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|ID||Project||Category||View Status||Date Submitted||Last Update|
|0002002||OpenFOAM||Bug||public||2016-02-19 11:17||2016-02-19 13:28|
|Fixed in Version||dev|
|Summary||0002002: Question regarding SuSp usage in kineticTheory.C|
|Description||I just noticed that in kineticTheory.C, ThetaEqn, there is a fvm::SuSp term on the right side of the equation, but it does not have a minus sign in front. However, in other places where I have seen SuSp being used, it is either added to the left side or it has a minus sign in front. So I'm wondering if the SuSp in ThetaEqn actually works as intended (aiding stability?), or should it be written as -fvm::SuSp(+((PsCoeff*I) && gradU), Theta_) instead?|
My interpretation of SuSp(kappa,phi): Generally it is preferable to have positive coeffs on the diagonal. SuSp looks the sign of kappa and if it is positive, it will put the coeffs on the diagonal, otherwise it is explicit. This is good, if the SuSp is on the left side of the equation. However, on the right side we want negative things go to diagonal (which are positive when the matrix is moved to the left side) and therefore we write leftSide == -SuSp(-kappa,phi).
This is merely a question and I don't currently have a test case, which would demonstrate possible stability issues. I'm just curious if there is some logic behind this that I'm missing or if I'm just confused with the signs.
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