Tips for Creating Ship Simulations

The FLIP Fluids simulator can be used to create ship simulations and ship wake effects. These effects often involve combining a smaller fluid simulation with a larger ocean plane, either through using procedural modifiers or compositing techniques.

These types of effects can be more on the advanced side of simulation and Blender, and are not recommended effects for beginners. This documentation will provide a basic overview, tips, and resource for how to get started. This is not a step by step guide and an intermediate to advanced knowledge of Blender's procedural tools or compositing techniques may be required.

Warning: Blender's procedural tools for combining simulation meshes into a larger ocean can be more difficult to use for these types of effects compared to other professional liquid simulation software.

• Example Animations
• Optimize your simulation setup
• More simulation tips
• Adding extra detail to the fluid surface

Example Animations

See these animation examples created using Blender and the FLIP Fluids addon:

• Shipwake | FLIP Fluids addon | Ocean Modifier by Blender Cinematic
• Ship Wake: Blender & FLIP Fluids by ArchiCraig CAD
• Liquid Methane Bunkering by Timx AS
• Bunkering Vessel Norway by Timx AS
• Riverboat by Tom Allen

Optimize your simulation setup

These types of effects often require simulating a high amount of physics detail, meaning you will likely need to use a high domain resolution. The resolution of these effects can often be in the range of 500 to 1500. Baking time takes significantly longer at high resolutions, so it will be important to optimize your scene setup:

• Simulate a thin layer of liquid rather than a deep pool. Less fluid reduces baking times. See this example showing a boat thin layer of liquid: Wake Test by Tom Allen
• Do not try to simulate a large ocean. To reduce the amount of liquid to simulate, the fluid bounds should be limited to the smallest area possible for your effect.
• Size the domain to fit as tight as possible around the fluid. If the fluid won't splash very high, it will be good idea to lower the domain ceiling. The simulator must make calculations over the entire domain volume, and less empty space will reduce baking time. Documentation topic: How large should I make my domain object?
• Does your ship model contain a large amount of geometry? You may want to model a simpler proxy object of just the ship's hull to use just for the simulation. Less geometry is quicker to compute.
  • Make sure that your ship geometry is manifold/closed/watertight, which is required for objects to be computed accurately within the simulator.
  • If your ship animation is more complex than keyframed location/rotation/scale or f-curves, you will need to enable Export Animated Mesh in the FLIP Fluid Obstacle settings for the animation to be exported correctly.
• For testing, you may want to decrease the Surface Subdivision Level in the FLIP Fluids Surface Panel to 0 for a lower amount of mesh generation quality and faster baking. Depending on the level of detail needed, you may also get away with decreasing the subdivision level for the final simulation as well.
• Using surface tension, sheeting effects, or viscosity is not recommended for these types of effects. These features are not very suitable for large scale simulations and will add a lot of extra simulation time if enabled.
• For large scale simulations, such as oceans, beaches, or other slow moving bodies of water, you can often get away with a higher CFL Number in the FLIP Fluid Advanced Panel such as 10 or 15 without affecting results. This can greatly improve simulation baking time, and even double or triple the speed in high resolution simulations. However, if you have thin obstacles or very quick moving obstacles, this may affect accuracy or result in leakage. A thick obstacle, such as a ship's hull moving through the water is a good situation for increasing the CFL number.
• More performance tips can be found here: Scene Troubleshooting: Baking is taking too long to compute!

More simulation tips

• For realistic results, it is suggested to model the simulation to a realistic scale. By default, 1 Blender unit is equal to 1 meter in the simulation. It is also important to make sure that the ship is animated at a realistic speed. Documentation topic: The Importance of Scale.
• The default FLIP Fluid Whitewater settings are usually good for this scale of simulation. You will usually just need to change a few settings to generate more or less foam: Scene Troubleshooting: Simulation not generating enough whitewater.
  • You may want to disable the Enable Emission Near Domain Boundary option in the Whitewater Advanced Settings. This will prevent whitewater from being generated near the edges of the domain.
• If combining the simulation with a larger plane, or if compositing the simulation into video, you may want to enable the Remove Mesh Near Boundary option in the FLIP Fluid Surface panel. This will generate a surface mesh without the sides and bottom of the domain which can make it easier to blend.
  • For an example workflow on how to combine a FLIP Fluids simulation with a larger ocean plane, see this tutorial series by Tom Allen: Ocean Modifier plus FLIP fluid sim equals greatness!

Adding extra detail to the fluid surface

Outside of the simulated wake pattern, the simulation surface may look flat and unlike the motion of an ocean. The generated fluid surface can be displaced to add extra ripple details:

• To add extra detail to the fluid surface it is common to add Blender's Ocean Modifier as a displacement to the fluid surface geometry. By setting wave alignment and direction on the ocean modifier, this can create the illusion that the ship is moving more quickly through the ocean than it actually is.
  • See these animation examples by Tom Allen: Without Displacement | With Displacement.
  • New: See this guide for How to blend FLIP simulation onto Ocean by Blender Cinematic.
  • See this Twitter thread on how to perfectly blend a simulation with the Ocean modifier without any compositing, displacement baking, weight painting or others complicated wizardry by Francis Jasmin (Original Tweet | Twitter Thread Reader).
  • See this Blender Artists comment from ArchiCraig with notes and example node groups for their ship wake animation.
  • See this Spaceship rising out of Ocean animation and breakdown by Blender Cinematic with notes and node groups used in the set up.
  • See this animation breakdown for how this can be set up on your fluid surface and whitewater: Dolphin: Blender + Flip Fluid by Artell Blender (Additional notes can be found in the pinned YouTube comment).
• Another method of adding detail, such as a larger wake pattern can be to use Blender's Dynamic Paint features.
  • See this tutorial on how to use dynamic paint for water effects: creating realistic ripples in water with dynamic painting in blender 2.8 by TopChannel1on1
  • See this animation example combining dynamic paint with a FLIP Fluids simulation: Bunkering Vessel Norway by Timx AS