Comparing buoyancy results between OF and DELFT Ship

Ryoko · June 21, 2020, 12:04

I'm trying to figure out why I have such a large difference in the measured buoyancy force between OpenFoam and Delft Ship. OF is showing the buoyancy to be 14230lbs and Delft is reporting 16850lbs in the hydrostatics report. Both are using the identical mesh and waterline. The forces from OF were done using two methods. The first was forces function inside the controlDict and the other was using paraview filters to integrate p dotted with the z_normal. Both gave the same answer. This has me puzzled. Any thoughts?

Ryoko · June 21, 2020, 12:49

On review, I realized that the OpenFoam solution was based on moving water past the hull at 5m/s. I dropped U to 1m/s and the models are now much closer. The amount of lift generated under the bilge from the moving water caught me be surprise given the extremely low aspect ratio for this 'wing'. So I'm curious if this really does happen to such a large degree and do hulls actually settle into the water to counter the downforce from the resulting lift. (ignoring any planing.)

June 21, 2020, 12:04	Comparing buoyancy results between OF and DELFT Ship	#1
Ryoko New Member M.Lewis Join Date: Jun 2020 Posts: 9 Rep Power: 6	I'm trying to figure out why I have such a large difference in the measured buoyancy force between OpenFoam and Delft Ship. OF is showing the buoyancy to be 14230lbs and Delft is reporting 16850lbs in the hydrostatics report. Both are using the identical mesh and waterline. The forces from OF were done using two methods. The first was forces function inside the controlDict and the other was using paraview filters to integrate p dotted with the z_normal. Both gave the same answer. This has me puzzled. Any thoughts?

June 21, 2020, 12:49		#2
Ryoko New Member M.Lewis Join Date: Jun 2020 Posts: 9 Rep Power: 6	On review, I realized that the OpenFoam solution was based on moving water past the hull at 5m/s. I dropped U to 1m/s and the models are now much closer. The amount of lift generated under the bilge from the moving water caught me be surprise given the extremely low aspect ratio for this 'wing'. So I'm curious if this really does happen to such a large degree and do hulls actually settle into the water to counter the downforce from the resulting lift. (ignoring any planing.)