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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.

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]

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]

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 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]