Hi Johan, I do not konw how you are familiar with FEM, if you are beginear my comment may helps you.
I think that your reported issue is quit know in transient FEM analysis. To my knowledge there are generally 2 methods to handdle mass matrix (matrix C in your case): 1. mass lumping (lumped mass) which is notihng else diagonilization of mass matrix (e.g., summation of off diagonal enties to diagonal one), it is usually more stable but not always more accuracy. main advantage is possiblity of fully explicit time integration 2. Consistent Mass Matrix: which is common result if we use interpolation of mass matrix like field. if you search by these keywords you can find sufficient information and idea. hope this helps B regards RT PS: in my case (couple of years ago): i solved nonlinear heat transfer, for it mass lumping works supperior. On Sun, Oct 12, 2008 at 9:32 PM, Johan Lorentzon <[EMAIL PROTECTED]>wrote: > I was not clear in previous mail the issue is that by rayleight C > non-diagonal i get matrix-matrix multilication thatbreaks the sparsity. I > am not sure what kind of approximation i should use, approximate > matrix-matrix, or go use diagonal c matrix or do anyone of you a better > suggestion to involve damping into the dynamical system. > > Best Regards > > Johan > > > _______________________________________________ >
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