Moored Ship Motions Research Articles

Mathematical Modeling of Moored Ship Motion in Arbitrary Harbor utilizing the Porous Breakwater

Mathematical Modeling of Moored Ship Motion in Arbitrary Harbor utilizing the Porous Breakwater

Experimental study of multi-buoy-assisted moored ship motion at open berth

Cable breaking and fender failure are frequently reported for the traditional moored ship at open berths. An effective mooring system is necessary to optimize the distribution of cable tension and reduce the impact force acting on the fender. In this paper, a multi-buoy-assisted mooring system is proposed to improve the safety performance of the moored ship. Based on the traditional mooring system, two or four buoys are added in the offshore direction of the ship and connected to the ship with the additional mooring lines. Physical model tests of a 180,000-dwt bulk cargo ship are carried out with the different mooring conditions. The cable tensions, the fender reaction forces and the corresponding ship motions in six degrees of freedom are measured under the different mooring conditions. By adjusting the number of buoys and the pretension of the buoy-assisted mooring lines, an effective mooring system for the tested ship is developed. The experimental results indicate that the developed mooring system can effectively prevent the cable breakage and the fender damage under the present test conditions. In addition, although the motion amplitude of the multi-buoy-assisted moored ship increases slightly, the motion velocity of the ship is considerably small, and the influence is limited for the load and unload operations of the bulk cargo ship.

The influence of infragravity waves, wind, and basin resonance on vessel movements and related downtime at the Outer Port of Punta Langosteira, Spain

The coupling of low-frequency oscillatory modes of a harbor with horizontal motions of moored ships can amplify the latter, causing operational and safety problems. The objectives of this study were to analyze infragravity waves and their effect on moored ship motions; to validate the Wavelet Transform Analysis (WTA) method for studying port-ship resonance in the Outer Port of Punta Langosteira, Spain; and to study the climatic forcing of downtimes. The excited resonant modes of the basin (102 and 132 s) were determined using a numerical model and high-frequency water level measurements at different points of the harbor. Yaw and sway motions of three bulk carriers were analyzed in the frequency-time domain using WTA. The results showed that the oscillation periods of the studied vessel motions are directly related to the water depth to vessel draft ratio. In addition, when the wind speeds exceeds 20 km/h, the ship moves away from the fenders, which lead to a lengthening of these periods. Based on our findings, yaw may induce oscillations of the same period in sway. Additionally, operational thresholds were proposed based on outer and inner waves data that will lead to optimize ship stays, avoiding downtimes, and to advance the safety of loading and unloading operations.

A Semi-Supervised Machine Learning Model to Forecast Movements of Moored Vessels

The good performance of the port activities in terminals is mainly conditioned by the dynamic response of the moored ship system at a berth. An adequate definition of the highly multivariate processes involved in the response of a moored ship at a berth is crucial for an appropriate characterization of port operability. The availability of an efficient forecast system of the movements of moored ships is essential for the planning, performance, and safety of the development of port operations. In this paper, an inference model to predict moored ship motions, based on a semi-supervised Machine Learning methodology, is presented. A comparison with different supervised and unsupervised Machine Learning techniques, as well as with existing Deep Learning-based models for predicting moored ship motions, has been performed. The highest performance of the semi-supervised Machine Learning-based model has been obtained. Additionally, the influence of infragravity wave parameters introduced as predictor variables in the model has been analyzed and compared with the typical ocean waves, wind, and sea level as predictor variables. The prediction model has been developed and validated with an available dataset of measured data from field campaigns in the Outer Port of Punta Langosteira (A Coruña, Spain).

Integrated approach to assess resonance between basin eigenmodes and moored ship motions with wavelet transform analysis and proposal of operational thresholds

Waves with periods between 25 s and some minutes can amplify the motions of moored ships, which may result in terminal downtimes and compromise safety. The purpose of this work is twofold: (i) studying infragravity waves and their influence on moored ship motions, including the definition of operational thresholds and (ii) developing a novel and integrated approach to identify and assess resonance situations using wavelet transform analysis. The resonant modes of the harbor basin were identified using a numerical model validated with full-scale data. The motions of five similar LPG vessels moored at two adjacent jetties were analyzed, both in the frequency and frequency–time domains. It was concluded that surge is the most important motion at the berth that has greater operational problems. Moreover, the infragravity motion periods vary with the mooring line pretension and are proportional to the ratio of water depth to vessel draft. Three episodes of mooring line breaking were attributed to large infragravity surge oscillations. In addition, operational thresholds for basin-vessel resonance situations were defined based on the port tide gauge data. A significant wave height of 0.075 and 0.010 m for the 30–65 s period band was established for LPGs and oil tankers, respectively.

Moored ship motion under the resonance conditions with breakwaters: A coupled numerical approach

A hybrid element model has been formulated to understand the wave interaction with moored ship motion using mild slope equation (MSE) including the influence of breakwaters and wave absorbers, under resonance conditions for variable bathymetry. In a hybrid element formulation, a combined approach with the finite element method (FEM) in an interior domain (port region) including moored ship region and an analytical approximation in the unbounded region (open sea) is utilized to determine the wave response of moored ship motion. Especially, in this approach, a FEM and analytical approximation are firstly utilized to solve MSE with the consideration of permeable breakwaters for moored ship motion under the resonance conditions. The non-uniform discretization pattern enhanced the numerical accuracy of the coupled numerical approach and is verified by using convergence analysis. Further, the simulation results are compared with existing studies to validate the applicability of the present numerical model. Wave absorbers and permeable breakwaters are employed to determine the incident wave response over moored ship motion inside the realistic Paradip port, Odisha, India. In addition, the efficacy of permeable breakwaters and wave absorbers on moored ship motion is investigated. It is shown that breakwaters and wave absorbers at appropriate locations play a significant role to induce/reduce the resonance inside the port. Therefore, the current numerical model provides the countermeasures tactics such as installing breakwaters, wave absorbers to mitigate the resonance in arbitrarily shaped ports for safe moorings.

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

Modelling and measurement of low-frequency surge motion associated with extreme storm conditions in the Port of Cape Town

Infra-gravity wave propagation into the Port of Cape Town (South Africa) was modelled with Delft3D-Surfbeat. The model was calibrated and verified against wave measurements outside the port and inside one of the main port basins. The numerical model results corresponded well to the measured data and theory on port basin oscillations.The calibrated model was used to develop a long wave forecasting tool, by parametrising a framework of simulations that covers the offshore wave climate. The forecasting tool relies only on the NCEP offshore wave forecasts as input and was shown to give reliable results 3 days in advance.Two storm events were analysed in detail and presented as case studies. The first event was an extreme storm with a measured significant swell wave height of 11.5 m offshore and a measured significant long wave height of 0.7 m inside the port. The second event was a significant storm with a measured significant swell wave height of 6.2 m offshore and a measured significant long wave height of 0.3 m inside the port basin.The surge motion of moored container vessels was measured during each of the two events. A tool was developed to detect and track user-defined objects on a vessel in a sequence of recorded images and then transform their positions to surge motion. The maximum surge motion measured during the first (extreme) event was 12.51 m and 3.14 m during the second (significant) event.The low-frequency motions of the vessels during the two storm events were modelled in the time domain with the moored ship motion model, Quaysim. The Delft3D-Surfbeat model output was used to determine the wave forces acting on the vessels. During the first (extreme) event, the moored vessel was under tug assistance and a line parting was observed. Several likely mooring scenarios were modelled to account for any uncertainty in the actual mooring arrangements.The modelled and measured surge motion was in good agreement, especially during the second event where there was less uncertainty about the mooring arrangement. Alternative mooring arrangements, including a dynamic tensioning system, were also modelled to determine whether vessels can be moored more effectively in such conditions.

Moored ship motion analysis in Paradip port under the resonance conditions using 3-D boundary element method

Loading and unloading of moored ship is difficult task during the extreme wave oscillation in a port during the seasonal weather conditions. Therefore, a mathematical model is developed based on Laplace equation to analyze the six different modes (surge, sway, heave, roll, pitch, and yaw) of the moored ship motion under resonance conditions utilizing the 3-D boundary element method (BEM). The domain of interest is divided as bounded (port region), unbounded (open sea) and ship region. The equation of motion with six degree of freedom is solved to analyze the moored ship motions with variable water depth. The present numerical scheme is validated with existing well-known studies. The current numerical model is implemented on realistic Paradip port to determine the resonance frequency for the moored ship motion at key location. In additional, the wave field with different resonance modes is also estimated inside the Paradip port. The safe locations inside the Paradip port are identified for the moored ships under the resonance conditions.

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.

An analysis methodology for the passing ship problem considering real-time simulations and moored ship dynamics: Application to the Port of Santos, in Brazil

An analysis methodology for the passing ship problem in ports combining a potential flow model, a dynamic simulator for moored ships and a real-time simulator is presented. Traditionally, the passing ship problem is approached by defining a criteria based on safe distances and maximum velocities, neglecting manoeuvring aspects that are crucial to verify whether the ship can meet such requirements or not. In order to overcome this limitation, the proposed methodology extends the standard one by including results of pilot guided real-time simulations into the analysis process. The method is applied to evaluate the manoeuvring feasibility of a 366 m long container ship in the Port of Santos, Brazil, taking into account the hydrodynamic effects that might be caused on small capesize vessels moored at different berths of the port. Results are discussed in terms of moored ship motions and mooring loads for different manoeuvring cases, including also possible improvements on the mooring arrangements in order to increase the port operational limits.

Moored Ship Motions due to Tropical Cyclone Linda

Moored Ship Motions due to Tropical Cyclone Linda

Modeling wave and spectral characteristics of moored ship motion in Pohang New Harbor under the resonance conditions

An integrated mathematical model is demonstrated to investigate the wave and spectral characteristics of the moored ship motion in an irregular geometrical domain due to diffraction, refraction, and partial reflection induced by incident ocean waves. The incidence angle of partial reflection boundary is assumed as zero. Fluid domain is divided into three regions entitled as bounded region (harbor), unbounded region (open sea), and ship region. A combined numerical approach including 3-D Boundary Element Method (BEM) in the ship region and a 2-D BEM in bounded region is performed to analyze the moored ship motion under the resonance conditions. Our proposed model is validated with existing well-known models, such as Sawaragi et al. (1989) and Takagi et al. (1993), revealing that it could efficiently capture the spectrum of waves. Then, the proposed numerical scheme is implemented in realistic Pohang New Harbor, which is situated in the southeast part of South Korea. The spectral characteristics of a moored ship motion are obtained under different directional incident waves with resonant frequencies. The reliable calculation results suggest that this method can be utilized for the safety and hazard mitigation of the moored ship in realistic harbor with complex geometry including sharp corners.

Review of Long Wave Dynamics over Reefs and into Ports with Implication for Port Operations

This paper reviews the dynamics of infragravity (long-period) waves over reef systems and the consequences of these waves for operations in ports located behind reefs with particular attention to Western Australia. Swells which originate in the Southern Ocean generate long (infragravity) waves, which propagate to the coast. On the reef edge, the swell waves are largely dissipated, transferring energy to turbulence and heat but also in that process generating long wave energy. The remaining swell waves are dominated by the infragravity waves and propagate towards the mainland and into port basins where they cause moored ship motions with consequences for the operational downtime of the port’s operations. When contemplating solutions to mitigate the impact of the long wave problems, these may be addressed from two sides: from the load side (waves) and the strength side (mooring). The former will be discussed in this paper.

ＧＰＳ位置データを用いた係留中の船体運動算出に関する一考察

Even now a casualty during ship berthing or cargo handling operation has being occurring. Furthermore it has been reported in ports exposed to high energy long-period wave conditions that an emergency unberthing operation was repeatedly conducted with mooring line and fender breakage due to the large ship motion. It is important for not only effective workability of cargo handling operation but also safe mooring of ship to measure and monitor the ship motions directly. In this study, we propose a conventional measurement method of moored ship motions by using GPS position data, which is observed at three positions on ship. A field observation has been conducted to confirm the accuracy of the method, and several considerations have been investigated.

항만공진주기와 선박동요량을 고려한 항만가동율 산정

This study proposed an estimation method of allowable wave height for loading and unloading of the ship and evaluation of effective working days considering moored ship motion that is affected by sip sizes, mooring conditions, wave periods and directions. The method was examined validity by comparison with wave field data at pier 8th in Pohang New Harbor. The wave field data obtained with wave height of 0.10~0.75 m and wave period of 7~13 s in ship sizes of 800~35,000 ton when a downtimes have occurred. On the other hand, the results of allowable wave height for loading and unloading of the ship in this method have obtained with wave heights of 0.19~0.50 m and wave periods of 8~12 s for ship sizes of 5,000, 10,000 and 30,000 ton. Thus this method well reproduced the field data respond to various a ship sizes and wave periods. And the results of this in Korea are didn’t respond to various the ship sizes and wave periods, and we h method tended to decrease in 16~62 percent when have considered long wave, and it is decreased in 0~46 percent when didn’t consider long wave than design standards in case of the ship sizes of 5,000~30,000 ton, wave period of 12 s and wave angle of 75o. The allowable wave heights for loading and unloading of the ship proposed by design standards in Korea have found that overestimated on smaller than 10,000 ton. On the other hand, the rate of effective working days considering ship motion at pier 8th in Pohang New Harbor reduced in 6.5 percent when compare with the results without considering ship motion. 핵심용어: Allowable wave height for loading and unloading of ship, Oscillation quantity of moored ship, ship model for analysis of moored ship motion, effective working days in a harbor, Pohang New harbor, í•˜ì—­í•œê³„íŒŒê³ , ì„ ë°•ë™ìš”ëŸ‰, ì„ ë°•ë™ìš”í•´ì„ëª¨í˜•, 항만가동율, í¬í•­ì‹ í•­

Hydrodynamic Modeling of Moored Ship Motion in an Irregular Domain

In this study, a hydrodynamic model for the analysis of moored ship motion is presented in a realistic harbor with highly irregular geometry. An accurate description of the harbor geometry, bathymetry and the associated wave's characteristics such as diffraction, refraction and partial reflection is required for the analysis of moored ship motion. Further, Fluid domain is divided into bounded, unbounded or open sea and ship region. In each region, wave field is determined by using Boundary Element Method (BEM) with the corner contribution and Chebyshev point discretization. Then, the hydrodynamic coefficient such as added mass and damping coefficients were determined based on the equation of motion with six degree of freedom, which represent the six different component of moored ship motion as surge, sway, heave, roll, pitch and yaw. The current numerical model is validated through previous well defined model based on moored ship motion. Moreover, current numerical scheme is implemented on realistic Pohang New Harbor (PNH), which is situated in Pohang city, South Korea to analyze the wave field in ship region under the various resonance frequencies for monochromatic incident waves.

Design of Safe Mooring Arrangement for Large Oil Tankers

In order to keep pace with the modern oil transport trends, the Indian ports are also developing terminal facilities for Very Large Crude Carrier (VLCC). A conceptual design methodology for marine oil terminal (MOT) including mooring system for large oil tankers has been evolved. The orientation of the MOT and mooring arrangements for 200000 DWT oil tanker were determined considering the environmental conditions prevailed at the site. Water flow velocity played an important role in the orientation of the MOT. Quick Fender Selection Method (QFSM) has been considered for the selection of fender system and it was found that supercone fenders of 2 m height or equivalent type of fenders were suitable for the oil tanker. The mooring arrangements comprising of steel ropes with nylon tails, sustained the effect of high winds of 60 knots associated with currents and waves. Finally, simulation of moored ship motions for moderate environmental conditions i.e., wind speed of 30 knots, current speed of 4 knots and 1 m wave height was carried out using quasi-static approach. The ship motions in six degrees of freedom were found within the permissible limit for safe cargo handling operation. The maximum rope tensions, fender compressions and bollard pull were found to be 195 ton, 0.51 m and 199 ton respectively.

EVALUATION OF EFFECTIVE WORKING DAYS CONSIDERING MOORED SHIP MOTION IN POHANG NEW HARBOR

This study proposes an estimation method for allowable wave heights for ship loading and unloading and evaluation of effective working days, considering moored ship motion that is affected by ship sizes, mooring conditions, and wave periods and directions. The method’s validity was examined with wave field data at pier 8th in Pohang New Harbor. The wave field data, obtained when downtimes had occurred, indicated wave heights of 0.10‒0.75 m and wave periods of 7‒13 s for ship sizes ranging between 800‒35,000 ton in weight. On the other hand, the estimated results for allowable wave heights for ship loading and unloading using this method yielded wave heights of 0.19–0.50 m and wave periods of 8‒12 s for ship sizes of 5,000, 10,000 and 30,000 ton in weight. Thus, this method reproduced well the field data responses of ships of various sizes and at different wave periods. But the allowable wave heights proposed by Korea’s technical standard are did not respond to various the ship sizes and wave periods. And the results of this method tended to decrease in 16–62 percent when have considered long wave, and it is decreased in 0‒46 percent when did not consider long wave than Korea’s technical standards in case of the ship sizes of 5,000‒30,000 ton, wave period of 12 s and wave angle of 75 degree. The allowable wave heights for ship loading and unloading proposed by Korea’s technical standards have indicated that overestimated for ships smaller than 10,000 ton in weight. On the other hand, the percentage rate of effective working days accounting for ship motion at pier 8th in Pohang New Harbor was 6.5 percent less compared to the corresponding results that did not consider ship motion.