[manoj_nav]

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

[fuzel]

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

[fuzel]

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

[manoj_nav]

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,



2. Drag,




3. Trim



4. Sinkage ,



5. Residuals,





Thanks in advance.


Manoj

[fuzel]

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

[manoj_nav]

Hi fuzel

Can you send me you email id.

Manoj

[alfaben]

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

[Tomilla]

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

[qingseshi]

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!

[liladhar]

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.