Hello, I am trying to perform topology optimization to minimize compliance on a wing, and I have modeled it in two parts--the skin and the inside structure, both solids. The skin is the non-design part, and the inside structure is the design part. The loads are however applied on the skin. When I try to perform optimization, optistruct shows the error 2148 "invalid design problem. all sensitivities of objective are zero." When i make the skin to be optimized as well, the optimization happens without any problems, but only the skin gets optimized, but i want to optimize the inside structure. In fact, the inside structure feels no stress/load at all in the result.
I want to be able to keep the skin as non-design, and the loads should be applied on the skin only, but i want the inside structure to be optimized, even though the loads are not directly applied onto it. Is there any way to rectify this situation? I also don't know if there is a way to sort of "connect" these surfaces without any bolts, screws, etc. so that the load is indirectly transferred. If there is such a facility please let me know so i can try it out. I have run the model without any objective, just by itself, and it runs fine. I have also attached the model below. Any suggestions are appreciated. Thanks.
