@Override
    public void write(JmeExporter ex) throws IOException {
        OutputCapsule oc = ex.getCapsule(this);
        oc.write(initialVelocity, "initialVelocity", Vector3f.ZERO);
        oc.write(velocityVariation, "variation", 0.2f);
    }
This method applies the variation to the particle with already set velocity.
@param particle
       the particle to be affected
jme3-core/src/main/java/com/jme3/effect/influencers/DefaultParticleInfluencer.java