> How small is the dt that you are using, and do the numbers change when you > reduce it further? > The time step dt = 0.001 when decreased to 5e-4 and even 1e-4 the change in error is no more 1%
pseudo-niters-max = 50 , using p-multigrid with vermiere pseudo integration I tried local-pi but it was either unstable or ineffective perhaps I need to do needs some fine-tuning of my chosen parameters > 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? > As for the matter of performance, using p-multigrid with pseudo-niters-max of 50 yields a wall clock time of 6 hours if dt is taken as low as 1e-4 for 8x8 mesh to run only 1s ( GPU utilization at less than 15%) Can you send plots of how the pseudo residuals are converging in each dt? > As for the residuals: p : 5e-5 ~ 1e-4 uv: 1e-6 ~ 1e-7 For reference, the residual history data and the corresponding ini file can be downloaded from the following link https://mega.nz/folder/jVZBwIBb#gk6J1zSTM-Hg8GgRzDYysw I included residual history for 0.25s only On Wed, Oct 7, 2020 at 22:21 Vincent, Peter E <[email protected]> wrote: > 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]> > 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]> > 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]> >> 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]> 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]> >>> 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]> >>> 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]> 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]. >>>> 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]. >>> 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. 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