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Comparison of Particle methods: SPH and MPS
(SPH: Smoothed Particle Hydrodynamics, MPS: Moving Particle Simulation)
Through co-simulation of RecurDyn and Particleworks, it is now possible to simulate complex mechanical system and fluid problems that were impossible to simulate in the past. You can find more about Particleworks and the features of RecurDyn x Particleworks co-simulation in the related links.
If you are interested in particle-based CFD simulation, you may have heard of either SPH or MPS. Or this might be the first time that you have heard of them. Both SPH and MPS are widely used in particle-based CFD simulation. In this article, the differences between MPS (Moving Particle Simulation Method) and SPH (Smoothed Particle Hydrodynamics) will be briefly introduced.
Though MPS and SPH are derived from different equations, they provide a very similar set of features for particle-based CFD simulation. Therefore, it is better to focus on the features and benefits of CFD software employing one method or the other rather than on the difference between MPS and SPH.
The basic differences between SPH and MPS are as follows.
SPH (Smoothed Particle Hydrodynamics)
- SPH was developed in the 70’s for astrophysics (Lucy, 1977)
- Formulation based on compressible fluids
- Nodes (particles) define mass distribution
- Kernel functions must be continuously differentiable
MPS (Moving Particle Simulation or Moving Particle Semi-Implicit)
- MPS was developed in the 90’s for free surface flows (Koshizuka and Oka, 1996)
- Formulation based on incompressible fluids
- Nodes (particles) define the volume of fixed density
- Kernel function can be discontinuous
For more information on Particleworks, a particle-based CFD simulation package, please visit the following links.
SPH
was developed more than 20 years before MPS, so SPH is more widely known than MPS. But because the words ‘Smoothed Particle Hydrodynamics’ lack an apparent meaning, most people cannot answer the question, “What is SPH?”
The term, ‘smoothed’ was originated from the kernel function, which is sometimes referred to as a ‘smoothing kernel function’ or ‘smoothing function’.
Hearing this, you might wonder, “So, what is smoothing function?”
However, let’s skip this question. It would significantly complicate this article.
The original SPH method was derived only for the simulation of compressible fluids. Recently, however, "ISPH"(Incompressible SPH) and "weakly compressible SPH" have also been derived.
On the other hand, MPS was developed much more recently than SPH. MPS is specifically for incompressible fluids. Most applications for fluid flow simulation in industry require modeling incompressible fluids. Since the MPS method was derived for the simulation of incompressible fluids, it has had numerical advantages compared to SPH for these incompressible problems. As a result, MPS has been rapidly adopted and used in various industries. In addition, recent additions to the MPS formulation partially support compressible fluids. Particleworks, for example, supports weakly compressible gas.
Initially, the equations of motion for SPH (Smoothed Particle Hydrodynamics) were almost exclusively solved using explicit methods. MPS, on the other hand, used implicit methods to calculate the pressure gradient and viscosity, and explicit methods for other calculations. As a result, MPS was able to support a more suitable time step size for simulation.
However, the difference between SPH and MPS has been reduced significantly because each method has incorporated the advantages of the other. So, unless you are developing your own particle-based CFD code, the differences between SPH and MPS are not significant now.
Most people aren’t concerned that SPH means Smoothed Particle Hydrodynamics and MPS means Moving Particle Simulation or Moving Particle Semi-Implicit. The differences between SPH and MPS are not significant now. Instead, it is more important to focus on the main features and benefits of any particular particle-based CFD simulation software that adopted MPS or SPH.
Simulation using Particle-based CFD (MPS)
For example, Particleworks is software based on the MPS method. It is encouraged to focus on the features of Particleworks rather than the features of MPS such as:
- Simulation of free surface flow using a particle-based method
- Fast calculation using GPU
- Solver - turbulence, heat transfer, viscosity, moving boundary
- Pre/Post – easy and intuitive modeling and post processing
- Co-simulation with RecurDyn, a Multibody Dynamics software package
Co-simulation examples between Particleworks and RecurDyn
For more information on Particleworks, a particle-based CFD simulation package, please visit the following links.
