Ship Mooring Research Articles

Experimental Study on the Motions of a Mooring Ship in Mixed Waves

By employing the method of bimodal spectral simulations, a series of experiments were performed on a 266,000 m3 LNG ship moored to an island berth in mixed waves. In the physical model experiments, a special effort was made to investigate how changing wave conditions affect the motion responses of the mooring ship in mixed waves. Therefore, this paper mainly engages in the analysis of such effects resulted from wave condition changes of mixed waves from such perspectives as the distribution of high- and low-frequency energy, the periodic changes of low-frequency swells, the wave-height changes of low-frequency swells, and the wave-height changes of high-frequency wind waves.

Analysis of fracture and cracks of oldham’s couplings used in anchor hoisting. Case study

The usual failure of an anchor hoisting assembly was investigated. The anchor ensures stability in cases of ship mooring in a harbor, anchorage or bay and provides adequate safety combined with convenient and easy handling. For the anchor hoisting a hydraulic motor is used consisting of a main two-speed crankshaft, the oldham’s coupling and a valve spool. The oldham’s coupling of a specific oil-tanker frequently fails during the anchor descent and blocks the whole hoisting system. Three pieces used to the same anchor were examined. Two of them exhibited total fracture while the third one had been plastically deformed. The study involved chemical analysis, hardness measurements and in-depth examination of microstructures and fracture morphologies of specimens derived from the failed parts. The paper presents conclusions related to the fracture mechanism and the type of fractures respectively. It was found that poor design and wrong material selection were the main causes of failure.

Experimental study of solutions to reduce downtime problems in ocean facing ports: the Port of Leixões, Portugal, case study

Downtime at ocean facing ports is often related to excessive moored ship motions caused by wave action. This paper discusses the influence of local conditions on the operational problems at Berth “A” of Leixoes Oil Terminal, Porto, Portugal, and analyses the efficacy and suitability of selected interventions, either on the north breakwater or on the mooring system, to reduce the amplitude of moored ship motions. Mooring practices are also analysed. It was concluded that friction forces at the interface between the ship and the fenders have a significant effect on the moored ship response and effectively reduce ship oscillation amplitudes (especially the surge); while a slight modification of the mooring arrangement has a negligible influence on the ship behaviour. In addition, modifications to the harbour breakwater configuration taking into account local conditions improved Berth “A” operational conditions.

Accident caused by dynamic overloading of a ship mooring rope

An accident of a passenger ship happened during a docking manoeuvre on a lake in Switzerland. After a regular mooring manoeuvre was completed, the ship was exposed to a wind gust pushing the ship away from the wharf. In that moment the mooring rope ruptured and hit the head of a child. An investigation was commissioned by the federal authority to answer several questions related to the accident.It had to be clarified whether the used rope could fail without being pre-damaged and if the failure could have been prevented by the use of a thicker rope. In addition, the influence of the wind exposure on the loading of the rope should be quantified. The acceleration of the ship by a wind gust was simulated by means of analytical and numerical analyses. Hereby the main goal was to quantify the drag due to water motion. The analysis showed that inertia effects of the water flow around the ship body (motion) have to be taken into account and can be described by an additional hydrodynamic mass which has to be added to the deadweight of the ship.Through the investigation it could be shown that rope failure was possible without a pre-damage of the rope. It was also shown that the use of a thicker rope would have led to a dynamic load condition that is even more critical than for the use of a thinner rope due to its larger stiffness.

Ship-based CO2 Injection into Subseabed Geological Formations Using a Flexible Riser Pipe Pickup System

This report presents details of one aspect, namely, the flexible riser pipe pickup system, of a proposed ship-based carbon dioxide capture and storage (CCS) method. The liquefied CO2 (LCO2) to be sequestered is directly injected into subseabed geological formations through a flexible riser pipe using injection facilities contained onboard an LCO2 carrier ship. The flexible riser pipe remains on the seabed, one end attached to the injection wellhead, until the other end is hoisted up and connected to the (dynamic positioning system (DPS)-controlled) LCO2 carrier ship arriving at the ocean injection site. This proposed system has various advantages over the use of stationary sea surface structures for ship mooring and CO2 injection: i) no need for stationary sea surface structures, e.g., ship-mooring-buoy or platform; ii) simplifies ship handling, especially in rougher sea states; and iii) the flexible riser pipe can remain on the seabed in rough seas. Details of a pickup buoy system for retrieving the riser from the seabed and the structure of the flexible riser pipe are presented in this paper. The riser pickup system consists basically of shipboard equipment such as a coupling valve, crane, winches and A-frame and offshore equipment such as a pickup buoy, pickup float, messenger line, sinker and pickup wire rope. The flexible riser pipe, outer diameter of 309mm, was designed with due consideration of the stresses encountered with repeated retrievals from the seabed.

港内係留船舶のかく坐による津波対策に関する基礎的研究

In the author's study, the disaster survey and analysis on a moored VLCC's behavior during the 2011 off the Pacific Coast of Tohoku Earthquake Tsunami at 14:46 JST, 11 March 2011 was done by using the numerical simulation methods on ship motions and tsunami. On the other hand, several questionnaires for the moored vessels encountered with the disaster were reported, and it has been recognized that emergency evacuation from harbor basin to outside harbor is very difficult due to the lack of tug assistance and supports of the ship mooring lines, and the black-out during tsunami and after earthquake. In order to find out an effective emergency ship handling against tsunami for the moored vessel under the circumstances, an intentional ship grounding (stranding) before tsunami attacking has been investigated.

Remote Measurement & Control of Ship Mooring System

Based on thoughts of ship safety, one novel scheme of ship mooring remote measurement & control system is proposed, including information obtaining subsystem and remote control subsystem. The former is to detect mooring system’s environmental parameters such as wind speed, water speed, and anchor chain stress, then to submit such parameters to remote control center by wireless channel more than 2.4 GHz. The latter ‘s main body is the aforementioned remote control center and it’s based on an embedded WEB server with functions such as calculating probability of mooring movement, emitting alarming signal, etc. Except an ocean water speed detector invented by ourselves, the hardware design in this paper is based on IC (integrated chip).

Research on Independent Coarse Alignment of Aircraft Carriers SINS

Carrier-based Aircraft closely watched as the aircraft carrier weapons, storms and other factors affect the generated carrier swing to sway.This will enable the gyro measurement to the Earth's rotation angular velocity signal to noise ratio dropped significantly, giving the aircraft carrier's initialaligned to bring difficulties. To solve this problem, the Earth gravity acceleration in the inertial space the SINS independent coarse alignment, and gives the process of acceleration due to gravity points vector of analytic coarse alignment and fine alignment algorithm. Theoretical analysis and simulation results show that the moving base SINS alignment method can effectively solve the initial alignment of the aircraft carrier in the state of the ship mooring.

COMPUTER SIMULATION OF MOORED SHIP MOTION INDUCED BY HARBOR RESONANCE IN POHANG NEW HARBOR

This paper proposes a computational method for estimating moored ship motion taking into consideration harbor resonance, and provides a way to estimate the effect that harbor resonance has on moored ship motion. The computation of harbor resonance used the CGWAVE model, and the computation of moored ship motion used the three-dimensional Green's function method. This method was verified with field motion measurement data from actual moored ships and wave field data and down time record data from Pohang New Harbor. The resonance periods obtained from wave field data in Pohang New Harbor were 80, 33, 23, and 8 min, which were the long waves, and 42, 54, and 60 s, which were the infra-gravity waves inside the harbor slip. The simulation results for harbor resonance were compared to the actual wave field data. This study investigated whether harbor resonance has an effect on moored ship motion using simulated results of ship motion both with and without harbor resonance included. In the case of harbor resonance included, moored ship motion increased by 10-30% when compared with the results without harbor resonance included. We found that harbor resonance has a greater effect on the surge and heave motion of a large-sized ship and on the roll and the yaw motion of a small-sized ship.

Some initial findings from the very shallow water GulfEx12 reverberation experiments

In April 2012, reverberation and clutter measurements were taken in very shallow water (~20 m) over a 40 hour period off Panama City, FL. This work describes the data from this recent sea trial called GULFEX12 designed to characterize reverberation and clutter from a very shallow water site in the 2500-5500 Hz band. The received data are taken from one aperture of the Five Octave Research Array (FORA) namely, the triplet sub-aperture. The array was fixed 2 m off the sea floor by mounting it to tripods using a clothes line and data were passed by cable to a nearby moored ship (the R/V Sharp). An ITC source transducer was located 3 m away from the array center. Data show a surprising amount of anisotropy. Five different pulses were used in this study. Matched filtered polar plots of the reverberation and clutter are presented using the FORA triplet beamformer to map out anisotropy. Some model data comparisons are made using the author?s normal mode based reverberation model. Help from D.J. Tang, T. Hefner and K. Williams of Applied Physics Lab at Univ. of Washington was crucial to this effort. [Work supported by ONR code 322OA.]

RESEARCH ON WORK METHODS FOR TUGS IN PORTS

Tug assistance in ports for increasing ship maneuverability, mooring and unmooring operations is a very important issue. New tugs are given increased possibilities; nevertheless, at the same time, work methods for tugs, including advantages and disadvantages must be carefully studied, evaluated and practically applied. The article presents the results of the carried out research on the work methods of a new type of tugs, thus offering recommendations for how to avoid drawbacks of working with new tugs during ship mooring operations.

EXPERIMENTAL FORMULA FOR THE WAVE-INDUCED SHIP MOORING FORCE

The wave force dose not considered at the formula of mooring ship cable force in the Load Code for Harbor Engineering[JTJ215-98]. This brought the inconvenience to the calculation of designed cable force for mooring ship. By means of analysis for the laboratory model test result of mooring ship cable force under wave effect, Wave force formula of mooring ship under wave effect was gained. This formula well reflected the influence of ship size, ship load , ship rolling period, ship pitch period, wave period and wave height. The formula can be used in the calculation of standard value of mooring ship cable force under the wave effection, also it can be used to instruct the wave model test for mooring ship.
 
 
 References
 
 Zhang Ri-xiang. Liu Zhong-bo. Zhang Ning-chuan. 2003 .An Experimental Study on the Mooring Line Forces & Impact Forces of a Moored Ship Under the Combined Action of Wind,Wave and Current [J].,China offshore Platform, (01).15-18.
 
 Li Yan. Zheng Bao-you.Gao Feng. Meng Xiang-wei.2007.Model test study on the impact forces and mooring line forces of a moored ship under the combined action of wave and current [J].;The Ocean Engineering, (02).57-63.
 
 Ministry of transport of the People's Republic of China(1998).The Load Code for Harbor Engineering(JTJ215-98). [S].
 
 Jiang Qing. Ge Hong-zheng.Xie Peng.2007.Influence of Ship's Type and Tonnage on the Ship's Mooring Force [J]. Port & Waterway Engineering, (09).51-59.
 
 Wu Xiuhuan. 1999.Ship and maneuverability and seakeeping [M]. Ministry of transport of the People's Republic of China. p220.
 
 Zhang Wen-zhong. Etc.(2006): Model test of Mooring LNG ship at Jiangsu Provence, Tianjin Port Engineering Institute Ltd. of CCCC.

The hydrodynamic model for simulating the motions of a ship moored near the quay in waves

In this study, a hydrodynamic mathematical model for simulating the motions of a ship moored near the quay in waves is presented. The related hydrodynamic coefficients such as the added mass, damping coefficient and wave exciting force are calculated by the two-dimensional source distribution method. The strip theory is then applied to integrate the whole ship hydrodynamic characteristics along the ship length and the ship motion behaviors in waves can be obtained through the equations of motions. The bank effects are treated by using the image method which is similar to the treatments of the twin hull ship except the differences on some coupled hydrodynamic forces. The time domain simulation technique is made to analyze the motions deeply by using the 4th order Runge-Kutta method. Different wave conditions are considered with respect to different clearances between the ship and bank and shallow water effect is neglected for simplicity. The present results will be helpful for the design on the ship mooring system arrangement near the quay or the wharf.

係留船舶の長周期動揺に関する基礎的研究

係留船舶の長周期動揺に関する基礎的研究

HYDRODYNAMIC PERFORMANCE CHARACTERISTICS OF SEMICIRCULAR BREAKWATER—WAVE RUN-UP AND RUN-DOWN

ABSTRACT Breakwaters are structures protecting a shore area, harbor, anchorage, or a basin from the fury of ocean waves. They create calm waters and give protection for safe mooring, operating and handling of ships, and provide protection to harbor facilities. Semicircular breakwaters are becoming increasingly popular these days, as they have high stability against the action of waves. The paper explains the physical model studies to evaluate the wave run-up (Rd/Hi) and wave run-down (Rd/Hi) on semicircular breakwater model for various incident wave heights H, wave periods T, water depths d and spacing (S) to diameter (D) ratios of perforations (S/D). It is found that relative wave run-up increases with the increase in wave steepness (Hi/gT2) and relative run-down decreases with the increase in wave steepness. Relative wave run-up and wave run-down values increase with the increase in depth parameter (d/gT2). The relative run-up and run-down values decrease with increasing perforations (decreasing S/D values) in breakwater.

Cause and countermeasure of long-period oscillations of moored ships and the quantification of surge and heave amplitudes

Long-period oscillations of moored ships whose periods are about 1 or 2 min cause many troubles in many ports and harbours. It is necessary to investigate these phenomena and verify their causes and countermeasures in each case because they are strongly dependent on the environment of each port and harbour. From this point of view, long-period oscillations of moored ships in the Port of Shibushi in Japan were investigated by means of wave observations, the image processing of moored ship motions using the video camera and motion-capture software and numerical simulations. From observation results, the relationship between offshore long-period waves and long-period oscillations of moored ships was recognized and surge and heave amplitudes were quantified by using wave data in order to forecast moored ship motions. Furthermore, from observation and numerical results, it was revealed that long-period waves with the peak period of 120 s from the offshore typhoon kept or exaggerated the local harbour oscillation of 60–70 s and it caused long-period oscillations of moored ships. Numerical results in case of reducing the reflection coefficient of the target berth implied that it ceased the local harbour oscillation and it would give an effective countermeasure to reduce long-period oscillations of moored ships in the Port of Shibushi.

A study on the optimal configuration of harbor structure under the combined loads

Response of harbor structure to environmental loads such as wave load, impact load, ship`s contacting load, is a fundamental factor in designing of the structure`s optimal configuration. In this paper, typical environmental loads against coastal structures are investigated for designing of the optimal harbor structure. Loads to be considered here are wave load, impact load and contacting load due to ship mooring. Statistical analysis for several harbor structure types under the corresponding loads is carried out, followed by investigation of effect of individual environmental load. Based on these, the optimal configuration for the harbor structure is obtained after considerable engineering process. Estimation of contacting load of the ship is suggested using effective energy concepts for the load, and analysis of structural behavior is done for the optimal designing of the structure in the particular load. A guideline for the design process of the harbor structure is established, and safety of the structure is examined by proposed scheme. For verification of the analytical approach, various steel-piled coastal structures and caissons are chosen and relevant structural analyses are carried out using the Finite Element Methods combined with MIDAS/GTS and ANSYS code. It is found using the Morison equation that impact load cannot be a major load in the typical harbor structure compared with the original wave load, and that configuration shape of the structure may play an important role in consideration of the response criteria.

In Situ Characterization and Noise Mapping of Ships Moored in the Port of Venice

The acoustical characterization and the mapping of noise emitted from ships were carried out on behalf of the Venice Port Authorithy in the frame of the European Project NoMEPorts (Noise Management in European Ports). According to the Directive 2002/49/CE (END), different noise sources (like roads, railways, aircraft, industrial sites, ports) have to be considered and mapped separately; so, in the first step, the acoustical characterization of ships is required. Annex IV of the Directive, in particular, establishes that the strategic noise maps for agglomerations shall put a special emphasis on the noise emitted by, inter alia, industrial activities, including ports. Three kinds of ships were investigated, using the Italian technical standards UNI 10855 and UNI 11143: 1. inland navigation ships (along wharves); 2. ferries (along wharves and when maneuvering); 3. cruises (along wharves and when maneuvering). As for the maneuvering, it could be said that a supplementary noise indicator is needed, as the END, Annex I, forsees in the case the average number of noise events in one or more of the day periods is very low (for example, less than one noise event an hour).

Effect of Structure Types of Quay Wall on Moored Ship Motions

The ship motions moored along quay wall depend on external forces such as waves and wind, ship's hull form, mooring system such as fender and mooring line, and structural type of quay wall. In this paper, the effect of the structure types of quay wall is investigated based on model test and numerical simulation which uses Green function; G = log R. In the numerical simulation, the accuracy of theory in low frequency region is also discussed.

Characteristics of low-frequency motions of ships moored inside ports and harbors on the basis of field observations

In order to understand characteristics of low-frequency motions of ships moored inside ports and harbors, analysis on actual cargo handling logbook of stevedoring services company, including events of interruption of cargo handling, and countermeasure for ship mooring problems are investigated by field observations at two ports and numerical simulation on moored ship motions. First model port concerns with interruption of cargo handling due to the low-frequency motions. Second model port relates to a resonant effect of long-period waves or harbor oscillations, and its countermeasure by mooring system. From the investigation, it is confirmed that the low-frequency motions of ships are induced by a resonance between surge motions and long-period waves or harbor oscillations and an asymmetry in the mooring system, and affect safe ship mooring and operation efficiency of cargo handling in ports and harbors significantly.