How to perform the base excitation random vibration analysis ( using input PSD) of beam and portal frame?

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Hello everyone, since i am new to the comsol multiphysics software and i want to perform the random vibration analysis ( using base excitation PSD) of beam ( cantilever and simply supported) , clamped rectangular plate and portal frame problems. I am able to perform the modal analysis of all the problems. Also, for random vibration part, i have given the input PSD in the interpolation function part of the global definition. But after that i don't know what are the steps that i have to followi.e what are the inputs given in global reduce model inputs and at finally obtained the response PSD in the desired direction and location. Can anyone help me in this mattter? Thanks in advance.


2 Replies Last Post Jul 25, 2021, 1:38 PM EDT
Henrik Sönnerlind COMSOL Employee

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Posted: 3 months ago Jun 23, 2021, 5:35 AM EDT

Here is an example with base excitation using an acceleration PSD:

https://www.comsol.com/model/random-vibration-test-of-a-motherboard-75781

The procedure used there is to replace the actual base excitation by a gravity load. That works, as long as all support points have the same acceleration (the by far most common case). You should however be aware of that while it makes no difference to stress quantities, displacements and accelerations are then computed relative to the base, and not relative to a space fixed coordinate system.

If the supports have different PSDs, then you can use what is usually called the 'large mass method'.

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Henrik Sönnerlind
COMSOL
Here is an example with base excitation using an acceleration PSD: The procedure used there is to replace the actual base excitation by a gravity load. That works, as long as all support points have the same acceleration (the by far most common case). You should however be aware of that while it makes no difference to stress quantities, displacements and accelerations are then computed relative to the base, and not relative to a space fixed coordinate system. If the supports have different PSDs, then you can use what is usually called the 'large mass method'.

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Posted: 2 months ago Jul 25, 2021, 1:38 PM EDT

Thankyou sir for this valuable information.

Thankyou sir for this valuable information.

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