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This paper summarises the main findings from the full-scale Computational Fluid Dynamics (CFD) analyses conducted at SINTEF Ocean on the case of MV REGAL, which is one of the benchmark vessels studied in the ongoing joint industry project JoRes. The numerical approach is described in detail, and comparative results are presented regarding the propeller open water characteristics, ship towing resistance, and ship self-propulsion performance. The focus of numerical investigations is on the assessment of the existing simulation best practises applied to a ship-scale case in a blind simulation exercise and the performance thereof with different turbulence modelling methods. The results are compared directly with full-scale performance predictions based on model tests conducted at SINTEF Ocean and sea trials data obtained in the JoRes project. [ABSTRACT FROM AUTHOR]

The dynamic coupling between the fluttering motions and hydrodynamic characteristics of codend is essential in understanding the trawl selectivity through fish response and the drag force acting on the whole trawl. This study investigated the effect of towing speed, warp length, warp tension, and catch size on the fluttering motions of Antarctic krill trawl codend during net shooting, towing, and hauling by using sea trial data. The time-periodicity of codend oscillation was analyzed by the Morlet wavelet transform method. Results indicated that the period of codend oscillation was between 50 s and 90 s and showed an increasing trend with the warp tension but a decreased value at the towing stage. The coefficient amplitude of codend oscillation was between 0 and 4 at the net shooting and hauling stages, and between 0.2 and 0.6 at the towing stage. The amplitude of codend oscillation increased with the warp tension, towing speed, and catch size, but decreased with the increase of the warp length. In addition, the period of codend oscillation increased with the towing speed at the net shooting and hauling stages, but decreased at the towing stage. These results from codend fluttering motions can improve the understanding of fish behavior and gear shape that modify the hydrodynamic force on the codend instantaneously. [ABSTRACT FROM AUTHOR]

The manoeuvring characteristics of the ships represent a complex phenomenon, which includes their capacity for both maintaining a steady course and turning ability. There are no simple methods for evaluating a ship's performance in these aspects. Furthermore, the flow patterns connected to these phenomena are complex and frequently coupled with other factors. The purpose of this study is to evaluate the course keeping and turning performance for a 37000 tdw chemical tanker. Course-keeping is evaluated based on stability criteria, while empirical relations and numerical simulations using hydrodynamic derivatives from both empirical and computational fluid dynamics (CFD) methods are employed to analyse the turning circle and then compared with data from actual sea trials. [ABSTRACT FROM AUTHOR]

The concept of manoeuvrability is very important for efficient ship operation but also in ship safety. The aim of this paper is to test and perform a comparative analysis of manoeuvrability performance of a 9000 tdw chemical/oil tanker. The comparative analysis has been performed between the results obtained based from two software’s, namely PHP and MPP, but also between the results obtained in the sea trials with the output data from MPP. In this way it will be shown the differences (if any) in terms of manoeuvrability., and if the two used platforms are effective for providing preliminary determination of performances of manoeuvrability. [ABSTRACT FROM AUTHOR]

This article investigates ship maneuverability by conducting and comparing calculations using two distinct computational platforms. The results obtained from these calculations are subsequently compared with real data from the sea trials. A detailed analysis of the discrepancies between theoretical and empirical results provides insights regarding the reliability and precision of each computational platform in assessing ship maneuverability in the naval domain. This research contributes to improving methods for evaluating ship performance and validating computational platforms used in the industry. [ABSTRACT FROM AUTHOR]

To mine the cobalt-rich crust deposits at the substrate of the slope of the seamount, the mining vehicle needs to walk on the slope and strip the cobalt-rich crust from the substrate. To achieve safety and control, the vehicle needs to stably walk on the slope. In this paper, we propose a modeling method for mining vehicle performance based on slope stability and antislip and antiskid conditions. The specific energy of three types of mining vehicles is compared based on dimensionless parameters. The dual-drum type is determined to be the best choice in terms of energy costs, followed by the down-milling type. The performance of the compact mining vehicle based on different slope angles and two sea trial results in the South China Sea indicate that the slope angle, substrate, and crust have significant effects on the stability. The modeling method proposed in this paper can help designers estimate the structure and power of mining vehicles based on mining stability. [ABSTRACT FROM AUTHOR]

Effective heading control can improve guidance efficiency and navigation accuracy of wave gliders. However, the weak maneuverability of wave gliders and the disturbance of the ocean environment make the heading errors and oscillations tend to be large. Hence a self-tuning incremental PID (IPID) based neural network (NN) control method is proposed for wave gliders in this paper, which contains a parameter self-tuning neural network (NN1) and a system identification neural network (NN2). An improved artificial jellyfish search algorithm (IAJS) is carried out to initialize the weights and thresholds of the network to improve the search accuracy of the IPID gains and the approximation accuracy of the unknown terms in dynamic heading control system. Additionally, the IPID is modified with a time-varying differential term coefficient to mainly avoid excessive overshooting and actuator saturation when subjected to environmental disturbances. At last, a closed-loop control method is proposed based on the dynamic model of a "Black Pearl" wave glider and the given desired heading. Sea trials are conducted based on simulations and compared with the conventional heading control method to verify the effectiveness and practicality of the control method. • A NN-based heading control is to solve the dynamic time-varying omnidirectional heading tracking problem of wave gliders. • An improved artificial jellyfish search algorithm for neural network initial weights and thresholds optimization. • A modified incremental PID controller was used to handle actuator saturation problem. • Simulations and experiments of the "Black Pearl" wave glider were put forward. [ABSTRACT FROM AUTHOR]

This paper presents the development of autonomy capability for an unmanned surface vehicle (USV). The development mainly focuses on the high-level autonomy on perception, path planning, guidance and control to achieve real sea applications of the USV. First, visual recognition and point cloud data processing techniques are utilized to achieve a real-time perception of the object in the sea environment. Second, detailed path planning strategies are illustrated to plan the easily reachable path for different missions, and the classic guidance and heading controller are adopted to implement the path following algorithm. Subsequently, these autonomy algorithms run in the high-level computer and render the actuator commands for the low-level embedded control system. Finally, sea trials of the USV are conducted by attending the 2020 Zhuhai Wanshan International Intelligent Vessel Competition (IIVC) in Dong Ao Island of South China Sea. The USV accomplish three missions: 1) path following, 2) navigating around the obstacle, and 3) rescuing the drowning. Sea trial results verify the autonomy of the USV in terms of the achieved performances.

Underwater acoustic (UWA) network protocol design is a challenging task due to several factors, such as slow propagation of acoustic waves, low frequency bandwidth and high bit error and frame error rates often encountered in real UWA environments. In this paper, we consider the design of a robust and scalable data gathering protocol for UWA sensor networks (UASNs), focusing on practical considerations and lessons learnt from multiple lake and sea trials. A cross-layer protocol is presented that integrates a network discovery process, intelligent routing, scheduling via Transmit Delay Allocation MAC (TDA-MAC) and multi-node Automatic Repeat Request (ARQ), to facilitate reliable data gathering in practical UASN deployments. Furthermore, this paper presents the details of a novel experimental testbed and underwater sensor node prototype that were used for the trials reported in this study. Based on the results of the trials, important conclusions are drawn on the protocol features required to achieve reliable networked communication in realistic UWA environments. The insights gained from the trials are valuable both for further development of the proposed data gathering protocol, and for the wider UWA networking research community concerned with developing practical solutions for real-world UASN deployments. [ABSTRACT FROM AUTHOR]

This paper summarises the main findings from the full-scale Computational Fluid Dynamics (CFD) analyses conducted at SINTEF Ocean on the case of MV REGAL, which is one of the benchmark vessels studied in the ongoing joint industry project JoRes. The numerical approach is described in detail, and comparative results are presented regarding the propeller open water characteristics, ship towing resistance, and ship self-propulsion performance. The focus of numerical investigations is on the assessment of the existing simulation best practises applied to a ship-scale case in a blind simulation exercise and the performance thereof with different turbulence modelling methods. The results are compared directly with full-scale performance predictions based on model tests conducted at SINTEF Ocean and sea trials data obtained in the JoRes project.

To better study the biology and ecology of hadal trenches for marine scientists, the Hadal Science and Technology Research Center (HAST) of Shanghai Ocean University proposed to construct a movable laboratory that includes a mothership, several full-ocean-depth (FOD) submersibles, and FOD landers to obtain samples in the hadal trenches. Among these vehicles, the project of an FOD autonomous and remotely-operated vehicle (ARV) named "Dream Chaser" was started in July 2018. The ARV could work in both remotely-operated and autonomous-operated modes, and serves large-range underwater observation, on-site sampling, surveying, mapping, etc. This paper proposed a novel three-body design of the FOD ARV. A detailed illustration of the whole system design method is provided. Numerical simulations and experimental tests for various sub-systems and disciplines have been conducted, such as resistance analysis using the computational fluid mechanics method and structural strength analysis for FOD hydrostatic pressure using the finite element method and pressure chamber tests. In addition, components tests and the entire system tests have been performed on land, underwater, and in the pressure chamber in the laboratory of HAST, and the results are discussed. Extensive experiments of two critical components, i.e., the thrusters and ballast-abandoning system, have been conducted and further analyzed in this paper. Finally, the procedures and results of lake trials, South China Sea trials and the first phase of Mariana Trench sea trials of the ARV in 2020 are also introduced. This paper provides a design method for the novel three-body FOD ARV. More importantly, the lessons learned from the FOD pressure test, lake tests, and sea trials, no matter the success or failure, will guide future endeavors and the application of ARV Dream Chaser and underwater vehicles of this kind. [ABSTRACT FROM AUTHOR]

• A partitioning control method based on distance error is designed to distinguish risk levels of WGs, which is divided into three areas: warning area, escape area and obstacle area. Different navigation methods are designed in different areas. • An AILOS algorithm is designed to make the WG follow the required circular path, and the lookahead distance can adaptively be adjusted based on external disturbances. A tan-type BLF is introduced into the AILOS algorithm to determine the warning area boundary. • Considering the extreme situation of WG within a period, the escape area navigation method is designed to prevent the WG entering the obstacle area. An obstacle mode station-keeping strategy that considers obstacles in the station-keeping center area is proposed for wave gliders (WGs) to cope with special applications such as oil spill monitoring on drilling platforms and observation around the island. Different from the traditional station-keeping strategy which requires closing in the preset position as much as possible, this strategy uses the adaptive integral line of sight (AILOS) algorithm to make the WG sail around the preset obstacle area. A partitioning control strategy based on distance error is introduced to divide three areas according to the risk level: warning area, escape area and obstacle area. A tan-type barrier Lyapunov function (BLF) is introduced into the warning area control method to determine the boundary. To avoid the potential risk of collision, the escape area control strategy is to make the WG move away from the obstacle area as quickly as possible. Simulation and sea trial results verified the capability of the proposed station-keeping strategy in a stable ocean environment and the station-keeping safety of the WG using this strategy under extreme situations. [ABSTRACT FROM AUTHOR]

Autonomous ships are promoted as the future of the maritime transport industry aiming to overcome conventional vessels in terms of performance, safety and environmental impact. Yet their tangled cyber-physical-social interactions and new emerging properties induce questions regarding their liability and trustworthiness. Digital simulations and sea trials are launched to assure the safety requirements and social expectations are met a priori. This paper presents the design of realistic testbed scenarios from huge historical data through a high-performance computational method to recommend a complete set of navigation scenarios for autonomy tests. The developed approach integrates traffic big data from Automatic Identification System (AIS) with high-resolution digital maps, vessel information registry, and digital nautical charts. All historical vessel-to-ground and vessel-to-vessel interactions are efficiently analyzed through a hierarchical method for collision and grounding conflicts assessment with a 15-minutes prediction horizon. Relative risk is evaluated accurately over full periods of predicted close-quarters situations subject to physical limits and sea-room availability for evasive maneuverers under COLREG rules and traffic separation schemes. Spatial dependencies among multiple conflicts define risky momentary traffic situations modelled through directed graph representation of nested interactions. Their temporal dependencies describe navigation scenarios through dynamic co-behaviors between multiple participating vessels over a period of time. Finally, we analyze negative/positive actions that increase/decrease the complexity. The presented algorithms are computationally very efficient, they scale to several (country*year)s where millions of scenarios are extracted, classified, and scored by their relative risk, complexity, and likelihood for firm post-test conclusions. [ABSTRACT FROM AUTHOR]

In this study, a model is developed to simulate the dynamics of an internal combustion engine, and it is calibrated and validated against reliable experimental data, making it a tool that can effectively be adopted to conduct emission predictions. In this work, the Ricardo WAVE software is applied to the simulation of a particular marine diesel engine, a four-stroke engine used in the maritime field. Results from the bench tests are used for the calibration of the model. Finally, the calibration of the model and its validation with full-scale data measured at sea are presented. The prediction includes not only the classic engine operating parameters for a comparison with surveys but also an estimate of nitrogen oxide emissions, which are compared with similar results obtained with emission factors. The calibration of the model made it possible to obtain an overlap between the simulation results and real data with an average error of approximately 7% on power, torque, and consumption. The model provides encouraging results, suggesting further applications, such as in the study on transient conditions, coupling of the engine model with the ship model for a complete simulation of the operating conditions, and optimization studies on consumption and emissions. The availability of the emission data during the sea trial and validated simulation results are the strengths and novelties of this work. [ABSTRACT FROM AUTHOR]

To mine the cobalt-rich crust deposits at the substrate of the slope of the seamount, the mining vehicle needs to walk on the slope and strip the cobalt-rich crust from the substrate. To achieve safety and control, the vehicle needs to stably walk on the slope. In this paper, we propose a modeling method for mining vehicle performance based on slope stability and antislip and antiskid conditions. The specific energy of three types of mining vehicles is compared based on dimensionless parameters. The dual-drum type is determined to be the best choice in terms of energy costs, followed by the down-milling type. The performance of the compact mining vehicle based on different slope angles and two sea trial results in the South China Sea indicate that the slope angle, substrate, and crust have significant effects on the stability. The modeling method proposed in this paper can help designers estimate the structure and power of mining vehicles based on mining stability.

Underwater acoustic (UWA) network protocol design is a challenging task due to several factors, such as slow propagation of acoustic waves, low frequency bandwidth and high bit error and frame error rates often encountered in real UWA environments. In this paper, we consider the design of a robust and scalable data gathering protocol for UWA sensor networks (UASNs), focusing on practical considerations and lessons learnt from multiple lake and sea trials. A cross-layer protocol is presented that integrates a network discovery process, intelligent routing, scheduling via Transmit Delay Allocation MAC (TDA-MAC) and multi-node Automatic Repeat Request (ARQ), to facilitate reliable data gathering in practical UASN deployments. Furthermore, this paper presents the details of a novel experimental testbed and underwater sensor node prototype that were used for the trials reported in this study. Based on the results of the trials, important conclusions are drawn on the protocol features required to achieve reliable networked communication in realistic UWA environments. The insights gained from the trials are valuable both for further development of the proposed data gathering protocol, and for the wider UWA networking research community concerned with developing practical solutions for real-world UASN deployments.

Tropical ocean environment teems with microorganisms, of which some adhere, either to the static ship hull or while en-route to the destination increasing roughness. A typical voyage analysis takes into account parameters like speed, power, propeller speed, displacement, fouling and weather conditions. Wind and wave data in the present study have been acquired from data buoys deployed along the voyage route from Chennai to Singapore. The differential equation of a ship undergoing acceleration is considered and solved to obtain voyage time and distance. Calculations to reach design speed were performed for various loading conditions. Limited experiments were performed in the towing tank using a ship model for various draft conditions. Granville's similarity law has been relied upon to arrive at the frictional resistance and is discussed in this paper. The loads due to wind and waves were specifically calculated for the ship with a fouled hull heading in its design speed. [ABSTRACT FROM AUTHOR]

Innovative underwater pipeline repair and inspection technologies utilising a dry chamber represent a novel approach. This technique involves injecting high-pressure air into a chamber to displace the surrounding medium. However, sealing becomes very challenging owing to the irregularity of the sealing surface, and diver operations pose significant risks at high gas pressures. This study presents a novel design that integrates inflation and drainage methods. It employs an air compressor for chamber inflation and submersible pumps, along with an air-operated diaphragm pump for water drainage. This system could effectively manage various degrees of leakage and maintain continuous drainage, thus establishing a normal pressure environment. Consequently, the sealing requirement is significantly reduced, and divers are allowed to perform multiple tasks within the chamber at atmospheric pressure. Furthermore, the inflation parameters were optimized during the inflation and drainage processes through a numerical method, and the designed system was validated via offshore experiments. The results indicated that the system could handle a leakage rate of 50 m3/h and maintain a dry chamber for at least 5 h. • By combining pumping and aerating, the system displaces seawater inside the dry chamber with air. • It can handle varying levels of sealing effectiveness and adapt to high flow rates, low flow rates, and intermittent leaks within the chamber. • The system can create a normal-pressure environment, allowing divers to work inside the chamber under normal atmospheric conditions. [ABSTRACT FROM AUTHOR]

To better study the biology and ecology of hadal trenches for marine scientists, the Hadal Science and Technology Research Center (HAST) of Shanghai Ocean University proposed to construct a movable laboratory that includes a mothership, several full-ocean-depth (FOD) submersibles, and FOD landers to obtain samples in the hadal trenches. Among these vehicles, the project of an FOD autonomous and remotely-operated vehicle (ARV) named “Dream Chaser” was started in July 2018. The ARV could work in both remotely-operated and autonomous-operated modes, and serves large-range underwater observation, on-site sampling, surveying, mapping, etc. This paper proposed a novel three-body design of the FOD ARV. A detailed illustration of the whole system design method is provided. Numerical simulations and experimental tests for various sub-systems and disciplines have been conducted, such as resistance analysis using the computational fluid mechanics method and structural strength analysis for FOD hydrostatic pressure using the finite element method and pressure chamber tests. In addition, components tests and the entire system tests have been performed on land, underwater, and in the pressure chamber in the laboratory of HAST, and the results are discussed. Extensive experiments of two critical components, i.e., the thrusters and ballast-abandoning system, have been conducted and further analyzed in this paper. Finally, the procedures and results of lake trials, South China Sea trials and the first phase of Mariana Trench sea trials of the ARV in 2020 are also introduced. This paper provides a design method for the novel three-body FOD ARV. More importantly, the lessons learned from the FOD pressure test, lake tests, and sea trials, no matter the success or failure, will guide future endeavors and the application of ARV Dream Chaser and underwater vehicles of this kind.

The paper considers the experience of upgrading a unified electric power system (UEPS) with an electric propulsion system (EPS) of the diesel–electric icebreaker Kapitan Kosolapov. The upgrading is caused by the need to replace the UEPS–EPS equipment and extend the icebreaker's service life. Technical inspection of the main UEPS–EPS electrical equipment has been carried out before the upgrading. When developing a technical project, a comparative circuit analysis and technical solutions have been carried out and the required electrical calculations have been performed. As part of the upgrading, the main diesel generators, controlled armature circuit rectifiers, and reversible controlled rectifiers of the propulsion motor excitation circuit have been replaced. A microprocessor controlled EPS system has been developed. An integrated control system for the technical means of the vessel has been introduced. Mooring, sailing, and ice tests of the icebreaker have been carried out. In the course of testing the UEPS, the quality of electricity in the ship's network, stability of the stand-alone and parallel operation of the diesel generators, and distribution of active and reactive loads have been checked. When testing the EPS, the quality of transient processes of the propulsion electric installation has been assessed. The transient acceleration, deceleration processes, and reversing of the propeller motor have been oscilloscoped. The successful upgrading and testing allowed the service life of the Kapitan Kosolapov diesel–electric icebreaker to be extended. [ABSTRACT FROM AUTHOR]

This paper presents sea trials on a 6-m boat specifically designed for kite propulsion. The kite control was automatic or manual, dynamic or static, depending on the point of sailing. The measurement system recorded boat motion and load generated by the kite. A particular attention was paid to wind measurement with several fixed and mobile locations directly on the kiteboat or in the vicinity. A high resolution weather modelling showed that a classical power law, describing the wind gradient, was not satisfactory to get the wind at kite location. 5-min measurement phases were systematically recorded. In the end, 101 runs were carried out. Data were processed with the phase-averaging method in order to produce reliable and accurate results. [ABSTRACT FROM AUTHOR]

Fiber-optic interferometric sensing is a very attractive approach for creating lightweight, high-sensitive, and fully passive fiber-optic hydrophone arrays. In this paper, results of sea trials of the thin cable fiber-optic hydrophone array for passive acoustic surveillance applications are presented. The performed trials consisted of two parts: the first part was devoted to the estimation of the array acoustic performance and the second part included the direction of arrival (DOA) estimation of the moving acoustic source. The estimation of the array acoustic performance showed that the average measured pressure sensitivity of fiber-optic hydrophones increased as the acoustic frequency increased from −122 dB re rad/ $ {\mu }$ Pa at 20 Hz to −116 dB re rad/ ${\mu }$ Pa at 495 Hz. The average minimum detectable pressure of hydrophones decreased from 78, 1 dB re $1~{\mu }$ Pa at 20 Hz to 28, 5 dB re $1~{\mu }$ Pa at 495 Hz. Obtained values of the minimum detectable pressure were below the sea state zero noise level in the considered frequency range. The average dynamic range of fiber-optic hydrophones was above 120 dB at 495 Hz. The proper capability of the DOA estimation was successfully demonstrated using the motor boat as the moving acoustic source. Trajectories of the moving boat were obtained by using the beamscan DOA estimation algorithm with additional Kalman filtering. Obtained results demonstrated the great potential of using fiber-optic interferometric sensors for hydroacoustic surveillance applications. The presented results might be helpful for the implementation of extended fiber-optic hydroacoustic surveillance systems. [ABSTRACT FROM AUTHOR]

The hydrodynamic characteristics and depth control of the towed sensors array system (TSAS) are investigated based on lumped mass method and computational fluid dynamics (CFD). Firstly, the flexible towed cable is discretized into multiple rigid links with the lumped mass point, and the terminal point is the towed underwater vehicle (TUV). Coupling analysis of each sensors integrated module to a finite length of towed cable is performed, taking the module as the lumped mass point. The variation of normal and tangential forces with the change of angle are discussed for different towed speeds. Then, the dynamics model of the TUV is established and solved. The equilibrium equation for each lumped mass point is established using the recursive method from the bottom up. The angle between each link and the horizontal plane is calculated. Finally, the coordinate of each node is derived, and the position of the towed cable is fitted. The study shows that the hydrodynamic characteristics of the module and towed cable significantly impact the depth control and profile measurement. Sea trials validate the reliability of the method proposed in this paper, which is a guide to the design and manipulation of the TSAS. • The hydrodynamic characteristics and depth control of the towed sensors array system are studied. • The lumped mass method and computational fluid dynamics are employed. • The dynamics and mathematical model are established by the recursive method. • The calculated position and plotted profile are validated by sea trials. [ABSTRACT FROM AUTHOR]

In this paper, a design method is presented for path following control of wave gliders (WGs) subject to velocity and rudder input constraints, as well as marine currents and wave disturbances. The control method integrates an adaptive integral line-of-sight (AILOS) guidance law, an adaptive target-path-switching control and a modified incremental PID heading control for WGs with the multi-straight-line path following, which can extremely overcome the influence of such marine currents interference and guarantee path following accuracy. For the control loop, adaptive adjustments on the parameters of the lookahead distance and the error-circle radius are built to provide a current-influenced position error compensation suitable for the time-varying velocity of the WG. Additionally, an online wave filter using an extended Kalman filter (EKF) is developed to address the issue of wave-induced disturbance influence worked on the position and heading of the WG. Further, simulations and sea trials demonstrate both tracking accuracy and high robustness under ocean disturbances with rudder constraints. • Adaptive path-following control is for wave gliders subject to velocity, rudder input constraints, and marine disturbances. • Adaptive adjustments in AILOS and target-path-switching control are to compensate a current-influenced error. • An online wave filter is used for avoiding wave-induced disturbance worked on the position and heading. • Simulations and sea trials of the experimental wave glider were put forward. [ABSTRACT FROM AUTHOR]

This paper presents sea trials on a 6-m boat specifically designed for kite propulsion. The kite control was automatic or manual, dynamic or static, depending on the point of sailing. The measurement system recorded boat motion and load generated by the kite. A particular attention was paid to wind measurement with several fixed and mobile locations directly on the kiteboat or in the vicinity. A high resolution weather modelling showed that a classical power law, describing the wind gradient, was not satisfactory to get the wind at kite location. 5-min measurement phases were systematically recorded. In the end, 101 runs were carried out. Data were processed with the phase-averaging method in order to produce reliable and accurate results.

As a new testing technology, large-scale ship model tests on the sea are advantageous in addressing the scale effect in ship models and in simulating ship navigation conditions. In this study, the uncertainty of a ship model propulsion test on the sea was analyzed using the Monte Carlo method, and the influence of the test environment was quantified. We used a 25 m-long ship model for the propulsion performance test. Based on the procedure recommended by the International Standardization Organization (ISO), several tests were conducted on the Yellow Sea (the northwestern part of the East China Sea). The results demonstrate that the wind and waves in the environment are the two factors that have the greatest influence on the test accuracy. This study will aid the development of sea trials, and the analysis method used in the propulsion test is also suitable for many complex ship tests.

In this paper author depicts the results of the sea trials of the operational test of a Hiload technology at sea waves with the numerical analysis for the dynamic forces and operational risk. The research was carried out on board MT “Navion Anglia” which was engaged in a towing operation through the Atlantic Ocean with a “Hiload DP1” prototype unit docked on her portside alongside, with different ship’s draft and in different weather conditions. Additionally in this paper author presents the methods that can be used for estimating the safety factor SF against sliding and/or operational risk for the towing and/or manoeuvring operation with a “Hiload DP1” unit docked alongside at the open sea.

The paper presents partitioned tightly coupled fluid-structure interaction (FSI) simulations for composite panel slamming of a high-speed planing hull, including comparison with full-scale experiments. Panels with different layout/stiffness are investigated. Computational fluid dynamics (CFD) is performed using the URANS code CFDShip-Iowa. Computational structural dynamics (CSD) uses modal expansion by ANSYS finite elements. One- and two-way tightly coupled FSI is performed. The complexity of sea-trial conditions is reduced by statistical/frequency analysis, allowing for a simplified representation by one regular wave. Simulations provide details of slamming, including correlation of re-entering pressure peaks with motions and strain peaks. Numerical/modeling issues are discussed. Expected value and associated uncertainty of experimental pressure/strain peak and duration are used for validation. The difference of panels’ dynamics is well predicted. Validation errors and uncertainties (average 25% and 14%) are quite large. Nevertheless, errors always fall within one standard deviation of experimental-data individual readings. Results are promising especially if compared to earlier slamming studies for regular/irregular waves in controlled towing tank tests, which show average error and validation uncertainty of 25% and 10%. The current study lays the groundwork for research on high-fidelity CFD/CSD FSI of real-world geometry slamming and ultimately multidisciplinary design optimization of structural and hull-form parameters. [ABSTRACT FROM AUTHOR]

Flexible/adaptive acoustic modems that are reprogrammable/reconfigurable at all layers of the communication stack, either by a user or by means of autonomous decisions, are considered as an important enabler for interoperability and cognitive networking in the underwater domain. In this paper, we review the existing literature on software-defined acoustic modems (SDAMs) for underwater communications and networking, considering past and ongoing academic efforts, as well as industrial developments and European collaborations centered on software-defined modem structures and functionalities. We then zoom in on relevant R&D efforts currently taking place in a defense cooperation between The Netherlands and Norway, targeting the design of a software-defined modem for the NILUS MK 2 sensor node. This modem is built using general-purpose (GP) computing architectures running open-source operating system and tools, thereby making a further step toward software-defined open-architecture underwater acoustic modems. The first field tests of the NILUS MK 2 node in multihop underwater acoustic networks are presented, showing satisfactory performance in shallow and open waters. [ABSTRACT FROM AUTHOR]

This paper compares the skill of two algorithms that enable real-time estimation of the directional wave spectra exciting a ship from its measured motions. One algorithm consists of a nonlinear optimization of a parametric or non-parametric spectral model and the other is a Kalman filter based observer. Sea trials have been conducted on an oceanographic vessel that was instrumented with a six degree of freedom fiber optic gyro, complemented with a rate gyro, several accelerometers, a dedicated GPS receiver and a bow mounted down-looking wave radar with motion compensation. The two algorithms are applied to the measured data and a discussion is provided on their skill to recover the properties of existing sea states. [ABSTRACT FROM AUTHOR]

Sigma Energy has performed its foremost prototype tests of scaled wave energy converter in a real sea environment. The prototype was a point absorber with a cylindrical buoy, a mechanical power take-off system with a counterweight, moored to the seabed as a tension leg platform (TLP) with three equal tendons. In these extensive experiments, numerous device characteristics were measured and analysed. The present paper focuses on the dynamic forces in the mooring lines, and some unexpected and rare data obtained. It is well known that TLP tendons are prone to a brief loss of tension (the slacking) and that, after such events, high snapping forces of short duration can arise. Partly by intention, and partly due to underestimation of the dynamical forces, several such slacking-snapping incidents were recorded during the experiments. In some severe storms, the snapping forces were up to six times higher than the tendon pretension. The paper presents several recordings of dynamic forces and platform motion during these critical events. It analysis them, and gives a typical scenario under which they occur. It gives also some theoretical explanations, and numerical predictions of dynamical tendon forces, with their comparison to the experimental results. • Sea trials of novel wave energy converter. • Dynamic forces in tension leg platform (TLP) mooring lines. • Slacking and snapping of TLP tendons. • Recordings of dynamical forces and platform motion in slacking-snapping incidents. • A typical scenario of critical slacking-snapping events. [ABSTRACT FROM AUTHOR]

The methodology and procedures are discussed on designing merchant ships to achieve fully-integrated and optimized hull-propulsion systems by using asymmetric aftbodies. Computational fluid dynamics (CFD) has been used to evaluate the powering performance through massive calculations with automatic deformation algorisms for the hull forms and the propeller blades. Comparative model tests of the designs to the optimized symmetric hull forms have been carried out to verify the efficiency gain. More than 6% improvement on the propulsive efficiency of an oil tanker has been measured during the model tests. Dedicated sea-trials show good agreement with the predicted performance from the test results. [ABSTRACT FROM AUTHOR]

Catamarans experience more types of global load than monohulls, these include pitch connecting moment, transverse bending moment, and split force. High-speed catamarans are widely used for passenger transportation but as the speed and size increase the severity of loads rises due to slam induced effects. In this study, full-scale CFD simulations are undertaken to investigate the loads acting on a 98m Incat wave-piercer catamaran (Hull 061) HSV2 Swift. Simulations are performed for conditions of a selected sea trial run in bow quartering seas at 20 knots forward speed undertaken by the Naval Surface Warfare Center, Carderock Division (NSWCCD), enabling comparisons and validation. In order to estimate internal global loads at different sections of the vessel, rigid body dynamics is applied based on the hydrodynamic and inertia forces. Those internal loads include longitudinal bending moment (LBM), pitch connecting moment (PCM), torsional moment (TorM), transverse bending moment (TBM), split force and prying moment. The estimated and measured global loads are also compared with design loads limits provided by DNV GL rules, and peak values of pitch and roll accelerations corresponding to each slam load are determined at the same wave height and wave period as the sea trial. The application of CFD to simulate sea trials runs in oblique seas is shown to provide a reliable estimation of slam induced loads for application in early design stages. • CFD simulations are beneficial for high-speed catamaran loads at full-scale. • Validation and verification of the proposed CFD model are performed. • JONSWAP spectrum is used to create a wave train in CFD as encountered in sea trials. • Global and torsional loads are computed using rigid body dynamics from CFD. • Slam loads are found to be within the range of DNV-GL design rules requirements. [ABSTRACT FROM AUTHOR]

Methane leakage at the interface between sediment and overlying seawater is an important basis for gas hydrate exploration. Therefore, a low disturbance in-situ encapsulation and pressure-retaining sampler for this interface with a working depth of 3000 m is developed recently, which can separate and transfer sediment and overlying water under pressure-retaining conditions. The tube-soil interaction during sampling process is investigated by the coupled Eulerian-Lagrangian (CEL) approach in the ABAQUS (a finite element analysis software), and the penetration resistance of the sampling tube is 599 N at a penetration depth of 150 mm without damage. The pressure-retaining transfer process of overlying water is investigated by the dynamic mesh technology in the Fluent (a computational fluid dynamics software), and the transfer scheme can ensure that the pressure fluctuation of the sample does not exceed 0.03%. Moreover, the laboratory pressure test verifies the strength and sealing performance (the pressure decreased from 30.77 MPa to 29.57 MPa) of the sampler. Furthermore, the pressure-retaining samples of more than 700 ml were obtained from sea trial, which verifies feasibility of the device application. [ABSTRACT FROM AUTHOR]

Heading control plays an essential role in improving accuracy of all kinds of navigations for wave gliders. However, the performance will exhibit large heading errors and oscillations caused by weak maneuverability and large ocean current disturbance when the wave glider is gliding at a time-varying velocity. A robust dynamic heading tracking control integrated a modified active disturbance rejection controller (MADRC) and an improved anti-windup (IAW) compensator was put forward in this paper, which could extremely guarantee heading tracking accuracy with appropriate actuator power consumption in real time. Focused on dynamically tracking a time-varying desired heading, a reduced-order extended state observer (RESO) was designed to estimate and compensate uncertain disturbance and reduce the computational complexity. The IAW was applied to deal with actuator saturation problem, which could further reduce convergence time and power consumption in the heading control. Following this, a closed-loop control was put forward with a dynamic model of "Black Pearl" wave glider and a given heading control. The proposed control was verified by simulations and sea trials compared with conventional heading controls, which demonstrated its effectiveness and practicability. • Robust dynamic heading tracking control was for dynamically time-varying omnidirectional heading tracking control. • The computational complexity is reduced by the RESO, and the actuator is real-time corrected with proper power consumption. • The disturbances are estimated and compensated based on the ADRC. [ABSTRACT FROM AUTHOR]

A dynamic positioning (DP) system includes different control functions for automatic positioning and guidance of marine vessels by means of thruster and propeller actions. This paper describes the control functions which provide station-keeping and tracking. The DP controller is designed using model-based control, where a new modified LQG feedback controller and a model reference feedforward controller are applied. A reference model calculates appropriate reference trajectories. Since it is not desirable nor even possible to counteract the wave-frequency movement caused by first-order wave loads, the control action of the propulsion system should be produced by the low frequency part of the vessel movement caused by current, wind and second-order mean and slowly varying wave loads. A Kalman filter based state estimator and a Luenberger observer are used to compute the low-frequency feedback and feedforward control signals. Full-scale experiments with a supply vessel demonstrate the performance of the proposed controller.

This work presents the main steps for the development of a multi-physic simulation platform, able to represent the dynamics of a twin-screw ship in 6 degrees of freedom, taking into account the complete propulsion system including automation effects. The simulation platform has to be used in the preliminary design phase in order to study and design the propulsion plant and its control system. The ship motion model has been developed including roll motion, in order to capture the ship heel angles during tight turning circles, which may be significant for a fast naval vessel. Moreover, the simulation model includes a simplified representation of the asymmetric behaviour of the two propeller shafts during manoeuvres, which cannot be neglected when dealing with the propulsion plant behaviour. Several sub-models have been developed and calibrated by means of a set of experimental tests, in model and full scale. The sea trial campaign is finally used to validate and tune the developed simulator; thus, the final version may be adopted as an optimization tool for other future designs (or sister ships) and training purposes. Although the presented case study has been validated on a specific ship, most of the discussed models have a general application. [ABSTRACT FROM PUBLISHER]

The squid resource is rich and widely distributed, which is an important economic cephalopod fishery resources. Squid jigging fishery is one of pillar industry in China ocean fisheries. There are 2 kinds of operation form in squid jigging fishery, one is hand line and the other is squid jigging machine. As a major component of squid jigging fishery, the squid jigging machine relies on import currently and the domestic research is still in a primary stage. To enhance the localization level of squid jigging machine, the improved design of power system, control system, control panel and protection device which are the main parts of squid jigging machine are discussed in detail. The overall structure is consisted of machine case and roller. The motor, reducer, control power, intelligent module, controller and a driver with protection circuit are installed in the machine case. The control power, intelligent module and driver connect with the controller through socket outlet, which is convenient for components maintenance and replacement. The power system of squid jigging machine adopts AC servo drive combined with AC servo permanent magnet synchronous motor. The encoder installed on the motor shaft back-end, which resolution is 210 pulses per revolution. The overload capacity is three times the rated torque. The response frequency of frequency converter is 2 kHz and the speed range is 1:10 000. The improved power system have the advantages of fast response, wide range of speed and complete protecting functions. The control system including fishing line releasing sub-control system, fishhook shaking sub-control system, fishing line rolling up sub-control system and the stop sub-control system. The control panel matches the digital tube display with graphic display screen, which is made of light emitting diode display, dot-matrix graphic liquid crystal display, status indicator lamp, alarm buzzer, main control chip, waterproof panel and waterproof box. The new graphic display can provide detailed technical data and real-time information of squid jigging machine. Through the compare of display content, operator can get more information of human-computer interaction, which improves the reliability and usability. The intelligent anti-overloading function, 0 position and limit position protection and the lack of phase alarm measures were designed as protection device. The intelligent anti-overloading function can limit the output of the power system to avoid overload operation, and can allow the machine operating over the rated torque under the low load rate condition to reduce the failure rate of power system. The sea trials were conducted in the waters off Peru squid fishing grounds from June 23 to July 12, 2014. The MY-7 squid jigging machine made by Japan Towa Denki Seisakusho CO, LTD was served as control machine. The results showed that the experimental squid jigging machine operated stability and the total catch was 2 493 kg. The total catch of control machine was 2 472 kg. T-test result shows that there was no significant difference between the experimental machine and the control machine (P>0.05). [ABSTRACT FROM AUTHOR]