Presentation is loading. Please wait.

Presentation is loading. Please wait.

Practical Animation of Turbulent Splashing Water SCA 2006 Janghee Kim Deukhyun Cha Byungjoon Chang Bonki Koo Insung Ihm.

Similar presentations

Presentation on theme: "Practical Animation of Turbulent Splashing Water SCA 2006 Janghee Kim Deukhyun Cha Byungjoon Chang Bonki Koo Insung Ihm."— Presentation transcript:

1 Practical Animation of Turbulent Splashing Water SCA 2006 Janghee Kim Deukhyun Cha Byungjoon Chang Bonki Koo Insung Ihm

2 Abstract ◇ Produce small-scale detail of turbulent water ◇ Integrate the dynamic behavior of splashing water easily into a fluid animation system ◇ Transform into water particles to represent subcell-level features ◇ Water particles create realistic turbulent splashing ◇ The particle agglomerates are smoothed, thickened, if necessary

3 Introduction ◇ Motivation : water spray, wave breaking, mist, foam ◇ An Eulerian grid often suffers from a difficulty in depicting the detailed turbulent behavior of splashing water ◇ leading to impractical requirements for computation time and memory space by increasing the resolution

4 Introduction ◇ Recently introduced particle-based techniques offer a computationally simple and versatile simulation scheme ◇ Particles are well suited to producing the small-sacale detail ◇ The primary goal of this work is to combine both grid-based and particle based simulation techniques in a fluid animation

5 Previous Work ◇ 3D Navier-Stokes equations for fluids - Foster and Metaxas 1997b - Stam Fedkiw et al ◇ Particle level set - Enright et al ◇ SPH technique - Muller M, Charypar D, and Gross M Muller M, Solenthaler B, Keiser R, and Gross M 2005

6 Previous Work ◇ Solid fluid coupling - Calson et al Guendelman et al ◇ CIP Method - Song O, Shin H, and Ko H Takahashi et al ◇ VOF (Volume Of Fluid) -Hong and Kim 2005 ◇ Multi-phase flow -Hong and Kim 2005

7 Previous Work ◇ MPS (Moving Particle Semi Implicit) - Koshizuka S, Tamako H, and Oka Y 1995 ◇ PIC and FLIP - Zhu Y and Bridson R Harlow F. H Brackbill J. U and Ruppel H. M 1986 ◇ Air Marker Particles (splash) - Enright et al Guendelman et al Selle et al. 2005

8 Our Contribution ◇ The massless marker particles escaped form the main body of water ◇ Seeds to produce the subcell level detail ◇ For generating droplets and bubbles, Estimate the volume loss and distributes it to water particles ◇ These physical particles are moved in the air by an advanced particle simulation system for turbulent splash ◇ We also present rendering techniques suitable for taking a close- up view of merging water drops with minimized aliases

9 Modeling of water particles ◇ Levelset simulator represents the main body of splashing water ◇ A particle simulator depict its small-scale detail ◇ phi 0 designs air in particle levelset ◇ Combined with an octree data structure, the levelset simulator create very detailed surfaces of dynamically evolving water

10 Identification of underresolved regions ◇ Rebuild the levelset in underresolved regions using massless marker particles ◇ It sometimes fails to recover subcell-level features which often occurs when water undergoes turbulent motion ◇ There still remain escaped negative particles near the shar conner even after the correction due to be resolved with the current grid resolution

11 Identification of underresolved regions ◇ The missing particles provide an excellent clue ◇ generation of various rendering effects for splashing water ◇ We explicitly transform these marker particles into physical particle ◇ Model small-scale detail that the given Eulerian grid fails to represent

12 Generation of water particles ◇ In the work Song et al.[SSK05] ◇ In order to detect small isolated regions ◇ A smeared Heaviside function was applied to dissipative cells ◇ Convert them into droplets or bubbles with an estimated volum

13 Generation of water particles ◇ The particle levelset method offers more information that helps correct poorly resolved regions of the flow ◇ It can the extraction of more charateristic information about the dissipating water ◇ We utilize the lost particles to treat subcell-level details ◇ The estimated volume is distributed to the water particles

14 Monte Carlo Integration ◇ For every cell that contains at least one escaped partcle ◇ A series of random three dimensional points are repeatedly generated within the cell checking if they fall in any of the escaped particles ◇ The ratio of inner points, multiplied by the cell’s volume ◇ Gives a good approximation to the actual minute volume of disappearing water

15 Generation of water particles ◇ n p is escaped marker particles in the cell ◇ The estimated volume V ◇ Each water particle inherits the position and velocity from the corresponding marker particle ◇ If any two particles overlap excessively, they are merged into a single particle with a radius

16 Generation of water particles ◇ Scene1 sampled 2048 times per volum-losing cell ◇ Scene3 sampled 256 times per the cell ◇ It can obtain reliable volume loss estimate ◇ The additional overhead by the integration process is not served

17 Advection of particles ◇ The SPH method is widely used for discrete particle systems ◇ MPS (Moving Particle Semi-implicit) ◇ Combining the PIC[Har64] and FLIP[BR86] Method, both recently introduced to the graphics part by Zhu and Bridson ◇ It lead to an effective and easy implementation for turbulent splashes ◇ we use a weighted average of PIC and FLIP when particle are updated after the nonadvection step

18 Advection of particles ◇ The particle velocities are transferred to an auxiliary Eulerain grid ◇ We extend the standard trilinear interpolation ◇ The particle’s mass is also reflected as a weighting factor ◇ The resolution of the auxiliary grid used in the adaptive levelset

19 Interaction of water particles with levelset surface and objects ◇ Water particle to water particle interaction ◇ Any two particles overlapping too much are merged into a single particle in the water particle generation step ◇ The masses and velocities of water particle are used in the PIC/FLIP-based particle simulator that the particles to interaction to each other

20 Interaction of water particles with levelset surface and objects ◇ Water particle to main body of water interaction ◇ As the returning water particle has mass, the velocity field of the Eulerian grid representing the levelset is affected near the hit point ◇ m p = mass particle, v p = velocity particle at the colision ◇ m ijk, v ijk denote the corresponding quantities for the surface cell hit by the particle

21 Interaction of water particles with levelset surface and objects ◇ In [SSK05], the inverse smeared Heaviside function ◇ Simple to implement update method is to find the edge of grid closest to the returning water particle, and adjust the levelset values (move upward by distance h) ◇ The entire volume increase induced by this modification can be approximated by summing the volume of all tetrahedra ◇ This process may often be omitted without making a visual difference in the animatio results ◇ Water particle to object(elasticity coeff a e ) interaction

22 Rendering of a close-up view of water particles ◇ This is difficult to achieve with sphere-based particle cluster in the resulting smoothness of the extracted surfaces ◇ Insufficient smoothing produces rough-looking surfaces ◇ Too much smoothing blur the small-scale detail ◇ Controlling the small-scale redering effects for creating turbulent spashes

23 Smoothing particle clusters ◇ [FF01,MCG03,PTB03,ZB05] employ an Eulerian grid to extract a set of iso-surface from a scalar field defined by the particles ◇ We designed a smoothing technique for tyny particle cluster ◇ It permits direct control over the smoothness of reconstructed water surfaces

24 Smoothing particle clusters ◇ p i = (x i, r i ), center x i = (x i, y i, z i ), radius r i ◇ W(x) as a weighted sum of contributions from near by particles ◇ W i (x) is a smoothing kernel whose detail is provided in the Appendix

25 Appendix ◇ Figure5 shows an example of cluster smoothing with alpha value ◇ The ray is marched from the intersection point x(0) with an initial step size ◇ This jump-and-check process is repeated with a halved step size ◇ Once that happens, the marching direction is reversed

26 Smoothing particle clusters ◇ Ray marching stops when the step size falls below a specified lower bound ◇ If no sign change occurs when the marching is finished, the ray does not intersect the smoothed surface

27 Thickening water agglomerates ◇ Sometimes, there are insufficient marker particles in the underresolved regions ◇ Entailing overall deficiencies in the distribution of water particles ◇ Seed more particles between them ◇ At every time step, the simulated water particles are partitioned ◇ All particles within distance d intra belong to the same group

28 Thickening water agglomerates ◇ The idea of the partitioning is to find regions automatically ◇ Particles are poorly distributed, therefore in need of more particles ◇ Once grouping is complete, nearby groups are interconnected ◇ Insert new particles between particles from different groups whose distance is less than d inter

29 Creating water spray ◇ Volume rendering for water mist [Takahashi et al. 03] ◇ The water particles are assumed to generate both external force and mist density in the air ◇ We use another Eulerian grid ◇ At every time step, each particle’s velocity is added onto grid points in its neighborhood ◇ The accumulated velocity v accum is then added to the external force

30 Creating water spray ◇ v accum also determines the amout of mist to be added at each step ◇ We use a simple linear function S(v accum ) as a source term ◇ Density d is moved along the velocity field using an advect- diffusion type equation

31 Experimental Results ◇ Environment - Navier-Stokes Equation - Eulerian velocity field - WENO, TVD Runge-Kuntta for integrate the marker particle - PIC and FLIP - Intel Xeon 3.6 GHz CPU

32 Experimental Results ◇ Our particle simulation component takes only a small portion of the computation time ◇ We observed that only 1.05% of the simulation time

33 Conclusion ◇ Hybrid water animation technique ◇ improving the visual realism of splashing water with turbulent ◇ Capturing detailed complex phenomena such as splash, mist, wave breaking, agglomerates, and spray ◇ We have not yet implemented bubbles

Download ppt "Practical Animation of Turbulent Splashing Water SCA 2006 Janghee Kim Deukhyun Cha Byungjoon Chang Bonki Koo Insung Ihm."

Similar presentations

Ads by Google