-
Notifications
You must be signed in to change notification settings - Fork 192
Limitations of the FLIP Fluids addon
Is the FLIP Fluids addon right for your project? The FLIP Fluids addon is a liquid simulation tool based on the popular FLIP simulation method which is short for FLuid Implicit Particle. You should always choose the right tool for the job, and like a hammer, this addon might not always be the right tool to use.
There may be limitations in the FLIP Fluids development project, limitations in the FLIP simulation method, or limitations of Blender that may affect success in creating your desired fluid effect. This document will detail common limitations of the FLIP Fluids addon and Blender.
If you want to try out the addon to see if it's right for you, install our Free FLIP Fluids Demo.
- Scale and Time Limitations
- Volume and Mass Preservation
- Usage in Scientific or Engineering simulations
- Usage in other software or export to other software
- Motion Blur Support
- Force Field Support
- Multiple Fluid Interaction and Mixing Fluid Materials
- UV Mapping Support
- Fluid and Rigid Body Interaction
- Distributed Computing
- Google Colab Support
Physical scale: The FLIP Fluids simulator is designed for small- to large-scale fluid effects. It is designed for physical scales ranging from a glass of water to large sections of a beach. The simulator is not designed for micro-scale phenomena such as accurately simulating the interaction between individual droplets of liquid. It is also not designed for very large scale simulations such as river networks, or entire seas and oceans.
Tip: If your effect involves a small area of dynamic liquid within a large ocean, you will likely need to resort to visual effects tricks. Rather than simulating the entire section of ocean, you will want to simulate smaller local fluid simulation effects and composite into larger ocean footage or blend with a larger ocean plane generated with the Blender Ocean Modifier.
Time Scale: The FLIP Fluids simulator is designed for time scales ranging from seconds to a low number of minutes. It is not designed for time scales of hours, days, or months.
These scale and time limitations are common to many fluid simulation systems that are used in computer graphics software.
Relevent documentation:
The FLIP Fluids simulator may not be able to perfectly preserve mass and volume liquid over time. This is a limitation of the FLIP simulation method and is one of the downsides of a FLIP-based simulator. The FLIP simulation method does not really have a concept of volume and tends to have a bias towards volume loss over time. Volume loss is more prevalent in simulations that involve large amounts of motion from obstacles, especially if the fluid is contained inside of a moving object.
Tips:
- In general, volume loss can be reduced by increasing the number of simulation subteps, which can improve accuracy of fluid-obstacle interaction. See this topic for more information: What are substeps?.
- Related topic: Does your liquid appear to lose volume when the liquid motion is calm or settling? See this topic for more information: Scene Troubleshooting: Volume Loss - Fluid amount shrinking while liquid is settling.
- If using a FLIP-based simulator in an effect where volume loss can be noticeable, a workaround can be to continuously emit fluid throughout the animation to hide the fact that the volume is decreasing.
- It is also possible that the volume of fluid can increase over time. Our Particle Sheeting Feature is an artificial simulation technique that helps create large thin splashes by adding more fluid to the simulation.
- If you require volume to be preserved over time, a particle-based simulation method such as SPH (Smoothed Particle Hydrodynamics) may be more suitable. The Blender particle system fluids and B3FX Studios' FluidLab addon are based on the SPH method and is able to preserve volume.
In general, the FLIP Fluids simulator and Blender simulation systems should not be used for scientific/engineering purposes where accuracy and validation is important. The simulator and simulation method is designed for use in computer graphics applications where complete accuracy is not needed and the fluid just needs to look plausible. Many shortcuts are taken during simulation in order to reduce processing time which also reduces simulation accuracy.
Some of the features/parameters in the simulator are not physically based, do not correspond to real-world physical values, and are just graphics tricks to help produce visually pleasing results. The simulator will not contain many of the parameters that you would find in a simulator aimed towards producing scientific/engineering simulations.
For simulation systems targeted for use in scientific and engineering, check out software packages such as OpenFOAM, SOLIDWORKS Flow Simulation, XFlow.
The FLIP Fluids addon and simulator is only designed to be installed and run within Blender. Installing into and using within other software outside of Blender is not supported.
Fluid simulation output can be exported from Blender for use in other software by using Blender's Alembic exporter. However, there may be compatibility issues upon import into other software. Not all software will support the Alembic structure that Blender imports. See this topic for more information Alembic Export Support > Alembic export for use in other software.
If you would like to test Alembic export using the FLIP Fluids addon in your workflow, try our free demo.
As of FLIP Fluids 1.5.0 (07-sep-2022) in Blender 3.1 or later, Cycles motion blur support has been improved and is supported on both the liquid surface and whitewater (foam/bubble/spray/dust) particles by exporting and using the FLIP Fluids velocity attribute. However, these features are hidden by default due to a current bug in Blender that can cause frequent render crashes or incorrect renders when using these features. See the FLIP Fluids Preferences > Developer Tools documentation for affected features, a workaround to this bug, and how to enable these features.
Related Documentation
- See the Domain Attributes and Data Settings > Motion Blur Rendering: Automatic Setup documentation for how to quickly get started with motion blur rendering.
- See our Motion Blur and Attributes example files for basic Blend file setups including notes.
- See the FLIP Fluids Sidebar Helper > Geometry Node Tools > Initialize Motion Blur operator to automatically set up motion blur rendering.
Alternative: A popular workaround is to add motion blur as a post-processing effect using software such as Adobe After Effects, DaVinci Resolve, and ReelSmart Motion Blur.
As of FLIP Fluids version 1.0.9 (26-nov-2020), a new force field feature set was introduced into the addon. See the Force Field Object Settings documentation for more info on our force field features.
However, there are some limitations to be aware about:
No, the built-in Blender force fields are not compatible with the FLIP Fluids addon. Our addon has limited access to Blender's force field system and due to this, we are not able to use these force fields within the simulator. Our force field system is a separate and custom built physics system that is implemented directly within our simulation engine.
In addition to the limitations of Blender's force field system, many of the force field modes we have implemented are for creating popular effects that are not possible using Blender's internal force fields. Our force field modes differ from Blender's in that they are specifically designed towards use in liquid physics and creating popular liquid effects.
Update: As of FLIP Fluids 1.5.0 (07-sep-2022), mixed/blended color attribute features and basic variable viscosity features have been added. However, these features are hidden by default due to a current bug in Blender that can cause frequent render crashes or incorrect renders when using these features. See the FLIP Fluids Preferences > Developer Tools documentation for affected features, a workaround to this bug, and how to enable these features.
At the moment, there is no support for multiple fluid simulation and mixing fluid materials in the FLIP Fluids simulator. The simulator is limited to a single fluid (and single viscosity) throughout the domain. Support for multiple fluid interaction is one of the most popular requests. We hope that we can add this in the future, but is not being actively worked on at the moment. This is a complex subject in fluid simulation and may require a significant amount of time for research and development, and some aspects of this feature may be outside of the scope of the FLIP Fluids project.
At the moment, multi-liquid simulation features only support color blending and variable viscosity. Features such as variable surface tension, variable density, volumetric liquid attributes, and separated liquid meshes are not implemented and some aspects of these features may be outside of the scope of the FLIP Fluids addon project.
At the moment, there is no support for generating UV Maps or applying textures to fluids created with the FLIP Fluids simulator. Support for UV mapping and applying textures to fluids and fluid parameters is a popular request and we hope to add this in the future, but is not actively being worked on at the moment. This is a complex subject in fluid simulation and may require a significant amount of time for research and development, and some aspects of this feature may be outside of the scope of the FLIP Fluids project.
Depending on the simulation effect, a workaround may be to use Blender's existing procedural texture features. In future development, support for mixing fluids and materials may be added which can expand how procedural textures can be used to render fluids.
Interaction between FLIP Fluids simulator and Blender's rigid body simulator is limited. Rigid body objects can push around the fluid, but the fluid is not able to push around the rigid body objects. This is because simulation systems in Blender are run separately and do not communicate with each other. This limitation also includes interaction with Blender's cloth and softbody simulation.
However, there are some convincing tricks that you can use to create the illusion of buoyancy where objects are floating around on your liquid surface. See this episode of our tutorial series for a detailed guide and example animations: Episode Seven: Buoyancy Tricks.
Distributing computation over multiple systems and CPUs is not supported in the FLIP Fluids simulator. The simulator is multi-threaded, but the FLIP simulation is not highly parallelizable and is often not able to benefit from distributed computation. There are methods to allow for distributed computing using the FLIP method, but have limited use and is outside of the scope of the FLIP Fluids project. Simulations large enough to benefit from distributed computing are likely too large to be displayed and rendered in Blender.
Relevant Documentation:
Running the FLIP Fluids addon on Google Colab is not supported. Both running a simulation and directly rendering a simulation is not supported. A workaround can be to export a FLIP Fluids addon simulation to Alembic so that the simulation results can be rendered without the use of the addon. See Alembic Export Support.
Warning: Not all Blender features or addons may be supported on Google Colab and the render results may differ from your home system. Google Colab is targeted towards researchers and students to run AI/ML tasks, data analysis and education, not rendering 3D scenes. You may be timed out or restricted from using Google Colab when misusing the service.