On Tue, Feb 27, 2018 at 4:03 AM, 吴家桦Gauvain <causegauv...@gmail.com> wrote:
> Hi all, > > I am trying to make a transient thermoelastic RB model. Both Internal heat > flux and external heat exchange described by Newton's law of cooling(Robin > boundary condition) are considered. It works well when the three thermal > conditions (heat flux, heat transfer coefficient and ambient temperature) > are chosen as parameters. However, abnormal results are observed when the > material properties (Young's modulus, Poisson's ratio, thermal expansion > coefficient and heat conductivity) are added as parameters: Three > displacement components remain 0 and the temperature increases drastically > as the time goes by. What's more, I notice that the difference between the > first and the second POD eigenvalues is extremely large: > > POD Eigenvalues: > eigenvalue 0 = 4.4536e+08 > eigenvalue 1 = 2.45303e-07 > ... > last eigenvalue = -1.90536e-07 > > The matrix assembly should not pose problem because it runs well in steady > case and I simply copy the assembly functions without any modification. > Thus I am really confused and I cannot figure out where the problem is. > Could you give me some suggestions? Thanks a lot. > Good to hear that it works well in the steady case. Regarding the transient case, I have a few comments: - The default implementation for transient RB that is used in the examples is intended for parabolic PDEs, like the heat equation. I guess your PDE is parabolic since you omit the hyperbolic parts (i.e. the inertia terms) from the elasticity part of the system? - 7 parameters is quite a lot of parameters, so you may just be having trouble with greedy convergence? My main suggestion would be to try to get a simple transient problem working first, then add more complexity to it until you reach the problem that you're interested in, e.g. you could start with the heat equation and then add elasticity terms. Regards, David ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Libmesh-users mailing list Libmesh-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-users
