# Fluid Particles Penetrating Piston?

Hello!

I am doing a 3D simulation, where I am generating 3D waves using a moving piston with regular 2nd order waves, but experiencing that fluid particles for some reason can enter the piston:

Orange is piston, blue is fluid and black is "beach"/floor. Side and top view. Has anyone experienced this before or is there an error when doing it in 3D? I have the simulation in 2D without a problem.

Kind regards

## Comments

can you paste here your XML input file?

Sure @Alex , I have uploaded it now

At time step "20" it is very evident, so no need to simulate the whole case.

Kind regards

Sorry I could not check this before

Please do not use coefh value="2", this value is to high so that your value of h will be also higher and therefore, 2h, the distance of interaction will be also too high. And this can be a problem with low resolution, as you are using now.

Let me explain this with an example:

you are using coefh=2 with dp=0.1m

therefore h=0.28m and 2h=0.56m

and the width of your piston is only of 0.2m

However using a smaller coefh:

such as using a recommended value of coefh=1.2 with dp=0.1m

therefore h=0.17m and 2h=0.34m

and the width of your piston is of 0.2m

On the other hand if you plan to simulate wave with H=0.3m you should use at least 10 particles per wave height so that dp=H/10=0.03m

Therefore you should use coefh=1.2 and wider piston (3-4 times dp) or higher resolution like dp=0.05m or dp=0.03m!!!

I see, thank you very much for your in-depth explanation! A lot of information I was not aware of in there.

Kind regards