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ANSYS CFX boat hull analysis/freesurface solution (Help)

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Old   April 12, 2014, 09:38
Default ANSYS CFX boat hull analysis/freesurface solution (Help)
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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?
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Old   April 12, 2014, 15:28
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In ANSYS CFX 13 Tutorial 9: “Free Surface Flow Over a Bump” can be helpful.
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Old   April 13, 2014, 08:20
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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?
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Old   April 13, 2014, 18:01
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Quote:
Originally Posted by RicochetJ View Post
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.
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Old   April 14, 2014, 18:24
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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!
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Old   August 30, 2018, 00:54
Default Fluent Boat Hull Tutorial
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Quote:
Originally Posted by idefix26 View Post
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.
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Old   August 30, 2018, 02:48
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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.
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Old   August 30, 2018, 02:56
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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 05:28.
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