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J. Mar. Sci. Eng., Volume 7, Issue 3 (March 2019)

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Cover Story (view full-size image) As foundations represent approximately 35% of the total cost of an offshore wind project, it is [...] Read more.
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Open AccessArticle
HAMS: A Frequency-Domain Preprocessor for Wave-Structure Interactions—Theory, Development, and Application
J. Mar. Sci. Eng. 2019, 7(3), 81; https://doi.org/10.3390/jmse7030081
Received: 14 February 2019 / Revised: 10 March 2019 / Accepted: 16 March 2019 / Published: 26 March 2019
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Abstract
This paper presents the theoretical background, the numerical implementation, and the applications of a new software that has been developed in recent years for the analysis of wave-structure interactions. The software is developed in the frequency domain, as a preprocessor of computing the [...] Read more.
This paper presents the theoretical background, the numerical implementation, and the applications of a new software that has been developed in recent years for the analysis of wave-structure interactions. The software is developed in the frequency domain, as a preprocessor of computing the wave excitation force, the added mass, and the wave radiation damping, for the input to a time-domain solver via the Fourier cosine and sine transforms. In addition, it can also predict the motion responses of a marine structure with sufficient accuracy, with or without the presence of a mooring system. Unlike other frequency-domain software, such as WAMIT® and Hydrostar®, the present software currently employs the least squares method in association with a partially extended boundary integral equation method to remove the so-called “irregular frequencies”. Calculation of the free-surface Green’s function employs a combination of fast-convergent series expansions in different parametric sub-regions. The solution of the resultant linear algebraic system employs the lower-upper (LU) decomposition method. Symmetry properties can be exploited, and the open multi-processing (OpenMP) parallelization technique can be applied to reduce the computation burden. The accuracy and the efficiency of the developed software are finally confirmed by numerical validations on three benchmark cases of a floating ellipsoid, a truncated circular cylinder and the OC4 DeepCwind semisubmersible floating wind turbine. A free executable version of the software is available to the research communities with a hope of facilitating the advancements in the researches that are relevant to ocean engineering and marine renewable energies. Full article
(This article belongs to the Special Issue Dynamics of Offshore Structures)
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Open AccessArticle
Robust Capon Beamforming against Steering Vector Error Dominated by Large Direction-of-Arrival Mismatch for Passive Sonar
J. Mar. Sci. Eng. 2019, 7(3), 80; https://doi.org/10.3390/jmse7030080
Received: 25 February 2019 / Revised: 21 March 2019 / Accepted: 22 March 2019 / Published: 26 March 2019
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Abstract
Capon beamforming is often applied in passive sonar to improve the detectability of weak underwater targets. However, we often have no accurate prior information of the direction-of-arrival (DOA) of the target in the practical applications of passive sonar. In this case, Capon beamformer [...] Read more.
Capon beamforming is often applied in passive sonar to improve the detectability of weak underwater targets. However, we often have no accurate prior information of the direction-of-arrival (DOA) of the target in the practical applications of passive sonar. In this case, Capon beamformer will suffer from performance degradation due to the steering vector error dominated by large DOA mismatch. To solve this, a new robust Capon beamforming approach is proposed. The essence of the proposed method is to decompose the actual steering vector into two components by oblique projection onto a subspace and then estimate the actual steering vector in two steps. First, we estimate the oblique projection steering vector within the subspace by maximizing the output power while controlling the power from the sidelobe region. Subsequently, we search for the actual steering vector within the neighborhood of the estimated oblique projection steering vector by maximizing the output signal-to-interference-plus-noise ratio (SINR). Semidefinite relaxation and Charnes-Cooper transformation are utilized to derive convex formulations of the estimation problems, and the optimal solutions are obtained by the rank-one decomposition theorem. Numerical simulations demonstrate that the proposed method can provide superior performance, as compared with several previously proposed robust Capon beamformers in the presence of large DOA mismatch and other array imperfections. Full article
(This article belongs to the Special Issue Signals and Images in Sea Technologies)
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Open AccessFeature PaperArticle
Effects of Swell on Wave Height Distribution of Energy-Conserved Bimodal Seas
J. Mar. Sci. Eng. 2019, 7(3), 79; https://doi.org/10.3390/jmse7030079
Received: 22 February 2019 / Revised: 16 March 2019 / Accepted: 19 March 2019 / Published: 22 March 2019
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Abstract
An understanding of the wave height distribution of a sea state is important in forecasting extreme wave height and lifetime fatigue predictions of marine structures. In bimodal seas, swell can be present at different percentages and different frequencies while the energy content of [...] Read more.
An understanding of the wave height distribution of a sea state is important in forecasting extreme wave height and lifetime fatigue predictions of marine structures. In bimodal seas, swell can be present at different percentages and different frequencies while the energy content of the sea state remains unaltered. This computational study investigates how the wave height distribution is affected by different swell percentages and long swell periods in an energy-conserved bimodal sea both near a wave maker and in shallow water. A formulated energy-conserved bimodal spectrum was created from unimodal sea states and converted into random waves time series using the Inverse Fast Fourier Transform (IFFT). The resulting time series was used to drive a Reynolds-Averaged Navier Stokes computational (RANS) model. Wave height values were then extracted from the model results (both away near and near the structure) using down-crossing analysis to inspect the non-linearity imposed by wave-wave interactions and through transformations as they propagate into shallow waters near the structure. It is concluded that the kurtosis and skewness of the wave height distribution very inversely with the swell percentage and peak periods. Non-linearities are greater in the unimodal seas compared to the bimodal seas with the same energy content. Also, non-linearities are greater structure side than at wave maker and are more dependent on the phases of the component waves at different frequencies. Full article
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Open AccessArticle
Morphodynamic Acceleration Techniques for Multi-Timescale Predictions of Complex Sandy Interventions
J. Mar. Sci. Eng. 2019, 7(3), 78; https://doi.org/10.3390/jmse7030078
Received: 14 February 2019 / Revised: 12 March 2019 / Accepted: 16 March 2019 / Published: 21 March 2019
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Abstract
Thirty one percent (31%) of the world’s coastline consists of sandy beaches and dunes that form a natural defense protecting the hinterland from flooding. A common measure to mitigate erosion along sandy beaches is the implementation of sand nourishments. The design and acceptance [...] Read more.
Thirty one percent (31%) of the world’s coastline consists of sandy beaches and dunes that form a natural defense protecting the hinterland from flooding. A common measure to mitigate erosion along sandy beaches is the implementation of sand nourishments. The design and acceptance of such a mitigating measure require information on the expected evolution at time scales from storms to decades. Process-based morphodynamic models are increasingly applied, together with morphodynamic acceleration techniques, to obtain detailed information on this wide scale of ranges. This study shows that techniques for the acceleration of the morphological evolution can have a significant impact on the simulated evolution and dispersion of sandy interventions. A calibrated Delft3D model of the Sand Engine mega-nourishment is applied to compare different acceleration techniques, focusing on accuracy and computational times. Results show that acceleration techniques using representative (schematized) wave conditions are not capable of accurately reproducing the morphological response in the first two years. The best reproduction of the morphological behavior of the first five years is obtained by the brute force simulations. Applying input filtering and a compression factor provides similar accuracy yet with a factor five gain in computational cost. An attractive method for the medium to long time scales, which further reduces computational costs, is a method that uses representative wave conditions based on gross longshore transports, while showing similar results as the benchmark simulation. Erosional behavior is captured well in all considered techniques with variations in volumes of about 1 million m 3 after three decades. The spatio-temporal variability of the predicted alongshore and cross-shore distribution of the morphological evolution however have a strong dependency on the selected acceleration technique. A new technique, called ’brute force merged’, which incorporates the full variability of the wave climate, provides the optimal combination of phenomenological accuracy and computational efficiency (a factor of 20 faster than the benchmark brute force technique) at both the short and medium to long time scales. This approach, which combines realistic time series and the mormerge technique, provides an attractive and flexible method to efficiently predict the evolution of complex sandy interventions at time scales from hours to decades. Full article
(This article belongs to the Special Issue Large-scale Coastal Behavior)
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Open AccessArticle
Understanding Hurricane Storm Surge Generation and Propagation Using a Forecasting Model, Forecast Advisories and Best Track in a Wind Model, and Observed Data—Case Study Hurricane Rita
J. Mar. Sci. Eng. 2019, 7(3), 77; https://doi.org/10.3390/jmse7030077
Received: 22 February 2019 / Revised: 15 March 2019 / Accepted: 15 March 2019 / Published: 21 March 2019
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Abstract
Meteorological forcing is the primary driving force and primary source of errors for storm surge forecasting. The objective of this study was to learn how forecasted meteorological forcing influences storm surge generation and propagation during a hurricane so that storm surge models can [...] Read more.
Meteorological forcing is the primary driving force and primary source of errors for storm surge forecasting. The objective of this study was to learn how forecasted meteorological forcing influences storm surge generation and propagation during a hurricane so that storm surge models can be reliably used to forecast actual events. Hindcasts and forecasts of Hurricane Rita (2005) storm surge was used as a case study. Meteorological forcing or surface wind/pressure fields for Hurricane Rita were generated using both the Weather Research and Forecasting (WRF) full-scale forecasting model along with archived hurricane advisories ingested into a sophisticated parametric wind model, namely Generalized Asymmetric Holland Model (GAHM). These wind fields were used to forecast Rita storm surges. Observation based wind fields from the OceanWeather Inc. (OWI) Interactive Objective Kinematic Analysis (IOKA) model, and Best track wind data ingested into the GAHM model were used to generate wind fields for comparison purposes. These wind fields were all used to hindcast Rita storm surges with the ADvanced CIRCulation (ADCIRC) model coupled with the Simulating Waves Nearshore (SWAN) model in a tightly coupled storm surge-wave model referred to as ADCIRC+SWAN. The surge results were compared against a quality-controlled database of observed data to assess the performance of these wind fields on storm surge generation and propagation. The surge hindcast produced by the OWI wind field performed the best, although some high water mark (HWM) locations were overpredicted. Although somewhat underpredicted, the WRF wind fields forecasted wider surge extent and wetted most HWM locations. The hindcast using the Best track parameters in the GAHM and the forecast using forecast/advisories from the National Hurricane Center (NHC) in the GAHM produced strong and narrow wind fields causing localized high surges, which resulted in overprediction near landfall while many HWM locations away from wind bands remained dry. Full article
(This article belongs to the Special Issue Hurricane Storm Surge Model Development)
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Open AccessArticle
Marine Coastline Polygonal Ridges and Surface Roughness Development on a Salt-Crusted Playa: Recognition by Structure-from-Motion Photogrammetry
J. Mar. Sci. Eng. 2019, 7(3), 76; https://doi.org/10.3390/jmse7030076
Received: 25 February 2019 / Revised: 13 March 2019 / Accepted: 14 March 2019 / Published: 20 March 2019
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Abstract
Salt crust is a normal landform in drying-out salt lake basins or marine regression coastlines, but the surface evolution processes over a decadal or even centenary period are not well understood due to poor data records. Microrelief characteristics control erodibility and erosivity, which [...] Read more.
Salt crust is a normal landform in drying-out salt lake basins or marine regression coastlines, but the surface evolution processes over a decadal or even centenary period are not well understood due to poor data records. Microrelief characteristics control erodibility and erosivity, which will significantly influence wind erosion and dust emission. It is essential to classify the microrelief pattern of salt crust for mapping its spatial distribution and evaluating the environmental process. A desiccated inland tail-end lake would be an example of the coastline surface evolution after regression and represent a good case study of salt crust because of the fewer exogenic process interruptions. For this paper, field work was performed in the Lop Nur playa in China, about 90° E, 40° N, which used to be a salt lake half a century ago. Ground-based photos of the salt crust were acquired and imported into structure-from-motion (SfM) software to produce a fine centimeter-scale digital elevation model (DEM). Two indexes were introduced and extracted from the digital elevation model to classify various types of salt crust: roughness was calculated to evaluate the magnitude and the gray-level co-occurrence matrix (GLCM) score was derived to describe the structure pattern of the salt crust. Moreover, in this paper, sedimentary features during different parts of a playa evaporation cycle are reviewed and peculiar kinds of salt crust found on Lop Nur are further discussed. Full article
(This article belongs to the Special Issue Coastal Zone Management)
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Open AccessArticle
Medicanes Triggering Chlorophyll Increase
J. Mar. Sci. Eng. 2019, 7(3), 75; https://doi.org/10.3390/jmse7030075
Received: 16 February 2019 / Revised: 6 March 2019 / Accepted: 14 March 2019 / Published: 20 March 2019
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Abstract
Studies have shown that hurricanes and typhoons, apart from being extreme weather phenomena, cause increases in marine chlorophyll-a concentrations and even phytoplankton blooms. Medicanes are the tropical-like Mediterranean cyclones that induce hazardous weather conditions as well. In this study, a couple of medicanes, [...] Read more.
Studies have shown that hurricanes and typhoons, apart from being extreme weather phenomena, cause increases in marine chlorophyll-a concentrations and even phytoplankton blooms. Medicanes are the tropical-like Mediterranean cyclones that induce hazardous weather conditions as well. In this study, a couple of medicanes, over the central and eastern parts of the Sea, are examined for the first time in respect to their possible influence on chlorophyll concentrations. The affected area was delineated with the use of numerical model data, while the sea surface temperature and chlorophyll variations were assessed based on satellite-derived data. The results showed that medicanes trigger surface chlorophyll increases; after the cyclones’ passage, the concentrations were higher compared both with those before and with the climatological monthly values over a large part of the affected area. The mechanisms proposed to explain hurricanes’ favorable influence on chlorophyll concentration seem to be valid for medicanes as well. Area averaged chlorophyll concentrations presented analogous increases to the ones reported for hurricanes, though on a smaller scale. Despite the much lower intensity of medicanes compared with hurricanes, the observed increase in surface chlorophyll after their passage points to their favorable influence. Full article
(This article belongs to the Section Physical Oceanography)
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Open AccessArticle
Vertical Structure of the Water Column at the Virgin Islands Shelf Break and Trough
J. Mar. Sci. Eng. 2019, 7(3), 74; https://doi.org/10.3390/jmse7030074
Received: 22 February 2019 / Revised: 16 March 2019 / Accepted: 17 March 2019 / Published: 20 March 2019
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Abstract
The steep US Virgin Islands Shelf Break (VISB) and the Virgin Islands Trough (VIT) at the Northeastern Caribbean Sea comprise a dynamic region of the Atlantic Ocean. In situ oceanographic data collected in the region during April 2017 were used to examine the [...] Read more.
The steep US Virgin Islands Shelf Break (VISB) and the Virgin Islands Trough (VIT) at the Northeastern Caribbean Sea comprise a dynamic region of the Atlantic Ocean. In situ oceanographic data collected in the region during April 2017 were used to examine the spatial variability in temperature, density, salinity, and relative Chlorophyll-a. Analysis of data from the upper 300 m of the water column, that include deep and shallow water stations in the shelf break region, shows strong stratification of the water column. Stations shallower than 800 m along the shelf break are more variable in temperature, density, and salinity than those that are deeper than 800 m along the trough. For shallow stations, the mixed layer depth deepens along-shelf from West to East while at the deep stations the opposite occurs. Salinity maxima exhibit more variability in depth and range of values in the shallow stations compared to deep stations. Six different types of water masses that contribute to the strong stratification in the region were identified in our study: Caribbean Surface Water, Subtropical Underwater, Sargasso Sea Water, Tropical Atlantic Central Water, Antarctic Intermediate Water, and North Atlantic Deep Water. The upper level Caribbean Surface Water, Subtropical Underwater, and Sargasso Sea Water are present in shallow stations, indicating potential meridional intrusions from the VIT to the VISB which may not be resolved by current ocean circulation models and are not captured in satellite data. The analysis presented here indicates that competing physical processes may be controlling the vertical structure of the water column in the region and merit further examination. Full article
(This article belongs to the Section Physical Oceanography)
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Open AccessArticle
Mesoscale Morphological Changes of Nearshore Sand Banks since the Early 19th Century, and Their Influence on Coastal Dynamics, Northern France
J. Mar. Sci. Eng. 2019, 7(3), 73; https://doi.org/10.3390/jmse7030073
Received: 13 February 2019 / Revised: 14 March 2019 / Accepted: 16 March 2019 / Published: 20 March 2019
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Abstract
Tidal sand banks are common along the coast of northern France facing the North Sea, where they form linear shore-parallel or slightly oblique sand bodies from shallow coastal areas to depths of tens of meters. Hydrographic surveys have been carried out since the [...] Read more.
Tidal sand banks are common along the coast of northern France facing the North Sea, where they form linear shore-parallel or slightly oblique sand bodies from shallow coastal areas to depths of tens of meters. Hydrographic surveys have been carried out since the 1830s for mapping the seabed of the coastal zone. An analysis of the bathymetry evolution shows significant morphological changes have occurred across the shoreface since the early 19th century, largely due to cross-shore and longshore sand bank migration. Our results show that nearshore sand banks mainly migrated onshore and gained sediment, especially during the 20th century; acting as temporary sediment sinks, which can in turn serve as sand sources for providing sediment to the coast. Alongshore, the migration and elongation of sand banks can be related to tidal asymmetry that is mostly directed to the east-north-east in the region. Shore-perpendicular movement can likely be explained by the action of shore-normal storm-waves in the nearshore zone after their refraction over shallow offshore sand banks. A seaward displacement of sand banks was also observed. This may be related to the combined action of waves and tidal currents which can induce erosion on one side of the bank, decreasing its width, and eventually leading to its seaward migration. Our observations point out that some nearshore sand banks respond to the action of currents and waves, and interact between each other via feedback morphodynamic processes induced by sand bank morphological changes. The substantial morphologic changes that affected the nearshore zone of northern France during the last centuries probably had large impacts on coastal hydrodynamics and associated shoreline evolution. Full article
(This article belongs to the Special Issue Large-scale Coastal Behavior)
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Open AccessArticle
Preliminary Study on the Contribution of External Forces to Ship Behavior
J. Mar. Sci. Eng. 2019, 7(3), 72; https://doi.org/10.3390/jmse7030072
Received: 15 January 2019 / Revised: 11 February 2019 / Accepted: 20 February 2019 / Published: 20 March 2019
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Abstract
Computational modeling has become a prominent tool to simulate physical processes for research and development projects. The coastal region of southern Brazil is very susceptible to oil spill accidents. Currently, oil is intensively transported in the region due to the presence of the [...] Read more.
Computational modeling has become a prominent tool to simulate physical processes for research and development projects. The coastal region of southern Brazil is very susceptible to oil spill accidents. Currently, oil is intensively transported in the region due to the presence of the Rio Grande Harbor, the Transpetro Waterway Terminal (Petrobras) and the Riograndense S/A Oil Refinery. Therefore, simulations under ideal navigation conditions for ships with potentially polluting loads are important because their use can reduce oil spills and toxic compound accidents in the environment. Therefore, the main objective of this work is to present a preliminary study of the contribution of external forces to a ship’s behavior over a simulation period of 5 h. The methodology is based on the development of a numerical model using LaGrangian formalism and the calculus of variations, besides Maneuvering Modeling Group (MMG Model). The external forces considered were the wind acting directly on the ship, waves driven by wind, the rudder, the force acting on the hull, inertial forces, and seawater density. The results indicate that at the beginning of the simulation, the inertial forces were of primary importance for controlling the trajectory of the ship. After 5 h of simulations, the ship had completely changed its trajectory due to forces suffered by the ship, classified according to MMG Model. Full article
(This article belongs to the Special Issue Engineering Mathematics in Ship Design)
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Open AccessArticle
The Efficient Application of an Impulse Source Wavemaker to CFD Simulations
J. Mar. Sci. Eng. 2019, 7(3), 71; https://doi.org/10.3390/jmse7030071
Received: 21 January 2019 / Revised: 9 March 2019 / Accepted: 12 March 2019 / Published: 19 March 2019
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Abstract
Computational Fluid Dynamics (CFD) simulations, based on Reynolds-Averaged Navier–Stokes (RANS) models, are a useful tool for a wide range of coastal and offshore applications, providing a high fidelity representation of the underlying hydrodynamic processes. Generating input waves in the CFD simulation is performed [...] Read more.
Computational Fluid Dynamics (CFD) simulations, based on Reynolds-Averaged Navier–Stokes (RANS) models, are a useful tool for a wide range of coastal and offshore applications, providing a high fidelity representation of the underlying hydrodynamic processes. Generating input waves in the CFD simulation is performed by a Numerical Wavemaker (NWM), with a variety of different NWM methods existing for this task. While NWMs, based on impulse source methods, have been widely applied for wave generation in depth averaged, shallow water models, they have not seen the same level of adoption in the more general RANS-based CFD simulations, due to difficulties in relating the required impulse source function to the resulting free surface elevation for non-shallow water cases. This paper presents an implementation of an impulse source wavemaker, which is able to self-calibrate the impulse source function to produce a desired wave series in deep or shallow water at a specific point in time and space. Example applications are presented, for a Numerical Wave Tank (NWT), based on the open-source CFD software OpenFOAM, for wave packets in deep and shallow water, highlighting the correct calibration of phase and amplitude. Furthermore, the suitability for cases requiring very low reflection from NWT boundaries is demonstrated. Possible issues in the use of the method are discussed, and guidance for accurate application is given. Full article
(This article belongs to the Special Issue Advances in Marine Dynamic Simulation)
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Open AccessFeature PaperArticle
The Snell’s Window Image for Remote Sensing of the Upper Sea Layer: Results of Practical Application
J. Mar. Sci. Eng. 2019, 7(3), 70; https://doi.org/10.3390/jmse7030070
Received: 28 February 2019 / Revised: 12 March 2019 / Accepted: 15 March 2019 / Published: 19 March 2019
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Abstract
Estimation of water optical properties can be performed by photo or video registration of rough sea surface from underwater at an angle of total internal reflection in the away from the sun direction at several depths. In this case, the key characteristic of [...] Read more.
Estimation of water optical properties can be performed by photo or video registration of rough sea surface from underwater at an angle of total internal reflection in the away from the sun direction at several depths. In this case, the key characteristic of the obtained image will be the border of the Snell’s window, which is a randomly distorted image of the sky. Its distortion changes simultaneously under the action of the sea roughness and light scattering; however, after correct “decoding” of this image, their separate determination is possible. This paper presents the corresponding algorithms for achieving these possibilities by the Snell’s window images. These images were obtained in waters with different optical properties and wave conditions under several types of illumination. Practical guidelines for recording, processing and analyzing images of the Snell’s window are also formulated. Full article
(This article belongs to the Special Issue Underwater Imaging)
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Open AccessArticle
Tool Use by Four Species of Indo-Pacific Sea Urchins
J. Mar. Sci. Eng. 2019, 7(3), 69; https://doi.org/10.3390/jmse7030069
Received: 5 February 2019 / Revised: 7 March 2019 / Accepted: 14 March 2019 / Published: 18 March 2019
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Abstract
We compared the covering behavior of four sea urchin species, Tripneustes gratilla, Pseudoboletia maculata, Toxopneustes pileolus, and Salmacis sphaeroides found in the waters of Malapascua Island, Cebu Province and Bolinao, Panagsinan Province, Philippines. Specifically, we measured the amount and type [...] Read more.
We compared the covering behavior of four sea urchin species, Tripneustes gratilla, Pseudoboletia maculata, Toxopneustes pileolus, and Salmacis sphaeroides found in the waters of Malapascua Island, Cebu Province and Bolinao, Panagsinan Province, Philippines. Specifically, we measured the amount and type of covering material on each sea urchin, and in several cases, the recovery of debris material after stripping the animal of its cover. We found that Tripneustes gratilla and Salmacis sphaeroides have a higher affinity for plant material, especially seagrass, compared to Pseudoboletia maculata and Toxopneustes pileolus, which prefer to cover themselves with coral rubble and other calcified material. Only in Toxopneustes pileolus did we find a significant corresponding depth-dependent decrease in total cover area, confirming previous work that covering behavior serves as a protection mechanism against UV radiation. We found no dependence of particle size on either species or size of sea urchin, but we observed that larger sea urchins generally carried more and heavier debris. We observed a transport mechanism of debris onto the echinoid body surface utilizing a combination of tube feet and spines. We compare our results to previous studies, comment on the phylogeny of sea urchin covering behavior, and discuss the interpretation of this behavior as animal tool use. Full article
(This article belongs to the Section Marine Biology)
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Open AccessArticle
The Hydrodynamic Noise Suppression of a Scaled Submarine Model by Leading-Edge Serrations
J. Mar. Sci. Eng. 2019, 7(3), 68; https://doi.org/10.3390/jmse7030068
Received: 1 February 2019 / Revised: 20 February 2019 / Accepted: 4 March 2019 / Published: 15 March 2019
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Abstract
High hydrodynamic noise is a threat to the survival of underwater vehicles. We investigated a noise suppression mechanism by putting leading-edge serrations on the sail hull of a scaled SUBOFF model, through numerical calculation and an experimental test. We found that the cone [...] Read more.
High hydrodynamic noise is a threat to the survival of underwater vehicles. We investigated a noise suppression mechanism by putting leading-edge serrations on the sail hull of a scaled SUBOFF model, through numerical calculation and an experimental test. We found that the cone shape of leading-edge serrations can decrease the intensity of the adverse pressure gradient and produce counter-rotation vortices, which destroy the formation of the horseshoe vortex and delay the tail vortex. To achieve the optimum hydrodynamic noise reduction, we summarized the parameters of leading-edge serrations. Then, two steel models were built, according to the simulation. We measured the hydrodynamic noise based on the reverberation method in a gravity water tunnel. The numerically calculated results were validated by the experimental test. The results show that leading-edge serrations with amplitudes of 0.025c and wavelengths of 0.05h can obtain hydrodynamic noise reduction of at least 6 dB, from 10 Hz to 2 kHz, where c is the chord length and h is the height of the sail hull. The results in our study suggest a new way to design underwater vehicles with low hydrodynamic noise at a high Reynolds number. Full article
(This article belongs to the Special Issue Underwater Technology—Hydrodynamics and Control System)
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Open AccessArticle
SCR Performance Evaluations in Relation to Experimental Parameters in a Marine Generator Engine
J. Mar. Sci. Eng. 2019, 7(3), 67; https://doi.org/10.3390/jmse7030067
Received: 9 February 2019 / Revised: 1 March 2019 / Accepted: 12 March 2019 / Published: 15 March 2019
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Abstract
Many researchers have conducted experiments on the position and nozzle conditions in the exhaust pipe of a stage/swirl mixer, as well as the injection position required to satisfy the International Maritime Organisation (IMO) regulations. In this study, an SCR (Selective catalytic reduction) system [...] Read more.
Many researchers have conducted experiments on the position and nozzle conditions in the exhaust pipe of a stage/swirl mixer, as well as the injection position required to satisfy the International Maritime Organisation (IMO) regulations. In this study, an SCR (Selective catalytic reduction) system was designed through basic and detailed designs. The performance of the components was verified through a single-component performance test for the detailed design components, and the total nitrogen oxide (NOx) reduction efficiency was predicted using the proven system. Subsequently, the system was applied to an actual engine, and the performance was verified according to the engine operating conditions using the experimental variables. The NOx reduction rate and NH3 slip characteristics in relation to MCR (Maximum Continuous Rating) conditions using the optimised SCR system indicate that the NOx reduction rate exceeds 80% in all MCR conditions. Finally, the SCR system developed in this study proves that the performance of the SCR system satisfies the IMO regulatory requirements. Full article
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Open AccessArticle
Two-Dimensional Numerical Study of Seabed Response around a Buried Pipeline under Wave and Current Loading
J. Mar. Sci. Eng. 2019, 7(3), 66; https://doi.org/10.3390/jmse7030066
Received: 4 March 2019 / Revised: 8 March 2019 / Accepted: 8 March 2019 / Published: 13 March 2019
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Abstract
The evaluation of the wave-induced seabed response around a buried pipeline has been widely studied. However, the analysis of seabed response around marine structures under the wave and current loadings are still limited. In this paper, an integrated numerical model is proposed to [...] Read more.
The evaluation of the wave-induced seabed response around a buried pipeline has been widely studied. However, the analysis of seabed response around marine structures under the wave and current loadings are still limited. In this paper, an integrated numerical model is proposed to examine the wave and current-induced pore pressure generation, for instance, oscillatory and residual pore pressure, around a buried pipeline. The present wave–current model is based on the Reynolds-Averaged Navier–Stokes (RANS) equation with k - ε turbulence while Biot’s equation is adopted to govern the seabed model. Based on this numerical model, it is found that wave characteristics (i.e., wave period), current velocity and seabed characteristics such as soil permeability, relative density, and shear modulus have a significant effect on the generation of pore pressure around the buried pipeline. Full article
(This article belongs to the Special Issue Coastal Geohazard and Offshore Geotechnics)
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Open AccessArticle
Physical Modelling of Blue Mussel Dropper Lines for the Development of Surrogates and Hydrodynamic Coefficients
J. Mar. Sci. Eng. 2019, 7(3), 65; https://doi.org/10.3390/jmse7030065
Received: 30 December 2018 / Revised: 26 February 2019 / Accepted: 6 March 2019 / Published: 12 March 2019
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Abstract
In this work, laboratory tests with live bivalves as well as the conceptual design of additively manufactured surrogate models are presented. The overall task of this work is to develop a surrogate best fitting to the live mussels tested in accordance to the [...] Read more.
In this work, laboratory tests with live bivalves as well as the conceptual design of additively manufactured surrogate models are presented. The overall task of this work is to develop a surrogate best fitting to the live mussels tested in accordance to the identified surface descriptor, i.e., the Abbott–Firestone Curve, and to the hydrodynamic behaviour by means of drag and inertia coefficients. To date, very few investigations have focused on loads from currents as well as waves. Therefore, tests with a towing carriage were carried out in a wave flume. A custom-made rack using mounting clamps was built to facilitate carriage-run tests with minimal delays. Blue mussels (Mytilus edulis) extracted from a site in Germany, which were kept in aerated seawater to ensure their survival for the test duration, were used. A set of preliminary results showed drag and inertia coefficients C D and C M ranging from 1.16–3.03 and 0.25 to 1.25. To derive geometrical models of the mussel dropper lines, 3-D point clouds were prepared by means of 3-D laser scanning to obtain a realistic surface model. Centered on the 3-D point cloud, a suitable descriptor for the mass distribution over the surface was identified and three 3-D printed surrogates of the blue mussel were developed for further testing. These were evaluated regarding their fit to the original 3-D point cloud of the live blue mussels via the chosen surface descriptor. Full article
(This article belongs to the Special Issue Selected Papers from Coastlab18 Conference)
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Open AccessFeature PaperReview
Gravity-Based Foundations in the Offshore Wind Sector
J. Mar. Sci. Eng. 2019, 7(3), 64; https://doi.org/10.3390/jmse7030064
Received: 27 December 2018 / Revised: 20 January 2019 / Accepted: 24 January 2019 / Published: 12 March 2019
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Abstract
In recent years, the offshore wind industry has seen an important boost that is expected to continue in the coming years. In order for the offshore wind industry to achieve adequate development, it is essential to solve some existing uncertainties, some of which [...] Read more.
In recent years, the offshore wind industry has seen an important boost that is expected to continue in the coming years. In order for the offshore wind industry to achieve adequate development, it is essential to solve some existing uncertainties, some of which relate to foundations. These foundations are important for this type of project. As foundations represent approximately 35% of the total cost of an offshore wind project, it is essential that they receive special attention. There are different types of foundations that are used in the offshore wind industry. The most common types are steel monopiles, gravity-based structures (GBS), tripods, and jackets. However, there are some other types, such as suction caissons, tripiles, etc. For high water depths, the alternative to the previously mentioned foundations is the use of floating supports. Some offshore wind installations currently in operation have GBS-type foundations (also known as GBF: Gravity-based foundation). Although this typology has not been widely used until now, there is research that has highlighted its advantages over other types of foundation for both small and large water depth sites. There are no doubts over the importance of GBS. In fact, the offshore wind industry is trying to introduce improvements so as to turn GBF into a competitive foundation alternative, suitable for the widest ranges of water depth. The present article deals with GBS foundations. The article begins with the current state of the field, including not only the concepts of GBS constructed so far, but also other concepts that are in a less mature state of development. Furthermore, we also present a classification of this type of structure based on the GBS of offshore wind facilities that are currently in operation, as well as some reflections on future GBS alternatives. Full article
(This article belongs to the Special Issue Offshore Wind Farms)
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Open AccessArticle
Low-Cost UAV for High-Resolution and Large-Scale Coastal Dune Change Monitoring Using Photogrammetry
J. Mar. Sci. Eng. 2019, 7(3), 63; https://doi.org/10.3390/jmse7030063
Received: 31 January 2019 / Revised: 27 February 2019 / Accepted: 1 March 2019 / Published: 7 March 2019
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Abstract
In this paper, coastal dune data are collected at Truc Vert, SW France, using photogrammetry via Unmanned Aerial Vehicles (UAVs). A low-cost GoPro-equipped DJI Phantom 2 quadcopter and a 20 MPix camera-equipped DJI Phantom 4 Pro quadcopter UAVs were used to remotely sense [...] Read more.
In this paper, coastal dune data are collected at Truc Vert, SW France, using photogrammetry via Unmanned Aerial Vehicles (UAVs). A low-cost GoPro-equipped DJI Phantom 2 quadcopter and a 20 MPix camera-equipped DJI Phantom 4 Pro quadcopter UAVs were used to remotely sense the coastal dune morphology over large spatial scales (4 km alongshore, i.e., approximately 1 km2 of beach-dune system), within a short time (less than 2 h of flight). The primary objective of this paper is to propose a low-cost and replicable approach which, combined with simple and efficient permanent Ground Control Point (GCP) set-up, can be applied to routinely survey upper beach and coastal dune morphological changes at high frequency (after each storm) and high resolution (0.1 m). Results show that a high-resolution and accurate Digital Surface Model (DSM) can be inferred with both UAVs if enough permanent GCPs are implemented. The more recent DJI Phantom 4 gives substantially more accurate DSM with a root-mean-square vertical error and bias of 0.05 m and −0.03 m, respectively, while the DSM inferred from the DJI Phantom 2 still largely meets the standard for coastal monitoring. The automatic flight plan procedure allows replicable surveys to address large-scale morphological evolution at high temporal resolution (e.g., weeks, months), providing unprecedented insight into the coastal dune evolution driven by marine and aeolian processes. The detailed morphological evolution of a 4-km section of beach-dune system is analyzed over a 6-month winter period, showing highly alongshore variable beach and incipient foredune wave-driven erosion, together with wind-driven inland migration of the established foredune by a few meters, and alongshore-variable sand deposition on the grey dune. In a context of widespread erosion, this photogrammetry approach via low-cost flexible and lightweight UAVs is well adapted for coastal research groups and coastal dune management stakeholders, including in developing countries where data are lacking. Full article
(This article belongs to the Special Issue Application of Remote Sensing Methods to Monitor Coastal Zones)
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Open AccessArticle
Numerical and Experimental Study on Trimaran Cross-Deck Structure’s Fatigue Characteristics Based on the Spectral Fatigue Method
J. Mar. Sci. Eng. 2019, 7(3), 62; https://doi.org/10.3390/jmse7030062
Received: 25 January 2019 / Revised: 25 February 2019 / Accepted: 1 March 2019 / Published: 7 March 2019
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Abstract
Spectral fatigue analysis is performed on the trimaran cross-deck structural detail. A global finite element (FE) model with local fine meshes at hot spot locations is built for the calculation of structural response. Three-dimensional linear potential flow theory and global FE analysis are [...] Read more.
Spectral fatigue analysis is performed on the trimaran cross-deck structural detail. A global finite element (FE) model with local fine meshes at hot spot locations is built for the calculation of structural response. Three-dimensional linear potential flow theory and global FE analysis are used for wave load and stress transfer function calculations. Then, the hot spots’ fatigue damage is calculated, considering various factors influencing spectral analysis, which includes cycle counting correction factors, wave scatter diagram, and the distribution coefficient of wave headings. A full-scale model fatigue test is used to investigate the fatigue behavior of the cross-deck structural detail. Using the fatigue test data, the S - N curve characteristic of the cross-deck structural detail is produced. Finally, the trimaran cross-deck structural detail’s fatigue characteristics are summarized and the effects of the factors influencing spectral fatigue analysis are reported. Full article
(This article belongs to the Section Ocean Engineering)
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Open AccessArticle
Assessment of Sea Level Rise at West Coast of Portugal Mainland and Its Projection for the 21st Century
J. Mar. Sci. Eng. 2019, 7(3), 61; https://doi.org/10.3390/jmse7030061
Received: 11 February 2019 / Revised: 27 February 2019 / Accepted: 1 March 2019 / Published: 7 March 2019
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Abstract
Based on the updated relative sea level rise rates, 21st-century projections are made for the west coast of Portugal Mainland. The mean sea level from Cascais tide gauge and North Atlantic satellite altimetry data have been analyzed. Through bootstrapping linear regression and polynomial [...] Read more.
Based on the updated relative sea level rise rates, 21st-century projections are made for the west coast of Portugal Mainland. The mean sea level from Cascais tide gauge and North Atlantic satellite altimetry data have been analyzed. Through bootstrapping linear regression and polynomial adjustments, mean sea level time series were used to calculate different empirical projections for sea level rise, by estimating the initial velocity and its corresponding acceleration. The results are consistent with an accelerated sea level rise, showing evidence of a faster rise than previous century estimates. Based on different numerical methods of second order polynomial fitting, it is possible to build a set of projection models of relative sea level rise. Applying the same methods to regional sea level anomaly from satellite altimetry, additional projections are also built with good consistency. Both data sets, tide gauge and satellite altimetry data, enabled the development of an ensemble of projection models. The relative sea level rise projections are crucial for national coastal planning and management since extreme sea level scenarios can potentially cause erosion and flooding. Based on absolute vertical velocities obtained by integrating global sea level models, neo-tectonic studies, and permanent Global Positioning System (GPS) station time series, it is possible to transform relative into absolute sea level rise scenarios, and vice-versa, allowing the generation of absolute sea level rise projection curves and its comparison with already established global projections. The sea level rise observed at the Cascais tide gauge has always shown a significant correlation with global sea level rise observations, evidencing relatively low rates of vertical land velocity and residual synoptic regional dynamic effects. An ensemble of sea level projection models for the 21st century is proposed with its corresponding probability density function, both for relative and absolute sea level rise for the west coast of Portugal Mainland. A mean sea level rise of 1.14 m was obtained for the epoch of 2100, with a likely range of 95% of probability between 0.39 m and 1.89 m. Full article
(This article belongs to the Special Issue Numerical Models in Coastal Hazards and Coastal Environment)
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Open AccessArticle
Statistical Analysis of the Stability of Rock Slopes
J. Mar. Sci. Eng. 2019, 7(3), 60; https://doi.org/10.3390/jmse7030060
Received: 26 November 2018 / Revised: 26 February 2019 / Accepted: 1 March 2019 / Published: 6 March 2019
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Abstract
Physical model tests were performed in a wave flume at Deltares with rock armoured slopes. A shallow foreshore was present. At deep water, the same wave conditions were used, but by applying different water levels, the wave loading on the rock armoured slopes [...] Read more.
Physical model tests were performed in a wave flume at Deltares with rock armoured slopes. A shallow foreshore was present. At deep water, the same wave conditions were used, but by applying different water levels, the wave loading on the rock armoured slopes increased considerably with increasing water levels. This allowed an assessment of the effects of sea level rise. Damage was measured by using digital stereo photography (DSP), which provides information on each individual stone that is displaced. Two test series were performed five times. This allowed for a statistical analysis of the damage to rock armoured slopes, which is uncommon due to the absence of statistical information based on a systematic repetition of test series. The statistical analysis demonstrates the need for taking the mean damage into account in the design of rock armoured slopes. This is important in addition to characterising the damage itself by erosion areas and erosion depths. The relation between damage parameters, such as the erosion area and erosion depth, was obtained from the tests. Besides tests with a straight slope, tests with a berm in the seaward slopes were also performed. A new method to take the so-called length effect into account is proposed to extrapolate results from physical model tests to real structures. This length effect is important, but is normally overlooked in the design of rubble mound structures. Standard deviations based on the presented model tests were used. Full article
(This article belongs to the Special Issue Selected Papers from Coastlab18 Conference)
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Open AccessArticle
Observations and Modelling of Shoreface Nourishment Behaviour
J. Mar. Sci. Eng. 2019, 7(3), 59; https://doi.org/10.3390/jmse7030059
Received: 24 December 2018 / Revised: 21 February 2019 / Accepted: 23 February 2019 / Published: 4 March 2019
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Abstract
Shoreface nourishments are commonly applied for coastal maintenance, but their behaviour is not well understood. Bathymetric data of 19 shoreface nourishments located at alongshore uniform sections of the Dutch coast were therefore analyzed and used to validate an efficient method for predicting the [...] Read more.
Shoreface nourishments are commonly applied for coastal maintenance, but their behaviour is not well understood. Bathymetric data of 19 shoreface nourishments located at alongshore uniform sections of the Dutch coast were therefore analyzed and used to validate an efficient method for predicting the erosion of shoreface nourishments. Data shows that considerable cross-shore profile change takes place at a shoreface nourishment, while an impact at the adjacent coast is hard to distinguish. The considered shoreface nourishments provide a long-term (3 to ∼30 years) cross-shore supply of sediment to the beach, but with small impact on the local shoreline shape. An efficient modelling approach is presented using a lookup table filled with computed initial erosion–sedimentation rates for a range of potential environmental conditions at a single post-construction bathymetry. Cross-shore transport contributed the majority of the losses from the initial nourishment region. This transport was driven partly by water-level setup driven currents (e.g., rip currents) and increased velocity asymmetry of the waves due to the geometrical change at the shoreface nourishment. Most erosion of the nourishment takes place during energetic wave conditions ( H m 0 3 m) as milder waves are propagated over the nourishment without breaking. A data-model comparison shows that this approach can be used to accurately assess the erosion rates of shoreface nourishments in the first years after construction. Full article
(This article belongs to the Special Issue Large-scale Coastal Behavior)
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Open AccessArticle
Experimental Study and Estimation of Groundwater Fluctuation and Ground Settlement due to Dewatering in a Coastal Shallow Confined Aquifer
J. Mar. Sci. Eng. 2019, 7(3), 58; https://doi.org/10.3390/jmse7030058
Received: 18 February 2019 / Revised: 22 February 2019 / Accepted: 25 February 2019 / Published: 1 March 2019
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Abstract
The coastal micro-confined aquifer (MCA) in Shanghai is characterized by shallow burial depth, high artesian head, and discontinuous distribution. It has a significant influence on underground space development, especially where the MCA is directly connected with deep confined aquifers. In this paper, a [...] Read more.
The coastal micro-confined aquifer (MCA) in Shanghai is characterized by shallow burial depth, high artesian head, and discontinuous distribution. It has a significant influence on underground space development, especially where the MCA is directly connected with deep confined aquifers. In this paper, a series of pumping well tests were conducted in the MCA located in such area to investigate the dewatering-induced groundwater fluctuations and stratum deformation. In addition, a numerical method is proposed for the estimation of hydraulic parameter, and an empirical prediction method is developed for dewatering-induced ground settlement. Test results show that groundwater drawdowns and soil settlement can be observed not only in MCA but also in the aquifers underneath it. This indicates that there is a close hydraulic connection among each aquifer. Moreover, the distributions and development of soil settlement at various depths are parallel to those of groundwater drawdowns in most areas of the test site except the vicinity of pumping wells, where collapse-induced subsidence due to high-speed flow may occur. Furthermore, the largest deformation usually occurs at the top of the pumping aquifer instead of the ground surface, because the top layer is expanded due to the stress arch formed in it. Finally, the proposed methods are validated to be feasible according to the pumping well test results and can be employed to investigate the responses of groundwater fluctuations and stratum deformations due to dewatering in MCA. Full article
(This article belongs to the Special Issue Coastal Geohazard and Offshore Geotechnics)
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Open AccessArticle
2D Numerical Study of the Stability of Trench under Wave Action in the Immersing Process of Tunnel Element
J. Mar. Sci. Eng. 2019, 7(3), 57; https://doi.org/10.3390/jmse7030057
Received: 16 January 2019 / Revised: 14 February 2019 / Accepted: 14 February 2019 / Published: 27 February 2019
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Abstract
The evaluation of the trench stability under the action of ocean waves is an important issue in the construction of an immersed tunnel. In this study, a two-dimensional coupling model of a wave-seabed-immersed tunnel is proposed for the dynamic responses of a trench [...] Read more.
The evaluation of the trench stability under the action of ocean waves is an important issue in the construction of an immersed tunnel. In this study, a two-dimensional coupling model of a wave-seabed-immersed tunnel is proposed for the dynamic responses of a trench under wave action in the immersing process of tunnel elements. The porous seabed is characterized by Biot consolidation equations. The k ε model and RANS equation are adopted to achieve the flow field simulation, and the level set method (LSM) is used to capture the free surface between the water and air. The proposed numerical model is verified using the experimental data and analytical results. Then, the transient liquefaction and shear failure in the vicinity of the trench are discussed at two different conditions, namely, after the foundation groove is excavated and after the tunnel element is placed. The pore pressure amplitude on the weather side slope is demonstrated to be significantly smaller than that on the lee side slope. Also, the distribution of the surrounding flow field and pressure field change dramatically after the tunnel element is settled, leading to the significant changes of seabed stability. Full article
(This article belongs to the Special Issue Coastal Geohazard and Offshore Geotechnics)
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Open AccessArticle
Loads and Response of a Tension Leg Platform Wind Turbine with Non-Rotating Blades: An Experimental Study
J. Mar. Sci. Eng. 2019, 7(3), 56; https://doi.org/10.3390/jmse7030056
Received: 31 December 2018 / Revised: 20 February 2019 / Accepted: 22 February 2019 / Published: 27 February 2019
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Abstract
This paper describes model testing of a Tension Leg Platform Wind Turbine (TLPWT) with non-rotating blades to better understand its motion and tendon responses when subjected to combined wind and unidirectional regular wave conditions. The TLPWT structure is closely based on the National [...] Read more.
This paper describes model testing of a Tension Leg Platform Wind Turbine (TLPWT) with non-rotating blades to better understand its motion and tendon responses when subjected to combined wind and unidirectional regular wave conditions. The TLPWT structure is closely based on the National Renewable Energy Laboratory (NREL) 5 MW concept. Multiple free decay tests were performed to evaluate the natural periods of the model in the key degrees of freedom, whilst Response Amplitude Operators (RAOs) were derived to show the motion and tendon characteristics. The natural periods in surge and pitch motions evaluated from the decay tests had a relatively close agreement to the theoretical values. Overall, the tested TLPWT model exhibited typical motion responses to that of a generalised TLP with significant surge offsets along with stiff heave and pitch motions. The maximum magnitudes for the RAOs of surge motion and all tendons occurred at the longest wave period of 1.23 s (~13.0 s at full-scale) tested in this study. From the attained results, there was evidence that static wind loading on the turbine structure had some impact on the motions and tendon response, particularly in the heave direction, with an average increase of 13.1% in motion amplitude for the tested wind conditions. The wind had a negligible effect on the surge motion and slightly decreased the tendon tensions in all tendons. The results also showed the set-down magnitudes amounting to approximately 2–5% of the offset. Furthermore, the waves are the dominant factor contributing to the set-down of the TLPWT, with a minimal contribution from the static wind loading. The results of this study could be used for calibrating numerical tools such as CFD codes. Full article
(This article belongs to the Special Issue Offshore Wind Farms)
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Open AccessArticle
Influence of Underwater Bar Location on Cross-Shore Sediment Transport in the Coastal Zone
J. Mar. Sci. Eng. 2019, 7(3), 55; https://doi.org/10.3390/jmse7030055
Received: 31 December 2018 / Revised: 19 February 2019 / Accepted: 21 February 2019 / Published: 26 February 2019
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Abstract
The effect of the underwater bar position on a sandy beach profile was studied on a timescale of one storm, using the XBeach numerical model. The largest shoreline regress occurred in the first hour of storm. For the chosen wave regime an underwater [...] Read more.
The effect of the underwater bar position on a sandy beach profile was studied on a timescale of one storm, using the XBeach numerical model. The largest shoreline regress occurred in the first hour of storm. For the chosen wave regime an underwater profile close to the theoretical Dean’s equilibrium profile is formed after 6 h. The position of the underwater bar affects the shoreline retreat rate. The lowest shore retreat occurs when the bar crest is located at a distance equal to 0.70–0.82 of the deep-water wavelength, corresponding to the period of the wave spectrum peak. The maximal shoreline retreat occurs when the bar is located at a distance that is close to a half wavelength. The shoreline recession depends on the heights of low-frequency waves. The smaller the mean wave period and the higher low-frequency waves’ height near the coast, the smaller the retreat of the shoreline. The distance of seaward sediment transfer is directly proportional to the significant wave height near shore. Full article
(This article belongs to the Special Issue Marine Sediments: Processes, Transport and Environmental Aspects)
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