Mooring of a Floating Container Terminal
 
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The terminal
 

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Location

Conditions

Dimensions

Forces

Before a mooring system can be designed, the desired dimensions and location of the terminal have to determined. These choices have a large influence on the design of the mooring system.

 

Location

The location of the floating terminal will be outside the harbour of Yokohama in the Tokyo Bay. Because land is scarce in the Yokohama port area, a container terminal on existing land is not an option. The waterdepth in the bay is relatively large (25 to 45 meters). The Tokyo bay is well protected from the Pacific ocean, thus reducing the significant waveheight, even during typhoons. Furthermore, the region is regularly subjected to earthquakes. Therefore a floating terminal is preferable over a land reclamation project.

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Conditions

The environmental conditions in the Tokyo Bay are as follows:

The tidal conditions are given in the table below:

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For a 100-year typhoon condition, the following applies:

 

Tokyo Bay soil conditions:

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Dimensions

The Yokohama harbour area handles 3.5 million TEU yearly. A new container terminal should be capable of increasing this with 10%. Therefore the capacity of the floating container terminal is set to 350,000 TEU each year. Based on previous studies, this will result in a terminal area of 100.000 square meters. Resulting from this, the dimensions are set to 200 x 500 meters. Draft is also taken from previous studies, resulting in an unloaded draft of 2.0 meters. The weight of the terminal's structure therefore is 205,000 tons. The terminal's maximum storage capacity is about 10,000 TEU. The terminal will be connected to the main land by means of an access bridge. This will also have implications on the mooring system.

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Forces

From the environmental conditions, the forces acting on the terminal can be calculated. These forces are important for the detailed design phase of the terminal's mooring system. The total environmental force is calculated by adding all different environmental components. Furthermore different design and ballast conditions have been taken into account. 

Environmental forces acting on the floating terminal

  • Second order wave forces
  • Wind forces
  • Current forces

Design conditions

  • Operational
  • Survival (100 year typhoon condition)

Ballast conditions

  • Unloaded
  • Fully loaded

The resulting environmental forces acting on the floating container terminal are given in the table below.

Ship mooring alongside

Another force the terminal will have to withstand is the "rough" mooring of a containership alongside the terminal. For this, a worst case scenario is chosen where a container vessel of 150,000 DWT collides sideways with the terminal at a speed of 0.5 m/s. This is a model for the ship not mooring smoothly alongside the terminal, but suddenly drifting into it (neglecting the fenders between ship and terminal). From the impuls conservation law the resulting speed of ship and terminal together can be established. This inelastic collision will result in a speed of approximately 0.21 m/s. This speed will be used in the final design of the mooring system.

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