Thanks for replying. I did omit the inertia terms in my PDE. Regarding the greedy convergence of 7 parameter transient case, the maximum error bound decreases as usual, from about 40000 to 0.00197 but the result is abnormal like what is described in my first mail. In fact, 3 parameter (thermal conditions) transient case works well and so does 7 parameter steady case. The problem arises when I attempt to combine them together by replacing the assembly function of the stiffness matrix in 3 parameter transient case with that of 7 parameter steady case.
Regards, Gauvain 2018-02-27 21:21 GMT+08:00 David Knezevic <[email protected]>: > On Tue, Feb 27, 2018 at 4:03 AM, 吴家桦Gauvain <[email protected]> > 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 [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
