Mesh Location This allows choosing between meshing the Interior Volumes, Exterior Volumes, or All Volumes. There are three options available in the drop down: Interior Volumes Exterior Volumes All Volumes

Figure 4.20 - Mesh location

Interior Volumes

This creates meshes in the interior of all volumes as defined by the closed CAD Surfaces. The selection of CAD Surfaces must be such that the volume is “water tight.” If not, the exterior volume mesh will “leak” inside and no interior volume will be created.

• The General Mesher first creates all volumes and then deletes any unwanted volume. Because it first creates all volumes (interior and exterior), the presence of neighboring volumes has an influence on the interior mesh of each other. If a “cleaner” mesh is desired, it is recommended to mesh each interior volume independently.

• The bounding box influences the size of the mesh formed in interior volumes. In this regard, meshing multiple volumes or changing the bounding box options will result in different meshes.

• In some cases, the relative position of the bounding box influences the resolution of the mesh formed in interior volumes. In some cases, an unwanted fine resolution of a boundary can be corrected by a slight displacement of the bounding box.

Note: Ensure that the interior volumes are “water tight.”

Exterior Volumes

This creates meshes on the exterior of all volumes as defined by selected closed CAD Surfaces.

• The extent of an exterior volume will depend on the limits set under the bounding box options. The outer surfaces of this bounding box will be meshed as boundaries.
• An external volume can be used to create a virtual “wind tunnel” around an object

Note: The General Mesher first creates all volumes and then deletes any interiors volume.

All Volumes

This creates meshes on both the interiors and exterior of all volumes as defined by the selected CAD Surfaces.

• Internal CAD Surfaces will be meshed as Interfaces.

• The extent of the exterior volume will depend on the limit set under the bounding box options. The outer surfaces of this bounding box will be meshed as boundaries.

• Interior volumes, as defined by selection of CAD Surfaces , must be “water tight.” If not, the external volume mesh will “leak” inside and no interior volume will be formed.

Note: Only CAD Surfaces and associated Volumes that are selected in the Geometric Entities Panel will be meshed.

 

Figure 4.21 - Interior volumes

Figure 4.22 - Exterior volumes

Figure 4.23 - All volumes

 

Bounding Box Margins This places a box around a volume to be meshed. It is used as the starting point for subsequent cell division by the binary tree logic in the General Mesher. The dimensions and orientation of the bounding box are dictated by the Bounding Box Margins and the Advanced Mode options, Tree Orientation X Axis and Tree Orientation Y Axis. The options are Uniform Margins, Nonuniform Margins and Diagonal Positions.         Figure 4.24 - Ellipsoid and Bounding box

Figure 4.25 - Bounding box margins

Note: The bounding box influences the distribution of the mesh formed in interior volumes. In this regard, meshing multiple volumes or changing the bounding box options will result in different meshes. In some cases, an unwanted fine resolution of a boundary can be corrected by a slight displacement of the bounding box.

Uniform Margins: The bounding box will be constructed using uniform margins. When it is selected, it requires to set the Size as a sub-parameter.

Figure 4.26 - Uniform-Relative size (0.5)

Figure 4.27 - Uniform-Absolute size (0.5)

	Note: If the Cell Size Specification is Absolute Size, the thickness of all margins will be equal to the input value of Size in meters.
	Note: If the Cell Size Specification is Relative Size, the thickness of the margins will be equal to the input value of size times the dimension of the object in each direction.

Nonuniform Margins:

The bounding box is constructed using non-uniform margins. When selected, it requires setting the Minimum Side Sizes and Maximum Side Sizes as a sub-parameter.

Diagonal Positions:

The bounding box is constructed using two points defining opposite corners of the box. When selected, it requires setting the Minimum Corner Position and Maximum Corner Position as a sub-parameter.

• If the Cell Size Specification is Relative Size, the location of the two corner points will off-set from the maximum and minimum of the object being modelled, such that the default of Minimum Corner Position = (0,0,0) and Maximum Corner Position = (1,1,1) results in a tightly wrapped bounding box, as shown in Figure 4.28.
• An example of Relative Size, using non-default settings of Minimum Corner Position = (-1,-1,-1) and Maximum Corner Position = (2,2,2) is shown in Figure 4.29. Note how the minimum and maximum corner values times the object’s <length, height, width> are added to the minimum corner of the object to get the max or min bounding box corners. In this case, the result is a box centered around the object. Also note that the reference lengths are different for each direction, based on the unequal dimensions of the cylinder.

Figure 4.28 - Minimum corner position = (0,0,0) and Maximum corner position = (1,1,1)

Figure 4.29 - Minimum corner position = (-1,-1,-1) and Maximum corner position = (2,2,2)

 

Cell Size Specification It is used to specify whether to use Relative Size or Absolute Size length scales for meshing parameters requiring length, such as the bounding box options, Maximum Cell Size, Minimum Cell Size, and Cell Size on Surfaces (see, Figure 4.31). The options are: Relative to All CAD Surfaces: The length scale is decided considering maximum dimension of all the CAD Surfaces. Relative to Selected CAD Surfaces: The length scale is decided considering maximum dimension of selected CAD Surfaces. Absolute: The Absolute cell size in meters.

Figure 4.30 - Cell size specification

 

 

 

 

Figure 4.31 - Relative cell size specification

Absolute Size

This means all coordinates and lengths (meters) to the model’s coordinate system.

Relative Size

This is used to specify the meshing parameters requiring length, such as the Bounding Box Margins, Maximum Cell Size, Minimum Cell Size, and Cell Size on Surfaces as a relative size to the CAD Surfaces.

 

Critical Edge Angle

This controls the accuracy with which the CAD Surfaces edge is resolved by the mesh.

• Smaller the edge angles, higher the resolution.

Figure 4.32 - Critical edge angle

Figure 4.33 - Critical edge angle (30° and 20°)

 

Curvature Resolution

This controls the accuracy with which the CAD Surfaces edge is resolved by the Mesh.

• Smaller the angles, higher the resolution.

Figure 4.34 - Curvature resolution angle

Figure 4.35 - Curvature resolution default (35°) and user defined (20°)

Figure 4.36 - Curvature resolution (Boundary) default (35°) and user defined (20°)

 

Maximum Cell Size

This controls the size of the cells throughout a mesh volume. Maximum Cell Size is a length scale specified in terms of Relative Size or Absolute Size.

• No cell in the volume can have a cell size larger than the Maximum Cell Size.
• This is applied throughout the Volume being meshed. For additional refinement inside a volume, the Create a Refinement Zone option can be used.

Figure 4.37 - Maximum cell size

Figure 4.38 - Minimum cell size

 

Minimum Cell Size

This limits how small cells can be in attempting to resolve the geometry using the general mesher. Minimum Cell Size is a length scale specified in terms of Relative Size or Absolute Size. It applies to all the cells in a volume (see, Figure 4.38).

• Smaller values provide higher resolution. If the general mesher hits the limit set by the Minimum Cell Size, then sub-features are formed. A small value of Minimum Cell Size is normally recommended to allow the general mesher, the flexibility to resolve fine features and prevent the formation of sub-features.
• Minimum Cell Size is a lower limit and will not be required if the general mesher is able to meet the resolution criteria ; Curvature Resolution and Critical Edge Angle using larger cells. (i.e. the cells may not be as small as the Minimum Cell Size).
• Large values of Minimum Cell Size is also used to “plug” holes in a “dirty” geometry, but at expense of the creation of sub-features and the possible loss of resolution in other areas.

 

Cell Size on Surfaces

This controls the size of the cells for all surfaces of a mesh volume. Cell Size on Surfaces is a length scale specified in terms of Relative Size or Absolute Size. No cell on the surface can have a cell size larger than the Cell Size on Surfaces.

• This parameter is applied for all the surfaces of the volume being meshed.
• Smaller values will provide higher resolution.

• Usually the Cell Size on Surfaces is specified smaller than the maximum cell size to capture the geometric features with higher resolution.

Figure 4.39 - Refined setting

Figure 4.40 - Coarse setting

 

Create a Refinement Zone

This controls the size of the mesh cells within defined zones of a volume. Any number of refinement zones can be created. Three types of zones are available: Cylindrical Zone Refinement, Box Zone Refinement and User Defined Refinement.

 

Cylindrical Zone Refinement and Box Zone Refinement

• Cells within a zone are subsequently based on Cell Size, which is similar in function to Maximum Cell Size.

• Once a refinement zone is created, the desired dimensions of the zone geometry and the Cell Size is set prior to the General Mesher operation. An example of two refinement zones (Box and Cylinder) is shown in Figure 4.41.

  The specified value of Cell Size is applied inside the meshed zone.

 

 

 

 

Figure 4.41 - Example of refinement zones (Box and Cylinder)

 

User Defined Refinement

This option is used, when user wants to refine any arbitrary region in the domain. User need to write a expression to define a particular region and cell setting to be used.

• An example of user defined refinement setting is shown in Figure 4.42. Here, rzone is the function used to refine the mesh in the triangular region.

• The value of 0.01 m Cell Size setting is applied inside the refinement zone, elsewhere 0.04 m is used.

• Mesh created using expression is shown in Figure 4.43.

 

Figure 4.42 - User Defined Zone Mesh settings

Figure 4.43 - User Defined Mesh Refinement

 

Cell Size on Boundaries This controls the size of the boundary cells generated next to an individual CAD Surface. It is a length scale specified in terms of Relative Size or Absolute Size. No boundary cell at the selected surface can have a cell size larger than the corresponding Cell Size on Boundaries. The User Input value of the Cell Size on boundaries is applied only for the selected surface. Smaller values will provide higher resolution.

Figure 4.44 - Cell size on boundaries

 

Min. Cell Refinement on Boundaries

This limits how small the cells can be in attempting to resolve a CAD geometry using the General Mesher. It controls the limiting size of the boundary cells generated next to an individual CAD Surface. Unlike, Minimum Cell Size, which is used to control the smallest cells in the entire volume, the Minimum Cell Refinement on Boundaries is used to provide local refinement on CAD Surfaces that present small features such as tight gaps, sharp curvature etc.

The Min. Cell Refinement on Boundaries is specified for a selected CAD Surface prior to the General Mesher. The operation as follows: Mesh Panel > General Mesher Geometric Entities Panel > CAD Surface > [Desired Surface] Properties Panel > Geometry Tab > Min. Cell Refinement on Boundaries > [User Input]   Three different levels of limiting are offered under Min. Cell Refinement on Boundaries: Refine One Level, Refine Two Levels and Refine Three Levels. Refine One Level: Binary tree mesh decreases the Minimum Cell Size by half for selected boundaries Refine Two Levels: Binary tree mesh decreases the Minimum Cell Size by four times for selected boundaries Refine Three Levels: Binary tree mesh decreases the Minimum Cell Size by eight times for selected boundaries

Figure 4.45 - Min. cell refinement on boundaries-options

 

Cell Size near Critical Edges

This controls the size of the cells near a critical edge. It is a length scale specified in terms of Relative Size or Absolute Size. No interior cell adjacent to a critical edge can have a cell side larger than the specified value of the Cell Size near Critical Edges.

• Smaller values will provide higher resolution.
• Cell Size near Critical Edges is applied for all critical edges of the volume being meshed.
• A critical edge is one that subtends an angle more acute than the Critical Edge Angle.

Figure 4.47 - Cell size near critical edges

Figure 4.48 - Cell size near critical points

 

Cell Size near Critical Points

This controls the size of the interior cells near critical points. Cell Size near Critical Points is a length scale specified in terms of Relative Size or Absolute Size. No interior cell near a critical point can have a cell size larger than the Cell Size near Critical Points (see, Figure 4.48).

• Cell Size near Critical Points is applied for all critical points of the volume being meshed.
• Smaller values will provide higher resolution.
• A critical point is the point connecting two or more critical edges.

 

Cell Size on Surface Near Edges

This controls the size of the boundary cells near the critical edge. It is a length scale specified in terms of Relative Size or Absolute Size.

• No boundary cells adjacent to a critical edge can have a cell side larger than the Cell Size on Surface Near Edges (see, Figure 4.47).
• Cell Size on Surface Near Edges is applied for all critical edges of the volume being meshed.
• Smaller values will provide higher resolution.
• Cell Size on Surface Near Edges is similar to Cell Size near Critical Edges, but the first applies to boundary cells and the second applies to interior cells.

 

Cell Size on Edge Near Points

This controls the size of the cells on edges near a critical points. It is a length scale specified in terms of Relative Size or Absolute Size.

• No Edge adjacent to a critical point can have a cell size larger than the Cell Size on Edge Near Points (see, Figure 4.48).
• Cell Size on Edge Near Points is applied for all critical points of the volume being meshed.
• Smaller values will provide higher resolution.

 

Volume Name by Surface Prefix

This allows to activate naming of volumes based on the prefix of the CAD Surface names. In conjugate heat transfer analysis, CAD domain may contains multiple solid components and a fluid volume, in such cases Volume Name by Surface Prefix is helpful.

For example, if a mesh is generated with the CAD Surfaces: inlet_inlet, inlet_walls, inlet_mgi, volute_mgi, volute_outlet and volute_walls, the Volumes are automatically generated as inlet and volute.

 

Tree Orientation X-Axis This gives the orientation of the bounding box used in the Binary Tree Mesh algorithm. The user provides the , and components of a vector that will become the new orientation of the X-Axis of the bounding box. The Tree Orientation X Axis and Tree Orientation Y Axis do not need to be orthogonal. The tree orientation for the Z axis is based on the cross product of the Tree Orientation Y Axis and Tree Orientation X Axis.         Figure 4.49 - Tree orientation X axis (default settings)           Figure 4.50 - Tree orientation X axis (User settings)

Figure 4.51 - Tree orientation settings

 

Tree Orientation Y-Axis

This gives the orientation of the bounding box used in the Binary Tree Mesh algorithm. The user provides the , and components of a vector that will become the new orientation of the Y-axis (see, Figure 4.50) of the bounding box.

 

Node Merge Tolerance (Distance)

This sets the tolerance at which two nodes would be merged into a single point. Node Merge Tolerance is a length scale specified in terms of Relative Size or Absolute Size.

• Smaller values will provide higher resolution.
• Node Merge Tolerance (Distance) is applied for all critical points of the volume being meshed.

Figure 4.52 - Critical points merged

Figure 4.53 - Refine cells next to boundary cells

 

Refine Cells next to Boundary Cells

This refines the cells in the transition from one boundary to the next such that they are of the same order in size.

• This is applied for all critical points of the volume being meshed (see, Figure 4.53).
• This is a length scale specified in terms of Relative Size or Absolute Size.

 

Parallel Cell Aspect Ratio

This controls the aspect ratio of the cells created by the Binary Tree Mesher. Parallel Cell Aspect Ratio controls mesh density near the control volume surfaces and has a value between 1 and 8.

 

Figure 4.54 - Aspect ratio = 4

Figure 4.55 - Aspect ratio = 1,2,8

 

Maximum Cell Proportion

This limits the aspect ratio of the cells generated by the General Mesher. The aspect ratio of cells can be controlled in , and direction. The default value for is 1,1,1 respectively. The aspect ratio can be relaxed in a particular direction depending on the geometry and flow physics. For e.g., in the case of a long pipe with smaller diameter, the aspect ratio can be relaxed to 2,1,1 in order to reduce the cell count.

 

Sub-feature Options

A sub-feature is a “stair-step” mesh created, when the Simerics Binary-Tree Mesh algorithm is unable to resolve a feature of the geometry. The Sub-feature Options are used to control the grouping of sub-features. The sub-features are grouped together as follows: Combined with Patches: Sub-features are combined with respective boundaries. Separate Patches: Sub-features are combined into a separate boundary. Separate Volumes: Sub-features are separated out as individual volume. To the extent that a sub-feature is a small deviation in the precision of the mesh it will have only a minor effect on accuracy of the solution. They can be combined with the appropriate adjacent boundary.   Note: Reducing the Minimum Cell Size usually reduces the number and size of sub-features.

Figure 4.56 - Sub-features options

 

 

 

 

 

Figure 4.57 - Sub-features

Volume Options When different closed volumes are meshed together, Volume Options gives the output for volumes. For example, if the meshing is carried out by selecting all CAD Surfaces of inlet and outlet which define two closed volumes, the output can be obtained using either of the following under Volume Options: Multiple Volume: Outputs all the volumes Biggest Volume: Outputs only the biggest volume of all volumes Single Volume: Outputs only one combined volume

Figure 4.58 - Volume options

 

Volume Order By Size

This allows ordering of Volumes in the Geometric Entities Panel based on the cell count (bigger volume to smaller).