In this link you can find some information about the initial model that used this method ( Smoothed-Particle Hydrodynamics), and it can be found in simulators that go from astrophysics modelling to educational packages (like the funny Algodoo). In the second case, particle systems, more simple local interactions are in use, but instead of solving one big/harder equation we have to solve a lot of small/simple equations. In this link you can find an introduction to physics and simulation of fluids with a videogame orientation. In any case, they are really interesting and the agent based modelling is usually inspired in them, so we encourage the reader to know a bit more about this mathematical modelling, commonly a variant of the Navier Stokes equations. In the first case, differential equations, the theory behind is too hard to be modelled with NetLogo, and it is far away from the agent modelling point of view, the real focus of this software. Both of them are high computing resources consuming, but provide very accurate ways to obtain dynamics very similar to real fluids, liquids or gasses. You can find very realistic and nice simulation of different fluids behaviours under several and more general assumptions, but here we will give only a fast and simple way to obtain a behaviour that we visually recognize as a liquid.Įssentially, there are two main approaches to the problem of liquids simulation: considering the differential equations that classically are behind them to provide mathematical models, or approximating the fluid as a set of particles with some attracting and repelling forces between them. In this post we will simplify so much the assumptions that the model we will obtain only will be useful to simulate liquids under some conditions, but not gasses. They require a huge amount of calculations in order to predict the dynamics of the whole system, and it is very common to try to reduce the complexity by statistical calculations. Because fluids take the shape of their container, they are always in collision with everything around them, including the fluid itself, hence a collision with one part of the fluid effectively means that the whole body of fluid must respond. But you can see them as a set of free particles with continuous interaction between them and the environment. Fluids: if you see them as one body, their shape/topology can change.Examples can be: chains in 1D, clothes in 2D, or soft bodies in 3D. Deformable bodies: can change shape but not with totally freedom, they keep their connectedness and adjacency of various points on the body.The behaviour is similar to the set of rigid bodies, but the collisions between them are restricted to a limited options (usually called constraints of the system). Articulated rigid bodies: are connected networks of rigid bodies.A set of rigid bodies are usually harder to simulate, because all the elements in the set can continuously collides between them. They are still easy to simulate under isolation, and the hard tasks come from detecting and responding to collisions with the environment. Rigid bodies: add shape and orientation to position, mass, and velocity.Usually are modelled using basic linear laws. Particles: points with position, mass, velocity.Usual modelling of physical objects follows an increasing chain of particularities, from more simple to more complex we can find: The distinction between liquids and gasses can determine how to model the fluid, but from a physical and mathematical point of view, both obey the same basic laws and their differences can be given by the values of some parameters that model them. Consequently, in the computer simulations to visualize a liquid, only this free surface is computed and rendered, as the other parts are occluded by the container. The difference between them is that a gas it is not (so) affected by the gravity and fills its container (if any) completely, whereas a liquid under gravity has a " free surface" (the top) whose shape does not depend on its container. Usually, the terms fluid and liquid are used interchangeable, but technically the term fluid can refer to either a liquid or a gas. right?īut, what is a fluid? A fluid is any substance that flows, and can take the shape of its container, and does not resist deformation, that is, it slides when receiving some pressure. After Earth, and to continue with the simulation of Classical Elements in NetLogo, in this post we will give some simple, but very graphical and good looking, models to simulate the behaviour of water.
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