Geometric imperfections are generated using synthetic random field models. Selecting the option for creating geometric perfections creates two nodes:
Synthetic random field (oSP3D)
- Boundary to be parameterized
The part of the boundary for which to find a random field parametrization. It can be a named selection of type face, element face, or node.
- Fixed boundary
The part of the boundary that is not to be modified (fixed). It can be a named selection of type face, element face, or node. All boundary parts that are not fixed or parametrized are "free" in the sense that oSP3D can modify them to interpolate between directly changed boundaries and fixed boundaries. It is recommended that the fixed boundary does not touch the directly parametrized boundary.
- Mesh part to be exported to oSP3D
The substructure that is to be exported to oSP3D. The boundary to be parametrized or fixed should belong to this substructure. The smaller the exported substructure, the smaller are the computational resources required by oSP3D. The scoping can be a named selection of type body or element.
- Definition
Desired variability (%)
Target value for the accuracy of the random field model in percent of the defined statistical variance.
Maximum number of parameters
An upper bound for the parameters to be used. The actual number of parameters may be less if the desired variability is to be obtained with a smaller number of shapes. If a greater number is required, the series is truncated here.
Correlation length
The correlation length parameter for the squared-exponential autocorrelation model. The larger the value, the larger the wave length. The smaller the value, the shorter the wave length. White noise is a correlation length of zero. The latter case must have more shape parameters.
Standard deviation of geometric variation
A constant value for the statistical standard deviation.
Mean geometric variation
A constant value for the statistical mean value. This is basically a constant shift around which the variation is applied in both directions.
- Visualization
Enable visualization
After creating the model, you can visualize the individual scatter shapes associated with the random field parameters as a colored contour plot. Use this parameter to turn visualization off (default) or on. For a larger model, you should turn visualization off because visualizing a large model can be slow.
Visible variation shape index
The number for the index of the shape. A special value of
0displays the mean, which should be a constant.
- Advanced options
Use mesh stabilization
When set to False, the computed geometric deviation is applied directly to the nodes. However, there is no check if the result is feasible. Thus, the result is fast, but it is very likely not solvable by Ansys Mechanical.
When set to True, an iterative algorithm tries to relax element distortions that are too strong. This avoids situations with negative volumes or negative Jacobians. The larger the applied deformations and the greater the number of nodes or elements, the more computation time that is needed.
Linearize Morphing for quadratic elements
This option affects only quadratic elements.
When set to True, for quadratic elements, oSP3D places the mid-edge nodes using a linear interpolation of the finite element geometry between the corner vertices. During morphing, some elements can be greatly distorted, leading to negative volumes or negative Jacobians. This option can help to avoid these problems and tends to produce more stable results.
When set to False, quadratic elements are morphed with quadratic curvature.
Erase degenerated shapes
When set to True, shapes with short wavelengths or short correlation lengths (that is with a very localized effect) are deleted. When set to False, all shapes are retained.
Test on mesh distortion
When set to True, oSP3D throws an error before the mesh is transferred to the Ansys Mechanical kernel. Because oSP3D uses a different FEM formulation, however, the test in oSP3D may be stricter than in Mechanical. You should use this option if the preparation in the Mechanical kernel takes a lot of time and if you do not want to start it when creating non-meaningful geometric variations.
Move nodes along
When set to Boundary normal, the variations are applied along the direction of the normal vector assigned with each FEM node on the boundary.
When set to Three coordinate axis, each variation pattern can be applied along the x, y, and z axis. This results in three times as many parameters, one parameter for each direction.
The variation along the normal direction is the default. The other option is more stable in the context of complex geometries.
- Solver options
Number of CPUs used by oSP3D
The number of CPU cores that oSP3D can use during the creation of the random field model. The default of
0means that oSP3D is to use all cores.Internal directory
This path is a local directory in the SYS/MECH path of the Workbench project directory. It contains all data that oSP3D requires to generate the random field model. You may also find the log files in there (in the sos_log subdirectory), which is a good starting point in case of errors. Also, you can open the sos_data.sdb file in that directory in the standalone oSP3D GUI for detailed analysis of the random field model.
Generate variations (oSP3D)
You must update the Synthetic random field model node before options are visible for defining or changing the second node.
See the previous option descriptions for Synthetic random field (oSP3D).
Caution: Never clear or reset the mesh. You may clear the generated data of the Generate variations node, but a reset of the Synthetic random field node also clears the random field model. Further, Ansys Mechanical cannot proceed with the Generate variations node automatically if the Synthetic random field mode is updated.