Topology optimization Warning

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Hi Everyone, I am working on a Topology Optimization setup of model (that consists of two materials) that undergoes Induction Heating(Physics involved: electromagnetic heating) in two step study ( Step1: Coil Geometry analysis, Step2: Frequency-Transient Solver, the optimization is applied for step 2). I have setup the settings for the required density model for topology optimization as following: theta_min: 0.01 theta_initial: 0.5

Control Variable Constraints: 0.9>=theta_average>=0.5 The optimization(MMA solver) starts properly at first iteration, but after that depending on the initial value given, after some iterations, I start getting this "Warning: Forward solution failed, requesting reduced step." This persists continuously and eventually I have to cancel the compute.

I would really grateful any help and please let me know if you need any further information regarding this.

Best, Ashok


2 Replies Last Post Apr 24, 2025, 1:38 p.m. EDT
Kristian Ejlebjærg Jensen COMSOL Employee

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Posted: 10 hours ago Apr 24, 2025, 5:04 a.m. EDT

Hi Ashok

If the behavior is deterministic, you can terminate the optimization solver on iterations, so that it stops for the controls that cause the problem.

You can then initialize a another study without optimization based on those "bad" controls and investigate the issue in a more time efficient manner. Alternatively, it might be possible to stop the computation by clicking the stop button next to the optimization solver on the progress tab (and waiting).

It sounds like the problem is nonlinear and the solver fails. You can change the nonlinear method on the solver configuration and enable plot while solving on the solver to get more information. Movelimits, larger filter length (or no filter), or better scaling are other possible solutions.

Best regards,

Kristian E. Jensen

Technical Product Manager, Optimization

Hi Ashok If the behavior is deterministic, you can terminate the optimization solver on iterations, so that it stops for the controls that cause the problem. You can then initialize a another study without optimization based on those "bad" controls and investigate the issue in a more time efficient manner. Alternatively, it might be possible to stop the computation by clicking the stop button next to the optimization solver on the progress tab (and waiting). It sounds like the problem is nonlinear and the solver fails. You can change the nonlinear method on the solver configuration and enable plot while solving on the solver to get more information. Movelimits, larger filter length (or no filter), or better scaling are other possible solutions. Best regards, Kristian E. Jensen Technical Product Manager, Optimization

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Posted: 1 hour ago Apr 24, 2025, 1:38 p.m. EDT
Updated: 1 hour ago Apr 24, 2025, 1:39 p.m. EDT

Hi Kristian, Thank you for your reply.

I believe I am using the linear solver, and think the forward solution warning appears during the "advanced" solver step as once the segregated solver starts, there will be a objective function result but if the advanced solver step has problem moving forward, I believe thats when the warning appears based on my observations. Right now, I am trying with stricter time steps(inital time step: 0.001) and manual absolute tolerance(0.001) in time solver and am attaching the screenshots of solver and solver config settings, so please go through them and let me know any recommended changes or things causing the issue(most of them are default settings).

Once again, I am really grateful any help and please let me know if you need any further information regarding this.

Best, Ashok

Hi Kristian, Thank you for your reply. I believe I am using the linear solver, and think the forward solution warning appears during the "advanced" solver step as once the segregated solver starts, there will be a objective function result but if the advanced solver step has problem moving forward, I believe thats when the warning appears based on my observations. Right now, I am trying with stricter time steps(inital time step: 0.001) and manual absolute tolerance(0.001) in time solver and am attaching the screenshots of solver and solver config settings, so please go through them and let me know any recommended changes or things causing the issue(most of them are default settings). Once again, I am really grateful any help and please let me know if you need any further information regarding this. Best, Ashok

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