Water Body

• The article on Water Mesh
• BodyWater class
• Fragment of the video tutorial on physics demonstrating the use of the Water body for simulation of various types of liquids

Liquidity defines the viscosity of water (or any other liquid): it determines how readily it splashes and affects wave formation. It multiplies the speed with which water particles pass velocity vectors to the neighboring ones.

• The higher the value, the more viscous the water is and the smaller are the waves risen by the objects (e.g. syrup).

• Low values provide higher surface waves (e.g. tap water).

  Notice

  Be careful not to set too high or too low values, because that may lead to unstable simulation and blowing up of the water. To regain stability, try to tweak Interaction.

Density of water determines the buoyancy of objects according to Archimedes' principle. Based on the volume of the submerged part of the shape and its mass, buoyancy force is applied to its center of mass and pushes the object upwards, whereto the mean normal of the grid covered by submerged shape points.

• By the minimum value of 0, the objects will not float in the water, but rather fall through it without any resistance.
• Higher values increase the buoyant force. If set too high, the immersed objects start to be pushed out in the air.

A physical object submerged into the water (or any other liquid) has its own velocity vector. On the other hand, all the water particles that are covered by this physical body or surround it, have their own integrated velocity vector, which approximates the state of water. The Interaction value is a coefficient that determines how much the object's velocity influences the velocities of water particles and thus generate waves.

• By the minimum value of 0, an object produces no disturbances on the water surface.

• Higher values make the disturbances of water surface more intense and the waves from moving objects become higher.

  Notice

  Too high values may blow the water up, as the law of conservation of energy does not constrain the system! Try decreasing damping values to regain stability.

Objects getting into the water are expected to slow down, as resistance of the water is higher than the drag in the air. Damping values work the other way around compared to the Interaction coefficient:

Linear Damping defines how much linear velocity of the submerged object is decreased over time when influenced by velocities of surrounding water particles. And similarly, Angular Damping defines the gradual decrease in the object's rotation. Both linear and angular damping forces are accumulated before being applied.

• By the minimum value of 0, objects movement is not hindered by the water. As a result, there are no waves in the water.

• Higher values make the damping of linear or angular velocities more intense, and objects slow down faster as they get into the water. The waves from the objects in this case become more pronounced, as the energy of the system increases.

  Notice

  The water may blow up in case the values are be very high. Try decreasing the Interaction value to regain stability.

It is possible to create an additional visual effect of small droplets, splashes or bubbles on the water when objects fall into it. To enable this effect perform the following steps:

1. Create a Particle system effect by clicking Create -> Effect -> Particle system in the main menu of UnigineEditor.
2. Go to the Parameters window.
3. In the Dynamic section, choose the Spark Emitter to spawn particles by selecting Emitter -> Spark.
4. Make Particle system a child of the Water Mesh object.

Particles will be generated only when the object first contacts the water surface, while already submerged bodies will float without generating them.

Depth determines the size of waves: high waves are formed in deep waters (e.g. a sea), while only a slight ripple is generated in shallow waters (e.g. a pool):

• With the minimum value of 0, the objects raise no waves in the water.
• Higher values result in higher waves generated by moving objects.

Intersection of water with the underlying terrain can be necessary, for example, to estimate the actual depth of the water basin. To enable ground intersection perform the following steps:

1. Make Water Mesh or Dynamic Mesh object a child node of the Terrain or Static Mesh
2. Check the Intersection box in the Parameters window -> Physics tab -> Body section.

Intersection is implemented in the following way: the rays are traced downwards from the water mesh surface, as far as the Depth distance. If a ray intersects the parent node, the obtained depth is used in calculations; otherwise the preset depth value is used.

Intersection is also traced upward to check if the water is under terrain and there is no need to render it.

Absorption is an option that creates either an effect of a limited basin or, on the contrary, of an open water surface that does not have marked boundaries.

• If Absorption is enabled, the waves are dispersed along the mesh perimeter. In this case the water level at mesh edges will gradually fall down to zero level.
• If disabled, the backwash from the wall is simulated: the wave when reaching the brink of the water is reflected and returns in the reversed direction.