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1
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.
11
Jia, Yan, Shuyi Liu, Yongqing Liu, Limin Zhai, Yifan Gong, and Xiangkun Zhang. "Echo-Level SAR Imaging Simulation of Wakes Excited by a Submerged Body." Sensors 24, no. 4 (February 7, 2024): 1094. http://dx.doi.org/10.3390/s24041094.
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The paper introduces a numerical simulation method for Synthetic Aperture Radar (SAR) imaging of submerged body wakes by integrating hydrodynamics, electromagnetic scattering, and SAR imaging simulation. This work is helpful for better understanding SAR images of submerged body wakes. Among these, the hydrodynamic model consists of two sets of ocean dynamics closely related to SAR imaging, namely the wake of the submerged body and wind waves. For the wake, we simulated it using computational fluid dynamics (CFD) numerical methods. Furthermore, we compared and computed the electromagnetic scattering characteristics of wakes under various navigation parameters and sea surface conditions. Following that, based on the operational principles and imaging theory of synthetic aperture radar (SAR), we established the SAR raw echo signal of the wake. Employing a Range-Doppler (RD) algorithm, we generated simulated SAR images of the wake. The results indicate that utilizing Computational Fluid Dynamics (CFD) numerical methods enables the simulation of wake characteristics generated by the motion of a submerged body with different velocities. The backscattering features of wakes are closely associated with the relative orientation between the wake and the radar line of sight. Under specific wind speeds, the wake gets masked within the sea surface background, resulting in less discernible characteristics of the wake in SAR images. This suggests that at lower speeds of submerged body or under specific wind conditions, the detectability of the wake in SAR images significantly diminishes.
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Bodini, Nicola, Dino Zardi, and Julie K. Lundquist. "Three-dimensional structure of wind turbine wakes as measured by scanning lidar." Atmospheric Measurement Techniques 10, no. 8 (August 14, 2017): 2881–96. http://dx.doi.org/10.5194/amt-10-2881-2017.
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Abstract. The lower wind speeds and increased turbulence that are characteristic of turbine wakes have considerable consequences on large wind farms: turbines located downwind generate less power and experience increased turbulent loads. The structures of wakes and their downwind impacts are sensitive to wind speed and atmospheric variability. Wake characterization can provide important insights for turbine layout optimization in view of decreasing the cost of wind energy. The CWEX-13 field campaign, which took place between June and September 2013 in a wind farm in Iowa, was designed to explore the interaction of multiple wakes in a range of atmospheric stability conditions. Based on lidar wind measurements, we extend, present, and apply a quantitative algorithm to assess wake parameters such as the velocity deficits, the size of the wake boundaries, and the location of the wake centerlines. We focus on wakes from a row of four turbines at the leading edge of the wind farm to explore variations between wakes from the edge of the row (outer wakes) and those from turbines in the center of the row (inner wakes). Using multiple horizontal scans at different elevations, a three-dimensional structure of wakes from the row of turbines can be created. Wakes erode very quickly during unstable conditions and can in fact be detected primarily in stable conditions in the conditions measured here. During stable conditions, important differences emerge between the wakes of inner turbines and the wakes of outer turbines. Further, the strong wind veer associated with stable conditions results in a stretching of the wake structures, and this stretching manifests differently for inner and outer wakes. These insights can be incorporated into low-order wake models for wind farm layout optimization or for wind power forecasting.
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Cao, Liushuai, Yanyan Pan, Gang Gao, Linjie Li, and Decheng Wan. "Review on the Hydro- and Thermo-Dynamic Wakes of Underwater Vehicles in Linearly Stratified Fluid." Journal of Marine Science and Engineering 12, no. 3 (March 15, 2024): 490. http://dx.doi.org/10.3390/jmse12030490.
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Wakes produced by underwater vehicles, particularly submarines, in density-stratified fluids play a pivotal role across military, academic, and engineering domains. In comparison to homogeneous fluid environments, wakes in stratified flows exhibit distinctive phenomena, including upstream blocking, pancake eddies, internal waves, and variations in hydrodynamic performance. These phenomena are crucial for optimizing the operation of underwater vehicles. This review critically assesses the hydrodynamic and thermodynamic aspects of these wakes through an integration of theoretical, experimental, and numerical approaches. The hydrodynamic wake evolution, comprising near-wake, non-equilibrium, and quasi-two-dimensional regimes, is scrutinized. The underlying physics, encompassing energy transformation, vertical motion suppression, and momentum dissipation, are analyzed in detail. Special emphasis is placed on numerical methods, encompassing diverse approaches and turbulence models and highlighting their differences in fidelity and computational cost. Numerical simulations not only provide insights into the intricate interplay among various factors but also emerge as a crucial focal point for future research directions. In the realm of thermodynamic wakes, we delve into the thermal wake induced by the discharge of high-temperature cooling water and the cold wake resulting from the stirring of seawater. The generation, evolution, and ascent to the free surface of these wakes are explored. Additionally, this review identifies and analyzes current research shortcomings in each aspect. By systematically addressing existing knowledge gaps, our study contributes novel insights that propel academic progress and bear significant implications for submarine engineering. This work not only enhances our understanding of the intricate dynamics involved but also provides a foundation for future research endeavors in this critical field.
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BANE, K. L. F. "WAKEFIELDS OF SUB-PICOSECOND ELECTRON BUNCHES." International Journal of Modern Physics A 22, no. 22 (September 10, 2007): 3736–58. http://dx.doi.org/10.1142/s0217751x07037391.
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We discuss wakefields excited by short bunches in accelerators. In particular, we review some of what has been learned in recent years concerning diffraction wakes, roughness impedance, coherent synchrotron radiation wakes, and the resistive wall wake, focusing on analytical solutions where possible. As examples, we apply formulas for these wakes to various parts of the Linac Coherent Light Source (LCLS) project. The longitudinal accelerator structure wake of the SLAC linac is an important ingredient in the LCLS bunch compression process. Of the wakes in the undulator region, the dominant one is the resistive wall wake of the beam pipe.
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Shi, Hui, Yao Luo, Fenghua Zhou, Chunhua Qiu, Dongxiao Wang, and Zhenqiu Zhang. "Abnormal Waves Observation and Analysis of the Mechanism in the Pearl River Estuary, South China." Water 15, no. 5 (March 6, 2023): 1001. http://dx.doi.org/10.3390/w15051001.
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The Pearl River Estuary is a typical estuary region in southern China, and the study of surface wave occurrence and characteristics is of great importance for shipping management, nearshore engineering, and monitoring shoreline changes and other human activities. Long-term and continuous observational data are critical for achieving a better understanding of waves. In this study, the wave measurements based on a high-precision wave gauge were analyzed and observation data over approximately two years at a sampling frequency of 2 Hz were obtained. The wave system in the Pearl River Estuary was found to deviate from the assumption of a stationary stochastic process similar to that in the open ocean, due to the effects of abnormal waves caused by human activities. Therefore, traditional distribution functions such as Rayleigh and Weibull were not suitable for accurately fitting the main wave parameters (Hs, Tp, etc.), particularly in the tail. Consequently, abnormal wave signals were extracted from all wave sets, and through the comparison and analysis of the wave spectral features, it was determined that these abnormal waves are caused by the ship wakes. The spectral characterization of these waves was performed to determine the characteristics of different ship wake processes. Ship wakes in the Pearl River Estuary are an important part of the wave system, and their wave height is significantly larger than the normal wave. Based on the spectral characteristics of ship wakes, this study proposed some news characteristics of ship wakes in the main channel of the Pearl River Estuary.
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Rosencrans, David, Julie K. Lundquist, Mike Optis, Alex Rybchuk, Nicola Bodini, and Michael Rossol. "Seasonal variability of wake impacts on US mid-Atlantic offshore wind plant power production." Wind Energy Science 9, no. 3 (March 14, 2024): 555–83. http://dx.doi.org/10.5194/wes-9-555-2024.
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Abstract. The mid-Atlantic will experience rapid wind plant development due to its promising wind resource located near large population centers. Wind turbines and wind plants create wakes, or regions of reduced wind speed, that may negatively affect downwind turbines and plants. We evaluate wake variability and annual energy production with the first yearlong modeling assessment using the Weather Research and Forecasting model, deploying 12 MW turbines across the domain at a density of 3.14 MW km−2, matching the planned density of 3 MW km−2. Using a series of simulations with no wind plants, one wind plant, and complete build-out of lease areas, we calculate wake effects and distinguish the effect of wakes generated internally within one plant from those generated externally between plants. We also provide a first step towards uncertainty quantification by testing the amount of added turbulence kinetic energy (TKE) by 0 % and 100 %. We provide a sensitivity analysis by additionally comparing 25 % and 50 % for a short case study period. The strongest wakes, propagating 55 km, occur in summertime stable stratification, just when New England's grid demand peaks in summer. The seasonal variability of wakes in this offshore region is much stronger than the diurnal variability of wakes. Overall, yearlong simulated wake impacts reduce power output by a range between 38.2 % and 34.1 % (for 0 %–100 % added TKE). Internal wakes cause greater yearlong power losses, from 29.2 % to 25.7 %, compared to external wakes, from 14.7 % to 13.4 %. The overall impact is different from the linear sum of internal wakes and external wakes due to non-linear processes. Additional simulations quantify wake uncertainty by modifying the added amount of turbulent kinetic energy from wind turbines, introducing power output variability of 3.8 %. Finally, we compare annual energy production to New England grid demand and find that the lease areas can supply 58.8 % to 61.2 % of annual load. We note that the results of this assessment are not intended to make nor are they suitable to make commercial judgments about specific wind projects.
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Chen, Ming Rong, Wei Chi, and Lian Gan Jin. "Extraction Method of the Contrast Feature of Ship Wake Images." Advanced Materials Research 712-715 (June 2013): 2403–6. http://dx.doi.org/10.4028/www.scientific.net/amr.712-715.2403.
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Since how to evaluate the ship wake images quality quantitatively and effectively, and achieve the purpose of the extraction of ship wakes optical signal characteristics rapidly, is an important base task for the ship optics-wakes elimination technology now. The method about quality evaluation of ship wake images is studied in this paper based on the contrast model. According to the characteristics of the obvious contrast between wake area and seawater background area in ship wake images, this paper uses the contrast parameter as the index of wake image quality evaluation, and also as the characterization of the strength of ship wakes optical signal characteristic. An experiment about the extraction of contrast feature and its results show that the contrast parameters can not only reflect the subjective visual perception of the human eye on the wake images actual quality, but also better reflect the application essence of the wake image processing. And the contrast parameters can describe the intensitys changing rules of ship wakes optical signal characteristics reliably and quantitatively.
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Grandpeix, Jean-Yves, and Jean-Philippe Lafore. "A Density Current Parameterization Coupled with Emanuel’s Convection Scheme. Part I: The Models." Journal of the Atmospheric Sciences 67, no. 4 (April 1, 2010): 881–97. http://dx.doi.org/10.1175/2009jas3044.1.
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Abstract The aim of the present series of papers is to develop a density current parameterization for global circulation models. This first paper is devoted to the presentation of this new wake parameterization coupled with Emanuel’s convective scheme. The model represents a population of identical circular cold pools (the wakes) with vertical frontiers. The wakes are cooled by the precipitating downdrafts while the outside area is warmed by the subsidence induced by the saturated drafts. The budget equations for mass, energy, and water yield evolution equations for the prognostic variables (the vertical profiles of the temperature and humidity differences between the wakes and their exterior). They also provide additional terms for the equations of the mean variables. The driving terms of the wake equations are the differential heating and drying due to convective drafts. The action of the convection on the wakes is implemented by splitting the convective tendency and attributing the effect of the precipitating downdrafts to the wake region and the effect of the saturated drafts to their exterior. Conversely, the action of the wakes on convection is implemented by introducing two new variables representing the convergence at the leading edge of the wakes. The available lifting energy (ALE) determines the triggers of deep convection: convection occurs when ALE exceeds the convective inhibition. The available lifting power (ALP) determines the intensity of convection; it is equal to the power input into the system by the collapse of the wakes. The ALE/ALP closure, together with the splitting of the convective heating and drying, implements the full coupling between wake and convection. The coupled wake–convection scheme thus created makes it possible to represent the moist convective processes more realistically, to prepare the coupling of convection with boundary layer and orographic processes, and to consider simulating the propagation of convective systems.
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Morozova, T. I., and S. I. Popel. "Modulational Interaction in a Dusty Plasma of Meteoroid Wakes." Geomagnetism and Aeronomy 61, no. 6 (November 2021): 888–95. http://dx.doi.org/10.1134/s0016793221060116.
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Abstract This is a study of the possible modulational instability of electromagnetic waves in meteoroid wakes associated with the dust acoustic mode at altitudes of 80–120 km, which is a linear stage of modulational interaction. The parameters of meteoroid wakes at different altitudes in the Earth’s ionosphere are considered. It is shown that the charging of dust particles of meteoric matter creates conditions for the occurrence of dust acoustic waves. Dust acoustic disturbances are excited due to the modulational instability of electromagnetic waves from the meteoric trail. The influence of neutrals on the development of modulational interaction is taken into account. The concentration of neutrals in meteoric wakes is higher than the concentration of neutrals in the Earth’s ionosphere. It has been found that the condition for the excitation of a dust acoustic wave is satisfied for the typical parameters of dusty plasma of meteoroid wakes at altitudes of 100–120 km. Due to collisions between dust and neutrals, the development of modulation instability is suppressed at altitudes of 80–90 km, while inelastic collisions of neutrals with electrons and ions do not affect the development of modulational instability. The modulational instability of electromagnetic waves can explain the occurrence of low-frequency noise during the passage of meteoric bodies in a frequency range characteristic of dust acoustic waves. It is shown that the modulation instability has time to develop for characteristic temperatures and particle concentrations in meteoroid wakes. Equations for the charging of dust particles in meteoroid wakes are given. It has been found that the dust is positively charged, both in the daytime and at night, due to intense emission currents from the surface of dust particles.
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Aird, Jeanie A., Eliot W. Quon, Rebecca J. Barthelmie, Mithu Debnath, Paula Doubrawa, and Sara C. Pryor. "Region-Based Convolutional Neural Network for Wind Turbine Wake Characterization in Complex Terrain." Remote Sensing 13, no. 21 (November 4, 2021): 4438. http://dx.doi.org/10.3390/rs13214438.
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We present a proof of concept of wind turbine wake identification and characterization using a region-based convolutional neural network (CNN) applied to lidar arc scan images taken at a wind farm in complex terrain. We show that the CNN successfully identifies and characterizes wakes in scans with varying resolutions and geometries, and can capture wake characteristics in spatially heterogeneous fields resulting from data quality control procedures and complex background flow fields. The geometry, spatial extent and locations of wakes and wake fragments exhibit close accord with results from visual inspection. The model exhibits a 95% success rate in identifying wakes when they are present in scans and characterizing their shape. To test model robustness to varying image quality, we reduced the scan density to half the original resolution through down-sampling range gates. This causes a reduction in skill, yet 92% of wakes are still successfully identified. When grouping scans by meteorological conditions and utilizing the CNN for wake characterization under full and half resolution, wake characteristics are consistent with a priori expectations for wake behavior in different inflow and stability conditions.
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Shuang, Sun, Li Wei, Lu Xin’gen, Zhang Yanfeng, Zhu Junqiang, and Tong Guoxiang. "A Comparison of the Wake Effects Generated by the Biased Triangle Bar and Traditional Cylinder Bar to the Boundary Layer on Suction Surface of LPT Blade." International Journal of Turbo & Jet-Engines 37, no. 2 (September 25, 2020): 153–66. http://dx.doi.org/10.1515/tjj-2017-0017.
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AbstractConsidering the asymmetry of the low pressure turbine blade (LPT) wake at a low Reynolds number, the influence of asymmetric wakes which are similar to LPT wakes on the boundary layer of downstream blade rows in the near field is studied in the present paper, in order to increase wake flow prediction accuracy of the downstream blade without increasing the difficulty of the experiment or calculation load. Packb high-lift LPT airfoil was studied with CFX software. Following the analysis of the similarities between the wake generated by the cylinder bar and the triangle bar and the LPT blade wake in the near-field, the boundary layer flow characteristics on the suction surface under the different wakes were compared. In this research, it was found that the wakes of biased triangle bar shared more similarities with the LPT blade wake in the near field than the cylinder bar. Furthermore, the biased triangle bar wake was asymmetrical in terms of its centerline, and the separation bubble was suppressed while the calming effect was reduced after the wake-induced transition due to the asymmetry. And the time-averaged momentum thickness decreased by 7 % compared to the cylinder wake.
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El Safty, Hoda, and Reza Marsooli. "Ship Wakes and Their Potential Impacts on Salt Marshes in Jamaica Bay, New York." Journal of Marine Science and Engineering 8, no. 5 (May 3, 2020): 325. http://dx.doi.org/10.3390/jmse8050325.
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Aerial photographs and field studies have revealed a rapid deterioration of salt marshes in Jamaica Bay, New York. Past studies have linked marsh deterioration to sediment supply, water quality, storms, and sea level rise. Yet ship wakes and their potential impacts on marsh edge erosion are not understood. Here, we study ship wake transformation in Jamaica Bay and their potential impacts on salt marsh erosion. We apply short-time, Fourier transform (spectrogram) on existing water level measurements collected during 2015 and 2016. Our analysis reveals the existence of typical wake components. Among the observed wake components is a long wave component which propagates over shallow areas where short wind waves do not reach. We further implement a phase-resolving wave model to study wake transformation in the vicinity of salt marsh islands Little Egg and Big Egg and the consequent morphological changes. The selected marshes are located near a deep shipping channel and a ferry station, making them exposed to wakes of vessels with different size and sailing speed. A series of numerical experiments show that ship wakes can result in erosion spots near the border of deep shipping channels and their banks, i.e., edges of mudflats and marsh substrates. We show that the cumulative erosion increases rapidly with the number of vessels that pass through the study area. For instance, the magnitude of final bed erosion after the passage of 10 vessels is two to three times larger than that after the passage of five vessels.
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Figlus, Jens, Fangzhou Tong, and William Fuller. "VESSEL WAKE INDUCED DYNAMICS IN A SHALLOW-BAY ENVIRONMENT." Coastal Engineering Proceedings, no. 37 (September 1, 2023): 53. http://dx.doi.org/10.9753/icce.v37.management.53.
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Ship wakes generated by large deep-draft vessels as well as those generated by smaller barges have the potential to cause significant compounding erosion and sedi-mentation issues, especially along high-traffic waterways. Yet, long-term in situ measurements of the actual hydro-dynamics initiated by ship wakes are rare. These data, however, are needed to optimize the design of erosion mitigation structures, to plan dredging efforts, to validate numerical modeling efforts, and to establish a basis from which the erosion and sedimentation potential of projected ship traffic can be estimated. This study is intended to help close some of these existing knowledge gaps through detailed analyses of measured velocity, water free-surface elevation change, and suspended sediment concentration caused by wind waves and ship wakes in the shallow-bay environment of Galveston Bay, Texas (GBT). In addition, numerical modeling efforts are being presented using the Boussinesq-type wave model FUNWAVE-TVD (Shi et al., 2012) to simulate individual vessel wake hydrodynamics and sediment-related dynamics and interactions with the local bathymetry and wetland edges based on the collected field data.
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Bich Ngoc, Hoang Thi. "Types of momentum defect diffusion at the begining of the wake and wake establishment zone for the coupled wake and comparison with the isolated wake." Vietnam Journal of Mechanics 20, no. 3 (September 30, 1998): 37–45. http://dx.doi.org/10.15625/0866-7136/10026.
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The article [10] has presented the necessity of the classification into two types: Isolated wakes and coupled wakes. In this report, different types of momentum defect diffusion at the beginning of wake are analyzed for the two types of coupled wake and isolated wake. According to ·numerical results obtained, we analyses the existence - long or short - of the wake establishment zone before the wake established zone, and this zone is very different between isolated wake and coupled wake.
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Soodak, Harry, and Martin S. Tiersten. "Wakes and waves in N dimensions." American Journal of Physics 61, no. 5 (May 1993): 395–401. http://dx.doi.org/10.1119/1.17230.
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Sherratt, Jonathan A. "Irregular wakes in reaction-diffusion waves." Physica D: Nonlinear Phenomena 70, no. 4 (February 1994): 370–82. http://dx.doi.org/10.1016/0167-2789(94)90072-8.
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Trabucchi, Davide, Lukas Vollmer, and Martin Kühn. "3-D shear-layer model for the simulation of multiple wind turbine wakes: description and first assessment." Wind Energy Science 2, no. 2 (November 22, 2017): 569–86. http://dx.doi.org/10.5194/wes-2-569-2017.
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Abstract. The number of turbines installed in offshore wind farms has strongly increased in the last years and at the same time the need for more precise estimations of the wind farm efficiency too. In this sense, the interaction between wakes has become a relevant aspect for the definition of a wind farm layout, for the assessment of its annual energy yield and for the evaluation of wind turbine fatigue loads. For this reason, accurate models for multiple overlapping wakes are a main concern of the wind energy community. Existing engineering models can only simulate single wakes, which are superimposed when they are interacting in a wind farm. This method is a practical solution, but it is not fully supported by a physical background. The limitation to single wakes is given by the assumption that the wake is axisymmetric. As an alternative, we propose a new shear-layer model that is based on the existing engineering wake models but is extended to also simulate non-axisymmetric wakes. In this paper, we present the theoretical background of the model and four application cases. We evaluate the new model for the simulation of single and multiple wakes using large-eddy simulations as reference. In particular, we report the improvements of the new model predictions in comparison to a sum-of-squares superposition approach for the simulation of three interacting wakes. The lower deviation from the reference considering single and multiple wakes encourages the further development of the model and promises a successful application for the simulation of wind farm flows.
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Schneemann, Jörge, Andreas Rott, Martin Dörenkämper, Gerald Steinfeld, and Martin Kühn. "Cluster wakes impact on a far-distant offshore wind farm's power." Wind Energy Science 5, no. 1 (January 3, 2020): 29–49. http://dx.doi.org/10.5194/wes-5-29-2020.
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Abstract. Our aim with this paper was the analysis of the influence of offshore cluster wakes on the power of a far-distant wind farm. We measured cluster wakes with long-range Doppler light detection and ranging (lidar) and satellite synthetic aperture radar (SAR) in different atmospheric stabilities and analysed their impact on the 400 MW offshore wind farm Global Tech I in the German North Sea using supervisory control and data acquisition (SCADA) power data. Our results showed clear wind speed deficits that can be related to the wakes of wind farm clusters up to 55 km upstream in stable and weakly unstable stratified boundary layers resulting in a clear reduction in power production. We discussed the influence of cluster wakes on the power production of a far-distant wind farm, cluster wake characteristics and methods for cluster wake monitoring. In conclusion, we proved the existence of wake shadowing effects with resulting power losses up to 55 km downstream and encouraged further investigations on far-reaching wake shadowing effects for optimized areal planning and reduced uncertainties in offshore wind power resource assessment.
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Soomere, Tarmo. "Nonlinear Components of Ship Wake Waves." Applied Mechanics Reviews 60, no. 3 (May 1, 2007): 120–38. http://dx.doi.org/10.1115/1.2730847.
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Nonlinear components of wakes from large high-speed ships at times carry a substantial part of the wake energy and behave completely differently compared to the classical Kelvin wave system. This overview makes an attempt to summarize the descriptions of nonlinear parts of a ship’s wake. For completeness, also the basic properties of the Kelvin wake are sketched. The central topic is the generation of solitons by ship motion both in channels and in unbounded sea areas. The discussion is mostly limited to disturbances on the surface of nonstratified water. The optional nonlinear components of the ship wake such as the very narrow V-like wake components, packets of monochromatic waves, ship-generated depression areas, and supercritical bores are also discussed. Specific features of solitonic ship waves and their interactions have numerous applications in naval and coastal engineering, and in adjacent areas of applied mechanics. An overview of the practical use of certain properties of phase shifts, and particularly high wave humps occurring during Mach reflection and nonlinear interaction of solitons in decreasing the wave resistance at supercritical speeds and in the freak wave theory, is also presented. The final part of the paper describes the results of studies of far-field properties of nonlinear wakes and possible consequences of the increase of local hydrodynamic activity. There are 263 references cited in this review article.
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Zhao, Chang Yu, Meng Xiao Bo, Jian Yong Zhu, and Guang Li Li. "Numerical Study of Wakes on Downstream Effects in Static Cascade Flow Field to Simulation of Rotor Wake." Advanced Materials Research 805-806 (September 2013): 1865–69. http://dx.doi.org/10.4028/www.scientific.net/amr.805-806.1865.
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The effects of moving wakes on the compressor cascade flow are discussed in this article, which can be regarded as the flow simulation between stages of compressor cascade. The moving wakes are simulated by moving cylinder before a compressor cascade flow. Different flow situations by changing the angle of wakes direction are presented by numerical simulation. The performance of cascade influenced by cylinder wakes can be related to several parameters, such as the distance between cascades in the shaft direction, the angle of wake direction. Loss of the cascade changes along with those parameters whose optimal direction is demonstrated.
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Jiang, Bing-Feng, De-Fu Hou, and Jia-Rong Li. "Wakes in viscous quark-gluon plasma." International Journal of Modern Physics: Conference Series 29 (January 2014): 1460217. http://dx.doi.org/10.1142/s2010194514602178.
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With the dielectric function derived from the chromohydrodynamic approach, we investigate wakes in induced charge density and wake potential induced by a fast parton traveling through the viscous quark-gluon plasma (QGP). When the fast parton moves with a speed v = 0.55c which is less than the phase velocity of plasmon vp in QGP, the equicharge lines show a sign flip in the backward-forward spaces. While for v = 0.99c which is larger than vp, the equicharge lines show an oscillatory behavior. A Lennard-Jones potential and an oscillatory wake potential are found in the backward direction for v = 0.55c and v = 0.99c respectively. In addition, the viscous effect on wakes is also speed-dependent. When v = 0.55c, shear viscosity has a trivial impact on the wakes. While for v = 0.99c, shear viscosity modifies the strength and structure of the wakes significantly.
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Orth, U. "Unsteady Boundary-Layer Transition in Flow Periodically Disturbed by Wakes." Journal of Turbomachinery 115, no. 4 (October 1, 1993): 707–13. http://dx.doi.org/10.1115/1.2929306.
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Boundary layers on turbomachinery blades develop in a flow that is periodically disturbed by the wakes of upstream blade cascades. These wakes have a significant effect upon laminar-turbulent boundary-layer transition. In order to study these effects, detailed velocity measurements using hot-wire probes were performed within the boundary-layer of a plate in flow periodically disturbed by wakes produced by bars moving transversely to the flow. The measurements were evaluated using the ensemble-averaging technique. The results show how the wake disturbance enters the boundary-layer and leads to a turbulent patch, which grows and is carried downstream. In favorable pressure gradients, transition due to wake turbulence occurred much earlier than predicted by linear stability theory. Between two wakes, laminar becalmed regions were observed far beyond the point at which the undisturbed boundary-layer was already turbulent.
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Valkov, T. V., and C. S. Tan. "Effect of Upstream Rotor Vortical Disturbances on the Time-Averaged Performance of Axial Compressor Stators: Part 1—Framework of Technical Approach and Wake–Stator Blade Interactions." Journal of Turbomachinery 121, no. 3 (July 1, 1999): 377–86. http://dx.doi.org/10.1115/1.2841330.
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In a two-part paper, key computed results from a set of first-of-a-kind numerical simulations on the unsteady interaction of axial compressor stators with upstream rotor wakes and tip leakage vortices are employed to elucidate their impact on the time-averaged performance of the stator. Detailed interrogation of the computed flow field showed that for both wakes and tip leakage vortices, the impact of these mechanisms can be described on the same physical basis. Specifically, there are two generic mechanisms with significant influence on performance: reversible recovery of the energy in the wakes/tip vortices (beneficial) and the associated nontransitional boundary layer response (detrimental). In the presence of flow unsteadiness associated with rotor wakes and tip vortices, the efficiency of the stator under consideration is higher than that obtained using a mixed-out steady flow approximation. The effects of tip vortices and wakes are of comparable importance. The impact of stator interaction with upstream wakes and vortices depends on the following parameters: axial spacing, loading, and the frequency of wake fluctuations in the rotor frame. At reduced spacing, this impact becomes significant. The most important aspect of the tip vortex is the relative velocity defect and the associated relative total pressure defect, which is perceived by the stator in the same manner as a wake. In Part 1, the focus will be on the framework of technical approach, and the interaction of stator with the moving upstream rotor wakes.
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Ding, Kaiyang, Junfeng Yang, Zhao Wang, Kai Ni, Xiaohao Wang, and Qian Zhou. "Specific Windows Search for Multi-Ship and Multi-Scale Wake Detection in SAR Images." Remote Sensing 14, no. 1 (December 22, 2021): 25. http://dx.doi.org/10.3390/rs14010025.
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Traditional ship identification systems have difficulty in identifying illegal or broken ships, but the wakes generated by ships can be used as a major feature for identification. However, multi-ship and multi-scale wake detection is also a big challenge. This paper combines the geometric and pixel characteristics of ships and their wakes in Synthetic Aperture Radar (SAR) images and proposes a method for multi-ship and multi-scale wake detection. This method first detects the highlight pixel area in the image and then generates specific windows around the centroid, thereby detecting wakes of different sizes in different areas. In addition, all wake components can be located completely based on wake clustering, the statistical features of wake axis pixels can be used to determine the visible length of the wake. Test results on the Gaofen-3 SAR image show the special potential of the method for wake detection.
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Ouyang, Xiaoqing, Zhijun Lei, Hanliu Deng, Hongrui Liu, Xingen Lu, Gang Xu, and Junqiang Zhu. "Influence of Upstream Sweeping Wake Number on the Unsteady Flow Mechanism in an Integrated Aggressive Intermediate Turbine Duct." Machines 11, no. 7 (July 10, 2023): 728. http://dx.doi.org/10.3390/machines11070728.
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This paper focuses on the dynamic internal flow in the integrated aggressive intermediate turbine duct (AITD) with different HPT wake numbers, using CFX Solver with dynamic Reynolds-averaged Navier–Stokes equations (RANS), the shear stress transmission κ-ω turbulence model (SST) and the γ-θ transition model. The HPT wakes are simulated using sweeping rods, with the number of rods ranging from 14 to 56 and a reduced frequency of 1.07. The increasing wake number reduces the radial pressure gradient in the integrated AITD, and then decelerates the radial migration and dissipation of wake vortices, so that some residual wakes can reach the integrated low-pressure turbine guide vane (LPT-GV) to enhance the suppression of flow separation to a certain extent. On the other hand, the increase in wake number can also weaken the skewness and stretching of the wake, thereby increasing the duration of flow separation suppression. When there are too many wakes, the mixing between adjacent wakes accelerates the dispersion of wake vortices, leading to increased total pressure loss and an enhanced turbulence intensity. This enhanced turbulence intensity promotes bypass transition on the suction surface of the LPT-GV in advance, thereby completely eliminating flow separation on the LPT-GV in the entire spatiotemporal domain, which is beneficial for reducing separation loss, but also increasing turbulent viscous loss. When N ≤ 28, the gross loss of the integrated AITD studied in this paper reaches a minimum value (around 0.22), as the benefits brought by the wake suppression of flow separation can offset the wake dissipation loss and the turbulent viscous loss caused by the wake-induced transition. Considering that wake loss is inherently present, using sweeping wakes to inhibit the flow separation on the integrated LPT-GV can bring certain aerodynamic benefits when the wake number is less than 28.
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Castorrini, A., L. Tieghi, V. F. Barnabei, S. Gentile, A. Bonfiglioli, A. Corsini, and F. Rispoli. "Wake interaction in offshore wind farms with mesoscale derived inflow condition and sea waves." IOP Conference Series: Earth and Environmental Science 1073, no. 1 (September 1, 2022): 012009. http://dx.doi.org/10.1088/1755-1315/1073/1/012009.
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Abstract Numerical simulation is an indispensable tool for the design and optimization of wind farms layout and control strategies for energy loss reduction. Achieving consistent simulation results is strongly related to the definition of reliable weather and sea conditions, as well as the use of accurate computational fluid dynamics (CFD) models for the simulation of the wind turbines and wakes. Thus, we present a case study aiming to evaluate the wake-rotor interaction between offshore multi-MW wind turbines modelled using the Actuator Line Model (ALM) and realistic wind inflow conditions. In particular, the interaction between two DTU10 wind turbines is studied for two orientations of the upstream turbine rotor, simulating the use of a yaw-based wake control strategy. Realistic wind inflow conditions are obtained using a multi-scale approach, where the wind field is firstly computed using mesoscale numerical weather prediction (NWP). Then, the mesoscale vertical wind profile is used to define the wind velocity and turbulence boundary conditions for the high-fidelity CFD simulations. Sea waves motion is also imposed using a dynamic mesh approach to investigate the interaction between sea waves, surface boundary layer, and wind turbine wakes and loads.
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Shao, Zhenzhou, Ying Wu, Li Li, Shuang Han, and Yongqian Liu. "Multiple Wind Turbine Wakes Modeling Considering the Faster Wake Recovery in Overlapped Wakes." Energies 12, no. 4 (February 20, 2019): 680. http://dx.doi.org/10.3390/en12040680.
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In a wind farm some wind turbines may be affected by multiple upwind wakes. The commonly used approach in engineering to simulate the interaction effect of different wakes is to combine the single analytical wake model and the interaction model. The higher turbulence level and shear stress profile generated by upwind turbines in the superposed area leads to faster wake recovery. The existing interaction models are all analytical models based on some simple assumptions of superposition, which cannot characterize this phenomenon. Therefore, in this study, a mixing coefficient is introduced into the classical energy balance interaction model with the aim of reflecting the effect of turbulence intensity on velocity recovery in multiple wakes. An empirical expression is also given to calculate this parameter. The performance of the new model is evaluated using data from the Lillgrund and the Horns Rev I offshore wind farms, and the simulations agree reasonably with the observations. The comparison of different interaction model simulation results with measured data show that the calculation accuracy of this new interaction model is high, and the mean absolute percentage error of wind farm efficiency is reduced by 5.3% and 1.58%, respectively, compared to the most commonly used sum of squares interaction model.
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Nie, Ruixin, Bin Wang, and Tengjiao He. "Extraction and analysis of three-dimensional sound scattering characteristics by body-generated internal waves." Journal of the Acoustical Society of America 154, no. 4_supplement (October 1, 2023): A41—A42. http://dx.doi.org/10.1121/10.0022737.
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The motion of an object submerged in a stratified fluid generates surface wakes, and simultaneously induces internal waves at the interface where there is a change in sound speed, known as the thermocline. As a result, spectral-temporal fluctuations occur in both the surface height and the distribution of sound velocity. While surface wakes primarily contribute to geometric acoustic scattering, the internal waves generated by the underwater object's motion can have diverse effects on sound propagation, leading to a prolonged acoustic impact that may have practical applications in underwater acoustic detection. This paper investigates the impact of body-generated internal waves on underwater acoustic propagation through the establishment of an “unfrozen field,” range-dependent model using the approximated Kelvin wake theory. The model allows numerical simulations to demonstrate the spatial-temporal coherence, time-frequency modulation and directional characteristics of the three-dimensional sound field scattered by the body-generated internal wave. By analyzing the influences of thermocline depth, target motion velocity and source depth, the results presented in this study indicate that the long-range acoustic propagation, modulated by the body-generated internal waves, can provide additional information for detecting moving targets.
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Arbie, M. Rizqie, Uwe Ehrenstein, and Christophe Eloy. "Stability of momentumless wakes." Journal of Fluid Mechanics 808 (October 28, 2016): 316–36. http://dx.doi.org/10.1017/jfm.2016.645.
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The caudal fin of swimming animals can be modelled as a thrust-producing flapping foil. When considered alone, such a foil produces on average a jet wake with a positive net momentum. It has been argued that the instability characteristics of these averaged wakes are linked to the propulsion efficiency of swimming animals. Here, we reconsider this question by taking into account both the thrust and the drag exerted on a self-propelled swimming body. To do so, we study the stability of a family of momentumless wakes, constructed as the Oseen approximation of a force doublet moving at constant velocity. By performing a local stability analysis, we first show that these wakes undergo a transition from absolute to convective instability. Then, using the time stepper approach by integrating the linearised Navier–Stokes system, we investigate the global stability and reveal the influence of a non-parallel base flow as well as the role of the locally absolutely unstable upstream region in the wake. Finally, to complete the global scenario, we address the nonlinear evolution of the wake disturbance. These results are then discussed in the context of aquatic locomotion. According to the present stability results, and assuming the Oseen approximation whose validity has been assessed only for moderate Reynolds number, the momentumless wake of aquatic animals is generally stable, whereas the corresponding thrust part is unstable. It is therefore essential to consider all forces exerted on a self-propelled animal when discussing its wake stability and its propulsion efficiency.
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Cho, H. H., M. Y. Jabbari, and R. J. Goldstein. "Mass Transfer With Flow Through an Array of Rectangular Cylinders." Journal of Heat Transfer 116, no. 4 (November 1, 1994): 904–11. http://dx.doi.org/10.1115/1.2911465.
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The mass transfer from an array of naphthalene-coated parallel rectangular cylinders, through which air passes in a slitlike flow, has been measured. The local Sherwood numbers indicate that the flow pattern is asymmetric in spite of using an array of two-dimensional, equally spaced identical cylinders. Smoke-wire flow visualization verifies this asymmetry, showing alternate short and long wakes around the cylinders, due probably to the instability of vortex shedding. On the side surfaces of the cylinders with the short wakes, the airflow deflects and reattaches, resulting in a high mass transfer. Also, a strong impinging effect is observed on the leeward (back) surface of these cylinders at high Reynolds numbers. Reattachment is not observed on the side surface for cylinders with the long wakes. On these, however, the mass transfer on the leeward surface is higher than on the short wake cylinders. This may be due to the relatively low naphthalene vapor concentration in the long wakes. The distribution of the short wakes (and the long wakes) is periodic and relatively stable. However, their position can be changed from one cylinder to the adjacent one by a disturbance. Measurements were taken over a moderate Reynolds number range of 300 to 3000 (based on the cylinder-to-cylinder pitch and approaching velocity). The laminar, transition, and turbulent nature in the wake flows can be inferred from the results.
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Morozova, T. I., and S. I. Popel. "Lower Hybrid Waves upon Interaction of Meteor Wakes with the Earth’s Ionosphere." Plasma Physics Reports 48, no. 7 (July 2022): 774–77. http://dx.doi.org/10.1134/s1063780x22600384.
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Abstract The possibility of generation of lower hybrid waves in meteoroid wakes upon their interaction with the Earth’s ionosphere is analyzed. The lower hybrid waves are driven as a result of development of the Buneman-type instability due to motion of meteoroid-wake plasma relative to the Earth’s magnetic field. Magneto-modulational processes that are induced by existence of the lower hybrid waves in plasma and leading to generation of quasi-stationary perturbations of magnetic field are discussed. It is demonstrated that these perturbations are of the same order of magnitude as magnetic fields induced by meteoroids passing through the Earth’s atmosphere.
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Didenkulova, I., and A. Rodin. "A typical wave wake from high-speed vessels: its group structure and run-up." Nonlinear Processes in Geophysics 20, no. 1 (February 26, 2013): 179–88. http://dx.doi.org/10.5194/npg-20-179-2013.
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Abstract. High-amplitude water waves induced by high-speed vessels are regularly observed in Tallinn Bay, the Baltic Sea, causing intense beach erosion and disturbing marine habitants in the coastal zone. Such a strong impact on the coast may be a result of a certain group structure of the wave wake. In order to understand it, here we present an experimental study of the group structure of these wakes at Pikakari beach, Tallinn Bay. The most energetic vessel waves at this location (100 m from the coast at the water depth 2.7 m) have amplitudes of about 1 m and periods of 8–10 s and cause maximum run-up heights on a beach up to 1.4 m. These waves represent frequency modulated packets where the largest and longest waves propagate ahead of other smaller amplitude and period waves. Sometimes the groups of different heights and periods can be separated even within one wave wake event. The wave heights within a wake are well described by the Weibull distribution, which has different parameters for wakes from different vessels. Wave run-up heights can also be described by Weibull distribution and its parameters can be connected to the parameters of the distribution of wave heights 100 m from the coast. Finally, the run-up of individual waves within a packet is studied. It is shown that the specific structure of frequency modulated wave packets, induced by high-speed vessels, leads to a sequence of high wave run-ups at the coast, even when the original wave heights are rather moderate. This feature can be a key to understanding the significant impact on coasts caused by fast vessels.
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ROGERS, MICHAEL M. "The evolution of strained turbulent plane wakes." Journal of Fluid Mechanics 463 (July 25, 2002): 53–120. http://dx.doi.org/10.1017/s0022112002008686.
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Direct numerical simulations of ten turbulent time-evolving strained wakes have been generated using a pseudo-spectral numerical method. In all the simulations, the strain was applied to the same (previously generated) initial developed self-similar wake flow field. The cases include flows in which the wake is subjected to various orientations of the applied mean strain, including both plane and axisymmetric strain configurations. In addition, for one particular strain geometry, cases with differing strain rates were considered. Although classical self-similar analysis does yield a self-similar solution for strained wakes, this solution does not describe the observed flow evolution. Instead, the wake mean velocity profiles evolve according to a different ‘equilibrium similarity solution’, with the strained wake width being determined by the straining in the inhomogeneous cross-stream direction. Wakes that are compressed in this direction eventually exhibit constant widths, whereas wakes in cases with expansive cross-stream strain ultimately spread at the same rate as the distortion caused by the applied strain. The shape of the wake mean velocity deficit profile is nearly universal. Although the effect of the strain on the mean flow is pronounced and rapid, the response of the turbulence to the strain occurs more slowly. Changes in the turbulence intensity cannot keep pace with changes in the mean wake velocity deficit, even for relatively low strain rates.
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Valkov, T. V., and C. S. Tan. "Effect of Upstream Rotor Vortical Disturbances on the Time-Averaged Performance of Axial Compressor Stators: Part 2—Rotor Tip Vortex/Streamwise Vortex–Stator Blade Interactions." Journal of Turbomachinery 121, no. 3 (July 1, 1999): 387–97. http://dx.doi.org/10.1115/1.2841331.
Full textAbstract:
In a two-part paper, key computed results from a set of first-of-a-kind numerical simulations on the unsteady interaction of axial compressor stator with upstream rotor wakes and tip leakage vortices are employed to elucidate their impact on the time-averaged performance of the stator. Detailed interrogation of the computed flowfield showed that for both wakes and tip leakage vortices, the impact of these mechanisms can be described on the same physical basis. Specifically, there are two generic mechanisms with significant influence on performance: reversible recovery of the energy in the wakes/tip vortices (beneficial) and the associated nontransitional boundary layer response (detrimental). In the presence of flow unsteadiness associated with rotor wakes and tip vortices, the efficiency of the stator under consideration is higher than that obtained using a mixed-out steady flow approximation. The effects of tip vortices and wakes are of comparable importance. The impact of stator interaction with upstream wakes and vortices depends on the following parameters: axial spacing, loading, and the frequency of wake fluctuations in the rotor frame. At reduced spacing, this impact becomes significant. The most important aspect of the tip vortex is the relative velocity defect and the associated relative total pressure defect, which is perceived by the stator in the same manner as a wake. In Part 2, the focus will be on the interaction of stator with the moving upstream rotor tip and streamwise vortices, the controlling parametric trends, and implications on design.
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Pillay, Kiara, and David Paul Mason. "Two-Fluid Classical and Momentumless Laminar Far Wakes." Symmetry 15, no. 5 (April 23, 2023): 961. http://dx.doi.org/10.3390/sym15050961.
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Two-dimensional two-fluid classical and momentumless laminar far wakes are investigated in the boundary layer approximation. The velocity deficit satisfies a linear diffusion equation and the continuity equation in the upper and lower parts of the wakes. By using the multiplier method, conservation laws for the system of partial differential equations (PDEs) in the upper and lower parts of the wake are derived. Lie point symmetries associated with the conserved vectors for the classical and momentumless wakes are obtained. The conserved quantity for the two-fluid classical wake is the total drag on the obstacle, which is rederived. A new conserved quantity for the two-fluid momentumless wake is obtained, which satisfies the condition that the total drag on the obstacle is zero. Using the conserved quantities, it is shown that the equation of the interface is y=kx12, where k is a constant and x and y are Cartesian coordinates with origin at the trailing edge of the obstacle. New invariant solutions for the two-fluid classical and momentumless wakes with k=0 are found. Both solutions depend on the dimensionless parameter χ=(ρ1μ1)/(ρ2μ2) where suffices 1 and 2 refer to the upper and lower parts of the wake. For the special case in which the kinematic viscosity ratio ν2/ν1=1, two further solutions for the two-fluid momentumless wake are derived with k=±6.
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Gilman, M., A. Soloviev, and H. Graber. "Study of the Far Wake of a Large Ship." Journal of Atmospheric and Oceanic Technology 28, no. 5 (May 1, 2011): 720–33. http://dx.doi.org/10.1175/2010jtecho791.1.
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Abstract A large dataset of high-resolution photographic images of far wakes of a volunteer observing ship (Royal Caribbean’s Explorer of the Seas) has been acquired under various meteorological conditions and ship operation modes. This work presents the description of instrumentation, methodology, and the results of the experiment. Environmental and ship operation factors that affect appearance and geometric properties of ship wakes in photographic and satellite-based radar images have been analyzed. The photo imagery reveals an asymmetry of the wake depending on wind direction relative to the ship course. In addition, a good agreement between the averaged shape of the wakes measured from the photographic images and a few available satellite-based radar images of the wake of the same ship has been found.
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Kumar, Dilip, and Soma Sanyal. "Magnetic Reconnection in the Wakes of Cosmic Strings." Astrophysical Journal 944, no. 2 (February 1, 2023): 183. http://dx.doi.org/10.3847/1538-4357/acb4ef.
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Abstract The motion of cosmic strings in the universe leads to the generation of wakes behind them. We study magnetized wakes of cosmic strings moving in the postrecombination plasma. We show that magnetic reconnection can occur in the postshock region. Since the width of the cosmic-string wake is very small, the reconnection occurs over a very short length scale. The reconnection leads to a large amount of kinetic energy being released in the postshock region of the cosmic-string wake. This enhances the kinetic energy released during the reconnection. We make a rudimentary estimate of the kinetic energy released by the magnetic reconnection in cosmic-string wakes and show that it can account for low-energy gamma-ray bursts in the postrecombination era.
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Videler, J. J., U. K. Muller, and E. J. Stamhuis. "Aquatic vertebrate locomotion: wakes from body waves." Journal of Experimental Biology 202, no. 23 (December 1, 1999): 3423–30. http://dx.doi.org/10.1242/jeb.202.23.3423.
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Vertebrates swimming with undulations of the body and tail have inflection points where the curvature of the body changes from concave to convex or vice versa. These inflection points travel down the body at the speed of the running wave of bending. In movements with increasing amplitudes, the body rotates around the inflection points, inducing semicircular flows in the adjacent water on both sides of the body that together form proto-vortices. Like the inflection points, the proto-vortices travel towards the end of the tail. In the experiments described here, the phase relationship between the tailbeat cycle and the inflection point cycle can be used as a first approximation of the phase between the proto-vortex and the tailbeat cycle. Proto-vortices are shed at the tail as body vortices at roughly the same time as the inflection points reach the tail tip. Thus, the phase between proto-vortex shedding and tailbeat cycle determines the interaction between body and tail vortices, which are shed when the tail changes direction. The shape of the body wave is under the control of the fish and determines the position of vortex shedding relative to the mean path of motion. This, in turn, determines whether and how the body vortex interacts with the tail vortex. The shape of the wake and the contribution of the body to thrust depend on this interaction between body vortex and tail vortex. So far, we have been able to describe two types of wake. One has two vortices per tailbeat where each vortex consists of a tail vortex enhanced by a body vortex. A second, more variable, type of wake has four vortices per tailbeat: two tail vortices and two body vortices shed from the tail tip while it is moving from one extreme position to the next. The function of the second type is still enigmatic.
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Biancofiore, L., and F. Gallaire. "Counterpropagating Rossby waves in confined plane wakes." Physics of Fluids 24, no. 7 (July 2012): 074102. http://dx.doi.org/10.1063/1.4729617.
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Schottler, Jannik, Jan Bartl, Franz Mühle, Lars Sætran, Joachim Peinke, and Michael Hölling. "Wind tunnel experiments on wind turbine wakes in yaw: redefining the wake width." Wind Energy Science 3, no. 1 (May 16, 2018): 257–73. http://dx.doi.org/10.5194/wes-3-257-2018.
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Abstract. This paper presents an investigation of wakes behind model wind turbines, including cases of yaw misalignment. Two different turbines were used and their wakes are compared, isolating effects of boundary conditions and turbine specifications. Laser Doppler anemometry was used to scan full planes of wakes normal to the main flow direction, six rotor diameters downstream of the respective turbine. The wakes of both turbines are compared in terms of the time-averaged main flow component, the turbulent kinetic energy and the distribution of velocity increments. The shape of the velocity increments' distributions is quantified by the shape parameter λ2. The results show that areas of strongly heavy-tailed distributed velocity increments surround the velocity deficits in all cases examined. Thus, a wake is significantly wider when two-point statistics are included as opposed to a description limited to one-point quantities. As non-Gaussian distributions of velocity increments affect loads of downstream rotors, our findings impact the application of active wake steering through yaw misalignment as well as wind farm layout optimizations and should therefore be considered in future wake studies, wind farm layout and farm control approaches. Further, the velocity deficits behind both turbines are deformed to a kidney-like curled shape during yaw misalignment, for which parameterization methods are introduced. Moreover, the lateral wake deflection during yaw misalignment is investigated.