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Passive vibration suppression |
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Has been proven in many applications |
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Accurate design and analysis methods exist |
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Implemented by several technologies |
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If the problem can be solved passively, it will
probably be less expensive and complex than active methods |
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If active methods are required, well-designed
passive methods can greatly ease the burden of active systems |
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Viscoelastic Materials (VEM) |
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Polymers |
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Rubbers |
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Pressure sensitive adhesives |
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Urethanes |
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Epoxies |
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Enamels |
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Viscous Fluids |
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Silicone oil |
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Other oils |
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Grease |
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Shearing of viscoelastic material dissipates
vibrational energy as heat |
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Viscoelastic materials have low shear modulus
but high loss factor |
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Shear modulus 20 to 10,000 psi |
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Loss factor up to 2 or more (Measure of energy
dissipation capability) |
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Properties are both temperature |
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and frequency dependent |
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Single treatment can damp |
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relatively wide frequency range |
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Typically, these force fluid through a precision
orifice or annulus |
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Moderately sensitive to temperature |
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Effective over relatively narrow frequency
bandwidths |
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Velocity-dependent damping |
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Operating Principle |
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Eddy currents in moving conductor dissipate
energy |
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Advantages |
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True linear viscous damping |
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Almost temperature invariant |
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Common, space-qualified
materials (no fluids) |
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Large damping constant in
compact device |
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Simple, robust construction |
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Good for TMD’s, strut dampers, and isolators |
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Advantages |
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Broad useful temperature ranges |
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Not mode/frequency specific |
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Non-outgassing |
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Variety of loss methods |
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Impact (particle-particle & particle/cavity) |
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Friction (particle-particle &
particle/cavity) |
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Caveats |
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Empirical based design |
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Amplitude dependent behavior |
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Behavior is also dependent on cavity orientation
to local quasi-static acceleration field |
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Multiple other parameters can influence damping
performance |
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Resistor shunted piezoelectrics produce frequency dependent material
properties much like VEM’s |
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Resonant shunted piezoelectrics add an extra
mode to the system, just like a TMD.
However, it counters potential strain energy instead of kinetic
energy. Modal strain energy
determines optimal location |
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Constrained-Layer Treatment |
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Tuned-Mass Damper (TMD) |
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High damping for single mode |
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Small weight penalty |
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Resonant motion amplification device |
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Can be retrofit |
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Link, Strut, or Shear Strap Dampers |
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Useful for damping and shifting
troublesome
modes |
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Small weight penalty |
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Joint or Interface Dampers |
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Small weight penalty |
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Low damping |
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Design issues |
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To achieve damping, two conditions must be met: |
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Significant strain energy must be directed into
the damping mechanism |
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Energy in damping mechanism must be dissipated |
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New “rigid” arrays for HST require increased
damping to accommodate attitude control bandwidth requirements |
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Passive damper integrated into existing
composite mast |
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Provides >3.5% critical damping to first two
bending modes |
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Damping provided for on-orbit operating
temperature range |
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Magnetically damped isolation |
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system for NICMOS |
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Very long stroke (10”) |
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All metal-design, no fluids |
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Low temperature sensitivity |
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Temp. range: -40 to +65 C |
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Passive damping and isolation are very
effective, if properly designed |
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Analysis and design tools have been developed
and proven |
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Select the proper passive technology to fit the
application |
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Use active solutions only when performance
improvements warrant an active solution |
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A good passive design should be integrated into
all active solutions |
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Notes
