Wall
Use the Wall node to prescribe the acoustic behavior of boundaries such as walls, absorbers, or diffusers, but also at the bottom of the ocean on the sea bed. The Wall node is the default boundary condition on all exterior boundaries. The condition has the most common conditions used in acoustics simulations. The default setting is for modeling a mixed diffuse and specular reflections. It has inputs for the scattering coefficient s and absorption coefficient α. For advanced and user-defined options see the General Wall condition.
The Accumulator (Boundary) subnode is available from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.
Wall Condition
Select the Wall condition option as Specular Reflection, Freeze, or Mixed diffuse and specular reflection (the default).
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For Mixed diffuse and specular reflection (the default), select to reflect rays at a wall either specularly or according to Lambert’s cosine law, based on the scattering coefficient s and absorption properties.
Enter values for the Scattering coefficient s (SI unit: 1). This is typically a frequency dependent property, but may also depend on the angle of incidence.
Select the Reflection coefficient model as Absorption coefficient (the default) or Reflection coefficient. Enter the value of the absorption coefficient α (SI unit: 1) or the reflection coefficient R (SI unit: 1), depending on the available data for the wall. The absorption coefficient is typically known and will depend on frequency (typically the diffuse field values). It can also depend on the angle of incidence, in this case use the actual absorption for the given angle and frequency.
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For Specular Reflection, rays will all be specularly reflect from the wall, so that the angle of incidence and the angle of reflection are equal. Select the Reflection coefficient model as Absorption coefficient (the default), Absorber, specified impedance, Reflection coefficient, Fluid-fluid interface, Fluid-solid interface, or Layered fluid half space. For the detailed settings see the General Wall.
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For Freeze, the ray position and wave vector is fixed at the instant a wall is struck. So, the ray position no longer changes after contact with the wall and the wave vector of the ray remains at the same value as when the ray struck the wall. This boundary condition is typically used to recover the ray intensity or phase at the instant contact was made with the wall.
To create detailed models the wall properties, for example, the surface reflection coefficient R, the absorption coefficient α, or scattering coefficient s, must depend on the properties of the incident ray. This is possible as all wall properties may depend on:
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The frequency of the ray rac.f
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The direction of the ray, the acute angle of incidence rac.phii
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Even the intensity of the ray rac.I
New Value of Auxiliary Dependent Variables
This section is available if an Auxiliary Dependent Variable has been added to the model.
When a ray crosses or touches a boundary, the values of the user-defined auxiliary dependent variables can be changed. The value can be a function of any combinations of ray variables and variables defined on the boundary.
Select the Assign new value to auxiliary variable checkbox or boxes based on the number of auxiliary variables in the model. Then enter the new value or expression in the field. For example, if there is an auxiliary variable, psi, then enter a value for psinew in the field. So, to increment the value of psi by 1 when a ray touches or crosses a boundary, enter psi+1 in the text field for psinew.