Geometric Sensitivity

The Geometric Sensitivity mesher allows you to calculate and visualize how sensitive a 3D-CAD model or CAD Client model is to the adjustment of specific shape parameters. The mesher applies an offset to the specified parameters and calculates how sensitive the surface is to changes in the parameter for each face on the surface, using a finite difference approximation.

In Gradient-Based Optimization studies (see Setting up a Gradient (Sensitivity)-Based Optimization Study), Simcenter STAR-CCM+ combines the geometric sensitivities with the adjoint sensitivities to optimize a set of geometric parameters. The goal of the optimization is a specific engineering objective, for example, minimizing or maximizing a physical quantity of interest. The sensitivity provides a direction for the optimization algorithm to follow, which leads to a reduction in the number of evaluations required by the study to reach the optimal design.
  1. Identify the geometric features for the optimization and create the corresponding global parameters under the Automation > Parameters node.
    NoteThe Geometric Sensitivity mesher requires global parameters.
In 3D-CAD, you can use these global parameters directly in the definition of the geometric features, using an expression. Alternatively you can link the global parameters to existing design parameters. For CAD model imported from a Simcenter STAR-CCM+ CAD Client, you link the global parameters to the imported CAD parameters.
  1. To link a parameter imported from a CAD Client (CAD Parameters) or exposed from 3D-CAD (Design Parameters) to a global parameter:
    1. Copy the Value of the CAD parameter or design parameter to the Value of the global parameter.
    2. Using an expression, set the Value of the CAD parameter or design parameter to the name of the global parameter.


    When you define the global parameters, make sure you specify the correct units. The Geometric Sensitivity mesher uses the specified units to define the step size for the parameter adjustment.
  2. Create a new automated mesh operation.
  3. Right-click the Operations > Automated Mesh and select Select Meshers.
  4. In the Select Meshers dialog, select the Surface Remesher. Then, from the Optional Surface Meshers, select Geometric Sensitivity.
  5. Select the Default Controls > Geometric Sensitivity node and set the following properties:
    • Parameters
    • Relative Step Size
    • Minimum Step Size


    The relative step size is a non-dimensional parameter unlike the minimum step size which is an absolute value. The step size is calculated for each parameter independently and takes into account the units defined on the specific parameter. When executed, the mesher applies an offset to the geometric parameters. The applied offset is equal to the largest offset produced by either the relative step size or the minimum step size. For example, if the minimum step size is larger than the relative step size, the minimum step size defines the offset.

    To obtain an accurate sensitivity analysis for the geometry, set the properties to ensure the geometry is perturbed between 2% and 25% of the original element size on the remeshed surface. When you optimize the properties remember the change in the parameter size is not the distance in which the geometry is moved. Optimizing these properties prevents the results from becoming increasingly inaccurate with each step size, and reduces the potential of discretization or tessellation errors. The overall step size depends on the geometry and the definition of the parameters. For more information see Geometric Sensitivity Properties.

    Before running the mesher, you can check whether the step size calculated for each parameter is appropriate. To preview the step size and offsets:

  6. Right-click the Meshers > Geometric Sensitivity node and select Print Step Sizes.
    The mesher uses the positive and negative offsets to determine the sensitivity of the geometry.

  7. Right-click the Operations > Automated Mesh node and select Execute Surface Meshers.
    On execution, the Geometric Sensitivity mesher applies the calculated positive and negative offsets to the specified parameters, then calculates the geometric sensitivity using a finite difference approximation.
You can visualize the calculated sensitivity field in either a scalar or vector scene. For this Simcenter STAR-CCM+ creates a separate sensitivity field function for each parameter. To visualize the sensitivities of a given parameter:
  1. Create a scalar or vector scene.
  2. In the scene, set the Scalar Field or Vector Field to Sensitivity of Position w.r.t. [Parameter].
  3. In the displayer, set the Representation to [Automated Mesh].Remesh