Robust Identification and Passive Control of Vibration of a Test Rig under Uncertain Conditions

Abstract

A continuous dynamical system under vibratory excitation may display several resonance situations. Therefore, a vibration absorber attached to the mechanical device can be quite important, especially when a projected operation point causes high vibration amplitudes. Health of equipment is also a main concern, or human comfort, when there is people near a machine the use of an absorber is a common solution in structure and machine dynamics. Ordinary vibration absorbers are designed as an additional degree of freedom that, theoretically, completely stops one of the other elements to vibrate at a specified frequency. So, in order to prevent more than one critical point, one may need to add the same number of absorbers as the number of harmful resonances. Also, each time you cancel one resonance frequency, the mechanical system increases in the same proportion the number of degrees of freedom. This work proposes to analyze theoretically and simulate a nonlinear absorber, which is capable to diminish the vibrations at more than one resonance frequency. It will be shown through simulations how the variation of the absorber parameters can modify the response of the system. Then, a stochastic modeling is also done to account for the applied force of the system that is considered a random process to test the efficiency of the nonlinear absorber. Further, an experimental set up will be presented that models a two-floor building with an ordinary absorber and also with a new concept of a non-linear absorber. The new absorber is assembled with two thin blades connecting a mass allowed to move only in one direction. Test data will be collected by accelerometers and the test rig is excited by a shaker for robust identification and to validate the model used in the simulation. The attached nonlinear absorber shall then reduce the vibration when an unbalanced rotor turning at variable speed is the source of perturbation.