To enhance the prediction accuracy of unsteady wakes behind wind turbines,a novel reduced-order model is proposed by integrating a multifunctional recurrent fuzzy neural network(MFRFNN)and proper orthogonal decom-posi...To enhance the prediction accuracy of unsteady wakes behind wind turbines,a novel reduced-order model is proposed by integrating a multifunctional recurrent fuzzy neural network(MFRFNN)and proper orthogonal decom-position(POD).First,POD is employed to reduce the di-mensionality of the wind field data,extracting spatiotempo-rally correlated modal coefficients and modes.These reduced-order variables can effectively capture the essential features of unsteady wake behaviors.Next,MFRFNN is utilized to predict the time series of modal coefficients.Fi-nally,by combining the predicted modal coefficients with their corresponding modes,a flow field is reconstructed,al-lowing accurate prediction of unsteady wake dynamics.The predicted wake data exhibit high consistency with large eddy simulation results in both the near-and far-wake re-gions and outperform existing data-driven methods.This ap-proach offers significant potential for optimizing wind farm design and provides a new solution for the precise prediction of wind turbine wake behavior.展开更多
With the rapid advancement of machine learning technology and its growing adoption in research and engineering applications,an increasing number of studies have embraced data-driven approaches for modeling wind turbin...With the rapid advancement of machine learning technology and its growing adoption in research and engineering applications,an increasing number of studies have embraced data-driven approaches for modeling wind turbine wakes.These models leverage the ability to capture complex,high-dimensional characteristics of wind turbine wakes while offering significantly greater efficiency in the prediction process than physics-driven models.As a result,data-driven wind turbine wake models are regarded as powerful and effective tools for predicting wake behavior and turbine power output.This paper aims to provide a concise yet comprehensive review of existing studies on wind turbine wake modeling that employ data-driven approaches.It begins by defining and classifying machine learning methods to facilitate a clearer understanding of the reviewed literature.Subsequently,the related studies are categorized into four key areas:wind turbine power prediction,data-driven analytic wake models,wake field reconstruction,and the incorporation of explicit physical constraints.The accuracy of data-driven models is influenced by two primary factors:the quality of the training data and the performance of the model itself.Accordingly,both data accuracy and model structure are discussed in detail within the review.展开更多
Regional turbofan aircraft,which are used for medium-short distances,have a heightened risk of high-altitude Wake Vortices(VV)because of their tail-mounted engines and high horizontal tail configurations.For some regi...Regional turbofan aircraft,which are used for medium-short distances,have a heightened risk of high-altitude Wake Vortices(VV)because of their tail-mounted engines and high horizontal tail configurations.For some regional medium-short-range turbofan aircraft,this threat is higher than that for conventionally designed aircraft.To analyze the flight safety of turbofan aircraft during cruise,this study developed a model to assess wake vortex encounters based on evolutionary high-altitude wake flow patterns.First,the high-altitude wake vortex aircraft dissipation patterns were analyzed by combining Quick Access Recorder(QAR)flight data with the wake vortex evolution model.Then,to consider the uniqueness of the medium-short-range turbofan aircraft,the severity of the wake vortex encounters was simulated using an induced roll moment coefficient.The proposed high-altitude wake vortex encounter model was able to identify and assess the highaltitude wake vortex changes,the bearing moments at different altitudes,and the atmospheric pressure conditions.Using the latest wake separation standards from the International Civil Aviation Organization(ICAO),acceptable safety wake intervals for follower aircraft in different scenarios were determined for the safety assessment.The results indicate that compared to mid and low altitudes,the high-altitude aircraft wake vortex dissipation rate is faster,the ultimate bearing moment is weaker,and the roll moment coefficient is higher,which confirm that there is elevated wake vortex encounter severity for regional turbofan aircraft.As safety is found to deteriorate when encountering wake vortices at altitudes higher than 8 km,new medium-short-range turbofan regional aircraft require higher safety margins than the latest wake separation standards.展开更多
In the Northern Hemisphere,cold wakes induced by tropical cyclones(TCs)are generally biased to the right of the storm track.However,a recent study found that a non-negligible proportion of cold wakes is actually leftw...In the Northern Hemisphere,cold wakes induced by tropical cyclones(TCs)are generally biased to the right of the storm track.However,a recent study found that a non-negligible proportion of cold wakes is actually leftward-biased.To further reveal the underlying physical mechanisms,the three-dimensional dynamic processes for the typical leftward cold wake of Hurricane Jova(2005)are investigated through a sequence of numerical simulations.Results reveal that the vertical advection in response to Jova(2005)is biased to the left of its track in the upper layer.In cooperation with the heterogenous ambient oceanic temperature stratification,the rightward vertical mixing is suppressed while the leftward feature of vertical advection is further intensified,which effectively promotes the formation of leftward cold wake.Additionally,the currents induced by Jova(2005)drive colder(warmer)water to the left(right)when coupled with background horizontal temperature gradients and then strengthen the leftward distribution of the temperature anomaly.These conclusions are substantiated by the control simulation,as the upper-layer temperature anomaly is restored to rightward disposition with homogeneous initial thermal structures.Based on three groups of sensitivity experiments,the leftward pattern of upwelling is found to be inextricably accompanied by the curl of wind stress caused by the movement of TCs.With the increase in translation speed from the stationary state,the symmetric structure of vertical velocity is gradually distorted to be leftward.Furthermore,the leftward bias distance of the upwelling center in the upper layer positively correlates with the radius of maximum wind,indicating that the wind structure can significantly influences the oceanic responses to TCs.展开更多
When a ship moves in an oblique flow,its hydrodynamic loads and wake characteristics vary substantially from those in straight-ahead motion.This dissimilarity can be even more complex when the ship operates in a seawa...When a ship moves in an oblique flow,its hydrodynamic loads and wake characteristics vary substantially from those in straight-ahead motion.This dissimilarity can be even more complex when the ship operates in a seaway of shallow water.In this paper,a numerical analysis of the shallow-water effect on the hydrodynamic forces and wake characteristics of an international ship model,KVLCC2,in oblique flows is conducted.Numerical simulations are performed based on the Reynolds Averaged NavierStokes equation in conjunction with the shear stress transport(SST)k-ωturbulence model.Four relative water depths(h=1.2T,1.5T,3.0T,and 24T;T is the ship draft)and five different drift angles(β=0°,5°,10°,15°,and 20°)are considered.Results reveal the following:i)The shallow-water effect is strong and leads to nonlinear increases in the longitudinal force regardless of drift angles and on the transverse force and yaw moment whenever the drift angle increases.ii)In shallow water,the mean wake fraction is sensitive to the drift angle,and the strength of the aft-body vortex on the leeward side increases.展开更多
The sedimentary bed morphology modulated by the wake flow of a wall-mounted flexible aquatic vegetation blade across various structural aspect ratios(A_(R)=l/b,where l and b are the length and width of the blade,respe...The sedimentary bed morphology modulated by the wake flow of a wall-mounted flexible aquatic vegetation blade across various structural aspect ratios(A_(R)=l/b,where l and b are the length and width of the blade,respectively)and incoming flow velocities was experimentally investigated in a water channel.A surface scanner was implemented to quantify bed topography,and a tomographic particle image velocimetry system was used to characterize the three-dimensional wake flows.The results showed that due to the deflection of incoming flow,the velocity magnitude increased at the lateral sides of the blade,thereby producing distinctive symmetric scour holes in these regions.The normalized morphology profiles of the sedimentary bed,which were extracted along the streamwise direction at the location of the maximum erosion depth,exhibited a self-similar pattern that closely followed a sinusoidal wave profile.The level of velocity magnitude enhancement was highly correlated to the postures of the flexible blade.At a given flow velocity,the blade with lower aspect ratios exhibited less significant deformation,causing more significant near-bed velocity enhancement in the wake deflection zone and therefore leading to higher erosion volumes.Further investigation indicated that when the blade underwent slight deformation,the larger velocity enhancement close to the bed can be attributed to more significant flow deflection effects at the lateral sides of the blade and stronger flow mixing with high momentum flows away from the bed.Supported with measurements,a basic formula was established to quantify the shear stress acting on the sedimentary bed as a function of incoming flow velocity and blade aspect ratio.展开更多
Dynamic wake field information is vital for the optimized design and control of wind farms.Combined with sparse measurement data from light detection and ranging(LiDAR),the physics-informed neural network(PINN)framewo...Dynamic wake field information is vital for the optimized design and control of wind farms.Combined with sparse measurement data from light detection and ranging(LiDAR),the physics-informed neural network(PINN)frameworks have recently been employed for forecasting freestream wind and wake fields.However,these PINN frameworks face challenges of low prediction accuracy and long training times.Therefore,this paper constructed a PINN framework for dynamic wake field prediction by integrating two accuracy improvement strategies and a step-by-step training time saving strategy.The results showed that the different performance improvement routes significantly improved the overall performance of the PINN.The accuracy and efficiency of the PINN with spatiotemporal improvement strategies were validated via LiDAR-measured data from a wind farm in Shandong province,China.This paper sheds light on load reduction,efficiency improvement,intelligent operation and maintenance of wind farms.展开更多
WT5 'BZThis paper presents an unsteady and nonlinear wake model based on th e widely used Peters He finite state dynamic wake model with improvements. The swirl component in the tip trace plane (TTP) can be pr...WT5 'BZThis paper presents an unsteady and nonlinear wake model based on th e widely used Peters He finite state dynamic wake model with improvements. The swirl component in the tip trace plane (TTP) can be predicted, nonlinear items are added into the linear theory, and the old small angle assumption use d in matrix prediction is removed. All of these enha ncements are aimed at the low speed flight phase and formulations for the induce d velocity field just in the TTP frame are derived. The corresponding FORTRAN pr ogram is tested and optimized for the real time applications on PCs.展开更多
This paper describes an improved model of curved vortex element on the circular arc (CVEC) for rotor wake analysis.As the key of the paper,two approximate formulas are derived by the series of limited terms to replace...This paper describes an improved model of curved vortex element on the circular arc (CVEC) for rotor wake analysis.As the key of the paper,two approximate formulas are derived by the series of limited terms to replace the Legendre incomplete elliptical integrals from the Biot-Savart integration,and the analytical solution of the induced velocity for the CVEC is obtained, which is more efficient in the complex rotor free wake calculation. Furthermore,the approximate formulas with the chosen factors are selected to avoid sigularity and give finite result of the induced velocity on the Vortex line,and an equivalent viscous vortex core radius might be evaluated.As examples, the induced velocity calculations on the vortex ring and two turns of a skew vortex helix are performed, and the comparisons between the circular-arc vortex element and the conventional straightline vortex element (SLVE) are given.It is shown that this curved vortex element model is advantageous over the SLVE model and is suitable for the rotor wake analysis.展开更多
The basal ganglia(BG) act as a cohesive functional unit that regulates motor function,habit formation,and reward/addictive behaviors. However,it is still not well understood how the BG maintains wakefulness and suppre...The basal ganglia(BG) act as a cohesive functional unit that regulates motor function,habit formation,and reward/addictive behaviors. However,it is still not well understood how the BG maintains wakefulness and suppresses sleep to achieve al these fundamental functions until genetical y engineered systems developed these years. Significant research efforts have recently been directed at developing genetic-molecular tools to achieve reversible and cell-type specific in vivo silencing or activation of neurons in behaving animals. Optogenetic tools can be used both to specifically activate or inhibit neurons of interest and identify functional synaptic connectivity between specific neuronal populations,both in vivo and in brain slices. Another recently developed system by Roth and colleagues permits the selective and ″remote″ manipulation(activation and silencing) of neuronal activity via all 3 major GPCR signaling pathways(G_i,G_s and G_q). These so-called ″ designer receptors exclusively activated by designer drugs″(DREADD) involve mutant GPCRs that do not respond to their endogenous ligands but are responsive to otherwise inert biological compounds. Recently,we demonstrated the essential roles and the neural pathways of the neurons expressing adenosine A_(2A) receptors or dopamine D_1 receptors in the BG for sleep-wake regulation using the genetically engineered systems including optogenetics and DREADD. We proposed a plausible model in which the caudate-putamen and the nucleus accumbens integrates behavioral processes with sleep/wakefulness through adenosine and dopamine receptors.展开更多
Rotor wake analysis,a fundamental research of helicopter technology,has been widely applied for rotor aerodynamic analysis. This paper summarizes the research of different rotor wake models at home and abroad and revi...Rotor wake analysis,a fundamental research of helicopter technology,has been widely applied for rotor aerodynamic analysis. This paper summarizes the research of different rotor wake models at home and abroad and reviews the development process of rotor wake methods as well as the research achievement obtained in each stage.Then,the new progress of helicopter rotor wake methods is described in detail. It includes constant circulation contours modeling method of rotor wake,pseudo-implicit relaxation iteration and time-accurate solution method,research on aerodynamic interaction characteristics of helicopter rotor/fuselage by wake method,research on the rotor blade-vortex interaction noise and interaction of coaxial rigid rotor aerodynamics by viscous vortex particle method,and application of free wake method to helicopter flight dynamics modeling. In the end,some prospects for the research of helicopter rotor wake method are put forward,which clarifies the ideas for the future development of rotor wake method.展开更多
Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, t...Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of un- steady Reynold-averaged Navier-Stokes （URANS） and de- tached eddy simulation （DES） are utilized, respectively. Re- suits reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.展开更多
A full-span free-wake method is coupled with an unsteady panel method to accurately predict the unsteady aerodynamics of helicopter rotor blades in hover and forward flight. The unsteady potential-based panel method i...A full-span free-wake method is coupled with an unsteady panel method to accurately predict the unsteady aerodynamics of helicopter rotor blades in hover and forward flight. The unsteady potential-based panel method is used to consider aerodynamics of finite thickness multi-bladed rotors, and the full-span free-wake method is applied to simulating dynamics of rotor wake. These methods are tightly coupled through trailing-edge Kutta condition and by converting doublet-wake panels to full-span vortex filaments. A velocity-field integration technique is also adopted to overcome singularity problem during the interaction between the rotor wake and blades. Helicopter rotors including Caradonna–Tung, UH-60A, and AH-1G rotors, are simulated in hover and forward flight to validate the accuracy of this approach. The predicted aerodynamic loads of rotor blades agree well with available measured data and computational fluid dynamics （CFD） results, and the unsteady dynamics of rotor wake is also well simulated. Compared to CFD, the present method obtains accurate results more efficiently and is suitable to rotorcraft aeroelastic analysis.展开更多
Accurate predictions of Shock Waves and Boundary Layer Interaction(SWBLI)and strong Shock Waves and Wake Vortices Interaction(SWWVI)in a highly-loaded turbine propose challenges to the currently widely used Reynolds-A...Accurate predictions of Shock Waves and Boundary Layer Interaction(SWBLI)and strong Shock Waves and Wake Vortices Interaction(SWWVI)in a highly-loaded turbine propose challenges to the currently widely used Reynolds-Averaged Navier-Stokes(RANS)model.In this work,the SWBLI and the SWWVI in a highly-loaded Nozzle Guide Vane(NGV)are studied using a hybrid RANS/LES strategy.The Turbulence Kinetic Energy(TKE)budget and the Proper Orthogonal Decomposition(POD)method are used to analyze flow mechanisms.Results show that this hybrid RANS/LES method can obtain detailed flow structures for flow mechanisms analysis.Strong shock waves induce boundary layer separation,while the presence of a separation bubble can in turn lead to a Mach reflection phenomenon.The shock waves cause trailing-edge vortices to break clearly,and the wakes,in turn,can change the shocks intensity and direction.Furthermore,the Entropy Generation Rate(EGR)is used to analyze the irreversible loss.It turns out that the SWWVI can reduce the flow field loss.There are several weak shock waves in the NGV flow field,which can increase the irreversible loss.This work offers flow mechanisms analysis and presents the EGR distribution in SWBLI and SWWVI areas in a transonic turbine blade.展开更多
A self-adaptive-grid method is applied to numerical simulation of the evolu- tion of aircraft wake vortex with the large eddy simulation （LES）. The Idaho Falls （IDF） measurement of run 9 case is simulated numerica...A self-adaptive-grid method is applied to numerical simulation of the evolu- tion of aircraft wake vortex with the large eddy simulation （LES）. The Idaho Falls （IDF） measurement of run 9 case is simulated numerically and compared with that of the field experimental data. The comparison shows that the method is reliable in the complex atmospheric environment with crosswind and ground effect. In addition, six cases with different ambient atmospheric turbulences and Brunt V^iis/il^i （BV） frequencies are com- puted with the LES. The main characteristics of vortex are appropriately simulated by the current method. The onset time of rapid decay and the descending of vortices are in agreement with the previous measurements and the numerical prediction. Also, sec-ondary structures such as baroclinic vorticity and helical structures are also simulated. Only approximately 6 million grid points are needed in computation with the present method, while the number can be as large as 34 million when using a uniform mesh with the same core resolution. The self-adaptive-grid method is proved to be practical in the numerical research of aircraft wake vortex.展开更多
Orexins, produced in the lateral hypothalamus, are important neuropeptides that participate in the sleep/wake cycle, and their expres- sion coincides with the projection area of the vagus nerve in the brain. Vagus ner...Orexins, produced in the lateral hypothalamus, are important neuropeptides that participate in the sleep/wake cycle, and their expres- sion coincides with the projection area of the vagus nerve in the brain. Vagus nerve stimulation has been shown to decrease the amounts of daytime sleep and rapid eye movement in epilepsy patients with traumatic brain injury. In the present study, we investigated whether vagus nerve stimulation promotes wakefulness and affects orexin expression. A rat model of traumatic brain injury was established using the free fall drop method. In the stimulated group, rats with traumatic brain injury received vagus nerve stimulation （frequency, 30 Hz, current, 1.0 mA; pulse width, 0.5 ms; total stimulation time, 15 minutes）. In the antagonist group, rats with traumatic brain injury were intracerebroventricularly injected with the orexin receptor type 1 （OXIR） antagonist SB334867 and received vagus nerve stimulation. Changes in consciousness were observed after stimulation in each group. Enzyme-linked immunosorbent assay, western blot assay and immunohistochemistry were used to assess the levels of orexin-A and OX1R expression in the prefrontal cortex. In the stimulated group, consciousness was substantially improved, orexin-A protein expression gradually increased within 24 hours after injury and OX1R expres- sion reached a peak at 12 hours, compared with rats subjected to traumatic brain injury only. In the antagonist group, the wake-promoting effect of vagus nerve stimulation was diminished, and orexin-A and OX1R expression were decreased, compared with that of the stim- ulated group. Taken together, our findings suggest that vagus nerve stimulation promotes the recovery of consciousness in comatose rats after traumatic brain injury. The upregulation of orexin-A and OXIR expression in the prefrontal cortex might be involved in the wake-promoting effects of vagus nerve stimulation.展开更多
The flow patterns of the wake of an oblique honeycombed grid fin were visualized by hydrogen bubbles technique in a water channel. It was found that the hairpin vortices existed in the wake of surfaces in the neighbor...The flow patterns of the wake of an oblique honeycombed grid fin were visualized by hydrogen bubbles technique in a water channel. It was found that the hairpin vortices existed in the wake of surfaces in the neighborhood of each crossing of intersecting elements at moderate angles of attack. They shed periodically following the flow separation on surfaces and connected each other into chains. The main features of the flow patterns are presented and the flow mechanism concerned is preliminarily discussed.展开更多
Presently developed two-phase turbulence models under-predict the gas turbulent fluctuation, because their turbulence modification models cannot fully reflect the effect of particles. In this paper, a two-time-scale d...Presently developed two-phase turbulence models under-predict the gas turbulent fluctuation, because their turbulence modification models cannot fully reflect the effect of particles. In this paper, a two-time-scale dis- sipation model of turbulence modification, developed for the two-phase velocity correlation and for the dissipation rate of gas turbulent kinetic energy, is proposed and used to simulate sudden-expansion and swirling gas-particle flows. The proposed two-time scale model gives better results than the single-time scale model. Besides, a gas tur- bulence augmentation model accounting for the finite-size particle wake effect in the gas Reynolds stress equation is proposed. The proposed turbulence modification models are used to simulate two-phase pipe flows. It can prop- erly predict both turbulence reduction and turbulence enhancement for a certain size of particles observed in ex- periments.展开更多
The maritime administrative department employs synthetic aperture radar (SAR) satellite remote sensing technology to obtain evidence of illegal discharge of ships. If the ship is discharged during navigation, it forms...The maritime administrative department employs synthetic aperture radar (SAR) satellite remote sensing technology to obtain evidence of illegal discharge of ships. If the ship is discharged during navigation, it forms a long dark wake on the SAR image due to the suppression of the Bragg wave by the oil fi lm. This study investigates key techniques for rapid detection of long ship wakes, thereby providing law enforcement agencies with candidate ships for possible discharge. This paper presents a rapid long ship wake detection method that uses satellite imaging parameters and the axial direction of the ship in images to determine the potential detection area of the wake. Then, the threshold of long ship wake detection is determined using statistical analysis, the area is binarized, and isolated points are removed using a morphological filter operator. The method was tested with ENVISAT Synthetic Aperture Radar and GF-3 SAR data, and results showed that the method was eff ective, and the overall accuracy of the decision reaches 71%. We present two innovations;one is a method that draws a Doppler shift curve, and uses the SAR imaging parameters to determine the detection area of the long wake to achieve rapid detection and reduce the image detection area. The other is where a classical linear fitting method is used to quickly and accurately determine whether the detected dark area is a long ship wake and realizes the twisted long ship wake detection caused by the sea surface flow field, which is otherwise diffi cult to detect by the traditional Radon and Hough transform methods. This method has good suppression performance for the dark spot false alarm formed by low speed wind region or upward flow. The method is developed for maritime ship monitoring system and will promote the operational application of maritime ship monitoring system.展开更多
基金The National Natural Science Foundation of China (No. 51908107)。
文摘To enhance the prediction accuracy of unsteady wakes behind wind turbines,a novel reduced-order model is proposed by integrating a multifunctional recurrent fuzzy neural network(MFRFNN)and proper orthogonal decom-position(POD).First,POD is employed to reduce the di-mensionality of the wind field data,extracting spatiotempo-rally correlated modal coefficients and modes.These reduced-order variables can effectively capture the essential features of unsteady wake behaviors.Next,MFRFNN is utilized to predict the time series of modal coefficients.Fi-nally,by combining the predicted modal coefficients with their corresponding modes,a flow field is reconstructed,al-lowing accurate prediction of unsteady wake dynamics.The predicted wake data exhibit high consistency with large eddy simulation results in both the near-and far-wake re-gions and outperform existing data-driven methods.This ap-proach offers significant potential for optimizing wind farm design and provides a new solution for the precise prediction of wind turbine wake behavior.
基金Supported by the National Natural Science Foundation of China under Grant No.52131102.
文摘With the rapid advancement of machine learning technology and its growing adoption in research and engineering applications,an increasing number of studies have embraced data-driven approaches for modeling wind turbine wakes.These models leverage the ability to capture complex,high-dimensional characteristics of wind turbine wakes while offering significantly greater efficiency in the prediction process than physics-driven models.As a result,data-driven wind turbine wake models are regarded as powerful and effective tools for predicting wake behavior and turbine power output.This paper aims to provide a concise yet comprehensive review of existing studies on wind turbine wake modeling that employ data-driven approaches.It begins by defining and classifying machine learning methods to facilitate a clearer understanding of the reviewed literature.Subsequently,the related studies are categorized into four key areas:wind turbine power prediction,data-driven analytic wake models,wake field reconstruction,and the incorporation of explicit physical constraints.The accuracy of data-driven models is influenced by two primary factors:the quality of the training data and the performance of the model itself.Accordingly,both data accuracy and model structure are discussed in detail within the review.
基金supported by the National Natural Science Foundation of China(Nos.U2333209,U1733203)the National Key R&D Program of China(No.2021YFF0603904)the Civil Aviation Administration of China(No.AQ20200019)。
文摘Regional turbofan aircraft,which are used for medium-short distances,have a heightened risk of high-altitude Wake Vortices(VV)because of their tail-mounted engines and high horizontal tail configurations.For some regional medium-short-range turbofan aircraft,this threat is higher than that for conventionally designed aircraft.To analyze the flight safety of turbofan aircraft during cruise,this study developed a model to assess wake vortex encounters based on evolutionary high-altitude wake flow patterns.First,the high-altitude wake vortex aircraft dissipation patterns were analyzed by combining Quick Access Recorder(QAR)flight data with the wake vortex evolution model.Then,to consider the uniqueness of the medium-short-range turbofan aircraft,the severity of the wake vortex encounters was simulated using an induced roll moment coefficient.The proposed high-altitude wake vortex encounter model was able to identify and assess the highaltitude wake vortex changes,the bearing moments at different altitudes,and the atmospheric pressure conditions.Using the latest wake separation standards from the International Civil Aviation Organization(ICAO),acceptable safety wake intervals for follower aircraft in different scenarios were determined for the safety assessment.The results indicate that compared to mid and low altitudes,the high-altitude aircraft wake vortex dissipation rate is faster,the ultimate bearing moment is weaker,and the roll moment coefficient is higher,which confirm that there is elevated wake vortex encounter severity for regional turbofan aircraft.As safety is found to deteriorate when encountering wake vortices at altitudes higher than 8 km,new medium-short-range turbofan regional aircraft require higher safety margins than the latest wake separation standards.
基金supported by the National Natural Science Foundation of China(Grant No.42192552)。
文摘In the Northern Hemisphere,cold wakes induced by tropical cyclones(TCs)are generally biased to the right of the storm track.However,a recent study found that a non-negligible proportion of cold wakes is actually leftward-biased.To further reveal the underlying physical mechanisms,the three-dimensional dynamic processes for the typical leftward cold wake of Hurricane Jova(2005)are investigated through a sequence of numerical simulations.Results reveal that the vertical advection in response to Jova(2005)is biased to the left of its track in the upper layer.In cooperation with the heterogenous ambient oceanic temperature stratification,the rightward vertical mixing is suppressed while the leftward feature of vertical advection is further intensified,which effectively promotes the formation of leftward cold wake.Additionally,the currents induced by Jova(2005)drive colder(warmer)water to the left(right)when coupled with background horizontal temperature gradients and then strengthen the leftward distribution of the temperature anomaly.These conclusions are substantiated by the control simulation,as the upper-layer temperature anomaly is restored to rightward disposition with homogeneous initial thermal structures.Based on three groups of sensitivity experiments,the leftward pattern of upwelling is found to be inextricably accompanied by the curl of wind stress caused by the movement of TCs.With the increase in translation speed from the stationary state,the symmetric structure of vertical velocity is gradually distorted to be leftward.Furthermore,the leftward bias distance of the upwelling center in the upper layer positively correlates with the radius of maximum wind,indicating that the wind structure can significantly influences the oceanic responses to TCs.
基金supported by the National Key R&D Plan Project(No.2019YFD0901003)。
文摘When a ship moves in an oblique flow,its hydrodynamic loads and wake characteristics vary substantially from those in straight-ahead motion.This dissimilarity can be even more complex when the ship operates in a seaway of shallow water.In this paper,a numerical analysis of the shallow-water effect on the hydrodynamic forces and wake characteristics of an international ship model,KVLCC2,in oblique flows is conducted.Numerical simulations are performed based on the Reynolds Averaged NavierStokes equation in conjunction with the shear stress transport(SST)k-ωturbulence model.Four relative water depths(h=1.2T,1.5T,3.0T,and 24T;T is the ship draft)and five different drift angles(β=0°,5°,10°,15°,and 20°)are considered.Results reveal the following:i)The shallow-water effect is strong and leads to nonlinear increases in the longitudinal force regardless of drift angles and on the transverse force and yaw moment whenever the drift angle increases.ii)In shallow water,the mean wake fraction is sensitive to the drift angle,and the strength of the aft-body vortex on the leeward side increases.
基金supported by the National Science Foundation under Grant No.2327916.
文摘The sedimentary bed morphology modulated by the wake flow of a wall-mounted flexible aquatic vegetation blade across various structural aspect ratios(A_(R)=l/b,where l and b are the length and width of the blade,respectively)and incoming flow velocities was experimentally investigated in a water channel.A surface scanner was implemented to quantify bed topography,and a tomographic particle image velocimetry system was used to characterize the three-dimensional wake flows.The results showed that due to the deflection of incoming flow,the velocity magnitude increased at the lateral sides of the blade,thereby producing distinctive symmetric scour holes in these regions.The normalized morphology profiles of the sedimentary bed,which were extracted along the streamwise direction at the location of the maximum erosion depth,exhibited a self-similar pattern that closely followed a sinusoidal wave profile.The level of velocity magnitude enhancement was highly correlated to the postures of the flexible blade.At a given flow velocity,the blade with lower aspect ratios exhibited less significant deformation,causing more significant near-bed velocity enhancement in the wake deflection zone and therefore leading to higher erosion volumes.Further investigation indicated that when the blade underwent slight deformation,the larger velocity enhancement close to the bed can be attributed to more significant flow deflection effects at the lateral sides of the blade and stronger flow mixing with high momentum flows away from the bed.Supported with measurements,a basic formula was established to quantify the shear stress acting on the sedimentary bed as a function of incoming flow velocity and blade aspect ratio.
基金supported by the National Natural Science Foundation of China(Grant Nos.12072105,11932006,and 52308498)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20220976).
文摘Dynamic wake field information is vital for the optimized design and control of wind farms.Combined with sparse measurement data from light detection and ranging(LiDAR),the physics-informed neural network(PINN)frameworks have recently been employed for forecasting freestream wind and wake fields.However,these PINN frameworks face challenges of low prediction accuracy and long training times.Therefore,this paper constructed a PINN framework for dynamic wake field prediction by integrating two accuracy improvement strategies and a step-by-step training time saving strategy.The results showed that the different performance improvement routes significantly improved the overall performance of the PINN.The accuracy and efficiency of the PINN with spatiotemporal improvement strategies were validated via LiDAR-measured data from a wind farm in Shandong province,China.This paper sheds light on load reduction,efficiency improvement,intelligent operation and maintenance of wind farms.
文摘WT5 'BZThis paper presents an unsteady and nonlinear wake model based on th e widely used Peters He finite state dynamic wake model with improvements. The swirl component in the tip trace plane (TTP) can be predicted, nonlinear items are added into the linear theory, and the old small angle assumption use d in matrix prediction is removed. All of these enha ncements are aimed at the low speed flight phase and formulations for the induce d velocity field just in the TTP frame are derived. The corresponding FORTRAN pr ogram is tested and optimized for the real time applications on PCs.
文摘This paper describes an improved model of curved vortex element on the circular arc (CVEC) for rotor wake analysis.As the key of the paper,two approximate formulas are derived by the series of limited terms to replace the Legendre incomplete elliptical integrals from the Biot-Savart integration,and the analytical solution of the induced velocity for the CVEC is obtained, which is more efficient in the complex rotor free wake calculation. Furthermore,the approximate formulas with the chosen factors are selected to avoid sigularity and give finite result of the induced velocity on the Vortex line,and an equivalent viscous vortex core radius might be evaluated.As examples, the induced velocity calculations on the vortex ring and two turns of a skew vortex helix are performed, and the comparisons between the circular-arc vortex element and the conventional straightline vortex element (SLVE) are given.It is shown that this curved vortex element model is advantageous over the SLVE model and is suitable for the rotor wake analysis.
文摘The basal ganglia(BG) act as a cohesive functional unit that regulates motor function,habit formation,and reward/addictive behaviors. However,it is still not well understood how the BG maintains wakefulness and suppresses sleep to achieve al these fundamental functions until genetical y engineered systems developed these years. Significant research efforts have recently been directed at developing genetic-molecular tools to achieve reversible and cell-type specific in vivo silencing or activation of neurons in behaving animals. Optogenetic tools can be used both to specifically activate or inhibit neurons of interest and identify functional synaptic connectivity between specific neuronal populations,both in vivo and in brain slices. Another recently developed system by Roth and colleagues permits the selective and ″remote″ manipulation(activation and silencing) of neuronal activity via all 3 major GPCR signaling pathways(G_i,G_s and G_q). These so-called ″ designer receptors exclusively activated by designer drugs″(DREADD) involve mutant GPCRs that do not respond to their endogenous ligands but are responsive to otherwise inert biological compounds. Recently,we demonstrated the essential roles and the neural pathways of the neurons expressing adenosine A_(2A) receptors or dopamine D_1 receptors in the BG for sleep-wake regulation using the genetically engineered systems including optogenetics and DREADD. We proposed a plausible model in which the caudate-putamen and the nucleus accumbens integrates behavioral processes with sleep/wakefulness through adenosine and dopamine receptors.
文摘Rotor wake analysis,a fundamental research of helicopter technology,has been widely applied for rotor aerodynamic analysis. This paper summarizes the research of different rotor wake models at home and abroad and reviews the development process of rotor wake methods as well as the research achievement obtained in each stage.Then,the new progress of helicopter rotor wake methods is described in detail. It includes constant circulation contours modeling method of rotor wake,pseudo-implicit relaxation iteration and time-accurate solution method,research on aerodynamic interaction characteristics of helicopter rotor/fuselage by wake method,research on the rotor blade-vortex interaction noise and interaction of coaxial rigid rotor aerodynamics by viscous vortex particle method,and application of free wake method to helicopter flight dynamics modeling. In the end,some prospects for the research of helicopter rotor wake method are put forward,which clarifies the ideas for the future development of rotor wake method.
基金supported by the National Key Technology R&D Program(2009BAG12A03)the Major State Basic Research Development Program of China(2011CB711101)
文摘Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of un- steady Reynold-averaged Navier-Stokes （URANS） and de- tached eddy simulation （DES） are utilized, respectively. Re- suits reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.
文摘A full-span free-wake method is coupled with an unsteady panel method to accurately predict the unsteady aerodynamics of helicopter rotor blades in hover and forward flight. The unsteady potential-based panel method is used to consider aerodynamics of finite thickness multi-bladed rotors, and the full-span free-wake method is applied to simulating dynamics of rotor wake. These methods are tightly coupled through trailing-edge Kutta condition and by converting doublet-wake panels to full-span vortex filaments. A velocity-field integration technique is also adopted to overcome singularity problem during the interaction between the rotor wake and blades. Helicopter rotors including Caradonna–Tung, UH-60A, and AH-1G rotors, are simulated in hover and forward flight to validate the accuracy of this approach. The predicted aerodynamic loads of rotor blades agree well with available measured data and computational fluid dynamics （CFD） results, and the unsteady dynamics of rotor wake is also well simulated. Compared to CFD, the present method obtains accurate results more efficiently and is suitable to rotorcraft aeroelastic analysis.
基金supported by the National Natural Science Foundation of China(No.51876098).
文摘Accurate predictions of Shock Waves and Boundary Layer Interaction(SWBLI)and strong Shock Waves and Wake Vortices Interaction(SWWVI)in a highly-loaded turbine propose challenges to the currently widely used Reynolds-Averaged Navier-Stokes(RANS)model.In this work,the SWBLI and the SWWVI in a highly-loaded Nozzle Guide Vane(NGV)are studied using a hybrid RANS/LES strategy.The Turbulence Kinetic Energy(TKE)budget and the Proper Orthogonal Decomposition(POD)method are used to analyze flow mechanisms.Results show that this hybrid RANS/LES method can obtain detailed flow structures for flow mechanisms analysis.Strong shock waves induce boundary layer separation,while the presence of a separation bubble can in turn lead to a Mach reflection phenomenon.The shock waves cause trailing-edge vortices to break clearly,and the wakes,in turn,can change the shocks intensity and direction.Furthermore,the Entropy Generation Rate(EGR)is used to analyze the irreversible loss.It turns out that the SWWVI can reduce the flow field loss.There are several weak shock waves in the NGV flow field,which can increase the irreversible loss.This work offers flow mechanisms analysis and presents the EGR distribution in SWBLI and SWWVI areas in a transonic turbine blade.
基金Project supported by the Boeing-COMAC Aviation Energy Conservation and Emissions Reduction Technology Center(AECER)
文摘A self-adaptive-grid method is applied to numerical simulation of the evolu- tion of aircraft wake vortex with the large eddy simulation （LES）. The Idaho Falls （IDF） measurement of run 9 case is simulated numerically and compared with that of the field experimental data. The comparison shows that the method is reliable in the complex atmospheric environment with crosswind and ground effect. In addition, six cases with different ambient atmospheric turbulences and Brunt V^iis/il^i （BV） frequencies are com- puted with the LES. The main characteristics of vortex are appropriately simulated by the current method. The onset time of rapid decay and the descending of vortices are in agreement with the previous measurements and the numerical prediction. Also, sec-ondary structures such as baroclinic vorticity and helical structures are also simulated. Only approximately 6 million grid points are needed in computation with the present method, while the number can be as large as 34 million when using a uniform mesh with the same core resolution. The self-adaptive-grid method is proved to be practical in the numerical research of aircraft wake vortex.
基金supported by the Natural Science Foundation of China,No.81260295the Graduate Student Innovation Fund of Jiangxi Province of China,No.YC2015-S090
文摘Orexins, produced in the lateral hypothalamus, are important neuropeptides that participate in the sleep/wake cycle, and their expres- sion coincides with the projection area of the vagus nerve in the brain. Vagus nerve stimulation has been shown to decrease the amounts of daytime sleep and rapid eye movement in epilepsy patients with traumatic brain injury. In the present study, we investigated whether vagus nerve stimulation promotes wakefulness and affects orexin expression. A rat model of traumatic brain injury was established using the free fall drop method. In the stimulated group, rats with traumatic brain injury received vagus nerve stimulation （frequency, 30 Hz, current, 1.0 mA; pulse width, 0.5 ms; total stimulation time, 15 minutes）. In the antagonist group, rats with traumatic brain injury were intracerebroventricularly injected with the orexin receptor type 1 （OXIR） antagonist SB334867 and received vagus nerve stimulation. Changes in consciousness were observed after stimulation in each group. Enzyme-linked immunosorbent assay, western blot assay and immunohistochemistry were used to assess the levels of orexin-A and OX1R expression in the prefrontal cortex. In the stimulated group, consciousness was substantially improved, orexin-A protein expression gradually increased within 24 hours after injury and OX1R expres- sion reached a peak at 12 hours, compared with rats subjected to traumatic brain injury only. In the antagonist group, the wake-promoting effect of vagus nerve stimulation was diminished, and orexin-A and OX1R expression were decreased, compared with that of the stim- ulated group. Taken together, our findings suggest that vagus nerve stimulation promotes the recovery of consciousness in comatose rats after traumatic brain injury. The upregulation of orexin-A and OXIR expression in the prefrontal cortex might be involved in the wake-promoting effects of vagus nerve stimulation.
文摘The flow patterns of the wake of an oblique honeycombed grid fin were visualized by hydrogen bubbles technique in a water channel. It was found that the hairpin vortices existed in the wake of surfaces in the neighborhood of each crossing of intersecting elements at moderate angles of attack. They shed periodically following the flow separation on surfaces and connected each other into chains. The main features of the flow patterns are presented and the flow mechanism concerned is preliminarily discussed.
基金State Key Development Program for Basic Research of China (No.2006CB200305), the National Natural Sci-ence Foundation of China (No.50376004), and Ph.D. Program Foundation of Ministry of Education of China (No.20030007028).
文摘Presently developed two-phase turbulence models under-predict the gas turbulent fluctuation, because their turbulence modification models cannot fully reflect the effect of particles. In this paper, a two-time-scale dis- sipation model of turbulence modification, developed for the two-phase velocity correlation and for the dissipation rate of gas turbulent kinetic energy, is proposed and used to simulate sudden-expansion and swirling gas-particle flows. The proposed two-time scale model gives better results than the single-time scale model. Besides, a gas tur- bulence augmentation model accounting for the finite-size particle wake effect in the gas Reynolds stress equation is proposed. The proposed turbulence modification models are used to simulate two-phase pipe flows. It can prop- erly predict both turbulence reduction and turbulence enhancement for a certain size of particles observed in ex- periments.
基金Supported by the National Natural Science Foundation of China(No.41476088)the National High Resolution Project of China(No.41Y30B12-9001-14/16)+1 种基金the 2016 Key Projects for Marine Environmental Security(No.2016YFC14032)the research grants of the Second Institute of Oceanography,MNR(No.JT1307)
文摘The maritime administrative department employs synthetic aperture radar (SAR) satellite remote sensing technology to obtain evidence of illegal discharge of ships. If the ship is discharged during navigation, it forms a long dark wake on the SAR image due to the suppression of the Bragg wave by the oil fi lm. This study investigates key techniques for rapid detection of long ship wakes, thereby providing law enforcement agencies with candidate ships for possible discharge. This paper presents a rapid long ship wake detection method that uses satellite imaging parameters and the axial direction of the ship in images to determine the potential detection area of the wake. Then, the threshold of long ship wake detection is determined using statistical analysis, the area is binarized, and isolated points are removed using a morphological filter operator. The method was tested with ENVISAT Synthetic Aperture Radar and GF-3 SAR data, and results showed that the method was eff ective, and the overall accuracy of the decision reaches 71%. We present two innovations;one is a method that draws a Doppler shift curve, and uses the SAR imaging parameters to determine the detection area of the long wake to achieve rapid detection and reduce the image detection area. The other is where a classical linear fitting method is used to quickly and accurately determine whether the detected dark area is a long ship wake and realizes the twisted long ship wake detection caused by the sea surface flow field, which is otherwise diffi cult to detect by the traditional Radon and Hough transform methods. This method has good suppression performance for the dark spot false alarm formed by low speed wind region or upward flow. The method is developed for maritime ship monitoring system and will promote the operational application of maritime ship monitoring system.
