overInterDyMFoam Floating Body Case Simulation Time Step Keeps Decreasing
 

Hello Everyone,


I am a student at the University of Bologna, Italy, and I am performing CFD simulations for a Wave Energy Converter (WEC) device that floats in water such that 90% of its vertical height is submerged into the water while the 10% is out of the water, as shown in the screenshot below:

Device:

https://i.imgur.com/mMe26iO.png

Device Floating in Water (Taken from ParaView)

https://i.imgur.com/lo8nQhB.png

Mesh:

https://i.imgur.com/SxD0BL7.jpg

Mesh with Opacity Less than 1 to Show the Insides:

https://i.imgur.com/OfkVqHE.jpg

I made the device's mesh using snappyHexMesh boxed into the overset mesh and then merge the meshes for the floating body and Numerical Wave Tank later (as done in the floatingBody case of the overInterDyMFoam).
The output for checkMesh (checkMesh_log.txt) is provided below. The checkMesh includes the result of the first two time steps as well, which are running quite fine, while the simulation tends to get stuck before the third time step, i.e., 0.3 s.

Attachment 84505

I am attaching my fvSchemes and fvSolution files. I am also attaching the controlDict file to let you know the startTime, endTime, Courant number used, etc.

Attachment 84506
Attachment 84507
Attachment 84508

For running the case, I am using OpenFOAM version 2012 on a HPC cluster with 64 cpus.

One thing to note: The original device is 10 meters in height, but I first performed the simulations on its reduced scale prototype (1:64), so it was 156.25 mm in height. The simulations went fine (I performed a lot of simulations, for free heave decay tests and also for the wave-structure-interaction tests).

Later on, we made another prototype (1:40 scale) with a height of 250 mm. For this prototype, I changed my mesh for the new bigger geometry, etc. However, the parameters of the simulations are kept all the same as before. For this simulation, after the 2nd time step is written, the simulation is not moving forward, instead, the time step keeps decreasing after 0.29 seconds (it should write 0.3 s, which is the third time step. The write interval is 0.1).

Kindly if someone can help me on this issue. I have tried changing my mesh dimensions (making the deltaX larger), but still, the simulation gets stuck after the 2nd timestep is written.

Right now, I am performing the free heave decay test, where I am releasing the body from the top with the water level around its mid-height. So it will try to achieve its design draft (of 90% of its height) by falling into the water and then popping back up and oscillating vertically up and down according to its natural period in heave.
The solver output for the last 3 time steps is here below: (The simulation is still going on, the time step decreases even to a magnitude of e-15 and so on.)
Attachment 84510

Time step 0, 0.1, and 0.2 screenshots of the mesh are here:

https://i.imgur.com/Hjlb4k6.jpg

https://i.imgur.com/bys46Fe.jpg

https://i.imgur.com/3J1WlAN.jpg

Thank you so much in anticipation. If you need more information to help me with, I am surely available to fully cooperate.

Have a good day you all and happy CFD :)


Kind Regards,
Ahsan

If you send me the .zip file maybe I can help you