InterFOAM instability at a certain flow speed
 

I have a free surface model in InterFOAM solving for a ship hull in open water. model works well as a model 'sandpit' where I can bring in different models run at different speeds look at different appendages etc. and look at different effects. I'm batch running at a certain set of speeds but the solver always goes unstable at a certain speed (in my case 12kts, but that is probably irrelevant) stable faster and slower than that speed.

My question is do you guys have any thoughts on what to check to get to the bottom of why it goes unstable at that particular speed. it seems to be upstream instability of the ship, but as I say most if the time its really stable.
Thoughts please?

At first I recommend to store the instability in short period to see what happens. Mostly, somewhere, ata small place, something strange happens and that catches all of the region.

If this is the case, you need to stabilize your simulation. More stable schemes and relaxation comes into mind. There is always a balance between stability and accuracy. An accurate but stabile simulation requires a very even mesh and a rather simple physics, no steep changes.

Life is a compromise.

It seems to work...

I extended some mesh refinements to the upstream areas, and seems to have more stability instead of just the progressive hull area and wake areas.

On the speeds that I had labelled successful I noted some minor turbulence on upstream mesh transition which seems fine for most of those run. following that through its like at 1 certain speed that instability resonates into a crashed run.

thanks for your guidance