Waveform design is one of the key technologies in radar signal processing for the netted collocated Multiple Input Multiple Output(MIMO)radar system.To improve the target detection capability of the system under clutter interference while taking into account hardware compatibility,good ambiguity and pulse compression properties of the designed waveform,the paper considers constructing a model for the radar output Signal to Clutter and Noise Ratio(SCNR)under constant modulus constraints and waveform similarity metrics;then by equivalent transformation of the original non-convex problem,a polynomial-time iterative algorithm based on successive convex approximation is proposed and analyzed for convergence.To further reduce the computational complexity,the paper also proposes an algorithm based on Gradient Projection(GP).Finally,the proposed method is simulated and verified,and the results show that the method can provide a new feasible method for the waveform design of each transmitting site under the netted radar system.
Path planning is one of the key technologies for UAVs to accomplish operation missions in complex battlefield environments.In this paper,we propose a UAV path planning method based on PER-D3QN,which realizes the path planning for UAVs in the battlefield environment through network model design,state space design,action space design and reward function design.The PER-D3QN algorithm combines the target network,dueling network and prioritized experience replay,which effectively solves the overfitting problem and unstable problem in deep reinforcement learning.In the end,it is verified through simulation experiments that the proposed method achieved better convergence,stability and applicability compared with double DQN and DQN algorithms,and better real-time performance compared with A* algorithm,which can efficiently realize the path planning of UAVs in the complex battlefield environment,and effectively help the UAVs to attempt the operational mission.
In order to meet the requirement of rapid prediction of fluid-structure interaction system in aircraft design,a data-driven unsteady flow field modeling strategy was explored to shorten the time spent on flow field evolution solution and accelerate the simulation speed of fluid-structure interaction system.The solution of flow field evolution in fluid-structure interaction system is partially equivalent to the evolution of unsteady flow field with moving boundary.This paper proposes a flow field prediction model based on neural networks to learn and predict the evolution of unsteady flow fields with moving boundaries.This neural network can predict the flow field at next timestep based on the current flow field and boundary motion information.The prediction accuracy and generalization ability of the proposed neural network model were tested by the flow around a moving cylinder under different vibration frequencies and amplitudes.The predicted flow fields of the neural network are in accordance with the computational fluid dynamics simulation results.The aerodynamic force obtained by integrating the pressure on the boundary of the predicted flow field data also has a high accuracy.The test results demonstrate that the good predictive performance of the neural network model,so this method can be used to quickly and accurately obtain the unsteady flow field state around the moving boundary.
The poor wear resistance of titanium alloys severely limits their application in the aerospace field.In order to study the mechanism of improving wear resistance of Ti-6Al-4V(TC4)titanium alloy after ultrasonic impact strengthening,ultrasonic impact strengthening test of Ti-6Al-4V(TC4)titanium alloy was conducted.The influence rule and sensitivity of ultrasonic impact treatment process parameters(tool diameter,air float table pressure,impact pass,tool head shape,feed step)on the surface quality and performance of titanium alloy were investigated.It was found that when the ball head tool was used,the pressure of air float table was 0.45MPa,and the feed step was 0.3mm,the ultrasonic impact strengthening had the most obvious improvement on the wear resistance of titanium alloy.Through the study and analysis of the tribological test results such as friction coefficient,ball grinding spot diameter,disk wear rate and surface topography,it is found that the wear resistance of titanium alloy after ultrasonic impact strengthening treatment is improved by the joint action of compressive stress suppression crack mechanism,surface hardening strengthening mechanism and gully oil storage mechanism.The actual enhancement effect of ultrasonic impact treatment on the wear resistance of titanium alloy was verified.
Flap-slat electromechanical actuator is a key motion part in the aircraft high lift system,and its speed control is very important for the opening and closing precision of the flap-slat.However,the speed control loop of electromechanical actuator is prone to periodic or aperiodic interference of external aerodynamic load and the traditional proportional integral speed controller cannot guarantee satisfactory control performance.Therefore,a speed controller based on a proportional resonance Active Disturbance Rejection Control(ADRC)is proposed.It can not only suppress aperiodic interference but also suppress specific periodic interference.The periodic interference is estimated by an extended state observer using a proportional resonance term.By comparing the control performance of proportional integral controller,traditional linear ADRC controller and proportional resonant controller,it is proved that the proposed method can significantly suppress the interference,improve the control performance of flap-slat electromechanical actuator,and enhance the smoothness of aircraft take-off and landing.
Analyzing the damage situation of typical ammunition warheads against airport targets is of great significance for improving the damage efficiency of air to ground ammunition against airport targets.Three typical targets related to combat aircraft,namely aircraft shelter targets,early warning aircraft targets on the apron,and airport runway targets,are selected to construct the damage assessment models,and the influence of typical ammunition warhead parameters on the damage effect is analyzed.The aircraft shelter targets are divided into external shelter targets and internal fighter targets,and the impact of drop angle on the damage effect of the invasion warhead is studied.Taking high precision early warning aircraft as the vulnerability model,the influence of aim point and blast height on the damage effect of detonating warhead is analyzed.The airport runway target takes the blockade probability as the evaluation index of damage effect,and the effects of bomb parameters,submunition parameters,runway dimensions and minimum leave window on the blocking effect of shrapnel on runways are studied.The feasibility and rationality of the constructed model are verified by the simulation examples.It also calculates and analyzes the optimal drop angle of the missile when striking the shelter target and the aircraft target inside the shelter,the optimal aim point and the optimal blast height of the missile when striking the target of the early warning aircraft,and the influence of typical parameters of submunitions on the damage effect when striking runway targets.
Quadrotor aircraft has been widely used in many fields.Due to the complex and changeable working environment,quadrotor aircraft is prone to structural damage faults,which brings great challenges to the safety of aircraft.Therefore,it is of great significance to study the structural damage faults of quadrotor aircraft for improving the reliability of quadrotor aircraft.Aiming at the problem of low diagnosis rate of structural damage small sample fault data of quadrotor aircraft in practical application,this paper proposes a siamese hybrid neural network(CNLS-MMD)quadcopter fault diagnosis method based on convolutional neural networks and long short-term memory network under small sample conditions.Firstly,an experiment is designed to obtain the multi-condition structural damage flight data of the quadrotor aircraft and to preprocess the data.Secondly,a siamese hybrid neural network based fault diagnosis model is established,and a CNLS hybrid model is constructed using Convolutional Neural Networks(CNN)and Long Short-Term Memory(LSTM)network to extract data features,and Maximum Mean Discrepancy(MMD)is used to measure the similarity of samples to achieve the prediction of fault labels.Finally,training sets with different sample sizes are selected to train the model,and the built model is tested for faults using a small sample data set with multiple working conditions.The results show that the fault diagnosis method has good diagnostic performance and generalization ability.
Aircraft often face the danger of icing during flight with urgent anti-icing needs,and energy-efficient superhydrophobic electro-thermal composite anti-icing skins have broad application prospects,but the superhydrophobic surface supercooled water droplet collection characteristics have not been considered in current design methods.In order to give full play to the role of superhydrophobic surfaces in aircraft anti-icing solutions,this paper firstly designs a spray device with accurate control of droplet diameter and flow rate,then determines a scheme for the experiments on the capture rate of supercooled water droplets,and finally explains the differences in surface capture rate under different experimental conditions and summarises the relevant laws by combining the theories related to heat transfer and surface properties.The results show that under the experimental conditions,the superhydrophobic surface supercooled water droplet capture rate is about 25%of that of the PI surface,which proves that the superhydrophobic surface reduces energy consumption due to the reduction of the total amount and duration of water droplets on the surface,and provides a basis for the accurate design of the minimum anti-icing power of the new generation superhydrophobic electro-thermal composite skin,which is of great significance for the normal operation of UAVs in harsh environments.
The integration method of far-field sound propagation based on the traditional acoustic analogy theory assumes that the acoustic medium is uniform,and it is difficult to account for the sound refraction in non-uniform media which causes large numerical errors in the prediction of noise field.In this paper,the acoustic perturbation equation is used to describe the sound wave motion,and the adjoint Green's function is constructed in the frequency domain to relate the near-field sound source and the far-field sound pressure based on the acoustic reciprocity principle,so that the refraction effect of the inhomogeneous media is included in the adjoint Green's function.By combining the numerical results of the adjoint Green's function and the source terms of the acoustic perturbation equations,the spatial propagation of aerodynamic noise is calculated by the integration method.Combined with the above method,numerical prediction research is carried out for the noise induced by flow around the two-dimensional cylinder and NACA0012 airfoil,and the far-field sound pressure prediction results are in good agreement with that directly obtained by CFD.The integral calculation method of aerodynamic noise propagation based on the acoustic disturbance equation takes into account the influence of non-uniform media on sound propagation,which can improve the prediction accuracy of aerodynamic noise.
Determining the fatigue limit of tube is important for avoiding fatigue failure of aviation engine fuel structures.In this paper,the rotational bending fatigue tests were conducted on empty tubes and pressurized tubes(13.5MPa)respectively.Two strain gauges were used to monitor the dynamic stress caused by inertia during eccentric rotation.Based on the Gerber model,stress corrections were made to the asymmetric cyclic load caused by internal pressure,and the differences in the fatigue failure forms between the empty tubes and pressurized tubes were obtained.The fatigue limits and their standard deviations of the empty pipe and the pressurized pipe were determined through the data of up-down method.Based on the up-down method data,several fatigue tests under high stress levels are supplemented,and the S-N curve of the two type tubes were fitted by the power function model.Finally,the probability statistical analysis method is used to process the test data,and the fatigue limits under different confidence levels and survival rates were obtain.The research results provide the reference for the stress severity values of aircraft fuel tubes design.
Aerodynamic gravity measurement is an effective means of quickly obtaining information about the earth's gravity field,and the data processing technology of high-precision extraction of gravity information from a wide range of noise plays an important role.This paper first analyzes the sources and error characteristics of measurement noise,and clarifies that commonly used FIR low-pass filters at present can effectively filter out high-frequency noise.Secondly,an error separation method based on Empirical Mode Decomposition(EMD)is proposed for dynamic characteristic errors and accidental errors.Then,a system adjustment method suitable for multiple repeated survey lines was proposed,which effectively suppresses the impact of low-frequency system errors.Finally,the measured aviation data is processed.The experimental results show that the EMD based error separation method improves the internal coincidence accuracy from 2.86mGal to 0.75mGal,and the repeated line system adjustment method further improves the accuracy to 0.28mGal.This study is of great significance for improving the maturity and practicality of airborne gravity measurement systems in data processing technology.
High-speed helicopter not only meets the new requirements of modern military war in helicopter technology,but also has considerable market demand prospects in civil fields such as emergency rescue because of its advantages of high speed and high load.This paper focuses on three types of high-speed helicopter:compound,dip transformation and stop transformation,and the current development status of high-speed helicopter at home and abroad is systematically introduced and analyzed.Combined with the performance advantages and limitations of high-speed helicopter configurations,the four development directions of high-speed helicopter in the future intelligent,unmanned,environmental protection and polar area are systematically analyzed and summarized.Combined with the future development trend,this paper points out the feasible research direction.
Air landing and airdrop is the basis of air force equipment development.To guarantee the safe landing of air drop equipment for long distance delivery,the heading attitude mode data of cargo platform are needed to obtain for real time descending attitude adjustment so as to avoid landing rollover accident.The present study envisaged the development of a vision-based method for calculating the heading attitude of airdrop cargo platform,in order to accurately estimate the attitude of the airdrop cargo platform during an airdrop landing.The landing distance of airdrop system was divided into two stages:Far-ground at 160m and near-ground at 20m.Signs of different scales were designed as visual reference for different landing stages,which effectively improved the autonomous landing height of airdrop cargo platform.When the airdrop cargo platform initially landed at an altitude of 160m,and the inherent geometric properties of the cooperative target were used to identify the overall cooperative target in the environment;When it reached 20m near the ground,the central cooperation target was screened by Hu-invariant moment as ground auxiliary features,and finally the motion of the airdrop cargo platform was estimated by homography.This algorithm effectively improved the accuracy,real-time performance and the robustness of the attitude calculation technology of the airdrop cargo platform.It also met the requirements of an accurate calculation of real-time attitude of airdrop cargo platform.The results showed the significance and feasibility of the vision-based heading attitude calculation technology of airdrop cargo platform with a good application prospect.
Flying wing UAVs has strong maneuverability and better stealth performances due to their special aerodynamic configurations.Nevertheless,the special aerodynamic configuration and complex flight environment bring the control system design with channel coupling and multi-source disturbance problems.Therefore,the flying wing UAV anti-disturbance control has become the key issue of its development limit.This paper investigates the command tracking control problem of the longitudinal dynamics in flying wing UAV with multi-source disturbances.Firstly,the command tracking problem in altitude and velocity channel is transformed into the stabilization of tracking errors.Secondly,the couplings between the altitude and velocity channels and the influences of multi-source disturbances are regarded as lumped disturbances,and then the High-order Sliding Mode Observer(HSMO)technique is introduced to estimate them.Finally,a composite nonlinear dynamic inverse output feedback controller is constructed based on the estimation information of HSMO.Simulation results validate that the proposed method not only guarantees high-precision tracking of the altitude and velocity commands,but also achieves good disturbance rejection performance.
Hydrogen energy is the inevitable direction and important branch of green aviation in the future.With the in-depth promotion of dual-carbon strategy,the development and flight safety of hydrogen-fueled general aircraft have attracted wide attention.Firstly,the development of hydrogen-powered general purpose aircraft is summarized,the hydrogen energy development strategy plans formulated and issued by various countries in the world are introduced,the basic concept of hydrogen-powered general purpose aircraft is explained,and the basic principle,application and development of hydrogen fuel cell and hydrogen combustion hydrogen propulsion technologies are expounded respectively.Then the application status of hydrogen powered aviation is introduced through several typical cases of hydrogen powered aircraft platform.Combined with hydrogen energy characteristics,the safety problems in the use of hydrogen-burning engine,the safety problems of hydrogen energy storage and transportation for general purpose aircraft and other safety problems of hydrogen powered general purpose aircraft are discussed.Finally,the safety standards of hydrogen-powered general aircraft are listed to provide reference for the design and development personnel of hydrogen-powered general aircraft and practitioners in related fields.
Addressing the challenges of slow inference speed and limited detection accuracy in small airborne target detection tasks,this paper investigated an enhanced detection algorithm grounded in the YOLOv7 model.Firstly,an encompassing benchmark dataset for aircraft targets was established,encapsulating varying scales,orientations,and weather conditions.Secondly,a novel detection approach was introduced,leveraging a generalized feature pyramid network and Wasserstein distance metric within the YOLOv7 framework.Finally,comparative evaluations encompassing public and self-constructed datasets validated the method against mainstream algorithms.The enhanced model exhibited a 7.3%boost in small target detection precision on self-constructed datasets,alongside accelerated inference speed surpassing mainstream counterparts.This research delivers a swift and highly precise detection algorithm tailored for small airborne target detection,contributing significantly to advancing the application of related algorithms in aerospace engineering.
自适应飞行器因其对于不同飞行阶段的空气动力学适应性,逐渐成为航空航天研究的重点领域.可变形蒙皮不仅需要具有良好的面内拉伸变形性能,同时材料结构也需要具有一定的刚度来应对飞行过程中的载荷.本文提出以由高性能工程塑料聚醚醚酮(PEEK)材料制备的折线形蜂窝和U形蜂窝材料作为蒙皮结构,通过数值模拟计算确定柔性蒙皮的面内拉伸变形模式及两种蜂窝材料的形状尺寸参数对其面内拉伸变形力学响应的影响.结果表明,折线形蜂窝和U形蜂窝材料的面内变形模式呈现高度一致性,同时,两者的面内拉伸变形性能与蜂窝胞元长度和高度成正比,而与蜂窝厚度成反比.本文研究结果可为变体结构的设计与制备提供理论支持.
碳材料以重量轻、比表面积大、机械强度高、导电性好等特性在隐身技术领域有巨大的应用潜力.本文基于化学气相沉积方法,通过优化生长温度、降温速率和氢气流量制备出厚度为500～700nm、表面褶皱且具有高结晶度的石墨薄膜.进一步通过构建夹层结构的中红外热辐射调制器,研究了离子插入对纳米石墨薄膜红外热辐射性能的影响,发现在0～4V电压调控范围,通过电控制离子液体插入,石墨薄膜的红外发射率可以从0.38降低到0.06,且红外发射率调谐性能可逆.这种纳米石墨薄膜可以作为一种新型的智能热表面材料,用于复杂背景下的动态热伪装或红外隐身,同时其发射率可动态调谐的性能使其在辐射冷却、个人热管理和红外通信等方面也有巨大的潜在应用价值.
可重复使用再入飞行器技术是航天领域的竞争热点,已成为世界航天强国发展战略中的重点.早在20世纪50-60年代,人类就已经开始了对重复使用运输系统相关技术的探索.本文介绍了20世纪50-60年代美国研究机构提出的多种可重复使用再入飞行器,重点分析了设计性能最为优越的Model 176的气动和结构方案.分析结果表明,Model 176采用可变机翼构型,在高超声速段升阻比达到3.5,亚声速段升阻比达6.5,远超其他类型再入飞行器,拥有优越的航向范围和横向范围,理论上可以从任何太空轨道再入在美国本土水平着陆;Model 176在结构方面采用完整的全金属结构和热防护系统,与陶瓷和碳-碳材料重量(质量)相当,且结构强度更高.Model 176作为一款性能优越的可重复使用再入飞行器,能为我国可重复使用高超声速技术研究提供一定的参考价值.
高速直升机因其独特构型造成过渡段操纵复杂,控制系统设计难度大.本文针对复合式共轴双旋翼高速无人直升机,设计了全飞行模式控制,为高速直升机的安全飞行提供理论基础.采取分块建模思路,搭建了无人直升机数学模型,设计了过渡模式的操纵策略.采用经典控制理论设计了低速模式和高速模式纵向飞行控制律,低速模式时,为提高位置响应的快速性,直接采用并行控制结构,将位置指令引入姿态通道;高速模式时,在俯仰通道引入航迹倾斜角补偿损失高度.针对过渡段的控制分配问题,分别考虑速度和操纵面反应速度快慢的影响,设计分配权值,采用加权伪逆法进行最优分配求解.仿真结果表明,所设计的纵向飞行控制律可以有效合理分配过渡段的不同操纵量,实现平滑过渡飞行.
