Mesh Generation Controls

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.

ASPECT                        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.

CURVEGRID                        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.)

GRIDARC                        default: 30 degrees

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

GRIDLIMIT                        default: 8

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

INITGRIDLIMIT                        default: 5

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

MERGEDIST                        default: 0

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.        (5.0.18)

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.

(These controls should be used only in unusual cases, when the default value performs incorrectly.)

MIN_FEATURE                        default: automatic

Prevents the mesh generator from generating cells with edges shorter that the specified value.        

NGRID        

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:

NODELIMIT                

Specifies the maximum node count.  If mesh refinement tries to create more nodes 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.        Default values are shown below:        

REGRID                        default: On

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

SMOOTHINIT                        default: On

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

STAGEGRID                        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                        default: automatic

  See MERGEDIST.

YMERGEDIST                        default: automatic

  See MERGEDIST.

ZMERGEDIST                        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.]