Abstract:For high speed aircrafts radome, the performance of guidance system is often affected with thermal and mechanical loads changing its original electromagnetic characteristics under actual flight conditions. A Thermo-Mechanical-Electrical (TME) coupling model based on hexahedral mesh partitioning and a simulation method are proposed, and these two methods being employed, the effects of dielectric temperature drift and structural deformation on the electrical performances of radome at high-speed flight can be characterized accurately. First, based on the TME Sharing Mesh Model (TME-SMM), the temperature field of radome is obtained by transient thermal simulation, and the deformation field of radome is obtained by static analysis. And then, the dielectric temperature drift and structural deformation of radome are accurately transferred into its electromagnetic simulation model, and the electrical performance of radome is calculated by three-dimensional ray tracing method. Last, a typical example is utilized for simulating and analyzing the variation of the electrical performance of radome at high-speed flight. The results show that the variation is obvious, and the feasibility and research necessity of the method are further illustrated.

Abstract:Energy Selective Surface (ESS) is an effective technology in blocking high-power microwave to damage electronic equipment systems through front-door coupling. Such a technology can adaptively respond to incident high-power waves by loading nonlinear components such as diodes in a “low-pass high-resistance” way through periodic structures. In this study, the impact of diode selection on the performance of ESS radome is investigated. Firstly, the damage threshold of the diodes is evaluated through injection experiments under high-power signal input and conducted corresponding damage testing and analysis. The experimental results show that the current being overloaded, BAP65 diode is out of use when the input power reaches 47 dBm. And then, four kinds of diodes are selected to assess their effects on the insertion loss and shielding effectiveness of the ESS radome. The experimental results show that the energy selective surface loaded with MMP4401 diodes exhibits a shielding effectiveness with insertion loss being below 0.5 dB and shielding effectiveness exceeding 15 dB within the frequency range of 0.75 to 0.9 GHz. Additionally, the dual-diode configuration shows a superior shielding effectiveness, whereas the single-diode configuration exhibits a good insertion loss.

Abstract:In view of a high temperature resistant radome setting special demands on root strength and matching of coefficient of thermal expansion between root material and metal connector, several kinds of quartz fiber fabric with needled structures for radome are designed, alumina fibers are introduced into the root of the needle punching fabric, and the properties of the composite materials at the root of the radome are studied systematically. The results show that the proper reduction of the content of felt in needle punching fabric can improve the tensile strength in the composite material but the inter-laminar shear strength and compressive strength of the composite can also be partly reduced. Although the coefficient of thermal expansion of the composite material at the root of radome can be improved by introducing the alumina fiber into the root of radome obviously, the tensile strength of the composite material at high temperature show a kind of U-shaped trend with the increasing content of alumina fibers, i.e. descending in advance and climbing behind. The research of the relevant technology provides a reference for the design of high temperature resistant radome.

Abstract:Functional structures are widely used in the field of aerospace and satellite communication,the machining of large curvature non-developable surface ectromagnetic functional structures is still a very important subject. In this paper, the laser control software and the guide rail motion control software are integrated and developed, and the method of zoned machining is combined to achieve laser etching of the electromagnetic functional structure of the spherical shell non-developable surface. The 304 stainless steel hemispherical surface with a diameter of 100 mm is divided into two areas. In the two areas, 3D projection and rotary processing are adopted respectively to better ensure the processing quality of the unit structure. 3D projection is applied to the area with angle β<45°of the cutting plane, which can form the laser machining track at one time, omits the multiple motions of layered machining, greatly improves the unit machining efficiency and ensures the machining accuracy. In the β>45°region, the sample rotation mode is used to adjust the position of the laser beam and the spherical element to be machined synchronously, so as to ensure that the laser beam and the spherical element to be machined coincide with the normal direction, reduce the laser incidence angle, and effectively improve the accuracy of the machining unit. Two quantization parameters, removal rate and root-mean-square difference of sample points, were selected to evaluate the machining quality. The results showed that the removal rate was basically in the range of 1.00~1.03, and the root-mean-square difference of sample points was basically kept in the range of 10~35 μm, and the overall machining effect was remarkable.

Abstract:Alumina fiber reinforced ceramic matrix composites are characterized by good mechanical properties, high temperature oxidation resistance, corrosion resistance and excellent dielectric properties. This material can be used as a kind of high temperature-resistant wave-transmitting functional material for radome. Taking Al2O3 and mullite slurry as basement, Al2O3 fiber as reinforcement, and LaPO4 as interface, Al2O3/Al2O3 composite is fabricated by repeating infiltration and high temperature treatment process. And then, the tensile strength of the composites at room temperature and 1 200 ℃ are measured, and the SEM is employed in observing the fracture microstructure. The tensile strength of Al2O3/Al2O3 composites with LaPO4 interface at room temperature is 148.3 MPa, and increment of tensile strength is 20.1% in comparison with Al2O3/Al2O3 composites without interface. The tensile strength of Al2O3/Al2O3 composites with LaPO4 interface at 1 200 ℃ is 129.6 MPa, and its increment is 24.9% in comparison with Al2O3/Al2O3 composites without LaPO4 interface. The SEM observation shows that the fracture surface of the composite without LaPO4 interface is smooth at crack, and brittle in fracture. A large number of fibers are pulled out in the fracture of alumina fiber reinforced ceramic matrix composites with LaPO4 interface phase, showing ductile fracture characteristics. The average dielectric constant of the composite material is 5.77 and the dielectric loss is 0.001 8 when the frequency is 10 GHz and RT; the average dielectric constant of the material at 1 300 ℃ is 6.18 with the dielectric loss is 0.002 0. The change rate of electric constant and dielectric loss is 7.10% and 11.1% respectively, meeting the needs of change rate <15%, and such a material is expected to be used in the field of wave-transparent composite materials.

Abstract:In order to realize the design of gas-thermal anti-icing/deicing system by the technology of micro-channel based on the design of electromagnetic function structure gas-thermal anti-icing/deicing system based on micro-channel technology closely related to the fluid flow behavior and heat transfer characteristics of the internal/external flow field,a coupled flow field-heat transfer analysis method is proposed. The flow field and heat transfer characteristic of typical wing-front edge electromagnetic functional structures are simulated and analyzed by using gas-thermal hallow quartz fiber reinforced resin matrix composites as the micro-channel implementation method. The results show that with ambient temperature being at 15℃, the anti-icing/deicing scheme based on the technology of micro-channel is satisfied with the needs of anti-icing/deicing potential, and a theoretical support is provided for the subsequent optimization design of gas-thermal anti-icing/deicing scheme.

Abstract:Aimed at the issues that a load angle limit function being added in permanent magnet synchronous motor (PMSM) model for predictive control, though it can prevent motor slip, the angle limit function makes the adjustment of control weight coefficients complicated, a weight coefficient-free model predictive control is proposed for PMSM with load angle limitation. This method is used to implement the model predictive control based on a dictionary approach, conduct the hierarchical sequence optimization of the objective function, and achieve the multi-objective optimization without weight coefficients. In order to verify the effectiveness of this method, the simulation and the experimental studies are made. The results show that this method can achieve the load angle limitation, and the performance of dynamic and static performance is consistent with the traditional methods. Compared to the traditional methods, the steadystate errors of torque and flux are similar, approximately 0.3 N·m and 0.005 V·s. And the elimination of weight coefficient adjustment can be omitted, there is a decrease in computational burden.

Abstract:The round-trip path planning problems remaining between the air search and rescue waiting area and the parachute jump area in the combat search and rescue mission scenario, a search and rescue channel planning method is proposed based on the improved ant colony algorithm and shared flight segments. First, in view of the shortcomings of the basic ant colony algorithm, such as local extreme values and slow convergence speed, the heuristic function, state transition strategy, and pheromone update strategy are improved, and its path planning performance is verified. And then, for the path planning problem of single starting point and multiple target points, a search and rescue channel planning method is proposed to set branch points to generate shared flight segments. The total path length is used to represent the mission preparation load and compared with separately planned routes. The experimental results show that in the test environment of this article, the path length planned is reduced by 15.4% and 14.2% respectively by the improved ant colony algorithm, and the task preparation load of the search and rescue channel is reduced by 25.4%.The proposed search and rescue channel planning method has a certain theoretical and application value.

Abstract:In order to systematically verify the ability to a domestic small bypass ratio turbofan engine in rainy days in application, a subject of study with an aero-engine being installed is made. And an adaption of test flight for three test systems is performed respectively, i.e. an engine water swallowing test with installed conditions, a simulated slippery running splash test in rainy day, and an adaptability of test flight in rain. In the test there is involved some surge under the conditions of installed water swallowing , and the engine is operating normally in the process of the splash test and the adaptability of test flight in the rain. The test results indicate that the designed engine rain environment verification technology can effectively identify the surge risk of engine after water swallowing, and systematically verify the engine's ability to use in the rainy day environment.

Abstract:Based on the integrated requirements of load-bearing and electrical functions of aviation wall panel, an optimized design and an experimental verification are conducted to heterogeneous composite material wall panel suitable for intelligent skin. By adding a glass fiber layer in the outer side of the high modulus carbon fiber skin, a wall panel load-bearing electrical functional integration design is carried out in the order of carbon fiber glass fiber metal structural unit array glass fiber composite. The layer optimization of heterogeneous composite material structures is in consideration of the zoning of co bonding and the process requirements for layer continuity. An optimization method based on layer dropping sequence is developed, and the geometric shape, number of ribs, geometric parameters of ribs, and layer angle between ribs and skin of the reinforced wall panel are optimized. The benefits of the structure in terms of load-bearing capacity and stability are verified through compression stability tests, and the buckling mode and post buckling failure mechanism under compression load are clarified.

Abstract:In view of space demand response problems for war zone in joint operations, this paper describes the background of space demand response task planning for war zone in joint operations, analyzes the main factors in consideration of task planning in its aspects of space resources ability, space demand response mechanism, space demand response beneficial result, and cost, defines and describes a task planning model, designs a planning implementation method, and conducts case simulation based on the actual situation for war zone in joint operations. And the model and the method are verified. A certain theoretical and methodological support is provided for effective response to space requirements in joint operations in theater of war.

Abstract:Based on the approximate dual relationship between the orbital angular momentum modal variable and the target azimuth variable, vortex electromagnetic wave radar can achieve two-dimensional highresolution imaging of stationary targets, but the Bessel function term in the target echo is able to seriously affect the azimuth focusing performance. The existing Bessel function compensation method based on inverse projection algorithm is computationally intensive and difficult to apply in practice. In view of the above-mentioned problems, this paper proposes a method by utilizing U-Net convolutional neural network for suppressing the influence of Bessel function and realizing high-resolution imaging of vortex electromagnetic wave radar. Firstly, the U-Net network is improved according to the sparse characteristics of radar targets in the observation space, and on the basis of this, the target defocus image is obtained by two-dimensional fast Fourier transform preprocessing of the target echo signal, and the target defocus image is further used as an input of the improved U-Net network, and the target ideal electromagnetic scattering model is used as the network output to supervise and train the network. Finally, based on the unknown target echo signal, the preprocessed target defocus image is input to the well-trained network model, and the well-focused high-resolution imaging results can be obtained. The simulation experiments show that the proposed method can effectively improve the focusing performance of target imaging, and the network model still is good in generalization ability in the presence of noise.

Abstract:Operation utilized by air support of drones at a close range is currently a research focus.The path and target allocation of Unmanned Aerial Vehicles (UAVs) for multi target firepower strikes require optimization under conditions of complex battlefield environments, and the following factors, such as UAV flight altitude, different weapon mounts, target types and various indicators, threat cost in threat zones, and operational time cost, should be taken into account. A comprehensive target damage index is constructed to improve asymmetric strike effectiveness, and a threat zone security threshold is set to improve path effectiveness analysis. The total cost of the optimal trajectory is planned by adopting the Adaptive Weighted Particle Swarm Collaborative Optimization (APSCO) algorithm for a single drone and a single target, and the imbalanced task allocation scheme is completed by adopting the 0-1 programming method for multiple drones against multiple targets,providing decision support for the allocation of multiple unmanned aerial vehicles to multiple targets at a close range in performing air support tasks.

Abstract:In order to achieve continuous remote communication between multiple source nodes and the Ground Control Station (GCS), a solution method is proposed for dynamic path planning of relay unmanned aerial vehicles based on the artificial potential field method. The relay cluster computation module is to dynamically divide the relay clusters according to the maximum density clustering, realizing the dynamic adjustment of the number of relay nodes. The dynamic path planning module for relay nodes employs in accordance with the concept of artificial potential fields, enabling the relay drones to mobilize to suitable positions based on the resultant force of the potential field while possessing dynamic obstacle avoidance and collision prevention capabilities. The simulation experiments are conducted on the constructed model with different task payload settings. The results demonstrate that the relay unmanned aerial vehicles can reliably achieve multi-hop relaying between multiple source nodes and the GCS, with a connectivity rate of communication links being no less than 99.83%, the number of source nodes being no greater than 10, and the number of threat zones in the airspace being no greater than 7.

Abstract:In view of the issue of model performance degradation caused by cross-domain transfer in fewshot learning, a lightweight adaptation strategy for few-shot SAR target recognition named SAR-LAM is proposed. This method is to utilize knowledge distillation for pre-training a generalized encoder and embedding an adaptation module trained only with very few target domain samples. The extracted features are then mapped into a more discriminative space, and finally, the query set samples are classified by taking a prototypical network as the baseline. This adaptation strategy is to increase at a few cost in learning parameters, and by so doing, the limitations of model transfer caused by data distribution differences is overcome, improving the model’s ability to extract features in the target domain, and simultaneously improving the accuracy of SAR target recognition by at least 1.93 percentage points under few-shot conditions. And this adaptation strategy is superior in performance to the other methods.

Abstract:Aimed at the problems that robot path planning problems being solved by the standard gray wolf algorithm, initial parameters are strong in dependence, lack of variety, and liable to sink into local extreme value, a Logistic-Tent based Grey Wolf Optimizer (LTGWO) is proposed. Firstly, by an elite method, the Logistic-Tent composite chaotic mapping is in combination with inverse learning to improve the population distribution. And then, by introducing the sigmoid function, the factor of concentration and balances between global exploration and local exploitation is adjusted, while the improved control parameters are fitted even more in line with the actual hunting behavior. Lastly, Proportional weights being in company with the changes of adaptable value are added to enhance the search ability of individual gray wolves. A population culling strategy is adopted to eliminate the individuals with poor fitness, promoting evolution. Three different groups of raster maps are selected for the experiments,and the experimental results show that the average path length and the standard deviation of the path length generated by the LTGWO algorithm are better than the comparison algorithm.

Abstract:A damage law of composite material structure under the action of warhead fragment group is studied experimentally. Taking the actual aircraft composite components as a research object, the ground static explosion test of the warhead of laminate and laminate reinforced structure is carried out. The real damage of composite materials under high-speed impact is detected and analyzed by nondestructive testing method. The test results show that the main damage forms for laminate structure subjected to high-speed impact of a single fragment serve as a broken hole + peripheral delamination + surface fiber tearing, the size of broken hole is equivalent to the size of fragment’s shrapnel, and the expansion area of peripheral delamination is 1.13~5.00 times larger than that of the broken hole. Finally, the repair suggestions in combination with the repair demand and strength analysis results are put forward. Under the same impact conditions, the residual strength of the laminate structure decreases more obviously than that of the stiffened composite structure, but, form the point of service, the residual carrying capacity of the stiffened composite structure may be lower than the ultimate strength, and the laminate structure can be used without repair or simply repair after the structural integrity is restored.