Lifting foils in Orca cfd

How well does this deal with say lifting foils as used by the likes of the Imoca 60s, ie will the boat be flown if the required speed is met? Presume this would be fixed heel/speed condition ??

Hi Hugh, the lift from the foils is accurately simulated and the boat will lift out of the water if there is enough lift. We don’t have an integrated controller to use feedback to adjust a trim tab, for example (you can prescribe the motion of a trim tab, for example as a function of time, but not as a function of heave for example). We have a number of users doing foil-borne or or foil-assisted multihulls, and often they will do runs at fixed values of heave and trim tab angles, and measure the lift and moments.

If you would like to try the software, please contact me and we can start with a demo/tutorial session, after which we can provide an evaluation license.

Thanks Bruce - so free to trim, applied rig moments, fixed heel and yaw condition would converge OK - assuming there is a natural stability point? Or can you constrain say the pitch limits to keep it from diverging?

Another question - I’ve been using Tdyn for CFD in the past and still do for some things - can you modify grid resolution for ( relatively ) quick and dirty solutions to save computational time?
Something I did with Tdyn when running appendage variations and was very worthwhile when I was interested in early relative comparisons and saved me a lot of time.


Yes; you can apply a rig moment, but you could also apply a thrust vector at the rig’s center of effort (for a self-propelled run), or move the towing point to the CE (for a resistance run). You could fix the pitch or perhaps apply a high pitch damping moment to avoid divergence.

You have complete control over the grid settings; there are “quick” settings (Coarse, Medium Coarse, Normal, Medium Fine, Fine, Extra Fine), but you can also do manual adjustments to the various settings if you are comfortable doing that. You can also use a quick setting (Normal, for example) but then draw a refinement zone around the foils.

My concern about “quick and dirty” runs is that if the grid is too coarse, there is the possibility of missing some flow phenomena somewhere. We suggest that users start the analysis process with a grid refinement study; that is, run the same analyis at multiple grid settings. Ideally, the answers would be close to the same. That study gives you some confidence in using the coarser grid settings.

Ok - that all sounds good - grid refinement I’m pretty comfortable with and it’s general possible side effects.
How long does an evaluation licence run for? Need to fit in with existing projects as we’ve got a bit on at the moment! Thanks Hugh


It’s good to be busy :slight_smile: The evaluation license is valid for 30 days. When you’re ready, please book at meeting at Calendly - Orca3D we can do a demo/tutorial.

Great - will do - cheers Hugh