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The underwater manipulator is a versatile tool commonly used for various underwater operations. In this study, we developed a heavy-duty hydraulic manipulator capable of operating at full ocean depth. The overall system design integrates both the mechanical structure and the electric control system. The master arm controls the slave arm by transmitting control signals to the controller and valve box. The structural design of the elbow and wrist joints has been optimized to enhance the manipulator's underwater performance and operational range. Laboratory tests demonstrated the manipulator’s excellent response consistency and tracking capability across a wide range of motion. During sea trials in the Mariana Trench, the manned submersible Fendouzhe successfully deployed the manipulator, showcasing its exceptional ability to complete complex tasks. [ABSTRACT FROM AUTHOR]

Flexible cages are widely used in marine aquaculture, yet their mechanical features in extreme seas are still unclear. This study proposes a numerical algorithm to solve the coupled response of the multiple cage systems. The net and mooring lines are modeled using the lumped-mass model, while the flexible floating collar system is assessed with the large-deformation FEM model, and the two models are coupled through an iterative scheme. Sea trials are conducted, and the motion of the cage is obtained using an image processing technique, which validates the numerical algorithm. Using the proposed numerical algorithm, a series of simulations are performed to investigate the response of flexible cages in extreme seas. Motions, line tensions, and structural sectional forces are studied, and the effects of factors such as the wavelength of incident waves and the diameter of collar pipes are investigated. [ABSTRACT FROM AUTHOR]

The innovative aquaculture equipment known as high-density polyethylene (HDPE) floating rafts has gained popularity among fishermen in the southeast coastal regions of China. Compared to deep-water anti-wave fish cages, the construction costs of HDPE floating rafts are 50% to 75% less. There is a dearth of comprehensive publicly available records of HDPE floating rafts sea trial data, despite substantial numerical studies on the motion response of aquaculture fish cages and scale model experiments under controlled-wave conditions. This study involves sea trial techniques under operational and extreme environmental conditions for motion responses of HDPE floating rafts, presents a comprehensive procedure for sea trials of HDPE floating rafts, summarizes the issues encountered during the trials, and suggests solutions. Using MATLAB for independent programming, motion videos and photos collected from the sea trials are processed for image capture, yielding the original time history curve of vertical displacement. Based on the sea trials' data, including motion displacement, acceleration, mooring line force, overall deformation patterns, and current and wave data, recommendations are provided for the design and layout of HDPE floating rafts. Based on the Fast Fourier Transform (FFT) method for spectral analysis, the influence of interference items on the observational data is eliminated; the rationality of the observational data is verified in conjunction with the results of the Gabor Transform. This study offers a scientific analytical method for the structural design and safe operation of HDPE floating rafts and provides a reference for subsequent numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract The pressure of the recovered sample is intricately connected to seawater temperature, the recovery velocity, and the pressure of the pre-charged gas. To better understand the sample pressure dynamics during the sampling recovery process, we focus on a gas-tight sediment sampler, delving into its pressure-compensation and pressure-retaining mechanisms. A comprehensive thermal and thermodynamic analysis is conducted throughout the entire pressure-retaining sampling process, examining the temporal variations in the temperatures of seawater and nitrogen within the sampler at various descending velocities. The heat transfer and thermodynamics are examined throughout the entire pressure-retaining sampling process to determine how changes in the temperatures of seawater and nitrogen, as well as the descent velocity, affect the pressure-retaining performance. The influence of pre-charging pressure and recovery velocities on the pressure-retaining performance of the sampler is examined. Then the proposed numerical model was well verified by the ultra-high-pressure vessel experiments of the sampler under 115 MPa. Finally, the sea trial results further verified the accuracy of the numerical model.

This paper explores the impact of sampling rates during sea trials on the estimation of hydrodynamic parameters in a nonlinear manoeuvring model. Sea trials were carried out using an offshore patrol vessel and test data were collected. A nonlinear manoeuvring model is introduced to characterise the ship's manoeuvring motion, and the truncated least squares support vector machine is employed to estimate nondimensional hydrodynamic coefficients and their corresponding uncertainties using the 25°–25° zigzag test. To assess the influence of the sampling rates, the training set is resampled offline with 14 sampling rates, ranging from 0.2 Hz to 5 Hz, encompassing a rate 10 times the highest frequency component of the signal of interest. The results show that the higher sampling rate can significantly diminish the parameter uncertainty. To obtain a robust estimation of linear and nonlinear hydrodynamic coefficients, the sampling rate should be higher than 10 times the highest frequency component of the signal of interest, and 3–5 Hz is recommended for the case in this paper. The validation is also carried out, which indicates that the proposed truncated least square support vector machine can provide a robust parameter estimation. [ABSTRACT FROM AUTHOR]

For bistatic detection, the desired target is always smeared by the direct blast, limited by the performance of direction-of-arrival (DOA) estimation algorithms. Thus, a deconvolved Multiple-Signal-Classification (D-MUSIC) DOA estimation algorithm is proposed. D-MUSIC beam power is obtained by deconvolving MUSIC beam power using the point-scattering-function (PSF) and Richardson-Lucy (R-L) iteration algorithm. Under low signal-to-noise ratios (SNRs), the background level of D-MUSIC beam power is much lower than that of MUSIC beam power. Besides, D-MUSIC can realize the weak target detection with an adjacent strong interferer in the mainlobe. Finally, via processing the actual data collected during the Sanya sea trial, we analyze the bearing time record (BTR) of MUSIC and D-MUSIC, verifying the superiority of D-MUSIC algorithm. [ABSTRACT FROM AUTHOR]

Flexible cages are widely used in marine aquaculture, yet their mechanical features in extreme seas are still unclear. This study proposes a numerical algorithm to solve the coupled response of the multiple cage systems. The net and mooring lines are modeled using the lumped-mass model, while the flexible floating collar system is assessed with the large-deformation FEM model, and the two models are coupled through an iterative scheme. Sea trials are conducted, and the motion of the cage is obtained using an image processing technique, which validates the numerical algorithm. Using the proposed numerical algorithm, a series of simulations are performed to investigate the response of flexible cages in extreme seas. Motions, line tensions, and structural sectional forces are studied, and the effects of factors such as the wavelength of incident waves and the diameter of collar pipes are investigated.

The innovative aquaculture equipment known as high-density polyethylene (HDPE) floating rafts has gained popularity among fishermen in the southeast coastal regions of China. Compared to deep-water anti-wave fish cages, the construction costs of HDPE floating rafts are 50% to 75% less. There is a dearth of comprehensive publicly available records of HDPE floating rafts sea trial data, despite substantial numerical studies on the motion response of aquaculture fish cages and scale model experiments under controlled-wave conditions. This study involves sea trial techniques under operational and extreme environmental conditions for motion responses of HDPE floating rafts, presents a comprehensive procedure for sea trials of HDPE floating rafts, summarizes the issues encountered during the trials, and suggests solutions. Using MATLAB for independent programming, motion videos and photos collected from the sea trials are processed for image capture, yielding the original time history curve of vertical displacement. Based on the sea trials’ data, including motion displacement, acceleration, mooring line force, overall deformation patterns, and current and wave data, recommendations are provided for the design and layout of HDPE floating rafts. Based on the Fast Fourier Transform (FFT) method for spectral analysis, the influence of interference items on the observational data is eliminated; the rationality of the observational data is verified in conjunction with the results of the Gabor Transform. This study offers a scientific analytical method for the structural design and safe operation of HDPE floating rafts and provides a reference for subsequent numerical simulations.

The sailboat architecture wave glider ( SWG) is a new type of single body underactuated ocean observation platform. Compared with traditional wave gliders, the SWG is powered by marine renewable energy: wind energy and wave energy. It overcomes the shortcomings of weak maneuverability and poor resistance to currents, effectively achieves continuous kinetic energy conversion, and performs tasks such as rapid cruising for a wide range of sea areas. Considering the dependence of the SWG on wind field environment, traditional path planning methods are not applicable to the SWG. Therefore, a local path planning algorithm for the SWG was proposed in the wind field environment. By improving the attractive potential field and repulsive potential field, the proposed algorithm overcomes the defects of traditional artificial potential field algorithm that the robot cannot reach the target point near the obstacles and may collide with the obstacles far away from the target point. In addition, a wind potential field was introduced into the proposed algorithm. The proposed algorithm can plan different paths for different wind fields, and the planned paths meet the kinematic constraints of the SWG. Finally, the applicability of the proposed local path planning algorithm for the SWG was verified by MATLAB simulation and sea trial. [ABSTRACT FROM AUTHOR]

The performance of underwater acoustic communication is significantly affected by multipath propagation and Doppler spread. In this paper, we propose a new communication technique called overlapped chirp spread carrier (OCSC) by modifying the existing sweep spread carrier (SSC) technique, which is robust in a multipath propagation environment. Our proposed OCSC technique uses a repeated carrier wave by combining up-chirp and down-chirp signals and estimates and corrects the Doppler shift frequency of the received signal by utilizing the characteristics of the correlation function of each up-chirp and down-chirp. To demonstrate the performance of the proposed OCSC technique, we provide the results of a simulation using an underwater channel simulator and sea trial conducted in the East Sea. As a result of the sea trial, when demodulating using only the estimated Doppler shift frequency, the uncoded bit error rate reached 0.135. However, when our proposed correction method was applied to the estimated Doppler frequency, the uncoded bit error rate decreased to 0.001.

Verification and validation of Computational Fluid Dynamics (CFD) simulations of a full-scale ship trial are presented in this study. Speed/power trials were carried out according to industry standards for three different power settings. Measured data was corrected for environmental effects to obtain ideal trial runs. Ship-scale unsteady RANS CFD simulations were conducted. Grid refinement sensitivity was evaluated for each power setting. Furthermore, time-step sensitivity was assessed for the selected grids. Finally, assumptions regarding symmetry condition and turbulence model were verified. Simulated results were in good agreement with the test data, thus illustrating the capabilities of numerical methods to determine ship performance at full scale.

This paper explores the impact of sampling rates during sea trials on the estimation of hydrodynamic parameters in a nonlinear manoeuvring model. Sea trials were carried out using an offshore patrol vessel and test data were collected. A nonlinear manoeuvring model is introduced to characterise the ship’s manoeuvring motion, and the truncated least squares support vector machine is employed to estimate nondimensional hydrodynamic coefficients and their corresponding uncertainties using the 25°–25° zigzag test. To assess the influence of the sampling rates, the training set is resampled offline with 14 sampling rates, ranging from 0.2 Hz to 5 Hz, encompassing a rate 10 times the highest frequency component of the signal of interest. The results show that the higher sampling rate can significantly diminish the parameter uncertainty. To obtain a robust estimation of linear and nonlinear hydrodynamic coefficients, the sampling rate should be higher than 10 times the highest frequency component of the signal of interest, and 3–5 Hz is recommended for the case in this paper. The validation is also carried out, which indicates that the proposed truncated least square support vector machine can provide a robust parameter estimation.

This work aims to develop a methodology for determining the hydrodynamic coefficients for ship maneuvering simulations. Finalized ship models are used to provide ship pilots accurate simulation and training scenarios. Results from the simulations are compared with sea trial data to assess accuracy. The simulations were run in WArtsi!8's Viitual Shipyard (VSY) using a test ship measuring 126 meters in length with a displaceinent of 4646 tons. The coefficients were fine-tuned based on turning circle, zigzag. and inertia open water sea trials. The tuning process i·equires modification of the added mass, sway force, damping force, and propeller side force coefficients. Each coefficient influences the forces and moments acting along a vessel. directly impacting the maneuverability. The sensitivity of each coefficient to the ovei·all inaneuverability was determined via inspection and iterative simulation mins. This methodology was applied to tile test ship to improve its accuracy against real-world data The final discrepancies between simulated and sea trial results for their respective parameters were between 3.6 and 18.0 meters during the turning circle test. There was less than a 1 -degree error for overshoot angles during the zigzag test, and a 6-meter difference in head reach during the inertia open water test. [ABSTRACT FROM AUTHOR]

Offshore drilling activities have been significantly impacted by extreme storm conditions as oil and gas development has moved into deeper water. Under the situation of the imminent arrival of a typhoon, retrieval of the whole drilling riser is time-consuming and tedious. A novel soft hang-off system under hang-off and transit operations is proposed and developed to solve the low-efficiency and time limitation for risers' retrieval. The hang-off joint system suspends the drilling riser and the hydraulic system is designed for dynamic load compensation. Sea trial for enhanced hang-off mode with hang-off joint, non-differential control dynamic load compensation mode at hang-off operation and passive compensation mode at transit operation are conducted to evaluate the load compensation effect equipped with novel soft hang-off system compared with conventional hard hang-off mode. Results on dynamic load compensation effect are discussed. The novel soft hang-off system is of high application value for deepwater drilling engineering. [ABSTRACT FROM AUTHOR]

Verification and validation of Computational Fluid Dynamics (CFD) simulations of a full-scale ship trial are presented in this study. Speed/power trials were carried out according to industry standards for three different power settings. Measured data was corrected for environmental effects to obtain ideal trial runs. Ship-scale unsteady RANS CFD simulations were conducted. Grid refinement sensitivity was evaluated for each power setting. Furthermore, time-step sensitivity was assessed for the selected grids. Finally, assumptions regarding symmetry condition and turbulence model were verified. Simulated results were in good agreement with the test data, thus illustrating the capabilities of numerical methods to determine ship performance at full scale. [ABSTRACT FROM AUTHOR]

The underwater glider has difficulty accessing the complex and narrow hadal trench for observation, which is affected by its limited regulation capability of pitch angle (−45°~45°). In this study, a compact attitude regulating mechanism is proposed to extend the regulation range of pitch angle from −90°to 90° and to install it on the hadal-class underwater glider Petrel-XPLUS. Subsequently, the dynamics model of Petrel-XPLUS is established using dual quaternions to solve the "gimbal lock" problem caused by the increased pitch angle range. Within the extended pitch range, the motion modes of the glider are enriched into long-range, virtual mooring, and Lagrangian float modes for long-range, small-area, and current-following observation missions, respectively, and are analyzed using the established dynamics model. Moreover, a ballast method was used to modify the pitch angle range and initial equilibrium state of a constructed underwater glider. Finally, Petrel-XPLUS achieved a pitch angle regulation range of −90°~90° in a water pool experiment and completed three consecutive profiles in a sea trial in the Challenger Deep, Mariana Trench, with all depths over 10,000 m, of which the maximum depth was 10,619 m. The proposed mechanism and methods can also be applied to other submersibles to facilitate ocean observations. [ABSTRACT FROM AUTHOR]

Marine current energy is recognized a promising energy source due to its inherent stability and high predictability. In the past decade, several milestones have been achieved in marine current turbine (MCT) research such as MeyGen and O2. However, compared with high-velocity currents, low velocity currents are more commonly distributed worldwide, which presents new challenges. The demand for low starting velocity and high efficiency necessitates some novel structure in the design of blade, power transmission, etc. To address these issues, taking a 50W MCT as research object, this paper firstly presents the MCT design of a new fan-shaped rotor configuration, a compact non-contact magnetic coupling, a low inertial power train and hollow-cup DC generator for easier starting. Furthermore, to realize the maximum power point tracking (MPPT) and sustainable power supply, the electrical system and its control strategy were designed. The hydrodynamic performance of the fan-shaped rotor was simulated and analyzed using CFD, and a simulation model of the electrical and control systems was constructed and tested to verify the performance. Finally, the tank and sea tests were respectively conducted to validate the performance of proposed MCT. The results indicate that the proposed MCT is capable of starting at velocities around 0.2 m/s and achieving a power coefficient (Cp) exceeding 0.4, making it well-suited for providing a continuous and stable power supply in areas with low flow velocities. • A comprehensive design of a marine current turbine (MCT) in low flow velocity was proposed. • The MCT was made and tank and sea tests were conducted. • The MCT can achieve a starting velocity of about 0.2 m/s, a power coefficient of above 0.4, showing good performance in low flow velocity areas. [ABSTRACT FROM AUTHOR]

High-efficiency pressure-retaining sampling technology for obtaining seabed sediments is required for studying marine geological history, the survival principles of marine microorganisms, and the evolution of earth life. In this paper, a novel submersible-mounted sampler capable of collecting pressure-retained samples at a full ocean depth is designed. The structure scheme is first presented, including the sampling unit, pressure-retaining unit, and pressure-compensation unit. The sampling kinematics model is then established, and the influences of pressing velocity, and the length and inner diameter of pressure pipe on the pressing force of the mechanical arm are determined, providing important guidance for the design of the sealing structure. The maximum working depth of the sampler is 11,000 m, the coring diameter of the sampler is 54 mm, the maximum coring depth is 500 mm, and obtained samples can keep close to in-situ pressures. The sampler can be mounted on a submersible and operated using a single mechanical arm. During cruise TS-21 from August to October 2021, the sampler was deployed 4 times at depth of 7700 m in the West Philippine Basin, and the high pressure sediment samples were successfully collected. The pressure change of the samples remained within ±6%, which verified the rationality of the design and the feasibility of this novel submersible-mounted pressure-retaining sampler.

Lifting coarse mineral particles from thousands of meters of seabed to the supportive vessSel is a crucial part of exploitation of deep-sea mineral resources, and the vertical transportation part is a key component of the deep-sea mining system. Three typical vertical transportation schemes are discussed and compared from the aspects of working mechanism, structural scheme, transportation capacity, system efficiency and implementation feasibility in the context of commercial exploitation of deep-sea polymetallic nodules. The conclusion is that the hydraulic pipeline lifting system with a centrifugal pump is a comprehensive scheme. Furthermore, the basic composition and function of the hydraulic lifting system are introduced, and the transportation performance indicators and technical requirements under commercial mining conditions are analyzed. As the key equipment of the lifting system, the structural characteristics, design theory, transportation performance analysis methods and research progress of the lifting pump are described. A 1000 m sea trial was carried out. The lifting system, the tests of the centrifugal pump and the sea trial are introduced. [ABSTRACT FROM AUTHOR]

Recently, shipyards have been booming in the product carrier (PC) market of the global shipbuilding industry. Due to the rising market conditions, orders for large container vessels and PCs are also steadily increasing. According to the industry, freight rates for LR tankers (70K) and MR tankers (50K) in the shipbuilding industry have rose to the highest level during the previous year. In order to secure the competitiveness of PCs, various core items are required, and Korean shipbuilders have been leading the market for a long time based on their knowledge of the design and production of low-fuel ships. In recent years, there have been frequent cases of coating cracks in the cargo hold after sea trial. All relevant rules presented by the classification so far are structural design, safety evaluation, and inspection standards, and coating cracks are considered a problem for coating makers. In other words, they must establish a standard coating measure agreed upon by all parties (owner, shipbuilder, and coating maker); therefore, solutions have been proposed by each shipping company. In this study, the causes of coating cracks occurring in the cargo hold of PCs during tank tests in sea trials were analyzed and measures to prevent them were studied. The main point of this study is assumed that coating crack are caused by mechanical load induced by structural behavior, and the numerical analysis methodology is newly introduced. Based on the results of the numerical analysis, it was confirmed that there is a high probability of coating cracks in the critical area where high stress occurs in the cargo hold. Therefore, the results obtained in this study will be useful to prevent coating cracks in future PC designs. [ABSTRACT FROM AUTHOR]

As an important green energy source for the future, deep-sea natural gas hydrate has attracted worldwide attention in recent years, and several trial exploitations have been carried out. Hydrates are prone to decomposition leading to terrain subsidence; hence, there is an urgent need to monitor terrain change during the exploration. In this study, a monitoring device based on six-axis Micro-Electro-Mechanical System array is developed to monitor the terrain subsidence during production of gas hydrate. The liability of the device has been tested both by lab experiments and a sea trial in the "Shenhu" area of the South China Sea with water-depth of 1,203 m. The device performed in-situ monitoring for 193 consecutive days; the deformation of the seafloor terrain has been successfully measured, and the seafloor topography has been obtained and reconstructed, showing that the overall average uplift of the seafloor terrain is 0.82 cm, with a maximum uplift of 5.98 cm and a maximum subsidence of 3.21 cm. The result shows that the geological conditions in the "Shenhu" area are stable, which provide a reference for the development of hydrates. [ABSTRACT FROM AUTHOR]

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Accurate depth control and prediction are fundamental for scientific observations on time and space scales. In this study, the depth control performance of Smartfloat, which is a novel observation platform that integrates Argo and Glider, was analyzed by integrating sea-trail data and the adaptive step-size least squares (ASLS) parameter identification algorithm. First, a one-dimensional Smartfloat submersible model that considers the nonlinear characteristics of the buoyancy drive system was established by accounting for the influences of seawater density and pressure shell contraction. The discrete motion model was then reconstructed using the expression form of the correlation function, to reduce the influence of external interference on the identification. The anti-data saturation function of the parameter identification algorithm was realized by adjusting the value of the covariance matrix. Finally, sea trial data with a large depth and full profile were analyzed following a trial conducted in the South China Sea in 2022, and the theoretical calculation results were compared with the parameter identification and depth prediction results. The results revealed that when compared with traditional least squares and support vector machine identification algorithms, the proposed ASLS algorithm demonstrates a higher convergence speed and smaller prediction error. The ASLS algorithm can predict the performance parameters of large-delay drive systems such as underwater vehicles, and provides certain models and data support for the accurate control and prediction of depth. • A Smartfloat model considering the buoyancy drive system was established taking water density and shell contraction into account. • The algorithm's anti-data saturation function is achieved by adjusting the covariance matrix value. • The comparison indicated that ASLS algorithm can predict the performance parameters of large-delay drive systems. [ABSTRACT FROM AUTHOR]

The automatic classification of fish species appearing in images and videos from underwater cameras is a challenging task, albeit one with a large potential impact in environment conservation, marine fauna health assessment, and fishing policy. Deep neural network models, such as convolutional neural networks, are a popular solution to image recognition problems. However, such models typically require very large datasets to train millions of model parameters. Because underwater fish image and video datasets are scarce, non-uniform, and often extremely unbalanced, deep neural networks may be inadequately trained, and undergo a much larger risk of overfitting. In this paper, we propose small convolutional neural networks as a practical engineering solution that helps tackle fish image classification. The concept of "small" refers to the number of parameters of the resulting models: smaller models are lighter to run on low-power devices, and drain fewer resources per execution. This is especially relevant for fish recognition systems that run unattended on offshore platforms, often on embedded hardware. Here, established deep neural network models would require too many computational resources. We show that even networks with little more than 12,000 parameters provide an acceptable working degree of accuracy in the classification task (almost 42% for six fish species), even when trained on small and unbalanced datasets. If the fish images come from videos, we augment the data via a low-complexity object tracking algorithm, increasing the accuracy to almost 49% for six fish species. We tested the networks with images obtained from the deployments of an experimental system in the Mediterranean sea, showing a good level of accuracy given the low quality of the dataset. [ABSTRACT FROM AUTHOR]

The wave glider is an ocean-wave-propelled autonomous marine vehicle with unique dual-body architecture, which can converse the energy obtained from the ocean wave into the forward thrust. In this paper, the dynamic models of the submerged glider based on dynamic characteristics of tandem hydrofoils and the surface float were separately established. The pitching angles of the hydrofoils and the submerged glider and the angle of attack between hydrofoils and relative current were considered for dynamic models and hydrodynamic coefficients. The translational hydrodynamic coefficient term for high-angle-of-attack passive motion of the submerged glider was calculated from static test simulations by using Computational Fluid Dynamics (CFD). Moreover, the rotational damping coefficients and added mass coefficients varying with the pitching angle of hydrofoils were analyzed by the simulation of the vertical planar motion mechanism (VPMM) tests. Furthermore, the numerical simulation of longitudinal motion with the computed hydrodynamic coefficients was performed, and the simulation results were compared with the sea trial data. The analysis was performed, and conclusions were drawn, which would provide a theoretical reference for the design of the wave glider. [ABSTRACT FROM AUTHOR]

A joint multiple-input multiple-output (MIMO) processing framework is proposed to exploit spatial diversity and moving cues for the enhancement of target detection in a shallow ocean environment. Orthogonal signals are transmitted to illuminate different aspects of a target and beamforming operation is carried out over the received data for estimating target bearing. The target range is achieved by a replica correlation integrator where the beamformer outputs are matched with transmitted signals. After meanshift clustering algorithm is carried out over the bearing-range spectrums to generate the clutter centers, the potential trajectories of targets can be tracked by an improved Bernoulli filter with inputs of these centers. The at-sea experimental results have shown the effectiveness of the joint processing framework in MIMO detection of moving targets.

As well known, ships which have complex production processes are subject to various tests made on every stage in many fields from the beginning to the end of the production. After the tests are completed successfully, the ship is delivered to the ship-owner. “Sea trial” being the last stage of these tests, is examined in detail in this study. The purpose of this study is to plan the tests performed in the sea trial by the means of computer programs and to suggest shorter completion period for the tests.Thus, reducing the total cost ofthe cruising. Moreover, shortening the duration ofthe cruise will be a factor that can speed up the delivery ofthe ship. For this purpose, the tests and processes performed during the sea trial are listed. A cruise process flow diagram including all the tests applied under normal conditions was created, and the data were entered into the SIMIO simulation program. As a result, it was determined that the total cruising time was 28,0989 hours. After that, a new flow diagram was created by making some improvements in the current testing process, and a new simulation model was built up. In the new simulation model, total time spent to complete the tests were 25,3567 hours, so the testing time was shortened by 2.75 (9,76%) hours.

The underwater glider has difficulty accessing the complex and narrow hadal trench for observation, which is affected by its limited regulation capability of pitch angle (−45°~45°). In this study, a compact attitude regulating mechanism is proposed to extend the regulation range of pitch angle from −90°to 90° and to install it on the hadal-class underwater glider Petrel-XPLUS. Subsequently, the dynamics model of Petrel-XPLUS is established using dual quaternions to solve the “gimbal lock” problem caused by the increased pitch angle range. Within the extended pitch range, the motion modes of the glider are enriched into long-range, virtual mooring, and Lagrangian float modes for long-range, small-area, and current-following observation missions, respectively, and are analyzed using the established dynamics model. Moreover, a ballast method was used to modify the pitch angle range and initial equilibrium state of a constructed underwater glider. Finally, Petrel-XPLUS achieved a pitch angle regulation range of −90°~90° in a water pool experiment and completed three consecutive profiles in a sea trial in the Challenger Deep, Mariana Trench, with all depths over 10,000 m, of which the maximum depth was 10,619 m. The proposed mechanism and methods can also be applied to other submersibles to facilitate ocean observations.

Recently, shipyards have been booming in the product carrier (PC) market of the global shipbuilding industry. Due to the rising market conditions, orders for large container vessels and PCs are also steadily increasing. According to the industry, freight rates for LR tankers (70K) and MR tankers (50K) in the shipbuilding industry have rose to the highest level during the previous year. In order to secure the competitiveness of PCs, various core items are required, and Korean shipbuilders have been leading the market for a long time based on their knowledge of the design and production of low-fuel ships. In recent years, there have been frequent cases of coating cracks in the cargo hold after sea trial. All relevant rules presented by the classification so far are structural design, safety evaluation, and inspection standards, and coating cracks are considered a problem for coating makers. In other words, they must establish a standard coating measure agreed upon by all parties (owner, shipbuilder, and coating maker); therefore, solutions have been proposed by each shipping company. In this study, the causes of coating cracks occurring in the cargo hold of PCs during tank tests in sea trials were analyzed and measures to prevent them were studied. The main point of this study is assumed that coating crack are caused by mechanical load induced by structural behavior, and the numerical analysis methodology is newly introduced. Based on the results of the numerical analysis, it was confirmed that there is a high probability of coating cracks in the critical area where high stress occurs in the cargo hold. Therefore, the results obtained in this study will be useful to prevent coating cracks in future PC designs.

When burying underwater cables using robots, heading control is one of the key functions for the robots to improve task efficiency. This paper addresses the heading control issue for URI-T, an ROV for underwater construction tasks, including the burial and maintenance of cables or small diameter pipelines. Through modeling and identifying the heading motion of URI-T, the dynamic characteristics and input limitation are analyzed. Based on the identification results, a PD type controller with appropriate input treatment is designed for the heading control of URI-T. The performance of the heading controller was verified in water tank experiments. The field applicability of the proposed controller was also evaluated through the sea trial of URI-T at the East Sea, with a water depth of 500 m.

The automatic classification of fish species appearing in images and videos from underwater cameras is a challenging task, albeit one with a large potential impact in environment conservation, marine fauna health assessment, and fishing policy. Deep neural network models, such as convolutional neural networks, are a popular solution to image recognition problems. However, such models typically require very large datasets to train millions of model parameters. Because underwater fish image and video datasets are scarce, non-uniform, and often extremely unbalanced, deep neural networks may be inadequately trained, and undergo a much larger risk of overfitting. In this paper, we propose small convolutional neural networks as a practical engineering solution that helps tackle fish image classification. The concept of “small” refers to the number of parameters of the resulting models: smaller models are lighter to run on low-power devices, and drain fewer resources per execution. This is especially relevant for fish recognition systems that run unattended on offshore platforms, often on embedded hardware. Here, established deep neural network models would require too many computational resources. We show that even networks with little more than 12,000 parameters provide an acceptable working degree of accuracy in the classification task (almost 42% for six fish species), even when trained on small and unbalanced datasets. If the fish images come from videos, we augment the data via a low-complexity object tracking algorithm, increasing the accuracy to almost 49% for six fish species. We tested the networks with images obtained from the deployments of an experimental system in the Mediterranean sea, showing a good level of accuracy given the low quality of the dataset.

The wave glider is an ocean-wave-propelled autonomous marine vehicle with unique dual-body architecture, which can converse the energy obtained from the ocean wave into the forward thrust. In this paper, the dynamic models of the submerged glider based on dynamic characteristics of tandem hydrofoils and the surface float were separately established. The pitching angles of the hydrofoils and the submerged glider and the angle of attack between hydrofoils and relative current were considered for dynamic models and hydrodynamic coefficients. The translational hydrodynamic coefficient term for high-angle-of-attack passive motion of the submerged glider was calculated from static test simulations by using Computational Fluid Dynamics (CFD). Moreover, the rotational damping coefficients and added mass coefficients varying with the pitching angle of hydrofoils were analyzed by the simulation of the vertical planar motion mechanism (VPMM) tests. Furthermore, the numerical simulation of longitudinal motion with the computed hydrodynamic coefficients was performed, and the simulation results were compared with the sea trial data. The analysis was performed, and conclusions were drawn, which would provide a theoretical reference for the design of the wave glider.

This paper proposed a compact design of the subsea cobalt-rich crust mining vehicle with a general purpose support vessel for subsea resource exploration, sample collection, and research. The necessary functions were considered in the concept design, including walk, crushing/mining, sample collection, cutter head adaptation, vehicle orientation, crust texture measurement, awareness, positioning, and navigation. The prototype was tested in both tank and subsea environment. The sea trials were carried out with the support of a general purpose support vessel. The track design worked well in both the tank and subsea environment and the mining vehicle walked smoothly in the sea trial. The crust was crushed to the size of 2 mm and 10 mm with different cutting parameters and successfully collected by the jet pump, 6 kg in total. The crust texture was measured by the onboard sonar successfully and can be used for cutting parameter selection. The cameras captured the images of the subsea environment, but the actions of crushing and sample collection produced plumes, which blocked the camera vision. In the situation, the front image sonar can be used to keep the vehicle away from big rocks. The mining vehicle is not limited to the mining and sampling of subsea cobalt-rich crust. Most of the subsea solid resources on the seabed can be considered to use the compact mining vehicle for sampling and related research. The only issues to be considered are the crushing ability and sample size required.

This paper suggests an estimation method for ship’s hydrodynamic coefficients, which is based on the system identification method that calculates an optimum value in a mathematical way. For the purpose of modelling existing ships, this study collects real ship sea trial data as benchmarks. Prior to the optimization, a sensitivity analysis is carried out for easy and effective optimization. The simulation results using optimized coefficients agree well with corresponding benchmarks. Following this, with various trim and draught conditions, this study suggests new estimation formulas that concern all trim and draught conditions. Simulation results applying the estimation formulas are satisfactory in regard to a corresponding benchmark, compared to a result obtained by using an existing regression formula.

A crucial issue that cannot be ignored in deep-sea resource surveys and scientific research is underwater positioning and navigation of deep-sea manned submersibles. Ultra-short baseline (USBL) is an important technical method for performing underwater positioning and tracking of manned submersibles and ensuring the safety of their underwater operations. Using USBL, the mothership can obtain the manned submersible's position in real time. Furthermore, the manned submersible can obtain its own position at longer time intervals using digital underwater acoustic communication to assist the pilot in driving. Long baseline (LBL) is a significant supplement to USBL because it is an independent positioning system that provides more accurate and real-time navigation and positioning data for manned submersibles in large areas and deep seas. In this paper, we analyzed USBL sea-trial calibration, its application in real diving, and details of LBL sea-trial using the Jiaolong deep-sea manned submersible as a case study. Data measured during 10 consecutive dives of the Jiaolong manned submersible are utilized to analyze the USBL positioning performance. We found that the positioning performance (relative slant range error, relative depth error, and data efficiency) is consistent with calibration results. Finally, a rectangular path with a length of 900 m and breadth of 300 mis designed to verify LBL performance in deep sea. The LBL sea-trial results show that the positioning accuracy of LBL is better than that of USBL. The USBL positioning performance is affected by the distance from the mothership and its heading.

The superior manoeuvrability of Z-drive equipped vessels is well known, though the comprehensive manoeuvring characteristics are seldom quantified. This paper presents the results of a sea trial on a 55 m ship equipped with twin Z-drive propulsion. Three manoeuvre types were conducted: turning circles, effective turning tests, and crash stops. Each were done for a range of ship speeds and thruster azimuth angles. For the turning circles, steering modes using both a single thruster and dual thrusters were also examined. The effective turning tests were used to determine the best or best-compromise thruster angles to achieve a high rate-of-turn with the least loss of ship speed. The crash stop tests investigated two different stopping methods: full reverse thrust and stopping by swinging the thrusters to 90°. • Manoeuvring sea trials were performed on a ship with twin Z-drive thrusters. • The data was analysed to quantify the turning and stopping metrics of the ship. • Results show performance changes based on helm configuration and stopping method. [ABSTRACT FROM AUTHOR]

Three-dimensional (3-D) power prediction method from model test has been widely accepted and used for many years. Form factor k is the most important characteristics of 3-D method and very crucial to the accurate power prediction. However, it's rather difficult to get the accurate value of k for those ships with pronounced bulbous or large transom from model test. In this paper, a new method to predict power is proposed, using k from CFD while other data from model test (or experimental fluid dynamics (EFD)). Delivered power prediction using the combination of CFD/EFD method agrees well with sea-trial results. [ABSTRACT FROM AUTHOR]

Tidal current energy is a promising renewable energy resource. Full scale tidal current turbines (TCT) have been deployed all over the world. To verify the design methods of large TCTs with high reliability and efficiency, a 600-kW tidal current turbine was designed and tested in this study. This turbine consisted of a two-blade rotor, a low speed ratio gearbox and a medium speed generator. The turbine was grid-connected through a full-rated converter, and its speed was controlled to capture the maximum power. First, to reach high turbine performance, system design details and maximum power point tracking (MPPT) control strategy were considered. Then, the 600-kW turbine was manufactured, and an onshore test was carried out to test power transmission and control performance. The power performance of the blades and control system were further tested in the sea trial carried out in Zhoushan. Good agreement was obtained between theoretical analyses and test results. Finally, to ascertain causes for observed power fluctuations, the power spectral density (PSD) was analyzed; the results indicated that power fluctuations may be due to stream shear. • The developing process and considerations of a two-blade TCT are presented offering valuable reference. • Sea trial results demonstrated high efficiency of designed TCT. • Power fluctuation may be produced by stream shear and may reveal fatigue load. [ABSTRACT FROM AUTHOR]

To improve the observation capability of the ocean, the combination of the static cabled ocean observatory network and the dynamic autonomous underwater vehicle has attracted more and more attention. In this paper, a non-contact docking system for the autonomous underwater vehicle is developed to combine the advantages of the cabled ocean observatory network and the autonomous underwater vehicle. The system includes both acoustic and optical navigation, underwater wireless communication, non-contact power transfer, and monitoring and controlling of the docking system. This docking system was verified by sea trials at depths of 50 and 105 m. The autonomous underwater vehicle successfully docked 11 times, during which non-contact power transfer and wireless communication were completed. The charging power reached 682 W, with a total efficiency of 78.5%, and the efficiency of the power transfer unit was 92%. The rate of wireless data transfer reached 3.1 MB/s. For the first time, this docking system has realized complete homing and docking navigation, wireless communication and charging in a water depth of more than 100 m, thus establishing a good foundation for the combination of the cabled ocean observatory network and autonomous underwater vehicles. [ABSTRACT FROM AUTHOR]

Abstract We develop the approach to simulate the experiments with surface and underwater vehicles in towing tanks for Reynolds numbers Re, corresponding to sea trials, using discrete injection of polymer additives. The complete dynamic similarity between full-scale and tank tests is possible if both Froude number and Re are equal for a ship and its model. In traditional experiments, the first condition is only satisfied and the viscous and wave resistances are independently studied. The Toms effect is widely used in marine engineering, e.g., to reduce energy cost. In this work, it is applied quite differently. Re is higher and the skin friction coefficient c f is hence less for sea trials than for towing tanks. Injection of polymer additives allows decreasing c f on ship model to full-scale values, providing the complete similarity and reproducing sea trials in that way. We report the selected results of such novel approach that, in particular, include velocity profiles and c f for sea trial, towing tank and pipe experiments, plane boundary layer and 3D flow around propeller, rough and smooth surfaces. The data for full-scale and tank experiments agree well with each other. Highlights • Novel approach in both application of Toms effect and marine engineering to simulate sea trials. • Complete dynamic similarity for sea trials and towing tank tests using polymer drag reduction. • Сoinciding data on viscous and total resistances of ships for full-scale and model experiments. [ABSTRACT FROM AUTHOR]

Abstract The unmanned wave glider (UWG) is a new kind of wave powered unmanned marine vehicle for persistent marine environment monitoring. However, the heading control of UWG is unusual, mainly about the heading control of the surface float body (Float), since it is indirectly actuated and with a large lag of the control response. The adaptive heading control method for the Float with heading information fusion is discussed. The basic and improved arrangement methods of the desired heading of Glider are proposed. Via direct heading control of Glider, the heading control of Float is realized indirectly. Simulation and sea trial results demonstrate that the proposed adaptive heading control method improves the heading control performance of UWG significantly. Highlights • The uniqueness of the heading control problem of UWG is analyzed. • The basic and improved arrangement methods of the desired heading of Glider are proposed. • Simulation and sea trial results verify the effectiveness of the proposed adaptive heading control method. • The proposed adaptive heading control method improves the heading control performance of UWG significantly. [ABSTRACT FROM AUTHOR]

Semi-submersible heavy-lift barges are widely used for transporting large offshore structures over long distances. The float-on and float-off operations of such vessels are considered as high-risk tasks even today. Improper flooding sequence may lead to accidents including loss of vessels and human lives. The main objective of this study is to provide valuable findings and guidelines for the design of submerging operations based on the case study of an unsuccessful submerging sea trial. A quasi-static time-domain simulation was conducted to investigate the unsuccessful trial and design a new flooding sequence. Based on the simulation results, the causes of the unsuccessful trial have been identified. Moreover, a new flooding sequence is proposed after examining various options. Since the vessel's dimensions and ballast tank layout are typical and similar to many other heavy-lift barges, general conclusions for the design of submerging operations are summarized. [ABSTRACT FROM AUTHOR]

In order to accurately predict wave induced motion and load responses of ships, a new experimental methodology is proposed. The new method includes conducting tests with large-scale models under natural environment conditions. The testing technique for large-scale model measurement proposed is quite applicable and general to a wide range of standard hydrodynamics experiments in naval architecture. In this study, a large-scale segmented self-propelling model allowed for investigating seakeeping performance and wave load behaviour as well as the testing systems were designed and experiments performed. A 2-hour voyage trial of the large-scale model aimed to perform a series of simulation exercises was carried out at Huludao harbour in October 2014. During the voyage, onboard systems, operated by crew, were used to measure and record the sea waves and the model responses. The post-voyage analysis of the measurements, both of the sea waves and the model’s responses, were made to predict the ship’s motion and load responses of short-term under the corresponding sea state. Furthermore, numerical analysis of short-term prediction was made by an in-house code and the result was compared with the experiment data. The long-term extreme prediction of motions and loads was also carried out based on the numerical results of short-term prediction.