Directed Meshing Properties

This topic describes the Properties of each of the nodes that are available for directed meshing.

Directed Mesh Properties

The following Properties are available when you select the Directed Mesh node. Some of these are only relevant to 1-1 Direct Meshing, as indicated.

Input Parts

Allows you to select one or more suitable parts from which to create a directed mesh. See Preparing CAD Parts For Directed Meshing and Preparing No-CAD Parts for Directed Meshing.

Mesher Execution Mode

Allows you to set the execution mode when running parallel servers. You can choose to run the mesh in two modes:

Serial – part collections are queued for meshing on the main processor only.
Concurrent –part collections are queued for meshing on multiple processes (see Concurrent Meshing).

Generate Internal Surfaces (1-1 Direct Meshing only)

Provides the option of creating internal surfaces within the directed mesh. There are two options for this:

Activated—creates a Directed Mesh > Internal Surfaces node which allows you to define an internal mesh faces between the channels of a directed mesh.
Deactivated—no internal faces are created within the directed mesh.

Rotational Sweep Coarsening

When activated, adds a Directed Mesh > Rotational Sweep Coarsening node by which you control the rotational sweep coarsening feature that adds successive layer transitions across which two or more cells are merged into a single cell.

Source Surfaces Properties

Source Surfaces: Allows you to select one or more surfaces to represent the source surface.

Target Surfaces Properties

Target Surfaces: Allows you to select one or more surfaces to represent the target surface.

Internal Surfaces Properties

Internal Surfaces (1-1 Direct Meshing only): Allows you to select a previously created empty part surface on which to create internal mesh faces. Mesh faces run along the internal and external sides of a channel running from a source mesh face, through the volume mesh, to the corresponding target mesh face.
If the part surface is assigned to a wall boundary, cross flow is not allowed between the channels. This functionality is useful when performing CFD analyses of heat exchangers which model hot and cold fluid streams through channels in a porous region between periodic interfaces.

Connected Parts – Part Properties

Each [part] node is named after the connected geometry parts that are selected for directed meshing.

Parts: Displays the names of the connected geometry parts that are selected for directed meshing.
Source Mesh Node: Displays the source mesh that is associated with the connected part.
Target Surface Mesh Smoothing: Controls whether the target surface mesh is smoothed. Activate this option to use the smoothing algorithms within the mesher. In some cases, such as simple cube and cylinder shapes, it is not necessary to smooth the target surface mesh. In other cases, smoothing a target surface mesh can deteriorate the surface mesh quality (this is especially true of M-1 direct meshing of more complex parts. In such cases, deactivate the smoothing of the target surface mesh.

Source Meshes – Existing Mesh Properties

Each source mesh node is named after the contacting part collection which the source mesh is defined on.

Source Mesh From

Specifies the source mesh. Choose from:

Contacting Volume Mesh – Extracts the mesh from a volume mesh that contacts the specified source surfaces.
Triangle Mesh – Extracts the latest triangle mesh of the part or parts being meshed. If the original triangulation is obtained, the source mesh that is extracted can be of poor quality if it contains long, narrow triangles. If the part is remeshed, the remeshed triangulation is obtained.
Quadrilateral Mesh – Obtained from the extracted triangulation. The mesh is dependent upon the quality of the extracted triangulation. The quadrilateral mesh that is obtained is quad-dominant with a mix of quads and triangles. The quadrilateral mesh does not faithfully replicate the extracted triangle mesh density.

Part Surfaces

Displays the part surfaces that are specified as the source surface meshes on the connected part.

Mesh Distributions

[Distribution] Properties

Part Collections

Sets the part collection to which this distribution is applied.

Mesh Controls

Allows you to create custom controls for each connected part in the directed mesh operation.

Use Default —allows you to specify the number and size of layers for all connected parts together.
Specify Custom—exposes the [Distribution] > Custom Controls node which allows you to create part controls for customizing the number of layers and stretching function for each connected part.

Size Specification

Sets the method by which the mesher determines the size of successive cell layers throughout the distribution. This choice affects the value nodes that you see under Default or Custom Controls.

Size Specification Method	[distribution] Parameters / Values for Custom Controls
Number of Layers Specify the number of layers and let the mesher determine the sizing.	Number of Layers Applies the specified Number of Layers between the source and target surfaces in the volume mesh. You can specify this property using a constant value or a global parameter. For a stack of connected parts, this is the sum of the cell layers through all the connected parts. When applied to a part control, the custom Number of Layers overrides the default Number of Layers and prints a warning message in the Output window if: The custom Number of Layers exceeds the default Number of Layers. All parts in the stack have a custom Number of Layers defined. When the custom Number of Layers for a part is subtracted from the default Number of Layers, the remaining number of layers are distributed to parts that are not in this Part Control. If a part is assigned to more than one Part Control, the highest value that is set for the Number of Layers is used for that part. Stretching Function See Stretching Function Properties. If you activate custom controls then this node is hidden for the default controls.
Size Specify size parameters and allow the mesher to calculate the number of layers.	Base Size Specifies the reference value for all relative size controls. Ignored when sizes are set as absolute values. Target Size Specifies the desired layer thickness you wish to achieve as a relative or absolute size. In the absence of any custom mesh control this size sets the layer thickness. If there are mesh controls for start and end thickness, for example, the layer thickness changes until the target size is achieved provided there is enough room to grow or shrink. Growth Rate The rate at which the layers grow within the volume distribution, defined as the ratio of the thickness of the current layer to the previous layer. Must be greater than 1.0. By default, this is set to 1.2. Spacing Gives you two options to activate: Customize Start - Specifies the layer thickness at the start of the part collection. Customize End - Specifies the layer thickness at the end of the part collection. Curvature Allows you to specify a number of divisions when generating mesh within curved portions of the geometry. Increasing the # Pts/Circle value increases the number of divisions. increases the divisions in curved areas of the geometry. By default this is set to 36.

Size Specification Method

[distribution] Parameters / Values for Custom Controls

Number of Layers: Specify the number of layers and let the mesher determine the sizing.

Number of Layers

Applies the specified Number of Layers between the source and target surfaces in the volume mesh. You can specify this property using a constant value or a global parameter. For a stack of connected parts, this is the sum of the cell layers through all the connected parts.

When applied to a part control, the custom Number of Layers overrides the default Number of Layers and prints a warning message in the Output window if:

The custom Number of Layers exceeds the default Number of Layers.
All parts in the stack have a custom Number of Layers defined.

When the custom Number of Layers for a part is subtracted from the default Number of Layers, the remaining number of layers are distributed to parts that are not in this Part Control.

If a part is assigned to more than one Part Control, the highest value that is set for the Number of Layers is used for that part.

Stretching Function

See Stretching Function Properties. If you activate custom controls then this node is hidden for the default controls.

Size: Specify size parameters and allow the mesher to calculate the number of layers.

Base Size

Specifies the reference value for all relative size controls. Ignored when sizes are set as absolute values.

Target Size

Specifies the desired layer thickness you wish to achieve as a relative or absolute size. In the absence of any custom mesh control this size sets the layer thickness. If there are mesh controls for start and end thickness, for example, the layer thickness changes until the target size is achieved provided there is enough room to grow or shrink.

Growth Rate

The rate at which the layers grow within the volume distribution, defined as the ratio of the thickness of the current layer to the previous layer. Must be greater than 1.0. By default, this is set to 1.2.

Spacing

Gives you two options to activate:

Customize Start - Specifies the layer thickness at the start of the part collection.
Customize End - Specifies the layer thickness at the end of the part collection.

Curvature: Allows you to specify a number of divisions when generating mesh within curved portions of the geometry. Increasing the # Pts/Circle value increases the number of divisions. increases the divisions in curved areas of the geometry. By default this is set to 36.

Number of Repetitions

Sets the number of times the volume mesh distribution is repeated between the source and the target surface. This repetition can be useful when meshing stacks of parts.

Stretching Function Properties

Stretching Method	Value Nodes
Constant No stretching applied.	None
One Sided Geometric Applies geometric progression to compute cell thickness.	One Sided Options Set the Stretching Mode to one of the following options and then set the required value in the child node: Stretching—ratio of spacing at layer n and layer n+1 Initial Wall Thickness—spacing at the first layer of cells Thickness Ratio—ratio of spacing between first layer and last layer of cells You can set the Stretch Value and Thickness Ratio using a constant value or a global parameter. To reverse the direction in which the stretching function applies, activate Reverse Direction.
One Sided Hyperbolic Hyperbolic-based stretching to compute cell distribution.	See One Sided Options above.
Two Sided Hyperbolic Hyperbolic stretching from both ends to compute cell distribution.	Two Sided Sets the following properties: Spacing at Source—initial spacing at the source surface Spacing at Target—initial spacing at the target surface Reverse Direction—activate in order to swap direction

When working with stacks of parts, and parts that are connected at the guide surface, Simcenter STAR-CCM+ attempts to fit the requested distribution to the stack of parts. The requested distribution in the resulting mesh cannot always be guaranteed since divisions close to the end of the part are moved to the end of that part.

Mesh Distributions – Custom Controls

When the Mesh Controls property for a Volume Distribution is set to Specify Custom, a Custom Controls node appears in which you can set specific property values for chosen parts.

Part Control Properties

Parts: Parts for which the custom control applies.
Enable Control: Activates the functionality of the Part Control.
Controls Display Mode: Choose to show All controls or only those you have already Customized.

[part control] Properties

Depending on your choice of Size Specification, you either see controls appropriate when setting the number of layers or those appropriate for size-based distributions. By default each control is set to Use Auto Computed Value. To define a custom value, set the option to Specify Custom Value, and then set the appropriate quantities beneath the Value node.

Custom Controls Node Right-Click Action

New Part Control: Creates a Part Control sub-node which allows you to customize the Properties of a part or parts that you select.

Rotational Sweep Coarsening – Mesh Coarsening Properties

The following Properties are available to set when you select the Directed Mesh > Rotational Sweep Coarsening node.

Part Collections

Sets the part collection to which this rotational sweep coarsening is applied.

Transition Controls

Defines the how the mesh transitions between the core mesh and the coarse mesh. There are two options for this:

Use Default—automatically computes where transitions are required in order to meet the constraints of the Aspect Ratio.
Specify Custom—Adds a Mesh Coarsening > Coarsening Transitions node which allows you to create one or more transitions manually.

Aspect Ratio

For a given mesh face on the guide surface the Aspect Ratio is the ratio of edge length in the radial direction to the edge length in the azimuthal direction. Coarsening tries to merge cells/faces such that the aspect ratio in the final mesh does not exceed the specified value. Transitions are computed automatically and the merge ratio at each transition is set to 2 by default. Specifying a smaller aspect ratio results in coarsening spreading further away from the rotational axis. The aspect ratio in the default setting is mainly intended to be used with constant stretching function in volume distribution.

Coarsening Transition Properties

Distance from rotational axis: The radial distance from the rotational axis at which this coarsening transition applies.
Merge ratio 1:: The number of cells that match a single cell, in the radial direction, across a transition.

Enable control: When activated, allows you to specify the properties of the transition in the window, and applies the transition when you generate the volume mesh.