# Sound Barrier

Here we will perform a 2D simulations concerning wave propagation over a sound barrier.

Thereby the wave is excited by a point source on the right side of the barrier in the origin $[x,y,z]=(0,0,0)$ of the domain.

For the analysis type, we chose a harmonic analysis in the frequency range of 34Hz to 680Hz with 10 linearly spaced samples.

Since we cannot create an infinitely large computational domain, we have to impose a model of free-radiation, in this example, we are using the PML (Perfectly Matched Layer) technique, described here.

## Meshing

As a preprocessor we use the free available software gmsh

The gmsh file is provided here and the mesh can be generated by executing

gmsh geometry.geo -2 -v 0 -format msh2 -o geometry.msh


## XML Simulation Setup

The ready-to-use xml file is provided here as well as the material xml file.

Here, we will just discuss the main parts of the XML description file (for a deeper introduction into the different analysis types, we refer to the Cantilever example)

• Domains with regions
<domain geometryType="plane">
<regionList>
<region material="air" name="prop"/>
<region material="air" name="plate"/>
<region material="air" name="pml"/>
</regionList>
<nodeList>
<nodes name="excite">
<coord x="0.0" y="0.0" z="0.0"/>
</nodes>
</nodeList>
</domain>

• Start the sequence and define analysis
<sequenceStep>
<analysis>
<harmonic>
<numFreq> 10 </numFreq>
<startFreq> 34 </startFreq>
<stopFreq> 680 </stopFreq>
<sampling>linear</sampling>
</harmonic>
</analysis>

• Define PDE for acoustics
  <pdeList>
<acoustic>
<regionList>
<region name="prop"/>
<region name="pml" dampingId="myPml"/>
</regionList>

     <dampingList>
<pml id="myPml">
<type> inverseDist </type>
<dampFactor>1.0</dampFactor>
</pml>
</dampingList>

• Define excitation and output result
    <bcsAndLoads>
<pressure value="1" name="excite"/>
<storeResults>
<nodeResult type="acouPressure">
<allRegions/>
</nodeResult>
</storeResults>


Perform the openCFS simulation by executing

cfs simulation


## Result

You can now investigate the results in paraview