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J. Mar. Sci. Eng., Volume 7, Issue 10 (October 2019)

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Cover Story (view full-size image) Large boulders have been found in marine cliffs from 7 study sites on Ibiza and Formentera Islands [...] Read more.
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Open AccessArticle
Numerical Analysis of Sandwich Composite Deep Submarine Pressure Hull Considering Failure Criteria
J. Mar. Sci. Eng. 2019, 7(10), 377; https://doi.org/10.3390/jmse7100377 - 22 Oct 2019
Abstract
The pressure hull is the primary element of submarine, which withstands diving pressure and provides essential capacity for electronic systems and buoyancy. This study presents a numerical analysis and design optimization of sandwich composite deep submarine pressure hull using finite element modeling technique. [...] Read more.
The pressure hull is the primary element of submarine, which withstands diving pressure and provides essential capacity for electronic systems and buoyancy. This study presents a numerical analysis and design optimization of sandwich composite deep submarine pressure hull using finite element modeling technique. This study aims to minimize buoyancy factor and maximize deck area and buckling strength factors. The collapse depth is taken as a base in the pressure hull design. The pressure hull has been analyzed using two composite materials, T700/Epoxy and B(4)5505/Epoxy, to form the upper and lower faces of the sandwich composite deep submarine pressure hull. The laminated control surface is optimized for the first ply failure index (FI) considering both Tsai–Wu and maximum stress failure criteria. The results obtained emphasize an important fact that the presence of core layer in sandwich composite pressure hull is not always more efficient. The use of sandwich in the design of composite deep submarine pressure hull at extreme depths is not a safe option. Additionally, the core thickness plays a minor role in the design of composite deep submarine pressure hull. The outcome of an optimization at extreme depths illustrates that the upper and lower faces become thicker and the core thickness becomes thinner. However, at shallow-to-moderate depths, it is recommended to use sandwich composite with a thick core to resist the shell buckling of composite submarine pressure hull. Full article
(This article belongs to the Special Issue Computer-Aided Marine Structures’ Design)
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Open AccessArticle
Design and Experiment of a Plateau Data-Gathering AUV
J. Mar. Sci. Eng. 2019, 7(10), 376; https://doi.org/10.3390/jmse7100376 - 21 Oct 2019
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Abstract
The design, control, and implementation of an autonomous underwater vehicle (AUV) for collecting hydrological information from plateau rivers and lakes are presented in this paper. The hardware and software structures of the control system were previously described. A novel sliding mode controller (SMC) [...] Read more.
The design, control, and implementation of an autonomous underwater vehicle (AUV) for collecting hydrological information from plateau rivers and lakes are presented in this paper. The hardware and software structures of the control system were previously described. A novel sliding mode controller (SMC) with combinational reaching law of vertical hovering motion is proposed to improve the robustness and stability. The S-plane control, a nonlinear controller with little parameters, is used in the horizontal motion. Besides, the navigation strategy based on the dead-reckoning algorithm, a path tracking based on the light-of-sight (LOS) algorithm, and a control allocation strategy considering saturation are present. Finally, experiments were performed in a tank and in a river in the Qinghai–Tibet Plateau to prove the feasibility and reliability of the AUV system. Full article
(This article belongs to the Section Ocean Engineering)
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Open AccessArticle
Investigation of Focusing Wave Properties in a Numerical Wave Tank with a Fully Nonlinear Potential Flow Model
J. Mar. Sci. Eng. 2019, 7(10), 375; https://doi.org/10.3390/jmse7100375 - 21 Oct 2019
Viewed by 74
Abstract
Nonlinear wave interactions and superpositions among the different wave components and wave groups in a random sea sometimes produce rogue waves with extremely large wave heights that appear unexpectedly. A good understanding of the generation and evolution of such extreme wave events is [...] Read more.
Nonlinear wave interactions and superpositions among the different wave components and wave groups in a random sea sometimes produce rogue waves with extremely large wave heights that appear unexpectedly. A good understanding of the generation and evolution of such extreme wave events is of great importance for the analysis of wave forces on marine structures. A fully nonlinear potential flow (FNPF) model is proposed in the presented paper to investigate the different factors that influence the wave focusing location, focusing time and focusing wave height in a numerical wave tank. Those factors include wave steepness, spectrum bandwidth, wave generation method, focused wave spectrum, and wave spreading functions. The proposed model solves the Laplace equation together with the boundary conditions on a σ -coordinate grid using high-order discretisation schemes on a fully parallel computational framework. The model is validated against the focused wave experiments and thereafter used to obtain insights into the effects of the different factors. It is found that the wave steepness contributes to changing the location and time of focus significantly. Spectrum bandwidth and directional spreading affect the focusing wave height and profile, for example, a wider bandwidth and a wider directional spread lead to a lower focusing wave height. A Neumann boundary condition represents the nonlinearity of the wave groups better than a relaxation method for wave generation. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics for Ocean Surface Waves)
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Open AccessArticle
Grid Type and Turbulence Model Influence on Propeller Characteristics Prediction
J. Mar. Sci. Eng. 2019, 7(10), 374; https://doi.org/10.3390/jmse7100374 - 20 Oct 2019
Viewed by 175
Abstract
This paper evaluates the applicability of the hexahedral block structured grids for marine propeller performance predictions. Hydrodynamic characteristics for Potsdam Propeller Test Case (PPTC), namely thrust and torque coefficients, were determined using numerical simulations in two commercial solvers: Ansys Fluent and STAR-CCM+. Results [...] Read more.
This paper evaluates the applicability of the hexahedral block structured grids for marine propeller performance predictions. Hydrodynamic characteristics for Potsdam Propeller Test Case (PPTC), namely thrust and torque coefficients, were determined using numerical simulations in two commercial solvers: Ansys Fluent and STAR-CCM+. Results were attained for hexahedral and tetrahedral hybrid grids equivalent in terms of cell count and quality, and compared to the experimental results. Furthermore, accuracy of Realizable k- ϵ and SST k- ω turbulent models when analyzing marine propeller performance was investigated. Finally, performance characteristics were assessed in cavitating flow conditions for a single advance ratio using Zwart–Gerber–Belamri and Schnerr and Sauer models. The resulting cavitation pattern was compared to cavity extents and shape noted during measurements. The results suggest that hexa and hybrid grids, in certain range of advance ratios, do provide similar results; however, for low and high ratios, structured grids in conjunction with Realizable k- ϵ model can achieve more accurate results. Full article
(This article belongs to the Special Issue Marine Propellers and Ship Propulsion)
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Open AccessArticle
Investigation of Oil Spills from Oil Tankers through Grey Theory: Events from 1974 to 2016
J. Mar. Sci. Eng. 2019, 7(10), 373; https://doi.org/10.3390/jmse7100373 - 19 Oct 2019
Viewed by 216
Abstract
An oil spill from a vessel is a critical maritime accident that can severely damage the environment. In this study; we utilize the basic construction of grey relational analysis to explore oil spill events statistics from 1974 to 2015 and successfully analyze the [...] Read more.
An oil spill from a vessel is a critical maritime accident that can severely damage the environment. In this study; we utilize the basic construction of grey relational analysis to explore oil spill events statistics from 1974 to 2015 and successfully analyze the causes of incidents in 2016. The results illustrate that grey relational analysis effectively identifies the factors causing oil spills with an accuracy of over 96%. The research is aimed to reduce the marine accidents and predict the cause of oil spill in advance. The analysis is dealing with the incidents to approach the circumstance in various intensity of oil spill in the last 40 years. Moreover, an application of grey theory demonstrates accurate and reliable methodology to decision maker. Thus, the investigation can predict the causes of pollution from oil spill accidents in the future. Full article
(This article belongs to the Special Issue Maritime Safety)
Open AccessArticle
Integrating Multiple-Try DREAM(ZS) to Model-Based Bayesian Geoacoustic Inversion Applied to Seabed Backscattering Strength Measurements
J. Mar. Sci. Eng. 2019, 7(10), 372; https://doi.org/10.3390/jmse7100372 - 18 Oct 2019
Viewed by 247
Abstract
The key to model-based Bayesian geoacoustic inversion is to solve the posterior probability distributions (PPDs) of parameters. In order to obtain PPDs more efficiently and accurately, the state-of-the-art Markov chain Monte Carlo (MCMC) method, multiple-try differential evolution adaptive Metropolis(ZS) (MT-DREAM(ZS)), [...] Read more.
The key to model-based Bayesian geoacoustic inversion is to solve the posterior probability distributions (PPDs) of parameters. In order to obtain PPDs more efficiently and accurately, the state-of-the-art Markov chain Monte Carlo (MCMC) method, multiple-try differential evolution adaptive Metropolis(ZS) (MT-DREAM(ZS)), is integrated to the inverse problem because of its excellent ability to fully explore the posterior space of parameters. The effective density fluid model (EDFM), which is derived from Biot–Stoll theory to approximate the poroelastic model, and the published field measurements of backscattering strength are adopted to implement the inversion. The results show that part of the parameters can be estimated close to the measured values, and the PPDs obtained by dual-frequency inversion are more concentrated than those of single-frequency inversion because of the use of more measured backscattering strength data. Otherwise, the comparison between the predicted backscattering strength of dual-frequency inversion results and Jackson’s prediction shows that the solutions of the inverse problem are not unique and may have multiple optimal values. Indeed, the difference between the two predictions is essentially the difference in the estimation of the contribution of volume scattering to the total scattering. Nevertheless, both results are reasonable due to the lack of measurement of volume scattering parameters, and the inversion results given by the posterior probabilities based on the limited measurements and the adopted model are still considered to be reliable. Full article
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Open AccessArticle
Benthic Habitat Morphodynamics-Using Remote Sensing to Quantify Storm-Induced Changes in Nearshore Bathymetry and Surface Sediment Texture at Assateague National Seashore
J. Mar. Sci. Eng. 2019, 7(10), 371; https://doi.org/10.3390/jmse7100371 - 18 Oct 2019
Viewed by 105
Abstract
This study utilizes repeated geoacoustic mapping to quantify the morphodynamic response of the nearshore to storm-induced changes. The aim of this study was to quantitatively map the nearshore zone of Assateague Island National Seashore (ASIS) to determine what changes in bottom geomorphology and [...] Read more.
This study utilizes repeated geoacoustic mapping to quantify the morphodynamic response of the nearshore to storm-induced changes. The aim of this study was to quantitatively map the nearshore zone of Assateague Island National Seashore (ASIS) to determine what changes in bottom geomorphology and benthic habitats are attributable to storm events including hurricane Sandy and the passage of hurricane Joaquin. Specifically, (1) the entire domain of the National Parks Service offshore area was mapped with side-scan sonar and multibeam bathymetry at a resolution comparable to that of the existing pre-storm survey, (2) a subset of the benthic stations were resampled that represented all sediment strata previously identified, and (3) newly obtained data were compared to that from the pre-storm survey to determined changes that could be attributed to specific storms such as Sandy and Joaquin. Capturing event specific dynamics requires rapid response surveys in close temporal association of the before and after period. The time-lapse between the pre-storm surveys for Sandy and our study meant that only a time and storm integrated signature for that storm could be obtained whereas with hurricane Joaquin we could identify impacts to the habitat type and geomorphology more directly related to that particular storm. This storm impacts study provides for the National Park Service direct documentation of storm-related changes in sediments and marine habitats on multiple scales: From large scale, side-scan sonar maps and interpretation of acoustic bottom types, to characterize as fully as possible habitats from 1 to 10 m up to many kilometer scales, as well as from point benthic samples within each sediment stratum and these results can help guide management of the island resources. Full article
(This article belongs to the Special Issue Remote Sensing in Coastline Detection)
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Open AccessFeature PaperEditorial
Use of Engineering Mathematics for Ship Design
J. Mar. Sci. Eng. 2019, 7(10), 370; https://doi.org/10.3390/jmse7100370 - 17 Oct 2019
Viewed by 173
Abstract
With over that 70% of the Earth submerged by seas, continents separated by oceans, two thousand major islands scattered throughout the World, hundreds of thousands of kilometers of navigable rivers, maritime or fluvial transport surely represents one of the most important ways of [...] Read more.
With over that 70% of the Earth submerged by seas, continents separated by oceans, two thousand major islands scattered throughout the World, hundreds of thousands of kilometers of navigable rivers, maritime or fluvial transport surely represents one of the most important ways of moving people, goods, and wealth around the globe [...] Full article
(This article belongs to the Special Issue Engineering Mathematics in Ship Design)
Open AccessArticle
Response of a Porous Seabed around an Immersed Tunnel under Wave Loading: Meshfree Model
J. Mar. Sci. Eng. 2019, 7(10), 369; https://doi.org/10.3390/jmse7100369 - 17 Oct 2019
Viewed by 116
Abstract
Seabed instability surrounding an immersed tunnel is a vital engineering issue regarding the design and maintenance for submarine tunnel projects. In this study, a numerical model based on the local radial basis function collocation method (LRBFCM) is developed to evaluate the seabed behaviour [...] Read more.
Seabed instability surrounding an immersed tunnel is a vital engineering issue regarding the design and maintenance for submarine tunnel projects. In this study, a numerical model based on the local radial basis function collocation method (LRBFCM) is developed to evaluate the seabed behaviour in a marine environment, in which the seabed is treated as the porous medium and governed by Biot’s “ u p ” approximation. As for the flow field above the seabed, the VARANS equations are used to simulate the fluid motion and properties. The present model is validated with analytical solutions and experimental data which show a good capacity of the integrated model. Both wave and current loading are considered in this study. Parametric studies are carried out to investigate the effects of wave characteristics and soil properties. Based on the numerical results, the maximum liquefaction depth around the immersed tunnel could be deeper under the wave loading with long wave period (T) and large wave height (H). Moreover, a seabed with lower permeability ( K s ) and degree of saturation ( S r ) is more likely to be liquefied. Full article
(This article belongs to the Special Issue New Advances in Marine Engineering Geology)
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Open AccessArticle
Watching the Beach Steadily Disappearing: The Evolution of Understanding of Retrogressive Breach Failures
J. Mar. Sci. Eng. 2019, 7(10), 368; https://doi.org/10.3390/jmse7100368 - 17 Oct 2019
Viewed by 122
Abstract
Retrogressive breach failures or coastal flow slides occur naturally in the shoreface in fine sands near dynamic tidal channels or rivers. They sometimes retrogress into beaches, shoal margins and riverbanks where they can threaten infrastructure and cause severe coastal erosion and flood risk. [...] Read more.
Retrogressive breach failures or coastal flow slides occur naturally in the shoreface in fine sands near dynamic tidal channels or rivers. They sometimes retrogress into beaches, shoal margins and riverbanks where they can threaten infrastructure and cause severe coastal erosion and flood risk. Ever since the first reports were published in the Netherlands over a century ago, attempts have been made to understand the geo-mechanical mechanism of flow slides. In this paper we have established that events, observed during the active phase, are characterized by a slow but steady retrogression into the shoreline, often continuing for many hours. This can be explained by the breaching mechanism, as will be clarified in this paper. Recently, further evidence has become available in the form of video footage of active events in Australia and elsewhere, often publicly posted on the internet. All these observations justify the new term ‘retrogressive breach failure’ (RBF event). The mechanism has been confirmed in flume tests and in a field experiment. With a better understanding of the geo-mechanical mechanism, current protection methods can be better understood, and new defense strategies can be envisaged. In writing this paper, we hope that the coastal science and engineering communities will better recognize and understand these intriguing natural events. Full article
(This article belongs to the Section Coastal Engineering)
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Open AccessArticle
Characterizing Wave Shape Evolution on an Ebb-Tidal Shoal
J. Mar. Sci. Eng. 2019, 7(10), 367; https://doi.org/10.3390/jmse7100367 - 16 Oct 2019
Viewed by 103
Abstract
Field measurements of waves and currents were obtained at ten locations on an ebb-tidal shoal seaward of Ameland Inlet for a six-week period. These measurements were used to investigate the evolution of the near-bed velocity skewness and asymmetry, as these are important drivers [...] Read more.
Field measurements of waves and currents were obtained at ten locations on an ebb-tidal shoal seaward of Ameland Inlet for a six-week period. These measurements were used to investigate the evolution of the near-bed velocity skewness and asymmetry, as these are important drivers for wave-induced sediment tranport. Wave shape parameters were compared to traditionally used parameterizations to quantify their performance in a dynamic area with waves and tidal currents coming in from different directions over a highly variable bathymetry. Spatially and temporally averaged, these parameterizations compared very well to observed wave shape. However, significant scatter was observed. The largest deviations from the parameterization were observed at the shallowest locations, where the contribution of wave-induced sediment transport was expected to be the largest. This paper shows that this scatter was caused by differences in wave-breaking, nonlinear energy transfer rate, and spatial gradients in tidal currents. Therefore, it is proposed to include the prior evolution of the wave before reaching a location in future parameterizations in numerical modeling instead of only using local parameters to predict wave shape. Full article
(This article belongs to the Section Coastal Engineering)
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Open AccessArticle
Concept Design of the Underwater Manned Seabed Walking Robot
J. Mar. Sci. Eng. 2019, 7(10), 366; https://doi.org/10.3390/jmse7100366 - 15 Oct 2019
Viewed by 164
Abstract
In this paper, a novel concept designed of a multi-legged underwater manned seabed walking robot is presented. The robot will be used in both shallow water current (1–2 m/sec) and deep water up to 500 m. It is powered by an external electric [...] Read more.
In this paper, a novel concept designed of a multi-legged underwater manned seabed walking robot is presented. The robot will be used in both shallow water current (1–2 m/sec) and deep water up to 500 m. It is powered by an external electric power source through tether cable. It walks on the seabed with six legs, which makes it distinct from conventional screw-propelled underwater robots. It can walk calmly without making the water turbid. Two anterior arms act as manipulators. All leg joints and manipulators are controlled by Brushless Direct Current Motors. Motivation for this concept comes from soldier crab that walk mostly forward and has an egg-shaped body. It is operated by a pilot sitting in a pressurized cabin, and promptly control operations of the robot and manipulator. Preliminary design of the pressurized cabin, using an empirical formula, “ASME PVHO-1 2007” standard, and validation was carried out through ANSYS Workbench. Hydrodynamic forces acting on the robot body and legs are utilized to withstand the water current and external forces to adjust legs and body posture for stability. Buoyancy rules are employed to control its rising and diving motion. All key technologies employed in the development of the robot and their approaching methods are explained. It will provide a safe operation space for humans in underwater operations. Full article
(This article belongs to the Section Ocean Engineering)
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Open AccessFeature PaperReview
River and Estuary Current Power Overview
J. Mar. Sci. Eng. 2019, 7(10), 365; https://doi.org/10.3390/jmse7100365 - 12 Oct 2019
Viewed by 196
Abstract
This paper presents a review of the stream current power sector, with a distinction made between the marine (MCP) and the river/estuary current power (RECP). Although scientific literature about MCP is actually well defined, that about RECP seems small, though this domain has [...] Read more.
This paper presents a review of the stream current power sector, with a distinction made between the marine (MCP) and the river/estuary current power (RECP). Although scientific literature about MCP is actually well defined, that about RECP seems small, though this domain has some research interest. This paper has thus a special emphasis on this latter, with comparative studies done between these domains. The assessment of the academic and industrial interests for the RECP is first addressed, based on two main scientific resources and a qualitative highlight of its potential. Then, a review of actual constraints restricting its development is introduced, followed by a non-exhaustive presentation of industrial projects. Finally, some development prospects allowing constraints to be mitigated are proposed. Globally, MCP and RECP are treated unconcernedly, with a primary interest on the mechanical converter study and the location energy potential estimation. It has been highlighted that countries with RECP potential are more plentiful, and that undertaken projects can be classified mainly into two categories following the nominal power of the production unit. Furthermore, the river current power growth has been confirmed in recent years, with a majority part of patented hydrokinetic technologies, although commercial deployments are still scarce. Full article
(This article belongs to the Section Ocean Engineering)
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Open AccessArticle
A Study on Cyber Security Threats in a Shipboard Integrated Navigational System
J. Mar. Sci. Eng. 2019, 7(10), 364; https://doi.org/10.3390/jmse7100364 - 12 Oct 2019
Viewed by 214
Abstract
The integrated navigational system (INS) enhances the effectiveness and safety of ship navigation by providing multifunctional display on the basis of integration of at least two navigational functions, the voyage route monitoring with Electronic Chart Display and Information System (ECDIS) and collision avoidance [...] Read more.
The integrated navigational system (INS) enhances the effectiveness and safety of ship navigation by providing multifunctional display on the basis of integration of at least two navigational functions, the voyage route monitoring with Electronic Chart Display and Information System (ECDIS) and collision avoidance with radar. The INS is essentially a software platform for fusion of data from the major ECDIS and radar systems with sensors for the additional navigation functions of route planning, status and data display, and alert management. This paper presents a study on cyber security resilience examination of a shipboard INS installed on a RoPax ship engaged in international trade. The study was based on a mixed-method approach, combining an interview of the ship’s navigational ranks and cyber security testing of the INS using an industry vulnerability scanner. The identified threats were analyzed qualitatively to study the source of cyber risks threatening the INS. The results obtained point out cyber threats related to weaknesses of the INS underlying operating system, suggesting a need for occasional preventive maintenance in addition to the regulatory compliance required. Full article
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Open AccessArticle
Robust Adaptive Heading Control for a Ray-Type Hybrid Underwater Glider with Propellers
J. Mar. Sci. Eng. 2019, 7(10), 363; https://doi.org/10.3390/jmse7100363 - 11 Oct 2019
Viewed by 186
Abstract
This paper presents the modeling of a new ray-type hybrid underwater glider (RHUG) and an experimental approach used to robustly and adaptively control heading motion. The motions of the proposed RHUG are divided into vertical-plane motions and heading motion. Hydrodynamic coefficients in the [...] Read more.
This paper presents the modeling of a new ray-type hybrid underwater glider (RHUG) and an experimental approach used to robustly and adaptively control heading motion. The motions of the proposed RHUG are divided into vertical-plane motions and heading motion. Hydrodynamic coefficients in the vertical-plane dynamics are obtained using a computational fluid dynamics (CFD) method for various pitch angles. Due to the difficulty of obtaining accurate parameter values for the heading dynamics, a robust adaptive control algorithm was designed containing an adaptation law for the unknown parameters and robust action for minimizing environmental disturbances. For robust action against bounded disturbances, such as waves and ocean currents, sliding mode control was applied under the assumption that the bounds of the external disturbances are known. A direct adaptive algorithm for heading motion was applied in an experiment. Computer simulations of the proposed robust adaptive heading control are presented to demonstrate the robustness of the proposed control system in the presence of bounded disturbances. To verify the performance of the proposed controller for heading dynamics, several heading control experiments were conducted in a water tank and in the sea. Full article
(This article belongs to the Special Issue Underwater Technology—Hydrodynamics and Control System)
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Open AccessFeature PaperArticle
Validation of Tidal Stream Turbine Wake Predictions and Analysis of Wake Recovery Mechanism
J. Mar. Sci. Eng. 2019, 7(10), 362; https://doi.org/10.3390/jmse7100362 - 11 Oct 2019
Viewed by 200
Abstract
This paper documents the predictive capability of rotating blade-resolved unsteady Reynolds averaged Navier-Stokes (URANS) and Improved Delayed Detached Eddy Simulation (IDDES) computations for tidal stream turbine performance and intermediate wake characteristics. Ansys/Fluent and OpenFOAM simulations are performed using mixed-cell, unstructured grids consisting of [...] Read more.
This paper documents the predictive capability of rotating blade-resolved unsteady Reynolds averaged Navier-Stokes (URANS) and Improved Delayed Detached Eddy Simulation (IDDES) computations for tidal stream turbine performance and intermediate wake characteristics. Ansys/Fluent and OpenFOAM simulations are performed using mixed-cell, unstructured grids consisting of up to 11 million cells. The thrust, power and intermediate wake predictions compare reasonably well within 10% of the experimental data. For the wake predictions, OpenFOAM performs better than Ansys/Fluent, and IDDES better than URANS when the resolved turbulence is triggered. The primary limitation of the simulations is under prediction of the wake diffusion towards the turbine axis, which in return is related to the prediction of turbulence in the tip-vortex shear layer. The shear-layer involves anisotropic turbulent structures; thus, hybrid RANS/LES models, such as IDDES, are preferred over URANS. Unfortunately, IDDES fails to accurately predict the resolved turbulence in the near-wake region due to the modeled stress depletion issue. Full article
(This article belongs to the Special Issue The Development of Marine Energy Extraction)
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Open AccessFeature PaperArticle
Evaluation of Lebanon’s Offshore-Wind-Energy Potential
J. Mar. Sci. Eng. 2019, 7(10), 361; https://doi.org/10.3390/jmse7100361 - 10 Oct 2019
Viewed by 235
Abstract
The only regional evaluation of Lebanese wind-energy potential (National Wind Atlas) dates back to 2011 and was carried out by a United Nations agency. In this work, data from the most recent reanalysis (ERA5) developed at the European Center for Medium Range Weather [...] Read more.
The only regional evaluation of Lebanese wind-energy potential (National Wind Atlas) dates back to 2011 and was carried out by a United Nations agency. In this work, data from the most recent reanalysis (ERA5) developed at the European Center for Medium Range Weather Forecast (ECMWF), corresponding to the 2010–2017 period, were used to evaluate Lebanese offshore-wind-energy potential. In the present study, wind power density associated to a SIEMENS 154/6 turbine was calculated with a horizontal resolution of 31 km and 1 hour time steps. This work incorporated the impact of air density changes into the calculations due to the seasonal evolution of pressure, temperature, and humidity. Observed average offshore air density ρ 0 was 1.19 kg / m 3 for the 2010–2017 period, but if instead of ρ 0 , hourly ρ values were used, seasonal oscillations of wind power density ( W P D ) represented differences in percentage terms ranging from −4% in summer to +3% in winter. ERA5 provides hourly wind, temperature, pressure, and dew-point temperature values that allowed us to calculate the hourly evolution of air density during this period and could also be used to accurately evaluate wind power density off the Lebanese coast. There was a significant gradient in wind power density along the shore, with the northern coastal area exhibiting the highest potential and reaching winter values of around 400 W / m 2 . Finally, this study suggests that the initial results provided by the National Wind Atlas overestimated the true offshore-wind-energy potential, thus highlighting the suitability of ERA5 as an accurate tool for similar tasks globally. Full article
(This article belongs to the Special Issue Offshore Wind Farms)
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Open AccessArticle
Analysis of Slope Failure Behaviour Based on Real-Time Measurement Using the x–MR Method
J. Mar. Sci. Eng. 2019, 7(10), 360; https://doi.org/10.3390/jmse7100360 - 10 Oct 2019
Viewed by 193
Abstract
A real-scale slope failure model experiment is performed to analyze the movement behavior of the slope during failure, and the results are analyzed through the x–MR control chart method, along with inverse displacement and various analysis sections such as K-values. As a result, [...] Read more.
A real-scale slope failure model experiment is performed to analyze the movement behavior of the slope during failure, and the results are analyzed through the x–MR control chart method, along with inverse displacement and various analysis sections such as K-values. As a result, the portent of failure can be identified to be about 7.7–18.3 min prior to the final slope failure. As a result of the analyses of changes in the control limit in the various analyses sections, it is considered that the application of K = 3 to the x-MR control chart is effective. It is observed that using the x-MR control chart technique of the inverse displacement is useful for the early prediction of the anomalous behavior of a slope, through a more quick and objective judgment. Henceforth, it is necessary to establish clear techniques for prediction and analyses of slope failure through continuous research, and those results can be used as the basic data of a slope instrumentation management standard that can contribute to the mitigation of life and property damage caused by slope failure hazards. Full article
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Open AccessArticle
Life Cycle Assessment of LNG Fueled Vessel in Domestic Services
J. Mar. Sci. Eng. 2019, 7(10), 359; https://doi.org/10.3390/jmse7100359 - 10 Oct 2019
Viewed by 126
Abstract
This research was focused on a comparative analysis of using LNG as a marine fuel with a conventional marine gas oil (MGO) from an environmental point of view. A case study was performed using a 50K bulk carrier engaged in domestic services in [...] Read more.
This research was focused on a comparative analysis of using LNG as a marine fuel with a conventional marine gas oil (MGO) from an environmental point of view. A case study was performed using a 50K bulk carrier engaged in domestic services in South Korea. Considering the energy exporting market for South Korea, the fuel supply chain was designed with the two largest suppliers: Middle East (LNG-Qatar/MGO-Saudi Arabia) and U.S. The life cycle of each fuel type was categorized into three stages: Well-to-Tank (WtT), Tank-to-Wake (TtW), and Well-to-Wake (WtW). With the process modelling, the environmental impact of each stage was analyzed based on the five environmental impact categorizes: Global Warming Potential (GWP), Acidification Potential (AP), Photochemical Potential (POCP), Eutrophication Potential (EP) and Particulate Matter (PM). Analysis results reveal that emission levels for the LNG cases are significantly lower than the MGO cases in all potential impact categories. Particularly, Case 1 (LNG import to Korea from Qatar) is identified as the best option as producing the lowest emission levels per 1.0 × 107 MJ of fuel consumption: 977 tonnages of CO2 equivalent (for GWP), 1.76 tonnages of SO2 equivalent (for AP), 1.18 tonnages of N equivalent (for EP), 4.28 tonnages of NMVOC equivalent (for POCP) and 26 kg of PM 2.5 equivalent (for PM). On the other hand, the results also point out that the selection of the fuel supply routes could be an important factor contributing to emission levels since longer distances for freight transportation result in more emissions. It is worth noting that the life cycle assessment can offer us better understanding of holistic emission levels contributed by marine fuels from the cradle to the grave, which are highly believed to remedy the shortcomings of current marine emission indicators. Full article
(This article belongs to the Special Issue Ship Lifecycle)
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Open AccessFeature PaperArticle
Direct Measurements of Bed Shear Stress under Swash Flows on Steep Laboratory Slopes at Medium to Prototype Scales
J. Mar. Sci. Eng. 2019, 7(10), 358; https://doi.org/10.3390/jmse7100358 - 09 Oct 2019
Viewed by 193
Abstract
Robust measurements of bed shear stress under wave runup flows are necessary to inform beachface sediment transport modelling. In this study, direct measurements of swash zone bed shear stress were obtained in medium and prototype-scale laboratory experiments on steep slopes. Peak shear stresses [...] Read more.
Robust measurements of bed shear stress under wave runup flows are necessary to inform beachface sediment transport modelling. In this study, direct measurements of swash zone bed shear stress were obtained in medium and prototype-scale laboratory experiments on steep slopes. Peak shear stresses coincided with the arrival of uprush swash fronts and high-resolution measurement of swash surface profiles indicated a consistently seaward sloping swash surface with minimal evidence of a landward sloping swash front. The quadratic stress law was applied to back-calculate time-varying friction factors, which were observed to decrease with increasing Reynolds number on smooth slopes, consistent with theory for steady flows. Additionally, friction factors remained relatively constant throughout the swash cycle (except around flow reversal), with a variation of approximately ±20% from the mean value and with only small differences between uprush and backwash. Measured friction factors were observed to be larger than expected when plotted on the Moody or wave friction diagram for a given Reynolds number and relative roughness, consistent with previous field and laboratory studies at various scales. Full article
(This article belongs to the Special Issue Dynamics of the Coastal Zone)
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Open AccessArticle
Dune Volume Changes at Decadal Timescales and Its Relation with Potential Aeolian Transport
J. Mar. Sci. Eng. 2019, 7(10), 357; https://doi.org/10.3390/jmse7100357 - 08 Oct 2019
Viewed by 135
Abstract
Long-term changes in dune volume at the Belgian coast are analyzed based on measured data by airborne surveys available from 1979. For most of the 65 km long coastal stretch, dune volume increases linearly in time at a constant rate. Dune growth varies [...] Read more.
Long-term changes in dune volume at the Belgian coast are analyzed based on measured data by airborne surveys available from 1979. For most of the 65 km long coastal stretch, dune volume increases linearly in time at a constant rate. Dune growth varies between 0–12.3 m3/m/year with an average dune growth of 6.2 m3/m/year, featuring large variations in longshore directions. Based on a wind data set from 2000–2017, it is found that potential aeolian sediment transport has its main drift from the west to southwest direction (onshore to oblique onshore). Based on a modified Bagnold model, onshore potential aeolian sediment transport ranges to a maximum of 9 m3/m/year, while longshore potential aeolian sediment transport could reach up to 20 m3/m/year. We found an important correlation between observed and predicted dune development at decadal timescales when zones with dune management activities are excluded. Most of the predicted data are within a factor of two of the measured values. The variability in potential transport is well related to the variability in dune volume changes at the considered spatial–temporal scale, suggesting that natural dune growth is primarily caused by aeolian sediment transport from the beach. It also suggests that annual differences in forcing and transport limiting conditions (wind and moisture) only have a modest effect on the overall variability of dune volume trends. Full article
(This article belongs to the Section Coastal Engineering)
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Open AccessArticle
Wave-Induced Seafloor Instability in the Yellow River Delta: Flume Experiments
J. Mar. Sci. Eng. 2019, 7(10), 356; https://doi.org/10.3390/jmse7100356 - 06 Oct 2019
Viewed by 262
Abstract
Geological disasters of seabed instability are widely distributed in the Yellow River Delta, posing a serious threat to the safety of offshore oil platforms and submarine pipelines. Waves act as one of the main factors causing the frequent occurrence of instabilities in the [...] Read more.
Geological disasters of seabed instability are widely distributed in the Yellow River Delta, posing a serious threat to the safety of offshore oil platforms and submarine pipelines. Waves act as one of the main factors causing the frequent occurrence of instabilities in the region. In order to explore the soil failure mode and the law for pore pressure response of the subaqueous Yellow River Delta under wave actions, in-lab flume tank experiments were conducted in this paper. In the experiments, wave loads were applied with a duration of 1 hour each day for 7 consecutive days; pore water pressure data of the soil under wave action were acquired, and penetration strength data of the sediments were determined after wave action. The results showed that the fine-grained seabed presented an arc-shaped oscillation failure form under wave action. In addition, the sliding surface firstly became deeper and then shallower with the wave action. Interestingly, the distribution of pores substantially coincided with that of sliding surfaces. For the first time, gas holes were identified along with their positioning and angle with respect to the sediments. The presence of gas may serve as a primer for submarine slope failures. The wave process can lead to an increase in the excess pore pressure, while the anti-liquefaction capacity of the sediments was improved, causing a decrease in the excess pore pressure resulting from the next wave process. Without new depositional sediments, the existing surface sediments can form high-strength formation under wave actions. The test results may provide a reference for numerical simulations and engineering practice. Full article
(This article belongs to the Special Issue New Advances in Marine Engineering Geology)
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Open AccessArticle
Effects of Different Temperatures on the Softening of Red-Bed Sandstone in Turbulent Flow
J. Mar. Sci. Eng. 2019, 7(10), 355; https://doi.org/10.3390/jmse7100355 - 06 Oct 2019
Viewed by 212
Abstract
The rates of chemical reactions are highly dependent on temperature, meaning that the actual geological rock mass is affected by different temperatures. Only when the temperature effect is considered can the mechanism of the influence of temperature on the interaction between water and [...] Read more.
The rates of chemical reactions are highly dependent on temperature, meaning that the actual geological rock mass is affected by different temperatures. Only when the temperature effect is considered can the mechanism of the influence of temperature on the interaction between water and rock be further understood. It was found that the condition of turbulent flow is more likely to promote the softening of red-bed sandstone than the conditions of laminar flow and static water in an experimental study on the softening effects of different flow patterns on red-bed sandstone. Therefore, based on a multi-functional self-circulating open channel hydraulic test system, this paper designs and completes equal volume saturated tests of red-bed sandstone at low temperature (1 °C), medium temperature (23 °C), and high temperature (45 °C) under the turbulent conditions of three equal temperature gradients. The chemical action of the circulating solution in water flow at different temperatures, the propagation of micro-cracks in rock and the changes in mechanical indexes are discussed. The influence laws and mechanisms of the different temperatures on the softening of red-bed sandstone in turbulent flow are revealed. The results show that low-temperature flow can inhibit the softening of red-bed sandstone in the range of 1–45 °C. With the increase in water flow temperature, the development degrees of micro-structures and the mechanical damage of the corresponding rock become more notable. That is, temperature affects the physical and chemical water-rock interactions and then changes the internal structure of rock, thus affecting the softening and failure processes of red-bed sandstone. The study provides a theoretical basis for the further investigation of the softening laws and mechanisms of other red layered soft rocks by temperature under turbulent conditions. Full article
(This article belongs to the Section Coastal Engineering)
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Open AccessArticle
A Study on the Estimation of Facilities in LNG Bunkering Terminal by Simulation—Busan Port Case
J. Mar. Sci. Eng. 2019, 7(10), 354; https://doi.org/10.3390/jmse7100354 - 03 Oct 2019
Viewed by 229
Abstract
Since 2020, the International Maritime Organization (IMO) has tightened regulations on the emissions of sulfur oxides from ships from less than 3.5% to less than 0.5%. As a countermeasure, shipping companies can adopt one of three potential solutions: using low sulfur fuel (LSFO), [...] Read more.
Since 2020, the International Maritime Organization (IMO) has tightened regulations on the emissions of sulfur oxides from ships from less than 3.5% to less than 0.5%. As a countermeasure, shipping companies can adopt one of three potential solutions: using low sulfur fuel (LSFO), installing scrubbers, or using liquefied natural gas (LNG) fuel. However, considering the environmental aspects such as the UN greenhouse gas (GHG) emission reduction program and the reduction of fine dust generation in port areas, LNG fuel is ultimately considered to be the most ideal method in the marine industry. In line with this international trend, major port authorities are considering building LNG bunkering stations, but the proper methods and criteria for estimating the size of LNG bunkering infrastructure are not clear. This study proposes a method of estimating the size of LNG infrastructure required with consideration for the operational status of ports according to the estimated amount of bunkering demand at a future time with the case study of Busan Port in Korea. In order to estimate the detailed demand amount by inbound vessels, a simulation modeling technique is applied as a tool of research. Full article
(This article belongs to the Special Issue Ports and Terminal Management)
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Open AccessArticle
A Data-Driven Approach Based on Multivariate Copulas for Quantitative Risk Assessment of Concrete Dam
J. Mar. Sci. Eng. 2019, 7(10), 353; https://doi.org/10.3390/jmse7100353 - 03 Oct 2019
Viewed by 137
Abstract
Risk assessment of dam’s running status is an important part of dam management. A data-driven method based on monitored displacement data has been applied in risk assessment, owing to its easy operation and real-time analysis. However, previous data-driven methods considered displacement data series [...] Read more.
Risk assessment of dam’s running status is an important part of dam management. A data-driven method based on monitored displacement data has been applied in risk assessment, owing to its easy operation and real-time analysis. However, previous data-driven methods considered displacement data series at each monitoring point as an independent variable and assessed the running status of each monitoring point separately, without considering the correlation between displacement of different monitoring points. In addition, previous studies assessed the dam’s running status qualitatively, without quantifying the risk probability. To solve the above two issues, a displacement-data driven method based on a multivariate copula function is proposed in this paper. Multivariate copula functions can construct a joint distribution which reveals the relevance structure of random variables. We assumed that the risk probability of each dam section is independent and took monitoring points at one dam section as examples. Starting from the risk assessment of single monitoring points, we calculated the residual between the monitored displacement data and the modelled data estimated by the statistical model, and built a risk ratio function based on the residual. Then, using the multivariate copula function, we obtained a combined risk ratio of multi-monitoring points which took the correlation between each monitoring point into account. Finally, a case study was provided. The proposed method not only quantitatively assessed the probability of the real-time dam risk but also considered the correlation between the displacement data of different monitoring points. Full article
(This article belongs to the Special Issue Monitoring of Coastal and Offshore Structures)
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Open AccessFeature PaperArticle
Climate Change Impact in the Ria de Aveiro Lagoon Ecosystem: A Case Study
J. Mar. Sci. Eng. 2019, 7(10), 352; https://doi.org/10.3390/jmse7100352 - 03 Oct 2019
Viewed by 181
Abstract
Climate change and global sea-level rise are major issues of the 21st century. The main goal of this study is to assess the physical and biogeochemical status of the Ria de Aveiro lagoon (Portugal) under future climate scenarios, using a coupled physical/ eutrophication [...] Read more.
Climate change and global sea-level rise are major issues of the 21st century. The main goal of this study is to assess the physical and biogeochemical status of the Ria de Aveiro lagoon (Portugal) under future climate scenarios, using a coupled physical/ eutrophication model. The impact on the lagoon ecosystem status of the mean sea level rise (MSLR), the amplitude rise of the M2 tidal constituent (M2R), the changes in the river discharge, and the rising of the air temperature was investigated. Under MSLR and M2R, the results point to an overall salinity increase and water temperature decrease, revealing ocean water dominance. The main lagoon areas presented salinity values close to those of the ocean waters (~34 PSU), while a high range of salinity was presented for the river and the far end areas (20–34 PSU). The water temperature showed a decrease of approximately 0.5–1.5 °C. The responses of the biogeochemical variables reflect the increase of the oceanic inflow (transparent and nutrient-poor water) or the reduction of the river flows (nutrient-rich waters). The results evidenced, under the scenarios, an overall decreasing of the inorganic nitrogen concentration and the carbon phytoplankton concentrations. A warm climate, although increasing the water temperature, does not seem to affect the lagoon’s main status, at least in the frame of the model used in the study. Full article
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Open AccessEditorial
Marine Structures
J. Mar. Sci. Eng. 2019, 7(10), 351; https://doi.org/10.3390/jmse7100351 - 03 Oct 2019
Viewed by 121
Abstract
Structural mechanics is an important field of engineering [...] Full article
(This article belongs to the Special Issue Marine Structures)
Open AccessArticle
Understanding the Vulnerabilities in Digital Components of an Integrated Bridge System (IBS)
J. Mar. Sci. Eng. 2019, 7(10), 350; https://doi.org/10.3390/jmse7100350 - 02 Oct 2019
Cited by 1 | Viewed by 178
Abstract
The adoption of the global positioning system (GPS) within the marine industry has revolutionized the marine operations by condensing the navigation of a vessel into an integrated bridge system (IBS). An IBS acts as the main command and control of a vessel as [...] Read more.
The adoption of the global positioning system (GPS) within the marine industry has revolutionized the marine operations by condensing the navigation of a vessel into an integrated bridge system (IBS). An IBS acts as the main command and control of a vessel as it interconnects various digital devices used for navigation in open seas and is also connected to other on-board systems of a vessel e.g., navigation and control, propulsion and machinery management system, cargo management system and safety management system, core infra structure systems, administrative and crew welfare systems, etc. Additionally, it also provides a gateway to the Internet, thus, leaving not only an IBS vulnerable but also all the on-board systems vulnerable to cyber-attacks. We, in this study, have collected historical evidences about various vulnerable digital components in an IBS to better understand the security and privacy challenges associated with the vulnerable IBS components. Our study is the first of its kind that involves collection and review of 59 historical accidents reported in literature and has highlighted various vulnerability patterns, their causes and consequences, with geographical as well as temporal relationships for different vulnerable IBS components. The vulnerabilities of IBS components were reportedly exploited using various cyber-attack techniques e.g., jamming, spoofing, hijacking, etc. This review paper also forms a baseline for future work on vulnerabilities of IBS and maritime cyber security. Full article
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Open AccessArticle
Simulation of Ice-Propeller Collision with Cohesive Element Method
J. Mar. Sci. Eng. 2019, 7(10), 349; https://doi.org/10.3390/jmse7100349 - 02 Oct 2019
Viewed by 193
Abstract
The existence of ice in ice-covered waters may cause damage to the propeller of polar ships, especially when massive ice floes are submerged around the hull. This paper aims to simulate an interaction process of a direct ice collision with a propeller based [...] Read more.
The existence of ice in ice-covered waters may cause damage to the propeller of polar ships, especially when massive ice floes are submerged around the hull. This paper aims to simulate an interaction process of a direct ice collision with a propeller based on the cohesive element method. A constitutive law is applied to model the ice material. The model of ice material is validated against model test results. The resulting impact loads acting on the contact surfaces and the corresponding ice block velocity are calculated in the time domain. The ice crushing, shearing and fracture failures are reproduced in the simulation. The convergence study with three meshing sizes of ice block is performed. To carry out a parametric study, five parameters are selected for analysis. These parameters are composed of rotational speed, direction of the propeller, initial speed of the ice block, contact position, and area between the ice and the propeller. The results show that the ice loads are affected by the five factors significantly. Ice loads tend to increase by decreasing the rotational speed, increasing the initial ice speed and the contact area, and changing the rotational direction from clockwise to counterclockwise. The effect of the contact position on the impact loads is relatively complex, depending on rotational speeds of the propeller. Full article
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Open AccessArticle
Numerical Modeling of Gas Migration and Hydrate Formation in Heterogeneous Marine Sediments
J. Mar. Sci. Eng. 2019, 7(10), 348; https://doi.org/10.3390/jmse7100348 - 02 Oct 2019
Viewed by 174
Abstract
The formation of marine gas hydrates is controlled by gas migration and accumulation from lower sediments and by the conditions of the hydrate stability zone. Permeability and porosity are important factors to evaluate the gas migration capacity and reservoir sealing capacity, and to [...] Read more.
The formation of marine gas hydrates is controlled by gas migration and accumulation from lower sediments and by the conditions of the hydrate stability zone. Permeability and porosity are important factors to evaluate the gas migration capacity and reservoir sealing capacity, and to determine the distribution of hydrates in the stable region. Based on currently available geological data from field measurements in the Shenhu area of Baiyun Sag in the northern South China Sea, numerical simulations were conducted to estimate the influence of heterogeneities in porosity and permeability on the processes of hydrate formation and accumulation. The simulation results show that: (1) The heterogeneity of the hydrate stability zone will affect the methane migration within it and influence the formation and accumulation of hydrates. This is one of the reasons for the formation of heterogeneous hydrates. (2) When the reservoir is layered heterogeneously, stratified differences in gas lateral migration and hydrate formation will occur in the sediment, and the horizontal distribution range of the hydrate in a high porosity and permeability reservoir is wider. (3) To determine the dominant enrichment area of hydrate in a reservoir, we should consider both vertical and lateral conditions of the sedimentary layer, and the spatial coupling configuration relationships among the hydrate stability region, reservoir space and gas migration and drainage conditions should be considered comprehensively. The results are helpful to further understand the rules of hydrate accumulation in the Shenhu area on the northern slope of the South China Sea, and provide some references for future hydrate exploration and the estimation of reserves. Full article
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