Newbie trying to get boat on water

Ryoko · June 11, 2020, 18:50

My google-fu has largely failed me. I'm trying to model a boat's hull on moving water. But I'm not sure I'm doing it right. The first question is whether it's possible to pre-flood the modeled test tank at Tzero. Right now, the tank starts empty and has to fill up before reaching the boat -- a lot a wasted simulation time there. I tried to specify a box filled with water in the setFieldsDict file to get things started. But it seems to be being ignored. The second question is whether the outlet has been specified correctly. In short, I just want water to run past my boat at a predefined level and speed so I can evaluate some hull shapes.

It's possible the issues I'm having are related to an exporter I wrote that exports models from Blender 3D directly into an fms file. From there, I run cartesianMesh on the fms file to get it into OpenFoam. The geometry looks correct in Paraview.

The project can be downloaded from here: http://www.roboticgladiator.com/Boat.zip

Yes, it's very crude right now just to speed things up until I get the config files sorted out. Any help will be appreciated.

JNSN · June 12, 2020, 03:21

Hi,

have a look at the DTCHull tutorial. This should be a good starting point for your case.

Best,

Jan

Ryoko · June 12, 2020, 11:44

That was very helpful. I hadn't thought of googling openFoam + hull. I was searching for boat and ship.

Things are working better, but the water still wants to pile up at the outlet to some extend rather than flowing out cleanly. Maybe this is normal? I'm also having trouble with the reconstructPar command. It's dying with an error "No times selected". I'm at a loss for this one. I have the 4 processor directories and decomposePar appears to run without any issues. Any ideas?

Edit: I looked in the various processor directories and it appears that there are no time steps inside of them other than 0. Why would this happen?

JNSN · June 13, 2020, 04:37

For the outlet issue, ensure correct mean velocity is set for the outlet BC, if using outletphasemeanvelocity.
ReconstructPar: Check the writeInterval.

Ryoko · June 13, 2020, 17:21

Things are working nicely as far as I can tell. I still haven't cranked the mesh resolution up yet mostly to keep the run times short while I expiriment with the software.

I do have one question as to why the DTCHull demo scaled the tanker ship so dramatically instead of using real world dimensions. It would seem to me that the significant scaling would cause issues with the dynamic similarity. (?) But I'm not an expert in fluid dynamics by any means.

June 11, 2020, 18:50	Newbie trying to get boat on water	#1
Ryoko New Member M.Lewis Join Date: Jun 2020 Posts: 9 Rep Power: 5	My google-fu has largely failed me. I'm trying to model a boat's hull on moving water. But I'm not sure I'm doing it right. The first question is whether it's possible to pre-flood the modeled test tank at Tzero. Right now, the tank starts empty and has to fill up before reaching the boat -- a lot a wasted simulation time there. I tried to specify a box filled with water in the setFieldsDict file to get things started. But it seems to be being ignored. The second question is whether the outlet has been specified correctly. In short, I just want water to run past my boat at a predefined level and speed so I can evaluate some hull shapes. It's possible the issues I'm having are related to an exporter I wrote that exports models from Blender 3D directly into an fms file. From there, I run cartesianMesh on the fms file to get it into OpenFoam. The geometry looks correct in Paraview. The project can be downloaded from here: http://www.roboticgladiator.com/Boat.zip Yes, it's very crude right now just to speed things up until I get the config files sorted out. Any help will be appreciated.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
How to use a UDF to set the volume fraction in the cells next to a wall?	DF15	Fluent UDF and Scheme Programming	33	August 20, 2020 13:36
Boat hydrodynamic forces estimation	CFD_fan	OpenFOAM Running, Solving & CFD	1	December 4, 2019 18:12
Problem condensation/ evaporation (condensate water vapor)	bigfoot47	FLUENT	0	October 21, 2019 08:07
air into box filled with water, outflow for water at bottom	dieterdanger	Fluent Multiphase	0	July 16, 2015 16:11
How to model Salinity, density, fresh water & sea water	grayback87	FLUENT	3	December 30, 2014 02:00

June 12, 2020, 03:21		#2
JNSN Senior Member Jan Join Date: Jul 2009 Location: Hamburg Posts: 137 Rep Power: 19	Hi, have a look at the DTCHull tutorial. This should be a good starting point for your case. Best, Jan

June 12, 2020, 11:44		#3
Ryoko New Member M.Lewis Join Date: Jun 2020 Posts: 9 Rep Power: 5	That was very helpful. I hadn't thought of googling openFoam + hull. I was searching for boat and ship. Things are working better, but the water still wants to pile up at the outlet to some extend rather than flowing out cleanly. Maybe this is normal? I'm also having trouble with the reconstructPar command. It's dying with an error "No times selected". I'm at a loss for this one. I have the 4 processor directories and decomposePar appears to run without any issues. Any ideas? Edit: I looked in the various processor directories and it appears that there are no time steps inside of them other than 0. Why would this happen?

June 13, 2020, 04:37		#4
JNSN Senior Member Jan Join Date: Jul 2009 Location: Hamburg Posts: 137 Rep Power: 19	For the outlet issue, ensure correct mean velocity is set for the outlet BC, if using outletphasemeanvelocity. ReconstructPar: Check the writeInterval.

June 13, 2020, 17:21		#5
Ryoko New Member M.Lewis Join Date: Jun 2020 Posts: 9 Rep Power: 5	Things are working nicely as far as I can tell. I still haven't cranked the mesh resolution up yet mostly to keep the run times short while I expiriment with the software. I do have one question as to why the DTCHull demo scaled the tanker ship so dramatically instead of using real world dimensions. It would seem to me that the significant scaling would cause issues with the dynamic similarity. (?) But I'm not an expert in fluid dynamics by any means.