万方数据知识服务平台期刊资源更新-中国航空学报（英文版）Wake structure and similar behavior of wake profiles downstream of a plunging airfoil
http://d.wanfangdata.com.cn/Periodical_hkxb-e201704001.aspx
Ali R.DAVARI2017-08-28 00:00:00Very limited attention has already been paid to the velocity behavior in the wake region in unsteady aerodynamic problems.A series of tests has been performed on a flapping airfoil in a subsonic wind tunnel to study the wake structure for different sets of mean angle of attack,plunging amplitude and reduced frequency.In this study,the velocity profiles in the wake for various oscillation parameters have been measured using a wide shoulder rake,especially designed for the present experiments.The airfoil under consideration was a critical section of a 660 kW wind turbine.The results show that for a flapping airfoil the wake structure can be of drag producing type,thrust producing or neutral,depending on the mean angle of attack,oscillation amplitude and reduced frequency.In a thrust producing wake,a high-momentum high-velocity jet flow is formed in the core region of the wake instead of the conventional low-momentum flow.As a result,the drag force normally experienced by the body due to the momentum deficit would be replaced by a thrust force.According to the results,the momentum loss in the wake decreases as the reduced frequency increases.The thrust producing wake pattern for the flapping airfoil has been observed for suffi ciently low angles of attack in the absence of the viscous effects.This phenomenon has also been observed for either high oscillation amplitudes or high reduced frequencies.According to the results,for different reduced frequencies and plunging amplitudes,such that the product of them be a constant,the velocity profiles exhibit similar behavior and coalesce on each other.This simi larity parameter works excellently at small angles of attack.However,at near stall boundaries,the similarity is not as evident as before.Self-sustained oscillation for compressible cylindrical cavity flows
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Kung-Ming CHUNG|Kuan-Huang LEE|Keh-Chin CHANG2017-08-28 00:00:00The presence of a cavity changes the mean and fluctuating pressure distributions.Simi larities are observed between a cylindrical cavity and a rectangular cavity for a compressible flow.The type of cavity flow field depends on the diameter-to-depth ratio and the length-to-depth ratio.The feedback loop is responsible for the generation of discrete acoustic tones.In this study,the selfsustained oscillation for a compressible cylindrical cavity flow was investigated experimentally.For open-type cavities,the power spectra show that the strength of resonance depends on the diameter to-depth ratio (4.43-43.0) and the incoming boundary layer thickness-to-depth ratio (0.72-7.0).The effective streamwise length is used as the characteristic length to estimate the Strouhal number.At higher modes,there is a large deviation from Rossiter's formula for rectangular cavities.The gradient-based searching method was used to evaluate the values of the empirical parameters.Less phase lag and a lower convection velocity are observed.Numerical studies of static aeroelastic effects on grid fin aerodynamic performances
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Chengde HUANG|Wen LIU|Guowei YANG2017-08-28 00:00:00The grid fin is an unconventional control surface used on missiles and rockets.Although aerodynamics of grid fin has been studied by many researchers,few considers the aeroelastic effects.In this paper,the static aeroelastic simulations are performed by the coupled viscous computational fluid dynamics with structural flexibility method in transonic and supersonic regimes.The developed coupling strategy including fluid-structure interpolation and volume mesh motion schemes is based on radial basis functions.Results are presented for a vertical and a horizontal grid fin mounted on a body.Horizontal fin results show that the deformed fin is swept backward and the axial force is increased.The deformations also induce the movement of center of pressure,caus ing the reduction and reversal in hinge moment for the transonic flow and the supersonic flow,respectively.For the vertical fin,the local effective incidences are increased due to the deformations so that the deformed normal force is greater than the original one.At high angles of attack,both the deformed and original normal forces experience a sudden reduction due to the interference of leeward separated vortices on the fin.Additionally,the increment in axial force is shown to correlate strongly with the increment in the square of normal force.A new vortex sheet model for simulating aircraft wake vortex evolution
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Mengda LIN|Guixiang CUI|Zhaoshun ZHANG2017-08-28 00:00:00A new vortex sheet model was proposed for simulating aircraft wake vortex evolution.Rather than beginning with a pair of counter-rotating cylindrical vortices as in the traditional models,a lift-drag method is used to initialize a vortex sheet so that the roll-up phase is taken into account.The results of this model report a better approximation to a real situation when compared to the measurement data.The roll-up induced structures are proved to influence the far-field decay.On one hand,they lead to an early decay in the diffusion phase.On the other hand,the growth of linear instability such as elliptical instability is suppressed,resulting in a slower decay in the rapid decay phase.This work provides a simple and practicable model for simulating wake vortex evolu tion,which combines the roll-up process and the far-field phase in simulation.It is also proved that the roll-up phase should not be ignored when simulating the far-field evolution of an aircraft wake vortex pair,which indicates the necessity of this new model.Linear stability analysis of interactions between mixing layer and boundary layer flows
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Fengjun LIU|Yifan WANG|Ying PIAO2017-08-28 00:00:00The linear instabilities of incompressible confluent mixing layer and boundary layer were analyzed.The mixing layers include wake,shear layer and their combination.The mean velocity profile of confluent flow is taken as a superposition of a hyperbolic and exponential function to model a mixing layer and the Blasius similarity solution for a flat plate boundary layer.The stability equation of confluent flow was solved by using the global numerical method.The unstable modes associated with both the mixing and boundary layers were identified.They are the boundary layer mode,mixing layer mode 1 (nearly symmetrical mode) and mode 2 (nearly anti-symmetrical mode).The interactions between the mixing layer stability and the boundary layer stability were examined.As the mixing layer approaches the boundary layer,the neutral curves of the boundary layer mode move to the upper left,the resulting critical Reynolds number decreases,and the growth rate of the most unstable mode increases.The wall tends to stabilize the mixing layer modes at low frequency.In addition,the mode switching behavior of the relative level of the spatial growth rate between the mixing layer mode 1 and mode 2 with the velocity ratio is found to occur at low frequency.Aerodynamic multi-objective integrated optimization based on principal component analysis
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Jiangtao HUANG|Zhu ZHOU|Zhenghong GAO|Miao ZHANG|Lei YU2017-08-28 00:00:00Based on improved multi-objective particle swarm optimization (MOPSO) algorithm with principal component analysis (PCA) methodology,an efficient high-dimension multiobjective optimization method is proposed,which,as the purpose of this paper,aims to improve the convergence of Pareto front in multi-objective optimization design.The mathematical efficiency,the physical reasonableness and the reliability in dealing with redundant objectives of PCA are verified by typical DTLZ5 test function and multi-objective correlation analysis of supercritical airfoil,and the proposed method is integrated into aircraft multi-disciplinary design (AMDEsign) platform,which contains aerodynamics,stealth and structure weight analysis and optimization module.Then the proposed method is used for the multi-point integrated aerodynamic optimization of a wide-body passenger aircraft,in which the redundant objectives identified by PCA are transformed to optimization constraints,and several design methods are compared.The design results illustrate that the strategy used in this paper is sufficient and multi-point design requirements of the passenger aircraft are reached.The visualization level of non-dominant Pareto set is improved by effectively reducing the dimension without losing the primary feature of the problem.Aerodynamic configuration integration design of hypersonic cruise aircraft with inward-turning inlets
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Jifei WANG|Jinsheng CAI|Chuanzhen LIU|Yanhui DUAN|Yaojie YU2017-08-28 00:00:00In this work,a novel airframe/propulsion integration design method of the wing-body configuration for hypersonic cruise aircraft is proposed,where the configuration is integrated with inward-turning inlets.With the help of this method,the major design concern of balancing the aerodynamic performance against the requirements for efficient propulsion can be well addressed.A novel geometric parametrically modelling method based on a combination of patched class and shape transition (CST) and COONs surface is proposed to represent the configuration,especially a complex configuration with an irregular inlet lip shape.The modelling method enlarges the design space of components on the premise of guaranteeing the configuration integrity via special constraints imposed on the interface across adjacent surfaces.A basic flow inside a cone shaped by a dual-inflection-point generatrix is optimized to generate the inward-turning inlet with improvements of both compression efficiency and flow uniformity.The performance improvement mechanism of this basic flow is the compression velocity variation induced by the variation of the generatrix slope along the flow path.At the design point,numerical simulation results show that the lift-to-drag ratio of the configuration is as high as 5.2 and the inlet works well with a high level of compression efficiency and flow uniformity.The design result also has a good performance on off-design conditions.The achievement of all the design targets turns out that the integration design method proposed in this paper is efficient and practical.Nutation instability of spinning solid rocket motor spacecraft
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Dan YANG|Yongliang XIONG|Qian REN|Xianyong WANG2017-08-28 00:00:00The variation of mass,and moment of inertia of a spin-stabilized spacecraft leads to concern about the nutation instability.Here a careful analysis on the nutation instability is performed on a spacecraft propelled by solid rocket booster (SRB).The influences of specific solid propellant designs on transversal angular velocity are discussed.The results show that the typical SRB of End Burn suppresses the non-principal axial angular velocity.On the contrary,the frequently used SRB of Radial Burn could amplify the transversal angular velocity.The nutation instability caused by a design of Radial Burn could be remedied by the addition of End Burn at the same time based on the study of the combination design of both End Burn and Radial Burn.The analysis of the results proposes the design conception of how to control the nutation motion.The method is suitable to resolve the nutation instability of solid rocket motor with complex propellant patterns.Numerical simulations of turbulent flows in aeroramp injector/gas-pilot flame scramjet
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Bing CHEN|Xu XU|Baoxi WEI|Yan ZHANG2017-08-28 00:00:00To uncover the internal flow characteristics in an ethylene-fueled aeroramp injector/gaspilot (ARI/G-P) flame scramjet,a Reynolds-averaged Navier-Stokes (RANS) solver is constructed under a hybrid polyhedral cell finite volume frame.The shear stress transport (SST) k-o model is used to predict the turbulence,while the Overmann's compressibility corrected laminar flamelet model is adopted to simulate the turbulent combustion.Nonreactive computations for Case 1 (G-P jet on),Case 2 (ARI jets on),and Case 3 (both ARI and G-P jets on) were conducted to analyze the mixing mechanism,while reactive Cases 4-7 at equivalent ratios of 0.380,0.278,0.199 and 0.167 respectively were calculated to investigate the flame structure and combustion modes.The numerical results are compared well to those of the experiments.It is shown that the G-P jet plays significant role in both the fuel/air mixing and flame holding processes;the combustion for the four reactive cases takes place intensively in the regions downstream of the ARI/G-P unit;Cases 4 and 5 are under subsonic combustion mode,whereas Cases 6 and 7 are mode transition critical and supersonic combustion cases,respectively;the mode transition equivalent ratio is approximately 0.20.Coupled Lagrangian impingement spray model for doublet impinging injectors under liquid rocket engine operating conditions
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Qiang WEI|Guozhu LIANG2017-08-28 00:00:00To predict the effect of the liquid rocket engine combustion chamber conditions on the impingement spray,the conventional uncoupled spray model for impinging injectors is extended by considering the couplingof the jet impingement process and the ambient gas field.The new coupled model consists of the plain-orifice sub-model,the jet-jet impingement sub-model and the droplet collision sub-model.The parameters of the child droplet are determined with the jet-jet impingement sub-model using correlations about the liquid jet parameters and the chamber conditions.The overall model is benchmarked under various impingement angles,jet momentum and offcenter ratios.Agreement with the published experimental data validates the ability of the model to predict the key spray characteristics,such as the mass flux and mixture ratio distributions in quiescent air.Besides,impinging sprays under changing ambient pressure and non-uniform gas flow are investigated to explore the effect of liquid rocket engine chamber conditions.First,a transient impingement spray during engine start-up phase is simulated with prescribed pressure profile.The minimum average droplet diameter is achieved when the orifices work in cavitation state,and is about 30％ smaller than the steady single phase state.Second,the effect of non-uniform gas flow produces off-center impingement and the rotated spray fan by 38°.The proposed model suggests more reasonable impingement spray characteristics than the uncoupled one and can be used as the first step in the complex simulation of coupling impingement spray and combustion in liquid rocket engines.A new stationary droplet evaporation model and its validation
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Fang WANG|Jie YAO|Shaofeng YANG|Rui LIU|Jie JIN2017-08-28 00:00:00The liquid droplet evaporation character is important for not only combustion chamber design process but also high-accuracy spray combustion simulation.In this paper,the suspended droplets' evaporation character was measured in a quiescent high-temperature environment by micro high-speed camera system.The gasoline and kerosene experimental results are consistent with the reference data.Methanol,common kerosene and aviation kerosene droplet evaporation characteristics,as well as their evaporation rate changing with temperature,were obtained.The evaporation rate experimental data were compared with the prediction result of Ranz-Marshall boiling temperature model (RMB),Ranz-Marshall low-temperature model (RML),drift flux model (DFM),mass analogy model (MAM),and stagnant film model (SFM).The disparity between the experimental data and the model prediction results was mainly caused by the neglect of the nat ural convection effect,which was never introduced into the droplet evaporation concept.A new droplet evaporation model with consideration of natural convection buoyancy force effect was proposed in this paper.Under the experimental conditions in this paper,the calculation results of the new droplet evaporation model were agreed with the experimental data for kerosene,methanol and other fuels,with less than 20％ relative deviations.The relative deviations between the new evaporation model predictions for kerosene and the experimental data from the references were within 10％.Theoretical aspects of selecting repeated unit cell model in micromechanical analysis using displacement-based finite element method
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Lijun GAO|Chengyu WANG|Zhanli LIU|Zhuo ZHUANG2017-08-28 00:00:00Repeated Unit Cell (RUC) is a useful tool in micromechanical analysis of composites using Displacement-based Finite Element (DFE) method,and merely applying Periodic Displacement Boundary Conditions (PDBCs) to RUC is almost a standard practice to conduct such analysis.Two basic questions arising from this practice are whether Periodic Traction Boundary Conditions (PTBCs,also known as traction continuity conditions) are guaranteed and whether the solution is independent of selection of RUCs.This paper presents the theoretical aspects to tackle these questions,which unify the strong form,weak form and DFE method of the micromechanical problem together.Specifically,the solution's independence of selection of RUCs is dealt with on the strong form side,PTBCs are derived from the weak form as natural boundary conditions,and the validity of merely applying PDBCs in micromechanical Finite Element (FE) analysis is proved by referring to its intrinsic connection to the strong form and weak form.Key points in the theoretical aspects are demonstrated by illustrative examples,and the merits of setting micromechanical FE analysis under the background of a clear theoretical framework are highlighted in the efficient selection of RUCs for UniDirectional (UD) fiber-reinforced composites.Optimal deployment schedule of an active twist rotor for performance enhancement and vibration reduction in high-speed flights
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Young H.YOU|Sung N.JUNG|Chang J.KIM2017-08-28 00:00:00The best active twist schedules exploiting various waveform types are sought taking advantage of the global search algorithm for the reduction of hub vibration and/or power required of a rotor in high-speed conditions.The active twist schedules include two non-harmonic inputs formed based on segmented step functions as well as the simple harmonic waveform input.An advanced Particle Swarm assisted Genetic Algorithm (PSGA) is employed for the optimizer.A rotorcraft Computational Structural Dynamics (CSD) code CAMRAD Ⅱ is used to perform the rotor aeromechanics analysis.A Computation Fluid Dynamics (CFD) code is coupled with CSD for verification and some physical insights.The PSGA optimization results are verified against the parameter sweep study performed using the harmonic actuation.The optimum twist schedules according to the performance and/or vibration reduction strategy are obtained and their optimization gains are compared between the actuation cases.A two-phase non-harmonic actuation schedule demonstrates the best outcome in decreasing the power required while a four-phase non-harmonic schedule results in the best vibration reduction as well as the simultaneous reductions in the power required and vibration.The mechanism of reduction to the performance gains is identified illustrating the section airloads,angle-of-attack distribution,and elastic twist deformation predicted by the present approaches.Stiffeners layout design of thin-walled structures with constraints on multi-fastener joint loads
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Jie HOU|Jihong ZHU|Fei HE|Weihong ZHANG|Wenjie GUO2017-08-28 00:00:00The purpose of this paper is to present an extended topology optimization method for the stiffeners layout design of aircraft assembled structures.Multi-fastener joint loads and manufacturing constraints are considered simultaneously.On one hand,the joint loads are calculated and constrained within a limited value to avoid the failure of fasteners.On the other hand,the manufacturing constraints of the material distribution in the machining directions of stiffeners are implemented by an improved piecewise interpolation based on a beveled cut-surface.It is proven that the objective function is strictly continuous and differentiable with respect to the piecewise interpolation.The effects of the extended method with two different constraints are highlighted by typical numerical examples.Compared with the standard topology optimization,the final designs have clearly shown the layout of stiffeners and the joint loads have been perfectly constrained to a satisfying level.A new structural reliability index based on uncertainty theory
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Pidong WANG|Jianguo ZHANG|Hao ZHAI|Jiwei QIU2017-08-28 00:00:00The classical probabilistic reliability theory and fuzzy reliability theory cannot directly measure the uncertainty of structural reliability with uncertain variables,i.e.,subjective random and fuzzy variables.In order to simultaneously satisfy the duality of randomness and subadditivity of fuzziness in the reliability problem,a new quantification method for the reliability of structures is presented based on uncertainty theory,and an uncertainty-theory-based perspective of classical Cornell reliability index is explored.In this paper,by introducing the uncertainty theory,we adopt the uncertain measure to quantify the reliability of structures for the subjective probability or fuzzy variables,instead of probabilistic and possibilistic measures.We utilize uncertain variables to uniformly represent the subjective random and fuzzy parameters,based on which we derive solutions to analyze the uncertainty reliability of structures with uncertainty distributions.Moreover,we propose the Cornell uncertainty reliability index based on the uncertain expected value and variance.Experimental results on three numerical applications demonstrate the validity of the proposed method.New reference trajectory optimization algorithm for a flight management system inspired in beam search
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Alejandro MURRIETA-MENDOZA|Bruce BEUZE|Laurane TERNISIEN|Ruxandra Mihaela BOTEZ2017-08-28 00:00:00With the objective of reducing the flight cost and the amount of polluting emissions released in the atmosphere,a new optimization algorithm considering the climb,cruise and descent phases is presented for the reference vertical flight trajectory.The selection of the reference vertical navigation speeds and altitudes was solved as a discrete combinatory problem by means of a graphtree passing through nodes using the beam search optimization technique.To achieve a compromise between the execution time and the algorithm's ability to find the global optimal solution,a heuristic methodology introducing a parameter called "optimism coefficient was used in order to estimate the trajectory's flight cost at every node.The optimal trajectory cost obtained with the developed algorithm was compared with the cost of the optimal trajectory provided by a commercial flight management system(FMS).The global optimal solution was validated against an exhaustive search algorithm(ESA),other than the proposed algorithm.The developed algorithm takes into account weather effects,step climbs during cruise and air traffic management constraints such as constant altitude segments,constant cruise Mach,and a pre-defined reference lateral navigation route.The aircraft fuel burn was computed using a numerical performance model which was created and validated using flight test experimental data.Heuristics of node selection criteria to assess robustness of world airport network
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Manel SORIA|Oriol LORDAN|José Maria SALLAN2017-08-28 00:00:00The world airport network (WAN) is one of the networked infrastructures that shape today's economic and social activity,so its resilience against incidents affecting the WAN is an important problem.In this paper,the robustness of air route networks is extended by defining and testing several heuristics to define selection criteria to detect the critical nodes of the WAN.In addition to heuristics based on genetic algorithms and simulated annealing,custom heuristics based on node damage and node betweenness are defined.The most effective heuristic is a multiattack heuristic combining both custom heuristics.Results obtained are of importance not only for advance in the understanding of the structure of complex networks,but also for critical node detection.On solving multi-commodity flow problems: An experimental evaluation
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Weibin DAI|Jun ZHANG|Xiaoqian SUN2017-08-28 00:00:00Multi-commodity flow problems (MCFs) can be found in many areas,such as transportation,communication,and logistics.Therefore,such problems have been studied by a multitude of researchers,and a variety of methods have been proposed for solving it.However,most researchers only discuss the properties of different models and algorithms without taking into account the impacts of actual implementation.In fact,the true performance of a method may differ greatly across various implementations.In this paper,several popular optimization solvers for implementations of column generation and Lagrangian relaxation are discussed.In order to test scalability and optimality,three groups of networks with different structures are used as case studies.Results show that column generation outperforms Lagrangian relaxation in most instances,but the latter is better suited to networks with a large number of commodities.Measuring air traffic complexity based on small samples
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Xi ZHU|Xianbin CAO|Kaiquan CAI2017-08-28 00:00:00Air traffic complexity is an objective metric for evaluating the operational condition of the airspace.It has several applications,such as airspace design and traffic flow management.Therefore,identifying a reliable method to accurately measure traffic complexity is important.Considering that many factors correlate with traffic complexity in complicated nonlinear ways,researchers have proposed several complexity evaluation methods based on machine learning models which were trained with large samples.However,the high cost of sample collection usually results in limited training set.In this paper,an ensemble learning model is proposed for measuring air traffic complexity within a sector based on small samples.To exploit the classification information within each factor,multiple diverse factor subsets (FSSs) are generated under guidance from factor noise and independence analysis.Then,a base complexity evaluator is built corresponding to each FSS.The final complexity evaluation result is obtained by integrating all results from the base evaluators.Experimental studies using real-world air traffic operation data demonstrate the advantages of our model for small-sample-based traffic complexity evaluation over other stateof-the-art methods.An optimal one-way cooperative strategy for two defenders against an attacking missile
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Qilong SUN|Naiming QI|Zheyao XU|Yanfang LIU|Yong ZHANG2017-08-28 00:00:00This paper investigates a cooperative strategy for protecting an aerial target.The problem is solved as a game among four players (a target,two defenders,and a missile).In this scenario,the target launches two defenders (defender-1 and defender-2) simultaneously,to establish a oneway cooperation system (OCS) against an attacking missile.A new optimal evasion strategy for the target is also derived.During the engagement,the target takes into account the reaction of the attacking missile,and guides defender-1 to the interception point by receiving information from defender-1.Depending on the control effort of the target,defender-2 can choose appropriate launch conditions and use very limited maneuvering capability to intercept the missile.For adversaries with first-order dynamics,simulation results show that the OCS allows two defenders to intercept the missile.During the engagement,even if one defender or communication channel is broken,the OCS still allows an interception to be made,thus increasing the target's survivability.Modified fast Fourier transform in FBMC for satellite communications
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Chaosan YANG|Rongke LIU|Ruifeng DUAN2017-08-28 00:00:00In this paper,a Doppler scaling fast Fourier transform (Doppler-FFT) algorithm for filter bank multi-carrier (FBMC) is proposed,which can efficiently eliminate the impact of the Doppler scaling in satellite communications.By introducing a Doppler scaling factor into the butterfly structure of the fast Fourier transform (FFT) algorithm,the proposed algorithm eliminates the differences between the Doppler shifts of the received subcarriers,and maintains the same order of computational complexity compared to that of the traditional FFT.In the process of using the new method,the Doppler scaling should be estimated by calculating the orbital data in advance.Thus,the inter-symbol interference (ISI) and the inter-carrier interference (ICI) can be completely eliminated,and the signal to interference and noise ratio (SINR) will not be affected.Simulation results also show that the proposed algorithm can achieve a 0.4 dB performance gain compared to the frequency domain equalization (FDE) algorithm in satellite communications.Extrinsic calibration of a laser displacement sensor in a non-contact coordinate measuring machine
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Chao BI|Jianguo FANG|Kun LI|Zhijun GUO2017-08-28 00:00:00In order to implement 3D scanning of those complicated parts such as blades in the aviation field,a non-contact optical measuring system is established in the paper,which integrates a laser displacement sensor,a probe head,the frame of a coordinate measuring machine (CMM),etc.As the output of the laser sensor directly obtained possesses the 1D length of the laser beam,it needs to determine the unit direction vector of the laser beam denoted as (l,m,n) by calibration so as to convert the 1D values into 3D coordinates of target points.Therefore,an extrinsic calibration method based on a standard sphere is proposed to accomplish this task in the paper.During the calibration procedure,the laser sensor moves along with the motion of the CMM and gathers the required data on the spherical surface.Then,both the output of the laser sensor and the grating readings of the CMM are substituted into the constraint equation of the spherical surface,in which an over-determined nonlinear equation group containing unknown parameters is established.For the purpose of solving the equation group,a method based on non-linear least squares optimization is put forward.Finally,the system after calibration is utilized to measure the diameter of a metallic sphere 10 times from different orientations to verify the calibration accuracy.In the experiment,the errors between the measured results and the true values are all smaller than 0.03 mm,which manifests the validity and practicality of the extrinsic calibration method presented in the paper.ABORT-like detector to combat active deceptive jamming in a network of LFM radars
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Yuan ZHAO|Zhi RAN|Ying XIONG|Bin TANG2017-08-28 00:00:00This paper studies an electronic counter-counter measures (ECCM) scheme combating against deceptive electronic counter measure (ECM) techniques.An adaptive detector exploiting generalized likelihood ratio test (GRLT) criterion is applied to detect the presence of deceptive jamming in fractional Fourier transform (FrFT) domain.First,the generating mechanism of spurious frequencies is analyzed based on the Volterra serial.The proposed nonlinear distortion model based on power amplifier behavior is robust in distortion analysis when the memory effect is considered.Second,a modified adaptive beamformer orthogonal rejection test (ABORT) like detector in closed form is built.The proposed detector can discriminate the echo and deceptive jamming adaptively by exploiting primary data and secondary data.This ECCM scheme is capable of guaranteeing the performance without the restriction of orthogonality,which is essential for the ABORT detectors.The expansion to radar network is discussed as a special case at the final part of this paper.Numerical simulations demonstrate the effectiveness of the proposed method.Research on a six-phase permanent magnet synchronous motor system at dual-redundant and fault tolerant modes in aviation application
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Xiaolin KUANG|Hong GUO|Jinquan XU|Tong ZHOU2017-08-28 00:00:00With the development of more/all electrical aircraft technology,an electro-mechanical actuator (EMA) is more and more used in an aircraft actuation system.The motor system,as the crucial part of an EMA,usually adopts the redundancy technology or fault tolerance technology to improve the reliability.To compare the performances of these two motor systems,a 10-pole/ 12-slot six-phase permanent magnet synchronous motor (PMSM) is designed with the concentrated single-layer winding,which is able to operate at dual-redundant and fault tolerant modes.Furthermore,the position servo performances of the six-phase PMSM at dual-redundant and fault tolerant modes are analyzed,including the normal and fault conditions.In addition,a variable structure proportional-integral-derivative (PID) control strategy is proposed to solve the performance degradation problem caused by phase current saturation.Simulation and experimental results show that the fault tolerant PMSM has a better position servo performance than the dual-redundant PMSM,and the variable structure PID control strategy is able to improve the performance due to phase current saturation.Rotorcraft flight endurance estimation based on a new battery discharge model
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Feng CHENG|Hua WANG|Pin CUI2017-08-28 00:00:00To avoid the numerical complexities of the battery discharge law of electric-powered rotorcrafts,this study uses the Kriging method to model the discharge characteristics of Li-Po batteries under standard conditions.A linear current compensation term and an ambient temperature compensation term based on radial basis functions are then applied to the trained Kriging model,leading to the complete discharged capacity-terminal voltage model.Using an orthogonal experimental design and a sequential method,the coefficients of the current and ambient temperature compensation terms are determined through robust optimization.An endurance calculation model for electric-powered rotorcrafts is then established,based on the battery discharge model,through numerical integration.Laboratory tests show that the maximum relative error of the proposed discharged capacity-terminal voltage model at detection points is 0.0086,and that of the rotorcraft endurance calculation model is 0.0195,thus verifying their accuracy.A flight test further demonstrates the applicability of the proposed endurance model to general electric-powered rotorcrafts.Distributed cooperative guidance for multiple missiles with fixed and switching communication topologies
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Qilun ZHAO|Xiwang DONG|Zixuan LIANG|Chen BAI|Jian CHEN|Zhang REN2017-08-28 00:00:00This study investigates cooperative guidance problems for multiple missiles with fixed and switching directed communication topologies.A two-step guidance strategy is proposed to realize the simultaneous attack.In the first step,a distributed cooperative guidance law is designed using local neighboring information for multiple missiles to achieve consensus on range-to-go and leading angle.The second step begins when the consensus of multiple missiles is realized.During the second step,multiple missiles disconnect from each other and hit the target using the proportional navigation guidance law.First,based on the local neighboring communications,a sufficient condition for multiple missiles to realize simultaneous attack with a fixed communication topology is presented,where the topology is only required to have a directed spanning tree.Then,the results are extended to the case of switching communication topologies.Finally,numerical simulations are provided to validate the theoretical results.Approach and landing guidance design for reusable launch vehicle using multiple sliding surfaces technique
http://d.wanfangdata.com.cn/Periodical_hkxb-e201704027.aspx
Xiangdong LIU|Fengdi ZHANG|Zhen LI|Yao ZHAO2017-08-28 00:00:00An autonomous approach and landing (A&L) guidance law is presented in this paper for landing an unpowered reusable launch vehicle (RLV) at the designated runway touchdown.Considering the full nonlinear point-mass dynamics,a guidance scheme is developed in threedimensional space.In order to guarantee a successful A&L movement,the multiple sliding surfaces guidance (MSSG) technique is applied to derive the closed-loop guidance law,which stems from higher order sliding mode control theory and has advantage in the finite time reaching property.The global stability of the proposed guidance approach is proved by the Lyapunov-based method.The designed guidance law can generate new trajectories on-line without any specific requirement on off-line analysis except for the information on the boundary conditions of the A&L phase and instantaneous states of the RLV.Therefore,the designed guidance law is flexible enough to target different touchdown points on the runway and is capable of dealing with large initial condition errors resulted from the previous flight phase.Finally,simulation results show the effectiveness of the proposed guidance law in different scenarios.A unifying approach in simulating the shot peening process using a 3D random representative volume finite element model
http://d.wanfangdata.com.cn/Periodical_hkxb-e201704028.aspx
Dianyin HU|Ye GAO|Fanchao MENG|Jun SONG|Yanfei WANG|Mengxi REN|Rongqiao WANG2017-08-28 00:00:00Using a modified 3D random representative volume (RV) finite element model,the effects of model dimensions (impact region and interval between impact and representative regions),model shapes (rectangular,square,and circular),and peening-induced thermal softening on resultant critical quantities (residual stress,Almen intensity,coverage,and arc height) after shot peening are systematically examined.A new quantity,i.e.,the interval between impact and representative regions,is introduced and its optimal value is first determined to eliminate any boundary effect on shot peening results.Then,model dimensions are respectively assessed for all model shapes to reflect the actual shot peening process,based on which shape-independent critical shot peening quantities are obtained.Further,it is found that thermal softening of the target material due to shot peening leads to variances of the surface residual stress and arc height,demonstrating the necessity of considering the thermal effect in a constitutive material model of shot peeing.Our study clarifies some of the finite element modeling aspects and lays the ground for accurate modeling of the SP process.Dynamic performance of a C/C composite finger seal in a tilting mode
http://d.wanfangdata.com.cn/Periodical_hkxb-e201704029.aspx
Hailin ZHAO|Guoding CHEN|Li'na WANG|Hua SU|Fei LU2017-08-28 00:00:00The complex operating state of aeroengines has an impact on the performance of finger seals.However,little work has been focused on the issue and the dynamic performance of finger seals is also rarely studied.Therefore,a distributed mass equivalent model considering working conditions is proposed in this paper for solving the existing problems.The effects of the fiber bundle density and the preparation direction of the fiber bundle of a C/C composite on the dynamic performance of a finger seal are investigated in rotor tilt based on the proposed model.The difference between the C/C composite finger seal performances under the rotor precession and nutation tilt cases is also investigated.The results show that the fiber bundle density and the preparation direction of the fiber bundle have an influence on the dynamic performance of the finger seal as rotor tilt is considered,and the dynamic performance of the finger seal is different in the two kinds of tilting modes.In addition,a novel method for design of finger seals is presented based on the contact pressure between finger boots and the rotor.Finger seals with good leakage rates and low wear can be acquired in this method.Investigation of high-speed abrasion behavior of an abradable seal rubber in aero-engine fan application
http://d.wanfangdata.com.cn/Periodical_hkxb-e201704030.aspx
Haijun XUAN|Na ZHANG|Bin LU|Lijun CHENG|Weirong HONG2017-08-28 00:00:00Abradable seal rubber has been widely used in aero-engine fans to improve their effi ciency by reducing the clearance between rotating and stationary components.To investigate the high-speed scraping behavior between a vulcanized silicone rubber and a Ti-6A1-4V fan blade and evaluate the abradable performance of seal rubber,abrasion tests were conducted at a blade tip velocity of 50-300 m/s with an incursion rate of 100 μm/s.The influences of the blade tip velocity on the wear mechanism and interaction forces were specially analyzed.It is shown that abrasive wear and pattern wear are the predominant wear mechanisms,and pattern wear can be seen as the emergence and propagation of cracks.With an increase of the blade tip velocity,both of the final incursion depth and wear mass loss of seal rubber exhibit growth trends.The gradual changes of rubbing forces with an increase of rubbing time are the characteristic of abrasive wear,and force curves with unstable mutations are a reflection of pattern wear.At a constant incursion rate of 100 tm/s,the maximum values of interaction forces decrease first and then grow with an increase of the blade tip velocity,and the blade tip velocity of 150 m/s becomes the cut-off point between abrasive wear and pattern wear.Simulation and experimental investigation on a dynamic lateral flow mode in trepanning electrochemical machining
http://d.wanfangdata.com.cn/Periodical_hkxb-e201704031.aspx
Dong ZHU|Zhouzhi GU|Tingyu XUE|Ao LIU2017-08-28 00:00:00An appropriate flow mode of electrolyte has a positive effect on process efficiency,surface roughness,and machining accuracy in the electrochemical machining (ECM) process.In this study,a new dynamic lateral flow mode,in which the electrolyte flows from the leading edge to the trailing edge,was proposed in trepanning ECM of a diffuser.Then a numerical model of the channel was set up and simulated by using computational fluid dynamics software.The result showed that the distribution of the flow field was comparatively uniform in the inter-electrode gap.Furthermore,a fixture was designed to realize this new flow mode and then corresponding experiments were carried out.The experimental results illustrated that the feeding rate of the cathode reached 2 mm/min,the best taper angle was about 0.4°,and the best surface roughness was up to Ra =0.115 μm.It reflects that this flow mode is suitable and effective,and can also be applied to machining other complex structures in trepanning ECM.Guide for Authors
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2017-08-28 00:00:00