[Sagun]

Hello everyone!

This is my first post on cfd-online and I would like to take this opportunity to thank all the members for making this website such a great information resource.

I am very new to openFoam (and CFD in general) and could really do with some help here. I am attempting a simple steady state modeling of water flow around a monopile which extends all the way to the sea bed. The overall intention is to calculate the hydrodynamic force acting on it. (At some point, I would also like to introduce the effect of sea waves but at the moment, I'm just going to stick with a steady current.)

As of now, I have been able to generate some preliminary simulations of steady flow using potentialFoam and the velocity distribution on the monopile surface appears as it should theoretically. Here are a few things that I wanted to ask:

1. What are the possible outputs of openFoam? Can we generate potentials of other fields apart from the velocity potential?

2. I see that my simulations run for only one 1s irrespective of the startTime, endTime and timeStep that I enter into the controlDict file. Is this some default setting in potentialFoam because of the flow being steady?

3. After the simulation is over, I see that a 'phi' file is generated in the 0 (initial conditions) folder and the 'U' is appended with a lot of values (which I probably think are velocity values at each grid point). Is this also expected?

4. Any leads on how can I use the generated 'phi' file to calculate the force acting on the monopile?

I would be extremely thankful to anyone who can answer my queries.

Thanks in advance,
Sagun

[Josh Yang]

Have you found out the answer yet? I am having a same question here.
Thank you very much.

[Sagun]

Hello Josh,

I have come a long way since I posted this but unfortunately, I haven't got all the answers that I was looking for. Not yet. I quickly realized that I was working with the wrong solver, since I'm basically attempting to simulate two-phase flow (water and air), which is initially transient in nature, around a monopile attached to the sea bed. The correct solver for this kind of application is interFoam. Waves can be generated in OpenFoam using either groovyBC or waves2Foam. You should be able to find plenty of information on both in the forums here or on their respective wiki-pages. As of now, I have only been able to generate the velocity potential around a cylinder including the effect of waves in 2D. I'm not sure if OpenFoam can generate potentials for other fields also (my first question) or if this problem can be solved in 3D too. I'm also working on a code to calculate the force on the structure from the velocity potential.

Hope this helps.
Sagun

[Josh Yang]

Sagun,

Thank you very much. I am using interFom to deal with two phase flow. My problem is not as complicated as yours. I am simulating water flowing downstair and calculate the force, says if someone want to ascends up. Still working on finding how to calculatet the drag force and visalizing the results with paraView. The usual equation F=0.5*pho*CD*Area seems not working in both your case and mine.

Josh

[Sagun]

Hi Josh,

I have seen some online tutorials on calculating lift and drag forces on an airfoil. Have you checked them out already? Although its a much simpler case, nevertheless it should give you some clues as to how to go about your problem.

Sagun

[Josh Yang]

Sagun,

Yes, I remember I saw it somewhere. Right now I am working on visualizing my results. It takes a lot of time to visualie it. Anyway, thanks a lot. Wish you luck on your part as well.