28-01-2013, 04:38 PM
FREQUENCY RESPONSE ANALYSIS
FREQUENCY RESPONSE.ppt (Size: 412 KB / Downloads: 272)
INTRODUCTION TO FREQUENCY RESPONSE ANALYSIS
Frequency response analysis is a method used to compute structural response to steady-state oscillatory excitation.
Examples of oscillatory excitation include rotating machinery, unbalanced tires, and helicopter blades.
In frequency response analysis the excitation is explicitly defined in the frequency domain.
All of the applied forces are known at each forcing frequency.
Forces can be in the form of applied forces and/or enforced motions (displacements, velocities, or accelerations).
FREQUENCY RESPONSE
For the cantilever beam shown here (figure at top), and a cosine (Harmonic) forcing function presented as a tip load, the Frequency Response procedure finds a solution that matches the theory. The first natural frequency is 325 Hz
Plotting the tip displacement magnitude as a function of the frequency of the harmonic excitation (figure at bottom) one can clearly see the static solution and the resonance when the first natural frequency is reached.
FREQUENCY RESPONSE
Frequency based dynamics should have the following characteristics:
The system should be linear. (but could have nonlinear preloading)
Linearized material behavior
No change in contact conditions
No nonlinear geometric effects other than those resulting from preloading.
The important results obtained from a frequency response analysis usually include the displacements, velocities, and accelerations of grid points as well as the forces and stresses of elements