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The optimisation starts with the modified geometry as the first iteration. At the end of the optimisation the strut is integrated completely removed and the rest of the structure completely integrated into the design. Because the new strut is now loaded with stresses other areas of the geometry are less loaded. The optimisation reduces the material accordingly at these areas, thus in most cases the new, modified design is as lightweight as the previous one. The algorithm might increase material elsewhere to compensate for the loss of the strut.
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You can check the status of the optimisation in the GD Status and get more information on Warning and Error messages. This can be done directly in the Post-Processing as well as in the Studies tab for an optimisation that has already run.
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