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Optimization of relaxation factor for simple solver, OpenFOAM Study Meeting for beginner@Kanto, 26th Aug. 2012

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Optimization of relaxation factor for simple solver, OpenFOAM Study Meeting for beginner@Kanto, 26th Aug. 2012

  1. 1. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Masashi Imano (OCAEL Co.Ltd.) Optimization of relaxation factor for simple solver 1
  2. 2. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) “Guidebook for Practical Applications of CFD to Pedestrian Wind Environment around Buildings” Working Group in Architectural Institute of Japan Web site (in Japanese and English)( in Japanese) Akashi Mochida, Yoshihide Tominaga, et al. Guideline for Practical Applications 2
  3. 3. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Case A (2:1:1 shape) Case B (4:4:1 shape) Case C (Simple blocks) Case D (High-rise bldg.) Case E (Niigata) Case F (Shinjuku, Tokyo) Benchmark tests 3
  4. 4. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Mesh Cartesian mesh (snappyHexMesh) Inflow Interpolate from wind tunnel results Top & Side wall Zero gradient Ground and bldg. wall Generalized log law for a smooth wall Turbulence model Standard k-epsilon Advection scheme Upwind Algorithm SIMPLE (simpleFoam) Wind direction NNE Building complexes with simple building shape in actual urban area (Niigata) Case E - Calculation condition 4
  5. 5. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Case E - Validation RMSE(Root Mean Square Error) Code O(Overlapping structured grid) 0.24 OpenFOAM (Unstructured grid) 0.22 NNE Code OExperiment Code O OpenFOAM Normalizedvelocity 5
  6. 6. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Test cluster condition • Project XL server @ Hokkaido University • Hardware: HITACH BladeSymphony BS 2000 • CPU: Intel Xeon E7-8870 2.4GHz, 10 cores • Node: 4CPUs (40 cores) • Memory: 128GB/node • HDD: 2TB/node • OS: Any OS (root account is available) • Rental fee: 21,000 yen/month • Other project server: ✓ L server: 10 cores(1CPU), 5,250 yen/month 6
  7. 7. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Accelerate simple solver • Relaxation parameters for pressure and velocity are important for steady state incompressible flows (solver: simpleFoam) relaxationFactors  //  0  <  relaxationFactors  <=  1 {        p                0.3;  //  for  pressure  (important)        U                0.5;  //  for  velocity  vectors  (important)        k                0.5;  //  for  turbulence  kinetic  energy        epsilon    0.5;  //  for  turbulence  kinetic  energy                                    //  dissipation  rate } system/fvSolution: 7
  8. 8. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Convergence criteria SIMPLE {                nNonOrthogonalCorrectors  0;        residualControl  //  convergence  criteria        {                "(p|U|k|epsilon|omega)"  2e-­‐3;        } } system/fvSolution: 8
  9. 9. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Results of speedup in SIMPLE 1 0 0.5 1 1.5 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.75 0.8 0.85 0.9 Speedupratio(baseαU=0.5,αp=0.8) Relaxation factor for velocity (αU) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Relaxation factor for pressure (αP) αP=0.1 αP=0.2 αP=0.3 9
  10. 10. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Results of speedup in SIMPLE 2 0.9 1 1.1 1.2 1.3 1.4 1.5 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.75 0.8 0.85 0.9 Speedupratio(baseαU=0.5,αp=0.8) Relaxation factor for velocity (αU) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Relaxation factor for pressure (αP) αP=0.1 αP=0.2 αP=0.3 αP=0.4αP=0.5 αP=0.6 αP=0.7 αP=0.8 αP=0.9 10
  11. 11. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Results of speedup in SIMPLEC 0 125 250 375 500 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Iterationnumber Relaxation factor for pressure (αU) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 SIMPLEC Relaxation factor for velocity (αP) αP=0.8 αP=0.9 αP=0.7 αP=0.6 αP=0.5 αP=0.4 αP=0.3 αP=0.2 αP=0.1 SIMPLEC is almost equivalance to SIMPLE when αU+αP=1 11
  12. 12. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Execution time per iteration 0 600 1200 1800 2400 3000 3600 4200 4800 0 600 1200 1800 2400 3000 Exectiontime[s] Number of iteration SIMPLE SIMPLEC 12
  13. 13. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Results of speedup in SIMPLEC 2 0 0.5 1 1.5 2 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Speedupratio(baseαU=0.5,αp=0.8) Relaxation factor for pressure (αU) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 SIMPLEC Relaxation factor for velocity (αP) αO=0.8 αP=0.9 αP=0.7 αP=0.6 αP=0.5 αP=0.4 αP=0.3 αP=0.2 αP=0.1 SIMPLEC is almost equivalance to SIMPLE when αU+αP=1 13
  14. 14. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) 0 0.5 1 1.5 2 2.5 3 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Maximumofvelocityrenewal[m/s] Relaxation factor for pressure (αU) Ux Uy Uz Maximum of velocity renewal 1 When solution is converged (i.e Initial residual for p and U are smaller than criteria) Inlet velocity at pedestrian level is about 3 m/s. Maximum of velocity renewal should be smaller than about 10% of 3 m/s, i.e. 0.3 m/s. 0.3 m/s 14
  15. 15. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) 0 0.5 1 1.5 2 2.5 3 0 1 2 3 4 5 6 7 8 9 Maximumofvelocityrenewal[m/s] Virtual time step (E=αU /(1-αU) Ux Uy Uz Maximum of velocity renewal 2 When solution is converged (i.e Initial residual for p and U are smaller than criteria) 15
  16. 16. Aug. 26th 2012 OpenFOAM Study Meeting for beginner @ Kanto Masashi Imano (OCAEL Co. Ltd.) Any Questions? 16

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