So it looks like errors saturate at 8x8 and don’t go down. So maybe due to the time integration?
How small is the dt that you are using, and do the numbers change when you reduce it further? Regarding: I tried different zeta values, different pseudo-dt,, more pseudo-niters-max going as high as 50 which is killing my performance Can you send plots of how the pseudo residuals are converging in each dt? What do you mean quantitatively by ‘killing performance’ Are you using local pseudo dt and PMG etc. for the inner iterations, or just plain RK4? Thanks Peter Professor of Computational Fluid Dynamics and EPSRC Fellow Department of Aeronautics Imperial College London South Kensington London SW7 2AZ UK On 7 Oct 2020, at 04:27, Mohamed M. Kamra <[email protected]<mailto:[email protected]>> wrote: When solver solver.order = 4 4x4 : Mesh DOFs = 400 Variable: U Error L1Norm = 0.000114383 Variable: U Error L2Norm = 0.000132731 8x8 : Mesh DOFs = 1600 Variable: U Error L1Norm = 3.8896e-05 Variable: U Error L2Norm = 4.86379e-05 16x16 : Mesh DOFs = 6400 Variable: U Error L1Norm = 3.90541e-05 Variable: U Error L2Norm = 4.82179e-05 32x32 : Mesh DOFs = 25600 Variable: U Error L1Norm = 3.91447e-05 Variable: U Error L2Norm = 4.81805e-05 Between the first two meshes, it is not even second order, after the order becomes almost 0! Vvisualizing the error shows high error everywhere, specifically at high gradient areas <image.png> Error distribution of U for Mesh 16x16 , order 4.0 <image.png> Distribution of U Numerical solution for Mesh 16x16 , order 4.0 <image.png> Distribution of U Exact solution for Mesh 16x16 , order 4.0 On Wed, Oct 7, 2020 at 11:28 AM Vincent, Peter E <[email protected]<mailto:[email protected]>> wrote: So what orders of accuracy do you get? Peter Professor of Computational Fluid Dynamics and EPSRC Fellow Department of Aeronautics Imperial College London South Kensington London SW7 2AZ UK On 7 Oct 2020, at 03:23, Mohamed M. Kamra <[email protected]<mailto:[email protected]>> wrote: Hi Peter, You're right. I left the source term in the ini file because it may not evaluate to zero depending on the choice of the length scale in the Reynolds number (since the domain is not a unit square). When the length scale is chosen to be 1 ( Re = 1/nu) which is the case in all of our simulations so far, then the source term vanishes and that's what's used in the ini file attached. So I don't think that the source term is the cause of the problem. I removed it now just in case but I got the exact same results. Regards, Mohamed Kamra On Wed, Oct 7, 2020 at 10:48 AM Vincent, Peter E <[email protected]<mailto:[email protected]>> wrote: Hi Mohamed, I am a little confused as to the test case you are using. The 2D TGV case in the paper you reference does not seem to use a method of manufactured solutions, it just solves the regular NS equations without a source term? Apologies if I missed something. Peter Professor of Computational Fluid Dynamics and EPSRC Fellow Department of Aeronautics Imperial College London South Kensington London SW7 2AZ UK On 6 Oct 2020, at 16:38, Mohamed M. Kamra <[email protected]<mailto:[email protected]>> wrote: Hi, Thanks for the prompt response I followed the case illustrated in Cox et al article https://www.sciencedirect.com/science/article/pii/S0021999116001686?casa_token=Vpk3uWyaxE0AAAAA:IGLI-wLZFaIwfIIOyPM1OZH6-TphsFXG3nTrgAbaSuJkzNJrUbAYDcL-qc9R1WINd9qGIA It is a double periodic 2D manufactured solution case, the u, v source terms are evaluated using Mathematica I attach the ini file here The Re = 10 I calculated the order of accuracy in the manner described in the article which is fairly straightforward <image.png> <image.png> where eps_k is the difference between the exact solution and the numerical solution. I used the same meshes resolutions as the article 4x4, 8x8, 16x16, 32x32 with double periodic bcs generated using gmsh For now, I am only trying to verify the spatial accuracy so following the article's example I am using very small dt I tried different zeta values, different pseudo-dt,, more pseudo-niters-max going as high as 50 which is killing my performance the only part I did not mess with is the LDG beta and tau I double-checked the source terms several times but it seems okay So I am not sure what could be the problem. Appreciate your help. M Kamra On Tue, Oct 6, 2020 at 23:51 Vincent, Peter E <[email protected]<mailto:[email protected]>> wrote: Hi M Karma, Could you provide more details of the test case, the way your are obtaining the order of accuracy, and the results that you are getting. Thanks Peter Professor of Computational Fluid Dynamics and EPSRC Fellow Department of Aeronautics Imperial College London South Kensington London SW7 2AZ UK On 6 Oct 2020, at 15:47, mkamra <[email protected]<mailto:[email protected]>> wrote: Hello Everyone, I have a question regarding the order of accuracy of the ACM method; Have you done any tests using the method of manufactured solutions ( published or otherwise) ? I tried the 2D taylor green benchmark but the order of accuracy I am getting is nowhere near what it should be. When comparing with exact solution I used the solution points directly not the subdivided solution in the vtu file to avoid interpolation issues polluting the order of accuracy Also regarding the ACM, how would one obtain the residual of the continuity and momentum equations? Pseudo-stats only report the change between two consecutive pseudo iterations Regards, M Kamra -- You received this message because you are subscribed to the Google Groups "PyFR Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]<mailto:[email protected]>. To view this discussion on the web, visit https://groups.google.com/d/msgid/pyfrmailinglist/fc58961d-02b2-4e7b-a05b-62af91f93537n%40googlegroups.com<https://groups.google.com/d/msgid/pyfrmailinglist/fc58961d-02b2-4e7b-a05b-62af91f93537n%40googlegroups.com?utm_medium=email&utm_source=footer>. -- You received this message because you are subscribed to the Google Groups "PyFR Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]<mailto:[email protected]>. To view this discussion on the web, visit https://groups.google.com/d/msgid/pyfrmailinglist/CAHrgCm7h18kXm-dUA%2BmfZH%2BK8bw1kfbpBnEdLyxORnpfV%3DFvrw%40mail.gmail.com<https://groups.google.com/d/msgid/pyfrmailinglist/CAHrgCm7h18kXm-dUA%2BmfZH%2BK8bw1kfbpBnEdLyxORnpfV%3DFvrw%40mail.gmail.com?utm_medium=email&utm_source=footer>. <tg2d.ini> -- You received this message because you are subscribed to the Google Groups "PyFR Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/pyfrmailinglist/BD78A613-33FB-4D8D-B6DE-5A4F998C84EF%40ic.ac.uk.
