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Minimum Value In a Transient Simulation

Posted 23 dic 2021, 16:41 GMT-5 General, Parameters, Variables, & Functions, Equation-Based Modeling 2 Replies

Matt Petroleum Engineering
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Hi all,

Is there a way to keep track of the minimum value in a transient simulation and use this value during solving? For example, at the first time step, the minimum value should be u_min=u(t1) and the subsequent time step should be u_min = min(u(t1), u(t2)) and so on until the last time step of u_min = min(u(t1),..., u(t)). I have tried defining an ODE to calcualte the minimum and have had no luck. Any help would be appreciated!

2 Replies Last Post 1 gen 2022, 16:23 GMT-5
Matt Petroleum Engineering
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Posted: 3 years ago 31 dic 2021, 08:37 GMT-5
Updated: 3 years ago 31 dic 2021, 08:46 GMT-5

** Update, the solution seems to be to define an ODE with the following weak form syntax:

where u is a variable from another PDE/physics interface, and umin is the dependent ODE variable. However, this method only works for Time Dependent solver where derivatives are continuous. This will not work for Time Discrete solver in which time derivatives are replaced by bdf() operator. I wonder if anyone has a solution for time discrete solver?

** Update, the solution seems to be to define an ODE with the following weak form syntax: \marthrm{0 = -d\left(umin,TIME\right)*test\left(umin\right) + \left(u\leq umin\right)*\left(d\left(u,TIME\right)\leq 0 \right)*d\left(u,TIME\right)*test\left(umin\right)} where u is a variable from another PDE/physics interface, and umin is the dependent ODE variable. However, this method only works for Time Dependent solver where derivatives are continuous. This will not work for Time Discrete solver in which time derivatives are replaced by bdf() operator. I wonder if anyone has a solution for time discrete solver?
Edgar J. Kaiser Certified Consultant
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Posted: 3 years ago 1 gen 2022, 16:23 GMT-5

Hi Matt,

have a look into this blog contribution by Walter Frei: https://www.comsol.de/blogs/using-the-previous-solution-operator-in-transient-modeling/

I have used this method in many transient and parametric studies. I think it should work in time-discrete as well, but haven't tried that so far.

Cheers Edgar

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Hi Matt, have a look into this blog contribution by Walter Frei: https://www.comsol.de/blogs/using-the-previous-solution-operator-in-transient-modeling/ I have used this method in many transient and parametric studies. I think it should work in time-discrete as well, but haven't tried that so far. Cheers Edgar

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