@Override
    public void read(JmeImporter im) throws IOException {
        InputCapsule ic = im.getCapsule(this);
        // NOTE: In previous versions of jME3, initialVelocity was called startVelocity
        if (ic.getSavableVersion(DefaultParticleInfluencer.class) == 0) {
            initialVelocity = (Vector3f) ic.readSavable("startVelocity", Vector3f.ZERO.clone());
        } else {
            initialVelocity = (Vector3f) ic.readSavable("initialVelocity", Vector3f.ZERO.clone());
        }
        velocityVariation = ic.readFloat("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