查看更多>>摘要：Unmanned Aerial Vehicles(UAVs)play increasing important role in modern battlefield.In this paper,considering the incomplete observation information of individual UAV in complex combat environment,we put forward an UAV swarm non-cooperative game model based on Multi-Agent Deep Reinforcement Learning(MADRL),where the state space and action space are constructed to adapt the real features of UAV swarm air-to-air combat.The multi-agent particle environment is employed to generate an UAV combat scene with continuous observation space.Some recently popular MADRL methods are compared extensively in the UAV swarm non-cooperative game model,the results indicate that the performance of Multi-Agent Soft Actor-Critic(MASAC)is better than that of other MADRL methods by a large margin.UAV swarm employing MASAC can learn more effective policies,and obtain much higher hit rate and win rate.Simulations under different swarm sizes and UAV physical parameters are also performed,which implies that MASAC owns a well generalization effect.Furthermore,the practicability and conver-gence of MASAC are addressed by investigating the loss value of Q-value networks with respect to individual UAV,the results demonstrate that MASAC is of good practicability and the Nash equi-librium of the UAV swarm non-cooperative game under incomplete information can be reached.
查看更多>>摘要：To design the optimum acceleration control schedule for the Adaptive Cycle Engine(ACE)in the full flight envelope,this paper establishes a direct simulation model of the ACE tran-sient state.In this model,geometric parameters are used to replace the component state parameters.The corresponding relationship between geometric parameters and component state parameters is determined by sensitivity analysis.The geometric variables are controlled when the geometric adjustment speed exceeds the limit,and at the same time the corresponding component state param-eters are iterated.The gradient optimization algorism is used to optimize the ground acceleration process of ACE,and the control schedule in terms of operating point of compression components and corrected acceleration rate is used as the full-envelope acceleration control schedule based on the similarity principle.The acceleration control schedules of the triple-bypass mode and the double-bypass mode are designed in this paper.The acceleration processes under various flight con-ditions are simulated using the acceleration control schedules.Compared with the acceleration pro-cess with the linear geometric adjustment schedule,the acceleration performance of ACE is improved by the acceleration control schedule,with the impulse of the acceleration process of the triple-bypass mode being increased by 8.7％-12.3％and the impulse of the double-bypass mode acceleration process being increased by 11.8％-14.1％.
查看更多>>摘要：The star identification algorithm usually identifies stars by angular distance matching.However,under high dynamic conditions,the rolling shutter effect distorts the angular distances between the measured and true star positions,leading to plethoric false matches and requiring com-plex and time-consuming verification for star identification.Low identification rate hinders the application of low-noise and cost-effective rolling shutter image sensors.In this work,we first study a rolling shutter distortion model of angular distances between stars,and then propose a novel three-stage star identification algorithm to identify distorted star images captured by the rolling shutter star sensor.The first stage uses a modified grid algorithm with adaptive error tolerance and an expanded pattern database to efficiently eliminate spurious matches.The second stage per-forms angular velocity estimation based on Hough transform to verify the matches that follow the same distortion pattern.The third stage applies a rolling shutter error correction method for further verification.Both the simulation and night sky image test demonstrate the effectiveness and effi-ciency of our algorithm under high dynamic conditions.The accuracy of angular velocity estimation method by Hough transform is evaluated and the root mean square error is below 0.5(°)/s.Our algorithm achieves a 95.7％identification rate at an angular velocity of 10(°)/s,which is much higher than traditional algorithms.
查看更多>>摘要：There are many types of radar active deception false target jamming that are highly cor-related with the real target.Recognizing the real and false targets under a low Signal-to-Noise Ratio(SNR)is difficult.To solve the above problem,this article proposes a real/false target recognition method based on the features of multi-pulse joint frequency response by analyzing the differences in the scattering characteristics and modeling real target echoes as a synthesis of multi-scattering cen-ter echoes.Firstly,in the range-doppler domain,the real and false targets are truncated along the range dimension,and a fast Fourier transform is performed to extract the features of multi-pulse joint frequency response.Then,a two-channel feature fusion network is designed for real and false target recognition.Finally,a Multi-Coherent Processing Interval Joint Decision Method(M-CPIJDM)based on temporal information is proposed to improve the recognition perfor-mance.Experiments using the measured data show that the proposed method can well recognize real and false target signals under four jamming backgrounds:distance false target,velocity false target,distance-velocity composite false target,and forwarding dense false target.
查看更多>>摘要：At present,aircraft taxiing at ground airports needs to be provided with a thrust by the main engine.The taxiing process is inefficient,has high fuel consumption and serious pollution,and is prone to safety risks.In this paper,a new configuration of aircraft autonomous traction taxiing system is proposed based on the principle of hydraulic secondary control,in which a hydraulic motor drive device is installed at the front wheels of the aircraft to drive the wheels to rotate for-ward or backward.Based on this,autonomous taxiing can be realized without relying on the main engines,thus greatly improving airport operation efficiency.Meanwhile,this paper analyzes the influencing factors of the autonomous traction taxiing process,and investigates the parameter matching design of the new configuration system.Besides,this paper develops the ground principle prototype,designs the aircraft longitudinal bonding force observer and the aircraft wheel distur-bance moment observer,and proposes the speed control method of the aircraft front wheel auton-omous traction taxiing by considering the ground bonding force saturation characteristics.Finally,the ground taxiing test is conducted,and the results show that the new configuration proposed in this paper presents a new solution for aircraft autonomous traction taxiing.
查看更多>>摘要：Detection and repair of composite damage is crucial to ensure the safety and reliability of aircraft structures.A novel approach to quantitatively evaluate the repair tolerance of composite structures in civil aircraft based on Bayesian updating is presented.The method incorporates his-torical damage inspection data to determine the prior distribution of damage size,which is then updated with newly collected damage size data using Bayesian theory.Monte Carlo simulation is employed to investigate the probability of failure and estimate maintenance costs,considering var-ious factors such as the frequency and timing of damage events,damage detection,structural strength,gust loads,and maintenance expenses throughout the lifecycle of composite structures.Safety and economic factors are considered to establish a lower threshold for repairs and an upper threshold for maintenance based on the occurrence of accidental impact damage.Verification of the effectiveness and feasibility of a quantitative assessment method for repair tolerance is conducted using damage statistics data from civil aircraft routes utilizing the structural skin panels of compos-ite outer wing.The results demonstrate that the method proposed in conjunction with extensive sim-ulations and full utilization of field damage inspection data can effectively simulate unexpected impact damage situations that may occur during civil aircraft service and evaluate the reliability and economic feasibility of the repair of structure.The research findings hold significant theoretical and practical value for the preparation of documents for continued airworthiness of composite structures,including structural repair manuals and maintenance programs.
查看更多>>摘要：In-situ consolidation forming of high-performance thermoplastic composites by Auto-mated Fiber Placement(AFP)is of significant interest in aerospace.During the laying process,the heating temperature has a great influence on the quality of the formed components.A three-dimensional heat transfer finite element model of Carbon Fiber(CF)/Polyether Ether Ketone(PEEK)heated by Slit Structure Nozzle Hot Gas Torch(SSNHGT)assisted AFP is proposed.The influence of gas flow rate,heat transfer distance,and laying speed on heating temperature is analysed.The results show that the overall temperature increases and then decreases as the gas flow rate increases.With the increase in heat transfer distance and laying speed,the overall temperature decreases.Meanwhile,the gas flow rate has the greatest influence on the temperature of CF/PEEK being heated,followed by the laying speed and finally the heat transfer distance.Furthermore,the model can also be extended to other fiber-reinforced polymer composites formed by hot gas torch assisted AFP,which can guide the optimization of process parameters for subsequent heating tem-perature control.
查看更多>>摘要：Predicting the thickness of Thermally Grown Oxide(TGO)and the residual stresses induced by TGO growth in the Thermal Barrier Coatings(TBCs)is significant work in analyzing the failure of TBCs.In practical applications,the operating temperature,oxygen partial pressure,aluminium content in TBCs,and porosity of the topcoat affect the oxidation rate.Therefore,a novel oxidation rate model is proposed to describe the effect of such factors.The parameters in the proposed model were fitted with isothermal degradation test data from prior literature.Then,a method for calculating the residual stress in a disk-shaped specimen was developed based on the oxidized growth strain model and the oxidized model.Finally,a variable-temperature oxidation experiment was performed to validate the new oxidation model.The average error between the pre-dicted and experimental thicknesses is approximately 10％,and the average error between the resid-ual stresses is 30％.Under the variable-temperature condition,the error between the predicted thickness and the average experimental thickness is 3.9％.
查看更多>>摘要：Flasher origami pattern has been widely utilized to improve the stowage efficiency of deployable structures.Nevertheless,flasher origami cannot be folded fully flat,and they still have great potential for optimization in terms of storage volume and folding creases.In this paper,a flat foldable equiangular spiral folding pattern inspired by the sunflower disk is introduced.Then,a parametric design method for this equiangular spiral crease diagram is introduced in detail.Subse-quently,a kinematic model of the equiangular spiral folding pattern is established based on the kinematic equivalence between rigid origami and spherical linkages.A simulation of the developed model demonstrates that the equiangular spiral folding pattern can be folded flat.Using the folded ratio as an evaluation index,the calculated results and experiments show that the equiangular spiral crease pattern can yield fewer creases and improve stowage efficiency in comparison to flasher ori-gami pattern.Equiangular spiral folding pattern can save a considerable amount of space and pro-vide a new approach to spatially deployable structures.
查看更多>>摘要：Thin-walled aerostructural components frequently get distorted after the machining pro-cess.Reworking to correct distortions or eventually rejecting parts significantly increases the cost.This paper proposes a new approach to correct distortions in thin-walled components by strategi-cally applying hammer peening on target surfaces of a machined component.Aluminium alloy 7475-T7351 was chosen for this research.The study was divided in two stages.First,the residual stresses(RS)induced by four different pneumatic hammer peening conditions(modifying the step-over distance and initial offset)were characterised in a test coupon,and one of the conditions was selected for the next stage.In the second stage,a FEM model was used to predict distortions caused by machining in a representative workpiece.Then,the RS induced by hammer peening were included in an FEM model to define two hammer peening strategies(varying the coverage area)to analyse the capability to reduce distortions.Two workpieces were machined and then treated with the simulated hammer peening strategies for experimental validation.Results in the test cou-pon showed that pneumatic hammer peening can generate high compressive RS(-50 to-350 MPa)up to 800 pm depth,with their magnitude increasing with a reduced stepover distance.Application of hammer peening over 4％of the surface of the representative workpiece reduced the machining-induced distortions by 37％,and a coverage area of 100％led to and overcorrection by a factor of five.This confirms that hammer peening can be strategically applied(in target areas and changing the percentage of coverage)to correct low or severe distortions.
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