hello researchers,
i am having question related to higher mode of vibration.
my question is that, does the all mode of continuous system excited under applied force? if not then how do we come to know that which mode is been excited under the applied force when higher modes are significant?
please help me in understanding that or provide some reference where do i find this
tha0nk you
regards
Hi
All modes are excited.
However, the contribution to response from some modes is small and can be neglected in the modal summation, i.e. the modal summation converges even when some modes are ignored in the summation. Such, ignored, modes are sometimes called higher modes.
Whether it is OK or not to neglect the contribution from a mode can be estimated using modal weight where the physical weight is compared with the weight provided by the modes you wish to use in the modal summation. See the discussion on MEFMASS here http://web.mscsoftware.com/support/prod_support/nastran/documentation/release2001.pdf
There are ways to approximate the contribution of higher modes using something called residuals. In this case, one makes a direct solution, e.g. at the highest analysis frequency, computed the modal response at the same frequency and uses the difference between the two solution sets as the residual. The residual has an appropriate frequency weighting function. One can repeat the trick also for lower frequencies.
Sincerely
Claes
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