6.12 ABC Box

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

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

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

The box name in the Name field can be set and the type of an absorbing box can be chosen in the Type drop-down list.

In the Geometry tab the user needs to define the dimensions of the absorbing box. It can be done in two ways. First one is using Bounding Box Offset option, where the absorbing box is drawn at the defined offset from the bounding box of the project structure. The offset is defined in project units for each direction and applies to each side from the structure.

Second solution is using Position option, where the user can choose Coordinates or Dimensions. While using Coordinates option the MinMax coordinates of the absorbing box in each direction should be defined. For the Dimensions option, length, width, and height of the absorbing box should be given together with the Min coordinates at which the box geometry starts.

In the Parameters tab the parameters for the absorbing box. Absorbing box 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 box 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.