FAQ

Here are some questions that might come up using the BEM acoustics Matlab toolbox. Of course there are much more. So please ask using the contact page. We will add than the most common questions to the FAQ.

What is BEM acoustics and what it be used for?

BEM acoustics is a toolbox for MATLAB that can solve acoustic scattering or radiation problems. It’s  a direct Boundary Element Method that performs the calculation in time domain.

Please keep in mind that BEM (like FEM) is a method based on the wave equation. So the computational effort will rise quadratic with frequency. This means you can only simulate low frequencies. The most limiting part of your hardware will be the memory. You can estimate the needed memory the following way: 3* number of elements^2 * 8 bytes (because of double precision)
The number 3 is a rough estimate of how many entries one element will produce and depends on your ratio of element size and time step size.
e.g. for a mesh with 20 000 elements you need about 90GB of memory (and a lot of time too)!!

How many elements do I need?

Please keep in mind that BEM (like FEM) is a method based on the wave equation. So the computational effort will rise quadratic with frequency. This means you can only simulate low frequencies. The most limiting part of your hardware will be the memory. You can estimate the needed memory the following way: 3* number of elements^2 * 8 bytes (because of double precision)
The number 3 is a rough estimate of how many entries one element will produce and depends on your ratio of element size and time step size.
e.g. for a mesh with 20 000 elements you need about 90GB of memory (and a lot of time too)!!

For an error smaller 1dB you will need about 6 elements per wavelength. This is a rough estimate and will depend on your problem!

Can the BEM acoustics toolbox be used with Octave or Scilab?

Honestly we have never tried!

Scilab and Octave are open source software for numerical computation quite similar to MATLAB. The core BEM functions should be easily portable because no special toolboxes are required. The GUI is probably not portable.

Please feel free to try and let us know how it works out. We are willing to help if you encounter any problems.

What data format can I use with BEM acoustics?

BEM acoustic Version 1.1 supports import compatibility with .cdb, .mphtxt and .nas meshes. For the examples we used it worked fine. But I’m sure that also depends a lot of the program versions that generated the mesh. So please try and let us know. If you improve the import functions please contribute them to the project!

How can I generate meshes that I can use with BEM acoustics?

BEM acoustic can handle flat quadrilateral or triangular elements (also a mixture of them). You need a mesh generator to produce a surface mesh. One of many open source tools is the Netgen Mesh Generator.

Importing the mesh to MATLAB is still quite difficult as there are no import functions. COMSOL has the possibility to connect with MATLAB and the mesh can be read into the MATLAB workspace.

Please always check the normal vectors of the surface! They should all point into the domain of interest!

How can I report a bug?

Please use the contact form to report a bug. Send us a detailed description of the error and your modified m-file. We will try to fix it as soon as we have time for it.

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If you have a question not answered here please use the contact form.