Download Doctoral Thesis on TD-BEM

You can download the thesis “Stabilitätsverhalten und Anwendungen der transienten Randelementmethode in der Akustik” (“Stability behaviour and application of the transient boundary element method in acoustics”) at the Digitales Repositorium der TU Berlin

The thesis is in German but nevertheless you may find the equations helpfull.

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BEM acoustics Version 1.1 released

Dear BEM acoustics users,

we are happy to announce that the new Version 1.1 has been released. We added quite a lot of new exciting features:

Version 1.1

  • added import compatibility with .cdb, .mphtxt and .nas meshes
    • You can now import some of the typical mesh file formats. 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.
  • added support for the parallel processing toolbox by MathWorks
    • If you have the parallel processing toolbox you can now speed up your simulations. The system matrix entries will than be calculated in parallel by the mkGH_parallel function.
  • added help entries on variable syntax, parallel processing
    • In the BEMacousticsV1.1\help folder you find BEMhelp. There you can browse through the documantation. Under Demos you find some examples how to use the CHIEF method or the parallel processing toolbox. You can access this information also via the MATLAB help by hitting the Help button in the GUI window.
  • added stability limit parameter
    • If the simulation is getting instable the algorithm will stop so you don’t have to waste your time.
  • added menu bar to main window
  • checkboxes are now displayed properly when loading a project
  • changed default window size to more appropriate for different screen sizes
  • GUIlayout updated
  • CHIEF points can now be added independently to different setups within the same project

If you did some improvements yourself please let us know so we can include it in the next version of BEM acoustics.

 

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Video tutorial on how to use the CHIEF method

Please watch our short introduction of the BEM acoustics MATLAB toolbox using the CHIEF method to improve results and stability.

Using a sphere the acoustic radiation of a monopol source will be simulated. The results show small disturbances because the internal eigenmodes of the sphere are exited and influence the outer sound field. For longer simulation times the results may also become instable. This effect strongly depends on the choosen time step Δt. If the sampling frequency 1/Δt coincides with the frequency of an internal eigenmode of the structure the simulation will get instable. In case of the sphere we know the eigenmodes. But for more complicated structures this is not the case and choosing the time step Δt will become kind of a lottery game. By increasing the spatial discretisation the influence of the internal eigenmodes will be reduced. This will also increase the computational time of course.

An other way is to use the CHIEF method. To do so define some points inside of the structure (the so called CHIEF points). In the solution process the solver trys to find a solution with a zero sound pressure in these CHIEF points. Use arround 30% of the number of surface elements as a estimate for the number of CHIEF points.

There is no forum so far as the BEM acoustics community is quite small so far. So if you have a question you can post it as a comment to this blog post. To do so you have to be logged in!

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