# Nonlinear Random vibration analysis

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Hi all,

I'm trying to learn about the random vibration analysis. From what I know, RVA uses the modal superposition method as its basis. Since it uses the modal superposition, it implies that random vibration analysis is a linear dynamic analysis. Lets say if you have a model with two or more parts, and you define some connection (spot-welds or elastic beams Rbe3) for them. The connection usually will introduce nonlinearity into the system. So then, in the end, I'm guessing the analysis will output nonlinear solutions.

The thing that I have trouble understanding is that how is it possible to start out with a linear analysis and end up with a nonlinear solutions? Doesn't the nonlinear random vibration analysis violate the superposition method that it uses as the basis?  Any comments or tips would greatly appreciated.

Regards,

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Hi,

What type of nonlinearities you think will be induced through spot welds and Beams?

RVA uses input from modal analysis which is linear and I think any non linearity will be ignored.

So RVA uses Linear natural frequencies and PSD curve.

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I'm not sure what type of nonlinearites. What I know is that not all the beam element formulation is linear. So if we choose a nonlinear element formulation and apply it to the connection beam with RBE3, I was thinking what will happen to the results then.

So What I get from your answer is that RVA has to be linear analysis. Is it right?

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Non linearities of three type:.

1. Non linear material (Rubber or elasto plastic material)

2.Contact based non linearity (component simply lying on other component without using any rigid)

3.Geometric non linearity (Even for small magnitude of load component will deform more)

I think in your case you have model connection with beam & rigid. Hence you can run randon response analysis.

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