Configuring advanced options

You can configure a shape optimization task.

  1. In the optimization task editor, click the Advanced tab.
  2. Choose the shape optimization algorithm.

    • Select General optimization (sensitivity-based) to use a sensitivity-based shape optimization that allows you to apply a range of constraints and objective functions to your model.
    • Select Condition-based optimization (default) to use a condition-based shape optimization that uses a strain energy objective function and volume constraint.

  3. Enter values specifying the Growth scale factor and the Shrink scale factor. The growth scale factor is applied to the displacement of nodes that are growing (increasing the volume of the model) as a result of the shape optimization. The shrink scale factor is applied to the displacements of nodes that are shrinking (decreasing the volume of the model) as a result of the shape optimization.

    It is recommended that you perform an optimization with default scale factors of 1.0 and examine the results before you attempt an optimization with modified scale factors. A value greater than 1.0 increases the incremental displacement of nodes and accelerates the optimization. Conversely, a value less than 1.0 decreases the incremental displacement of nodes and slows down the optimization.

    You should consider increasing the scale factors if the first few iterations of the optimization produce little change in the position of the surface nodes; for example, if you have a dense mesh with small element edge lengths. Conversely, if the scale factor is too large, mesh quality will suffer, individual elements might collapse, and the optimization might not be able to converge on the optimal solution.

    You should consider decreasing the scale factors if the original model is close to being optimal. Decreasing the scale factor and slowing down the optimization is also beneficial when the optimization includes many geometric restrictions and when the beginning mesh quality is poor.

    To optimize regions that are in contact, you might want to enter a negative value to reverse the direction of the optimization. As a result, areas of high stress will shrink and areas of low stress will grow.

  4. Choose whether to update the optimization shape vectors after every optimization cycle (default) or only after the first cycle.

    The Optimization module determines an optimization displacement vector for every node in the design area. The vector lies along the normal to the outer surface at the node and indicates the direction of displacement during the optimization. If you choose to update the optimization shape vectors after every optimization cycle, the Optimization module adjusts the vectors to account for changing conditions, such as changes in the shape of the structure, the mesh quality, and design variable restrictions. If you choose to update the optimization shape vectors only after the first optimization cycle, the vectors remain fixed in subsequent cycles.

    In most cases, the default value of updating the optimization shape vectors after every optimization cycle provides better results because the mesh smoothing algorithm is less restricted, resulting in an improved mesh quality.

  5. Choose whether the step size should be determined by the minimum displacement of the nodes in the design area during the optimization or the average displacement.

    The Optimization module examines your mesh and limits the amount of displacement of the nodes in the design area during each optimization cycle. This limit prevents the large displacement of one node from causing the collapse of a neighboring element. In addition, the condition-based optimization algorithm provides control of the displacement of the nodes in the design area after every design cycle—the step size. The step size depends on the limit that the Optimization module has applied to the nodes. For example, if the Optimization module decreases the allowed displacement, the condition-based optimization algorithm decreases the increment size.

    This option allows you to choose which displacement is used by the condition-based optimization algorithm to determine the step size. You can choose the average value of the allowed displacement of the nodes in the design area during the optimization or the minimum value (default). Selecting the average value results in a larger step size and a faster calculation of the optimum solution. However, selecting the average value can result in limited displacement of nodes for which only small displacements are allowed causing undesirable corners in the design area.

  6. Choose the method that the Optimization module will use to interpolate the midside nodes.

    If you select Linearly by position (default), the optimization linearly interpolates the position of the midside node from the optimized position of the connected corner nodes. If you select By optimization displacement of corner nodes, the optimization interpolates the position of the midside node from the optimization displacement of the connected corner nodes.

    If the nodes are in their original position, the midside node sits on the line between the corner nodes and there is no difference between the two interpolation methods. However, to prevent element bending, you must select By optimization displacement of corner nodes.

  7. If desired, toggle on Edge length for movement vector and enter a value.

    The Optimization module modifies the displacement of nodes in areas of high curvature to prevent the mesh from collapsing because of a large volume change. In effect, sharp corners are smoothed out. The default value of the minimum element edge length that triggers smoothing is 5.0. A larger value results in a larger radius for the smoothed region.

  8. The Optimization module can use a filter to smooth out local stress peaks. You can define the filter function by toggling on Max. influence radius for equivalent stress and entering the following:

    • A value for the maximum distance between nodes that are influenced by the filter.

    • A value that determines how much the local surface curvature will be used to adjust the maximum distance between nodes that are influenced by the filter. The default value is 0.2; a smaller value increases the effect of the surface curvature.

    • A weighting value that controls the effect of the filter depending on the distance from the node.

  9. Volume is the only constraint you can apply to a shape optimization, and you can specify that the volume be reduced to a specified value or to a fraction of the initial value. The Equality constraint tolerance specifies the minimum difference between the specified volume constraint and the calculated volume that results in the Optimization module assuming the solution has converged. The Optimization module compares the absolute value of the difference with the tolerance value you enter. The default value is 0.001.
  10. If you selected General optimization (sensitivity-based), you can select Use Abaqus sensitivities when possible to use Abaqus to compute the design responses and their sensitivities whenever possible. This workflow modification improves the optimization process performance.
  11. If you selected General optimization (sensitivity-based), you can choose Use Group Operator when possible to use large groups of more than 5000 elements or nodes in the design response definition in an efficient way. This workflow modification uses a new algorithm based on Abaqus sensitivities.