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This page provides some useful tips for working with the Phoenix FD Active Bodies feature.

Overview

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Setup Guide

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Column width 40%  A Phoenix FD Liquid Simulation with Active Bodies consists of the following elements: A Liquid Simulator – used for the simulation of water. One or more scene objects – converted to Active Bodies at simulation time. An Active Body Solver – used to specify the scene objects which will be converted to Active Bodies and to set some global options for the Active Body simulation. A Center of Mass gizmo – automatically generated for each object when included in the Active Body simulation through the solver. Column width 60%

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Column width 40% To add an Active Bodies Body Solver, go to Command Panel → Create → PhoenixFD → Active Bodies. Add your scene geometry to the Active Bodies list. Finally, link the Active Bodies Body Solver to the Phoenix FD Liquid Simulator from the Dynamics roll-out. UI Text Box size medium type info The Active Bodies Body Solver is separated from the Phoenix FD Simulator to allow extra flexibility when setting up the simulation. Multiple Liquid Simulators can be set up to use the same solver, or alternatively, you can switch between several Active Body solvers with different settings and geometries with the same Simulator. Column width 60%

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Column width 40% When you start the simulation, the Active Bodies solver Body Solver will create a duplicate of your object and keyframe its Position and Rotation for every single frame. A couple of things to note here: The ship is sinking - this happens because its Density too high. The Density of the Active Body can be tweaked from the original object's Phoenix FD Properties. The Center of Mass Gizmo is above the ship's deck, right at the base of the middle mast - this is causing the ship to tilt to the side. Instead of relying on the Active Bodies solver Body Solver to guess the correct position for the Center of Mass gizmo, its position can be overriden from the Phoenix FD Properties of the original object and tweaked manually.   UI Text Box size medium type warning When tweaking the Phoenix FD Properties of an object, take extra care to select the original, source object, rather than the clone. Existing clones are deleted when a simulation is re-started, thus any changes made in the Phoenix FD Properties window of the clone are lost. Column width 60% Videoautoplayloop 0 001_base_sim0000.mp4 1 100% 2 100% 3 true 4 false 5 true

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Column width 40% With a lower density, the object does not now sink entirely underwater. The erratic spinning of the ship is caused by the incorrectly placed Center of Mass gizmo. Placing the Center of Mass somewhere close to the center of an object would make sense for a sphere but not for a ship which is usually bottom-heavy. UI Text Box size medium type info The Active Bodies solver Body Solver will compute the Center of Mass of an object by looking at its volume. To simplify things, an assumption is made that all parts of the object have an equal weight. In the case of a ship, however, this is not true. The masts and sails of a ship make up a large portion of its volume but contribute little to its total mass. Column width 60% Videoautoplayloop 0 002_tweak_density0000.mp4 1 100% 2 100% 3 true 4 false 5 true

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Column width 40% The ship is now behaving as expected. You may continue this setup by adding a Phoenix FD Wave Force with an Ocean Texture to generate waves in the simulator. Column width 60% Videoautoplayloop 0 006_moveCenterOfMassBack_0000.mp4 1 100% 2 100% 3 true 4 false 5 true

 

 

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