Ship Mooring Research Articles

New evaluation of ship mooring with friction effects on mooring rope and cost-benefit estimation to improve port safety

Abstract To ensure safe port operations around the world, it is important to solve mooring problems. In particular, the many ports that face open seas have difficulties with long-period waves. As a countermeasure, the installation of a breakwater is proposed for mooring safety. However, this often cannot be put into practice because of financial issues. Instead, port terminals control berthing schedules with weather forecasting. However, mooring problems remain unsolved, because of inaccurate wave forecasting. To quantify the current situation, numerical simulations are presented with ship motions, fender deflections, and rope tensions. In addition, novel simulations for mooring ropes are proposed considering tension, friction, bending fatigue, and temperature. With this novel simulation, the optimal mooring method in terms of safety and economic efficiency was confirmed. In terms of safety, the optimal mooring method is verified to minimize dangerous mooring situations. Moreover, the optimal mooring method shows economic benefits and efficiency. It can help to reinforce the safety of port terminals and improve the efficiency of port operations.

LONG-WAVE MITIGATION STUDY FOR THE PORT OF NGQURA

Solutions to the long-wave induced moored ship motion problems at the Port of Ngqura were investigated in this study. Long-wave mitigation options were modelled with various layout modifications to the present model of the port, which has been validated with measured data. The numerical model simulations were used to derive long-term data sets inside the Port. Several moored ship motion simulations, using alternative conventional and dynamic mooring options, were performed for an extreme wave and wind condition for each berth at the port. Preferred port layout options and optimal mooring solutions were then determined for each berth. A complete framework of wave and ship motion simulations were performed for the preferred mitigation options. The ship motions and mooring line forces were determined for the relevant vessels at selected berths. This allowed for berth operability and downtime statistics to be determined, taking the limiting wave height and allowable mooring line criteria into account. Since several port layout options and different mooring arrangements were assessed, a Multi-Criteria-Analysis (MCA) was followed to determine the best possible solution.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/y79b158riGE

PREDICTING INFRAGRAVITY WAVES IN HARBOURS - AN EVALUATION OF PUBLISHED EQUATIONS AND THEIR USE IN FORECASTING OPERATIONAL THRESHOLDS

Infragravity (IG) waves have received considerable study since the 1950s (Munk, 1949, Bertin, 2018), allowing their generation, propagation and impacts to be more effectively quantified. Here, we are concerned with the frequencies that directly excite motion in moored ships, thereby creating problematic and often unsafe conditions. Operational knowledge gained in surge-affected ports in Australia and New Zealand revealed IG height thresholds common to all locations (McComb, 2011), with wave periods from 25 to 120-150s being causative. A further observation that the IG spectral shapes at berths remain relatively constant regardless of the incident short wave spectra (McComb, 2014) allows robust predictive methodologies to be developed to forecast the onset and the passing of these empirically-derived values. The governing IG height thresholds are: Hsless than 0.10m is safe and manageable for a well-tendered vessel; at Hs 0.10-0.15m caution is advised and additional management is recommended, and at Hsgreater than 0.15m active management is required. Management options include shore moorings, pneumatic fendering, ShoreTension, MoorMaster etc. Without intervention, IG conditions greater than 0.20m are universally considered dangerous. Further, IG heights are strongly modulated by tide at certain locations (Thomson, 2006), which creates rapidly changing conditions that compound the difficulties ensuring safe and effective operations. We selected five published methods to predict nearshore IG height (Lara 2004, McComb 2005, Okihiro 1992, Arduin 2014 and Cuomo 2017) and undertook an evaluation of their efficacy at two energetic ports on opposite sides of the Earth. The ports of Gijon in Spain and Taranaki in New Zealand both experience problematic moored ship motions and have been subject to numerous studies of their wave dynamics over previous decades. Consequently, there is a body of knowledge, operational experience and local data to make an evaluation. The purpose of this work is to offer pragmatic guidance to the developers of operational forecasting systems on the optimal method to predict IG heights for safe mooring of ships at berth. Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/8oCRQkMdcIo

On the reliability of the 3D steady RANS approach in predicting microscale wind conditions in seaport areas: The case of the IJmuiden sea lock

Coastal areas and seaport areas are exposed to high wind speeds which may involve risks for the ships and people working in the area. Therefore, knowledge of the microscale wind conditions is essential for safe maneuvering and mooring of ships and optimizing harbor design. In the present study, 3D steady RANS CFD simulations with the realizable k-ε turbulence model are performed for the new configuration of the “IJmuiden sea lock” in Amsterdam, the largest sea lock in the world at the time of writing this article. The computed wind speed and turbulence intensity amplification factors and the local wind directions are validated with on-site measurements for the old configuration of the sea lock. For the wind speed amplification factor and local wind direction, a satisfactory agreement is obtained with 90% of CFD data within ±30% from the measured data. Conversely, for the turbulence intensity amplification factor, less satisfactory agreement is found with 74% of CFD data within ±30% from the measured data. Overall, the 3D steady RANS approach shows a sufficiently high reliability for predicting the wind conditions in the seaport area under neutral atmospheric conditions.

Cyber-physical System to Help Moor a Ship

A method of organizing an information cyber- physical system to assist in the mooring process has been considered in the article. It describes ways to organize the mooring of ships to the berth. The problems that occur during this operation have been listed. As the mooring process is labor- intensive and depends on the human factor, a system that will provide up-to-date real-time information to facilitate the mooring operation has been regarded. The structure and stages of development of the proposed solution have been described. The features of the selected elements have been indicated. Obtaining preliminary sensory results from two ports makes it possible to begin the next stage of system development.

Optimization of Continuous Berth Scheduling by Taking into Account Double-Line Ship Mooring

“Double-Line Ship Mooring” (DLSM) mode has been applied as an initiative operation mode for solving berth allocation problems (BAP) in certain giant container terminals in China. In this study, a continuous berth scheduling problem with the DLSM model is illustrated and solved with exact and heuristic methods with an objective to minimize the total operation cost, including both the additional transportation cost for vessels not located at their minimum-cost berthing position and the penalties for vessels not being able to leave as planned. First of all, this problem is formulated as a mixed-integer programming model and solved by the CPLEX solver for small-size instances. Afterwards, a particle swarm optimization (PSO) algorithm is developed to obtain good quality solutions within reasonable execution time for large-scale problems. Experimental results show that DLSM mode can not only greatly reduce the total operation cost but also significantly improve the efficiency of berth scheduling in comparison with the widely used single-line ship mooring (SLSM) mode. The comparison made between the results obtained by the proposed PSO algorithm and that obtained by the CPLEX solver for both small-size and large-scale instances are also quite encouraging. To sum up, this study can not only validate the effectiveness of DLSM mode for heavy-loaded ports but also provide a powerful decision support tool for the port operators to make good quality berth schedules with the DLSM mode.

Modeling a Berth with a Moored Ship under Wind Wave Loads

The algorithm and results of calculating the impact of the moored ship under the wind, current and wave loads on the berth are presented. The methodology is presented on the case study of calculating the mooring system of a massive floating object in the Kola Bay, for which numerical modeling and forecasting of hydrometeorological factors have been carried out. The calculations are performed using the SCAD complex with a simplified modeling of mooring lines. In the conclusions, the regulatory methodology for finding the loads from weather factors on the ship is analyzed; problems of using regulatory documents are formulated.

The Propagation of Landslide‐Generated Impulse Waves and Their Impacts on the Moored Ships: An Experimental Investigation

The effective prevention and reduction of the hazardous impact of landslide‐generated impulse waves on the moored ships are crucial for the sustainable operation of the reservoirs. Although the investigations of landslide‐generated impulse waves have been widely studied in the past decades, few efforts involved their impacts on the moored ships. The authors in this paper specifically examine the hazardous impact of the impulse waves on the moored ships by applying the physical experiments. Considering that the impulse wave was an external force acting on the mooring line, the impulse wave generation, propagation, and its impact on the moored ships are hence explored in detail. The results indicate that the impact of impulse waves on the moored ships was mainly due to the first wave amplitude and height, and an exponential function relationship between the relative wave height and wave crest amplitude was revealed. Furthermore, the attenuation of the maximum wave crest amplitude was approximated by a power exponential function. On this basis, the mooring tension could be calculated based on the linear relationship between the mooring tension and wave height. Ultimately, the safety of the moored ships in the port can be evaluated.

Experimental and modelling study on the response of mooring container ships in port under medium to long period waves

For understanding the influence of medium to long period waves on the dynamic response of ships, the hydrodynamic analysis of three typical moored container ships under wave interaction is carried out based on potential flow theory. The calculated and experimental results comparison shows that the numerical calculation is more suitable for simulation of long-period wave, as the dynamic response of ship is larger, but more accurate. For the larger ship, the peak response period of the mooring system usually reaches 100 s because the mooring stiffness is relatively small. With extended wave period, the ship motion response increases almost linearly. The symmetrical mooring arrangement and the similar mooring stiffness can effectively reduce the inhomogeneity of mooring forces. In addition, the ship motion and mooring force response can reach a minimum value at a special angle between ship and wave.

General Principles of Constructing a Motion Control System for a Remotely Operated Sea Vessel in the Port Area Based on the NMEA-2000 Network Protocol

The paper is concerned with the current state of the question of using unmanned ships in the field of water transport, as well as the most promising areas for applying remote ship piloting technology. The organization of information systems for data transmission is considered in detail, and relevant protocols are proposed. Technical solutions for equipping specialized unmanned transport vessels for piloting and mooring of heavy cargo ships are also proposed.

APPLICATION OF CFD FOR CALCULATION AND SIMULATION OF ANCHOR-CABLE TENSIONS IN MOORING SHIP

Computational Fluid Dynamics was applied to early hydrodynamics research, and the name CFD originated here. CFD has been developed, applied, and highly effective in the fields of fluid mechanics and deformation and elastic environments. CFDs are widely applied in advanced sciences and high technology as well as maritime sciences. In recent years, many scientists have effectively exploited and applied CFD and numerical methods for calculating and simulating the hydrodynamics of ocean current on ships. Simulating studies on the effect of ocean current on the tension of anchor-cable by CFD are becoming more and more popular. In this paper, from the theoretical basis related to the tension problem of mooring cables, the authors have proposed a simulation model that applies CFD to research and develop simulation model and calculate tension of cables in mooring ship. The goal of this study is to build a simulation model that is closest to reality so that we can study assumptions of different situations. Also, the achieved results will be the basis for proposing warnings to minimize marine accidents at the mooring area at the ports in Vung Tau, especially for tanker fleets. The authors have developed general implementation procedures, and specific calculations for several different input cases on a ship hull based on data of wind and flow characteristics at Vung Tau anchorage area, namely the oil tanker M/T AULAC JUPITER of Au Lac Joint Stock Company.

Physical Modelling of Motions and Forces on a Moored Ship at the Leixões Port

This paper describes the physical model, experimental setup and tests performed at the Portuguese Civil Engineering Laboratory (LNEC), to study the motions and forces of a moored ship at the Leixões port, for different sea states in irregular waves. The tests were carried out at one of the wave tanks of LNEC, where the Leixões port layout was implemented at scale 1:80 with the detailed model similar to the prototype bathymetry and surrounding structures. The moored ship is a 3.43 m long scale model of the well-known “Esso Osaka” tanker and is moored to the pier A of the oil terminal at 0.135 m draft. Several types of measurements were recorded in this study. The free-surface elevation and wave direction were measured with a set of resistive wave gauges. The wave velocities at the entrance of the harbour were measured with an acoustic Doppler velocimeter. Motions of the moored ship were measured with the OptiTrackTM motion capture system whereas forces on fenders and mooring lines were measured with load cells attached to a complex spring system developed at LNEC. Several tests were carried out for a number of incident sea states characterized by a JONSWAP spectrum, with different significant wave heights and peak periods. The measurement, analysis and results obtained for the incident wave conditions characterized by a significant wave height of 6 m and a peak wave period of 14 s are presented and discussed in this paper.

Application of Fuzzy Fault Tree Analysis (FFTA) to maritime industry: A risk analysing of ship mooring operation

Risk assessment has always been a serious concern in maritime transportation since shipping activities can pose potential harm to human life, commodity and maritime environment. Maritime safety researchers, in this context, are trying to enhance risk mitigation measures. This paper attempts to provide an insight into a process of accident development related to risks in ship mooring operation which presents a great challenge for ship's crew. A Fuzzy Fault Tree Analysis (FFTA) is adopted to perform systematic risk analysing on the case of ship mooring operation. The FFTA is capable of tackling limitations of conventional Fault Tree Analysis (FTA) where handling the uncertainties is possible with fuzz logic theory. A real maritime accident is analysed considering potential risks: the case of M/T Zarga which occurred during berthing manoeuvring to LNG (Liquefied Neutral Gas) terminal. The ship crew was seriously injured on his head during accident. To this end a risk model is developed and some risk control options are proposed. Besides handling data shortage in maritime risk assessment, this paper provides practical contributions to maritime professionals in course of risk mitigation and accident prevention.

A site-specific CFD study of passing ship effects on multiple moored ships

A site-specific CFD study of passing ship effects on multiple moored ships

Simulation of Mooring Lines Based on Position-Based Dynamics Method

The Position-Based Dynamics (PBD) method considers the rope as a series of particles in rope simulation. This paper introduces the PBD method and simulates mooring line in ship mooring simulation training system with four constraints, which are distance constraint, bending constraint, Long Range Attachment (LRA) constraint and pin constraint. In this paper, the LRA constraint method is applied to solve the overstretch problem of mooring line simulation caused by distance constraint and bending constraint. A pin constraint which combines two particles into one is put forward to achieve the connection effect between cable and the eye splice as well as the interaction between anchor and chain. Moreover, the method of Continuous Collision Detection (CCD) constraint is proposed to realize the collision detection between mooring lines and other objects. Compared with Newton's method, our adopted method is more efficient and robustness. Since it has sufficient visual plausibility and can realize real-time visualization, the simulation system developed by PBD method has a good training effect for crew.

A SLACK MOORING FOR A LARGE SHIP UNDER BEAM SEAS IN PORT

As an empirical and traditional ship mooring method, a pretension mooring (a hard mooring) or slack mooring (without pretension in mooring line) is performed for large ship or small ship, respectively. However, the slack mooring is applied to a large ship under beam seas in port to avoid large roll and sway motions, and excessive loads in mooring lines and fenders. In this study, the mechanism and validity of the slack mooring for large ship is investigated by a physical model test and a numerical simulation method of the moored ship motions and mooring loads under beam seas.

WAVE FORECASTING AT THE SITE -- A PRACTICAL SOLUTION FOR TERMINAL OPERATION AND PLANNING

Due to the capital investment cost, procurement and construction schedule, and in some cases the permissions and environmental restrictions, the oil and LNG terminals tend to move more offshore nowadays. Survivability of the facility and operational downtime becomes an issue because of the considerably more challenging metocean conditions. In most cases, metocean conditions (typically related to swell) that dictate terminal operations are determined from ship mooring studies. A slight variation in wave height, period or direction could shift the condition from ‘operational’ to ‘downtime’. However, how do commissioned terminals make critical decisions on whether or when to shut down operations? A precise wave forecast at the terminal site becomes more critical than ever for terminal planning and operation.

Management Control Systems in port waste management: Evidence from Italy

This study investigates Management Control Systems (MCS) in supporting Port Authority (PA) decision-making processes to prevent and reduce negative environmental effects from seaports. We focus on information management (data collecting, processing and reporting) in the inter-organisational relationships system established among the stakeholders involved in the arrival, mooring and departure of ships in port destinations, evidencing whether the control function exclusively consists of compliance with the MARPOL 73/78 convention and port regulations. Drawing on a deep review of the regulations and literature on environmental issues in seaports and MCS for environmental sustainability and energy efficiency in the port sector, we conducted semi-structured interviews with port users in one Italian seaport. The results show that more detailed information and reporting are needed to improve performance, especially during the mooring of the ships, as well as, MCS could support information for all players, especially the PA, in making developmental decisions about seaports. Key Performance Indicators (KPIs) are provided for measuring and controlling the effectiveness and efficiency of the waste management process in the port sector. Theoretical and managerial implications are discussed.

A Comparative Study on the Motions of a Mooring LNG Ship in Bimodal Spectral Waves and Wind Waves

By adopting the method of a series of physical model tests, a study has been conducted to compare the motion responses of a mooring ship under the action of bimodal spectral waves and pure wind waves. The results show that the low-frequency waves in the bimodal spectrum waves control the motion responses of the mooring ship. When the energy of bimodal spectral waves equals the one of pure wind waves, the amount of mooring ship motions under the action of bimodal spectral waves is significantly larger than that of pure wind waves. Under such circumstances, even when the energy of the low-frequency waves accounts for only 20% of the total energy of the bimodal spectral waves and the low spectral peak period is 12s, the movement quantity of sway can reach 1.5 times in bimodal spectral waves than in pure wind waves. The movement quantities of surge, heave, and roll in bimodal can reach more than 2 times of those in pure wind waves. Under the action of transverse waves, the mooring ship’s movement of pitch is not affected by the wave height of bimodal spectral waves and the period of low-frequency bimodal spectral waves.

Prediction of the mean heading of a turret moored FPSO in bi-modal and bi-directional sea states

Ship-shaped platforms like Floating Production Storage and Offloading (FPSO) vessels are deployed in many offshore locations where the sea states are dominated by wind driven local seas combined with long period swells that are incident from different directions. Many of these vessels are held in station by a mooring system that is connected to the platform by a rotating turret. The heading stability of the vessel and its ability to self-align with respect to oncoming environmental forces is studied in this paper. Experiments at 1:120 scale conducted in a wave basin facility for two storm conditions offshore Brazil and West of Africa show that the heading angle is self-limiting to a range of ±20° with respect to head sea direction. Time domain simulations conducted using industry-standard software by modeling the wind-sea and swell with suitable spectrum models approaching from different directions show almost double the heading range seen in experiments. If similar numerical analyses were part of a design process, it is conceivable that this could result in incorrect predictions of the weathervaning of the platform, and hence the latter’s global motions in response to design storm conditions.Previous studies by the authors have confirmed that the delicate balance between various mean wave drift forces and moments is the main contributor to the heading stability of a single-point moored ship shaped vessel. It is shown here that in a bi-directional seastate, the interaction between the two wave components can significantly alter the drift loads on the platform. A simple cross-wave correction is added to the time domain simulations to account for the interaction. Implementing this correction brings the numerical results more in line with the experimental findings. The cross-wave correction term is quantified and recommendations are made for better simulations and experiments of such platforms.