Tips & Tricks

Here you will find articles on how to solve specific issues related to ESI's software solutions. Missing ESI products will be added progressively. Each article has a short abstract which is accessible to everyone. As logged users you can see the full article with all attached screenshots, and you can post comments related to each article.

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...
Emna Ben Ali
Vibro-Acoustics
8

What is <Sqq> ?
<Sqq> is an exact expression for the ensemble average response of a system of coupled subsystems with uncertain boundaries...
Emna Ben Ali
Vibro-Acoustics
22

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...
Emna Ben Ali
Vibro-Acoustics
41

What is a stiffness multiplier in SEA?
Essentially it’s about adjusting the Young’s modulus to fit modes in band.
Emna Ben Ali
Vibro-Acoustics
28

 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
Emna Ben Ali
Vibro-Acoustics
31

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 ...
Emna Ben Ali
Vibro-Acoustics
23

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.
Emna Ben Ali
Vibro-Acoustics
12

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...
Emna Ben Ali
Vibro-Acoustics
11

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.
Emna Ben Ali
Vibro-Acoustics
11

Workaround for using VPS 2014 DMP modal data in VA One (internal)
It is possible to export the modes in erfh5 format of type 1. You have for that to setup the following environment variable: PAM_OCTRL_ERFVERSION=1 PSM is much faster than BLOCK_IRAM.
Emna Ben Ali
Vibro-Acoustics
13