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Old   May 31, 2012, 06:37
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  #181
ngj
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Niels Gjoel Jacobsen
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Hi Flowris

My common settings deviate from yours. From my experience I use:

relTol = 0.0; in all pressure corrections.

nAlphaSubCycles = 1;

cAlpha = 1;

Using these I get nice results and it runs pretty stable for long times (hundres of wave periods).

Furthermore, I use GAMG for the pressure solution.

Kind regards,

Niels
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Old   June 9, 2012, 03:47
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  #182
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Quote:
Originally Posted by ngj View Post
Hi Flowris

What does your fvSolution file look like? With respect to schemes, I have been happy using MUSCL for div(rho*phi,U) and div(phi.aplha).

Best regards,

Niels
Hie Niels, I try MUSCL for div(rho*phi,U) and div(phi, alpha) but my test crash. The best combination I found is this:

ddtSchemes
{
default localEuler rDeltaT;
}

gradSchemes
{
default Gauss linear;
grad(p) Gauss MUSCL 1.0 phi;
}

divSchemes
{
div(rho*phi,U) Gauss limitedLinear 1.0 phi;
div(phi,alpha) Gauss vanLeer;
div(phirb,alpha) Gauss interfaceCompression;
div(phi,k) Gauss upwind;
div(phi,omega) Gauss upwind;
}

laplacianSchemes
{
default Gauss linear corrected;
}

interpolationSchemes
{
default linear;
}

snGradSchemes
{
default corrected;
}

fluxRequired
{
default no;
p_rgh;
pcorr;
alpha1;
}

Any idea why if I replace by MUSCL, my calculation diverge?

Best regard

Vince
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Old   August 3, 2012, 04:20
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  #183
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Vince, Niels,

I tried all of your tips and many other things, but nothing took away the oscillations. Is any of you willing to take a look at my case? I can send it by e-mail, since it is too large to post on the forum.

Greetings and thanks for your help so far.
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Old   August 7, 2012, 06:01
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  #184
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Hi Flowris

You can send your case on my mail: vincent.jacob@greenflow2358.fr.

Kind regards,

Vince
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Old   October 7, 2012, 19:20
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  #185
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Hey all,

I have a rather rushed project to complete. I wish to model a ship on the free surface, eventually with 2DOF (heave/sink + pitch), self-propelled and in a seaway.

I would be happy if I can get just the 2DOF bit working

I am new to openFOAM and have literally no idea where to start. If I can show that my methods are working I will have access to very large computing power (up to 40m cells). Could someone give me some pointers as to where to start?

Thanks,
James
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Old   October 8, 2012, 02:20
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Ralph Moolenaar
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Hello James,

What kind of timeframe do you have for your project?

Regards,

Ralph
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Old   October 8, 2012, 04:17
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Hi Ralph,

I have about 2 weeks to get a 2 DOF system working, with a further month to add a seaway and self-propulsion effects.

James
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Old   October 8, 2012, 04:24
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Hi James,

In that case I think you should change your plans.... currently there are only between two-five OF-solvers in the world capable of simulating a moving ship and none of them are available for public. I've been working on this matter for a long time now and still working hard to develop such a code myself. Unless you're a genius I doubt that you'll be able to fix a code in such a short time.

Hopefully you'll be able to simplify your problem towards a fixed ship, then I recommend you to go for the latest OF version (2.1) and use the LTSInterFOAM solver. Setting up a working case will already take you a few weeks... so good luck!

Ralph
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Old   October 8, 2012, 05:11
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Hi Ralph,

Thanks for your feedback. I am aware that tools like overset grids would hugely assist in this problem. Is the issue with dynamic meshing or with calculating the motions of the vessel?

I planned to use sliding meshes for the selfpropulsion (I believe they are public domain) and a numerical beach to solve the wave outflow boundary... But I'm looking a long way in advance here.

Is this problem solvable straightforwardadly in tools like star ccm or ansys cfx?

James
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Old   October 8, 2012, 06:05
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James,

Everything is possible in OF.... if you have enough time! Most of the stuff you need is indeed already available somewhere, but it takes a lot of effort to combine and check.

I even think that two weeks time isn't very much for a commercial package like Fine/Marine or StarCCM. But if you could use something like that I would certainly go for the commercial packages instead OF. Again you have to invest a lot of time, but it's certainly less time than learning how to use OF!

Ralph
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Old   October 8, 2012, 15:54
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Thanks Ralph,

I will speak to my supervisor who has some experience with OF and see what he thinks. I worry that dynamic meshing won't be enough for the amplitudes of motion I am considering.

I'm quite daunted by how much there is to learn - I should probably just get started!

James
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Old   October 20, 2012, 08:10
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I am trying to determine Power Number using ANSYS CFX for Rushton impeller vessel

I am looking for tutorial or procedure how to do it.

thanks
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Old   December 10, 2012, 19:23
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Hi Ben,

I am starting play with interDyMFoam and I am curious about how do you print out the trim and sinkage data ?

Regards
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Old   December 11, 2012, 05:40
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Hi Angela,

I'll try to send you the gnuplot file tonight.

Ben
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Old   December 11, 2012, 10:48
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Thanks, Ben. What I mean is how do you get the trim and heave output? From the log file? Or any setup just like the force in controldict ?

Quote:
Originally Posted by bouclette View Post
Hi Angela,

I'll try to send you the gnuplot file tonight.

Ben
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Old   December 11, 2012, 10:53
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I take it from the log file.
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Old   December 11, 2012, 13:47
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Thanks, Ben. I checked the log file and it only gave out Linear velocity and Angular velocity. Do you use them and the timestep to calculate heave displacement and pitch angle?
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Old   December 12, 2012, 16:40
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Hi Ben,

I just realized yesterday that the heave data can be fetched from the log file (CoM, center of mass). And the trim can be calculated with the coordinates of CoM and any other point on the moving boundary. But it seems the pointDisplacement is only dumped at write interval instead of every time step. Then how can we easily see if a calm water problem goes to convergence if any degree of motion is allowed?

Angela
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Old   January 18, 2013, 09:46
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Hi

I make some test with LTSInterFoam on sailing hull with appendages. The result close to the theory is obtain with in fvScheme file:
div(rho*phi,U) Gauss limitedLinear 1.0 phi

With a refinement level 6 on surface and volume, is not very good. With a refinement level 7, it's better. But now, when I test with a level 8, the calculation stop after 3 iterations with an error message.

What's wrong? Anybody have an idea?

Vince
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Old   January 18, 2013, 09:53
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Hi vince,

it is hard to say what is wrong with your calculation since you dont provide
all necessary information.

Eventually you want to post:

- the Error Message

- your snappyHexMeshDict file since I assume youre using sHM

- type: "checkMesh > log" and post the content of new
created log file here

This will increase the chance that someone is willing to help you

regards

Colin
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