Many FEA applications can benefit from the ability to strategically modify a mesh during solution, in order to simulate challenging geometry distortions which otherwise cannot be solved. Unlike manual rezoning, mesh nonlinear adaptivity is completely automatic, requiring no user input during solution.
To activate mesh nonlinear adaptivity within Workbench-Mechanical, insert ‘Nonlinear Adaptive Region’ in the Environment Branch.
Scope the Geometric features to be included in adaptive remeshing
Define the Criterion that triggers mesh modification
Define the checking frequency and range of application
Equally Spaced Points
Specified Recurrence Rate
This same technology is also available in MAPDL via the NLADAPTIVE and NLMESH commands.
To use nonlinear adaptivity most effectively, it is very important to understand the meaning and limitations of the criterion that will trigger a modification of the mesh during the solution.
There are three criterion currently exposed in ANSYS Workbench Mechanical:
Energy: When an element’s strain energy is greater than or equal to the mean strain energy of components to which the element belongs during a time increment (or substep), the element is split and remeshed. The energy based criteria will cause the mesh to be strategically refined in regions where a high concentration of stress exists and elements are too large. It applies to current technology 2D elements and 3-D linear tetrahedral elements (SOLID285).
Box: When nodes of an element are within a user defined region (or “Box”), the element is split and remeshed. This is useful for refining the mesh in regions where it is difficult to predict which elements of the model will be present, or move in to. For example, a small cavity filled by the deformation of a compressed seal. This criteria also applies to current technology 2D elements and 3-D linear tetrahedral elements (SOLID285).
Skewness: A mesh quality check that compares the volume of an element to that of a standard tetrahedral inscribed in the same sphere as the element under consideration. The numerical value of the skewness represents the ratio of volume difference of the two elements to that of the standard element. For an ideally shaped element, the skewness approaches zero as the volume of element under consideration approaches that of the standard element. For a poorly shape element, the skewness approaches 1 as the volume of the element under consideration is approaching zero. Skewness only applies to 3-D linear tetrahedral elements (SOLID285).
When the defined criteria are met, mesh modification occurs either by a combination of splitting followed by morphing or by general remeshing. During splitting, the current elements are divided into elements having a half-edge length. Splitting applies to Energy and box criterion. General remeshing only applies to Skewness criterion on 3-D linear tetrahedral elements (SOLID285). During remeshing, the selected region is completely remeshed to obtain a high quality mesh. For each mesh modification, mesh quality matrics stats are recorded in the Solver output comparing previous mesh with new mesh
Post processing procedure is same as for any conventional Structural Analysis with multiple results sets. All results are automatically saved to one jobname.rst file in working directory.
It is important to note that mesh nonlinear adaptivity via splitting or refinement, in general, cannot repair an already distorted mesh. In some cases, it can exacerbate mesh distortion by creating smaller elements. Most nonlinear material models, especially those employing hyperelastic materials, have their own applicable ranges. When a deformation is too large or a stress state exceeds the applicable range, the material may become unstable. The instability can manifest itself as a mesh distortion, but nonlinear adaptive region cannot help in such cases.
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