Positive:

They do not depend on external power source for their operation.

They can respond to small level of excitation.

Their properties can be adjusted in the field.

They can also be introduced in upgrading structure.

They require low maintenance.

Negative:

A large mass or a large space is needed for installation.

The effectiveness of a TMD is constrained by the maximum weight that can be practically placed on top of the structure.

Their effectiveness depends on the accuracy of their tuning, but natural frequency of a structure cannot be predicted with great accuracy.

Read the attachment on tune mass damper.

Thank you Mr. Girish it is always a pleasure to hear from IIT's researchers.

Warm regards

Hi

I concur with the above listed points.

Perhaps we can add as general information that

• The highest Q-value you get in practice is about Q=25 and hence, the smallest weight (mass or intertia as appropriate) you can use is about (100*1/Q=) 4%of the modal weight.
• The heavier the TMD, the wider its effective bandwidth.
• A TMD can be tuned for dissipation or maximum counteraction at a point (dof). 
• TMDs exist for translation and rotation (torsion dampers).
• A Hemholtz resonator and panel resonators are acoustic versions of TMD.
• In theory, a TMD can be tuned for 6 dofs as its moving weight has 6 dofs. In practice and with skill, you might get away tuning 3 dofs. Most TMDS are tuned for a single dof. By dof is implied direction and frequency.

Sincerely

Claes

Thank you Mr. Claes Richard Fredö.

I am not agree with Mr. Fredo. The smaller mass will be more effective if you are controlling the earthquake exciations. His statment is correct in case of wind engineering only. 

If you compare TMD with other devices you will find its advantages more as compared to ... 

Said

If you run simulation, you can  have a Q of, say 10000 and at a narrow frequency interval tune a very small mass to oppose vibration.If you want to do this in real life, you need to keep things like losses from radiation, non linear spring stiffness, etc. at bay. Q = 25, maybe 30 usually is what you end up with, which sets the limit for linear maximum tuning. After all, the TMD will loose energy to the system it is acting upon, so it is difficult to get a very high Q factor.

For a Helmholtz resonator, i.e. an acoustic TMD, the theoretical limit for Q, if memory correctly serves me, is Q=28 and this limit is set by the sound radiation from the acoustic plug's oscillatory motion. A mechanical TMD can get a higher Q if it acts upon a very rigid object, but my guess is that it ends up in the ballpark Q = 25-30 for structures containing several resonance in the vicinity of the TMD resonance frequency.

However, if you use a small mass and drive it to high response, you can provoke a lock-in response, where the mass has to oppose vibration also away from its tuned resonance frequency. This counteracting force, at least at the tuned frequency, will not be as large as the linear case, but lock-in has its own merits in that the TMD follows excitation also to other frequencies.The physical mechanism underpinning lock-in is that once excited into high response, it is unable to step down in amplitude as it does not have the damping mechanisms required to do so. The situation then resembles that of so called stepping frequencies that are found in corrugated pipes.

Perhaps you are referring to such a situation?

/Claes