Particle fluid emission rate cannot be keyed

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Symptom

I would like to animate the emission rate (i.e. shut the effect off) on disc and square fluid emitters. I cannot close the emitter using animated Rate (i.e. keying the Rate at zero), nor use the old workaround of scaling the emitter to Zero. Is there a way to animate a fluid emitter rate in the SOFTIMAGE|XSI (V2.0 & V2.0.1).



Cause

The behavior is a characteristic of the SOFTIMAGE|XSI simulation engine, as the rate parameter is not used in the context of Particle Fluids. With the Fluid operator, the Emission Rate property is always ignored, since the number of emitted particles depends on the Mean Distance (Fluid Density) property.

Note: The Emission Rate should be grayed out, and unavailable to Fluids at all. There is bug logged for this problem: Bug 75330

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Solution

There are two workaround options available to circumvent this issue. In both cases, no slave particles will be emitted, and there will be no emission rate:

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  1. Fully key-able option

    This workaround involves keying the scale of the emitter object to values of zero for XYZ, and setting the Emission Speed parameter value also to zero ( 0.0 ).

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    Note for Cube Emitters only: If you also add a key to the Particle size set to zero ( 0.0 ), you will still obtain a lone particle emitted from somewhere out in the volume - but in this case it will not render. Disc/Square emitters do not appear to need this extra parameter/key.

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  2. Slave ratio option
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    As in the first option, scale the emitter object XYZ values to zero. But, set the Slave Ratio parameter to zero ( 0.0 ).

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    Note: If the Slave ratio value is less than 1.0, there still can be some particles that will be emitted. So, in such cases, a value of 0.99 should be used. Also, the Slave ratio parameter is a non-key-able parameter, setting this parameter to zero might impact on the overall Particle effect and behavior in your scene.

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    References

    SOFTIMAGE|XSI-Simulation document

    chapter: Fluid Simulation, page 63.



    Applies To: XSI 2.0,XSI 2.0.1 on NT,Win2K,Irix

    Posted: 1/17/2002

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