We will make use of particles, in order to carry out this simulation. At first, we will need a particles emitter object, placed at the top of the scene, hovering like a cloud. For example, a plane slightly banked (or not) will be fine, as it is not necessary to see it subdivided.

makerain-01.png

The other objects in our example scene: a ground (just a plan) and the main focus of the scene (a simple cube), would be obstacles for the particles (at least), and reactors for the particles (ideally), because they would interact with the rain drops.

You can also make sure that you will have at hand a very last object as the rain drop of your simulation.

makerain-02.png

Normals of the objects: the normals of the cloud should be orientated toward the ground, those of the ground orientated toward the cloud, and those of the cube should radiate outside of it. This will ease the management of the direction the particles will be emitted.

Location of the objects on the layers: to insure correct interaction, make sure that the emitters and reactors (or any object which would collide with the particles) belong to the same layers.

Name of the objects: they will be of importance, later, so please name your object a decent way.

The particles emitter

Select the particles emitter (here, this is our object named Cloud) and in the Object F7 menu, in the Particle Buttons, click on the Add New button from the Particle System panel. A new particle system named PSys is then attached to the emitter. Make sure this a Emitter system type. The other parameters of the panel could be set like this:

  • Amount: 5000 (enough to provide a dense rain)
  • Emit from, Random (to make sure that the water falls are not too regular nor artificial)
  • Emit from, Faces
  • Emit from, Even (for a proportional distribution of the drops, if the emitter is built from many faces with uneven dimensions)
  • Emit from, Jittered (for a random distribution of the drops emitted by a single face)

makerain-03.png

In the Physics panel, we should mainly set the influence of the emitter's normal (especially if it is banking, in order to simulate rain drops submitted to wind), and to set the direction of the gravity.

  • Newtonian
  • Initial velocity, Normal: 10.000 (or any high value that leads to good visual effects)
  • Global effects, AccZ: -9.81 (in order to stay close to the earth gravity)

makerain-04.png

Finally, in the Visualization panel, select Object, and in the OB: field, type the name of the water drop object. In the Extras panel, activate the Effectors, Die on hit button.

makerain-05.png

The reactor particles

Basically, all the objects that could be hit by any rain drop should be considered as a reactor. You will select them one after the other, and apply the same kind of settings to each of them.

In the Object F7 menu, in the Physics Buttons and the Collision tab, activate the Collision and Kill buttons. As an option, specify some value for the Damping and Friction parameters, but this is not really necessary there.

makerain-08.png

In the Particle Buttons, add a new system using the Add New button from the Particle System tab. Select Reactor as the system type, and set the other parameters as follow:

  • Amount: 5000 (in order to generate enough particles to react to the rain drops)
  • Life: 5.0 (the droplets will have a very short span life...)
  • Rand: 0.5 (... that could vary a lot from time to time)
  • Emit from, Particle (so that the system will react to particles...)
  • Target, OB: Cloud (...emitted by the target emitter Cloud)
  • Target, Psys 1 (and we specify the number id of the particle system in case the emitter has many of them)

makerain-06.png

In the Physics panel, specify a Global effects, AccZ positive value, for example 10.00. Because you would like to see the reactor object showing on the render, do not forget to activate the Render, Emitter button in the Visualization panel.

As a final step, in the Children tab, we will enable the spawning, at each collision, of a cluster of particles instead of just one. Please set the panels parameters like this:

  • Particles and Nothing
  • Amount: 3 (in order to spawn 3 child droplets by parent droplet emitted during the collision)
  • Round: 1.000 (to obtain a circular distribution of the particles)

makerain-07.png

You can know play the animation Ctrl+A or use the Bake button from the Bake tab in the Particle Buttons.

makerain-09.png

Obviously, before rendering your animation, remember to set materials for your rain drops, especially the droplets emitted by the reactors. Those ones should stay discreet in order to remain realist.

makerain-10.png

Article written on December the 24th, 2004.
Updated on November the 16th, 2008 for Blender 2.48a. Comments re-initialized