Introduction
Tianjin Port is situated at a central position on the west coast of Bohai Bay. It is 66 km away from the downtown of Tianjin city and roughly a distance of 170 km to the city of Beijing. The port owns a total quay line length of about 14,464 m and about 76 berths of various types which are operated by 11 terminal companies.
In recent years, Tianjin Port has seen continuous rapid growth of cargo throughput. In the period from 2000 to 2005, the total throughput of the port has been growing at an average annual rate of 20.3 per cent. In 2005, the total cargo throughput of the port reached 240 million tonnes, including 4.80 million TEUs of containerized cargoes.
Tianjin Port is ranked in top 10 in the world’s largest ports according to throughput capacity and is the largest man-made port in China, with its approach channel (40 km in length, 234 m in bottom width and –17.4m in water depth) formed entirely by dredging.
It is planned that between 2006 and 2010, a fund of 27.68 billion yuan will be invested in the construction of port facilities, including a number of bulk cargo berths in the South Harbour Zone accommodating ships such as oil tankers up to 250,000 dwt, as well as more than ten container berths of 100,000 dwt class in the North and East Harbour Zone.
Meanwhile Tianjin Port is planning to upgrade the approach channel to allow access by ships up to 250,000 dwt. It is wondered, with the exception of satisfying the requirements of creating access for ships of 250,000 dwt, how effective the new channel conditions will be in cutting short the average time ships wait for channel availability? Will the channel still be able to meet the demand from the fleet of ships accessing the port when the port is further developed with increased throughput?
If the answer is negative, when should the second channel be dredged?
To answer the question, a joined theme study group was set up by Tianjin Port Group Ltd and the First Design Institute of Navigation Engineering (FDINE) to specifically study the navigation capacity of the approach channel of Tianjin Port against three phases of port development by using a mathematic modeling method.
Computing method
A port system that consists of factors such as ship, channel, berths and handling operation is a random service system with multiple random factors and complex dynamic relations. Within this system, affected by the random factors such as ship arriving time and duration at berth, the operation of the channel is rendered into a status of an unbalanced busy-idle pattern that has certain impacts on the normal utilisation of the navigability of the channel.
On the other hand, the constrains of channel conditions and natural conditions will also prolong the non-production waiting time of ships (at berth or anchorage), generating a ‘bottle neck’ phenomenon, which, at serious status, will affect the throughput capacity of the wharves and cause a great waste of the transportation capacity of the ships. For such a complex system with multiple factors interacting with each other, the conventional system analytic method would fail to make quantitive analysis. Therefore, the theme study was performed by using the computer simulation method.
The study was performed in the following process: The port system was first analysed. By means of theoretical analysis, data statistics and field investigation, mathematic models were established for the subsystems and components that constitute the complete system. Then the math models of the subsystems were converted into a simulation model of the complete integral system.
The model was then used on a computer to dynamically simulate the port system operation for a certain period of time, so as to calculate out the technical indexes that reflect the status of the system operation. Finally, the navigability of the channel was evaluated by analysis of the affects of the factors of the channel on the system operation.
System analysis
The process of analysis on the system is the effort to describe, from viewpoint of mathematical regularity, each element that constitutes the integral system, and to quantify the system regulations. The components of the Tianjin Port system are described as follows:
1. Navigation Channel
In the math model, the Main Channel and the Northern Branch Channel are chosen as the object of study. The configuration of the channel system is shown in Figure 1.
(I) Major Dimensions of the Main Channel
Channel class: 250,000 dwt
Length: 44 km
Bottom width: 315m
Water depth: -19.7m
The Northern Branch Channel is about 8.9 km long, capable of allowing two fully loaded container carriers up to 100,000 dwt to access the port and leave the port at the same time. The North Branch Channel joins the Main Channel axis at the location of mileage of 9.8 km of the Main Channel.
