Discussion Forum

Hi all,

I´m trying to apply topology optimization to the design of compliant mechanisms using COMSOL optimization interface.

As a first exercise I´m working on an Inverter Mechanism (please see this paper for more details: R. Ansola et al. A simple evolutionary topology optimization procedure for compliant mechanism design. Finite Elements in Analysis and Design 44 (2007) 53–62).

I think I set up the problem correctly but for some reason COMSOL optimization solver can never converge ("Returned solution is not converged." / "Forward solution failed: requesting reduced step." / "Adjoint solution failed: requesting reduced step." / ), though the solution isn´t too far from the expected one (check the result in 2D Plot Group 6) .

This is a very simple problem and there must exist a solution in the form of the attached figure. I might be wrong about the definition of the MPE, but the SE is probably correct because it is automatically calculated by COMSOL as solid.Ws .

I based my model on the Model Library Example called "Topology Optimization of a Loaded Knee Structure". However the example model focus on maximizing the structural stiffness (by minimizing the Strain Energy - SE). For compliant mechanism, which is my case, we need also to consider the maximization of Mutual Potential Energy - MPE. To simultaneously accomplish the two requirements of maximizing MPE and minimizing SE a multicriteria objective needs to be defined. I used the following formulation: Min ( - MPE/SE ), which is the same as Max ( MPE/SE ).

I also wanted to plot the values of SE1 (Strain Energy for load case 1), MPE2 (Mutual Potencial Energy for load case 2) and the objective function for each iteration of the optimization routine, in order to be able to check the values and the convergence of the solution. I defined the Global Variable Probe for each variable but when I plot them (1D Plot -> Global) I get an error.

In case anyone wants to check, my model file is attached. I can give more details on the physics involved if needed.

Has anyone ever solved a similar problem using COMSOL?

Thanks in advance,
Andre Teves