Natural frequencies and mode shapes


by reast_reast
Tags: frequencies, mode, natural, shapes
reast_reast
reast_reast is offline
#1
Feb13-12, 07:28 PM
P: 1
Hi people, we were doing an experiment in lab where we excite a plate clamped at the circumference at various frequencies to detect natural frequencies. My questions are:

1. Sometimes at certain frequencies, we were observing multiple mode-shapes (an overlap of two mode shapes, to be exact). What is the reason? It probably has to do something with the imperfection in our set-up. Does anyone have a more definitive answer?

2. The first theoretical natural frequency was 160 Hz. However, in reality, we observed the same mode shape at 80 Hz and 160 Hz. What may be a reason?

3. Why amplitude of vibration at natural frequencies decreases with increasing natural frequencies? i.e. first mode shape (and lowest natural frequency) has the highest amplitude, and the later shapes have lower amplitude. I was thinking frequency is proportional to the square root of the elastic modulus. But it's not the complete answer (TA told me). Does it have anything to do with energy and power?

Thank you a lot for your help!
Phys.Org News Partner Science news on Phys.org
NASA's space station Robonaut finally getting legs
Free the seed: OSSI nurtures growing plants without patent barriers
Going nuts? Turkey looks to pistachios to heat new eco-city

Register to reply

Related Discussions
Draw the mode shapes and get the natural frequencies of the cantilever beam(with a fo Mechanical Engineering 5
MATLAB FEM for natural frequencies and mode shapes of a beam Engineering, Comp Sci, & Technology Homework 1