Mode localization is often an unexpected dynamic phenomenon in weakly-coupled symmetric structures, and it arises from small imperfections (less than 5%) which perturb the symmetry of a structure. Such imperfections typically result from random manufacturing or assembly imprecision. Mode localization prediction is an important issue in T-tail structure design because drastic localized vibration phenomena may occur during the ground vibration test of a T-tail aircraft. Mode localization is dependent not only on parameter mistuning, but also on coupling degree. In this article the definition of mode localization is improved according to the peak amplitude ratio. The coupling degree is defined according to the effect of the stiffness of the horizontal stabilizer and fin on the modal frequencies of the T-tail structure. The mode localization and frequency loci veering phenomena for a T-tail structure is then studied and the effects of mistuned mass, mistuned stiffness and the location of mistuning on the mode localization of the horizontal stabilizer are investigated. Numerical simulation results for a T-tail structure model indicate that mode localization is most likely to occur in a T-tail structure consisting of weakly coupled substructures—a horizontal stabilizer and a fin. Moreover, when mode localization occurs, the first two bending vibration modes in the T-tail structure are prone to localization, and only one of the two modal frequencies is changed by parameter mistuning to induce frequency loci veering. The simulation also demonstrates that if mass or stiffness mistuning occurs to a horizontal stabilizer, the amplitude of the bigger mass side or smaller stiffness side is greater than that of the peer side. The study suggests that mode localization design is easy to achieve in T-tail structures by introducing mass mistuning on the tip of the horizontal stabilizer or stiffness mistuning on the root of the horizontal stabilizer.

Recent years have witnessed extensive discussions on the change of warfare forms and the development of post-4th generation fighters against the background of great power competition and batches of 4th generation fighters entering service. This paper reviews the origin of fighter generation classification and the driving elements behind each generational leap, outlining the evolution of Observe, Orient, Decision, Act (OODA) loops for air combat and proposing the essence of OODA 3.0. After a summary of the supportive and progressive relations among mechanization, informatization and intelligentization, it explores the dialectical relationship among autonomy and manned/unmanned, as well as that among platform, system of systems, and distributed operation, followed finally by a discussion of an agile and efficient development approach of future fighters.

Over the past two decades, surrogate modeling has received much attention from the researchers in the area of aerospace science and engineering due to its capability of greatly improving the efficiency of design optimization when high-fidelity numerical analysis is employed. Design optimization via surrogate models is intensively researched and eventually leads to a new type of optimization algorithm which is called surrogate-based optimization (SBO). Among the available surrogate models, such as polynomial response surface model, radial-basis functions, artificial neutral network, support-vector regression, multivariate interpolation or regression, and polynomial chaos expansion, Kriging model is the most representative surrogate model which has great potential in engineering design and optimization. In the context of aircraft design, this paper reviews the theory, algorithm and recent progress for researches on the Kriging surrogate model. First, the fundamental theory and algorithm of Kriging model are briefly reviewed and the experience about how to improve the robustness and efficiency is presented. Second, three major breakthroughs of Kriging model in recent years are reviewed, including gradient-enhanced Kriging, CoKriging and hierarchical Kriging. Third, the optimization mechanism and framework of surrogate-based optimization using Kriging model are discussed. In the meanwhile, the concept of infill-sampling criterion and sub optimization is presented. Five infill-sampling criteria as well as the dedicated constraint handling methods are described. Furthermore, the newly developed local EI (expected improvement) method and termination criteria for SBO are introduced. Fourth, a number of test cases including benchmark optimization problems as well as aerodynamic and multidisciplinary design optimization problems are given to demonstrate the excellent performance and great potential of the surrogate-based optimization using Kriging model. At last, the key challenges as well as future directions about the theory, algorithm and applications are discussed.

A real-time and accurate health condition prediction for an inertial platform is essential for cost-effective and timely maintenance planning and scheduling. Due to the fact that the true health condition of the inertial platform cannot be observed directly, it is assumed that the observations of characteristic parameters are available from monitoring, and the characteristic parameters correlate with health condition of the inertial platform. In this article, a health condition prediction system for the inertial platform is established based on belief rule base (BRB), where the characteristic parameters of the inertial platform are used as the inputs of BRB system and the health condition of platform as the output consequence. To overcome the drawbacks of current parameter optimization algorithms for BRB and satisfy real-time prediction, a parameter estimation algorithm is investigated for online updating BRB prediction system based on the expectation maximization (EM) algorithm. When the new input-output information of system operation is available, the model parameter can be updated online. Real-time health condition prediction for the inertial platform system is validated using the established model and the algorithm under investigation. The experimental results show that the proposed method can implement online parameter estimation of health condition prediction for the inertial platform effectively. In addition, compared with offline parameter optimization method, the proposed method can generate better results in terms of prediction accuracy and operating time, and thus has great potential in engineering practice.

To deal with the path planning problems of irregularly shaped objects in complex environment, a genetic collision avoidance algorithm with kinematics constraint is developed. This algorithm is then applied to the path planning operations on carrier-based aircraft scheduling on carrier flight deck. Moreover, it can be extended to solve other path planning cases under such constraints. For the problems resulting from these objects, which are characterized by complex shape and the bending radius constraint while moving in complicated obstacle situations, the technique proposed is proved to be effective. Based on the traditional genetic path planning algorithm, a three-dimensional position and orientation coding method, a three-stage path decoding method and an approach specific to the collision detection and distance calculation of a track bounding box are presented. Also, a penalty term and a gene repairing strategy are brought into the genetic process to seek the optimum. Finally, simulated verifications are conducted using VC++ platform to obtain the optimal paths. The results show that the optimal collision avoidance paths in complex obstacle environment are achieved utilizing the proposed algorithm, with the pre-set bending radius constraints satisfied. It is indicated that the design yields effective solutions to the collision avoidance path planning problems correlated with this kind of objects.

Euler/RANS-based CFD methods have been rapidly developed and widely used in aeronautics since the 1980s, making remarkable achievements and playing an important role in aircraft development and aerodynamic research. This article reviews the achievements of CFD in military and civil aeronautics in the past four decades and analyzes its shortcomings, particularly the problem in separation flow simulation due to the turbulence modeling. The development of aeronautics CFD is discussed from the perspectives of turbulence models and numerical schemes. Finally, a brief conclusion and suggestions on future development are presented.

In single channel SAR, the echo from a slow moving target is confused with ground clutter in time、space and frequency domains. If the information about fixed clutter in SAR image can be used to suppress the background clutter, the detection of moving target will be easy. The fractional Fourier transform is a linear operator, and will not be influenced by cross terms. The FrFT is a way to concentrate the energy of the echo from a ground moving target. In two symmetry fractional Fourier domains with two inverse rotation angles of every SAR image tangential line, the static clutter’s spectrums are same, while the moving target’s are different. The absolute value subtracting of the two signals can be expected to have superior moving target detection performance. The experiment result proveds the validity of this method.

The prediction of residual life (RL) is the key of the predictive maintenance for engineering equipment. Accurate and real-time prediction can provide more effective decision support to the subsequent maintenance schedule and avoid the failure effectively. In engineering practice, the performance index reflecting the degradation process of the equipment is generally not observed directly. To tackle the residual life problem under hidden degradation, a prediction method based on semi-stochastic and expectation maximization (EM) algorithm is proposed in this paper. First, the residual life is taken as the hidden state and the prediction model is constructed by building the stochastic relationship between the residual life and monitoring data. Secondly, based on the monitoring data up to the current time, a collaborative method by the extended Kalman filter (EKF) and expectation maximization algorithm is presented to achieve a real-time estimation and updating of the residual life distribution and unknown model parameters. Finally, the proposed method is validated by the application to the inertial measurement unit (IMU) and the results indicate that the method can improve the accuracy and reduce the uncertainty of the estimated residual life.

This article establishes a general numerical scheme which incorporates the accurate transport and thermodynamic property calculations of a fluid under supercritical pressures based on a modified corresponding-state method and the fundamental thermodynamic relationships with the Soave-Redlich-Kwong (SRK) equation of state. A comprehensive numerical investigation of the turbulent convective heat transfer with n-heptane, a typical hydrocarbon fuel, under supercritical pressures is systematically conducted. This heat transfer phenomenon is closely related to engine cooling technique in rocket and hypersonic propulsion systems. The effect of the supercritical pressure on fluid flows and heat transfer phenomena is examined in detail. Variations of the Nusselt number are elucidated and compared with those obtained from the available empirical formulae. Numerical results indicate that under supercritical pressures, the Nusselt number decreases with decreasing pressure, and that turbulent heat transfer becomes weakened and slightly oscillated near the critical region.

In this paper investigate the alignment problem of a stationary based strapdown inertial navigation system . In order to improve the aligning accuracy and shorten the aligning time, a Gauss-Hermite filter (GHF) is adopted in the alignment model based on large azimuth misalignment angles. The nonlinear Gauss integration of multi-variables to the mean and covariance computation in the GHF is addressed. Since large azimuth misalignment angles will introduce the nonlinearity in the alignment error equations, this paper employs linear state transformation approach to obtain the analytic solution of the linear state vector in the underlying equations. The integration of multi-variables is thus converted to the integration of a single-variable. Hence the so called "dimension problem" in the application of GHF to alignment is solved without loss of accuracy. The proposed method is applied to a SINS, and it shows that the aligning accuracy of path angle is improved by 16% and the aligning time is reduced by 75% compared with extended Kalman filter (EKF) and unscented Kalman filter (UKF).

Based on uniform circular arrays (UCAs), a high-precision estimation of 2D direction angle for multiple sources is proposed. First, exploiting information of source in 2D space-time domain forms the space-time rotational matrix, so that the multiple sources are separated. Second, based on a direct array manifold in UCA, the azimuth and elevation are estimated by Least Squares (LS). Finally, the removal method of cyclic ambiguity is presented. Numerical results show that the advantages of estimator are high precision and robustness to amplitude and phase error of sensor gain.

Object detection is one of the key technologies in improving the autonomous sensing ability of Unmanned Aerial Vehicles (UAVs). Research on object detection is of critical significance in UAV applications. Compared with traditional methods based on manual features, deep learning based on the convolutional neural network has a powerful capability of feature learning and expression, therefore becoming the mainstream algorithm in object detection. In recent years, object detection research has achieved a series breakthrough in the field of natural scene and the research in UAVs has increasingly become a hotspot simultaneously. This paper reviews the research progress of object detection algorithms based on deep learning, summarizing their advantages and disadvantages. Then, some typical aerial image datasets and the method of transfer learning are introduced, and relevant algorithms are analyzed aiming at the complex background, small and rotating objects, large fields of view in UAV imagery. The existing problems and possible future development directions are finally discussed.

The combustion characteristics of single boron particle in forced convective flow in ramjet engines are investigated systemically. A physical and mathematical model is proposed taking into consideration the gas flow around the particle, the gas diffusion and the surface finite reaction dynamics. The two-dimensional axi-symmetric Navier-Stokes equations with species reactions are solved using the finite volume technique. And the numerical simulation method is validated. Then influencing factors such as the free stream velocity, particle radius, the ambient oxygen mass fraction and the ambient pressure on the combustion characteristics of single boron particle are studied by numerical simulations. And the effect mechanism for each factor is analyzed in detail. The numerical prediction results show that in forced convective flow, both the mass rate and the mass flux of the buring boron particle increase with the increase in the free stream velocity, the particle radius, the ambient oxygen mass fraction and the ambient pressure. A comprehensive analysis of the results is conducted and it is found that the mass flux of the buring boron increases with the stream Reynolds number. Then the mass flux of the buring boron particle in the static atmosphere is modified based on abundant numerical results to describe the combustion characteristics of the boron particle in forced convective flow.

The erosion wear resistance is one of the most important properties of abradable seal coating. The erosion wear behaviour and mechanism of several kinds of middle temperature abradable seal coatings were investigated by a CMS 100 self made vacuum sand erosion machine. The results show that the relationship between the erosion weight loss and the erosion time is linear, the coatings hold a maximum erosion rate at 60° impact angle, and the relation between the erosion rate and the impact speed is an exponential function. The speed exponent increases with the increase of the impact angle. At 90° impact, the abrasive particles impinging on the coating surface produce indents and extrude lips, then the lips are work hardened and fall off; and flattened metal phase grains are impinged repeatedly, loosen and exfoliate. At 30° impact, the micro cutting, plowing and tunneling via pores and non metal phase are involved. The model of the erosion mechanism is advanced on the basis of the above mentioned erosion behaviour.

Friction drag is the major part of the total drag of a transport, so reducing it is essential for improving the performance and reducing the cost of a transport. Since laminar friction drag is much less than the turbulent one, one of the important measures for reducing it is to increase the laminar flow extent, and if possible, to realize a fully laminar flow. For that, three types of laminar flow control technology, i.e., natural laminar flow, fully laminar flow and hybrid laminar flow controls, are formed. In the present paper, drag reducing analysis, the concepts, methods, potential benefits and design methods of laminar flow control technology, and operational maintenance of a laminar flow aircraft (including protection of insect contamination and ice accumulation) are systematically described; Summary of researches of laminar flow control technology during 1930-2000 is briefly introduced and the progress in this field is shown by using examples of X-21A slotted suction flight tests, simulated airlines flight tests of Jetstar HLFC leading edge systems and Boeing 757 HLFC flight tests, and future research is also pointed out.

The autonomous navigation technology is essential for the automated and intelligent operation of various motion carriers. This article briefly introduces the basic concepts of autonomous navigation technology, and illustrates the research progress of the technology in the fields of aerospace, aviation, ships, vehicles, and individual soldiers at home and abroad. The key technologies for autonomous navigation such as inertial navigation, inertial-based integrated navigation, geomagnetic navigation, gravity gradient navigation, celestial navigation and multi-source information fusion are analyzed. Then, the development trend of the technology is discussed, which can provide reference for the development of various mainstream autonomous navigation systems in China and assistance for the overall design of a variety of autonomous navigation tasks in the future.

In the analysis of the development cost of an aircraft there are usually only small samples with a large number of cost drive factors. In view of this fact and considering the advantages of hierarchical partial least squares regression (Hi-PLS) in building a regressive model in the condition of a large number of variables, an application of Hi-PLS to aircraft development cost prediction is proposed using the development cost prediction of a fighter plane fuselage as an example. After the cost drive factors of the fighter plane fuselage development cost are grouped, Hi-PLS is applied to the regress of the grouped cost drive factors, and a fuselage development cost prediction model is established. The calculated results in the example show that Hi-PLS model can reflect satisfactorily the correlation between fuselage development cost and performance parameters of a military aircraft.

A CFD study on the reduction of aerodynamic heating on the nose of a reentry vehicle by an opposing jet thermal protection system is conducted, by means of which the flow field parameters, reattachment point position, surface pressure distribution and heat flux distribution are obtained. The physical mechanism of the reduction of heat flux is analyzed. The opposing jet interacts with the freestream to form a Mach disk which enables the freestream to flow to the edges rather than interact with the surface to produce aerodynamic heating. In addition, the jet flows back to form a cool recirculation region, which reduces the difference in temperature between the surface and the nearby gas, and thus reduces the heat flux. The larger the total pressure ratio, the lower is the aerodynamic heating. To study the effect of the intensity of the opposing jet more appropriately, a new parameter RPA is defined by combining the flux and the total pressure ratio. The study shows that the same shock wave position, reattachment point position, peak heat flux position and total heat load can be obtained with the same RPA with different fluxes and total pressure ratios, which means the new ratio parameter may account for the intensity of the opposing jet and be used to analyze its influence on the flow field and total heat load at the nose of a reentry vehicle.

With the Shenzhou spacecraft entering into the stage of maturity, it is of necessity to launch the research and development of a new-generation multi-purpose manned spacecraft. In this paper, we firstly generalize the technological characteristics, the design concept and the status quo of the foreign new-generation manned spacecraft. Based on this, we summarize their technological trend, i.e., multi-task adaption, cost reduction, bluntbody aerodynamic configuration, high safety reliability and new lightweight materials. Then, we primarily analyze the task requirements of China's new-generation manned spacecraft, including low earth orbit flight mission, as well as manned flights to the Moon, the asteroid and the Mars. We basically set the parameters of the overall performance. Finally, we sort out the technological approaches of it and propose two design schemes, which could provide some reference for the research of China's new-generation manned spacecraft.

In complex environments with high dynamics, uncertainty and resource constraints, the unmanned swarm system will face challenges in all fields of the "Observation-Orientation-Decision-Action (OODA)" loop when performing complicated tasks such as collaborative area search and swarm optimal scheduling. To improve the adaptability of unmanned swarm systems to different scenarios, it is necessary to break through the key technologies for autonomous cooperation of unmanned swarm systems in complex environments. Based on the theory of robust autonomous cooperation of large-scale heterogeneous unmanned swarm systems in complex environments, this paper gives a review of the design and modeling methods of adaptive heterogeneous architecture for unmanned swarm systems, and discusses three problems:high-dimensional situation distributed perception and cognition, intelligent decision-making with guiding, trusting and evolving ability, and autonomous cooperative control of the unmanned swarm system in complex environments. Firstly, the research progress of autonomous cooperation of unmanned swarm system in complex environment is summarized. Secondly, the challenges faced by OODA task loop of unmanned swarm system are analyzed. Then, the key technologies involved in autonomous cooperation of unmanned swarm system in complex environment and their progress are reviewed. Finally, the future development of autonomous cooperation of unmanned swarm system is given.