grasshopper 1 Report post Posted September 1, 2017 Greetings, I have a basic question about the optimization in Inspire 2017 7305. It is possible to maximize the stiffness as well as the natural frequency of structures in Inspire, but how can I decide the weighting function of these two objective functions? In general, in such multi-objective optimizations, I think it is necessary to adjust a weighting function. Maybe it is performed automatically by Inspire, but how is it done? On which is focused more - maximization of stiffness, or maximization of natural frequency? Thanks in advance. Share this post Link to post Share on other sites

Felix Radisch 9 Report post Posted September 4, 2017 Hi Grasshopper, you can maximize both simutaniously, but you can't manipulate the weightening function (which is set automatically). Inspire is using Altair Optistruct as a solver, which is calculating a compliance for each mode and the static compliance. Please see below an abstract from the topoOpt.out , located in the Inspire Scratch directory. Combined Compliance Index The combined compliance index is a method to consider multiple frequencies and static subcases (loadsteps, load cases) combined in a classical topology optimization. The index is defined as follows: This is a global response that is defined for the whole structure. The normalization factor, NORM, is used to normalize the contributions of compliances and eigenvalues. A typical structural compliance value is of the order of 1.0e4 to 1.0e6. However, a typical inverse eigenvalue is on the order of 1.0e-5. If NORM is not used, the linear static compliance requirements dominate the solution. The quantity NORM is typically computed using the formula: Where, Cmax is the highest compliance value in all subcases (loadsteps, load cases) and is the lowest eigenvalue included in the index. In a new design problem, you may not have a close estimate for NORM. If this happens, OptiStruct automatically computes the NORM value based on compliances and eigenvalues computed in the first iteration step. Abstract from topoOpt.out ITERATION 39 Subcase: 1 -------------------------------------------------------------------------- Label x-force y-force z-force x-moment y-moment z-moment -------------------------------------------------------------------------- Sum-App. 0.000E+00 1.000E+03 0.000E+00 -2.000E+01 0.000E+00 1.870E+02 Sum-SPCF -6.333E-09 -1.000E+03 2.689E-11 2.000E+01 -6.171E-11 -1.870E+02 -------------------------------------------------------------------------- the 2nd satisfied convergence ratio = 2.8748E-03 Objective Function (Minimize COMB ) = 1.47125E-02 % change = -0.29 Maximum Constraint Violation % = 0.20159E-05 Design Volume Fraction = 3.00000E-001 Mass = 5.61149E+000 Subcase Weight Compliance Epsilon Weight*Comp. 1 1.000E+00 8.520537E-03 -2.098521E-03 8.520537E-03 ------------ Sum of Weight*Compliance 8.520537E-03 Note : Epsilon = Residual Strain Energy Ratio. Subcase Mode Weight Frequency Eigenvalue Weight/Eigen 2 1 1.000E+00 3.823884E+02 5.772571E+06 1.732330E-07 2 2 1.000E+00 9.579818E+02 3.623050E+07 2.760106E-08 2 3 1.000E+00 9.707180E+02 3.720026E+07 2.688153E-08 2 4 1.000E+00 1.466867E+03 8.494565E+07 1.177223E-08 2 5 1.000E+00 1.667356E+03 1.097531E+08 9.111363E-09 2 6 1.000E+00 1.821137E+03 1.309317E+08 7.637568E-09 ------------ Sum of (Weight/Eigenvalue) / Sum of Weights 4.270613E-08 Mode Normalization Factor x 1.450E+05 ------------ Weighted Inverse Eigenvalues 6.191977E-03 Weighted Compliances 8.520537E-03 ------------ Combined Compliance Index 1.471251E-02 Hope this helps! Kind Regards, Felix Share this post Link to post Share on other sites

grasshopper 1 Report post Posted September 10, 2017 I'm sorry for my late reply... Thank you very much for your detailed explanation. Share this post Link to post Share on other sites