Modeling Technique of the Aircraft Unsteady Aerodynamics Due to the Travelling Gust

The main equations for computing the unsteady aerodynamics of the aircraft undergoing the travelling gust are derived.Research and simulation on a specific example aircraft are performed,the results indicate that the modeling technique of the aircraft unsteady aerodynamics is correct,and it can meet the requirements due to the head⁃on and tail⁃on travelling gusts.

Determination of Dynamic Load Condition of Aircraft Carrier based on Multivariable Distribution of Flight Parameters

In order to solve the design problem of dynamic load of a carrier-based aircraft,according to the relevant criteria of national military standards,eight key flight parameters of the dynamic load conditions for the aircraft carrier were selected.Based on the multivariable distribution data of landing flight parameters obtained from flight test,the distribution form and range limitation of each flight parameter were determined by using the probability distribution of each flight parameter and the spatial relationship among variables.Furthermore,100000 sets of data were constructed to simulate the landing condition of aircraft in the form of random number.After the envelope is screened by multivariable joint probability distribution,the boundary conditions were compared and merged,and finally the dynamic load conditions were obtained.In this paper,a set of dynamic load condition design method based on the aircraft requirements is constructed,which systematically covers all kinds of situations that occur in the process of aircraft landing,and improves the conventional design process of aircraft dynamic load.

Elastic Buckling of Bionic Cylindrical Shells Based on Bamboo

High load-bearing efficiency is one of the advantages of biological structures after the evolution of billions of years. Biomimicking from nature may offer the potential for lightweight design. In the viewpoint ofrnechanics properties, the culm of bamboo comprises of two types of cells and the number of the vascular bundles takes a gradient of distribution. A three-point bending test was carried out to measure the elastic modulus. Results show that the elastic modulus of bamboo decreases gradually from the periphery towards the centre. Based on the structural characteristics of bamboo, a bionic cylindrical structure was designed to mimic the gradient distribution of vascular bundles and parenchyma cells. The buckling resistance of the bionic structure was compared with that of a traditional shell of equal mass under axial pressure by finite element simulations. Results show that the load-bearing capacity of bionic shell is increased by 124.8%. The buckling mode of bionic structure is global buckling while that of the conventional shell is local buckling.

Environmentally Friendly and Multifunctional Shaddock Peel-Based Carbon Aerogel for Thermal-Insulation and Microwave Absorption

Eco-friendly electromagnetic wave absorbing materials with excellent thermal infrared stealth property,heat-insulating ability and compression resistance are highly attractive in practical applications.Meeting the aforesaid requirements simultaneously is a formidable challenge.Herein,ultra-light carbon aerogels were fabricated via fresh shaddock peel by facile freeze-drying method and calcination process,forming porous network architecture.With the heating platform temperature of 70℃,the upper surface temperatures of the as-prepared carbon aerogel present a slow upward trend.The color of the sample surface in thermal infrared images is similar to that of the surroundings.With the maximum compressive stress of 2.435 kPa,the carbon aerogels can provide favorable endurance.The shaddock peel-based carbon aerogels possess the minimum reflection loss value(RLmin)of−29.50 dB in X band.Meanwhile,the effective absorption bandwidth covers 5.80 GHz at a relatively thin thickness of only 1.7 mm.With the detection theta of 0°,the maximum radar cross-sectional(RCS)reduction values of 16.28 dB m^(2) can be achieved.Theoretical simulations of RCS have aroused extensive interest owing to their ingenious design and time-saving feature.This work paves the way for preparing multi-functional microwave absorbers derived from biomass raw materials under the guidance of RCS simulations.

UAV cooperative air combat maneuver decision based on multi-agent reinforcement learning

In order to improve the autonomous ability of unmanned aerial vehicles(UAV)to implement air combat mission,many artificial intelligence-based autonomous air combat maneuver decision-making studies have been carried out,but these studies are often aimed at individual decision-making in 1 v1 scenarios which rarely happen in actual air combat.Based on the research of the 1 v1 autonomous air combat maneuver decision,this paper builds a multi-UAV cooperative air combat maneuver decision model based on multi-agent reinforcement learning.Firstly,a bidirectional recurrent neural network(BRNN)is used to achieve communication between UAV individuals,and the multi-UAV cooperative air combat maneuver decision model under the actor-critic architecture is established.Secondly,through combining with target allocation and air combat situation assessment,the tactical goal of the formation is merged with the reinforcement learning goal of every UAV,and a cooperative tactical maneuver policy is generated.The simulation results prove that the multi-UAV cooperative air combat maneuver decision model established in this paper can obtain the cooperative maneuver policy through reinforcement learning,the cooperative maneuver policy can guide UAVs to obtain the overall situational advantage and defeat the opponents under tactical cooperation.

On Nonlinear Evolution of C-type Instability in Nonparallel Boundary Layers

The process of evolution, especially that of nonlinear evolution, of C-type instability of laminar-turbulent flow transition in nonparallel boundary layers are studied by means of a newly developed method called parabolic stability equations （PSE）. Initial conditions, which are very important for the nonlinear problem, are investigated by computing initial solution of the harmonic waves, modifying the mean-flow-distortion, and giving initial value of TS wave and its subharmonic waves at initial station by solving linear PSE. A numerical method with high-order accuracy are developed in the text, the key normalization conditions in the PSE are satisfied, and nonlinear PSE are solved efficiently and implemented stably by the spatial marching. It has been shown that the computed process of nonlinear evolution of C-type instability in Blasius boundary layer is in good agreement with the experimental results.

复合材料韧性评定的新方法——关于损伤阻抗性能的研究(英文)

从复合材料结构设计的角度 ,指出了目前在韧性复合材料评定技术中存在的问题 ,特别是指出了用冲击后压缩强度值作为判别复合材料韧性的缺点 ,提出了应采用损伤阻抗和损伤容限共同评定复合材料韧性的观点。对 7种不同韧性的复合材料进行了冲击与静压痕等试验 ,在对试验数据分析的基础上 ,确定了对损伤阻抗最敏感的损伤参数 。

Robust airfoil optimization based on improved particle swarm optimization method

A robust airfoil optimization platform is constructed based on the modified particle swarm optimization method （i.e., the second-order oscillating particle swarm method）, which consists of an efficient optimization algorithm, a precise aerodynamic analysis program, a high accuracy surrogate model, and a classical airfoil parametric method. There are two improvements for the modified particle swarm method compared with the standard particle swarm method. First, the particle velocity is represented by the combination of the particle position and the variation of position, which makes the particle swarm algorithm a second-order precision method with respect to the particle po- sition. Second, for the sake of adding diversity to the swarm and enlarging the parameter searching domain to improve the global convergence performance of the algorithm, an oscillating term is introduced to the update formula of the particle velocity. At last, tak- ing two airfoils as examples, the aerodynamic shapes are optimized on this optimization platform. It is shown from the optimization results that the aerodynamic characteristic of the airfoils is greatly improved in a broad design range.

Static solution on four-region spherial cavity expansion model in a pressure sensitive medium

Spherical cavity expansion model is often used to study the mechanic characteristics of pressure sensitive mediums. The most important one we do in the paper is that we construct a four-region model with σθ≠0 in damage region,which is different from what Satapathy did before and is more reasonable. By adopting this model,different constitutive equations were constructed by different method-elastic mechanics in elastic region,damage mechanics and fracture mechanics in damage region,and macro-micro mechanics theory in plastic region. Then using Durban's self-similarity assumption,the control differential equations with boundary conditions were established,and the static numerical solution of stress field and displacement field in the three different regions of elastic,damage and plastic area were discussed respectively. Results showed that this four-region model can describe precisely the mechanic characteristics of pressure sensitive mediums under initial pressure.

Experimental study of a porous electrospray thruster with different number of emitterstrips

The electrospray thruster is becoming popular in space propulsion due to its low power and high specific impulse.Before this work,an electrospray thruster based on a porous emitter was developed.In order to achieve larger and more stable thrust,the thruster was redesigned,and the influence of the space between strips on thrust was studied.Four types of emitter were tested,and they had 1,3,4 and 14 emitter-strips on the emission surface of the same size respectively.According to the experimental results,the maximum extraction voltage and emission current of the four thrusters are different under stable operational conditions.The measured stable emission currents and extraction voltages were-500μA/-5000 V,-1570μA/-3800 V,-1200μA/-3800 V,and-650μA/-4500 V,respectively.Increasing the number of strips may not result in the emission current increasing,but changing the stable operational range of the emission current per strip and the extraction voltage.The maximum stable operational extraction voltages of 3 and 4 emitter-strips are lower than those of 1 and 14 emitter-strips,but the emission currents are higher than those of 1 and 14 emitter-strips.Time-of-flight mass spectrometry was used to analyze the mass distribution and obtain the performance of the thruster in the case of thrusters with 1 and 3 emitter-strips.Both of their plumes were composed of very small ion cluster(the pure-ion regime),and their thrusts were 80.1μN,219.2μN with specific impulses of 5774 s,5047 s,respectively.

Interesting Beat Phenomenon for Airfoil

The airfoil with two degrees is simulated to get the beat phenomenon.The results indicate that the occurrence of beat phenomenon is very sensitive to the equivalent frequency and damping,contributed by the structural and aerodynamic ones.Only the equivalent damping approaches to zero and the equivalent frequency is very close to the gust frequency which the beat phenomenon occurs.

Structural Reliability Analysis Method in Fuzzy Environment

In this paper, the fuzzy-set-based structural possibility theory is investigated, and this theory can be used to deal with the subjective uncertainties in the design of engineering structures. Furthermore, a comprehensive model of structural safety assessment, which can merge subjective uncertainties with objective uncertainties, is presented. In this model, the fuzziness of stress-strength inference model, safety margin functions of single or multiple limit-state, structural failure state and the final assessment result are taken into account. This continuous model can be transformed into an equivalent model of probability-based and solved by the present structural reliability analysis method and parallel algorithm. An example is given to show the main idea of the method presented in this paper.

System of systems oriented flight vehicle conceptual design: Perspectives and progresses

In order to obtain optimized flight vehicle concepts which meet system of systems （SOS） operation requirements, designers have to pay high attention to the impact of SoS at conceptual design stage since operation environment goes increasingly complex. Based on this tendency, per- spectives and progre,;ses of SoS oriented flight vehicle conceptual design, which is abbreviate as SoSed design, are reviewed in this paper. Such basic concepts of SoS as definition, characteristics, differences between systems engineering and SoS engineering, as well as SoSed design process are introduced, then SoS engineering process model for research and development of flight vehicles and SoSed design wheel model for conceptual design are proposed. Related literature is classified and analyzed in accordance with four major elements including requirements, design concept, design analysis, and trade studies and optimization： typical SoS architectures, description and quan- tization of indexes are introduced; Application of inverse design in designing concept is analyzed; Modeling and simulation （M＆S）-based methods and their applications in SoSed effectiveness evaluation are highlighted; According to SoSed trade studies and optimization related research, the importance of such points as decision-making and using multidisciplinary design optimization for reference are emphasized. Finally, the value of SoSed design is concluded, and five directions which are worthy of .attention in this field are presented.

Gain self-scheduled H_∞ control for morphing aircraft in the wing transition process based on an LPV model

This article investigates gain self-scheduled H 1 robust control system design for a tailless fold- ing-wing morphing aircraft in the wing shape varying process. During the wing morphing phase, the aircraft＇s dynamic response will be governed by time-varying aerodynamic forces and moments. Nonlinear dynamic equations of the morphing aircraft are linearized by using Jacobian linearization approach, and a linear parameter varying （LPV） model of the morphing aircraft in wing folding is obtained. A multi-loop controller for the morphing aircraft is formulated to guarantee stability for the wing shape transition process. The proposed controller uses a set of inner-loop gains to provide stability using classical techniques, whereas a gain self-scheduled H 1 outer-loop controller is devised to guarantee a specific level of robust stability and performance for the time-varying dynamics. The closed-loop simulations show that speed and altitude vary slightly during the whole wing folding process, and they converge rapidly after the process ends. This proves that the gain self-scheduled H 1 robust controller can guarantee a satisfactory dynamic performance for the morphing aircraft during the whole wing shape transition process. Finally, the flight control system＇s robustness for the wing folding process is verified according to uncertainties of the aerodynamic parameters in the nonlinear model.

Evaluation of simulation-based training for aircraft carrier marshalling with learning cubic and Kirkpatrick's models

Simulation-based training is a promising way to train a carrier flight deck crew because of the complex and dangerous working environment. Quantitative evaluation of simulation-based training quality is vital to make simulation-based training practical for aircraft carrier marshalling.This paper develops a personal computer-based aircraft carrier marshalling simulation system and a cave automatic virtual environment（CAVE）-based immersive environment. In order to compare the training effectiveness of simulation-based training and paper-based training, a learning cubic model is proposed and a contrast experiment is carried out as well. The experimental data is analyzed based on a simplified Kirkpatrick＇s model. The results show that simulation-based training is better than paper-based training by 26.80% after three rounds of testing, which prove the effectiveness of simulation-based aircraft carrier marshalling training.

Oscillation quenching and physical explanation on freeplay-based aeroelastic airfoil in transonic viscous flow

Limit Cycle Oscillation(LCO)quenching of a supercritical airfoil(NLR 7301)considering freeplay is investigated in transonic viscous flow.Computational Fluid Dynamics(CFD)based on Navier-Stokes equations is implemented to calculate transonic aerodynamic forces.A loosely coupled scheme with steady CFD and an efficient graphic method are developed to obtain the aerodynamic preload.LCO quenching phenomenon is observed from the nonlinear dynamic aeroelastic response obtained by using time marching approach.As the airspeed increases,LCO appears then quenches,forming the first LCO branch.Following the quenching region,LCO occurs again and sustains until the divergence of the response,forming the second LCO branch.The quenching of LCOs was addressed physically based on the aerodynamic preload and the linear flutter characteristic.An“island”of stable region is observed in the flutter boundary,i.e.the flutter speed versus the mean Angle of Attack(AoA).The LCO quenches when the aerodynamic preload crosses this stable region with the increasing of airspeed.The LCO quenching of this model in transonic flow is essentially induced by destabilizing effect from aerodynamic preload,since the flutter speed is sensitive to AoA due to aerodynamic nonlinearity.

Reconfigurable intelligent surface with high optical-transparency based on metalmesh

Reconfigurable intelligent surfaces(RISs)have aroused extensive attentions from academic and wireless communication communities due to their abilities to customize the electromagnetic(EM)characteristics of the propagation channels flexibly and rapidly.Recent advances in theoretical innovations and prototype systems have demonstrated the advantages of RISs in terms of low cost,low power consumption,and easy deployment.Meanwhile,the optically transparent RISs are demanded in some application scenarios.In this paper,we propose a 2-bit metalmesh-based RIS with high optical-transparency.By analyzing the surface current distributions on the element,we employ the metalmesh-grid patterns and metalmesh-stripe patterns on the top and ground layers respectively.The metalmesh patterns can help improve the optical transparency of RISs,while maintaining similar microwave characteristics.The RIS can reach the optical transparency of 79%,and the reflection amplitude is greater than3.2 dB within the operating band.Finally,to verify the capability of the proposed RIS in wavefront controls,the far-field scattering patterns of the RIS with different coding sequences are investigated and the simulation results are in good agreement with the theoretical results.

激光冲击处理对铆接结构疲劳性能的影响(Ⅱ)

文 [1]对 LY12 (2 0 2 4 ) T6 2薄板铆钉孔进行激光冲击处理 ,装配成铆接结构后发现其疲劳寿命有稳定地提高 ,本文通过对疲劳断口的宏观和微观形貌的分析 。

The effect of leading-edge sweep angle asymmetry on lateral aerodynamics

Based on the results of force measurement experiment in a low speed wind tunnel, the effect of asymmetrical leading-edge sweep angle on aerodynamic load was investigated with the commonswift’s wing model. The wing model was divided into three segments, i.e., arm wing, hand wingin and hand wingout, and the roll moment produced by the variation of asymmetrical change of wing segment’s leading-edge sweep angle was analyzed.

Aerodynamics and dynamic stability of micro-air-vehicle with four flapping wings in hovering flight

Recently,a novel concept of flapping Micro-Air-Vehicles(FMAVs)with four wings has been proposed,which potentially utilizes the clap-and-fling effect for lift enhancement and agile maneuvers through an adjustment of wing kinematics.However,the application of the clap-and-fling effect in the four-winged FMAVs is underexplored and the dynamic stability is still unclear.In this paper,aerodynamics and flight dynamic stability of the four-winged FMAVs are studied experimentally and numerically.Results show that the clap-and-fling effect is observed when the flapping frequency is above 18 Hz.Due to the clap-and-fling effect,the lift generation and aerodynamic efficiency are both improved,which is mainly attributed to the fling phase.Further studies show that the clap-and-fling effect becomes weaker as the wing root spacing increases and is almost absent at a wing root spacing of 1.73 chord length.In addition,a wing with an aspect ratio of 3 can increase both lift generation and efficiency due to the clap-and-fling effect.Finally,according to the dynamic stability analysis of the four-winged FMAV,the divergence speed of the lateral oscillation mode is about 4 times faster than that of the longitudinal oscillation mode.Our results can provide guidance on the design and control of four-winged FMAVs.