Computational fluid dynamics
Computational fluid dynamics can be expensive, and interactions between multiple fluid bodies or with external objects/forces can require complex logic to evaluate. Fluid simulation is generally achieved in video games by simulating only the height of bodies of water to create the effect of waves, ripples, or other surface features. For relatively free bodies of liquid, Lagrangian or semi-Lagrangian methods are often used to speed up the simulation by treating particles as finite elements of fluid (or carriers of physical properties) and approximating the Navier-Stokes equations