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Old   May 26, 2021, 06:53
Default Floating Body Forces
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Furkan Türkmen
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Hello sir,

When I use the floating body solver options, I get the following forces from the file REEF3D_6DOF_S_force.dat. Normally, my expectation is that Fz is close to +3000N which is the weight of the ship but as you can see from the figure, the z force convergences to zero. So, I think this parameters mean something else such as net force on floating body. Could you tell me what do they mean? (also Ks Ms Ns)

In addition I would like to see both viscous and pressure force, is there any possibilities to do that?

Thank you,

Best regards
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Old   May 28, 2021, 04:21
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Arun Kamath
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Dear Furkan,
From the filename that you name, I see that you are not using the newest version of the floating algorithm implemented in the model.
I would advice you to get the latest version from Github (there will also be a new release soon).
In addition, if you see this persists, it would be useful to have a look at your input files.
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Old   May 28, 2021, 04:36
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Furkan Türkmen
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Thank you very much. I will look for the newest version.


Regards
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Old   May 28, 2021, 10:55
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Furkan Türkmen
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Hello again Mr Kamath,


I have tried to solve floating body problem with the latest version, however, the result have not converged. The critical velocity was exceeded. I used the direct forcing setting for X 13 (X 13 2) and as you mentioned before, I saw that the forces.dat file is new notation now, which is more clear, thank you.



Am I missing something for the solution I think. If there were a example case I would compare with it. Will you do a tutorial case for floating body?


In attachment you can find my case settings


Thank you,

Best regards


Furkan
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File Type: txt ctrl.txt (423 Bytes, 21 views)
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Old   May 29, 2021, 08:08
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Dear Furkan,


we can have a look, but you need to send us the stl file as well so that we can run the actual simulation.
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Old   May 31, 2021, 07:08
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Furkan Türkmen
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Hello Dr Martin,

I want to simulate a ship resistance analyze as you can see in the attached picture.
My main objective is to get the x direction forces on the floating body.

When the 6DOF is not allowed i can get the forces as i want. They are strongly acceptable.

When 6DOF is allowed i cannot get the forces.
In 6 DOF analyzes i want these:
Translation through x axis is not allowed.
Translation through y axis is not allowed.
Translation through z axis is allowed.
Rotation around x axis is not allowed.
Rotation around y axis is allowed.
Rotation around z axis is not allowed.

The mass is 320kg.
The center of rotation is 5.66643,4,2.4297 (as meter).
The moment of inertia values are 38.44, 357.24, 357.24.

I am sending you the control.txt and ctrl.txt and floatig.stl files.
In this situation i do not get any error. And i can get free surface as i want. But i cannot read the x direction forces on the body.
In this situation REEF3D_6DOF_S_force.dat folder is created. There are Xs, Ys, Zs, Ks, Ms, Ns. But their values are not as i expect. They all goes to zero.

When i change X 13 0 option to X 13 2 the solution diverges.
I also tried different options for X 40. But could not get the x direction forces on the floating body.

In my opinion my mistakes are in X 10, X 13, X 40 options.

Could you please help me? What should i change in my ctrl.txt file to get the x direction forces on the hull (ship resistance value)?

By the way i use version 21.02.



In addition, I can not send stl file due to size is too large. I have sent you an e mail to your mail address (tobias.martin@ntnu.no)


Best regards.
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File Type: txt control.txt (242 Bytes, 12 views)
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Last edited by fturkmen; May 31, 2021 at 09:57.
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