Moored Ship Motions Research Articles

Basic Research on the Relation Between Mooring Criteria and Typhoons at Harbour Facing to the Pacific Ocean

Mooring troubles due to moored ship motions in a harbour facing the open sea are very serious problem from the point of view of the port operation. Some studies about a wave prediction are carried out, however, the accuracy of the prediction isn't still enough exact, especially in case of a rapid wave growth at stormy weathers. In this study, we focus on a harbour facing the Pacific Ocean, and research on mooring troubles which are happened in 1997-1998. Furthermore, observed wave data by NOWPHAS system and typhoon data are analyzed. Thus, we consider the relations among mooring troubles, observed wave conditions, and typhoons from the point of view of the mooring criteria.

長周期波作用下でのRoll共振動揺により誘発される港内係留船舶の長周期動揺特性について

長周期波作用下でのRoll共振動揺により誘発される港内係留船舶の長周期動揺特性について

BASIC RESEARCH ON THE CONSTRUCTION OF WEATHER-PROOF MARITIME TRANSPORTATION SYSTEM USING THE MEASUREMENT EQUIPMENT OF SHIP MOTIONS

In harbours facing to the open sea, long breakwaters tend to be built to decrease wave heights. Also, it is cleared that the influence of moored ship motions has to be considered. On the other hand, ship motions at harbour entrances due to waves are one of the most serious problems in ship handling. However, ship motions near harbour entrances are not discussed and observed so much. Therefore, it is necessary to research on ship motions offshore and near harbour entrance. In this study, we observe ship motions during the navigation, entering to and departing from harbours. Ship motions are measured by the new type of measurement equipment consisted of GPS, optical fiber gyro and gyro compass. Observed data at the departure from the harbour shows that the rapid growth of ship motions can be recognized as the important factor, which causes the difficulty of ship handling near the harbour entrance. So, it is verified that harbours should be constructed and operated based on the numerical influence of ship motions due to waves near harbour entrances and offshore.

大型船・小型船における船体運動に与える初期張力の影響について

A suitable ship mooring achieves not only a safe mooring but also an economical and effective cargo handling operation. Moored ship motions are generated during waves, winds and other external forces. The excessive motions disturb the cargo handling operation and happen to derive some damages of the mooring lines and fenders. An empirical and traditional role of mooring such as a pretension mooring (a hard mooring) or a slacked mooring is operated on each size of ships on site. In this paper, field observations for 250, 000DWT class VLCC (Very Large Crude Carrier) and 3, 590DWT cargo ship were carried out. We observed the moored ship motions, waves and winds. As the results, the mooring methods for VLCC and 3, 590DWT ship were the pretension and slacked mooring which were as same as the empirical methods. Then, we tried to reproduce the moored ship motions of each observation using a numerical simulation method of moored ship motions. The objective of this study was to evaluate whether the empirical and traditional role of mooring was a suitable and reasonable mooring using the simulation. It focussed therefore on the ship motions and mooring loads corresponding to the pretensions of mooring lines.

BASIC RESEARCH ON THE PLANNING AND THE OPERATION OF MOORING EQUIPMENT AT CONTAINER TERMINALS THAT FACES THE OPEN SEA

Moored ship motions due to long period waves become the serious problem, those phenomenon are happened in harbors which faces the open sea. Container terminals have been built in harbors at inside bay by now, however, some container terminals are planned and built in a harbor which faces the open sea area because of container carriers of larger sizes. Container carriers have more serious limit values of cargo handling than bulk carriers, tankers, etc. In this study, firstly, we research about the operation situation of container terminals which are working now and operational plans of new container terminals that which faces the open sea. Secondly, we examine about the design of mooring equipment of container terminals by using numerical simulations of moored ship motions considering long period waves, swells and winds. At last, we consider about the facility design of container terminals which faces open sea in the future.

湾水振動を考慮した港内係留船舶の時系列解析

湾水振動を考慮した港内係留船舶の時系列解析

3Dトラッカーによる新しい係留船動揺監視システムの提案

The wharf operation efficiency should be defined based on the allowable ship motions for cargo handling. Especially it is very important to estimate the long period horizontal motions, surge and sway, at the berth. Some mathematical models have been developed and many experiments were carried out to simulate the motions in waves. But these results should be compared with more exact actual field data. Because of the ability of instrument and an operational cost, a few field observations of moored ship motions have been carried out. Moreover it was impossible to measure the long period horizontal motions by the conventional instrument using an accelerometer. In this study, the observation method of three dimensional positions of the targets using the "3D-Tracker" is described as well as the 6-component motions of ship. We propose two new motion monitoring system of moored ship. One is "absolute system" in which there are two CCD-cameras on a quay wall and the targets on a ship. The other is "relative system" in which the cameras are on a ship and the targets are on a quay wall. The field measurements are carried out, while the accuracy of the motions is confirmed by the indoor experiments.

係留限界を支配する諸要因に関する基礎的研究 : うねりと季節風が卓越する海域に立地する港湾の場合

A lot of studies about mooring ship motions have done in recent decades, but they are focused on cargo handling criteria. At some ports in open sea, mooring ships move so hard and sometimes mooring lines or fenders are broken. So, when we think about mooring criteria, we have to consider a lot of parameters. In this paper, we study about these parameters and we pick up some cases of mooring accidents at the harbor face to Pacific Ocean. And we find out the results as follows : (1) We can't argue about the mooring criteria correctly if we focus only on ship motions. (2) We can clear up the relation between cargo handling criteria and the mooring criteria. (3) Mooring accidents tend to take place in winter season than other seasons in these cases. (4) In most of those accident cases, mooring ships should shift to offshore earlier stage. (5) The required time length when ships shift to offshore depends on the ship type, the cargo handling way, etc. (6) The difficulty of wave prediction makes so hard to make out mooring criteria. (7) We have to consider long period wave in case of considering the mooring criteria. (8) There are trade off relations between the safety of mooring ship and the berth efficiency. (9) It is necessary to grasp the effect of moored ship motions by wave and wind correctly, if we want to avoid mooring accidents.

Basic Research on Progressing Safety of a Sea Berth in Open Sea and a Berth Operation Support System

Suspending of cargo handling caused by moored ship motions is serious problem at sea berths facing to open sea area. In this paper, we focus on a tanker sea berth facing to the Pacific Ocean. And we research about the berth operation of the sea berth firstly. Secondly, we measure and analyze the wind waves and swell data at the berth. We simulate mooring ship motions under these waves and winds, then we compared with the hearing result from the berth master and the simulation result. Finally, we propose a berth operation support system for a safe berth operation.

Field Observation of Ship Motions using 3D Tracker

A few field observations of moored ship motions have been carried out. But it was impossible to measure long period horizontal motions by using a accelerometer. In this study, the observation system of three dimensional motions of moored ship using 3D traker is described. The field measurement of a small craft motions is carried out and the results are compared with those by the other equipment. The applications of the system are also discussed in the paper.

湾内港湾と湾外港湾の年間稼働率の比較に関する研究

In Japan, large main ports are located in the area where sea conditions are good and they are near the big cities. But recently it is pointed out that this area is not necessarily desirable as harbours in all aspects. The Ministry of Transport is planning to build new ports outside bay. But the outside ports have serious natural conditions than inside ones. Then we simulate one-year workabilities by using the harbour tranquility and a moored ship motion. We introduced the "ASYMMETRICAL AMPLIFICATION FUNCTION", which explains easily a phenomenon of Subharmonic Motion. The obtained results can be summarized as follows : (1) When we simulate one-year workability of harbours, we have to consider the wave height in a harbour, ship entry into port, and moored ship motions. (2) The maximum value of the amplitude of Subharmonic Motion X_<max> can be expressed as the sum of the maximum value of amplitude in case of free vibration X'_<max> and the amplitude in case of symmetrical mooring ζ_<max>. (3) We consider the Subharmonic Motion. Then we introduce AS (T) : "ASYMMETRICAL AMPLIFICATION FUNCTION" which can explain this complicated phenomenon easily. The value of AS (T) increase rapidly from about 40 of spring constant ratio. AS (T) is 1 at harbours inside bay as the incident wave period is short, but it becomes several times as the wave period is long at harbours outside bay.

船体離岸防止装置作用下での船体動揺の近似計算手法について

In the previous paper, we carried out model tests under wave action in order to investigate motions of a ship moored by the prevention system of ship separation from quay wall. In this paper, we introduce an approximate calculation method of ship motions under system. The obtained results are summarized as follows : (1) Excluding the wave force and moment over a range of the prevention system, we can calculate the moored ship motions under the system. (2) The ratio of dynamic wave force to static force of the system can be calculated, and our experiments are performed under the condition of same order of both forces. (3) Even if horizontal wave moment is larger than the static moment of the system, roll motions become small by an increased damping force due to the ship side wall contact with fender.

岸壁前面での船体運動におけるストリップ法の改善について

Authors proposed the strip method of ship motions moored along quay walls. But its calculation method is not good in quartering seas. It is considered that the estimation method of the exciting forces is not appropriate in that case. In this paper, an improved calculation method of the exciting forces is proposed and the experiments of moored ship motions are carried out to verify the method.

THE TIME DOMAIN ANALYSIS ON MOORED SHIP MOTIONS

The ship refuge inside a harbor in storm requires the analysis of moored ship motions along a quay wall. In this case the time domain analysis with the convolution integral method becomes effective. But the calculation accuracy is not enough and must be improved to analyze actual moored ship motions. In this paper some methods of the improvement are proposed and their efficiency is verified by comparing the calculation results with the experimental ones.

斜面前面における係留船の船体運動について

The moored ship motions depend on hull forms, mooring systems, the structual type of quay walls and so on. In this paper, particularly, concerning with the ship motions moored along a quay wall which has a slope, two-dimensional analysis proposed by Ijima and the experiments are carried out. The obtained results are summarized as follows: (1) The agreements of the theoretical and experimental results of the ship motions are fairly well. (2) The results obtained on the assumption that a distance between an imaginary boundary line and a floating body is equal to an incident wave length are almost similar to those obtained when the distance is given by Eq. (15). (3) The ship motions moored along a slope are approximated by those moored along a vertical solid quay wall.

岸壁前面における三次元浮体の流体力係数の周波数特性について

The time domain analysis with the retardation functions is important in the research of moored ship motions. The hydrodynamic coefficients are required in a whole range of frequenies to calculate the retardation functions. Few examples of 3-D floating body moored along a quay wall exist, and those calculations are not satisfactory. In this paper are proposed, the calculation methods are proposed to improve the accuracy of hydrodynamic coefficients and the retardation functions.

Dash-Potによる短周期船体運動の低減化に関する一考察

In harbors attacked by swells, cargo handlings are often interrupted by severe ship motions in waves. Furthermore, mooring lines of ships are sometimes broken due to ship motions. Authors develop a new mooring system containing dash-pots in order to reduce the moored ship motions. The system is investigated experimentally and analytically. The results obtained from this analytical model indicate a good agreement with the experimental ones. So the moored ship motions with various kind of dash pots are calculated by this analytical model. As the results, it is clarified that the mooring system with dash pots is very useful for the ship to reduce the moored ship motions. Further the design of optimum dash pot is proposed.