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Water Drops on Surfaces Huamin Wang, Peter J. Mucha and Greg Turk Georgia Institute of Technology From SIGGRAPH 2005 Presented by Huamin Wang (whmin@cc.gatech.edu) Motivation Film special effects Motivation Scientific Visualization Motivation Game industry (eventually) Motivation

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water drops on surfaces

Water Drops on Surfaces

Huamin Wang, Peter J. Mucha and Greg Turk

Georgia Institute of Technology

From SIGGRAPH 2005

Presented by Huamin Wang (whmin@cc.gatech.edu)

motivation
Motivation

Film special effects

motivation3
Motivation

Scientific Visualization

motivation4
Motivation

Game industry (eventually)

motivation5
Motivation

Game industry (eventually)

overview
Overview
  • Background
  • The virtual surface method
  • Dynamic contact angle model
  • Results and Analysis
  • Future work
background
Background

Small-scale liquid-solid Interactions

Q: Why small water behaves naturally different from large water?

A1: Surface Tension (water: 72 dynes/cm at 25º C).

A2: Viscosity (water: 1.0020 × 10-3 N·s/m2 at 20º C).

Lake view ( >1 meter)

Water drops (in millimeters)

background8
Background
  • To calculate surface tension force:

: Tension coefficient (always positive)

: Mean curvature

: Normal (always pointing outward)

(Laplace’s Law)

Uniform curvature

Water sphere: photo taken on the International Space Station. Courtesy NASA

background9
Background

Stable contact angle satisfies Young’s Relation:

background10
Background
  • Our work is based on fluid simulation using Computational Fluid Dynamics (CFD).
    • Solve the Navier-Stokes equations for the velocity field
    • Use the particle Level-Set method
overview11
Overview
  • Background
  • The virtual surface method
  • Dynamic contact angle model
  • Results and Analysis
  • Future work
the virtual surface method
The virtual surface method
  • Solution:
    • Place a virtual surface beneath the solid plane
    • Estimate the surface tension using the new combined surface
  • Problem:
    • Real World: a stable contact front with contact angle
    • Simulation: Curvature at contact front is positive, thus always pushes inward:

Air

Liquid

Virtual Liquid

Solid

Virtual Surface

the virtual surface method13
The virtual surface method
  • Create a virtual surface
  • Estimate curvature on the contact front
  • A kink cause the curvature to “push” the fluid front

Air

Air

Liquid

Virtual Liquid

Solid

Virtual Liquid

Solid

Virtual Surface

Virtual Surface

Advancing to right

Receding to left

the virtual surface method14
The virtual surface method

Details? Please read our paper.

overview15
Overview
  • Background
  • The virtual surface method
  • Dynamic contact angle model
  • Results and Analysis
  • Future work
dynamic contact angle model
Dynamic contact angle model

Contact angle hysteresis: Small water drops can stay on a vertical plane, while large water drops will flow down.

dynamic contact angle model17
Dynamic contact angle model
  • Stable contact angles bounds:
    • Advancing
    • Receding
  • a valid stable contact angle:
  • Final pressure P is:

Pa: pressure calculated using Pr: pressure calculated using

dynamic contact angle model18
Dynamic contact angle model
  • Dry/Wet conditions
    • wetting history map
    • Contact angles based on surface wetness

(wet advancing angle smaller than the dry advancing angle)

Dusted region is dry, transparent region is wet.

overview19
Overview
  • Background
  • The virtual surface method
  • Dynamic contact angle model
  • Results and Analysis
  • Future work
results and analysis
Results and Analysis
  • Physics phenomena:

Capillary Action

results and analysis21
Results and Analysis
  • Drop impacts, rivulets, dripping drops, and more…
results and analysis22
Results and Analysis
  • Drop impacts, rivulets, dripping drops, and more…
results and analysis23
Results and Analysis
  • Video

(playback speed 10 times slower than real world speed)

results and analysis24
Results and Analysis
  • Grid resolution: 400×400×400
  • Simulation speed: 20 minutes per frame
  • Each sequence has 500 frames
  • The total running time is:

20 × 500 / (60 × 24) ≈7 days

results and analysis25
Results and Analysis
  • Why is it relatively computational expensive?
    • High grid solution (400×400×400)
    • Large viscosity effects
      • Implicit Euler method
      • The condition number of the linear system increased.
overview26
Overview
  • Background
  • The virtual surface method
  • Dynamic contact angle model
  • Results and Analysis
  • Future work
future work
Future Work
  • Octree data structure
  • Virtual surface reconstruction based on particles
  • Distributed computing
acknowledgements
Acknowledgements

We would like to thank:

  • Mark Carlson, Chris Wojtan, Howard Zhou, Spencer Reynolds, Nathan Sisterson
  • Everyone supporting our work, including reviewers.
  • Gatech Computational Perception Laboratory, Geometry Group
  • CMU graphics lab

Funded:

  • In part by NSF grant DMS 0204309.

Rendering :

  • Physically Based Ray tracer (pbrt), Matt Pharr & Greg Humpheys
  • Light Probe Image Gallery, Paul Debevec
slide29

Fin

Any questions?

Water Drops on Surfaces

Huamin Wang, Peter J. Mucha and Greg Turk

Georgia Institute of Technology

From SIGGRAPH 2005

Presented by Huamin Wang (whmin@cc.gatech.edu)