GTD-PO 6.3

10.1. Create Mesh

In the GTD-PO module, the mesh generation is a required step that is performed immediately before simulating. In the Meshing Parameters window, represented in the next Figure, the following options are available:

 

Parameters panel

 

  • Bands Per Octave. Set the different meshes to be generated, according to the bands per octave divisions. If no options are chosen, just a mesh at the lowest simulation frequency is generated. This option is only highlighted when previously a frequency shift or a distance to source sweep are selected.
    • On R: the octaves are considered according to the distance to the source. This option only can be set when the source is defined by spherical coordinates.
    • On Frequency: the octaves are considered according to the frequency range. 
  • Number of processors. Sets the number of processors for the meshing process.
  • GTD Advanced Parameters: the user can change the curvature angle and the angular margin in order to control how the curved surfaces of the geometry will be partitioned. The contributions are previously evaluated on a parametric internal mesh of the geometry where the curved surfaces are simplified. The resolution of this mesh may be edited according to the below parameters, which are set by default with the recommended values.
    • Parametric Steps: accuracy in the curvature evaluation, normalized. Decrease this parameter to get a higher precision in the parametric discretization. 
    • Curvature angle (deg): maximum curvature considered on targets. It indicates the maximum curvature allowed in the input surfaces for the meshing step. Decrease this parameter to get a higher resolution mesh.
    • Angular Margin (deg): maximum deviation allowed around the curvature reference angle. The curvature discretization is achieved by an approximated iterative method, so an angular error around the previous parameter is allowed. Decrease this parameter to increase the precision in the curvature discretization.
  • PO Advanced Parameters:
    • Regular Meshing. The size of the generated elements is selected by the user. Regular meshing is the common algorithm used in other modules such as MOM. It provides a mesh of triangles of similar sizes with a distribution as uniform as possible. It enables the user to set the exact size edge of the triangles to be generated, given in lambda units. However, a huge number of mesh elements may results when the geometry contains large surfaces.
      • Multilevel. Use Multilevel to automatically generate the mesh 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. This value is the desired size for the edge of the elements, in wavelengths.

Regular meshing

    • Curvature Meshing. The size of the generated elements 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. This technique provides a non-regular mesh with patches generated to discretize the curvatures and edges of the geometry with a quasi-adaptive method. The generated meshes usually are less dense than the ones provided with the Regular Meshing strategy. The curvature meshing has been developed with the aim of solving the limitations that uniform meshes may cause in PO and GTD-PO modules. By using this technique, the planar surfaces are discretized with the minimum number of triangles that is possible; and the curved surfaces are discretized in a set of flat triangles. The criterion of curvature meshing converts the curved surfaces in planar triangles meshes where the maximum deviation between any planar triangle and the original surfaces is lower than the wavelength multiplied by the Surface Error factor.
      • Distance error: increasing this parameter creates a denser mesh in planar surfaces (smaller size of elements).
      • Surface error (lambda): decreasing this parameter creates a denser mesh in curved surfaces (smaller size of elements).
  • Advanced Parametersthis parameter is used to classify the geometry in order to apply GTD or PO.

The table below shows a comparison of meshing PO-criterions with different configurations for meshing a cylinder with a radius of 0.25 m. and height of 1 m. at 3 GHz.

Regular

1 lambda

0.5 lambda

0.01 lambda

Curvature

0.2 surface error

0.1 surface error

0.01 surface error

 

 

The user may select the number of processors used to run the simulation and press the Mesh button to start the meshing process. This process may take a while (depending on the number of processors selected and the computing power of the machine running the simulation).

 

While running, the status of the meshing process is reported in the process log panel. From this panel, it is possible to abort the running meshing process or save the log to a text file.

 

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