Ship Resistance – KCS(KRISO Container Ship)

Introduction

This is an example of mesh generation for the resistance analysis of a ship with a free surface. The target ship is the KCS , a model with many published experimental and analytical results. For the calculation of the free surface, the directional level increment function is used to densify the mesh in the direction of the water surface height.

The calculation results using the created grid are as follows

Drag coefficient	Experiment	Baram	Difference
Pressure, Cr	7.25E-04	7.46E-04	2.83%
Friction, Cf	2.83E-03	2.79E-03	-1.55%
Total, Ct	3.56E-03	3.54E-03	-0.62%

Ref) Measurement of flows around modern commercial ship models, Kim,W J.Kim, Van, S H, Kim, D H, Experiments in Fluids, 2001

Geometry

After unzipping the downloaded file, you will have two stl files named hull and deck.

Click the [Import] button at the bottom to select the two files.

The farfield boundary is created using Hex6. Set the density of the mesh using three hexahedra around the ship, near the free surface, and near the free surface around the ship.

Create farfield boundary

Create a farfield boundary using Hex6. In the window that appears when you click the [Add] button, select [Hex6] and set the following settings.

Name : Hex6_1
Type : None
MIn. : (-18 0 -15)
Max. : (18 18 5)

Since it is a left-right symmetric shape, we give it a minimum y coordinate of 0 to make the mesh only half in the +y direction.

Rename the six surfaces below Hex6 as follows

Hex6_1_xMin -> far_outlet
Hex6_1_xMax -> far_inlet
Hex6_1_yMin -> centerplane
Hex6_1_yMax -> far_side
Hex6_1_zMin -> far_bottom
Hex6_1_zMax -> far_top

Create Refinement Regions

To specify the area around the ship, press the [Add] button to add a hexahedron.

Name : near_hull
Type : None
MIn. : (-6 0 -1)
Max. : (5 1.5 0.5)

Adding the hexahedron creates a near_hull_surface, which we change its property to None.

To specify the area around the free water surface, click the Add button to add a hexahedron.

Name : near_vof
Type : None
MIn. : (-10 0 -0.1)
Max. : (18 10 0.1)

Adding the hexahedron creates a near_vof_surface, which we will change its property to None.

To specify the free surface area around the ship, click the [Add] button to add a hexahedron.

Name : near_hull_vof
Type : None
MIn. : (-6 0 -0.1)
Max. : (5 1.5 0.1)

Adding the hexahedron creates a near_hull_vof_surface, which we will change its property to None.

The final result is as follows

Click the [Next] button to move on to the next step.

Region

Click the (+) icon at the top to create a region. Move the mouse to the intersection of the lines that appear in light green color in the graphics window and position them outside the wing. Click the [Update] button to complete the setup.

Click the [Next] button to move on to the next step.

Base Grid

Select [Use Hex6] and set the number of grids to 20, 10, and 20. Click the [Generate] button to generate the base grid.

Click the [Next] button to move on to the next step.

Castellation

[Configuration] and [Advanced] use the default conditions.

Define the mesh refinement of the ship, hull and deck.

Click the (+) icon in [Surface/Feature Refinement] and set the following for the hull

Surface Refinement
- Minimum Level : 7
- Maximum Level : 7
Feature Edge Refinement Level : 7

Click the (+) icon in [Surface/Feature Refinement] and set the following for the deck.

Surface Refinement
- Minimum Level : 6
- Maximum Level : 6
Feature Edge Refinement Level : 6

Define a mesh refinement for the hexahedron near the submarine and near the free water surface.

[Click the (+) icon under Volume Refinement and set the following settings for near_hull and near_vof

Volume Refinement Level : 5

Define a mesh refinement for the hexahedron near the submarine.

[Click the (+) icon under Volume Refinement and set the following settings for near_hull_vof

Level Increment On
Split Count per Direction : (0 0 2)
Min. Level is 5, Max. Level is 6

To enable parallelization, click [Parallel] – [Environment] in the menu and enter the desired value for [Number of Cores].

Click the Refine button to refine mesh.

Click the [Next] button to move on to the next step.

Snap

With the default settings, click [Snap] button.

Click the [Next] button to move on to the next step.

Boundary Layer

Create a boundary layer mesh for the hull.

Click the (+) icon under [Configuration] to add a [Setting] and set it to the following set

Number of Layers : 4
Thickness Model Specification : First and Expansion
Size Specification : Absolute( Off the Relative)
First Layer Thickness : 0.0014
Expansion Ratio : 1.2
Min. Total Thickness : 0.003
Boundary : hull, deck