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Heaviside function help
Posted 3 giu 2010, 16:13 GMT-4 0 Replies
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I am having a technical problem with the heaviside step function in COMSOL.
My model is composed of a transient, Darcy flow (pressure) problem. I have attached the model.
There are two subdomains; namely rock and fluid. The permeabilities are 1e-22 and 1e-10, respectively. This is a pressure decay experiment, i.e. the fluid is given an initial pressure of 1 (normalized) and the rock is maintained at 0 (t=0).
I noticed that the pressure oscillates when being solved and realize that this is a stability problem (a numerical abberation) which generates a negative pulse wave and a sudden drop inside the fluid cavity at the first timestep.
I realize that this can be solved with brute force, i.e. mesh discretization and timestep control. But this will only work for unidirectional flow patterns and not bi-directional flow patterns. bi-directional flow would occur if the fluid cavity was smaller than the rock sample.
Could anyone help me define a heaviside step function that can control the negative pressure fluctuations in this problem?
my email address is pa.selvadurai@gmail.com
Thanks,
Paul Selvadurai
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Hello Paul Selvadurai
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