Case study – Heavy Cargo carrier Conversion to Container carrier

Case Study – Heavy Cargo carrier Conversion to Container carrier update

1. Main outline of the project

The project consists of three major steps:

• Assessment of ship compliance with the applicable requirements of Part II “Hull” of Rules for the Classification and Construction of Sea-Going Ships of Russian Register with increased draft and new cargo
• Cargo Securing manual to be amended to include containers as a type of cargo.
• Arrangement of the container securing devices on deck

Ship particulars:

• Length (LOA)………………….……..… 123.0 m
• Length (LPP).…………………………… 118.0 m
• Breadth (MLD).………………………… 16.5 m
• Breadth NET ……………………………. 16.7 m
• Depth Main ……………………………… 5.6 m
• Max. Draught …………………..………. 3.4 m

2. Container plan and design loads

Based on the requirements of the client firstly we determine the available container positions. In general, there are two options when deciding this:

• On top of the hatch covers
• In the Cargo hold.

After performing strengths calculations in this particular case the containers are positioned in the Cargo holds. Below is the General Arrangement showing the positions of the containers that will be placed on deck.

3.Container Socket Installation

Reinforcements are installed into deck structure, in places where container sockets are installed, and in places where deck lashing points are arranged. There are two types of locking sockets:

• Twistlock pockets
• Lashing pots

4.Loads on container fittings and external lashing

The purpose of this step is to determine racking, compressive, and lifting loads of containers. Loads from external lashing on deck are determinate as well. All forces are applied at container COG.

Calculations were performed in ANSYS – Workbench 19.0*

The calculations are being performed on:

• Central stacks
• Side stacks

  4.1. Central stacks

  There are three types of loads acting on the central stacks:

• Central stacks Weight
• Central stacks Wind
• Central stacks Motion

 

 

 

 

 

 

 

 

 

                                               Central stacks weight                                                                      Central stacks wind load

 

 

 

 

 

 

 

                                           Central stacks motion

 

 4.2. Side stacks

There are three types of loads acting on the side stacks:

• Side stacks Weight
• Side stacks Wind
• Side stacks Motion

 

 

 

 

 

 

 

 

 

                                      Side stacks weight                                                                                                 Side stacks wind load

 

 

 

 

 

 

 

                                 Side stacks motion

5. Deck stiffening strength check-up

One of the most integral parts of the ship is its bottom structure. It is designed not only to give the hull the required strength to withstand the weight of the cargo but also to withstand the external hydrostatic loads that act on the bottom of the hull.

A calculation model is created based on the vessel‘s structural drawings. Aft part of cargo deck is used, as in this area deck plate thickness and under deck structure thicknesses are smallest. Calculations were performed in ANSYS – Workbench 19.0.

5.1. Geometry

 

 

 

 

 

 

 

                                                  Deck structure                                                     Additional Deck reinforcement

5.2. Loads on deck

 

 

 

 

 

 

 

                      Calculation model – Container weights                                     Calculation model – Wind forces

 

 

 

 

 

 

 

                  Calculation model – External lashing forces                         Calculation model – Motion forces

5.3. Results

 

 

 

 

 

 

 

                                                                                 Calculation model – Deformations under deck detail  

 

 

 

 

 

 

 

                                                                                          Calculation model – Shear stress

The main purpose of the stress calculations is to prove the sufficiency of the designed structure according to RMRS rules. Some peak extreme values are concentrated in very small areas on the surface of the elements or in areas with big swaps in the geometry parameters and are judged to be non-physical, but rather a result of numerical approximations. Therefore, such values are ignored and actual values are considered to be around the average values of the stresses outside the peak extreme values areas.