[al_th]

Hello there,

I am currently implementing my own SPH solver and I do have some questions that maybe some of you could answer to. Please do not hesitate if anything said is wrong and correct me.


1. When performing a SPH simulation, we compute a pressure force. This pressure force is calculated using the SPH formalism in order to solve the momentum equation. The different SPH paper use different methods to compute the pressure :

• WCSPH : Equation of states is used to compute the pressure
• PCISPH : Pressure is updated in order to correct the density during each sub-iterations

What is the physical relationship between the pressure computed and the real world pressure ?

2. My second question is focusing on the actual velocity field carried by the particles. Assuming you want to obtain an incompressible fluid, you have to have a strong pressure force. This is obtained by increasing the stiffness parameter in the equation of state or in the predictive corrective scheme of the PCISPH algorithm. Doing so actually increase the contribution of the force that acts to enforce incompressibility. At a small timestep, though, the effect will be that we see particles "pulling and pushing" their neighbors. The analogy I make is the same as molecules of fluids interacting with each other. The question is the following

How should I compute the macro flow field ? If I look at a very tiny time step, the particle could very well go backward if it helps enforce incompressibility, even if during the simulation the particle is going foward. Should I estimate the velocity using the SPH estimator at some known positions in the domain ?


Thanks in advance for taking the time to answer to my questions,

Best