Structured mesh Properties

Structured mesh generation and adjustment

The structured mesh can be applied in combination with an unstructured one. The unstructured mesh must be already generated before. The structured mesh will overlap the unstructured one with a second layer. The structured mesh is useful when a high spatial resolution is required. Additional advantage is a small computational time required for one iteration on the structured mesh in comparison with the unstructured mesh. The stability of the fluid flow solution algorithm on the structured mesh is essentially higher than on the unstructured mesh.

The preprocessing for the structured mesh is generally more elaborated than for the unstructured mesh. The higher effort is caused by the specific requirements which should be satisfied for the mesh applied for the fluid flow calculation. Also the smoothness and orthogonality requirements should be achieved.

mesh parameter

Default value

Description

Boundary layer thickness (m)

0.01

The structured mesh generator compresses the mesh density in the boundary layers if the corresponding option grid refinement in the boundary layer is activated. The distribution of the distances between the nodes inside of the boundary layer is adjusted in order to achieve the required target distance between the last node in the fluid before the interface liquid-solid.

The band along the interface liquid-solid in which the mesh adaption takes place has a thickness defined by this parameter. The grid refinement in the boundary layer parameter should be defined before the structured mesh is generated because it affects the auxiliary CAD drawing associated with the structured mesh. The necessary thickness of the boundary layer can be estimated using the characteristic numbers dialog, see Definitions and Explanations of Characteristic Numbers. for details. The thickness of boundary layers can be estimated as L/sqrt(Re) with L characteristic length and Re Reynolds number.

At least 3-5 nodes should located within the mesh reserved for the boundary layer resolution.

The parameter is applied only if the checkbox grid refinement in the boundary layer is activated.

Last CV size towards wall (m)

0.001

Defines the distance between the last central node in the fluid and the interface liquid-solid. This value affects the number of the control volumes to be placed within the boundary layer. This parameter exactly as Boundary layer thickness (m) should be defined before the structured mesh is generated because it affects the auxiliary CAD drawing associated with the structured mesh. The number of the control volumes in the boundary layer for the prescribed boundary layer thickness can be controlled by means of the Last CV size towards wall .

The parameter is applied only if the checkbox grid refinement in the boundary layer is activated.

This setting is irreversible and should be set properly once before the structured mesh is generated first time.

grid refinement in the boundary layer

checked

Activates the automatic refinement of the structured mesh in the boundary layer. The locations of boundary layers are found automatically while the structured mesh is generated. The boundary layer is supposed everywhere along the interfaces between liquid and solid materials.

Activation of the automatic refinement procedure affects the auxiliary CAD drawing associated with the structured mesh. Additional segments are introduced on the drawing lines crossing boundary layers if this measure is required for the mesh control.

This setting is irreversible and should be set properly once before the structured mesh is generated first time.

Default Grid: edge length (m)

0.005

Target distance between the neighboring nodes in the inner part of the structured mesh.

This parameter is applied if there are no other requirements for the mesh density such as boundary layer condition or phase transition constrains.

In opposite to the Boundary layer thickness (m) and Last CV size towards wall (m) parameters the edge length acts reversible. After the structured mesh was generated, this parameter can be modified and the mesh generation can be repeated. Then the mesh density will be updated everywhere on the block boundaries and in the block inner where no special constrains are applied.

Default Grid: generate default grid

5 cm

causes the mesh generated to repeat generation whereas such mesh parameters as boundary layers and phase transition remains not affected. The recently prescribed Boundary layer thickness (m) is taken over and applied for the mesh distribution along the block boundaries.

Phase boundary: phase transition

not checked

The phase transition crystal-melt can be treated on the hybrid mesh.

Usually the melt is meshed by block-structured and the crystal only by unstructured mesh. The phase boundary coincides with the region boundary. This boundary separates the specified regions of the crystal and melt domains.

The specified phase transition will affect the crystallization or melting heat at this boundary during the thermal modeling.

Additionally the phase tracking procedure can be switched on and the shape of the phase boundary for the thermal equilibrium can be calculated.

The checking of the phase transition affects also properties of the structured mesh. The mesh lines at the phase boundary are aligned with the unstructured mesh there. Therefore first the appropriate density of the unstructured mesh should be set at the region boundary coinciding with the presumed phase boundary. The structured mesh generation can be then done after the unstructured mesh is prepared.

This setting is irreversible and should be set properly once before the structured mesh is generated first time.

Phase boundary: crystal

 

Number of region where the crystal is intended.

The region number is visible in the bottom part of the main CrysMAS window if the cursor is located inside of the region (The indication of the computation results should be switched of for this). This region should have at least one shared CAD line with the melt. In the case if more regions are included into the crystal only the number of the region in direct contact with the intended melt should be entered.

Phase boundary: melt

 

Number of region where the melt is intended.

The region number is visible in the bottom part of the main CrysMAS window if the cursor is located inside of the region (The indication of the computation results should be switched of for this). This region should have at least one shared CAD line with the intended crystal. In the case if more regions are included into the melt only the number of the region in direct contact with the intended crystal should be entered.

Phase boundary: discard phase tracking result

 

return the crystal and melt to the initial configuration before the phase tracking was started.

This option is available only if the structured mesh with the defined phase transition is already created and the thermal computation with phase tracking was already done.

The button push moves positions of the nodes in the affected crystal and melt regions to their start locations as it was after the last mesh generation.

This operation should be done before the structured mesh is going to be deleted and generated again, because otherwise the CAD geometry of the affected regions will stay in conflict with new generated mesh.

grid properties at the line: number of edges at line

 

Indicates number of control volumes at the selected line of the auxiliary CAD drawing. The CAD line of the CrysMAS drawing may contain one or more lines of the auxiliary drawing. The selection of the auxiliary lines acts simultaneously with the selection of the main lines. If one single auxiliary line is selected then the number of control volumes appears in the dialog field.

If the structured mesh was already generated, its density can be adjusted locally at the selected line. Change the indicated number of control volumes and press the Default Grid: generate default grid button. The number of control volumes will be changed at the selected auxiliary line.

The change of the mesh density will be propagated automatically until the end of the structured domain if it is required for preservation of the equality condition of the mesh size for each numerical block.

grid properties at the line: refinement factor

1.0

Prescribes the factor of geometrical progression for distribution of the mesh density along the selected auxiliary line. The default value 1 of the refinement factor affects nothing. If it deviates from 1 then the geometrical progression will be applied, also if the refinement rules of the boundary layer are applied for the line, while the refinement factor has a higher priority than the automatic mesh refinement in the boundary layer method. Therefore the refinement factor method can be applied if the automatic refinement should be adjusted.

The manual refinement factor doesn't work for lines of the phase boundary because the mesh distribution is attached to the fixed unstructured mesh there.

The change of the refinement factor will be accounted after the button Default Grid: generate default grid will be pressed.

grid properties at the line: recalc line

 

recalulates and displays line length and length of first mesh element on the line, as it would result from applying the current settings, but does not regenerate yet

grid properties at the line: accept and regenerate grid

 

repeat the mesh generation. It can be applied after the mesh was generated at least once. This doesn't affect the the options for the boundary layer and for the phase transition which were applied during previous mesh generation.

The repeated mesh generation applies changes in the manual refinement factor and number of control volumes at the selected single auxiliary line.

shift edges between 2 selected lines: number of edges to shift

2

Transfer of the edges between two recently selected auxiliary lines. This operation redistributes the mesh density along the side of the structured block without change of the total mesh size of the block. It can be useful for manual improvement of the mesh orthogonality of the single block.

At least two auxiliary lines should be selected. Both lines should belong to the same numerical block and to the same side of the block. The operation is not possible if at least one of the selected pair is shared by two numerical blocks.

The number of the edges transferred between the selected lines is defined in the dialog window and can be any positive number which doesn't affect zero or negative number of edges at the auxiliary line which is treated as a "source" of edges.

The transfer of the edges to the last selected line is activated by the button "> >" press. The transfer in opposite direction takes place by the "< <" button press. The operation is reversible and has an advantage that no reallocation of degrees of freedom at the structured mesh is required afterwards.

HELP

 

A brief user guidance about the generation and application of structured mesh can be found here.