Learning Forum

[toeztuerk]

Hello everybody,

I want to carry out a numerical impact analysis on a structure which behaves like a beam clamped on side (cantilever beam). Before doing the transient analysis, I performed successfully a modal analysis and got the first six natural frequencies which are plausible to me. However, for performing the transient impact analysis I set up a Force Load behaving like an impulse as shown in the screenshot

[Chris Quan]

2KHz is the frequency of free vibrations, where there is no external loading. When a structural system vibrates under external loading (forced vibration), its vibration frequency will not be the same as free vibration. It will be affected by the frequency and magnitude of the external loading.n

[toeztuerk]

Hello cxquan,thanks for the fast reply. I agree with you, but my external loading is not a constant harmonic excitation. The intention was to apply an impulse excitation to the structure and if you apply an external force in form of an impulse, similar to an Dirac impulse, then the structure is been excited with a frequency bandwidth of approx. 1/Tp, where Tp is the pulse width of the force impulse. So I expect, at least, the first mode shape with its natural frequency, which is in this case study of about 2kHz. Furthermore, I would expect higher harmonics within the response signal, since not only the first natural frequency is been excited (approx. 1/Tp).nFor test purposes, I just carried out this numerical experiment using an alternative FEM Software and I got the expected results...nBest regards,nTugruln