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Hi

A prescribed value means to force the variable (displacement in structural solid) to this value, of you leave a direction unchecke it remains free to move

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Good luck
Ivar

Dear Ivar,
Thanks for you reply. But I get the opposing conclusion. That is if I clear the "Prescribed value" after input a value for dirichlet BC, the variable then is forced to be the input value. However, when I check it, the variable is free and the BC may change.Anyway, I have obtained a correct result by clear the prescribed value,which has been confirmed by my own code.

I am new to comsol. Could you help me to answer a new question?

I have three variables(say A, B, C), and have constructed three PDEs by comsol for one dimensional geometry. I carefully choose the initial values from a set of simplified PDEs for the variables. And then the solutions is converged. That is ok. However,physically, I need to impose two extral constraints by fixxing the integrals of two variables (say, A, and B) to be constants.I have tried two methods.

Method1:right click the corresponding PDE, and choose weak constraint for domain. Use defined intop1() to let intop1(A)=constant1,and intop1(B)=constant2.

Method2:define two new variables(say, D and E), and construct two new ODEs. The derivatives of the two new varibes are equal to A and B respectively.Then Let D and E to be zero at one bounday and constants at the other boundary.

Those methods are both failed.Failure message shows "fail to find consistent inistial values".It is really strange t me since I have used the good initial values, which can guarantee the convergence of solutions if the constaines are not imposed.So how can I solve the problem?
Regards
WL

HI, Ivar, I found the global constraint can solve the problem. Maybe in the weak constraint, the inital value of lagrange multiplier variable is too far away from the real value, resutling in "failed to find the consistent value".In the global constraint, no any initial value should be given.Thanks.