Passive vibration absorber

When the force F is narrow band, attenuation can be achieved with a passive vibration absorber which has to be tuned to the disturbance fre-... 

Fig. 6.9. Vibration attenuation using a passive vibration absorber...

The principle structure of the active vibration absorber corresponds approximately to the structure of the passive vibration absorber shown in Fig. 6.9 whereby the passive elastic material between mi and m2 has been replaced by a piezoelectric actuator and a displacement amplification system to increase the achievable displacement of m2. The amplification system is given in this example by elastic joints, similar to those illustrated in Fig. 6.9. 

Os... 0.1 s the controller is idle, so that the vibration absorber operates passively. The maximum amplitude of the acceleration ai emerging due to the excitation by F amounts in this operating state to about 5m/s. The controller is switched on at t = 0.1 s which excites the dynamics of the whole system. 

Hunt JB (1979) Dynamic vibration absorbers. Mechanical Engineering Publications, London Ibrahim R (2008) Recent advances in nonlinear passive vibration isolators. J Sound Vib 314(3) 371-452 Ibrahim RA (2009) Vibro-impact dynamics modeling, mapping and applications, vol 43. Springer, Berlin... 

Tissue Properties. The properties of human tissues when the body is considered a linear, passive mechanical system are summarized in Table 10.1 (von Gierke et al., 2002 Goldstein et al., 1993). The values shown for soft tissues are typical of muscle tissue, while those for bone depend on the structure of the specific bone. Cortical bone is the dominant constituent of the long bones (e.g., femiu, tibia), while trabecular bone, which is more elastic and energy absorbent, is the dominant constituent of the vertebrae. The shear viscosity and bulk elasticity of soft tissue are from a model for the response in vivo of a human thigh to the vibration of a small-diameter piston (von Gierke et al., 1952)... 

Vibration reduction based on an eneigy transfer from a main system to a passive absorber with sufficient energy dissipation. 

These systems consist of a combination (series of parallel) of active (or semi-active) and passive systems. The efficiency of such co-operation lies in the fact that the passive system can provide the gross reduction of response (by absorbing or deflecting energy) while the active one is used for further lowering (for protection of sensitive equipment, for example) of displacements or accelerations. Figure 2 illustrates an example where an actuator complements passive isolation to reduce high-frequency low-displacement vibrations. 

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