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Method for solving for High frequency modes

Method for solving for High frequency modes

Method for solving for High frequency modes

(OP)
Hi everyone, this is my first post, so if I messed up on some form rules, just let me know.

I’m trying to solve for higher frequencies of a structure. The problem involves plates attached to a complicated base. From vibration testing, the bending modes were measured and I’m trying to measure them in the model for validation. I was given a model to use, so I don’t have a lot of flexibility with it.

The model has many nodes (10k’s across the plate, about 1M nodes), so I shouldn’t be getting to high frequencies relative to the total number. But these modes are going to be at least a hundred modes shapes in due to intra-plate motion and back structure, so I don’t want to solve for the first 300 modes (file size would also be a problem due to the size of the model, about 0.1GB per mode).

Right now I’m running NX Nastran generated by FEMAP for Normal Modes/Eigenvalues. I’ve been using Lanczos with lower and upper frequencies and number of modes to solve for. The solution is run on a linux cluster. All systems are 64bit. Sometimes the solution will be just wrong and re-exporting and running the analysis would fix it.

Are there better ways of getting these high frequencies? Such as other methods that offer better accuracy/efficiency (I’m doing a run on the modified Householder now)? The base interaction with the plate is assumed to be important, so doing the plate alone doesn’t seem to be an option.

Thanks a bunch!

RE: Method for solving for High frequency modes

You may be able to apply a "shift" to solution, such that is iterates about the shift point. This should allow it to converge faster and give more accurate results.

Brian
www.espcomposites.com

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