One obvious way to simulate a fluid on a computer is to model the
individual molecules which make up the fluid. Then, provided the
inter-molecular interactions are modelled correctly, the system should
behave as a fluid [3].
Different situations can be modelled by changing the
average energy of the molecules and their separation.
The main disadvantage with such an approach is that large computer resources are required, many simulations taking hours to evolve a fraction of a second [4]. The system must be updated in small time-steps, the new position and velocity of all particles being calculated, at every time-step, from a knowledge of their previous position and velocity, taking into account any external forces which are acting on them. Any particles which collided during the previous time-step have to be identified and their new trajectories calculated. This can be restrictively time consuming when considering even a very small volume of fluid. Even when a gas is being considered where there are fewer molecules and a larger time-step can be used, because of the longer mean free path of the molecules, the number of molecules which can be considered is severely limited.