MOM 6.3

10.1. Create Mesh

The most common parameters for the meshing process may be edited in this window.

meshing panel

Meshing panel

The following parameters may be edited:

  • Divisions per wavelength: This section specifies the size of the elements to be generated in the meshing process. 
    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
    The larger is the number of divisions specified the denser are the generated meshes.
    Different meshing resolution is considered for planar and curved surfaces. Also, a specific number of divisions may be assigned to different used by using the Specify Divisions option within the Advanced Simulation parameters section.
    • Planar surfaces: To set the number of divisions to be applied on planar surfaces which are contained in a single plane.
    • Curved surfaces: To set the number of divisions to be applied on curved surfaces which are not contained in a single plane.
  • Mesh Mode: This section specifies how the meshing frequencies are assigned. It allows considering different frequencies in the meshing process than the specified in Simulation parameters section.
    • Octaves: When a frequency swept is enabled, the meshing frequencies are different to the simulation ones. An automatic frequency range per octaves is performed, that depends on the Initial frequency, the Final frequency set in the Simulation parameters panel, and the number of Bands per octave specified. The higher is this parameter, the more frequencies are considered for the meshing process.
    • Frequency: Select this option to set the desired Frequency for the meshing process, in GHz. If a Frequency Sweep has been enabled within the Simulation parameters panel, all the steps in the sweep will consider the mesh generated at the Frequency value. 

      All frequencies: a meshing by each frequency is built, so it is the more accurate option. This option will only be chosen when the user needs a very accurate mesh.

  • Processors: To set the number of processors used in the meshing process.
  • More Options:
    • Mesh Repair: Select this option to evaluate and repair the generated mesh. It is recommended for analyzing complex geometries, especially whenever a good convergence is not achieved. Several problems will be studied and solved: isolated and spurious 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 with 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 depend 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

    • Click on Advanced Settings button to edit more complex meshing parameters. The available options are detailed in next subsection.
  • Mesh: click on this button to save the parameters and start the meshing process.

10.1.1. Advanced Settings

The advanced meshing parameters are detailed within this section, separated in so many sections as available tabs. 

Click on OK button to save the changes performed on every tab. Otherwise, the last configuration will not be taken into account. General

The most common advanced parameters are resumed in the General section.

General advanced parameters.

The following options are available within this panel:

  • Multilevel Meshing: This option generates the mesh automatically in several steps, and it is usually more efficient (in terms of runtime) than common mesh generation, so it is selected by default. However, minor differences may appear between the meshes obtained with and without multilevel mode. 
    • Use Multilevel Meshing: enable this option to use the multilevel mode.
    • First frequency: The frequency of the first step may be specified by the user with this parameter. If this field is empty, the first frequency is automatically computed. It is only considered when the Multilevel Meshing is enabled.
  • Memory Factor: This option allows a reduction of the memory resources required in the mesh generation process. The memory allocation is an automatic feature in this process, so the highest one is selected by default to ensure that the mesh will be successfully obtained.
    If the memory resources exceed the available memory, the message "ERROR: Not enough memory. Please, try decreasing Memory Factor" will appear to suggest decreasing this factor. Sometimes, a short factor may lead in not enough allocation for the required mesh resolution.
  • Volumetric Meshing: When a dielectric material is assigned to any geometric object, it may be defined as a volume, so it will be meshed with hexaedrons instead of quads. If there are any volume in the geometry, this section is enabled.
    • 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.
    • Divisions: Different divisions per wavelength for the X, Y and Z dimensions may be considered for meshing the volumetric objects. If some of this field is empty, the divisions specified in the main Meshing Parameters window are assigned.
  • Topology: If the electrical continuity between the surfaces have 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 as virtual fissures are introduced.
  • Edge Refinement: Within this section, the border effect in the mesh generation may be configured. The border effect consist on generating thiner elements in the boundary of the surfaces than the meshing size, so currents analysis is more accurate. This function is recommended for analyzing planar structures.
    • Edge Refinement: This option allows enabling the modelling of border effect in the mesh generation.
    • Edge Factor: It represents the portion of size of the final elements to model the border effect: the higher is this value the are the boundary elements. This parameter may be higher than 3. It is only enabled when Edge Refinement is selected. Surfaces Replication

During the meshing process, open objects may be replicated in the meshing process to approximate them as two thin parallel layers. It may be useful to analyze open structures by using the CFIE formulation, as the thin layer replication allows to consider its objects at approximate volumes.

Meshing advanced parameters - Surfaces Replication

The following options may be edited within this section:

  • Replicate Open Surfaces: Select this option to activate the replication and the to enable rest of paremeters in the window. If replication is enabled, the elements of the open objects are replicated to an automatic frequency-dependent distance from the original ones. 
  • Replication Area: This section defines the criterion to select the open objects that would be replicated or not, according to its dimensions. To force any open objects to not be replicated, use the Surfaces to not duplicate option included in the Method of Moments advanced parameters. The criterion may be edited:
    • Automatic replication: Any object with a total area greater than

      square meters is replicated, where div_plane and div_curve are the number of divisions per wavelength for planar and curved surfaces.. It is the default option.
    • Replicate all open objects: every open objects are replicated.
    • Objects with area greater than: To specify manually the threshold of the minimum total area of the open objects to be replicated, in square meters.
  • Replication Distance: The distance between the original objects and their parallel replicas can also be edited. Two different methods are available:
    • Automatically calculate: By default, the distance (in meters) is given by the following expression:
    • Specified distance: To specify manually the desired distance, in meters. Geometry

Within section, several parameters may be modified to set how the input geometry is preprocessed before the meshing process. It may result on getting or not electrical continuity between surfaces, or discarding spurious shapes.

Meshing advanced parameters geometry tab 

Note that every option that may be enabled has at the right side its corresponding parameter to set the maximum threshold allowed. The following parameters are included in this panel:

  • Study geometry: enable this option to carry out the input geometry preprocessing. Some features such as the surface sizes or electrical continuities may be evaluated.
    • Study edges: enable this option to delete the edges of the input surfaces that are shorter than the Minimum Edge parameter (in meters), extending its adjacent edges. It is only enabled when the Study geometry option is enabled.
    • Study loops: enable this option to delete the loops of the input surfaces that are shorter than the Minimum Loop parameter (in meters). It is only enabled when the Study geometry option is enabled.
    • Study areas: enable this option to delete the input surfaces that are smaller than the Minimum Area parameter (in square meters). It is only enabled when the Study geometry option is enabled.
    • Detect topolgy: enable this option 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). It is only enabled when the Study geometry option is enabled.
    • Split curves: enable this option to divide the curved borders of the input surfaces that describe curvatures greater than the Maximum Arc parameter (in degrees). It is only enabled when the Study geometry option is enabled.
    • Scale geometry: enable this option to  scale internally the geometry during the meshing process by the given factor. 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. It is only enabled when the Study geometry option is enabled. 

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