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4.4 Mesh Movement

Mesh movement is the time dependent change of volume mesh to solve transient flows. This is achieved using the Volume Remesh feature in Simerics-MP/Simerics-MP+.

Specify the method of mesh movement as follows:

Geometric Entities Panel > Volumes > [Desired Volume]

Properties Panel > Model Tab > Common > Volume Remesh > [Desired Method]

Volume can be re-meshed by the following methods:

  

Figure 4.107 - Volume remesh-method
 

Note: The effect of boundary motion due to remesh is not automatically included in the shear terms for the flow module. Shear effects must be accounted for by correct specification of the corresponding Boundary Condition (BC) in the flow module. (For example, a rotating wall must be given the Flow BC = Rotating Wall.)

For brief description of each method, click the respective Method or click Description drop-down list.

ClosedDescription

Translation

This method translates a selected volume and associated mesh. The motion is defined by a Displacement or a Velocity. The associated methods under Options are:

  1. Displacement: This translates a selected volume based on a function of a displacement vector. The displacement is specified in terms vector or as a function of time (using the expression editor). For both Transient and Steady State Simulation, this is relative to the position of the volume in the original Mesh file (*.sgrd), even for a restart using Start from Solution. This applies as follows:
    • For a Steady State Simulation, the displacement is applied once at the start of the simulation.
    • For a transient simulation, the displacement is applied at the beginning of each time-step but is not cumulative.
  2. Velocity: This translates a selected volume based on a function of a velocity vector. The displacement is calculated based on the velocity which is specified in terms of vector or as a function of time (using the Expression Editor). This is not relevant for a Steady State Simulation. It only translates the volume for a Transient simulation.
  

Figure 4.108 - Method-Translation

 

Example:

The Translation motion, using volume remesh is simulated as follows:

  1. Open the project file “cylinder_translation.spro” from the mesh_movement tutorial folder in the working directory.
  2. Select Volumes in Geometric Entities Panel.
  3. Verify Value as 0,0.1,0 for co-ordinates under Volume Remesh in the Model Tab of Properties Panel.
  4. Run the simulation to see the translation of volume based on Value.

 

  

Figure 4.109 - Animation-Translation

 

Rotation

This method rotates a selected volume and associated mesh as a function of time. The parameters associated with Rotation are:

  • Rotational Direction: Determines the direction of rotation for the rotating volume. The direction can be chosen as Clockwise, Counter Clockwise and Both Directions.
  • Rotational Speed: Determines the magnitude (and in some cases, the direction) of the volume rotation. A negative value of Rotational Speed corresponds to a counter clockwise rotation when the Rotational Direction is set to Both Direction. This value can be specified in terms of rpm or Expressions (in the Edit Expressions ).
  • Rotational Center: Specifies the rotational center for the rotating volume. This is specified in terms of an coordinate lying on the rotational axis.
  • Rotational Axis Vector: Used to specify the Rotational Axis Vector for the volume’s rotation. The values are the components of the Rotational Axis Vector.

The flow field for a re-meshing volume is displayed in terms of the stationary (laboratory) reference frame. Stationary volumes and those with remeshing can be connected using the MGI algorithm.

  

Figure 4.110 - Method-Rotation

 

Example:

The Rotation motion, using volume remesh is simulated as follows:

  1. Open the project file “cylinder_rotation.spro” from the mesh_movement tutorial folder in the working directory.
  2. Select Volumes in Geometric Entities Panel.
  3. Verify Rotational Speed as 1 under Volume Remesh in the Model Tab of Properties Panel.
  4. Run the simulation to see the rotation of volume based on Rotational Speed.
  

Figure 4.111 - Animation-Rotation

 

Compression/Expansion

This method deforms a volume based on a Scale Length and Reference Point. Compression/Expansion motion stretches the shape of the selected volume uniformly in all three directions around a Reference Point using the following equations shown in Figure 4.112:

 

 

 

 

Figure 4.112 - Compression/Expansion

The parameters associated with the Compression/Expansion are Scale Length and Reference Point.

  Note: An user defined expression can be input for the scale length as a function of time.
 

Figure 4.113 - Method-Compression/Expansion

 

Example:

The Compression/Expansion motion, using volume remesh is simulated as follows:

  1. Open the project file “cylinder_compression.spro” from the mesh_movement tutorial folder in the working directory.
  2. Select Volumes in Geometric Entities Panel.
  3. Click Edit Expressions to view the Global Expression for Scale Length under Volume Remesh in the Model Tab of Properties Panel.
  4. Run the simulation to see the compression of volume based on the scale length and reference point.
  5. Similarly, the scale length expression (s=1-time/20) can be changed to see the expansion of volume.

 

  

Figure 4.114 - Animation-Compression

 

Composite Motion

This method deforms a volume based on a Reference Point and One, Two, or Three direction points. This method stretches the shape of the selected volume using a reference point and one, two, or three “tug” points that stretch the coordinate system as if elastic.

  

Figure 4.115 - Method-Composite motion

 

 

 

 

Figure 4.116 - Composite motion

There are three methods under Option for Composite Motion:

  • Two Points: This has a Reference Point and a First Direction Point.
  • Three Points: This has a Reference Point, a First Direction Point and a Second Direction Point.
  • Four Points: This has a Reference Point, a First Direction Point, a Second Direction Point and a Third Direction Point.

The Directional Points are defined as functions of time using the expression editor. The Reference Point can be stationary or a function of time.

  

Figure 4.117 - Composite motion-Parameters

For example, the effect of a direction point, , on a point A in the volume is based on the Reference Point, , as follows:

4.1  

4.2  

4.3  

Example:

The Composite motion, using volume remesh is simulated as follows:

  1. Open the project file “cylinder_composit_motion.spro” from the mesh_movement tutorial folder in the working directory.
  2. Select Volumes in Geometric Entities Panel.
  3. Click to view the Global Expression for First Direction Point under Volume Remesh in the Model Tab of Properties Panel

    4. f=2

    xx=0.2+0.1*sin(2*3.14*time*f)

  4. Run the simulation to see the composite motion of volume based on First Direction Point.
  

Figure 4.118 - Animation-Composite

 

By Dynamics

This method deforms/moves a volume as a function of time based on motion defined using a selected Dynamic module.

 

Note: At least one Dynamics module (e.g. Translation (1-DOF) or Rotation (1-DOF)) must have been activated for By Dynamics to have an option for controlling the motion.

Example:

The Dynamics motion, using volume remesh is simulated as follows:

  1. Open the project file “cylinder_by_dynamics.spro” from the mesh_movement tutorial folder in the working directory.
  2. Select Volumes in Geometric Entities Panel.
  3. Verify Dynamics as Translation (1 DOF) under Volume Remesh in the Model Tab of Properties Panel.
  4. Run the simulation to see the dynamics of volume based on Dynamics.
  

Figure 4.119 - Animation-By dynamics

 

Radial Motion(Cylinder)

This method deforms the annulus volume based on movement of inner cylinder with respect to stationary outer cylinder. The control parameters associated with Radial Motion(Cylinder) are:

  • Displacement: The function to displace the moving cylinder.
  • Center of Cylinder: Center of the moving cylinder.
  • Cylinder Axis Vector: The common axis of the moving and stationary cylinder.
  • Radius of Moving Cylinder: The radius of the cylinder to be moved.
  • Radius of Stationary Cylinder: The radius of the stationary (outer) cylinder.
  • Minimum Gap: The minimum gap allowed between the two cylinders.
  

Figure 4.120 - Method-Radial motion(Cylinder)
 

Note: When creating the mesh, it is compulsory to create a concentric annulus and then deform it.

 

 

 

 

Figure 4.121 - Radial motion(Cylinder)

The Radial Motion (Cylinder) option was originally developed for the relative motion between a journal bearing and its shaft (a deforming annulus such as shown above), but can be used to deform any mesh between two reference cylinders. Only radial displacement of the moving cylinder has any effect on the mesh/ volume deformation.

Example:

The Radial motion (Cylinder), using volume remesh is simulated as follows:

  1. Open the project file “cylinder_annulus.spro” from the mesh_movement tutorial folder in the working directory.
  2. Select Volumes in Geometric Entities Panel.
  3. Click Edit Expressions to view the Global Expression for Displacement under Volume Remesh in the Model Tab of Properties Panel

    4. f= 2

    amp=0.01

    xx=amp*sin(2*3.14*time*f)

    yy=amp*cos(2*3.14*time*f)

  4. Run the simulation to see the motion of volume based on Displacement
  

Figure 4.122 - Animation-Annulus

The Displacement of the moving cylinder is defined using the Expression Editor as follows:

 

 

 

 

Figure 4.123 - Moving cylinder-Expression editor

As illustrated for the cube below, only the /volume between the reference cylinders is deformed:

 

 

 

 

Figure 4.124 - Mesh/Volume between the reference cylinders

 

Expression

This method is used to deform a volume based on user-defined expressions for the coordinates. This moves the coordinates of a selected volume and associated mesh as a function of time, based on expressions for each coordinate. The new coordinate positions are based on their original coordinates which themselves do not change during remeshing. To find the example using expressions, see this reference.

Example:

The motion using an expression is simulated using the following steps.

  1. Open the project file “cylinder_expression.spro” from the mesh_movement tutorial folder in the working directory.
  2. Select Volumes in Geometric Entities Panel.
  3. Verify Method as Expression under Volume Remesh in the Model Tab of Properties Panel.
  4. Run the simulation to see the motion of volume based on Method.
  

Figure 4.125 - Animation-Expression

 

External Grid File

The deformation of a volume is specified through external files in this method. The coordinates of a selected volume and associated mesh move as specified by an External Grid File.

The entries associated with External Grid File are:

  • Base Name: Base name of all the external files.
  • Files Found: Number of files to be read.
  • Header Lines: Number of lines preceding the coordinates in the external file.
  • Cyclic: The files are read repeatedly for each cycle if Yes is selected.
  

Figure 4.126 - Method-External grid file
 

Note: The name of the external grid file should in the format of <BaseName><number>. The file contains the coordinates with header line indicating the number of points in the corresponding file.

 

 

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