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This rollout controls the FireSmoke dynamics parameters. It , which affect the fluid’s behavior when simulating. The Dynamics rollout can be accessed in the Modify panel when a FireSmokeSim object is selected. |
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UI UI Path: ||Select Select Fire Smoke Simulator| FireSmokeSim|| > Modify panel > Dynamics rollout |
Parameters
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General
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Motion Inertia | ext_wind – When enabled, moving the simulator object over a series of frames causes inertial forces in the opposite direction of the movement. This allows you to link the simulator to a moving object and keep the size of the grid relatively small, as opposed to creating a large grid that covers the entire path of the moving object. Motion Inertia can be used for moving ground and water vehicles, torches, fireballs, rockets, etc. | ||||||||||||||||||||||||||||||||||
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| TimeScale
Time Scale * Time in frames / Frames per second | |||||||||||||||||||||||||||||||||
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| Cooling
| SmokeDissipation
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Smoke Buoyancy | smoke_bcy – The buoyancy of the smoke. Positive values make the smoke move upwards. Negative values make it move downwards. |
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Vorticity
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Vorticity
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the fluid excessively and stops the fluid's motion.
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Example: Vorticity
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Example: Vorticity
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Randomize
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These options add random fluctuations in the fluid's velocity for each grid voxel. It works in combination with the Vorticity parameters. |
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Fluidity (Conservation)
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The conservation process gives the fluid its characteristic swirling motion. It transforms straight-line movement of the fluid into swirling vortices. The higher the strength of the conservation, the farther the motion forces will be propagated throughout the container, so a movement in one point will cause the fluid to start moving at a distance too. The conservation directs smoke and fire into realistic shapes and helps liquids to support their own weight when at rest, and to fill up a volume they are poured into. |
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Internally, the conservation updates the directions and magnitudes of the velocities of each cell in the grid, preparing them for the Advection step when the content will be moved between cells. Basically it tries to equalize the velocities coming in and going out from each cell, and does this in many passes, getting closer to the perfect equilibrium. The number of passes is the conservation strength (quality). In nature, conservation has an infinite strength and is always perfect. In Phoenix FD, the better the quality of the conservation is, the farther the movement from one point will be propagated, making the simulation more realistic, but at the expense of longer simulation time for each frame. There are a number of conservation methods in Phoenix FD that you can choose between, depending on the type of your simulation. Each of them comes with pros and cons for the given situation. |
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Example: Conservation Method Types
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Example: Conservation Quality
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Anchor Advection Advection
Transport (Advection)
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The advection Advection is the process that moves the fluid along its velocity inside the grid. A problem of all grid-based simulators is that moving the content of one cell to a new place in the grid will blur the result when the destination lies between cells (and it usually does), thus losing the fine details with each new frame. Phoenix FD has a number of advection methods that battle this problem in different ways, each one with its own pros and cons depending on the situation.
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Phoenix FD may perform advection more than once per frame, or once in a number of frames, depending on the the Steps per frame Per Frame (SPF) parameter. To get the best detail for smoke and fire, it is best to keep the SPF low. On the other hand a higher SPF works better to keep liquids steady and smooth, and is better for quickly moving fluids in general. |
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Method | advtype – Specifies the algorithm used for calculating the advection. For more information, see the Advection Method Types example below.
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parameter. When you press simulate, the activity of the fluid in all of the voxels is calculated in sequential steps, representing the passage of time. The order of steps is always sequential, meaning the simulator will calculate fluid properties sequentially from one step to the next, until you have a series of steps that map out the fluid’s behavior over time. The number of steps can be modified using the Steps Per Frame (SPF) parameter, which determines how time is subdivided, and has a significant impact on the behavior, quality and performance of the simulation. |
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To get the most detail for fire and smoke simulations, it is best to keep the Steps Per Frame (SPF) low. On the other hand, a higher SPF works better to keep liquid simulations smooth and steady, and can also produce better results for fast moving fluids in general. |
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Signs that this parameter needs to be increased are:
More often than not, those issues will be caused by the simulation moving too quickly (e.g. the emission from the source is very strong or the objects in the scene are moving very fast). In such cases you should use a higher SPF. Keep in mind that higher Steps Per Frame decreases the performance in a linear way, i.e. if you increase the SPF twice, your simulation will go twice as slow. However, the quality does not have a linear relation to the SPF. Each simulation step kills fine details, and thus for maximum detail it's best to use the lowest possible SPF that runs without any of the issues mentioned above. For additional information, please refer to Phoenix FD Explained.
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Example: Advection Method Types
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Example: Steps Per Frame (SPF)
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Active Bodies
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Interaction between Active Bodies and the Phoenix FD Fire/Smoke Simulator is not supported yet. |
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For more information on Active Bodies, please check out the Active Body Solver and the Active Bodies Setup Guide. |
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Texture UVW
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The main purpose of the Texture UVW feature is to provide dynamic UVW coordinates for texture mapping that follow the simulation. If such simulated texture coordinates are not present for mapping, textures assigned to your simulation will appear static, with the simulated content moving through the image. This undesired behavior is often referred to as 'texture swimming'. UVW coordinates are generated by simulating an additional Texture UVW Grid Channel which has to be enabled under the Output roll-out rollout for the settings below to have any effect. The custom UVW texture coordinates can be used for advanced render-time effects, such as recoloring of mixing fluids, modifying the opacity or fire intensity with a naturally moving texture, or natural movement of displacement over fire/smoke and liquid surfaces. Some examples uses are:
The Texture UVW channel values represent the UVW coordinates of each Cell in the Simulator, with a range of [ 0 - 1 ]. The channel is initialized when a simulation is started in one of two ways:
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Interpolation | texuvw_interpol_influence – Blends between the UVW coordinates of the liquid particle at time of birth and its UVW coordinates at the current position in the Simulator. When set to 0, no interpolation will be performed - as a consequence, textures assigned to the fluid mesh will be stretched as the simulation progresses. This is best used for simulations of melting objects. When set to 1, the UVW coordinates of the fluid mesh will be updated with a frequency based on the Interpol.Step parameter - this will essentially re-project the UVWs to avoid stretching but cause the textures assigned to the fluid to 'pop' as the re-projection is applied. If you intend to apply e.g. a displacement map to a flowing river, set this parameter to a value between 0.1 and 0.3 - this will suppress both the effects of stretching and popping. See the Interpolation example below.
Interpol. Step | texuvw_interpol_step – Specifies the update frequency for the UVW coordinates. When set to 1, the UVWs are updated on every frame, taking into account the Interpolation parameter. See the Interpolation Step example below.
Antitear | texuvw_antitear_influence – Use this option when the assigned texture appears twisted, torn apart or otherwise distorted. This may happen when the simulation is moving very fast, therefore increase both the Antitear and A-tear Iterations to let Phoenix FD attempt to resolve the distortion.
A-tear Iterations | texuvw_antitear_iterations – The number of Antitear iterations performed for every Step of the simulation. Increasing this parameter will help resolve UVW distortion issues by allowing Phoenix FD to run the Antitear operation multiple times. Note that this may slightly increase the time it takes for the simulation to complete.
Example: Interpolation
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The following video provides examples to show the differences of Interpolation values of 0, 0.1, and 1, and an Interpolation Step of 1. |
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For more information, please check the Texture mapping, moving textures with fire/smoke/liquid, and TexUVW page. |
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Example: Interpolation
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Example: Interpolation Step
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