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The following is a partial list of abstracts from technical papers authored or co-authored by CSA Engineering personnel. Please contact CSA if you would like copies of the papers that are not available as PDFs. Short Course: Design and Application of Passive Vibration Suppression. |
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Jonathan Hall
Roger M. Glaese
Eric M. Flint
CSA Engineering, Inc.
2565 Leghorn St.
Mountain View, CA
43rd AIAA / ASME / ASCE / AHS / ASC Structures, Structural Dynamics, and Materials Conference
Denver, Colorado, April 22-25 2002
ABSTRACT
In this paper, results of work addressing the dynamic characterization of thin membrane strips is presented. While apparently 'simple', the behavior of such strips offers a wide range of interesting effects to be independently modeled and significant challenges for testing. It is felt that these results will offer a valuable insight into the considerable complexities involved with modeling and testing thin film membrane structures, both strips, and by extension, more complicated structures. The body of the paper concentrates first on analytical and numerical predictive techniques for membrane strips, followed by detailed discussions of the testing of thin film strips and the associated already developed test apparatus. The experimentally observed results are then compared in terms of frequency/mode shape agreement and forced response to predictions from progressively more detailed modeling approaches ranging from classical closed form solutions to detailed finite element modeling approaches. In all cases agreement was good to with in 6% across multiple modes and preloads.
Eric H. Anderson
Jason E. Lindler
Marc E. Regelbrugge, Associate Fellow
CSA Engineering, Inc.
Rhombus Consultants Group
2565 Leghorn Street
Mountain View, CA
43rd AIAA / ASME / ASCE / AHS / ASC Structures, Structural Dynamics, and Materials Conference
Denver, Colorado, April 22-25 2002
ABSTRACT
The paper describes an actuator that makes use of high energy density smart materials, specifically piezoelectrics, in a non-standard way. Large displacements are produced, while high force capacity is retained, for a net high power output. Piezoelectrics are combined with a closed hydraulic system that acts as a transmission to convert smart material output to useful mechanical work. The paper reviews basic concepts in hybrid solid-fluid actuation. It then presents the design concept employed in the smart material - hydraulic hybrid technology. The basic design tradeoffs and major technical issues are discussed in the areas of materials, mechanical design, power delivery, electronics and control. This is followed by reviews of piezoelectric properties, subsystem and overall device test approaches, and results. Several prototype devices are presented. Test results quantifying actuator force and velocity are summarized. Potential applications in unmanned aircraft and elsewhere are discussed.
Conor D. Johnson
Paul S. Wilke
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Proceedings of SPIE Conference on Smart Structures and Materials
San Diego, CA, March 2002
ABSTRACT
Spacecraft are subjected to shock loads in the several thousands of g's level during their trip to orbit. These high shock loads usually result from some separation event, such as staging, spacecraft separation, and fairing separation. Shock loads are very detrimental to spacecraft components, instruments and electronics. A new type of shock isolation system is discussed. This shock system, referred to as the SoftRide ShockRing, is a whole-spacecraft isolation system, i.e., it shock isolates the complete spacecraft from the launch vehicle. Seven whole-spacecraft vibration isolation systems (SoftRide) have flown to date and flight data confirms large reductions of the dynamic loads on the spacecraft. The standard SoftRide system is a lower frequency isolation system than the ShockRing, vibration isolating the spacecraft starting in the approximately 25 Hz range. The ShockRing is targeted at shock leads and is set to isolate above approximately 75 Hz. Component tests have been performed on the ShockRing using a specially built pneumatic gun that can generate 10,000 g's on the test article. Results from these tests demonstrate substantial reductions of the shock being transmitted to the payload. Results from a system test consisting of a spacecraft simulator, payload attachment fittings, avionics section, and shock plate are discussed. In the system tests, pyrotechnic devices were used to obtain the high levels of shock for the tests.
Jason E. Lindler
Eric H. Anderson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
SPIE Paper 4698-53, Industrial and Commercial Applications of Smart Structures Technologies
San Diego, CA, March 2002
ABSTRACT
A single-stage servovalve using direct piezoelectric actuator drive is described. The single-stage servovalve design offers higher bandwidth than conventional two-stage valves. It takes advantage of the high energy density in piezoelectric materials while addressing the need for internal amplification of stroke. When used alone, the valve can regulate pressure, and when used in combination with a hydraulic output device it forms part of an effective servohydraulic actuator. Development of a direct drive prototype valve is described. Discussion includes design issues related to low stroke smart material actuators such as piezoelectrics. Component and subsystem testing and results are reviewed. Electronic drive and control of the piezoelectric and overall device along with performance in the control of fluid flow is discussed. The value of the new servovalve is shown in the combination of the valve with a hydraulic output device. Data are supplied for this servohydraulic actuator. The new actuator shows promise for a motion simulator application and more generally for motion control at higher bandwidth than is possible with currently available servohydraulics.
Keith K. Denoyer
Conor Johnson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Presented at the 52nd International Astronautical Congress
Toulouse, France, October 1-5, 2001
ABSTRACT
This paper presents successful recent applications of several vibration mitigation technologies to space and launch systems. These technologies include: whole-spacecraft vibration isolation and shock protection during launch, an innovative fluid-free magnetic isolation system for the Hubble Space Telescope servicing mission, precision isolation and pointing platforms for on-orbit applications, and pneumatic isolation technology for 0-g ground test systems.
Shawn P. Kelso
Ross Blankinship
CSA Engineering, Inc.
1300 Britt Street SE, Suite 201
Albuquerque, NM
Presented at the AIAA Space 2001 Conference,
Albuquerque, NM, August 28-30, 2001
ABSTRACT
Precision controlled vibration isolation utilizing magnetorheological (MR) fluid technology for potential space optical applications, such as surveillance and directed energy, is addressed. This research includes the design, development and preliminary testing of a semi-active, proof-of-concept, MR vibration isolator. Base disturbances designed to produce payload vibration responses were employed in a single degree-of-freedom test apparatus. The MR vibration isolator served as the load-coupling element between the payload and the base disturbance input. The three-parameter isolator consists of two passive spring elements combined with one MR damping element. The MR damper control algorithm uses relative rate between damper cylinder and piston to dynamically vary the effective coefficient of damping. The result of this technology is ability to tune isolation frequency within a given range. Through intelligent modulation of the damping element alone, dynamic changes in both apparent stiffness and damping of the isolator are achieved. For applications where the ability to vary stiffness and damping would improve pointing accuracy and jitter control, this technology holds great appeal.
Eric Flint
Eric Anderson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Presented at the AIAA Space 2001 Conference, Albuquerque, NM, August 28-30, 2001,
Paper # AIAA-2000-4750
ABSTRACT
This paper discusses multi-degree of freedom parallel actuator systems that can provide motion control authority, i.e. systems that provide pointing/positioning and/or active vibration isolation functionality using parallel, rather than serial/staged system level configurations. Such systems, commonly referred to as bi-, tri-, hexa- or octo-pods, are becoming more prevalent in aerospace and other high end applications where full authority over all of a payload's rigid body modes of motion are desired. Additionally, the sophistication of such systems has advanced to make them competitive with the more traditional staged several degree of freedom systems for certain applications, especially where both pointing/positioning and vibration isolation are simultaneously required. In the body of the paper, important considerations that must be taken into account when specifying such a system are first discussed. Next, the way these specifications cascade down into system level design and then sub-system level design aspects / component selection is reviewed. The resolution of the resulting, often conflicting, demands and issues are then illustrated through reference to a wide range of example systems that have been developed over the years. The chosen examples cover a range from extremely precise to large stroke applications for payloads ranging from 10 to 7200 lbs but the principles and systems discussed are certainly capable of being extended to larger payloads.
Eric H. Anderson
Mike E. Evert
Patrick Flannery
Bryce L. Fowler
Roger M. Glaese
Paul C. Janzen
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Presented at SPIE Aerospace Sensing Conference, Orlando, FL, April 2001,
Paper # 4366-24
ABSTRACT
The Image Stabilization Testbed (ISTAT) is a high-bandwidth angular motion system for the simulation of missile dynamics with capability beyond that of current flight motion simulators (FMS). This paper describes the development and initial laboratory integration of the ISTAT. The intention is to mount a missile seeker and any associated inertial measurement sensors, and then allow ISTAT to replicate the dynamic boundary conditions at the base of the seeker resulting from both airframe vibrations (flexible body motion) as well as rigid body motion resulting from vehicle control forces or the flight environment. ISTAT will be driven by the output of deterministic simulations and will replicate the time history of the command signals. It can be used in a standalone mode or possibly in conjunction with a conventional large motion lower bandwidth FMS. ISTAT makes use of high bandwidth hydraulic actuation and advanced feedback and feedforward control algorithms to deliver two- and three-axis motion control at frequencies from DC to greater than 500 Hz. The largest motions, achieved at lower frequencies, are about two degrees. The paper describes the motivation, the servohydraulic, mechanical, and electronic subsystems, control software and algorithms, and the software user interface for the testbed. An initial report on the system integration is also provided.
Eric H. Anderson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Bowie Houghton
Newport Corporation
1791 Deere Avenue, Irvine, CA
Mountain View, CA
Proceedings of SPIE Conference on Smart Structures and Materials,
Paper # 4332-23,
Newport Beach, CA, March, 2001
ABSTRACT
This paper describes the development and capabilities of ELITE-3, a product that incorporates piezoelectric actuators to provide ultrastable work surfaces for very high resolution wafer production, metrology, microscopy, and other applications. The electromechanical, electronic, and software/firmware parts of the ELITE-3 active workstation are described, with an emphasis on considerations relating to the piezoelectric transducers. Performance of the system and its relation to the smart materials is discussed. As the floor beneath a vibration-sensitive instrument supported by ELITE-3 moves, piezoelectrics are controlled to minimize the motion of the instrument. A digital signal processor (DSP) determines the appropriate signals to apply to the actuators. A PC-based interface allows reprogramming of control algorithms and resetting of other parameters within the firmware. The modular product allows incorporation of vibration isolator, actuator and sensor modules into original equipment manufacturer (OEM) products. Alternatively, a workstation can be integrated as an integrated standalone system. The paper describes the system architecture, overall approach to vibration isolation, and various system components, and summarizes motivations for key design approaches.
Conor D. Johnson, Paul S. Wilke
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Kenneth R. Darling
Orbital Sciences Corporation
3380 South Price Road, Chandler, AZ
Mountain View, CA
Proceedings of SPIE Conference on Smart Structures and Materials,
Paper # 4331-16,
Newport Beach, CA, March, 2001
ABSTRACT
Small launch vehicles present an economically viable method for placing small satellites into orbit. These launch vehicles would be even more attractive to satellite customers if they could provide a softer ride to orbit. Passive whole-spacecraft vibration isolation systems have been developed for small launch vehicles to greatly reduce dynamic launch loads. To date, two types of isolation systems have been designed. The first is a single-axis "SoftRide" axial isolation system that provides isolation for predominatly axial loads. This type of system has been flown successfully three times on the Taurus/GFO mission in February 1998, the Taurus/STEX mission in October 1998, and the Taurus/MTI mission in March 2000. The second type of isolation system is a multi-axis device that provides vibration isolation in three axes. This type of system is needed to alleviate dynamic launch loads on the Minotaur vehicle. This multi-axis "SoftRide" system inserts flexibility and damping in three orthogonal axes between the launch vehicle and the satellite. The result is that dynamic launch loads with both axial and lateral components can be effectively mitigated. Additionally, these isolation systems provide extreme reductions to shock and structure-borne acoustic loads. The multi-axis isolation system is a logical extension of the single-axis system and has the same qualities of being simple, passive, small, lightweight, reliable, and highly effective. Two flights have demonstrated this new isolation system to date: these are the Minotaur/JAWSAT mission in January of 2000 and the Minotaur/MightySat mission in July 2000. Coupled loads analyses and flight telemetry data indicate that the new multi-axis vibration isolation system performed as expected and greatly reduced dynamic launch loads for the satellites. This new isolation system can be sized for any satellite and is being considered for other small and large launch vehicle missions.
Joseph R. Maly, Roger M. Glaese
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
P. J. Keas
Orbital Sciences Corporation
NASA/Ames Research Center, Moffett Field, CA
Mountain View, CA
Proceedings of SPIE Conference on Smart Structures and Materials,
Paper # 4331-07, Newport
Beach, CA, March, 2001
ABSTRACT
The stratospheric Observatory For Infared Astronomy, SOFIA, is being developed by NASA and the German space agency, Deutschen Zentrum Für Luft- and Raumfahrt (DLR), with an international contractor team. The 2.5 meter reflecting telescope of SOFIA will be the worlds largest airborne telescope. Flying in an open cavity on a modified 747 aircraft, SOFIA will perform infared astronomy while cruising at 41,000 feet and while being buffetted by a 550-mile-an-hour slipstream. A primary system requirement of SOFIA is tracking stability of 0.2 arc-seconds, and a 3-axis pointing control model shows that increased levels of damping in certain elastic modes of the telescope assembly will help achieve the tracking stability goal and also expand the bandwidth of the attitude controller. This paper describes the preliminary work that has been done to approximate the reduction in image motion yielded by various structure configurations that use reaction masses to attenuate the flexible motions of the telescope structure. Three approaches are considered: passive and tuned-mass dampers, active-mass dampers, and attitude control with reaction-mass actuators. Expected performance improvements for each approach, and practical advantages and disadvantages associated with each, are presented.
Bryce L. Fowler, Eric M. Flint
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Proceedings of SPIE Conference on Smart Structures and Materials,
Paper # 4331-20, Newport
Beach, CA, March, 2001
ABSTRACT
Focused research in the area of Multi-Particle Impace Damping (MPID) has resulted in new methods of characterization and prediction. An analytical method has been developed, based on the particle dynamics method, that uses characterized particle damping data to predict damping in structural systems. A methodology to design particle damping for dynamic structures will be discussed. The complete design methodology has been validated in "proof-of-methodology" testing on a structural component in the laboratory.
Shawn P. Kelso
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Proceedings of SPIE Conference on Smart Structures and Materials,
Paper # 4332-34, Newport
Beach, CA, March, 2001
ABSTRACT
As technologies for magnetorheological (MR) fluid hardware further evolve towards commercial adoption, the appeal for simpler, more cost effective solutions becomes evident. While the skills involved in methods of manufacturing and cost-reduction efforts for mass production lie within the manufacturing community, practical and cost-effective MR technologies must first exist. As part of a "whole approach" MR solution, the MR damper technology presented in this paper illustrates the development of a fast-response, low-power cost-effective solution. Fundamentally a competitive "whole approach" active or semi-active MR solution can be viewed as a system of separate components: parameter sensing, intelligent control, power delivery, and MR hardware technology. The development of any single component should not successfully evolve without addressing the cost efficiency and commercialization concerns of the other three. The MR hardware component should be predictable in performance behavior, capable of high damping force at minimal power, and fast in time response to complement simplified control schemes. The design effort is further challenged to meet these requirements within a simple, cost-effective package that holds commercial development appeal.
This research includes the characterization of a new prototype MR damper including a description of the device technology, characterization test results and current work. It is evident by these results that this MR technology, comprising simple, commercial-off-the-shelf (COTS) components where possible, presents an attractive, practical and cost-effective component of the "whole approach" MR solution.
Joseph R. Maly, Kirsten A. Bender, Scott C. Pendleton
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Presented at the International ModalAnalysis Conference, IMAC-XVIII,
San Antonio, Texas, February 2000
ABSTRACT
As vibration suppression technology has matured, the application of viscoelastic materials in passive damping mechanisms has proven to be a reliable means towards improved structural dynamics. This paper discusses general steps required in characterization of viscoelastic damping elements and presents several successful passive damping devices as examples of the approach. Sample devices include a damper for the Hubble Space Telescope Solar Array 3, a damped strut built for the FORTÉ satellite a viscoelastic isolator, and a cocured viscoelastic/composite strut.
When damping is built into a structure with a damped element, it is necessary to measure the element of stiffness to understand its effect on the system dynamics. The stiffness measurement is complex because of the level of damping. The complex stiffness function, with both real and imaginary components, characterizes the behavior of a damping device, a damped structural element, or a sample of viscoelastic material. Stiffness characterization of structural elements with viscoelastic damping is presented in terms of real stiffness and loss (imaginary stiffness/real stiffness).
Bradley R. Allen, Eric Ruhl, Bryce Fowler
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Dino Sciulli
Air Force Research Laboratory
Kirtland Air Force Base, NM
Presented at Smart Structures and Materials Conference, San Diego, CA, March 2000
ABSTRACT
Research to create advanced vibration isolator designs and practical design techniques for Launch Vehicle (LV) manufacturers is discussed. Avionics of launch vehicles have unique requirements for isolation since many generate heat and cannot use convection cooling for dissipation. Nearly all isolation systems are ineffective thermal conductors unless expensive custom modifications are performed. The cost of a custom isolation design can rarely be justified, particularly on expendable vehicles. While viscoelastic isolators offer simplicity and affordability, such materials with high loss factors (greater than 0.25) also exhibit aggressive changes in stiffness with both temperature and frequency. Materials having new and unique formulations are introduced which have an order of magnitude higher thermal conductivity than today's materials of similar stiffness. This enables appreciable heat conduction with nominal temperature increases to isolated packages. The formulation of nearly all elastomeric vibration isolators creates heavy coupling between their loss factors and the rate of change in their storage moduli. High loss factors result in an aggressive temperature-dependant shift in the resonant frequencies of an isolated element. New compounds introduced in this paper address this limitation. A software utility has also been developed that greatly simplifies isolation design. The utility solves the equations of motion for a rigid body on flexible mounts and allows performance predictions using base vibration inputs. New progress in material technology and design techniques enables LV manufacturers to implement affordable designed vibration isolation systems on avionics and similar systems.
Roger M. Glaese, Eric H. Anderson, Paul C. Janzen
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
ABSTRACT
The Airborne Laser (ABL) system has extremely tight jitter requirements. Acoustic disturbances, such as those caused by the pressure recovery system of the high power laser, are a significant jitter source. Several technologies may be appropriate for reducing the acoustically induced jitter. The first choice for mitigation will be passive approaches, such as acoustic blankets. There is, however, some uncertainty whether these approaches will provide sufficient attenuation and there is concern about the weight of these approaches. A testbed that captured the fundamental physics of the ABL acoustically induced optical jitter problem was developed. This testbed consists of a flexure-mounted mirror exposed to an acoustic field that is generated outside a beam tube and then propagates within the tube. Both feedback and adaptive feedforward control topologies were implemented on the testbed using either of two actuators (a fast steering mirror and a secondary acoustic speaker located near the precision mirror), and a variety of sensors (microphones measuring the acoustic disturbance, accelerometers, and microphones mounted on the precision optic, and an optical position sensing detector). This paper summarizes the results from these control topologies for reducing the acoustically induced jitter with some control topologies achieving in excess of 40 dB jitter reduction at a single frequency. This work was performed under an SBIR Phase I funded by the Air Force Research Laboratory Space Vehicles Directorate.
Joseph R. Maly, Scott Pendleton
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
S. M. Anandakrishnan, E. Shade, J. W. Sills Jr.
Lockheed Martin Technical Operations
Greenbelt, MD
Presented at Smart Structures and Materials 2000: Passive Damping and Isolation,
Newport Beach,
CA March 2000
ABSTRACT
The Hubble Space Telescope (HST) is currently operating with two flexible solar arrays (or "wings"), referred to as SA2, that were installed during Servicing Mission 1. These flexible solar arrays are to be replaced with two rigid solar arrays, SA3, during Servicing Mission 3B which is currently scheduled for May, 2001. The key requirements for these arrays are to: (1) increase long term power to support the HST mission, (2) improve the jitter performance while maintaining stability margin requirements, and (3) withstand re-boost loads without astronaut or ground intervention. Analysis of the original SA3 design showed that the Pointing Control System (PCS) stability margin requirements would be violated because of the modal characteristics of the SA3 fundamental bending modes. One of the options to regain the stability margins was to increase the damping of these modes. Damping of 1.5% of critical of theSA3 fundamental bending modes, at the HST system level, is needed to meet the stability margin requirements. Therefore, the development of a discrete damping device was undertaken to provide adequate damping of the SA3 fundamental bending modes for all operational conditions.
Top (Download PDF)Bryce L. Fowler, Eric M. Flint
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Steven E. Olson
University of Dayton Research Institute
Dayton, OH
ABSTRACT
In this paper, recent results of ongoing studies into the effectiveness and predictability of particle damping are discussed. Efforts have concentrated on characterizing and predicting the behavior of a wide range of potential particle materials, shapes and sizes in the laboratory environment, as well as at elevated temperature. Methodologies used to generate data and extract the characteristics of the nonlinear damping phenomena are illustrated with interesting test results. Experimental results are compared to predictions from analytical simulations performed with an explicit code, based on the particle dynamics method, that has been developed in support of this work.
Conor D. Johnson, Paul S. Wilke
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Patrick J. Grosserode
Orbital Sciences Corporation
Chandler, AZ
Dino Sciulli
AFRL/VSDV
Kirtland AFB, NM
ABSTRACT
Small launch vehicles historically provide a very rough ride to spacecraft during launch. This is particularly true of solid-fueled launch vehicles. In order for the spacecraft to survive such a trip to orbit, one of two choices must be made: (1) design all structure, payloads, and systems on the spacecraft to be strong enough to survive the high launch loads, or (2) reduce the magnitude of the high launch loads. The former is not a good choice because it typically requires additional cost, schedule, and weight. The latter is the preferred choice because it allows the focus of the spacecraft design to be primarily for on-orbit performance rather than for launch survival.
Under a number of contracts from the Air Force Research Laboratory, Space Vehicles Directorate, whole-spacecraft vibration isolation systems have been in development since 1993. This work has resulted in two whole-spacecraft isolation systems (SoftRide) that have been flown on Taurus launch vehicles, the first in February 1998 with the GFO spacecraft and the second in October 1998 with the STEX spacecraft. Both of these isolation systems were designed primarily to reduce axial dynamic responses on the spacecraft due to resonant burn excitations from the motors of the solid-fueled booster. Full coupled-loads analyses were used to predict the performance of the SoftRide systems. Using the isolation requirements derived from these analyses, hardware having the correct damping and stiffness was designed to implement the isolation system. All isolation system components were extensively tested and characterized. Typical results show 85% attenuation (i.e., only 15% of original) for the worst case resonant burn condition and 59% attenuation for combination of static plus worst case resonant burn condition in the axial spacecraft c.g. location. No detrimental effects from the SoftRide system were observed. Limited flight data from the two flights agree with the predictions. SoftRide systems are now under development for the first and second OSP launches and for the Taurus/MTI launch. Additionally, isolation systems are being designed for larger liquid-fueled launch vehicles. This isolation system technology will greatly further the goal of better, faster, cheaper, and lighter spacecraft.
Eric H. Anderson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
John P. Fumo
Trisys Inc.
Phoenix, AZ
R. Scott Erwin
Air Force Research Laboratory
Kirtland AFB, NM
IEEE Aerospace Conference, Big Sky, Montana, March 19-25, 2000
ABSTRACT
An experimental active vibration isolation called Satellite Ultraquiet Isolation Technology Experiment (SUITE) is described in detail. SUITE is a piezoelectric-based technology demonstration scheduled to fly in 2000 or 2001 on board the PICOSat spacecraft. SUITE is designed to show that the effect of small vibrations on spacecraft instrument effectiveness can be reduced significantly. Control from the ground station is planned for the first year after launch. A description of the PICOSat spacecraft and the other considerations influencing the development of the flight hardware begins the paper. Experimental goals are listed. The mechanical and electromechanical construction of the SUITE hexapod assembly is described, including the piezoelectric actuators, motion sensors, and electromagnetic actuators. The data control system is also described, including the digital signal processor and spacecraft communication. The main features of the software used for real-time control and the Matlab software used for control system development and data processing are summarized. Initial test results are presented.
Joseph R. Maly, Paul S. Wilke, Emily C. Fowler
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Capt. S. A. Haskett
Space Test Program, USAF Space and Missile System Center
Kirtland Air Force Base, NM
Dino Sciulli
Space Vehicles Directorate, Air Force Research Laboratory
Kirtland Air Force Base, NM
T. E. Meink
Space Vehicles Directorate, Air Force Research Laboratory
Kirtland Air Force Base, NM
Smart Structures and Materials: Passive Damping and Isolation, Newport Beach, CA March 2000
ABSTRACT
ESPA, the Secondary Payload Adapter for Evolved Expendable Launch Vehicles, addresses two of the major problems currently facing the launch industry: the vibration environment of launch vehicles, and the high cost of putting satellites into orbit. (1) During the 1990s, billions of dollars have been lost due to satellite malfunctions, resulting in total or partial mission failure, which can be directly attributed to vibration loads experienced by payloads during launch. Flight data from several recent launches have shown that whole-spacecraft launch isolation is an excellent solution to this problem. (2) Despite growing worldwide interest in small satellites, launch costs continue to hinder the full exploitation of small satellite technology. Many small satellite users are faced with shrinking budgets, limiting the scope of what can be considered an "affordable" launch opportunity.
Joseph R. Maly, Scott Pendleton, Jason Salmanoff
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
G. J. Blount
NASA/Goddard Space Flight Center
Greenbelt, MD
K. Mathews
Lochheed Martin Technical Operations
Greenbelt, MD
Smart Structures and Materials: Passive Damping and Isolation, Newport Beach, CA March 1999
ABSTRACT
This paper describes the design of solar array damper that will be built into each of two new solar arrays to be installed on the Hubble Space Telescope (HST) during Servicing Mission 3. On this mission, currently scheduled for August, 2000, two "rigid" solar array wings will replace the "flexible" wings currently providing power for HST. In addition to increased power, the new arrays will provide the capability for HST to survive re-boost to a higher orbit. The objective of the damper is to reduce the dynamic interaction of these new wings with the Telescope spacecraft.
The damper, which is integral to the mast of the solar array, suppresses the fundamental bending modes of the deployed wings at 1.2 Hz (in-plane) and 1.6 Hz (out-of-plane). With the flight version of the damper, modal damping of 2.3% of critical is expected over the temperature range of -4 C to 23 C with a peak damping level of 3.9%. The unique damper design, a combination of titanium spring and viscoelastic damper, was developed using a system finite element model of the solar array wing and measured viscoelastic material properties. Direct complex stiffness (DCS) testing was performed to characterize the frequency - and temperature-dependant behavior of the damper prior to fixed-base modal testing of the wing at NASA/Goddard Space Flight Center (GSFC).
Eric M. Flint, Patrick Flannery, Michael Evert, Eric Anderson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Proceedings of the SPIE Conference # 3989, paper # 64, Newport Beach, CA, March 6-9
ABSTRACT
Cryocoolers are well known sources of harmonic disturbance forces. In this paper two miniaturized, add-on, vacuum compatible, active vibration control systems for cryocoolers are discussed. The first, called VIS6, is an active/passive isolation hexapod and has control authority in all six degrees of freedom. This capability is desirable when reduction of all cryocooler disturbance loads, including the radial loads, is required. Each of the six identical hexapod struts consists of a miniature moving coil electromagnetic proof mass actuator, custom piezoelectric wafer load cell, viscoelastic passive isolation stage, and axial end flexures. The first five disturbance tones are reduced over a bandwidth of 250 Hz using a filtered-x least mean square algorithm. Load reductions of 30-40 dB were measured both axially and radially. The second system, called VRS1, is a pure active control system designed to reduce axial expander head disturbance loads. It works on the basis of a counter-force developed from an electromagnetic proof mass actuator. Error signals are provided from a commercial accelerometer to a standalone digital signal processor, on which a filtered-x least means square control algorithm is implemented. Over the 500 Hz control bandwidth, the 11 disturbance tones were reduced on between 14 to 40 dB.
Eric Flint, Michael E. Evert, Eric Anderson, Patrick Flannery
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Proceedings of the IEEE 2000 Aerospace Conference, Paper # 432,
Big Sky, Montana, March 19-25,
ABSTRACT
Active counter-force control has significant advantages over the more traditional motion based active vibration suppression for isolation of disturbance sources. In this paper, features of four specific actuators, two hybrid isolation struts, and three system level realizations are reviewed with a focus on vibration isolation/suppression to reduce cryocooler disturbance forces. All of the discussed hardware and systems are based on electromagnetic reaction mass actuators. Significant vibration reductions can be achieved with such systems. The best measured tonal performance for all three systems discussed exceeds two orders of magnitude (40 dB) of vibration reduction. Control bandwidth can exceed 500 Hz. The necessary actuators are also robust, compact, and lightweight. Two of the systems were realized with miniature actuators weighing 3.8 ounces (107 grams) and 3.12 ounces (88 grams) respectively. Such systems have significant promise for addressing critical vibration isolation needs for upcoming space missions such as SIM, NGST, TPF, SBL, etc., through isolation of on-orbit noise sources such as cryocoolers and reaction wheels. They could also be quite useful for terrestrial applications in telecommunication, manufacturing, and semiconductor processing industries.
Eric Flint, Eric Ruhl
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Steven E. Olson
University of Dayton Research Institute
300 College Park
Dayton, OH
Proceedings of the 5th National Turbine Engine High Cycle Fatigue Conference
Chandler, AZ, March 6-9, 2000
ABSTRACT
In this paper, analytical and experimental studies of particle damping behavior are discussed. These studies have focused on the development of an analytical model to predict particle damping behavior and on determination of the effects of centrifugal loading on the behavior. An analytical model, based on the particle dynamics method, has been developed and is being correlated with results from experimental testing. A novel test facility is being established which enables laboratory based evaluation of the damping effectiveness of blade-like objects under centrifugal loading. Depending on the test article, this facility will be capable of exposing test specimens to centrifugal accelerations of up to 124,000 G’s.
Paul Wilke, Conor Johnson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Patrick Grosserode
Orbital Sciences Corporation
3380 South Price Road
Chandler,
Dino Sciulli
Air Force Research Lab
AFRL/VSDV
Kirtland AFB, NM
Presented at the IEEE Aerospace Conference, Big Sky, Montana, March 19-25, 2000
ABSTRACT
Launch vehicles impart high levels of vibration to spacecraft during launch. The vibration environments are defined over several frequency bands: (1) transient vibration < 80 Hz, (2) random vibration 20 to 2000 Hz, and (3) pyrotechnic shock 100 to 10000 Hz. Loads from transient vibration define spacecraft design of primary structures such as spacecraft bus, solar panel and antenna supports, instrument mounts, ect. Loads from random vibration define the design for spacecraft light structures such as antennas and solar panels, and shock loads define the design of electronic components and instruments. The spacecraft must survive the combination of all vibration environments. This requires spacecraft structures, instruments, and components to be designed to minimize vibration across a broad frequency range. Spacecraft are designed for the short launch to orbit, which is well beyond the requirements for on-orbit performance. A better choice is to reduce the magnitude of the high launch loads across all frequency bands and design smaller and less costly spacecraft.
Satya M. Anandaksishnan, Chris T. Connor, Steve Lee, Ed Shade, Joel Sills
Lockheed Martin Technical Operations
7474 Greenway Center Drive
Greenbelt, MD 20770
Joseph R. Maly, Scott C. Pendleton
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Presented at the IEEE Aerospace Conference, Big Sky, Montana, March 19-25, 2000
ABSTRACT
Analysis of the rigid solar array, SA-3, design showed that the Pointing Control System stability margin requirements would be violated because of the modal characteristics of the SA-3 fundamental bending modes. A damping of 1.5% of critical of the SA-3 fundamental bending modes, at the HST system level, is needed to meet the stability margin requirements.
A damper, consisting of a titanium flexure and viscoelastic damping material, has been designed, built, and tested, and is an integral part of the SA-3 mast. The viscoelastic material properties are temperature-sensitive, and Direct Complex Stiffness testing was performed to characterize the frequency-and temperature-dependant behavior of the damper. Fixed-base modal testing showedthat the optimized damper is expected to provide modal damping of at least 2.25% of critical (fixed base extrapolated to zero excitation force levels) over the temperature range of 0°C to 25°C.
Conor D. Johnson, Paul S. Wilke
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Presented at the AIAA Space Technology Conference and Exposition,
September 28-30, 1999, Albuquerque, NM
ABSTRACT
Spacecraft typically are hard-mounted to the launch vehicle for launch. Therefore, all of the high dynamic loads from the launch are transmitted directly from the launch vehicle to the spacecraft. The launch events include lift-off, motor excitation, buffet, staging and fairing separation, ect. A whole-spacecraft vibration isolation system is an isolation system that vibration-isolates the complete spacecraft from the launch vehicle. Unlike many typical isolation systems, this isolation system must couple two dynamically rich structures in the same frequency range as the individual components. Therefore, a coupled-loads approach must be used for its design characteristics. This paper discusses two whole-spacecraft systems: a shear-type designed for large, liquid-fueled vehicle. And an axial system, designed for small, solid-fueled launch vehicles. A prototype shear-type of system was designed, built and tested for a Delta II class of launch vehicle. Coupled-loads analyses predicted that the RMS lateral accelerations on the spacecraft were reduced by a factor of two to six. The axial-type of system has been flown on two flights: the Taurus/GFO and the Taurus/STEX. Flight data shows that the dynamic responses on the spacecraft were reduced by up to a factor of 5.
Eric H. Anderson, Michael E. Evert, Roger M. Glaese, James C. Goodding, Scott C. Pendleton
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Richard G. Cobb, R. Scott Erwin, Johnathan Jensen
Air Force Research Laboratory
Kirtland AFB, NM
Donald Camp, John Fumo, Marty Jessen
Trisys, Inc.
Phoenix, AZ
Presented at the Industrial and Commercial Applications of Smart Structures and Technologies,
Newport Beach, CA,
March 2-4, 1999
ABSTRACT
Spacecraft carry instruments and sensors that gather information from distant points, for example, from the earth's surface several hundred kilometers away. Small vibrations on the spacecraft can reduce instrument effectiveness significantly. Vibration isolation systems are one means of minimizing the jitter of sensitive instruments. This paper describes one such system, the Satellite Ultraquiet Isolation Technology Experiment (SUITE). SUITE is a piezoelectric-based technology demonstration scheduled to fly in 2000 on the PICOSat, a microsatellite fabricated by Surrey Satellite Technology, Ltd. Control from the ground station is planned for the first year after launch. SUITE draws on technology from previous research programs as well as commercial piezoelectric vibration solation system. The paper details the features of SUITE, with particular emphasis on the active hexapod assembly. A description of the PICOSat spacecraft and the other considerations preceding the development of the flight hardware begins the paper. Experiment goals are listed. The mechanical and electromechanical construction of the SUITE hexapod assembly is described, including the piezoelectric actuators, motion sensors, electromagnetic actuators. The data control system is also described briefly, including the digital signal processor and spacecraft communication. The main features of the software used for real-time control and the supporting Matlab software used for control system development and data processing are summarized.
Conor D. Johnson, Paul S. Wilke
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Patrick J. Grosserode
Orbital Sciences Corporation
3380 South Price Road
Chandler, AZ
Presented at the Smart Structures and Materials Conference, Passive Damping and Isolation,
Vol. 3045, pgs 23-30,
March 1999, San Diego, CA
ABSTRACT
A whole-spacecraft isolation system for the GFO/Taurus mission was designed, fabricated, tested, and subsequently flown on February 10, 1998. This isolation system was designed to reduce dynamic responses on the GFO spacecraft caused by the resonant burn dynamic load introduced by the Castor 120 solid rocket motor. Longitudinal (flight direction) response of the GFO spacecraft center of gravity, due to the resonant burn load, was reduced by a factor of seven. The isolation system was designed very nonintrusive to existing hardware, lightweight and effective. Flight data indicates that the isolation system performed as designed. The GFO spacecraft had a successful launch and is currently operational on-orbit. A second flight of this type of isolation system occurred in October 1998. Similar isolation systems are planned for other flights in 1999 an 2000. This whole-spacecraft isolation technology was highly successful for the GFO/Taurus mission.
Eric H. Anderson, Roger M. Glaese
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
ABSTRACT
Launch loads, both mechanical and acoustic, are the prime driver of spacecraft structural design. Passive approaches for acoustic attenuation are limited in their low frequency effectiveness by constraints on total fairing mass and payload volume constraints. Active control offers an attractive approach for low frequency acoustic noise attenuation inside the payload fairing. Smart materials such as piezoceramics can be exploited as actuators for structural-acoustic control. In one active approach, structural actuators are attached to the walls of the fairing and measurements from structural sensors and/or acoustic sensors are fed back to the actuators to reduce the transmission of acoustic energy into the inside of the payload fairing. In this paper, structural-acoustic modeling and test results for a full scale composite launch vehicle payload fairing are presented. These analytical and experimental results fall into three categories: structural modal analysis, acoustic modal analysis, and coupled structural-acoustic transmission analysis. The purpose of these analysis and experimental efforts is to provide data and validated models that will be used for active acoustic control of the payload fairing. In the second part of the paper, this closed-loop acoustic transmission reduction is implemented and measured on a full-scale composite payload fairing.
Roger M. Glaese, Eric H. Anderson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
ABSTRACT
Launch loads, both mechanical and acoustic, are the prime driver of spacecraft structural design. Passive approaches for acoustic attenuation are limited in their low frequency effectiveness by constraints on total fairing mass and payload volume constraints. Active control offers an attractive approach for low frequency acoustic noise attenuation inside the payload fairing. Smart materials such as piezoceramics can be exploited as actuators for structural-acoustic control. In one active approach, structural actuators are attached to the walls of the fairing and measurements from structural sensors and/or acoustic sensors are fed back to the actuators to reduce the transmission of acoustic energy into the inside of the payload fairing. In this paper, structural-acoustic modeling and test results for a full scale composite launch vehicle payload fairing are presented. These analytical and experimental results fall into three categories: structural and modal analysis, acoustic modal analysis and coupled structural-acoustic transmission analysis. The purpose of these analysis and experimental efforts is to provide data and validated models that will be used for active acoustic control of the payload fairing. In the second part of the paper, this closed-loop acoustic transmission reduction is implemented and measured on a full-scale composite payload fairing.
David A. Kienholz
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Presented at SPIE, Smart Structures and Materials Conference, San Diego, CA, March, 2000
ABSTRACT
Airborne optical or electro-optical systems may be too large for all elements to be mounted on a single integrated structure, other than the aircraft fuselage itself. An active system must then be used to maintain the required alignment between elements. However the various smaller integrating structures (benches) must still be isolated from high-frequency airframe disturbances that could excite resonances outside the bandwidth of the alignment control system. The combined active alignment and vibration isolation functions must be performed by flight-weight components, which may have to operate in vacuum. A testbed system developed for the Air Force Airborne Laser program is described. The payload, a full-scale 1650-lb simulated bench, is mounted in six degrees of freedom to a vibrating platform by a set of isolator-actuators. The mounts utilize a combination of pneumatics and magnetics to perform the dual functions of low-frequency alignment and high-frequency isolation. Test results are given and future directions for development are described.
Eric M. Flint
CSA Engineering, Inc.
2565 Leghorn Street
Mountian View, CA
Proceedings of the 4th National Turbine Engine High Cycle Fatigue Conference,
HCF '99 (CD-ROM), Monterey, California, February 9-11
ABSTRACT
Particle damping is believed to be a promising loss mechanism for engine turbine blades, as some particle damping materials have the capability to withstand the extremely high temperatures inherent with operational aircraft engines turbines. The ability to provide damping under centrifugal loads however had never been shown experimentally. In this paper, initial measurement results from a series of particle damping configurations tested under true centrifugal loads are reported upon. The interplay of various parameters such as fill ratio, particle size, shape, and material on achieved damping levels were investigated with nine different particle damping configurations loaded up to 5,000 G's. Damping, in terms of frequency domain peak response reduction, was seen at this G loading for one configuration with no indication of reduction due to centrifugal load. This best performing particle damper, based on irregular tungsten carbide granules, was also proof tested to more than 50,000 G's with no noticeable degredation. While damping still remains to be shown at centrifugal load levels comparable with real engines, these initial test results show the particle damping is worthy of further consideration.
Steven E. Olson, Michael L. Drake
University of Dayton Research Institute
300 College Park
Dayton, OH
Eric M. Flint, Bryce L. Fowler
CSA Engineering, Inc.
2565 Leghorn Street
Mountian View, CA
Proceedings of the 4th National Turbine Engine High Cycle Fatigue Conference
Monterey, CA, February 9-11,
1999
ABSTRACT
Particle dampers are highly nonlinear auxiliary mass dampers whose energy dissipation, or damping, is derived from a combination of mechanisms including plastic deformations, external and internal friction, and momentum transfer. To complicate matters, the predominate energy dissipation mechanism may vary depending on parameters such as cavity fill ratio, vibration amplitude levels, ect. Research has indicated that particle dampers could be a viable option for extreme environment applications, such as elevated temperatures and/or under centrifugal loading. However, to date, the lack of robust design methodology has limited particle damper usage to “trial and error” applications. The objective of this effort is to develop the necessary design methodology to enable the successful design and application of particle dampers. Experimental and analytical efforts toward this goal are presented.
Eric H. Anderson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Donald J. Leo
University of Toledo
Toledo, OH
Proceedings of the 3rd National Turbine Engine High Cycle Fatigue Conference,
HCF '98 (CD-ROM), San Antonio, Texas, February 2-5
ABSTRACT
Low frequency active acoustic attenuation is examined for the payload fairing of a representative small launch vehicle. The feasibility of using structural sensors and actuators for active acoustic control is assessed with a numerical model of the fairing. The results of the numerical analysis indicate that broadband damping decreases the interior overall sound pressure level between 4 db and 10 db, depending on the amount of structural damping that is added to the vibration modes. Singular value analyses demonstrate that point force actuators and in-plane strain actuators have the control authority for active acoustic control. Control studies indicate that the local velocity feedback reduces the average level of the fairing by roughly 50%, and that the force levels required of the control system are within the range of conventional point force and piezoceramic actuators.
Conor D. Johnson, Paul S. Wilke
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Patrick J. Grosserode
Orbital Sciences Corporation
3380 South Price Road
Chandler, AZ
Presented at the 12th Annual AIAA/USU Conference on Small Satellites, September 1998, Logan UT
ABSTRACT
A whole-spacecraft isolation system for the GFO/Taurus mission was designed, fabricated, tested, and subsequently flown on February 10, 1998. This isolation system was designed to reduce dynamic responses on the GFO spacecraft caused by the resonant burn dynamic load introduced by the Castor 120 solid rocket motor. Longitudinal (flight direction) response of the GFO spacecraft center of gravity, due to the resonant burn load, was reduced by a factor of seven. The isolation system was designed very nonintrusive to existing hardware, lightweight, and effective. Flight data indicates that the isolation system performed as designed. The GFO spacecraft had a successful launch and is currently operational on-orbit. Similar isolation systems are planned for other flights in 1998 and 1999. This whole-spacecraft isolation technology was highly successful for the GFO/Taurus mission.
Paul S. Wilke, Conor D. Johnson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
E. R. Fosness
Air Force Research Laboratory
Kirtland Air Force Base, NM
Presented at the Journal of Spacecraft and Rockets. Vol. 35, No. 5,
pgs 690-694, September-October 1998
ABSTRACT
A spacecraft is subjected to very large dynamic forces from its launch vehicle during its ascent into orbit. These large forces place stringent design requirements on the spacecraft and its components to insure that the trip to orbit will be survived. The severe launch environment accounts for much of the expense of designing, qualifying, and testing satellite components. Reduction of launch loads would allow for more sensitive equipment to be included in missions, reduce risk of equipment of component failure, and possibly allow the mass of the spacecraft bus to be reduced. These benefits apply to military as well as commercial satellites. The design and testing is reported of a prototype whole-spacecraft isolation system that will replace current payload attach fittings, is passive only in nature, and provides lateral isolation to a spacecraft that is mounted on it. This isolation system is being designed for a medium launch vehicle and a 3000-kg (6600-lb) spacecraft, but the isolation technology is applicable to practically all launch vehicles and spacecraft, small and large. The isolator significantly reduces the launch loads seen by the spacecraft.
Lyn M. Greenhill
DynaTech Engineering
Citrus Heights, CA
Scott C. Pendleton
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Jerry Hunt
EIMCO Process Equipment
Salt Lake City, UT
Proceedings from the Vibration Institute, 22nd Annual Meeting,
Dearborne, MI, June 23-25, 1998
ABSTRACT
Excessive vibration was encountered during the prototype development of a large, low speed vertical process machine. The characteristics of this vibration was a discrete peak nearly 0.70 inches/sec, and was identified as a nonsyncronous resonance. This paper describes the analysis, design, and testing effort that led to the creation of a unique damper which resulted in an order of magnitude reduction in the vibration. The application of this device, which is referred to as a Tuned Mass Damper, is thought to be unprecedented with rotating machinery.
Nicholas M. Jedrich
Jackson and Tull
7375 Executive Place, Suite 200
Seabrook, MD
Scott C. Pendleton
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Presented at Technology Overview,
International Symposium on Smart Structures and Materials, March 3, 1998
ABSTRACT
Servicing the Hubble Space Telescope (HST) requires the safe transportation of electronic Orbital Replacement Units (ORUs) on the Space Transportation System (STS) to replace or enhance the capability of existing units. The delicate design of these ORUs makes it imperative to provide isolation from the STS launch random vibration, while maintaining fundamental modes above the transient load environment. Two methods were developed and used exclusively, on Servicing Mission 2 (SM2), to isolate the ORUs from the environmental launch loads imposed by the STS. The first load isolation system utilizes a refined open/closed cell foam design to provide the required damping and corner frequency, while the second method uses an innovative Viscoelastic Material (VEM) design. This paper addresses both systems as initially designed including finite element (FE) model analysis of the VEM system. Vibration testing of prototype systems and modifications to the design resulting from test will be discussed. The final design as flown on HST SM2 with recommendations for future applications of these technologies in transporting electronic black boxes to orbit will conclude the paper.
Doanld L. Edberg, Bruce Bartos
Boeing
5301 Bolsa Ave., MS H013-C3316
Huntington Beach, CA
James Goodding, Paul S. Wilke
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Torey Davis
Honeywell Satellite Systems Operations
Phoenix, AZ
Presented at SPIE Smart Structures Conference, March 1998, San Diego, CA
ABSTRACT
A U.S. Air Force-sponsored team consisting of Boeing (formerly McDonnell Douglas), Honeywell Satellite Systems, and CSA Engineering has developed technology to reduce the vibration felt by an isolated payload during launch. Spacecraft designers indicate that a launch vibration isolation system (LVIS) could provide significant cost benefits in payload design, testing, launch, and lifetime. This paper contains developments occurring since those reported previously. Simlations, which included models of a 6,500 pound spacecraft, an isolating payload attach fitting (PAF) to replace an existing PAF, and the Boeing Delta II launch vehicle, were used to generate PAF performance requirements for the desired levels of attenuation. Hardware was designed to meet the requirements. The isolating PAF concept replaces portions of a conventional metallic fitting with hydraulic-pneumatic struts featuring a unique hydraulic cross-link feature that stiffens under rotation to meet rocking restrictions. The pneumatics provide low-stiffness longitudinal support. Two demonstrating isolating PAF struts were designed, fabricated, and tested to their dertermine stiffness and damping characteristics and to verify the performance of the hydraulic crosslink concept. Measurements matched analytical predictions closely. An active closed-loop control system was simulated to assess its potential isolation performance. A factor of 100 performance increase over the passive case was achieved with minor weight addition and minimal power consumption.
Eric M. Flint, Lynn Rogers, Bryce L. Fowler
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA 94043
Presented at the 3rd National Turbine Engine High Cycle Fatigue Conference,
San Antonio, Texas, February
2-5, 1998
ABSTRACT
Hardware representative of viscoelastic damping material in a cavity in a spinning jet engine blade was investigated. Specimens representing jet engine fan blades were analyzed, designed, fabricated and spun to establish that elastomer filled cavities can be designed for service in high-g environments. It was also shown that such systems can be analyzed using conventional finite element analysis. Spin rates of 7500 RPM were achieved which at a radius of 14 inches resulted in a g-level of 22,400 in the outer edge of a constrained viscoelastic material (VEM) damping treatment. Static strain readings were taken for the cavity walls. Dynamic testing was conducted and some excitation and response vibration data was acquired during spin. The elastic constants and elastomeric properties such as shear modulus, youngs modulus, bulk modulus, and Poisson's ratio of the VEM were also experimentally investigated in the laboratory. Initial results from these investigations are reported upon here.
Eric H. Anderson, Mark D. Holcomb, Donald J. Leo
CSA Engineering, Inc.
Mountain View, CA
Adam X. Bogue, Farla R. Russo
Active Control eXperts, Inc.
Cambridge MA
Presented at the International Mechanical Engineering Congress and Exposition,
Dallas, Texas, November 16-21, 1997
ABSTRACT
Advances in transducers and electronics have made possible integrated electromechanical devices for active vibration and noise control. This paper describes one such system which makes use of piezoelectric materials. An integrated device employing piezoceramic actuators and sensors, analog electronic signal conditioning, programmable control components, and a voltage amplifier is described. Issues driving design of each functional subsystem are addressed. The device is packaged using flex circuit technology and other electronics industry methods. The means of integrating transducers and other components are noted. Test results indicating the vibration suppression capability are presented, and the considerably greater possibilities for the more sophisticated control designs using the same system are summarized. Potential applications in active vibration and sound control are described, and uses of the broader technology, beyond the specific device design, are summarized.
Top (Download PDF)Paul S. Wilke, Conor D. Johnson
CSA Engineering, Inc.
2565 Leghorn, Street
Mountain View, CA
Eugene R. Fosness
Air Force Phillips Laboratory, PL/VTVD
3550 Aberdeen Ave.
SE, Kirtland AFB, NM
Presented at the 38th Structures, Structural Dynamics and Materials Conference and Exhibit, Adaptive Structures Forum, April 1997, Kissimmee, FL
ABSTRACT
A Spacecraft is subjected to very large dynamic forces from its launch vehicle during its ascent into orbit. These large forces place stringent design requirements on the spacecraft and its components to assure that the trip to orbit will be survived. The severe launch environment accounts for much of the expense of designing, qualifying, and testing satellite components. Reduction of launch loads would allow more sensitive equipment to be included in missions. Reduce risk of equipment or component failure, and possibly allow the mass of the spacecraft bus to be reduced. These benefits apply to military as well as commercial satellites. This paper reports the design and testing of a prototype whole-spacecraft isolation system which will replace current payload attach fittings, is passive-only in nature and provides lateral isolation to a spacecraft which is mounted on it. This isolation system is being designed for a medium launch vehicle and a 6500 lb spacecraft, but the isolation technology is applicable to practically all launch vehicles and spacecraft, small and large. The isolator significantly reduces the launch loads seen by the spacecraft. Follow-on contracts will produce isolating payload attach fittings for commercial and government launches.
Donald J. Leo
Mechanical, Industrial, and Manufacturing Engineering
University of Toledo
Toledo, Ohio
Christian A. Smith
CSA Engineering, Inc.
5495 Arapahoe Ave.
Boulder, CO 80303
Presented at the Eleventh Symposium on Structural Dynamics and Control,
Blacksburg, VA, May 12-14, 1997
ABSTRACT
Several important tradeoffs exist in the design of vibration isolation systems for expendable launch vehicles. This paper presents an optimal control approach that allows these tradeoffs to be efficiently studied as a finite-dimensional quadratic optimization that is solved with standard numerical techniques. Peak response specifications are shown to be linear matrix functions of the design variables, which allows them to be incorporated within the design framework without increasing the complexity of the optimization. The quadratic optimization approach is illustrated on a simple mathematical model of a single-degree-of-freedom isolation system. The analysis demonstrates that the quadratic optimization technique is useful for studying the explicit tradeoffs between several practical performance requirements, such as mean-square mitigation and peak response of the payload acceleration and actuator stroke.
D. L. Edberg
McDonnell Douglas Aerospace – Phantom Works
Paul S. Wilke
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
T. Davis
Honeywell Space Systems
E. Fosness
USAF Phillips Laboratory
Presented at the 38th Structures, Structural Dynamics, and Materials Conference and Exhibit,
Adaptive Structures Forum, April 1997, Kissimmee, FL
ABSTRACT
The Airforce’s Phillips Laboratory has sponsored a program to isolate payloads during launch. Called LVIS, for Launch Vibration Isolation System, the programs goals are to reduce the RMS accelerations felt by and isolated payload by a factor of 5 compared to an unisolated payload. Its secondary goals are to use minimal launch vehicle services, fit within existing payload attach fittings’ dimension and mass envelope. And provide fail-safe operation. The LVIS system must provide this mechanical osolation while at the same time not allowing its host spacecraft to “rattle” too much and make contact with the external payload fairing, which protects the payload against heat, aerodynamic, and acoustic loads during ascent. The LVIS program intends to accomplish this goal using an innovative suspension system which is specially designed to be compliant in the vertical and lateral directions, but stiff in the rotational directions to prevent payload fairing contact. An overview of the LVIS design and predicted performance will be given.
Eric H. Anderson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Jonathan P. How
Stanford University
Palo Alto, CA
Presented at the American Control Conference, Albuquerque, NM, June 1997. Paper I-97115B
ABSTRACT
The structure and performance requirements for active vibration isolation control systems motivate the use of adaptive control. This is especially true for spacecraft platforms subject to uncertainties inherent in on-orbit operation. This paper is an initial investigation into adaptive control strategies and algorithms that may have application to isolation on spacecraft platforms. Analysis of the algorithms, numerical simulation, and laboratory test data are used to evaluate adaptive feedforward control. Of particular interest are the performance characteristics and limitations of the filtered-x LMS (FXLMS) algorithm. The Augmented Error algorithm and combination feedback/feedforward control are two means investigated to extend the capabilities of FXLMS by desensitizing the algorithm to the specific dynamics of the plant. Several experiments were conducted on a laboratory testbed which serves as the prototype for a planned active vibration isolation flight demonstration.
TopEugene R. Fosness
Air Force Phillips Laboratory
Kirtland AFB, NM
Presented at SPIE Conference, San Diego, CA, March 1997
ABSTRACT
A spacecraft is subjected to very large dynamic forces from its launch vehicle during its ascent into orbit. These large forces place stringent design requirements on the spacecraft and its components to assure that the trip to orbit will be survived. The severe launch environment accounts for much of the expense of designing, qualifying, and testing satellite components. Reduction of launch loads would allow more sensitive equipment to be included in missions, reduce risk of equipment or component failure, and possibly allow more sensitive equipment to be included in missions, reduce risk of equipment or component failure, and possibly allow the mass of the spacecraft bus to be reduced. These benefits apply to military as well as commercial satellites. This paper reports the design and testing of a prototype whole-spacecraft isolation system which will replace current payload attach fittings, is passive-only in nature, and provides lateral isolation to a spacecraft which is mounted on it. This isolation system is being designed for a medium launch vehicle and a 6500 lb spacecraft, but th eisolation technology is applicable to practically all launch vehicles and spacecraft, small and large. The feasibility of such a system on a small launch vehicle has been demonstrated with a system-level analysis which shows great improvements. The isolator significantly reduces the launch loads seen by the spacecraft. Follow-on contracts will produce isolating payload attach fittings for commercial and government launches.
TopAndrew S. Bicos
McDonnell Douglas Aerospace
Huntington Beach, CA
L. Porter Davis
Honeywell Satellite Systems
Glendale, AZ
Presented at SPIE Conference, San Diego, CA, March 1997
ABSTRACT
Spacecraft designs are driven by the necessity of the spacecraft to survive being launched into orbit. This launch environment consists of structure-borne vibrations transmitted to the payload through the payload attach fitting (PAF) and acoustic excitation. Here we present a discussion on the need for and benefit of isolating the structure-borne vibrations. If the PAF were replaced with an isolator with the correct characteristics the potential benefits would be significant. These benefits include reduced spacecraft structural weight and cost, as well as increased life and reliability. This paper will present an overview of the problem of vibration on a launch vehicle payload and the benefits that an isolating PAF would provide. The structure-borne vibrations experienced by a spacecraft during launch are made up of transient, shock, and periodic oscillations originating in the engines, pyrotechnic separation systems, and from aerodynamic loading. Any isolation system used by the launch vehicle must satisfy critical launch vehicle constraints on weight, cost, and rattle space. A discussion of these points is presented from the perspective of both a launch vehicle manufacturer and a spacecraft manufacturer/user.
TopDonald L. Edberg
McDonnell Douglas
Huntington Beach, CA
L. Porter Davis
Honeywell Satellite Systems Operation
Phoenix, AZ
Eugene R. Fosness
U.S.A.F. Phillips Laboratory
Albuquerque, NM
Presented at SPIE Conference, San Diego, CA, March 1997
ABSTRACT
The U.S. Air Force's Phillips Laboratory has sponsored several programs to isolate payloads from mechanical vibrations during launch. This paper details a program called LVIS (for Launch Vibration Isolation System). LVIS' goals are to reduce the RMS accelerations felt by an isolated payload by a factor of 5 compared to an unisolated payload while using minimal launch vehicle services, fitting within existing payload attach fittings' dimension and mass envelopes and providing fail-safe operation.
The LVIS system must provide axial isolation while at the same time not allowing its host spacecraft to "rattle" too much and make contact with the launch vehicle's external payload fairing, which is present to protect against heat aerodynamic, and acoustic loads. This challenging set of goals will be accomplished using an innovative suspension system specially designed to be relatively soft in the vertical and lateral directions and stiff in the rotational directions to prevent payload fairing contact. An overview of the LVIS design and predicted performance is given. TopLynn C. Rogers, Joseph R. Maly
CSA Engineering, Inc.
Palo Alto, CA
Ian R. Searle,
Roy Ikegami, Wes Owen
Boeing Defense/& Space Group
Robert W. Gordon, David Conley
US Air Force/Wright Lab/FIB; WPAFB, OH 45433
Presented at The First Joint DoD/FAA/NASA Conference on Aging Aircraft
ABSTRACT
The Durability Patch Program addresses the repair and life enhancement of nuisance cracks which have been induced into secondary structure by resonant high cycle fatigue from aerovibroacoustics. For this type of damage, safety of flight concerns are virtually non-existant, but maintenance and repair costs are high. Conventional repair techniques consist of mechanically fastened, single sided doublers. For significant static in-plane loads and/or for significant vibration levels due to out-of-plane dynamic loads, the repair does not last long because new cracks will form and emanate from the repair. Eventually, large areas of skin and substructure will have to be replaced. The Durability Patch consists of a bonded pair region which is an elastic elliptical laminate overlaid by and surrounded by a thoroughly integrated damping treatment. In some configurations the transition from the elastic repair region to the damping region is accomplished by the use of a viscoelastic material instead of a structural adhesive in one layer; thus, the other layers are multi-functional. The bonded repair does not introduce stress concentrations, does reduce static and dynamic stresses, and does reduce crack tip stress intensities. The damping further reduces dynamic stresses and stress intensities. Damping is maximized within thickness and area constraints in order to enhance the life of adjoining structure with undetected damage. The life improvement goal is 600x. Finite element analysis results comparing static and vibratory stresses will be presented. High cycle fatigue and crack growth rates will be compared. The design and use of a miniature autonomous damage dosimeter to obtain service temperature and vibration environmental data at low cost will be described. Selection of structural materials and processes to attain a goal of field installation will be described. Comparison of analysis and laboratory results will be presented. Dpatch configurations will be described and compared using a numerical measure of merit system.
David A. Kienholz
CSA Engineering, Inc.
Palo Alto, CA
19th Space Simulation Conference, Baltimore, MD, October 1996
ABSTRACT
Simulation of unconstrained (free-free) boundary conditions is a longstanding problem in ground vibration testing of spacecraft. The test article weight must be supported without introducing constraining forces due to stiffness, inertia, or friction from the suspension system. High-fidelity simulation of the space environment requires that such constraint forces be kept small compared to forces inherent in the experiment. A multipoint, six degree of freedom suspension system for dynamic testing is described. Intended primarily for highly flexible space structures, it uses a combination of passive pneumatic and active electromagnetic subsystems. The suspension offers a wide payload range, near-zero stiffness, zero static deflection, small added mass, and zero friction. The electromagnetic system can also provide active cancellation of added mass, accurate ride-height control, and integrated disturbance input. Several versions of the system are described, aimed at test articles ranging from very flexible solar arrays to a 7000-lb simulated optical truss. The concept and hardware are described, test results are given, and applications experience from several industry, government, and university installations is discussed.
Eugene R. Fosness
Air Force Phillips Laboratory, PL/VTVD
3550 Aberdeen Ave. SE
Kirtland AFB, NM
Paul S. Wilke, Conor D. Johnson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Presented at the Fifth International Conference on Space, Vol. 2, ASCE Engineering, Construction, and Operations in Space V, June 1996, Albuquerque, NM
ABSTRACT
One of the most severe environments that a satellite will be subjected to during its lifetime will occur during qualification testing and launch. This paper summarizes the results and status of research efforts in the area of satellite isolation from the launch environment. The objective of this effort was to reduce the launch induced-dynamic acceleration of the satellite by insertion of a passive isolator. Isolation issues involving the use of passive elements and launch vehicle system-level requirements will be discussed.
Paul S. Wilke, Conor D. Johnson
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Proceedings from the ASCE Engineering Mechanics Conference, Fort Lauderdale, Florida, May 1996.
ABSTRACT
One of the most severe environment that a satellite will be subjected to during its lifetime will occur during launch. This paper summarizes the results and status of research efforts in the area of satellite isolation from the launch environment. The objective of this effort was to reduce the launch-induced dynamic acceleration of the satellite by insertion of an isolator. Isolation issues involving the use of passive elements and launch vehicle system-level requirements will be discussed.
Donald J. Leo
CSA Engineering, Inc.
Palo Alto, CA
Daniel J. Inman
Dept. of Engineering Science
and Mechanics
Presented at the Virginia Polytechnic Institute and State University
Blacksburg, VA
Presented at the SPIE Conference on Smart Structures & Materials, San Diego, Feb. 96
ABSTRACT
Smart material systems enable near collocation of sensors and actuators for controlled structures. Distributed sensors and actuators, placed in close priximity to one another, yield high bandwidth control systems that exhibit passivity characteristics that can be exploited in the design of robust structural control laws. Transfer function properties of Single-Input-Single-Output (SISO) systems with collocated sensors and actuators are well understood. In this paper, analogies between the SISO case and Multiple-Input-Multiple-Output systems with collocated sensors and actuators are developed. The analogies are based on the eigenproperties of complex symmetric matrices; namely, that the eigenvectors of complex symmetric matrices are orthogonal to their simple transpose, and that the eigenvalues of complex symmetric matrices are bounded by the definiteness of their real and imaginary components. These theorems are derived and applied to the analysis and control of nongyroscopic, noncirculatory mechanical ystems. Transfer matrics of mechanical systems with collocated sensors and actuators are shown to be complex symmetric matrices whose eigenproperties are determined by the type of collocated feedback. These properties are derived for both the general damping case and for the case of modal dmaping. An optimal control technique based on the eigenproperties of complex symmetric systems is developed. The technique is a constrained convex optimization program that can incorporate many different types of performance and constraint specifications. The technique is derived in the paper and a design example is included.
Bradley R. Allen
CSA Engineering, Inc.
Palo Alto, CA
Presented at the SPIE Conference on Smart Structures & Materials, San Diego, Feb. 96
ABSTRACT
A test system designed specifically to acquire the complex moduli of viscoelastic materials in shear is described. Unique and innovative approaches in the mechanical design, temperature control system, and data acquisition methods provide a standard of accuracy that is rarely seen in dynamic mechanical properties of viscoelastic materials. The system operates on the principle of direct complex stiffness measurements. Unique sensors, hardware layout, and data acquisition and reduction methods maximize the frequency bandwidth and the dynamic range of stiffness, data acquisition speed, and temperature uniformity. Forced liquid convection temperature control also provides unparalleled speed and uniformity in specimen temperatures. Results are demonstrated and scrutinized using characterization software. Characterized data are stored in a database that provides the designer with the capability of searching based on the mechanical parameters commonly needed for damping designs. The end product is an end-to-end system capable of superior data accuracy and acquisition rates, and software that enables the most critical evaluation of results and ready storage in a manner that is efficient for damping design applications.
David A. Kienholz, Christian A. Smith
CSA Engineering, Inc.
Palo Alto, CA
William B. Haile
Swales and Associates
Beltsville, MD
Presented at the SPIE Conference on Smart Structures & Materials, San Diego, Feb. 96
ABSTRACT
A new vibration isolation system for a Space Shuttle payload is described. Designed for a large optical instrument to be launched aboard the next Hubble Telescope servicing mission, the system uses a set of eight telescoping struts to mount the payload to a shuttle pallet. Each strut is a combination of a titanium coil spring and a passive damper. The latter dissipates energy through eddy currents induced in a conductor moving in a DC magnetic field. The result is a simple, robust, all-metal isolation mount that is linear over a long stroke, relatively insensitive to temperature, and contains no fluids. Design of the system is described and strut-level test results are given along with predictions for system-level isolation under flight loads.
Eric H. Anderson, Donald J. Leo, Mark D. Holcomb
CSA Engineering, Inc.
Palo Alto, CA
Presented at the 19th Annual AAS Guidance and Control Conference, Breckenridge, CO, February 7-11, 1996
ABSTRACT
This paper describes the development of a system designed to provide a stable, vibration-isolated platform for spacecraft sensors and instruments. The UltraQuiet Platform if made up of three subsystems: a six-strut, six-axis passive-active vibration isolation mount, a damped support bench, and specialized vibration isolation mounts which reduce transmission of narrowband vibration from individual noisy components on the quiet platform. this paper emphasizes the six-axis Stewart platform active isolation system, which uses a novel series approach to active-passive isolation within each strut. the stiff electromagnetic actuator and geophone velocity sensors in the struts are described. Control design and active vibration isolation performance are summarized. Vibration reduction of up to 20 dB was demonstrated over a 100 Hz bandwidth. The change in isolation performance which resulted when the system was mated with a highly flexible base structure in noted.
Eric H. Anderson, Donald J. Leo, Mark D. Holcomb
CSA Engineering, Inc.
Palo Alto, CA
Presented at the SPIE Conference on Smart Structures & Materials, San Diego, Feb. 1996
Paper No. 436/SPIE Vol. 2717
ABSTRACT
This paper describes an active/passive system designed to provide a stable, isolated platform for vibration-sensitive equipment. The UltraQuiet Platform includes three subsystems: a six-strut, six-axis passive-active vibration isolation mount, a damped support bench, and specialized vibration isolation mounts which reduce transmission of narrowband vibration from individual noisy components on the quiet platform. This paper emphasizes the six-axis Stewart platform active isolation system, which uses a novel series approach to active-passive isolation within each strut. The stiff electromagnetic actuator and geophone velocity sensors in the struts are described. Control design and active vibration isolation performance are summarized. Vibration reduction of up to 20 dB was demonstrated over a 100 Hz bandwidth. Reduction in isolation performance which resulted when the system was mated with a highly flexible base structure is noted.
Joseph R. Maly, Conor D. Johnson
CSA Engineering, Inc.
Palo Alto, CA
Presented at the SPIE Conference on Smart Structures & Materials, San Diego, Feb. 1996
ABSTRACT
Conventional composite materials have high stiffness-to-weight ratios but exhibit little damping; many viscoelastic materials provide high levels of energy dissipation with minimal structural stiffness. The objective of this work was to combine these two material types to produce highly damped structural elements with favorable stiffness and weight characteristics. Cocuring refers to the inclusion of one or more layers of viscoelastic damping material sandwiched between composite plies prior to curing of the composite. Cocured viscoelastic/composite layups were studied experimentally at the material level, modeled analytically, and used to build optimized damped structural components. Measured cocured material properties were used in finite element models to design damped components which were built and tested individually and as part of a truss test structure. Load-carrying and highly damped struts and panels were fabricated. The curing process modified the viscoelastic behavior to some degree, but the materials retained significant, and predictable, damping capability.
Joseph R. Maly
CSA Engineering, Inc.
Palo Alto, CA
Thomas A. Butler
Los Alamos National Laboratory
Los Alamos, New Mexico
Presented at the SPIE Conference on Smart Structures & Materials, San Diego, Feb. 1996
ABSTRACT
FORTE is a small satellite being developed by Los Alamos National Laboratory (LANL) and Sandia National Laboratories Albuquerque (SNLA). It will be placed into orbit via a Pegasus launch in 1996. Testing a full-scale engineering model of the structure using the proto-qualification, system-level vibration spectrum indicated that acceleration levels caused by structural resonances exceed component levels to which certain sensitive components had previously been qualified. Viscoelastic struts were designed to reduce response levels associated with these resonances by increasing the level of damping in key structural modes of the spacecraft. Four identical shear-lap struts were fabricated and installed between the two primary equipment decks. The struts were designed using a system finite element model (FEM) of the spacecraft, a component FEM of the strut, and measured viscoelastic properties. Direct complex stiffness testing was performed to characterize the frequency- dependent behavior of the struts, and these measured properties (shear modulus and loss factor) were used to represent the struts in the spacecraft model. System-level tests were repeated with the struts installed and the response power spectral densities at critical component locations were reduced by as much as 10 dB in the frequency range of interest.
S. K. Thampi, D. N. Le
Martin Marietta Services
Houston, TX
Paul S. Wilke
CSA Engineering, Inc.
2565 Leghorn Street
Mountain View, CA
Presented at the 36th Structures, Structural Dynamics, and Materials Conference,
April 1995, New Orleans, LA
ABSTRACT
The high level vibroacoustic environment, typical for launch vehicles. Can result in excessive loads and fatigue problems for space payloads. Extensive analysis and testing requirements are imposed on the payload developer to ensure the flight worthiness of the payload element. To alleviate these requirements and reduce the long lead times involved in analytical verification, a soft ride capability was proposed for transporting experiment payloads to the Space Station. This paper presents the results of a study to determine the feasibility of using viscoelastic treatments to suppress structure borne vibrations and provide soft-ride capability. Finite element analysis and the modal strain energy method are used to design a damping treatment for an equipment drawer with a representative payload mass. The response of the damped and undamped system to simulated launch loads are determined and compared with test results. The resultsshowed good agreement and also confirmed the effectiveness of the damping treatment in controlling vibrations.
Joseph R. Maly, Warren C. Gibson
CSA Engineering, Inc.
Palo Alto, CA
Craig F. Chang
AlliedSignal Aircraft Landing Systems
South Bend, IN
SPIE Conference on Smart Structures & Materials, San Diego, 1995
ABSTRACT
A "torque tube," part of an aircraft braking system, was investigated both experimentally and analytically, as part of a larger project with the goal of developing finite element models for the prediction of aircraft brake dynamics to frequencies as high as 2 kHz. This paper presents a case history of this effort, and covers the following tasks: pre-test finite element analysis (FEA) including Guyan reduction; experiemental modal analysis (EMA) including data acquisition, parameter estimation, and development of a test-analysis model (TAM); correlation of FEA results with EMA; and tuning of the FE model. Correlation and tuning were used to improve the fidelity of the component models and hence their suitability for predicting overall response when joined together in a system model.
TopSalvatore L. Liguore, Theodor Beier
McDonnell Douglas
Aerospace
St. Louis, MO
Bradley R. Allen
CSA Engineering, Inc.
Palo Alto, CA
Michael L. Zeigler
Wright Laboratory
Dayton, OH
Smart Structures 1995
ABSTRACT
This paper describes the development of damped structure for the Supportable Technology for Affordable Fighter Structures (STAFS) Program. The study started with analytical design trade studies and progressed through a series of tests to characterize adhesive behavior, performance testing a a component level integrally damped panel concept, and full scale design integration. Analyses were performed on finite element panel models with viscoelastic elements in the bond areas to determine the sensitivities of configuration and adhesive type to overall damping achieved. The concepts studied showed that as much as 10 percent fabricated using super plastically formed-adhesive bonded 2095 aluminum, and tested to measure the comparative response improvement in the damped panels. A substantial weight savings was realized in comparison to the monolithic metal panels which would be required to withstand the acoustic environment.
TopRobert E. Holman, Steven M. Spencer
Hughes Space Company
Los Angeles, CA
Eric M. Austin, Conor D. Johnson
CSA Engineering, Inc.
Palo Alto, CA
Smart Structures 1995
ABSTRACT
A Hughes Space Company study was unertaken to (1) acquire the analytical capability to design effective passive damping treatments and to predict the damped dynamic performance with reasonable accuracy; (2) demonstrate reasonable test and analysis agreement for both baseline and damped baseline hardware; and (3) achieve a 75% reduction in peak transmissibility and 50% reduction in RMS random vibration response. Hughes Space Company teamed with CSA Engineering to learn how to apply passive damping technology to their products successfully in a cost-effective manner.
Existing hardware was selected for the demonstration because (1) previous designs were lightly damped and had difficulty in vibration test; (2) multiple damping concepts could be investigated; (3) the finite element model, hardware, and test fixture would be available; and (4) damping devices could be easily implemented.
Bracket, strut, and sandwich panel damping treatments that met the performance goals were developed by analysis. The baseline, baseline with damped bracket, and baseline with damped strut designs were built and tested. The test results were in reasonable agreement with the anlytical predictions and demonstrated that the desire reduction in dynamic response could be achieved. Having successfully demonstrated this approach, it can be used with confidence for future designs as a means for reducing weight and enhancing reliability.
TopTheodore J. Norbut
Advanced Propulsion Division
Wright-Patterson AFB, OH
Jeffrey A. Pearce
Universal Technology Corporation
Dayton, OH
Timothy R. Knowles
Energy Science Laboratories, Inc.
San Diego, CA
Joseph K.
Weeks
Technical Research Associates, Inc.
Salt Lake City,
Utah
Jatin C. Parekh
CSA Engineering, Inc.
Palo Alto,
CA
JANNAS Propulsion and Subcommittee Joint Meetings
Tampa,
Florida, December 1995
ABSTRACT
With the emergence of high temperature coatings capable of protecting carbon-carbon (C/C) from oxidation attack, C/C's prospects as a material for high speed propulsion applications are improving. However, the results of applications research undertaken under the NASP program over the past seven years have revealed other limitations accompanying the application of this material in the thermo-structural design of advanced fuel cooled panels. Of particular concern are through-thickness thermal conductivityy, interlaminar tensile and shear strength, porosity effects, and heat transfer at joints between C/C and candidate metallic tubing materials. Alternative approaches to overcome these limitations were sought and developed under the auspices of the Air Force Small Business Innovative Research (SBIR) program and two separate concepts were developed. The first concept involved the development of specialized carbon tubing incorporating flock, small carbon fibers oriented normal to the tube wall, to enhance radial heat transfer. The second concept involved treating a carbon-carbon (C/C) perform to allow wetting of the preform by molten copper. Refractory metal tubes could then effectively be brazed into holes drilled in the C/C preform with high conductivity copper. This paper summarizes the key limitations, describes two concepts by which the limitations can be overcome, and gives the results of an analytical performance assessment performed on each of the heat exchanger concepts.
TopConor D. Johnson
CSA Engineering, Inc.
Palo Alto, CA
Contributed by the Design Engineering Division for publication in the Special
50th Anniversary
Design Issue, June 1995
ABSTRACT
This paper presents a brief review of technicques for designed-in passive damping for vibration control. Designed-in passive damping for structures is usually based on one of four damping technologies: viscoelastic materials, viscous fluids, magnetics, or passive piezoelectrics. These methods are discussed and compared. The technology of using viscoelastic materials for passive damping is discussed in more detail than the other methods since it is presently the most widely used type of damping technology. Testing and characterization of viscoelastic materials and design methods for passive damping are discussed. An example showing the benefits of a passive damping treatment applied to a stiffened panel under an acoustic load presented.
TopChristian A. Smith, Eric H. Anderson
CSA Engineering, Inc.
Palo Alto, CA
SPIE Conference on Smart Structures & Materials, San Diego, March 1995
Paper No. 136/SPIE
Vol. 2445
ABSTRACT
This paper examines the use of smart materials for passive damping. Among the smart materials considered are electrorheological and magnetorheological (ER and MR) fluids, piezoelectrics, electrostrictives, magnetostrictives, and shape memory alloys. The specific mechanism exploited for energy dissipation by passive or semi-passive means is described for each material. A distinction is made between internal and external energy dissipation. The external stimuli required for each of the semi-passive mechanisms are noted. Selected examples of damping results with each material are provided. Practical limitations for engineering design and implementation are considered, and recommendations are made for the more promising materials.
TopPaul S. Wilke
CSA Engineering, Inc.
Palo Alto, CA
S. K. Thampi
Martin Marietta Services
Houston, TX
SPIE Conference, San Diego, CA, February 1995
ABSTRACT
Experiments performed aboard the space shuttle often utilize sensitive scientific equipment which cannot withstand high launch loads without damage. It would be highly advantageous to reduce the severity of the dynamic launch environment so that space-qualification of such equipment would be faster and less expensive. This is the goal of the Soft Ride to Orbit program. This program has identified passive damping as one technology which will reduce loads seen by equipment and thereby provide a softer ride. Finite element structural modeling was used to predict both undamped and damped responses to simulated launch loads. The modal strain energy method was used to design the passive damping treatment. This treatment was manufactured and applied to the drawer. All analyses were verified by modal and vibration testing. It was found that predicted and tested frequencies, damping values, and vibration response levels agreed reasonably well, thus showing that passive damping may be designed into future equipment drawers to reduce launch loads on sensitive equipment.
TopWarren C. Gibson, Christian A. Smith
CSA Engineering, Inc.
Palo Alto, CA
Donald J. McTavish
Dynacon Enterprises Ltd.
Downsview, Ontario, Canada
SPIE Conference, San Diego, CA, February 1995
ABSTRACT
Representation of frequency-dependent viscoelastic material properties has long been problematical in the frequency domain and especially in the time domain. The method of Golla, Hughes, and McTavish (GHM) addresses this problem with a Laplace-domain model of the complex material modulus, in which a number of parameters are determined by curve-fitting to experimental data. The result is well suited to finite element formulations because the equations of motion retain the familiar second-order, constant-coefficient form, at the expense of some extra scalar degrees of freedom. This paper reports on an implementation of GHM in MATLAB, using FEM data imported from NASTRAN. Sample problem demonstrate the efficacy and practicality of the method.
TopPaul S. Wilke
CSA Engineering, Inc.
Palo Alto, CA
T.A. Decker, L.C. Hale
Lawrence Livermore National Laboratory
Livermore, CA
SPIE Conference, San Diego, CA, February 1995
ABSTRACT
Instruments and machines requiring very high stability should be isolated from their normally less stable environment. Exact constraint mounting using six, single-constraint flexures provides a stiff connection between the instrument and its environment while isolating the instrument from low frequency deformations of the environment, such as thermal expansion. Higher frequency disturbances, however, transfer through the flexures and excite vibration modes of the instrument. Traditionally, passive or active vibration isolation is employed to attenuate environmental disburbances reaching the instrument. However, strict alignment requirements for the instrument preclude the use of low-frequency isolation, unless active methods are used. Therefore, the solution is to provide damping in parallel with the flexures to reduce the vibration amplitudes of the instrument. Flexures concentrate strain energy in blades making them excellent candidates for damping treatments. A properly-designed damping treatment across the flexures can provide as much as 8% to 10% viscous damping to the isolation modes and will also help attenuate the instrument vibration modes. Thus, through the use of six damped single-constraint flexures the instrument's requirements for stability, alignment, stress, and vibration may be met.
An application of this approach will be employed on the Reflection Grating Array (RGA) for the X-ray Multi-mirror Mission for the European Space Agency. The RGA is an array of 200 diffraction gratings aligned to sub-micron and sub-arc-second tolerances relative to each other. This produces a coherent wavefront for spectrum analysis. The launch vehicle will be an Ariane 5 scheduled for 1998.
TopEric H. Anderson
CSA Engineering, Inc.
Palo Alto, CA
SEM Micro-Integrated Smart Materials and Structures Conference, Williamsburg, VA, Oct. 1995
ABSTRACT
Active control of physical systems requires sensing, actuation, and a control system connecting the two. Physical integration of the electromechanical components which perform these functions has the potential to reduce the total size, weight, and cost of active systems. Smart materials are well-suited to integration in certain active vibration suppression systems. An intermediate or mesoscale is suggested as the appropriate level for integration leading to near-term development of vibration suppression devices incorporating peizoelectric transducers. Five main areas -- actuation, sensing, power amplification, signal conditioning, and control -- are needed for an integrated system. The implications of combining each function with the four others are addressed. Actuation is shown to be the main driver for an integrated device. The paper concludes by referring to an ongoing product development which has created a device incorporating all five functions.
TopEric H. Anderson
CSA Engineering, Inc.
Palo Alto, CA
15th Biennial Conference on Vibration and Noise, Boston, MA, September 17-21, 1995
ABSTRACT
This paper develops analogies between discrete devices that achieve damping by active and passive means. It describes the simplest models useful for inclusion in larger system design. Lumped-parameter models for representing passive dampers are given, and the similarity to local active feedback is shown. A model for active damper components containing piezoelectrics or similar materials is developed for force feedback compensation. This system is similar to the passive damper model when its parameters are allowed to vary. An active damper with direct feedback of the integral of measured force is represented by a model containing a single spring and a gain-dependent dashpot. Further aspects of the active damper are illustrated using a one-mode model of a vibrating structure. The effects of a feedforward modification to the system, and the analogy to changes in passive parameters, are illustrated by tracking the locus of the closed loop system poles with feedback gain.
TopDonald J. Leo and Eric H. Anderson
CSA Engineering, Inc.
Palo Alto, CA
ASME International Mechanical Engineering Conference and Exhibition,
Symposium on Adaptive Structures,
San Francisco, CA, November 1995
ABSTRACT
This paper compares two mechanical architectures useful for active vibration isolation and discusses factors which limit performance in each case. Nondimensional equations of motion for two types of single-axis isolators are developed. Parallel and series active-passive combinations are considered. Isolator models are mated to six degree-of-freedom representations of rigid body payload dynamics. Multiaxis isolator transmissibilities and open loop transfer functions are examined for each case. The impact of actuator/sensor dynamics and reduced-order control on the achievable performance is studied. Additional dynamics, such as sensor signal conditioning and phase lag due to controller discretization, introduce constraints on the isolator design and further limit the achievable performance. The effects of sensor noise and controller simplification are demonstrated on a model of a three-axis isolation system.
TopJoseph R. Maly, Warren C. Gibson
CSA Engineering, Inc.
Palo Alto, CA
Craig F. Chang
Allied Signal Aircraft Landing Systems
South Bend, IN
October 1994
ABSTRACT
A ``torque tube,'' part of an aircraft braking system, was investigated both experimentally and analytically, as part of a larger project with the goal of developing finite element models for the prediction of aircraft brake dynamics to frequencies as high as 2 kHz. This paper presents a case history of this effort, and covers the following tasks: pre-test finite element analysis (FEA) including Guyan reduction; experimental modal analysis (EMA) including data acquisition, parameter estimation, and development of a test-analysis model (TAM); correlation of FEA results with EMA; and tuning of the FE model. Correlation and tuning were used to improve the fidelity of the component models and hence their suitability for predicting overqll response when joined together in a system model.
TopWarren C. Gibson
Christian A. Smith
CSA Engineering, Inc.
Palo Alto, CA
Donald J. McTavish
Dynacon Enterprises Ltd.
Downsview, Ontario, Canada
SPIE Conference on Smart Structures & Materials, Orlando, FLA, Feb. 1994
ABSTRACT
Representation of frequency-dependent viscoelastic material properties has long been problematical in the frequency domain and especially inthe time domain. The method of Golla, Hughes, and McTavish (GRM) addresses this problem with a Laplace-domain model of the complex material modulus, in which a number of parameters are determined by curve-fitting to experiemental data. The result is well suited to finite element formulations because the equations of motion retain the familiar second-order, constant-coefficent form, at the expense of some extra scalar degrees of freedom. This paper reports on an implementation of GHM in MATLAB, using FEM data imported from NASTRAN. Sample problems demonstate the efficacy and practiality of the method.
TopDavid A. Kienholz
CSA Engineering, Inc.
Palo Alto, CA
12th Int'l Modal Analysis Conference, Honolulu, Hawaii, Jan. 31-Feb. 3, 1994
ABSTRACT
A multipoint suspension system is described for supporting test articles such that their unconstrained modal properties will not be altered by stiffness, inertia, or friction forces from the suspension. Intended primarily for flexible space structures, it is suitable for test items with natural frequencies as low as one Hz. Using a combination of passive pneumatic and active electromagnetic subsystems, the suspension offers a wide payload range, near-zero stiffness, zero static deflection, small added mass, and zero friction. The electromagnetic system can also provide active cancellation of added mass, accurate ride-height control, and controlled disturbance input. The concept and hardware are described, test results are given, and applications experience from several installations is discussed. Current development efforts are described, aimed at testing of payloads such as solar arrays and large beam-pointing experiments.
TopDavid A. Kienholz, Scott C. Pendleton
CSA Engineering, Inc.
Palo Alto, CA
Kenneth E. Richards, Jr., Daniel R. Morgenthaler
Martin Marietta Astronautics
Denver, CO
SPIE Conference on Smart Structures & Materials, Orlando, FLA, Feb. 1994
ABSTRACT
An adaptive passive damping system is described for the low-order modes of spacecraft large solar arrays. The work is motivated by the stringent sensor pointing requirements of several current satellite programs. Realistic system-level requirements are developed relating pointing error of a representative spacecraft to damping of its solar arrays. Performance is specified in terms of gain envelopes on open-loop frequency response functions for the structure with dampers. A family of remotely tunable, eddy-current tuned mass dampers (TMDs) is described which suppress several modes of a 430-lb solar array simulator in the frequency range of 0.1-1.0 Hz. The magnetic dampers are ground demonstration units, suitable for use in 1-G, but are designed around traceable, system-level dynamic requirements. The damper design is intended from the outset to be evolved into flight hardware. Tuning to TMD natural frequency and damping ratio to their optimum values is demonstrated through component-level base transmissibility test results. System-level tests using the solar array simulator demonstrate that resonant peaks for two target modes are reduced by 25-30 dB using an array of three dampers, each with a moving mass of about four pounds. Future work towards flight hardware is described.
TopPaul S. Wilke
Lockheed Missles & Space Company, Inc.
1111 Lockheed Way
Sunnyvale, CA
Presented at the 11th International Modal Analysis Conference, Vol. 1, pgs 77-80,
February 1993, Kissimmee, Florida
ABSTRACT
This paper presents the results of the correlation between the finite element modal test data for the SPace Integrated Control Experiment (SPICE) truss structure. For structural control experiments such as SPICE, the control system requires accurate knowledge of a large number of modes, thereby placing a greater demand on the modal test and on the fidelity of the finite element model. Excellent correlation results were obtained as demonstrated in the test-to-analysis orthogonality matrix, which was within 95% on the diagonal and 10% for off diagonals covering the first 25 modes over 60-Hz frequency bandwidth. Incremental model improvements were performed with the aid of design sensitivities and optimization. Component level testing, pretest analysis, and close analysis/test engineering collaboration were the keys to this success.
TopWarren C. Gibson, Eric M. Austin
CSA Engineering, Inc.
Palo Alto, CA
Finite Elements in Analysis and Design, [ISBN #: 0168-874X], Vol. 14
pp. 337-351, Elsevier Science Publishers,
1993
ABSTRACT
Damping can be one of the more perplexing aspects of structural dynamics becuase it is much less intuitive and 'clean-cut' than concepts like stiffness and mass. Nevertheless, analysts should not view damping simply as an unfortunate side issue in structural dynamics, but as an opportunity for creative design work aimed at suppression of unwanted vibrations. This paper presents a review of some basic concepts in damping and how damping is treated in finite element analysis. It also presents some new techniques that have been developed to support optimization of damping for structures.
TopDavid A. Kienholz
CSA Engineering, Inc.
Palo Alto, CA
Paper prepared for Sandia National Laboratories, May 1993
ABSTRACT
Helium-filled balloons are sometimes used as suspension devices to simulate zero-gravity in dynamic testing of space structures. This application note compares the performance of balloons with that of the CSA pneumatic-magnetic suspension devices in terms of mass added to the test article by the suspension. Such added mass degrades the fidelity of the zero-G simulation by changing the normal modes of the payload.
TopJoseph R. Maly, David A. Kienholz
CSA Engineering, Inc.
Palo Alto, CA
39th International Instrumentation Symposium, Aerospace Industries and Measurement Division, Instrument Society of America, Albuquerque, NM, May 1993
ABSTRACT
Dynamic pressure measurements are made in all phases of testing, qualification, and production of turbine engine and rocket propulsion systems. These measurements require use of various sensors, including complex transducer/tubing configurations. Analytical estimates of measurement system frequency response need to be verified experimentally, and to ensure measurement reliability, frequent transducer calibrations are required. Excitation devices used for frequency response characterizations are limited in ultimate peak pressure, bandwidth, and accuracy.
In response to the need for an improved calibrator, a system has been developed for pressure levels ranging to 1.0 psi over the bandwidth of 2-2500 Hz. A prototype calibrator was built that is capable of achieving accurate and controlled pressure for several sensor configurations, including flush-mounted, rake, and tube-type. Controlled pressure can be provided, in sine or random waveform, to a reference transducer and a transducer under test. For the frequency bands of 2-150 Hz and 1600-2400 Hz, acoustic pressure levels of 1.0 psi RMS can be attained.
The application to acoustic-mechanical systems of a hybrid modeling technique known as admittance modeling is demonstrated. The technique combines test results with finite element analysis; here it is applied for a system with an acoustic pressure source driving various acoustic cavities.
TopWarren C. Gibson, Kevin L. Napolitano, Bradley Allen
CSA Engineering, Inc.
Mountain View, CA
Roger E. Scholl
CounterQuake Corporation
Redwood City, CA
Damping '93, San Francisco, CA, February 1993
ABSTRACT
Viscoelastic materials have been used successfully to reduce building deformations due to wind. Research has also indicated their suitability for counteracting small to moderate earthquake motions. Viscoelastic solutions are attractive in several ways. A completely passive solution is obviously desirable for earthquake dampers since power can't be relied on. Another advantage is that they work over moderately wide frequency ranges, unlike tuned devices.
The large motions and forces associated with severe earthquake pose a serious problem. Large blocks of viscoelastic are needed to provide large forces. If the consequent heat isn't dissipated fast enough, the temperature may rise far enough that the material begins to lose stiffness and ceases ro provide the required damping forces.
TopKevin L. Napolitano, Conor D. Johnson
CSA Engineering, Inc.
Palo Alto, CA
John B. Andriulli
Oak Ridge National Laboratory
Oak Ridge, TN
Damping '93, San Francisco, CA, February 1993
ABSTRACT
Many space vehicles under consideration at the present time will contain sensors whose performance is affected by vibrations. One commom solution to vibration problems is to increase passive damping levels. A viscoelastically-damped thermoplastic box-platform representing a primary structural component with sensors was designed, built, and tested to demonstrate the feasibility of using advanced materials to both save weight and reduce the vibrations environment. The resulting structure was lighter in weight, stiffer, and achieved over an order-of-magnitude increase in passive damping when compared to a baseline aluminum structure.
TopBryce Fowler
CSA Engineering, Inc.
Palo Alto, CA
Dr. Lynn Rogers
Oak Ridge National Laboratory
Jamestown, OH
Damping '93, San Francisco, CA, February 1993
ABSTRACT
An approach to successfully characterize a wide range of viscoelastic material data is discussed. Computer programs that implement the characterization process and allow the database storage and retrieval of materials based on dynamic properties are also discussed.
TopJoseph R. Maly, Kevin L. Napolitano
CSA Engineering, Inc.
Palo Alto, CA
Damping '93, San Francisco, CA, February 1993
ABSTRACT
Vibrations are an inherent problem for aircraft structures, especially military aircraft that perform high-speed maneuvers causing extreme acceleration levels. A form of unwanted vibration called buffet occurs when an aircraft surface is directly exposed to an unsteady, vortex flow generated upstream during high-angle-of-attack maneuvers. In the case of the F/A-18 aircraft, buffeting of the twin vertical stabilizers excites the bending and torsional modes of these structures, and, over time, fatigue failures occur. Failures of this nature are unpredictable and result in millions of dollars every year in maintenance costs.
A tuned mass damper solution for this problem is proposed. Analysis indicates that an array of dampers employing eddy currents induced by rare earth magnets for the damping mechanism will provide sufficient damping to significantly reduce the dynamic response of the twin-vertical-tail buffet. A prototype damper was built, and it was determined by testing that this concept is a valid approach to solve this problem. The prototype was tested on a simple structure, selected so that the mass ratio with the prototype applied to the structure is equal to the mass ratio of the TMD array applied to the F/A-18 tail. The amplitude of the undamped response was reduced by a factor of 20 when the magnetic TMD was applied.
TopWarren C. Gibson, Eric M. Austin
CSA Engineering, Inc.
Palo Alto, CA
MSC World Users' Conference, Deerborn, Michigan, May 18-22, 1992
ABSTRACT
Damping can be one of the more perplexing aspects of structural dynamics because it is much less intuitive and ``clean-cut'' than concepts like stiffness and mass. Nevertheless, analysts should not view damping simply as an unfortunate side issue in structural dynamics, but as an opportunity for creative design work aimed at suppression of unwanted vibrations. This paper presents a review of some basic concepts in damping and how damping is treated in finite element analysis. It also presents some new techniques that have been developed to support optimization of damping for structures.
TopEric M. Austin
CSA Engineering, Inc.
Palo Alto, CA
James C. Goodding
CSA Engineering, Inc.
Palo Alto, CA
63rd Annual Shock and Vibration Symposium, November 1992
ABSTRACT
Passive damping hardware has been fabricated, installed, and tested on a large optical system required to meet a stringent RMS specification for closed-loop residual jitter due to ground and coolant flow excitations. Over the course of the study, constrained layer treatments, tuned-mass dampers, and link dampers were analyzed. It was shown through analysis that one type of treatment alone was not sufficient to solve the problem due to the number of harmful modes spread over a relatively wide frequency range. The final solution incorporated constrained layer damping treatments on an interface component between the mirrors and their mounts, link dampers between selected locations on the optical bench, and constrained layer treatments on some mirror support plates. Tests were performed before and after the application of the damping hardware to demonstrate its effectiveness and applicability to this class of problem. The primary focus of this paper is the dynamic testing of the optical system and design, fabrication, installation, and qualification of the passive damping hardware.
TopEric A. Austin, James C. Goodding
CSA Engineering, Inc.
Palo Alto, CA
Timothy L. Flora
Lockheed Missiles and Space Company, Inc.
Sunnyvale, CA
Damping '91, San Diego, CA, February 1991
ABSTRACT
Passive damping has been demonstrated to be an effective and efficient means for limiting the effects of on-board excitations on the dynamics of space vehicles. High-precision applications require these treatments to both be effective at very low excitation levels and not affect the dimensional stability of the structure under quasistatic and thermal-mechanical loads. This work documents a study of two important issues facing structures damped with viscoelastic materials: hysteresis and loss at low deflection levels.
The test article is an I-beam-like structure designed to simulate an experimental method of fabricating graphite-epoxy/honeycomb structures without using any mechanical fasteners. After identifying the most critical vibrational modes from a separate system-level analysis, a damping treatment was designed for the test joint using standard finite element techniques. A modal test using very low random excitation levels was performed on the resulting damped structure. Statistical methods were used to determine that the maximum displacement level of the free-free structure was of the order of nano-meters. Subsequently, hysteresis tests were performed on the same damped beam. Laser interferometry was used to measure displacements of the joint after undergoing cyclic static loads of varying magnitudes. Percent hysteresis was measured while the joint was loaded in three-point bending. Hysteresis behaviour during displacements as small as 150 nano-meters was recorded.
TopA.H. von Flotow, N.W. Hagood
Massachusetts Institute of Technology
Boston, Massachusetts
K.L. Napolitano, E.M. Austin
CSA Engineering, Inc.
Palo Alto, CA
L.P. Davis
Honeywell, Inc.
Glendale, AZ
AMAS Conference, November 4, 1991
ABSTRACT
This paper presents a comparison of three approaches for the passive damping of the ASTREX structure. Open loop performance from specified disturbances (thrusters) to specified responses (line-of-sight) is considered. A computational model is used to select important eigenmodes on the basis of their contribution to the line-of-sight weighted modal strain energy fraction. Damped replacements for these components are designed using piezoceramic, viscous, and viscoelastic damping mechanisms. The components incorporated into the model and the relative improvement in structural damping response are compared.
No subtleties are attempted. The paper does not consider either structural configuration redesign for damping or possible synergism between passive damping and active control.
TopBryce L. Fowler
CSA Engineering, Inc.
Palo Alto, CA
Damping '91, San Diego, CA, February 1991
ABSTRACT
The development and use of an interactive computer program for the characterization of complex modulus data is described. The program uses the collocation process which accurately fits the real part of the complex modulus data and then uses the lack of fit of the loss factor to adjust the temperature shift function. This iterative method, which has converged when both the real modulus and the loss factor are fit simultaneously (the real directly and the loss factor indirectly), yields the most accurate estimate of the temperature shift function possible.
TopBradley Allen
CSA Engineering, Inc.
Palo Alto, CA
David Cunningham
Honeywell Satellite Systems
Glendale, AZ
Damping '91, San Diego, CA, February 1991
ABSTRACT
It is essential that accurate methods for testing mechanical properties be employed during the development of precision spacecraft isolation systems. Mechanical properties of the isolator will determine force transmission to the spacecraft; thus they are critical to its performance. This paper documents component-level tests performed on viscous-damped isolators developed by Honeywell Satellite Systems for a spacecraft reaction wheel isolator system.
Two types of component-level tests were performed on the elements: direct stiffness measurements (often called mechanical impedance) and transmissibility tests. Direct stiffness measurements indicated linearity, linear stiffness, damping, and hysteresis. A custom test apparatus was designed for accuracy and repeatability. Stiffness deviations as small as 5 percent could be detected, and loss factors as low as 0.01 could be resolved with the direct stiffness measurements.
Motion transmissibility measurements determined high-frequency isolation and verified stiffness and damping near the predicted resonance of the sprung payload. Although the suspension system consisted of eight isolators, tests were performed on a single unit. Motion was constrained to a single degree of freedom using a system of air bearings sliding on rails. The air bearing design possessed less than 0.4 grams of friction allowing verification of isolation properties to above 300 Hz and enabled transmissibility to be accurately measured over 4 orders-of-magnitude of input excitation.
TopKevin E. Smith, Joseph R. Maly, Conor D. Johnson
CSA Engineering, Inc.
Palo Alto, CA
AMAS Conference, November 4, 1991
ABSTRACT
Passive damping using tuned-mass dampers (TMDs) is well-known, weight-efficient approach to suppress vibrations of a single mode (or a group of modes). A TMD produces a high level of damping with a small amount of added weight if kept tuned to the frequency of the offending mode. A prototype TMD that will tune itself to an offending mode has been designed, built, and tested. It can keep itself tuned to the offending mode, even if that mode changes frequency. The prototype confirmed that a "smart" TMD could be built.
TopConor D. Johnson
CSA Engineering, Inc.
Palo Alto, CA
The 30th IEEE Conference on Decision and Control, Brighton, United Kingdom, December 1991
ABSTRACT
This paper presents a brief review of techniques for designed-in passive damping for space structures. Although the main topic of the paper is passive damping using viscoelastic materials, other methods are discussed and compared. The testing and characterization of viscoelastic materisla and design methods for passive damping are discussed. An example showing the benefits of a passive damping treatment for an actual space structure is presented.
TopEric M. Austin, Conor D. Johnson
CSA Engineering, Inc.
Palo Alto, CA
Sound and Vibration, 1991
ABSTRACT
This paper presents a brief review of techniques for designed-in passive damping for noise and vibration control. Designed-in passive damping for structures is uaually based on one of four damping technologies: viscoelastic materials, viscous fluids, magnetics, or passive piezoelectrics. These methods are discussed and compared. The technology of using viscoelastic materials for passive damping is discussed in more detail than the other methods since it is presently the most applicable for surface treatments for noise control. Testing and characterization of viscoelastic materials and design methods for passive damping are discussed. An example showing the benefits of a passive damping treatment for an acoustic problem is presented.
TopWarren C. Gibson
CSA Engineering, Inc.
Palo Alto, CA
Presented on November 5, 1991
ABSTRACT
Sensitivity analysis is a key element of structural optimization and optimization-based methods of parameter identification. Sensitivities of responses to dynamic loads pose special challenges because of the volume and complexity of data in a complete frequency spectrum or time record. An efficient method for computing the sensitivity of one or more peaks in a frequency spectrum or time domain is presented. The method accounts for shifts in peak location as well as changes in peak magnitude as design variables are varied. Brief examples are included.
TopWarren C. Gibson, Conor D. Johnson
Csa Engineering, Inc.
Palo Alto, CA
ASME Vibration and Noise Conference, Boston, MA, Sept. 1987
ABSTRACT
The modal strain energy method, implemented in finite elements, is the best method for designing viscoelastic damping treatments and predicting modal damping for complex structures. This mehtod uses real normal modes and estimates damping as a function of the viscoelastic material's strain energy and its loss factor. Designs in the past have been optimized manually, i.e., by running a number of analyses and using the results of each analysis to attempt manual improvements of the design. This paper reports on an automated optimization method which couples MSC/NASTRAN with the ADS optimizer. Design parameters are computed to maximize the effectiveness of modal damping treatments while observing weight constrains, frequency constraints, and side constraints. The design parameters considered are the viscoelastic shear modulus and thickness, and constraining layer thickenss for constrained layer treatments. This optimization software speeds up the design process, and allows engineers to explore more design concepts than they migh totherwise. Examples are presented to show the effectiveness of the procedure.
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