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problem in initial value in matlab
Posted 5 nov. 2012, 05:30 UTC−5 Interfacing, Heat Transfer & Phase Change, Computational Fluid Dynamics (CFD), LiveLink for MATLAB, Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers Version 4.3a 1 Reply
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I'm simulating a model in matlab for a sampling time 3 s. After this i use the last simulation as initial condition for the next iteration. I use the following code (as the tutorial):
for k = 1:nit
model.study('std1').run;
temp = mpheval(model,'T','edim','edge','selection',3);
% update initial time for next iteration
t0 = mphglobal(model,'t','solnum','end');
model.param.set('t0',t0);
% initial condition for the next iteration
model.physics('nipfl').feature('init1').set('p', 1, 'p');
model.physics('nipfl').feature('init1').set('u', 1, 'u');
model.physics('nipfl').feature('init1').set('T', 1, 'T');
model.physics('ge').feature('init1').set('Tm',1, 'Tm');
v1 = model.sol('sol1').feature('v1');
v1.set('initsol', 'sol1');
data = [data;temp.d1(end,3)]; % store in a vector the output
end
My dependent variables are p, u, T and Tm, as can be seen. But when I plot the temperature i have a wrong result (blue line).
I compare this result with other simulation, without use a loop 'for' (in red line). For this case I run the model from time = 0 to time final, don't using the interpolation.
The image is in attach.
Anyone have the same problem?
best regards
Geovani
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very unlikely you'll find someone who has got the same problem of you, so (for the next time) I suggest you to formulate the question in a more general fashion :-)
I believe you are having problems when applying the initial conditions. To me the weird blue line sounds like numerical instability due, in your case, to the application of a not suitable initial conditions. What I image is that you have a solution for time t, and for t+1 you impose as a solution the field at time t. That's in principle obvious, but I guess you're doing it wrongly. To ensure this hypothesis of mine you can try to vary the time step's length.
My only suggestion, not that useful though, is to try with another simpler problem (maybe of lower dimension) and practise yourself with the technique of "using the last simulation as initial condition for the next iteration".
Hope it helps,
Mattia