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Hydraulic drive is one of the main driving methods of traditional bionic fish, which has the disadvantages of high driving pressure and significant radial expansion of the fishtail. In this research, two innovative structures are introduced in the fishtail design to overcome these drawbacks. Firstly, high-flexible origami technology is applied to the fishtail, significantly reducing the unwanted radial expansion of the fishtail and improving energy efficiency. Based on the experiments, the origami-structured fishtail can save up to 92.3% energy compared with the traditional fishtail. Secondly, according to the bionic principles, the hybrid neutral layer of the fishtail which is sandwich-structured with knitting methods was designed. The test results show that this novel hybrid neutral layer could save up to 56.7% energy compared to the fishtail with a rigid neutral layer. A bionic fish in BCF model (Body and/or Caudal Fin propulsion) is fabricated and tested in a water tank. The results prove that the new bionic fish with the innovative fishtail obtain a good straight-line swimming direction and turning ability. This study could provide an important reference for the bionic design to mimic real fish. • A new type of fishtail is designed with an origami-style driven structure and a neutral layer that mimics a real fish's bone. • The structure of the elastic fluid driver adopts the folding paper structure to expand and contract efficiently. • Inspired by traditional Chinese knot structure, the neutral layer of the original rigid body structure was scattered first and then connected by knot structure to form a whole structure. • The novel fishtail shows excellent energy efficiency in experiments. [ABSTRACT FROM AUTHOR]

The increased application of Information and Communications Technology in automation and digitization is the driving concept towards the actualization of the Industrial Revolution 4.0. Many aspects of industrial design and operations including offshore engineering have been automated. However, the selection procedure of mooring design parameters including azimuth angle, pretension, diameter, fairlead slope, and mooring radius, which is a critical aspect of mooring system design has remained heavily based on a manual approach despite the availability of sophisticated hydrodynamic analysis software. Up to date, there is no proper review on optimisation techniques that have the potential of automating these procedures. In the past, some of the few available mooring optimisation procedures consider only the mooring lines for the prediction of optimal platform offset without due consideration to the integrity of the risers. Thus, the significance of adopting an integrated riser-mooring design methodology in the optimisation of mooring design variables is discussed in this paper where the integrity of the riser is adequately represented using a Safe Operation (SAFOP) zone polar diagram. We also review the developmental transition from the use of classical to Evolutionary Algorithms (EA) in the optimisation procedure. EA has been acknowledged as a practical alternative for solving mooring optimisation problems. Hence, some of the EA techniques are presented and their computational capabilities explored. In the last part, a concise review of the application of optimisation techniques for mooring optimisation of the different offshore floating platforms is presented based on their capabilities in minimizing platform offset and efficiency in terms of simulation time. So far, EA techniques like the Differential Evolution (DE), variants of Genetic Algorithms (GA) and Particle Swarm Optimisation (PSO) have been used to optimize mooring line design variables. Based on the discussions, the potentials of DE, RegPSO and other variants of PSO can be further explored for better efficiency. • Previous studies addressing differential evolution (DE), genetic algorithm (GE) and particle swarm optimisation (PSO) techniques used for optimisation of mooring parameters have been critically reviewed. • The integrated riser -mooring design methodology is effective in accounting for integrity of riser and mooring systems. • The application of evolutionary algorithms, particularly the variants and hybrids of DE ,PSO and GA, have proven to be efficient optimisation of mooring systems. • Some variants of PSO like the RegPSO have demonstrated improved capability in terms of escaping premature convergence , thereby resulting in better computational efficiency. [ABSTRACT FROM AUTHOR]

Autonomous ships are vulnerable to a spectrum of potential faults, including propeller damage, shaft-line failures, and electrical supply disruptions. Swift fault detection is critical to minimize the potentially catastrophic consequences of these issues. In this paper, we introduce an innovative digital twin-based method for diagnosing faults in autonomous ships. Our digital twin system collects data from the ship's sensor array, conducts comprehensive analysis, computes fault parameters, and provides real-time visualizations of the findings. To achieve this, we utilize the ship's dynamical model and employ a novel adaptive extended Kalman filter (AEKF) algorithm to estimate the severity of these faults. We evaluate the effectiveness of this approach through numerical simulations and practical implementation in an autonomous surface vehicle called the Otter, developed by Maritime Robotics. The experimental results, which consider both normal and faulty ship propulsion systems, underscore the significant potential of this novel approach to improve ship condition monitoring during operational activities. • This paper presents digital twin-based fault diagnosis architecture. • The fault diagnosis algorithm is based on a novel AEKF method. • The approach is demonstrated in a real-world scenario using a small autonomous vessel. [ABSTRACT FROM AUTHOR]

Aiming at the problem that the distribution of explosion load in the cabin and the propagation law of structural impact response was unclear, this paper established the numerical calculation model of explosion in a closed cabin by ALE (Arbitrary Lagrangian Eulerian) method. There was an apparent convergence of shock waves at the cabin's corners, and the pressure relief hole's area and its position significantly affected the peak of quasi-static pressure. The peak acceleration of the deck structure decreased exponentially as the distance from the location of charge increased. Peak acceleration decreased by approximately 50% for each bulkhead crossing. There was a "paper window effect" during the cabin interior explosion on the whole ship. It meant there was a limit to the value for the energy generated by the explosion to be transmitted along the frame structure. When the charge was 150 kg, it reached the limit of the energy transferred by the structure in this paper. The response of the distant structure did not change significantly with the increase in the charge quality. The research revealed the impact response propagation mechanism in the structure and provided a reference for designing protective structures. • The shock wave shows noticeable convergence in the cabin corner, where the area and position of the pressure relief hole significantly affect the peak quasi-static pressure. • The existence of a bulkhead greatly affects the maximum acceleration, each additional bulkhead results in approximately a 50% reduction. • The investigation reveals a remarkable "paper window effect" during the localized explosion of the entire vessel. [ABSTRACT FROM AUTHOR]

Research on fishing vessels worldwide began in the 1850s and continues to increase to this day. In Turkey, academic studies on fishing vessels commenced with the establishment of the Ata Nutku Ship Model Experiment Laboratory in 1953. Academic studies on fishing vessels in Turkey can be divided into three periods: the early period studies, the İTU fishing vessel series studies, and the Black Sea type fishing vessels studies. The early period studies started in the 1950s and continued until the 1970s, focusing on Taka, Çektirme, and Alametro type fishing vessels. The İTU fishing vessel series studies began in 1979 under the leadership of Prof. Dr. Kemal KAFALI, in collaboration with İTU and TÜBİTAK, based on fishing vessel forms developed through model experiments, and have continued to the present day. The third period, the Black Sea type fishing vessels studies, started in the 1990s and research on these forms is still ongoing. These fishing vessels, generally built in the Black Sea region, are now used in all seas and oceans. This study examined master's and doctoral theses, articles, and conference papers from these three periods. The subjects were analyzed in a cause-and-effect relationship, and the information contained was summarized. • Academic studies on fishing vessels in Turkey. • Doctoral and master's theses, articles and conference papers from 1950 to the present. • Studies on Taka, Çektirme, Alametro. • Studies on ITU fishing boats series. • Studies on the Black Sea type fishing vessel. [ABSTRACT FROM AUTHOR]

This paper aims at the identification and assessment of High-Impact Research Papers (HIRPs) on the Berth Allocation Problem (BAP) research at marine terminals. The BAP objective is to optimally assign and schedule ships at berthing positions along a quay, as well as to determine the berthing times and positions of ships at a port. The purpose of this study is to facilitate the work of the relevant research community and ultimately promote the research quality in this area. In meeting this objective, the paper utilizes a systematic and fair method to determine HIRPs of the BAP, which is based on the h -index and the g -index. An in-depth bibliometric analysis of the identified studies reveals their key features and characteristics. The analysis was conducted using the VOSviewer and bibliometrix R-package software programs. The main findings provide many useful insights on the BAP research development. The adopted approach and associated analysis results present an up-to-date detailed picture of the BAP research and constitute a valuable tool for its applications into other relevant research areas. The common trends in the reviewed HIRPs and important future research needs are discussed in a comprehensive manner. This survey study can be viewed as the first attempt for a comprehensive bibliometric survey of the high-impact BAP literature, which will be of a great value to researchers and industry practitioners. Furthermore, the proposed methodology for the identification of HIRPs can be used not only for the BAP research but for the literature surveys in other domains as well. [Display omitted] • A comprehensive analysis is conducted for the Berth Allocation Problem (BAP) research. • High Impact Research Papers (HIRPs) in the BAP research are identified and analyzed. • The co-authorship relations among countries, institutes, and authors are investigated. • Trending models of HIRPs and their solution techniques are discussed. • The statistical techniques for mapping and network analysis of HIRPs are presented. [ABSTRACT FROM AUTHOR]

This paper develops a novel unscented Kalman filter-model free adaptive predictive control (UKF-MFAPC) method for an underactuated hovercraft speed and heading stabilization under the influence of measurement noise. First, the proposed method is based on the compact form dynamic linearization (CFLD) technique, which involves an analysis of the tight format dynamic linearization method. This approach specifically addresses the unique non-real-time scalability of the heading control subsystem, rendering the CFDL method unsuitable. Through redefining the linear combination of lateral velocity and heading as output to fulfill all assumptions of CFDL methods, this scheme effectively mitigates the lateral velocity vibration problem of the hovercraft. Secondly, this controller introduces the measurement noise during the data collection process into the optimization function and combines the unscented Kalman filtering method with data-driven models, the influence of error suppression noise on the controller is suppressed, ensuring that the output can still be controlled within a certain range of expected values. This paper also delves into the convergence of tracking errors and examines the stability of bounded inputs and outputs. Finally, the noise suppression effect and stability of the UKF-MFAPC scheme are demonstrated through a comparative analysis of simulation results with proposed model-free methods. • This paper proposes a UKF-MFAPC method for the complex modeling problem of hovercraft, which does not need to consider the mechanism model of the controlled system in the controller design process. In response to the issues of slow convergence speed of the MFAC method, and sensitivity of adaptive parameter changes to control effectiveness, the controller design of the MFAPC method introduces I/O information for future time when obtaining data from hovercraft. The simulation indicates that Compared with the PID method, it has a smaller overshoot and is less sensitive to the selection of adaptive coefficients, and faster convergence speed compared with the MFAC method. • The UKF-MFAPC proposed in this paper uses UT transformation to increase the accuracy of data sampling and the interference suppression ability of the hovercraft controller in response to the issues of process noise and measurement noise interference in the control process of hovercraft. The simulation indicates that the UKF-MFAPC approach has higher noise resistance and a faster response speed when compared to the TD-MFAC method. • This paper proposes a redefinition method to define longitudinal and transverse velocities as data-driven outputs for the lateral velocity oscillation problem of hovercraft under high speed and high turning, which satisfies the quasi linear assumption of data-driven methods and solves the lateral vibration problem of hovercraft. [ABSTRACT FROM AUTHOR]

Tanker ships carry volatile cargo, presenting inherent risks of fire and explosion. Inert gas systems (IGS) are pivotal in mitigating risks by displacing oxygen in cargo tanks. However, failure of IGS components may lead to fatal consequences such as loss of life and marine pollution. This paper prompts a systematic approach integrating Quantitative Hazard and Operability (HAZOP) analysis under D-S (Dempster–Shafer) evidence theory and Fault Tree Analysis (FTA) to predict and quantify the fire and explosion risk associated with IGS malfunction on tanker ships. The methodology systematically evaluates failure probabilities, and consequences using HAZOP to identify critical scenarios. D-S evidence theory is employed to address uncertainties and incorporate expert knowledge into the analysis. FTA is applied to model fault propagation and assesses the likelihood of fire and explosion events based on the identified failure scenarios. A case study is presented to demonstrate the application of the proposed methodology, illustrating effectiveness in identifying high-risk scenarios and providing insights for enhancing operational safety minimising the risk of IGS on tanker ships. The findings show that the risk of fire and explosion in the inert gas system due to the high concentration of oxygen entering the tank was found to be 2.86E-01. Besides its robust theoretical background, the findings of the paper provide the utmost contribution to ship crew, ship inspectors, HSEQ managers and safety professionals for proactive risk mitigation strategies, contributing to the advancement of safety management practices in the maritime industry. • A systematic risk analysis for fire and explosion associated with IGS failure on tanker ships is conducted. • Quantitative Hazard and Operability (HAZOP) analysis under D-S (Dempster-Shafer) theory of evidence and Fault Tree Analysis (FTA) is proposed. • The risk of fire and explosion in the shielding gas system from the high concentration of oxygen entering the tank is 28%. • The most important root cause of this high risk of 28% is incorrect air and fuel line pressure measurement entering the boiler. [ABSTRACT FROM AUTHOR]

This paper explores the disturbance observer based adaptive trajectory tracking control strategy of Unmanned Surface Vehicle with input and state quantization. To devise the controller without prior knowledge of quantization parameters, a linear analytical model of input quantization is introduced, facilitating adaptive parameter estimation. Estimations of external disturbances and quantized states are obtained through the application of a disturbance observer. Additionally, the control law is constructed using a combination of backstepping control and dynamic surface techniques. By leveraging Lyapunov stability theory, this paper demonstrates the stability of the trajectory tracking control system for Unmanned Surface Vehicle with input and state quantization, as well as the boundedness of errors between quantized and non-quantized variables within the closed-loop control system. Finally, the effectiveness of the proposed tracking approach is validated through comprehensive simulation experiments. • This paper incorporates signal quantization into the USV trajectory tracking method. • Disturbance observer is used for estimating quantized states and external disturbances. • This paper introduces a linear analytical model of the input quantization. [ABSTRACT FROM AUTHOR]

In this paper, data-driven models for wind speed forecasting are established by incorporating atmospheric variables, such as temperature, humidity divergence and etc. as input, and using forecasted wind speed as the output. Input data, statistics in every 3-h interval, utilized in this study are from CERA-20C within a period from the year 2001–2010. In the models, a feature selection technique is proposed to identify the relative dependence of each input to the output. Through a comparison between results with and without the selection technique, it is observed that the technique helps to select the most pertinent inputs, and thus further improve the forecast performance, accuracy and efficiency. In addition, three data-driven models are further revealed to acquire the best forecast accuracy, by including temporal effect, spatial effect, or coupled temporal and spatial effects on atmospheric conditions, which are named as temporal-based, spatial-based and hybrid data-driven models, respectively. By comparing the forecast performance among different models, it is revealed that the newly proposed hybrid data-driven model with feature selection technique is more suitable in dealing with wind speed forecasting. Moreover, an additional case study further reinforces the feasibility of the newly proposed hybrid data-driven model for forecasting of wind direction. The proposed date-driven models in the paper provide a high-cost efficiency alternative for wind speed forecast using machine learning instead of physical models. This approach can assist engineers in making prompt and informed decisions even when resources are constrained during emergency conditions. • Cost-efficiency wind speed forecast methods are developed by incorporating atmospheric variables into data-driven models. • Data-driven models are generated by considering temporal and spatial effects of atmospheric conditions on wind fields. • The feature selection is utilized to select the appropriate inputs and to enhance the accuracy of wind speed forecasts. • The important atmospheric variables that significantly affect wind fields are identified. • The feasibility of the newly proposed hybrid data-driven model for wind direction forecasting is demonstrated. [ABSTRACT FROM AUTHOR]

The deep-sea environment restricts the collection of reliable data for subsea connectors, leading to a lack of available failure data to develop connection fault detection processes and maintenance strategies. Therefore, this paper proposes an FMECA-BN model. The model developed an algorithm for mapping Risk Priority Number (RPN) to Bayesian network (BN) parameters and enhanced the details for mapping BN structures to match the diversity of FMEA. This enables the establishment of a BN based on a given Failure Mode, Effects, and Criticality Analysis (FMECA). The model was applied to the development of the Subsea Horizontal Clamp Connector (SHCC) to quantify and evaluate failure modes during the connection stage, creating an effective detection process. Then, the system's reliability variations caused by component degradation were analyzed using transformed dynamic BN, offering information for maintenance strategies based on availability. The reliability analysis results of the FMECA-BN model demonstrate a statistical error of 4.5% compared to actual data samples, proving the model's efficacy in addressing issues of information asymmetry, incomplete reliability data, and uncertainty. The analysis revealed that the developed SHCC requires a maintenance cycle of 14,892 h to maintain a 0.99 reliability level, with a cumulative failure probability of 4.6% after 20 years. • This paper presents an FMECA-BN model that incorporates the functionality of mapping Risk Priority Number (RPN) to Bayesian network node parameters to address the challenge of insufficient prior data. • This paper is based on the engineering context and delves into the specific process and characteristics of failure modes occurring in the developed subsea horizontal clamp connector (SHCC). The conversion of static Bayesian networks to dynamic Bayesian networks has been employed to accomplish the reliability analysis and data update for the SHCC. • For the first time, a quantitative analysis of SHCC is conducted at both the system and component levels, effectively addressing the issues related to connection fault detection and formulating service and maintenance strategies based on availability. [ABSTRACT FROM AUTHOR]

The combined wellhead has the advantage of high bearing capacity and broad prospects for application in the construction of deep water surface wells; therefore, it is important to conduct relevant research to guide the construction of combined wellheads. The aim of this paper is to study the mechanical characteristics of the combined wellhead in the longitudinal direction and establish the method for real-time calculation of the bearing capacity of the combined wellhead taking into account the effects of installation. The variations of external wall pressure and internal soil pressure during installation and the waiting process of the combined wellhead were investigated by indoor experiments. The installation efficiency of the combined wellhead at different negative pressure conditions was also compared. The experimental results show that the pressure on the outer wall of the combined wellhead facility gradually increases as the depth of the combined wellhead facility increases, and the closer it is to the bottom, the greater the soil pressure. The pressure on the inner soil will increase rapidly during the installation process to almost the same level, while the pressure on the outer soil will increase slightly. During the waiting process of the combined wellhead, as the waiting time increases, the soil damaged during the installation process gradually recovers, and the external wall pressure gradually rises. Moreover, the pressure on the outer wall gradually increases, the pressure on the inner soil decreases slightly leveling off within about 24 h. An appropriate increase in suction pressure facilitates the installation of the combined wellhead, and approximately 2.0 L/min is the optimal option for installation. The computational model developed in this paper and the experimental measurements corroborate each other. These combined wellheads significantly improve the stability of deep water soft-soil well construction and provide a theoretical benchmark for developing oil, gas and hydration in deep water. • The pressure at the outside wall exhibited an exponential function during the installation of the combined wellhead. • During the installation of the combined wellhead, the pressure on the inner wall is slightly higher than that on the outer wall. • The combined wellhead is in place, the fluid from the outside gradually enters the combined wellhead inside. • Increasing the suction power appropriately can guarantee both the operating effect and the efficiency. [ABSTRACT FROM AUTHOR]

In maritime search and rescue (SAR), the boat swarm mode can greatly improve the success rate, but because of the influence of the curvature of the earth, the communication distance on the ground is short. Relay communication using unmanned surface vehicles (USVs) is the main means of maritime SAR, but communication speed and reliability are the core difficulties. To solve the problem, this paper proposes a trajectory planning aided unmanned surface vehicle optimization communication method with hierarchical reinforcement learning (TP–OC–HRL), which introduces relay USVs into the maritime SAR system and uses trajectory planning and the adaptive orthogonal frequency-division multiplexing (OFDM) technology as variables to optimize the communication rate of the SAR system. The paper proposes a communication optimization scheme based on hierarchical reinforcement learning, which divides the modulation coding scheme and the trajectory planning of the USVs into two hierarchical subproblems to improve the communication rate of the maritime SAR system through reinforcement learning. The experimental verification in the island area of the South China Sea shows that the TP–OC–HRL algorithm proposed in this paper has a faster convergence speed compared with that of the existing relay communication optimization methods, and can improve the communication rate of the maritime SAR system under the condition of meeting the reliability. • We established a high-speed maritime search and rescue communication method utilizing USV relays. • We established a surface USV communication optimization scheme based on hierarchical reinforcement learning. • Our method can adjust the MCS in real time based on the motion status of the USV, effectively improving the communication speed. [ABSTRACT FROM AUTHOR]

In the paper, a 3-D numerical model based on the olaFlow solver to study the vegetation effects on flow characteristics and turbulent structure as well as wave attenuation under combined regular wave-unidirectional current conditions. The results show that following currents can either promote or suppress wave attenuation within the velocity magnitude specified in the paper, whereas opposing currents always enhance wave damping. Moreover, the emergent canopy and a staggered configuration resulted in increased wave-height attenuation. The time-averaged velocity patterns are various for submerged and emergent scenarios with different configurations. Furthermore, the time-averaged velocity magnitude inside the canopy decreases as the wave height increases for following flow conditions, while it increases in opposing currents. The time-averaged turbulent kinetic energy (TKE) inside the canopy follows the same distribution pattern as that of time-averaged velocity, and the maximum values of time-averaged TKE for the submerged and emergent canopies appear at the free surface, and above, respectively. The flow field characteristics show different patterns for various wave-current combinations and vegetation configurations, which provides a microscopic perspective to understand the interaction of vegetation-wave-current. • A three-dimensional numerical model using cyclic boundary based on the OlaFlow solver was developed. • Time-averaged velocity and turbulent kinetic energy within submerged/emergent canopy present different patterns. • Microscopic flow fields characteristic within the vegetation in following and opposing currents are presented. [ABSTRACT FROM AUTHOR]

Control room operators on offshore platforms play an important role in realizing the safety instrumentation functions of the high integrity pressure protection system (HIPPS) during overpressure emergencies. Human reliability analysis is critical to the overpressure operation of offshore HIPPS, yet there are few studies. To remedy this gap, the paper proposes an integrated human reliability analysis method to analyse the impact of human intervention on offshore HIPPS safety. Considering the effects of context and cognitive performance on human reliability comprehensively, the improved cognitive reliability and error analysis model (CREAM) is established; The correction effect of external environmental factors on response failure probability is quantified, and the improved human cognitive reliability (HCR) model is developed; The two improved models are organically combined to form an integrated methodology. Based on the behaviour characteristics of personnel emergency response, human error probability is calculated in stages to analyse human reliability. The findings indicate that the overall human error probability for HIPPS overpressure operations is 0.124 and particular attention needs to be paid to observation and decision-making operations. Besides the theoretical background, the paper provides practical contributions to personnel training, mission planning, and risk management of HIPPS to minimize the possibility of human error. • An integrated human reliability analysis method for offshore HIPPS is proposed. • The cognitive performance correction coefficient is introduced to improve CREAM. • The modification effect of external environmental factors is quantified to improve the HCR model. • Human error probabilities are calculated in stages based on personnel task characteristics. [ABSTRACT FROM AUTHOR]

An accurate prediction of motion responses of a moored floating structure requires high-fidelity coupled analysis between the structure and its mooring system in waves, which involves both mooring line dynamics and fluid dynamics. In this paper, we develop a nonlinear finite element dynamic mooring analysis module that allows large axial stretching of mooring lines under the open source CFD framework OpenFOAM, and couple it with an Overset CFD solver to establish a fully coupled finite element mooring-CFD analysis model for floating structures. The coupled model is advantageous over existing models in that it is able to deal with large axial mooring stretching and complex mesh motions induced by significant structure responses under severe operating conditions. The developed dynamic mooring analysis method is firstly validated against publicly available data. In order to validate the coupled model, a series of experimental tests were carried out for a semi-submersible platform moored by eight catenary lines under different operating conditions, including free decay, regular and irregular wave tests. The dynamic responses of the floating structure and mooring tension are analyzed and compared with experimental data. Results show that numerically predicted structure responses and mooring tension are generally in good agreement with experimental measurements. Meanwhile, the strongly nonlinear large-amplitude resonant motions generated by the interaction of irregular waves with the moored floating structure are also investigated. Comparisons reveal that the coupled model can accurately predict the resonant spectral peaks of the structure responses, indicating that the it is capable of simulating large-amplitude motions of moored floating structures. The coupled model developed in this paper can be further applied to study the survivability of moored floating structures under harsh sea conditions. • A finite element mooring dynamics module was developed in OpenFOAM. • The developed mooring module was coupled with an Overset CFD solver in OpenFOAM. • The coupled model was validated against model tests of a moored platform. • The coupled model can accurately predict large-amplitude motion responses. [ABSTRACT FROM AUTHOR]

According to the Novak's plane strain theory and Biot's wave equation, this paper proposes an analytical model for horizontal vibration of partially embedded offshore piles under distribution effect of wave loads (DEWL) incorporating the diffraction effects of waves. Firstly, for the pile above the mudline, the wave force acting on the pile is obtained through the method of separation of variables. Secondly, for the embedded section of offshore piles, the governing equations of the seabed are decoupled by introducing potential functions, and then the boundary condition of the seabed and the continuity condition at the soil-pile contact surface are combined to obtain the frequency domain analysis of the soil reaction forces. Furthermore, by applying the continuity condition of displacement at mudline and using the matrix transfer method, the analytical solution for the horizontal vibration characteristics (HVC) is derived. Finally, a comparison analysis with existing theoretical solutions is conducted to validate the rationality and accuracy of the analytical solution proposed in this paper. Based on this, a parametric analysis is conducted to discuss the effects of the parameters of the soil, the pile and the wave on the HVC of partially embedded offshore piles. • An analytical solution for the horizontal vibration of partially embedded offshore piles considering the distribution effect of wave loads is proposed. • The analytical solution is derived by the separation of variables technique and the transfer-matrix method. • The effect of wave load distribution on the horizontal vibration of partially embedded offshore piles is investigated. [ABSTRACT FROM AUTHOR]

The paper proposes a fleet size and mix vehicle routing model to optimize the river-sea liner shipping service. A mixed integer linear programming model is adopted as a rapid screening tool for strategic fleet planning to determine the type and number of river-sea vessels to deal with the fluctuation of the demand over the year, guaranteeing the efficiency and effectiveness of the shipping service. Moreover, the model provides a better-informed decision on the logistic infrastructure design, demand allocation and fleet size and composition in scenarios of demand uncertainty. Thus, the quantified decision support model increases the service level of the shipping service, reducing the frequent mismatches between fleet capacity and demand. A verification step aiming to test the behaviour of the model solution in a realistic case study is presented to analyse the impact of the demand fluctuation on the fleet composition. In conclusion, river-sea vessels enable door-to-door transport via coastal and inland waterways without transhipment. This approach offers a reliable and cost-effective solution. The findings of the work may enhance the state of the art, expanding the narrow studies on river-sea liner shipping services and demonstrating the advantages of river-sea vessels. • The paper proposes a fleet size and mix vehicle routing model to optimize the river-sea liner shipping service. • A mixed integer linear programming is adopted as a tool for strategic fleet planning i.e. the type and number of vessels. • A decision support model increases the level of the shipping service reducing mismatches between fleet capacity and demand. • A verification step aiming to test the behaviour of the model solution in a realistic case study is presented. • The river-sea transport without transhipment was shown to be a sustainable, reliable, and cost-effective. [ABSTRACT FROM AUTHOR]

Water-air trans-media flying submersible is a new type of unmanned vehicle with important engineering applications. This paper describes pool towing experiment and numerical calculation methods conducted to study the influence of the submersible's velocity on the free water-surface, the hydrodynamic characteristics, and the flow field structure. The working conditions researched in this paper include the water-surface navigation and underwater diving. The results show that the lift and drag of the submersible increase with velocity, but the trend and range are greatly affected by the water depth, especially those of the lift. The high-pressure area on the surface is mainly distributed in the bow and appendage structure inflow area, and the low-pressure area is distributed behind the high-pressure area and the back-flow area. The influence of the free water-surface causes the wake field to dissipate rapidly and become asymmetric when water-surface navigation. The free water-surface is a Kelvin wave system. The Kelvin angle decreases and the wavelength and amplitude increase with velocity. When navigating on the water-surface, the bow wave and tail wave form a double-row Kelvin wave. When diving underwater, a Bernoulli dome appears on the water-surface above the bow, and the surface forms a regular single-row Kelvin wave. • Hydrodynamic performance of a water–air trans-media flying submersible vehicle is studied. • The free water-surface evolution of the flying submersible vehicle at different velocities is analyzed. • The flow structure over the vehicle and the force of the vehicle are discussed. [ABSTRACT FROM AUTHOR]

This paper introduces an adaptive sampling strategy for a multi-vehicle sensor network to explore an underwater biological system known as the pelagic scattering layer, which is a region in the water column with a high density of marine organisms that reflect sound. Ever-changing ocean flow presents a challenge to multi-vehicle coordination in this process. The presence of an ocean flow field may disrupt inter-vehicle spacing so that the group loses communication, strays from a desired formation, or ends up with reduced area of coverage, especially for robotic drifting vehicles whose motion is largely influenced by the ambient flow field. However, those vehicles may also take advantage of the vertical variation of the flow to form a desired cohesive configuration since they can tune their vertical position via depth control. A motion-control algorithm, therefore, is a key element of the adaptive sampling strategy. The paper derives a decentralized coordination algorithm to stabilize a cohesive formation in a two-dimensional flow field with an initial unknown vertical distribution. The algorithm works with a distributed extended Kalman filter that generates a local estimate of the flow from pairwise range measurements between vehicles. Another component of the sampling strategy is the modeling of organism density dynamics using estimation of the density with local optical measurements, such as from onboard cameras. The density evolution is estimated using an ensemble Kalman filter and the results are fed into the motion-coordination algorithm. Numerical simulations illustrate the efficacy of this strategy and motivate ongoing and future efforts to extend the result to a three-dimensional geophysical flow. • A decentralized depth control algorithm guides multiple drifting vehicles to varying depths, ensuring cohesive, collision-free formation in shear flow. • Buoyancy control extends to unknown shear flow using extended Kalman filter for parameter estimation, enabling formation. • Ensemble Kalman filter estimates scattering layer density from depth predictions using operator and local measurements. [ABSTRACT FROM AUTHOR]

Pump-jet propulsion is a kind of propeller with excellent performance. Because of its high working efficiency and good anti-cavitation performance, it has been widely concerned and studied by scholars at home and abroad. This paper takes the self-designed pump-jet propulsion as the research object. The hydrodynamic and noise experiment of pump-jet propulsion was carried out based on the towing tank and the cavitation tunnel. It analyzes the mechanical characteristics and noise performance of pump-jet propulsion, compares and verifies the test results with CFD calculation results. The results show that the calculated values of hydrodynamic force and noise of pump-jet propulsion are in good agreement with the experimental test results, which further verifies the reliability of the calculation strategy in this paper. At the same time, it provides theoretical basis and data support for the performance forecast and optimization design of the subsequent pump-jet propulsion. • Hydrodynamic and noise experiment of pump-jet propulsion was carried out based on towing tank and cavitation tunnel in this paper. • The whole and rotor components in the axial and radial plane show obvious line spectrum characteristics at the axial frequency, blade frequency and their harmonic frequency. • The fluctuating range of the sound pressure level in the radial plane is approximately circular distribution, and there is no obvious sound field directivity. • The sound pressure directionality shows an approximate "8" shape distribution on the axial plane, showing the characteristics of the dipole sound source. [ABSTRACT FROM AUTHOR]

In offshore production platforms, horizontal three-phase separator is common process equipment. Its main function is to complete the dehydration and degassing of crude oil. Separator system is more complex, and its failure may cause significant economic losses and disastrous consequences. Therefore, it is critical to accurately and quickly identify where and why faults occur in the separator system. In this study, separator fault diagnosis model based on Bayesian networks is developed. Moreover, Sequential Monte Carlo simulation and physical model are introduced to overcome field problems such as missing separator failure data and the inability of experts to provide accurate empirical knowledge. Using this model, 13 faults in a separator in an offshore crude oil processing system are successfully diagnosed. Meanwhile, the proposed model is compared with deep neural network, convolutional neural network, and deep residual network, with accuracy rates of 100%, 91.34%, 87.99%, and 94.62%, respectively. Then, the diagnostic accuracy of each model for different faults is also compared in this paper under various signal-to-noise ratios. The results show that the method proposed in this paper has better noise immunity compared to the other three models. Therefore, the accuracy and robustness of the proposed model is further demonstrated. Finally, to analyze the fault-tolerance of the proposed model, 2–3 error evidence is randomly entered. The results show that the proposed model has better fault tolerance compared to data-driven Bayesian networks. • A Bayesian network-based fault diagnosis method for separators is proposed. • Overcome the problem of lack of separator fault data in the field. • Overcome the inability of experts to provide expert experience for separator. • Use physical model instead of human expert to improve modelling efficiency. • Use physical model to compensate for the shortcomings of Sequential Monte Carlo. [ABSTRACT FROM AUTHOR]

The dynamic analysis for nonlinear floating systems has been traditionally conducted in the time domain. Although the time-domain method can obtain a sufficiently accurate result, it is usually time-consuming in computation. This paper proposes a novel hybrid Laplace-time domain method for computing the response of nonlinear floating systems. In the proposed method, the nonlinearities of the system are treated as an additional external load. The external excitation is then divided into a number of segments, of which the response of the floating structure under each segment is computed by the pole-residue method operated in the Laplace domain. Along with the pole-residue method in each segment computation, the iterative technique is employed for dealing with system nonlinearities in the time domain. As the pole-residue method computes the response through simple algebraic operations in the complex plane and obtains analytical solutions, the proposed hybrid Laplace-time domain method is more efficient and accurate. Two numerical examples are carried out in this paper, in which one is an analytical single-degree-of-freedom (SDOF) nonlinear floating system and the other is a semi-submersible floating offshore wind turbine (FOWT) foundation with nonlinear damping. Both computational accuracy and efficiency of the proposed method are demonstrated through these numerical examples, by comparing the responses with those obtained by traditional time-domain methods. • A novel hybrid Laplace-time domain method is proposed for nonlinear system responses. • Analytical solutions are obtained by pole-residue operations in the complex plane. • The proposed method is more efficient than traditional time methods. [ABSTRACT FROM AUTHOR]

Due to the early stage of development for floating offshore wind turbines (FOWTs), there's a scarcity of effective methods and procedures for determining the overall dimensions of floating foundation. Moreover, the comprehensive dynamic response features of various foundation configurations remain inadequately understood. To tackle these limitations, this paper presents a global design approach for semi-submersible platform used to support a large-scale wind turbine. In this paper, the distance between offset column and main column (R OI), the radius of offset column (R O), the height of heave plate (H HP), the total draft of platform (H dft), the ratio of heave plate radius to offset column radius (R HP), and the ratio of the horizontal distance from anchor to fairlead to the water depth (x M) were selected as the initial design variables of the platform. A design of experiment based on the Taguchi method was performed to construct various combinations of design variables. Then, the physical properties and hydrodynamics of the platform, and controller dynamics were determined for each combination. The correlations between the variables and key outputs were studied. Finally, the multi-objective optimization for the foundation dimensions was performed based on the Taguchi method. Compared to other experimental cases, the FOWT with optimal variables (R OI = 29 m, R HP = 2.0, R O = 7 m, H HP = 6.0 m, H dft = 21 m, and x M = 4.0) exhibits excellent comprehensive performance, particularly outperforming the OC4 model overall, with a 26% increase in platform mass (excluding ballast mass). This study offers an insight into the nature of the design variables and the response outputs, and provides a optimization framework to optimize the foundation dimensions, which can then serve as initial points for a more detailed design. • Natural frequency and output of a FOWT with various platform parameters were studied. • Taguchi method is used to perform the DOE. • The correlations between variables and key outputs were studied. • The multi-objective optimization of the platform structure was performed and validated. [ABSTRACT FROM AUTHOR]

Floating bridges are economically attractive alternatives used for crossing wide and deep straits or fjords. They have played a crucial role in transportation since the early 20th century. Although several floating bridges are currently in operation worldwide, their design standards are not mature, especially associated with the dynamic response analysis. To this end, a review of the relevant advances and research directions of floating bridges is presented. In this paper, the development and types of floating bridges are briefly introduced. To evaluate the dynamic responses of floating bridges, research advances are reviewed from the perspectives of numerical simulations, model tests, and field measurements. It has shown that floating bridges are exposed to complex coastal environmental conditions in which combinations of various loads can induce significant load effects. Challenges can come from environmental inhomogeneity, structural flexibility, coupled effects, and multi-disasters. Besides, the existing research methods have more or less shortcomings, making it difficult to effectively analyze their dynamic responses. This paper summarizes the previous methods for the dynamic response analysis of floating bridges, with an emphasis on loads and load effects. Some recommendations and research opportunities for future work are also proposed. • Development and types of floating bridges are briefly summarized. • Relevant advances in design and analysis of floating bridges are reviewed. • Numerical simulations, model tests, and field measurements are addressed. • Challenges come from environmental modeling, load modeling, and response assessment. • Recommendations and research opportunities are identified. [ABSTRACT FROM AUTHOR]

As a mesh-free approach, the incompressible Smoothed Particle Hydrodynamics (ISPH) method has been often used for simulating wave-structure interaction problems. In the conventional ISPH method, the pressure-projection phase of solving the pressure Poisson's equation (PPE) is the most time-consuming. In recent years, the machine learning (ML) techniques has gradually shown their potential in accelerating the computational fluid dynamics. In this paper, the graph neural network (GNN) supported ISPH method (ISPH_GNN), in which the GNN replaces solving the PPE for the fluid pressure in the conventional ISPH, is adopted for numerical simulations of wave-floater interactions. To the best of the authors' knowledge, this is the first work to study the wave-floater interactions by using GNN supported ISPH method. More importantly, this paper demonstrates that the GNN trained only on data for simpler wave-only cases (i.e. no structure in the wave fields) can be satisfactorily applied to the cases for wave-floater interactions. More specifically, the paper will show this by using the ISPH_GNN with such trained GNN model to simulate various different cases, including the decay tests of a box, a floating box subjected to a wave, the interaction between wave and a moored floating breakwater and the violent green water impact on a floating structure. In most of the cases, the numerical results are validated by comparing with experimental data. Agreement between them is surprisingly satisfactory, being as good as those obtained by the conventional ISPH. The paper will also show that the ISPH_GNN requires much less computational time (97 times less for the cases concerned) than the conventional ISPH for estimating pressure involved in wave-floater interactions. This reveals a great potential that one can train the GNN using the datasets for simpler cases and then use the ISPH_GNN to simulate wave-floater interaction problems. • The first work to study the wave-floater interactions by using the graph neural network (GNN) supported ISPH method. • The GNN trained only on data for simpler wave-only cases can be applied to more complex cases for wave-floater interactions. • The ISPH_GNN can give satisfactory results for the relatively complex cases involving wave-floater interactions. • The ISPH_GNN takes much less computation time than the conventional ISPH for estimating pressure. [ABSTRACT FROM AUTHOR]

This paper proposes a novel fixed-time output feedback trajectory tracking control method suitable for autonomous surface vehicles (ASVs). Firstly, various complex uncertainty terms, such as unknown external disturbances, unmodeled errors, and actuator faults are considered in this paper. And these terms are uniformly converted into the total uncertainty terms through model transformation for convenience. Then, a fixed-time extended state observer (FTESO) with the newly expanded state is designed to observe and estimate the total uncertainty terms. Next, the saturation dynamic filter (SDF) is adopted to address the input saturation, and the saturation factors of SDF are incorporated into the trajectory error calculation to reduce the torque mutation caused by an excessive error in the control input. Finally, a fixed-time control law is proposed by taking into account the ASV system error and FTESO estimation state. Simulation experiments show that this method has excellent control performance, and this conclusion is validated through stability proof and case comparison. • A FTESO is designed to estimate the unknown states of ASVs. • A SDF is employed to address input saturation. • A novel FTOFC method is proposed for the stable and efficient operation of ASVs. [ABSTRACT FROM AUTHOR]

Floatover method has been widely applied in the installation of both fixed and floating platforms, which has the advantages of high efficiency, economy, and large lifting capacity compared with other installation methods. Few studies could numerically and experimentally simulate the continuous load transfer process which shows significant nonstationary characteristics. This paper conducts experimental research on the nonstationary mating process of the floatover system. The ballasting system based on the control logic of feedback adjustment is developed to adjust the draft and inertia properties of the floatover vessel, and the validation tests are conducted to verify the feasibility and reliability of the system. The load buffer devices are designed carefully and the piecewise linear spring simulation method is applied to simulate the nonlinear stiffnesses of the elastic cushion. The stationary model for 0% and 100% load transfer stages and the nonstationary model for continuous load transfer process are established and tested in the model tests, and the dynamic responses are analyzed by using statistical and spectral methods respectively. Stationary model tests indicate that the spectral characteristics and distribution of LMU (Leg Mating Unit) dynamic loads in transverse symmetric positions are similar, and the statistical values are also relatively close under different wave heads. The nonstationary dynamic responses are segmented according to the physical process, time-frequency spectrum and piecewise statistics diagram to find the critical stage. The greatest dynamic load occurs in the intermediate stage of the mating process when the larger stiffness of the LMU acts and the steel-to-steel contact will also occur. • A brief introduction and the main procedures of the floatover installation operation are presented. • The paper reviews the numerical and experimental modeling of floatover installation systems. • The hydrodynamic analysis and the nonstationary nonlinear dynamical system of the floatover system are introduced. • The strength and weaknesses along with the challenges of each modeling and method are discussed. [ABSTRACT FROM AUTHOR]

In recent times, marine engineers have progressively turned to collaborative efforts involving multiple ships to accomplish intricate tasks at sea and enhance the efficacy of maritime transportation. This trend is also observed in the context of surface ships, where coordinated actions among multiple vessels can enhance combat capabilities. Nevertheless, the assessment of ship formation coordination's effectiveness has emerged as a significant challenge. Consequently, this research paper presents a quantitative evaluation framework for ship performance indicators and develops a ship formation model grounded in multi-objective constraints that account for the complexities of the marine environment. This paper presents the establishment of a ship evaluation system that encompasses the impact of auxiliary equipment, the ship's platform, and trained personnel. The study utilizes aircraft carrier battle groups from four distinct countries as case examples to obtain quantitative evaluation results regarding combat performance. Furthermore, the analysis examines the effects of two extreme marine environments on surface ships. The organization of new surface ship formations is conducted based on a multi-objective planning model that is tailored to specific surface ship formations. All kinds of combat performance indexes are better than the formation of this particular surface ship. The experimental results show that the model can integrate different kinds of equipment performance parameters into a unified system and consider the comprehensive factors of equipment, platform and people. According to the requirements of task formation and the limitations of the actual Marine environment, a stable formation can be formed quickly, which can be superior to a specific formation in all aspects. Good results are obtained and the effectiveness of the model is verified. • We quantitatively assessed the operational effectiveness of the ship formation. • Different kinds of parameters are incorporated into a unified system. • The final result accords with the actual formation efficiency through comparative analysis. • Multi-objective programming model is used for autonomous formation research. [ABSTRACT FROM AUTHOR]

This paper presents an energy efficiency improvement scheme for offshore wind farms. This scheme uses learning-based nonlinear model predictive control (NMPC) and does not require wake modeling. The main feature is that each wind turbine can independently complete all optimal control, without the need for wind farm wake model calculation and iterative optimization. Specifically, this paper studies the critical factors for increasing the active power of wind farms and reducing the structural load of wind turbines, and reconstructs the optimal control objectives of wind turbines. Furthermore, combined with the nonlinear model of wind turbines containing uncertainty, a nonlinear model predictive control algorithm based on deep neural networks was designed, which can achieve multi-objective optimal control at the wind turbine level. The simulation results show that the uncertainty estimation method can effectively improve the nonlinear control performance, achieve an increase in the active power of the wind farm without wake iterative optimization, and at the same time suppress the structural loads of all wind turbines. • Propose a solution to improve wind farm energy efficiency without requiring wake modeling. • A nonlinear model of wind turbines considering uncertainty was established. • A deep neural network was used for uncertainty estimation. • Nonlinear model predictive control is used to achieve optimal control of wind turbines. [ABSTRACT FROM AUTHOR]

This paper presents a dynamic analysis model for a catenary anchor leg mooring (CALM) system based on the absolute nodal coordinate formulation (ANCF) method, combined with continuum mechanics and finite element theory. This model uses absolute slope coordinates instead of traditional angle coordinates to better describe the large deformation and large displacement of the cables. The paper derives the element mass matrix, generalized stiffness matrix, and the element external load matrix, including the Morison force transformed into the ANCF framework, based on the virtual work principle. The accuracy and reliability of the ANCF program are validated using static and dynamic beam models, as well as submerged tether models. Furthermore, a comparative analysis of the ANCF mooring cable model with OpenFAST and MoorDyn accentuates the program's practical value in real engineering applications. Finally, we systematically analyzed the dynamic characteristics of a CALM single-point mooring system, revealing that the mooring forces in the cables significantly influence the high-frequency motion of the buoy. Additionally, the reduction in the length of the mooring cables, to an appropriate extent, enhances the stability of the system, which further attests to the effectiveness and practicality of the ANCF model that has been developed. [ABSTRACT FROM AUTHOR]

Offshore wind turbines (OWTs) are dynamically sensitive structures to low-frequency wind-wave loadings due to their low damping and high flexibility. This makes them vulnerable to unwanted vibrations in ocean environments. Therefore, there is a need to implement innovative vibration control devices to suppress undesired vibration and ensure their structural safety. A tuned mass damper (TMD) has been a promising solution to control excessive vibrations recently in OWTs due to higher efficiency and low installation cost. However, TMD performance in vibration mitigation of OWTs when placed at a nacelle is still challenging to investigate because the generator torque and pitch control may affect the dynamics of the overall system. In this paper, an optimal multiple TMD system is designed by placing TMDs at optimal locations along the tower, which are defined using the maximum amplitude of the displacements for the first three natural frequencies of the tower. In addition, extensive simulations are carried out with integrated OWT-TMD systems to find the optimal mass ratio values and quantity of the TMDs. The TMD system is also tuned for several scenarios, including operating, parked, and idling conditions under the combined wind-wave loadings. A numerical model of the 5 MW NREL OWT developed in OpenFAST is considered as the baseline in this study. The results show a root mean square (RMS) response reduction of 10.2% and 42% in fore-aft (FA) and side-side (SS) tower displacement with optimally designed multiple TMDs. Moreover, improved mitigation effects on tower base moment of RMS 43.6% and 20.8% are observed in orthogonal directions, respectively. The findings of this paper may have the potential for designing passive TMD systems for vibration reductions in OWT. • A novel bi-directional MTMD is proposed for vibration suppression of a 5 MW OWT. • The proposed MTMD shows a significant improvement in vibration control of the OWT compared to a single TMD. • Optimized MTMD distributed along the tower can effectively suppress the tower base moment. • The performance of the proposed MTMD is evaluated under parked, idling, and operational conditions. [ABSTRACT FROM AUTHOR]

Effective coverage path planning for USVs is essential to optimize the performance of bathymetric surveys. Traditionally, it is well recognized that the best sweep direction for coverage path planning is the parallel direction that finds the minimum span of the region of interest (ROI). However, the results in this paper first reveals that it is not always the case when the water current is involved. In this paper, we first formulate an energy consumption estimation model for USV and introduce a novel coverage path planning strategy. Then, we investigate the relationship between sweep direction and USV energy consumption under the influence of water currents, referred to as the E - β curve. We then systematically analyze the variations of the E - β curve under different shapes of ROIs, various water current attacking angles, and different coverage strategies. Finally, the model is extended to more realistic scenarios involving non-convex ROIs. The practicality of the model is validated USV semi-physical model. The results indicate that, under water currents, our proposed model allows for an optimal sweep direction that minimizes the energy consumption of USVs. This contrasts with traditional methods, which fail to achieve the optimal energy cost. The results hold significant implications for the design of USV mapping strategies in inland river. • This paper is the first to unveil the relationship between sweep direction and USV energy consumption under water currents, referred to as E - β curve. • Systematical analysis has been conducted on the factors that may impact the E - β curve. • An energy consumption estimation model for USV is constructed. • The model is extended to realistic scenarios involving non-convex polygonal ROIs and semi-physical simulation. [ABSTRACT FROM AUTHOR]

Internal solitary waves propagation perturbing the sound velocity field, causes fluctuations in the sound field. This paper proposes to process the sound pressure data by the Product of the Slope and the even square of the Difference between two points of the acoustic parameter-time curve (PSD). The PSD processed data are processed to time-frequency analysis to extract the frequencies of the fluctuations in sound field. In this paper, numerical simulations and laboratory experiments are carried out on the process of internal solitary wave propagation in the sound field, and the characteristics of the sound field perturbation by internal solitary waves of different amplitudes are investigated. Results are both showing that the method can extract the dominant frequency of fluctuations in the sound field caused by internal solitary waves in real conditions. The method can be applied to the inversion of internal solitary wave phase speed which related to other parameters such as amplitude and characteristic width by theory. It is anticipated that this method can help realize the monitoring of internal solitary waves using acoustic paths. • A Product of Slop and Difference (PSD) method used to extract the fluctuation of sound field. • Considering the effects on sound field with internal solitary wave propagating. • The method to extract fluctuations in the sound field is validated by experiments in the tank. • Both simulation and experiments results showed the method can be applied in inversion of internal solitary waves. [ABSTRACT FROM AUTHOR]

The application of Random Matrix Theory to study the spectral statistics of bubble dynamics near a curved perforated plate in an infinite liquid domain is presented in this work. The simulation of bubble dynamics is conducted in the vicinity of a circular opening in the bilge. Empirical interpolation distribution is employed to quantify the chaoticity of the simulation results, while the boundary element method combined with RMT is utilized to evaluate the level spacing of different opening sizes and standoff distances. The objective of this study is to gain a deeper insight into the internal dynamics and to determine the presence of chaotic or regular behavior. The findings reveal that chaotic behavior emerges in the presence of jet formation in bubbles, while regular behavior dominates when jet formation is not observed. • The paper investigates the bubble dynamics by adopting simulation approaches and boundary element method. • The effects of the two key parameters including opening size and standoff distance, were numerically studied on the bubble dynamics near a curved perforated plate in an infinite liquid domain. • The results reveal the complexity of bubble dynamics and the capability of the boundary element method to predict the bubble dynamics. • The paper opens up new avenues to understand the chaos and regularity in the bubble dynamics. [ABSTRACT FROM AUTHOR]

Floating offshore wind turbines (FOWTs) offer a significant opportunity for harnessing wind energy and achieving clean energy goals. This paper investigates the effects of mooring line failure in semisubmersible FOWTs under normal and extreme environmental conditions. The OC4 DeepCwind type semisubmersible with an NREL 5 MW wind turbine is considered for investigating the behavior of FOWT under intact and failed mooring lines. This study covers a wide range of environmental conditions, operational conditions of wind turbines, and mooring line failure scenarios. This paper investigates the mooring line failure effects on platform responses, mooring line fairlead tensions, and tower responses. The results show that the platform surge, heave, pitch responses, tower fore-aft displacement, base shear force in X -direction, and base moment in Y -direction are increased for upwind side mooring line failure during the operational condition of FOWT. Subsequently, the platform sway, roll, yaw responses, tower side-to-side displacement, base shear force in Y -direction, and base moment in X -direction are more during downwind side mooring line failure in the same environment. On the other hand, the impact of upwind side mooring line failure affects all 6 Degrees of Freedom (DOF) platform responses significantly during the parked state of FOWT. The maximum fairlead tensions observed in the remaining mooring lines remain below the mooring line breaking strength even after a mooring line failure during both operational and parked states of FOWT. It is also observed that the platform responses (excluding heave), tower responses, and fairlead tensions exhibit greater values when an extreme turbulence wind model is employed. The platform surge, heave, pitch responses, maximum fairlead tension, tower fore-aft displacement, and tower base moment in Y -direction show higher values under severe sea state condition. • Effects of mooring line failure under normal and extreme environmental conditions • Simulation of intact and mooring line failure scenarios using coupled analysis • Covering wide range of environmental conditions and mooring line failure scenarios • Effects of failure on platform responses, fairlead tensions, and tower responses [ABSTRACT FROM AUTHOR]

Icebreaker assistance is a common yet intricate operation in ice-covered waters, frequently leading to collisions between ships and icebreakers. This underscores the need for advanced kinematic models to improve safety and coordination in convoy operations. Consequently, this paper introduces a kinematic model for guiding intelligent ships under icebreaker assistance. The model, grounded in the Traffic Factor State Network (TFSN), evaluates the safety state of a fleet in various ice conditions, using data from actual convoy operations. An enhanced Proportional Integral Derivative (PID) algorithm is integrated to formulate a multi-ship following model, which accounts for the kinematic characteristics of ships in ice. The model also incorporates the transmission process of ship maneuvering commands. Its validity is confirmed through application to two ships under icebreaker assistance. The findings show that the model effectively simulates safe speeds and maintains proper inter-ship distances over time, and it generates safe kinematic instructions for the fleet. This model may contribute to navigational safety in ice-covered waters and demonstrates the potential for inclusion in ice navigation support systems. • The paper introduces a kinematic model for the collaborative operation of multiple ships. • This method is grounded in the evaluation of kinematic features of ships in various ice conditions. • The effectiveness is illustrated through actual convoy operations in the Baltic Sea. • The proposed approach has the potential to support intelligent decision-making systems. [ABSTRACT FROM AUTHOR]

This paper presents a study in which both the control and the shape of a Wave Energy Converter (WEC) are optimized simultaneously. A heaving point absorber WEC is assumed. To optimize the shape of the WEC's buoy, nonlinear hydrodynamics need to be evaluated. One main contribution of this paper is the integration of nonlinear hydrodynamics and nonlinear control during the optimization of the WEC's buoy shape. This approach is referred to as Control Co-Design (CCD). In this work, we present a control co-designed nonlinear heaving point absorber WEC that leverages the nonlinear dynamic, static Froude–Krylov (FK) forces to maximize power extraction. The nonlinear FK forces are approximated using a variation of the algebraic solution; the hydrodynamic forces of the body are computed using an analytic formulation leveraging the methods of eigenfunction expansion and separation of variables. The nonlinear geometry of the buoy is modeled as a series of inclined panels; the inclination angles are optimized to arrive at the optimal shape. The performance of the optimized shape is compared to that of a nonlinear spherical WEC. It is found that an average of 20% improvement is achieved by the optimized geometry over the spherical device. • The highlight of the research is that, generally, the dynamic equation of WECs are used to formulate innovative control methods to ensure the efficient operation of the devices. • The design of optimal control often comes at the last stage of the design process, after the mechanical, electrical, and other subsystems are completely defined. • During the earlier stages, simplified controls are employed for designing the subsystems, which may not match the final system's control requirements. • This study introduces an approach to the WEC device design process that integrates the ultimate control method and all other pertinent engineering considerations from the outset. [ABSTRACT FROM AUTHOR]

Autonomous underwater vehicle (AUV) is currently the mainstream equipment for ocean exploration due to its long endurance and large operating range. However, the torpedo profile of traditional AUVs limits their maneuverability and hovering capabilities. This hinders the application and popularity of AUVs in near-seabed operations and accurate detection in small areas. This paper presents a novel disc-shaped micro AUV characterized by using a multi-core heterogeneous architecture to integrate control and positioning systems to obtain a lightweight design with complete functionality. Through the special structure and adaptive sliding mode controller, it can achieve high maneuvering navigation and stable hovering under different working conditions. A passive inverted ultra-short baseline (piUSBL) underwater positioning system is developed to provide accurate and instantaneous underwater position at low cost and power consumption. Field experiments, including special circular cruising and acoustic docking, were conducted in an open-water environment. The experimental results show that this vehicle has a depth control accuracy of 5 cm and a heading control accuracy of 3°, which well proves that this prototype can carry out accurate detection in a small range. In addition, this vehicle has a diameter of only 42 cm, a height of 23 cm, and a weight of 14 kg, making it easy to deploy and recover. To the best of our knowledge, this is the first AUV to be successfully tested in the field using a multi-core heterogeneous architecture with such small size and light weight. • This paper presents a novel disc-shaped micro AUV characterized by using a multi-core heterogeneous architecture to integrate control and positioning systems to obtain a lightweight design with complete functionality. • A passive inverted ultra-short baseline (piUSBL) underwater positioning system is developed to provide accurate and instantaneous underwater position at low cost and power consumption. • Field experiments, including special circular cruising and acoustic docking, were conducted in an open-water environment. The experimental results show that this vehicle has a depth control accuracy of 5 cm and a heading control accuracy of 3°, which well proves that this prototype can carry out accurate detection in a small range. • This vehicle has a diameter of only 42 cm, a height of 23 cm, and a weight of 14 kg, making it easy to deploy and recover. To the best of our knowledge, this is the first AUV to be successfully tested in the field using a multi-core heterogeneous architecture with such small size and light weight. [ABSTRACT FROM AUTHOR]

To ensure that underwater remotely operated vehicles have the ability to complete trajectory tracking in the presence of external disturbances and model parameter uncertainties, this paper proposes a double-closed-loop integrative sliding mode ROV tracking control based on the nonlinear expansion state observer. Firstly, to address the issue of oscillatory vibrations in the stable state of the dual closed-loop sliding mode structure, the inner loop control adopts a combinatorial reaching rate that leverages both exponential and variable convergence rates. Secondly, addressing the impact of external disturbances and model parameter uncertainties on the ROV, this paper proposes a novel nonlinear disturbance observer inspired by active disturbance rejection control principles. The stability of the complete closed-loop cascaded system is substantiated. Simulation outcomes demonstrate that the presented scheme significantly enhances the control system's transient response, disturbance rejection capacity, and ability to suppress jitter vibrations within sliding mode control, thereby proving the robustness, viability, and effectiveness of the control strategy outlined herein. • Proposed a dual loop sliding mode control strategy based on a nonlinear extended state observer. • Designed a nonlinear extended state observer based on the ROV model to handle external disturbances. • Application of a composite convergence rate to solve the problem of inner-loop jitter in a double-loop control structure. [ABSTRACT FROM AUTHOR]

In response to the intricate marine environment and the need for diverse, intelligent, and large-scale operations, clustered Autonomous Underwater Vehicles (AUVs) have emerged as a pivotal trend in AUV oceanic applications. This paper delves into three key aspects of clustered AUV control: optimal formation assembly, dynamic cooperative control, and autonomous obstacle avoidance. The formation assembly is approached as a target point allocation problem, employing an F-Norm and Dubins Path (FNDP) based method for efficient path planning and optimal allocation. A novel hybrid control strategy, LFVS, combines leader–follower (LF) and virtual structure (VS) approaches, facilitating cohesive formation maintenance with minimal communication. Additionally, the paper introduces an intelligent adaptive artificial potential field (IA2PF) method. This technique, enhancing energy efficiency and obstacle avoidance, dynamically adjusts to current conditions, thereby overcoming limitations of traditional APF methods like unreachable targets , oscillation, and dead zones. The efficacy and applicability of these methods are corroborated through extensive simulations and practical experiments using three 260 AUVs, and compared with formation control based on the LF strategy, proving their utility and stability in real-world formation assembly and maintenance tasks. • This study developed LFVS-IA2PF, a new multi-AUV formation control strategy. • FNDP is introduced for effective target point allocation in AUV operations. • This paper proposed an adaptive algorithm for AUV formation and obstacle avoidance. • The proposed algorithms are validated with both simulations and actual experiments. [ABSTRACT FROM AUTHOR]

In this paper, oblique water wave interaction with a surface piercing box-type porous structure placed in front of a vertical rigid wall is investigated in the presence of current, which flows parallel to vertical wall. The current speed is considered distinct in different subdomains. However, in a particular subdomain current speed is uniform throughout the water depth. In this analysis, Sollitt and Cross model is used for the study of wave motion inside the porous structure. Employing small amplitude linear water wave theory, the present model of our interest is developed into a boundary value problem and solved analytically using the eigenfunction expansion method. Using the developed solution, the reflection coefficient and hydrodynamic wave forces on porous structure are computed for different values of parameters: the dimension of porous structure, the friction coefficient of porous structure, the current speed of following current and opposing current. This research paper suggests that suitable arrangement of rigid walls and surface-piercing partially extended porous structures can be an effective and economical approach for guiding ocean currents and protecting marine facilities against wave attacks. • Oblique wave trapping in the presence of current and porous structure is discussed. • Boundary value problem solved analytically using the eigenfunction expansion method. • Wave forces are higher for following current speed than the opposing current speed. • Node of standing waves are formed on the rear face of the porous breakwater. [ABSTRACT FROM AUTHOR]

Array shape calibration is commonly categorized into active calibration and self-calibration, yet both methods have their drawbacks and are generally considered less optimal. This paper proposes a novel approach based on the coherence of noise radiated from non-cooperative ships. Firstly, the time-varying law of the frequency domain coherence of ocean ambient noise received by a titled hydrophone pair when a ship passes by is investigated, which reveals the relative location of the hydrophones and passing ship. The array shape can be calibrated by analyzing the ambient noise coherence and horizontal acoustic path difference between passing ships and different hydrophones. The calibration results are consistent which are obtained from the three sections of data collected near the shipping lanes in the Qingdao offshore. One of the calibrated result is employed to simulate the coherogram of ambient noise when the ship passes by. It is shown that the simulation is in good agreement with the measured results. The main error sources are also analyzed and simulated in this paper, and the results show that the method is basically feasible and reliable. • Noise coherence coefficient model in water near shipping lanes. • Array shape calibration based on coherence coefficients of ship-radiated noise. • Simulation of noise coherogram during ships passage. [ABSTRACT FROM AUTHOR]

The current paper investigates the path following control problem for marine vehicles with multiple disturbances and input saturation. First, considering that marine vehicles exposed to the marine environment always contain stochastic components, which were ignored in most of the previous studies, the multiple disturbances in this paper are decomposed into complex nonlinear terms, slow-varying disturbances, and stochastic disturbances. Accordingly, an appropriate stochastic differential model is constructed. Second, a new stochastic path following control strategy based on the fuzzy logic system, the stochastic disturbance observer, and the auxiliary dynamic compensators is established. The fuzzy logic system is adopted for approximating the complex nonlinear terms, the stochastic disturbance observer is constructed to estimate the slow-varying disturbances in stochastic situation, and the auxiliary dynamic compensators are designed to tackle input saturation. In the end, the stability of the entire system is proven through linear matrix inequalities and Lyapunov functions. The simulation results demonstrate the proposed controller's effectiveness and robustness. • The multiple disturbances are divided into three categories, and astochastic differential model is proposed. • The fuzzy logic system is adopted for approximating the marine vehicle model's complex nonlinear terms. • The stochastic disturbance observer is constructed to estimate the slow-varying disturbances in stochastic situation. • The auxiliary dynamic compensators are adopted to overcome the input saturation. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of automatic berthing of unmanned surface vehicles (USVs) in complex scenarios and proposes a multitask optimal control berthing method (MT-OCBM). The berthing process is divided into stages, each with distinct goal constraints and path restrictions. Through a combination of topology and computational geometry, a sparse Delaunay triangulation map segmentation (SDTMS) is introduced. SDTMS reduces map complexity while preserving accuracy by extracting map feature points and dividing the map into multiple triangular regions. The application of the traditional hp-Radau pseudospectral method (hp-RPM) to solve optimal control problems (OCPs) in complex marine environments is restricted by problems such as slow convergence and susceptibility that arise because of greatly different magnitudes of path constraints. To overcome these problems, we propose the hp-normalized Radau pseudospectral method (hp-NRPM). Normalizing the path constraints equalizes the magnitudes of path constraints, thereby significantly reducing the computational complexity of solving the OCPs. In contrast to traditional approaches that separate control from path planning, the optimal control algorithm employed in this paper integrates the control variables of unmanned vessels into the planning process of berthing paths. This integration allows the planned berthing paths to reflect the motion characteristics and constraints experienced by the unmanned vessel. It uses the KCS ship model to construct the Maneuvering Modeling Group ship motion model, and using the power spectrum given in the NORSOK standard, it establishes a slow, time-varying wind field model. The hp-NRPM algorithm is used to adjust the control inputs within the constraint region, thereby deriving a berthing route that optimizes the performance function. For validating the method, Qingdao Port was used as a simulation environment, and multiple sets of experiments were performed. The experimental results confirmed that MT-OCBM is robust and effective against disturbances and various obstacles encountered during berthing. • Pseudospectral method can effectively solve the optimal control berthing problem. • Using Delaunay triangulation for map segmentation can mitigate problem complexity. • Multitasking method allows algorithm focusing on different goals at various stages. • Normalizing path constraints can expedite the convergence speed of berthing problem. [ABSTRACT FROM AUTHOR]

In almost every practical scenario, the shape of towed linear array (TLA) is always affected by current, tug vehicle speed, and other factors, resulting in the deviation of sensor positions. Furthermore, maneuvers bring significant changes to array shape, i.e., array mismatch, which will greatly degrade the performance of array processing system. To deal with this problem, this paper first establishes a hydrodynamic model to fit the law of motion of turning cables. Then, a time difference of arrival (TDOA) method is utilized to estimate the real-time array shape, which exploits the near-field tug vehicle noise. Finally, the array shape is estimated by combining the hydrodynamic model and the TDOA method. The simulation results exhibit that the proposed array shape estimation method can resolve the array mismatch problem when turnings happen. Compared with the state-of art array shape estimation methods, this paper provides similar estimation accuracy without extra gyros or auxiliary sources. The lake trial results validate its feasibility and stability for estimating far-field target bearings in practical applications. • Different motion states of towed linear array during turning is derivated and classified. • Tug vehicle noise is utilized to estimate array shape other than gyros or auxiliary sources. • Time difference of arrival method (TDOA) combining hydrodynamic model. • Lake trial data support with practical significance. [ABSTRACT FROM AUTHOR]

In this paper, a new adaptive maximum correntropy unscented Kalman filter (AMCUKF) Time-Difference-of-Arrival (TDOA) tracking algorithm is proposed for autonomous underwater vehicles (AUVs) in the complex and variable marine environment. Firstly, the measurement model of the acoustic tracking system is established based on the multi-layer isogradient sound speed profile (SSP) model to correct tracking errors caused by the bending of sound transmission trajectory. To resist the impact of measurement gross errors caused by instrument measurement anomalies or accidental environmental interference, the maximum correntropy unscented Kalman filter (MCUKF) TDOA tracking algorithm is constructed by introducing the maximum correntropy criterion into the UKF. Then, this paper introduces the innovation-based covariance-matching method and moving window method to improve the algorithm's adaptability, which can reduce the influence of covariance variable measurement noise caused by marine environmental changes. Finally, we compare the effectiveness of the proposed AMCUKF algorithm with the UKF algorithm, adaptive unscented Kalman filter (AUKF) algorithm, and MCUKF algorithm, which indicates the AMCUKF algorithm has better tracking performance in the marine environment with covariance variable measurement noise, measurement gross errors, and Gaussian mixture noise. [ABSTRACT FROM AUTHOR]

Digital Twins have much attention in the shipping industry, attempting to support all phases of a vessel's life cycle. With several tools appearing in Digital Twin software suites, high-quality manoeuvring and performance prediction remain cornerstones. Propulsion efficiency is in focus while in service. Simulator-based training is in focus to ensure safety of manoeuvring in confined waters and harbours. Prediction of ships' velocity and turn rate are essential for correct look and feel during training, but phenomena like dynamic inflow to propellers, bank and shallow water effects limit simulators' accuracy, and master mariners often comment that simulations could be in better agreement with actual behaviours of their vessel. This paper focuses on digital twin enhancements to better match reality. Using data logged during in-service operation, we first consider a system identification perspective, employing a first-principles model structure. Showing that a complete first-principles model is not identifiable under the excitation met in service, we employ a Recurrent Neural Network to predict deviations between measured velocities and the model output. The outcome is a hybrid of a first-principles model with a machine learning generic approximator add-on. The paper demonstrates significant improvements in prediction accuracy of both in-harbour manoeuvring and shallow water passage conditions. • Identifiability analysis to highlight challenges in identification of first-principle hydrodynamics models. • Hybrid model for velocity prediction that combines a first-principles and Recurrent Neural Networks. • Training and validation using full-scale data collected from an operational Roll-ON/Roll-Off ferry. • Systematic evaluation of the obtained model accuracy and comparison to an industrial state-of-the-art ship simulator. [ABSTRACT FROM AUTHOR]

Due to tiny edge and texture details of harmful algae blooms(HABs), existing segmentation networks are not effective for HABs segmentation. In order to solve the above problems, this paper proposes a Multi-scale Feature extraction and TrasMLP Encoder Fusion-based network (MFTS). To tackle the complex morphological characteristics and the complex backgrounds of HABs, a TrasMlp module which can effectively identify long-range patterns and adapt network parameters is introduced, enabling accurately parsing of complex algae images. Secondly, the deep convolution module is constructed by combining deep separable convolution with a two-channel attention mechanism to separate the target region from the background. In addition, this paper proposes a Weighted Feature Fusion of Deep Convolution and INRS Encoder Module classification network(FDIR) is proposed to quantify the performance of the image segmentation network. The segmentation results on HABs dataset from AICO Lab show that our proposed MFTS model achieves a miou of 90.02%, outperforming the performance of classical segmentation networks such as U-Net and Mask R-CNN. Compared to original HABs dataset, the segmented result shows a 5.1% improvement in the classification accuracy of the FDIR model. • Proposes a novel method for automatic detection of harmful algal blooms. • Development of a novel network architecture for harmful algal blooms segmentation and classification. • Achieves the best performance on the AICO labs dataset. • Shows the effectiveness of using multi-scale feature methods. • Demonstrates that the TrasMLP Encoder is helpful for improving model accuracy. [ABSTRACT FROM AUTHOR]

Safe execution of a Marine operation (MO) depends on accurate values of operational limits and forecasting quality of environmental parameters, especially wave spectral parameters (significant wave height, peak period, and peak direction). Since offshore sites are generally characterized by the presence of more than one wave system e.g. wind seas and swells, it becomes challenging to assess accurate multimodal spectral parameters. Apart from forecasts, buoy or vessel motions can be used to estimate wave spectral parameters. This paper deals with an assessment of trimodal wave spectral parameters using three machine learning (ML) methods, i.e. Random forest, Extra trees, and Convolutional neural networks, for an offshore site in the Norwegian Sea. The methods use synthetic statistics of vessel responses as features and spectral parameters computed from a spectrum partitioning method, for training the ML algorithms. It is found that the Extra trees method has the best performance and is very accurate for predicting spectral parameters of three wave systems. Findings from this paper can be used to further develop efficient on-board safety systems and help superintendents make more informed decisions. • Multi-output machine learning algorithms are used to assess trimodal wave spectral parameters. • Vessel response statistics and spectral parameters from wave partitioning are used for training algorithms. • The Extra trees method can accurately predict trimodal wave spectral parameters. • Predicted wave spectral parameters can be used to support on-board decision-making. [ABSTRACT FROM AUTHOR]