Journal of Marine Science and Engineering

23 pages, 8777 KiB

Open AccessArticle

Sensitivity of Storm Response to Antecedent Topography in the XBeach Model

by Rangley C. Mickey, Patricia S. Dalyander, Robert McCall and Davina L. Passeri

J. Mar. Sci. Eng. 2020, 8(10), 829; https://doi.org/10.3390/jmse8100829 - 21 Oct 2020

Cited by 7 | Viewed by 3678

Antecedent topography is an important aspect of coastal morphology when studying and forecasting coastal change hazards. The uncertainty in morphologic response of storm-impact models and their use in short-term hazard forecasting and decadal forecasting is important to account for when considering a coupled [...] Read more.

Antecedent topography is an important aspect of coastal morphology when studying and forecasting coastal change hazards. The uncertainty in morphologic response of storm-impact models and their use in short-term hazard forecasting and decadal forecasting is important to account for when considering a coupled model framework. This study provided a methodology to investigate uncertainty of profile response within the storm impact model XBeach related to varying antecedent topographies. A parameterized island Gaussian fit (PIGF) model generated an idealized baseline profile and a suite of idealized profiles that vary specific characteristics based on collated observed LiDAR data from Dauphin Island, AL, USA. Six synthetic storm scenarios were simulated on each of the idealized profiles with XBeach in both 1- and 2-dimensional setups and analyzed to determine the morphological response and uncertainty related to the varied antecedent topographies. Profile morphologic response tends to scale with storm magnitude but among the varied profiles there is greater uncertainty in profile response to the medium range storm scenarios than to the low and high magnitude storm scenarios. XBeach can be highly sensitive to morphologic thresholds, both antecedent and time-varying, especially with regards to beach slope. Full article

(This article belongs to the Special Issue Beach-Dune System Morphodynamics)

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23 pages, 6224 KiB

Open AccessArticle

Development of the Physics–Based Morphology Model as the Platform for the Optimal Design of Beach Nourishment Project: A Numerical Study

by Yong Jun Cho

J. Mar. Sci. Eng. 2020, 8(10), 828; https://doi.org/10.3390/jmse8100828 - 21 Oct 2020

Cited by 7 | Viewed by 2270

Abstract

In this study, a physics-based morphology model is developed and to test the feasibility of the morphology model proposed in this study as the platform for the optimal design of the beach nourishment project, the beach restoration process by the infra-gravity waves underlying [...] Read more.

In this study, a physics-based morphology model is developed and to test the feasibility of the morphology model proposed in this study as the platform for the optimal design of the beach nourishment project, the beach restoration process by the infra-gravity waves underlying the swells in a mild sea is numerically simulated. As a hydrodynamic module, the IHFOAM wave toolbox having its roots in the OpenFoam is used. Speaking of the morphology model, a transport equation for suspended load and the Exner type equation constitute the morphology model. In doing so, the probability theory first introduced by Einstein and the physical model test by Bagnold are used as the constituent sub-model of the morphology model. Numerical results show that among many flow features that are indispensable in forming sand bars over the flat bottom and swash zone, the partially skewed and asymmetric bottom shearing stresses, a shoreward Stokes drift near the free surface, boundary layer streaming near the seabed, and undertow toward the offshore were successfully simulated using the morphology model proposed in this study. It was also shown that plunging type breaker occurring at the final stage of the shoaling process, and its accompanying second breaker, sediment entrainment at the seabed, and the redistribution of suspended load by the down rush of preceding waves were successfully reproduced in the numerical simulation, and agreements with our experience in the field were very encouraging. In particular, the sand bar formation process over the flat bottom and backshore were successfully reproduced in the numerical simulation, which has been regarded as a challenging task. Full article

(This article belongs to the Section Coastal Engineering)

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16 pages, 6589 KiB

Open AccessArticle

Derivation of Engineering Design Criteria for Flow Field Around Intake Structure: A Numerical Simulation Study

by Lee Hooi Chie and Ahmad Khairi Abd Wahab

J. Mar. Sci. Eng. 2020, 8(10), 827; https://doi.org/10.3390/jmse8100827 - 21 Oct 2020

Cited by 9 | Viewed by 5720

Abstract

The primary environmental impact caused by seawater intake operation is marine life impingement resulting from the intake velocity. Environmental Protection Agency (EPA) of United State has regulated the use of velocity cap fitted at intake structures to reduce the marine life impingement. The [...] Read more.

The primary environmental impact caused by seawater intake operation is marine life impingement resulting from the intake velocity. Environmental Protection Agency (EPA) of United State has regulated the use of velocity cap fitted at intake structures to reduce the marine life impingement. The engineering design parameters of velocity cap has not been well explored to date. This study has been set to determine the fundamental relationships between intake velocity and design parameters of velocity cap, using computational fluid dynamic (CFD) model. A set of engineering design criteria for velocity cap design are derived. The numerical evidence yielded in this study show that the velocity cap should be designed with vertical opening (H_vc) and horizontal shelf (ℓ_vc). The recommended intake opening ratio (O_r) shall be 0.36 V_r^−0.31, where O_r = H_vc/ℓ_vc and V_r =V₀/V_pipe. V_o is the velocity at the intake window and V_pipe is the suction velocity at the intake pipe. The volume ratio (ω_r) between the velocity cap (ω_vc) and intake tower (ω_IT) is recommended at 0.11 V_r^−1.23. The positive outlooks that yielded from this study can be served as a design reference for velocity cap to mitigate the detrimental impacts from the existing intake structure. Full article

(This article belongs to the Special Issue Fluid/Structure Interactions)

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20 pages, 6071 KiB

Open AccessFeature PaperArticle

SPH Simulations of Real Sea Waves Impacting a Large-Scale Structure

by Corrado Altomare, Angelantonio Tafuni, José M. Domínguez, Alejandro J. C. Crespo, Xavi Gironella and Joaquim Sospedra

J. Mar. Sci. Eng. 2020, 8(10), 826; https://doi.org/10.3390/jmse8100826 - 21 Oct 2020

Cited by 38 | Viewed by 5776

Abstract

The Pont del Petroli is a dismissed pier in the area of Badalona, Spain, with high historical and social value. This structure was heavily damaged in January 2020 during the storm Gloria that hit southeastern Spain with remarkable strength. The reconstruction of the [...] Read more.

The Pont del Petroli is a dismissed pier in the area of Badalona, Spain, with high historical and social value. This structure was heavily damaged in January 2020 during the storm Gloria that hit southeastern Spain with remarkable strength. The reconstruction of the pier requires the assessment and characterization of the wave loading that determined the structural failure. Therefore, a state-of-the-art Computational Fluid Dynamic (CFD) code was employed herein as an aid for a planned experimental campaign that will be carried out at the Maritime Engineering Laboratory of Universitat Politècnica de Catalunya-BarcelonaTech (LIM/UPC). The numerical model is based on Smoothed Particle Hydrodynamics (SPH) and has been employed to simulate conditions very similar to those that manifested during the storm Gloria. The high computational cost for a full 3-D simulation has been alleviated by means of inlet boundary conditions, allowing wave generation very close to the structure. Numerical results reveal forces higher than the design loads of the pier, including both self-weight and accidental loads. This demonstrates that the main failure mechanism that led to severe structural damage of the pier during the storm is related to the exceeded lateral soil resistance. To the best of the authors’ knowledge, this research represents the first known application of SPH open boundary conditions to model a real-world engineering case. Full article

(This article belongs to the Special Issue Wave Interactions with Coastal Structures)

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30 pages, 3750 KiB

Open AccessFeature PaperArticle

Real-Time Wave Excitation Forces Estimation: An Application on the ISWEC Device

by Mauro Bonfanti, Andrew Hillis, Sergej Antonello Sirigu, Panagiotis Dafnakis, Giovanni Bracco, Giuliana Mattiazzo and Andrew Plummer

J. Mar. Sci. Eng. 2020, 8(10), 825; https://doi.org/10.3390/jmse8100825 - 21 Oct 2020

Cited by 26 | Viewed by 4761

Abstract

Optimal control strategies represent a widespread solution to increase the extracted energy of a Wave Energy Converter (WEC). The aim is to bring the WEC into resonance enhancing the produced power without compromising its reliability and durability. Most of the control algorithms proposed [...] Read more.

Optimal control strategies represent a widespread solution to increase the extracted energy of a Wave Energy Converter (WEC). The aim is to bring the WEC into resonance enhancing the produced power without compromising its reliability and durability. Most of the control algorithms proposed in literature require for the knowledge of the Wave Excitation Force (WEF) generated from the incoming wave field. In practice, WEFs are unknown, and an estimate must be used. This paper investigates the WEF estimation of a non-linear WEC. A model-based and a model-free approach are proposed. First, a Kalman Filter (KF) is implemented considering the WEC linear model and the WEF modelled as an unknown state to be estimated. Second, a feedforward Neural Network (NN) is applied to map the WEC dynamics to the WEF by training the network through a supervised learning algorithm. Both methods are tested for a wide range of irregular sea-states showing promising results in terms of estimation accuracy. Sensitivity and robustness analyses are performed to investigate the estimation error in presence of un-modelled phenomena, model errors and measurement noise. Full article

(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters)

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23 pages, 3365 KiB

Open AccessArticle

Microbial Abundance and Enzyme Activity Patterns: Response to Changing Environmental Characteristics along a Transect in Kongsfjorden (Svalbard Islands)

by Gabriella Caruso, Alice Madonia, Simone Bonamano, Stefano Miserocchi, Federico Giglio, Giovanna Maimone, Filippo Azzaro, Franco Decembrini, Rosabruna La Ferla, Viviana Piermattei, Daniele Piazzolla, Marco Marcelli and Maurizio Azzaro

J. Mar. Sci. Eng. 2020, 8(10), 824; https://doi.org/10.3390/jmse8100824 - 21 Oct 2020

Cited by 9 | Viewed by 3334

Abstract

Svalbard archipelago is experiencing the effects of climate changes (i.e., glaciers’ thickness reduction and glacier front retreat), but how ice melting affects water biogeochemistry is still unknown. Microbial communities often act as environmental sentinels, modulating their distribution and activity in response to environmental [...] Read more.

Svalbard archipelago is experiencing the effects of climate changes (i.e., glaciers’ thickness reduction and glacier front retreat), but how ice melting affects water biogeochemistry is still unknown. Microbial communities often act as environmental sentinels, modulating their distribution and activity in response to environmental variability. To assess microbial response to climate warming, within the ARctic: present Climatic change and pAst extreme events (ARCA) project, a survey was carried out along a transect in Konsfjorden from off-shore stations towards the Kronebreen glacier. Total bacterial abundance and the fraction of actively respiring cells (labelled by cyanotetrazolium chloride, CTC), cultivable heterotrophic bacterial abundance, and extracellular enzymatic activities (leucine aminopeptidase (LAP), beta-glucosidase (GLU), and alkaline phosphatase (AP)) were measured. In addition, water temperature, salinity, dissolved oxygen, turbidity, total suspended matter (TSM), particulate and chromophoric dissolved organic matter (CDOM), chlorophyll-a (Chl-a), and inorganic compounds were determined, in order to evaluate whether variations in microbial abundance and metabolism were related with changes in environmental variables. Colder waters at surface (3.5–5 m) depths and increased turbidity, TSM, and inorganic compounds found at some hydrological stations close to the glacier were signals of ice melting. CDOM absorption slope values (275–295 nm) varied from 0.0077 to 0.0109 nm⁻¹, and total bacterial cell count and cultivable heterotrophic bacterial abundance were in the order of 10⁶ cells/mL and 10³ colony forming units/mL, respectively. Enzymatic rates <1.78, 1.25, and 0.25 nmol/L/h were recorded for AP, LAP, and GLU, respectively. Inorganic compounds, TSM, and turbidity correlated inversely with temperature; AP was significantly related with CDOM absorption spectra and heterotrophic bacteria (r = 0.59, 0.71, p < 0.05); and LAP with Chl-a, Particulate Organic Carbon (POC) and Particulate Organic Nitrogen (PON) (0.97, 0.780, 0.734, p < 0.01), suggesting that fresh material from ice melting stimulated the metabolism of the cultivable fraction. Full article

(This article belongs to the Special Issue Distribution and Metabolic Activities of Marine Microbes in Response to Natural and Anthropogenic Stressors)

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Graphical abstract

26 pages, 1543 KiB

Open AccessReview

Review of Systems Engineering (SE) Methods and Their Application to Wave Energy Technology Development

by Pablo Ruiz-Minguela, Vincenzo Nava, Jonathan Hodges and Jesús M. Blanco

J. Mar. Sci. Eng. 2020, 8(10), 823; https://doi.org/10.3390/jmse8100823 - 20 Oct 2020

Cited by 3 | Viewed by 3993

Abstract

The design of effective and economically viable wave energy devices involves complex decision-making about the product based on conceptual design information, including stakeholder requirements, functions, components and technical parameters. The great diversity of concepts makes it extremely difficult to create fair comparisons of [...] Read more.

The design of effective and economically viable wave energy devices involves complex decision-making about the product based on conceptual design information, including stakeholder requirements, functions, components and technical parameters. The great diversity of concepts makes it extremely difficult to create fair comparisons of the relative merits of the many different designs. Conventional design approaches have proved insufficient to guarantee wave energy technologies meet their technical and economic goals. Systems engineering can provide a suitable framework to overcome the obstacles towards a successful wave energy technology. The main objective of this work is to review the well-established systems engineering approaches that have been successfully implemented in complex engineering problems and to what extent they have been applied to wave energy technology development. The paper first reviews how system information can be organised in different design domains to guide the synthesis and analysis activities and the definition of requirements and metrics, as well as the search for solutions and decision-making. Then, an exhaustive literature review on the application of systems engineering approaches to wave energy development is presented per design domain. Finally, a set of conclusions is drawn, along with some suggestions for improving the effectiveness of wave energy technology development. Full article

(This article belongs to the Special Issue From High-Fidelity Models towards Engineering Tools for the Design of Offshore Renewable Energy Technologies)

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14 pages, 2311 KiB

Open AccessArticle

Effects of Low pH and Low Salinity Induced by Meltwater Inflow on the Behavior and Physical Condition of the Antarctic Limpet, Nacella concinna

by Eunchong Sin, In-Young Ahn, Seojeong Park and Taewon Kim

J. Mar. Sci. Eng. 2020, 8(10), 822; https://doi.org/10.3390/jmse8100822 - 20 Oct 2020

Cited by 12 | Viewed by 4177

Abstract

Seawater acidification and freshening in the intertidal zone of Marian Cove, Antarctica, which occurs by the freshwater inflow from snow fields and glaciers, could affect the physiology and behavior of intertidal marine organisms. In this study, we exposed Antarctic limpets, Nacella concinna, [...] Read more.

Seawater acidification and freshening in the intertidal zone of Marian Cove, Antarctica, which occurs by the freshwater inflow from snow fields and glaciers, could affect the physiology and behavior of intertidal marine organisms. In this study, we exposed Antarctic limpets, Nacella concinna, to two different pH (8.00 and 7.55) and salinity (34.0 and 27.0 psu) levels and measured their righting ability after being flipped over, mortality, condition factor, and shell dissolution. During the 35-day exposure, there was no significant difference in behavior and mortality between different treatments. However, the condition factor was negatively affected by low salinity. Both low pH and low salinity negatively influenced shell formation by decreasing the aragonite saturation state (Ω_arg) and enhancing shell dissolution. Our results suggest that, though limpets can tolerate short-term low pH and salinity conditions, intrusions of meltwater accompanied by the glacial retreat may act as a serious threat to the population of N. concinna. Full article

(This article belongs to the Special Issue Drivers and Consequences of Ocean Acidification on Different Temporal and Spatial Scales)

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15 pages, 4163 KiB

Open AccessArticle

The Effects of Ocean Acidification and Warming on Growth of a Natural Community of Coastal Phytoplankton

by Bonggil Hyun, Ja-Myung Kim, Pung-Guk Jang, Min-Chul Jang, Keun-Hyung Choi, Kitack Lee, Eun Jin Yang, Jae Hoon Noh and Kyoungsoon Shin

J. Mar. Sci. Eng. 2020, 8(10), 821; https://doi.org/10.3390/jmse8100821 - 20 Oct 2020

Cited by 11 | Viewed by 4639

Abstract

An in situ mesocosm experiment was performed to investigate the combined effects of ocean acidification and warming on the coastal phytoplankton standing stock and species composition of a eutrophic coastal area in the temperate-subtropical region. Experimental treatments of natural seawater included three CO [...] Read more.

An in situ mesocosm experiment was performed to investigate the combined effects of ocean acidification and warming on the coastal phytoplankton standing stock and species composition of a eutrophic coastal area in the temperate-subtropical region. Experimental treatments of natural seawater included three CO₂ and two temperature conditions (present control: ~400 μatm CO₂ and ambient temperature, acidification conditions: ~900 μatm CO₂ and ambient temperature, and greenhouse conditions: ~900 μatm CO₂ and ambient temperature +3 °C). We found that increased CO₂ concentration benefited the growth of small autotrophic phytoplankton groups: picophytoplankton (PP), autotrophic nanoflagellates (ANF), and small chain-forming diatoms (DT). However, in the greenhouse conditions, ANF and DT abundances were lower compared with those in the acidification conditions. The proliferation of small autotrophic phytoplankton in future oceanic conditions (acidification and greenhouse) also increased the abundance of heterotrophic dinoflagellates (HDF). These responses suggest that a combination of acidification and warming will not only increase the small autotrophic phytoplankton standing stock but, also, lead to a shift in the diatom and dinoflagellate species composition, with potential biogeochemical element cycling feedback and an increased frequency and intensity of harmful algal blooms. Full article

(This article belongs to the Section Marine Biology)

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22 pages, 6257 KiB

Open AccessArticle

Analysis of the Impact of Split Injection on Fuel Consumption and NO_x Emissions of Marine Medium-Speed Diesel Engine

by Vladimir Pelić, Tomislav Mrakovčić, Radoslav Radonja and Marko Valčić

J. Mar. Sci. Eng. 2020, 8(10), 820; https://doi.org/10.3390/jmse8100820 - 20 Oct 2020

Cited by 12 | Viewed by 3382

Abstract

The medium-speed diesel engine in diesel-electric propulsion systems is increasingly used as the propulsion engine for liquefied natural gas (LNG) ships and passenger ships. The main advantage of such systems is high reliability, better maneuverability, greater ability to optimize and significant decreasing of [...] Read more.

The medium-speed diesel engine in diesel-electric propulsion systems is increasingly used as the propulsion engine for liquefied natural gas (LNG) ships and passenger ships. The main advantage of such systems is high reliability, better maneuverability, greater ability to optimize and significant decreasing of the engine room volume. Marine propulsion systems are required to be as energy efficient as possible and to meet environmental protection standards. This paper analyzes the impact of split injection on fuel consumption and NO_x emissions of marine medium-speed diesel engines. For the needs of the research, a zero-dimensional, two-zone numerical model of a diesel engine was developed. Model based on the extended Zeldovich mechanism was applied to predict NO_x emissions. The validation of the numerical model was performed by comparing operating parameters of the basic engine with data from engine manufacturers and data from sea trials of a ship with diesel-electric propulsion. The applicability of the numerical model was confirmed by comparing the obtained values for pressure, temperature and fuel consumption. The operation of the engine that drives synchronous generator was simulated under stationary conditions for three operating points and nine injection schemes. The values obtained for fuel consumption and NO_x emissions for different fuel injection schemes indicate the possibility of a significant reduction in NO_x emissions but with a reduction in efficiency. The results showed that split injection with a smaller amount of pilot fuel injected and a smaller angle between the two injection allow a moderate reduction in NO_x emissions without a significant reduction in efficiency. The application of split injection schemes that allow significant reductions in NO_x emissions lead to a reduction in engine efficiency. Full article

(This article belongs to the Special Issue Marine Power Systems)

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23 pages, 5194 KiB

Open AccessArticle

A Real-Time Detection System for the Onset of Parametric Resonance in Wave Energy Converters

by Josh Davidson and Tamás Kalmár-Nagy

J. Mar. Sci. Eng. 2020, 8(10), 819; https://doi.org/10.3390/jmse8100819 - 20 Oct 2020

Cited by 12 | Viewed by 2827

Abstract

Parametric resonance is a dynamic instability due to the internal transfer of energy between degrees of freedom. Parametric resonance is known to cause large unstable pitch and/or roll motions in floating bodies, and has been observed in wave energy converters (WECs). The occurrence [...] Read more.

Parametric resonance is a dynamic instability due to the internal transfer of energy between degrees of freedom. Parametric resonance is known to cause large unstable pitch and/or roll motions in floating bodies, and has been observed in wave energy converters (WECs). The occurrence of parametric resonance can be highly detrimental to the performance of a WEC, since the energy in the primary mode of motion is parasitically transferred into other modes, reducing the available energy for conversion. In addition, the large unstable oscillations produce increased loading on the WEC structure and mooring system, accelerating fatigue and damage to the system. To remedy the negative effects of parametric resonance on WECs, control systems can be designed to mitigate the onset of parametric resonance. A key element of such a control system is a real-time detection system, which can provide an early warning of the likely occurrence of parametric resonance, enabling the control system sufficient time to respond and take action to avert the impending exponential increase in oscillation amplitude. This paper presents the first application of a real-time detection system for the onset of parametric resonance in WECs. The method is based on periodically assessing the stability of a mathematical model for the WEC dynamics, whose parameters are adapted online, via a recursive least squares algorithm, based on online measurements of the WEC motion. The performance of the detection system is demonstrated through a case study, considering a generic cylinder type spar-buoy, a representative of a heaving point absorber WEC, in both monochromatic and polychromatic sea states. The detection system achieved 95% accuracy across nearly 7000 sea states, producing 0.4% false negatives and 4.6% false positives. For the monochromatic waves more than 99% of the detections occurred while the pitch amplitude was less than 1/6 of its maximum amplitude, whereas for the polychromatic waves 63% of the detections occurred while the pitch amplitude was less than 1/6 of its maximum amplitude and 91% while it was less than 1/3 of its maximum amplitude. Full article

(This article belongs to the Special Issue Optimization and Energy Maximizing Control Systems for Wave Energy Converters)

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13 pages, 1927 KiB

Open AccessConcept Paper

Assisting Maritime Search and Rescue (SAR) Personnel with AI-Based Speech Recognition and Smart Direction Finding

by Aylin Gözalan, Ole John, Thomas Lübcke, Andreas Maier, Maximilian Reimann, Jan-Gerrit Richter and Ivan Zverev

J. Mar. Sci. Eng. 2020, 8(10), 818; https://doi.org/10.3390/jmse8100818 - 20 Oct 2020

Cited by 8 | Viewed by 4224

Abstract

Communication for processing relevant information plays a paramount role in developing a comprehensive understanding of Search and Rescue (SAR) situations and conducting operations in a successful and reliable manner. Nevertheless, communication systems have not changed considerably in the context of simplifying very high [...] Read more.

Communication for processing relevant information plays a paramount role in developing a comprehensive understanding of Search and Rescue (SAR) situations and conducting operations in a successful and reliable manner. Nevertheless, communication systems have not changed considerably in the context of simplifying very high frequency (VHF) maritime communication and enhancing the value of SAR practices. The Automated Transcription of Maritime VHF Radio Communication for SAR Mission Coordination (ARTUS) project approaches this problem with the development of an assistance system which employs AI-based speech recognition and smart direction finding. First, ideas and specified needs of end users for designing the user interface are presented in this paper. Further, preliminary accomplishments of domain specific language training for maritime speech recognition, and the direction-finding algorithms for localizing senders are sketched out. While the preliminary results build a solid ground, additional field experiments will be conducted in order to enhance the accuracy and reliability of speech recognition and direction finding. The identified end user requirements across different personnel groups show commonalities, but call for a differentiated approach in order to meet the challenges and peculiar needs of the various working contexts. Full article

(This article belongs to the Special Issue Human-Automation Integration in the Maritime Sector)

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19 pages, 1286 KiB

Open AccessArticle

Ballast Water Treatment Performance Evaluation under Real Changing Conditions

by Pung-Guk Jang, Bonggil Hyun and Kyoungsoon Shin

J. Mar. Sci. Eng. 2020, 8(10), 817; https://doi.org/10.3390/jmse8100817 - 20 Oct 2020

Cited by 25 | Viewed by 4838

Abstract

We conducted a shipboard ballast water test using seawater of extreme turbidity collected from Shanghai Port (China) (>300 mg total suspended solids (TSS)/L), and normal seawater collected in other ports (<100 mg TSS/L). All three types of International Maritime Organization (IMO)-approved ballast water [...] Read more.

We conducted a shipboard ballast water test using seawater of extreme turbidity collected from Shanghai Port (China) (>300 mg total suspended solids (TSS)/L), and normal seawater collected in other ports (<100 mg TSS/L). All three types of International Maritime Organization (IMO)-approved ballast water management system (BWMS) tested failed to properly operate because of filter clogging or insufficient generation of oxidants under near-fresh water conditions with extremely high concentration of suspended solid during ballasting. It was also found that the number of microorganisms increased with longer ballast water retention time, with higher numbers in the treated discharge water. The results suggest that when operating a BWMS involving a filter unit in areas with water having high concentrations of suspended solids, the filter unit should be used during ballast water discharge, rather than during ballasting. This method has the advantage of removing ≥50 µm organisms at discharge that could not be removed by a filter during ballasting. For ballast water retained for long storage times, the results suggest the use of BWMSs involving UV units or electrolysis during deballasting. In addition, BWMSs involving electrolysis units provide the opportunity to maintain residual total residual oxidant (TRO) levels, using a partial ballast tank. Although the BWMSs tested are a small subset of the large number of IMO-approved BWMSs, the results demonstrate that there is a significant gap between the technology currently available and capacity to meet IMO and US Coast Guard standards. Full article

(This article belongs to the Section Marine Biology)

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21 pages, 13052 KiB

Open AccessFeature PaperArticle

Static Behaviors of a Long-span Cable-Stayed Bridge with a Floating Tower under Dead Loads

by Minseo Jang, Yunwoo Lee, Deokhee Won, Young-Jong Kang and Seungjun Kim

J. Mar. Sci. Eng. 2020, 8(10), 816; https://doi.org/10.3390/jmse8100816 - 20 Oct 2020

Cited by 9 | Viewed by 4270

Abstract

Owing to the structural characteristics of floating-type structures, they can be effectively applied to overcome the limitation of conventional long-span bridges in deep water. Unlike cable-supported bridges with fixed towers, floating cable-supported bridges show relatively large displacements and rotations under the same load [...] Read more.

Owing to the structural characteristics of floating-type structures, they can be effectively applied to overcome the limitation of conventional long-span bridges in deep water. Unlike cable-supported bridges with fixed towers, floating cable-supported bridges show relatively large displacements and rotations under the same load because of floating towers; moreover, the difference in the support stiffness causes differences in the behavior of the superstructures. In addition, the risk of overturning is greater than in conventional floating offshore structures because the center of gravity of the tower is located above the buoyancy center of the floater. A floating cable-supported bridge in which the tether supports the floating main tower is directly influenced by the tether arrangement, which is very important for the stability of the entire structure. In this study, according to the inclined tether arrangement, the outer diameter of the floater, and the buoyancy vertical load ratio (BVR), the static behavioral characteristics of the long-span cable-stayed bridges with floating tower are evaluated through nonlinear finite-element analysis. When the intersection of the tension line of the tether and a pivot point of the tower coincide, the tethers can no longer resist the tower’s rotation. For this reason, a large displacement occurs to equilibrate the structure, and further increases as it approaches the specific slope, even if it is not exactly the specific tether slope. The analytical model of this study indicates that, in terms of increasing the rotational stiffness of the main tower, it is advantageous to increase the floater diameter until a BVR of 1.8 is reached and to increase the axial stiffness of the tether from a BVR of 2.0 or higher. Full article

(This article belongs to the Special Issue Ocean and Shore Technology (OST))

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29 pages, 3017 KiB

Open AccessArticle

Coastal Ecosystem Services, Social Equity, and Blue Growth: A Case Study from South-Eastern Bangladesh

by Mohammad Mahmudul Islam, Shuvo Pal, Mohammad Mosarof Hossain, Mohammad Mojibul Hoque Mozumder and Petra Schneider

J. Mar. Sci. Eng. 2020, 8(10), 815; https://doi.org/10.3390/jmse8100815 - 19 Oct 2020

Cited by 15 | Viewed by 5771

Abstract

By employing empirical and secondary data (qualitative and quantitative), this study demonstrates how social equity (with its three dimensions) can meaningfully address the conservation of the coastal social–ecological system (SES), without losing diverse ecosystem services (ES) in south-east coastal Bangladesh. Based on this [...] Read more.

By employing empirical and secondary data (qualitative and quantitative), this study demonstrates how social equity (with its three dimensions) can meaningfully address the conservation of the coastal social–ecological system (SES), without losing diverse ecosystem services (ES) in south-east coastal Bangladesh. Based on this proposition, this study assesses the available ES and identifies the drivers responsible for ES changes, arguing for the application of social equity for resource conservation. The findings show that communities along Bangladesh’s south-eastern coast use several ES for food, medicine, income, livelihoods, and cultural heritage. However, this valuable ecosystem is currently experiencing numerous threats and stressors of anthropogenic and natural origin. In particular, large-scale development activities, driven by the blue growth agenda, and neoliberalism policy, pose a risk to the local communities by degrading coastal ecosystem services. Escaping this situation for coastal natural resource-dependent communities in Bangladesh will require a transformation in the governance structure. Implementing the Small-Scale Fisheries (SSF) Guidelines that call for initiating policy change to deliver social justice to small-scale fisheries would help to address coastal ecosystem service conservation in Bangladesh. Full article

(This article belongs to the Special Issue Integrated Coastal Zone Management)

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17 pages, 3321 KiB

Open AccessArticle

A Study on the Minimization of Mooring Load in Fish-Cage Mooring Systems with a Damping Buoy

by Gun-Ho Lee, Bong-Jin Cha and Hyun-young Kim

J. Mar. Sci. Eng. 2020, 8(10), 814; https://doi.org/10.3390/jmse8100814 - 19 Oct 2020

Cited by 3 | Viewed by 3419

Abstract

This study established the conditions in which mooring load is minimized in a fish cage that includes a damping buoy in specific wave conditions. To derive these conditions, numerical simulations of various mooring contexts were conducted on a fish cage (1/15 scale) using [...] Read more.

This study established the conditions in which mooring load is minimized in a fish cage that includes a damping buoy in specific wave conditions. To derive these conditions, numerical simulations of various mooring contexts were conducted on a fish cage (1/15 scale) using a simplified mass-spring model and fifth-order Stokes wave theory. The simulation conditions were as follows: (1) bridle-line length of 0.8–3.2 m; (2) buoyancy of 2.894–20.513 N for the damping buoy; and (3) mooring-rope thickness of 0.002–0.004 m. The wave conditions were 0.333 m in height and 1.291–2.324 s of arrival period. Consequently, the mooring tensions tended to decrease with decreasing mooring line thickness and increasing bridle-line length and buoyancy of the buoy. Accordingly, it was assumed to be advantageous to minimize the mooring tension by designing a thin mooring line and long bridle line and for the buoyancy of the buoy to be as large as possible. This approach shows a valuable technique because it can contribute to the improvement of the mooring stability of the fish cage by establishing a method that can be used to minimize the load on the mooring line. Full article

(This article belongs to the Special Issue Application of Flexible Structure in Marine Engineering)

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19 pages, 4080 KiB

Open AccessArticle

Rhodolith Beds Heterogeneity along the Apulian Continental Shelf (Mediterranean Sea)

by Giovanni Chimienti, Lucia Rizzo, Sara Kaleb, Annalisa Falace, Simonetta Fraschetti, Francesco De Giosa, Angelo Tursi, Enrico Barbone, Nicola Ungaro and Francesco Mastrototaro

J. Mar. Sci. Eng. 2020, 8(10), 813; https://doi.org/10.3390/jmse8100813 - 19 Oct 2020

Cited by 23 | Viewed by 3435

Abstract

Rhodolith beds represent a key habitat worldwide, from tropical to polar ecosystems. Despite this habitat is considered a hotspot of biodiversity, providing a suite of ecosystem goods and services, still scarce quantitative information is available thus far about rhodolith beds occurrence and ecological [...] Read more.

Rhodolith beds represent a key habitat worldwide, from tropical to polar ecosystems. Despite this habitat is considered a hotspot of biodiversity, providing a suite of ecosystem goods and services, still scarce quantitative information is available thus far about rhodolith beds occurrence and ecological role, especially in the Mediterranean Sea. This study reports the composition and patterns of distribution of rhodolith assemblages found in four study areas along ca. 860 km of coast in the Central Mediterranean Sea. These rhodolith beds were studied for the first time and significant differences at all spatial scales have been highlighted, documenting the high variability of this habitat. Rhodolith species composition, morphology and distribution have been discussed considering the potential role of environmental factors in driving these patterns. The need for improving their protection is discussed to complement present conservation and management initiatives, particularly in the frame of the EU Marine Strategy Framework Directive. Full article

(This article belongs to the Special Issue Benthic Species and Habitats)

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18 pages, 6957 KiB

Open AccessArticle

Coastal Boulders on the SE Coasts of Cyprus as Evidence of Palaeo-Tsunami Events

by Niki Evelpidou, Christos Zerefos, Costas Synolakis, Christos Repapis, Anna Karkani, Miltiadis Polidorou and Giannis Saitis

J. Mar. Sci. Eng. 2020, 8(10), 812; https://doi.org/10.3390/jmse8100812 - 19 Oct 2020

Cited by 10 | Viewed by 3242

Abstract

Cyprus has a long history of tsunami events, as noted by archaeological and geological records. At Cape Greco (southeastern Cyprus) large boulders have been noted, however, no detailed geomorphological research has taken place so far and the related high energy event was undated [...] Read more.

Cyprus has a long history of tsunami events, as noted by archaeological and geological records. At Cape Greco (southeastern Cyprus) large boulders have been noted, however, no detailed geomorphological research has taken place so far and the related high energy event was undated until now. Our research aims to record in detail and interpret these large boulders deposits. The boulders, located between ≈3 and 4.5 m a.m.s.l., are fragments of an upper Pleistocene aeolianite, which is overlaying unconformly a lower Pleistocene calcarenite. Dimensions and spatial distribution of 272 small, medium, and large boulders were documented, while their precise distance from the coastline was recorded by field mapping and remote sensing, using Differential GPS (DGPS), drone, and Geographic Information Systems (GIS) technics. Field data were subsequently combined with hydrodynamic equations, in order to determine the extreme event(s) that caused their transport inland, and radiocarbon dating was accomplished on three samples of Vermetus sp. to determine the chronological context. Our findings appear to broadly correlate with the 1303 AD tsunami, which has displaced at least part of the studied boulders, and one other undocumented event at AD 1512-1824. The large number of boulders and sizes in our study area further indicate that their dislocation is most likely owed to multiple events from various sources. Full article

(This article belongs to the Special Issue Tectonics and Sea-Level Fluctuations)

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21 pages, 1267 KiB

Open AccessArticle

Investment Analysis of Waste Heat Recovery System Installations on Ships’ Engines

by Eunice O. Olaniyi and Gunnar Prause

J. Mar. Sci. Eng. 2020, 8(10), 811; https://doi.org/10.3390/jmse8100811 - 19 Oct 2020

Cited by 21 | Viewed by 5966

Abstract

This study considers incentive provisions for investment decisions related to waste heat recovery system (WHRS) installations on ships to reduce CO₂ emissions and improve ships’ engine efficiency. The economic assessment of WHRS installations in the shipping sector is not widely covered in [...] Read more.

This study considers incentive provisions for investment decisions related to waste heat recovery system (WHRS) installations on ships to reduce CO₂ emissions and improve ships’ engine efficiency. The economic assessment of WHRS installations in the shipping sector is not widely covered in the literature. A reason for this might be that the conventional financial evaluation of sensitive choices is commonly done through capital budgeting methods, which are not flexible enough to integrate future changes in fuel prices and long-term aspects of other costs. Thus, this work evaluates the WHRS investment using the classical budgeting instruments as well as the real-options approach (a more sophisticated approach) to accommodate the presumed expected future changes in the volatile maritime markets. Following the methodology of triangulation, three case studies of ships with varying operational conditions empirically validate the result to depict the practical use of the real-options evaluation method in investment assessment. The capital budgeting analysis reveals that the investment in maritime WHRS technology is only economically favorable under certain frame conditions projected in the work that shows a more realistic assessment of the project. Full article

(This article belongs to the Special Issue Marine Alternative Fuels and Environmental Protection)

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17 pages, 2786 KiB

Open AccessArticle

Tidal and Storm Impacts on Hydrodynamics and Sediment Dynamics in an Energetic Ebb Tidal Delta

by Kehui Xu, P. Ansley Wren and Yanxia Ma

J. Mar. Sci. Eng. 2020, 8(10), 810; https://doi.org/10.3390/jmse8100810 - 19 Oct 2020

Cited by 4 | Viewed by 2688

Abstract

Bottom-mounted instrumentation was deployed at two sites on a large sandy shoal of an ebb tidal delta offshore of the Port Royal Sound of South Carolina of USA to collect hydrodynamics and sediment dynamics data. One site (“borrow site”) was 2 km offshore [...] Read more.

Bottom-mounted instrumentation was deployed at two sites on a large sandy shoal of an ebb tidal delta offshore of the Port Royal Sound of South Carolina of USA to collect hydrodynamics and sediment dynamics data. One site (“borrow site”) was 2 km offshore in a dredge pit for nearby beach nourishment and the other site (“reference site”) was 10 km offshore. In situ time-series data were collected during two periods after the dredging: 15 March–12 June (spring) and 18 August–18 November (fall) of 2012. Data at the reference site indicated active migrating bedforms from centimeters to decimeters tall, and sediment concentrations were highly associated with semidiurnal and fortnightly tidal cycles. In the fall deployment, waves at the reference site were higher than those at the shallow borrow site. Both Tropical Storm Beryl and Hurricane Sandy formed high waves and strong currents but did not generate the greatest sediment fluxes. The two sites were at different depths and distances offshore, and waves contributed more to sediment mobility at the reference site whereas tidal forcing was the key controlling factor at the borrow site. This study provides valuable datasets for the selection of sites, prediction of pit infilling, and the modeling of storm impact in future beach nourishment and coastal restoration projects. Full article

(This article belongs to the Special Issue Observational and Numerical Approaches in Coastal Sediment Dynamics and Hydrodynamics)

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25 pages, 21123 KiB

Open AccessFeature PaperArticle

A Discrete-Forcing Immersed Boundary Method for Moving Bodies in Air–Water Two-Phase Flows

by Haixuan Ye, Yang Chen and Kevin Maki

J. Mar. Sci. Eng. 2020, 8(10), 809; https://doi.org/10.3390/jmse8100809 - 19 Oct 2020

Cited by 2 | Viewed by 3314

Abstract

For numerical simulations of ship and offshore hydrodynamic problems, it is challenging to model the interaction between the free surface and moving complex geometries. This paper proposes a discrete-forcing immersed boundary method (IBM) to efficiently simulate moving solid boundaries in incompressible air–water two-phase [...] Read more.

For numerical simulations of ship and offshore hydrodynamic problems, it is challenging to model the interaction between the free surface and moving complex geometries. This paper proposes a discrete-forcing immersed boundary method (IBM) to efficiently simulate moving solid boundaries in incompressible air–water two-phase flows. In the present work, the air–water two-phase flows are modeled using the Volume-of-Fluid (VoF) method. The present IBM is suitable for unstructured meshes. It can be used combined with body-fitted wall boundaries to model the relative motions between solid walls, which makes it flexible to use in practical applications. A field extension method is used to model the interaction between the air–water interface and the immersed boundaries. The accuracy of the method is demonstrated through validation cases, including the three-dimensional dam-break problem with an obstacle, the water exit of a circular cylinder, and a ship model advancing with a rotating semi-balanced rudder. The flow field, free-surface profile and force on the immersed boundaries (IBs) are in good agreement with experimental data and other numerical results. Full article

(This article belongs to the Special Issue CFD Simulations of Marine Hydrodynamics)

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14 pages, 1227 KiB

Open AccessArticle

Sublethal Effects of Crude Oil and Chemical Dispersants on Multiple Life History Stages of the Eastern Oyster, Crassostrea virginica

by Sara M. Garcia, Kevin T. Du Clos, Olivia H. Hawkins and Brad J. Gemmell

J. Mar. Sci. Eng. 2020, 8(10), 808; https://doi.org/10.3390/jmse8100808 - 19 Oct 2020

Cited by 10 | Viewed by 2941

Abstract

The eastern oyster Crassostrea virginica is an ecologically and economically important species that is vulnerable to oil pollution. We assessed sublethal effects of soluble fractions of crude oil alone (WAF) and crude oil in combination with Corexit 9500 dispersant (CEWAF) on oysters at [...] Read more.

The eastern oyster Crassostrea virginica is an ecologically and economically important species that is vulnerable to oil pollution. We assessed sublethal effects of soluble fractions of crude oil alone (WAF) and crude oil in combination with Corexit 9500 dispersant (CEWAF) on oysters at three life history stages. Veliger swimming, pediveliger settlement, and adult clearance rates were quantified after 24 h exposures to the contaminants. Veliger swimming speeds were not significantly impacted by 24 h exposures to WAF or CEWAF. A larger proportion of veligers were inactive following WAF and CEWAF exposure as compared to the control, but the effect was greater for pediveligers, and pediveliger settlement in the highest concentration CEWAF treatment decreased by 50% compared to controls. Thus, pediveligers may be particularly vulnerable to oil exposure. In the adults, we found significant clearance rates reductions that persisted 33 days after acute exposure to CEWAF. Knowledge of sublethal effects of oil and dispersant at multiple life history stages aids understanding of how this important species will respond to an oil spill. Full article

(This article belongs to the Special Issue Degradation of Marine Oil Pollution)

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15 pages, 1349 KiB

Open AccessArticle

Coupling between Benthic Nutrient Cycling and Pelagic Phytoplankton Community in Taiwan Strait in Spring 2018

by Xiaowen Li, Xiaojie Chai, Lingling Zheng, Qinghui Deng, Xiaoyan Chen, Qi Zhang, Lingling Wan, Chunlei Song, Lirong Song, Yiyong Zhou and Xiuyun Cao

J. Mar. Sci. Eng. 2020, 8(10), 807; https://doi.org/10.3390/jmse8100807 - 18 Oct 2020

Cited by 3 | Viewed by 2453

Abstract

Although the nutrient as a driving force for the red tide was intensively studied, the spatial patterns of the phytoplankton community and its response to benthic nutrient cycling remain unclear. We determined the pelagic phytoplankton community and its extracellular alkaline phosphatase qualitatively using [...] Read more.

Although the nutrient as a driving force for the red tide was intensively studied, the spatial patterns of the phytoplankton community and its response to benthic nutrient cycling remain unclear. We determined the pelagic phytoplankton community and its extracellular alkaline phosphatase qualitatively using enzyme-labeled fluorescence (ELF) technique, concomitantly with the concentrations of phosphorus (P) and nitrogen (N) in the water and sediments in the Taiwan Strait in spring 2018. A total of 30 phytoplankton genera were identified with a higher abundance of the abundance of Prorocentrum and Trichodesmium being observed at the north coast and the center of the southern strait, respectively. Both phytoplankton abundances and Trichodesmium were negatively correlated with the ratios of dissolved inorganic N and ammonium to soluble reactive P (DIN/SRP, NH₄⁺/SRP) in the bottom. Furthermore, the ELF-labeling percentage in Trichodesmium was negatively correlated with total P and SRP but positively correlated with TN/TP, DIN/SRP, and NH₄⁺/SRP in the bottom. In contrast to high DIN/SRP of the surface, lower DIN/SRP in the bottom was owing to a high P release potential and weak sequestration of P as evidenced by the distribution of P solubilizing bacteria and P content. Our findings indicated that the benthic nutrient regime might shape the structure of the pelagic phytoplankton community. Full article

(This article belongs to the Special Issue Distribution and Metabolic Activities of Marine Microbes in Response to Natural and Anthropogenic Stressors)

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Graphical abstract

23 pages, 8417 KiB

Open AccessArticle

An Analytical Model for Rock Cutting with a Chisel Pick of the Cutter Suction Dredger

by Yiping Ouyang, Qi Yang, Xinquan Chen and Yongfu Xu

J. Mar. Sci. Eng. 2020, 8(10), 806; https://doi.org/10.3390/jmse8100806 - 16 Oct 2020

Cited by 8 | Viewed by 3680

Abstract

Cutter suction dredgers are important pieces of rock excavation equipment in port and waterway construction. It is valuable but difficult to properly estimate the cutting force on the chisel pick of the cutter suction dredger. In this paper, an analytical model, called the [...] Read more.

Cutter suction dredgers are important pieces of rock excavation equipment in port and waterway construction. It is valuable but difficult to properly estimate the cutting force on the chisel pick of the cutter suction dredger. In this paper, an analytical model, called the crushed zone expansion induced tensile failure model (CEIT model), is proposed for rock cutting with a chisel pick in order to predict the peak cutting force (Fc) more accurately. First, a review of the existing models for rock cutting with a chisel pick is presented. Next, based on the tensile breakage theory, cavity expansion theory and some hypotheses, the mathematical formula of the CEIT model is obtained. Different from that in the previous models, the effect of the rock on both sides of the chisel pick on Fc, defined as the sidewall effect is considered in the CEIT model. Then, the predicted Fc by the CEIT model is compared with the predicted Fc by existing theoretical models and experimental results to check the validity of the CEIT model. The results show that the CEIT model can well capture the relationships of Fc to the cutting parameters, including cutting width, cutting depth, and rake angle, and can predict the experimental results much better than the existing models. Finally, the sidewall effect and its influence factors according to the CEIT model are discussed. Full article

(This article belongs to the Section Coastal Engineering)

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24 pages, 5887 KiB

Open AccessArticle

Prediction of Ocean Weather Based on Denoising AutoEncoder and Convolutional LSTM

by Ki-Su Kim, June-Beom Lee, Myung-Il Roh, Ki-Min Han and Gap-Heon Lee

J. Mar. Sci. Eng. 2020, 8(10), 805; https://doi.org/10.3390/jmse8100805 - 16 Oct 2020

Cited by 38 | Viewed by 5175

Abstract

The path planning of a ship requires much information, and one of the essential factors is predicting the ocean environment. Ocean weather can generally be gathered from forecasting information provided by weather centers. However, these data are difficult to obtain when satellite communication [...] Read more.

The path planning of a ship requires much information, and one of the essential factors is predicting the ocean environment. Ocean weather can generally be gathered from forecasting information provided by weather centers. However, these data are difficult to obtain when satellite communication is unstable during voyages, or there are cases where forecast data for a more extended period of time are needed for the operation of the fleet. Therefore, shipping companies and classification societies have attempted to establish a model for predicting the ocean weather on its own. Historically, ocean weather has been primarily predicted using empirical and numerical methods. Recently, a method for predicting ocean weather using deep learning has emerged. In this study, a deep learning model combining a denoising AutoEncoder and convolutional long short-term memory (LSTM) was proposed to predict the ocean weather worldwide. The denoising AutoEncoder is effective for removing noise that hinders the training of deep learning models. While the LSTM could be used as time-series inputs at specific points, the convolutional LSTM can use time-series images as inputs, making them suitable for predicting a wide range of ocean weather. Herein, using the proposed model, eight parameters of ocean weather were predicted. The proposed learning model predicted ocean weather after one week, showing an average error of 6.7%. The results show the applicability of the proposed learning model for predicting ocean weather. Full article

(This article belongs to the Special Issue Smart Technologies for Shipbuilding)

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17 pages, 2586 KiB

Open AccessArticle

Developing a Universal and Efficient Method for the Rapid Selection of Stable Fluorescent Protein-Tagged Pathogenic Vibrio Species

by Candice A. Thorstenson and Matthias S. Ullrich

J. Mar. Sci. Eng. 2020, 8(10), 804; https://doi.org/10.3390/jmse8100804 - 16 Oct 2020

Cited by 2 | Viewed by 2967

Abstract

World-wide increases in Vibrio-associated diseases have been reported in aquaculture and humans in co-occurrence with increased sea surface temperatures. Twelve species of Vibrio are known to cause disease in humans, but three species dominate the number of human infections world-wide: Vibrio cholerae [...] Read more.

World-wide increases in Vibrio-associated diseases have been reported in aquaculture and humans in co-occurrence with increased sea surface temperatures. Twelve species of Vibrio are known to cause disease in humans, but three species dominate the number of human infections world-wide: Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio vulnificus. Fluorescent protein (FP)-labelled bacteria have been used to make great progress through in situ studies of bacterial behavior in mixed cultures or within host tissues. Currently, FP-labelling methods specific for Vibrio species are still limited by time-consuming counterselection measures that require the use of modified media and temperatures below the optimal growth temperature of many Vibrio species. Within this study, we used a previously reported R6K-based suicide delivery vector and two newly constructed transposon variants to develop a tailored protocol for FP-labelling V. cholerae, V. parahaemolyticus, and V. vulnificus environmental isolates within two days of counterselection against the donor Escherichiacoli. This herein presented protocol worked universally across all tested strains (30) with a conjugation efficiency of at least two transconjugants per 10,000 recipients. Full article

(This article belongs to the Section Marine Biology)

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24 pages, 11137 KiB

Open AccessArticle

Shape Characteristics of Coral Sand from the South China Sea

by Xing Wang, Yang Wu, Jie Cui, Chang-Qi Zhu and Xin-Zhi Wang

J. Mar. Sci. Eng. 2020, 8(10), 803; https://doi.org/10.3390/jmse8100803 - 15 Oct 2020

Cited by 71 | Viewed by 4827

Abstract

The particle shape of coral sand is a crucial factor that affects its accumulation characteristics. Two-dimensional particle images of coral sand with different particle sizes were obtained through optical imaging, and the basic size parameters of particles were measured by digital image processing. [...] Read more.

The particle shape of coral sand is a crucial factor that affects its accumulation characteristics. Two-dimensional particle images of coral sand with different particle sizes were obtained through optical imaging, and the basic size parameters of particles were measured by digital image processing. The particle shape parameters were created, and on this basis, the variation of shape parameters with size, the distribution characteristics, and the sensitivity of shape parameters were analyzed by mathematical statistics and the fractal theory. In addition, a comparative analysis was conducted for the particle shape and bulk density of coral sand and quartz sand with the same particle size. The results show that (1) for coral sand with particle size ranging from 0.5 to 5.0 mm, as the particle size augments, its overall profile coefficient grows, while the flatness, angularity, and roughness diminish and the particle shape deviates more from the regular circle. (2) The shape of coral sand particles exhibits good fractal characteristics, and the particle shape gets more complex as the particle size grows as evidenced by the fact that the fractal dimension enlarges. (3) All the shape parameters obey a skewed distribution. Concerning the sensitivity to the change in particle shape, the flatness occupies the first place, the overall profile coefficient and angularity come second, and the roughness ranks third, accordingly. It is suggested that flatness should be preferred as the evaluation parameter of the particle shape. (4) Compared with that of quartz sand, the particle shape of coral sand is more irregular, and the intergranular pores are larger under the same accumulation conditions, which is the primary reason why the specific gravity of coral sand is greater than that of quartz sand while the bulk density is smaller than that of quartz sand. Full article

(This article belongs to the Section Physical Oceanography)

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22 pages, 4696 KiB

Open AccessArticle

Application of Reference Voltage Control Method of the Generator Using a Neural Network in Variable Speed Synchronous Generation System of DC Distribution for Ships

by Hyeonmin Jeon and Jongsu Kim

J. Mar. Sci. Eng. 2020, 8(10), 802; https://doi.org/10.3390/jmse8100802 - 15 Oct 2020

Cited by 6 | Viewed by 3193

Abstract

In the case of DC power distribution-based variable speed engine synchronous generators, if the output reference voltage is kept constant regardless of the generator engine operating speed, it may cause damage to the internal device and windings of the generator due to over-flux [...] Read more.

In the case of DC power distribution-based variable speed engine synchronous generators, if the output reference voltage is kept constant regardless of the generator engine operating speed, it may cause damage to the internal device and windings of the generator due to over-flux or over-excitation. The purpose of this study is to adjust the generator reference voltage according to the engine speed change in the DC distribution system with the variable speed engine synchronous generator. A method of controlling the generator reference voltage according to the speed was applied by adjusting the value of the variable resistance input to the external terminal of the automatic voltage regulator using a neural network controller. The learning data of the neural network was measured through an experiment, and the input pattern was set as the rotational speed of the generator engine, and the output pattern was set as the input current of the potentiometer. Using the measured input/output pattern of the neural network, the error backpropagation learning algorithm was applied to derive the optimum connection weight to be applied to the controller. For the test, the variable speed operation range of the generator engine was set to 1100–1800 rpm, and the input current value of the potentiometer according to the speed increase or decrease within the operation range and the output of the voltage output from the actual generator were checked. As a result of neural network control, it was possible to confirm the result that the input current value of the potentiometer accurately reached the target value 4–20 mA at the point where the initial speed change occurred. It was confirmed that the reference voltage was also normally output in the target range of 250–440 V. Full article

(This article belongs to the Special Issue Marine Alternative Fuels and Environmental Protection)

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14 pages, 263 KiB

Open AccessReview

Impact of Neonicotinoids to Aquatic Invertebrates—In Vitro Studies on Mytilus galloprovincialis: A Review

by Maria Pagano, Alzbeta Stara, Valbona Aliko and Caterina Faggio

J. Mar. Sci. Eng. 2020, 8(10), 801; https://doi.org/10.3390/jmse8100801 - 15 Oct 2020

Cited by 84 | Viewed by 5118

Abstract

The use of pesticides in agriculture has always had a strong impact on environmental contamination. Since the 1990s, neonicotinoids have grown increasingly more popular, targeting specific receptors for insects, especially bees, which is why the use of some neonicotinoids has been banned. Much [...] Read more.

The use of pesticides in agriculture has always had a strong impact on environmental contamination. Since the 1990s, neonicotinoids have grown increasingly more popular, targeting specific receptors for insects, especially bees, which is why the use of some neonicotinoids has been banned. Much is known about the effects they have on insects, but very little about the effect they can have on non-target organisms. Several studies have shown how these neonicotinoids interact negatively with the normal physiology of aquatic organisms. For the genus Mytilus, even though the neonicotinoids did not show an interaction with specific receptors, a chronic and acute exposure to them causes damage. In these animals, a reduced production of byssus, alteration of the normal antioxidant systems and tissue damage have been found. Therefore, an analysis of the entire ecosystem in which the pollutant enters is of great importance in evaluating any possible alterations. Full article

(This article belongs to the Special Issue Effects of Emerging Contaminants to Marine Organisms: In Vitro and In Vivo Studies)

21 pages, 11313 KiB

Open AccessArticle

Flexible Pile Group Interaction Factors under Arbitrary Lateral Loading in Sand

by Miloš Marjanović, Mirjana Vukićević and Diethard König

J. Mar. Sci. Eng. 2020, 8(10), 800; https://doi.org/10.3390/jmse8100800 - 15 Oct 2020

Cited by 8 | Viewed by 5274

Abstract

Marine and harbor structures, wind turbines, bridges, offshore platforms, industrial chimneys, retaining structures etc. can be subjected to significant lateral loads from various sources. Appropriate assessment of the foundations capacity of these structures is thus necessary, especially when these structures are supported by [...] Read more.

Marine and harbor structures, wind turbines, bridges, offshore platforms, industrial chimneys, retaining structures etc. can be subjected to significant lateral loads from various sources. Appropriate assessment of the foundations capacity of these structures is thus necessary, especially when these structures are supported by pile groups. The pile group interaction effects under lateral loading have been investigated intensively in past decades, and the most of the conducted studies have considered lateral loading that acts along one of the two orthogonal directions, parallel to the edge of pile group. However, because of the stochastic nature of its source, the horizontal loading on the pile group may have arbitrary direction. The number of studies dealing with the pile groups under arbitrary loading is very limited. The aim of this paper is to investigate the influence of the arbitrary lateral loading on the pile group response, in order to improve (extend) the current design approach for laterally loaded pile groups. Free head, flexible bored piles in sand were analyzed through the extensive numerical study. The main hypothesis of the research is that some critical pile group configurations, loading directions, and soil conditions exist, which can lead to the unsafe structural design. Critical pile positions inside the commonly used pile group configurations are identified with respect to loading directions. The influence of different soil conditions was discussed. Full article

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