Tips & Tricks

MUMPS error when solving my SEA model

I'm getting a MUMPS error when solving my SEA model - what may be the cause?, Reason for this is un-allowed or un-physical combination of physical properties in some NCTs. Correct those and the solve should go through.

Why PEM disappears when solving for coupled modes ?

PEM subsystems are nodal, whereas acoustic and structural ss are modal. The PEM ss adds to the global dynamic stiffness matrix, just as any SEA etc objects; so the PEM ss is taken into account when solving for the coupled mode. But one won't be able to visualize any modes, as there is no modal data for PEM ss, (same in coupled/uncoupled modes).

What is <Sqq> ?

is an exact expression for the ensemble average response of a system of coupled subsystems with uncertain boundaries...

Difference between using a cavity constraint vs. a Diffuse Acoustic Field source

If I apply a Diffuse Acoustic Field (DAF) source on a panel instead of constraining the pressure in an adjacent cavity, will I obtain the same results?, The results from the DAF and the constrained cavity are almost identical. The two main differences between the results will be a 3 dB offset and the fill factor effect

What is a stiffness multiplier in SEA?

Essentially it’s about adjusting the Young’s modulus to fit modes in band.

Imported modal damping from NASTRAN

How do I use imported modal damping from NASTRAN?, VA One can read the modal damping matrix from Nastran (KHH or BHH matrix). The KHH or BHH matrix needs to be in the.op2 file with the modes

I have a DAF and a cavity wetting the same plate, and get unexpected cavity mass law - why?

A model like this is not valid, i.e. a DAF is not intended to be combined with a cavity like this ...

How do I work with only imported geometry for creating temporary nodes for subsystem creation?

In order to import the geometry, and use this for creating new temporary nodes, select to import “Geometry (nodes and elements)”. Then in the visibility tree, uncheck “Imported nodes” under Imported “CAD/FE Geometry”, and make “Nodes on Visible Objects” checked.

Difference in BEM solve times when recovering Radiation Efficiency. Is this expected?

I see a drastic difference in BEM solve times when recovering Rad Eff. Is this expected?, Yes, computing the BEM radiation efficiency is very expensive as it has to recover the velocity at every wetted node and multiply by the mode shape at that mode, then sum that all up.

What is the recommended mesh density for RAYON BEM and FMM BEM?

For standard BEM one can start with 6-8 elements, and refine from there. For collocation (used by the FMM solver) the guideline should be 6 to 10 elements.