Rocker Arm Design Example
Step 5: Fine-tune the design
Working Model Shape is used to fine-tune the design created in the previous step. Before doing so, a new mesh is created with a larger element size (increased from 0.04 in to 0.135 in). The results from the simulation are shown in Figure 9. Note that the maximum stress decreased from about 33 ksi to about 27 ksi.
Figure 9: Simulation results with larger elements.
The larger elements are used for shape optimization to increase performance and to help reduce the chance of mesh distortion. To account for the errors that are introduced with using larger elements, the design constraint will be adjusted.
The design criteria specify the maximum stress must be less than 42 ksi. Therefore, the design constraint is adjusted according to the simulation results to 42*27/33 = 34 ksi. This constraint will apply to the entire model. The objective is to minimize the total volume of the part and 7 design variables are defined for the width and thickness of the flanges and thickness of the web.
Working Model Shape converged to an optimal solution in 3 design cycles. The stress constraint was satisfied with a maximum stress of about 34 ksi and the total volume was reduced by 23%. Using Working Model Shape, the parametric geometry is automatically altered to this final design, shown in Figure 10.
Figure 10: The parametric part after shape optimization.
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