Because mesh generation is such a critical step in performing an accurate simulation, and because nonlinear adaptivity automatically modifies the mesh, there are there are a variety of limitations associated with its use and how it interacts with other simulation specifications. Carefully review the limitations described below when you use this feature.
Solution Limitations
The purpose of nonlinear adaptive region is to repair a distorted mesh to overcome convergence problems caused by the distortion. It is effective only when the mesh distortion is caused by a large, nonuniform deformation. Nonlinear adaptivity cannot help if the divergence occurs for any other reason such as unstable material, unstable structures, or numerical instabilities.
- Unstable Material
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. While it is sometimes difficult to determine when a material instability occurs, you can check the strain values, stress states, and convergence patterns. A sudden convergence difficulty could indicate material instability. The program also issues a warning at the beginning of the solution indicating when a hyperelastic material could be unstable, although such a warning is very preliminary and applies only to cases involving simple stress states.
- Unstable Structures
For some geometries and loads, a deformation may cause a "snap-through," or local buckling. Such behavior can also manifest itself as a mesh distortion, that nonlinear adaptive region cannot repair. The effect is usually easy to detect by closely checking the deformed region or the load-versus- time (displacement) curve.
- Numerical Instabilities
A condition of numerical instability can occur when a problem is nearly overconstrained. The constraints can include kinematic constraints such as applied displacements, couplings, constraint equations, and volumetric constraints introduced by fully incompressible material in mixed u-P elements. In many cases, numerical instability is apparent even in the early stages of an analysis.
General Limitations
Nonlinear adaptivity cannot be specified:
For Convergence.
On a part that is also scoped to a Cyclic Symmetry object.
Material Limitations
You cannot apply nonlinear adaptivity to a body that includes the following materials properties:
Cast Iron
Concrete
Cohesive Zone
Damage Initiation Criteria and Damage Evolution Law
Microplane
Shape Memory Alloy
Swelling
Contact Limitations
Nonlinear adaptivity cannot be applied to a part that includes any of the following contact property definitions or applications:
Behavior property set to .
Formulation property set to .
Point Mass, Beam Connection, Joints, Spring, and Bearings.
Mesh Limitations
Mesh specification limitations include:
When there is a hexahedral mesh for a multibody part, the Nonlinear Adaptive Region can only be scoped to a single body.
Nonlinear adaptivity is not supported if your model is a multibody part or multibody assembly with a mixture of linear and quadratic elements.
Boundary Conditions Limitations
Nonlinear adaptivity does not support:
Spatially varying boundary conditions
An analysis that includes a Pressure or an Imported Pressure that has the following combination of settings:
Applied By property set to Direct option.
Loaded Area property set to Initial.
Large Deflection property set to .
Any of the following:
Coupling
Constraint Equation
Remote Displacement, Remote Force, and Moment specified with the Behavior property set to .
Results Limitations
Because nonlinear adaptivity modifies the mesh throughout the solution process, note the following limitations:
Only Body scoping is permitted (for bodies whose meshes will change). Therefore, if you scope any result or probe on a vertex, edge, or face of a body that experiences a mesh change, the analysis will not solve. This limitation is a result of the base mesh of the body being represented by nodes only. This limitation also applies to probes scoped to boundary conditions (via Location Method property).
Element selection on a result is not supported. However, if you 1) have an element-based named selection and 2) activate the Preserve During Solve property, you can specify results for the named selection using the Solver Component Names option of the Solution Quantities and Result Summary page of the Worksheet (accessed via the Solution object).
If you have a result object selected, certain mesh-based features are not available, including mesh selection filters (nodes, elements, and element faces), as well as the ability to display a Node ID in the probe label, and Selecting Nodes and Elements by ID.
The multiple result set options of the By property: / or /.
Penetration plot following remesh may show the curve discontinuity.
When transferring the deformed geometry and mesh of a Deformation result, nonlinear adaptivity is not supported.
When using the Deformation result tracker to graph displacement, note there is a display limitation for the graph. The tracker reads and displays data contained in the jobname.nlh file. This file contains incremental displacement data collected after re-meshing occurs. That is, the re-meshed model is considered as a new reference.