[HHK]

Hi everyone,

I am working on shallow water effects on Planar Motion Mechanism simulations.
I have used default PMM module in Star-CCM+ which is a part of DFBI set up.

Meshing is done in Star itself (PFA). In my preliminary simulations, I have used the same boundary conditions as that in KCS resistance prediction tutorial (i.e. Pressure outlet at the back & rest are velocity inlets). I face the following problems.

1) To get the shallow water effects, I merely reduced the distance between ship and bottom boundary (as in the fig). Is it the correct way of modelling shallow water effects?

2)Isn't no-slip wall more appropriate than velocity inlet at the bottom? Especially when I need the boundary layer effects of ocean bottom? But when I use it, I get negative volume cell errors.

Please post your suggestions on this.
Thanks in advance.

[rishabhk28]

yea , the bottom surface should be given wall as boundary condition, with no-slip!

hope this answers your query!

[Seervan]

Greetings

I have performed shallow water tests on KVLCC2 which seems you are studying the KCS model,
For some guidelines you should definitely use "wall" boundary condition for bottom as you want to see the depth variation effects. And also according to some references you better use "moving wall" condition at bottom with the wall moving with the far field flow velocity.
I assume you are modelling the free surface and thus you are running your tests in time domain yes?

And as I see in your picture, I see you have extended the domain in the Air region too much. It can cost you a lot of computation power. You can lower it much more which an extenstion of 1 to 1.5 LPP to the air domain at maximum should be enough.
And as for the mesh, your mesh your mesh is kinda good. Trimmer mesh is adequately optimum for most runs, but you can also use Polyhedral meshing instead since PMM tests can have immense turbulence generations in Y direction. You can reach a fine mesh with Polyhedral with much less elements compared to Trimmer but bare in mind that Polyhedral takes more time to generate the mesh.

Make sure to have a look of the works done by Toxopeous which include very good procedures for shallow water CFD runs.
Papers such as: "VISCOUS-FLOW CALCULATIONS FOR KVLCC2 IN DEEP AND SHALLOW WATER" , "Calculation of the Flow around the KVLCC2M Tanker", "Investigation of water depth and basin wall effects on KVLCC2 in manoeuvring motion using viscous-flow calculations" and "VALIDATION OF CALCULATIONS OF THE VISCOUS FLOW AROUND A SHIP IN OBLIQUE MOTION".

I hope it helps.
Best regards

[HHK]

Hi guys,

Thank you so much for the suggestions.
Sure I will look into those articles.

[823811603]

Hello, have you solved your problem？I also encountered the same problem. How did you solve it?

[Nazir426]

I am facing problems for using the PMM module in Star-CCM+ for my analysis of DARPA Suboff. I do not know the required steps in star ccm even for Rotating Arm Analysis of DARPA model. Please help me. What are the steps in order to calculate the Hydrodynamics coefficients of DARPA Suboff in star ccm+?

Regards
Nazir Ahmed

Originally Posted by HHK

Hi everyone,

I am working on shallow water effects on Planar Motion Mechanism simulations.
I have used default PMM module in Star-CCM+ which is a part of DFBI set up.

Meshing is done in Star itself (PFA). In my preliminary simulations, I have used the same boundary conditions as that in KCS resistance prediction tutorial (i.e. Pressure outlet at the back & rest are velocity inlets). I face the following problems.

1) To get the shallow water effects, I merely reduced the distance between ship and bottom boundary (as in the fig). Is it the correct way of modelling shallow water effects?

2)Isn't no-slip wall more appropriate than velocity inlet at the bottom? Especially when I need the boundary layer effects of ocean bottom? But when I use it, I get negative volume cell errors.

Please post your suggestions on this.
Thanks in advance.