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J. Mar. Sci. Eng., Volume 11, Issue 1 (January 2023) – 233 articles

Cover Story (view full-size image):

The proposed cover represents the essential elements of the study by means of four graphical elements: incoming wave profile (blue), C2s hull bow flare impact image, added resistance time series (orange), and an adimensional spectrum of both incoming wave and added resistance on top.

The bow flare impact of the planing hull represents the added resistance in waves, the main topic of the paper. The two timeseries represent the added resistance phase analysis results. The frequency-domain analysis used in the study and the presence of nonlinear effects such as the added resistance second harmonic content are shown in the spectra on top.

An image of regular waves generated in the Naples towing tank during the experiments fills the background. View this paper

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12 pages, 4980 KiB  
Article
Numerical Simulation on the Local Scour Processing and Influencing Factors of Submarine Pipeline
by Ke Hu, Xinglan Bai and Murilo A. Vaz
J. Mar. Sci. Eng. 2023, 11(1), 234; https://doi.org/10.3390/jmse11010234 - 16 Jan 2023
Cited by 2 | Viewed by 2159
Abstract
To investigate the different influencing characteristics of local scour around submarine pipelines, hydrodynamic and sediment transport two-dimensional models based on Flow-3D are used to numerically simulate the local scour around the pipeline under steady currents. An RNG k-ε turbulence model is applied to [...] Read more.
To investigate the different influencing characteristics of local scour around submarine pipelines, hydrodynamic and sediment transport two-dimensional models based on Flow-3D are used to numerically simulate the local scour around the pipeline under steady currents. An RNG k-ε turbulence model is applied to simulate the turbulent flow field around the pipeline. The instantaneous shear stress of the bed surface is taken as the starting and transporting conditions of the sediment. The simulation results of the equilibrium scour depth and terrain around the pipeline are verified with the previous experimental results, which perform with good agreement. Then, the numerical simulation method is applied to investigate the local scour process around the pipeline. The results show that shear stress is the main driving force of scour around a pipeline. The velocity, sediment grain size, pipeline diameter, and the initial gap between the pipeline and the seabed, significantly affects submarine pipeline equilibrium scour depth and terrain in varying degrees. Full article
(This article belongs to the Section Ocean Engineering)
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14 pages, 3414 KiB  
Article
Material and Production Optimization of the Ship Design Process by Introducing CADs from Early Design Stages
by Jaime Perez-Martinez and Rodrigo Perez Fernandez
J. Mar. Sci. Eng. 2023, 11(1), 233; https://doi.org/10.3390/jmse11010233 - 16 Jan 2023
Viewed by 2906
Abstract
Since the introduction of scientific disciplines into the shipbuilding process, there has been a search for optimisation of human and material resources. The current environmental crisis is putting additional pressure on global resource management and special attention to materials sourcing and utilisation. This [...] Read more.
Since the introduction of scientific disciplines into the shipbuilding process, there has been a search for optimisation of human and material resources. The current environmental crisis is putting additional pressure on global resource management and special attention to materials sourcing and utilisation. This paper discusses the potential solution for the current lack of effectiveness at early design stages, which are still based on 2D drawings. The industry is demanding a new 3D approach, which implies, first, a change in the procedures, and second, having a suitable CAD/CAM tool for the early generation of a digital mock-up, from which the project is developed throughout all design and production phases, from conceptual design to operation. The proposed solution shown in this paper would improve the general arrangement definition, with the use of CAD for the 3D definition of the compartments and the main equipment positioning; improve the naval architecture calculation; and finally improve the basic/class design stage, with better reuse of data already developed in the general arrangement model and in the definition of a 3D model of structure, with the main equipment positioning, pipes, and electrical equipment already into the model. Intelligent P&I diagrams and single-wire electric diagrams would be used at this stage and connected to the 3D model. Additionally, it will allow for early estimating of materials, weights, and associated processes. This will be further supported by the use of topology to consider design alternatives and produce early information on materials for procurement and production. The cost reduction associated with the definition of the early design stages in 3D has been estimated at around 15% of the overall design and production stages. Full article
(This article belongs to the Special Issue Sustainable Ship Design and Digital Twin Yard)
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19 pages, 15619 KiB  
Article
Offshore Measurements and Numerical Validation of the Mooring Forces on a 1:5 Scale Buoy
by Jens Engström, Zahra Shahroozi, Eirini Katsidoniotaki, Charitini Stavropoulou, Pär Johannesson and Malin Göteman 
J. Mar. Sci. Eng. 2023, 11(1), 231; https://doi.org/10.3390/jmse11010231 - 16 Jan 2023
Viewed by 1855
Abstract
Wave energy conversion is a renewable energy technology with a promising potential. Although it has been developed for more than 200 years, the technology is still far from mature. The survivability in extreme weather conditions is a key parameter halting its development. We [...] Read more.
Wave energy conversion is a renewable energy technology with a promising potential. Although it has been developed for more than 200 years, the technology is still far from mature. The survivability in extreme weather conditions is a key parameter halting its development. We present here results from two weeks of measurement with a force measurement buoy deployed at Uppsala University’s test site for wave energy research at the west coast of Sweden. The collected data have been used to investigate the reliability for two typical numerical wave energy converter models: one low fidelity model based on linear wave theory and one high fidelity Reynolds-Averaged Navier–Stokes model. The line force data is also analysed by extreme value theory using the peak-over-threshold method to study the statistical distribution of extreme forces and to predict the return period. The high fidelity model shows rather good agreement for the smaller waves, but overestimates the forces for larger waves, which can be attributed to uncertainties related to field measurements and numerical modelling uncertainties. The peak-over-threshold method gives a rather satisfying result for this data set. A significant deviation is observed in the measured force for sea states with the same significant wave height. This indicates that it will be difficult to calculate the force based on the significant wave height only, which points out the importance of more offshore experiments. Full article
(This article belongs to the Special Issue Advanced Marine Energy Harvesting Technologies)
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26 pages, 10165 KiB  
Article
Research on the Karhunen–Loève Transform Method and Its Application to Hull Form Optimization
by Haichao Chang, Chengjun Wang, Zuyuan Liu, Baiwei Feng, Chengsheng Zhan and Xide Cheng
J. Mar. Sci. Eng. 2023, 11(1), 230; https://doi.org/10.3390/jmse11010230 - 16 Jan 2023
Cited by 3 | Viewed by 1518
Abstract
Hull form optimization becomes prone to the curse of dimensionality as the number of design variables increases. The traditional sensitivity analysis method requires massive computational fluid dynamics (CFD) computations and analyzing the effects of all variables on the output; thus, it is extremely [...] Read more.
Hull form optimization becomes prone to the curse of dimensionality as the number of design variables increases. The traditional sensitivity analysis method requires massive computational fluid dynamics (CFD) computations and analyzing the effects of all variables on the output; thus, it is extremely time-consuming. Considering this, the development of a rapid and effective dimensionality reduction method is particularly important. The Karhunen–Loève (K–L) transform method projects data from a high-dimensional space onto a low-dimensional space in the direction of the eigenvectors corresponding to large-variance eigenvalues. It extracts the principal components that represent the hull offset information to represent the hull geometric characteristics by analyzing the relationship between the variables in the sample offset matrix. The geometric information matrices of new hull forms can be rapidly reconstructed from the principal components. Compared with direct optimization methods, fewer variables are used to control the deformation of the hull form from the perspective of geometric deformation, avoid a large number of CFD calculations, and improve the efficiency of optimization. This study examined the relevant K–L matrix solution methods and the corresponding hull form reconstruction methods and proposed eigenvalue-based hull form reconstruction equations. The K–L transform method was combined with a previously developed multidisciplinary platform for a comprehensive optimization of ship hydrodynamic performance for hull form optimization, and its effectiveness was verified by using it to optimize DTMB 5415. The results showed that the K–L transform–based dimensionality reduction method significantly reduces the time consumption of optimization while maintaining an acceptable optimization performance. Full article
(This article belongs to the Special Issue Ship Dynamics and Hydrodynamics)
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26 pages, 9688 KiB  
Article
A Techno-Economic Analysis of a Cargo Ship Using Flettner Rotors
by Gianluca Angelini, Sara Muggiasca and Marco Belloli
J. Mar. Sci. Eng. 2023, 11(1), 229; https://doi.org/10.3390/jmse11010229 - 16 Jan 2023
Cited by 4 | Viewed by 2110
Abstract
In the last twenty years, the global shipping transport demand has strongly increased (around 4% per year since the 1990s), together with the request for new green propulsion technologies to break down carbon emissions and face the costs deriving from the usage of [...] Read more.
In the last twenty years, the global shipping transport demand has strongly increased (around 4% per year since the 1990s), together with the request for new green propulsion technologies to break down carbon emissions and face the costs deriving from the usage of conventional diesel fuels. Flettner rotors (hereafter: FRs) have been identified by several researchers as a promising solution to exploit wind energy on commercial ships, reducing fuel consumption. The present work presents a six-degree-of-freedom (6DOF) ship performance model set up to evaluate the best way of using a pair of Flettner rotors. The study analyses the performance of this propulsion system in consideration of weather and sea conditions, evaluating the related reduction in fuel consumption. A discussion about the economic and environmental advantages of the usage of FRs is provided, considering the costs linked to their installation and the new emission restrictions. Relevant results have been obtained for different routes, speed ranges and rotor dimensions while investigating the best Flettner rotor arrangement to minimise both the emissions and the installation cost payback period. Full article
(This article belongs to the Special Issue Marine Fuels and Green Energy)
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15 pages, 5116 KiB  
Article
Experimental Investigation into the Erosion Performance of Water Jets on Marine Hydrate-Bearing Sediment
by Dongbin Pan, Lin Yang, Chen Chen and Xitong Li
J. Mar. Sci. Eng. 2023, 11(1), 228; https://doi.org/10.3390/jmse11010228 - 16 Jan 2023
Cited by 1 | Viewed by 1575
Abstract
Fine-grained natural gas hydrate (NGH) reservoirs are widely distributed across the world and bear more than 90% of global NGH. However, it is difficult to exploit this kind of NGH reservoir economically and environmentally using conventional methods. Water-jet cutting is an efficient and [...] Read more.
Fine-grained natural gas hydrate (NGH) reservoirs are widely distributed across the world and bear more than 90% of global NGH. However, it is difficult to exploit this kind of NGH reservoir economically and environmentally using conventional methods. Water-jet cutting is an efficient and environmentally friendly technique for mining such hydrate reservoirs, as the production process does not depend on mass and heat transfer within the formations. In this work, a series of physical experiments were conducted to clarify the erosion performance of marine hydrate-bearing sediment (HBS) impacted by water jets. The results show that the accumulation of sediment particles and hydrate particles at the bottom of erosion hole severely inhibits the vertical erosion of HBS by water jet. For a particular jet flow rate, the jet distance has an optimal value, which is between 4 mm and 28 mm. Moreover, the upwelling flow containing solid particles has a significant impact on the erosion of the hole top. In reservoirs with a low hydrate saturation (20–40%) and reservoirs with a high hydrate saturation (60–80%), the erosion holes exhibit a gourd shape and a bamboo shape, respectively. In addition, the volume erosion efficiency and the depth erosion efficiency are more sensitive to the variation in jet flow rate than jet distance and hydrate saturation. This study can provide theoretical and technical support for the application of water-jet cutting in the exploitation of marine HBS. Full article
(This article belongs to the Section Ocean Engineering)
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19 pages, 7522 KiB  
Article
Seismic Multiple Attenuation in the Continent–Ocean Transition Zone of the Northern South China Sea
by Nan Chen, Chun-Feng Li, Yong-Lin Wen, Peng Wang, Xiu-Lian Zhao and Xiao-Li Wan
J. Mar. Sci. Eng. 2023, 11(1), 227; https://doi.org/10.3390/jmse11010227 - 15 Jan 2023
Cited by 4 | Viewed by 2106
Abstract
In this study, we process four new multichannel reflection seismic profiles acquired in 2015 and 2016 in the continent–ocean transition zone (COT) of the northern South China Sea (SCS). We apply a multi-domain, progressive, and seabed-controlled denoising technique and obtain a good denoising [...] Read more.
In this study, we process four new multichannel reflection seismic profiles acquired in 2015 and 2016 in the continent–ocean transition zone (COT) of the northern South China Sea (SCS). We apply a multi-domain, progressive, and seabed-controlled denoising technique and obtain a good denoising effect. Combining velocity analysis in the multi-round time domain and forward modeling, we analyze the types and characteristics of multiples in the study area and formulate an effective demultiple technique to attenuate strong seabed multiples, diffracted multiples from rough seafloor, and other multiples from deep reflectors. The processing results show that the sea surface-related multiple elimination technique predicts the sea surface-related multiples accurately by data convolution, and has a good effect in attenuating seabed multiples. Diffracted multiple attenuation method extracts high-frequency and high-energy diffracted multiples, and suppresses multiples by the energy ratios of multiples to primary events. To attenuate deep multiples, we select predictive deconvolution to attenuate periodic deep multiples after many trials and detailed analysis. The combination of these different techniques in sequence proves to be quite effective in attenuating different seismic multiples in the COT. The imaged crustal structures near the COT often show strong magmatism and/or basement uplifting. The faulted and thinned continental crust adjacent to the COT corresponds to the lowest free-air gravity anomalies. Gravity anomalies often increase from the COT to the oceanic crust. An exception is to the northeast of the SCS, where the relatively wide COT shows very high gravity anomalies, likely induced by mantle upwelling and serpentinization. Full article
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21 pages, 4445 KiB  
Article
Analytical Eddy Viscosity Model for Turbulent Wave Boundary Layers: Application to Suspended Sediment Concentrations over Wave Ripples
by Rafik Absi and Hitoshi Tanaka
J. Mar. Sci. Eng. 2023, 11(1), 226; https://doi.org/10.3390/jmse11010226 - 15 Jan 2023
Cited by 3 | Viewed by 2616
Abstract
Turbulence related to flow oscillations near the seabed, in the wave bottom boundary layer (WBBL), is the phenomenon responsible for the suspension and transport of sediments. The vertical distribution of turbulent eddy viscosity within the WBBL is a key parameter that determines the [...] Read more.
Turbulence related to flow oscillations near the seabed, in the wave bottom boundary layer (WBBL), is the phenomenon responsible for the suspension and transport of sediments. The vertical distribution of turbulent eddy viscosity within the WBBL is a key parameter that determines the vertical distribution of suspended sediments. For practical coastal engineering applications, the most used method to parameterize turbulence consists in specifying the shape of the one-dimensional-vertical (1DV) profile of eddy viscosity. Different empirical models have been proposed for the vertical variation of eddy viscosity in the WBBL. In this study, we consider the exponential-type profile, which was validated and calibrated by direct numerical simulation (DNS) and experimental data for turbulent channel and open-channel flows, respectively. This model is generalized to the WBBL, and the period-averaged eddy viscosity is calibrated by a two-equation baseline (BSL) k-ω model for different conditions. This model, together with a β-function (where β is the inverse of the turbulent Schmidt number), is used in modeling suspended sediment concentration (SSC) profiles over wave ripples, where field and laboratory measurements of SSC show two kinds of concentration profiles depending on grain particles size. Our study shows that the convection–diffusion equation, for SSC in WBBLs over sand ripples with an upward convection term, reverts to the classical advection–diffusion equation (ADE) with an “apparent” sediment diffusivity εs*=α εs related to the sediment diffusivity εs by an additional parameter α associated with the convective sediment entrainment process over sand ripples, which is defined by two equations. In the first, α depends on the relative importance of upward convection related to coherent vortex shedding and downward settling of sediments. When the convective transfer is very small, above low-steepness ripples, α1. In the second, α depends on the relative importance of coherent vortex shedding and random turbulence. When random turbulence is more important than coherent vortex shedding, α1, and “apparent” sediment diffusivity reverts to the classical sediment diffusivity εs* εs. Comparisons with experimental data show that the proposed method allows a good description of both SSC for fine and coarse sand and “apparent” sediment diffusivity εs*. Full article
(This article belongs to the Special Issue Latest Advances in Physical Oceanography)
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21 pages, 937 KiB  
Article
Causality of Risk Assessment Attributes under Uncertainty in Taiwan’s Offshore Wind Farms Development
by Feng-Ming Tsai, Sheng-Long Kao, Raditia Yudistira Sujanto, Ming-Lang Tseng, Tai-Wen Hsu and Chien-Chang Chou
J. Mar. Sci. Eng. 2023, 11(1), 225; https://doi.org/10.3390/jmse11010225 - 15 Jan 2023
Viewed by 1641
Abstract
This study contributes to investigating the causality of risk assessment attributes under uncertainty for the offshore wind farms development in Taiwan. The investigation of risk assessment attributes for the offshore wind farms development has increasingly attracted more notice as multifaceted challenges from socioeconomic, [...] Read more.
This study contributes to investigating the causality of risk assessment attributes under uncertainty for the offshore wind farms development in Taiwan. The investigation of risk assessment attributes for the offshore wind farms development has increasingly attracted more notice as multifaceted challenges from socioeconomic, safety, and environmental perspectives emerged. Yet, the literature is lacking a multi-perspective viewpoint of the determining attributes and an examination of the attributes’ interrelationships using qualitative information. To fill this gap, this study aims to identify the valid attributes based on the multi-perspectives of feasibility, environment, economic, and safety risks, and investigate the attributes’ interrelationships. Thus, this study employs the fuzzy Delphi method to obtain valid risk assessment attributes and adopts a fuzzy decision-making trial and evaluation laboratory method to examine the attributes’ interrelationships while identifying the multi-perspective-based crucial attributes. The results indicate that human safety, impact on marine environment, and navigation safety are crucial risk aspects to be assessed. From the practical point of view, this study found that safety of ship crews and passengers, safety of maintenance crews, local fishery industry, public trust in environmental regulations, and change of income for fishermen are the important risk criteria to be prioritized when developing offshore wind farms. Full article
(This article belongs to the Special Issue Contemporary Shipping Logistics and Port Management)
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18 pages, 15903 KiB  
Article
Analysis of the Descent Process and Multi-Objective Optimization Design of a Benthic Lander
by Qiao Zhang, Chunming Dong, Zongze Shao and Donghui Zhou
J. Mar. Sci. Eng. 2023, 11(1), 224; https://doi.org/10.3390/jmse11010224 - 15 Jan 2023
Viewed by 1414
Abstract
The growing need for deep-sea biological research and environmental monitoring has expanded the demand for benthic landers. Compared with remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs), benthic landers can reduce overall operation cost and also possess longer endurance. Configuring a suitable [...] Read more.
The growing need for deep-sea biological research and environmental monitoring has expanded the demand for benthic landers. Compared with remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs), benthic landers can reduce overall operation cost and also possess longer endurance. Configuring a suitable descent velocity is important for benthic lander designs, helping them avoid retrieval failure and improve sea trial efficiencies. In this study, an effective scheme for the configuration and optimization of a self-developed benthic lander was outlined. First, the structural characteristics of the benthic lander were analyzed, and then a dynamic model was established. Second, the hydrodynamic coefficients of the benthic lander during its descent process were calculated using computational fluid dynamics (CFD) methods. Third, the MATLAB Simulink simulation environment was used to solve the dynamic model, and then the multi-objective optimization algorithm was introduced for the optimization design. Finally, the model was validated based on sea trial data, which demonstrated that the designed configuration and optimization scheme were correct and efficient. Collectively, this work provides a useful reference for the rational configuration and practical application of benthic landers. Full article
(This article belongs to the Special Issue Frontiers in Deep-Sea Equipment and Technology II)
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17 pages, 17182 KiB  
Article
Experimental Investigation on the Cyclic Shear Mechanical Characteristics and Dynamic Response of a Steel–Silt Interface in the Yellow River Delta
by Peng Yu, Jie Dong, Yong Guan, Qing Wang, Shixiang Jia, Meijun Xu, Hongjun Liu and Qi Yang
J. Mar. Sci. Eng. 2023, 11(1), 223; https://doi.org/10.3390/jmse11010223 - 15 Jan 2023
Cited by 3 | Viewed by 1486
Abstract
The shear behavior and dynamic response of a steel–silt interface are significant for the safety and stability of offshore structures in the Yellow River Delta. A series of steel–silt interface cyclic shear tests under constant normal load conditions (CNL) were carried out to [...] Read more.
The shear behavior and dynamic response of a steel–silt interface are significant for the safety and stability of offshore structures in the Yellow River Delta. A series of steel–silt interface cyclic shear tests under constant normal load conditions (CNL) were carried out to explore the effects of normal stress, shear amplitude, roughness, and water content on the interface shear strength, shear stiffness, and damping ratio using a large interface shear apparatus. The preliminary results showed that the amplitude of normal stress and shear amplitude affected the interface’s shear strength, stiffness, and damping ratio in a dominant manner. The roughness and water content were also crucial factors impacting the rule of shear strength, shear stiffness, and damping ratio, changing with the number of cycles. Under various scenarios, the steel–silt interface weakened distinctively, and the energy dissipation tended to be asymptotic with the cyclic shear. Full article
(This article belongs to the Special Issue Advances in Marine Engineering: Geological Environment and Hazards II)
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24 pages, 9213 KiB  
Article
Design of Control System for Multistage Distillation Seawater Desalination Device Driven by Photovoltaic-Thermal
by Jiaqi Yan, Chengjun Qiu, Yuangan Wang, Ning Wu, Wei Qu, Yuan Zhuang, Guohui Yan, Ping Wang, Ruoyu Zhang, Yirou Yan, Ruonan Deng, Jiuqiang Luo, Jiaqi Gao and Yuxuan Wu
J. Mar. Sci. Eng. 2023, 11(1), 222; https://doi.org/10.3390/jmse11010222 - 14 Jan 2023
Cited by 1 | Viewed by 1936
Abstract
This research proposes a seawater desalination system driven by photovoltaic and solar thermal energy for remote regions such as islands and seaside villages where fresh water is not accessible. The performance of this system is demonstrated through experiments, and the main concerns are [...] Read more.
This research proposes a seawater desalination system driven by photovoltaic and solar thermal energy for remote regions such as islands and seaside villages where fresh water is not accessible. The performance of this system is demonstrated through experiments, and the main concerns are the output of the photovoltaic power generation system, power quantity, water yield, and the loads under different solar irradiance and temperature. In this system, a PLC is used as the controller to adjust the water pump by the collection and processing of sensor data. A load switching time system is designed to select different operating schemes under different environments in order to save energy. The control method of this system is developed to ensure that the photovoltaic power generation system does not undervoltage while maintaining the normal operation of the desalination system. An improved Perturbation and Observation (P&O) algorithm is also proposed as a new Maximum Point Power Tracking (MPPT) method to solve the problem of misjudgment and oscillation after tracking the maximum power point (MPP) in the traditional P&O algorithm. The simulation test in the MATLAB/Simulink environment shows that when external irradiance changes, the improved P&O algorithm can track the MPP faster than the traditional P&O algorithm, and the amplitude of oscillation on the MPP is smaller. The hardware experiments show that this system can operate stably and flexibly, and it is capable of producing 5.18 kWh of electric energy and 335.81 kg of freshwater per day. The maximum yield of the unit can reach 565.75 kg per day and the maximum daily power generation is 8.12 kWh. Full article
(This article belongs to the Special Issue Advanced Marine Electronic Applications in Smart Ocean)
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20 pages, 9223 KiB  
Article
A Marine Hydrographic Station Networks Intrusion Detection Method Based on LCVAE and CNN-BiLSTM
by Tianhao Hou, Hongyan Xing, Xinyi Liang, Xin Su and Zenghui Wang
J. Mar. Sci. Eng. 2023, 11(1), 221; https://doi.org/10.3390/jmse11010221 - 14 Jan 2023
Cited by 4 | Viewed by 1579
Abstract
Marine sensors are highly vulnerable to illegal access network attacks. Moreover, the nation’s meteorological and hydrological information is at ever-increasing risk, which calls for a prompt and in depth analysis of the network behavior and traffic to detect network attacks. Network attacks are [...] Read more.
Marine sensors are highly vulnerable to illegal access network attacks. Moreover, the nation’s meteorological and hydrological information is at ever-increasing risk, which calls for a prompt and in depth analysis of the network behavior and traffic to detect network attacks. Network attacks are becoming more diverse, with a large number of rare and even unknown types of attacks appearing. This results in traditional-machine-learning (ML)-based network intrusion detection (NID) methods performing weakly due to the lack of training samples. This paper proposes an NID method combining the log-cosh conditional variational autoencoder (LCVAE) with convolutional the bi-directional long short-term memory neural network (LCVAE-CBiLSTM) based on deep learning (DL). It can generate virtual samples with specific labels and extract more significant attack features from the monitored traffic data. A reconstructed loss term based on the log-cosh model is introduced into the conditional autoencoder. From it, the virtual samples are able to inherit the discrete attack data and enhance the potential features of the imbalance attack type. Then, a hybrid feature extraction model is proposed by combining the CNN and BiLSTM to tackle the attack’s spatial and temporal features. The following experiments evaluated the proposed method’s performance on the NSL-KDD dataset. The results demonstrated that the LCVAE-CBiLSTM obtained better results than state-of-the-art works, where the accuracy, F1-score, recall, and FAR were 87.30%, 87.89%, 80.89%, and 4.36%. The LCVAE-CBiLSTM effectively improves the detection rate of a few classes of samples and enhances the NID performance. Full article
(This article belongs to the Section Ocean Engineering)
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25 pages, 9488 KiB  
Article
Study of Safety Auxiliary Facilities to Prevent the Start-Up Failure of Large Axial Flow Pump Systems under Gate Failure Working Conditions
by Xiaowen Zhang, Chenglin Yang, Xijie Song, Fangping Tang, Chongyang Hu, Fan Yang and Lijian Shi
J. Mar. Sci. Eng. 2023, 11(1), 220; https://doi.org/10.3390/jmse11010220 - 14 Jan 2023
Cited by 1 | Viewed by 1331
Abstract
Large axial flow pump systems are used in coastal pump stations. It is common and very dangerous for large axial flow pump systems to encounter the failure of the fast hydraulic gate during start-up operations. Methods for equipping LAPS with reasonable safety aids [...] Read more.
Large axial flow pump systems are used in coastal pump stations. It is common and very dangerous for large axial flow pump systems to encounter the failure of the fast hydraulic gate during start-up operations. Methods for equipping LAPS with reasonable safety aids for start-up operations in order to deal with the unexpected situation that the quick gate cannot be opened, limiting the safety and stability of LAPS, have become a key focus of research. We aim to investigate the effect of safety aids on the LAPS’s start-up characteristics under gate rejection conditions and to find the best safety aid allocation method to solve the LAPS’s start-up failure problem. Based on the verification of the model test, a numerical simulation of the start-up process of the large axial flow pump system equipped with auxiliary safety features was carried out under the condition of gate rejection. The results show that under the condition of gate rejection, the auxiliary FLVA or OVHO can help LAPS reduce the risk of start-up failure to a certain extent. The FLVA will play the main protective role during the start-up operations of the LAPS if the LAPS is equipped with both the OVHO and FLVA of unrestricted size under the gate rejection condition. LAPS equipped with OVHO (1.27 Hm) and FLVA (49.1% Ag) and LAPS equipped with FLVA (49.1% Ag) have comparable start-up safety. The latter has an His of 1.783 Hr and a Pis of 1.30 Pr. The former has an instantaneous shock head of 1.772 Hr and a Pis of 1.30 Pr, which exhibit a decrease of 0.38% and 0 %, respectively. The research results will provide an important reference value for the prevention of pump station start-up failures under gate rejection conditions. Full article
(This article belongs to the Section Ocean Engineering)
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29 pages, 10093 KiB  
Article
Field Measurement and Numerical Study on the Effects of Under-Excavation and Over-Excavation on Ultra-Deep Foundation Pit in Coastal Area
by Jifei Cui, Zhenkun Yang and Rafig Azzam
J. Mar. Sci. Eng. 2023, 11(1), 219; https://doi.org/10.3390/jmse11010219 - 14 Jan 2023
Cited by 15 | Viewed by 2444
Abstract
An ultra-deep L-shape foundation pit in a coastal area has recently been constructed and monitored. The project overview, geological conditions, excavation sequence and monitoring scheme are introduced in detail. The deformation of the retaining structure and surrounding strata are analyzed in detail through [...] Read more.
An ultra-deep L-shape foundation pit in a coastal area has recently been constructed and monitored. The project overview, geological conditions, excavation sequence and monitoring scheme are introduced in detail. The deformation of the retaining structure and surrounding strata are analyzed in detail through the measured data and 3D numerical simulation. The results show that the exceptional performance of the current project is due to the combination of under-excavation and over-excavation during construction. The under-excavation procedure restrained the wall deflections at the middle part of the diaphragm wall, making the corner effects at the corresponding side inapparent. Both the under-excavation and over-excavation procedure can only influence the performance of the excavation in close proximity, while having negligible impacts on the normally excavated areas. Based on the results of this study, practical suggestions are given to improve the performance of similar excavations in the future. Full article
(This article belongs to the Special Issue Advances in Offshore Geotechnics)
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19 pages, 5015 KiB  
Article
Dynamic Responses of the Cylindrical Floating Drilling Production Storage and Offloading System with Annular Anti-Motion Structures under the Survival Sea Scenario
by Yan Li, Yaolong Li, Zhimin Zhao, Yougang Tang, Haoran Li, Yijian Zhang and Yinan Hu
J. Mar. Sci. Eng. 2023, 11(1), 218; https://doi.org/10.3390/jmse11010218 - 14 Jan 2023
Cited by 1 | Viewed by 1339
Abstract
At present, dry wellheads are usually adopted on small-storage TLP and SPAR platforms to develop offshore oil and gas because of the robust hydrodynamic performance under severe-wind seas. On the other hand, FPSO and FDPSO platforms that have a larger storage capacity can [...] Read more.
At present, dry wellheads are usually adopted on small-storage TLP and SPAR platforms to develop offshore oil and gas because of the robust hydrodynamic performance under severe-wind seas. On the other hand, FPSO and FDPSO platforms that have a larger storage capacity can hardly use this cost-saving facility due to their relatively poor vertical motion performance. Cylindrical FPSOs are proposed to improve the heave performance of ship-type FPSOs, but their behaviors are still too large to adopt the dry wellheads. In the present work, a cylindrical FDPSO platform is proposed based on the FWPSO platform, adding an extension cylinder and a new damping structure at the bottom. Their hydrodynamic performances are calculated by the potential theory and compared in the frequency domain. Taking two particular mooring systems, including both catenary and ‘chain-polyester-chain’ types, and the survival sea scenario in the South China Sea into account, a time-domain coupling analysis was adopted to simulate the dynamic performance of the platform-mooring system. The feasibility of dry wellhead adoption on the FDPSO is discussed by investigating the platform motion and the mooring tension. The results show that the FCDS platform with the ‘chain-polyester-chain’-type mooring system can meet the motion response requirements, and the mooring system can also meet the requirements of the specification. Full article
(This article belongs to the Special Issue Offshore Structures and Hydrodynamic Modeling)
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18 pages, 3583 KiB  
Article
Assessing Efficacy of “Eco-Friendly” and Traditional Copper-Based Antifouling Materials in a Highly Wave-Exposed Environment
by Clara Arboleda-Baena, Nicole Osiadacz, Mirtala Parragué, Andrés E. González, Miriam Fernández, Gerhard R. Finke and Sergio A. Navarrete
J. Mar. Sci. Eng. 2023, 11(1), 217; https://doi.org/10.3390/jmse11010217 - 13 Jan 2023
Cited by 2 | Viewed by 2280
Abstract
Biofouling control on human-made structures and seagoing technologies that minimize environmental impacts is a major focus of research in marine industries. However, the most widely used antifouling (AF) method is still copper-based coatings. Some “eco-friendly” approaches are commercially available but have been scarcely [...] Read more.
Biofouling control on human-made structures and seagoing technologies that minimize environmental impacts is a major focus of research in marine industries. However, the most widely used antifouling (AF) method is still copper-based coatings. Some “eco-friendly” approaches are commercially available but have been scarcely tested in natural conditions, especially high-energy environments. We conducted a replicated long-term field experiment in a highly wave-exposed, high productivity coastal environment to test three untreated materials used in maritime industries, two traditional copper-based AF coatings, and two materials offered as “eco-friendly” AF in the market (i.e., a slow-copper release and a self-adhesive, fiber-covered, skin-like coating). We showed that biofouling cover and biomass increased at similar rates over time among all untreated materials, including the skin-like AF. The two traditional copper-based AF coatings and the slow-release AF paint both showed similarly low biofouling biomass and richness, demonstrating their efficacy after 12 months in the field. Although the “eco-friendly” slow-release technologies are not completely innocuous to the environment, we suggest this approach over the more environmentally aggressive traditional copper paints, which are the most widely used in aquaculture and shipping industries today. However, further research is needed to test whether their environmental impact is significantly lower in the long-term than traditional AF paints, and therefore the search for non-toxic coating must continue. The fortuitous settlement and growth of sea urchins in our experiments also suggest that a combination of “eco-friendly” AF and biological control would be possible and should be further investigated. The skin-like coatings must be tested under different environmental conditions, and they are not recommended in wave-exposed coastal habitats. Full article
(This article belongs to the Section Marine Environmental Science)
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15 pages, 1315 KiB  
Article
Trajectory Data Compression Algorithm Based on Ship Navigation State and Acceleration Variation
by Junbo Gao, Ze Cai, Wangjing Yu and Wei Sun
J. Mar. Sci. Eng. 2023, 11(1), 216; https://doi.org/10.3390/jmse11010216 - 13 Jan 2023
Cited by 4 | Viewed by 1413
Abstract
An active area of study under the dual carbon target, which is based on automatic identification systems (AIS), is the emission inventory of pollutants from ships. Data compression is required because there is currently so much data that it has become difficult to [...] Read more.
An active area of study under the dual carbon target, which is based on automatic identification systems (AIS), is the emission inventory of pollutants from ships. Data compression is required because there is currently so much data that it has become difficult to transmit, process, and store it. A trajectory simplification method considering the ship sailing state and acceleration rate of change is developed in this paper to assure the validity of the compressed data used in the emission inventory analysis. By carefully examining the integral relationship between acceleration and pollution emissions, the algorithm constructs an acceleration rate of change function for data compression and categorizes AIS data by ship navigation status. By dynamically altering the amount of acceleration change, the developed function can stabilize the pollutant emission calculation error and adaptively calculate the threshold value. The experimental results show that the emission calculation error of the proposed algorithm is only 0.185% when the compression rate is 90.28%. Full article
(This article belongs to the Section Ocean Engineering)
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23 pages, 7915 KiB  
Article
A Modified MPS Method with a Split-Pressure Poisson Equation and a Virtual Particle for Simulating Free Surface Flows
by Date Li, Huaixin Zhang and Guangfei Qin
J. Mar. Sci. Eng. 2023, 11(1), 215; https://doi.org/10.3390/jmse11010215 - 13 Jan 2023
Cited by 1 | Viewed by 1681
Abstract
As a Lagrangian mesh-free method, the moving particle semi-implicit (MPS) method can easily handle complex incompressible flow with a free surface. However, some deficiencies of the MPS method, such as inaccurate results, unphysical pressure oscillation, and particle thrust near the free surface, still [...] Read more.
As a Lagrangian mesh-free method, the moving particle semi-implicit (MPS) method can easily handle complex incompressible flow with a free surface. However, some deficiencies of the MPS method, such as inaccurate results, unphysical pressure oscillation, and particle thrust near the free surface, still need to be further resolved. Here, we propose a modified MPS method that uses the following techniques: (1) a modified MPS scheme with a split-pressure Poisson equation is proposed to reproduce hydrostatic pressure stably; (2) a new virtual particle technique is developed to ensure the symmetrical distribution of particles on the free surface; (3) a Laplacian operator that is consistent with the original gradient operator is introduced to replace the original Laplacian operator. In addition, a two-judgment technique for distinguishing free surface particles is introduced in the proposed MPS method. Four free surface flows were adopted to verify the proposed MPS method, including two hydrostatic problems, a dam-breaking problem, and a violent sloshing problem. The enhancement of accuracy and stability by these improvements was demonstrated. Moreover, the numerical results of the proposed MPS method showed good agreement with analytical solutions and experimental results. Full article
(This article belongs to the Special Issue Computational Fluid Mechanics II)
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17 pages, 6741 KiB  
Article
Experimental Study of the Dynamic Shear Modulus of Saturated Coral Sand under Complex Consolidation Conditions
by Weijia Ma, You Qin, Fei Gao and Qi Wu
J. Mar. Sci. Eng. 2023, 11(1), 214; https://doi.org/10.3390/jmse11010214 - 13 Jan 2023
Cited by 3 | Viewed by 1701
Abstract
The shear modulus is an essential parameter that reflects the mechanical properties of the soil. However, little is known about the shear modulus of coral sand, especially under complex consolidation conditions. In this paper, we present the results of a multi-stage strain-controlled undrained [...] Read more.
The shear modulus is an essential parameter that reflects the mechanical properties of the soil. However, little is known about the shear modulus of coral sand, especially under complex consolidation conditions. In this paper, we present the results of a multi-stage strain-controlled undrained cyclic shear test on saturated coral sand. The influences of several consolidation state parameters: effective mean principal stress (p0), consolidation ratio (kc), consolidation direction angle (α0), and coefficient of intermediate principal stress (b) on the maximum shear modulus (G0), the reference shear strain (γr) and the reduction of shear modulus (G) have been investigated. For a specified shear strain level, G will increase with increasing p0 and kc, but decrease with increasing α0 and b. However, the difference between G for various α0 and b can be reduced by the increase of shear strain amplitude (γa). G0 shows an increasing trend with the increase of p0 and kc; on the contrary, with the increase of α0 and b, G0 shows a decreasing trend. To quantify the effect of consolidation state parameters on G0, a new index (μG0) with four parameters (λ1, λ2, λ3, λ4) which is related to p0, kc, α0, b is proposed to modify the prediction model of G0 in literature. Similarly, the values of γr under different consolidation conditions are also evaluated comprehensively by the four parameters, and the related index (μγr) is used to predict γr for various consolidation state parameters. A new finding is that there is an identical relationship between normalized shear modulus G/G0 and normalized shear strain γa/γr for various consolidation state parameters and the Davidenkov model can describe the G/G0γa/γr curves. By using the prediction model proposed in this paper, an excellent prediction of G can be obtained and the deviation between measured and predicted G is all within ±10%. Full article
(This article belongs to the Special Issue Advance in Marine Geotechnical Engineering)
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21 pages, 8653 KiB  
Article
Effect of Rigid Vegetation Arrangement on the Mixed Layer of Curved Channel Flow
by Tianwei Huang, Mengxing He, Kan Hong, Yingtien Lin and Pengcheng Jiao
J. Mar. Sci. Eng. 2023, 11(1), 213; https://doi.org/10.3390/jmse11010213 - 13 Jan 2023
Cited by 3 | Viewed by 1381
Abstract
Curved channels and aquatic vegetation are commonly present in the riverine environment. In this study, the effects of vegetation density and distribution on the hydrodynamic characteristics of a mixed layer developed over a 180-degree curved channel were investigated through flume experiments. Wooden sticks [...] Read more.
Curved channels and aquatic vegetation are commonly present in the riverine environment. In this study, the effects of vegetation density and distribution on the hydrodynamic characteristics of a mixed layer developed over a 180-degree curved channel were investigated through flume experiments. Wooden sticks were used to simulate rigid vegetation distributed along the half side of the channel, and a 200 Hz acoustic Doppler velocimeter (ADV) was employed to measure the three-dimensional instantaneous velocity at five selected cross sections along the curved channel. Experimental results show that the vegetation covering the half of the channel significantly affects the hydrodynamic structure of the curved channel flow, and the unequal vegetation resistance induces the K-H instability at the vegetation and non-vegetation interface, resulting in a standard hyperbolic tangent function of streamwise velocity distribution along the lateral direction. The influence of curve position on turbulence kinetic energy is far greater than that of vegetation density and vegetation distribution. The peak value of turbulent kinetic energy is comprehensively affected by vegetation density and distribution, and the peak position of turbulent kinetic energy at the interface is changed by different vegetation distribution. The combined effect of the curve and the partly covered vegetation increases the mixing between the water bodies, enhancing turbulent kinetic energy, and vegetation along the concave bank plays a more significant role. For turbulent bursting, the inward and outward interactions are mainly bursting events in the vegetation area, while ejections and sweeps are dominant in the non-vegetation area. However, the critical vegetation condition to initiate large-scale coherent structure (LSS) in the mixed layer and the influence of flexible vegetation need to be further studied in the future. Full article
(This article belongs to the Special Issue Fluid/Structure Interactions II)
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25 pages, 4082 KiB  
Review
Progress of Combined Wind and Wave Energy Harvesting Devices and Related Coupling Simulation Techniques
by Feifei Cao, Mingqi Yu, Bing Liu, Zhiwen Wei, Lei Xue, Meng Han and Hongda Shi
J. Mar. Sci. Eng. 2023, 11(1), 212; https://doi.org/10.3390/jmse11010212 - 13 Jan 2023
Cited by 5 | Viewed by 2922
Abstract
The use of combined wind and wave energy harvesting devices (CWWHDs) is an effective way to synergistically capture offshore wind and wave energy. However, the form of combined energy harvesting and coupled simulation techniques limit the development of CWWHDs. This paper classifies the [...] Read more.
The use of combined wind and wave energy harvesting devices (CWWHDs) is an effective way to synergistically capture offshore wind and wave energy. However, the form of combined energy harvesting and coupled simulation techniques limit the development of CWWHDs. This paper classifies the existing CWWHDs based on wave energy converters and offshore wind turbines, summarizes the theoretical background and implementation forms of the numerical simulation of CWWHDs, and focuses on the technical details of wind-wave coupling and multi-body coupling simulation, which fills the gap in the research of the wind-wave coupling and multi-body coupling numerical simulation of CWWHDs. Finally, the current research focus and development direction of CWWHDs and their numerical simulation technology are summarized to provide a reference for the future development and application of CWWHDs and numerical simulation technology. Full article
(This article belongs to the Special Issue Advances in Offshore Wind and Wave Energies)
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16 pages, 1638 KiB  
Article
Low-Frequency Sound Propagation in an Underwater Waveguide with a Giant Gassy Pockmark
by Alexander A. Komissarov, Denis V. Makarov, Andrey O. Kholmogorov and Renat B. Shakirov
J. Mar. Sci. Eng. 2023, 11(1), 211; https://doi.org/10.3390/jmse11010211 - 13 Jan 2023
Cited by 5 | Viewed by 1449
Abstract
Bottom formations known as pockmarks basically arise due to extensive gas emission. Active pockmarks are characterized by exceptionally high gas saturation and substantially reduced sound speed. The latter circumstance leads to strong attenuation of sound waves contacting with a pockmark. In the present [...] Read more.
Bottom formations known as pockmarks basically arise due to extensive gas emission. Active pockmarks are characterized by exceptionally high gas saturation and substantially reduced sound speed. The latter circumstance leads to strong attenuation of sound waves contacting with a pockmark. In the present paper, we study low-frequency sound propagation in a 10-km long waveguide crossing a giant pockmark. A new method of acoustic waveguide scanning based on measurement of the wavefield propagator is represented. This method allows one to explore attenuation anomalies associated with the presence of the gas-saturated bottom region. In particular, one can find out which beams fall into a pockmark area and therefore experience strong losses. Identifying such beams, as well as beams which avoid pockmark-assisted losses, one can estimate probable locations of the pockmark segment in the waveguide, provided information about the background medium is sufficient. Full article
(This article belongs to the Special Issue Sound Scattering in the Ocean)
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10 pages, 1967 KiB  
Article
Differences in the Fate of Surface and Subsurface Microplastics: A Case Study in the Central Atlantic
by Igor Zhdanov, Svetlana Pakhomova, Anfisa Berezina, Ksenia Silvestrova, Natalia Stepanova and Evgeniy Yakushev
J. Mar. Sci. Eng. 2023, 11(1), 210; https://doi.org/10.3390/jmse11010210 - 13 Jan 2023
Cited by 3 | Viewed by 1691
Abstract
Plastic is recognized as a threat to marine ecosystems, and estimating the level of plastic and microplastics (MPs) pollution of the World Ocean is, nowadays, the goal of many studies. However, the use of different methods for the sampling and analysis of MPs [...] Read more.
Plastic is recognized as a threat to marine ecosystems, and estimating the level of plastic and microplastics (MPs) pollution of the World Ocean is, nowadays, the goal of many studies. However, the use of different methods for the sampling and analysis of MPs leads to the problem of comparing the results obtained. Studies on surface MPs pollution of the surface sea water are based on the application of the manta or neuston nets that collect water from the upper 10–20 cm layer (the “surface” MPs) or submersible pumping systems that collect water from the water layer 3 to 5 m below the sea surface (the “subsurface” MPs). These two techniques allow the collection of particles of different size fractions, i.e., >300 µm for the surface MPs and >100 µm for the subsurface MP. However, it is shown that microplastics found in the surface and subsurface layers differ not only in the size of the items found, but also in morphology, types of polymers, abundance, weight concentration and their spatial distribution. Different hydrodynamic processes affect the fate of the plastic found exactly at the sea surface and several meters deeper. The aim of this work was to study the distribution of surface and subsurface MPs and to reveal an influence of oceanographic conditions on their spatial distribution, using as an example the open ocean waters of the Central Atlantic. Full article
(This article belongs to the Special Issue Marine Litter and Sustainability of Ocean Ecosystems)
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17 pages, 5656 KiB  
Article
The Interannual Variations of Summer Ichthyoplankton in the Pearl River Estuary as a Response to Climate Change
by Shuofu Li, Jianguo He and Zhigang Lai
J. Mar. Sci. Eng. 2023, 11(1), 209; https://doi.org/10.3390/jmse11010209 - 13 Jan 2023
Cited by 2 | Viewed by 2795
Abstract
The impacts of climate change on ichthyoplankton have barely been examined in the Pearl River estuary (PRE). Using the fish larvae and eggs caught in the estuary in the summer from 2003 to 2018 (except for the years 2004 and 2008), the spatial [...] Read more.
The impacts of climate change on ichthyoplankton have barely been examined in the Pearl River estuary (PRE). Using the fish larvae and eggs caught in the estuary in the summer from 2003 to 2018 (except for the years 2004 and 2008), the spatial and temporal variations in ichthyoplankton’s abundance, species composition, and community structure were examined and linked to the variability of the climate system. A positive/negative correlation was found between the abundance and taxonomic diversity of the fish larvae and the monthly Oceanic Niño Index. However, the variation in larval fish’s species diversity was in phase with climate change, while the variation in larval fish’s abundance had a 3-month lag behind the climate variability. The different phases of the correlations reflect a progressive change in the ichthyoplankton dynamics under the influence of climate. Furthermore, during the period of the study, the regional climate underwent an obvious transition from a “cold” to a “warm” state in the early 2010s. Associated with that, it was found that both the abundance and species composition of the ichthyoplankton exhibit a significant change around that time, particularly for the fish larvae. A further examination of the ichthyoplankton’s horizontal distributions suggests that the assemblage of ichthyoplankton in the PRE is sensitive to the La Niña conditions. This leads to an overall reduction in ichthyoplankton’s abundance and less seaward spreading of the assemblage, implying the possible impact of climate change on river discharge and then the estuarine environment. Full article
(This article belongs to the Section Marine Ecology)
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18 pages, 5335 KiB  
Article
Optimization of a Regional Marine Environment Mobile Observation Network Based on Deep Reinforcement Learning
by Yuxin Zhao, Yanlong Liu and Xiong Deng
J. Mar. Sci. Eng. 2023, 11(1), 208; https://doi.org/10.3390/jmse11010208 - 12 Jan 2023
Cited by 1 | Viewed by 1303
Abstract
The observation path planning of an ocean mobile observation network is an important part of the ocean mobile observation system. With the aim of developing a traditional algorithm to solve the observation path of the mobile observation network, a complex objective function needs [...] Read more.
The observation path planning of an ocean mobile observation network is an important part of the ocean mobile observation system. With the aim of developing a traditional algorithm to solve the observation path of the mobile observation network, a complex objective function needs to be constructed, and an improved deep reinforcement learning algorithm is proposed. The improved deep reinforcement learning algorithm does not need to establish the objective function. The agent samples the marine environment information by exploring and receiving feedback from the environment. Focusing on the real-time dynamic variability of the marine environment, our experiment shows that adding bidirectional recurrency to the Deep Q-network allows the Q-network to better estimate the underlying system state. Compared with the results of existing algorithms, the improved deep reinforcement learning algorithm can effectively improve the sampling efficiency of the observation platform. To improve the prediction accuracy of the marine environment numerical prediction system, we conduct sampling path experiments on a single platform, double platform, and five platforms. The experimental results show that increasing the number of observation platforms can effectively improve the prediction accuracy of the numerical prediction system, but when the number of observation platforms exceeds 2, increasing the number of observation platforms will not improve the prediction accuracy, and there is a certain degree of decline. In addition, in the multi-platform experiment, the improved deep reinforcement learning algorithm is compared with the unimproved algorithm, and the results show that the proposed algorithm is better than the existing algorithm. Full article
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26 pages, 4077 KiB  
Article
Date-Driven Tracking Control via Fuzzy-State Observer for AUV under Uncertain Disturbance and Time-Delay
by Chengxi Wu, Yuewei Dai, Liang Shan and Zhiyu Zhu
J. Mar. Sci. Eng. 2023, 11(1), 207; https://doi.org/10.3390/jmse11010207 - 12 Jan 2023
Cited by 3 | Viewed by 1432
Abstract
This paper focuses on developing a data-driven trajectory tracking control approach for autonomous underwater vehicles (AUV) under uncertain external disturbance and time-delay. A novel model-free adaptive predictive control (MFAPC) approach based on a fuzzy state observer (FSO) was designed to achieve high precision. [...] Read more.
This paper focuses on developing a data-driven trajectory tracking control approach for autonomous underwater vehicles (AUV) under uncertain external disturbance and time-delay. A novel model-free adaptive predictive control (MFAPC) approach based on a fuzzy state observer (FSO) was designed to achieve high precision. Concretely, the mathematical model of AUV motion was analyzed, and simplified via model decoupling, thus providing the model basis with an explicit physical explanation for the controller. Second, the MFAPC scheme for a multiple-inputs and multiple-outputs (MIMO) discrete time system was derived, that estimates system external disturbance. The controller can online estimate and predictive time-varying parameter pseudo-Jacobian matrix (PJM) to establish equivalent state space data-model for AUV motion system. Third, the Takagi–Sugeno (T–S) fuzzy model based state observer was designed to combine with the MFAPC scheme for the first time, which was used to online decline the state error generated by system uncertain time-delay. In addition, the stability of the proposed control scheme was analyzed. Finally, two trajectory tracking scenarios were designed to verify the effectiveness and robustness of the proposed FMFAPC scheme, and the simulations are implemented using the realistic parameters of T-SEA AUV. Full article
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13 pages, 5627 KiB  
Article
Development of Electromagnetic Current Meter for Marine Environment
by Shizhe Chen, Yushang Wu, Shixuan Liu, Yingdong Yang, Xiaozheng Wan, Xianglong Yang, Keke Zhang, Bo Wang and Xingkui Yan
J. Mar. Sci. Eng. 2023, 11(1), 206; https://doi.org/10.3390/jmse11010206 - 12 Jan 2023
Cited by 1 | Viewed by 2370
Abstract
Ocean current is one of the most important parameters in ocean observation, and ocean current measurement based on electromagnetic induction is becoming more and more important because of its advantages such as simple structure and high measurement accuracy. However, it is difficult to [...] Read more.
Ocean current is one of the most important parameters in ocean observation, and ocean current measurement based on electromagnetic induction is becoming more and more important because of its advantages such as simple structure and high measurement accuracy. However, it is difficult to detect weak current signals in a complex marine environment. In this paper, an electromagnetic induction current measurement scheme based on lock-in amplification technology is proposed. Key technologies such as the evaluation of induced current intensity, overall design, circuit design, and orientation design of the current meter were studied. The prototype of the electromagnetic current meter was developed and tested in the laboratory and at sea. The repeatability of current velocity and current direction was higher than 1.5 cm/s and 1.5°, respectively. A comparison test between the electromagnetic current meter prototype and Nortek ADCP (Acoustic Doppler Current Profiler) installed on a buoy at sea was carried out, and the correlation coefficients of the current velocity and current direction datum were 0.90 and 0.96, respectively. Through continuous on-site and fault-free operations at sea, the experimental data show that the electromagnetic current meter has good adaptability at sea, which provides feasible technical and equipment support for ocean current observation. Full article
(This article belongs to the Special Issue Advances in Sensor Technology in Smart Ships and Offshore Facilities)
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17 pages, 6125 KiB  
Article
A Simple Bias Correction Scheme in Ocean Data Assimilation
by Changxiang Yan and Jiang Zhu
J. Mar. Sci. Eng. 2023, 11(1), 205; https://doi.org/10.3390/jmse11010205 - 12 Jan 2023
Cited by 2 | Viewed by 1614
Abstract
The mode bias is present and time-dependent due to imperfect configurations. Data assimilation is the process by which observations are used to correct the model forecast, and is affected by the bias. How to reduce the bias is an important issue. This paper [...] Read more.
The mode bias is present and time-dependent due to imperfect configurations. Data assimilation is the process by which observations are used to correct the model forecast, and is affected by the bias. How to reduce the bias is an important issue. This paper investigates the roles of a simple bias correction scheme in ocean data assimilation. In this scheme, the misfits between modeled and monthly temperature and salinity with interannual variability from the Met Office Hadley Centre subsurface temperature and salinity data set (EN4.2.2) are used for the innovations in assimilation via the Ensemble Optimal Interpolation method. Two assimilation experiments are implemented to evaluate the impacts of bias correction. The first experiment is a data assimilation system without bias correction. In the second experiment, the bias correction is applied in assimilation. For comparison, the nature run with no assimilation and no bias correction is also conducted. When the bias correction is not applied, the assimilation alone leads to a rising trend in the heat and salt content that is not found in the observations. It is a spurious temporal variability due to the effect of the bias on the data assimilation. Meanwhile, the assimilation experiment without bias correction also produces significant negative impacts on the subsurface salinity. The experiment with bias correction performs best with notable improvements over the results of the other two experiments. Full article
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18 pages, 3916 KiB  
Article
Analysis of the Sabellaria spinulosa Bioconstruction Growth in a Laboratory
by Stefania Lisco, Tamara Lazic, Cataldo Pierri, Daniela Mele, Alessia de Luca and Massimo Moretti
J. Mar. Sci. Eng. 2023, 11(1), 204; https://doi.org/10.3390/jmse11010204 - 12 Jan 2023
Cited by 1 | Viewed by 1395
Abstract
Sabellaria spinulosa (Leukhart, 1849) is a suspension feeding polychaeta that lives in tubes consisting of terrigenous particles captured by the worm itself. They form impressive reefs containing millions of worm tubes. In temperate marine areas, under optimal environmental conditions, these structures can become [...] Read more.
Sabellaria spinulosa (Leukhart, 1849) is a suspension feeding polychaeta that lives in tubes consisting of terrigenous particles captured by the worm itself. They form impressive reefs containing millions of worm tubes. In temperate marine areas, under optimal environmental conditions, these structures can become natural breakwaters and can play an active role in sandy beaches’ defense. In this work, we report procedures aimed to analyze the growth of S. spinulosa bioconstructions in laboratory. By collecting biological replicas from a wild reef, this study aimed to identify sedimentological characteristics of sands that induce faster tube growth. During the tank experiments, the grain size and mineralogy of the sand were modified. By employing thin sections and X-ray microtomography analyses, the structures observed and measured during and after the tests were analogous to those naturally formed. The fastest growth was recorded in the presence of bioclastic sands with a grain size between 125 and 350 μm. Defining the physical conditions that induce faster growth is fundamental for the defense of these vulnerable habitats but also the surrounding marine environment. This study also lays the foundations for coastal protection interventions in which bioconstructions grown in the tank could be directly implanted on submerged natural and artificial substrates that are already present in situ. Full article
(This article belongs to the Section Marine Environmental Science)
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