6.11 ABC Wall

The  command from Add section in  button in Model tab and I/O Ports->Absorbing Boundary Conditions->(Add) MUR Wall... command from main menu invoke ABC Wall dialogue for adding abc wall port with default settings for MUR.

The  command from Add section in  button in Model tab and I/O Ports->Absorbing Boundary Conditions->(Add) PML Wall... command from main menu invoke ABC Wall dialogue for adding abc wall port with default settings for PML.

This dialogue can be also opened for adding or editing the abc wall port from ABCs dialogue.

The wall name in the Name field can be set and the type of an absorbing wall can be chosen in the Type drop-down list. Activity drop-down list allows choosing the wall activity (Plus or Minus), which depends on the wall’s position with respect to the considered structure.

In the Geometry tab the user sets the port Orientation by choosing an appropriate axis. In the Position frame the position and dimensions of the port are set. To set the port position the Use position option needs to be checked and the position is defined explicitly. The in plane dimensions of the port can be set in three ways. Full Plane option sets the port dimensions equal to the bounding dimensions of the entire project in the directions perpendicular to the port orientation. Coordinates option allows introducing MinMax coordinates between which the port will be created/stretched out. Dimensions option allows defining port dimensions explicitly but requires also Min coordinates indicating where the port geometry starts.

In the Parameters tab the parameters for the absorbing wall. Absorbing wall of MUR type needs the effective permittivity of the medium in which the wave propagates. It is used by the software to calculate the correct phase velocity of the wave. Incorrect assumption of the effective permittivity increases the level of spurious reflections from the ABC. By default it is assumed that the medium is air and the effective permittivity value is set to 1.

Absorbing wall of PML type needs to specify the PML thickness (in the number of cells) and to select the conductivity profile from the following:

·        Parabolic (used in most usual applications) - its conductivity varies as: A*x^2, where x=(distance from PML edge)/(PML thickness) and A set in the dialogue,

·        Exponential - its conductivity varies as: A*exp(B*x) with x defined as above, and A, B set in the dialogue.

It is advised to refer to Absorbing Boundary Conditions for more information regarding both types of absorbing boundary conditions.