Flow around a ship hull with trim and sinkage
 

Hi,

I am trying to simulate flow around a ship hull. I get good wave patern when I run the simulate without rigid body motion using DFBI translation and rotation activation (for trim and sinkage calculation). But when I activate rigid body motion, the converged wave patern formed earlier gets distorted and drag, trim and sinkage values starts to oscillate. I ran the simulation till 50 sec and there is no convergence of drag, trim and sinkage.

Kindly help.
Thanks

Manoj

Hi manoj_nav,

could you specify your settings? So I assume you are running transient? What convergence do you expect in drag and sinkage? Whats your solver settings, timestep?

Could you plot your values for sinkage,trim, residuals and maybe attach a picture of your domain and mesh?

If your project allows you too, you could also just send me the sim file and I'll have a look at it after work, or send me your settings with a different geometry if your data is confidential.

Hope I will be able to help.

Cheers

Kons

p.s:

how do you realize the 6DOF (or 3 in your case). Is it a moving, morphing mesh or overset? that's probably where you get in trouble with your free surface. (eg. timestep too big for the accelerations) but hard to say without more information

Hi fuzel

Thanks you for the reply.

The setting can be read here - http://www.scribd.com/doc/149664686/summary-report-pdf .The sim file size is large, so I have uploaded the setting summery above. I am running transient simulation with Implicit Unsteady solver time step 0.005 sec, temporal discretization 1st order; K-Epsilon Turbulence - under relaxation factor 0.8; AMG Linear Solver, max inner iteration 8. 6DOF has been realised using a moving mesh.

Following are the plots

1. Free surface,

http://s20.postimg.org/dmknw9cy5/free_surface.jpg

2. Drag,

http://s20.postimg.org/vbcenvop9/drag.jpg


3. Trim

http://s20.postimg.org/m9xva9qrx/trim.jpg

4. Sinkage ,

http://s20.postimg.org/efx9oviz1/sinkage.jpg

5. Residuals,


http://s20.postimg.org/67vc3vr2l/residuals.jpg


Thanks in advance.


Manoj

Hey Manoj,

I ll have a look at it after work. Still, if you could send me the sim file it would make it a lot easier and faster finding your problem... Maybe delete Solution and Mesh, it shouldnt be to big then.... Dropbox,Rapidshare....

Cheers

Kons

Hi fuzel

Can you send me you email id.

Manoj

Hi,

is there any solution for this problem?
I have same problem.
But I think I have a solution for this problem.
I switched under region --> Physics Value form Lab Reference Frame to Ship Reference Frame.
With this settings I get a very good convergence and accordance to the towing tank tests.
Difference trim computation to towing tank 0,001°; sink 0,001m
The same with Rf und Rp.

alfaben

Settings link PDF
 

Hello

Thanks for the interesting discussion. Do you find/ have the pdf with the settings, somewhere else, because the scribd links seams to be dead?! Thanks a lot in advance.

BR Thomas

Hi manoj_nav,
I am calculating the resistance of DTMB 5415 without rigid body motion using STAR CCM+,my wave patern is bad,can you give me some advise or your sim file without generated mesh? thank you!

Resistance calculation using potential flow in Star CCM+
 

Dear all
Good day!

I am trying to calculate resistance of ship using potential (inviscid) flow method, although one can go for RANS calculations.

Objective of this calculation is to get trim table for a tanker hull form.

1. Can anybody suggest me settings for inviscid resistance calculation in STAR-CCM+ using DFBI.
2. CPU time required for such calculations. Though time depends on mesh density, i just wanted to know rough estimate.