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J. Mar. Sci. Eng., Volume 6, Issue 2 (June 2018)

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Research

Open AccessFeature PaperArticle Wave-Created Mud Suspensions: A Theoretical Study
J. Mar. Sci. Eng. 2018, 6(2), 29; https://doi.org/10.3390/jmse6020029
Received: 1 February 2018 / Revised: 13 March 2018 / Accepted: 21 March 2018 / Published: 27 March 2018
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Abstract
We studied wave-created high-density mud suspensions (fluid mud) using a one-dimensional water column (1DV) model that includes k-ε turbulence closure at a high vertical resolution with a vertical grid spacing of 1 mm. The k-ε turbulence model includes two sediment-related dissipation
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We studied wave-created high-density mud suspensions (fluid mud) using a one-dimensional water column (1DV) model that includes k-ε turbulence closure at a high vertical resolution with a vertical grid spacing of 1 mm. The k-ε turbulence model includes two sediment-related dissipation terms associated with vertical density stratification and viscous drag of flows around sediment particles. To this end, the calibrated model reproduces the key characteristics (maximum concentration and thickness) of fluid mud layers created in laboratory experiments over a large range of wave velocities from 10 to 55 cm/s. The findings demonstrate that the equilibrium near-bed mud concentration, Cb, is solely determined from the balance between erosion and deposition fluxes, whereas the thickness of the fluid mud layer is mainly controlled by sediment-induced density stratification, which dissipates turbulence and hence eliminates turbulent sediment diffusivity at the top of the fluid mud layer, the lutocline. Our model stands in contrast to those that suggest that upward sediment diffusion is close to zero at the interface between the fluid mud layer and the overlying fluid. Instead, our model suggests that the upward diffusive flux of fluid mud flows peak at the lutocline and is compensated for enhanced settling fluxes just above it. Our model findings also support the existence of the gelling-ignition process, which is critical for the development of fluid mud beds in modern sedimentary environments. Full article
(This article belongs to the Special Issue Advances in Sediment Transport under Combined Waves and Currents)
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Open AccessArticle The Implications of Oil Exploration off the Gulf Coast of Florida
J. Mar. Sci. Eng. 2018, 6(2), 30; https://doi.org/10.3390/jmse6020030
Received: 6 March 2018 / Revised: 21 March 2018 / Accepted: 30 March 2018 / Published: 2 April 2018
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Abstract
In the United States (U.S.), oil exploration and production remain critical economic engines for local, state, and federal economies. Recently, the U.S. Department of the Interior expressed interest in expanding offshore oil production by making available lease areas in the U.S. Gulf of
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In the United States (U.S.), oil exploration and production remain critical economic engines for local, state, and federal economies. Recently, the U.S. Department of the Interior expressed interest in expanding offshore oil production by making available lease areas in the U.S. Gulf of Mexico, the U.S. West Coast and East Coast, as well as offshore Alaska. With the promise of aiding in energy independence, these new lease areas could help solidify the U.S. as one of the world’s largest oil-producing countries, while at the same time bolstering the local and regional energy job sectors. Of all the newly proposed lease areas, the Gulf Coast of Florida is particularly contentious. Opponents of drilling in the area cite the sensitive ecosystems and the local and state tourism economy that depends heavily on the numerous beaches lining Florida’s coast. In this analysis, we use a data-driven spatial analytic approach combined with advanced oil spill modeling to determine the potential impact of oil exploration off of Florida’s Gulf Coast given a loss-of-control event. It is determined that plume behavior varies drastically depending on the location of the spill but that overall impacts are comparable across all spill scenario sites, highlighting the necessity of contingency-type analyses. Implications for spill response are also discussed. Full article
(This article belongs to the Special Issue Marine Oil Spills 2018)
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Open AccessArticle Control of Wave Energy Converters with Discrete Displacement Hydraulic Power Take-Off Units
J. Mar. Sci. Eng. 2018, 6(2), 31; https://doi.org/10.3390/jmse6020031
Received: 7 February 2018 / Revised: 2 March 2018 / Accepted: 26 March 2018 / Published: 2 April 2018
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Abstract
The control of ocean Wave Energy Converters (WECs) impacts the harvested energy. Several control methods have been developed over the past few decades to maximize the harvested energy. Many of these methods were developed based on an unconstrained dynamic model assuming an ideal
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The control of ocean Wave Energy Converters (WECs) impacts the harvested energy. Several control methods have been developed over the past few decades to maximize the harvested energy. Many of these methods were developed based on an unconstrained dynamic model assuming an ideal power take-off (PTO) unit. This study presents numerical tests and comparisons of a few recently developed control methods. The testing is conducted using a numerical simulator that simulates a hydraulic PTO. The PTO imposes constraints on the maximum attainable control force and maximum stroke. In addition, the PTO has its own dynamics, which may impact the performance of some control strategies. Full article
(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)
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Open AccessArticle Basic Heat Exchanger Performance Evaluation Method on OTEC
J. Mar. Sci. Eng. 2018, 6(2), 32; https://doi.org/10.3390/jmse6020032
Received: 1 January 2018 / Revised: 15 February 2018 / Accepted: 11 March 2018 / Published: 3 April 2018
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Abstract
Ocean thermal energy conversion (OTEC) harvests the power from the thermal energy in the ocean, which is reserved in the ocean as the temperature difference between warm surface and cold deep seawaters. In the energy conversion, the heat exchangers transfer the thermal energy
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Ocean thermal energy conversion (OTEC) harvests the power from the thermal energy in the ocean, which is reserved in the ocean as the temperature difference between warm surface and cold deep seawaters. In the energy conversion, the heat exchangers transfer the thermal energy to the heat engine, which converts it into power. The pressure drops yielded by piping, valve and heat exchangers cause pump loads, which show significant negative power with respect to net power in OTEC. The heat transfer performance and the pressure drop in heat exchanger depend on the types and shapes of each heat transfer area. Generally, heat exchangers with higher friction factors yield higher heat transfer performance and vice versa. However, heat transfer performance and pressure drop are separately evaluated and there is no comprehensive performance evaluation index for OTEC power take-off. Therefore, this research proposes a new simplified overall performance evaluation method for heat exchangers, which can be comprehensively and easily applied and takes into consideration the heat transfer performance and the pressure drop. The evaluation results on plate-type heat exchangers show that the overall performance in each heat exchanger are elucidated and are quantitatively compared. Full article
(This article belongs to the Special Issue Ocean Thermal Energy Conversion)
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Open AccessArticle In Vitro Inhibition of Acetylcholinesterase, Alphaglucosidase, and Xanthine Oxidase by Bacteria Extracts from Coral Reef in Hainan, South China Sea
J. Mar. Sci. Eng. 2018, 6(2), 33; https://doi.org/10.3390/jmse6020033
Received: 18 February 2018 / Revised: 15 March 2018 / Accepted: 27 March 2018 / Published: 5 April 2018
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Abstract
Acetylcholinesterase is one of the most important enzymes in living organisms, which is responsible for the synapse cholinergic and other nervous processes. However, its inhibiting effects have proven to have pharmacological applications in the treatment of different diseases, as well as in the
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Acetylcholinesterase is one of the most important enzymes in living organisms, which is responsible for the synapse cholinergic and other nervous processes. However, its inhibiting effects have proven to have pharmacological applications in the treatment of different diseases, as well as in the control of insect pests; thus, the search for inhibitors is a matter of interest for biomedical and agrochemical fields. Alzheimer’s is a progressive neurodegenerative disease, which can be seen as a wide degeneration of synapses, as well as neurons, in the cerebral cortex, hippocampus, and subcortical structures. Acetylcholinesterase inhibition is an important target for the management of Alzheimer’s. Additionally, diabetes mellitus is a chronic disease with clinical manifestation of hyperglycemia, due to the ineffective production of insulin that controls the level of blood glucose. Alphaglucosidaseinhibitors could retard the uptake of dietary carbohydrates and have shown significant therapeutic effects in clinical application. Fifty-five ethyl acetate extracts from nine bacterial families from Hainan (China) were evaluated to observe their acetylcholinesterase, alphaglucosidase, and xanthine oxidase inhibitory activity. Moreover, a screening of inhibitory activity against the pathogens fungi Fusarium oxysporum and Colletotrichum gloeosporioides was performed. The best acetylcholinesterase and alphaglucosidase inhibitory activity was shown by Vibrio neocaledonicus (98.95%). This is the first report of inhibition of both enzymes by ethyl acetate extract from this strain. Full article
(This article belongs to the Section Marine Biology)
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Open AccessArticle Nominal vs. Effective Wake Fields and Their Influence on Propeller Cavitation Performance
J. Mar. Sci. Eng. 2018, 6(2), 34; https://doi.org/10.3390/jmse6020034
Received: 27 February 2018 / Revised: 25 March 2018 / Accepted: 29 March 2018 / Published: 5 April 2018
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Abstract
Propeller designers often need to base their design on the nominal model scale wake distribution because the effective full scale distribution is not available. The effects of such incomplete design data on cavitation performance are examined in this paper. The behind-ship cavitation performance
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Propeller designers often need to base their design on the nominal model scale wake distribution because the effective full scale distribution is not available. The effects of such incomplete design data on cavitation performance are examined in this paper. The behind-ship cavitation performance of two propellers is evaluated, where the cases considered include propellers operating in the nominal model and full scale wake distributions and in the effective wake distribution, also in the model and full scale. The method for the analyses is a combination of RANS for the ship hull and a panel method for the propeller flow, with a coupling of the two for the interaction of ship and propeller flows. The effect on sheet cavitation due to the different wake distributions is examined for a typical full-form ship. Results show considerable differences in cavitation extent, volume, and hull pressure pulses. Full article
(This article belongs to the Special Issue Marine Propulsors)
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Open AccessArticle Simulating Storm Surge Impacts with a Coupled Atmosphere-Inundation Model with Varying Meteorological Forcing
J. Mar. Sci. Eng. 2018, 6(2), 35; https://doi.org/10.3390/jmse6020035
Received: 14 February 2018 / Revised: 8 March 2018 / Accepted: 26 March 2018 / Published: 5 April 2018
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Abstract
Storm surge events have the potential to cause devastating damage to coastal communities. The magnitude of their impacts highlights the need for increased accuracy and real-time forecasting and predictability of storm surge. In this study, we assess two meteorological forcing configurations to hindcast
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Storm surge events have the potential to cause devastating damage to coastal communities. The magnitude of their impacts highlights the need for increased accuracy and real-time forecasting and predictability of storm surge. In this study, we assess two meteorological forcing configurations to hindcast the storm surge of Hurricane Sandy, and ultimately support the improvement of storm surge forecasts. The Weather Research and Forecasting (WRF) model is coupled to the ADvanced CIRCulation Model (ADCIRC) to determine water elevations. We perform four coupled simulations and compare storm surge estimates resulting from the use of a parametric vortex model and a full-physics atmospheric model. One simulation is forced with track-based meteorological data calculated from WRF, while three simulations are forced with the full wind and pressure field outputs from WRF simulations of varying resolutions. Experiments were compared to an ADCIRC simulation forced by National Hurricane Center best track data, as well as to station observations. Our results indicated that given accurate meteorological best track data, a parametric vortex model can accurately forecast maximum water elevations, improving upon the use of a full-physics coupled atmospheric-surge model. In the absence of a best track, atmospheric forcing in the form of full wind and pressure field from a high-resolution atmospheric model simulation prove reliable for storm surge forecasting. Full article
(This article belongs to the Special Issue Coastal Hazards Related to Water)
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Open AccessArticle Description and Mechanisms of the Mid-Year Upwelling in the Southern Caribbean Sea from Remote Sensing and Local Data
J. Mar. Sci. Eng. 2018, 6(2), 36; https://doi.org/10.3390/jmse6020036
Received: 6 February 2018 / Revised: 23 March 2018 / Accepted: 27 March 2018 / Published: 5 April 2018
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Abstract
The southern Caribbean Sea experiences strong coastal upwelling between December and April due to the seasonal strengthening of the trade winds. A second upwelling was recently detected in the southeastern Caribbean during June–August, when local coastal wind intensities weaken. Using synoptic satellite measurements
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The southern Caribbean Sea experiences strong coastal upwelling between December and April due to the seasonal strengthening of the trade winds. A second upwelling was recently detected in the southeastern Caribbean during June–August, when local coastal wind intensities weaken. Using synoptic satellite measurements and in situ data, this mid-year upwelling was characterized in terms of surface and subsurface temperature structures, and its mechanisms were explored. The mid-year upwelling lasts 6–9 weeks with satellite sea surface temperature (SST) ~1–2° C warmer than the primary upwelling. Three possible upwelling mechanisms were analyzed: cross-shore Ekman transport (csET) due to alongshore winds, wind curl (Ekman pumping/suction) due to wind spatial gradients, and dynamic uplift caused by variations in the strength/position of the Caribbean Current. These parameters were derived from satellite wind and altimeter observations. The principal and the mid-year upwelling were driven primarily by csET (78–86%). However, SST had similar or better correlations with the Ekman pumping/suction integrated up to 100 km offshore (WE100) than with csET, possibly due to its influence on the isopycnal depth of the source waters for the coastal upwelling. The mid-year upwelling was not caused by dynamic uplift but it might have been enhanced by the seasonal intensification of the Caribbean Current during that period. Full article
(This article belongs to the Special Issue Applications of Satellite Remote Sensing in Marine Science)
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Open AccessFeature PaperArticle Numerical Analysis of Azimuth Propulsor Performance in Seaways: Influence of Oblique Inflow and Free Surface
J. Mar. Sci. Eng. 2018, 6(2), 37; https://doi.org/10.3390/jmse6020037
Received: 28 February 2018 / Revised: 18 March 2018 / Accepted: 27 March 2018 / Published: 5 April 2018
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Abstract
In the present work, a generic ducted azimuth propulsor, which are frequently installed on a wide range of vessels, is subject to numerical investigation with the primary focus on performance deterioration and dynamic loads arising from the influence of oblique inflow and the
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In the present work, a generic ducted azimuth propulsor, which are frequently installed on a wide range of vessels, is subject to numerical investigation with the primary focus on performance deterioration and dynamic loads arising from the influence of oblique inflow and the presence of free surface. An unsteady Reynolds-Averaged Navier-Stokes (RANS) method with the interface Sliding Mesh technique is employed to resolve interaction between the propulsor components. The VOF formulation is used to resolve the presence of free surface. Numerical simulations are performed, separately, in single-phase fluid to address the influence of oblique inflow on the characteristics of a propulsor operating in free-sailing, trawling and bollard conditions, and in multi-phase flow to address the influence of propulsor submergence. Detailed comparisons with experimental data are presented for the case of a propulsor in oblique flow conditions, including integral propulsor characteristics, loads on propulsor components and single blade loads. The results of the study illustrate the differences in propulsor performance at positive and negative heading angles, reveal the frequencies of dynamic load peaks, and provide quantification of thrust losses due to the effect of a free surface without waves. The mechanisms of ventilation inception found at different propulsor loading conditions are discussed. Full article
(This article belongs to the Special Issue Marine Propulsors)
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Open AccessArticle Peridynamic Analysis of Marine Composites under Shock Loads by Considering Thermomechanical Coupling Effects
J. Mar. Sci. Eng. 2018, 6(2), 38; https://doi.org/10.3390/jmse6020038
Received: 15 February 2018 / Revised: 18 March 2018 / Accepted: 31 March 2018 / Published: 6 April 2018
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Abstract
Nowadays, composite materials have been increasingly used in marine structures because of their high performance properties. During their service time, they may be exposed to extreme loading conditions such as underwater explosions. Temperature changes induced by pure mechanical shock loadings cannot to be
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Nowadays, composite materials have been increasingly used in marine structures because of their high performance properties. During their service time, they may be exposed to extreme loading conditions such as underwater explosions. Temperature changes induced by pure mechanical shock loadings cannot to be neglected especially when smart composite materials are employed for condition monitoring of critical systems in a marine structure. Considering this fact, both the thermal loading effect on deformation and the deformation effect on temperature need to be taken into consideration. Consequently, an analysis conducted in a fully coupled thermomechanical manner is necessary. Peridynamics is a newly proposed non-local theory which can predict failures without extra assumptions. Therefore, a fully coupled thermomechanical peridynamic model is developed for laminated composites materials. In this study, numerical analysis of a 13 ply laminated composite subjected to an underwater explosion is conducted by using the developed model. The pressure shocks generated by the underwater explosion are applied on the top surface of the laminate for uniform and non-uniform load distributions. The damage is predicted and compared with existing experimental results. The simulation results obtained from uncoupled case are also provided for comparison. Thus the coupling term effects on crack propagation paths are investigated. Furthermore, the corresponding temperature distributions are also investigated. Full article
(This article belongs to the Special Issue Marine Structures)
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Open AccessArticle Deployment and Maintenance of Wave Energy Converters at the Lysekil Research Site: A Comparative Study on the Use of Divers and Remotely-Operated Vehicles
J. Mar. Sci. Eng. 2018, 6(2), 39; https://doi.org/10.3390/jmse6020039
Received: 15 February 2018 / Revised: 20 March 2018 / Accepted: 26 March 2018 / Published: 12 April 2018
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Abstract
Ocean renewable technologies have been rapidly developing over the past years. However, current high installation, operation, maintenance, and decommissioning costs are hindering these offshore technologies to reach a commercialization stage. In this paper we focus on the use of divers and remotely-operated vehicles
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Ocean renewable technologies have been rapidly developing over the past years. However, current high installation, operation, maintenance, and decommissioning costs are hindering these offshore technologies to reach a commercialization stage. In this paper we focus on the use of divers and remotely-operated vehicles during the installation and monitoring phase of wave energy converters. Methods and results are based on the wave energy converter system developed by Uppsala University, and our experience in offshore deployments obtained during the past eleven years. The complexity of underwater operations, carried out by either divers or remotely-operated vehicles, is emphasized. Three methods for the deployment of wave energy converters are economically and technically analyzed and compared: one using divers alone, a fully-automated approach using remotely-operated vehicles, and an intermediate approach, involving both divers and underwater vehicles. The monitoring of wave energy converters by robots is also studied, both in terms of costs and technical challenges. The results show that choosing an autonomous deployment method is more advantageous than a diver-assisted method in terms of operational time, but that numerous factors prevent the wide application of robotized operations. Technical solutions are presented to enable the use of remotely-operated vehicles instead of divers in ocean renewable technology operations. Economically, it is more efficient to use divers than autonomous vehicles for the deployment of six or fewer wave energy converters. From seven devices, remotely-operated vehicles become advantageous. Full article
(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)
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Open AccessArticle Fault-Tolerant Control for ROVs Using Control Reallocation and Power Isolation
J. Mar. Sci. Eng. 2018, 6(2), 40; https://doi.org/10.3390/jmse6020040
Received: 7 March 2018 / Revised: 4 April 2018 / Accepted: 10 April 2018 / Published: 12 April 2018
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Abstract
This paper describes a novel thruster fault-tolerant control system (FTC) for open-frame remotely operated vehicles (ROVs). The proposed FTC consists of two subsystems: a model-free thruster fault detection and isolation subsystem (FDI) and a fault accommodation subsystem (FA). The FDI subsystem employs fault
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This paper describes a novel thruster fault-tolerant control system (FTC) for open-frame remotely operated vehicles (ROVs). The proposed FTC consists of two subsystems: a model-free thruster fault detection and isolation subsystem (FDI) and a fault accommodation subsystem (FA). The FDI subsystem employs fault detection units (FDUs), associated with each thruster, to monitor their state. The robust, reliable and adaptive FDUs use a model-free pattern recognition neural network (PRNN) to detect internal and external faulty states of the thrusters in real time. The FA subsystem combines information provided by the FDI subsystem with predefined, user-configurable actions to accommodate partial and total faults and to perform an appropriate control reallocation. Software-level actions include penalisation of faulty thrusters in solution of control allocation problem and reallocation of control energy among the operable thrusters. Hardware-level actions include power isolation of faulty thrusters (total faults only) such that the entire ROV power system is not compromised. The proposed FTC system is implemented as a LabVIEW virtual instrument (VI) and evaluated in virtual (simulated) and real-world environments. The proposed FTC module can be used for open frame ROVs with up to 12 thrusters: eight horizontal thrusters configured in two horizontal layers of four thrusters each, and four vertical thrusters configured in one vertical layer. Results from both environments show that the ROV control system, enhanced with the FDI and FA subsystems, is capable of maintaining full 6 DOF control of the ROV in the presence of up to 6 simultaneous total faults in the thrusters. With the FDI and FA subsystems in place the control energy distribution of the healthy thrusters is optimised so that the ROV can still operate in difficult conditions under fault scenarios. Full article
(This article belongs to the Special Issue Intelligent Marine Robotics Modelling, Simulation and Applications)
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Open AccessArticle Modelling a Propeller Using Force and Mass Rate Density Fields
J. Mar. Sci. Eng. 2018, 6(2), 41; https://doi.org/10.3390/jmse6020041
Received: 23 February 2018 / Revised: 28 March 2018 / Accepted: 3 April 2018 / Published: 12 April 2018
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Abstract
A method to replace a propeller by force and mass rate density fields has been developed. The force of the propeller on the flow is calculated using a boundary element method (BEM) program and used to generate the force and mass rate fields
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A method to replace a propeller by force and mass rate density fields has been developed. The force of the propeller on the flow is calculated using a boundary element method (BEM) program and used to generate the force and mass rate fields in a Reynolds-averaged Navier–Stokes (RANS) solver. The procedures to calculate the fields and to allocate them to the cells of a RANS grid are described in detail. The method has been implemented using the BEM program PROCAL and the RANS solver OpenFOAM and tested using the propeller DTMB P4384 operating in open water. Close to the design advance coefficient, the time-average flow fields generated by PROCAL and by OpenFOAM with the force and mass rate fields match to within 1.5% of the inflow speed over almost all of the flow field, including the swept volume of the blades. At two-thirds of the design advance coefficient, the match is about 4% of the inflow speed. The sensitivity of the method to several of its free parameters is investigated. Full article
(This article belongs to the Special Issue Marine Propulsors)
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Open AccessArticle Photogrammetric Surveys and Geometric Processes to Analyse and Monitor Red Coral Colonies
J. Mar. Sci. Eng. 2018, 6(2), 42; https://doi.org/10.3390/jmse6020042
Received: 1 February 2018 / Revised: 28 February 2018 / Accepted: 26 March 2018 / Published: 12 April 2018
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Abstract
This article describes the set of photogrammetric tools developed for the monitoring of Mediterranean red coral Corallium rubrum populations. The description encompasses the full processing chain: from the image acquisition to the information extraction and data interpretation. The methods applied take advantage of
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This article describes the set of photogrammetric tools developed for the monitoring of Mediterranean red coral Corallium rubrum populations. The description encompasses the full processing chain: from the image acquisition to the information extraction and data interpretation. The methods applied take advantage of existing tools and new, innovative and specific developments in order to acquire data on relevant ecological information concerning the structure and functioning of a red coral population. The tools presented here are based on: (i) automatic orientation using coded quadrats; (ii) use of non-photorealistic rendering (NPR) and 3D skeletonization techniques; (iii) computation of distances between colonies from a same site; and (iv) the use of a plenoptic approach in an underwater environment. Full article
(This article belongs to the Special Issue Underwater Imaging)
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Open AccessArticle Coupling Numerical Methods and Analytical Models for Ducted Turbines to Evaluate Designs
J. Mar. Sci. Eng. 2018, 6(2), 43; https://doi.org/10.3390/jmse6020043
Received: 27 February 2018 / Revised: 31 March 2018 / Accepted: 11 April 2018 / Published: 16 April 2018
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Abstract
Hydrokinetic turbines extract energy from currents in oceans, rivers, and streams. Ducts can be used to accelerate the flow across the turbine to improve performance. The objective of this work is to couple an analytical model with a Reynolds averaged Navier–Stokes (RANS) computational
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Hydrokinetic turbines extract energy from currents in oceans, rivers, and streams. Ducts can be used to accelerate the flow across the turbine to improve performance. The objective of this work is to couple an analytical model with a Reynolds averaged Navier–Stokes (RANS) computational fluid dynamics (CFD) solver to evaluate designs. An analytical model is derived for ducted turbines. A steady-state moving reference frame solver is used to analyze both the freestream and ducted turbine. A sliding mesh solver is examined for the freestream turbine. An efficient duct is introduced to accelerate the flow at the turbine. Since the turbine is optimized for operation in the freestream and not within the duct, there is a decrease in efficiency due to duct-turbine interaction. Despite the decrease in efficiency, the power extracted by the turbine is increased. The analytical model under-predicts the flow rejection from the duct that is predicted by CFD since the CFD predicts separation but the analytical model does not. Once the mass flow rate is corrected, the model can be used as a design tool to evaluate how the turbine-duct pair reduces mass flow efficiency. To better understand this phenomenon, the turbine is also analyzed within a tube with the analytical model and CFD. The analytical model shows that the duct’s mass flow efficiency reduces as a function of loading, showing that the system will be more efficient when lightly loaded. Using the conclusions of the analytical model, a more efficient ducted turbine system is designed. The turbine is pitched more heavily and the twist profile is adapted to the radial throat velocity profile. Full article
(This article belongs to the Special Issue Marine Propulsors)
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Open AccessArticle Residence Time of a Highly Urbanized Estuary: Jamaica Bay, New York
J. Mar. Sci. Eng. 2018, 6(2), 44; https://doi.org/10.3390/jmse6020044
Received: 22 January 2018 / Revised: 16 April 2018 / Accepted: 17 April 2018 / Published: 20 April 2018
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Abstract
Using a validated coupled hydrodynamic-tracer transport model, this study quantified the mean residence time in Jamaica Bay, a highly eutrophic lagoonal estuary in New York City. The Bay is a well-mixed to partially-stratified estuary with heavily-dredged bathymetry and substantial wastewater treatment plant effluent
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Using a validated coupled hydrodynamic-tracer transport model, this study quantified the mean residence time in Jamaica Bay, a highly eutrophic lagoonal estuary in New York City. The Bay is a well-mixed to partially-stratified estuary with heavily-dredged bathymetry and substantial wastewater treatment plant effluent inputs that lead to seasonal hypoxia in some poorly-flushed deep-water basins. Residence time was computed for Jamaica Bay and its largest isolated deep basin, Grassy Bay. The response of residence time to freshwater discharge and wind forcing during summer 2015 was also investigated. The model results showed that the mean residence time, which represents the time required to flush out 63% of tracers released into the region of interest, was 17.9 days in Jamaica Bay and 10.7 days in Grassy Bay. The results also showed that some regions in Jamaica Bay retained their tracers much longer than the calculated residence time and, thus, are potentially prone to water quality problems. Model experiments demonstrated that summertime wind forcing caused a small increase in residence time, whereas freshwater discharge substantially reduced residence time. Freshwater inputs were shown to strongly enhance the two-layer estuarine gravitational circulation and vertical shear, which likely reduced residence time by enhancing shear dispersion. Due to the Bay’s small, highly-urbanized watershed, freshwater inputs are largely derived from the municipal water supply, which is fairly uniform year-round. This water helps to promote bay flushing, yet also carries a high nitrogen load from wastewater treatment. Lastly, the tidal prism method was used to create a simple calibrated model of residence time using the geometry of the study area and the tidal range and period. Full article
(This article belongs to the Section Physical Oceanography)
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Open AccessArticle Experimental and Numerical Investigation of Propeller Loads in Off-Design Conditions
J. Mar. Sci. Eng. 2018, 6(2), 45; https://doi.org/10.3390/jmse6020045
Received: 27 February 2018 / Revised: 21 March 2018 / Accepted: 4 April 2018 / Published: 24 April 2018
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Abstract
The understanding of the performance of a propeller in realistic operative conditions is nowadays a key issue for improving design techniques, guaranteeing safety and continuity of operation at sea, and reducing maintenance costs. In this paper, a summary of the recent research carried
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The understanding of the performance of a propeller in realistic operative conditions is nowadays a key issue for improving design techniques, guaranteeing safety and continuity of operation at sea, and reducing maintenance costs. In this paper, a summary of the recent research carried out at CNR-INSEAN devoted to the analysis of propeller loads in realistic operative scenarios, with particular emphasis on the in-plane loads, is presented. In particular, the experimental results carried out on a free running maneuvering model equipped with a novel force transducer are discussed and supported by C F D (Computational Fluid Dynamics) analysis and the use of a simplified propeller model, based on Blade Element Momentum Theory, with the aim of achieving a deeper understanding of the mechanisms that govern the functioning of the propeller in off-design. Moreover, the analysis includes the scaling factors that can be used to obtain a prediction from model measurements, the propeller radial force being the primary cause of failures of the shaft bearings. In particular, the analysis highlighted that cavitation at full scale can cause the increment of in-plane loads by about 20% with respect to a non-cavitating case, that that in-plane loads could be more sensitive to cavitation than thrust and torque, and that Reynolds number effect is negligible. For the analysis of cavitation, an alternative version of the B E M T solver, improved with cavitation linear theory, was developed. Full article
(This article belongs to the Special Issue Marine Propulsors)
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Open AccessArticle Influence of Propulsion Type on the Stratified Near Wake of an Axisymmetric Self-Propelled Body
J. Mar. Sci. Eng. 2018, 6(2), 46; https://doi.org/10.3390/jmse6020046
Received: 1 March 2018 / Revised: 30 March 2018 / Accepted: 23 April 2018 / Published: 1 May 2018
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Abstract
To better understand the influence of swirl on the thermally-stratified near wake of a self-propelled axisymmetric vehicle, three propulsor schemes were considered: a single propeller, contra-rotating propellers (CRP), and a zero-swirl, uniform-velocity jet. The propellers were modeled using an Actuator-Line model in an
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To better understand the influence of swirl on the thermally-stratified near wake of a self-propelled axisymmetric vehicle, three propulsor schemes were considered: a single propeller, contra-rotating propellers (CRP), and a zero-swirl, uniform-velocity jet. The propellers were modeled using an Actuator-Line model in an unsteady Reynolds-Averaged Navier–Stokes simulation, where the Reynolds number is R e L = 3.1 × 10 8 using the freestream velocity and body length. The authors previously showed good comparison to experimental data with this approach. Visualization of vortical structures shows the helical paths of blade-tip vortices from the single propeller as well as the complicated vortical interaction between contra-rotating blades. Comparison of instantaneous and time-averaged fields shows that temporally stationary fields emerge by half of a body length downstream. Circumferentially-averaged axial velocity profiles show similarities between the single propeller and CRP in contrast to the jet configuration. Swirl velocity of the CRP, however, was attenuated in comparison to that of the single propeller case. Mixed-patch contour maps illustrate the unique temperature distribution of each configuration as a consequence of their respective swirl profiles. Finally, kinetic and potential energy is integrated along downstream axial planes to reveal key differences between the configurations. The CRP configuration creates less potential energy by reducing swirl that would otherwise persist in the near wake of a single-propeller wake. Full article
(This article belongs to the Special Issue Marine Propulsors)
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Open AccessArticle Using Live-Stream Video from an Artificial Reef to Increase Interest in Marine Biology
J. Mar. Sci. Eng. 2018, 6(2), 47; https://doi.org/10.3390/jmse6020047
Received: 18 March 2018 / Revised: 21 April 2018 / Accepted: 24 April 2018 / Published: 1 May 2018
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Abstract
New methods are needed to attract more interest to natural sciences among the public and young people. We established an underwater laboratory by placing cameras on an artificial reef (a sunken ferry) to create a new and inspiring way of teaching marine biology
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New methods are needed to attract more interest to natural sciences among the public and young people. We established an underwater laboratory by placing cameras on an artificial reef (a sunken ferry) to create a new and inspiring way of teaching marine biology and showing science to the public. Here we describe the process and solutions to the technical challenges in designing the laboratory. Live-streaming from the underwater environment has great potential for teaching marine biology in new and exciting ways, and it could also be used more widely for stimulating interest among the general public in aquariums and museums. Full article
(This article belongs to the Special Issue Methodologies for Outreach in the Marine Sciences)
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Open AccessArticle Probabilistic Assessment of Overtopping of Sea Dikes with Foreshores including Infragravity Waves and Morphological Changes: Westkapelle Case Study
J. Mar. Sci. Eng. 2018, 6(2), 48; https://doi.org/10.3390/jmse6020048
Received: 19 March 2018 / Revised: 4 April 2018 / Accepted: 23 April 2018 / Published: 1 May 2018
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Abstract
Shallow foreshores in front of coastal dikes can reduce the probability of dike failure due to wave overtopping. A probabilistic model framework is presented, which is capable of including complex hydrodynamics like infragravity waves, and morphological changes of a sandy foreshore during severe
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Shallow foreshores in front of coastal dikes can reduce the probability of dike failure due to wave overtopping. A probabilistic model framework is presented, which is capable of including complex hydrodynamics like infragravity waves, and morphological changes of a sandy foreshore during severe storms in the calculations of the probability of dike failure due to wave overtopping. The method is applied to a test case based on the Westkapelle sea defence in The Netherlands, a hybrid defence consisting of a dike with a sandy foreshore. The model framework consists of the process-based hydrological and morphological model XBeach, probabilistic overtopping equations (EurOtop) and the level III fully probabilistic method ADIS. By using the fully probabilistic level III method ADIS, the number of simulations necessary is greatly reduced, which allows for the use of more advanced and detailed hydro- and morphodynamic models. The framework is able to compute the probability of failure with up to 15 stochastic variables and is able to describe feasible physical processes. Furthermore, the framework is completely modular, which means that any model or equation can be plugged into the framework, whenever updated models with improved representation of the physics or increases in computational power become available. The model framework as described in this paper, includes more physical processes and stochastic variables in the determination of the probability of dike failure due to wave overtopping, compared to the currently used methods in The Netherlands. For the here considered case, the complex hydrodynamics like infragravity waves and wave set-up need to be included in the calculations, because they appeared to have a large influence on the probability of failure. Morphological changes of the foreshore during a severe storm appeared to have less influence on the probability of failure for this case. It is recommended to apply the framework to other cases as well, to determine if the effects of complex hydrodynamics as infragravity waves and morphological changes on the probability of sea dike failure due to wave overtopping as found in this paper hold for other cases as well. Furthermore, it is recommended to investigate broader use of the method, e.g., for safety assessment, reliability analysis and design. Full article
(This article belongs to the Special Issue Climate Change, Coasts and Coastal Risk)
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Open AccessArticle A Semi-Empirical Prediction Method for Broadband Hull-Pressure Fluctuations and Underwater Radiated Noise by Propeller Tip Vortex Cavitation
J. Mar. Sci. Eng. 2018, 6(2), 49; https://doi.org/10.3390/jmse6020049
Received: 27 February 2018 / Revised: 13 April 2018 / Accepted: 26 April 2018 / Published: 2 May 2018
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Abstract
A semi-empirical method is presented that predicts broadband hull-pressure fluctuations and underwater radiated noise due to propeller tip vortex cavitation. The method uses a hump-shaped pattern for the spectrum and predicts the centre frequency and level of this hump. The principal parameter is
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A semi-empirical method is presented that predicts broadband hull-pressure fluctuations and underwater radiated noise due to propeller tip vortex cavitation. The method uses a hump-shaped pattern for the spectrum and predicts the centre frequency and level of this hump. The principal parameter is the vortex cavity size, which is predicted by a combination of a boundary element method and a semi-empirical vortex model. It is shown that such a model is capable of representing the variation of cavity size with cavitation number well. Using a database of model- and full-scale measured hull-pressure data, an empirical formulation for the maximum level and centre frequency has been developed that is a function of, among other parameters, the cavity size. Acceptable results are obtained when comparing predicted and measured hull-pressure and radiated noise spectra for various cases. The comparison also shows differences that require adjustments of parameters that need to be further investigated. Full article
(This article belongs to the Special Issue Marine Propulsors)
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Open AccessArticle Experimental Investigation of Propeller Wake Velocity Field to Determine the Major Factors Affecting Propeller Wake Wash
J. Mar. Sci. Eng. 2018, 6(2), 50; https://doi.org/10.3390/jmse6020050
Received: 30 March 2018 / Revised: 23 April 2018 / Accepted: 1 May 2018 / Published: 7 May 2018
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Abstract
The propeller jet from a ship has a significant component directed upwards towards the free surface of the water, which can be used for ice management. This paper describes a comprehensive laboratory experiment where the operational factors affecting a propeller wake velocity field
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The propeller jet from a ship has a significant component directed upwards towards the free surface of the water, which can be used for ice management. This paper describes a comprehensive laboratory experiment where the operational factors affecting a propeller wake velocity field were investigated. The experiment was conducted using a steady wake field to investigate the characteristics of the axial velocity of the fluid in the wake and the corresponding variability downstream of the propeller. The axial velocities and the variability recorded were time-averaged. Propeller rotational speed was found to be the most significant factor, followed by propeller inclination. The experimental results also provide some idea about the change of the patterns of the mean axial velocity distribution against the factors considered for the test throughout the effective wake field, as well as the relationships to predict the axial velocity for known factors. Full article
(This article belongs to the Section Ocean Engineering)
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Open AccessArticle Experimental Validation of Fluid–Structure Interaction Computations of Flexible Composite Propellers in Open Water Conditions Using BEM-FEM and RANS-FEM Methods
J. Mar. Sci. Eng. 2018, 6(2), 51; https://doi.org/10.3390/jmse6020051
Received: 29 March 2018 / Revised: 16 April 2018 / Accepted: 24 April 2018 / Published: 7 May 2018
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Abstract
In the past several decades, many papers have been published on fluid–structure coupled calculations to analyse the hydro-elastic response of flexible (composite) propellers. The flow is usually modelled either by the Navier–Stokes equations or as a potential flow, by assuming an irrotational flow.
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In the past several decades, many papers have been published on fluid–structure coupled calculations to analyse the hydro-elastic response of flexible (composite) propellers. The flow is usually modelled either by the Navier–Stokes equations or as a potential flow, by assuming an irrotational flow. Phenomena as separation of the flow, flow transition, boundary layer build-up and vorticity dynamics are not captured in a non-viscous potential flow. Nevertheless, potential flow based methods have been shown to be powerful methods to resolve the hydrodynamics of propellers. With the upcoming interest in flexible (composite) propellers, a valid question is what the consequences of the potential flow simplifications are with regard to the coupled fluid–structure analyses of these types of propellers. This question has been addressed in the following way: calculations and experiments were conducted for uniform flows only, with a propeller geometry that challenges the potential flow model due to its sensitivity to leading edge vortex separation. Calculations were performed on the undeformed propeller geometry with a Reynolds-averaged-Navier–Stokes (RANS) solver and a boundary element method (BEM). These calculations show some typical differences between the RANS and BEM results. The flexible propeller responses were predicted by coupled calculations between BEM and finite element method (FEM) and RANS and FEM. The applied methodologies are briefly described. Results obtained from both calculation methods have been compared to experimental results obtained from blade deformation measurements in a cavitation tunnel. The results show that, even for the extreme cases, promising results have been obtained with the BEM-FEM coupling. The BEM-FEM calculated responses are consistent with the RANS-FEM results. Full article
(This article belongs to the Special Issue Marine Propulsors)
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Open AccessArticle Prediction of Propeller-Induced Hull Pressure Fluctuations via a Potential-Based Method: Study of the Effects of Different Wake Alignment Methods and of the Rudder
J. Mar. Sci. Eng. 2018, 6(2), 52; https://doi.org/10.3390/jmse6020052
Received: 4 April 2018 / Revised: 28 April 2018 / Accepted: 2 May 2018 / Published: 8 May 2018
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Abstract
In order to predict ship hull pressure fluctuations induced by marine propellers, a combination of several numerical schemes is used. The propeller perturbation flow is solved by the boundary element method (BEM), while the coupling between a BEM solver and a Reynolds-averaged Navier-Stokes
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In order to predict ship hull pressure fluctuations induced by marine propellers, a combination of several numerical schemes is used. The propeller perturbation flow is solved by the boundary element method (BEM), while the coupling between a BEM solver and a Reynolds-averaged Navier-Stokes (RANS) solver can efficiently predict the effective wake. Based on the BEM solution under the predicted effective wake, the propeller-induced potential on the ship hull can be evaluated. Then, a pressure-BEM solver is used to solve the diffraction pressure on the hull in order to obtain the solid boundary factor which leads to the total hull pressure. This paper briefly introduces the schemes and numerical models. To avoid numerical instability, several simplifications need to be made. The effects of these simplifications are studied, including the rudder effect and the wake alignment model effect. Full article
(This article belongs to the Special Issue Marine Propulsors)
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Open AccessArticle Marine Turbine Hydrodynamics by a Boundary Element Method with Viscous Flow Correction
J. Mar. Sci. Eng. 2018, 6(2), 53; https://doi.org/10.3390/jmse6020053
Received: 30 March 2018 / Revised: 27 April 2018 / Accepted: 1 May 2018 / Published: 8 May 2018
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Abstract
A computational methodology for the hydrodynamic analysis of horizontal axis marine current turbines is presented. The approach is based on a boundary integral equation method for inviscid flows originally developed for marine propellers and adapted here to describe the flow features that characterize
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A computational methodology for the hydrodynamic analysis of horizontal axis marine current turbines is presented. The approach is based on a boundary integral equation method for inviscid flows originally developed for marine propellers and adapted here to describe the flow features that characterize hydrokinetic turbines. For this purpose, semi-analytical trailing wake and viscous flow correction models are introduced. A validation study is performed by comparing hydrodynamic performance predictions with two experimental test cases and with results from other numerical models in the literature. The capability of the proposed methodology to correctly describe turbine thrust and power over a wide range of operating conditions is discussed. Viscosity effects associated to blade flow separation and stall are taken into account and predicted thrust and power are comparable with results of blade element methods that are largely used in the design of marine current turbines. The accuracy of numerical predictions tends to reduce in cases where turbine blades operate in off-design conditions. Full article
(This article belongs to the Special Issue Marine Propulsors)
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Open AccessArticle Storm Surge and Wave Impact of Low-Probability Hurricanes on the Lower Delaware Bay—Calibration and Application
J. Mar. Sci. Eng. 2018, 6(2), 54; https://doi.org/10.3390/jmse6020054
Received: 9 March 2018 / Revised: 30 April 2018 / Accepted: 4 May 2018 / Published: 10 May 2018
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Abstract
Hurricanes pose major threats to coastal communities and sensitive infrastructure, including nuclear power plants, located in the vicinity of hurricane-prone coastal regions. This study focuses on evaluating the storm surge and wave impact of low-probability hurricanes on the lower Delaware Bay using the
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Hurricanes pose major threats to coastal communities and sensitive infrastructure, including nuclear power plants, located in the vicinity of hurricane-prone coastal regions. This study focuses on evaluating the storm surge and wave impact of low-probability hurricanes on the lower Delaware Bay using the Delft3D dynamically coupled wave and flow model. The model comprised Overall and Nested domains. The Overall model domain encompassed portions of the Atlantic Ocean, Delaware Bay, and Chesapeake Bay. The two-level Nested model domains encompassed the Delaware Estuary, its floodplain, and a portion of the continental shelf. Low-probability hurricanes are critical considerations in designing and licensing of new nuclear power plants as well as in establishing mitigating strategies for existing power facilities and other infrastructure types. The philosophy behind low-probability hurricane modeling is to establish reasonable water surface elevation and wave characteristics that have very low to no probability of being exceeded in the region. The area of interest (AOI) is located on the west bank of Delaware Bay, almost 16 miles upstream of its mouth. The model was first calibrated for Hurricane Isabel (2003) and then applied to synthetic hurricanes with very low probability of occurrence to establish the storm surge envelope at the AOI. The model calibration results agreed reasonably well with field observations of water surface elevation, wind velocity, wave height, and wave period. A range of meteorological, storm track direction, and storm bearing parameters that produce the highest sustained wind speeds were estimated using the National Weather Service (NWS) methodology and applied to the model. Simulations resulted in a maximum stillwater elevation and wave height of 7.5 m NAVD88 and 2.5 m, respectively, at the AOI. Comparison of results with the U.S. Army Corps of Engineers, North Atlantic Coastal Comprehensive Study (USACE-NACCS) storm surge values at the AOI demonstrates that the estimated elevation has an annual exceedance probability of less than 10 4 . Full article
(This article belongs to the Section Ocean Engineering)
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Open AccessFeature PaperArticle An Effective Modelling Approach to Support Probabilistic Flood Forecasting in Coastal Cities—Case Study: Can Tho, Mekong Delta, Vietnam
J. Mar. Sci. Eng. 2018, 6(2), 55; https://doi.org/10.3390/jmse6020055
Received: 12 March 2018 / Revised: 3 May 2018 / Accepted: 4 May 2018 / Published: 11 May 2018
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Abstract
Probabilistic flood forecasting requires flood models that are simple and fast. Many of the modelling applications in the literature tend to be complex and slow, making them unsuitable for probabilistic applications which require thousands of individual simulations. This article focusses on the development
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Probabilistic flood forecasting requires flood models that are simple and fast. Many of the modelling applications in the literature tend to be complex and slow, making them unsuitable for probabilistic applications which require thousands of individual simulations. This article focusses on the development of such a modelling approach to support probabilistic assessment of flood hazards, while accounting for forcing and system uncertainty. Here, we demonstrate the feasibility of using the open-source SWMM (Storm Water Management Model), focussing on Can Tho city, Mekong Delta, Vietnam. SWMM is a dynamic rainfall-runoff simulation model which is generally used for single event or long-term (continuous) simulation of runoff quantity and quality and its application for probabilistic riverflow modelling is atypical. In this study, a detailed SWMM model of the entire Mekong Delta was built based on an existing ISIS model containing 575 nodes and 592 links of the same study area. The detailed SWMM model was then systematically reduced by strategically removing nodes and links to eventually arrive at a level of detail that provides sufficiently accurate predictions of water levels for Can Tho for the purpose of simulating urban flooding, which is the target diagnostic of this study. After a comprehensive assessment (based on trials with the varying levels of complexity), a much reduced SWMM model comprising 37 nodes and 40 links was determined to be able to provide a sufficiently accurate result while being fast enough to support probabilistic future flood forecasting and, further, to support flood risk reduction management. Full article
(This article belongs to the Special Issue Climate Change, Coasts and Coastal Risk)
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Open AccessArticle DDES of Wetted and Cavitating Marine Propeller for CHA Underwater Noise Assessment
J. Mar. Sci. Eng. 2018, 6(2), 56; https://doi.org/10.3390/jmse6020056 (registering DOI)
Received: 29 March 2018 / Revised: 23 April 2018 / Accepted: 3 May 2018 / Published: 21 May 2018
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Abstract
In this paper we present results of delayed detached eddy simulation (DDES) and computational hydroacoustics (CHA) simulations of a marine propeller operating in a cavitation tunnel. DDES is carried out in both wetted and cavitating conditions, and we perform the investigation at several
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In this paper we present results of delayed detached eddy simulation (DDES) and computational hydroacoustics (CHA) simulations of a marine propeller operating in a cavitation tunnel. DDES is carried out in both wetted and cavitating conditions, and we perform the investigation at several propeller loadings. CHA analyses are done for one propeller loading both in wetted and cavitating conditions. The simulations are validated against experiments conducted in the cavitation tunnel. Propeller global forces, local flow phenomena, as well as cavitation patterns are compared to the cavitation tunnel tests. Hydroacoustic sources due to the propeller are evaluated from the flow solution, and corresponding acoustic simulations utilizing an acoustic analogy are made. The propeller wake flow structures are investigated for the wetted and cavitating operating conditions, and the acoustic excitation and output of the same cases are discussed. Full article
(This article belongs to the Special Issue Marine Propulsors)
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