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From: Laila Bahgat (firstname.lastname@example.org)
Actually my question is not directly related to ASIM software specifically. However I'll very much appreciate any information about the following point regarding your experience with ASIM 4.0: I've noticed while simulating model ASM2d using MATLAB, that the initial conditions, number of reactors used and their volumes can lead to simulation failure in some cases. In such cases the simulation fails as the state variable Xpao reaches zero value whereas three equations of the set of ODEs that make up the model contain the term (Xpp/Xpao) or (Xpha/Xpao). Thus the simulation fails due to divide by zero error while it may complete in some other cases using the same initial conditions but a fewer number of reactors or where the volume of the aerobic reactors is decreased. I would like to know whether what I am experiencing is the result of some error and if not how ASIM handles this issue and what is the best set of typical values to use as initial conditions. Thank you very much for your help.
We solved this problem in ASIM as follows: the process is of the form: rho = (X1/X2) / (Kx + (X1/X2)), in case of X2=0 we set rho=1 because you can write rho in the form: rho = 1 / (Kx*X2/X1 + 1) and for X2=0 => rho=1 I hope this answers your question. Kind regards, Rolf
Many thanks for the quick response.