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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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20 pages, 5413 KiB  
Review
A Comprehensive Review on Design, Monitoring, and Failure in Fixed Offshore Platforms
by Nima Amiri, Mohammad Shaterabadi, Kazem Reza Kashyzadeh and Mahmoud Chizari
J. Mar. Sci. Eng. 2021, 9(12), 1349; https://doi.org/10.3390/jmse9121349 - 30 Nov 2021
Cited by 37 | Viewed by 6144
Abstract
Offshore platforms have had diverse applications in the marine industry, for example, oil or gas platforms can provide facilities to store the oil and gas before transport those to refineries. Offshore wind turbines are another well-known use of the offshore platform for generating [...] Read more.
Offshore platforms have had diverse applications in the marine industry, for example, oil or gas platforms can provide facilities to store the oil and gas before transport those to refineries. Offshore wind turbines are another well-known use of the offshore platform for generating power. As platforms encounter various strong forces from water and wind currents, the materials used for these structures are mainly steel or concrete. These platforms are classified into different types, according to the depth of water and their applications. In addition, offshore platforms, as artificial reefs may be used for decades at different marine conditions. Consequently, their design and maintenance are very important, otherwise, they can cause irreparable damage to the environment. This paper presents the latest and most significant design and monitoring methods, such as the optimal probabilistic seismic demand model, multi-objective optimization, dynamic response assessment, robust fault-tolerant control, etc., under different environmental and geographical conditions. Moreover, the effective factors on the life and failure of these offshore structures are comprehensively introduced to enhance awareness of them, which can be very helpful to improve the design and construction of more reliable and durable structures. Full article
(This article belongs to the Special Issue Failure Analysis of Marine Structure)
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33 pages, 12259 KiB  
Article
Assessment of Extreme Wave Impact on Coastal Decks with Different Geometries via the Arbitrary Lagrangian-Eulerian Method
by Tao Xiang and Denis Istrati
J. Mar. Sci. Eng. 2021, 9(12), 1342; https://doi.org/10.3390/jmse9121342 - 29 Nov 2021
Cited by 47 | Viewed by 4128
Abstract
Given the documented wave-induced damage of elevated coastal decks during extreme natural hazards (e.g., hurricanes) in the last two decades, it is of utmost significance to decipher the wave-structure-interaction of complex deck geometries and quantify the associated loads. Therefore, this study focuses on [...] Read more.
Given the documented wave-induced damage of elevated coastal decks during extreme natural hazards (e.g., hurricanes) in the last two decades, it is of utmost significance to decipher the wave-structure-interaction of complex deck geometries and quantify the associated loads. Therefore, this study focuses on the assessment of solitary wave impact on open-girder decks that allow the air to escape from the sides. To this end, an arbitrary Lagrangian-Eulerian (ALE) numerical method with a multi-phase compressible formulation is used for the development of three-dimensional hydrodynamic models, which are validated against a large-scale experimental dataset of a coastal deck. Using the validated model as a baseline, a parametric investigation of different deck geometries with a varying number of girders Ng and three different widths, was conducted. The results reveal that the Ng of a superstructure has a complex role and that for small wave heights the horizontal and uplift forces increase with the Ng, while for large waves the opposite happens. If the Ng is small the wave particles accelerate after the initial impact on the offshore girder leading to a more violent slamming on the onshore part of the deck and larger pressures and forces, however, if Ng is large then unsynchronized eddies are formed in each chamber, which dissipate energy and apply out-of-phase pressures that result in multiple but weaker impacts on the deck. The decomposition of the total loads into slamming and quasi-static components, reveals surprisingly consistent trends for all the simulated waves, which facilitates the development of predictive load equations. These new equations, which are a function of Ng and are limited by the ratio of the wavelength to the deck width, provide more accurate predictions than existing empirical methods, and are expected to be useful to both engineers and researchers working towards the development of resilient coastal infrastructure. Full article
(This article belongs to the Special Issue Performance of Transportation Systems Subjected to Extreme Hydrodynamic Events)
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21 pages, 9006 KiB  
Article
Unprecedented Outbreak of Harmful Algae in Pacific Coastal Waters off Southeast Hokkaido, Japan, during Late Summer 2021 after Record-Breaking Marine Heatwaves
by Hiroshi Kuroda, Tomonori Azumaya, Takashi Setou and Natsuki Hasegawa
J. Mar. Sci. Eng. 2021, 9(12), 1335; https://doi.org/10.3390/jmse9121335 - 27 Nov 2021
Cited by 29 | Viewed by 4508
Abstract
Unprecedented large-scale harmful algae blooms (HABs) were reported in coastal waters off the south-eastern coast of Hokkaido, Japan, in mid-to-late September 2021, about a month after very intense and extensive marine heatwaves subsided. To understand the physical–biological processes associated with development of the [...] Read more.
Unprecedented large-scale harmful algae blooms (HABs) were reported in coastal waters off the south-eastern coast of Hokkaido, Japan, in mid-to-late September 2021, about a month after very intense and extensive marine heatwaves subsided. To understand the physical–biological processes associated with development of the HABs, we conducted analyses via a combination of realistic ocean circulation models, particle-tracking simulations, and satellite measurements. The satellite-derived chlorophyll concentrations (SCCs) and areal extent of the high SCCs associated with the HABs were the highest recorded since 1998. More specifically, the extent of SCCs exceeding 5 or 10 mg m−3 started to slowly increase after 20 August, when the marine heatwaves subsided, intermittently exceeded the climatological daily maximum after late August, and reached record-breaking extremes in mid-to-late September. About 70% of the SCCs that exceeded 10 mg m−3 occurred in places where water depths were <300 m, i.e., coastal shelf waters. The high SCCs were also tightly linked with low-salinity water (e.g., subarctic Oyashio and river-influenced waters). High-salinity subtropical water (e.g., Soya Warm Current water) appeared to suppress the occurrence of HABs. The expansion of the area of high SCCs seemed to be synchronized with the deepening of surface mixed layer depths in subarctic waters on the Pacific shelves. That deepening began around 10 August, when the marine heatwaves weakened abruptly. However, another mechanism was needed to explain the intensification of the SCCs in very nearshore waters off southeast Hokkaido. Particle-tracking simulations based on ocean circulation models identified three potential source areas of the HABs: the Pacific Ocean east of the Kamchatka Peninsula, the Sea of Japan, and the Sea of Okhotsk east of the Sakhalin Island. Different processes of HAB development were proposed because distance, time, and probability for transport of harmful algae from the potential source areas to the study region differed greatly between the three source areas. Full article
(This article belongs to the Special Issue Advances in Ocean Monitoring and Modeling for Marine Biology)
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30 pages, 6701 KiB  
Article
A Review of Maximum Power Point Tracking Algorithms for Wind Energy Conversion Systems
by Jayshree Pande, Paresh Nasikkar, Ketan Kotecha and Vijayakumar Varadarajan
J. Mar. Sci. Eng. 2021, 9(11), 1187; https://doi.org/10.3390/jmse9111187 - 27 Oct 2021
Cited by 83 | Viewed by 7967
Abstract
Renewable energy resources are gaining a lot of popularity. Several researchers have worked on the tracking and extraction of energy from these sources. In the past few decades, among the available green energy resources, wind energy has been the most attractive option among [...] Read more.
Renewable energy resources are gaining a lot of popularity. Several researchers have worked on the tracking and extraction of energy from these sources. In the past few decades, among the available green energy resources, wind energy has been the most attractive option among the resources available. It is imperative to use the maximum power available in the wind to achieve the wind turbine (WT) operation at maximum power. The maximum power point tracking (MPPT) algorithms are a pioneer in this context. Many research papers are contributed in this domain which necessitates a thorough review while choosing an appropriate technique. This paper comprehensively focuses on reviewing different algorithms in the past and present for tracking maximum power point, and capturing maximized output power from the wind energy conversion system (WECS). In this paper, the algorithms are classified based on the direct and indirect power measurement, hybrid and smart algorithms for tracking maximum power point, and they are compared, considering the parameters like complexity, convergence speed, use of sensors, memory requirement, need for knowledge of system parameters, etc. The immense popularity of the different versions of perturb and observe (P&O) based algorithms due to their various features is evident from the literature. The review reveals that the hybrid maximum power point tracking algorithms can use the advantages of the conventional methods and eliminate their drawbacks. Full article
(This article belongs to the Section Marine Energy)
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25 pages, 9463 KiB  
Article
Vertebrate Palaeoecology of the Pisco Formation (Miocene, Peru): Glimpses into the Ancient Humboldt Current Ecosystem
by Alberto Collareta, Olivier Lambert, Felix G. Marx, Christian de Muizon, Rafael Varas-Malca, Walter Landini, Giulia Bosio, Elisa Malinverno, Karen Gariboldi, Anna Gioncada, Mario Urbina and Giovanni Bianucci
J. Mar. Sci. Eng. 2021, 9(11), 1188; https://doi.org/10.3390/jmse9111188 - 27 Oct 2021
Cited by 23 | Viewed by 6202
Abstract
The northward-flowing Humboldt Current hosts perpetually high levels of productivity along the western coast of South America. Here, we aim to elucidate the deep-time history of this globally important ecosystem based on a detailed palaeoecological analysis of the exceptionally preserved middle–upper Miocene vertebrate [...] Read more.
The northward-flowing Humboldt Current hosts perpetually high levels of productivity along the western coast of South America. Here, we aim to elucidate the deep-time history of this globally important ecosystem based on a detailed palaeoecological analysis of the exceptionally preserved middle–upper Miocene vertebrate assemblages of the Pisco Formation of the East Pisco Basin, southern Peru. We summarise observations on hundreds of fossil whales, dolphins, seals, seabirds, turtles, crocodiles, sharks, rays, and bony fishes to reconstruct ecological relationships in the wake of the Middle Miocene Climatic Optimum, and the marked cooling that followed it. The lowermost, middle Miocene Pisco sequence (P0) and its vertebrate assemblage testify to a warm, semi-enclosed, near-shore palaeoenvironment. During the first part of the Tortonian (P1), high productivity within a prominent upwelling system supported a diverse assemblage of mesopredators, at least some of which permanently resided in the Pisco embayment and used it as a nursery or breeding/calving area. Younger portions of the Pisco Formation (P2) reveal a more open setting, with wide-ranging species like rorquals increasingly dominating the vertebrate assemblage, but also local differences reflecting distance from the coast. Like today, these ancient precursors of the modern Humboldt Current Ecosystem were based on sardines, but notably differed from their present-day equivalent in being dominated by extremely large-bodied apex predators like Livyatan melvillei and Carcharocles megalodon. Full article
(This article belongs to the Special Issue Feature Papers in Marine Biology)
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27 pages, 4632 KiB  
Article
Explaining a Deep Reinforcement Learning Docking Agent Using Linear Model Trees with User Adapted Visualization
by Vilde B. Gjærum, Inga Strümke, Ole Andreas Alsos and Anastasios M. Lekkas
J. Mar. Sci. Eng. 2021, 9(11), 1178; https://doi.org/10.3390/jmse9111178 - 26 Oct 2021
Cited by 13 | Viewed by 3161
Abstract
Deep neural networks (DNNs) can be useful within the marine robotics field, but their utility value is restricted by their black-box nature. Explainable artificial intelligence methods attempt to understand how such black-boxes make their decisions. In this work, linear model trees (LMTs) are [...] Read more.
Deep neural networks (DNNs) can be useful within the marine robotics field, but their utility value is restricted by their black-box nature. Explainable artificial intelligence methods attempt to understand how such black-boxes make their decisions. In this work, linear model trees (LMTs) are used to approximate the DNN controlling an autonomous surface vessel (ASV) in a simulated environment and then run in parallel with the DNN to give explanations in the form of feature attributions in real-time. How well a model can be understood depends not only on the explanation itself, but also on how well it is presented and adapted to the receiver of said explanation. Different end-users may need both different types of explanations, as well as different representations of these. The main contributions of this work are (1) significantly improving both the accuracy and the build time of a greedy approach for building LMTs by introducing ordering of features in the splitting of the tree, (2) giving an overview of the characteristics of the seafarer/operator and the developer as two different end-users of the agent and receiver of the explanations, and (3) suggesting a visualization of the docking agent, the environment, and the feature attributions given by the LMT for when the developer is the end-user of the system, and another visualization for when the seafarer or operator is the end-user, based on their different characteristics. Full article
(This article belongs to the Special Issue Explainable AI and Evaluation of Algorithms for Autonomous Marine Vehicles)
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18 pages, 1961 KiB  
Article
Walleye Pollock Gadus chalcogrammus, a Species with Continuous Range from the Norwegian Sea to Korea, Japan, and California: New Records from the Siberian Arctic
by Alexei M. Orlov, Maxim O. Rybakov, Elena V. Vedishcheva, Alexander A. Volkov and Svetlana Yu. Orlova
J. Mar. Sci. Eng. 2021, 9(10), 1141; https://doi.org/10.3390/jmse9101141 - 17 Oct 2021
Cited by 21 | Viewed by 3530
Abstract
The first records of walleye pollock Gadus chalcogrammus Pallas, 1814 in the seas of the Siberian Arctic (the Laptev Sea, the Kara Sea, the southeastern Barents Sea), are documented. Information about the external morphology (morphometric and meristic characters), photos of sagittal otoliths and [...] Read more.
The first records of walleye pollock Gadus chalcogrammus Pallas, 1814 in the seas of the Siberian Arctic (the Laptev Sea, the Kara Sea, the southeastern Barents Sea), are documented. Information about the external morphology (morphometric and meristic characters), photos of sagittal otoliths and fish, and data on the sequences of the CO1 mtDNA gene are presented. The results of a comparative analysis indicate that walleye pollock caught in the Siberian Arctic do not differ in principle from North Pacific and North Atlantic individuals. Previous conclusions about the conspecificity of the walleye and Norwegian pollock Theragra finnmarchica are confirmed. New captures of walleye pollock in the Siberian Arctic allow us to formulate a hypothesis about its continuous species’ range from the coasts of Norway in the North Atlantic to the coasts of Korea, Japan, and California in the North Pacific. The few records of walleye pollock in the North Atlantic originate from the North Pacific due to the transport of early pelagic juveniles to the Arctic by currents through the Bering Strait and further active westward migrations of individuals which have switched to the bentho-pelagic mode of life. Full article
(This article belongs to the Special Issue Deepwater Fishes)
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19 pages, 1960 KiB  
Article
Applying Artificial Intelligence Methods to Detect and Classify Fish Calls from the Northern Gulf of Mexico
by Emily E. Waddell, Jeppe H. Rasmussen and Ana Širović
J. Mar. Sci. Eng. 2021, 9(10), 1128; https://doi.org/10.3390/jmse9101128 - 15 Oct 2021
Cited by 14 | Viewed by 3638
Abstract
Passive acoustic monitoring is a method that is commonly used to collect long-term data on soniferous animal presence and abundance. However, these large datasets require substantial effort for manual analysis; therefore, automatic methods are a more effective way to conduct these analyses and [...] Read more.
Passive acoustic monitoring is a method that is commonly used to collect long-term data on soniferous animal presence and abundance. However, these large datasets require substantial effort for manual analysis; therefore, automatic methods are a more effective way to conduct these analyses and extract points of interest. In this study, an energy detector and subsequent pre-trained neural network were used to detect and classify six fish call types from a long-term dataset collected in the northern Gulf of Mexico. The development of this two-step methodology and its performance are the focus of this paper. The energy detector by itself had a high recall rate (>84%), but very low precision; however, a subsequent neural network was used to classify detected signals and remove noise from the detections. Image augmentation and iterative training were used to optimize classification and compensate for the low number of training images for two call types. The classifier had a relatively high average overall accuracy (>87%), but classifier average recall and precision varied greatly for each fish call type (recall: 39–91%; precision: 26–94%). This coupled methodology expedites call extraction and classification and can be applied to other datasets that have multiple, highly variable calls. Full article
(This article belongs to the Special Issue Fish Acoustic Communities in a Conservation Perspective)
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21 pages, 5116 KiB  
Review
Natural Processes and Anthropogenic Activity in the Indus River Sedimentary Environment in Pakistan: A Critical Review
by Usman Khan, Hammad Tariq Janjuhah, George Kontakiotis, Adnanul Rehman and Stergios D. Zarkogiannis
J. Mar. Sci. Eng. 2021, 9(10), 1109; https://doi.org/10.3390/jmse9101109 - 12 Oct 2021
Cited by 25 | Viewed by 11109
Abstract
The Indus River is Asia’s longest river, having its origin in the Tibet Mountain northwest of Pakistan. Routed from northern Gilgit and flowing to the plains, the river passes through several provinces and is connected by numerous small and large tributaries. The river [...] Read more.
The Indus River is Asia’s longest river, having its origin in the Tibet Mountain northwest of Pakistan. Routed from northern Gilgit and flowing to the plains, the river passes through several provinces and is connected by numerous small and large tributaries. The river was formed tectonically due to the collusion of the Indian and Eurasian plates, which is referred to as the Indus suture Plains zone (ISPZ). The geological setting of the study area is mainly composed of igneous and metamorphic rocks. The river passed through a variety of climatic zones and areas, although the predominant climate is subtropic arid and sub arid to subequatorial. Locally and globally, anthropogenic activities such as building, dams, and water canals for irrigation purposes, mining exploration, and industries and factories all affected the physical and chemical behaviors of the sediments in various rivers. The main effect of human activities is the reworking of weathered soil smectite, a chemical weathering indicator that rises in the offshore record about 5000 years ago. This material indicates increased transport of stronger chemically weathered material, which may result from agriculture-induced erosion of older soil. However, we also see evidence for the incision of large rivers into the floodplain, which is also driving the reworking of this type of material, so the signal may be a combination of the two. Sediments undergo significant changes in form and size due to clashing with one another in the high-charge river. Full article
(This article belongs to the Special Issue Recent Advances in Geological Oceanography)
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37 pages, 4797 KiB  
Review
Buckling Mechanism of Offshore Pipelines: A State of the Art
by Debtanu Seth, Bappaditya Manna, Jagdish Telangrao Shahu, Tiago Fazeres-Ferradosa, Francisco Taveira Pinto and Paulo Jorge Rosa-Santos
J. Mar. Sci. Eng. 2021, 9(10), 1074; https://doi.org/10.3390/jmse9101074 - 1 Oct 2021
Cited by 15 | Viewed by 7989
Abstract
The buckling analysis of an offshore pipeline refers to the analysis of temperature-induced uplift and lateral buckling of pipelines by analytical, numerical, and experimental means. Thus, the current study discusses different research performed on thermal pipe-buckling and the different factors affecting the pipeline’s [...] Read more.
The buckling analysis of an offshore pipeline refers to the analysis of temperature-induced uplift and lateral buckling of pipelines by analytical, numerical, and experimental means. Thus, the current study discusses different research performed on thermal pipe-buckling and the different factors affecting the pipeline’s buckling behaviour. The current study consists of the dependency of the pipe-buckling direction on the seabed features and burial condition; the pre-buckling and post-buckling load-displacement behaviour of the pipeline; the effect of soil weight, burial depth, axial resistance, imperfection amplitude, temperature difference, interface tensile capacity, and diameter-to-thickness ratio on the uplift and lateral resistance; and the failure mechanism of the pipeline. Moreover, the effect of external hydrostatic pressure, bending moment, initial imperfection, sectional rigidity, and diameter-to-thickness ratio of the pipeline on collapse load of the pipeline during buckling were also included in the study. This work highlights the existing knowledge on the topic along with the main findings performed up to recent research. In addition, the reference literature on the topic is given and analysed to contribute to a broad perspective on buckling analysis of offshore pipelines. This work provides a starting point to identify further innovation and development guidelines for professionals and researchers dealing with offshore pipelines, which are key infrastructures for numerous maritime applications. Full article
(This article belongs to the Section Ocean Engineering)
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12 pages, 3678 KiB  
Article
1D–3D Coupling Algorithm of Gas Flow for the Valve System in a Compression Ignition Engine
by Kyeong-Ju Kong
J. Mar. Sci. Eng. 2021, 9(10), 1061; https://doi.org/10.3390/jmse9101061 - 27 Sep 2021
Viewed by 2234
Abstract
Emission control devices such as selective catalytic reduction (SCR), exhaust gas recirculation (EGR), and scrubbers were installed in the compression ignition (CI) engine, and flow analysis of intake air and exhaust gas was required to predict the performance of the CI engine and [...] Read more.
Emission control devices such as selective catalytic reduction (SCR), exhaust gas recirculation (EGR), and scrubbers were installed in the compression ignition (CI) engine, and flow analysis of intake air and exhaust gas was required to predict the performance of the CI engine and emission control devices. In order to analyze such gas flow, it was inefficient to comprehensively analyze the engine’s cylinder and intake/exhaust systems because it takes a lot of computation time. Therefore, there is a need for a method that can quickly calculate the gas flow of the CI engine in order to shorten the development process of emission control devices. It can be efficient and quickly calculated if only the parts that require detailed observation among the intake/exhaust gas flow of the CI engine are analyzed in a 3D approach and the rest are analyzed in a 1D approach. In this study, an algorithm for gas flow analysis was developed by coupling 1D and 3D in the valve systems and comparing with experimental results for validation. Analyzing the intake/exhaust gas flow of the CI engine in a 3D approach took about 7 days for computation, but using the developed 1D–3D coupling algorithm, it could be computed within 30 min. Compared with the experimental results, the exhaust pipe pressure occurred an error within 1.80%, confirming the accuracy and it was possible to observe the detailed flow by showing the contour results for the part analyzed in the 3D zone. As a result, it was possible to accurately and quickly calculate the gas flow of the CI engine using the 1D–3D coupling algorithm applied to the valve system, and it was expected that it can be used to shorten the process for analyzing emission control devices, including predicting the performance of the CI engine. Full article
(This article belongs to the Special Issue Experiments and Numerical Analysis of Flow)
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14 pages, 3493 KiB  
Article
Optimal Ways of Unloading and Loading Operations under Arctic Conditions
by Marat Eseev and Dmitry Makarov
J. Mar. Sci. Eng. 2021, 9(10), 1050; https://doi.org/10.3390/jmse9101050 - 24 Sep 2021
Viewed by 2669
Abstract
Usually, loading and unloading of cargo ships takes place in ports that are equipped with the infrastructure necessary to carry out such operations. In the Arctic, often a helicopter is the only way to get the cargo to the right place. Finding the [...] Read more.
Usually, loading and unloading of cargo ships takes place in ports that are equipped with the infrastructure necessary to carry out such operations. In the Arctic, often a helicopter is the only way to get the cargo to the right place. Finding the optimal geographic location for unloading a ship using helicopters is an important task. It is necessary to create a support system for making the right decisions in such situations. Mathematical modeling has been used to find the geographical location that ensures the most favorable and quickest delivery of cargo from a vessel to its destination, using a helicopter. A criterion has also been found in which the search for the optimum point is a more rational way of unloading the vessel compared to other discharge options. The maps of the economic benefits of loading and unloading operations in this model have been developed. Using the example of the developed model, it is shown that during the transportation of goods in Ob Bay, significant economic and temporary advantages can be obtained. The developed model can be extended to the case of cargo delivery not only in the Arctic conditions, but also where the transport infrastructure is insufficiently developed. Full article
(This article belongs to the Special Issue Modern Technologies and Methods of Development for the Maritime Industry)
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18 pages, 4959 KiB  
Article
Bathymetric Data Requirements for Operational Coastal Erosion Forecasting Using XBeach
by Nashwan Matheen, Mitchell D. Harley, Ian L. Turner, Kristen D. Splinter, Joshua A. Simmons and Mandi C. Thran
J. Mar. Sci. Eng. 2021, 9(10), 1053; https://doi.org/10.3390/jmse9101053 - 24 Sep 2021
Cited by 17 | Viewed by 4445
Abstract
There is an increasing interest in the broad-scale implementation of coastal erosion early warning systems (EWS) with the goal of enhancing community preparedness to extreme coastal storm wave events. These emerging systems typically rely on process-based models to predict the storm-induced morphological change. [...] Read more.
There is an increasing interest in the broad-scale implementation of coastal erosion early warning systems (EWS) with the goal of enhancing community preparedness to extreme coastal storm wave events. These emerging systems typically rely on process-based models to predict the storm-induced morphological change. A key challenge with incorporating these models in EWSs is the need for up-to-date nearshore and surf zone bathymetry data, which is difficult to measure routinely, but potentially important for accurate erosion forecasting. This study evaluates the degree to which up-to-date bathymetry is required for accurate coastal erosion predictions using the morphodynamic model XBeach and, subsequently, whether a range of “representative” and/or “synthetic” bathymetries can be used for the bottom boundary, when a survey of the immediate pre-storm bathymetry is not available. Twelve storm events at two contrasting sites were modelled using six different bathymetry scenarios, including the expected “best case” bathymetry surveyed immediately pre-storm. These results indicate that alternative bathymetries can be used to obtain sub-aerial erosion predictions that are similar (and in some cases better) than those resulting from the use of an immediately pre-storm surveyed bathymetry, provided that rigorous model calibration is undertaken prior. This generalized finding is attributed to specific parametrizations in the XBeach model structure that are optimized during the calibration process to match the particular bottom boundary condition used. This study provides practical guidance for the selection of suitable nearshore bathymetry for use in operational coastal erosion EWSs. Full article
(This article belongs to the Special Issue Monitoring and Modelling of Coastal Environment)
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11 pages, 2130 KiB  
Article
Soil Fabric and Transitional Behavior in Completely Decomposed Granite: An Example of Well-Graded Soil
by Elsayed Elkamhawy, Huabin Wang, Tarek N. Salem, František Vranay and Martina Zelenakova
J. Mar. Sci. Eng. 2021, 9(10), 1046; https://doi.org/10.3390/jmse9101046 - 23 Sep 2021
Viewed by 2082
Abstract
Unlike sedimentary soils, limited studies have dealt with completely decomposed granite (CDG) soils, even though they are plentiful and used extensively in several engineering applications. In this paper, a set of triaxial compression tests have been conducted on well-graded intact and disturbed CDG [...] Read more.
Unlike sedimentary soils, limited studies have dealt with completely decomposed granite (CDG) soils, even though they are plentiful and used extensively in several engineering applications. In this paper, a set of triaxial compression tests have been conducted on well-graded intact and disturbed CDG soils to study the impact of the fabric on soil behavior. The soil behavior was robustly affected by the soil fabric and its mineral composition. The intact soil showed multiple parallel compression lines, while a unique isotropic compression line was present in the case of disturbed soil. Both the intact and disturbed soils showed unique critical state lines (CSL) in both the e-log p′ and q-p′ spaces. The intact soil showed behavior unlike other transitional soils that have both distinct isotropic compression lines ICLs and CSLs. The gradient of the unique ICL of the disturbed soil was much more than that of the parallel compression lines of the intact soil. In the intact soil, the slope of the unique CSL (M) in the q-p′ space was higher than that of the disturbed soil. The isotropic response was present for both the intact and disturbed soils after erasing the inherited anisotropy as the stress increased with irrecoverable volumetric change. Soil fabric is considered the dominant factor in the transitional behavior and such a mode of soil behavior is no longer restricted to gap-graded soil as previously thought. Full article
(This article belongs to the Section Geological Oceanography)
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19 pages, 692 KiB  
Article
Challenges for Zero-Emissions Ship
by Carlos A. Reusser and Joel R. Pérez Osses
J. Mar. Sci. Eng. 2021, 9(10), 1042; https://doi.org/10.3390/jmse9101042 - 22 Sep 2021
Cited by 31 | Viewed by 5517
Abstract
Due to the increasing impact of ship emissions on the environment and the preventive measures of current regulations introduced by the International Maritime Organization to significantly reduce them, the development of ocean-going all-electric ships has been addressed as a concept applied to achieve [...] Read more.
Due to the increasing impact of ship emissions on the environment and the preventive measures of current regulations introduced by the International Maritime Organization to significantly reduce them, the development of ocean-going all-electric ships has been addressed as a concept applied to achieve it. Being a promising technology considers the use of technology alternatives such as fuel cells, batteries, and supercapacitors together with the use of zero-carbon alternative fuels such as hydrogen (H2) and ammonia (NH3) as main energy sources. This article addresses a state-of-the-art on several challenges related to the ocean-going zero-emissions ship to achieve a zero-emissions shipping, based on the technology associated with hybrid and all-electric ship, and the zero-carbon fuels alternatives. In this respect, a transition from fossil fuel-based propulsion and auxiliary systems to a zero-emissions ship concept are related to the challenges to overcome the needs of energy density for these new alternatives energy sources compared to current fossil fuel options. The transitional process should consider a first step of hybridization of the propulsion and auxiliary systems of existing ships to get a baseline from where to move forward to a zero-emissions configuration for new designs. Full article
(This article belongs to the Special Issue Zero Emission Shipping)
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15 pages, 8359 KiB  
Article
The North Equatorial Countercurrent East of the Dateline, Its Variations and Its Relationship to the El Niño Event
by Yusuf Jati Wijaya, Ulung Jantama Wisha and Yukiharu Hisaki
J. Mar. Sci. Eng. 2021, 9(10), 1041; https://doi.org/10.3390/jmse9101041 - 22 Sep 2021
Cited by 4 | Viewed by 2262
Abstract
Using forty years (1978–2017) of Ocean Reanalysis System 4 (ORAS4) dataset, the purpose of this study is to investigate the fluctuation of the North Equatorial Countercurrent (NECC) to the east of the dateline in relation to the presence of three kinds of El [...] Read more.
Using forty years (1978–2017) of Ocean Reanalysis System 4 (ORAS4) dataset, the purpose of this study is to investigate the fluctuation of the North Equatorial Countercurrent (NECC) to the east of the dateline in relation to the presence of three kinds of El Niño events. From spring (MAM) through summer (JJA), we found that the NECC was stronger during the Eastern Pacific El Niño (EP El Niño) and the MIX El Niño than during the Central Pacific El Niño (CP El Niño). When it comes to winter (DJF), on the other hand, the NECC was stronger during the CP and MIX El Niño and weaker during the EP El Niño. This NECC variability was affected by the fluctuations of thermocline depth near the equatorial Pacific. Moreover, we also found that the seasonal southward shift of the NECC occurred between winter and spring, but the shift was absent during the CP and MIX El Niño events. This meridional shift was strongly affected by the local wind stress. Full article
(This article belongs to the Special Issue Sea Surface Temperature: From Observation to Applications)
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18 pages, 8438 KiB  
Article
A Design Method to Assess the Primary Strength of the Delta-Type VLFS
by Roy Gafter and Nitai Drimer
J. Mar. Sci. Eng. 2021, 9(9), 1026; https://doi.org/10.3390/jmse9091026 - 18 Sep 2021
Cited by 1 | Viewed by 2055
Abstract
Very large floating structure (VLFS) is a sustainable concept centered around creating solid platforms at sea. The Delta is a new type of VLFS, designed to withstand open-sea conditions and to form, in addition to a broad deck areas, a sheltered basin of [...] Read more.
Very large floating structure (VLFS) is a sustainable concept centered around creating solid platforms at sea. The Delta is a new type of VLFS, designed to withstand open-sea conditions and to form, in addition to a broad deck areas, a sheltered basin of year-round operability. The design of this unique hull relies on direct calculations in order to identify critical load cases and assess their load effects. This study formulates a theoretical procedure for the initial assessment of the primary strength. The procedure analytically integrates the floatation loads while the hull rests at hydrostatic equilibrium on a wave surface and obtains the vertical and horizontal bending moment. This preliminary assessment tool enables a fast review of many load cases and provides the basic insights necessary for a reasonable initial design. Using the procedure, we conducted a primary load assessment for the design of Delta. By calculating the load response to 588 load cases, we identified the critical load scenario and the maximal axial stress. As the stress was too high, we improved the geometry in order to reduce loads and assessed proper scantlings for the critical section. We present the formulation of the procedure, the validation of the results, and the implementation for the structural design of the Delta VLFS. Full article
(This article belongs to the Section Ocean Engineering)
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32 pages, 15064 KiB  
Review
AUV Trajectory Tracking Models and Control Strategies: A Review
by Daoliang Li and Ling Du
J. Mar. Sci. Eng. 2021, 9(9), 1020; https://doi.org/10.3390/jmse9091020 - 17 Sep 2021
Cited by 85 | Viewed by 11789
Abstract
Autonomous underwater vehicles (AUVs) have been widely used to perform underwater tasks. Due to the environmental disturbances, underactuated problems, system constraints, and system coupling, AUV trajectory tracking control is challenging. Thus, further investigation of dynamic characteristics and trajectory tracking control methods of the [...] Read more.
Autonomous underwater vehicles (AUVs) have been widely used to perform underwater tasks. Due to the environmental disturbances, underactuated problems, system constraints, and system coupling, AUV trajectory tracking control is challenging. Thus, further investigation of dynamic characteristics and trajectory tracking control methods of the AUV motion system will be of great importance to improve underwater task performance. An AUV controller must be able to cope with various challenges with the underwater vehicle, adaptively update the reference model, and overcome unexpected deviations. In order to identify modeling strategies and the best control practices, this paper presents an overview of the main factors of control-oriented models and control strategies for AUVs. In modeling, two fields are considered: (i) models that come from simplifications of Fossen’s equations; and (ii) system identification models. For each category, a brief description of the control-oriented modeling strategies is given. In the control field, three relevant aspects are considered: (i) significance of AUV trajectory tracking control, (ii) control strategies; and (iii) control performance. For each aspect, the most important features are explained. Furthermore, in the aspect of control strategies, mathematical modeling study and physical experiment study are introduced in detail. Finally, with the aim of establishing the acceptability of the reported modeling and control techniques, as well as challenges that remain open, a discussion and a case study are presented. The literature review shows the development of new control-oriented models, the research in the estimation of unknown inputs, and the development of more innovative control strategies for AUV trajectory tracking systems are still open problems that must be addressed in the short term. Full article
(This article belongs to the Section Ocean Engineering)
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12 pages, 1671 KiB  
Article
A Comparison of Traditional and Locally Novel Fishing Gear for the Exploitation of the Invasive Atlantic Blue Crab in the Eastern Adriatic Sea
by Luka Glamuzina, Alexis Conides, Giorgio Mancinelli and Branko Glamuzina
J. Mar. Sci. Eng. 2021, 9(9), 1019; https://doi.org/10.3390/jmse9091019 - 17 Sep 2021
Cited by 18 | Viewed by 3158
Abstract
The Atlantic Blue Crab Callinectes sapidus has been recognized as invasive in the Mediterranean Sea, where it now provides a significant contribution to artisanal fisheries. In this study, we compared the efficiency, selectivity, and productivity of American wire crab traps and traditional fyke [...] Read more.
The Atlantic Blue Crab Callinectes sapidus has been recognized as invasive in the Mediterranean Sea, where it now provides a significant contribution to artisanal fisheries. In this study, we compared the efficiency, selectivity, and productivity of American wire crab traps and traditional fyke nets for the capture of Blue Crabs in a study conducted from June to December 2019 in the Parila Lagoon (River Neretva Estuary, Croatia). A total of 7707 specimens were caught in 15 wire traps, comprising 6959 males and 749 females. The total catch using 50 traditional fyke traps was 1451 crabs, of which 1211 were males and 240 were females. In general, wire crab traps showed a higher capture selectivity and economic performance compared to fyke nets. The catch per unit effort (CPUE) was 102.76 kg for the American wire crab trap and 5.96 kg for the traditional fyke net. The CPUE of gravid female Blue Crabs was lower for the wire traps than the fyke nets. Herein, the utility of crab traps as selective fishing gear for the capture of Blue Crabs, and management tools for control of the reproductive and recruitment phases of the crab, are discussed, with the perspective of future exploitation of the species as a commercially valuable shellfish product in the Mediterranean. Full article
(This article belongs to the Special Issue Marine Fisheries Management)
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23 pages, 384 KiB  
Review
In Situ Aerobic Bioremediation of Sediments Polluted with Petroleum Hydrocarbons: A Critical Review
by Efsevia Fragkou, Eleftheria Antoniou, Ioannis Daliakopoulos, Thrassyvoulos Manios, Marianna Theodorakopoulou and Nicolas Kalogerakis
J. Mar. Sci. Eng. 2021, 9(9), 1003; https://doi.org/10.3390/jmse9091003 - 14 Sep 2021
Cited by 20 | Viewed by 5261
Abstract
Oil pollution has been a worldwide concern especially in environments where treatment is quite difficult to apply. Marine polluted sediments, in particular, constitute one of the most recalcitrant environments for bioremediation and are often the final repository of petroleum contaminants, as a result [...] Read more.
Oil pollution has been a worldwide concern especially in environments where treatment is quite difficult to apply. Marine polluted sediments, in particular, constitute one of the most recalcitrant environments for bioremediation and are often the final repository of petroleum contaminants, as a result of runoff and deposition. Aerobic hydrocarbon degraders present in the sediments are tackling the pollution under oxygen-limited or oxygen-depleted conditions. Research has focused on new ways to enhance bioremediation under anoxic conditions, however aerobic bioremediation is faster, and hence more effort should be made to sustain oxygen concentration levels. In this review, the different bioremediation techniques used for the decontamination of marine sediments are briefly discussed, and focus is primarily given to the different oxygenation methods used for enhancing aerobic bioremediation and the aeration methods that are suitable for in situ application, as well as state of the art technologies that make in situ aeration an appealing approach. Based on the technologies analyzed, suggestions are made for sediment bioremediation techniques in different marine environments. Full article
(This article belongs to the Topic From Coastal Engineering to Integrated Coastal Zone Management)
14 pages, 3367 KiB  
Article
Fin Whale (Balaenoptera physalus) in the Ligurian Sea: Preliminary Study on Acoustics Demonstrates Their Regular Occurrence in Autumn
by Laura Pintore, Virginia Sciacca, Salvatore Viola, Cristina Giacoma, Elena Papale and Giacomo Giorli
J. Mar. Sci. Eng. 2021, 9(9), 966; https://doi.org/10.3390/jmse9090966 - 6 Sep 2021
Cited by 5 | Viewed by 3570
Abstract
The patterns of movement of the fin whale (Balaenoptera physalus (Linnaeus, 1758)) in the Mediterranean Sea are still a matter of debate. Feeding aggregations are well known in the Corso-Liguro-Provençal Basin from July to September, but little is known for the autumn [...] Read more.
The patterns of movement of the fin whale (Balaenoptera physalus (Linnaeus, 1758)) in the Mediterranean Sea are still a matter of debate. Feeding aggregations are well known in the Corso-Liguro-Provençal Basin from July to September, but little is known for the autumn and winter seasons. Passive acoustic monitoring (PAM) was implemented in the Ligurian Sea to overcome this gap and to investigate the temporal and spatial variation of fin whale acoustic presence. From July to December 2011, five autonomous recorders were deployed at between 700 and 900 m depths. Fin whale calls were automatically detected almost every day, with higher vocalization rates in October, November, and December. Furthermore, daily vocalization rates were higher during light hours, and closer to the coast. These outcomes suggest that not all the individuals migrate, staying in the area also during autumn for feeding or breeding purposes. The dial cycle of vocalization might be related to feeding activities and zooplankton vertical migration, whereas the proximity to the coast can be explained by the morphology of the area that promotes the upwelling system. Although this work only represents a six-month period, certainly it suggests the need for a larger spatial and temporal PAM effort, crucial for species management and for mitigating possible impact of anthropogenic activities at the basin level. Full article
(This article belongs to the Special Issue Passive Acoustics to Study Marine and Freshwater Ecosystems)
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26 pages, 12618 KiB  
Article
Analysis of Composite Scrubber with Built-In Silencer for Marine Engines
by Myeong-rok Ryu and Kweonha Park
J. Mar. Sci. Eng. 2021, 9(9), 962; https://doi.org/10.3390/jmse9090962 - 3 Sep 2021
Cited by 6 | Viewed by 2563
Abstract
The International Maritime Organization (IMO) is strengthening regulations on reducing sulfur oxide emissions, and the demand for reducing exhaust noise affecting the environment of ships is also increasing. Various technologies have been developed to satisfy these needs. In this paper, a composite scrubber [...] Read more.
The International Maritime Organization (IMO) is strengthening regulations on reducing sulfur oxide emissions, and the demand for reducing exhaust noise affecting the environment of ships is also increasing. Various technologies have been developed to satisfy these needs. In this paper, a composite scrubber for ships that can simultaneously reduce sulfur oxide and noise was proposed, and the flow characteristics and noise characteristics were analyzed. For the silencer, vane type and resonate type were applied. In the case of the vane type, the effects of the direction, size, and location of the vane were analyzed, and in the case of the resonate type, the effects of the hole location and the number of holes were analyzed. The result shows that the length increase of the vane increased the average transmission loss and had a great effect, especially in the low frequency region. The transmission loss increased when the vane was installed outside, and the noise reduction effect was excellent when the vane was in the reverse direction. In the resonate type, increasing the number of holes is advantageous for noise reduction. The condition for maximally reducing noise in the range not exceeding 840 Pa, which is 70% of the allowable back pressure, is a vane length of 225 mm in the outer vane reverse type. The pressure drop under this condition was 777 Pa, and the average transmission losses in the low frequency region and the entire frequency region were 43.5 and 54.5 dB, respectively. Full article
(This article belongs to the Special Issue Marine Engines Performance and Emissions II)
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14 pages, 1909 KiB  
Article
Benthic Diatoms on Sheltered Coastal Soft Bottoms (Baltic Sea)—Seasonal Community Production and Respiration
by Ulf Karsten, Kana Kuriyama, Thomas Hübener and Jana Woelfel
J. Mar. Sci. Eng. 2021, 9(9), 949; https://doi.org/10.3390/jmse9090949 - 31 Aug 2021
Cited by 3 | Viewed by 2808
Abstract
Benthic diatom communities dominate sheltered shallow inner coastal waters of the atidal Southern Baltic Sea. However, their photosynthetic oxygen production and respiratory oxygen consumption is rarely evaluated. In the Baltic Sea carbon budget benthic diatom communities are often not included, since phytoplankton is [...] Read more.
Benthic diatom communities dominate sheltered shallow inner coastal waters of the atidal Southern Baltic Sea. However, their photosynthetic oxygen production and respiratory oxygen consumption is rarely evaluated. In the Baltic Sea carbon budget benthic diatom communities are often not included, since phytoplankton is regarded as the main primary producer. Therefore, two wind-protected stations (2–49-cm depths) were investigated between July 2010 and April 2012 using undisturbed sediment cores in combination with planar oxygen optodes. We expected strong fluctuations in the biological activity parameters in the incubated cores over the course of the seasons. The sediment particles at both stations were dominated by fine sand with a median grain size of 131–138 µm exhibiting an angular shape with many edges, which were less mobile compared to exposed coastal sites of the Southern Baltic Sea. These sand grains inhabited dense communities of rather small epipsammic diatoms (<10 µm). Chlorophyll a as a biomass parameter for benthic diatoms fluctuated from 64.8 to 277.3-mg Chl. a m−2 sediment surface. The net primary production and respiration rates exhibited strong variations across the different months at both stations, ranging from 12.9 to 56.9 mg O2 m−2 h−1 and from −6.4 to −137.6 mg O2 m−2 h−1, respectively. From these data, a gross primary production of 13.4 to 59.5 mg C m−2 h−1 was calculated. The results presented confirmed strong seasonal changes (four-fold amplitude) for the activity parameters and, hence, provided important production biological information for sheltered sediments of the Southern Baltic Sea. These data clearly indicate that benthic diatoms, although often ignored until now, represent a key component in the primary production of these coastal habitats when compared to similar studies at other locations of the Baltic Sea and, hence, should be considered in any carbon budget model of this brackish water ecosystem. Full article
(This article belongs to the Special Issue Coastal Lagoon Ecology)
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24 pages, 14245 KiB  
Article
Round Robin Testing: Exploring Experimental Uncertainties through a Multifacility Comparison of a Hinged Raft Wave Energy Converter
by Thomas Davey, Javier Sarmiento, Jérémy Ohana, Florent Thiebaut, Sylvain Haquin, Matthieu Weber, Sebastien Gueydon, Frances Judge, Eoin Lyden, Michael O’Shea, Roman Gabl, Laura-Beth Jordan, Martyn Hann, Daming Wang, Keri Collins, Daniel Conley, Deborah Greaves, David M. Ingram and Jimmy Murphy
J. Mar. Sci. Eng. 2021, 9(9), 946; https://doi.org/10.3390/jmse9090946 - 30 Aug 2021
Cited by 14 | Viewed by 4319
Abstract
The EU H2020 MaRINET2 project has a goal to improve the quality, robustness and accuracy of physical modelling and associated testing practices for the offshore renewable energy sector. To support this aim, a round robin scale physical modelling test programme was conducted to [...] Read more.
The EU H2020 MaRINET2 project has a goal to improve the quality, robustness and accuracy of physical modelling and associated testing practices for the offshore renewable energy sector. To support this aim, a round robin scale physical modelling test programme was conducted to deploy a common wave energy converter at four wave basins operated by MaRINET2 partners. Test campaigns were conducted at each facility to a common specification and test matrix, providing the unique opportunity for intercomparison between facilities and working practices. A nonproprietary hinged raft, with a nominal scale of 1:25, was tested under a set of 12 irregular sea states. This allowed for an assessment of power output, hinge angles, mooring loads, and six-degree-of-freedom motions. The key outcome to be concluded from the results is that the facilities performed consistently, with the majority of variation linked to differences in sea state calibration. A variation of 5–10% in mean power was typical and was consistent with the variability observed in the measured significant wave heights. The tank depth (which varied from 2–5 m) showed remarkably little influence on the results, although it is noted that these tests used an aerial mooring system with the geometry unaffected by the tank depth. Similar good agreement was seen in the heave, surge, pitch and hinge angle responses. In order to maintain and improve the consistency across laboratories, we make recommendations on characterising and calibrating the tank environment and stress the importance of the device–facility physical interface (the aerial mooring in this case). Full article
(This article belongs to the Special Issue Marine Renewables–Infrastructures and Physical Testing)
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21 pages, 3670 KiB  
Article
Emission Abatement Technology Selection, Routing and Speed Optimization of Hybrid Ships
by Antti Ritari, Kirsi Spoof-Tuomi, Janne Huotari, Seppo Niemi and Kari Tammi
J. Mar. Sci. Eng. 2021, 9(9), 944; https://doi.org/10.3390/jmse9090944 - 30 Aug 2021
Cited by 10 | Viewed by 2976
Abstract
This paper evaluates the effect of a large-capacity electrical energy storage, e.g., Li-ion battery, on optimal sailing routes, speeds, fuel choice, and emission abatement technology selection. Despite rapid cost reduction and performance improvement, current Li-ion chemistries are infeasible for providing the total energy [...] Read more.
This paper evaluates the effect of a large-capacity electrical energy storage, e.g., Li-ion battery, on optimal sailing routes, speeds, fuel choice, and emission abatement technology selection. Despite rapid cost reduction and performance improvement, current Li-ion chemistries are infeasible for providing the total energy demand for ocean-crossing ships because the energy density is up to two orders of magnitude less than in liquid hydrocarbon fuels. However, limited distance zero-emission port arrival, mooring, and port departure are attainable. In this context, we formulate two groups of numerical problems. First, the well-known Emission Control Area (ECA) routing problem is extended with battery-powered zero-emission legs. ECAs have incentivized ship operators to choose longer distance routes to avoid using expensive low sulfur fuel required for compliance, resulting in increased greenhouse gas (GHG) emissions. The second problem evaluates the trade-off between battery capacity and speed on battery-powered zero-emission port arrival and departure legs. We develop a mixed-integer quadratically constrained program to investigate the least cost system configuration and operation. We find that the optimal speed is up to 50% slower on battery-powered legs compared to the baseline without zero-emission constraint. The slower speed on the zero-emission legs is compensated by higher speed throughout the rest of the voyage, which may increase the total amount of GHG emissions. Full article
(This article belongs to the Special Issue Modelling and Optimisation of Ship Energy Systems II)
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12 pages, 5740 KiB  
Article
Broadband Characteristics of Zooplankton Sound Scattering Layer in the Kuroshio–Oyashio Confluence Region of the Northwest Pacific Ocean in Summer of 2019
by Minghua Xue, Jianfeng Tong, Siquan Tian and Xuefang Wang
J. Mar. Sci. Eng. 2021, 9(9), 938; https://doi.org/10.3390/jmse9090938 - 29 Aug 2021
Cited by 11 | Viewed by 3093
Abstract
Acoustic technology, as an important investigation method for fishery resources, has been widely used in zooplankton surveys. Since the Kuroshio–Oyashio confluence region has an extensive distribution of zooplankton, describing and analyzing the characteristic of the zooplankton sound scattering layer (SSL) in this area [...] Read more.
Acoustic technology, as an important investigation method for fishery resources, has been widely used in zooplankton surveys. Since the Kuroshio–Oyashio confluence region has an extensive distribution of zooplankton, describing and analyzing the characteristic of the zooplankton sound scattering layer (SSL) in this area is essential for marine ecology research. To understand its spatial–temporal distribution, acoustic data of the Kuroshio–Oyashio confluence region at the Northwest Pacific Ocean, obtained by a Simrad EK80 broadband scientific echosounder in 2019, were used on board the research vessel (RV) Songhang. After noise removal, the volume backscattering strength (SV) was measured to plot the broadband scattering spectrogram of each water layer and to exhibit zooplankton distribution. The results show that the main sound scattering within 0–200 m originate from the zooplankton, and the SV of each layer increases with the rise of the transducer frequency. The magnitude of SV was closely synchronized with the solar altitude angle, which gets smaller when the angle is positive, then larger when the angle is negative. It means that the SSL has a diel vertical migration (DVM) behavior with the variation of solar height. Meanwhile, scattering strength was positively correlated with temperature in the vertical direction and showed a maximum of −54.31 dB at 20–40 m under the influence of the thermocline. The Kuroshio and Oyashio currents had an obvious influence on the scattering strengths in this study, indicating a low value when next to the Oyashio side and a high value on the Kuroshio side. The scattering strength near the warm vortex center was higher than that at the vortex edge. The results of this study could provide references for a long-term study on ecological environment variation and its impacts on zooplankton distribution. Full article
(This article belongs to the Special Issue Marine Environment Monitoring)
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17 pages, 10684 KiB  
Article
A Novel Cargo Ship Detection and Directional Discrimination Method for Remote Sensing Image Based on Lightweight Network
by Pan Wang, Jianzhong Liu, Yinbao Zhang, Zhiyang Zhi, Zhijian Cai and Nannan Song
J. Mar. Sci. Eng. 2021, 9(9), 932; https://doi.org/10.3390/jmse9090932 - 28 Aug 2021
Cited by 2 | Viewed by 2844
Abstract
Recently, cargo ship detection in remote sensing images based on deep learning is of great significance for cargo ship monitoring. However, the existing detection network is not only unable to realize autonomous operation on spaceborne platforms due to the limitation of computing and [...] Read more.
Recently, cargo ship detection in remote sensing images based on deep learning is of great significance for cargo ship monitoring. However, the existing detection network is not only unable to realize autonomous operation on spaceborne platforms due to the limitation of computing and storage, but the detection result also lacks the directional information of the cargo ship. In order to address the above problems, we propose a novel cargo ship detection and directional discrimination method for remote sensing images based on a lightweight network. Specifically, we design an efficient and lightweight feature extraction network called the one-shot aggregation and depthwise separable network (OSADSNet), which is inspired by one-shot feature aggregation modules and depthwise separable convolutions. Additionally, we combine the RPN with the K-Mean++ algorithm to obtain the K-RPN, which can produce a more suitable region proposal for cargo ship detection. Furthermore, without introducing extra parameters, the directional discrimination of the cargo ship is transformed into a classification task, and the directional discrimination is completed when the detection task is completed. Experiments on a self-built remote sensing image cargo ship dataset indicate that our model can provide relatively accurate and fast detection for cargo ships (mAP of 91.96% and prediction time of 46 ms per image) and discriminate the directions (north, east, south, and west) of cargo ships, with fewer parameters (model size of 110 MB), which is more suitable for autonomous operation on spaceborne platforms. Therefore, the proposed method can meet the needs of cargo ship detection and directional discrimination in remote sensing images on spaceborne platforms. Full article
(This article belongs to the Special Issue Machine Learning and Remote Sensing in Ocean Science and Engineering)
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13 pages, 1188 KiB  
Article
Improving the Performance of Mode-Based Sound Propagation Models by Using Perturbation Formulae for Eigenvalues and Eigenfunctions
by Alena Zakharenko, Mikhail Trofimov and Pavel Petrov
J. Mar. Sci. Eng. 2021, 9(9), 934; https://doi.org/10.3390/jmse9090934 - 28 Aug 2021
Cited by 4 | Viewed by 2196
Abstract
Numerous sound propagation models in underwater acoustics are based on the representation of a sound field in the form of a decomposition over normal modes. In the framework of such models, the calculation of the field in a range-dependent waveguide (as well as [...] Read more.
Numerous sound propagation models in underwater acoustics are based on the representation of a sound field in the form of a decomposition over normal modes. In the framework of such models, the calculation of the field in a range-dependent waveguide (as well as in the case of 3D problems) requires the computation of normal modes for every point within the area of interest (that is, for each pair of horizontal coordinates x,y). This procedure is often responsible for the lion’s share of total computational cost of the field simulation. In this study, we present formulae for perturbation of eigenvalues and eigenfunctions of normal modes under the water depth variations in a shallow-water waveguide. These formulae can reduce the total number of mode computation instances required for a field calculation by a factor of 5–10. We also discuss how these formulae can be used in a combination with a wide-angle mode parabolic equation. The accuracy of such combined model is validated in a series of numerical examples. Full article
(This article belongs to the Special Issue Modeling Techniques for Underwater Acoustic Scattering and Propagation (including 3D Effects))
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26 pages, 3913 KiB  
Article
A Numerical Study of Sheet Flow Driven by Skewed-Asymmetric Shoaling Waves Using SedWaveFoam
by Yeulwoo Kim, Ryan S. Mieras, Dylan Anderson and Timu Gallien
J. Mar. Sci. Eng. 2021, 9(9), 936; https://doi.org/10.3390/jmse9090936 - 28 Aug 2021
Cited by 1 | Viewed by 2599
Abstract
SedWaveFoam, an OpenFOAM-based two-phase model that concurrently resolves the free surface wave field, and the bottom boundary layer is used to investigate sediment transport throughout the entire water column. The numerical model was validated with large-scale wave flume data for sheet flow driven [...] Read more.
SedWaveFoam, an OpenFOAM-based two-phase model that concurrently resolves the free surface wave field, and the bottom boundary layer is used to investigate sediment transport throughout the entire water column. The numerical model was validated with large-scale wave flume data for sheet flow driven by shoaling skewed-asymmetric waves with two different grain sizes. Newly obtained model results were combined with previous nonbreaking and near-breaking wave cases to develop parameterization methods for time-dependent bed shear stress and sediment transport rate under various sediment sizes and wave conditions. Gonzalez-Rodriguez and Madsen (GRM07) and quasi-steady approaches were compared for intra-wave bed shear stress. The results show that in strongly asymmetric flows, considering the separated boundary layer development processes at each half wave-cycle (i.e., GRM07) is essential to accurately estimating bed shear stress and highlights the impact of phase-lag effects on sediment transport rates. The quasi-steady approach underpredicts (∼60%) sediment transport rates, especially for fine grains under large velocity asymmetry. A modified phase-lag parameter, incorporating velocity asymmetry, sediment stirring, and settling processes is proposed to extend the Meyer-Peter and Mueller type power law formula. The extended formula accurately estimated the enhanced net onshore sediment transport rate observed under skewed-asymmetric wave conditions. Full article
(This article belongs to the Special Issue Recent Advances in Coastal Sediment Dynamics and Transport)
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13 pages, 4704 KiB  
Article
A Comparative Study on the Hydrodynamic-Energy Loss Characteristics between a Ducted Turbine and a Shaftless Ducted Turbine
by Ke Song and Bangcheng Yang
J. Mar. Sci. Eng. 2021, 9(9), 930; https://doi.org/10.3390/jmse9090930 - 27 Aug 2021
Cited by 6 | Viewed by 2280
Abstract
The shaftless ducted turbine (abbreviated as SDT), as an extraordinary innovation in tidal current power generation applications, has many advantages, and a wide application prospect. The structure of an SDT resembles a ducted turbine (abbreviated as DT), as both contain blades and a [...] Read more.
The shaftless ducted turbine (abbreviated as SDT), as an extraordinary innovation in tidal current power generation applications, has many advantages, and a wide application prospect. The structure of an SDT resembles a ducted turbine (abbreviated as DT), as both contain blades and a duct. However, there are some structural differences between a DT and a SDT, which can cause significant discrepancy in the hydrodynamic characteristics and flow features. The present work compares the detailed hydrodynamic-energy loss characteristics of a DT and a SDT by means of computational fluid dynamics (CFD), performed by solving the 3D steady incompressible Reynolds-averaged Navier-Stokes (RANS) equations in combination with the Menter’s Shear Stress Transport (SST k−ω) turbulence model and entropy production model. The results show the SDT features a higher power level at low tip speed ratio (TSR) and a potential reduction in potential flow resistance and disturbance with respect to the DT. Moreover, a detail entropy production analysis shows the energy loss is closely related to the flow separation and the reverse flow, and other negative flow factors. The entropy production of the SDT is lessened than that of the DT at different TSR. Unlike the DT, the SDT allows a large mass flow of water to leak through the open-center structure, which plays an important role in improving the wake structure and avoiding the negative flow along the central axis. Full article
(This article belongs to the Topic Marine Renewable Energy)
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28 pages, 18776 KiB  
Article
Prediction of Changes in Seafloor Depths Based on Time Series of Bathymetry Observations: Dutch North Sea Case
by Reenu Toodesh, Sandra Verhagen and Anastasia Dagla
J. Mar. Sci. Eng. 2021, 9(9), 931; https://doi.org/10.3390/jmse9090931 - 27 Aug 2021
Cited by 3 | Viewed by 2359
Abstract
Guaranteeing safety of navigation within the Netherlands Continental Shelf (NCS), while efficiently using its ocean mapping resources, is a key task of Netherlands Hydrographic Service (NLHS) and Rijkswaterstaat (RWS). Resurvey frequencies depend on seafloor dynamics and the aim of this research is to [...] Read more.
Guaranteeing safety of navigation within the Netherlands Continental Shelf (NCS), while efficiently using its ocean mapping resources, is a key task of Netherlands Hydrographic Service (NLHS) and Rijkswaterstaat (RWS). Resurvey frequencies depend on seafloor dynamics and the aim of this research is to model the seafloor dynamics to predict changes in seafloor depth that would require resurveying. Characterisation of the seafloor dynamics is based on available time series of bathymetry data obtained from the acoustic remote sensing method of both single-beam echosounding (SBES) and multibeam echosounding (MBES). This time series is used to define a library of mathematical models describing the seafloor dynamics in relation to spatial and temporal changes in depth. An adaptive, functional model selection procedure is developed using a nodal analysis (0D) approach, based on statistical hypothesis testing using a combination of the Overall Model Test (OMT) statistic and Generalised Likelihood Ratio Test (GLRT). This approach ensures that each model has an equal chance of being selected, when more than one hypothesis is plausible for areas that exhibit varying seafloor dynamics. This ensures a more flexible and rigorous decision on the choice of the nominal model assumption. The addition of piecewise linear models to the library offers another characterisation of the trends in the nodal time series. This has led to an optimised model selection procedure and parameterisation of each nodal time series, which is used for the spatial and temporal predictions of the changes in the depths and associated uncertainties. The model selection results show that the models can detect the changes in the seafloor depths with spatial consistency and similarity, particularly in the shoaling areas where tidal sandwaves are present. The predicted changes in depths and uncertainties are translated into a probability risk-alert map by evaluating the probabilities of an indicator variable exceeding a certain decision threshold. This research can further support the decision-making process when optimising resurvey frequencies. Full article
(This article belongs to the Special Issue Spatial and Spatiotemporal Methods in Marine Science)
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16 pages, 4613 KiB  
Article
Comparative Analysis of Two Approaches for Correcting the Systematic Ocean Temperature Bias of CAS-ESM-C
by Mengjiao Du, Fei Zheng, Jiang Zhu, Renping Lin and Kan Yi
J. Mar. Sci. Eng. 2021, 9(9), 925; https://doi.org/10.3390/jmse9090925 - 26 Aug 2021
Cited by 2 | Viewed by 2131
Abstract
Currently, several ocean data assimilation methods have been adopted to increase the performance of air–sea coupled models, but inconsistent adjustments between the sea temperature with other oceanic fields can be introduced. In the coupled model CAS-ESM-C, inconsistent adjustments for ocean currents commonly occur [...] Read more.
Currently, several ocean data assimilation methods have been adopted to increase the performance of air–sea coupled models, but inconsistent adjustments between the sea temperature with other oceanic fields can be introduced. In the coupled model CAS-ESM-C, inconsistent adjustments for ocean currents commonly occur in the tropical western Pacific and the eastern Indian Ocean. To overcome this problem, a new ensemble-based bias correction approach—a simple modification of the Ensemble Optimal Interpolation (EnOI) approach for multi-variable into a direct approach for a single variable—is proposed to minimize the model biases. Compared with the EnOI approach, this new approach can effectively avoid inconsistent adjustments. Meanwhile, the comparisons suggest that inconsistent adjustment mainly results from the unreasonable correlations between temperature and ocean current in the background matrix. In addition, the ocean current can be directly corrected in the EnOI approach, which can additionally generate biases for the upper ocean. These induced ocean biases can produce unreasonable ocean heat sinking and heat storage in the tropical western Pacific. It will generate incorrect ocean heat transmission toward the east, further amplifying the inconsistency introduced through the tropical air–sea interaction process. Full article
(This article belongs to the Special Issue Earth System Modeling, Data Assimilation, Artificial Intelligence, Deep Learning and Ocean Information Engineering)
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15 pages, 3268 KiB  
Article
Experimental Study of Large-Temperature-Range and Long-Period Monitoring for LNG Marine Auxiliary Based on Fiber Bragg Grating Temperature Measurement
by Fenghui Han, Zhe Wang, Hefu Zhang, Dongxing Wang, Wenhua Li and Wenjian Cai
J. Mar. Sci. Eng. 2021, 9(9), 917; https://doi.org/10.3390/jmse9090917 - 24 Aug 2021
Cited by 7 | Viewed by 2609
Abstract
Temperature is a key variable to evaluate the energy consumption and thermodynamic performance of traditional marine auxiliary machinery, chillers and piping systems. In particular, for the cryogenic storage tanks and fuel gas supply systems of LNG ships, explosion-proof and low-temperature-resistance properties bring new [...] Read more.
Temperature is a key variable to evaluate the energy consumption and thermodynamic performance of traditional marine auxiliary machinery, chillers and piping systems. In particular, for the cryogenic storage tanks and fuel gas supply systems of LNG ships, explosion-proof and low-temperature-resistance properties bring new challenges to the onboard temperature measurement and monitoring. In order to promote the development of high-performance and safer monitoring systems for LNG ships, this paper adopted fiber Bragg grating (FBG) technology to ensure the measurement safety and accuracy of temperature sensors, and performs a series of experiments in a large temperature range on the chiller, pipeline, and cryogenic storage tank of an LNG ship and their long-term reliabilities. Firstly, the principle and composition of the designed FBG temperature sensors are introduced in detail, and the measurement accuracy and range of different metal-coated optical fibers were tested in a large temperature range and compared against the traditional thermistors. Then, the effects of different operating conditions of the LNG marine chiller system and cryogenic storage tank on the temperature measurements were investigated. In addition, the drift degrees of the optical fibers and industrial thermistors were analyzed to figure out their reliabilities for long-term temperature measurements. The results showed that for the long-period (16 months) monitoring of LNG ships in a large temperature range (105–315 K) under different shipping conditions, the optical temperature measurement based on FBG technology has sufficient accuracy and dynamic sensitivity with a higher safety than the traditional thermoelectric measurement. Besides, the ship vibration, ambient humidity, and great temperature changes have little impact on its measurement reliability and drifts. This research can provide references and technical supports to the performance testing systems of LNG ships and other relevant vessels with stricter safety standards. Full article
(This article belongs to the Section Ocean Engineering)
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18 pages, 4742 KiB  
Article
A Universal Simulation Framework of Shipborne Inertial Sensors Based on the Ship Motion Model and Robot Operating System
by Qianfeng Jing, Haichao Wang, Bin Hu, Xiuwen Liu and Yong Yin
J. Mar. Sci. Eng. 2021, 9(8), 900; https://doi.org/10.3390/jmse9080900 - 20 Aug 2021
Cited by 7 | Viewed by 2870
Abstract
A complete virtual test environment is a powerful tool for Autonomous Surface Vessels (ASVs) research, and the simulation of ship motion and shipborne sensors is one of the prerequisites for constructing such an environment. This paper proposed a universal simulation framework of shipborne [...] Read more.
A complete virtual test environment is a powerful tool for Autonomous Surface Vessels (ASVs) research, and the simulation of ship motion and shipborne sensors is one of the prerequisites for constructing such an environment. This paper proposed a universal simulation framework of shipborne inertial sensors. A ship motion model considering environmental disturbances is proposed to simulate the six-degrees-of-freedom motion of ships. The discrete form of the inertial sensor stochastic error model is derived. The inertial measurement data are simulated by adding artificial errors to a simulated motion status. In addition, the ship motion simulation, inertial measurement simulation, and environment simulation nodes are implemented based on the computational graph architecture of the Robot Operating System (ROS). The benefit from the versatility of the ROS messages, the format of simulated inertial measurement is exactly the same as that of real sensors, which provides a research basis for the fusion perception algorithm based on visual–inertial and laser–inertial sensors in the research field of ASVs. Full article
(This article belongs to the Special Issue Explainable AI and Evaluation of Algorithms for Autonomous Marine Vehicles)
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20 pages, 25025 KiB  
Article
Verification and Validation of a Methodology to Numerically Generate Waves Using Transient Discrete Data as Prescribed Velocity Boundary Condition
by Rafael P. Maciel, Cristiano Fragassa, Bianca N. Machado, Luiz A. O. Rocha, Elizaldo D. dos Santos, Mateus N. Gomes and Liércio A. Isoldi
J. Mar. Sci. Eng. 2021, 9(8), 896; https://doi.org/10.3390/jmse9080896 - 19 Aug 2021
Cited by 8 | Viewed by 2717
Abstract
This work presents a two-dimensional numerical analysis of a wave channel and a oscillating water column (OWC) device. The main goal is to validate a methodology which uses transient velocity data as a means to impose velocity boundary condition for the generation of [...] Read more.
This work presents a two-dimensional numerical analysis of a wave channel and a oscillating water column (OWC) device. The main goal is to validate a methodology which uses transient velocity data as a means to impose velocity boundary condition for the generation of numerical waves. To achieve this, a numerical wave channel was simulated using regular waves with the same parameters as those used in a laboratory experiment. First, these waves were imposed as prescribed velocity boundary condition and compared with the analytical solution; then, the OWC device was inserted into the computational domain, aiming to validate this methodology. For the numerical analysis, computational fluid dynamics ANSYS Fluent software was employed, and to tackle with water–air interaction, the nonlinear multiphase model volume of fluid (VOF) was applied. Although the results obtained through the use of discrete data as velocity boundary condition presented a little disparity; in general, they showed a good agreement with laboratory experiment results. Since many studies use regular waves, there is a lack of analysis with ocean waves realistic data; thus, the proposed methodology stands out for its capacity of using realistic sea state data in numerical simulations regarding wave energy converters (WECs). Full article
(This article belongs to the Special Issue Wind and Wave Climate)
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19 pages, 62076 KiB  
Article
Real-Time Nonlinear Model Predictive Controller for Multiple Degrees of Freedom Wave Energy Converters with Non-Ideal Power Take-Off
by Ali S. Haider, Ted K. A. Brekken and Alan McCall
J. Mar. Sci. Eng. 2021, 9(8), 890; https://doi.org/10.3390/jmse9080890 - 18 Aug 2021
Cited by 14 | Viewed by 3047
Abstract
An increase in wave energy converter (WEC) efficiency requires not only consideration of the nonlinear effects in the WEC dynamics and the power take-off (PTO) mechanisms, but also more integrated treatment of the whole system, i.e., the buoy dynamics, the PTO system, and [...] Read more.
An increase in wave energy converter (WEC) efficiency requires not only consideration of the nonlinear effects in the WEC dynamics and the power take-off (PTO) mechanisms, but also more integrated treatment of the whole system, i.e., the buoy dynamics, the PTO system, and the control strategy. It results in an optimization formulation that has a nonquadratic and nonstandard cost functional. This article presents the application of real-time nonlinear model predictive controller (NMPC) to two degrees of freedom point absorber type WEC with highly nonlinear PTO characteristics. The nonlinear effects, such as the fluid viscous drag, are also included in the plant dynamics. The controller is implemented on a real-time target machine, and the WEC device is emulated in real-time using the WECSIM toolbox. The results for the successful performance of the design are presented for irregular waves under linear and nonlinear hydrodynamic conditions. Full article
(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters)
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18 pages, 4977 KiB  
Article
Functionality Investigation of the UAV Arranged FMCW Solid-State Marine Radar
by Saulius Rudys, Andrius Laučys, Dainius Udris, Raimondas Pomarnacki and Domantas Bručas
J. Mar. Sci. Eng. 2021, 9(8), 887; https://doi.org/10.3390/jmse9080887 - 18 Aug 2021
Cited by 4 | Viewed by 2876
Abstract
Some models of marine radars are light-weight enough and thus are attractive for potential applications when arranged on UAVs. Elevating a marine radar to high altitudes provides a much wider field of view, however, this could lead to a higher radio interference level. [...] Read more.
Some models of marine radars are light-weight enough and thus are attractive for potential applications when arranged on UAVs. Elevating a marine radar to high altitudes provides a much wider field of view, however, this could lead to a higher radio interference level. The practical estimation of the radio interferences affecting the solid-state FMCW marine radar at altitudes up to 120 m was the main objective of this contribution. A rotary-wing octocopter UAV was developed and built for the experiments. Two different kinds of interferences were observed at higher altitudes. Ray-like interferences were caused by signals, which are received by the radar’s antenna. Circle-like interferences appear due to the low frequency interfering signal directly penetrating the detector due to insufficient receiver screening. Full article
(This article belongs to the Section Ocean Engineering)
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12 pages, 5313 KiB  
Article
Chained Data Acquisition and Transmission System Protype for Cabled Seafloor Earthquake Observatory
by Jingyang Qiao, Wu Liu, Jingquan Liu and Jianping Zhou
J. Mar. Sci. Eng. 2021, 9(8), 880; https://doi.org/10.3390/jmse9080880 - 15 Aug 2021
Cited by 1 | Viewed by 2233
Abstract
Seafloor observatories can provide long-term, real-time submarine monitoring data, which has great significance for the study of major scientific technology in marine science, especially in the seafloor earthquake observation. The chained submarine data sampling and transmission system is the prototype and foundation of [...] Read more.
Seafloor observatories can provide long-term, real-time submarine monitoring data, which has great significance for the study of major scientific technology in marine science, especially in the seafloor earthquake observation. The chained submarine data sampling and transmission system is the prototype and foundation of cabled seafloor earthquake observatories. This paper designs and builds a chained data sampling and transmission system (SQSTS) based on Zynq-7000 Soc (System on chip) and clock synchronization. At the beginning, we realized high-precision submarine data (24 bit) sampling based on Zynq-7000 Soc and ADS 1256. Using the PPS (Pulse per second) signal provided by the P88 1588 PTP (Precise time protocol) clock synchronization board and the inner crystal oscillator of the Zynq-7000 Soc, the time stamp up to the microsecond level, for the seismic data sampled in each seismometer node can support subsequent inversion of seismic data. In addition, a high-speed data transmission link connecting nodes in SQSTS, which is based on the Gigabit transceiver and optical cable, has been investigated. The transmission link has been realized by using the Aurora IP core. The theoretical calculations indicate that the data transmission bus bandwidth can reach 4 Gbps, while in the meantime its reliability has been proved by experiments. The experimental results show that the system owns the characteristics of high data sampling accuracy, stable and reliable high-speed transmission, and has promising application prospects. Full article
(This article belongs to the Section Ocean Engineering)
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16 pages, 7020 KiB  
Article
Real-Time Management of Vessel Carbon Dioxide Emissions Based on Automatic Identification System Database Using Deep Learning
by Yongpeng Wang, Daisuke Watanabe, Enna Hirata and Shigeki Toriumi
J. Mar. Sci. Eng. 2021, 9(8), 871; https://doi.org/10.3390/jmse9080871 - 13 Aug 2021
Cited by 11 | Viewed by 3211
Abstract
In this study, we propose an effective method using deep learning to strengthen real-time vessel carbon dioxide emission management. We propose a method to predict real-time carbon dioxide emissions of the vessel in three steps: (1) convert the trajectory data of the fixed [...] Read more.
In this study, we propose an effective method using deep learning to strengthen real-time vessel carbon dioxide emission management. We propose a method to predict real-time carbon dioxide emissions of the vessel in three steps: (1) convert the trajectory data of the fixed time interval into a spatial–temporal sequence, (2) apply a long short-term memory (LSTM) model to predict the future trajectory and vessel status data of the vessel, and (3) predict the carbon dioxide emissions. Automatic identification system (AIS) database of a liquefied natural gas (LNG) vessel were selected as the sample and we reconstructed the trajectory data with a fixed time interval using cubic spline interpolation. Applying the interpolated AIS data, the carbon dioxide emissions of the vessel were calculated based on the International Towing Tank Conference (ITTC) recommended procedures. The experimental results are twofold. First, it reveals that vessel emissions are currently underestimated. This study clearly indicates that the actual carbon dioxide emissions are higher than those reported. The finding offers insight into how to accurately measure the emissions of vessels, and hence, better execute a greenhouse gases (GHGs) reduction strategy. Second, the LSTM model has a better trajectory prediction performance than the recurrent neural network (RNN) model. The errors of the trajectory endpoint and carbon dioxide emissions were small, which shows that the LSTM model is suitable for spatial–temporal data prediction with excellent performance. Therefore, this study offers insights to strengthen the real-time management and control of vessel greenhouse gas emissions and handle those in a more efficient way. Full article
(This article belongs to the Special Issue Advanced Research in Shipping Informatics and Communications)
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14 pages, 3281 KiB  
Article
Desulfurizing of Pyrolysis Oil of Used Tires Using a 3D-Printed Vortex Diode and Modeling of Process
by Jochen Uebe, Žilvinas Kryževičius, Jolanta Janutėnienė, Audronė Žukauskaitė, Eugenijus Bertašius, Rokas Rapolavičius, Valdas Jankūnas and Audrius Senulis
J. Mar. Sci. Eng. 2021, 9(8), 876; https://doi.org/10.3390/jmse9080876 - 13 Aug 2021
Cited by 2 | Viewed by 2315
Abstract
The use of pyrolysis oil can be seen as an alternative fuel for maritime transport. However, pyrolysis oil from tires must be desulfurized for this. Recently, this can be done by hydrodynamic cavitation. This process does not require oxidation chemicals but only water, [...] Read more.
The use of pyrolysis oil can be seen as an alternative fuel for maritime transport. However, pyrolysis oil from tires must be desulfurized for this. Recently, this can be done by hydrodynamic cavitation. This process does not require oxidation chemicals but only water, a cavitation generator, and a pump to drive it. In the literature, this concept has been successfully tested on model fuels. In this study, the cavitation generator for the desulfurization of waste tire pyrolysis oil was printed from polylactic acid-based on simulations of the optimal design, which allows for much cheaper production and easy replacement in case of wear or testing of alternative designs. After 60 min of treatment at 5 bar inlet pressure, a desulfurization of almost 33% was achieved. Furthermore, an interaction analysis showed that only from a pyrolysis oil content of 5.5 to 6% does hydrodynamic cavitation have an effective effect on desulfurization. Full article
(This article belongs to the Section Ocean Engineering)
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12 pages, 5683 KiB  
Article
Microscopic Anatomy of the Lining of Hemal Spaces in the Penaeid Shrimp, Sicyonia ingentis
by Rachel Brittany Sidebottom, Sabi Bang and Gary Martin
J. Mar. Sci. Eng. 2021, 9(8), 862; https://doi.org/10.3390/jmse9080862 - 11 Aug 2021
Cited by 1 | Viewed by 4297
Abstract
The purpose of this paper is to present a morphological description of three different types of acellular material lining hemal spaces in a shrimp, providing a background for addressing future questions. The vasculature of the penaeid shrimp, Sicyonia ingentis, includes vessels leading [...] Read more.
The purpose of this paper is to present a morphological description of three different types of acellular material lining hemal spaces in a shrimp, providing a background for addressing future questions. The vasculature of the penaeid shrimp, Sicyonia ingentis, includes vessels leading from the heart into arteries which branch and expand into sinuses before returning hemolymph back to the heart. Early work showed that an endothelium was absent, and a basement membrane (BM) separated tissues from the hemolymph. Therefore, it was suggested that hemocytes could identify anything other than the BM as a “foreign” entity. This study demonstrates three major types of acellular material lining the hemal spaces of S. ingentis. Cardiomyocytes, digestive gland tubules, and abdominal muscle fibers are covered by BMs. Major arteries are lined by a fibrillin-like fibrous material. Finally, sheaths of collagenous connective tissues cover the heart and digestive gland as well as the outer surface of arteries, the gut, and gonad. Our understanding of hemocyte receptors and extracellular matrices in general have greatly expanded but the biochemical composition of the matrices lining crustacean hemal spaces, their role in regulating nutrient uptake, and the cells responsible for their deposition deserve further attention. Full article
(This article belongs to the Special Issue New Research Advances on Marine Invertebrates)
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22 pages, 7680 KiB  
Article
Assessment of and Adaptation to Beach Erosion in Islands: An Integrated Approach
by Olympos Andreadis, Antonis Chatzipavlis, Thomas Hasiotis, Isavela Monioudi, Evangelia Manoutsoglou and Adonis Velegrakis
J. Mar. Sci. Eng. 2021, 9(8), 859; https://doi.org/10.3390/jmse9080859 - 10 Aug 2021
Cited by 12 | Viewed by 2871
Abstract
Island beaches, which form significant natural and economic resources, are under increasing erosion risk due to sea level rise. The present contribution proposes an integrated methodological framework for the evaluation of the socio-economic significance of beaches and their vulnerability to sea level rise [...] Read more.
Island beaches, which form significant natural and economic resources, are under increasing erosion risk due to sea level rise. The present contribution proposes an integrated methodological framework for the evaluation of the socio-economic significance of beaches and their vulnerability to sea level rise and the design of effective adaptation measures. The approach comprises four steps: (i) beach ranking on the basis of their socio-economic significance and vulnerability in order to prioritize adaptation responses; (ii) monitoring of the hydro- and morphodynamic regime of the most highly ranking beaches using field observations and modelling, (iii) assessment of the sediment volumes required for beach nourishment under different scenarios of sea level rise and nourishment designs; (iv) evaluation of the marine aggregate potential of the adjacent areas that can be used for beach nourishment. The framework was applied to the Greek island of Chios, which has many beaches that are already under erosion. The methodology was shown to provide a structured approach for the assessment and response to erosion of the most vulnerable beach. Full article
(This article belongs to the Section Coastal Engineering)
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20 pages, 4022 KiB  
Article
What Speleothems Tell Us about Long-Term Rainfall Oscillation throughout the Holocene on a Planetary Scale
by Jean-Louis Pinault and Ligia Pereira
J. Mar. Sci. Eng. 2021, 9(8), 853; https://doi.org/10.3390/jmse9080853 - 8 Aug 2021
Cited by 3 | Viewed by 2293
Abstract
Within the context of anthropogenic warming, rainfall oscillations may induce especially important societal impacts worldwide. In this article, we propose to study potential underlying mechanisms related to precipitation changes on a planetary scale by taking advantage of the recent theory of Rossby waves [...] Read more.
Within the context of anthropogenic warming, rainfall oscillations may induce especially important societal impacts worldwide. In this article, we propose to study potential underlying mechanisms related to precipitation changes on a planetary scale by taking advantage of the recent theory of Rossby waves of long periods winding around subtropical gyres, the Gyral Rossby Waves (GRWs). The stable oxygen isotopic compositions of speleothems are used to regionalize and reconstruct the evolution of long-term rainfall oscillation during the Holocene. The method applied here consists in estimating the wavelet power of dated series of stable oxygen isotopic composition (δ18O) in speleothems within period bands representative of subharmonic modes. Our findings highlight: (1) hydrological processes resulting from friction between the North Equatorial Current (NEC) and the North Equatorial Counter Current (NECC) to explain the weakening of ENSO activity in mid-Holocene, and (2) the quasi-resonance of the equatorward migration of the summer Inter Tropical Convergence Zone (ITCZ) during the Holocene, because of the progressive decrease of the thermal gradient between the low and high latitudes of the gyres. The results of this study suggest that the spatial and temporal variations in the amplitude of the rainfall oscillations are related both on the acceleration/deceleration phases of the western boundary currents and on the shrinkage of the Hadley cell. The latitudinal shift of the summer ITCZ in response to changes in the thermal gradient is of the utmost importance in predicting the expansion of deserts resulting from anthropogenic warming. Full article
(This article belongs to the Special Issue Hydroclimatic Events in Regions Subject to Rainfall Oscillation)
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18 pages, 3721 KiB  
Article
Estimation of Maneuverability of Trawl Fishing Vessel Using an Analytical Method
by Su-Hyung Kim and Chun-Ki Lee
J. Mar. Sci. Eng. 2021, 9(8), 854; https://doi.org/10.3390/jmse9080854 - 8 Aug 2021
Cited by 3 | Viewed by 2671
Abstract
Most fishing vessels are less than 100 m in length between the perpendiculars, for which adherence to the International Maritime Organization maneuverability standards are not mandatory. In the design stage of fishing vessels, maneuverability is estimated using empirical formulas—mainly analytical methods—rather than costly [...] Read more.
Most fishing vessels are less than 100 m in length between the perpendiculars, for which adherence to the International Maritime Organization maneuverability standards are not mandatory. In the design stage of fishing vessels, maneuverability is estimated using empirical formulas—mainly analytical methods—rather than costly and time-consuming model tests. However, the empirical formula is developed through the process of regression analysis on the model test results from merchant ships’ hull form and applying the same to the fishing vessels’ hull form may result in an estimation error due to the differences in the vessels’ characteristics—e.g., L/B, B/d and Cb·B/L—. In a previous study, the authors of this paper derived a modified empirical formula by adding the hull form parameters of trawl fishing vessels to the existing empirical formula based on those of merchant ships. This study analyzes the validity of the modified empirical formula in depth by applying it to a newly-built training vessel that has the hull form of a trawl fishing vessel. As a result of the study, the estimation results were improved by including the parameters of the hull form of trawl fishing vessels in the empirical formula developed for merchant ships. Full article
(This article belongs to the Special Issue Manoeuvring and Control of Ships and Other Marine Vehicles)
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20 pages, 2501 KiB  
Article
The Fate of Nitrogen in Dredged Material Used for Tidal Marsh Restoration
by Lorie W. Staver, Jeffrey C. Cornwell, Nicholas J. Nidzieko, Kenneth W. Staver, J. Court Stevenson, Michael Owens, Walter Boynton and Leysa Lopez-Gonzalez
J. Mar. Sci. Eng. 2021, 9(8), 849; https://doi.org/10.3390/jmse9080849 - 6 Aug 2021
Cited by 4 | Viewed by 2267
Abstract
Tidal marsh restoration using dredged material is being undertaken in many coastal areas to replace lost habitat and ecosystem services due to tidal marsh loss. The fate of high levels of nitrogen (N) in fine-grained dredged material used as a substrate for marsh [...] Read more.
Tidal marsh restoration using dredged material is being undertaken in many coastal areas to replace lost habitat and ecosystem services due to tidal marsh loss. The fate of high levels of nitrogen (N) in fine-grained dredged material used as a substrate for marsh restoration is uncertain, but if exported tidally may cause subtidal habitat degradation. In this study, a mass balance was developed to characterize N fluxes in a two-year-old restored tidal marsh constructed with fine-grained dredged material at Poplar Island, MD, in Chesapeake Bay, and to evaluate the potential impact on the adjacent submersed aquatic vegetation (SAV) habitat. Denitrification and N accumulation in Spartina organic matter were identified as the major sinks (21.31 and 28.5 mg N m−2 d−1, respectively), while tidal export of TN was more modest (9.4 mg N m−2 d−1) and inorganic N export was low (1.59 mg N m−2 d−1). Internal cycling helped retain N within the marsh. Mineralization of N associated with labile organic matter in the dredged material was likely a large, but unquantified, source of N supporting robust plant growth and N exports. Exceedances of SAV water quality habitat requirements in the subtidal region adjacent to the marsh were driven by elevated Chesapeake Bay concentrations rather than enrichment by the marsh. Full article
(This article belongs to the Special Issue Organic Matter and Nutrient Cycling in Coastal Wetlands and Submerged Aquatic Ecosystems in an Age of Rapid Environmental Change – the Anthropocene)
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13 pages, 1157 KiB  
Review
Modeling Multiscale and Multiphysics Coastal Ocean Processes: A Discussion on Necessity, Status, and Advances
by Hansong Tang, Charles Reid Nichols, Lynn Donelson Wright and Donald Resio
J. Mar. Sci. Eng. 2021, 9(8), 847; https://doi.org/10.3390/jmse9080847 - 5 Aug 2021
Cited by 4 | Viewed by 3405
Abstract
Coastal ocean flows are interconnected by a complex suite of processes. Examples are inlet jets, river mouth effluents, ocean currents, surface gravity waves, internal waves, wave overtopping, and wave slamming on coastal structures. It has become necessary to simulate such oceanographic phenomena directly [...] Read more.
Coastal ocean flows are interconnected by a complex suite of processes. Examples are inlet jets, river mouth effluents, ocean currents, surface gravity waves, internal waves, wave overtopping, and wave slamming on coastal structures. It has become necessary to simulate such oceanographic phenomena directly and simultaneously in many disciplines, including coastal engineering, environmental science, and marine science. Oceanographic processes exhibit distinct behaviors at specific temporal and spatial scales, and they are multiscale, multiphysics in nature; these processes are described by different sets of governing equations and are often modeled individually. In order to draw the attention of the scientific community and promote their simulations, a Special Issue of the Journal of Marine Science and Engineering entitled “Multiscale, Multiphysics Modelling of Coastal Ocean Processes: Paradigms and Approaches” was published. The papers collected in this issue cover physical phenomena, such as wind-driven flows, coastal flooding, turbidity currents, and modeling techniques such as model comparison, model coupling, parallel computation, and domain decomposition. This article outlines the needs for modeling of coastal ocean flows involving multiple physical processes at different scales, and it discusses the implications of the collected papers. Additionally, it reviews the current status and offers a roadmap with numerical methods, data collection, and artificial intelligence as future endeavors. Full article
(This article belongs to the Special Issue Multiscale, Multiphysics Modelling of Coastal Ocean Processes: Paradigms and Approaches)
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16 pages, 6509 KiB  
Article
Spatiotemporal Variability and Trends of Marine Heat Waves in the Red Sea over 38 Years
by Bayoumy Mohamed, Hazem Nagy and Omneya Ibrahim
J. Mar. Sci. Eng. 2021, 9(8), 842; https://doi.org/10.3390/jmse9080842 - 4 Aug 2021
Cited by 21 | Viewed by 6013
Abstract
Marine heat waves (MHWs) can have catastrophic consequences for the socio-environmental system. Especially in the Red Sea, which has the world’s second longest coral reef system. Here, we investigate the sea surface temperature (SST) variability and trends, as well as the spatiotemporal characteristics [...] Read more.
Marine heat waves (MHWs) can have catastrophic consequences for the socio-environmental system. Especially in the Red Sea, which has the world’s second longest coral reef system. Here, we investigate the sea surface temperature (SST) variability and trends, as well as the spatiotemporal characteristics of marine heat waves (MHWs) in the Red Sea, using high resolution daily gridded (1/20°) SST data obtained from the Copernicus Marine Environment Monitoring Service (CMEMS) for the period 1982–2019. Results show that the average warming rate was about 0.342 ± 0.047 °C/decade over the entire Red Sea over the whole study period. The Empirical Orthogonal Function (EOF) analysis reveals that the maximum variability is over the central part of the Red Sea, while the minimum variability is in the southernmost part of the Red Sea. Over the last two decades (2000–2019), we have discovered that the average MHW frequency and duration increased by 35% and 67%, respectively. The results illustrate that the MHW frequency and duration trends have increased by 1.17 counts/decade and 1.79 days/decade, respectively, over the study period. The highest annual MHW frequencies were detected in the years 2018, 2019, 2010, and 2017. A strong correlation (R = 0.89) was found between the annual MHW frequency and the annual mean SST. Full article
(This article belongs to the Special Issue Sea Surface Temperature: From Observation to Applications)
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21 pages, 5201 KiB  
Article
Considering the Effect of Land-Based Biomass on Dune Erosion Volumes in Large-Scale Numerical Modeling
by Constantin Schweiger and Holger Schuettrumpf
J. Mar. Sci. Eng. 2021, 9(8), 843; https://doi.org/10.3390/jmse9080843 - 4 Aug 2021
Cited by 3 | Viewed by 2221
Abstract
This paper presents and validates a novel root model which accounts for the effect of belowground biomass on dune erosion volumes in XBeach, based on a small-scale wave flume experiment that was translated to a larger scale. A 1D-XBeach model was calibrated by [...] Read more.
This paper presents and validates a novel root model which accounts for the effect of belowground biomass on dune erosion volumes in XBeach, based on a small-scale wave flume experiment that was translated to a larger scale. A 1D-XBeach model was calibrated by using control runs considering a dune without vegetation. Despite calibration, a general model–data mismatch was observed in terms of overestimated erosion volumes around the waterline. Furthermore, the prediction of overwash had to be induced by increasing the maximum nearshore wave height within the XBeach simulation. Subsequently, applying the root model resulted in a good agreement with the belowground biomass cases, and the consideration of spatially varying rooting depths further improved the results. Predictions of the root model while using locally increased friction coefficients were in line with the aboveground and belowground biomass cases. However, the effect of the root model on the erosion predictions varied among the hydrodynamic conditions, so further improvements are required. Therefore, future research should focus on quantifying the effects of land-based biomass and individual plant characteristics, such as root density, on dune erodibility at large scales, along with their influences on the temporal evolution of dune scarping and avalanching. Full article
(This article belongs to the Special Issue Morphodynamic Evolution and Sustainable Development of Coastal Systems)
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17 pages, 2104 KiB  
Article
COLREGs: Compliant Dynamic Obstacle Avoidance of USVs Based on the Dynamic Navigation Ship Domain
by Fang Deng, Leilei Jin, Xiuhui Hou, Longjin Wang, Boyang Li and Hualin Yang
J. Mar. Sci. Eng. 2021, 9(8), 837; https://doi.org/10.3390/jmse9080837 - 1 Aug 2021
Cited by 18 | Viewed by 4174
Abstract
Dynamic obstacle avoidance is essential for unmanned surface vehicles (USVs) to achieve autonomous sailing. This paper presents a dynamic navigation ship domain (DNSD)-based dynamic obstacle avoidance approach for USVs in compliance with COLREGs. Based on the detected obstacle information, the approach can not [...] Read more.
Dynamic obstacle avoidance is essential for unmanned surface vehicles (USVs) to achieve autonomous sailing. This paper presents a dynamic navigation ship domain (DNSD)-based dynamic obstacle avoidance approach for USVs in compliance with COLREGs. Based on the detected obstacle information, the approach can not only infer the collision risk, but also plan the local avoidance path trajectory to make appropriate avoidance maneuvers. Firstly, the analytical DNSD model is established taking into account the ship parameters, maneuverability, sailing speed, and encounter situations regarding COLREGs. Thus, the DNSDs of the own and target ships are utilized to trigger the obstacle avoidance mode and determine whether and when the USV should make avoidance maneuvers. Then, the local avoidance path planner generates the new avoidance waypoints and plans the avoidance trajectory. Simulations were implemented for a single obstacle under different encounter situations and multiple dynamic obstacles. The results demonstrated the effectiveness and superiority of the proposed DNSD-based obstacle avoidance algorithm. Full article
(This article belongs to the Special Issue Maritime Autonomous Vessels)
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19 pages, 10530 KiB  
Article
Hindcasting Soundscapes before and during the COVID-19 Pandemic in Selected Areas of the North Sea and the Adriatic Sea
by Hüseyin Özkan Sertlek
J. Mar. Sci. Eng. 2021, 9(7), 702; https://doi.org/10.3390/jmse9070702 - 26 Jun 2021
Cited by 8 | Viewed by 2486
Abstract
The national measures in several European countries during the COVID-19 pandemic also affected offshore human activities, including shipping. In this work, the temporal and spatial variations of shipping sound are calculated for the years before and during the pandemic in selected shallow water [...] Read more.
The national measures in several European countries during the COVID-19 pandemic also affected offshore human activities, including shipping. In this work, the temporal and spatial variations of shipping sound are calculated for the years before and during the pandemic in selected shallow water test areas from the Southern North Sea and the Adriatic Sea. First, the monthly sound pressure level maps of ships and wind between 2017 and 2020 are calculated for frequencies between 100 Hz to 10 kHz. Next, the monthly changes in these maps are compared. The asymptotic approximation of the hybrid flux-mode propagation model reduces the computational requirements for sound mapping simulations and facilitates the production of a large number of sound maps for different months, depths, frequencies, and ship categories. After the strictest COVID-19 measures were applied in April 2020, the largest decline was observed for the fishing, passenger and recreational ships. Although the changes in the number of fishing vessels are large, their contribution to the soundscape is minor due to their low source level. In both test areas, the spatial exceedance levels and acoustic energies were decreased in 2020 compared to the average of the previous three years. Full article
(This article belongs to the Special Issue Ocean Noise: From Science to Management)
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