To get a smooth wave surface, the object needs a certain amount of detail: the more points/polygons it has, the better the waves.

1. At the obj level, put down a Torus and double-click it to dive into the node.

2. Select the torus and set Rows to 60 and Columns to 120 to get enough resolution.

For this step you’ll create a point selection and displace the points to determine the waves' origin. Before you start, hover the mouse cursor over the viewport and press 3 to switch to Front mode. You might also want to press W the turn on a shaded mode. This will help you to select the points.

1. Add a Group SOP and connect its input with the output of the Torus node.

2. Go to Group Name and replace the default entry with wave_origin (or any other name).

3. Change the Group Type to Points, and click the icon beside the Base Group parameter.

4. ⇧ Shift-click the points you want to select or draw a rectangle around the with the mouse.

   Note that the selection tool will also select hidden points form the rear surfaces. If you want to get rid off them, move the mouse over the viewport again and press 0 for the Perspective mode. To deselect a point, ⌃ Ctrl-click it or draw a rectangle around a group of points. Press Enter to confirm your selection and the point indices will appear in the Base Group parameter.

The pattern could be a cross-shaped selection as shown below.

1. Add a Soft Peak SOP and connect it to the Group SOP.

2. On the Group parameter, type wave_origin to restrict the node’s effect to the previously selected points.

3. Set Distance to 0.15 to displace the selected points. This is important because without initial deformations, nothing will happen when you press play.

4. Turn off Translate Along Lead Normals to get a smooth surface.

5. The Soft Radius parameters flattens the polygons around the point selection and turns the cross-shaped selection into a bubble. For hard edges, decrease the value.

What you have now is an original rest state and a deformed version with displaced points.

The solver calculates the difference between both versions to create the ripples.

1. Add a Ripple Solver SOP and connect its first input with the Torus SOP’s output.

2. Connect the solver’s second input (Deformed Geometry) with the Soft Peak SOP’s output.

3. On the playbar, click the Play forward icon to start a first simulation.

Here is what you can get with the Ripple Solver’s default settings. The colors represent the displacement values.

On the Ripple Solver’s Setup tab you can find two parameters for controlling the ripples' speed: Wave Speed and Rest Spring. Wave Speed defines how fast the ripples travel from point to point. Rest Spring is a force that tries to pull the displaced points towards their rest position. When Wave Speed is 0 and Rest Spring is set to 1 (or greater), it will create a back and forth movement, similar to a pumping or breathing effect. Increasing the Rest Spring value to 10 or higher will create more up and down cycles.

Conservation doesn’t contribute to the ripples' speed, but lets the waves fade out over time. A value of 1, will result in the ripples keeping their entire energy and move infinitely. Values less than 1 will cause the waves to lose energy. For example, a value of 0.7 will cause the waves to lose 30% of their initial energy after one second. A value of 0.2, will cause the waves to lose 80%.

Substeps define the simulation’s accuracy. The Ripple Solver’s substeps are adaptive. The solver calculates how many substeps are required to keep the simulation stable. The actual number lies between the Min Substeps and Max Substeps. One of the first things you can do when you observe stability issues is increase the solver’s Min Substeps. If the solver requires more maximum substeps than adjusted, then Wave Speed and Rest Spring will be clamped internally to maintain stability.

To check if speed and spring force are clamped, go to the solver’s Output tab and turn on Substep Clamped. Open the Geometry Spreadsheet and simulate. If the substepclamped point attribute is 1, then speed and spring force are clamped.

The thickness attribute is positive number that indicates how thick the geometry is at this point. It is used to clamp the height of waves at each point and to determine the amount of distortion due to collisions. If this attribute is not present, the point thickness is determined by settings on the Thickness tab.

The parameters on the Clamping tab are associated with thickness. Clamping means that all displacement values greater than Thickness are cut off. Cutting off the values can create hard edges. To restore a smooth and more organic look, use Soft Clamp Falloff.

1. To see the effect of clamping, turn off Enable Clamping and set Soft Clamp Falloff to 0.

2. Additionally, set Thickness to 0.1. The actual displacement determined in the Soft Peak SOP’s Distance value is 0.25. When you look at the viewport, the object looks as before. If you turn on Enable Clamping again, and you will see that the bubble’s shape has changed.

3. To restore the smooth look, increase Soft Clamp to 1 and Soft Clamp Falloff to 2.

The water surface in this project is a high-resolution grid to get enough details. Then you’ll randomly place spheres with variable size on the grid. The spheres will act as colliders and the “impact” creates the waves.

1. At the obj level, put down a Grid SOP and double-click it to dive into the node.

2. Select the grid node and set the Size parameters (width and height) to 7.5.

3. Increase Rows and Columns to 500 to get enough resolution for small ripples.

4. Add a Sphere SOP and decrease Uniform Scale to 0.1. This object will be instanced to create the raindrops.

5. Play down a Scatter SOP and connect its input with the Grid SOP’s output.

6. On the scatter node, change Force Total Count to 7. This parameter specifies the number of sphere instances. To introduce new spheres with each frame and delete the previous objects, change Global Seed to $F. This expression changes the spheres' distribution over time. However, the number of new spheres per frame remains constant.

When you turn on the scatter node’s blue Display/Render flag, you should see seven black dots in the viewport. Drag the timeline slider to see how the points' distribution changes over times.

To create the instances, copy the spheres onto the scatter points. Here’s a preview of the complete network.

1. Add a Copy to Points SOP and connect its first input with the sphere’s output. The second input is linked to the grid’s output.

2. Put down a Ripple Solver SOP.Connect its first and second input with the output of the grid. The third input goes to the output of the Copy to Points SOP.

3. To dampen the ripples and make them vanish over times, change Conservation to 0.3 on the Setup tab.

4. Click the Play forward button to start the simulation.

You can see the sphere instances as blue wireframe objects. The solver recognizes the spheres as collision objects and creates waves around them. When you render the scene, the blue instances won’t be considered. In the image below the number of rain drops was increased for illustration purposes.

To change the uniform look of the rain drops' distribution you can apply a dynamic mask. The mask spares out certain areas and you get zones with more or less drops.

1. Add an Attribute Noise SOP and place it between the grid and scatter SOPs to connect it.

2. Beside the Attribute Names parameter, turn off the Y and Z buttons to keep only the Cd attribute’s red color.

3. From the Range Values dropdown menu, choose Zero Centered.

4. Change the Offset parameter value to $F. Again. this expression uses the current frame to change the noise pattern over time.

5. On the Scatter SOP, turn on Density Attribute and replace density with Cd. The red parts of the noise pattern will determine where the scatterer creates rain drops.

6. To delete the colors after the creation of the instances, put down an Attribute Delete SOP and place it between the copy to point and solver nodes to connect it.

7. Go to Point Attributes and enter Cd.

8. Press the Play forward button to simulate.

Here’s a screenshot from the color mask.

You can also randomize the size of the drops for even more realism.

1. Add an Attribute Randomize SOP and place it between the attribute noise and copy nodes to connect it.

2. Under Attribute Name replace Cd with pscale.

3. On the Distribution tab, choose Two Values from the Distribution dropdown menu to define the drops' minimum and maximum size.

4. Set Dimensions to 1, because pscale is a scalar.

5. For Value A, enter 0.6. The Value A/B parameters are multiplied with the sphere’s current scale to get the actual value.

6. Simulate again.