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The characteristics of coherent structures in turbulent boundary layers were investigated experimentally using PIV and hydrogen bubble visualisation techniques. Turbulent boundary layers were generated and tested in two flumes with different scale, for two Reynolds numbers: $$\hbox {Re}=32{,}000$$ and 71,200, both over a smooth bed. Measurements from the PIV technique and hydrogen bubble visualisation lead to the same research findings, suggesting a linear relationship between the instantaneous integral spatial scale and the instantaneous spacing between turbulent streaks. This new approach to determining the streak spacing provides some guidance for experimentalists in terms of experimental methodology. Results of hydrogen bubble visualisations provide additional evidence that streamwise vortices reside near low-speed streaks. Detailed statistical analysis further demonstrates the better performance of Burr distribution for the probability density function of streak spacing. Combining the measurements of flow field in the horizontal and vertical plane, streamwise vortices are observed to be tilted $$\pm ~8^\circ $$ in the (x, z) plane and shear layers are inclined to the wall at $$30^\circ $$ in the (x, y) plane.

This paper sheds light on the mechanism of post equilibrium sea bed scour around dynamically active marine structures such as wind turbines. Exposure of a fully developed scour hole (at equ...

Vertical surface piercing cylinders, such as typical coastal wind turbine foundations and basic elements of many coastal structures, are often exposed to combined loading from waves and currents. Accurate prediction of hydrodynamic loads on a vertical cylinder in a combined wave-current flow is a challenging task. This work describes and compares two different approaches for numerical modelling of the interaction between focussed wave groups and a sheared current, and then their interactions with a vertical piercing cylinder. Both approaches employ an empirical methodology to generate a wave focussed at the location of the structure in the presence of sheared currents and use OpenFOAM, an open source Computational Fluid Dynamics (CFD) package. In the first approach, the empirical wave-on-current focussing methodology is applied directly in the OpenFOAM domain, replicating the physical wave-current flume. This approach is referred to as the Direct Method. In the second approach, a novel Lagrangian model is used to calculate the free surface elevation and flow kinematics, which are then used as boundary conditions for a smaller 3-D OpenFOAM domain with shorter simulation time. This approach is referred to as the Coupling Method. The capabilities of the two numerical methods have been validated by comparing with the experimental measurements collected in a wave-current flume at UCL. The performance of both approaches is evaluated in terms of accuracy and computational effort required. It is shown that both approaches provide satisfactory predictions in terms of local free surface elevation and nonlinear wave loading on the vertical cylinders with an acceptable level of computational cost. The Coupling Method is more efficient because of the use of a smaller computational domain and the application of the iterative wave-current generation in the faster Lagrangian model. Additionally, it is shown that a Stokes-type perturbation expansion can be generalized to approximate cylinder loads arising from wave groups on following and adverse sheared currents, allowing estimation of the higher-order harmonic shapes and time histories from knowledge of the linear components alone.

This paper highlights the importance of spilling breaking waves in the design of offshore structures. Although wave loading on offshore structures due to non-breaking waves has been extensively studied, wave loading due to breaking waves is uncertain and not very well understood. Plunging breaking waves in deep water are very unusual, whereas spilling breaking waves are very common in extreme seas. Nevertheless, no significant research efforts have been made to study the effects of spilling breaking waves. The present study addresses this, comparing the wave loading from highly nonlinear non-breaking waves and spilling breaking waves. Focused wave groups have been used to generate the non-breaking and spilling breaking wave conditions in a wave tank. The experiments have shown that spilling breaking waves generate significantly larger forces on the cylindrical model than highly non-linear non-breaking waves of equivalent size. This is shown to be due to the direct excitation at high frequency as well as the resonant and impact excitation of higher natural frequency modes. It is concluded that spilling breaking waves can generate very significant forces and should therefore be considered in the design of offshore structures.

The functional design of submerged breakwaters is still developing, particularly with respect to modelling of the nearshore wave field behind the structure. This paper describes a method for predicting the wave transmission coefficients behind submerged breakwaters using machine learning algorithms. An artificial neural network using the radial-basis function approach has been designed and trained using laboratory experimental data expressed in terms of non-dimensional parameters. A wave transmission coefficient calculator is presented, based on the proposed radial-basis function model. Predictions obtained by the radial-basis function model were verified by experimental measurements for a two dimensional breakwater. Comparisons reveal good agreement with the experimental results and encouraging performance from the proposed model. Applying the proposed neural network model for predictions, guidance is given to appropriately calculate wave transmission coefficient behind two dimensional submerged breakwaters. It is concluded that the proposed predictive model offers potential as a design tool to predict wave transmission coefficients behind submerged breakwaters. A step-by-step procedure for practical applications is outlined in a user-friendly form with the intention of providing a simplified tool for preliminary design purposes. Results demonstrate the model’s potential to be extended to three dimensional, rough, permeable structures.

Focused waves are often used in physical and numerical studies as a representative condition for extreme waves or as a means to generate very steep and breaking waves at a prescribed location in space and time. They have also been combined with depth-varying currents in investigations of incipient wave breaking, wave breaking–induced energy dissipation, and wave–current induced loads on marine structures. A focused wave is created when all the components in a transient wave group come into phase. In the past, linear wave theory and iterative methodologies coupled with the linear Doppler-shifted dispersion relationship have been suggested to account for the presence of a current and achieve the required phase and amplitude focusing. In the majority of cases, linear or constant steepness spectra are used, which, compared to measured or theoretical spectra like the Joint North Sea Wave Project (JONSWAP), Gaussian, and Pierson-Moskowitz (PM) can be termed unrealistic. The effectiveness of these methodologies also decreases as the nonlinearity increases; therefore, in most studies, either weakly nonlinear conditions are used or the focus location is determined empirically. Here, an iterative methodology is suggested that can focus waves of any height at a predetermined temporal and spatial location even for wave groups propagating on a strong following or adverse current. An experimental apparatus developed to generate relatively stable sheared velocity profiles is also described. The depth-varying profile of the resulting currents diverges from that of classical wind-driven currents and comes closer to profiles measured in field sites important for the deployment of, for instance, tidal and wind energy converters. The methodology is successfully applied to wave groups traveling on still water, following, and adverse currents, and the results presented refer to linear, weakly nonlinear, and strongly nonlinear–focused waves generated for a range of realistic target spectra. The capability to generate wave groups with the same amplitude spectrum at a fixed location for a variety of flow conditions—still water, following, and adverse sheared currents—is also illustrated.

Offshore gravity base foundations (GBFs) are often designed with complex geometries. Such structures interact with local hydrodynamics, creating an adverse pressure gradient that is responsible for flow and scour phenomena, including the bed shear stress amplification. In this study, a method is presented for predicting clear-water scour around cylindrical structures with nonuniform geometries under the force of a unidirectional current. The interaction of the flow field with the sediment around these complex structures is described in terms of nondimensional parameters that characterize the similitude of water-sediment movement. The paper presents insights into the influence the streamwise depth-averaged Euler number has on the equilibrium scour around uniform and nonuniform cylindrical structures. Here, the Euler number is based on the depth-averaged streamwise pressure gradient (calculated using potential flow theory), the mean flow velocity, and the fluid density. Following a dimensional analysis, the controlling parameters were found to be the Euler number, pile Reynolds number, Froude number, sediment mobility number, and nondimensional flow depth. Based on this finding, a new scour-prediction equation was developed. This new method shows good agreement with the database of scour depths acquired in this study (R2=0.91)(R2=0.91). Measurements of the equilibrium scour depth around nonuniform cylindrical structures were used to show the importance of the Euler number in the scour process. Finally, the importance of the remaining nondimensional quantities with respect to scour was also investigated in this study.

The functional design of submerged breakwaters is still developing, particularly with respect to modeling of the nearshore wave field behind the structure. An effective design tool needs to calculate both 2D and 3D effects. A numerical method for predicting the spatial transmission coefficient for regular waves in the shadow region of a 3D submerged breakwater is proposed in this paper. Two distinct models have been developed using machine learning algorithms; these artificial neural networks, based on multi-layer perceptron (MLP) and radial-basis function (RBF) methods, have been designed and trained against new laboratory experimental data expressed in terms of both dimensional and non-dimensional parameters. Comparisons between the experimental data and predictions from the trained models show that the non-dimensional RBF model is able to best predict the 3D wave field around the submerged breakwater. The performance of the model was validated in interpolation, extrapolation and at larger scale using different laboratory facilities, revealing sufficient agreement with the experimental results to suggest that it has potential as a design tool in real applications.

This paper presents insights into the structure of turbulence in combined wave-current boundary layers, based on experiments performed in flumes of different scale using Particle Image Velocimetry and hydrogen bubble visualisation. Flow conditions covered a range of wave frequencies, wave amplitudes and mean flow conditions. Results show that the spacing between turbulent streaks varies periodically with the passage of each wave, increasing when the flow accelerates and decreasing when the flow decelerates. A new formula has been put forward, relating the streak spacing variation and the wave-induced orbital displacements. The near-wall flow structure suggests a rhythmic pattern in terms of the velocity gradients across the flume. Waves with higher frequencies and larger amplitudes lead to a greater reduction of mean streak spacing, together with a greater increase of the maximum Reynolds shear stress induced by ejections. These results can be useful for better predictions of the hydrodynamics and sediment transport in combined wave-current flows.

When designing any artificial beach, it’s desirable to avoid (or minimise) future maintenance commitments by arranging the initial beach planshape so that it remains in equilibrium given the incident wave climate. Headlands bays, or embayments, where a sandy beach is held between two erosion resistant headlands, tend to evolve to a stable beach planshape with little movement of the beach contours over time. Several empirical bay shape equations have been derived to fit curves to the shoreline of headland bay beaches. One of the most widely adopted empirical equations is the parabolic bay shape equation, as it is the only equation that directly links the shoreline positions to the predominant wave direction and the point of diffraction. However, the main limitation with the application of the parabolic bay shape equation is locating the downcoast control point. As a result of research presented in this paper a new equation, based on the hyperbolic tangent shape equation was developed, which eliminates the requirement of placing the down coast control point and relies on defining a minimum beach width instead. This modified equation was incorporated into a new ArcGIS tool.

The characteristics of dense gravity currents in coastal regions, where free-surface gravity waves are dominant, have yet to be studied in the laboratory. This paper provides a first insight into the dynamics of dense saline gravity currents moving beneath regular progressive free-surface water waves. The gravity currents were generated by releasing a finite volume of saline into a large wave tank with an established periodic wave field. After the initial collapse, the gravity currents propagated horizontally with two fronts, one propagating in the wave direction and the other against the wave direction. The fronts of the gravity currents oscillated with an amplitude and phase that correlated with the orbital velocities within a region close to the bed. To leading order, the overall length of the gravity current was found to be weakly affected by the wave action and the dynamics of the current could be approximated by simply considering the buoyancy of the released fluid. Other characteristics such as the position of the gravity current centre and the shape of the two leading profiles were found to be significantly affected by the wave action. The centre was displaced at constant speed dependent on the second-order wave-induced mean Lagrangian velocity. For long waves, the centre was advected downstream in the direction of wave propagation owing to the dominance of Stokes drift. For short waves, the gravity current centre moved upstream against the wave direction, as under these wave conditions Stokes drift is negligible at the bed. An asymmetry in the shape of the upstream and downstream current heads was observed, with the gravity current front moving against the waves being much thicker and the front steeper, similar to the case of a current moving in a stream.

The cost of process equipment has exploded in recent decades. Enhanced document requirements and more strict environmental and safety requirements are facts. In practice, too much overdesign and an overload of technical specifications, which are in many cases contradictive, have created a substantial CAPEX increase. The big question nowadays is: "How to bring down the CAPEX of projects and create healthy and sustainable upstream projects for the coming future?" The industry calls for a cost reduction, which is often translated into a "standardized approach". But how should an operator approach standardized processes and equipment, while a fit-for-purpose design seems necessary to cope with different field conditions? The present paper deals with these questions in order to investigate how to achieve substantial cost reductions without compromising safety, operability and efficiency. Based on projects for several operating companies, a study was performed to compare three built onshore, marginal gas plants with different design philosophies: Design fully according operator specifications;Design according reduced specifications by combined operator/suppliers team;Design according engineering practice standards. All plants were normalized for comparison. The conclusion is that a cost reduction of nearly 50% for option c is proven, and that there is a method to achieve this for other projects. Besides the influence of specifications, some critical aspects were identified which contribute in attaining low CAPEX projects: A real cooperation in small, focused teams of operators, contractors and suppliers. This should start in an early stage, to link conceptual selection to basic design and project execution.Use pre-designed standardized process building blocks that are proven in use to create a fit-for-purpose solution, while being flexible enough to allow the end user influence where necessary.Approach process packages as black boxes and rely on the experience of the supplier to design the most cost-effective solution. These principles can be strengthened by a different contracting strategy and trust-based engineering. Although most applicable for smaller projects, the principles may be more broadly applicable. We present and discuss in detail the pathways to come to structural CAPEX reductions for oil & gas projects, thereby coming up to par with the 21st century.

Many offshore foundations are composed of non-uniform cylindrical geometries such as cones and different diameter composite cylinders. However, little is known about how these types of structure respond with regards to scour under the forcing of a unidirectional current. The present paper describes a series of laboratory experiments that have been performed to examine the effect that the geometry of a marine structure has on the evolution and equilibrium depth of scour under different hydrodynamic conditions. It was found that the hydrodynamic scour response of the non-uniform cylindrical structures is fundamentally different to that of a uniform cylinder.

The 33 papers and posters presented at the sixth Young Coastal Scientists and Engineers Conference held at University College London in March 2010 were of a high standard, typical of that expected at a leading international conference. They gave a good indication of the breadth of basic and applied research currently being pursued in UK universities and consultancies. Topics included coastal management, dunes, saltmarshes, beaches, swash, renewable energy, gravity-driven currents, freak waves, sediment transport, morphological modelling, nutrient and pollution transport, scour protection, liquefied natural gas facilities and submerged breakwaters. The paper below reproduces the abstracts of the keynote Peregrine Lecture and of five presentations judged by the organising committee to be of particular merit. The next UK Young Coastal Scientists and Engineers Conference will be held at the National Oceanography Centre in Liverpool and is scheduled for 30–31 March 2011.

Offshore Gravity Base Foundations (GBFs) are often designed with non-uniform cylindrical geometries. Such structures interact with the local hydrodynamics which amplify the adverse dynamic pressure gradient, which is responsible for all flow and scour phenomena including the bed shear stress amplification. In this study a method for predicting the effect non-uniform cylindrical structure geometries have on local scour around offshore structures under the forcing of a unidirectional current is presented. The interaction of the flow field with the sediment around these complex structures is described in terms of non-dimensional parameters that characterize the similitude of water-sediment movement. The paper presents insights in the influence a form of the Euler number has on the equilibrium scour around uniform and non-uniform cylindrical structures. Here the Euler number is defined as the depth averaged pressure gradient (calculated using potential flow theory) divided by the product of the square of mean flow velocity and the fluid density. The insights are confirmed through a series of experiments where the equilibrium scour was monitored for different types of structures and flow conditions. The results of this study show that the Euler number is a more appropriate parameter for describing the scour potential of a structure compared to using the equivalent pile diameter. The experimental data show that an increasing Euler number yields an increase in the non-dimensional equilibrium scour. The results of this study also suggest that an increase in the water depth yields a decrease in the equilibrium scour depth for the conical, cylindrical base structures and truncated cylinders and an increase in the equilibrium scour depth for the uniform cylinders which can also be explained in terms of changes in the Euler number. Finally, the Buckingham π theorem in conjunction with the experimental data was used to derive a simple shape correction factor that could be used to determine the scour depth of a non-uniform cylindrical structure based on the equilibrium scour produced for the same flow conditions by a uniform cylinder.

BACKGROUND: Injury rates and injury mortality rates are generally higher in rural and remote communities compared with urban jurisdictions as has been shown to be the case in the rural-remote area of Northwest (NW) British Columbia (BC). The purpose of study was to identify: (1) the place and timing of death following injury in NW BC, (2) access to and quality of local trauma services, and (3) opportunities to improve trauma outcomes. METHODS: Quantitative data from demographic and geographic databases, the BC Trauma Registry, Hospital discharge abstract database, and the BC Coroner's Office, along with qualitative data from chart reviews of selected major trauma cases, and interviews with front-line trauma care providers were collated and analyzed for patients sustaining injury in NW BC from April 2001 to March 2006. RESULTS: The majority of trauma deaths (82%) in NW BC occur prehospital. Patients arriving alive to NW hospitals have low hospital mortality (1.0%), and patients transferring from NW BC to tertiary centers have better outcomes than matched patients achieving direct entry into the tertiary center by way of geographic proximity. Access to local trauma services was compromised by: incident discovery, limited phone service (land lines/cell), incomplete 911 emergency medical services system access, geographical and climate challenges compounded by limited transportation options, airport capabilities and paramedic training level, dysfunctional hospital no-refusal policies, lack of a hospital destination policies, and lack of system leadership and coordination. CONCLUSION: Improving trauma outcomes in this rural-remote jurisdiction requires a systems approach to address root causes of delays in access to care, focusing on improved access to emergency medical services, hospital bypass and destination protocols, improved transportation options, advanced life support transfer capability, and designated, coordinated local trauma services. Language: en

There is a need for decadal predictions of the seabed evolution, for example to inform resurvey strategies when maintaining navigation channels. The understanding of the physical processes involved in morphological evolution, and the viability of process models to accurately model evolution over these time scales, are currently limited. As a result, statistical approaches are used to supply long-term forecasts. In this paper, we introduce a novel statistical approach for this problem: the autoregressive Hilbertian model (ARH). This model naturally assesses the time evolution of spatially-distributed measurements. We apply the technique to a coastal area in the East Anglian coast over the period 1846 to 2002, and compare with two other statistical methods used recently for seabed prediction: the autoregressive model and the EOF model. We evaluate the performance of the three methods by comparing observations and predictions for 2002. The ARH model enables a reduction of 10% of the root mean squared errors. Finally, we compute the variability in the predictions related to time sampling using the jackknife, a method that uses subsamples to quantify uncertainties.

There has been a steady transition towards the representation, analysis and modelling of dynamic spatio-temporal relationships in geographical information systems (GISs). These developments open up opportunities for investigating and modelling the dynamic relationships that occur in the coastal and marine environments and how these relate to human activities. Such a spatio-temporal approach is applied in this research to address an issue faced by the bodies responsible for maintaining navigation safety in territorial waters and this paper introduces the developed resurvey decision support system. The developed system models morphological change in response to hydrodynamic conditions and determines the seabed locations that require resurvey based on the modelled change and navigation characteristics. System validation tests indicate that the morphological modelling tool is under-predicting the magnitude and lateral extent of the change which then influences the locations that require resurvey. Additional sensitivity tests of the morphological modelling parameters highlight the influence of the parameters on the outputs and derived predictions. The achieved modelling results and resurvey decision indicate the applicability of utilising a GIS to model seabed change as an input into decision support systems for planning and management purposes. The results also suggest the applicability of the modelling and decision support methodology to similar problems in the coastal and marine environments.

In this paper, the vertical diffusion was measured from line source injector under neutral boundary condition over rib-roughened wall in a water channel. The variation in gap distance between the rib-roughened wall characterized skimming flow (ribs closely spaced), wake interference flow and isolated roughness flow (ribs widely spaced). The effect of change in local bed geometry was noticed with the increase in turbulence energy production, which was correlated with the vertical diffusion.

Offshore gravity foundations are often designed with complex geometries. Such structures interact with the local hydrodynamics and generate enhanced bed shear stresses and flow turbulence capable of scouring the seabed or destabilizing bed armour where deployed. In the present study a novel bed shear stress measurement method has been developed from the camera and laser components of a Particle Image Velocimetry (PIV) system. The bed shear stress amplification was mapped out around six models of gravity foundations with different geometries. Tests were repeated for two bed roughness conditions. The structures tested included uniform cylinders, cylindrical base structures and conical base structures. The flow field around the models was also measured using PIV. The results of this study reveal that the conical base structures generate a different hydrodynamic response compared to the other structures. For uniform cylinders the maximum bed shear stress amplification occurs upstream, at an angle of 45° relative to the flow direction, and measurements were found to agree well with numerical results obtained by Roulund et al. (2005). In the case of the cylindrical base structure the maximum amplification occurs upstream at a similar location to the uniform cylinder case. For the conical base structures the maximum amplification of the bed shear stress occurs on the lee side of the structure, with the magnitude dependent on the side slope of the cone. The bed shear stress results were validated against stresses derived from analysis of the flow fields obtained by the PIV measurements performed under the same test conditions. Conclusions from the study are that the structure with the cylindrical base foundation produces the lowest bed shear stress amplification and that an increase in the bed roughness results in an increase in the amplification of the bed shear stress. These findings have direct implications for design of scour protection. In addition the flow reattachment point behind the foundation is dependent on pile Reynolds number (ReD). This suggests that the results of this study may be extrapolated for higher pile Reynolds using the method described in Roulund et al. (2006).

Experiments have been carried out to investigate turbulence at and above roof-level in an urban environment, and to predict the behaviour of street pollution from experiments using dye dispersion, for different roughness conditions and bed geometries. The flow in the boundary layer above an idealised urban environment has been simulated in a laboratory water flume. Comparisons have been made for the same model street canyon with and without the presence of upstream roughness. In the tests reported here, model street canyons were aligned perpendicular to the flow direction, and velocity measurements made within and above the model street canyons using a laser Doppler velocimeter (LDV). Flow visualisation techniques have also been used to confirm the gross flow features from streak images. Turbulence generated from the upstream roughness has a significant effect on the turbulence production and dispersion behaviour of the dye simulating pollution in street canyons.

Flow regimes were investigated in the cavity formed between the roughness elements in a laboratory water flume. Further tests were carried out on similar aspect ratio of the cavity to study the effect on turbulence production because of change in local bed geometry. The idealized 2-D bed roughness has been aligned perpendicular to the flow direction, and velocity measurements were made using a laser Doppler velocimeter. Skimming and transition regime has been identified between the roughness elements with the help of flow visualization. Turbulence production was investigated at test section with and without the presence of urban approach roughness. The effect on turbulence production in the boundary layer was significantly influenced by the upstream roughness and height of the roughness element.

A laboratory flume experiment was performed to investigate the time development of scour around a vertical cylinder acting as a scaled model of an offshore wind turbine monopile in tidal currents. The tidal current was simulated by resolving each half-cycle into three time steps, between which flow velocity and depth were varied. Flow direction was reversed between half-cycles, which were otherwise identical. Between them, the three time steps exhibited clear water, transitional, and live-bed conditions. The experiment was run over two full-simulated tidal cycles. The scour hole formed tended to a symmetrical shape after two half-cycles and was both shallower and slower developing than the scour hole in a unidirectional current test carried out in the same flume. This was due mainly to the variable rates of scour caused by the variable flow conditions within each half-cycle, and to a lesser extent to the infilling of the scour hole when the current direction reversed. The lower scour depth recorded in tidal conditions implies that the amount of scour protection required may be less than previous studies suggest.

A full-depth numerical model solving the free surface flow induced by linear water waves propagating with collinear vertically sheared turbulent currents is presented. The model is used to estimate the wave amplitude decay rate in combined wave current flows. The decay rates are compared with data collected in wave flumes by Kemp and Simons [J Fluid Mech, 116 (1982) 227; 130 (1983) 73] and Mathisen and Madsen [J Geophys Res, 101 (C7) (1996) 16,533]. We confirm the main experimental finding of Kemp and Simons that waves propagating downstream are less damped, and waves propagating upstream significantly more damped than waves on fluid at rest. A satisfactory quantitative agreement is found for the decay rates of waves propagating upstream, whereas not more than a qualitative agreement has been observed for waves propagating downstream. Finally, some wave decay rates in the presence of favourable and adverse currents are provided in typical field conditions.

Bottom friction in random waves plus current flow is presented. The model is an extension of the Myrhaug [Coastal Eng. 24 (1995) 259] approach for random waves alone. The effect of random waves on the bottom friction is studied by assuming the wave motion to be a stationary Gaussian narrow-band random process, and by using friction coefficient formulas for sinusoidal waves. The data used for comparison are obtained from statistical analysis of direct measurements of bottom shear stresses made in the UK Coastal Research Facility under combined random waves and orthogonal as well as near-orthogonal currents.

This paper describes a simple method for determining the wavelength of small amplitude waves under laboratory conditions where reflected wave components are present both with and without a mean current flow superimposed. It assumes a locally horizontal bed but requires no a priori assumption concerning the form of the dispersion relation with a coexisting current. Synchronous measurements of the water surface recorded along any straight line are analysed to yield Fourier coefficients at each location. It is then shown that for all practical conditions excluding a perfect standing wave, the average rate of change of wave phase in the chosen direction can be related directly to the component of incident wave number in that direction, irrespective of reflection coefficient or relative current strength. The technique has been applied to regular and bichromatic waves in a flume with an absorbing wave generator, and can also be applied in 3-D wave basins where waves and currents intersect at arbitrary angles. In combined wave–current experiments, by assuming the linear dispersion relation, it is also possible to estimate the effective current velocity.

This paper describes the extension of an engineering model (Harris et al., 2010) developed to predict the time evolution of scour around a monopile in uniform granular soils in the marine environment to layered granular soils. The model is capable of looking at cylindrical, square and rectangular structures. It is capable of representing both the scouring and backfilling process and has been modified to incorporate the ability to predict the effect of scouring in layered soils making use of the results from recent experimental studies into scouring in non-uniform sediment beds. Output from the model is compared with the laboratory results and extended to look at potential implications at field-scale. The model is of use on those occasions when knowledge of the likely variation in depth of scour is important. Examples include predictions of scour development to inform the evaluation of the duration of time after pile driving for a fully developed scour hole to form for installation of scour protection, or to determine the likely exposure of cables entering and exiting offshore turbine foundations.

This paper reviews the state-of-the-art as perceived by the Wave-Current Interaction (WCI) group which forms part of the MAST G6M Coastal Morphodynamics project, and includes some new results arising out of that project. Those processes which affect the vertical profiles of current and wave kinematics, and the bed shear-stresses, are discussed, but “horizontal” processes such as refraction of waves by currents, and generation of longshore currents, are not included. Among the group's conclusions are recommendations for the calculation of wave-induced bottom orbital velocities with and without WCI, and direct parameterisations of the bed shear-stresses produced by WCI. The latter is the results of a comprehensive intercomparison of WCI boundary-layer models and data. The results are aimed at aiding the formulation of numerical models of coastal morphodynamics.

2-6 July 2007 This paper reports results from experiments carried out in a laboratory flume to investigate the process of seabed scour around cylinders of finite length under the action of currents close to the threshold of motion for the bed sediment. The conditions relate to the design of large caisson foundations for offshore oil and gas installations and wind turbines. Results show that depth and extent of scour are much reduced for cylinders that stand less than one diameter above the seabed compared to tests with a surface-piercing cylinder. When truncated cylinders stand on shallow foundations, scour patterns are not sensitive to skirt depth, even when the cylinder has been undermined. For the present tests, maximum scour depth around truncated cylinders in a tidally reversing current was found to be less than 50% of equilibrium scour depth for an equivalent unidirectional flow.

A laboratory study of the effect of wave action on turbulent gravity currents generated by an instantaneous release of dense fluid is described. Dense fluid is released in the centre of the flume, generating a gravity current propagating horizontally with two fronts. This gravity current type, in the absence of waves, spreads symmetrically and propagating with the length scales according to the standard box models. In the presence of gravity waves the length of the gravity current is, to leading order unchanged, but the centre is advected in the direction of the wave motion. The shear of the mean flow generated by the oscillatory wave motion modifies the shape of the gravity current, inducing an asymmetry in the current height. Copyright ASCE 2006.

The mechanism responsible for asymmetric sediment accretion around an idealized, symmetrical headland is clearly the Coriolis force. What is not evident, however, is how the Coriolis force manifests itself in the headland dynamics to promote asymmetric depositional patterns. In this study, patterns of scour and accretion, topographic and advective vorticity, bed load, and suspended load transport pathways around a theoretical coastal headland are examined. Previous studies have emphasized the contribution of the Coriolis force to a secondary flow mechanism, "tidal stirring." This investigation provides evidence to suggest that secondary flow dynamics are not significant in sandbank generation associated with headlands. It further demonstrates the direct contribution of the Coriolis force in reinforcing inertial terms, near-headland scour, and asymmetric accretion. Examination of the vorticity balance throughout the simulations reveals that high levels of slope-induced topographic vorticity act in direct opposition to advective vorticity near a headland tip. It is also demonstrated that the Coriolis force manifests itself in the production of vorticity. This has been used in the investigation as a means of detecting the sensitivity of the flow to the Coriolis force. In regimes where advective and topographic vorticity production is very similar ( flat bed cases), it is found that bed evolution is more sensitive to the Coriolis force. In regimes where topographic vorticity clearly dominates the vorticity balance ( in seabed slope case), the influence of the Coriolis force becomes less important.

[1] A unique experiment to investigate the transformation of near-linear gravity waves propagating across a narrow horizontally sheared jet-like current, typical of those found in the nearshore, coastal, and ocean regions, is described. A single wave condition was studied, propagating across the current orthogonally and at oblique incidence in both a following and opposing sense to the current. The length scale of the current shear layers was comparable to the incident wavelength. The experiment is the first attempt to assess the kinematics and dynamics of the interaction of regular waves and currents in three dimensions at a physically realistic scale. The resulting data set provides direct quantitative measurements of the spatial variation of the primary flow variables. Negligible reflection of the incident wave at the current shear layers was observed. Typical refraction behavior was observed: A following wave is refracted to a more current-parallel direction with an increased wavelength and reduced wave height as it moves onto the current, while the opposing wave becomes more current normal with a shortened wavelength and enhanced wave height. The experimental data are compared with predictions of a wave ray model, assuming a depth-averaged current and slowly varying horizontal shear, and a new model that incorporates the influence of vertical shear.

Reports of infectious diseases to local and state public health agencies are often delayed and incomplete. Some of the clinicians charged with the responsibility for making notifications encounter various difficulties in reporting. These may include heavy patient loads that make it easy to forget to file reports, or cumbersome disease reporting mechanisms and systems. For some percentage of practitioners, knowledge of what and when to report infectious diseases is less than optimal. However, it is not clear how reporting methods or systems could be designed or improved, owing to lack of data on physicians' knowledge and views about them. We conducted a survey of resident physicians at three university teaching hospitals in Pennsylvania to ascertain their knowledge about reporting timeframe and responsibility, as well as their attitudes toward various methods to enhance disease reporting.

Laboratory studies form an integral part of scour research, yet there is no standard technique for monitoring scour depth development during testing. This paper investigates the advantages and disadvantages of a variety of techniques, and compares results from three methods: photogrammetry, an echosounder, and a calibrated pile. A novel system involving an underwater camera is presented. This produces results in close agreement with the other techniques, and has the advantage of providing accurate measurements over the full scour hole while at the same time enabling qualitative information to be gained from the photographs.