Mesh Generation Controls

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Mesh Generation Controls

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The following controls can be used in the SELECT section to modify the behavior of the mesh generator.

Logical selectors can be turned on by selector = ON, or merely mentioning the selector
Logical selectors can be turned off by selector = OFF.
Numeric selectors are set by selector = number.
Some selectors can be STAGED.

 

ASPECT                type: Numeric        default: 2.0        

Maximum cell aspect ratio for mesh generation in 2D problems and 3D surface meshes.  Cells may be stretched to this limit of edge-size ratio.

 

CELL_LIMIT                type: Numeric        default: See below

Specifies the maximum cell count.  (Note that in version 7 this selector has replaced the NODELIMIT selector of previous versions.)  If mesh refinement tries to create more cells than the limit, the cell-merge threshold will be raised to try to balance errors across a mesh of the specified size.  This control cannot be used to reduce the size if the initial mesh construction, which is dictated by NGRID, user density controls, and domain boundary feature sizes.   This selector can be STAGED.  Default values are shown below, although these limits will likely not be reachable within the resources of most computers :

 

1D

2D

3D

Professional

1,000,000

10,000,000

50,000,000

Lite

100

400

1200

 

CURVEGRID                type: Logical        default: On        

If ON, cells will be bent to follow curved boundaries, and a 3D mesh will be refined to resolve surface curvature.

If OFF, neither of these modifications will be attempted, and the computation will proceed with straight-sided triangles or flat-sided tetrahedra.  (It may be necessary to turn this option OFF when surfaces are defined by TABLES, because the curvature is infinite at table breaks.)

 

FEATURE_INDUCTION        type: Numeric        default: 2

In the initial domain layout, FlexPDE attempts to discover cell sizes necessary to resolve domain elements, iterating to propagate the influence of small features. In complex domains this can become expensive. If feature sizes are relatively uniform, or if the user controls the cell size manually, the iteration can be bypassed by setting FEATURE_INDUCTION to 0.
         

GRIDARC                type: Numeric        default: 30 degrees

Arcs will be gridded with no cell exceeding this angle.  Other factors may cause the sizes to be smaller.
         

GRIDLIMIT                type: Numeric        default: 8

Maximum number of regrids before a warning is issued. Batch runs stop at this limit.
         

INITGRIDLIMIT        type: Numeric        default: 5

Maximum number of regridding passes in the initial refinement to define initial values. INITGRIDLIMIT=0 suppresses initial refinement.        

 

MERGEDIST                type: Numeric        default: Automatic

In the initial domain layout, points closer than MERGEDIST will be coalesced into a single point.  This helps overcome the effects of roundoff and input number precision in generation of domains.  A default merge distance is computed during initial layout. MERGEDIST will over-ride this default value.  Individual values for X, Y and Z coordinates can be set with XMERGEDIST, YMERGEDIST and ZMERGEDIST respectively.  (These controls should be used only in unusual cases, when the default value performs incorrectly.)

 

NGRID                type: Numeric        default: See below

Specifies the number of mesh rows in each dimension.  Use this control to set the maximum cell size in open areas.  This is a convenient way to control the overall mesh density in a problem.  Default values are shown below:

 

1D

2D

3D

Professional

100

15

10

Student/Lite

25

10

5

         

REGRID                type: Logical        default: On

By default, FlexPDE implements adaptive mesh refinement.  This selector can be used to turn it off and proceed with a fixed mesh.    This selector can be STAGED.        

 

SMOOTHINIT        type: Logical        default: On

Implements a mild initial-value smoothing for time dependent problems, to help ameliorate discontinuous initial conditions.

                 

STAGEGRID                type: Logical        default: Off

Forces regeneration of mesh with each stage of a staged problem.  FlexPDE attempts to detect stage dependencies in the domain and regenerate the mesh, but this selector may be used to override the automatic detection.

         

XMERGEDIST        type: Numeric        default: Automatic

See MERGEDIST.

 

YMERGEDIST        type: Numeric        default: Automatic

See MERGEDIST.

 

ZMERGEDIST        type: Numeric        default: Automatic

See MERGEDIST.

 

                                 

Note: See the "Mesh Control Parameters" section in this manual and the "Controlling Mesh Density" section in the User Guide for more discussion of mesh control.