Tuned mass dampers (TMDs) can be an effective and practical means for reducing resonant vibration in structures. Shown schematically in Figure 1, a TMD is a modular device composed of a spring, mass, and dashpot. These three components can each be implemented in a number of different ways, as are illustrated here through examples.

A TMD is itself a single degree-of-freedom resonant system. It adds a mode of vibration to the base structure. Mounted to a rigid base, the TMD would have a natural frequency of √(k/m) and damping ratio of c/(2√(km)).

The stiffness k and mass m of the TMD are chosen to put the TMD natural frequency just below the frequency of the "target" mode of the base structure, i.e. the mode to be damped. This causes a strong dynamic interaction between the TMD and the target mode. The target mode is replaced by two modes, one slightly above and one slightly below the original frequency. Most important, both of these "split modes" will be damped by the dashpot of the TMD. In essence, the TMD attracts to itself the vibrational energy of the target mode and dissipates it into heat through the action of its dashpot.

As a solution to a vibration problem, TMDs have a number of very attractive features:

- They are inherently compact, modular devices that can have a simple interface to the base structure.

- They can be readily added to a base structure that is already designed or even built.

- A well-designed TMD can add high damping with minimal weight. Figures 2 and 3 shows the relationship. Figure 3 shows that a TMD having even 1% of the base structure weight  can produce high damping: over 5% of critical when tuned correctly.

- The TMD does not impact the static strength or stiffness of the base structure.

- For designing the TMD, it is often possible to characterize the base structure by inexpensive test or analysis. In effect, the base structure is modeled simply in terms of a single mode: the target mode.

The primary limitation of a TMD is that it is a narrow-band device. It will add high damping only to modes with natural frequencies close to its own. This means that multiple TMDs may be needed to obtain high damping of modes if the frequency range is too large.

The practical challenge in designing and implementing TMDs is usually concerned with the dashpot mechanism, i.e. the part of the TMD that produces a retarding force proportional to relative velocity and therbeby dissipates mechanical energy into heat.

Additional information is available in a paper on resonant vibration control devices.