MESH_SMOOTH

Definition of parameters for the mesh smoothing algorithm for shape optimization.

ID_NAME

= <name_of_mesh_smooth>

Name of the MESH_SMOOTH definition.

EL_GROUP

= <name_of_element_group>

Name of the element group for which MESH_SMOOTH is done.

MS_LAYER

= <name_of_node_group>, <number_of_elementlayers>

The mesh smooth element group is defined automatically. Starting with the referenced node group and the defined number of grouped element layers.

FREE_SF

= FIX, 0

= FIX, <number_of_node_layers>

Free surface nodes of the MESH_SMOOTH area which is completely fixed (number of node layers <number_of_node_layers> depending upon the remaining free design nodes).
 

= FREE

Free surface nodes of the MESH_SMOOTH remaining free area (not fixed).

BOUNDARY

= FIX

Nodes on the border of the mesh smooth area are fixed.
 

= FREE

No nodes are automatically fixed.

STRATEGY

= CONSTRAINED_LAPLACIAN

Use constrained Laplacian MESH_SMOOTH strategy.
 

= LOCAL_GRADIENT

Use local gradient mesh smooth strategy; not recommended for models with many nodes in mesh smooth area.

LEVEL_QUAL

= NOT

= LOW

= MEDIUM

= HIGH

Parameter to set the quality of the mesh. Increasing mesh quality with NOT -> LOW -> MEDIUM -> HIGH.

QUAL_LIST

= YES

List of the qualitative bad elements.
 

= NO

No list of the qualitative bad elements.

QUAD_LOW_ANGLE

= <value>

= 20

Angle between 0 and 89 degrees.

QUAD_HIGH_ANGLE

= <value>

= 160

Angle between 91 and 180 degrees.

TRIA_LOW_ANGLE

= <value>

= 20

Angle between 0 and 59 degrees.

TRIA_HIGH_ANGLE

= <value>

= 140

Angle between 61 and 180 degrees.

TETRA_LOW_ASPECT

= <value>

= 0.222

Value between 0.00177 and 1.30.

TETRA_ HIGH_ASPECT

= <value>

= 8

Value between 1.36 and 999.

SOLVER_CHECK

= YES

The solver quality criteria are checked.
 

= NO

The solver quality criteria are not checked.

SOLVER_STOP

= YES

Optimization will be stopped if quality criteria are not satisfied.
 

= NO

No stop.

Q4TAPER

= <value>

= 0.5

Value for Q4TAPER (greater or equal 0).

Q4SKEW

= <value>

= 30

Angle for Q4SKEW (greater or equal 0).

TETRAAR

= <value>

= 100

Value for TETRAAR (greater or equal 0).

T3SKEW

= <value>

= 10

Angle for T3SKEW (greater or equal 0).

CORRECT_ ELEMENTS

= YES

= NO

Correct tetrahedral elements that got inverted or too high aspect ratios during optimization.

CE_CORRECTION_FACTOR

0 <= (<value>) < 1

= 0.5

Correct elements by multiplication of optimization displacements with this factor.

CE_CORRECTION_LOOPS

= <int_value>

= 4

Trying to correct a single element <int_value> times.

CE_FAIL_ACTION

= RESET

= CONTINUE

Handling of not correctable elements:

RESET: Optimization displacement is set to zero for the current iteration.

CONTINUE: Do nothing and risk a solver crash.

Items for STRATEGY = CONSTRAINED_LAPLACIAN

LEVEL_CONV

= LOW

= MEDIUM

= HIGH

Convergence parameter of MESH_SMOOTH.

LEVEL_DVCON

= NOT

= LOW

= MEDIUM

= HIGH

Parameter for checking frequency of DVCON_SHAPE entries during MESH_SMOOTH.

Items for STRATEGY = LOCAL_GRADIENT

FEATURE_RECOGNITION

= <value>

= 30

Angle used for recognition of edges and corners (greater or equal 0).

Remarks

  1. In MESH_SMOOTH certain elements are not permitted (e.g. beam elements, for more information please refer to the User Manual). From the user-defined element group a system-defined element group with the name Mesh_smooth_id_name_'ELEM' is created in which the non-permitted elements are eliminated and a system-defined node group Mesh_smooth_id_name_'NODE' is generated that contains all the necessary boundary nodes.
  2. The calculation time for MESH_SMOOTH increases with an increase in the number of iterations, i.e. LEVEL_CONV=LOW is faster as HIGH. A higher convergence parameter gives a better result in MESH_SMOOTH. The aim for the user is: to work with the lowest convergence parameter as possible and only switch to the next highest convergence parameter when having problems.
  3. BOUNDARY: MESH_SMOOTH is working on an element group and changes due to mesh smoothing should remain within this group. The BOUNDARY=FIX option is used to fix the nodes (inner and surface nodes) at the border of the mesh smooth area defined by the element group. In common, this behavior is preferred. All nodes fixed due to this settings are stored a node group with the name <Mesh_smooth_id_name>_BOUN. If you do not want the "border" nodes to be fixed, you can select the BOUNDARY = FREE option. Then you are responsible to fix the proper nodes by yourself via DVCON_SHAPE entries.
  4. FREE_SF: Free surface nodes include all surface nodes of the MESH_SMOOTH area that are neither design nodes (command DV_SHAPE operator ND_GROUP) or restricted in any way (command DVCON_SHAPE operator ND_GROUP). The specified number of node layers <number_of_node_layers> controls the area which is used for remeshing. If surface nodes are fixed with FREE_SF=FIX, a node group <Mesh_smooth_id_name>_SF is automatically created and a DVCON_SHAPE entry <Mesh_smooth_id_name>_SFIX is generated. The relevant entry for DVCON_SHAPE is then automatically activated in OPTIMIZE.
  5. Calculation time for MESH_SMOOTH increases when the sequence is changed, LEVEL_DVCON = NOT -> LOW -> MEDIUM -> HIGH. The user should work with the lowest parameter possible and only switch to the next highest parameter when problems arise.
  6. LEVEL_QUAL: Calculation time for MESH_SMOOTH increases in the sequence LEVEL_QUAL = NOT -> LOW -> MEDIUM -> HIGH. The user should work with the lowest parameter possible and only switch to the next highest parameter when problems arise. With LEVEL_QUAL=NOT the entries for QUAL_LIST, QUAD_LOW_ANGLE, QUAD_HIGH_ANGLE, TRIA_LOW_ANGLE, TRIA_HIGH_ANGLE, TETRA_LOW_ASPECT, TETRA_HIGH_ASPECT do not have any influence.
  7. Determining quality: To determine the quality of an element, the angle of the element is determined. Tetrahedron elements have the additional quality determination of the aspect ratio. The value of quality is between 1 (the best element quality) and 0 (the worst element quality). Using the parameter QUAL_LIST the list of specifications of the worst elements are controlled with a quality of zero. The values shown with the help of QUAL_LIST are only internal values for MESH_SMOOTH and may be different from values of preprocessors.

    QUAD surfaces (QUAD element, side surfaces from HEXA elements):

    Optimal angle is 90 degrees:

    Quality=1

    Angle less than and equal to QUAD_LOW_ANGLE:

    Quality=0

    Angle greater than and equal to QUAD_HIGH_ANGLE:

    Quality=0

    TRIA surfaces (TRIA elements):

    Optimal angle is 60 degrees:

    Quality=1

    Angle less than and equal to TRIA_LOW_ANGLE:

    Quality=0

    Angle greater than and equal to TRIA_HIGH_ANGLE:

    Quality=0

    TRIA surfaces (side surfaces from TETRA elements):

    Optimal aspect ratio is 1.33 degrees:

    Quality=1

    Aspect ratio less than and equal to TETRA_LOW_ASPECT:

    Quality=0

    Aspect ratio greater than and equal to TETRA_HIGH_ASPECT:

    Quality=0
  8. Solver criteria of quality: SOLVER_CHECK must be activated so SOLVER_STOP can be executed. With SOLVER_CHECK=NO the entries SOLVER_STOP, Q4TAPER, Q4SKEW, TETRAAR, T3SKEW have no effect. The values found in SIMULIA Tosca Structure should be identical to the values which have been set in the solver. A meaningful program stop in SIMULIA Tosca Structure due to bad mesh quality is better than having errors in the solver!

Example

MESH_SMOOTH
 ID_NAME = my_mesh_smooth
 EL_GROUP = all_elements
 FREE_SF = FIX, 3
END_