With nParticles, you can use dynamic wind generated by the Maya Nucleus solver to affect the motion of your particles. Gravity and Wind forces generated by the Nucleus system are different from the Maya dynamic forces that you create with Maya Fields. Nucleus forces are internal, meaning that they only affect Nucleus objects. Nucleus object that are assigned to the same Nucleus solver are affected by the same intensity of the solver’s wind and gravity.

In this section of this lesson, you create an Axial Magnitude ramp to control the field’s magnitude at various points in the field volume. You specify that the field’s magnitude gradually increases from the bottom of the volume to its top, so that as the nParticles travel through the field volume, the field’s influence on the nParticles increases. To finish the smoke simulation, you use the Nucleus Wind to make the smoke drift as it rises.

To create an Axial Magnitude ramp

1. In the Outliner, select Field_Smoke1.
2. In the Attribute Editor, expand the Volume Control Attributes section, and go to the Axial Magnitude section.
3. Click in the Axial Magnitude ramp to create two new markers, and create a ramp by setting the following:

   Marker	Selected Position	Selected Value	Interpolation
   1	0.055	0.520	Linear
   2	0.315	0.900	Linear
   3	0.961	1.0	Linear

   
4. Play your simulation.

To add Nucleus Wind in your simulation.

1. In the Outliner, select nParticle_Smoke.
2. In the Attribute Editor, click the nucleus1 tab.
3. In the Gravity and Wind section, set Wind Speed to 0.85.

   Wind Speed determines the force and intensity of the wind. A higher value means a faster wind speed, which has more of an effect on the smoke.

   
4. To set Wind Direction, do the following:
   • Set wind direction to 0 in the X-axis.
   • Set wind direction to -1 in the Y-axis.
   • Set wind direction to -1 in the Z-axis.
5. Set Wind Noise to 0.686.

   This adds some randomization to the wind direction.

6. Play the simulation.
   

   To make the smoke simulation more realistic, you can set up your effect so that the cigarette smoke is rising in the first frame of the simulation. You do this by setting the nParticle object’s initial state.

To set the nParticle Object’s initial state

1. Play the simulation and stop the playback at or around frame 200.
2. In the Outliner, select nParticle_Smoke.
3. Select nSolver > Initial State > Set From Current.
4. Rewind the simulation to the start frame and play it back.