ANSYS CFX boat hull analysis/freesurface solution (Help)

idefix26 · April 12, 2014, 10:38

Hi.

I want to calculate hull resistance in Ansys CFX. I can calculate hull resistance in Fluent but I want to try CFX.

I can set up CFX for single phase solutions.

How can I set up in CFX for multiphase solution for a boat analysis? (freesurface calculation)
(Fluid flows: Above waterline air, below waterline water)

Boundary conditions, domains, interfaces, values etc?

Can anybody help me about setting up the CFX for boat analysis?
Or is there any tutorial for my topic?

Abou ali · April 12, 2014, 16:28

In ANSYS CFX 13 Tutorial 9: “Free Surface Flow Over a Bump” can be helpful.

JuPa · April 13, 2014, 09:20

Before diving into CFD do some engineering calculations by hand and try to get a rough ball park of the hull resistance. It will serve as a sanity check when you have a CFD result.

The free surface flow over a bump can be useful. But when you go multiphase you're dealing with a totally different beast. Is there a way you can do your problem single phase? I.e. just model the water?

idefix26 · April 13, 2014, 19:01

Quote:

Originally Posted by RicochetJ

Is there a way you can do your problem single phase? I.e. just model the water?

To calculate the wave resistance, I should set up the problem as multiphase. In Fluent, I can do it with this way. I want to do it in CFX.

idefix26 · April 14, 2014, 19:24

I understood the multiphase fluid defining from bump tutorial. Thanks.
I want to try it with rigid body motion together. Namely, i want to see the motion of ship hull by itself generated wave. No external wave. I dont know this is possible. I will try to do it. Do you have suggestion/opion about this case?

Thank so much!

jvoi_boy · August 30, 2018, 01:54

Quote:

Originally Posted by idefix26

I can calculate hull resistance in Fluent but I want to try CFX.

Is it fine if you can provide me with a tutorial/video/post that goes step by step into this process? I've been trying to do this for a month and I don't know what I'm doing. I am new to this program so a meticulous step-by-step guide would be greatly appreciated.

ghorrocks · August 30, 2018, 03:48

A meticulous step by step guide? See FAQ: https://www.cfd-online.com/Wiki/Ansy...ible_answer.3F

To be honest, I find boat hull analysis in Gerris very easy. If at all possible I would do it there (http://gfs.sourceforge.net/wiki/index.php/Main_Page). It has a nice tutorial example of a ship wave model.

urosgrivc · August 30, 2018, 03:56

It can be done in cfx yes.

Your domain needs to include water, air, and gravity.
You must initialize the water level height with two expressions based on height (air above and the water below some value)
and it is good to use rigid body motion and mesh deformation so you can have nice inflation layers near the boat hull.
Do not use immersed solid for this.
with rigid body motion setting, you can define free and fixed movement plus define moments of inertia in all directions.

a similar simulation I have done in CFX in the link
https://drive.google.com/open?id=166...ZpxJxceEj_Bo3I

In this case, it is a transient one but a lot of cases were done this is a bit of a fail to be honest,
but it works nicely
While I was doing it in the steady state I think I set it to a fixed timescale to drive the solution towards convergence
(i would have to check this one)

April 12, 2014, 10:38	ANSYS CFX boat hull analysis/freesurface solution (Help)	#1
idefix26 New Member Join Date: Apr 2014 Posts: 3 Rep Power: 12	Hi. I want to calculate hull resistance in Ansys CFX. I can calculate hull resistance in Fluent but I want to try CFX. I can set up CFX for single phase solutions. How can I set up in CFX for multiphase solution for a boat analysis? (freesurface calculation) (Fluid flows: Above waterline air, below waterline water) Boundary conditions, domains, interfaces, values etc? Can anybody help me about setting up the CFX for boat analysis? Or is there any tutorial for my topic?

August 30, 2018, 03:48		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	A meticulous step by step guide? See FAQ: https://www.cfd-online.com/Wiki/Ansy...ible_answer.3F To be honest, I find boat hull analysis in Gerris very easy. If at all possible I would do it there (http://gfs.sourceforge.net/wiki/index.php/Main_Page). It has a nice tutorial example of a ship wave model. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

August 30, 2018, 03:56		#8
urosgrivc Senior Member urosgrivc Join Date: Dec 2015 Location: Slovenija Posts: 365 Rep Power: 12	It can be done in cfx yes. Your domain needs to include water, air, and gravity. You must initialize the water level height with two expressions based on height (air above and the water below some value) and it is good to use rigid body motion and mesh deformation so you can have nice inflation layers near the boat hull. Do not use immersed solid for this. with rigid body motion setting, you can define free and fixed movement plus define moments of inertia in all directions. a similar simulation I have done in CFX in the link https://drive.google.com/open?id=166...ZpxJxceEj_Bo3I In this case, it is a transient one but a lot of cases were done this is a bit of a fail to be honest, but it works nicely While I was doing it in the steady state I think I set it to a fixed timescale to drive the solution towards convergence (i would have to check this one) Last edited by urosgrivc; August 30, 2018 at 06:28.

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April 12, 2014, 16:28		#2
Abou ali Member Join Date: Nov 2009 Posts: 49 Rep Power: 17	In ANSYS CFX 13 Tutorial 9: “Free Surface Flow Over a Bump” can be helpful.

April 13, 2014, 09:20		#3
JuPa Senior Member Mr CFD Join Date: Jun 2012 Location: Britain Posts: 361 Rep Power: 15	Before diving into CFD do some engineering calculations by hand and try to get a rough ball park of the hull resistance. It will serve as a sanity check when you have a CFD result. The free surface flow over a bump can be useful. But when you go multiphase you're dealing with a totally different beast. Is there a way you can do your problem single phase? I.e. just model the water?

April 14, 2014, 19:24		#5
idefix26 New Member Join Date: Apr 2014 Posts: 3 Rep Power: 12	I understood the multiphase fluid defining from bump tutorial. Thanks. I want to try it with rigid body motion together. Namely, i want to see the motion of ship hull by itself generated wave. No external wave. I dont know this is possible. I will try to do it. Do you have suggestion/opion about this case? Thank so much!