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Chapter 4: Rezoning

In a finite large-deformation analysis, mesh distortion reduces simulation accuracy, causes convergence difficulties, and can eventually terminate an analysis. Rezoning allows you to repair the distorted mesh and continue the simulation.

The program's manual rezoning capability allows you to decide when to use rezoning, what region(s) to rezone, and what remeshing method to use on the selected region(s).

During the rezoning process, the program updates the database as necessary, generates contact elements if needed, transfers boundary conditions and loads from the original mesh, and maps all solved variables (node and element solutions) to the new mesh automatically. Afterwards, with equilibrium achieved based on the mapped variables, you can continue solving using the new mesh.

The following rezoning topics are available:

4.1.Benefits and Limitations of Rezoning

4.2.Rezoning Requirements

4.3.Understanding the Rezoning Process

4.4.Step 1: Determine the Substep to Initiate Rezoning

4.5.Step 2. Initiate Rezoning

4.6.Step 3: Select a Region to Remesh

4.7.Step 4: Perform the Remeshing Operation

4.8.Step 5: Verify Applied Contact Boundaries, Surface-Effect Elements, Loads, and Boundary Conditions

4.9.Step 6: Automatically Map Variables and Balance Residuals

4.10.Step 7: Perform a Multiframe Restart

4.11.Repeating the Rezoning Process if Necessary

4.12.Postprocessing Rezoning Results

4.13.Rezoning Restrictions

4.14.Rezoning Examples

For related information, see Mesh Nonlinear Adaptivity.

4.1. Benefits and Limitations of Rezoning

Even when an analysis terminates due to severe mesh distortion, rezoning allows you to continue the analysis and complete the simulation. You can also use rezoning to improve analysis accuracy and convergence when the mesh is distorted but does not terminate the analysis.

To illustrate how rezoning works in a case where the analysis terminates, assume that the following initial mesh and boundary conditions exist:

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The simulation terminates at TIME = 0.44. Rezoning begins on the deformed mesh at substep 7 (TIME = 0.40):

After remeshing the selected region, an acceptable new mesh is ready:

 

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Benefits and Limitations of Rezoning

Based on the new mesh, the simulation concludes successfully at TIME = 1.0:

For a more detailed example, see Rezoning Examples (p. 124).

4.1.1. Rezoning Limitations

The purpose of rezoning is to repair a distorted mesh in order to overcome convergence problems caused by the distortion.

Rezoning is effective only when the mesh distortion is caused by a large, nonuniform deformation. Rezoning cannot help if 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 rezoning cannot help in such cases. While it is sometimes

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