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Academic literature on the topic 'Wakes'

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Published: 4 June 2021
Last updated: 13 April 2024

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Journal articles on the topic "Wakes"

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Tings, Björn. "Non-Linear Modeling of Detectability of Ship Wake Components in Dependency to Influencing Parameters Using Spaceborne X-Band SAR." Remote Sensing 13, no. 2 (January 6, 2021): 165. http://dx.doi.org/10.3390/rs13020165.

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The detection of the wakes of moving ships in Synthetic Aperture Radar (SAR) imagery requires the presence of wake signatures, which are sufficiently distinctive from the ocean background. Various wake components exist, which constitute the SAR signatures of ship wakes. For successful wake detection, the contrast between the detectable wake components and the background is crucial. The detectability of those wake components is affected by a number of parameters, which represent the image acquisition settings, environmental conditions or ship properties including voyage information. In this study the dependency of the detectability of individual wake components to these parameters is characterized. For each wake component a detectability model is built, which takes the influence of incidence angle, polarization, wind speed, wind direction, sea state (significant wave height, wavelength, wave direction), vessel’s velocity, vessel’s course over ground and vessel’s length into account. The presented detectability models are based on regression or classification using Support Vector Machines and a dataset of manually labelled TerraSAR‑X wake samples. The considered wake components are: near‑hull turbulences, turbulent wakes, Kelvin wake arms, Kelvin wake’s transverse waves, Kelvin wake’s divergent waves, V‑narrow wakes and ship‑generated internal waves. The statements derived about wake component detectability are mainly in good agreement with statements from previous research, but also some new assumptions are provided. The most expressive influencing parameter is the movement velocity of the vessels, as all wake components are more detectable the faster vessels move.
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Wang, Letian, Min Zhang, and Jiong Liu. "Electromagnetic Scattering Model for Far Wakes of Ship with Wind Waves on Sea Surface." Remote Sensing 13, no. 21 (November 3, 2021): 4417. http://dx.doi.org/10.3390/rs13214417.

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A comprehensive electromagnetic scattering model for ship wakes on the sea surface is proposed to study the synthetic aperture radar (SAR) imagery for ship wakes. Our model considers a coupling of various wave systems, including Kelvin wake, turbulent wake, and the ocean ambient waves induced by the local wind. The fluid–structure coupling between the ship and the water surface is considered using the Reynolds–averaged Navier–Stokes (RANS) equation, and the wave–current effect between the ship wake and wind waves is considered using the wave modulation model. The scattering model can better describe the interaction of the ship wakes on sea surface and illustrates well the features of the ship wakes with local wind waves in SAR images.
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SPEDDING, G. R. "The evolution of initially turbulent bluff-body wakes at high internal Froude number." Journal of Fluid Mechanics 337 (April 25, 1997): 283–301. http://dx.doi.org/10.1017/s0022112096004557.

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Coherent vortex structures are formed in the late wakes of towed spheres for all values of the internal Froude number, F≡2U/ND∈ [10, 240] (U is the body speed, D its diameter, and N is the buoyancy frequency). The eventual emergence of the long-lived and stable pattern of alternating-signed patches of vertical vorticity is characteristic of all towed-sphere wakes, from those dominated by internal lee waves at F=1, to initially fully turbulent early wakes at F[ges ]4. At late times, the local Froude number is always low, and a characteristic stratified wake structure and dynamics result. These wakes have high mean wake defect velocities compared with non-stratified wakes, but the decay rates of energy and enstrophy are similar. Experimental evidence is presented for the existence of an intermediate non-equilibrium (NEQ) regime with very low decay rates of kinetic energy, that precedes the late wake. The NEQ regime is the period when the initial turbulence reorganizes under the increasingly (relative to the decaying turbulent kinetic energy) powerful influence of the background density gradient, accompanied by conversion of potential to kinetic energy as the wake turbulence collapses. The stable long-lived late-wake structure that eventually emerges has a high degree of order and coherence that reflects the initial wake instability. A universal curve for the energy decay of all stratified drag wakes at high Froude and Reynolds numbers is proposed.
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Liu, Yingfei, and Ruru Deng. "Ship Wakes in Optical Images." Journal of Atmospheric and Oceanic Technology 35, no. 8 (August 2018): 1633–48. http://dx.doi.org/10.1175/jtech-d-18-0021.1.

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AbstractShip wakes are more distinct than the hulls and can be visually observed in optical images. In this paper the wakes of 2836 ships in 32 optical images with different resolutions are observed and summarized. The ships are divided into four types according to the hull and wake features: fishing vessels, motorboats, cargo ships, and warships. The results show that each ship type has characteristic wakes, and there are significant differences among the categories. The probabilities of occurrence of different types of wakes and their components are shown. Turbulent wakes are inevitable. The probability of occurrence of Kelvin wakes is small and less than 40%. The visibilities of internal waves that are generated by only cargo ships are very low as a result of the harsh formation conditions. Turbulent wakes should be preferentially detected. Low-resolution images are more suitable for the detection and positioning of hulls and wakes, while high-resolution images with more details are convenient for further analysis of the size, velocity, and draft of ships. The study on the cause of the formation of the features of ship wakes in optical images proves that the classification of the wakes is reasonable and that the features of wakes can be used to initially identify the type of ship.
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Doorly, D. J., and M. L. G. Oldfield. "Simulation of the Effects of Shock Wave Passing on a Turbine Rotor Blade." Journal of Engineering for Gas Turbines and Power 107, no. 4 (October 1, 1985): 998–1006. http://dx.doi.org/10.1115/1.3239847.

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The unsteady effects of shock waves and wakes shed by the nozzle guide vane row on the flow over a downstream turbine rotor have been simulated in a transient cascade tunnel. At conditions representative of engine flow, both wakes and shock waves are shown to cause transient turbulent patches to develop in an otherwise laminar (suction-surface) boundary layer. The simulation technique employed, coupled with very high-frequency heat transfer and pressure measurements, and flow visualization, allowed the transition initiated by isolated wakes and shock waves to be studied in detail. On the profile tested, the comparatively weak shock waves considered do not produce significant effects by direct shock-boundary layer interaction. Instead, the shock initiates a leading edge separation, which subsequently collapses, leaving a turbulent patch that is convected downstream. Effects of combined wake- and shock wave-passing at high frequency are also reported.
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Torsvik, T., I. Didenkulova, T. Soomere, and K. E. Parnell. "Variability in spatial patterns of long nonlinear waves from fast ferries in Tallinn Bay." Nonlinear Processes in Geophysics 16, no. 2 (April 29, 2009): 351–63. http://dx.doi.org/10.5194/npg-16-351-2009.

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Abstract. High-speed ferries are known to generate wakes with unusually long periods, and occasionally large amplitudes which may serve as a qualitatively new forcing factor in coastal regions that are not exposed to a sea swell. An intrinsic feature of such wakes is their large spatial variation. We analyze the variability of wake conditions for the coasts of Tallinn Bay, the Baltic Sea, a sea area with very intense fast ferry traffic. The modelled ship wave properties for several GPS-recorded ship tracks reasonably match the measured waves in terms of both wave heights and periods. It is shown that the spatial extent of the wake patterns is very sensitive to small variations in sailing conditions. This feature leads to large variations of ship wave loads at different coastal sections with several locations regularly receiving high ship wave energy. The runup of the largest ship wakes on the beach increases significantly with an increase in wave height whereas shorter (period <2–5 s) waves merge into longer waves in the shoaling and runup process.
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Balachandar, R., M. F. Tachie, and V. H. Chu. "Concentration Profiles in Shallow Turbulent Wakes." Journal of Fluids Engineering 121, no. 1 (March 1, 1999): 34–43. http://dx.doi.org/10.1115/1.2822007.

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The present study deals with the noninvasive measurement of concentration in the intermediate shallow turbulent wake region using a video-imaging technique. The flow depths considered in the present study are small compared to the width of the channel and the generated wakes are categorized as shallow. On the basis of the observed behavior, the waves are classified as deep-shallow wakes and shallow-shallow wakes. The topology of the dye concentration distribution in the near and intermediate wake region indicates that the vortex structure tends to be preserved when the flow depth is relatively high and the dominant eddy structures are similar to that noticed in conventional two-dimensional wakes. In shallow-shallow wakes, the conventional Karman vortex street appears to be annihilated or intermittent. The lateral concentration distribution at several axial stations covering the first thirty body widths are considered for analysis. The instantaneous concentrations are observed to be several times higher than the corresponding mean values. Attempts are also made to determine the paths traversed by the vortex cores and the vortex core convection velocity. The axial variation of the wake half-width with depth of flow is also examined. A model is developed to predict the spread of the wake with downstream distance from the test body. A friction length scale is introduced in the model to account for the influence of depth and bed friction on the development of the wake.
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Griffin, Owen M. "Ship Wave Modification by a Surface Current Field." Journal of Ship Research 32, no. 03 (September 1, 1988): 186–93. http://dx.doi.org/10.5957/jsr.1988.32.3.186.

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One potential contribution to the formation of the narrow-V patterns observed remotely in the wakes of surface ships is discussed. This is the interaction between the ship-generated waves and a surface current pattern in the ship's wake. This surface current field in turn is primarily a manifestation of the turbulent wake caused by the passage of the ship itself. It can be shown by means of relatively simple theoretical arguments that such an interaction can lead directly to a V-wake pattern which is included within a smaller angular region than that of the classical Kelvin waves produced by the steady motion of a surface ship in still water. Predictions of V-wake patterns are obtained which are in qualitative agreement with some of the recently observed ship wakes.
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BRUCKER, KYLE A., and SUTANU SARKAR. "A comparative study of self-propelled and towed wakes in a stratified fluid." Journal of Fluid Mechanics 652 (April 12, 2010): 373–404. http://dx.doi.org/10.1017/s0022112010000236.

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Direct numerical simulations (DNS) of axisymmetric wakes with canonical towed and self-propelled velocity profiles are performed atRe= 50 000 on a grid with approximately 2 billion grid points. The present study focuses on a comparison between towed and self-propelled wakes and on the elucidation of buoyancy effects. The development of the wake is characterized by the evolution of maxima, area integrals and spatial distributions of mean and turbulence statistics. Transport equations for mean and turbulent energies are utilized to help understand the observations. The mean velocity in the self-propelled wake decays more rapidly than the towed case due to higher shear and consequently a faster rate of energy transfer to turbulence. Buoyancy allows a wake to survive longer in a stratified fluid by reducing the 〈u1′u3′〉 correlation responsible for the mean-to-turbulence energy transfer in the vertical direction. This buoyancy effect is especially important in the self-propelled case because it allows regions of positive and negative momentum to become decoupled in the vertical direction and decay with different rates. The vertical wake thickness is found to be larger in self-propelled wakes. The role of internal waves in the energetics is determined and it is found that, later in the evolution, they can become a dominant term in the balance of turbulent kinetic energy. The non-equilibrium stage, known to exist for towed wakes, is also shown to exist for self-propelled wakes. Both the towed and self-propelled wakes, atRe= 50000, are found to exhibit a time span when, although the turbulence is strongly stratified as indicated by small Froude number, the turbulent dissipation rate decays according to inertial scaling.
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Nadaf, E., J. M. Brown, and T. Radko. "Turbulent wakes in a non-uniformly stratified environment." Physics of Fluids 34, no. 10 (October 2022): 105123. http://dx.doi.org/10.1063/5.0108064.

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This study explores the behavior of turbulent wakes generated by a sphere propagating with constant speed in a non-uniformly stratified fluid. The investigation is based on a series of high-resolution direct numerical simulations in which the background stratification is systematically varied. We consider one linear and three nonlinear density profiles and discover that even modest, spatially localized non-uniformities of stratification can profoundly influence the wake dynamics, structure, and evolution. The analysis of microstructure signatures shows that wakes in non-uniformly stratified fluids tend to be more spread horizontally, and internal waves are much stronger than in linear stratification. Simulations performed with Gaussian perturbations are characterized by a vertically asymmetric energy distribution, which is attributed to internal wave reflections from low-gradient regions. Using microstructure decay rates, we estimate the effective persistence period of wakes, showing that it substantially increases with the increasing Froude number. We also find that wakes persist much longer in high-gradient profiles, whereas weak local gradients can substantially reduce the wake longevity.
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Dissertations / Theses on the topic "Wakes"

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Acreman, D. M. "Galaxy wakes." Thesis, University of Birmingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403583.

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Cicatelli, Giancarlo. "Time warying wake flow characteristics behind turbine blade wakes." Doctoral thesis, Universite Libre de Bruxelles, 1998. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212070.

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Nilsson, Karl. "Numerical computations of wind turbine wakes and wake interaction." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-166658.

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When wind turbines are placed in farms, wake effects reduce the overall power production. Also, turbine loads are significantly increased since turbulence levels are high within the wake flow. Therefore, when planning for a wind farm, it is imperative to have an understanding of the flow conditions in the farm in order to estimate the power losses and to optimize the durability of the turbines to be selected for the farm. The possibilities granted by numerical modeling and the development of computational capabilities give an opportunity to study these flow conditions in detail, which has been the key focus of this doctoral work. The actuator disc method is used for predicting the power production of the Lillgrund wind farm. The results of the simulations are compared to measurements from the actual wind farm, which are found to be in very good agreement. However, some uncertainties are identified in the modeling of the turbine. One of the uncertainties is that a generic rotor is used in the Lillgrund case. In order to quantify the errors resulting from this generalization three different rotor configurations are simulated in various flow conditions. Generally, it can be stated that the choice of rotor configuration is not crucial if the intention of the simulations is to compute the mean wake characteristics subject to turbulent inflow. Another uncertainty is that the turbines in the Lillgrund case were simulated without a power controller. Therefore, a power controller is implemented and used in simulations. Generally, the controller reduces the thrust of the turbines, reduces turbulence intensity and increases velocity levels in the wake flow. However, the use of a controller was observed to have a small impact on the power production. The effects of using the technique of imposing pregenerated turbulence and a prescribed boundary layer in the simulation are analyzed in order to verify its applicability in very long domains. It is observed that close to the plane of imposed turbulence, the conditions are mainly dependent on the imposed turbulence while far downstream the turbulence, regardless of its initial characteristics, is in near equilibrium with the prescribed wind shear. The actuator line method is validated using measurements of the near wake behind the MEXICO rotor. The analysis is performed by comparing position, size and circulation of the tip vortices, as well as velocity distributions in the wake flow. The simulations and measurements are generally found to be in good agreement apart from the tip vortex size, which is greatly overestimated in the simulations.

QC 20150519

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Baille, Kevin. "Fine-scale structures in Saturn's rings waves, wakes and ghosts." Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4840.

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The Cassini mission provided wonderful tools to explore Saturn, its satellites and its rings system. The UVIS instrument allowed stellar occultation observations of structures in the rings with the best resolution available (around 10 meters depending on geometry and navigation), bringing our understanding of the physics of the rings to the next level. In particular, we have been able to observe, dissect, model and test the interactions between the satellites and the rings. We first looked at kilometer-wide structures generated by resonances with satellites orbiting outside the main rings. The observation of structures in the C ring and their association with a few new resonances allowed us to estimate some constraints on the physical characteristics of the rings. However, most of our observed structures could not be explained with simple resonances with external satellites and some other mechanism has to be involved. We located four density waves associated with the Mimas 4:1, the Atlas 2:1, the Mimas 6:2 and the Pandora 4:2 Inner Lindblad Resonances and one bending wave excited by the Titan -1:0 Inner Vertical Resonance. We could estimate a range of surface mass density from 0.22 ([plus or minus]0.03) to 1.42 ([plus or minus]0.21) g cm[super-2] and mass extinction coefficient from 0.13 ([plus or minus]0.03) to 0.28 ([plus or minus]0.06) cm[super2] g[super-1]. These mass extinction coefficient values are higher than those found in the A ring (0.01 - 0.02 cm[super2] g[super-1]) and in the Cassini Division (0.07 - 0.12 cm[super2] g[super-1] from Colwell et al. (2009), implying smaller particle sizes in the C ring. We can therefore imagine that the particles composing these different rings have either different origins or that their size distributions are not primordial and have evolved differently.; Using numerical simulations for the propeller formation, we estimate that our observed moonlets belong to a population of bigger particles than the one we thought was composing the rings: Zebker et al. (1985) described the ring particles population as following a power-law size distribution with cumulative index around 1.75 in the Cassini Division and 2.1 in the C ring. We believe propeller boulders follow a power-law with a cumulative index of 0.6 in the C ring and 0.8 in the Cassini Division. The question of whether these boulders are young, ephemeral and accreted inside the Roche limit or long-lived and maybe formed outisde by fragmentation of a larger body before migrating inward in the disk, remains a mystery. Accretion and fragmentation process are not yet well constrained and we can hope that Cassini extended mission will still provide a lot of information about it.; We also estimate the mass of the C ring to be between 3.7 ([plus or minus]0.9) x 10[super16] kg and 7.9 ([plus or minus]2.0) x 10[super16] kg, equivalent to a moon of 28.0 ([plus or minus]2.3) km to 36.2 ([plus or minus]3.0) km radius (a little larger than Pan or Atlas) with a density comparable to the two moons (400 kg m[super-3]). From the wave damping length and the ring viscosity, we also estimate the vertical thickness of the C ring to be between 1.9 ([plus or minus]0.4) m and 5.6 ([plus or minus]1.4) m, which is consistent with the vertical thickness of the Cassini Division (2 - 20 m) from Tiscareno et al. (2007) and Colwell et al. (2009). Conducting similar analysis in the A, B rings and in the Cassini Division, we were able to estimate consistent masses with previous works for the these rings. We then investigated possible interactions between the rings and potential embedded satellites. Looking for satellite footprints, we estimated the possibility that some observed features in the Huygens Ringlet could be wakes of an embedded moon in the Huygens gap. We discredited the idea that these structures could actually be satellite wakes by estimating the possible position of such a satellite. Finally, we observed a whole population of narrow and clear holes in the C ring and the Cassini Division. Modeling these holes as depletion zones opened by the interaction of a moonlet inside the disk material (this signature is called a "propeller"), we could estimate a distribution of the meter-sized to house-sized objects in these rings. Similar objects, though an order of magnitude larger, have been visually identified in the A ring. In the C ring, we have signatures of boulders which sizes are estimated between 1.5 and 14.5 m, whereas similar measures in the Cassini Division provide moonlet sizes between 0.36 and 58.1 m.
ID: 030422748; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 269-295).
Ph.D.
Doctorate
Physics
Sciences
Planetary Science
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Nedic, Jovan. "Fractal-generated wakes." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/12632.

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This thesis aims at getting a better understanding of the properties, scalings and similarities of turbulent axisymmetric wakes, as well as possible applications that arise from the information learnt. Over the last 60 years, axisymmetric wakes have been generated using axisymmetric bodies, such as disks, spheres and bodies of revolution, and key parameters such as the drag coefficient, shedding frequency and similarity and scaling of the wake width and velocity deficit have been documented and verified by numerous experimental and numerical studies. However, in this thesis the aim is to use asymmetric wake generators to generate the axisymmetric wakes and see if this has any effect on the results. These asymmetric wake generators are made up of a square plate and a number of fractal plates, where the perimeter of the plates can be increased by as much as 16 times that of the square. As well as increasing the perimeter, the irregularity, or fractal dimension, is also increased. It is found that the drag coefficient of the fractal plates is increased to beyond the values observed for regular polygons and a theory is presented that could explain this possible change in the drag coefficient, whereby the drag coefficient is the product of the volume of the wake and the dissipation of the turbulent kinetic energy within the wake. Wake profiles were taken over a moderate downstream distance of up to 50l, where l is the characteristic length of the plates, defined as the square root of the frontal area. Using the measured integral width of the wake directly, it was found that the volume of the wake decreased with increasing fractal dimension and iteration. Using these values, the similarity and scaling of the wake was carried out and a new high local Reynolds number scaling for turbulent axisymmetric wakes was discovered and for which the data from the fractal plates fit very well. The intensity of the vortex shedding is also shown to decrease with increasing perimeter and fractal dimension and it is found that the rate at which these vortices are shed is the same for all plates if the characteristic length is used to normalise the frequency. It is also discussed how the decrease in the energy of the vortex shedding is linked to the volume of the wake. Finally, the use of fractal geometries to manipulate the wake to reduce noise is also investigated, with emphasis placed on various aspects of an aircrafts wing.
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Rigas, Georgios. "Modelling of turbulent wakes." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/26590.

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The dynamics of the turbulent three-dimensional wake generated by an axisymmetric bluff body with blunt trailing edge are experimentally and theoretically investigated at a diameter based Reynolds number of 188,000. A detailed analysis of the base pressure measurements shows that the large scale structures of the turbulent three-dimensional wake retain the structure of the laminar instabilities observed in the transitional regimes, in a statistical sense. These persisting instabilities at the turbulent regime, are associated with spatial and temporal symmetry breaking, giving rise to spatial reflectional symmetry and quasi-periodic vortex shedding. The influence of turbulence recovers the lost temporal and spatial symmetries in the long-time average. It is shown that the turbulent spatial dynamics are reproduced by a simple stochastic model the deterministic part of which accounts for the spatial symmetry breaking and gives rise to steady large scale structures through a supercritical pitchfork bifurcation, and the stochastic part modelling in a phenomenological sense the turbulent fluctuations acting on the large scale structures. The axisymmetric body wake is further investigated when axisymmetric slot-jet zero-net-mass-flux forcing is applied on the rear base. Landau-like models that capture the weakly nonlinear interaction between the global vortex shedding mode and axisymmetric forcing are derived from the phase-averaged Navier-Stokes equations. The Landau-like models describe accurately the forced response by means of measured base pressure of the global vortex shedding mode. With the present analysis it is demonstrated that the concept of weakly nonlinear global modes can be extended to a fully turbulent flow, far from the critical bifurcation Reynolds number, and a general framework for the description of systems with broken symmetries---giving rise to global dynamics---and turbulent dynamics is provided. The novel results presented here advance the understanding of the dynamics of three-dimensional turbulent wakes and pave the way for turbulence prediction and control.
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Smith, David Andrew Robert. "Pertubation of vortex wakes for amelioration of the vortex wake hazard." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.406670.

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Onur, Cagla. "Acoustic Tracking Of Ship Wakes." Phd thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615656/index.pdf.

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Theories about ship wake structure, bubble dynamics, acoustic propagation through bubble clouds, backscattering and target strength of bubble clouds have been investigated and related Matlab simulations have been carried on. Research has been carried on algorithms for ship wake acoustic detection and tracking. Particle filter method has been simulated with Matlab for target tracking using wake echo measurements. Simulation results are promising.
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Rind, Elad. "Turbulent wakes in turbulent streams." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/193955/.

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Direct numerical simulation and wind tunnel experiments have been used to study the effects of free-stream turbulence on axisymmetric wakes. In both cases the wake was introduced to various turbulent streams having various levels of turbulence intensity and length scales. It was found that the presence of the free-stream turbulence changes the wake’s decay rate and does not allow self-similarity to occur (unless maybe very far downstream and way beyond the current measurements reached). Also, the free-stream turbulence was found to be causing a significant transformation in the turbulence structure inside the wake, where the latter was found to be gradually evolving towards the former. Last, the fact that the two approaches were modelling two different problems led to some differences in their results emphasising the importance of the flow structure around the wake generating body in shaping the far wake region.
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Parslew, Ben. "Simulating avian wingbeats and wakes." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/simulating-avian-wingbeats-and-wakes(038035c2-fe9e-4104-92dc-544579c7011b).html.

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Analytical models of avian flight have previously been used to predict mechanical and metabolic power consumption during cruise. These models are limited, in that they neglect details of wing kinematics, and model power by assuming a fixed or rotary wing (actuator disk) weight support mechanism. Theoretical methods that incorporate wing kinematics potentially offer more accurate predictions of power consumption by calculating instantaneous aerodynamic loads on the wing. However, the success of these models inherently depends on the availability and accuracy of experimental kinematic data. The predictive simulation approach offers an alternative strategy, whereby kinematics are neither neglected nor measured experimentally, but calculated as part of the solution procedure. This thesis describes the development of a predictive tool for simulating avian wingbeat kinematics and wakes. The tool is designed in a modular format, in order to be extensible for future research in the biomechanics community. The primary simulation module is an inverse dynamic avian wing model that predicts aerodynamic forces and mechanical power consumption for given wing kinematics. The model is constructed from previous experimental studies of avian wing biomechanics. Wing motion is defined through joint kinematic time histories, and aerodynamic forces are predicted using blade element momentum theory. Mechanical power consumption at the shoulder joint is derived from both aerodynamic and inertial torque components associated with the shoulder joint rotation rate. An optimisation module is developed to determine wing kinematics that generate aerodynamic loads for propulsion and weight support in given flight conditions, while minimising mechanical power consumption. For minimum power cruise, optimisation reveals numerous local minima solutions that exhibit large variations in wing kinematics. Validation of the model against wind tunnel data shows that optimised solutions capture qualitative trends in wing kinematics with varying cruise speed. Sensitivity analyses show that the model outputs are most affected by the defined maximum lift coefficient and wing length, whereby perturbations in these parameters lead to significant changes in the predicted amount of upstroke wing retraction. Optimised solutions for allometrically scaled bird models show only small differences in predicted advance ratio, which is consistent with field study observations. Accelerating and climbing flight solutions also show similar qualitative trends in wing kinematics to experimental measurements, including a reduction in stroke plane inclination for increasing acceleration or climb angle. The model predicts that both climb angle and climb speed should be greater for birds with more available instantaneous mechanical power. Simulations of the wake using a discrete vortex model capture fundamental features of the wake geometry that have been observed experimentally. Reconstruction of the velocity field shows that this method overpredicts induced velocity in retracting-wing wakes, and should therefore only be applied to extended-wing phases of an avian wingbeat.
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Books on the topic "Wakes"

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Minerva Wakes. Riverdale NY: Baen Books, 1994.

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Soper, Michael. Xavier wakes. Middletown, DE: [publisher not identified], 2012.

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Magic wakes. [Place of publication not identified]: Wido Publishing, 2012.

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James S. A. Corey. Leviathan wakes. New York: Orbit, 2011.

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ill, Davie Helen, ed. He wakes me. New York: Orchard Books, 1991.

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ill, Jenkins Steve 1952, ed. Volcano wakes up! New York: Henry Holt and Company, 2009.

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Marlene, Freethy, ed. The Wakes resorts. [S.l.]: [Aurora], 1997.

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Merriton wakes up. Toronto: Lugus, 1994.

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Schubert, Leda. Winnie wakes up. London: Walker, 2000.

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Harwood, Seth. Jack wakes up. Barrington, NH: Breakneck Books Pub. Co., 2008.

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Book chapters on the topic "Wakes"

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Harris, Claire. "She Wakes." In Ancestral House, 246–55. New York: Routledge, 2021. http://dx.doi.org/10.4324/9780429039348-29.

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Yamazaki, Y. "Wakes, Dynamic Screening." In Interaction of Charged Particles with Solids and Surfaces, 423–41. Boston, MA: Springer US, 1991. http://dx.doi.org/10.1007/978-1-4684-8026-9_18.

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Neunaber, Ingrid. "Turbulence of Wakes." In Handbook of Wind Energy Aerodynamics, 881–911. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-31307-4_45.

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Neunaber, Ingrid. "Turbulence of Wakes." In Handbook of Wind Energy Aerodynamics, 1–34. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-05455-7_45-1.

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Fares, E., and W. Schröder. "Analysis of Wakes and Wake-Jet Interaction." In Flow Modulation and Fluid—Structure Interaction at Airplane Wings, 57–84. Berlin, Heidelberg: Springer Berlin Heidelberg, 2003. http://dx.doi.org/10.1007/978-3-540-44866-2_4.

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Massey, B. S. "Boundary Layers and Wakes." In Mechanics of Fluids, 235–84. Boston, MA: Springer US, 1989. http://dx.doi.org/10.1007/978-1-4899-3126-9_8.

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Feldmeier, Achim. "Jets, Wakes, and Cavities." In Theoretical and Mathematical Physics, 161–206. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-31022-6_5.

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Uddin, Naseem. "Wakes and Separated Flows." In Fluid Mechanics, 337–74. Boca Raton: CRC Press, 2022. http://dx.doi.org/10.1201/9781003315117-13.

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Dörenkämper, Martin, and Gerald Steinfeld. "Wind Farm Cluster Wakes." In Handbook of Wind Energy Aerodynamics, 1039–76. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-31307-4_52.

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Rosenblatt, Paul C., and Beverly R. Wallace. "Visitations, Wakes, and Funerals." In African American Grief, 29–42. New York: Routledge, 2021. http://dx.doi.org/10.4324/9781003169758-4.

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Conference papers on the topic "Wakes"

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Potts, Douglas, Zhi Leong, Jonathan Binns, Hayden Marcollo, and Alex Skvortsov. "Wakes of Surface-Piercing Cylinders." In ASME 2023 42nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/omae2023-101473.

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Abstract The hydrodynamics of surface-piercing cylinders differ from fully submerged cylinders due to the generation of surface wakes and under increasing flow velocities the formation of a ventilated pocket in the lee of the cylinder, both of which grow with increasing velocity, with concomitant effects on the hydrodynamic loading. Laboratory testing of surface-piercing cylinders to date has predominantly been confined to characterising the wakes of a rigid cylinder cantilevered down into the water from a towing tank carriage, which under certain test conditions will exhibit significant Vortex-Induced-Vibration (VIV). The wake characteristics of cylindrical structures such as those protruding through the free surface from a submerged platform do alter substantially depending on the structure, geometrical properties, and operating parameters. The relative length of submergence, or immersed aspect ratio (AR) and end conditions of the cylinder do also impact the wake formation. The wake characteristics can be described by two major regions: above and below the waterline. Where the above waterline wakes are derivatives of the bow wave run-up on the leading face of the cylinder, and the below waterline wakes are derivatives of the ventilation, which is the entrapment of air of the rear face of the cylinder. This paper presents an experimental programme in a towing tank to characterise the wake of cylindrical structures of different diameters, submergence, and forward speeds. Conventional experiments have the model attached from above the surface, however, this method is not representative of some real-world applications such as structures that are bottom mounted. [To the best of our knowledge] The authors developed the novel design of a bottom mount test platform, where the model is cantilevered from a single connection pointed up through the water column. The experiments collected a range of results including the forces, motions and wakes of the models where this paper will focus on presenting and defining the different wakes and insights into these phenomena.
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Izsak, Michael S., and Hsiao-Wei D. Chiang. "Turbine and Compressor Wake Modeling for Blade Forced Response." In ASME 1993 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1993. http://dx.doi.org/10.1115/93-gt-236.

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A key ingredient in turbine and compressor forced response analyses is the prediction of wake strength. An empirical wake model and a 3D CFD flow solver have been used for this purpose. The empirical wake model predictions were compared with wake data obtained from low speed turbine and compressor rigs, and from a high speed turbine facility for a high pressure turbine nozzle with cooling flows. The CFD flow solver is used to predict the turbine low speed and high speed wakes, and to provide a basis of comparison for transonic fan wakes. The wake data and predictions were Fourier decomposed to compare the harmonic content of the wakes. Although the empirical wake model adequately predicts the compressor wakes, turbine wake predictions need improvements. The CFD wake model needs additional data for calibration, in particular with regard to turbulence and transition. This paper provides a guide for applying empirical and CFD methods to model turbine and compressor wakes for blade forced response analysis.
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Mannikus, R., T. Soomere, and T. Torsvik. "Optimizing breakwater configuration for vessel wakes and wind waves." In 2012 IEEE/OES Baltic International Symposium (BALTIC). IEEE, 2012. http://dx.doi.org/10.1109/baltic.2012.6249201.

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Jordan, Stephen A. "Resolving Turbulent Wakes." In ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/fedsm2002-31282.

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Accurate resolution of turbulent wakes is a formidable task. Herein, we challenge this task by testing several compact schemes for approximating the convective derivative of the direct numerical and large-eddy simulation (DNS and LES) methodologies. The stencils house the needed resolution efficiency and numerical stability characteristics to properly resolve turbulent wakes while concurrently maintaining convergent solutions. Turbulent wakes of the circular cylinder are computed for Re = 1260 and 3900 with the results verified by the experimental evidence.
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Womack, Kristofer M., Ralph J. Volino, and Michael P. Schultz. "Combined Effects of Wakes and Jet Pulsing on Film Cooling." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27921.

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Pulsed film cooling jets subject to periodic wakes were studied experimentally. The wakes were generated with a spoked wheel upstream of a flat plate. Cases with a single row of cylindrical film cooling holes inclined at 35 degrees to the surface were considered at blowing ratios, B, of 0.50, and 1.0 with jet pulsing and wake Strouhal numbers of 0.15, 0.30, and 0.60. Wake timing was varied with respect to the pulsing. Temperature measurements were made using an infrared camera, thermocouples, and constant current (cold wire) anemometry. The local film cooling effectiveness and heat transfer coefficient were determined from the measured temperatures. Phase locked flow temperature fields were determined from cold wire surveys. With B = 0.5, wakes and pulsing both lead to a reduction in film cooling effectiveness, and the reduction is larger when wakes and pulsing are combined. With B = 1.0, pulsing again causes a reduction in effectiveness, but wakes tend to counteract this effect somewhat by reducing jet liftoff. At low Strouhal numbers, wake timing had a significant effect on the instantaneous film cooling effectiveness, but wakes in general had very little effect on the time averaged effectiveness. At high Strouhal numbers, the wake effect was stronger, but the wake timing was less important. Wakes increased the heat transfer coefficient strongly and similarly in cases with and without film cooling, regardless of wake timing. Heat transfer coefficient ratios, like the time averaged film cooling effectiveness, did not depend strongly on wake timing for the cases considered.
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Praisner, T. J., J. P. Clark, T. C. Nash, M. J. Rice, and E. A. Grover. "Performance Impacts Due to Wake Mixing in Axial-Flow Turbomachinery." In ASME Turbo Expo 2006: Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-90666.

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One of the last loss mechanisms remaining to be quantified and correlated for inclusion in meanline predictive systems concerns the mixing of wakes across downstream airfoil rows. Here, we demonstrate that the unsteady losses incurred as turbomachinery wakes mix in downstream rows are a function of the velocity ratio across the downstream row as calculated in the frame of reference of wake generation. Analytical and computational results, compared to measurements of wakes mixing under variable free-stream velocity conditions, reveal that wake-loss modification is primarily a result of an inviscid dilation of the stream tubes that comprise the wake fluid. Further, simulations of wakes exposed to a range of turbomachinery-specific velocity ratios indicate that wake-loss augmentation caused by stream-tube dilation is significantly more pronounced than wake-loss reductions imparted by stream-tube contraction. It is demonstrated that wakes in turbines are dilated in the adjacent downstream row, whether it is a vane or a blade row, through a work extraction process that occurs in the wake-generation reference frame. Finally, comparisons between rig data and CFD simulations suggest that wake-mixing losses, enhanced by downstream rows, can contribute as much as 1.5 percent of lost efficiency in multistage low-pressure turbines.
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Kraft, Wayne N., and Malcolm J. Andrews. "Experimental Investigation of Stratified, Buoyant Wakes." In ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56623.

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The development of a buoyant plane wake has been investigated experimentally. A water channel has been used as a statistically steady experiment to investigate the plane wakes. Parallel streams of hot and cold water are initially separated by a splitter plate. The streams are oriented such that the cold fluid is above the hot fluid, resulting in an unstable stratification. At the end of the splitter plate, the two streams are allowed to mix and a buoyancy driven mixing layer develops. Downstream of the splitter plate, growth of the turbulent buoyancy-driven mix is disrupted by a cylinder. The cylinder is located at the centerline of the mixing layer and associated wake. As a result the dynamic flows of the plane wake and buoyancy driven mixing layer interact. Particle image velocimetry (PIV), and a high-resolution thermocouple system are used to measure the response of the plane wake to buoyancy driven turbulence. Velocity and density measurements are used as a basis from which we describe the transition, and return to equilibrium, of the buoyancy driven mixing layer. We found for wakes where buoyancy is driving the motion, a remarkably fast recovery of a Rayleigh-Taylor mix in the wake region.
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Womack, Kristofer M., Ralph J. Volino, and Michael P. Schultz. "Measurements in Film Cooling Flows With Periodic Wakes." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27917.

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Film cooling flows subject to periodic wakes were studied experimentally. The wakes were generated with a spoked wheel upstream of a flat plate. Cases with a single row of cylindrical film cooling holes inclined at 35 degrees to the surface were considered at blowing ratios of 0.25, 0.50, and 1.0 with a steady freestream and with wake Strouhal numbers of 0.15, 0.30, and 0.60. Temperature measurements were made using an infrared camera, thermocouples, and constant current (cold wire) anemometry. Hot wire anemometry was used for velocity measurements. The local film cooling effectiveness and heat transfer coefficient were determined from the measured temperatures. Phase locked flow temperature fields were determined from cold wire surveys. Wakes decreased the film cooling effectiveness for blowing ratios of 0.25 and 0.50 when compared to steady freestream cases. In contrast, effectiveness increased with Strouhal number for the 1.0 blowing ratio cases, as the wakes helped mitigate the effects of jet liftoff. Heat transfer coefficients increased with wake passing frequency, with nearly the same percentage increase in cases with and without film cooling. The time resolved flow measurements show the interaction of the wakes with the film cooling jets. Near-wall flow measurements are used to infer the instantaneous film cooling effectiveness as it changes during the wake passing cycle.
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Rose, Martin G., and Neil W. Harvey. "Turbomachinery Wakes: Differential Work and Mixing Losses." In ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/99-gt-025.

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In this paper the mixing of stator wakes in turbomachinery is considered. An extension is made to the existing model of Denton (1993), which addresses the effects of acceleration before mixing. Denton showed that if a total pressure wake was accelerated mixing loss diminished and vice versa. Here a total temperature wake is shown to exhibit a reverse trend. An attempt is also made to better understand the work transfer process between a stator wake and a rotor. The paper concentrates on axial turbines, but a brief look at compressors is included. It is argued that the freestream work is not the same as the wake work and the concept of ‘Differential Work’ is introduced. A simple steady velocity triangle based model is proposed to give an estimate of the ratio of wake work to freestream work (μ see later). The model is compared to an unsteady CFD result to offer some verification of the assumptions. It is concluded that the rotodynamic work process tends to reduce total pressure wake depths in turbines and compressors and therefore mixing losses. The mixing loss due to total temperature wakes is less strongly affected by the differential work process.
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McCroskey, W. "Vortex wakes of rotorcraft." In 33rd Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1995. http://dx.doi.org/10.2514/6.1995-530.

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Reports on the topic "Wakes"

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Kelley, Christopher Lee, David Charles Maniaci, and Brian R. Resor. Wind Turbine Wakes. Office of Scientific and Technical Information (OSTI), October 2015. http://dx.doi.org/10.2172/1331504.

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Bain, Rachel, Richard Styles, and Jared Lopes. Ship-induced waves at Tybee Island, Georgia. Engineer Research and Development Center (U.S.), December 2022. http://dx.doi.org/10.21079/11681/46140.

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Commercial vessels transiting the Savannah entrance channel intermittently generate large wake events at Tybee Island, Georgia, creating a potential hazard for beachgoers. However, not all commercial vessels generate large wakes, and the relationship between vessel dimensions, operating conditions, wake height, and drawdown magnitude is unclear. This study evaluates bathymetric data, high-frequency wave and vessel wake measurements, and broadcast vessel identification over a 4-month period with the goal of providing a quantitative characterization of vessel wake conditions at Tybee Island. Data from 1,386 cargo vessel passages and 202 tanker passages indicate that vessel dimensions (length and beam) are positively correlated with drawdown magnitude and secondary wake height, although large vessels do not consistently generate large wakes. Container ships, which tended to travel faster than tankers, corresponded to the largest wakes in the dataset. A further hypothesis is that tidally modulated energy dissipation may favor smaller vessel wake uprush at low tide and larger uprush at high tide, but this idea cannot be confirmed without additional measurements to quantify nonlinear wave propagation on the beach face. Based on the collected data, the study concludes with four recommendations for reducing risk to beachgoers.
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Burov, Alexey, and Timofey Zolkin. TMCI with Resonator Wakes. Office of Scientific and Technical Information (OSTI), June 2018. http://dx.doi.org/10.2172/1480111.

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Spedding, Geoffrey R. Experiments in Developing Wakes. Fort Belvoir, VA: Defense Technical Information Center, April 2014. http://dx.doi.org/10.21236/ada619192.

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Ramsdell, J. V. Jr, and C. A. Simonen. Atmospheric relative concentrations in building wakes. Office of Scientific and Technical Information (OSTI), May 1997. http://dx.doi.org/10.2172/481848.

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Jayne, Steven R. Observing the Evolution of Typhoon Wakes. Fort Belvoir, VA: Defense Technical Information Center, September 2009. http://dx.doi.org/10.21236/ada531982.

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Jayne, Steven R. Observing the Evolution of Typhoon Wakes. Fort Belvoir, VA: Defense Technical Information Center, September 2010. http://dx.doi.org/10.21236/ada542476.

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Ramsdell, J. V. Jr, C. A. Simonen, and S. B. Smyth. Atmospheric relative concentrations in building wakes. Office of Scientific and Technical Information (OSTI), May 1995. http://dx.doi.org/10.2172/70706.

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Blaskiewicz, Michael. Simple formula for surface roughness wakes. Office of Scientific and Technical Information (OSTI), July 2019. http://dx.doi.org/10.2172/1542781.

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Jayne, Steven R. Observing the Evolution of Typhoon Wakes. Fort Belvoir, VA: Defense Technical Information Center, March 2012. http://dx.doi.org/10.21236/ada560220.

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