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Old   November 30, 2012, 19:56
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  #241
ngj
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Niels Gjoel Jacobsen
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Hi Sagun

Without knowing the dimensions of your test case, it looks correct. What do you mean by no flow at all? When I ran the test with the same parameters, everything worked as it should.

1. Try to visualise the pressure field.

2. If your Courant number is not very small, then there is probably a certain flow, but you might be looking at the wrong number/data range.

3. You have a quite small wave height relative to the other spatial dimensions, so it might be hard to see.

Kind regards,

Niels
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Old   December 3, 2012, 06:00
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Hello Niels,

Good morning. I wanted to let you know that the case finally worked. The problem was indeed with the wave height and its velocity. They were too small with respect to the other spatial dimensions. I fixed those and it worked like a charm.

Now that I have been able to generate waves around an offshore structure, could you possibly tell me how can I extract the velocity potential only on the surface of the structure? I have tried to find some info on the forums here on this topic but to no avail. It would be great if you can point me in the right direction.

Thanks for all your help.
Sagun
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Old   December 3, 2012, 09:03
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  #243
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Niels Gjoel Jacobsen
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Hi Sagun,

If you want the velocity potential (irrotational), then why are you using a solution based on the Navier-Stokes equations? You already have the velocities and the pressure, wouldn't that suffice your requirements?

Kind regards,

Niels
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Old   December 3, 2012, 11:43
Default wave theories and wave2Foam
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Albert Tong
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Hi Niels,

This maybe not relevant to this topic, but I would much appreciate if you can confirm or correct the following list of my understandings about the wave theories used in wave2Foam.

1, some wave theories were derived based on assumptions such as irrotational and inviscid flow (airy and stokes wave theories, for instance), but as they are only served as an inlet boundary condition to NS equations, the solution is a rotational and viscous flow field.

2, The reason to use these wave theories as inlet condition is because that the wave in reality can be roughly described by the equations in different wave theory (or cannot be precisely describe by a standard and general method).

3, different wave theory has its own validity range, which can be found here: http://en.wikipedia.org/wiki/File:Wa...e_theories.svg

4, the "potential current" as defined at the inlet or outlet is really a uniformly distributed velocity, and has nothing to do with potential flow.

5, Even with wave theory based on potential flow, wave breaking around ocean structure (highly non-linear) can be achieved.

Many thanks.
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Kind regards,

Albert
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Old   December 3, 2012, 12:16
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Hi Niels,

I suppose my question was incorrect. If I want to extract any field on the surface of the structure, say pressure with a view to calculate the net hydrodynamic force acting on it, then could you tell me how should I go about it?

Thanks,
Sagun
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Old   December 3, 2012, 16:25
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  #246
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Niels Gjoel Jacobsen
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Hi Albert,

On the contrary I find the questions very relevant, so let me try to answer them:

Quote:
Originally Posted by tfuwa View Post
1, some wave theories were derived based on assumptions such as irrotational and inviscid flow (airy and stokes wave theories, for instance), but as they are only served as an inlet boundary condition to NS equations, the solution is a rotational and viscous flow field.
All the wave theories, which to present date are implemented (as of revision 1984; Big Brother is watching!), are based on irrotational theory also termed potential wave theory. This is a reasonable approximation as the effect of internal friction and wave boundary layers only has a minor effect of the wave. Wind, on the other hand, as already discussed somewhere above, has an important effect on the wave shape and kinematics, but it is not considered in waves2Foam (as of revision 1984 ).

Quote:
Originally Posted by tfuwa View Post
2, The reason to use these wave theories as inlet condition is because that the wave in reality can be roughly described by the equations in different wave theory (or cannot be precisely describe by a standard and general method).
Yes, they roughly describe the kinematics, however, irregular waves are still limited to low order wave theories. As far as I know, potential wave theory is also used in all laboratory facilities around the world to describe the motion of the paddle (however, these might also include evanescence modes, but that would be a very elongated story to tell on this forum).

Quote:
Originally Posted by tfuwa View Post
3, different wave theory has its own validity range, which can be found here: http://en.wikipedia.org/wiki/File:Wa...e_theories.svg
Yes, and they are not necessarily derived from the same fundamental equation. E.g. first order stokes (Airy) theory carries an assumption of infinitesimal wave height, whereas first order cnoidal wave theory accept a finite wave height. This also means that whereas the first order Stokes theory originates from a linear set of equations, even the first order cnoidal theory is a solution to a non-linear PDE.

Quote:
Originally Posted by tfuwa View Post
4, the "potential current" as defined at the inlet or outlet is really a uniformly distributed velocity, and has nothing to do with potential flow.
The potential current is a horizontal velocity, which is constant in time and space. This is a solution to the potential wave theory (e.g. the Laplace equation), so it has all to do with potential wave theory; hence the name.

Quote:
Originally Posted by tfuwa View Post
5, Even with wave theory based on potential flow, wave breaking around ocean structure (highly non-linear) can be achieved.
Yes, out of many examples you can consult our paper, which describe the release of this toolbox. Please find the reference on the wiki: http://openfoamwiki.net/index.php/Contrib/waves2Foam
You will also find references to previous works on the modelling of wave breaking using VOF and other methods in this paper.

Hope this helps,

Niels
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Old   December 3, 2012, 16:30
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  #247
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Niels Gjoel Jacobsen
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Hi Sagun,

You should investigate the many post-processing utilities available in the standard OF distribution. Especially, what you request are either available through the sample utility:

<OF-path>/applications/utilities/postProcessing/sampling/sample

or the forces application:

<OF-path>/src/postProcessing/functionObjects/forces

As far I know, the latter is best run during the simulation, but I might be mistaken, as I have never used it myself.

Plenty information on the use of these utilities are available on this Forum.

Kind regards

Niels
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Old   December 11, 2012, 06:58
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  #248
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Luca Bonfiglio
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Quote:
Originally Posted by rosswin View Post
I have been getting this error in my log files for waveFoam.
Hi Ross,
I'm stuck in the same trouble with OF171. Have you finally solved your problem?
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Old   December 12, 2012, 13:59
Default Solitary wave velocity components derivation
  #249
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Qicheng
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Hi Niels,

Thank you very much for your wonderful work.

I am a new PhD student. And I am going to do research on solitary wave. I have sucessfully operated the solitary wave tutorial. I am now learning the program you have made.

But I face the same problem as Masoud. I cannot understand how you derived the velocity components of particle. I have worked it on several days and there is no clue to derive the form you use in the program.

Could you please give me some detailed derivation about it?

Yours,
Qicheng Meng
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Old   December 13, 2012, 05:28
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Niels Gjoel Jacobsen
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Good morning,

Please do read the description in

waves2Foam/src/waveTheories/solitary/solitaryFirst/solitaryFirst.H

on how the vertical velocity field is derived.

Kind regards,

Niels
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Old   December 13, 2012, 07:59
Default The horizontal particle velocity
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Qicheng
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Dear Niels,

Many thanks for your reply.

What I cannot understand is the horizontal particle velocity field, for it is different from what is taught in the text book about the first order solitary wave theory. The horizontal velocity is only the first order of expansion without magnitude change in the vertical direction. However, your expression contains the vertical coordinate in the expression. So I tried to include the second order of the velocity expansion. But I still cannot derive your expression.

So could you help me to understand the derivation of the horizontal particle velocity? The problem is neither can I find the reference nor can I derive it by myself.

Best regards!

Qicheng

Quote:
Originally Posted by ngj View Post
Good morning,

Please do read the description in

waves2Foam/src/waveTheories/solitary/solitaryFirst/solitaryFirst.H

on how the vertical velocity field is derived.

Kind regards,

Niels
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Old   December 14, 2012, 10:32
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  #252
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Good evening Qicheng,

I have not derived the solitary wave theory myself and I do unfortunately not have the reference in a digital format.

I suggest that you implement your favourite solitary wave theory, which should not be difficult once you have a set of algebraic equations, and you will know, where the terms originate from. I will gladly incorporate such an implementation of yours into waves2Foam.

Kind regards,

Niels
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Old   December 15, 2012, 08:27
Default The gratitude for Niels' suggestions
  #253
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Dear Niels,

Thank you very much! I will follow your instructions, modify the code and validate the results. I believe I will have fun with it. Your code does give me a lot of help for the research. I am going to study the internal solitary wave. So it would be great if we could exchange the ideas in the future.

Yours,
Qicheng

Quote:
Originally Posted by ngj View Post
Good evening Qicheng,

I have not derived the solitary wave theory myself and I do unfortunately not have the reference in a digital format.

I suggest that you implement your favourite solitary wave theory, which should not be difficult once you have a set of algebraic equations, and you will know, where the terms originate from. I will gladly incorporate such an implementation of yours into waves2Foam.

Kind regards,

Niels
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Old   December 15, 2012, 08:47
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  #254
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Niels Gjoel Jacobsen
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Your are welcome.

Good luck,

Niels
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Old   December 19, 2012, 09:26
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Galchenko Olga
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Good afternoon!

I'm having problems with coupling waves2Foam with dynamic mesh motion. I've followed all the instructions, but still can't compile my waveDyMFoam solver. When I type wmake, I got this error message: "command not found".
I tried to "make" it, but I was told that thereis nothing needed to be done with this files. Though when I try to run this solver, I stil got same message "command not found" .

can someone help me to solve this problem?

Regards,
Olga

Last edited by Galchenko; December 19, 2012 at 09:46.
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Old   December 20, 2012, 05:57
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  #256
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Niels Gjoel Jacobsen
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Hi Olga,

You need to source the entire OpenFoam, before you can compile anything. Please look on the descriptions on how to set-up OpenFoam on your computer here (Section: Setting Environment Variables):

http://openfoam.org/download/source.php

Just to be clear, the problems you encounter have nothing to do with waves2Foam in specific, but rather the initiation of system variables, which are related to OpenFoam.

Kind regards,

Niels
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Old   December 20, 2012, 12:11
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Galchenko Olga
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Thanks a lot for your answer, Niels.

But I have no problems with using waveFoam(also a grand thanks for a great work you've done) or any other solvers, so I suppose the problem is coonected exactly with implementing waveDyMFoam. Anyway,I repeated all the actions to set the environment variables, but it didn't help.

Regards,
Olga
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Old   December 21, 2012, 03:41
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  #258
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Niels Gjoel Jacobsen
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Good morning Olga,

It sounds a bit weird, however, I do not have the faintest idea about the actual problem, since the error "command not found" would suggest that "wmake" is not in the search path.

As you have compiled waves2Foam successfully disprove that wmake cannot be found. Try to compile a fresh interDymFoam in the new waveDymFoam directory and see if it works, i.e. do not make any changes to the files (except the output location in Make/files). This must work.

Kind regards

Niels
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Old   January 4, 2013, 16:10
Default Problems compiling waves2Foam
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Hi All!,

I have been straggling to compile waves2Foam for a long time with no success.
I use cae-linux and my openFoam instalation is in /opt/openfoam211.
waves2Foam was placed in /home/carlos/OpenFOAM/carlos-2.1.1/waves2Foam and a copy of all files is in
/opt/openfoam211/applications/solvers/multiphase
I attach the errors reported.
Thanks a lot for your help!
Carlos.
Attached Files
File Type: zip Errors compiling waveFoam.zip (1.8 KB, 11 views)
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Old   January 5, 2013, 05:35
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  #260
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Hi Carlos,

I would recommend that you do not add any solvers to begin with - this is not necessary to begin with for version 2.1.1. If you need dynamic meshes then you need to follow the instructions on the wiki, however, take this step, when the basic package is compiled correctly.

Make a new checkout from the svn, and you should be able to compile it all without any problems.

E.g. the library libwaves2Foam.so is compiled correctly and so are all of the utilities.

Kind regards,

Niels
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