Journal of Marine Science and Engineering

13 pages, 4997 KiB

Open AccessArticle

Numerical Study on the Influence of Drift Angle on Wave Properties in a Two-Layer Flow

by Xiaoxing Zhao, Liuliu Shi and Eryun Chen

J. Mar. Sci. Eng. 2024, 12(12), 2139; https://doi.org/10.3390/jmse12122139 (registering DOI) - 23 Nov 2024

This study examines the influence of drift angle on the wave and flow field generated by a submarine navigating through a density-stratified fluid. Employing a numerical methodology, this research computed the viscous flow field around the SUBOFF bare hull under conditions of oblique [...] Read more.

This study examines the influence of drift angle on the wave and flow field generated by a submarine navigating through a density-stratified fluid. Employing a numerical methodology, this research computed the viscous flow field around the SUBOFF bare hull under conditions of oblique shipping maneuvers. The analytical framework relies on the Reynolds-Averaged Navier–Stokes (RANS) equations, supplemented by the Re-Normalization Group (RNG) k-ε turbulence model and the Volume of Fluid (VOF) method. The initial phases of this study involved verifying grid convergence and the accuracy of the numerical methods used. Subsequently, numerical simulations were performed across a spectrum of drift angles while maintaining a fixed Froude number of F_n = 0.5, with submergence depths set at 1.1 D and 2.0 D. The analysis focused on the wave profiles at both the free surface and the internal surface. The results indicate that the presence of a drift angle produces significant alterations in the characteristics of the free surface and internal surface when compared with straight-ahead motion. Specifically, the asymmetry in the flow field is enhanced, and the variability in the roughness of the free surface is pronounced. Full article

(This article belongs to the Section Ocean Engineering)

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25 pages, 4279 KiB

Open AccessArticle

Dynamic Response Assessment of Floating Offshore Wind Turbine Mooring Systems with Different In-Line Tensioner Configurations Based on Fully Coupled Load Calculations

by Wenhua Li, Guanlin Du, Shanying Lin, Zhenju Chuang and Fei Wang

J. Mar. Sci. Eng. 2024, 12(12), 2138; https://doi.org/10.3390/jmse12122138 (registering DOI) - 23 Nov 2024

Abstract

In-line tensioning technology has significantly reduced the cost barriers that previously hindered the expansion of the floating offshore wind industry. However, assessing the impact of in-line tensioners on the dynamic response of floating offshore wind turbines (FOWTs) lacks effectiveness, and the relevant mooring [...] Read more.

In-line tensioning technology has significantly reduced the cost barriers that previously hindered the expansion of the floating offshore wind industry. However, assessing the impact of in-line tensioners on the dynamic response of floating offshore wind turbines (FOWTs) lacks effectiveness, and the relevant mooring configuration specifications are not complete. Thus, a fully coupled calculation method is introduced in this paper to solve the relevant issues in mooring systems with in-line tensioners using a classic spar platform model. Three distinct design scenarios were selected to study the variation in mooring configurations of in-line tensioners along different mooring lines and at varied positions within each line. The potential occurrence of reverse tension phenomena was deliberated and assessed. We identified the varying tension patterns at the fairlead and in-line tensioner locations in mooring systems with in-line tensioners, and the influence of such variations on platform dynamics. The findings also demonstrate that the appropriate configuration of in-line tensioners should be selected to avoid the risk of reverse tension. This research has potential to contribute to the security and economy of the deployment of this emerging in-line mooring method. Full article

(This article belongs to the Section Ocean Engineering)

13 pages, 4339 KiB

Open AccessArticle

Experimental Investigation on Wave Dissipation of Perforated Pipe Breakwater Under Regular Wave Conditions

by Shaopeng Yang, Lipeng Yang, Bing Shi, Jing Na and Yakun Guo

J. Mar. Sci. Eng. 2024, 12(12), 2137; https://doi.org/10.3390/jmse12122137 (registering DOI) - 23 Nov 2024

Abstract

The permeable breakwater is an innovative, eco-friendly coastal protection structure that reduces wave impact while minimizing “dead water” and environmental harm. This study introduces a perforated pipe breakwater design with an increasing pipe diameter from top to bottom, evaluated through physical model tests [...] Read more.

The permeable breakwater is an innovative, eco-friendly coastal protection structure that reduces wave impact while minimizing “dead water” and environmental harm. This study introduces a perforated pipe breakwater design with an increasing pipe diameter from top to bottom, evaluated through physical model tests using transmission coefficient K_t and reflection coefficient K_r serving as the primary parameters. The results indicate that K_t decreases as the relative width (B/L), wave steepness (H/L), and relative water depth (h/L) increase, but rises with a steeper breakwater slope. When B/L exceeds 0.3, H/L surpasses 0.06, or the h/L ratio is greater than 0.3, K_t gradually declines until reaching a stable state, resulting in a more pronounced wave reduction. As B/L and H/L increase, the coefficient K_r initially drops, then rises. The slope ratio of 1:1.5 demonstrates the most effective wave energy dissipation, with primary dissipation occurring on the front slope. The mixed pipe diameter design shows superior wave absorption over a uniform diameter. Compared to a porous horizontal plate, the perforated pipe breakwater exhibits better wave absorption. These findings offer valuable guidance for designing eco-friendly coastal protection projects. Full article

(This article belongs to the Section Ocean Engineering)

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34 pages, 21017 KiB

Open AccessArticle

Operation Analysis of the Floating Derrick for Offshore Wind Turbine Installation Based on Machine Learning

by Jia Yu, Honglong Li, Shan Wang and Xinghua Shi

J. Mar. Sci. Eng. 2024, 12(12), 2136; https://doi.org/10.3390/jmse12122136 - 22 Nov 2024

Abstract

To investigate the influencing factors on the operation of an offshore wind turbine installation ship, a neural network, as a machine-learning method, is built to predict and analyze the motion response of a floating derrick in the process of a lifting operation under [...] Read more.

To investigate the influencing factors on the operation of an offshore wind turbine installation ship, a neural network, as a machine-learning method, is built to predict and analyze the motion response of a floating derrick in the process of a lifting operation under an external environmental load. The numerical method for the double floating body, from the software SESAM/SIMA, is validated against the experiments. The numerical method is used to establish the floating derrick-lifting impeller model to obtain the motions of the ship and impeller and the coupling effect. Based on the numerical results, the BP neural network model is built to predict the ship’s operation. The results show that the BP neural network model for the floating derrick and impeller motion prediction is very feasible. Combined with the Rules for Lifting Appliances of Ships and Offshore Installations and the Noble Denton Guidelines for Marine Lifting Operations, the operation of the floating crane system can be determined based on the environmental parameters. Full article

(This article belongs to the Special Issue Impact of Ocean Wave Loads on Marine Structures)

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24 pages, 5064 KiB

Open AccessArticle

High-Precision Permeability Evaluation of Complex Carbonate Reservoirs in Marine Environments: Integration of Gaussian Distribution and Thomeer Model Using NMR Logging Data

by Hengyang Lv, Jianhong Guo, Baoxiang Gu, Yuhan Liu, Li Wang, Long Wang, Zuomin Zhu and Zhansong Zhang

J. Mar. Sci. Eng. 2024, 12(12), 2135; https://doi.org/10.3390/jmse12122135 - 22 Nov 2024

Abstract

Accurate evaluation of permeability parameters is critical for the exploration and development of oil and gas fields. Among the available techniques, permeability assessment based on nuclear magnetic resonance (NMR) logging data is one of the most widely used and precise methods. However, the [...] Read more.

Accurate evaluation of permeability parameters is critical for the exploration and development of oil and gas fields. Among the available techniques, permeability assessment based on nuclear magnetic resonance (NMR) logging data is one of the most widely used and precise methods. However, the rapid biochemical variations in marine environments give rise to complex pore structures and strong reservoir heterogeneity, which diminish the effectiveness of traditional SDR and Timur–Coates models. To address these challenges in complex carbonate reservoirs, this study proposes a high-precision permeability evaluation method that integrates the Gaussian distribution model with the Thomeer model for more accurate permeability calculations using NMR logging data. Multimodal Gaussian distributions more accurately capture the size and distribution of multiscale pores. In this study, we innovatively employ the Gaussian distribution function to construct NMR-derived pseudo-pore size distribution curves. Subsequently, Thomeer model parameters are derived from Gaussian distribution parameters, enabling precise permeability calculation. The application of this method to the marine dolomite intervals of the Asmari Formation, Section A, within Oilfield A in southeastern Iraq, demonstrates its superior performance under both bimodal and unimodal pore size distributions. Compared to traditional models, this approach significantly reduces errors, providing crucial support for the accurate evaluation of complex reservoirs and the development of hydrocarbon resources. Full article

(This article belongs to the Special Issue Petroleum and Gas Hydrate Exploration and Marine Geology)

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23 pages, 8542 KiB

Open AccessArticle

Graphics Processing Unit-Accelerated Propeller Computational Fluid Dynamics Using AmgX: Performance Analysis Across Mesh Types and Hardware Configurations

by Yue Zhu, Jin Gan, Yongshui Lin and Weiguo Wu

J. Mar. Sci. Eng. 2024, 12(12), 2134; https://doi.org/10.3390/jmse12122134 - 22 Nov 2024

Abstract

Computational fluid dynamics (CFD) has become increasingly prevalent in marine and offshore engineering, with enhancing simulation efficiency emerging as a critical challenge. This study systematically evaluates the application of graphics processing unit (GPU) acceleration technology in CFD simulation of propeller open water performance. [...] Read more.

Computational fluid dynamics (CFD) has become increasingly prevalent in marine and offshore engineering, with enhancing simulation efficiency emerging as a critical challenge. This study systematically evaluates the application of graphics processing unit (GPU) acceleration technology in CFD simulation of propeller open water performance. Numerical simulations of the VP1304 propeller model were performed using OpenFOAM v2312 integrated with the NVIDIA AmgX library. The research compared GPU acceleration performance against conventional CPU methods across various hardware configurations and mesh types (tetrahedral, hexahedral-dominant, and polyhedral). Results demonstrate that GPU acceleration significantly improved computational efficiency, with tetrahedral meshes achieving over 400% speedup in a 4-GPU configuration, while polyhedral meshes reached over 500% speedup with a fixed mesh count. Among the mesh types, hexahedral-dominant meshes performed best in capturing flow field details. The study also found that GPU acceleration does not compromise simulation accuracy, but its effectiveness is closely related to mesh type and hardware configuration. Notably, GPUs demonstrate more significant advantages when handling large-scale problems. These findings have important practical implications for improving propeller design processes and shortening product development cycles. Full article

(This article belongs to the Section Ocean Engineering)

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24 pages, 8531 KiB

Open AccessArticle

Optimization of a Dual-Channel Water-Cooling Heat Dissipation System for PMSM in Underwater Unmanned Vehicles Using a Multi-Objective Genetic Algorithm

by Wenlong Tian, Chen Zhang, Zhaoyong Mao and Bo Cheng

J. Mar. Sci. Eng. 2024, 12(12), 2133; https://doi.org/10.3390/jmse12122133 - 22 Nov 2024

Abstract

To minimize the temperature of the propulsion motor and reduce flow loss in the water-cooling structure during the operation of an underwater unmanned vehicle, this paper employs a multi-objective genetic algorithm to optimize the dimensions of the inner and outer dual-channel water-cooling structure [...] Read more.

To minimize the temperature of the propulsion motor and reduce flow loss in the water-cooling structure during the operation of an underwater unmanned vehicle, this paper employs a multi-objective genetic algorithm to optimize the dimensions of the inner and outer dual-channel water-cooling structure as well as the flow rate of the cooling water. Firstly, the influence of design variables on response variables was examined through sensitivity analysis. Subsequently, a model sample library for simulating the coupled temperature and flow fields of the motor was constructed, and a response surface model between the variables was developed. Finally, appropriate sample points were selected from the Pareto solution set to verify the validity of the optimization results through CFD simulation and error analysis. The sensitivity analysis results indicate that the cooling water flow rate had the greatest impact on both the maximum motor temperature and the flow losses of the water-cooling structure, with values of 77.79% and 99.84%, respectively. On the other hand, the optimal design parameters for the four dimensions of the channel and the cooling water flow rate were obtained. Compared with the initial dimensions of the water-cooling structure, the maximum temperature of the motor decreased from 332.86 K to 331.46 K. Simultaneously, the flow loss of the water-cooling structure decreased from 100.02 kPa to 59.58 kPa, with a maximum reduction rate of 40.43%. The optimization effect of the motor cooling system is significant, which provides valuable insights for system design under the premise of ignoring multi-objective interactions. Full article

(This article belongs to the Section Ocean Engineering)

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26 pages, 28817 KiB

Open AccessArticle

Hydrodynamic Performance of Toroidal Propeller Based on Detached Eddy Simulation Method

by Pei Xu, Yingchun Guo, Liyu Ye and Kewei Song

J. Mar. Sci. Eng. 2024, 12(12), 2132; https://doi.org/10.3390/jmse12122132 - 22 Nov 2024

Abstract

Toroidal propellers hold significant potential as underwater propulsion systems compared to traditional propellers, primarily due to their unique shape, which effectively reduces and minimizes hydrodynamic noise and enhances structural stability and overall strength. To investigate hydrodynamic loads, flow fields, and vortex characteristics of [...] Read more.

Toroidal propellers hold significant potential as underwater propulsion systems compared to traditional propellers, primarily due to their unique shape, which effectively reduces and minimizes hydrodynamic noise and enhances structural stability and overall strength. To investigate hydrodynamic loads, flow fields, and vortex characteristics of toroidal propellers, numerical simulations were conducted on both toroidal and conventional propellers using the detached eddy simulation (DES) method in Star CCM+ computational fluid dynamics software. Results show that at low advance coefficients, the primary thrust generated by toroidal blades comes from pressure difference in the front section, whereas at high advance coefficients, it originates in the back section. A high-velocity region exists between the front and back sections of the toroidal propeller, with the range and intensity of this region gradually increasing from front to back. The wake vortex of the toroidal propeller comprises two parts: the tip vortex, where the front section tip vortex, back section tip vortex, and transition section leakage vortex merge, and the trailing edge vortex, which forms from the fusion of the front and back section leakage vortices. The fusion of these vortices is influenced by the advance coefficient. Compared to conventional propellers, the toroidal propellers exhibit a more extensive and intense trailing edge vortex in the wake flow field. These findings provide guidance for the optimization design research of toroidal propellers. Full article

(This article belongs to the Section Ocean Engineering)

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26 pages, 11337 KiB

Open AccessArticle

Comparative Study on Hydrodynamic Characteristics of Under-Water Vehicles Near Free Surface and Near Ice Surface

by Pei Xu, Jixiang Chen, Yingchun Guo and Wanzhen Luo

J. Mar. Sci. Eng. 2024, 12(12), 2131; https://doi.org/10.3390/jmse12122131 - 22 Nov 2024

Abstract

In this paper, the commercial computational fluid dynamics software STAR-CCM+ (18.04.008-R8) is utilized to analyze the hydrodynamic performance of BB2 underwater vehicles under various navigation conditions, as well as the flow field disturbances caused by the free surface and ice surface during navigation. [...] Read more.

In this paper, the commercial computational fluid dynamics software STAR-CCM+ (18.04.008-R8) is utilized to analyze the hydrodynamic performance of BB2 underwater vehicles under various navigation conditions, as well as the flow field disturbances caused by the free surface and ice surface during navigation. After dividing the computational domains based on different navigation scenarios, numerical simulations are conducted for BB2 underwater vehicles (without a propeller) at infinite depth, near the free surface, and near the ice surface under various operating conditions. The analysis focuses on changes in resistance, velocity fields, and pressure fields of the BB2 at different velocities and navigation depths, followed by a comparison of the navigation differences of BB2 vehicles under varying operating conditions. Furthermore, to simulate realistic navigation conditions for underwater vehicles, numerical simulations are performed for BB2 underwater vehicles equipped with a propeller under different operating conditions. The results indicate that both the free surface and ice surface significantly influence the resistance, velocity field, and pressure field of the BB2. When the navigation depth exceeds 2D, the impact of ice on the vehicle can be nearly disregarded, and when the navigation depth exceeds 3D, the influence of the free surface on the vehicle can also be considered negligible. Full article

(This article belongs to the Section Ocean Engineering)

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18 pages, 2646 KiB

Open AccessArticle

Improved RT-DETR for Infrared Ship Detection Based on Multi-Attention and Feature Fusion

by Chun Liu, Yuanliang Zhang, Jingfu Shen and Feiyue Liu

J. Mar. Sci. Eng. 2024, 12(12), 2130; https://doi.org/10.3390/jmse12122130 - 22 Nov 2024

Abstract

Infrared cameras form images by capturing the thermal radiation emitted by objects in the infrared spectrum, making them complex sensors widely used in maritime surveillance. However, the broad spectral range of the infrared band makes it susceptible to environmental interference, which can reduce [...] Read more.

Infrared cameras form images by capturing the thermal radiation emitted by objects in the infrared spectrum, making them complex sensors widely used in maritime surveillance. However, the broad spectral range of the infrared band makes it susceptible to environmental interference, which can reduce the contrast between the target and the background. As a result, detecting infrared targets in complex marine environments remains challenging. This paper presents a novel and enhanced detection model developed from the real-time detection transformer (RT-DETR), which is designated as MAFF-DETR. The model incorporates a novel backbone by integrating CSP and parallelized patch-aware attention to enhance sensitivity to infrared imagery. Additionally, a channel attention module is employed during feature selection, leveraging high-level features to filter low-level information and enabling efficient multi-level fusion. The model’s target detection performance on resource-constrained devices is further enhanced by incorporating advanced techniques such as group convolution and ShuffleNetV2. The experimental results show that, although the enhanced RT-DETR algorithm still experiences missed detections under severe object occlusion, it has significantly improved overall performance, including a 1.7% increase in mAP, a reduction in 4.3 M parameters, and a 5.8 GFLOPs decrease in computational complexity. It can be widely applied to tasks such as coastline monitoring and maritime search and rescue. Full article

(This article belongs to the Special Issue AI-Empowered Marine Energy)

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29 pages, 18764 KiB

Open AccessArticle

Analytical Modeling of the Lazy-Wave Hydrogen Production Riser (HPR) with Incorporation of Seabed Interaction in the Touchdown Zone

by Mohammad Mahdi Hajitaheriha and Hodjat Shiri

J. Mar. Sci. Eng. 2024, 12(12), 2129; https://doi.org/10.3390/jmse12122129 - 22 Nov 2024

Abstract

Hydrogen production risers (HPRs) connected to floating offshore wind turbines (FOWTs) must be properly configured to minimize both the top-end tension at the hang-off point and the oscillation amplitude in the touchdown zone (TDZ) under environmental loads. One of the best riser configurations [...] Read more.

Hydrogen production risers (HPRs) connected to floating offshore wind turbines (FOWTs) must be properly configured to minimize both the top-end tension at the hang-off point and the oscillation amplitude in the touchdown zone (TDZ) under environmental loads. One of the best riser configurations to meet these requirements is the lazy-wave configuration, where the riser is lifted midway by buoyancy tanks to create a negative curvature, mitigating the motion dependency of the catenary part and the TDZ. Analytical solutions can be effectively used in riser optimization and configuration studies, where a large number of analyses need to be conducted iteratively. In this paper, an analytical model for HPRs has been developed by combining different approaches for the hanging and touchdown zones to improve the accuracy and continuity of shear force, bending moment, and axial tension distribution along the riser, which are the key parameters governing fatigue damage accumulation in the TDZ. Modified catenary equations were used for the hanging part, and a boundary layer model was implemented in the touchdown zone to model the seabed interaction, preventing stress discontinuity between the two sections. The model was used to assess a case study and compared with numerical simulations to ensure accuracy and viability. The proposed model can be used in daily engineering practice for preliminary investigations and optimization studies of HPRs. Full article

(This article belongs to the Special Issue Sustainable Offshore Pipeline Operations)

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19 pages, 623 KiB

Open AccessArticle

Critical Success Factors for Green Port Transformation Using Digital Technology

by Zhenqing Su, Yanfeng Liu, Yunfan Gao, Keun-Sik Park and Miao Su

J. Mar. Sci. Eng. 2024, 12(12), 2128; https://doi.org/10.3390/jmse12122128 - 22 Nov 2024

Abstract

Ports are the main arteries of global trade, handling goods circulation and serving as hubs for information, capital, and technology. Integrating digital technology has become the key for green port development to achieve resource efficiency and ecological balance. The current literature overlooks how [...] Read more.

Ports are the main arteries of global trade, handling goods circulation and serving as hubs for information, capital, and technology. Integrating digital technology has become the key for green port development to achieve resource efficiency and ecological balance. The current literature overlooks how digital technology can facilitate greener port operations. This study integrates sustainable supply chain management and system dynamics theories based on an in-depth analysis of existing research results and expert interviews. The analysis focuses on three key dimensions: integrating digital technologies with infrastructure, optimizing digital management and operations, and improving environmental and safety management in a digitally driven setting. Using the fuzzy Decision Making Trial and Evaluation Laboratory (Fuzzy Dematel) methodology, we collaborated with domain experts in port logistics to identify and confirm 12 pivotal factors that support the green digital transformation of ports. The research shows that the most critical success factors for using digital technology to drive ports’ green transformation are green supply chain information platforms, intelligent vessel scheduling, traffic optimization, and digital carbon emission monitoring. This study significantly contributes to the literature on green port transformation, offering indispensable practical insights for port operators, government entities, and shipping firms in identifying and deploying these key success factors. The findings will help maritime supply chain stakeholders develop actionable digital strategies, improving port efficiency and ecological resilience. Full article

(This article belongs to the Section Ocean Engineering)

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23 pages, 4326 KiB

Open AccessReview

Stromatolites and Their “Kin” as Living Microbialites in Contemporary Settings Linked to a Long Fossil Record

by Ed Landing and Markes E. Johnson

J. Mar. Sci. Eng. 2024, 12(12), 2127; https://doi.org/10.3390/jmse12122127 - 22 Nov 2024

Abstract

Organo-sedimentary deposits that result from fine-grained sediment trapping, binding, and likely precipitation (of carbonate) by microbes in flat-mat, branching, and dome-shaped constructions are termed microbialites. They were first identified as stromatolites by paleontologists well before the discovery of cyanobacteria that build the same [...] Read more.

Organo-sedimentary deposits that result from fine-grained sediment trapping, binding, and likely precipitation (of carbonate) by microbes in flat-mat, branching, and dome-shaped constructions are termed microbialites. They were first identified as stromatolites by paleontologists well before the discovery of cyanobacteria that build the same kinds of structures in contemporary settings around the world. Earth’s earliest life forms were prokaryotes (bacteria and bacteria-like forms) that reproduced under anaerobic conditions and later produced increasingly aerobic conditions. Stromatolites persisted through later Archean and Proterozoic times through the subsequent Phanerozoic to the present. At the start of the Cambrian Period 538 million years ago, stromatolites continued alongside rapidly diversifying plant and animal phyla during the Cambrian explosion of eukaryotic life, which have complex cells with internal structures and tissue-grade organization in multicellular taxa. The type locality exhibiting clear examples of stromatolite structures is conserved at Lester Park near Saratoga Springs in northeastern New York State. Paleontologist James Hall (1811–1898) was the first in 1884 to assign a Latin binomen (Cryptozoon proliferum) to stromatolite fossils from Lester Park. Thereafter, reports on formally named stromatolites proliferated, as did examples from virtually all subsequent geological time intervals including the Pleistocene Epoch. However, recognition that living cyanobacteria formed stromatolites identified as Cryptozoon took place much later in 1961 with the announcement by geologist Brian W. Logan (1933–2008) who described modern constructions in Hamlin Pool, Shark Bay, Western Australia. Initially, Shark Bay was regarded as a one-of-a-kind sanctuary for stromatolites living under restricted conditions with elevated levels of salinity that prohibited competition or grazing by eukaryotes. Most notably, among other settings with living stromatolites discovered and described since then are the Bahamas, East African rift lakes, Mexico’s Baja California, and saline lakes in Argentina. This report reviews the history of discoveries of modern-day stromatolites, more commonly called microbialites by biologists. All are predicated on the ground-breaking efforts of geologists and paleontologists who first described fossil stromatolites but were unaware of their living counterparts. The Lester Park locality is highlighted together with a master list of other North American localities that feature purported Cryptozoons. Full article

(This article belongs to the Special Issue Feature Review Papers in Geological Oceanography)

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18 pages, 1666 KiB

Open AccessArticle

Experimental Investigation on Wave and Bed Profile Evolution in a Sandbar-Lagoon Coast with Submerged Vegetation

by Wei Xing, Xin Cong, Cuiping Kuang, Dan Wang, Zhenzhen An and Qingping Zou

J. Mar. Sci. Eng. 2024, 12(12), 2126; https://doi.org/10.3390/jmse12122126 - 21 Nov 2024

Abstract

Better understanding of the hydro- and morphodynamic processes within vegetated sandbar-lagoon coasts is important for assessing the coastal protection capability of vegetation meadow for the coastal environments. Eighteen flume tests were conducted in a mobile-bed sandbar-lagoon with mimicked submerged vegetation under different water [...] Read more.

Better understanding of the hydro- and morphodynamic processes within vegetated sandbar-lagoon coasts is important for assessing the coastal protection capability of vegetation meadow for the coastal environments. Eighteen flume tests were conducted in a mobile-bed sandbar-lagoon with mimicked submerged vegetation under different water depths and wave conditions. It was found that wave attenuation by submerged vegetation near the breaking point is significant. An empirical linear expression for the total wave energy change ratio is proposed with a determination coefficient of 0.84. Moreover, the quantitative formulae for the erosion volume and maximum erosion thickness of sandbars and foredunes, as well as the total sediment transport volume, were proposed to demonstrate the implications of submerged vegetation meadows. These findings provide scientific references for coastal management and conservation planning, especially for sandbar-lagoon coasts. Nevertheless, additional physical experiments or field data are necessary to further validate those formulae. Full article

(This article belongs to the Section Coastal Engineering)

17 pages, 5533 KiB

Open AccessArticle

Numerical Study on the Hydrodynamics of Manta Rays Exiting Water

by Dong-Hui Zhou, Min-Hui Zhang, Xiao-Yang Wu, Yu Pei, Xue-Jing Liu, Cheng Xing, Yong Cao, Yong-Hui Cao and Guang Pan

J. Mar. Sci. Eng. 2024, 12(12), 2125; https://doi.org/10.3390/jmse12122125 - 21 Nov 2024

Abstract

Observation of manta rays exiting water has been rarely reported, as there are various difficulties in observing and obtaining data on their behavior in a marine environment. Therefore, the movement mechanism of manta rays exiting water is still unclear. This paper proposes the [...] Read more.

Observation of manta rays exiting water has been rarely reported, as there are various difficulties in observing and obtaining data on their behavior in a marine environment. Therefore, the movement mechanism of manta rays exiting water is still unclear. This paper proposes the idea of using CFD (based on Ansys Fluent, version 2022) to simulate the water-exit process of the manta ray. The study discusses the changes in the mechanical and kinematic parameters of the manta ray over time and obtains the evolution of vortex structures during the underwater movement phase of the manta ray. Time history variations of the mechanical and kinematics parameters in the vertical water-exit motion are discussed. The evolution of vortex structures during the underwater movement of the manta ray is obtained. The direction in which the manta ray approaches the free surface is the X-direction and the direction of its flapping motion is the Z-direction. V_X and V_Z are the velocities of the manta ray in the X- and Z-directions, respectively. F_X and F_Z represent the forces acting on the manta ray in the X- and Z-directions, respectively. The results indicate that the vertical water-exit of the manta ray mainly undergoes three stages: underwater acceleration, crossing the free surface, and aerial movement. During the underwater acceleration phase, the force F_X of the manta ray fluctuates, but its average value is positive within one cycle. V_X also shows a stepwise increase, while F_Z and V_Z exhibit periodic changes. During the stage of crossing the free liquid surface, F_X first increases and then sharply decreases, V_X also shows an increase and then decrease, F_Z fluctuates greatly, producing a peak, and the swimming speed V_Z of the manta ray is negative. During the aerial motion phase, F_X is mainly affected by gravity, V_X decreases linearly, F_Z approaches 0, and V_Z remains constant. During the process of swimming underwater, the tail vortex of the manta ray presents a double row staggered structure to generate thrust. Increasing the flapping frequency and decreasing the wave number can improve the swimming speed of the manta ray, and then increase its water-exit height. The findings may provide an important hydrodynamics basis for biomimetic trans-media vehicle designs. Full article

(This article belongs to the Section Ocean Engineering)

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14 pages, 2821 KiB

Open AccessArticle

Global Mean Sea Level Change Projections up to 2100 Using a Weighted Singular Spectrum Analysis

by Fengwei Wang, Yunzhong Shen, Jianhua Geng and Qiujie Chen

J. Mar. Sci. Eng. 2024, 12(12), 2124; https://doi.org/10.3390/jmse12122124 - 21 Nov 2024

Abstract

This paper forecasts global mean sea level (GMSL) changes from 2024 to 2100 using weighted singular spectrum analysis (SSA) that considers the formal errors of the previous GMSL time series. The simulation experiments are first carried out to evaluate the performance of the [...] Read more.

This paper forecasts global mean sea level (GMSL) changes from 2024 to 2100 using weighted singular spectrum analysis (SSA) that considers the formal errors of the previous GMSL time series. The simulation experiments are first carried out to evaluate the performance of the weighted and traditional SSA approaches for GMSL change prediction with two evaluation indices, the root mean square error (RMSE) and mean absolute error (MAE). The results show that all the RMSEs and MAEs of the weighted SSA are smaller than those of the traditional SSA, indicating that the weighed SSA can predict GMSL changes more accurately than the traditional SSA. The real GMSL change rate derived from weighted SSA is approximately 1.70 ± 0.02 mm/year for 1880–2023, and the predicted GMSL changes with the first two reconstructed components reaches 796.75 ± 55.92 mm by 2100, larger than the 705.25 ± 53.73 mm predicted with traditional SSA, with respect to the baseline from 1995 to 2014. According to the sixth Assessment Report of Intergovernmental Panel on Climate Change (IPCC AR6), the GMSL change by 2100 is 830.0 ± 152.42 mm/year with the high-emission scenarios is closer to weighted SSA than traditional SSA, though SSA predictions are within the prediction range of IPCC AR6. Therefore, the weighted SSA can provide an alternative future GMSL rise prediction. Full article

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

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25 pages, 1758 KiB

Open AccessArticle

Collision Avoidance for Unmanned Surface Vehicles in Multi-Ship Encounters Based on Analytic Hierarchy Process–Adaptive Differential Evolution Algorithm

by Zhongming Xiao, Baoyi Hou, Jun Ning, Bin Lin and Zhengjiang Liu

J. Mar. Sci. Eng. 2024, 12(12), 2123; https://doi.org/10.3390/jmse12122123 - 21 Nov 2024

Abstract

Path planning and collision avoidance issues are key to the autonomous navigation of unmanned surface vehicles (USVs). This study proposes an adaptive differential evolution algorithm model integrated with the analytic hierarchy process (AHP-ADE). The traditional differential evolution algorithm is enhanced by introducing an [...] Read more.

Path planning and collision avoidance issues are key to the autonomous navigation of unmanned surface vehicles (USVs). This study proposes an adaptive differential evolution algorithm model integrated with the analytic hierarchy process (AHP-ADE). The traditional differential evolution algorithm is enhanced by introducing an elite archive strategy and adaptively adjusting the scale factor F and the crossover factor

C R

to balance global and local search capabilities, preventing premature convergence and improving the search accuracy. Additionally, the collision risk index (CRI) model is optimized and combined with the quaternion ship domain, enhancing the precision of CRI calculations and USV autonomous collision avoidance capabilities. The improved CRI model, the International Regulations for Preventing Collisions at Sea, and the optimal collision avoidance distance were incorporated as evaluation factors in a fitness function assessment, with weights determined through the AHP to enhance the rationality and accuracy of the fitness function. The proposed AHP-ADE algorithm was compared with the improved particle swarm algorithm, and the performance of the algorithm was comprehensively evaluated using safety, economy, and operational efficiency. Simulation experiments on the MATLAB platform demonstrated that the proposed AHP-ADE algorithm exhibited better performance in scenarios involving multiple ship encounters, thus proving its effectiveness. Full article

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

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16 pages, 3056 KiB

Open AccessArticle

Exploration of the Formation Mechanism of Underground Brine Based on Hydrodynamic Environment Analysis Using Grain-Size Data of One Drilling Core

by Qiao Su, Ying Yu, Mingjun Chen, Tengfei Fu, Wenzhe Lyu and Wenquan Liu

J. Mar. Sci. Eng. 2024, 12(12), 2122; https://doi.org/10.3390/jmse12122122 - 21 Nov 2024

Abstract

The Laizhou Bay area in China harbors a significant amount of Quaternary brine resources, which have been gradually depleted due to intensive long-term exploitation. It is widely accepted that underground Quaternary brine in Laizhou Bay originates from seawater. However, there are disputes regarding [...] Read more.

The Laizhou Bay area in China harbors a significant amount of Quaternary brine resources, which have been gradually depleted due to intensive long-term exploitation. It is widely accepted that underground Quaternary brine in Laizhou Bay originates from seawater. However, there are disputes regarding the specific form of seawater concentration and the geological processes leading to brine formation. Revealing the genesis of shallow brine in different geological environments is of great scientific significance for resource production and environmental protection. This study analyzed the hydrodynamic conditions of underground brine and adjacent strata based on grain size data, and the possible formation mechanisms of brine layers at different depths were discussed. The mineralization of underground brine is a complex process controlled by various factors, such as specific meteorological and paleogeographic environments, topography, and hydrogeological conditions. On the southern coast of Laizhou Bay, there are three ways in which underground brine layers are formed: residual evaporation from lagoons during the initial regression stage, the hypersaline zone in estuarine lagoons during high-sea-level periods, and brine formation from seawater evaporation on intertidal flats. Turbulent sea–land interactions and the development of river deltas are also necessary conditions for brine mineralization, as they are favorable for replenishing, transporting, and storing underground brine layers. Full article

(This article belongs to the Section Marine Environmental Science)

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30 pages, 1672 KiB

Open AccessReview

Review on Maximum Power Point Tracking Control Strategy Algorithms for Offshore Floating Photovoltaic Systems

by Lei Huang, Baoyi Pan, Shaoyong Wang, Yingrui Dong and Zihao Mou

J. Mar. Sci. Eng. 2024, 12(12), 2121; https://doi.org/10.3390/jmse12122121 - 21 Nov 2024

Abstract

Floating photovoltaic systems are rapidly gaining popularity due to their advantages in conserving land resources and their high energy conversion efficiency, making them a promising option for photovoltaic power generation. However, these systems face challenges in offshore environments characterized by high salinity, humidity, [...] Read more.

Floating photovoltaic systems are rapidly gaining popularity due to their advantages in conserving land resources and their high energy conversion efficiency, making them a promising option for photovoltaic power generation. However, these systems face challenges in offshore environments characterized by high salinity, humidity, and variable irradiation, which necessitate effective maximum power point tracking (MPPT) technologies to optimize performance. Currently, there is limited research in this area, and few reviews analyze it comprehensively. This paper provides a thorough review of MPPT techniques applicable to floating photovoltaic systems, evaluating the suitability of various methods under marine conditions. Traditional algorithms require modifications to address the drift phenomena under uniform irradiation, while different GMPPT techniques exhibit distinct strengths and limitations in partial shading conditions (PSCs). Hardware reconfiguration technologies are not suitable for offshore use, and while sampled data-based techniques are simple, they carry the risk of erroneous judgments. Intelligent technologies face implementation challenges. Hybrid algorithms, which can combine the advantages of multiple approaches, emerge as a more viable solution. This review aims to serve as a valuable reference for engineers researching MPPT technologies for floating photovoltaic systems. Full article

(This article belongs to the Special Issue Offshore Renewable Energy, Second Edition)

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