ISAR 6.2.10

10.1. Create Mesh

The meshing options in the ISAR module depend on the solver that has previously been selected. In both cases the mesh generation is a required step that is performed immediately before simulating.

If the PO solver has been selected in the Solver menu, the following options are available:

 

Meshing Parameters panel

 

 In the Meshing Options panel the following options are available:

  • Number of processors. To set the number of processors for the meshing process.
  • Meshing Strategy:
    • Regular Meshing. The size of the generated elements is selected by the user.
      • Multilevel. Use Multilevel to generate the mesh automatically in several sequenced steps. This option is usually more efficient (in terms of runtime) than the common mesh generation option, so it is selected by default. However, there may be minor differences between the meshes obtained with and without the Multilevel mode.
      • Edge size. Desired size for the edge of the elements, in meters.
    • Curvature Meshing. The size of the elements generated is automatically computed in the meshing progress. However, it depends on the global bounding box of the targets, their curvatures, and the Distance error and Surface error (lambda) parameters.
      • Distance error: Increasing this parameter creates a denser mesh (smaller size of elements).
      • Surface error (lambda): Decreasing this parameter creates a denser mesh (smaller size of elements).

If the MoM approach has been selected in the Solver menu, the following options are available:

 

meshing panel

Meshing Parameters panel 

In the Meshing Options panel the following options are available:

  • Divisions per wavelength: The user may specify different mesh density in planar and curved surfaces. Planar surfaces are contained in a single plane, otherwise surfaces are curved. Let c be the speed of light in the vacuum (meters per second), given a number of divisions D and a frequency f, the size of the generated elements L is given by:

L = lambda / D ; lambda = c / f

  • Processors: Use this to set the number of processors used for the meshing process 
  • Mesh Repair: Select this option to evaluate and repare the generated mesh. It is recommended for analyzing complex geometries, specially whenever a good convergence is not achieved. Several problems will be studied and solved: isolated and spurius elements are removed, and overlapped regions are repaired. The detection of this defects on the mesh depends on two parameters that are explained below, and can be edited by clicking on Options button. Elements wit smaller area than the minimum allowed, isolated elements, or parallel elements closer than a minimum distance are deleted from the output mesh. The minimum area and distance depends on the wavelength, the number of divisions per wavelength selected, and the Area and Border factors, and they are determined as:

meshing repairing

Meshing Repairing options

area factor

border factor

The Advanced Settings are explained below.

  • General: there are some options to specify in this tab.
    • Multilevel Meshing. Enable this option to automatically generate the mesh in several steps. This option is usually more efficient (in terms of runtime) than common mesh generation, so it is selected by default. However, there may be minor differences between the meshes obtained with and without multilevel mode. The frequency of the first step may be specified by the user in the First freq field, but when this field is empty, the first frequency is automatically computed.
    • Memory Factor. This option allows reducing the memory resources required in the mesh generation process. The memory allocation is an automatic feature in that process, so the largest one is selected by default to ensure that the mesh will be obtained successfully. If the memory resources required are higher than the memory available in the machine, the message represented in the next Figure will appear to suggest decreasing this factor.

Warning  panel

    • Volumetric Mode. This option allows to change the algorithm used in the mesh generation process of dielectric objects (defined as Volumes). Two different modes are available:
      • Structured Mesh: All elements of the volumetric mesh are perfect parallelepipeds. This method is an approximation of the real shape of the dielectric objects by simple cubes. Some parts of the mesh can be out of the volume and other regions can have incomplete regions, but the average volume of the mesh is very similar to the volume of the original dielectric objects. This algorithm is the fastest one.
      • Conformed Mesh: Most of elements of the volumetric mesh are perfect parallelepipeds, but only in the completely inner regions of them. The inner structured mesh is joined with the boundaries of the volume by using hexahedrons of variable shapes. This method is more accurate than the Structured Mesh, but is also slower and irregular elements may appear in specific cases.

Different divisions per wavelength for the X, Y and Z dimensions may be considered for meshing the volumetric objects.

    • Topology. If the electrical continuity between the surfaces has to be broken, the option Disable topology must be selected. Note that the accuracy may be reduced when the electrical continuities are not correctly analyzed because virtual fissures are introduced.
    • Edge Refinement. This option allows enabling the modeling of border effect in the mesh generation when this option is selected. The Edge Factor field represents the portion of size of the final elements to model the border effect. It is only enabled when Edge Refinement is selected.

 advanced meshing paramaters

Meshing advanced parameters general tab

  •  Surfaces Replication: there is only one check box called Parameters in this tab that is composed by some options:
    • By marking the Replicate Open Surfaces option, a parallel near layer of open objects is generated in the mesh generation process. If replication is marked, the elements of all open objects are replicated to an automatic frequency-dependent distance from the original ones.
    • Replication Area. The criterion used to replicate open objects can be configured.
      • Automatic Replication. The replication will be applied to any object with a total surface greater than:

      • Replicate all open objects. Any object is replicated, by default.
      • Replicate objects with area greater than. To manually specify the threshold of the minimum total area of the objects to be replicated, in square meters.
    • Replication Distance. The distance between the original objects and their parallel replicas can also be edited.
      • Automatically calculate. By default, the distance is given by the following expression:

      • Specified distance. To specify manually the desired distance, in meters.

Meshing advanced parameters surface replication tab

 

  • Geometry: the followings parameters can be specified.
    • Study Geometry. To pre-process the input geometry, evaluating some features such as its sizes or electrical continuities.
    • Study Edges. To delete the edges of the input surfaces that are lower than the Minimum Edge parameter (in meters), extending their adjacent edges. This option is only enabled when the Study Geometry button is enabled.
    • Study Loops. To delete the loops of the input surfaces that are shorter than the Minimum Loop parameter (in meters). This option is only enabled when the Study Geometry button is enabled.
    • Study Areas. To delete the input surfaces that are smaller than the Minimum Area parameter (in square meters). This option is only enabled when the Study Geometry button is enabled.
    • Detect Topology. To detect automatically electrical continuity between neighboring surfaces that are very close but have not been modeled with precise continuity. The maximum separation allowed to set the electrical continuity is the Maximum Distance parameter (in meters). This option is only enabled when the Study Geometry button is enabled.
    • Split Curves. To divide the curved borders of the input surfaces that have a curvature greater than the Maximum Arc parameter (in degrees). This option is only enabled when the Study Geometry button is enabled.
    • Scale Geometry. To scale internally the geometry during the meshing process. When the mesh generation finishes, the output mesh has the same sizes as the original geometry. This option is useful for meshing very small structures. This option is only enabled when the Study Geometry button is activated.

Meshing advanced parameters geometry tab

  • Output: This option is no longer within the Meshing Advanced Parameters window. It has been moved to the main Meshing window, as it is recommended whenever a good convergence is not achieved. 

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