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Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 When the convergence gets rough… MIGAL for PHOENICS.

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Presentation on theme: "Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 When the convergence gets rough… MIGAL for PHOENICS."— Presentation transcript:

1 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 When the convergence gets rough… MIGAL for PHOENICS

2 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Migal How to What’s happening Conclusion MFRDC is specialized in numerical methods and embedded scientific software MIGAL is a coupled multigrid solver that…

3 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Turns hours 8 hours 12 minutes into minutes Migal How to What’s happening Conclusion

4 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 And the more cells… the better… Migal How to What’s happening Conclusion

5 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 the better… Because segregated algorithms are at least N² because MIGAL is a fully coupled multi-grid solver almost N Migal How to What’s happening Conclusion

6 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Why? Migal How to What’s happening Conclusion

7 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 The Equations for U,V,W,P Migal How to What’s happening Conclusion

8 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Segregated Approach 1.Linearize, discretize and solve x- momentum equation for U 2.Linearize, discretize and solve y- momentum equation for V 3.Linearize, discretize and solve z- momentum equation for W 4.Linearize, discretize and solve mass equation for P 5.Back to step 1 until convergence Migal How to What’s happening Conclusion

9 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Segregated Approach LinearizeDiscretizeSolve Migal How to What’s happening Conclusion

10 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Segregated Approach LinearizeDiscretize Solve Migal How to What’s happening Conclusion

11 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Coupled Approach 1.Linearize and discretize momentum and mass equations in the same way than segragted approach 2.Solve by coupled solver for U,V,W,P 3.Back to step 1 until convergence Migal How to What’s happening Conclusion

12 Migal How to What’s happening Convergence Parameters Conclusion Coupled Approach Dr Michel Ferry September 2002 Migal How to What’s happening Conclusion

13 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Advantages 1.Segregated approach needs small time steps, especially when cell sizes diminish 2.Improving segregated solvers does not improve the over all convergence 3.Almost no time step restiriction for linear flows with the coupled approach 4.Improving the coupled solver (multi- grid) directly improves the over all convergence. Migal How to What’s happening Conclusion

14 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 How to… How to What’s happening Conclusion

15 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 How to control MIGAL? 2- by changing parameters 3- by extending to single variables 1- by Editing the q1 file 4- that’s all… How to What’s happening Conclusion

16 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 How to… How to What’s happening Conclusion

17 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 How to check MIGAL? 1- by openning the RESULT file 2- by looking for the MIGAL header 3- by looking for the sweeps outputs 4- that’s all… How to What’s happening Conclusion

18 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 How to check MIGAL? How to What’s happening Conclusion

19 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 What’s happening? How to What’s happening Conclusion

20 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Flow Past a Flat Plate UINI = WINI = 0 Z X How to What’s happening Conclusion

21 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 SIMPLEST’s first sweep How to What’s happening Conclusion

22 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 MIGAL’s first sweep How to What’s happening Conclusion

23 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 More sweeps with SIMPLEST? How to What’s happening Conclusion

24 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 More sweeps with SIMPLEST What for How to What’s happen New features More examples Conclusion isweep=1isweep=2isweep=3isweep=4isweep=15isweep=30isweep=45isweep=60isweep=300isweep=450isweep=1000isweep=1500

25 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Phew… How to What’s happening Conclusion

26 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 More sweeps with MIGAL? How to What’s happening Conclusion

27 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 More sweeps with MIGAL isweep=1isweep=2isweep=3isweep=4isweep=5isweep=10 How to What’s happening Conclusion

28 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Converged How to What’s happening Conclusion

29 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Flow Past a Flat Plate UINI = 0 WINI = 1 Z X How to What’s happening Conclusion

30 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 SIMPLEST’s first sweep How to What’s happening Conclusion

31 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 MIGAL’s first sweep How to What’s happening Conclusion

32 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 More sweeps with SIMPLEST? How to What’s happening Conclusion

33 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 More sweeps with SIMPLEST isweep=1isweep=2isweep=3isweep=4isweep=15 How to What’s happening Conclusion

34 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 More sweeps with SIMPLEST … How to What’s happening Conclusion

35 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 More sweeps with SIMPLEST isweep=1500 How to What’s happening Conclusion

36 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 More sweeps with MIGAL? How to What’s happening Conclusion

37 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 More sweeps with MIGAL isweep=1isweep=2isweep=3isweep=4isweep=10 How to What’s happening Conclusion

38 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Converged How to What’s happening Conclusion

39 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Free Convection in Cavity Laminar Ra=1.E5 How to What’s happening Conclusion

40 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 SIMPLEST convergence? How to What’s happening Conclusion

41 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 SIMPLEST (velocity) isweep=1isweep=2isweep=3isweep=4isweep=50isweep=100isweep=200isweep=500 How to What’s happening Conclusion

42 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 SIMPLEST (temperature) isweep=1isweep=2isweep=3isweep=4isweep=50isweep=100isweep=200isweep=500 How to What’s happening Conclusion

43 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 MIGAL convergence? How to What’s happening Conclusion

44 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 MIGAL (velocity) isweep=1isweep=2isweep=3isweep=4isweep=10isweep=20 How to What’s happening Conclusion

45 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 MIGAL (temperature) isweep=1isweep=2isweep=3isweep=4isweep=10isweep=20 How to What’s happening Conclusion

46 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 When the convergence gets rough Convergence

47 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Correct setting RELAX(V1,FALSDT, 1.000000E+10) RELAX(W1,FALSDT, 1.000000E+10) RELAX(TEMP,FALSDT, 1.000000E+00) SPEDAT(SET,MIGAL,SOLVED1,C,HYDRO) SPEDAT(SET,MIGAL,LINRLX1,R,1.0000E+00) SPEDAT(SET,MIGAL,SOLVED2,C,TEMP) SPEDAT(SET,MIGAL,LINRLX2,R,1.0000E+00) RELAX(V1,FALSDT, 1.000000E-02) RELAX(W1,FALSDT, 1.000000E-02) RELAX(TEMP,FALSDT, 1.000000E+00) SPEDAT(SET,MIGAL,SOLVED1,C,HYDRO) SPEDAT(SET,MIGAL,LINRLX1,R,1.0000E+00) SPEDAT(SET,MIGAL,SOLVED2,C,TEMP) SPEDAT(SET,MIGAL,LINRLX2,R,1.0000E+00) Ambitious setting Convergence

48 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 MIGAL (velocity) isweep=1isweep=2isweep=3isweep=4isweep=5isweep=6isweep=7 Convergence

49 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 MIGAL (temperature) isweep=1isweep=2isweep=3isweep=4isweep=5isweep=6isweep=7 Convergence

50 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Why? ok Convergence

51 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 RELAX(V1,FALSDT, 1.000000E+10) RELAX(W1,FALSDT, 1.000000E+10) RELAX(TEMP,FALSDT, 1.000000E+00) SPEDAT(SET,MIGAL,SOLVED1,C,HYDRO) SPEDAT(SET,MIGAL,LINRLX1,R,5.0000E-01) SPEDAT(SET,MIGAL,SOLVED2,C,TEMP) SPEDAT(SET,MIGAL,LINRLX2,R,1.0000E+00) Alternative setting Convergence

52 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Non-linearities Convergence Convection -Momentum convection => quadradtic terms in momentum equations

53 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Non-linearities Convergence Buoyancy –Heat convection => density dependence to velocity field

54 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Non-linearities Convergence Turbulence –Convection of turbulent quantities (k,  ) –Production term highly dependent on velocity gradients

55 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Non-linearities Convergence Non-Orthogonality –Missing terms in correction operator P E N S SE NE e x y P E N S SE NE e x y

56 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Non-linearities Convergence High-order schemes –Missing terms in correction operator P E W WW w

57 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Parameters When facing non-linear oscillations –Reduce time step –RELAX(U1,FALSDT,...) –RELAX(V1,FALSDT,...) –RELAX(W1,FALSDT,...) –Under-relax corrections –SPEDAT(MIGAL,LINRLX1,R,...) Parameters

58 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Parameters When facing poor linear convergence –Increase effort on each grid (very large grids) –SPEDAT(MIGAL,NBRELAX1,I,...) –SPEDAT(MIGAL,NBPRER1,I,...) –SPEDAT(MIGAL,LITER1,I,...) –SPEDAT(MIGAL,RESFAC1,R,...) Parameters cycle max mean rms 0 0.2801E+00 0.2192E-02 0.9848E-02 1 0.1027E-01 0.8624E-03 0.1276E-02 2 0.1238E-01 0.4684E-03 0.8903E-03 3 0.1137E-01 0.4586E-03 0.8563E-03 4 0.1098E-01 0.4405E-03 0.8341E-03 5 0.1063E-01 0.4337E-03 0.8187E-03 Restriction Prolongation Pre-Restriction relaxations Post-Prolongation relaxations Last level relaxations

59 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Parameters When facing strong local convergence issue –Use the multi-grid preconditionned GMRES facility –SPEDAT(MIGAL,IGMRES1,I,...) –SPEDAT(MIGAL,NBPRECO1,I,...) NB: Increase memory footprint! Parameters

60 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Parameters : GMRES cycle max mean rms 0 0.2801E+00 0.2192E-02 0.9848E-02 1 0.1027E-01 0.8624E-03 0.1276E-02 2 0.1238E-01 0.4684E-03 0.8903E-03 3 0.1137E-01 0.4586E-03 0.8563E-03 4 0.1098E-01 0.4405E-03 0.8341E-03 5 0.1063E-01 0.4337E-03 0.8187E-03 IGMRES = 0 cycle max mean rms 0 0.2801E+00 0.2192E-02 0.9848E-02 1 0.7377E-03 2 0.1734E-03 3 0.1133E-03 4 0.1087E-02 0.7057E-04 0.9309E-04 IGMRES = 5 1 order 2 orders Parameters

61 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 More Examples? Parameters

62 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Turbulent (k-  ) open cavity RELAX(V1,FALSDT, 3.000000E-02) RELAX(W1,FALSDT, 3.000000E-02) RELAX(KE,FALSDT, 3.000000E-02) RELAX(EP,FALSDT, 3.000000E-02) SPEDAT(SET,MIGAL,SOLVED1,C,HYDRO) SPEDAT(SET,MIGAL,LINRLX1,R,8.0000E-01) SPEDAT(SET,MIGAL,SOLVED2,C,KEMODL) SPEDAT(SET,MIGAL,LINRLX2,R,1.0000E+00) Parameters

63 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Comfort in a supermarket VARMAX(TEM1 ) =50.000000 VARMIN(TEM1 ) =12.000000 RELAX(U1,FALSDT, 5.000000E+3) RELAX(V1,FALSDT, 5.000000E+3) RELAX(W1,FALSDT, 5.000000E+3) SPEDAT(MIGAL,SOLVED1,C,HYDRO) SPEDAT(MIGAL,LINRLX1,R,0.4) SPEDAT(MIGAL,IGMRES1,I,5) SPEDAT(MIGAL,RESFAC1,R,0.O) SPEDAT(MIGAL,SOLVED2,C,TEM1) SPEDAT(MIGAL,RESFAC2,R,0.0) SPEDAT(MIGAL,SOLVED3,C,KEMODL) SPEDAT(MIGAL,LINRLX3,R,0.8) SPEDAT(MIGAL,RESFAC3,R,0.0) Parameters

64 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Racing Car Model RELAX(U1,FALSDT, 1.000000E+10) RELAX(V1,FALSDT, 1.000000E+10) RELAX(W1,FALSDT, 1.000000E+10) SPEDAT(MIGAL,SOLVED1,C,HYDRO) SPEDAT(MIGAL,LINRLX1,R,0.6) SPEDAT(MIGAL,IGMRES1,I,5) SPEDAT(MIGAL,RELAX1,R,0.85) SPEDAT(MIGAL,SOLVED2,C,KEMODL) SPEDAT(MIGAL,LINRLX2,R,0.8) SPEDAT(MIGAL,NBRELAX2,I,10) Parameters

65 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Conclusion

66 Migal How to What’s happening Convergence Parameters Conclusion Michel Ferry June 2008 Conclusion MIGAL boosts your convergence. MIGAL proceeds only few sweeps. Parameters can overcome usual convergence issues. mf@mfrdc.com Conclusion

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