Acusolve doesn't stop after reaching convergence
Altair EmployeeHello,
I am quite new to Acusolve and I need to clear my doubts about convergence and residual ratio. My simulation has maximum time steps set to 300 and convergence tolerance set to 0.001. I am monitoring residuals in AcuProbe (see attachment). Correct me if I am wrong - shouldn't the simulation have already stopped at about 60 Time Step? Does it have other stop criteria? Thanks for any help.
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Answers
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By default, AcuSolve looks at both Residual Ratio (a measure of how well the overall solution matches the equations) and Solution Ratio (a measure of how much the overall solution is changing from time step to time step). By default the Solution Ratio can be an order of magnitude larger than the Residual Ratio. If you look at the plots for Solution Ratio, you'll probably have one or more variables that is too high. For Solution Ratio, with convergence tolerance at 0.001, eddy-viscosity would need to be below 0.1, pressure and velocity below 0.01. High values of solution ratio indicate the solution is changing a lot from time step to time step - thus indicating it's probably not really a steady flow.
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Thanks a lot for your reply! Indeed, solution ratios are about 0,1. Thus, the flow I am simulating is not a steady flow. I am working on a quadcopter model and its propellers are modeled by fan components. Are steady state results even possible to obtain in this case? Or should I perform transient analysis?
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You also need to determine what results are of interest. If those have stabilized to what you would term 'steady' maybe that is enough. These automatic settings are just tools for guidance. Would more mesh in some regions help? Would a higher relaxation factor help? (If you have it as 0 now, maybe try 0.3.) You could also try running transient, but a higher relaxation factor would probably be my first look.
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