Parallel MPS Method for Violent Free Surface Flows

Transcription

1 2013 International Research Exchange Meeting of Ship and Ocean Engineering (SOE) in Osaka Parallel MPS Method for Violent Free Surface Flows Yuxin Zhang and Decheng Wan State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Eng. Shanghai Jiao Tong University

2 Outline Introduction Parallel modified MPS Applications Dam break Sloshing Green Water Ship-Wave interaction Conclusions

3 Introduction Characteristics of violent free surface flows Large deformed free surface Strong nonlinearity Sloshing (Ship Research Institute in Tokyo) Green Water (Greco, 2001) It is a challenging task to simulate violent free surface flow.

4 The research object: Develop a MPS(Moving Particle Semi-Implicit) solver for simulations of violent free surface flows.

5 Advantages of MPS Very effective in handling large deformed free surfaces Easy to deal with moving boundary Perfect mass conservation Simple to program

6 Disadvantages of MPS Strong Pressure oscillation Modified MPS High Computational Cost Parallel computation

7 Modified MPS 1. Mixed source term for pressure Poisson equation 2. Precise surface detection method

8 Pressure Poisson Equation Original MPS + ρ < n > n t n 2 n 1 < P > i = Modified MPS( Tanaka, Lee) ρ >= γ V γ ρ 2 t t 2 n+ 1 * < P i (1 ) * 0 i 2 0 * < n > i 0 The introduction of velocity divergence in source term improves the pressure field since the velocity field is smoother than the field of particle number density, n n 0 where: γ * is a parameter, V is temporal velocity, * n is temporal particle number density.

9 numerical test : sloshing Geometry of tank Unit : mm

10 Experiment (DSME) Original MPS Mixed Source term method

11 Surface detection method Original MPS < n> < β n * 0 i Modified MPS D 1 < F >= ( r r ) W ( r ) i 0 i j ij n j i ri rj F represents the asymmetry of arrangements of neighbor particles. < F > > i α where: is particle number density, D is the number of dimensions. n W is the kernel function, r is the position vector, β, α are parameters.

12 Mixed Source Term Mixed Source Term + precise Surface Detection Surface particle Pressure field

13 Comparison of pressure Experiment (DSME) Modified MPS (Mixed Source Term + precise Surface Detection)

14 Disadvantages of MPS Strong Pressure oscillation Modified MPS High Computational Cost Parallel computation

15 Parallel computation

16 Parallel computation Strategy: Domain decomposition

17 Parallel computation Strategy: Domain decomposition Node 0 Node 1 Node 2 Node 3

18 Dynamic Load balance n0 n1 n2 n3 n4 n5 n6 n7 n8 n9 Node 0 Node 1 Node 2 Node 3 N _ proc N _ total / np where: N _ proc N _ total np Particle number in each processor Particle number in the whole computation Number of processors

19 Dynamic Load balance n0 n1 n2 n3 n4 n5 n6 n7 n8 n9 Node0 Node1 Node2 Node 3 N _ proc N _ total / np where: N _ proc N _ total np Particle number in each processor Particle number in the whole computation Number of processors

20 without dynamic load balance with dynamic load balance

21 Speed-up Ideal Measured Speed-up Number of processors Load is redistributed in every 100 time steps

22 Outline Introduction Parallel modified MPS Applications Dam break Sloshing Green Water Ship-Wave interaction Conclusions

23 Dam break Computational model water Obstacle

24 Dam break Number of particle Fluid particle Wall particle Particle spacing 1.01 million 0.67 million 0.33 million 0.01 m

25 Animation

26 Wave height H2 Exp. (Kleefsman, 2005) Modified MPS VOF (Kleefsman, 2005)

27 Wave height H4 Exp. (Kleefsman, 2005) Modified MPS VOF (Kleefsman, 2005)

28 Impact Pressure Evolution P1 Exp. Modified MPS Original MPS VOF P5

29 Comparison of pressure fields (a1) t=0.35 s (b1) t=0.35 s (a2) t=0.70 s Original MPS (b2) t=0.70 s Modified MPS

30 Sloshing Geometry of tank Unit: mm

31 Animation

32 Snapshots Exp. Modified MPS t=nt+1/20t t=nt+9/10t

33 Impact pressure Exp. Modified MPS P1 P3

34 Sloshing with baffle

35 Wave height Left wall Exp. MPS VOF Right wall Exp. MPS VOF

36 Sloshing with baffle

37 Green water Computational model Damping region Unit: m Regular wave: Period (s) Height (m)

38 Early stage of wave shipping Experiment (Greco, 2001) Modified MPS

39 Impact pressure P1 Experiment (Greco, 2001) Modified MPS Original MPS VOF (Nielsen, 2004) P2

40 3D green water

41 Snapshots t=4.25s t=4.7s t=4.9s

42 Impact pressure P1 P2

43 Ship-wave interaction

44 T=10.2 s T=10.4 s T=10.6 s T=10.8 s

45 Conclusions The present MPS method is robust in handling violent free surface flows; Reliability of the present MPS is good in terms of pressure prediction and surface tracking; A large number of particles can be simulated by use of parallel computation.

46 Thank you for your attention!