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Using Max/Min Nonlocal Couplings and Selecting specific location when Max/Min occurs at multiple points

Posted Apr 1, 2024, 2:04 p.m. EDT General, Equation-Based Modeling Version 5.6 0 Replies

Mark JoFa

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I am using the Equations-based modeling to solve for the evolution of a two-layer drop. As part of the solution, I need to track the contact lines of the drop. I do this by using the Domain ODEs and DAEs feature in comsol, and specifically by tracking the minimum of the total height - some threshold value. This works fine for most cases, however, I have noticed a convergence issue for certain parameter values as the dynamics evolve such that the total height is equal to this threshold value at 3 different points. I think this is the source of the convergence issue as Comsol doesn't know which of these 3 points to choose (note that I am saving the location of this as a variable called xcut which is then used in the next time step to determine evolution of the drop).

My question is if fmin(function,x) attains at minimum at multiple locations, then what is comsol's default method of determining which location it ouputs? Further, can I force it to always spit out the smallest location (x value) at which this occurs.

Has anyone run into an issue such as this? Is there a simple way to get around this problem?

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