Abstract

Elastic mooring lines can keep stable bearing force even if the position of the attachment point on the floating body side move up and down and it is possible to suppress the motion of the floating structure. But it has never been applied to floating structures over 500m. Although the motion response of LFTS (Large-scale Floating Transposition Station for Loading Coal) moored with elastic mooring lines has been analyzed so far; it can be said that it is still insufficient to confirm whether or not it can actually be operated. Therefore; in this study; a parametric study was conducted due to changes in the conditions of elastic mooring lines and the sea conditions of the installation sea area. And then; the applicability of the elastic mooring system to a large floating body was examined by comparing the results of the motion response by the elastic mooring system and the catenary mooring.

Introduction

In recent years; Japan has been importing more than 90% of the coal it needs; with 80% supplied by Australia and Indonesia. Indonesia; which is the second-largest exporter of coal to Japan; is the main coal supplier in the Asia-Pacific region. Currently; Indonesia adopted a national coal policy that seeks to promote the development of the country's coal resources to meet domestic requirements and increase exports (Mitsumuroto; 2001). Therefore; increasing the efficiency of coal transportation in Indonesia is beneficial not only for Japan and Indonesia; but for other countries that import Indonesian coal. However; the shallow depth of the Markham River; by which coal is transported to coastal areas; is challenging for bulk carriers. Therefore; the LFTS system (Eto; 2016); which is used as a relay station between coal-barging barges for land and bulk carriers; was proposed.

LFTS is located about 10 km away from the land area; it stores coal carried by barge from the land area; and it is a facility that efficiently loads stored coal into bulk carriers. Therefore; it reduces the waiting time of bulk carrier; improvement of operation rates and profitability is expected. The LFTS system is designed to have a total coal storage capacity of 500;000 tons; which is equivalent to the total capacity of five bulk carriers. Depending on the loading condition of this coal; the draft of LFTS changes from 1.8m to 7.0m during operation; and the tidal range of this sea area is about 4.0m. Therefore; the attachment point of the mooring line on the LFTS side moves up and down about 9m under the influence of this; so it is important to consider a position holding control method that can respond to that movement. Examples of the method for controlling the position holding of the floating structure include elastic mooring which are examined in this study; dolphin mooring; chain catenary mooring; and application of DPS. Here; since LFTS is large and is installed in the sea area at a depth of about 30 m; it is necessary to prepare large dolphin piles in order to apply the mooring method by dolphin mooring to LFTS. In addition; position holding control by DPS is a system that can be moored regardless of water depth and draft; but it is considered difficult to apply it to LFTS from the viewpoint of the cost of installation and maintenance of the propulsion device. And since catenary mooring is a system in which position holding control is performed by its own weight; it may not be possible to fully utilize its characteristics at a water depth of 30m in the sea area where the LFTS is installed. Since sufficient water depth is not secured; it is expected that catenary mooring will be difficult to respond to changes in water depth and draft.

This content is only available via PDF.
You can access this article if you purchase or spend a download.