Virtual Canoe: Real-Time Realistic Water Simulation for Haptic Interaction

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Virtual Canoe Real-Time Realistic Water
Simulation for Haptic Interaction
Shoichi Hasegawa Tokyo Institute of
Technology/PRESTO JST Yoshinori Dobashi Hokkaido
University Mitsuaki Kato Tokyo Institute of
Technology Makoto Sato Tokyo Institute of
Technology Tsuyoshi Yamamoto Hokkaido
University Tomoyuki Nishita The University of
Tokyo
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Motivation

• My physics simulations for haptic interaction
• Virtual basket
• SIGGRAPH97 Ball and other static objects
• Real-time Rigid Body Simulation for Haptic
  Interactions Based on Contact Volume (SPRINGHEAD
  used in KOBITO)
• Euro Graphics 2004 Multiple rigid objects
• Human Scale Haptic Interaction with a Reactive
  Virtual Human in a Realtime Physics Simulator
• ACE 2005 Upper part of virtual human
• Virtual canoe
• SIGGRAPH 2005 Water and rigid bodies

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Interaction with Fluid

• 3D Computational Fluid Dynamics takes a lot of
  computation time.
• Haptic interaction with Fluid
• The numbers of cells must be small.
• Faster methods realize more applications

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Realtime simulation

• Computation time is limited.
• Generic model takes too much computation time.
• Approximations and specific models are required.
• Example
• Contact model for realtime rigid body simulation
• A rigid body model itself is an approximation.
• Real objects deform when they contact.

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Realtime fluid model

• Requirements for haptic interaction
• Realtime simulation 100Hz-
• Fluid surface
• Forces between fluid and objects.
• Our realtime model
• Realtime 2D wave simulation
• Pre-computation of fluid resistance of objects.

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Decomposing dynamics

• Linear flow
• Wave equations
• Non-linear flow
• NS equations

Realtime simulation
Fluid Resistance Map, FRM
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Wave equations
Navier-Storkes
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Wave equations
Navier-Storkes Long gravity wave assumption
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Wave equations
(Equations of continuity)
(Wave equations)
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Wave equations
(Equations of continuity)
We use this equation to set the velocity of fluid
(Wave equations)
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Boundary conditions

• Velocities of fluid cells around object
  velocity of the object.

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Fluid resistance map

• Limitation of 2D wave equations
• Effects of non linear effects such as vortices
  are not considered.
• Waves from objects are not realistic.

Fluid resistance map
Boundary condition only
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Fluid resistance map
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Related presentation

• For detail of the fluid modelingplease
  participate to our sketch
• A Fluid-Resistance-Map Method for Real-Time
  Haptic Interaction With Fluids
• Prof. Yoshinori Dobashi
• Interactive InteractionTomorrow 920 - 945 am
  Room 511 AB

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Other parts of the system
Simulation of rigid bodies
Human scale haptic interface SPIDAR
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Haptic interface SPIDAR

• SPIDAR
• SPace Interface for Artificial Reality
• Since 1990

Motor and encoder Present force to
user. Measure length of string.
SPIDAR
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Reconfigurable haptic interface

• Any DOF and arrangements are designable.
• Same control algorithm is used for position and
  torque calculations.

7DOF 8Strings
6DOF 8Strings
3DOF 4Strings
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SPIDAR for virtual canoe
To avoid interferences of strings,we need string
anchor apart from the user
To create rotation force We need these
directionsof strings
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Simulation of rigid bodies

• Rigid body simulation
• Equation of motion
• Contact model
• Analytical method (David Baraff 89)
• Stable, rigid
• Much computation for one step
• Penalty method
• Time step must be very small
• Less computation for one step
• The same algorithm can be used for haptic
  rendering

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Simulation of rigid bodies

• Penalty method for 3D convex shapes
• Contact volume based penalty method

Contact part
Suppose distributed spring-damper model Integrate
force and torque for each triangles
A cube on a floor
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Fluid and rigid
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Conclusion

• Haptic interaction with water and rigid bodies.
• Water was modeled by realtime 2D simulation and
  pre-computed FRM.
• For detail of the fluid modeling please
  participate to
• A Fluid-Resistance-Map Method for Real-Time
  Haptic Interaction With Fluids
• Interactive InteractionTomorrow 920 - 945 am
  Room 511 AB

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Fluid and rigid
Rigid body(canoe)
Rigid body(stone)
2D fluid model