"Algebraic Loop" Question
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Hi!
I am working on a school project using Simulink and I would like to ask if anyone knows why can't Simulink solve the following system.
I have tried using "Trust-Region" and "Line-Search" solvers, changed the stepsize, tolerances without any luck. Here is the error I get:
Algebraic state in algebraic loop containing 'test_valve_10/Pressure Valve1/Sum2' computed at time 0.0 is Inf or NaN. There may be a singularity in the solution. If the model is correct, try reducing the step size (either by reducing the fixed step size or by tightening the error tolerances)
I have also uploaded an image of the formula and the Simulink file, I need to find out p2.
It would be great if any of you knew about this.
Thank you so much in advance!
Best Regards,
David
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Accepted Answer
Martin Brown
on 1 Jul 2015
From a very quick look, you appear to be computing p2 as the dependent variable in the Simulink simulation, but you're also giving it an initial value of 100000, without it being a dynamic equation? I'd imagine Simulink can't make the equation consistent which is giving the error message. p1, p3 etc appear to be constants, so if this really is an algebraic equation, you probably should be using "solve" (symbolic) or "fzero" (numeric) in Matlab.
3 Comments
Martin Brown
on 1 Jul 2015
OK, to better understand the question, p1, p3 and flow2 are really variables which can change and this algebraic equation allows you to compute p2 based on their values? Calculating p2 in a larger simulation is necessary?
The square roots probably make it difficult to get a closed form solution (symbolic) so why not just include a Matlab "User Defined Function" where you pass in p1, p3, flow 2, ... (or whatever is appropriate) and then call fzero to numerically calculate p2? This allows you to do this type of root finding in Simulink. There may be more efficient ways to do this.
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