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[zyao1]

Brief introduction on the issue:nFLUENT’s shape optimizer doesn’t appear to be giving the correct direction for optimizing the case with an energy objective function, but works fine with a momentum based objective function. nSection 1: Model introductionnThe model is a tunnel, with the liquid flowing through it as shown in the figure 1.nBoundary conditions:nThe objective function is minimizing the temperature of the bottom surface.nI already did a parametric study to validate the direction the optimizer should go: I simulate a case with smaller thickness and find that the smaller thickness can lead to the bottom surface temperature smaller as shown in table 1.n To do the shape optimization for this case, I use the adjoint based shape optimization in FLUENT.nSection 2: Sensitivity of optimal displacementnI made vector plots of sensitivity of optimal displacement for two cases, one is the case with the objective function that minimizing the bottom surface’s temperature, same as the section 1, and the other one is the case with objective function that maximizing the pressure drop between inlet and outlet.nFrom the plots, the geometry cannot change in y direction (thickness direction) when the objective function is temperature, but for objective function as the pressure drop, the design will be changed in y direction. These plots are also shown in the figure 2.nSection 3 Optimization processnFor the case, the objective function is minimizing the temperature of the bottom surface, I set all the surfaces, except for the bottom surface, can be moved and the surfaces movement is constrained only in y direction, which is the thickness direction. The movement freedom is 1. The optimization results are shown table 2:nThere are two steps during the optimization, first running with -1% as target change and subsequently running with -0.3%. The residuals for first step are below 1e-10. As for the second step, the continuity residual is around 1e-5, other residuals are below 1e-7. nWhen I set larger target change, there is an error: negative cell volume detected. nBased on the optimized design, there is negligible change of the design, I also cannot find the expected design change in y direction (thickness direction).nIssue: nBased on the sections above, My question is why the optimizer does not make the geometry of energy on case (objective is minimizing the temperature) change in y direction(thickness direction) but can make the geometry of energy off case (objective is maximizing the pressure drop) change in y direction(thickness direction)?nHow to resolve the error properly: negative cell volume detected so that I can use larger target change.  nnThank you for any reply!nnZhengda Yaon

[Karthik Remella]

Hi,nThis question is being answered here. n

Dear everyone,I have an issue when using the Ansys FLUENT Optimizer.The case is a tunnel, with the water flowing through it.The top surface is the wall, the bottom surface is wall with heat flux.The two side surfaces are symmetry.The objective function is minimizing the temperature of the bottom surface.I already made a case with smaller thickness proving the bottom surface temperature is smaller, showing in the picture below.https://us.v-cdn.net/6032193/uploads/A3832RP88RRT/shape-optimization-issue-1-png.pngBut when I try to optimize the same case, there is negligible change for the geometry and the thickness does not change. (for the optimization, I set the constraint that the geometry could only change in y direction, which is the thickness direction)https://us.v-cdn.net/6032193/uploads/9FOBNBO1X53A/shape-optimization-issue-2-png.pngI also made vector plots of sensitivity of optimal displacement for this energy case (objective function is minimizing temperature) and case without energy(objective function is maximizing the pressure drop between inlet and outlet),From the plots, the geometry can not change in y direction (thickness direction) with energy on, but for no energy case, the design will be changed in y direction. These plots are also shown in the picture below.https://us.v-cdn.net/6032193/uploads/TQ9TKKGCUVBJ/shape-optimization-issue-3-png.pngMy question is why the optimizer does not make the geometry of energy on case change in y direction(thickness direction) and can make the geometry of energy off case change in y direction(thickness direction)?Thank you for any reply!zyao/forum/discussion/22544/shape-optimizing-the-tunnel-case-with-energy-on-in-fluent

Thanks.nKarthikn