On Tue, Feb 27, 2018 at 8:55 AM, 吴家桦Gauvain <causegauv...@gmail.com> wrote:
> 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. > Sounds like you need to do some debugging... e.g. set parameters to have min=max and see if it's still abnormal, or view the "truth solve" solution or other things like that to try to identify where the problem is. David > 2018-02-27 21:21 GMT+08:00 David Knezevic <david.kneze...@akselos.com>: > >> 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
