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Volume 11
Issue 9
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J. Mar. Sci. Eng., Volume 11, Issue 9 (September 2023) – 206 articles

Cover Story (view full-size image): This paper presents a stereo reconstruction method for three-dimensional (3D) surface wave fields around floating bodies in a wave tank. Styrofoam markers were attached to a flexible net in a regular grid (marker net) and were placed on the water surface to be used as targets for stereo cameras (SCs). A thin plate spline was applied to the markers detected by the SCs to reconstruct the 3D surface wave profile around a floating body model. The proposed method was used in a tank experiment to reconstruct 3D wave profiles around a cylindrical floating body model with a footing at its bottom. The experiment was conducted under three different configurations: (1) without the model, (2) with a fixed model, and (3) with a freely oscillating model. The incident, scattering, and radiation waves were successfully acquired from the wave fields measured under these three configurations. View this paper
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24 pages, 5461 KiB  
Article
Contrastive Learning for Graph-Based Vessel Trajectory Similarity Computation
by Sizhe Luo, Weiming Zeng and Bowen Sun
J. Mar. Sci. Eng. 2023, 11(9), 1840; https://doi.org/10.3390/jmse11091840 - 21 Sep 2023
Cited by 1 | Viewed by 1047
Abstract
With the increasing popularity of automatic identification system AIS devices, mining latent vessel motion patterns from AIS data has become a hot topic in water transportation research. Trajectory similarity computation is a fundamental issue to many maritime applications such as trajectory clustering, prediction, [...] Read more.
With the increasing popularity of automatic identification system AIS devices, mining latent vessel motion patterns from AIS data has become a hot topic in water transportation research. Trajectory similarity computation is a fundamental issue to many maritime applications such as trajectory clustering, prediction, and anomaly detection. However, current non-learning-based methods face performance and efficiency issues, while learning-based methods are limited by the lack of labeled sample and explicit spatial modeling, making it difficult to achieve optimal performance. To address the above issues, we propose CLAIS, a contrastive learning framework for graph-based vessel trajectory similarity computation. A combined parameterized trajectory augmentation scheme is proposed to generate similar trajectory sample pairs and a constructed spatial graph of the study region is pretrained to help model the input trajectory graph. A graph neural network encoder is used to extract spatial dependency from the trajectory graph to learn better trajectory representations. Finally, a contrastive loss function is used to train the model in an unsupervised manner. We also propose an improved experiment and three related metrics and conduct extensive experiments to evaluate the performance of the proposed framework. The results validate the efficacy of the proposed framework in trajectory similarity calculation. Full article
(This article belongs to the Section Ocean Engineering)
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19 pages, 6202 KiB  
Article
Tide-Induced Upwelling and Its Three-Dimensional Balance of the Vertical Component of Vorticity in the Wider Area of the Bohai Strait
by Yinfeng Xu, Xiaohui Liu, Feng Zhou, Xueen Chen, Ruijie Ye and Dake Chen
J. Mar. Sci. Eng. 2023, 11(9), 1839; https://doi.org/10.3390/jmse11091839 - 21 Sep 2023
Cited by 1 | Viewed by 920
Abstract
Upwelling is a widespread phenomenon in the ocean and plays key roles in the marine environment, marine fishery and air–sea carbon exchange. In coastal regions, the upwelling is usually modulated by tides and complex topography, but the dynamical mechanism is still unclear and [...] Read more.
Upwelling is a widespread phenomenon in the ocean and plays key roles in the marine environment, marine fishery and air–sea carbon exchange. In coastal regions, the upwelling is usually modulated by tides and complex topography, but the dynamical mechanism is still unclear and yet to be quantified. In this study, a three-dimensional (3D) regional ocean model is used to investigate tide-induced upwelling and its mechanisms quantitatively in the mouth of a semi-closed bay, the Bohai Strait, which is a tide-dominated coastal region. The results show that the upwelling mainly occurs near the tidal front in the north of the Laotieshan Channel and the southern region of the front, with the most active upwelling existing off promontories and small islands. Numerical sensitivity experiments indicate that the upwelling in the study area is mainly caused by tides, accounting for approximately 86% of the total. The 3D balance of the vertical component of the vorticity based on the model results quantifies the dynamic processes of the upwelling and reveals that tides induce the upwelling through tidal mixing and nonlinear effects. In the tidal front zone, the upwelling is mainly caused by baroclinic processes related to tidal mixing. Off promontories and small islands, we first reveal that the upwelling is driven by both the tidal mixing and nonlinear effect related to centrifugal force rather than just one of the two mechanisms, and the latter plays a dominant role in producing the upwelling. The strong nonlinear effect is attributed to the periodic movement of barotropic tidal currents rather than the mean flow. Full article
(This article belongs to the Special Issue Monitoring and Assessing the Changing Coastal Ecosystem in Response to Global Change)
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14 pages, 3811 KiB  
Article
Revisiting Enhanced AIS Detection Range under Anomalous Propagation Conditions
by Irina Sirkova
J. Mar. Sci. Eng. 2023, 11(9), 1838; https://doi.org/10.3390/jmse11091838 - 21 Sep 2023
Viewed by 1741
Abstract
Two clear-air over-the-horizon propagation mechanisms affecting the Automatic Identification System (AIS) detection range are considered. Comparison results are presented between the path loss due to tropospheric ducting and path loss due to tropospheric scattering (troposcatter) for the AIS frequencies. The calculations are based [...] Read more.
Two clear-air over-the-horizon propagation mechanisms affecting the Automatic Identification System (AIS) detection range are considered. Comparison results are presented between the path loss due to tropospheric ducting and path loss due to tropospheric scattering (troposcatter) for the AIS frequencies. The calculations are based on the well-known parabolic equation approximation to the wave equation, in which a simple troposcatter formula is incorporated. In most studied cases, the ducting ensures a significantly greater reduction in path loss than troposcatter even when the AIS frequencies are not well trapped in the duct. Emphasis is placed on the elevated trapping layers, and some features that may make ducting propagation less favorable in terms of increasing the AIS detection range are discussed. Full article
(This article belongs to the Section Ocean Engineering)
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16 pages, 5396 KiB  
Article
Visual-Aided Shared Control of Semi-Autonomous Underwater Vehicle for Efficient Underwater Grasping
by Tianlei Wang, Fei Ding and Zhenxing Sun
J. Mar. Sci. Eng. 2023, 11(9), 1837; https://doi.org/10.3390/jmse11091837 - 21 Sep 2023
Cited by 2 | Viewed by 771
Abstract
Human intelligence has the advantage for making high-level decisions in the remote control of underwater vehicles, while autonomous control is superior for accurate and fast close-range pose adjustment. Combining the advantages of both remote and autonomous control, this paper proposes a visual-aided shared-control [...] Read more.
Human intelligence has the advantage for making high-level decisions in the remote control of underwater vehicles, while autonomous control is superior for accurate and fast close-range pose adjustment. Combining the advantages of both remote and autonomous control, this paper proposes a visual-aided shared-control method for a semi-autonomous underwater vehicle (sAUV) to conduct flexible, efficient and stable underwater grasping. The proposed method utilizes an arbitration mechanism to assign the authority weights of the human command and the automatic controller according to the attraction field (AF) generated by the target objects. The AF intensity is adjusted by understanding the human intention, and the remote-operation command is fused with a visual servo controller. The shared controller is designed based on the kinematic and dynamic models, and model parameter uncertainties are also addressed. Efficient and stable control performance is validated by both simulation and experiment. Faster and accurate dynamic positioning in front of the target object is achieved using the shared-control method. Compared to the pure remote operation mode, the shared-control mode significantly reduces the average time consumption on grasping tasks for both skilled and unskilled operators. Full article
(This article belongs to the Section Ocean Engineering)
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11 pages, 2836 KiB  
Article
The Influence of Geological Conditions in the Hangzhou Bay Area on the Deformation Behavior of Deep Excavations
by Yihong Zhu, Mingming Wu, Gangping Zhang, Jianlin Yu, Qiliang Xu, Riqing Xu and Tianci Yu
J. Mar. Sci. Eng. 2023, 11(9), 1836; https://doi.org/10.3390/jmse11091836 - 21 Sep 2023
Viewed by 745
Abstract
The deformation behavior of deep excavations is affected by many factors, among which the geological conditions are greatly affected. Hangzhou Bay is affected by marine siltation and river alluvium, and the geological conditions within the urban area of Hangzhou are quite different. In [...] Read more.
The deformation behavior of deep excavations is affected by many factors, among which the geological conditions are greatly affected. Hangzhou Bay is affected by marine siltation and river alluvium, and the geological conditions within the urban area of Hangzhou are quite different. In this paper, the geological and deformation data of 79 deep excavation cases in the Hangzhou urban area were collected, and the statistical analysis showed that the deformation control of excavations in the silt area was poor. The average maximum lateral wall displacement of deep excavations of the Hangzhou urban area was 0.41%H (H was the depth of the excavation), the average value of the alluvial area was 0.22%H, and the average value of the silted area was 0.55%H. The influence of geological conditions, wall type, and construction period on the deformation of excavations was compared, and the deformation behavior of excavations in the silted area was clearly affected by various factors. Full article
(This article belongs to the Special Issue Geological Environment and Engineering in Coastal Region)
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15 pages, 5133 KiB  
Article
When Time Is of the Essence—Recording an Underwater Excavation at 110 m
by Timmy Gambin, Maja Sausmekat, John Wood and Kari Hyttinen
J. Mar. Sci. Eng. 2023, 11(9), 1835; https://doi.org/10.3390/jmse11091835 - 20 Sep 2023
Viewed by 918
Abstract
Underwater archaeological excavations present unique challenges, particularly when conducted at significant depths where divers face limited time on the archaeological site. Traditional methods of recording excavation progress, such as manual documentation and drawings, are too time-consuming when the time on the site totals [...] Read more.
Underwater archaeological excavations present unique challenges, particularly when conducted at significant depths where divers face limited time on the archaeological site. Traditional methods of recording excavation progress, such as manual documentation and drawings, are too time-consuming when the time on the site totals no more than 12 min. To address these limitations, this paper introduces an innovative approach for daily recording and observation of underwater archaeological excavations using 3D photogrammetric models and point of view (PoV) cameras developed specifically for the excavation of a shipwreck situated at a depth of 110 m. The proposed system leverages advancements in photogrammetry and 3D modelling techniques to capture and analyse detailed visual data of the excavation site on a daily basis. Three-dimensional photogrammetric models offer a comprehensive and easily accessible representation of the excavation site, enabling the team to record and analyse excavation levels and features in a highly precise and detailed manner. By comparing the 3D models captured on consecutive days, researchers can precisely measure changes in the excavation area, identify new artifacts or structures, and record the progress of the excavation. The PoV cameras contribute to the planning of daily tasks required on the site. Overall, this paper showcases innovative methods for underwater archaeological excavations at significant depths, employing 3D photogrammetric models for daily recording as well as PoV cameras for observation. The proposed system represents a substantial advancement in the field of underwater archaeology, offering a more accurate, efficient, and reliable approach to documenting and analysing excavation progress, whilst also producing results that can be subsequently adapted and applied to other deep water archaeological sites. Full article
(This article belongs to the Special Issue Recent Advances in Maritime Archaeology)
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18 pages, 5734 KiB  
Article
Energy Management Strategy of Hybrid Ships Using Nonlinear Model Predictive Control via a Chaotic Grey Wolf Optimization Algorithm
by Long Chen, Diju Gao and Qimeng Xue
J. Mar. Sci. Eng. 2023, 11(9), 1834; https://doi.org/10.3390/jmse11091834 - 20 Sep 2023
Cited by 1 | Viewed by 884
Abstract
Reducing energy consumption and carbon emissions from ships is a major concern. The development of hybrid technologies offers a new direction for the rational distribution of energy. Therefore, this paper establishes a torque model for internal combustion engines and motors based on first [...] Read more.
Reducing energy consumption and carbon emissions from ships is a major concern. The development of hybrid technologies offers a new direction for the rational distribution of energy. Therefore, this paper establishes a torque model for internal combustion engines and motors based on first principles and fitting the data collected from the test platform; in turn, it develops a model for fuel consumption and carbon emissions. Furthermore, the effect of irregular waves using an extended Kalman filter is estimated as well as feedback to the controller as a disturbance variable. Then, a parallel hybrid ship energy management strategy based on a new real-time nonlinear model of predictive control is designed to achieve energy conservation and emission decrease. A hybrid algorithm of chaotic optimization combined with grey wolf optimization is utilized to solve the nonlinear optimization problem in the nonlinear model predictive control strategy and a local refined search is performed using sequential quadratic programming. Through the comparison of fuel consumption, carbon emissions, real-time performance, and the engine load path, the superiority of the nonlinear model predictive control energy management strategy based on the chaotic grey wolf optimization algorithm is verified. Full article
(This article belongs to the Section Ocean Engineering)
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22 pages, 15349 KiB  
Article
Structural Analysis Procedure and Applicability Review of Spudcan Considering Soil Types
by Joo-Shin Park, Dong-Hun Lee and Myung-Su Yi
J. Mar. Sci. Eng. 2023, 11(9), 1833; https://doi.org/10.3390/jmse11091833 - 20 Sep 2023
Cited by 2 | Viewed by 1009
Abstract
As interest in eco-friendly energy development continues to rise, the offshore wind turbine market is growing at a high rate of increase every year. In line with this, the demand for installation vessels with large capacity is also increasing rapidly. WTIVs (Wind Turbine [...] Read more.
As interest in eco-friendly energy development continues to rise, the offshore wind turbine market is growing at a high rate of increase every year. In line with this, the demand for installation vessels with large capacity is also increasing rapidly. WTIVs (Wind Turbine Installation Vessels) employ spudcans in the seabed for the installation of wind turbines. Currently, the assessment of spudcans is an important issue in ensuring structural safety in the entire structure system. This study examines the current procedure suggested by classification societies and a new procedure that accounts for the new loading scenarios based on realistic operating conditions. This new procedure is further validated through an FEA (Finite Element Analysis). The current procedure yields maximum stress values below the allowable criteria because it does not consider the effect of the seabed slope, the leg bending moment, and the spudcan shape. However, the results of some load conditions as defined in the new procedure confirm the need for reinforcement under actual preload conditions. Therefore, the new procedure considers a broader range of real-world operating conditions, and the possible problems were verified through a detailed FEA. Full article
(This article belongs to the Special Issue The Stability of Offshore Structures)
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22 pages, 20855 KiB  
Article
The Impact of Coastline and Bathymetry Changes on the Storm Tides in Zhejiang Coasts
by Xiaoxiao Gou, Huidi Liang, Tinglu Cai, Xinkai Wang, Yining Chen and Xiaoming Xia
J. Mar. Sci. Eng. 2023, 11(9), 1832; https://doi.org/10.3390/jmse11091832 - 20 Sep 2023
Viewed by 1006
Abstract
Coastal evolutions are expected to have a significant impact on storm tides, disproportionately aggravating coastal flooding. In this study, we utilize a nested storm tide model to provide an integrated investigation of storm tide responses to changes in coastline and bathymetry along the [...] Read more.
Coastal evolutions are expected to have a significant impact on storm tides, disproportionately aggravating coastal flooding. In this study, we utilize a nested storm tide model to provide an integrated investigation of storm tide responses to changes in coastline and bathymetry along the Zhejiang coasts. We selected coastline and bathymetry data from 1980 and 2016, as well as data from three typical typhoon events (i.e., Winnie, Haikui, and Chan-hom) for simulating the storm surge processes. The results indicate that changes in the coastline and bathymetry from 1980 to 2016 have resulted in an increase in storm tides in the northern part and a decrease in the central part of Zhejiang. Specifically, storm tides in Hangzhou Bay have increased significantly, with an average increase of about 0.3 m in the maximum storm tides primarily attributed to coastline changes. On the contrary, in smaller basins like Sanmen Bay, while reclamation itself has reduced peak storm surges, rapid siltation has consequently exacerbated the storm surge. By decomposing storm tides into astronomical tides and storm surges, we discovered that the change in tidal levels was twice as significant as the surge change. Moreover, the nonlinear tide–surge interaction was nearly four times that of the pure surge, significantly contributing to storm surge variation. Alterations in the momentum balance reveal that the water depth-induced bottom friction and wind stress increase contributes to the local enlargement of storm tides at the bay head, while the coastline changes exaggerate nearshore storm tides through an increase in the advection term. Full article
(This article belongs to the Section Coastal Engineering)
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23 pages, 9766 KiB  
Article
Unmanned Vessel Collision Avoidance Algorithm by Dynamic Window Approach Based on COLREGs Considering the Effects of the Wind and Wave
by Xiaoyu Yuan, Chengchang Tong, Guoxiang He and Hongbo Wang
J. Mar. Sci. Eng. 2023, 11(9), 1831; https://doi.org/10.3390/jmse11091831 - 20 Sep 2023
Cited by 3 | Viewed by 970
Abstract
In recent years, the rapid development of artificial intelligence algorithms has promoted the intelligent transformation of the ship industry; unmanned surface vessels (USVs) have become a widely used representative product. The dynamic window approach (DWA) is an effective robotic collision avoidance algorithm; however, [...] Read more.
In recent years, the rapid development of artificial intelligence algorithms has promoted the intelligent transformation of the ship industry; unmanned surface vessels (USVs) have become a widely used representative product. The dynamic window approach (DWA) is an effective robotic collision avoidance algorithm; however, there are deficiencies in its application to the ship field. First, the DWA algorithm does not consider International Regulations for Preventing Collisions at Sea (COLREGs), which must be met for ship collision avoidance to ensure the navigational safety of the USV and other ships. Second, the DWA algorithm does not consider the influence of wind and waves on the collision avoidance of USVs in actual navigational environments. Reasonable use of windy and wavy environments not only improves navigational safety but also saves navigational time and fuel consumption, thereby improving the economy. Therefore, this paper proposes an improvement algorithm by DWA referred to as utility DWA (UDWA) based on COLREGs considering the sailing environment. The velocity sampling area was improved by dividing the priority, and the velocity function in the objective function was enhanced to convert the effect of wind and waves on the USVs into a change in velocity. The simulation results showed that the UDWA algorithm optimized the distance to the obstacle ship by 43.25%, 31.36%, and 67.81% in a head-on situation, crossing situation, and overtaking situation, respectively, compared to the COLREGs-compliant DWA algorithm, which considers the COLREGs. The improved algorithm not only follows the COLREGs but also has better flexibility in emergency collision avoidance and can safely and economically navigate and complete collision avoidance in windy and wavy environments. Full article
(This article belongs to the Special Issue Young Researchers in Ocean Engineering)
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28 pages, 13021 KiB  
Article
Hydrodynamic Analysis of a Multi-Pile-Supported Offshore Wind Turbine Integrated with an Aquaculture Cage
by Zhisheng Tu, Cailiang Zhang, Hanqiu Liu and Ronghua Zhu
J. Mar. Sci. Eng. 2023, 11(9), 1830; https://doi.org/10.3390/jmse11091830 - 20 Sep 2023
Cited by 1 | Viewed by 1039
Abstract
The integrated development of offshore wind power and marine aquaculture is becoming increasingly important. However, the impact mechanism of integrating a net cage on the dynamic characteristics of offshore wind turbines remains unclear. This paper presents a design scheme for a multi-pile-supported offshore [...] Read more.
The integrated development of offshore wind power and marine aquaculture is becoming increasingly important. However, the impact mechanism of integrating a net cage on the dynamic characteristics of offshore wind turbines remains unclear. This paper presents a design scheme for a multi-pile-supported offshore wind turbine integrated with an aquaculture net cage and conducts a preliminary theoretical analysis of the influence of an additional net cage on the wind turbine. The analysis reveals that the primary effect is an increase in hydrodynamic loads on the wind turbine foundation, while the structural frequency of the wind turbine remains largely unaffected. Furthermore, computational fluid dynamics (CFD) numerical models, whose accuracy is verified by physical experiments, are utilized to compare the hydrodynamic characteristics of the offshore wind turbine foundation with and without the net cage, considering different net solidities. The simulations identify significant changes in the flow field surrounding the foundation due to the presence of the net cage, resulting in a considerable increase in the overall hydrodynamic load on the foundation. Moreover, the mutual interference between the netting and the foundation amplifies their respective hydrodynamic loads and concentrates these loads at the upstream section of the structure. The maximum increase in hydrodynamic load for a single pile reaches 6.32 times its original value, posing significant risks to the structure. Finally, a preliminary feasibility analysis of the scheme was conducted. The results presented in this article can serve as a theoretical basis for the design of such innovative structures. Full article
(This article belongs to the Section Ocean Engineering)
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16 pages, 2539 KiB  
Article
A Cost–Benefit Approach to Assess the Physical and Economic Feasibility of Sand Bypassing Systems
by Márcia Lima, Ana Margarida Ferreira and Carlos Coelho
J. Mar. Sci. Eng. 2023, 11(9), 1829; https://doi.org/10.3390/jmse11091829 - 19 Sep 2023
Viewed by 766
Abstract
The artificial sand bypassing systems are coastal interventions designed to transfer sediments from areas of accretion to areas where erosion is observed. The goal of these systems is to reduce the littoral drift gradients where sediment transport is interrupted (vicinity of river mouths [...] Read more.
The artificial sand bypassing systems are coastal interventions designed to transfer sediments from areas of accretion to areas where erosion is observed. The goal of these systems is to reduce the littoral drift gradients where sediment transport is interrupted (vicinity of river mouths or port structures) and maintain a balanced sediment distribution along the shoreline. However, these systems present high initial investment costs as well as ongoing expenses for operation and maintenance. To assess the feasibility of sand bypassing systems in mitigating coastal erosion from a long-term perspective (decades), a comprehensive understanding of their performance is necessary, considering both physical and economic aspects. Thus, a cost–benefit assessment numerical tool, COAST, is applied to evaluate and discuss the effectiveness of bypassing systems during their life cycle. First, a comprehensive analysis is conducted for a generic study area, and then, the feasibility of the systems is discussed for two real study areas of the Portuguese West coast (Barra-Vagueira and Figueira da Foz-Leirosa). The generic results demonstrate as the importance of systems location or transposed flow volumes. On the other hand, the analysis of the two real case studies revealed that, under similar conditions, the results of the cost–benefit analysis can be contradictory. For the Barra-Vagueira stretch, the work indicates that the bypass system is not economically viable, whereas for Figueira da Foz-Leirosa, it is cost-effective. The study shows the importance of the site-specific conditions to evaluate the best option for a medium to long-term planned coast, highlighting the relevance of the proposed approach to assess the physical and economic feasibility of sand bypassing systems. Full article
(This article belongs to the Special Issue Sandy Beach Erosion and Protection: Past, Present and Future)
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23 pages, 14467 KiB  
Article
On the Added Modal Coefficients of a Rotating Submerged Cylinder Induced by a Whirling Motion—Part 2: Numerical Investigation
by Rafel Roig, Xavier Sánchez-Botello and Xavier Escaler
J. Mar. Sci. Eng. 2023, 11(9), 1828; https://doi.org/10.3390/jmse11091828 - 19 Sep 2023
Viewed by 710
Abstract
Part 2 of this work presents a numerical methodology, validated using the experimental results presented in Part 1, to calculate the added modal coefficients of a submerged cylinder in water both when it oscillates and when it rotates with a whirling motion. The [...] Read more.
Part 2 of this work presents a numerical methodology, validated using the experimental results presented in Part 1, to calculate the added modal coefficients of a submerged cylinder in water both when it oscillates and when it rotates with a whirling motion. The numerical methodology is based on computational fluid dynamic simulations that obtain the added modal forces on the cylinder when it is forced to vibrate with mode shapes calculated using acoustic-structural modal analysis. Then, these forces are processed with a curve-fitting algorithm to extract all the coefficients. Most numerical coefficients presented a close agreement with the corresponding experimental ones, although the added modal damping was overestimated. In general, the added modal mass was found to be independent of both the rotating speed and the whirling frequency except for low whirling frequencies when it increased. The added modal damping was found to depend on both parameters, and the rest of the coefficients were independent of the whirling frequency and only depended on the rotating speed. As a conclusion, this numerical approach has permitted the study of particular conditions that could not be experimentally tested and thus broadened the knowledge of the behavior of the added modal coefficients of rotating submerged cylinders. Full article
(This article belongs to the Topic Advanced Technology of Full Lifecycle Service for Hydraulic Machinery)
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17 pages, 1038 KiB  
Article
SPACNet: A Simulation Platform of an Acoustic Cognitive Network
by Xiaoyu Yang, Siyuan Zheng, Yanfeng Zhao, Dongsheng Chen, Feng Tong and Shuaifeng Hao
J. Mar. Sci. Eng. 2023, 11(9), 1827; https://doi.org/10.3390/jmse11091827 - 19 Sep 2023
Viewed by 838
Abstract
Originating from the concept of cognitive networks (CNs), which are becoming popular in wireless terrestrial communication scenarios, underwater acoustic cognitive networks (UACNs) are drawing more and more attention in the field of the Internet of Underwater Things (IoUT). However, as the implementation of [...] Read more.
Originating from the concept of cognitive networks (CNs), which are becoming popular in wireless terrestrial communication scenarios, underwater acoustic cognitive networks (UACNs) are drawing more and more attention in the field of the Internet of Underwater Things (IoUT). However, as the implementation of cognitive mechanisms in underwater acoustic networks is different from that of wireless scenarios, it is impossible or difficult for traditional simulation platforms to carry out simulations of UACNs. There is a lack of specialized simulation tools in terms of UACNs. To enable the quantitative evaluation of the effectiveness and performance enhancement of a UACNs in an adverse underwater environment, a simulation platform of acoustic cognitive networks (SPACNet) was designed and investigated in this article. First, based on a state machine-based protocol programming framework, the SPACNet is capable of supporting the implementation of different state-transform types associated with cognitive networking protocols. Moreover, to facilitate the realization of cognitive function at comprehensive levels of signal, information, and link, an underwater acoustic channel model with an environmental parameter input is integrated in SPACNet to generate underwater environment-driven multiple-aspect behaviors. Moreover, a simplified collision model consisting of an environment factor, channel response, and node location is used to reduce the complexity of the simulation of UACNs signal reception. A simulation was carried out to verify the effectiveness of SPACNet in evaluating the cognitive capabilities of UACNs. Finally, a field UACNs experiment was performed to validate the general consistency between the conclusion obtained with the SPACNet-based simulation and that from the field test. Full article
(This article belongs to the Special Issue Underwater Acoustic Communication and Network)
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18 pages, 1341 KiB  
Article
Is the Plant Bolboschoenus maritimus an Adequate Biomonitor for Trace Metal Contamination in Saltmarshes? A Field Study from the Óbidos Lagoon (Portugal)
by Márcia S. S. Santos, Carmen A. Pedro, Susana M. F. Ferreira and Sílvia C. Gonçalves
J. Mar. Sci. Eng. 2023, 11(9), 1826; https://doi.org/10.3390/jmse11091826 - 19 Sep 2023
Viewed by 700
Abstract
Monitoring the negative impacts of trace metals is crucial to assess the health and stability of ecosystems. In salt marshes, halophyte plants were reported as possible bioaccumulators of these elements. The aim of this work was to explore the bioaccumulation potential of Bolboschoenus [...] Read more.
Monitoring the negative impacts of trace metals is crucial to assess the health and stability of ecosystems. In salt marshes, halophyte plants were reported as possible bioaccumulators of these elements. The aim of this work was to explore the bioaccumulation potential of Bolboschoenus maritimus as a tool for monitoring the presence of metals in coastal environments. Bolboschoenus maritimus were collected from a brackish water lagoon, and the presence of the trace metals lead, cadmium, and nickel were seasonally evaluated in distinct parts of the plants, and in water and sediment samples. Lead was the trace metal with the highest concentration detected in water and sediments of the sampling site. The highest lead concentrations in B. maritimus were recorded in the spring season. The transport index indicated an accumulation of lead in the leaves of around 70% in the spring of 2009. Cadmium in leaves in spring and summer of 2009 reached values above 5 mg Cd. kg−1. Nickel was not detected in most samples collected. Bolboschoenus maritimus was considered an adequate biomonitor for lead and cadmium, since it bioaccumulates both metals with seasonally distinct results, as the bioaccumulation factor results indicated. Full article
(This article belongs to the Special Issue Chemical Contamination on Coastal Ecosystems)
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21 pages, 8730 KiB  
Article
Experimental Investigation on Particle Breakage Behavior of Marine Silica Sand under High-Stress Triaxial Shear
by Rong Chen, Tong Zhao, Zhiyong Wu, Dongxue Hao, Nan Xue and Chi Yuan
J. Mar. Sci. Eng. 2023, 11(9), 1825; https://doi.org/10.3390/jmse11091825 - 19 Sep 2023
Viewed by 822
Abstract
There is often obvious particle breakage for silica sand under high-stress, which will lead to the bearing capacity reduction and excessive settlement of the foundation. This paper focuses on the particle breakage characteristics of marine silica sand from the East China Sea under [...] Read more.
There is often obvious particle breakage for silica sand under high-stress, which will lead to the bearing capacity reduction and excessive settlement of the foundation. This paper focuses on the particle breakage characteristics of marine silica sand from the East China Sea under high-stress conditions. A series of conventional triaxial tests for silica sand, including consolidated drained (CD) and consolidated undrained (CU) shear tests, were conducted under the confining pressures in the range of 2–8 MPa to investigate the breakage rule during the shearing process. The developments of particle breakage index Br with axial strain ε1 and volumetric strain εv present hyperbolic and linear trends, respectively. A hyperbolic model was adopted to describe the relationship of Br and ε1 and the corresponding model parameters were obtained. The particle breakage index also has a good correlation with the input work per unit volume under various average stresses, regardless of the stress history. Furthermore, the relationship between the fractal dimension and the particle breakage was studied based on the particle size distribution curve. It is concluded that the fractal dimension increases in an up–convex hyperbolic trend with the increase of particle breakage index. The dividing radius for whether the silica sand particles exhibit the fractal features is determined as approximately 0.4 mm. This is anticipated to provide reference and supplementary test data for analyzing sand constitutive models/environments regarding particle crushing. Full article
(This article belongs to the Special Issue Engineering Properties of Marine Soils and Offshore Foundations)
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31 pages, 9523 KiB  
Review
State-of-the-Art Review and Future Perspectives on Maneuvering Modeling for Automatic Ship Berthing
by Song Zhang, Qing Wu, Jialun Liu, Yangying He and Shijie Li
J. Mar. Sci. Eng. 2023, 11(9), 1824; https://doi.org/10.3390/jmse11091824 - 19 Sep 2023
Cited by 2 | Viewed by 1268
Abstract
Automatic berthing is at the top level of ship autonomy; it is unwise and hasty to hand over the control initiative to the controller and the algorithm without the foundation of the maneuvering model. The berthing maneuver model predicts the ship responses to [...] Read more.
Automatic berthing is at the top level of ship autonomy; it is unwise and hasty to hand over the control initiative to the controller and the algorithm without the foundation of the maneuvering model. The berthing maneuver model predicts the ship responses to the steerage and external disturbances, and provides a foundation for the control algorithm. The modular MMG model is widely adopted in ship maneuverability studies. However, there are two ambiguous questions on berthing maneuver modeling: What are the similarities and differences between the conventional MMG maneuvering model and automatic berthing maneuvering model? How can an accurate automatic berthing maneuvering model be established? To answer these two questions, this paper firstly performs bibliometric analysis on automatic berthing, to discover the hot issues and emphasize the significance of maneuver modeling. It then demonstrates the similarities and differences between the conventional MMG maneuvering model and the automatic berthing maneuvering model. Furthermore, the berthing maneuver specifications and modeling procedures are explained in terms of the hydrodynamic forces on the hull, four-quadrant propulsion and steerage performances, external disturbances, and auxiliary devices. The conclusions of this work provide references for ship berthing mathematical modeling, auxiliary device utilization, berthing aid system improvement, and automatic berthing control studies. Full article
(This article belongs to the Special Issue Intelligent Ships and Waterways: Design, Operation and Advanced Technology)
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18 pages, 4012 KiB  
Article
Numerical Simulations of Effects of the Layout of Permeable Pile Groin Systems on Longshore Currents
by Rong Zhang, Yongping Chen, Peng Yao, Marcel J. F. Stive and Jian Zeng
J. Mar. Sci. Eng. 2023, 11(9), 1823; https://doi.org/10.3390/jmse11091823 - 19 Sep 2023
Viewed by 917
Abstract
Coastal permeable groins have been used to protect beaches from erosion for centuries. However, the hydraulic functioning of permeable groins has not been fully understood and their design heavily depends on engineering experiences. In this study, numerical experiments were executed to investigate the [...] Read more.
Coastal permeable groins have been used to protect beaches from erosion for centuries. However, the hydraulic functioning of permeable groins has not been fully understood and their design heavily depends on engineering experiences. In this study, numerical experiments were executed to investigate the effects of layout configurations of a permeable groin system on longshore currents. The non-hydrostatic SWASH (Simulating WAve till SHore) model was employed to carry out the numerical simulations. Two data sets obtained from physical laboratory experiments with different permeable groin layouts on different slopes are used to validate the accuracy of the model. Then, the longshore current reduction by the permeable groin system with varying configuration parameters (e.g., groin spacing, groin length) was numerically investigated under different environmental conditions (e.g., a slight or a moderate wave climate). From the calculation results of numerical experiments, it is indicated that permeable groins function efficiently to reduce the maximal longshore current velocity under the condition that the groin length ranges from 84% and 109% of the wave breaker zone width. The longshore current reduction rate monotonously decreases with the increase in groin spacing; permeable pile groin functions best to reduce longshore current with the minimal groin spacing-groin length ratio 1:1 among the range between 1:1 and 2:1. When the groin spacing–groin length ratios are 1:1 and 1.5:1, the longshore current reduction is not sensitive to the investigated wave conditions in this study. When the spatial ratio is 2:1, the permeable pile groin system functions worse under a moderate wave climate than under a slight wave climate, from the view of longshore current reduction. Full article
(This article belongs to the Special Issue Wave Interactions with Coastal Structures II)
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13 pages, 1092 KiB  
Article
Kelp Aquaculture as a Nature-Based Solution for Coastal Protection: Wave Attenuation by Suspended Canopies
by Roma Bodycomb, Andrew W. M. Pomeroy and Rebecca L. Morris
J. Mar. Sci. Eng. 2023, 11(9), 1822; https://doi.org/10.3390/jmse11091822 - 19 Sep 2023
Viewed by 1592
Abstract
Suspended kelp canopies have the potential to provide a coastal protection service in addition to their primary function of generating a sustainable resource. In this study, the attenuation of incident waves by kelp suspended from the surface was quantified. We adapted an analytical [...] Read more.
Suspended kelp canopies have the potential to provide a coastal protection service in addition to their primary function of generating a sustainable resource. In this study, the attenuation of incident waves by kelp suspended from the surface was quantified. We adapted an analytical 1D cross-shore wave attenuation model and tested the effect of (1) water depth, (2) vegetation density, and (3) longline density. The results show that as the percentage of vegetation in the water column increases, wave attenuation by the canopy also increases. However, this attenuation is affected by seasonal variations in kelp growth as well as harvesting strategies. Careful choice of the adopted harvesting strategy was found to be important to maintain optimal wave attenuation by kelp aquaculture farms throughout the year. Partial and targeted removal of the vegetation along longlines is preferred to harvesting all laterals on longlines. This study demonstrates that there is an opportunity for the emerging global kelp aquaculture industry to provide a coastal protection service in addition to resource production, which will help to affect how coastal protection is realized and scaled globally. Full article
(This article belongs to the Section Marine Environmental Science)
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18 pages, 4553 KiB  
Article
A Machine-Learning Approach Based on Attention Mechanism for Significant Wave Height Forecasting
by Jiao Shi, Tianyun Su, Xinfang Li, Fuwei Wang, Jingjing Cui, Zhendong Liu and Jie Wang
J. Mar. Sci. Eng. 2023, 11(9), 1821; https://doi.org/10.3390/jmse11091821 - 19 Sep 2023
Cited by 3 | Viewed by 1285
Abstract
Significant wave height (SWH) is a key parameter for monitoring the state of waves. Accurate and long-term SWH forecasting is significant to maritime shipping and coastal engineering. This study proposes a transformer model based on an attention mechanism to achieve the forecasting of [...] Read more.
Significant wave height (SWH) is a key parameter for monitoring the state of waves. Accurate and long-term SWH forecasting is significant to maritime shipping and coastal engineering. This study proposes a transformer model based on an attention mechanism to achieve the forecasting of SWHs. The transformer model can capture the contextual information and dependencies between sequences and achieves continuous time series forecasting. Wave scale classification is carried out according to the forecasting results, and the results are compared with gated recurrent unit (GRU) and long short-term memory (LSTM) machine-learning models and the key laboratory of MArine Science and NUmerical Modeling (MASNUM) numerical wave model. The results show that the machine-learning models outperform the MASNUM within 72 h, with the transformer being the best model. For continuous 12 h, 24 h, 36 h, 48 h, 72 h, and 96 h forecasting, the average mean absolute errors (MAEs) of the test sets were, respectively, 0.139 m, 0.186 m, 0.223 m, 0.254 m, 0.302 m, and 0.329 m, and the wave scale classification accuracies were, respectively, 91.1%, 99.4%, 86%, 83.3%, 78.9%, and 77.5%. The experimental results validate that the transformer model can achieve continuous and accurate SWH forecasting, as well as accurate wave scale classification and early warning of waves, providing technical support for wave monitoring. Full article
(This article belongs to the Special Issue The Application of Artificial Intelligence and Machine Learning in a Marine Context)
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29 pages, 10527 KiB  
Article
Application of Machine Learning Techniques to the Maritime Industry
by Miguel Ángel Gómez Ruiz, Iván Martín de Almeida and Rodrigo Pérez Fernández
J. Mar. Sci. Eng. 2023, 11(9), 1820; https://doi.org/10.3390/jmse11091820 - 18 Sep 2023
Viewed by 1788
Abstract
The maritime industry is displaying notable interest in the adoption of cutting-edge technologies within the scope of Industry 4.0, aiming to digitalize both companies and processes. At the core of data science lies machine learning, which serves as the focal point of this [...] Read more.
The maritime industry is displaying notable interest in the adoption of cutting-edge technologies within the scope of Industry 4.0, aiming to digitalize both companies and processes. At the core of data science lies machine learning, which serves as the focal point of this article. This study seeks to accomplish two main objectives: firstly, an exploration of various machine learning algorithms, and subsequently, the application of these techniques to analyze predictions within the propulsion system of a 9500 TEU container ship. The outcomes of the study reveal that utilizing distinct machine learning algorithms for predicting braking performance yields a lower mean square error (MSE) when compared to the discrepancy introduced by the J. Mau formula, as evident in the container ship database. The selection of propulsion engines was based on predictions for a 9500 TEU container ship. Similarly, promising outcomes were achieved in predicting propeller diameter in comparison to conventional methods. Thus, these predictions can also effectively guide the appropriate choice of propeller diameter. Full article
(This article belongs to the Section Ocean Engineering)
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22 pages, 5006 KiB  
Article
A Decision Support System Using Fuzzy Logic for Collision Avoidance in Multi-Vessel Situations at Sea
by Tanja Brcko and Blaž Luin
J. Mar. Sci. Eng. 2023, 11(9), 1819; https://doi.org/10.3390/jmse11091819 - 18 Sep 2023
Cited by 1 | Viewed by 1455
Abstract
The increasing traffic and complexity of navigation at sea require advanced decision support systems to ensure greater safety. In this study, we propose a novel decision support system that employs fuzzy logic to improve situational awareness and to assist navigators in collision avoidance [...] Read more.
The increasing traffic and complexity of navigation at sea require advanced decision support systems to ensure greater safety. In this study, we propose a novel decision support system that employs fuzzy logic to improve situational awareness and to assist navigators in collision avoidance during multi-vessel encounters. The system is based on the integration of the rules of the Convention on International Regulations for Preventing Collisions at Sea (COLREGs) and artificial intelligence techniques. The proposed decision model consists of two main modules to calculate the initial encounter conditions for the target vessels, evaluate the collision risk and navigation situation based on COLREG rules, sort the target vessels, and determine the most dangerous vessel. Fuzzy logic is used to calculate the collision avoidance maneuver for the selected ship, considering the closest point of approach, relative bearing, and the ship’s own speed. Simulation tests demonstrate the effectiveness of the fuzzy-based decision model in scenarios with two ships. However, in complex situations with multiple ships, the performance of the model is affected by possible conflicts between evasive maneuvers. This highlights the need for a cooperative collision avoidance algorithm for all vessels in high traffic areas. Full article
(This article belongs to the Special Issue Maritime Security and Risk Assessments)
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18 pages, 6123 KiB  
Article
Time–Frequency Analysis of Nonlinear Dynamics of an Aquaculture Cage Array in Waves
by Liu Zhu, Yuan Cheng, Jinfang Wang, Hongyu Zhu and Zhijing Xu
J. Mar. Sci. Eng. 2023, 11(9), 1818; https://doi.org/10.3390/jmse11091818 - 18 Sep 2023
Viewed by 751
Abstract
The nonlinear dynamic response of an aquaculture cage array caused by wave-frequency and low-frequency excitations coupled with the nonlinearity of the mooring and the netting system is a complicated problem. So far, this problem still has not been completely understood. To address this [...] Read more.
The nonlinear dynamic response of an aquaculture cage array caused by wave-frequency and low-frequency excitations coupled with the nonlinearity of the mooring and the netting system is a complicated problem. So far, this problem still has not been completely understood. To address this issue, we consider the nonlinear interaction of an extreme wave with an aquaculture cage array containing 16 net cages in a 2 × 8 configuration. This paper aims to provide insight into understanding the nonlinear dynamics of an aquaculture cage array via time–frequency analysis. Time-domain analysis shows that the cage array exhibits weak nonlinearity in the surge and heave motions. On the contrary, there is strong nonlinearity in the sway motion under 45° and 90° wave attacks. Aside from this, the frequency-domain analysis indicates that nonlinearities exist in all three of these different responses (surge/sway/heave). Particularly, the low-frequency component has a predominant effect on the nonlinearity of the sway motion under 45° and 90° wave attacks. With this understanding, future aquaculture fish farms that contain multiple cages (i.e., cage array) can be potentially designed to withstand severe conditions in the open ocean. Full article
(This article belongs to the Special Issue Next-Generation Sustainable Marine Fisheries and Aquaculture Engineering)
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36 pages, 898 KiB  
Article
Fit-for-Purpose Information for Offshore Wind Farming Applications—Part-II: Gap Analysis and Recommendations
by Johannes Schulz-Stellenfleth, Anouk Blauw, Lauri Laakso, Baptiste Mourre, Jun She and Henning Wehde
J. Mar. Sci. Eng. 2023, 11(9), 1817; https://doi.org/10.3390/jmse11091817 - 18 Sep 2023
Cited by 2 | Viewed by 1209
Abstract
Offshore wind energy installations in coastal areas have grown massively over the last decade. This development comes with a large number of technological, environmental, economic, and scientific challenges, which need to be addressed to make the use of offshore wind energy sustainable. One [...] Read more.
Offshore wind energy installations in coastal areas have grown massively over the last decade. This development comes with a large number of technological, environmental, economic, and scientific challenges, which need to be addressed to make the use of offshore wind energy sustainable. One important component in these optimization activities is suitable information from observations and numerical models. The purpose of this study is to analyze the gaps that exist in the present monitoring systems and their respective integration with models. This paper is the second part of two manuscripts and uses results from the first part about the requirements for different application fields. The present solutions to provide measurements for the required information products are described for several European countries with growing offshore wind operations. The gaps are then identified and discussed in different contexts, like technology evolution, trans-European monitoring and modeling initiatives, legal aspects, and cooperation between industry and science. The monitoring gaps are further quantified in terms of missing observed quantities, spatial coverage, accuracy, and continuity. Strategies to fill the gaps are discussed, and respective recommendations are provided. The study shows that there are significant information deficiencies that need to be addressed to ensure the economical and environmentally friendly growth of the offshore wind farm sector. It was also found that many of these gaps are related to insufficient information about connectivities, e.g., concerning the interactions of wind farms from different countries or the coupling between physical and biological processes. Full article
(This article belongs to the Special Issue Advanced Studies in Coastal Ocean Observation)
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30 pages, 15742 KiB  
Article
Fast Reconstruction Model of the Ship Hull NURBS Surface with Uniform Continuity for Calculating the Hydrostatic Elements
by Kaige Zhu, Guoyou Shi, Jiao Liu and Jiahui Shi
J. Mar. Sci. Eng. 2023, 11(9), 1816; https://doi.org/10.3390/jmse11091816 - 18 Sep 2023
Viewed by 1089
Abstract
The fast reconstruction of the ship hull nonuniform rational B-spline (NURBS) surface with uniform continuity is essential for calculating hydrostatic elements such as waterplane area and molded volume in real time. Thus, this study proposes a fast reconstruction model with uniform continuity to [...] Read more.
The fast reconstruction of the ship hull nonuniform rational B-spline (NURBS) surface with uniform continuity is essential for calculating hydrostatic elements such as waterplane area and molded volume in real time. Thus, this study proposes a fast reconstruction model with uniform continuity to solve the problem of uniform continuity and splicing in the separate model of hull bow and stern surfaces. The proposed model includes the NURBS curve generation (UCG) algorithm with uniform continuity and the hybrid NURBS surface generation (HSG) algorithm. The UCG algorithm initially fits the feature points using the global interpolation algorithm and then precisely constructs straight-line segments in the curve using the improved flattening algorithm. In comparison, the HSG algorithm adaptively selects the surface knot vectors according to the parameters of the section curves. In this study, the profile of discontinuous compartments is uniformly expressed, effectively avoiding various articulation problems in separation modeling. The results of comparative experiments show that the NURBS surface generated using the HSG algorithm can accurately express the characteristics of various parts of the hull with uniform continuity, and the calculation speed of the proposed model can be increased by up to 8.314% compared with the existing best-performing algorithms. Thus, the proposed model is effective and can improve computational efficiency to a certain extent. The NURBS surfaces generated by the proposed model can be further applied to calculating the hydrostatic elements of hulls and compartments. Full article
(This article belongs to the Topic Ship Dynamics, Stability and Safety)
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21 pages, 5619 KiB  
Article
Proportioning Test on the Similar Materials of the Rock Mass Physical Model Test Considering Seepage and Dynamic Characteristics
by Wanpeng Shi, Jianwei Zhang, Chunlei Xin, Danqing Song, Nan Hu and Bowei Li
J. Mar. Sci. Eng. 2023, 11(9), 1815; https://doi.org/10.3390/jmse11091815 - 18 Sep 2023
Viewed by 790
Abstract
With the development of infrastructure construction, an increasing number of projects are faced with the problem of hydraulic and dynamic coupling. However, traditional physical model materials mainly consider the single factor influence and lack comprehensive research on the hydraulic and dynamic parameters of [...] Read more.
With the development of infrastructure construction, an increasing number of projects are faced with the problem of hydraulic and dynamic coupling. However, traditional physical model materials mainly consider the single factor influence and lack comprehensive research on the hydraulic and dynamic parameters of similar materials. Based on the dimensionless criterion and Buckingham π theorem, the dimension and similarity relation of physical model tests of rock masses under seepage and dynamic coupling are derived. A new type of similar material considering hydraulic and dynamic properties was developed by using quartz sand, barite powder, cement, water glass, rosin, and glycerol as raw materials through a large number of orthogonal tests. Meanwhile, the sensitivity analysis of the physical and mechanical properties of similar materials was carried out and the influence of each component factor on the physical properties was revealed. A material preparation scheme was developed to meet the physical and hydraulic characteristics of different rock and soil physical models. An empirical matching formula considering each parameter is proposed. This work can provide an important reference for physical model tests of similar rock masses. Full article
(This article belongs to the Special Issue Advances in Offshore Geotechnics)
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19 pages, 10659 KiB  
Article
CCGAN as a Tool for Satellite-Derived Chlorophyll a Concentration Gap Reconstruction
by Leon Ćatipović, Frano Matić, Hrvoje Kalinić, Shubha Sathyendranath, Tomislav Županović, James Dingle and Thomas Jackson
J. Mar. Sci. Eng. 2023, 11(9), 1814; https://doi.org/10.3390/jmse11091814 - 18 Sep 2023
Cited by 2 | Viewed by 864
Abstract
This work represents a modification of the Context Conditional Generative Adversarial Network as a novel implementation of a non-linear gap reconstruction approach of missing satellite-derived chlorophyll a concentration data. By adjusting the loss functions of the network to focus on the structural credibility [...] Read more.
This work represents a modification of the Context Conditional Generative Adversarial Network as a novel implementation of a non-linear gap reconstruction approach of missing satellite-derived chlorophyll a concentration data. By adjusting the loss functions of the network to focus on the structural credibility of the reconstruction, high numerical and structural reconstruction accuracies have been achieved in comparison to the original network architecture. The network also draws information from proxy data, sea surface temperature, and bathymetry, in this case, to improve the reconstruction quality. The implementation of this novel concept has been tested on the Adriatic Sea. The most accurate model reports an average error of 0.06mgm−3 and a relative error of 3.87%. A non-deterministic method for the gap-free training dataset creation is also devised, further expanding the possibility of combining other various oceanographic data to possibly improve the reconstruction efforts. This method, the first of its kind, has satisfied the accuracy requirements set by scientific communities and standards, thus proving its validity in the initial stages of conceptual utilisation. Full article
(This article belongs to the Special Issue Technological Oceanography Volume II)
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26 pages, 12241 KiB  
Article
Hydrodynamic Characteristics of Floating Photovoltaic Systems under Ocean Loads
by Jiahui Song, Hasan Imani, Jinchao Yue and Shaolin Yang
J. Mar. Sci. Eng. 2023, 11(9), 1813; https://doi.org/10.3390/jmse11091813 - 18 Sep 2023
Viewed by 1268
Abstract
The floating photovoltaic (FPV) array, which consists of tens or hundreds of rows of floating photovoltaic systems, exhibits great economic and environmental benefits. An FPV array arranged in the ocean will be subjected to the combined action of wind, waves, and currents during [...] Read more.
The floating photovoltaic (FPV) array, which consists of tens or hundreds of rows of floating photovoltaic systems, exhibits great economic and environmental benefits. An FPV array arranged in the ocean will be subjected to the combined action of wind, waves, and currents during the installation, service, and maintenance processes; however, systematic research in this field is still lacking. As a representative of the FPV array, this study on the hydrodynamic characteristics of a single-row FPV system is a fundamental prerequisite for the safe design of large-scale FPV arrays in the near future. In this paper, based on the potential theory, a numerical model of a single-row FPV system with ten floating platforms is established with ANSYS-AQWA software. Following this, the hydrodynamic coefficients of a single floating platform are calculated and evaluated. After that, the dynamic responses of the FPV system under different load combinations are explored. Finally, the influence mechanism of wave parameters on the hydrodynamic characteristics of the FPV system is discussed in detail, including the wavelength and wave height. The results indicate that, within the scope of this study, the floating platforms have good seakeeping and stability. The wave load dominates for all conditions, and the presence of the current will affect the parameters of the wave. In addition, the relative relationship between the wavelength and the length of FPV system will affect their resonance effect, and the increase in wave height will significantly enhance the dynamic response of the FPV system. This study can help to provide references for the safety design of FPV arrays. Full article
(This article belongs to the Section Ocean Engineering)
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21 pages, 8370 KiB  
Article
Determination of Formulae for the Hydrodynamic Performance of a Fixed Box-Type Free Surface Breakwater in the Intermediate Water
by Guoxu Niu, Yaoyong Chen, Jiao Lv, Jing Zhang and Ning Fan
J. Mar. Sci. Eng. 2023, 11(9), 1812; https://doi.org/10.3390/jmse11091812 - 17 Sep 2023
Viewed by 970
Abstract
A two-dimensional viscous numerical wave tank coded mass source function in a computational fluid dynamics (CFD) software Flow-3D 11.2 is built and validated. The effect of the core influencing factors (draft, breakwater width, wave period, and wave height) on the hydrodynamic performance of [...] Read more.
A two-dimensional viscous numerical wave tank coded mass source function in a computational fluid dynamics (CFD) software Flow-3D 11.2 is built and validated. The effect of the core influencing factors (draft, breakwater width, wave period, and wave height) on the hydrodynamic performance of a fixed box-type free surface breakwater (abbreviated to F-BW in the following texts) are highlighted in the intermediate waters. The results show that four influence factors, except wave period, impede wave transmission; the draft and breakwater width boost wave reflection, and the wave period and wave height are opposite; the draft impedes wave energy dissipation, and the wave height is opposite; the draft and wave height boost the horizontal extreme wave force; four influence factors, except the draft, boost the vertical extreme wave force. Finally, new formulas are provided to determine the transmission, reflection, and dissipation coefficients and extreme wave forces of the F-BW by applying multiple linear regression. The new formulas are verified by comparing with existing literature observation datasets. The results show that it is in good agreement with previous datasets. Full article
(This article belongs to the Special Issue Advances in Marine Engineering: Geological Environment and Hazards II)
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23 pages, 8041 KiB  
Article
Affine Formation Maneuver Control for Multi-Heterogeneous Unmanned Surface Vessels in Narrow Channel Environments
by Yeye Liu, Xiaogong Lin and Chao Zhang
J. Mar. Sci. Eng. 2023, 11(9), 1811; https://doi.org/10.3390/jmse11091811 - 16 Sep 2023
Cited by 4 | Viewed by 1105
Abstract
This paper investigates the affine formation maneuver control for multi-heterogeneous unmanned surface vessels (USV), aiming to enable them to navigate through narrow channels in the near-sea environment. The approach begins with implementing an affine transformation to facilitate flexible configuration adjustments within the formation [...] Read more.
This paper investigates the affine formation maneuver control for multi-heterogeneous unmanned surface vessels (USV), aiming to enable them to navigate through narrow channels in the near-sea environment. The approach begins with implementing an affine transformation to facilitate flexible configuration adjustments within the formation system. The affine transformation of the entire formation is achieved by controlling the leaders’ positions. Second, this article introduces an anti-perturbation formation tracking controller for the underactuated vessels, which assume the role of leaders, to accurately follow the arbitrary formation transformation. Third, the followers consist of fully actuated vessels with the same kinematic model as the leaders but different dynamic models. This paper utilizes the affine localizability theorem to derive an expected virtual time-varying trajectory based on the leaders’ trajectory. The followers achieve the desired formation maneuver control by tracking this expected virtual time-varying trajectory through an anti-perturbation formation tracking controller. Finally, the efficacy of the introduced control law is confirmed and supported by the results obtained from rigorous simulation experiments. Full article
(This article belongs to the Section Ocean Engineering)
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