Configuring mesh smoothing quality

Mesh smoothing attempts to improve the quality of the mesh despite the mesh distortion that results from the displacement of the design nodes during the shape optimization. You can specify the relative quality of the smoothed mesh, and you can specify the range of angles (quadrilateral and triangular elements) or the range of aspect ratios (tetrahedral elements) that define an element that is considered good quality. Elements that are considered poor are given a quality rating. The poorer an element is rated, the greater the consideration it will be given in improving the element quality.

  1. In the optimization task editor for a shape optimization, click the Mesh Smoothing Quality tab.
  2. Do either of the following:

    • Toggle on Target mesh quality, and select a setting (Low, Medium, or High).

      In most cases you should accept the default setting of Low. You should select a higher convergence level only after you have determined the mesh quality is not satisfactory. Even though it is computationally expensive, you may want to select a higher convergence level if your mesh contains a large number of tetrahedral elements; otherwise, the mesh quality may not be acceptable.

      If you are unable to obtain a satisfactory mesh quality, even with a convergence level of High, you should consider reducing the amount of displacement during the shape optimization by reducing the Growth scale factor and the Shrink scale factor, as described in Configuring advanced options.

    • Toggle off Target mesh quality to deactivate the algorithm that calculates the element quality.

  3. Toggle on Report poor quality elements to generate a list of elements that fall outside the ranges defined in the element quality table.
  4. Toggle on Report solver quality criteria violation to report elements that Abaqus considers to be of poor quality.
  5. If you toggled on Report solver quality criteria violation, you can choose to stop the optimization process if Abaqus encounters elements of poor quality. It is possible that the Optimization module will generate a poor quality mesh that will not allow the Abaqus analysis to complete successfully, especially as the number of design cycles increases. If Abaqus stops the analysis prematurely, no results are available to the Optimization module, and the optimization ends prematurely. If you allow the Optimization module to stop the optimization because the Abaqus element quality criteria is violated, it will be easier for you to troubleshoot the optimization and determine why it failed.
  6. If you chose to allow the Optimization module to adjust mesh quality, you can use the table to specify the range of angles (quadrilateral and triangular elements) or the range of aspect ratios (tetrahedral elements) that define an element that is considered good quality. You can also enter the maximum skew angle for quadrilateral and tetrahedral elements and the maximum taper for quadrilateral elements. In most cases, you should not modify the default values. Modifying the range of angles or aspect ratios has a minimal effect on the quality of the mesh. You should try to match the acceptable mesh quality in the Optimization module with the acceptable mesh quality in Abaqus. It is preferable to have your optimization process end because of degrading mesh quality rather than allowing Abaqus to end the optimization process or generate meaningless results.
  7. Choose the strategy or algorithm that the mesh smoothing operation will use. By default, the Optimization module uses the Constrained Laplacian mesh smoothing algorithm. If you have a relatively small model (less than 1000 nodes in the mesh smooth area), you can select the Local gradient mesh smoothing algorithm.
  8. If you selected a strategy of Constrained Laplacian, do the following:
    1. Select the Convergence level, a measure of the amount of time the Optimization module should spend trying to improve the quality of the mesh. In most cases you should accept the default value of Low, which results in the Optimization module applying a few iterations with large increments. Selecting Medium or High will result in more iterations with smaller increments; however, the computational time will increase significantly. You should use the Mesh Smoothing Quality tabbed page to adjust the target mesh quality before you modify the convergence level.
    2. Select the Frequency of evaluating geometric restrictions, which determines how often the Optimization module applies any geometric restrictions while the mesh smoothing algorithm is executing. In most cases you should accept the default value of Low. Selecting Medium or High will result in the Optimization module applying the geometric restrictions more often, and the computation time will increase significantly.
  9. If you selected a strategy of Local gradient, enter the Feature recognition angle, which is the angle that the Optimization module uses during the mesh smoothing operation to recognize features by detecting edges and corners. The default value is 30°, which provides good results in most cases.