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Objective function missing after computing optimization

Posted 30 mars 2023, 08:30 UTC−4 Optimization, Structural Mechanics Version 6.1 1 Reply

Hendrik Mechanical Engineering
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Hi all,

I am trying to optimize (topology optimization) a plate structure, in order to maximize the lowest eigenfrequency.

When selecting my objective function in Study > Topology optimization, I am able to choose comp1.plate.freq , as well as "maximization".

However, right after running the study, it says the variable is undefined. After this, the variable also has disappeared from the list of variables (model>plate>global).

Does anyone know what could be the cause of this?

Kind Regards,

1 Reply Last Post 31 mars 2023, 03:30 UTC−4
Kristian Ejlebjærg Jensen COMSOL Employee

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Posted: 3 years ago 31 mars 2023, 03:30 UTC−4

Hi Kaap H.

I cannot reproduce your problem using the shell_eigenfrequency_shape_optimization library model. The solution is probably to use the global freq variable instead of the variable defined by the shell interface, but keep in mind that COMSOL 6.1 only supports gradient based optimization over a Eigenvalue/Eigenfrequency study step (and this is unsupported in 6.0). This means that it is not possible to use the Helmholtz filter in the Density Model or the regularization functionality in the shape optimization features, because these all require support for optimization over a Stationary->Eigenvalue combination.

You might be able to address the checkboard issue by avoiding linear discretization for the displacement. Alternatively, you can use the Polynomial Shell feature or derivative free optimization to maximize the lowest eigenfrequency.

Best regards, Kristian E. Jensen Technical Product Manager, Optimization

Hi Kaap H. I cannot reproduce your problem using the shell_eigenfrequency_shape_optimization library model. The solution is probably to use the global freq variable instead of the variable defined by the shell interface, but keep in mind that COMSOL 6.1 only supports gradient based optimization over a Eigenvalue/Eigenfrequency study step (and this is unsupported in 6.0). This means that it is not possible to use the Helmholtz filter in the Density Model or the regularization functionality in the shape optimization features, because these all require support for optimization over a Stationary->Eigenvalue combination. You might be able to address the checkboard issue by avoiding linear discretization for the displacement. Alternatively, you can use the Polynomial Shell feature or derivative free optimization to maximize the lowest eigenfrequency. Best regards, Kristian E. Jensen Technical Product Manager, Optimization

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