Journal of Marine Science and Engineering

22 pages, 4648 KiB

Open AccessArticle

Obstacle Avoidance Control for Autonomous Surface Vehicles Using Elliptical Obstacle Model Based on Barrier Lyapunov Function and Model Predictive Control

by Pengfei Zhang, Yuanpei Ding and Shuxin Du

J. Mar. Sci. Eng. 2024, 12(6), 1035; https://doi.org/10.3390/jmse12061035 - 20 Jun 2024

Viewed by 272

Abstract

This study explores positioning and obstacle avoidance control for autonomous surface vehicles (ASVs) by considering equivalent elliptical-shaped obstacles. Firstly, compared to most Barrier Lyapunov function (BLF) methods that approximate obstacles as circles, a novel BLF is improved by introducing an elliptical obstacle model. [...] Read more.

This study explores positioning and obstacle avoidance control for autonomous surface vehicles (ASVs) by considering equivalent elliptical-shaped obstacles. Firstly, compared to most Barrier Lyapunov function (BLF) methods that approximate obstacles as circles, a novel BLF is improved by introducing an elliptical obstacle model. This improvement uses ellipses instead of traditional circles to equivalent obstacles, effectively resolving the issue of excessive conservatism caused by over-expanded areas during the obstacle equivalence process. Secondly, unlike traditional obstacle avoidance approaches based on BLF, to achieve constraint control of angle and angular velocity, a method based on model predictive control (MPC) is introduced to optimize local angle planning. By incorporating angular error constraints, this ensures that the directional error of the ASV remains within a restricted range. Furthermore, an auxiliary function of directional error is introduced into the ASV’s linear velocity, ensuring that the ASV parks and adjusts its direction when the deviation in angle becomes too large. This innovation guarantees the linearization of the ASV system, addressing the complexity of traditional MPC methods when dealing with nonlinear second-order ASV systems. Ultimately, the efficacy of our proposed approach is validated through rigorous experimental simulations conducted on the MATLAB platform. Full article

(This article belongs to the Special Issue Unmanned Marine Vehicles: Perception, Planning, Control and Swarm)

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20 pages, 1000 KiB

Open AccessArticle

Federated Learning for Maritime Environments: Use Cases, Experimental Results, and Open Issues

by Anastasios Giannopoulos, Panagiotis Gkonis, Petros Bithas, Nikolaos Nomikos, Alexandros Kalafatelis and Panagiotis Trakadas

J. Mar. Sci. Eng. 2024, 12(6), 1034; https://doi.org/10.3390/jmse12061034 - 20 Jun 2024

Viewed by 245

Abstract

Maritime transportation is crucial for global trade and responsible for the majority of goods movement worldwide. The optimization of maritime operations is challenged by the complexity and heterogeneity of maritime nodes. This paper presents the emerging deployment of federated learning (FL) in maritime [...] Read more.

Maritime transportation is crucial for global trade and responsible for the majority of goods movement worldwide. The optimization of maritime operations is challenged by the complexity and heterogeneity of maritime nodes. This paper presents the emerging deployment of federated learning (FL) in maritime environments to address these challenges. FL enables decentralized machine learning model training, ensuring data privacy and security while overcoming issues associated with non-i.i.d. data. This paper explores various maritime use cases, including fuel consumption reduction, predictive maintenance, and just-in-time arrival. Experimental results using real datasets demonstrate the superiority of FL in predicting the fuel consumption of large cargo ships in terms of accuracy and spatiotemporal complexity over traditional collaborative machine learning approaches. The findings indicate that FL can significantly improve the performance of fuel consumption models in a collaborative way, while ensuring data privacy preservation and no data transmission during the learning process. Finally, this paper discusses open issues and future research directions necessary for the widespread adoption of FL in maritime transportation and settings. Full article

(This article belongs to the Section Ocean Engineering)

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20 pages, 30272 KiB

Open AccessArticle

A Pruning and Distillation Based Compression Method for Sonar Image Detection Models

by Chensheng Cheng, Xujia Hou, Can Wang, Xin Wen, Weidong Liu and Feihu Zhang

J. Mar. Sci. Eng. 2024, 12(6), 1033; https://doi.org/10.3390/jmse12061033 - 20 Jun 2024

Viewed by 241

Abstract

Accurate underwater target detection is crucial for the operation of autonomous underwater vehicles (AUVs), enhancing their environmental awareness and target search and rescue capabilities. Current deep learning-based detection models are typically large, requiring substantial storage and computational resources. However, the limited space on [...] Read more.

Accurate underwater target detection is crucial for the operation of autonomous underwater vehicles (AUVs), enhancing their environmental awareness and target search and rescue capabilities. Current deep learning-based detection models are typically large, requiring substantial storage and computational resources. However, the limited space on AUVs poses significant challenges for deploying these models on the embedded processors. Therefore, research on model compression is of great practical importance, aiming to reduce model parameters and computational load without significantly sacrificing accuracy. To address the challenge of deploying large detection models, this paper introduces an automated pruning method based on dependency graphs and successfully implements efficient pruning on the YOLOv7 model. To mitigate the accuracy degradation caused by extensive pruning, we design a hybrid distillation method that combines output-based and feature-based distillation techniques, thereby improving the detection accuracy of the pruned model. Finally, we deploy the compressed model on an embedded processor within an AUV to evaluate its performance. Multiple experiments confirm the effectiveness of our proposed method in practical applications. Full article

(This article belongs to the Special Issue Autonomous Marine Vehicle Operations—2nd Edition)

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19 pages, 6901 KiB

Open AccessArticle

Response Extremes of Floating Offshore Wind Turbine Based on Inverse Reliability and Environmental Contour Method

by Da Li, Botao Xie, Tao Liu, Zhuolantai Bai, Bigui Huang and Junrong Wang

J. Mar. Sci. Eng. 2024, 12(6), 1032; https://doi.org/10.3390/jmse12061032 - 20 Jun 2024

Viewed by 184

Abstract

Floating structures are subject to complex marine conditions. To ensure their safety, reliability analysis needs to be conducted during the design phase. However, because of the complexity of traditional full long-term analysis, the environmental contour method (ECM) based on the inverse reliability method, [...] Read more.

Floating structures are subject to complex marine conditions. To ensure their safety, reliability analysis needs to be conducted during the design phase. However, because of the complexity of traditional full long-term analysis, the environmental contour method (ECM) based on the inverse reliability method, which can combine accuracy and efficiency, is extensively used. Due to the unique environment in the South China Sea, the probabilistic characteristics of three-dimensional (3D) environmental parameters of wind, wave and current are investigated. The ECs of the target sea are established via the ECM based on both the inverse first-order reliability method (IFORM) and inverse second-order reliability method (ISORM). It is found that the sea state forecasted by ISORM is more extreme and may lead to a more conservative design than IFORM. Furthermore, the wind–wave–current combination coefficient matrixes developed using the 3D ECs are proposed for the design of FOWTs in the South China Sea. The validity and practicality of the contours and matrixes are tested by using a floating offshore wind turbine (FOWT) as a numerical example. Then, the short-term response of the structure under the combined wind, wave and current conditions is calculated, providing a theoretical reference for the design of FOWTs. Full article

(This article belongs to the Section Ocean Engineering)

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15 pages, 6148 KiB

Open AccessArticle

Influence of Melt Supply on the Spreading State of a Slow–Ultraslow-Spreading Ridge: The Reykjanes Ridge, North Atlantic

by Lihong Zhao, Yingzi Liu, Zilong Ling, Pengyao Zhi, Faqiang Zhao, Hongqin Liu and Jinwei Zhang

J. Mar. Sci. Eng. 2024, 12(6), 1031; https://doi.org/10.3390/jmse12061031 - 20 Jun 2024

Viewed by 285

Abstract

Although recent research suggests that the morphology and crustal structure of slow–ultraslow-spreading ridges are mainly controlled by melt supply, there is a lack of quantitative understanding of the effect of systematic changes in melt supply on the seafloor spreading state of mid-ocean ridges. [...] Read more.

Although recent research suggests that the morphology and crustal structure of slow–ultraslow-spreading ridges are mainly controlled by melt supply, there is a lack of quantitative understanding of the effect of systematic changes in melt supply on the seafloor spreading state of mid-ocean ridges. In this study, we used bathymetry, free-air gravity anomaly, and sediment thickness data to calculate the residual bathymetry, mantle Bouguer gravity and crustal thickness of the Reykjanes Ridge. According to the gradient of changes in crustal thickness and residual bathymetry along the axis, the influence of melt supply on the spreading state of the Reykjanes Ridge can be divided into three zones: ultra-strong effect zone (0–160 km), strong effect zone (160–610 km), and weak effect zone (610–930 km). In the ultra-strong effect zone, excess melt supply and a higher melting degree result in a strong upwelling and large melt eruption. The change in relative position between the Reykjanes Ridge and the Iceland hotspot results in the spreading state of the Reykjanes Ridge transforming from asymmetric spreading to symmetric spreading. In the strong effect zone, the decrease in melt supply and melting degree weakens the mantle upwelling and enhances the viscosity of the dehydrated mantle layer. Sufficient viscosity of the dehydrated mantle layer forces asymmetric asthenosphere rise along the sloping boundary of the lithosphere, resulting in symmetric spreading. In the weak effect zone, the pattern of magma upwelling becomes a focused magma supply pattern similar to that of the slow–ultraslow-spreading of the mid-ocean ridge, and tectonics dominate the spreading process. The asymmetry of this weak effect zone may be due to the concentration of tectonic and magmatic activity on one flank of the ridge. Full article

(This article belongs to the Section Geological Oceanography)

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30 pages, 39898 KiB

Open AccessArticle

Inundation Characteristics’ Prediction of Storm Surge under Relative Sea Level Rise Scenarios: A Case Study of Taizhou, Zhejiang Province

by Tangqi Zhao, Xiaomin Li, Suming Zhang, Qi Hou, Xuexue Du and Jie Zhang

J. Mar. Sci. Eng. 2024, 12(6), 1030; https://doi.org/10.3390/jmse12061030 - 20 Jun 2024

Viewed by 363

Abstract

Storm surge is the most serious marine disaster in China, and the inundation characteristics of storm surge are the key indicators of disaster severity. Especially in the context of relative sea level rise (RSLR), it is very important to rapidly and accurately estimate [...] Read more.

Storm surge is the most serious marine disaster in China, and the inundation characteristics of storm surge are the key indicators of disaster severity. Especially in the context of relative sea level rise (RSLR), it is very important to rapidly and accurately estimate the inundation characteristics of storm surge for the risk assessment and emergency management of storm surge disasters. Taking Taizhou city, Zhejiang Province, as the study area, this paper constructed an RSLR scenario library considering absolute sea level rise, land subsidence and storm surge water increase. The scenario library includes 72 scenarios, consisting of a combination of four absolute sea level rise scenarios, three land subsidence scenarios, three timescales (2030, 2050 and 2100) and two storm surge water increase scenarios. Then, an improved passive inundation method was used to predict and analyze the inundation characteristics of storm surge under each scenario. This improved method combines the advantages of the accurate active inundation method and the rapid passive inundation method, and is suitable for rapid and accurate estimation of the storm surge inundation characteristics, which can meet the needs of a storm surge disaster risk assessment and emergency response. The prediction and analysis results show that a minor RSLR can also cause a large-scale inundation in coastal areas of Taizhou. When the value of RSLR exceeds the critical value (0.6 m), it may significantly increase the expansion of the inundation area of storm surge. At a relative sea level rise of 1.57 m (extreme scenario in 2100), the inland storm surge inundation of low-risk areas may become high-risk areas. Finally, the quantitative measures for preventing storm surge disasters were put forward according to the current situation of the coast in Taizhou. Without considering storm surge and superimposed general surge, the existing 20-year return period standard seawall can effectively protect against storm surge under various scenarios. In the case of maximum water increase, it is expected that effective protection will remain until 2030, but the standard of the seawall defense will need to be improved in 2050 and 2100. Full article

(This article belongs to the Special Issue Sea Level Rise and Related Hazards Assessment)

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16 pages, 5260 KiB

Open AccessArticle

Confined Compressibility of Fine-Grained Marine Sediments with Cavities after Complete Dissociation of Noduled Natural Gas Hydrates

by Lei Yang, Lele Liu, Tao Liu, Jinbo Lin, Yizhao Wan, Yongchao Zhang, Zhihui Wang and Xiang Liu

J. Mar. Sci. Eng. 2024, 12(6), 1029; https://doi.org/10.3390/jmse12061029 - 20 Jun 2024

Viewed by 221

Abstract

Due to natural and anthropogenic disturbances, natural gas hydrates with morphologies of nodules and chunks dissociate and release massive free gas, creating large cavities within fine-grained marine sediments. However, it is still a challenge to quantify the impact of gas cavities on mechanical [...] Read more.

Due to natural and anthropogenic disturbances, natural gas hydrates with morphologies of nodules and chunks dissociate and release massive free gas, creating large cavities within fine-grained marine sediments. However, it is still a challenge to quantify the impact of gas cavities on mechanical properties of cavitied fine-grained marine sediments as there is a lack of efforts focusing on the inner structure visualization. In this study, an oedometer test and X-ray computed tomography scans are jointly conducted on marine clayey silt with gas cavities, and the confined compressibility as well as the inner structure change under an undrained condition are explored, followed by development of a theoretical model depicting the void ratio change. The results show that vertical loading induces a void ratio reduction, and the reduced void ratio can fully recover after being unloaded. Although being fully recovered, unrecovered changes of the inner structure still remain after being unloaded. Examples include closed cracks in the lower matrix, new occurring cracks in the upper matrix, and the fragmented gas cavity. In addition, the void ratio linearly increases with the increasing inverse of normalized pore gas pressure, while the coefficient of the effective stress linearly decreases with the increasing inverse of normalized vertical loading stress. The proposed theoretical model captures the essential physics behind undrained confined deformation of fine-grained marine sediments with gas cavities when subjected to loading and unloading. Full article

(This article belongs to the Special Issue Analytical and Experimental Technology for Marine Gas Hydrate)

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11 pages, 1908 KiB

Open AccessArticle

Effect of Bivalves’ Sand Burial Capacity on Predation in the Invasive Blue Crab, Callinectes sapidus

by Patricia Prado, Ignasi Gairin and Silvia Falco

J. Mar. Sci. Eng. 2024, 12(6), 1028; https://doi.org/10.3390/jmse12061028 - 20 Jun 2024

Viewed by 380

Abstract

In the Ebro Delta (Catalonia, Spain), the abundance of burrowing bivalves has dramatically decreased, with the blue crab, Callinectes sapidus, being blamed by shellfish collectors. Trends from 2010 evidence a decrease in the capture of clams (Ruditapes spp.) before 2016 (start [...] Read more.

In the Ebro Delta (Catalonia, Spain), the abundance of burrowing bivalves has dramatically decreased, with the blue crab, Callinectes sapidus, being blamed by shellfish collectors. Trends from 2010 evidence a decrease in the capture of clams (Ruditapes spp.) before 2016 (start of blue crab fisheries), although a further decline in both clams and cockles (Cerastoderma glaucum) occurred in 2018. In contrast, captures of razor clams (Ensis siliqua) have increased by 3.6-fold since 2016. Predation risk for these taxa, with contrasting burrowing capacities (1.7 ± 0.3 cm, 0.4 ± 0.2 cm, and 26.3 ± 0.1 cm, respectively), was assessed using predation preference (N = 5 tanks; 5 individuals of each species) and no-choice experiments (N = 5 tanks; 15 individuals of the same taxa) in the absence and presence of sand. The results showed that, in the absence of sand, razor clams were fully preyed upon in 24 h, clams in 96 h, and cockles reached 60% after 144 h. Conversely, when sand was present, only 4% of razor clams were predated, while clams and cockles reached 60–100% in 120–144 h. The no-choice results featured similar patterns, depending on substrate availability. Overall, clams and cockles appear to be greatly vulnerable to blue crab predation, whereas razor clams may escape thanks to their deeper burrowing capacity. Full article

(This article belongs to the Section Marine Ecology)

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18 pages, 4401 KiB

Open AccessArticle

Comparative FEM Analysis of Vacuum and Perlite Insulation Techniques on the Structural Integrity of Independent Type C Liquefied Natural Gas Tank

by Šimun Sviličić, Smiljko Rudan, Helena Galić, Emil Weigand and Vedran Slapničar

J. Mar. Sci. Eng. 2024, 12(6), 1027; https://doi.org/10.3390/jmse12061027 - 20 Jun 2024

Viewed by 275

Abstract

In light of escalating global energy demands and the imperative to reduce greenhouse gas emissions, the efficient transportation of liquefied natural gas (LNG) has become increasingly critical. As the evaporation of LNG from storage tanks represents a significant energy loss, improving tank insulation [...] Read more.

In light of escalating global energy demands and the imperative to reduce greenhouse gas emissions, the efficient transportation of liquefied natural gas (LNG) has become increasingly critical. As the evaporation of LNG from storage tanks represents a significant energy loss, improving tank insulation is crucial to optimize storage efficiency. This paper conducts a structural assessment of a smaller-sized Type C independent tank made of AISI 304L steel and examines the impact of two insulation techniques—vacuum and perlite—on their heat, structural, and fatigue behavior. Utilizing the finite element method (FEM), this study performs a heat transfer analysis followed by a structural analysis under combined loads in accordance with the International Gas Carrier (IGC) code. The subsequent fatigue analysis follows IGC procedures and is performed using third-party software. This article presents a detailed analysis of the heat transfer throughout the entire LNG tank and the stress levels under various combined load scenarios while providing insights into the critical stress points and the areas with the lowest fatigue life. Finally, this study confirms the viability of using both novel materials, perlite as an insulation material and Durolight for the tank support, because they meet the required limits. Full article

(This article belongs to the Section Ocean Engineering)

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16 pages, 5878 KiB

Open AccessArticle

Modeling and Research on Offshore Casing Cutting of Hydraulic Internal Cutting Device

by Qiaolei Sun, Jie Tian, Yujie Jin, Ding Feng and Lingxia Hou

J. Mar. Sci. Eng. 2024, 12(6), 1026; https://doi.org/10.3390/jmse12061026 - 20 Jun 2024

Viewed by 264

Abstract

A mechanical model for offshore casing cutting based on the field application of a mechanical cutting device in the South China is presented in this paper. The proposed model includes the calculation of the piston acting on the cutter and the calculation of [...] Read more.

A mechanical model for offshore casing cutting based on the field application of a mechanical cutting device in the South China is presented in this paper. The proposed model includes the calculation of the piston acting on the cutter and the calculation of the cutting torque and wellhead driving torque. The influence of structural parameters on cutting extension distance, cutting torque, wellhead driving torque, and the proportion of cutting torque to wellhead driving torque are analyzed. The required extension distance is related to piston displacement and cutter face angle, the cutter face angle and cutting depth (water depth) have obvious influence on the cutting torque and wellhead driving torque, and the drilling revolution affects the inertia torque and wellhead driving torque. Since the proportion of cutting torque to wellhead driving torque decreased with the increase in the cutting depth, we cannot determine whether the casing cutting is completed based on the sudden decrease in the wellhead driving torque with cutting depths greater than 800 m. The numerical simulation results of the cutting tool cutting the casing show that if the revolution speed is too high, the initial cutting melting of the casing may affect the cutting force, and it is recommended to increase the rake angle as much as possible within a certain range. The field example shows the limitation of judging casing cutting by a sudden drop in torque. Full article

(This article belongs to the Section Ocean Engineering)

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26 pages, 14766 KiB

Open AccessArticle

Complete Coverage Path Planning Based on Improved Genetic Algorithm for Unmanned Surface Vehicle

by Gongxing Wu, Mian Wang and Liepan Guo

J. Mar. Sci. Eng. 2024, 12(6), 1025; https://doi.org/10.3390/jmse12061025 - 19 Jun 2024

Viewed by 339

Abstract

Complete Coverage Path Planning (CCPP) is a key technology for Unmanned Surface Vehicles (USVs) that require complete coverage on the water surface, such as water sample collection, garbage collection, water field patrol, etc. When facing complex and irregular boundaries, the traditional CCPP-based boustrophedon [...] Read more.

Complete Coverage Path Planning (CCPP) is a key technology for Unmanned Surface Vehicles (USVs) that require complete coverage on the water surface, such as water sample collection, garbage collection, water field patrol, etc. When facing complex and irregular boundaries, the traditional CCPP-based boustrophedon method may encounter many problems and challenges, such as multiple repeated regions, multiple turns, and the easy occurrence of local optima. The traditional genetic algorithm also has some shortcomings. The fixed fitness function, mutation operator and crossover operator are not conducive to the evolution of the population and the production of better offspring. In order to solve the above problems, this paper proposes a CCPP method based on an improved genetic algorithm, including a stretched fitness function, an adaptive mutation operator, and a crossover operator. The algorithm combines the key operators in the fireworks algorithm. Then, the turning and obstacle avoidance during the operation of the Unmanned Surface Vehicle are optimized. Simulation and experiments show that the improved genetic algorithm has higher performance than the exact unit decomposition method and the traditional genetic algorithm, and has more advantages in reducing the coverage path length and repeating the coverage area. This proves that the proposed CCPP method has strong adaptability to the environment and has practical application value in improving the efficiency and quality of USV related operations. Full article

(This article belongs to the Special Issue Unmanned Marine Vehicles: Perception, Planning, Control and Swarm)

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23 pages, 2335 KiB

Open AccessArticle

Enhanced Target Localization in the Internet of Underwater Things through Quantum-Behaved Metaheuristic Optimization with Multi-Strategy Integration

by Xiaojun Mei, Fahui Miao, Weijun Wang, Huafeng Wu, Bing Han, Zhongdai Wu, Xinqiang Chen, Jiangfeng Xian, Yuanyuan Zhang and Yining Zang

J. Mar. Sci. Eng. 2024, 12(6), 1024; https://doi.org/10.3390/jmse12061024 - 19 Jun 2024

Viewed by 318

Abstract

Underwater localization is considered a critical technique in the Internet of Underwater Things (IoUTs). However, acquiring accurate location information is challenging due to the heterogeneous underwater environment and the hostile propagation of acoustic signals, especially when using received signal strength (RSS)-based techniques. Additionally, [...] Read more.

Underwater localization is considered a critical technique in the Internet of Underwater Things (IoUTs). However, acquiring accurate location information is challenging due to the heterogeneous underwater environment and the hostile propagation of acoustic signals, especially when using received signal strength (RSS)-based techniques. Additionally, most current solutions rely on strict mathematical expressions, which limits their effectiveness in certain scenarios. To address these challenges, this study develops a quantum-behaved meta-heuristic algorithm, called quantum enhanced Harris hawks optimization (QEHHO), to solve the localization problem without requiring strict mathematical assumptions. The algorithm builds on the original Harris hawks optimization (HHO) by integrating four strategies into various phases to avoid local minima. The initiation phase incorporates good point set theory and quantum computing to enhance the population quality, while a random nonlinear technique is introduced in the transition phase to expand the exploration region in the early stages. A correction mechanism and exploration enhancement combining the slime mold algorithm (SMA) and quasi-oppositional learning (QOL) are further developed to find an optimal solution. Furthermore, the RSS-based Cramér–Raolower bound (CRLB) is derived to evaluate the effectiveness of QEHHO. Simulation results demonstrate the superior performance of QEHHO under various conditions compared to other state-of-the-art closed-form-expression- and meta-heuristic-based solutions. Full article

(This article belongs to the Special Issue Advances in Underwater Acoustic Communication and Ocean Sensor Networks)

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25 pages, 14216 KiB

Open AccessArticle

Autonomous Underwater Vehicle Cruise Positioning and Docking Guidance Scheme

by Zhuoyu Zhang, Wangjie Ding, Rundong Wu, Mingwei Lin, Dejun Li and Ri Lin

J. Mar. Sci. Eng. 2024, 12(6), 1023; https://doi.org/10.3390/jmse12061023 - 19 Jun 2024

Viewed by 288

Abstract

The Autonomous Underwater Vehicle (AUV) is capable of autonomously conducting underwater cruising tasks. When combined with docking operations, the AUV can replenish its electric power after long-distance travel, enabling it to achieve long-range autonomous monitoring. This paper proposes a positioning method for the [...] Read more.

The Autonomous Underwater Vehicle (AUV) is capable of autonomously conducting underwater cruising tasks. When combined with docking operations, the AUV can replenish its electric power after long-distance travel, enabling it to achieve long-range autonomous monitoring. This paper proposes a positioning method for the cruising and docking stages of AUVs. Firstly, a vision guidance algorithm based on monocular vision and threshold segmentation is studied to address the issue of regional noise that commonly occurs during underwater docking. A solution for regional noise based on threshold segmentation and proportional circle selection is proposed. Secondly, in order to enhance the positioning accuracy during the cruising stage, a fusion positioning algorithm based on particle filtering is presented, incorporating the Doppler Velocity Log (DVL) and GPS carried by the AUV. In simulation, this algorithm improves positioning accuracy by over 56.0% compared to using individual sensors alone. Finally, experiments for cruising and docking were conducted in Qingjiang, Hubei, China. The effectiveness of both methods is demonstrated, with successful docking achieved in four out of five attempts. Full article

(This article belongs to the Section Ocean Engineering)

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21 pages, 912 KiB

Open AccessReview

Applications of Voronoi Diagrams in Multi-Robot Coverage: A Review

by Meng Zhou, Jianyu Li, Chang Wang, Jing Wang and Li Wang

J. Mar. Sci. Eng. 2024, 12(6), 1022; https://doi.org/10.3390/jmse12061022 - 19 Jun 2024

Viewed by 306

Abstract

In recent decades, multi-robot region coverage has played an important role in the fields of environmental sensing, target searching, etc., and it has received widespread attention worldwide. Due to the effectiveness in segmenting nearest regions, Voronoi diagrams have been extensively used in recent [...] Read more.

In recent decades, multi-robot region coverage has played an important role in the fields of environmental sensing, target searching, etc., and it has received widespread attention worldwide. Due to the effectiveness in segmenting nearest regions, Voronoi diagrams have been extensively used in recent years for multi-robot region coverage. This paper presents a survey of recent research works on region coverage methods within the framework of the Voronoi diagram, to offer a perspective for researchers in the multi-robot cooperation domain. First, some basic knowledge of the Voronoi diagram is introduced. Then, the region coverage issue under the Voronoi diagram is categorized into sensor coverage and task execution coverage problems, respectively, considering the sensor range parameter. Furthermore, a detailed analysis of the application of Voronoi diagrams to the aforementioned two problems is provided. Finally, some conclusions and potential further research perspectives in this field are given. Full article

(This article belongs to the Special Issue Unmanned Marine Vehicles: Navigation, Control and Sensing)

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21 pages, 10368 KiB

Open AccessReview

A Critical Review of Constitutive Models Applied to Ice-Crushing Simulations

by Mojtaba Mokhtari and Bernt Johan Leira

J. Mar. Sci. Eng. 2024, 12(6), 1021; https://doi.org/10.3390/jmse12061021 - 19 Jun 2024

Viewed by 453

Abstract

In marine engineering, understanding the compressive behaviour of ice is crucial for accurately modelling ice loads on ships and offshore structures in ice-prone waters. Over the past few decades, numerous studies have focused on numerically simulating the ice-crushing process using various material models. [...] Read more.

In marine engineering, understanding the compressive behaviour of ice is crucial for accurately modelling ice loads on ships and offshore structures in ice-prone waters. Over the past few decades, numerous studies have focused on numerically simulating the ice-crushing process using various material models. A significant source of contention among these models lies in the representation of ice strength envelopes and their evolution with pressure and strain rate. Moreover, there is ongoing debate regarding whether plasticity or viscoelasticity more effectively captures the rheology of ice. Additionally, various flow rules have been implemented in plasticity models and different damage models have been used in viscoelasticity models, all of which play a critical role in simulating ice loads. This critical review aims to shed light on the reasons behind these disagreements and to evaluate the advantages and limitations of the most commonly used models, based on established theories in ice mechanics and empirical evidence. Full article

(This article belongs to the Special Issue Design of Marine Structures against Ice Actions)

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23 pages, 11659 KiB

Open AccessArticle

Cooling Improvement for High-Power-Density Shell-Mounted Underwater Propulsion Motors with Heat Bridges

by Huanyu Ou, Yuli Hu, Zhaoyong Mao, Wenlong Tian and Bo Cheng

J. Mar. Sci. Eng. 2024, 12(6), 1020; https://doi.org/10.3390/jmse12061020 - 19 Jun 2024

Viewed by 274

Abstract

Subject to an autonomous underwater vehicle (AUV) with rigorously limited space and weight, the high-power-density propulsion motor urgently needs an efficient cooling method to improve reliability and stability. In this paper, a cooling improvement method based on heat bridges (HBs) is proposed for [...] Read more.

Subject to an autonomous underwater vehicle (AUV) with rigorously limited space and weight, the high-power-density propulsion motor urgently needs an efficient cooling method to improve reliability and stability. In this paper, a cooling improvement method based on heat bridges (HBs) is proposed for the shell-mounted propulsion motor (SmPM) of the AUVs. First, the electromagnetic and thermal characteristics of a 150 kW SmPM are analyzed using a numerical method. Then, a prototype was developed and tested to verify the accuracy of the numerical calculation. Subsequently, in order to further improve the cooling performance of the motor with minimal weight increment, this paper proposes HBs mounted on the end winding. The maximum winding temperature of the motor containing the proposed HBs is decreased by 20 K at the rated operation state. Based on the validated numerical method, the effects of topologies, materials, and geometric parameters on the cooling effect are investigated. Furthermore, according to the required operating time, the SmPM is optimized based on the cooling performance improvement provided by the proposed HBs. The results show that in addition to the benefit of the cooling improvement contributed by the proposed HB, the weight of the propulsion motor is reduced by 7.14%. Full article

(This article belongs to the Section Ocean Engineering)

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14 pages, 3950 KiB

Open AccessArticle

A Novel Method for Estimating the Undrained Shear Strength of Marine Soil Based on CPTU Tests

by Sai Fu, Yanghai Shen, Xianlin Jia, Zhiqing Zhang and Xibin Li

J. Mar. Sci. Eng. 2024, 12(6), 1019; https://doi.org/10.3390/jmse12061019 - 19 Jun 2024

Viewed by 296

Abstract

The undrained shear strength is an essential parameter in the foundation design of marine structures. Due to the complex marine environment and technical limitations, it is difficult and costly to obtain offshore samples. Piezocone penetration tests (CPTU) are relatively low-cost compared to drilling [...] Read more.

The undrained shear strength is an essential parameter in the foundation design of marine structures. Due to the complex marine environment and technical limitations, it is difficult and costly to obtain offshore samples. Piezocone penetration tests (CPTU) are relatively low-cost compared to drilling and sampling methods. Therefore, based on the soil behavior type index (I_c) derived from CPTU results, a model for estimating cone factors (N_kt, N_ke) is proposed to improve the accuracy of estimation of undrained shear strength. The result shows that the soil behavior type index (I_c) and cone factors take on a negatively correlated exponential relation. Incorporating a cone factor that varies with the soil behavior type index (I_c) significantly enhances the accuracy of undrained shear strength predictions compared to the conventional method of using a constant cone factor. This approach reduces the root mean square error (RMSE) for N_kt (N_ke) from 0.124 (0.126) MPa to 0.056 (0.06) MPa, and the mean absolute error (MAE) from 0.0154 (0.016) MPa to 0.0032 (0.0036) MPa. The method was validated at an additional location and the predictions were in high agreement with the results of the consolidated quick direct shear test. The developed method can serve as an effective tool used in the design of foundations of marine structures. Full article

(This article belongs to the Special Issue Advance in Sedimentology and Coastal and Marine Geology—2nd Edition)

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15 pages, 1626 KiB

Open AccessArticle

Research on Time-Cooperative Guidance with Evasive Maneuver for Multiple Underwater Intelligent Vehicles

by Zuoe Fan, Hao Ding, Linping Feng, Bochen Li and Lei Song

J. Mar. Sci. Eng. 2024, 12(6), 1018; https://doi.org/10.3390/jmse12061018 - 19 Jun 2024

Viewed by 237

Abstract

In order to achieve the precise attack of multiple underwater intelligent vehicles (UIVs) on the same target ship at a fixed impact time, and to improve the penetration capability of the UIVs themselves, this study investigated the guidance law for the time-cooperative guidance [...] Read more.

In order to achieve the precise attack of multiple underwater intelligent vehicles (UIVs) on the same target ship at a fixed impact time, and to improve the penetration capability of the UIVs themselves, this study investigated the guidance law for the time-cooperative guidance of UIVs with maneuvering evasion. The evasive maneuver of the UIV increases the line-of-sight angle between the UIV and the target, which decreases the guidance precision of the UIV. A segmented control strategy is proposed to solve the problem of decreasing guidance precision caused by evading maneuvers, which is also the main contribution of this paper. This control strategy is dividing the guidance trajectory into two segments. The first segment allows for intelligent underwater vehicles to make evasion maneuvers and penetrate the defense, while the second segment controls the terminal time and achieves precision strike. Different desired target-vehicle distances are designed for each segment, unifying the impact time control issue and evasion maneuver problem into the pursuit of desired target-vehicle distances. Finally, based on feedback linearization control theory, a time-cooperative guidance law with evasion maneuver capability is proposed. Simulation results validate the effectiveness of the proposed method in attacking-moving targets. Full article

(This article belongs to the Special Issue Advanced Condition Monitoring and Intelligent Operation & Maintenance Technologies in Ships and Offshore Facilities)

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35 pages, 13522 KiB

Open AccessArticle

Life Assessment of Deep-Sea Observation Windows under Different Design Considerations

by Zhihao He, Fang Wang, Jinfei Zhang, Bingxiong Zhao, Yu Wu, Ruilong Luo and Fengluo Chen

J. Mar. Sci. Eng. 2024, 12(6), 1017; https://doi.org/10.3390/jmse12061017 - 18 Jun 2024

Viewed by 345

Abstract

As a key component of deep-sea manned submersibles, the observation window is usually constructed with polymethyl methacrylate (PMMA) material. During the design of the observation windows, the consideration of actual lifespan and its influential factors is insufficient. There are no clear provisions in [...] Read more.

As a key component of deep-sea manned submersibles, the observation window is usually constructed with polymethyl methacrylate (PMMA) material. During the design of the observation windows, the consideration of actual lifespan and its influential factors is insufficient. There are no clear provisions in the widely applied specifications. In this paper, based on the continuum damage mechanics model, combined with the viscoelastic relationship of PMMA material, a series of calculations were performed on the PMMA observation window. The parametric analysis of the fatigue crack-initiation life of the observation window at various thickness-to-diameter ratios (1.6, 1.4, 1.2, and 1.0), different friction coefficients (0.1, 0.2, and 0.3), and different transition arc radii (4000 mm and 6000 mm) was carried out. The calculated crack positions in the numerical mode used for validation closely align with those in the tested window. And simulation results show that the fatigue life of the observation window gradually decreases with the decrease in the thickness–diameter ratio and the increase in the friction coefficient. However, the increase in the transition arc radius will prolong the fatigue life of the observation window, which is higher than that of the original structure. Full article

(This article belongs to the Special Issue Structural Analysis and Failure Prevention in Offshore Engineering)

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18 pages, 1098 KiB

Open AccessArticle

Prediction of Drift Trajectory in the Ocean Using Double-Branch Adaptive Span Attention

by Chenghao Zhang, Jing Zhang, Jiafu Zhao and Tianchi Zhang

J. Mar. Sci. Eng. 2024, 12(6), 1016; https://doi.org/10.3390/jmse12061016 - 18 Jun 2024

Viewed by 199

Abstract

The accurate prediction of drift trajectories holds paramount significance for disaster response and navigational safety. The future positions of underwater drifters in the ocean are closely related to their historical drift patterns. Additionally, leveraging the complex dependencies between drift trajectories and ocean currents [...] Read more.

The accurate prediction of drift trajectories holds paramount significance for disaster response and navigational safety. The future positions of underwater drifters in the ocean are closely related to their historical drift patterns. Additionally, leveraging the complex dependencies between drift trajectories and ocean currents can enhance the accuracy of predictions. Building upon this foundation, we propose a Transformer model based on double-branch adaptive span attention (DBASformer), aimed at capturing the multivariate time-series relationships within drift history data and predicting drift trajectories in future periods. DBASformer can predict drift trajectories more accurately. The proposed adaptive span attention mechanism exhibits enhanced flexibility in the computation of attention weights, and the double-branch attention structure can capture the cross-time and cross-dimension dependencies in the sequences. Finally, our method was evaluated using datasets containing buoy data with ocean current velocities and Autonomous Underwater Vehicle (AUV) data. The raw data underwent cleaning and alignment processes. Comparative results with five alternative methods demonstrate that DBASformer improves prediction accuracy. Full article

(This article belongs to the Section Ocean Engineering)

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17 pages, 5874 KiB

Open AccessArticle

Spatial Distribution and Abundance of a Pelagic Squid during the Evolution of Eddies in the Southeast Pacific Ocean

by Xiaoci Wu, Pengchao Jin, Yang Zhang and Wei Yu

J. Mar. Sci. Eng. 2024, 12(6), 1015; https://doi.org/10.3390/jmse12061015 - 18 Jun 2024

Viewed by 255

Abstract

The Humboldt squid (Dosidicus gigas), is a significant economic species off Peru. The abundance and distribution of the species are highly susceptible to fluctuations in marine environmental conditions. The evolution of mesoscale eddies represents one of the dynamic processes in the [...] Read more.

The Humboldt squid (Dosidicus gigas), is a significant economic species off Peru. The abundance and distribution of the species are highly susceptible to fluctuations in marine environmental conditions. The evolution of mesoscale eddies represents one of the dynamic processes in the ocean, exerting varying degrees of influence on regional biogeochemical processes from generation to dissipation. However, the mechanisms governing the regulation of abundance and spatial distribution of D. gigas off Peru during this evolution remain unclear. Therefore, this study employed normalization techniques and the habitat suitability index (HSI) model, utilizing data from the D. gigas fishery, mesoscale eddies, and marine environmental factors (including sea surface temperature, temperature at 50 m depth, and chlorophyll-a concentration) to analyze the environmental changes and the abundance, spatial distribution, and habitat changes of D. gigas during the evolution of mesoscale eddies. The results indicate that eddies undergo four stages: formation, intensification, maturity, and decay. During eddy evolution, the abundance of D. gigas exhibited an initial increase and a subsequent decrease within cyclonic eddies (CEs), whereas, within anticyclonic eddies (AEs), abundance showed a gradual decline. The outcome of the HSI model revealed that, the habitat suitability and the proportion of suitable habitat areas within eddies were highly consistent with the abundance of D. gigas during all stages of the eddies other than the intensification stage of AEs. The study speculated that both CEs and AEs can create favorable environmental conditions during the maturity stage, thereby leading to an increase in suitable habitat and abundance of D. gigas. These findings emphasize the significant impact of mesoscale eddy evolution on the abundance and habitat distribution of D. gigas. Full article

(This article belongs to the Section Marine Ecology)

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23 pages, 5247 KiB

Open AccessArticle

Robust Prescribed-Time ESO-Based Practical Predefined-Time SMC for Benthic AUV Trajectory-Tracking Control with Uncertainties and Environment Disturbance

by Yufei Xu, Ziyang Zhang and Lei Wan

J. Mar. Sci. Eng. 2024, 12(6), 1014; https://doi.org/10.3390/jmse12061014 - 18 Jun 2024

Viewed by 263

Abstract

The aim of this study is to address the trajectory-tracking control problem of benthic autonomous underwater vehicles (AUVs) subjected to model uncertainties and extra disturbance. In order to estimate lumped uncertainties and reconstruction speed information, this paper designs a robust prescribed-time extended state [...] Read more.

The aim of this study is to address the trajectory-tracking control problem of benthic autonomous underwater vehicles (AUVs) subjected to model uncertainties and extra disturbance. In order to estimate lumped uncertainties and reconstruction speed information, this paper designs a robust prescribed-time extended state observer (RPTESO), and its prescribed time can be directly designed as an explicit parameter, without relying on the initial state of the system and complex parameter settings. In addition, an adaptive law is designed to improve the robustness of RPTSEO and reduce overshoot on the premise of ensuring convergence speed. Then, a non-singular robust practical predefined-time sliding mode control (RPPSMC) considering the hydrodynamic characteristics of AUV is designed, and the predefined time can be directly set by an explicit parameter. The RPPSMC is designed based on the lumped uncertainties estimated using RPTESO, so as to improve the control accuracy of the controller in a complex environment. Theoretical analysis and simulations demonstrated the effectiveness and superiority of the proposed method. Full article

(This article belongs to the Section Ocean Engineering)

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17 pages, 9987 KiB

Open AccessArticle

DSE-NN: Discretized Spatial Encoding Neural Network for Ocean Temperature and Salinity Interpolation in the North Atlantic

by Shirong Liu, Wentao Jia and Weimin Zhang

J. Mar. Sci. Eng. 2024, 12(6), 1013; https://doi.org/10.3390/jmse12061013 - 18 Jun 2024

Viewed by 264

Abstract

The precise interpolation of oceanic temperature and salinity is crucial for comprehending the dynamics of marine systems and the implications of global climate change. Prior neural network-based interpolation methods face constraints related to their capacity to delineate the intricate spatio-temporal patterns that are [...] Read more.

The precise interpolation of oceanic temperature and salinity is crucial for comprehending the dynamics of marine systems and the implications of global climate change. Prior neural network-based interpolation methods face constraints related to their capacity to delineate the intricate spatio-temporal patterns that are intrinsic to ocean data. This research presents an innovative approach, known as the Discretized Spatial Encoding Neural Network (DSE-NN), comprising an encoder–decoder model designed on the basis of deep supervision, network visualization, and hyperparameter optimization. Through the discretization of input latitude and longitude data into specialized vectors, the DSE-NN adeptly captures temporal trends and augments the precision of reconstruction, concurrently addressing the complexity and fragmentation characteristic of oceanic data sets. Employing the North Atlantic as a case study, this investigation shows that the DSE-NN presents enhanced interpolation accuracy in comparison with a traditional neural network. The outcomes demonstrate its quicker convergence and lower loss function values, as well as the ability of the model to reflect the spatial and temporal distribution characteristics and physical laws of temperature and salinity. This research emphasizes the potential of the DSE-NN in providing a robust tool for three-dimensional ocean temperature and salinity reconstruction. Full article

(This article belongs to the Special Issue Recent Scientific Developments in Ocean Observation)

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16 pages, 39802 KiB

Open AccessArticle

Intelligent Detection of Marine Offshore Aquaculture with High-Resolution Optical Remote Sensing Images

by Di Dong, Qingxiang Shi, Pengcheng Hao, Huamei Huang, Jia Yang, Bingxin Guo and Qing Gao

J. Mar. Sci. Eng. 2024, 12(6), 1012; https://doi.org/10.3390/jmse12061012 - 18 Jun 2024

Viewed by 397

Abstract

The rapid and disordered expansion of artificial marine aquaculture areas has caused severe ecological and environmental problems. Accurate monitoring of offshore aquaculture areas is urgent and significant in order to support the scientific and sustainable management and protection of coastal marine resources. Artificial [...] Read more.

The rapid and disordered expansion of artificial marine aquaculture areas has caused severe ecological and environmental problems. Accurate monitoring of offshore aquaculture areas is urgent and significant in order to support the scientific and sustainable management and protection of coastal marine resources. Artificial intelligence provides a valuable tool to improve marine resource monitoring. Deep learning methods have been widely used for marine object detection, but You Only Look Once (YOLO) models have not been employed for offshore aquaculture area monitoring. This study therefore evaluated the capacity of two well-known YOLO models, YOLOv5 and YOLOv7, to detect offshore aquaculture areas based on different high-resolution optical remote sensing imagery. Compared with YOLOv7 based on a satellite dataset, YOLOv5 increased the Precision value by approximately 3.29% (to 95.33%), Recall value by 3.02% (to 93.02%), mAP_0.5 by 2.03% (to 96.22%), and F1 score by 2.65% (to 94.16%). Based on the Google Earth dataset, YOLOv5 and YOLOv7 showed similar results. We found that the spatial resolution could affect the deep learning models’ performances. We used the Real-ESRGAN method to enhance the spatial resolution of satellite dataset and investigated whether super-resolution (SR) methods improved the detection accuracy of the YOLO models. The results indicated that despite improving the image clarity and resolution, the SR methods negatively affected the performance of the YOLO models for offshore aquaculture object detection. This suggests that attention should be paid to the use of SR methods before the application of deep learning models for object detection using remote sensing imagery. Full article

(This article belongs to the Special Issue Sustainable Development and Resource Management of Marine Aquaculture)

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23 pages, 20878 KiB

Open AccessArticle

Heterogeneous Reservoir Petrophysical Property and Controlling Factors in Semi-Restricted Depositional Setting: A Case Study of Yamama Formation, X Oilfield, Middle East

by Fengfeng Li, Lei Li, Haowei Chen, Wenyu Wang and Yang Wan

J. Mar. Sci. Eng. 2024, 12(6), 1011; https://doi.org/10.3390/jmse12061011 - 18 Jun 2024

Viewed by 277

Abstract

The Early Cretaceous Yamama Formation of X oilfield, deposited in a semi-restricted setting, holds considerable oil reserves. However, the reservoir is extremely heterogeneous and is poorly studied. Integrating outcrops, cores, cast thin sections, regular or special core analysis, wireline logging data from six [...] Read more.

The Early Cretaceous Yamama Formation of X oilfield, deposited in a semi-restricted setting, holds considerable oil reserves. However, the reservoir is extremely heterogeneous and is poorly studied. Integrating outcrops, cores, cast thin sections, regular or special core analysis, wireline logging data from six wells, and seismic data, this study provides an improved understanding of reservoir petrophysical characteristics and geological controlling factors including sedimentation, diagenesis, and sequence. The results showed that eight lithologies are developed in the Yamama Formation, of which packstone and wackstone are dominant. The physical properties span a wide range, with porosity mainly distributed between 10% and 25%, and the permeability mainly distributed between 0.1 mD and 1 mD. Nine types of pores are developed, with moldic pores, micropores, and skeletal pores being the most developed. The reservoir has six types of microstructures, of which the poorly sorted with mega-throat represent the best reservoir. The Yamama Formation was mainly deposited in a lagoon, along with five other facies, such as supratidal flat, patchy reef, back shoal, shoal, and open shelf. Six types of diageneses are developed, with dissolution during the penecontemporaneous stage being the most beneficial to the reservoir and cementation being the most destructive. Three sequences were recognized in the Yamama Formation. It concluded that the hydrodynamics in semi-restricted depositional setting is weak overall and does not have the potential to develop large-scale high-quality reservoirs. A wide range of bioclasts were selectively dissolved to form a large number of secondary pores. Sediments rich in Algae, Bacinella, and peloids tend to form moldic pores, skeletal pores, and intergranular pores, respectively, which are prone to be favorable reservoirs. Controlled by the coupling of sedimentation and diagenesis driven by sequence, the reservoir is extremely heterogenous. Full article

(This article belongs to the Special Issue Exploration and Development of Marine Energy)

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14 pages, 5331 KiB

Open AccessTechnical Note

A New Workflow for Instance Segmentation of Fish with YOLO

by Jiushuang Zhang and Yong Wang

J. Mar. Sci. Eng. 2024, 12(6), 1010; https://doi.org/10.3390/jmse12061010 - 18 Jun 2024

Viewed by 308

Abstract

The application of deep-learning technology for marine fishery resource investigation is still in its infancy stage. In this study, we applied YOLOv5 and YOLOv8 methods to identify and segment fish in the seabed. Our results show that both methods could achieve superior performance [...] Read more.

The application of deep-learning technology for marine fishery resource investigation is still in its infancy stage. In this study, we applied YOLOv5 and YOLOv8 methods to identify and segment fish in the seabed. Our results show that both methods could achieve superior performance in the segmentation task of the DeepFish dataset. We also expanded the labeling of specific fish species classification tags on the basis of the original semantic segmentation dataset of DeepFish and completed the multi-class instance segmentation task of fish based on the newly labeled tags. Based on the above two achievements, we propose a general and flexible self-iterative fish identification and segmentation standard workflow that can effectively improve the efficiency of fish surveys. Full article

(This article belongs to the Special Issue Underwater Observation Technology in Marine Environment)

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17 pages, 8157 KiB

Open AccessArticle

The Effects of Acute Ammonia Nitrogen Stress on Antioxidant Ability, Phosphatases, and Related Gene Expression in the Kidney of Juvenile Yellowfin Tuna (Thunnus albacares)

by Yongyue Sun, Zhengyi Fu and Zhenhua Ma

J. Mar. Sci. Eng. 2024, 12(6), 1009; https://doi.org/10.3390/jmse12061009 - 18 Jun 2024

Viewed by 333

Abstract

This study investigated the effects of acute ammonia nitrogen (NH₃-N) exposure on kidney antioxidant ability and phosphatases and related gene expression in juvenile yellowfin tuna (Thunnus albacares). The 180 juvenile yellowfin tuna (260.39 ± 55.99 g, 22.33 ± 2.28 [...] Read more.

This study investigated the effects of acute ammonia nitrogen (NH₃-N) exposure on kidney antioxidant ability and phosphatases and related gene expression in juvenile yellowfin tuna (Thunnus albacares). The 180 juvenile yellowfin tuna (260.39 ± 55.99 g, 22.33 ± 2.28 cm) were exposed to ammonia for 6, 24, and 36 h using natural seawater (0 mg/L) as a control and NH₃-N at 5 and 10 mg/L. The lipid peroxidation byproduct malondialdehyde (MDA) and the levels of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX), alkaline phosphatase (AKP), and acid phosphatase (ACP), were measured using the colorimetric method in the trunk kidney to determine changes in antioxidant ability and phosphatase activity of juvenile yellowfin tuna exposed to NH₃-N. Results indicated that, at 36 h, MDA, SOD, CAT, and GSH-PX levels rose in the 5 mg/L group versus the control. In the 10 mg/L group, MDA and SOD, CAT, and GSH-PX activities significantly increased after 24 and 36 h exposure compared to the control. Phosphatases play a pivotal role in the immune system. AKP activity significantly increased at 6 h, and ACP activity markedly rose at 36 h in the 5 mg/L group versus the control. Real-time fluorescence quantitative PCR was applied to detect alterations in the antioxidant genes SOD2, CAT, and glutathione peroxidase 1b (GPX1b) and immune cytokines-related genes Interleukin 10 (IL-10) and Interleukin 6 receptor (IL-6r) expression in the head kidney in juvenile tuna. Relative to the control, antioxidant gene expression in the 5 mg/L group significantly rose at 6 and 36 h, and in the 10 mg/L group, SOD2 and GPX1b were significantly elevated at 36 h. Compared to the control group, IL-10 expression in the 5 mg/L group significantly increased at 6 h, whereas IL-6r expression decreased. In the 10 mg/L group, both IL-10 and IL-6r levels were observed to be lower. Low ammonia nitrogen concentrations boost antioxidant defenses, phosphatase activities, and gene expression levels, whereas higher levels may induce suppressive effects. In yellowfin tuna juvenile farming, NH₃-N concentration significantly affects the health of the juveniles. When the NH₃-N concentration is between 5–10 mg/L, the stress duration should be limited to 24 h; if the concentration is below 5 mg/L, the stress duration can be extended to 36 h. Full article

(This article belongs to the Special Issue New Techniques and Equipment in Large Offshore Aquaculture Platform)

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20 pages, 14363 KiB

Open AccessArticle

Seasonal Phytoplankton Characteristics Related with Region-Specific Coastal Environments in the Korean Peninsula

by Chung Hyeon Lee, Young Kyun Lim, Mungi Kim, Seongjin Hong and Seung Ho Baek

J. Mar. Sci. Eng. 2024, 12(6), 1008; https://doi.org/10.3390/jmse12061008 - 17 Jun 2024

Viewed by 309

Abstract

The seasonal dynamics of phytoplankton communities in Korean coastal waters (KCWs) are influenced by complex interactions between ocean currents and nearshore human activities. Despite these influences, the understanding of seasonal phytoplankton changes and their environmental relationships in KCWs remains limited. We investigate the [...] Read more.

The seasonal dynamics of phytoplankton communities in Korean coastal waters (KCWs) are influenced by complex interactions between ocean currents and nearshore human activities. Despite these influences, the understanding of seasonal phytoplankton changes and their environmental relationships in KCWs remains limited. We investigate the influence of the distinct characteristics of the three seas surrounding the KCWs (the Yellow Sea, the South Sea, and the East Sea) on seasonal phytoplankton communities based on field surveys conducted at 23 stations between 2020 and 2021. The East Sea exhibited higher winter temperatures due to the Jeju and Tsushima warm currents, while summer temperatures were lower compared to the other regions, highlighting the role of currents and deeper oceanic waters. The Yellow Sea showed significant freshwater influence with low salinity levels from major rivers, contrasting with the higher salinity in the East Sea. These differences led to a disparity in the productivity of the two regions: the highest value of Chl. a was observed to be 6.05 µg L⁻¹ in the Yellow Sea in summer. Diatoms dominated in nutrient-rich conditions, particularly in the Yellow Sea, where they comprised up to 80–100% of the phytoplankton community in summer, winter, and spring. PCA analysis revealed positive correlations between diatoms and Chl. a, while cryptophytes, which thrive in the absence of diatom proliferation, showed no such correlation, indicating their opportunistic growth in nutrient-limited conditions. This study highlights the significant impact of region-specific hydrographic factors on phytoplankton communities in KCWs, with diatoms dominating in summer and cryptophytes and dinoflagellates showing seasonal and regional variations. Understanding these dynamics is crucial for predicting phytoplankton bloom dynamics and their ecological implications in coastal ecosystems. Full article

(This article belongs to the Section Marine Biology)

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25 pages, 2188 KiB

Open AccessArticle

Systems-Based Safety Analysis for Hydrogen-Driven Autonomous Ships

by Mir Md Ashfaque Sumon, Hyungju Kim, Seong Na, Choungho Choung and Elisabeth Kjønsberg

J. Mar. Sci. Eng. 2024, 12(6), 1007; https://doi.org/10.3390/jmse12061007 - 17 Jun 2024

Viewed by 481

Abstract

In the maritime domain, hydrogen fuel cell propulsion and autonomous vessels are two important issues that are yet to be implemented together because of a few challenges. It is obvious that there are several individual safety studies on Maritime Autonomous Surface Ships and [...] Read more.

In the maritime domain, hydrogen fuel cell propulsion and autonomous vessels are two important issues that are yet to be implemented together because of a few challenges. It is obvious that there are several individual safety studies on Maritime Autonomous Surface Ships and hydrogen storage as well as fuel cells based on various risk assessment tools but the combined safety studies that include hydrogen fuel cells on autonomous vessels with recent risk analysis methods are extremely limited. This research chooses the “System-Theoretic Process Analysis” (STPA) method which is a recent method for potential risk identification and mitigation. Both hydrogen and autonomous vessels are analyzed and assessed together with the STPA method. Results are not speculative but rather flexible compared to conventional systems. The study finds a total of 44 unsafe control actions (UCAs) evolved from human and central control unit controllers through STPA. Further, the loss scenarios (LS) are identified that lead to those UCAs so that loss scenarios can be assessed and UCAs can be mitigated for safe operation. The objective of this study is to ensure adequate safety for hydrogen fuel cell propulsion on autonomous vessels. Full article

(This article belongs to the Special Issue Risk Assessment in Maritime Transportation)

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29 pages, 2805 KiB

Open AccessArticle

Port Accessibility Depends on Cascading Interactions between Fleets, Policies, Infrastructure, and Hydrodynamics

by Floor P. Bakker, Solange van der Werff, Fedor Baart, Alex Kirichek, Sander de Jong and Mark van Koningsveld

J. Mar. Sci. Eng. 2024, 12(6), 1006; https://doi.org/10.3390/jmse12061006 - 17 Jun 2024

Viewed by 413

Abstract

Reducing waiting times is crucial for ports to be efficient and competitive. Important causes of waiting times are cascading interactions between realistic hydrodynamics, accessibility policies, vessel-priority rules, and detailed berth availability. The main challenges are determining the cause of waiting and finding rational [...] Read more.

Reducing waiting times is crucial for ports to be efficient and competitive. Important causes of waiting times are cascading interactions between realistic hydrodynamics, accessibility policies, vessel-priority rules, and detailed berth availability. The main challenges are determining the cause of waiting and finding rational solutions to reduce waiting time. In this study, we focus on the role of the design depth of a channel on the waiting times. We quantify the performance of channel depth for a representative fleet rather than the common approach of a single normative design vessel. The study relies on a mesoscale agent-based discrete-event model that can take processed Automatic Identification System and hydrodynamic data as its main input. The presented method’s validity is assessed by hindcasting one year of observed anchorage area laytimes for a liquid bulk terminal in the Port of Rotterdam. The hindcast demonstrates that the method predicts the causes of 73.4% of the non-excessive laytimes of vessels, thereby correctly modelling 60.7% of the vessels-of-call. Following a recent deepening of the access channel, cascading waiting times due to tidal restrictions were found to be limited. Nonetheless, the importance of our approach is demonstrated by testing alternative maintained bed level designs, revealing the method’s potential to support rational decision-making in coastal zones. Full article

(This article belongs to the Special Issue Management and Control of Ship Traffic Behaviours)

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J. Mar. Sci. Eng., Volume 12, Issue 6 (June 2024) – 187 articles

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