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About The 'Reuse Solution From Previous Step' In Parametric Sweep And Time-Dependent Solver

Posted Apr 29, 2024, 8:29 a.m. EDT General, Studies & Solvers, Modeling Workflow 0 Replies

HC L solid mechanics

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Hi there,

I am trying to modeling the buckling and post-buckling process using the parameteric sweep and time-dependent solver like in this presentation about psudo-dynamic approach. We may take the buckling of a compressed bar as an extremely simplified example. Suppose a bar measured is fixed at the left end and loaded through displacement control in terms of nominal compressive strain at the right end (as shown by the graph below). Due to the strong nonlinearity of the original problem, the steady problem is passed to a time-dependent one like in this presentation. The modeling is based on the time-dependent solver with parameteric sweep over . In each time-dependent study step, initial conditions like are prescribed and then the system is allowed to evolve for a sufficiently long time period , say, .

During the trail run, I encounter several questions:

1) The system doesn't seem to start from the initial conditions. For example, the result of at (shown belown) is quite different from the prescribed initial condition . And the profile at changes as varies, though the box of 'reuse solution from previous step' is unchecked under the node of 'parametric sweep'. This is important because the steady configuration can be sensitive to initial conditions when the system have multiple energetic minimum.

2) How to perturbe the solution of previous step when the box of 'resue solution from previous step' is checked? In modeling of a system with strong nonlinearity, it's hard for the model to directly evolve from an arbitrary initial condition into the realistic final configuration in a single time-dependent study step, for the final configuration may depend on the intermediate process. So, I suppose the 'reuse solution from previous step' is needed. Neverthless, only reusing previous results can lead to trivial solution for all parameters. In the above compressed bar example, with 'reuse solution from previous step', comsol keeps giving the trivial solution even as increases far beyond its critical value (shown below), maybe because the system only has trivial solution at small and this trivial solution keeps being passed on to the next parametric sweep step as initial condition. As a result, the system is stucked in the trivial solution. Maybe a perturbation needs to be added into the previous solution before it is passed on to the next sweep step as initial condition.

Thank you so much for your reading. I would appreciate it if anyone could shed lights on these questions.

Best regards,

HC L

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