Next Issue
Previous Issue

Table of Contents

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

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
Cover Story (view full-size image) Accurate numerical prediction of the flow characteristics near a marine propeller and in its wake [...] Read more.
View options order results:
result details:
Displaying articles 1-45
Export citation of selected articles as:
Open AccessArticle Analysis of Different Methods for Wave Generation and Absorption in a CFD-Based Numerical Wave Tank
J. Mar. Sci. Eng. 2018, 6(2), 73; https://doi.org/10.3390/jmse6020073
Received: 30 April 2018 / Revised: 6 June 2018 / Accepted: 10 June 2018 / Published: 14 June 2018
PDF Full-text (4083 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, the performance of different wave generation and absorption methods in computational fluid dynamics (CFD)-based numerical wave tanks (NWTs) is analyzed. The open-source CFD code REEF3D is used, which solves the Reynolds-averaged Navier–Stokes (RANS) equations to simulate two-phase flow problems. The
[...] Read more.
In this paper, the performance of different wave generation and absorption methods in computational fluid dynamics (CFD)-based numerical wave tanks (NWTs) is analyzed. The open-source CFD code REEF3D is used, which solves the Reynolds-averaged Navier–Stokes (RANS) equations to simulate two-phase flow problems. The water surface is computed with the level set method (LSM), and turbulence is modeled with the k-ω model. The NWT includes different methods to generate and absorb waves: the relaxation method, the Dirichlet-type method and active wave absorption. A sensitivity analysis has been conducted in order to quantify and compare the differences in terms of absorption quality between these methods. A reflection analysis based on an arbitrary number of wave gauges has been adopted to conduct the study. Tests include reflection analysis of linear, second- and fifth-order Stokes waves, solitary waves, cnoidal waves and irregular waves generated in an NWT. Wave breaking over a sloping bed and wave forces on a vertical cylinder are calculated, and the influence of the reflections on the wave breaking location and the wave forces on the cylinder is investigated. In addition, a comparison with another open-source CFD code, OpenFOAM, has been carried out based on published results. Some differences in the calculated quantities depending on the wave generation and absorption method have been observed. The active wave absorption method is seen to be more efficient for long waves, whereas the relaxation method performs better for shorter waves. The relaxation method-based numerical beach generally results in lower reflected waves in the wave tank for most of the cases simulated in this study. The comparably better performance of the relaxation method comes at the cost of larger computational requirements due to the relaxation zones that have to be included in the domain. The reflections in the NWT in REEF3D are generally lower than the published results for reflections using the active wave absorption method in the NWT based on OpenFOAM. Full article
(This article belongs to the Special Issue Advances in Ocean Wave Energy Conversion)
Figures

Figure 1

Open AccessArticle Obtaining Reflection Coefficients from a Single Point Velocity Measurement
J. Mar. Sci. Eng. 2018, 6(2), 72; https://doi.org/10.3390/jmse6020072
Received: 11 May 2018 / Revised: 6 June 2018 / Accepted: 8 June 2018 / Published: 13 June 2018
PDF Full-text (987 KB) | HTML Full-text | XML Full-text
Abstract
The quantification of the reflection of water waves is of paramount importance in coastal and marine engineering. Reflected waves are produced as a result of an incident wave meeting a reflective boundary e.g., in a wave basin. While reflection can be seen as
[...] Read more.
The quantification of the reflection of water waves is of paramount importance in coastal and marine engineering. Reflected waves are produced as a result of an incident wave meeting a reflective boundary e.g., in a wave basin. While reflection can be seen as an undesirable disturbance, for example in experimental tests performed in confined tanks, it can also have a useful purpose such as being directed towards wave energy converters (WECs). Whether useful or not, reflection needs to be accurately quantified. For cases effected by directional spreading such as WECs, the wave height of a reflected wave will be spatially variable. The majority of quantification methods are based on frequency domain analysis of surface elevation data at more than one discrete location over approximately one wavelength. Thus, a method which requires a single point measurement is desirable. This paper presents a novel method derived from Linear Wave theory to quantify reflection coefficients using orbital velocity measurements at one discrete location. An additional advantage of this method is it only requires data over a single wave cycle and thus will be particularly suitable for numerical simulations. In the present form the method is only applicable to monochromatic waves. The theoretical background of the method is explained in detail. An application is demonstrated through a comparison to reflections quantified using surface elevation measurements in Computational Fluid Dynamics (CFD) numerical simulations. It is found that the results of the new proposed method compare to surface elevation methods within the levels of experimental accuracy. Full article
(This article belongs to the Section Ocean Engineering)
Figures

Figure 1

Open AccessArticle Numerical Simulation and Uncertainty Analysis of an Axial-Flow Waterjet Pump
J. Mar. Sci. Eng. 2018, 6(2), 71; https://doi.org/10.3390/jmse6020071
Received: 30 March 2018 / Revised: 1 June 2018 / Accepted: 5 June 2018 / Published: 11 June 2018
Cited by 1 | PDF Full-text (9828 KB) | HTML Full-text | XML Full-text
Abstract
Unsteady Reynolds-averaged Navier–Stokes simulations of an axial-flow pump for waterjet propulsion are carried out at model scale, and the numerical uncertainties are analyzed mainly according to the procedure recommended by the twenty-eighth International Towing Tank Conference. The two-layer realizable k-ε model is
[...] Read more.
Unsteady Reynolds-averaged Navier–Stokes simulations of an axial-flow pump for waterjet propulsion are carried out at model scale, and the numerical uncertainties are analyzed mainly according to the procedure recommended by the twenty-eighth International Towing Tank Conference. The two-layer realizable k-ε model is adopted for turbulence closure, and the flow in viscous sub-layer is resolved. The governing equations are discretized with second-order schemes in space and first-order scheme in time and solved by the semi-implicit method for pressure-linked equations. The computational domain is discretized into block-structured hexahedral cells. For an axial-flow pump consisting of a seven-bladed rotor and a nine-bladed stator, the uncertainty analysis is conducted by using three sets of successively refined grids and time steps. In terms of the head and power over a range of flow rates, it is verified that the simulation uncertainty is less than 4.3%, and the validation is successfully achieved at an uncertainty level of 4.4% except for the lowest flow rate. Besides this, the simulated flow features around rotor blade tips and between the stator and rotor blade rows are investigated. Full article
(This article belongs to the Special Issue Marine Propulsors)
Figures

Figure 1

Open AccessArticle Frequency Analysis of Storm-Surge-Induced Flooding for the Huangpu River in Shanghai, China
J. Mar. Sci. Eng. 2018, 6(2), 70; https://doi.org/10.3390/jmse6020070
Received: 14 May 2018 / Revised: 1 June 2018 / Accepted: 5 June 2018 / Published: 11 June 2018
PDF Full-text (8537 KB) | HTML Full-text | XML Full-text
Abstract
Shanghai, as a coastal city, is vulnerable to various types of flooding. The floodwalls along the Huangpu River provide protection against typhoon-induced flooding. However, there is limited insight into the actual safety level of the flood defences in Shanghai, and recent failures have
[...] Read more.
Shanghai, as a coastal city, is vulnerable to various types of flooding. The floodwalls along the Huangpu River provide protection against typhoon-induced flooding. However, there is limited insight into the actual safety level of the flood defences in Shanghai, and recent failures have highlighted their vulnerability. Therefore, the aims of this paper are to derive a series of new flood frequency curves for the Huangpu River, and to evaluate the level of protection of the floodwall system. This paper analysed over 100 years (1912–2013) of annual maximum water levels for three stations at near-sea, mid-stream and inland locations along the Huangpu River. Best-fit curves were determined for a number of selected probability distributions using statistical performance indicators. As a result, new flood frequency curves of the water levels for different storm surge return periods were produced. The results showed that generalised extreme value (GEV) was identified as the most suitable probability distribution for the datasets. Analysis showed that the current design water levels correspond to exceedance probabilities of 1/500 per year at the near-sea and mid-stream stations, and no more than 1/50 per year at the inland station of the Huangpu River, whereas the intended safety standard is 1/1000 per year. A comparison of the findings with a dataset of the crest heights of the floodwalls showed that the current protection level of the floodwalls along the Huangpu River is expected to be around 1/50 per year in terms of overtopping for the lowest sections. The results of this study can be utilized to provide future recommendations for flood risk management in Shanghai. Full article
(This article belongs to the Special Issue Coastal Hazards Related to Water)
Figures

Figure 1

Open AccessFeature PaperArticle Ballast Water Management in the Black Sea’s Ports
J. Mar. Sci. Eng. 2018, 6(2), 69; https://doi.org/10.3390/jmse6020069
Received: 9 May 2018 / Revised: 30 May 2018 / Accepted: 7 June 2018 / Published: 9 June 2018
PDF Full-text (942 KB) | HTML Full-text | XML Full-text
Abstract
The objective of this work is to develop a case study in order to improve the ballast water management in the Black Sea’s ports. From this perspective, the present paper provides an extensive explanation about the main issues related to the control of
[...] Read more.
The objective of this work is to develop a case study in order to improve the ballast water management in the Black Sea’s ports. From this perspective, the present paper provides an extensive explanation about the main issues related to the control of marine non-indigenous species introduction through ballast water discharged by ships during their operations in the ports. Thereafter, it quantifies the amount of the ballast water discharged in the major ports of the Black Sea and the amount of the invading species that could reach these ports. Although, globally speaking, the problem of ballast water management is a reality, only three of the six neighboring countries in the Black Sea basin have signed, in 2004, the ratification of the International Convention on Management of Ships’ Ballast Water and Sediments. This is also known as the Water Ballast Management Convention, and it provides regulations concerning ballast water management generated by the shipping activities through a common set of rules. Full article
(This article belongs to the Section Ocean Engineering)
Figures

Figure 1

Open AccessFeature PaperArticle Seiching Induced by Bichromatic and Monochromatic Wave Conditions: Experimental and Numerical Analysis in a Large Wave Flume
J. Mar. Sci. Eng. 2018, 6(2), 68; https://doi.org/10.3390/jmse6020068
Received: 27 April 2018 / Revised: 30 May 2018 / Accepted: 1 June 2018 / Published: 6 June 2018
PDF Full-text (8358 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes a set of spectral and eigen analysis in order to identify seiche generation from a large-scale laboratory dataset. The experiments were performed in the large-scale “Canal d’Investigació i Experimentació Marítima” wave flume at the Universitat Politècnica de Catalunya in Spain.
[...] Read more.
This paper describes a set of spectral and eigen analysis in order to identify seiche generation from a large-scale laboratory dataset. The experiments were performed in the large-scale “Canal d’Investigació i Experimentació Marítima” wave flume at the Universitat Politècnica de Catalunya in Spain. Erosive and accretive wave regimes have been analyzed, including monochromatic waves and bichromatic wave groups with different bandwidths. Each test started with approximately the same underlying beach conditions. Video runup measurements are also used to better understand the role of the bandwidth in the generation of swash oscillation. Some evidence of the influence of low frequency waves on runup and sediment transport pattern is found. Good agreements between eigenmode families for volume flux and sediment volume variations are also shown. Full article
(This article belongs to the Section Ocean Engineering)
Figures

Figure 1

Open AccessArticle Boundary Element Modelling Aspects for the Hydro-Elastic Analysis of Flexible Marine Propellers
J. Mar. Sci. Eng. 2018, 6(2), 67; https://doi.org/10.3390/jmse6020067
Received: 10 April 2018 / Revised: 30 May 2018 / Accepted: 1 June 2018 / Published: 5 June 2018
Cited by 1 | PDF Full-text (995 KB) | HTML Full-text | XML Full-text
Abstract
Boundary element methods (BEM) have been used for propeller hydrodynamic calculations since the 1990s. More recently, these methods are being used in combination with finite element methods (FEM) in order to calculate flexible propeller fluid–structure interaction (FSI) response. The main advantage of using
[...] Read more.
Boundary element methods (BEM) have been used for propeller hydrodynamic calculations since the 1990s. More recently, these methods are being used in combination with finite element methods (FEM) in order to calculate flexible propeller fluid–structure interaction (FSI) response. The main advantage of using BEM for flexible propeller FSI calculations is the relatively low computational demand in comparison with higher fidelity methods. However, the BEM modelling of flexible propellers is not straightforward and requires several important modelling decisions. The consequences of such modelling choices depend significantly on propeller structural behaviour and flow condition. The two dimensionless quantities that characterise structural behaviour and flow condition are the structural frequency ratio (the ratio between the lowest excitation frequency and the fundamental wet blade natural frequency) and the reduced frequency. For both, general expressions have been derived for (flexible) marine propellers. This work shows that these expressions can be effectively used to estimate the dry and wet fundamental blade frequencies and the structural frequency ratio. This last parameter and the reduced frequency of vibrating blade flows is independent of the geometrical blade scale as shown in this work. Regarding the BEM-FEM coupled analyses, it is shown that a quasi-static FEM modelling does not suffice, particularly due to the fluid-added mass and hydrodynamic damping contributions that are not negligible. It is demonstrated that approximating the hydro-elastic blade response by using closed form expressions for the fluid added mass and hydrodynamic damping terms provides reasonable results, since the structural response of flexible propellers is stiffness dominated, meaning that the importance of modelling errors in fluid added mass and hydrodynamic damping is small. Finally, it is shown that the significance of recalculating the hydrodynamic influence coefficients is relatively small. This fact might be utilized, possibly in combination with the use of the closed form expressions for fluid added mass and hydrodynamic damping contributions, to significantly reduce the computation time of flexible propeller FSI calculations. Full article
(This article belongs to the Special Issue Marine Propulsors)
Figures

Figure 1

Open AccessFeature PaperArticle Modelling Hydrodynamic Impacts of Sea-Level Rise on Wave-Dominated Australian Estuaries with Differing Geomorphology
J. Mar. Sci. Eng. 2018, 6(2), 66; https://doi.org/10.3390/jmse6020066
Received: 20 April 2018 / Revised: 21 May 2018 / Accepted: 31 May 2018 / Published: 5 June 2018
PDF Full-text (4626 KB) | HTML Full-text | XML Full-text
Abstract
Sea-level rise (SLR) will affect the hydrodynamics and flooding characteristics of estuaries which are a function of the geomorphology of particular estuarine systems. This study presents a numerical modelling of coastal flooding due to drivers such as spring-tides, storm surges and river inflows
[...] Read more.
Sea-level rise (SLR) will affect the hydrodynamics and flooding characteristics of estuaries which are a function of the geomorphology of particular estuarine systems. This study presents a numerical modelling of coastal flooding due to drivers such as spring-tides, storm surges and river inflows and examines how these will change under sea-level increases of 0.4 m and 0.9 m for two estuaries that are at different geomorphological evolutionary stages of infill. Our results demonstrate that estuarine response to SLR varies between different types of estuaries, and detailed modelling is necessary to understand the nature and extent of inundation in response to SLR. Comparison of modelling results indicates that floodplain elevation is fundamental in order to identify the most vulnerable systems and estimate how inundation extents and depths may change in the future. Floodplains in mature estuarine systems may drown and experience a considerable increase in inundation depths once a certain threshold in elevation has been exceeded. By contrast, immature estuarine systems may be subject to increases in relative inundation extent and substantial changes in hydrodynamics such as tidal range and current velocity. The unique nature of estuaries does not allow for generalisations; however, classifications of estuarine geomorphology could indicate how certain types of estuary may respond to SLR. Full article
(This article belongs to the Special Issue Climate Change, Coasts and Coastal Risk)
Figures

Figure 1

Open AccessFeature PaperArticle Exchange Flow Variability between Hypersaline Shark Bay and the Ocean
J. Mar. Sci. Eng. 2018, 6(2), 65; https://doi.org/10.3390/jmse6020065
Received: 22 May 2018 / Revised: 22 May 2018 / Accepted: 29 May 2018 / Published: 1 June 2018
PDF Full-text (7571 KB) | HTML Full-text | XML Full-text
Abstract
In Shark Bay, a large hypersaline bay in Western Australia, longitudinal density gradients force gravitational circulation that is important for Bay-ocean exchange. First-time observations of vertical stratification and velocity are presented, confirming the presence of a steady, near-bed dense water outflow from Shark
[...] Read more.
In Shark Bay, a large hypersaline bay in Western Australia, longitudinal density gradients force gravitational circulation that is important for Bay-ocean exchange. First-time observations of vertical stratification and velocity are presented, confirming the presence of a steady, near-bed dense water outflow from Shark Bay’s northern Geographe Channel that persisted through all stages of the tide. Outflow velocities were 2–3 times stronger than the outflows recorded previously in Naturaliste Channel (in the west), and were more resistant to breakdown by tidal mixing. Estimates of turbulent kinetic energy production derived from the variance method showed a more complex structure in the Geographe Channel, due to shear between surface and bottom layers. Turbulence varied between flood and ebb tide, with peak levels of turbulence occurring during reversal of tidal flows. For both channels, the main source of turbulence was tidal flow along the seabed, with the bottom current speed cubed, |Ub3|, providing a reasonable proxy for tidal mixing and prediction of dense water outflows from Shark Bay majority of the time. Orientation and deeper water of the Geographe Channel along the main axis of the longitudinal density gradient provided an explanation for the predominant outflow from the Bay’s northern entrance. These density-driven currents could potentially influence recruitment of commercially fished scallops and prawns through the dispersal and flushing of larvae. Full article
(This article belongs to the Section Physical Oceanography)
Figures

Figure 1

Open AccessArticle Coastal Defence Integrating Wave-Energy-Based Desalination: A Case Study in Madagascar
J. Mar. Sci. Eng. 2018, 6(2), 64; https://doi.org/10.3390/jmse6020064
Received: 10 April 2018 / Revised: 9 May 2018 / Accepted: 25 May 2018 / Published: 1 June 2018
PDF Full-text (3259 KB) | HTML Full-text | XML Full-text
Abstract
In arid, coastal cities, water demand is often met through large-scale desalination systems. However, the energy required to run desalination plants remains a drawback. Further, numerous low-density population areas lack not only fresh water availability, but in most of the cases electrical grid
[...] Read more.
In arid, coastal cities, water demand is often met through large-scale desalination systems. However, the energy required to run desalination plants remains a drawback. Further, numerous low-density population areas lack not only fresh water availability, but in most of the cases electrical grid connection or any other energy source as well. The challenge, consequently, is to ensure adequate fresh water supplies at the lowest possible cost. The main objective of this work is to assess the freshwater production from a reverse osmosis desalination system powered by a wave energy converter, the Overtopping Breakwater for Wave Energy Conversion (OBREC). The desktop analysis is illustrated through a case study on the Fenoarivo Atsinanana coast, along north-eastern Madagascar. The novel aspect of the analysis method is the application of a specific numerical code calibrated using preliminary results from a two-year monitoring campaign of the first OBREC prototype in operation in Naples Harbour (Italy). Instead of dissipating the incoming wave energy, the system collects the overtopping water above the sea level and the potential energy is converted into electricity through low head turbines. Then, the flow will be driven towards the desalination system. This configuration seems like a promising opportunity for developing countries to meet their water supply needs while at the same time developing their renewable energy potential. Full article
(This article belongs to the Section Ocean Engineering)
Figures

Figure 1

Open AccessArticle The Anticipation of the ENSO: What Resonantly Forced Baroclinic Waves Can Teach Us (Part II)
J. Mar. Sci. Eng. 2018, 6(2), 63; https://doi.org/10.3390/jmse6020063
Received: 27 April 2018 / Revised: 19 May 2018 / Accepted: 25 May 2018 / Published: 1 June 2018
Cited by 2 | PDF Full-text (2992 KB) | HTML Full-text | XML Full-text
Abstract
The purpose of the paper is to take advantage of recent work on the study of resonantly forced baroclinic waves in the tropical Pacific to significantly reduce systematic and random forecasting errors resulting from the current statistical models intended to predict El Niño.
[...] Read more.
The purpose of the paper is to take advantage of recent work on the study of resonantly forced baroclinic waves in the tropical Pacific to significantly reduce systematic and random forecasting errors resulting from the current statistical models intended to predict El Niño. Their major drawback is that sea surface temperature (SST), which is widely used, is very difficult to decipher because of the extreme complexity of exchanges at the ocean-atmosphere interface. In contrast, El Niño-Southern Oscillation (ENSO) forecasting can be performed between 7 and 8 months in advance precisely and very simply from (1) the subsurface water temperature at particular locations and (2) the time lag of the events (their expected date of occurrence compared to a regular 4-year cycle). Discrimination of precursor signals from objective criteria prevents the anticipation of wrong events, as occurred in 2012 and 2014. The amplitude of the events, their date of appearance, as well as their potential impact on the involved regions are estimated. Three types of ENSO events characterize their climate impact according to whether they are (1) unlagged or weakly lagged, (2) strongly lagged, or (3) out of phase with the annual quasi-stationary wave (QSW) (Central Pacific El Niño events). This substantial progress is based on the analysis of baroclinic QSWs in the tropical basin and the resulting genesis of ENSO events. As for cold events, the amplification of La Niña can be seen a few months before the maturation phase of an El Niño event, as occurred in 1998 and 2016. Full article
(This article belongs to the Section Physical Oceanography)
Figures

Figure 1

Open AccessArticle Implementation of an Implicit Solver in ADCIRC Storm Surge Model
J. Mar. Sci. Eng. 2018, 6(2), 62; https://doi.org/10.3390/jmse6020062
Received: 30 April 2018 / Revised: 24 May 2018 / Accepted: 25 May 2018 / Published: 1 June 2018
PDF Full-text (12019 KB) | HTML Full-text | XML Full-text
Abstract
The current state of science does not offer any remedy to stop a hurricane from occurring. Therefore, accurate storm surge models capable of predicting water velocity and elevation are indispensable. In this paper, the implementation of an implicit solver in the Advanced Circulation
[...] Read more.
The current state of science does not offer any remedy to stop a hurricane from occurring. Therefore, accurate storm surge models capable of predicting water velocity and elevation are indispensable. In this paper, the implementation of an implicit solver in the Advanced Circulation (ADCIRC) storm surge model is presented. The implemented implicit solver uses hybrid finite element and finite volume techniques for solving shallow water equations. Objectives of this research include: Enhancing numerical stability, providing an option of using large timesteps, and the usage of a relatively easier mathematical formulation than the existing one in ADCIRC. The storm surge hindcast of Hurricane Katrina that hit Louisiana and Mississippi in 2005 is used as a case study. Stability of the solver, comparison of water elevation and velocity against observed data, impact of timestep sizes, and execution times of solvers are thoroughly investigated in this study. Results of the implemented implicit solver are compared with those of existing lumped explicit and semi-implicit solvers of ADCIRC; the findings appear to be very promising. Full article
Figures

Figure 1a

Open AccessArticle Optimal Transmission of Interface Vibration Wavelets—A Simulation of Seabed Seismic Responses
J. Mar. Sci. Eng. 2018, 6(2), 61; https://doi.org/10.3390/jmse6020061
Received: 19 April 2018 / Revised: 11 May 2018 / Accepted: 12 May 2018 / Published: 29 May 2018
PDF Full-text (6798 KB) | HTML Full-text | XML Full-text
Abstract
Seismic interface waves generated by seabed impacts are believed to have biological importance. Previous work on the effects of ocean piling and dredging studied water motion adjacent to the seabed, using sediment measurements as reviewed in the literature. This new modelling work has
[...] Read more.
Seismic interface waves generated by seabed impacts are believed to have biological importance. Previous work on the effects of ocean piling and dredging studied water motion adjacent to the seabed, using sediment measurements as reviewed in the literature. This new modelling work has idealised the sediment data to a simple model with few parameters, and has shown how this leads to filtration of the applied energy to propagate simple seismic vibration wavelets. These special wavelets remain compact with high peak levels of the associated water particle velocity as they ripple outward, and provide a means of assessing the worst-case environmental impact. The form of this wavelet morphs from a hump shape to a dip and back, via intermediate forms which are here described in mathematical terms based on the Ricker form. Whilst the model structure is idealised it is much closer to reality than the Rayleigh and Scholte half-space models, but with only two more parameters required. The resultant wavelet peaks are propagated with values given by the optimal limit case of cylindrical spreading (ignoring absorption) which results in a relatively widespread impact. Full article
Figures

Figure 1

Open AccessArticle The Effect of Propeller Scaling Methodology on the Performance Prediction
J. Mar. Sci. Eng. 2018, 6(2), 60; https://doi.org/10.3390/jmse6020060
Received: 28 February 2018 / Revised: 27 April 2018 / Accepted: 4 May 2018 / Published: 24 May 2018
Cited by 1 | PDF Full-text (380 KB) | HTML Full-text | XML Full-text
Abstract
In common model testing practise, the measured values of the self propulsion test are split into the characteristics of the hull, the propeller and into the interaction factors. These coefficients are scaled separately to the respective full scale values and subsequently reassembled to
[...] Read more.
In common model testing practise, the measured values of the self propulsion test are split into the characteristics of the hull, the propeller and into the interaction factors. These coefficients are scaled separately to the respective full scale values and subsequently reassembled to give the power prediction. The accuracy of this power prediction depends inter alia on the accuracy of the measured values and the scaling procedure. An inherent problem of this approach is that it is virtually impossible to verify each single step, because of the complex nature of the underlying problem. In recent years the scaling of the open-water characteristics of propeller model tests attracted a renewed interest, fuelled by competitive tests, which became the norm due to requests of the customer. This paper shows the influence of different scaling procedures on the predicted power. The prediction is compared to the measured trials data and the quality of the prediction is judged. The procedures examined are the standard ITTC 1978 procedure plus derivatives of it, the Meyne method, the strip method developed by the Hamburgische Schiffbau-Versuchsanstalt (HSVA) and the β i -method by Helma. Full article
(This article belongs to the Special Issue Marine Propulsors)
Figures

Figure 1

Open AccessArticle Projected 21st Century Coastal Flooding in the Southern California Bight. Part 1: Development of the Third Generation CoSMoS Model
J. Mar. Sci. Eng. 2018, 6(2), 59; https://doi.org/10.3390/jmse6020059
Received: 24 April 2018 / Revised: 11 May 2018 / Accepted: 11 May 2018 / Published: 24 May 2018
Cited by 1 | PDF Full-text (7006 KB) | HTML Full-text | XML Full-text
Abstract
Due to the effects of climate change over the course of the next century, the combination of rising sea levels, severe storms, and coastal change will threaten the sustainability of coastal communities, development, and ecosystems as we know them today. To clearly identify
[...] Read more.
Due to the effects of climate change over the course of the next century, the combination of rising sea levels, severe storms, and coastal change will threaten the sustainability of coastal communities, development, and ecosystems as we know them today. To clearly identify coastal vulnerabilities and develop appropriate adaptation strategies due to projected increased levels of coastal flooding and erosion, coastal managers need local-scale hazards projections using the best available climate and coastal science. In collaboration with leading scientists world-wide, the USGS designed the Coastal Storm Modeling System (CoSMoS) to assess the coastal impacts of climate change for the California coast, including the combination of sea-level rise, storms, and coastal change. In this project, we directly address the needs of coastal resource managers in Southern California by integrating a vast range of global climate change projections in a thorough and comprehensive numerical modeling framework. In Part 1 of a two-part submission on CoSMoS, methods and the latest improvements are discussed, and an example of hazard projections is presented. Full article
(This article belongs to the Special Issue Climate Change, Coasts and Coastal Risk)
Figures

Figure 1

Open AccessArticle Using Coupled Hydrodynamic Biogeochemical Models to Predict the Effects of Tidal Turbine Arrays on Phytoplankton Dynamics
J. Mar. Sci. Eng. 2018, 6(2), 58; https://doi.org/10.3390/jmse6020058
Received: 3 April 2018 / Revised: 14 May 2018 / Accepted: 17 May 2018 / Published: 22 May 2018
PDF Full-text (3770 KB) | HTML Full-text | XML Full-text
Abstract
The effects of large scale tidal energy device (TED) arrays on phytoplankton processes owing to the changes in hydrodynamic flows are unknown. Coupled two-dimensional biogeochemical and hydrodynamic models offer the opportunity to predict potential effects of large scale TED arrays on the local
[...] Read more.
The effects of large scale tidal energy device (TED) arrays on phytoplankton processes owing to the changes in hydrodynamic flows are unknown. Coupled two-dimensional biogeochemical and hydrodynamic models offer the opportunity to predict potential effects of large scale TED arrays on the local and regional phytoplankton dynamics in coastal and inshore environments. Using MIKE 21 Software by DHI (https://www.dhigroup.com), coupled two-dimensional biogeochemical and hydrodynamic models were developed with simulations including no turbines or an array of 55 turbines with four solar radiation scenarios to assess the temporal and spatial changes of phytoplankton dynamics in an idealised domain. Results suggest that the effect of TEDs on phytoplankton dynamics accounted for up to 25% of the variability in phytoplankton concentrations, most likely associated with an increased residence time in an inshore basin. However, natural variation, such as the intensity of photosynthetically active radiation, had a larger effect on phytoplankton dynamics than an array of TEDs. Full article
Figures

Figure 1

Open AccessEditorial Announcing the 2018 JMSE Travel Awards for Postdoctoral Researchers and Ph.D. Students
J. Mar. Sci. Eng. 2018, 6(2), 57; https://doi.org/10.3390/jmse6020057
Received: 18 May 2018 / Revised: 18 May 2018 / Accepted: 18 May 2018 / Published: 22 May 2018
PDF Full-text (545 KB) | HTML Full-text | XML Full-text Figures

Figure 1

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
Received: 29 March 2018 / Revised: 23 April 2018 / Accepted: 3 May 2018 / Published: 21 May 2018
Cited by 1 | PDF Full-text (16667 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

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
PDF Full-text (8321 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

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
PDF Full-text (15433 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

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
Cited by 1 | PDF Full-text (4062 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

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
Cited by 1 | PDF Full-text (4576 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

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
Cited by 3 | PDF Full-text (12339 KB) | HTML Full-text | XML Full-text
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.
[...] Read more.
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)
Figures

Figure 1

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
PDF Full-text (3599 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

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
Cited by 1 | PDF Full-text (5459 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

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
PDF Full-text (2974 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

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
PDF Full-text (3268 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

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
Cited by 1 | PDF Full-text (14699 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

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
Cited by 1 | PDF Full-text (4050 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

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
PDF Full-text (7874 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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)
Figures

Figure 1

Back to Top