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Volume 6
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J. Mar. Sci. Eng., Volume 6, Issue 3 (September 2018) – 34 articles

Cover Story (view full-size image): Numerous types of marine fouling organisms may be found on the submerged part of offshore structures, as depicted in this cover image. Identification of marine species on-site allows assumptions to be made about their growth rate and coverage, which helps engineers to obtain more accurate estimates of the wave loading. The main objective of this study was to capitalize on recent advances in deep learning by developing a technique that could detect and segment marine growth in imagery captured during underwater inspection campaigns. A key feature of this study was that the deep network was trained using thousands of synthetic images. The team behind this research has a long-held interest in measuring the extent of marine growth and assessing its impact from a structural loading standpoint. View this paper.
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23 pages, 4156 KiB  
Article
Modulated Response of Subtropical Gyres: Positive Feedback Loop, Subharmonic Modes, Resonant Solar and Orbital Forcing
by Jean-Louis Pinault
J. Mar. Sci. Eng. 2018, 6(3), 107; https://doi.org/10.3390/jmse6030107 - 19 Sep 2018
Cited by 15 | Viewed by 4545
Abstract
Evidence of long-term variability in the upper ocean has emerged for two decades. Most of the issues discussed raise a lot of questions. What is the driver of the decadal oscillation of rainfall in Europe that has been observed since the end of [...] Read more.
Evidence of long-term variability in the upper ocean has emerged for two decades. Most of the issues discussed raise a lot of questions. What is the driver of the decadal oscillation of rainfall in Europe that has been observed since the end of the 20th century? How to explain low-frequency variability as observed in the Atlantic Multidecadal Oscillation (AMO)? More generally, how does solar and orbital forcing occur during very long-term climate change? The observations suggest that both a positive feedback loop amplifies the effects of the insolation gradient on the climate system and a resonance phenomenon occurs, filtering out some frequencies in favour of others. Throughout this paper, some answers to these problems are given from a new concept based on the modulated response of subtropical gyres to solar and orbital forcing. Subtropical gyres turn out to be the main driver of long-term climate variability because they tightly control, via the western boundary currents, heat transport from the tropics into middle and high latitudes. Specifically, the theoretical foundations of long-period Rossby waves winding around the subtropical gyres are laid, suggested by the observations of persistent sea surface temperature anomalies at mid-latitudes. Multi-frequency Gyral Rossby Waves (GRWs) exhibit properties resulting from their annular structure and their coupling. Using a β-cone approximation, the momentum equations are solved in polar coordinates. The gradient β of the Coriolis parameter depends on the mean radius of the annulus and remains constant all around the latter. GRWs result from the variation in the Coriolis Effect with the mean radius of the annulus. The speed of the anti-cyclonically wind-driven circulation being higher than the phase velocity of cyclonically propagating GRWs, amplified forcing effects occur as well as resonances for periods consistent with the observations. Full article
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20 pages, 10031 KiB  
Article
A Modeling Study on the Oil Spill of M/V Marathassa in Vancouver Harbour
by Xiaomei Zhong, Haibo Niu, Yongsheng Wu, Charles Hannah, Shihan Li and Thomas King
J. Mar. Sci. Eng. 2018, 6(3), 106; https://doi.org/10.3390/jmse6030106 - 17 Sep 2018
Cited by 11 | Viewed by 6147
Abstract
The M/V Marathassa oil spill occurred on 8 April 2015 in the English Bay. In the present study, the trajectory and the transport mechanism of the spilled oil have been studied by using the three-dimensional and particle-based Oil Spill Contingency and Response (OSCAR) [...] Read more.
The M/V Marathassa oil spill occurred on 8 April 2015 in the English Bay. In the present study, the trajectory and the transport mechanism of the spilled oil have been studied by using the three-dimensional and particle-based Oil Spill Contingency and Response (OSCAR) model forced by the Finite-Volume Community Ocean Model (FVCOM). FVCOM provided the hydrodynamic variables used by the oil spill model of OSCAR. The results showed that the fraction of the oil on the water surface and on the shoreline, as well as the amount of oil recovered were affected by the time of the initial release, the overall duration of the discharge, wind and recovery actions. The hindcast study of the M/V Marathassa oil spill showed that the likely starting time for the discharge was between 14:00 and 15:00, on 8 April 2015. The release may have lasted for a relatively long time (assumed to be 22 h in this study). The results of modeling in this study were found reasonably acceptable allowing for further application in risk assessment studies in the English Bay and Vancouver Harbour. The trajectory of the spill was mainly controlled by the tidal currents, which were strongly sensitive to the local coastline and topography of First Narrows and that in the central harbour. The model results also suggested that a high-resolution model, which was able to resolve abrupt changes in the coastlines and topography, was necessary to simulate the oil spill in the harbour. Full article
(This article belongs to the Special Issue Marine Oil Spills 2018)
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23 pages, 2424 KiB  
Article
Free Surface Reconstruction for Phase Accurate Irregular Wave Generation
by Ankit Aggarwal, Csaba Pákozdi, Hans Bihs, Dag Myrhaug and Mayilvahanan Alagan Chella
J. Mar. Sci. Eng. 2018, 6(3), 105; https://doi.org/10.3390/jmse6030105 - 13 Sep 2018
Cited by 22 | Viewed by 5911
Abstract
The experimental wave paddle signal is unknown to the numerical modellers in many cases. This makes it quite challenging to numerically reproduce the time history of free surface elevation for irregular waves. In the present work, a numerical investigation is performed using a [...] Read more.
The experimental wave paddle signal is unknown to the numerical modellers in many cases. This makes it quite challenging to numerically reproduce the time history of free surface elevation for irregular waves. In the present work, a numerical investigation is performed using a computational fluid dynamics (CFD) based model to validate and investigate a non-iterative free surface reconstruction technique for irregular waves. In the current approach, the free surface is reconstructed by spectrally composing the irregular wave train as a summation of the harmonic components coupled with the Dirichlet inlet boundary condition. The verification is performed by comparing the numerically reconstructed free surface elevation with theoretical input waves. The applicability of the present approach to generate irregular waves by reconstructing the free surface is investigated for different coastal and marine engineering problems. A numerical analysis is performed to validate the free surface reconstruction approach to generate breaking irregular waves over a submerged bar. The wave amplitudes, wave frequencies and wave phases are modelled with good accuracy in the time-domain during the higher-order energy transfers and complex processes like wave shoaling, wave breaking and wave decomposition. The present approach to generate irregular waves is also employed to model steep irregular waves in deep water. The free surface reconstruction method is able to simulate the irregular free surface profiles in deep water with low root mean square errors and high correlation coefficients. Furthermore, the irregular wave forces on a monopile are investigated in the time-domain. The amplitudes and phases of the force signal under irregular waves generated by using the current technique are modelled accurately in the time-domain. The proposed approach to numerically reproduce the free surface elevation in the time-domain provides promising and accurate results for all the benchmark cases. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics for Ocean Surface Waves)
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39 pages, 25607 KiB  
Article
Simulation of the 2003 Foss Barge - Point Wells Oil Spill: A Comparison between BLOSOM and GNOME Oil Spill Models
by Rodrigo Duran, Lucy Romeo, Jonathan Whiting, Jason Vielma, Kelly Rose, Amoret Bunn and Jennifer Bauer
J. Mar. Sci. Eng. 2018, 6(3), 104; https://doi.org/10.3390/jmse6030104 - 11 Sep 2018
Cited by 26 | Viewed by 8415
Abstract
The Department of Energy’s (DOE’s) National Energy Technology Laboratory’s (NETL’s) Blowout and Spill Occurrence Model (BLOSOM), and the National Oceanic and Atmospheric Administration’s (NOAA’s) General NOAA Operational Modeling Environment (GNOME) are compared. Increasingly complex simulations are used to assess similarities and differences between [...] Read more.
The Department of Energy’s (DOE’s) National Energy Technology Laboratory’s (NETL’s) Blowout and Spill Occurrence Model (BLOSOM), and the National Oceanic and Atmospheric Administration’s (NOAA’s) General NOAA Operational Modeling Environment (GNOME) are compared. Increasingly complex simulations are used to assess similarities and differences between the two models’ components. The simulations presented here are forced by ocean currents from a Finite Volume Community Ocean Model (FVCOM) implementation that has excellent skill in representing tidal motion, and with observed wind data that compensates for a coarse vertical ocean model resolution. The comprehensive comparison between GNOME and BLOSOM presented here, should aid modelers in interpreting their results. Beyond many similarities, aspects where both models are distinct are highlighted. Some suggestions for improvement are included, e.g., the inclusion of temporal interpolation of the forcing fields (BLOSOM) or the inclusion of a deflection angle option when parameterizing wind-driven processes (GNOME). Overall, GNOME and BLOSOM perform similarly, and are found to be complementary oil spill models. This paper also sheds light on what drove the historical Point Wells spill, and serves the additional purpose of being a learning resource for those interested in oil spill modeling. The increasingly complex approach used for the comparison is also used, in parallel, to illustrate the approach an oil spill modeler would typically follow when trying to hindcast or forecast an oil spill, including detailed technical information on basic aspects, like choosing a computational time step. We discuss our successful hindcast of the 2003 Point Wells oil spill that, to our knowledge, had remained unexplained. The oil spill models’ solutions are compared to the historical Point Wells’ oil trajectory, in time and space, as determined from overflight information. Our hindcast broadly replicates the correct locations at the correct times, using accurate tide and wind forcing. While the choice of wind coefficient we use is unconventional, a simplified analytic model supported by observations, suggests that it is justified under this study’s circumstances. We highlight some of the key oceanographic findings as they may relate to other oil spills, and to the regional oceanography of the Salish Sea, including recommendations for future studies. Full article
(This article belongs to the Special Issue Marine Oil Spills 2018)
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21 pages, 8477 KiB  
Article
Modeling the Transport and Fate of Sediments Released from Marine Construction Projects in the Coastal Waters of British Columbia, Canada
by David B. Fissel and Yuehua Lin
J. Mar. Sci. Eng. 2018, 6(3), 103; https://doi.org/10.3390/jmse6030103 - 6 Sep 2018
Cited by 4 | Viewed by 4759
Abstract
Major marine construction projects, resulting in the release of sediments, are subject to environmental assessment and other regulatory approval processes. An important tool used for this is the development of specialized numerical methods for these marine activities. An integrated set of numerical methods [...] Read more.
Major marine construction projects, resulting in the release of sediments, are subject to environmental assessment and other regulatory approval processes. An important tool used for this is the development of specialized numerical methods for these marine activities. An integrated set of numerical methods addresses four distinct topics: (1) The near-field release and mixing of suspended sediments into the water column (i.e., the initial dilution zone); (2) the transport of the suspended sediments under the influence of complex ocean currents in the far-field; (3) the settling of the transported suspended sediments onto the seabed; and (4) the potential for resuspension of the deposited sediments due to sporadic occurrences of unusually large near-bottom currents. A review of projects subjected to environmental assessment in the coastal waters of British Columbia, from the year 2006 to 2017, is presented to illustrate the numerical models being used and their ongoing development. Improvements include higher resolution model grids to better represent the near-field, the depiction of particle size dependent vertical settling rates and the computation of resuspension of initially deposited sediments, especially in relation to temporary subsea piles of sediments arising from trenching for marine pipelines. The ongoing challenges for this numerical modeling application area are also identified. Full article
(This article belongs to the Special Issue Selected Papers from the 15th Estuarine and Coastal Modeling Conference)
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22 pages, 7326 KiB  
Article
Semi-Active Structural Control of Offshore Wind Turbines Considering Damage Development
by Arash Hemmati and Erkan Oterkus
J. Mar. Sci. Eng. 2018, 6(3), 102; https://doi.org/10.3390/jmse6030102 - 5 Sep 2018
Cited by 29 | Viewed by 6167
Abstract
High flexibility of new offshore wind turbines (OWT) makes them vulnerable since they are subjected to large environmental loadings, wind turbine excitations and seismic loadings. A control system capable of mitigating undesired vibrations with the potential of modifying its structural properties depending on [...] Read more.
High flexibility of new offshore wind turbines (OWT) makes them vulnerable since they are subjected to large environmental loadings, wind turbine excitations and seismic loadings. A control system capable of mitigating undesired vibrations with the potential of modifying its structural properties depending on time-variant loadings and damage development can effectively enhance serviceability and fatigue lifetime of turbine systems. In the present paper, a model for offshore wind turbine systems equipped with a semi-active time-variant tuned mass damper is developed considering nonlinear soil–pile interaction phenomenon and time-variant damage conditions. The adaptive concept of this tuned mass damper assumes slow change in its structural properties. Stochastic wind and wave loadings in conjunction with ground motions are applied to the system. Damages to soil and tower caused by earthquake strokes are considered and the semi-active control device is retuned to the instantaneous frequency of the system using short-time Fourier transformation (STFT). The performance of semi-active time-variant vibration control is compared with its passive counterpart in operational and parked conditions. The dynamic responses for a single seismic record and a set of seismic records are presented. The results show that a semi-active mass damper with a mass ratio of 1% performs significantly better than a passive tuned mass damper with a mass ratio of 4%. Full article
(This article belongs to the Special Issue Marine Structures)
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19 pages, 20825 KiB  
Article
Numerical Assessment of Roll Motion Characteristics and Damping Coefficient of a Ship
by S.S. Kianejad, Jaesuk Lee, Yi Liu and Hossein Enshaei
J. Mar. Sci. Eng. 2018, 6(3), 101; https://doi.org/10.3390/jmse6030101 - 1 Sep 2018
Cited by 22 | Viewed by 6807
Abstract
Accurate calculation of the roll damping moment at resonance condition is essential for roll motion prediction. Because at the resonance condition, the moment of inertia counteracts restoring moment and only the damping moment resists increase in the roll angle. There are various methods [...] Read more.
Accurate calculation of the roll damping moment at resonance condition is essential for roll motion prediction. Because at the resonance condition, the moment of inertia counteracts restoring moment and only the damping moment resists increase in the roll angle. There are various methods to calculate the roll damping moment which are based on potential flow theory. These methods have limitations to taking into account the viscous effects in estimating the roll motion, while, CFD as a numerical method is capable of considering the viscous effects. In this study, a CFD method based on a harmonic excited roll motion (HERM) technique is used to compute the roll motion and the roll damping moment of a containership’s model in different conditions. The influence of excitation frequency, forward speed and degrees of freedom at beam-sea and oblique-sea realizations are considered in estimating the roll damping coefficients. The results are validated against model tests, where a good agreement is found. Full article
(This article belongs to the Special Issue Engineering Mathematics in Ship Design)
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12 pages, 937 KiB  
Article
Onset of Motion of Sediment underneath Scour Protection around a Monopile
by Anders Wedel Nielsen and Thor Ugelvig Petersen
J. Mar. Sci. Eng. 2018, 6(3), 100; https://doi.org/10.3390/jmse6030100 - 29 Aug 2018
Cited by 10 | Viewed by 3917
Abstract
The stability of scour protections is, potentially, an important issue during the design of fixed foundations for offshore wind turbines. One of the failure mechanisms observed at placed scour protection around offshore foundations is suction of sediment through the scour protection and subsequent [...] Read more.
The stability of scour protections is, potentially, an important issue during the design of fixed foundations for offshore wind turbines. One of the failure mechanisms observed at placed scour protection around offshore foundations is suction of sediment through the scour protection and subsequent sinking of the scour protection. Incipient motion of sediment and the initiation of suction underneath scour protections around piles in the marine environment were studied under waves, current and combined waves and current conditions. The motion of a thin layer of sediment underneath the scour protection was studied through the glass bottom of the test flume, which provided a clear view of the initiation of the motion of the sediment. The results show that the mobility depends on the Keulegan–Carpenter ( K C ) number for the pile, the ratio between waves and current flow and the ratio between the thickness of the scour protection and the base sediment. The critical mobility number is smaller for the wave-dominated situation compared to current-dominated conditions, which again are smaller than for combined waves and current conditions. Consequently, larger K C -numbers cause larger critical mobility numbers than smaller K C -numbers. Design diagrams are presented for the threshold of incipient motion of sediment underneath a scour protection in waves, current and combined waves and current. Full article
(This article belongs to the Special Issue Offshore Wind Structures)
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24 pages, 7645 KiB  
Article
Impact Assessment of a Major River Basin in Bangladesh on Storm Surge Simulation
by Md. Abdul Al Mohit, Masaru Yamashiro, Noriaki Hashimoto, Md. Bodruddoza Mia, Yoshihiko Ide and Mitsuyoshi Kodama
J. Mar. Sci. Eng. 2018, 6(3), 99; https://doi.org/10.3390/jmse6030099 - 28 Aug 2018
Cited by 20 | Viewed by 5596
Abstract
A two-dimensional bay and river coupled numerical model in Cartesian coordinates was developed to find the impact of the river on the simulated water levels associated with a storm along the coast of Bangladesh. The shallow water models developed for both the bay [...] Read more.
A two-dimensional bay and river coupled numerical model in Cartesian coordinates was developed to find the impact of the river on the simulated water levels associated with a storm along the coast of Bangladesh. The shallow water models developed for both the bay and river were discretized by the finite difference method with forward in time and central in space. The boundaries for the coast and islands were approximated through proper stair steps representation and solved by a conditionally stable semi-implicit manner on a staggered Arakawa C-grid. A one-way nested scheme technique was used in the bay model to include coastal complexities as well as to save computational costs. A stable tidal condition was made by forcing the sea levels with the most energetic tidal constituent, M2, along with the southern open boundary of the bay model omitting wind stress. The developed model was then applied to foresee the sea-surface elevation associated with the catastrophic cyclone of 1991 and cyclone MORA. A comparative study of the water levels associated with a storm was made through model simulations with and without the inclusion of the river system. We found that the surge height in the bay-river junction area decreased by 20% and the surge height reduced by about 3–8% outside the junction area from this study. The obtained results were found to have a satisfactory similarity with some of the observed data. Full article
(This article belongs to the Special Issue Coastal Zone Management)
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26 pages, 10742 KiB  
Article
Autonomous Minimum Safe Distance Maintenance from Submersed Obstacles in Ocean Currents
by Timothy Sands, Kevin Bollino, Isaac Kaminer and Anthony Healey
J. Mar. Sci. Eng. 2018, 6(3), 98; https://doi.org/10.3390/jmse6030098 - 22 Aug 2018
Cited by 13 | Viewed by 4644
Abstract
A considerable volume of research has recently blossomed in the literature on autonomous underwater vehicles accepting recent developments in mathematical modeling and system identification; pitch control; information filtering and active sensing, including inductive sensors of ELF emissions and also optical sensor arrays for [...] Read more.
A considerable volume of research has recently blossomed in the literature on autonomous underwater vehicles accepting recent developments in mathematical modeling and system identification; pitch control; information filtering and active sensing, including inductive sensors of ELF emissions and also optical sensor arrays for position, velocity, and orientation detection; grid navigation algorithms; and dynamic obstacle avoidance, amongst others. In light of these modern developments, this article develops and compares integrative guidance, navigation, and control methodologies for the Naval Postgraduate School’s Phoenix submerged autonomous vehicle, where these methods are assumed available. The measure of merit reveals how well each of several proposed methodologies cope with known and unknown disturbances, such as currents that can be constant or harmonic, while maintaining a safe passage distance from underwater obstacles, in this case submerged mines. Classical pole-placement designs establish nominal baseline behaviors and are subsequently compared to performance of designs that are optimized to satisfy linear quadratic cost functions in regulators as well as linear-quadratic Gaussian designs. Feed-forward architectures and integral control designs are also evaluated. A noteworthy contribution is a very simple method to mimic optimal results with a “rule of thumb” criteria based on the design’s time constant. Since the rule-of-thumb method uses the assumed system model for computation of the control, it is particularly generic. Cited references each contain methods for online system parameter identification (with a motivation of use in the finding the control signal), permitting the rule of thumb’s generic applicability, since it is expressed in terms of the system parameters. This proposed method permits control design at sea where significant computation abilities are not available. Very simple waypoint guidance is also introduced to guide a vehicle along a preplanned path through a field of obstacles placed at random locations. The linear-quadratic Gaussian design proves best when augmented with integral control, and works well with reduced-order equations, while the “rule of thumb” design is seen to closely mimic the optimal performance. Feed-forward augmentation proves particularly efficient at rejecting constant disturbances, while augmentation with integral control is necessary to counter periodic disturbances, where the augmentations are also optimized in the linear-quadratic Gaussian procedures, yet can be closely mimicked by the proposed “rule of thumb” technique. Full article
(This article belongs to the Special Issue Intelligent Marine Robotics Modelling, Simulation and Applications)
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2 pages, 148 KiB  
Editorial
Marine Propulsors
by Sverre Steen and Kourosh Koushan
J. Mar. Sci. Eng. 2018, 6(3), 97; https://doi.org/10.3390/jmse6030097 - 22 Aug 2018
Cited by 1 | Viewed by 3232
Abstract
This Special Issue is following up the success of the latest Symposium on Marine Propulsors (www.marinepropulsors.com, smp’17) by publishing extended or improved versions of the selected papers presented at the symposium[…] Full article
(This article belongs to the Special Issue Marine Propulsors)
23 pages, 1813 KiB  
Article
Coupled and Decoupled Force/Motion Controllers for an Underwater Vehicle-Manipulator System
by Corina Barbalata, Matthew W. Dunnigan and Yvan Petillot
J. Mar. Sci. Eng. 2018, 6(3), 96; https://doi.org/10.3390/jmse6030096 - 21 Aug 2018
Cited by 30 | Viewed by 5146
Abstract
Autonomous interaction with the underwater environment has increased the interest of scientists in the study of control structures for lightweight underwater vehicle-manipulator systems. This paper presents an essential comparison between two different strategies of designing control laws for a lightweight underwater vehicle-manipulator system. [...] Read more.
Autonomous interaction with the underwater environment has increased the interest of scientists in the study of control structures for lightweight underwater vehicle-manipulator systems. This paper presents an essential comparison between two different strategies of designing control laws for a lightweight underwater vehicle-manipulator system. The first strategy aims to separately control the vehicle and the manipulator and hereafter is referred to as the decoupled approach. The second method, the coupled approach, proposes to control the system at the operational space level, treating the lightweight underwater vehicle-manipulator system as a single system. Both strategies use a parallel position/force control structure with sliding mode controllers and incorporate the mathematical model of the system. It is demonstrated that both methods are able to handle this highly non-linear system and compensate for the coupling effects between the vehicle and the manipulator. The results demonstrate the validity of the two different control strategies when the goal is located at various positions, as well as the reliable behaviour of the system when different environment stiffnesses are considered. Full article
(This article belongs to the Special Issue Intelligent Marine Robotics Modelling, Simulation and Applications)
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23 pages, 3712 KiB  
Article
Simulation of the Arctic—North Atlantic Ocean Circulation with a Two-Equation K-Omega Turbulence Parameterization
by Sergey Moshonkin, Vladimir Zalesny and Anatoly Gusev
J. Mar. Sci. Eng. 2018, 6(3), 95; https://doi.org/10.3390/jmse6030095 - 18 Aug 2018
Cited by 13 | Viewed by 4149
Abstract
The results of large-scale ocean dynamics simulation taking into account the parameterization of vertical turbulent exchange are considered. Numerical experiments were carried out using k − ω turbulence model embedded to the Institute of Numerical Mathematics Ocean general circulation Model (INMOM). Both the [...] Read more.
The results of large-scale ocean dynamics simulation taking into account the parameterization of vertical turbulent exchange are considered. Numerical experiments were carried out using k − ω turbulence model embedded to the Institute of Numerical Mathematics Ocean general circulation Model (INMOM). Both the circulation and turbulence models are solved using the splitting method with respect to physical processes. We split k − ω equations into the two stages describing transport-diffusion and generation-dissipation processes. At the generation-dissipation stage, the equation for ω does not depend on k. It allows us to solve both turbulence equations analytically that ensure high computational efficiency. The coupled model is used to simulate the hydrophysical fields of the North Atlantic and Arctic Oceans for 1948–2009. The model has a horizontal resolution of 0.25 ∘ and 40 σ -levels along the vertical. The numerical results show the model’s satisfactory performance in simulating large-scale ocean circulation and upper layer dynamics. The sensitivity of the solution to the change in the coefficients entering into the analytical solution of the k − ω model which describe the influence of some physical factors is studied. These factors are the climatic annual mean buoyancy frequency (AMBF) and Prandtl number as a function of the Richardson number. The experiments demonstrate that taking into account the AMBF improves the reproduction of large-scale ocean characteristics. Prandtl number variations improve the upper mixed layer depth simulation. Full article
(This article belongs to the Special Issue Large-Eddy Simulations and Direct Numerical Simulations of the Turbulent Ocean)
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32 pages, 14562 KiB  
Article
Wave and Tidal Controls on Embayment Circulation and Headland Bypassing for an Exposed, Macrotidal Site
by R. Jak McCarroll, Gerd Masselink, Nieves G. Valiente, Tim Scott, Erin V. King and Daniel Conley
J. Mar. Sci. Eng. 2018, 6(3), 94; https://doi.org/10.3390/jmse6030094 - 7 Aug 2018
Cited by 30 | Viewed by 7023
Abstract
Headland bypassing is the transport of sediment around rocky headlands by wave and tidal action, associated with high-energy conditions and embayment circulation (e.g., mega-rips). Bypassing may be a key component in the sediment budget of many coastal cells, the quantification of which is [...] Read more.
Headland bypassing is the transport of sediment around rocky headlands by wave and tidal action, associated with high-energy conditions and embayment circulation (e.g., mega-rips). Bypassing may be a key component in the sediment budget of many coastal cells, the quantification of which is required to predict the coastal response to extreme events and future coastal change. Waves, currents, and water levels were measured off the headland of a sandy, exposed, and macrotidal beach in 18-m and 26-m depths for 2 months. The observations were used to validate a Delft3D morphodynamic model, which was subsequently run for a wide range of scenarios. Three modes of bypassing were determined: (i) tidally-dominated control during low–moderate wave conditions [flux O (0–102 m3 day−1)]; (ii) combined tidal- and embayment circulation controls during moderate–high waves [O (103 m3 day−1)]; and (iii) multi-embayment circulation control during extreme waves [O (104 m3 day−1)]. A site-specific bypass parameter is introduced, which accurately (R2 = 0.95) matches the modelled bypass rates. A 5-year hindcast predicts bypassing is an order of magnitude less than observed cross-shore fluxes during extreme events, suggesting that bypassing at this site is insignificant at annual timescales. This work serves a starting point to generalise the prediction of headland bypassing. Full article
(This article belongs to the Section Physical Oceanography)
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15 pages, 4665 KiB  
Article
Semantic Segmentation of Underwater Imagery Using Deep Networks Trained on Synthetic Imagery
by Michael O’Byrne, Vikram Pakrashi, Franck Schoefs and Bidisha Ghosh
J. Mar. Sci. Eng. 2018, 6(3), 93; https://doi.org/10.3390/jmse6030093 - 4 Aug 2018
Cited by 51 | Viewed by 7725
Abstract
Recent breakthroughs in the computer vision community have led to the emergence of efficient deep learning techniques for end-to-end segmentation of natural scenes. Underwater imaging stands to gain from these advances, however, deep learning methods require large annotated datasets for model training and [...] Read more.
Recent breakthroughs in the computer vision community have led to the emergence of efficient deep learning techniques for end-to-end segmentation of natural scenes. Underwater imaging stands to gain from these advances, however, deep learning methods require large annotated datasets for model training and these are typically unavailable for underwater imaging applications. This paper proposes the use of photorealistic synthetic imagery for training deep models that can be applied to interpret real-world underwater imagery. To demonstrate this concept, we look at the specific problem of biofouling detection on marine structures. A contemporary deep encoder–decoder network, termed SegNet, is trained using 2500 annotated synthetic images of size 960 × 540 pixels. The images were rendered in a virtual underwater environment under a wide variety of conditions and feature biofouling of various size, shape, and colour. Each rendered image has a corresponding ground truth per-pixel label map. Once trained on the synthetic imagery, SegNet is applied to segment new real-world images. The initial segmentation is refined using an iterative support vector machine (SVM) based post-processing algorithm. The proposed approach achieves a mean Intersection over Union (IoU) of 87% and a mean accuracy of 94% when tested on 32 frames extracted from two distinct real-world subsea inspection videos. Inference takes several seconds for a typical image. Full article
(This article belongs to the Special Issue Underwater Imaging)
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30 pages, 5083 KiB  
Article
Optimized Reliability Based Upgrading of Rubble Mound Breakwaters in a Changing Climate
by Panagiota Galiatsatou, Christos Makris and Panayotis Prinos
J. Mar. Sci. Eng. 2018, 6(3), 92; https://doi.org/10.3390/jmse6030092 - 2 Aug 2018
Cited by 24 | Viewed by 7932
Abstract
The present work aims at presenting an approach on implementing appropriate mitigation measures for the upgrade of rubble mound breakwaters protecting harbors and/or marinas against increasing future marine hazards and related escalating exposure to downtime risks. This approach is based on the reliability [...] Read more.
The present work aims at presenting an approach on implementing appropriate mitigation measures for the upgrade of rubble mound breakwaters protecting harbors and/or marinas against increasing future marine hazards and related escalating exposure to downtime risks. This approach is based on the reliability analysis of the studied structure coupled with economic optimization techniques. It includes the construction of probability distribution functions for all the stochastic variables of the marine climate (waves, storm surges, and sea level rise) for present and future conditions, the suggestion of different mitigation options for upgrading, the construction of a fault tree providing a logical succession of all events that lead to port downtime for each alternative mitigation option, and conclusively, the testing of a large number of possible alternative geometries for each option. A single solution is selected from the total sample of acceptable geometries for each upgrading concept that satisfy a probabilistic constraint in order to minimize the total costs of protection. The upgrading options considered in the present work include the construction or enhancement of a crown wall on the breakwater crest, the addition of the third layer of rocks above the primary armor layer of the breakwater (combined with crest elements), the attachment of a berm on the primary armor layer, and the construction of a detached low-crested structure in front of the breakwater. The proposed methodology is applied to an indicative rubble mound breakwater with an existing superstructure. The construction of a berm on the existing primary armor layer of the studied breakwater (port of Deauville, France), seems to be advantageous in terms of optimized total costs compared to other mitigation options. Full article
(This article belongs to the Special Issue Climate Change, Coasts and Coastal Risk)
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19 pages, 5210 KiB  
Article
A Novel Gesture-Based Language for Underwater Human–Robot Interaction
by Davide Chiarella, Marco Bibuli, Gabriele Bruzzone, Massimo Caccia, Andrea Ranieri, Enrica Zereik, Lucia Marconi and Paola Cutugno
J. Mar. Sci. Eng. 2018, 6(3), 91; https://doi.org/10.3390/jmse6030091 - 1 Aug 2018
Cited by 26 | Viewed by 5611
Abstract
The underwater environment is characterized by hazardous conditions that make it difficult to manage and monitor even the simplest human operation. The introduction of a robot companion with the task of supporting and monitoring the divers during their activities and operations underwater can [...] Read more.
The underwater environment is characterized by hazardous conditions that make it difficult to manage and monitor even the simplest human operation. The introduction of a robot companion with the task of supporting and monitoring the divers during their activities and operations underwater can help to solve some of the problems that usually arise in this scenario. In this context, a proper communication between the diver and the robot is imperative for the success of the dive. However, the underwater environment poses a set of technical challenges which are not readily surmountable thus limiting the spectrum from which possibilities can be chosen. This paper presents the design and development of a gesture-based communication language which has been employed for the entire duration of the European project CADDY (Cognitive Autonomous Diving Buddy). This language, the Caddian, was built upon consolidated and standardized underwater gestures that are commonly used in recreational and professional diving. Its use and integration during field tests with a remotely operated underwater vehicle (ROV) is also shown. Full article
(This article belongs to the Special Issue Intelligent Marine Robotics Modelling, Simulation and Applications)
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28 pages, 13595 KiB  
Article
CMIP5-Derived Single-Forcing, Single-Model, and Single-Scenario Wind-Wave Climate Ensemble: Configuration and Performance Evaluation
by Alvaro Semedo, Mikhail Dobrynin, Gil Lemos, Arno Behrens, Joanna Staneva, Hylke De Vries, Andreas Sterl, Jean-Raymond Bidlot, Pedro M. A. Miranda and Jens Murawski
J. Mar. Sci. Eng. 2018, 6(3), 90; https://doi.org/10.3390/jmse6030090 - 1 Aug 2018
Cited by 24 | Viewed by 6567
Abstract
A Coupled Model Intercomparison Project Phase 5 (CMIP5)-derived single-forcing, single-model, and single-scenario dynamic wind-wave climate ensemble is presented, and its historic period (1979–2005) performance in representing the present wave climate is evaluated. A single global climate model (GCM)-forcing wave climate ensemble was produced [...] Read more.
A Coupled Model Intercomparison Project Phase 5 (CMIP5)-derived single-forcing, single-model, and single-scenario dynamic wind-wave climate ensemble is presented, and its historic period (1979–2005) performance in representing the present wave climate is evaluated. A single global climate model (GCM)-forcing wave climate ensemble was produced with the goal of reducing the inter GCM variability inherent in using a multi-forcing approach for the same wave model. Seven CMIP5 EC-Earth ensemble runs were used to force seven WAM wave model realizations, while future wave climate simulations, not analyzed here, were produced using a high-emission representative concentration pathway 8.5 (RCP8.5) set-up. The wave climate ensemble’s historic period was extensively compared against a set of 72 in situ wave-height observations, as well as to ERA-Interim reanalysis and Climate Forecast System Reanalysis (CFSR) hindcast. The agreement between the wave climate ensemble and the in situ measurements and reanalysis of mean and extreme wave heights, mean wave periods, and mean wave directions was good, in line with previous studies or even better in some areas of the global ocean, namely in the extratropical latitudes. These results give a good degree of confidence in the ability of the ensemble to simulate a realistic climate change signal. Full article
(This article belongs to the Section Ocean Engineering)
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22 pages, 20593 KiB  
Article
Panel Method for Ducted Propellers with Sharp Trailing Edge Duct with Fully Aligned Wake on Blade and Duct
by Seungnam Kim, Spyros A. Kinnas and Weikang Du
J. Mar. Sci. Eng. 2018, 6(3), 89; https://doi.org/10.3390/jmse6030089 - 23 Jul 2018
Cited by 21 | Viewed by 6255
Abstract
A low-order panel method is used to predict the performance of ducted propellers. A full wake alignment (FWA) scheme, originally developed to determine the location of the force-free trailing wake of open propellers, is improved and extended to determine the location of the [...] Read more.
A low-order panel method is used to predict the performance of ducted propellers. A full wake alignment (FWA) scheme, originally developed to determine the location of the force-free trailing wake of open propellers, is improved and extended to determine the location of the force-free trailing wakes of both the propeller blades and the duct, including the interaction with each other. The present method is applied on a ducted propeller with sharp trailing edge duct, and the predicted results over a wide range of advance ratios, with or without full alignment of the duct wake, are compared with each other, as well as with results from RANS simulations and with measurements from an experiment. Full article
(This article belongs to the Special Issue Marine Propulsors)
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14 pages, 3844 KiB  
Article
Numerical Simulation of a Sandy Seabed Response to Water Surface Waves Propagating on Current
by Dagui Tong, Chencong Liao, Jinjian Chen and Qi Zhang
J. Mar. Sci. Eng. 2018, 6(3), 88; https://doi.org/10.3390/jmse6030088 - 20 Jul 2018
Cited by 7 | Viewed by 4075
Abstract
An integrated numerical model is developed to study wave and current-induced seabed response and liquefaction in a flat seabed. The velocity-inlet wave-generating method is adopted in the present study and the finite difference method is employed to solve the Reynolds-averaged Navier-Stokes equations with [...] Read more.
An integrated numerical model is developed to study wave and current-induced seabed response and liquefaction in a flat seabed. The velocity-inlet wave-generating method is adopted in the present study and the finite difference method is employed to solve the Reynolds-averaged Navier-Stokes equations with k-ε turbulence closure. The model validation demonstrates the capacity of the present model. The parametrical study reveals that the increase of current velocity tends to elongate the wave trough and alleviate the corresponding suction force on the seabed, leading to a decrease in liquefaction depth, while the width of the liquefaction area is enlarged simultaneously. This goes against previous studies, which ignored fluid viscosity, turbulence and bed friction. Full article
(This article belongs to the Special Issue Coastal Geohazard and Offshore Geotechnics)
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12 pages, 1873 KiB  
Article
Model Uncertainties for Soil-Structure Interaction in Offshore Wind Turbine Monopile Foundations
by Lars Vabbersgaard Andersen, Thomas Lykke Andersen and Lance Manuel
J. Mar. Sci. Eng. 2018, 6(3), 87; https://doi.org/10.3390/jmse6030087 - 18 Jul 2018
Cited by 9 | Viewed by 4583
Abstract
Monopiles are the most common type of foundation used for bottom-fixed offshore wind turbines. This investigation concerns the influence of uncertainty related to soil–structure interaction models used to represent monopile–soil systems. The system response is studied for a severe sea state. Three wave-load [...] Read more.
Monopiles are the most common type of foundation used for bottom-fixed offshore wind turbines. This investigation concerns the influence of uncertainty related to soil–structure interaction models used to represent monopile–soil systems. The system response is studied for a severe sea state. Three wave-load cases are considered: (i) irregular waves assuming linearity; (ii) highly nonlinear waves that are merged into the irregular wave train; (iii) slamming loads that are included for the nonlinear waves. The extreme response and Fourier amplitude spectra for external moments and mudline bending moments are compared for these load cases where a simpler static pile-cap stiffness and a lumped-parameter model (LPM) are both considered. The fundamental frequency response of the system is well represented by the static pile-cap stiffness model; however, the influence of higher modes (i.e., the second and third modes with frequencies of about 1 Hz and 2 Hz, respectively) is significantly overestimated with the static model compared to the LPM. In the analyzed case, the differences in the higher modes are especially pronounced when slamming loads are not present. Full article
(This article belongs to the Special Issue Offshore Wind Structures)
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23 pages, 5840 KiB  
Article
Potential Impacts of Sea Level Rise and Coarse Scale Marsh Migration on Storm Surge Hydrodynamics and Waves on Coastal Protected Areas in the Chesapeake Bay
by Alayna Bigalbal, Ali M. Rezaie, Juan L. Garzon and Celso M. Ferreira
J. Mar. Sci. Eng. 2018, 6(3), 86; https://doi.org/10.3390/jmse6030086 - 16 Jul 2018
Cited by 12 | Viewed by 5483
Abstract
The increasing rate of sea level rise (SLR) poses a major threat to coastal lands and natural resources, especially affecting natural preserves and protected areas along the coast. These impacts are likely to exacerbate when combined with storm surges. It is also expected [...] Read more.
The increasing rate of sea level rise (SLR) poses a major threat to coastal lands and natural resources, especially affecting natural preserves and protected areas along the coast. These impacts are likely to exacerbate when combined with storm surges. It is also expected that SLR will cause spatial reduction and migration of coastal wetland and marsh ecosystems, which are common in the natural preserves. This study evaluates the potential impacts of SLR and marsh migration on the hydrodynamics and waves conditions inside natural protected areas during storm surge. The study focused on four protected areas located in different areas of the Chesapeake Bay representing different hydrodynamic regimes. Historical and synthetic storms are simulated using a coupled storm surge (ADCIRC) and wave (SWAN) model for the Bay region for current condition and future scenarios. The future scenarios include different rates of local SLR projections (0.48 m, 0.97 m, 1.68 m, and 2.31 m) and potential land use changes due to SLR driven marsh migration, which is discretized in the selected preserve areas in a coarse scale. The results showed a linear increase of maximum water depth with respect to SLR inside the protected areas. However, the inundation extent, the maximum wave heights, and the current velocities inside the coastal protected areas showed a non-linear relationship with SLR, indicating that the combined impacts of storm surge, SLR, and marsh migration depend on multiple factors such as storm track, intensity, local topography, and locations of coastal protected areas. Furthermore, the impacts of SLR were significantly greater after a 1 m threshold of rise, suggesting the presence of a critical limit for conservation strategies. Full article
(This article belongs to the Special Issue Climate Change, Coasts and Coastal Risk)
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24 pages, 1936 KiB  
Article
Response-Spectrum Uncoupled Analyses for Seismic Assessment of Offshore Wind Turbines
by Giuseppe Failla, Fabio Santangelo, Gabriele Foti, Fabio Scali and Felice Arena
J. Mar. Sci. Eng. 2018, 6(3), 85; https://doi.org/10.3390/jmse6030085 - 9 Jul 2018
Cited by 14 | Viewed by 3877
Abstract
According to International Standards and Guidelines, the seismic assessment of offshore wind turbines in seismically-active areas may be performed by combining two uncoupled analyses under wind-wave and earthquake loads, respectively. Typically, the separate earthquake response is calculated by a response-spectrum approach and, for [...] Read more.
According to International Standards and Guidelines, the seismic assessment of offshore wind turbines in seismically-active areas may be performed by combining two uncoupled analyses under wind-wave and earthquake loads, respectively. Typically, the separate earthquake response is calculated by a response-spectrum approach and, for this purpose, structural models of various degrees of complexity may be used. Although response-spectrum uncoupled analyses are currently allowed as alternative to time-consuming fully-coupled simulations, for which dedicated software packages are required, to date no specific studies have been presented on whether accuracy may vary depending on key factors as structural modelling, criteria to calculate wind-wave and earthquake responses, and other relevant issues as the selected support structure, the considered environmental states and earthquake records. This paper will investigate different potential implementations of response-spectrum uncoupled analyses for offshore wind turbines, using various structural models and criteria to calculate the wind-wave and earthquake responses. The case study is a 5-MW wind turbine on two support structures in intermediate waters, under a variety of wind-wave states and real earthquake records. Numerical results show that response-spectrum uncoupled analyses may provide non-conservative results, for every structural model adopted and criteria to calculate wind-wave and earthquake responses. This is evidence that appropriate safety factors should be assumed when implementing response-spectrum uncoupled analyses allowed by International Standards and Guidelines. Full article
(This article belongs to the Special Issue Offshore Wind Structures)
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11 pages, 4939 KiB  
Article
Capturing Physical Dispersion Using a Nonlinear Shallow Water Model
by Rozita Kian, Juan Horrillo, Andrey Zaytsev and Ahmet Cevdet Yalciner
J. Mar. Sci. Eng. 2018, 6(3), 84; https://doi.org/10.3390/jmse6030084 - 9 Jul 2018
Cited by 6 | Viewed by 3538
Abstract
Predicting the arrival time of natural hazards such as tsunamis is of very high importance to the coastal community. One of the most effective techniques to predict tsunami propagation and arrival time is the utilization of numerical solutions. Numerical approaches of Nonlinear Shallow [...] Read more.
Predicting the arrival time of natural hazards such as tsunamis is of very high importance to the coastal community. One of the most effective techniques to predict tsunami propagation and arrival time is the utilization of numerical solutions. Numerical approaches of Nonlinear Shallow Water Equations (NLSWEs) and nonlinear Boussinesq-Type Equations (BTEs) are two of the most common numerical techniques for tsunami modeling and evaluation. BTEs use implicit schemes to achieve more accurate results compromising computational time, while NLSWEs are sometimes preferred due to their computational efficiency. Nonetheless, the term accounting for physical dispersion is not inherited in NLSWEs, calling for their consideration and evaluation. In the present study, the tsunami numerical model NAMI DANCE, which utilizes NLSWEs, is applied to previously reported problems in the literature using different grid sizes to investigate dispersion effects. Following certain conditions for grid size, time step and water depth, the simulation results show a fairly good agreement with the available models showing the capability of NAMI DANCE to capture small physical dispersion. It is confirmed that the current model is an acceptable alternative for BTEs when small dispersion effects are considered. Full article
(This article belongs to the Special Issue Tsunami Science and Engineering II)
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16 pages, 7409 KiB  
Article
Wave (Current)-Induced Pore Pressure in Offshore Deposits: A Coupled Finite Element Model
by Chencong Liao, Dongsheng Jeng, Zaibin Lin, Yakun Guo and Qi Zhang
J. Mar. Sci. Eng. 2018, 6(3), 83; https://doi.org/10.3390/jmse6030083 - 6 Jul 2018
Cited by 8 | Viewed by 4224
Abstract
The interaction between wave and offshore deposits is of great importance for the foundation design of marine installations. However, most previous investigations have been limited to connecting separated wave and seabed sub-models with an individual interface program that transfers loads from the wave [...] Read more.
The interaction between wave and offshore deposits is of great importance for the foundation design of marine installations. However, most previous investigations have been limited to connecting separated wave and seabed sub-models with an individual interface program that transfers loads from the wave model to the seabed model. This research presents a two-dimensional coupled approach to study both wave and seabed processes simultaneously in the same FEM (finite element method) program (COMSOL Multiphysics). In the present model, the progressive wave is generated using a momentum source maker combined with a steady current, while the seabed response is applied with the poro-elastoplastic theory. The information between the flow domain and soil deposits is strongly shared, leading to a comprehensive investigation of wave-seabed interaction. Several cases have been simulated to test the wave generation capability and to validate the soil model. The numerical results present fairly good predictions of wave generation and pore pressure within the seabed, indicating that the present coupled model is a sufficient numerical tool for estimation of wave-induced pore pressure. Full article
(This article belongs to the Special Issue Coastal Geohazard and Offshore Geotechnics)
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10 pages, 545 KiB  
Article
Possible Criterion to Estimate the Juvenile Reference Length of Common Sardine (Strangomera bentincki) off Central-Southern Chile
by Karen Walker, Antonio Aranis and Javier E. Contreras-Reyes
J. Mar. Sci. Eng. 2018, 6(3), 82; https://doi.org/10.3390/jmse6030082 - 5 Jul 2018
Cited by 3 | Viewed by 3244
Abstract
In the last century, the growing evidence that global fisheries are depleting natural resources much faster than they can recover has led to negative processes, like overfishing, being addressed with increasingly complex models and thus mitigating or regulating actions that aim to protect [...] Read more.
In the last century, the growing evidence that global fisheries are depleting natural resources much faster than they can recover has led to negative processes, like overfishing, being addressed with increasingly complex models and thus mitigating or regulating actions that aim to protect stocks. Said negative processes contain two components: (i) they can diminish the reproductive potential of fish stocks, called over exploitation by recruitment, and (ii) the effect of early capture prevents the full realization of the growth potential, called overfishing by growth. In this article, the structure of common sardine sizes is analyzed. Due to the precise moment in which pre-recruits are incorporated into the exploited phase of the stock is unknown, the estimation of a recruitment size is a hard problem. This problem is addressed by modeling the mean size via a stochastic process, applying models of structural change. A time series (2001–2015) was analyzed on a weekly time scale based on the size structure of the pelagic fishery landings in the central-southern zone of Chile (32∘10′–40∘14′ LS), from the V. to the XIV. Region. Specifically, the evolution of sizes according to macro-zones was studied for the conglomerates identified in two sub-zones, the V.–VIII. and IX.–XIV. Regions. In this context, the reference size for juveniles to cautiously allow the recruitment process of the common sardine from the central-southern zone of Chile was estimated, and the behavior of these sizes was spatially analyzed. Finally, a statistical inferential criterion was established that confirms the mean size of juveniles with a certain margin of error, which allows nonetheless later on to define a fraction that could be protected to avoid overfishing by growth. Full article
(This article belongs to the Section Marine Biology)
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12 pages, 1059 KiB  
Project Report
A Collaborative European Approach to Accelerating Translational Marine Science
by Philip Brennecke, Maria I. Ferrante, Ian A. Johnston and David Smith
J. Mar. Sci. Eng. 2018, 6(3), 81; https://doi.org/10.3390/jmse6030081 - 5 Jul 2018
Cited by 7 | Viewed by 3850
Abstract
Marine environments account for over 90% of the biosphere and hold tremendous potential for biotechnological applications and drug discovery. To fully exploit this potential and develop interesting discoveries into useful molecular tools and successful products, a multidisciplinary approach is indispensable. Here, we introduce [...] Read more.
Marine environments account for over 90% of the biosphere and hold tremendous potential for biotechnological applications and drug discovery. To fully exploit this potential and develop interesting discoveries into useful molecular tools and successful products, a multidisciplinary approach is indispensable. Here, we introduce the European Marine Biological Research Infrastructure Cluster (EMBRIC), a novel collaborative initiative that aims to facilitate translational marine science and remove existing bottlenecks that are currently impeding blue innovation. In the context of this initiative, pilot projects have been designed to test the functionality of the cluster focusing on two specific sectors of marine biotechnology: (i) the discovery and exploitation of marine natural products and (ii) the marker-assisted selection of desirable traits in aquaculture. EMBRIC brings together the expertise of six European Research Infrastructures on accessing the potential of marine organisms, specifically on the 99% of bacteria yet to be grown in culture, the microalgae, finfish, and shellfish. It improves the throughput and efficiency of workflows for discovery of novel marine products and facilitates projects that require an interdisciplinary approach. The objective is to develop coherent chains of high quality services for access to biological, analytical, and data resources by deploying common underpinning technologies and practices. The connection of academic science with industry is being strengthened by engaging companies, as well as geographically separated public and private-sector communities in the domain of marine biotechnology, and by federating technology transfer services amongst the players involved. Full article
(This article belongs to the Special Issue Methodologies for Outreach in the Marine Sciences)
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25 pages, 12901 KiB  
Article
Shoreline Change around a River Delta on the Cox’s Bazar Coast of Bangladesh
by Upal Mahamud and Satoshi Takewaka
J. Mar. Sci. Eng. 2018, 6(3), 80; https://doi.org/10.3390/jmse6030080 - 4 Jul 2018
Cited by 16 | Viewed by 6465
Abstract
A recent erosional problem around a river delta on the Cox’s Bazar coast was analyzed in this study. The coastline extends from south to north. Rapid erosion has affected some portions of a 24-km road along the coast, and local authorities have attempted [...] Read more.
A recent erosional problem around a river delta on the Cox’s Bazar coast was analyzed in this study. The coastline extends from south to north. Rapid erosion has affected some portions of a 24-km road along the coast, and local authorities have attempted to protect the road via revetment. However, the structure was soon buried with sediment because of a growing sand spit along the river delta, and a new area was eroded. Shoreline positions for a 44-year (1972–2016) period were digitized using Landsat images. From the time stack images, we observed a sand spit growing in a northward direction from 2000 to 2015, and the adjacent erosion area extended in the same direction. We employed a numerical model (MIKE21FM SM) for the computation of wave-driven currents and sediment transport along the coast, and attempted to reproduce recent erosional processes. The numerical result shows that net littoral drift is dominant in the northward direction along the coast, which is the same direction of the spit growth observed in the satellite images. A higher amplitude spit induces higher sediment transport compared to a low amplitude spit because of the difference in local incident wave angles resulting in greater positive gradient of the longshore sediment flux distribution, causing erosion in the downcoast. Full article
(This article belongs to the Special Issue Coastal Zone Management)
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12 pages, 1406 KiB  
Article
Significance of Fluvial Sediment Supply in Coastline Modelling at Tidal Inlets
by Janaka Bamunawala, Shreedhar Maskey, Trang Minh Duong and Ad Van der Spek
J. Mar. Sci. Eng. 2018, 6(3), 79; https://doi.org/10.3390/jmse6030079 - 3 Jul 2018
Cited by 12 | Viewed by 3915
Abstract
The sediment budget associated with future coastline change in the vicinity of tidal inlets consists of four components; sea level rise-driven landward movement of the coastline (i.e., the Bruun effect), basin infilling effect due to sea level rise-induced increase in accommodation space, basin [...] Read more.
The sediment budget associated with future coastline change in the vicinity of tidal inlets consists of four components; sea level rise-driven landward movement of the coastline (i.e., the Bruun effect), basin infilling effect due to sea level rise-induced increase in accommodation space, basin volume change due to variation in river discharge, and coastline change caused by change in fluvial sediment supply. These four components are affected by climate change and/or anthropogenic impacts. Despite this understanding, holistic modelling techniques that account for all the aforementioned processes under both climate change and anthropogenic influences are lacking. This manuscript presents the applications of a newly-developed reduced complexity modelling approach that accounts for both climate change and anthropogenically-driven impacts on future coastline changes. Modelled results corresponding to the year 2100 indicate considerable coastline recessions at Wilson Inlet (152 m) and the Swan River system (168 m) in Australia and Tu Hien Inlet (305 m) and Thuan An Inlet (148 m) in Vietnam. These results demonstrate that coastline models should incorporate both climate change and anthropogenic impacts to quantify future changes in fluvial sediment supply to coasts to achieve better estimates of total coastline changes at tidal inlets. Omission of these impacts is one of the major drawbacks in all the existing coastline models that simulate future coastline changes at tidal inlets. A comparison of these modelled future coastline changes with the predictions made by a relevant existing modelling technique (Scale Aggregated Model for Inlet-interrupted Coasts (SMIC)) indicates that the latter method overestimates total coastline recessions at the Swan River system, and the Tu Hien and Thuan An Inlets by 7%, 10%, and 30%, respectively, underlining the significance of integrating both climate change and anthropogenic impacts to assess future coastline changes at tidal inlets. Full article
(This article belongs to the Special Issue Climate Change, Coasts and Coastal Risk)
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25 pages, 3812 KiB  
Article
Resonantly Forced Baroclinic Waves in the Oceans: Subharmonic Modes
by Jean-Louis Pinault
J. Mar. Sci. Eng. 2018, 6(3), 78; https://doi.org/10.3390/jmse6030078 - 2 Jul 2018
Cited by 12 | Viewed by 3826
Abstract
The study of resonantly forced baroclinic waves in the tropical oceans at mid-latitudes is of paramount importance to advancing our knowledge in fields that investigate the El Niño–Southern Oscillation (ENSO), the decadal climate variability, or the resonant feature of glacial-interglacial cycles that are [...] Read more.
The study of resonantly forced baroclinic waves in the tropical oceans at mid-latitudes is of paramount importance to advancing our knowledge in fields that investigate the El Niño–Southern Oscillation (ENSO), the decadal climate variability, or the resonant feature of glacial-interglacial cycles that are a result of orbital forcing. Indeed, these baroclinic waves, the natural period of which coincides with the forcing period, have a considerable impact on ocean circulation and in climate variability. Resonantly Forced Waves (RFWs) are characterized by antinodes at sea surface height anomalies and nodes where modulated geostrophic currents ensure the transfer of warm water from an antinode to another, reflecting a quasi-geostrophic motion. Several RFWs of different periods are coupled when they share the same node, which involves the geostrophic forces at the basin scale. These RFWs are subject to a subharmonic mode locking, which means that their average periods are a multiple of the natural period of the fundamental wave, that is, one year. This property of coupled oscillator systems is deduced from the Hamiltonian (the energy) of the Caldirola–Kanai (CK) oscillator. In this article, it is shown how the CK oscillator, which is usually used to develop a phenomenological single-particle approach, is transposable to RFWs. Subharmonic modes ensure the durability of the resonant dissipative system, with each oscillator transferring as much interaction energy to all the others that it receives periodically. Full article
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