Chinese Journal of Aeronautics最新文献

Track-Before-Detect (TBD) is an efficient method to detect dim targets for radars. Conventional TBD usually follows an approximate motion model of the target, which may cause an inaccurate integration of the target energy. A TBD technique on basis of pseudo-spectrum in mixed coordinates adopting an accurate motion model for bistatic radar system is developed in this paper. The predicted position in bistatic polar plane is derived according to a nonlinear function that exactly describes the constant Cartesian velocity motion. Then around the predicted position, a pseudo-spectrum is formulated and its samples are accumulated to the integration frame for energy integration. The evolution of the state and the procedure of accumulation of the target energy are derived elaborately. The superior performance of the proposed method is demonstrated by some simulations.

The wheel brake system of an aircraft is the key to ensure its safe landing and rejected takeoff. A wheel’s slip state is determined by the brake torque and ground adhesion torque, both of which have a large degree of uncertainty. It is this nature that brings upon the challenge of obtaining high deceleration rate for aircraft brake control. To overcome the disturbances caused by the above uncertainties, a braking control law is designed, which consists of two parts: runway surface recognition and wheel’s slip state tracking. In runway surface recognition, the identification rules balancing safety and braking efficiency are defined, and the actual identification process is realized through recursive least square method with forgetting factors. In slip state tracking, the LuGre model with parameter adaptation and a brake torque compensation method based on RBF neural network are proposed, and their convergence are proven. The effectiveness of our control law is verified through simulation and ground experiment. Especially in the experiments on the ground inertial test bench, compared to the improved pressure-biased-modulation (PBM) anti-skid algorithm, fewer wheel slips occur, and the average deceleration rate is increased by 5.78%, which makes it a control strategy with potential for engineering applications.

The large manipulator outside the space cabin is a multi-degree of freedom actuator for space operations. In order to realize the automatic control and flexible operation of the space manipulator, a novel spoke structure piezoelectric six-dimensional force/torque sensor with redundancy ability, high stiffness and good decoupling performance is innovatively proposed. Based on the deformation coordination relationship, the redundancy measurement mechanism is revealed. The mathematical models of the sensor with and without branch fault are established respectively. The finite element model is established to verify the feasibility of structure and redundancy measuring principle of the sensor. Depending on the theoretical analysis and simulation analysis, the prototype of the sensor is developed. Static and dynamic calibration experiments are carried out. The actual output voltage signal of the six-dimensional force/torque sensor is collected to establish the equation between the standard input applied load and the actual output voltage signal. Based on ant colony optimized BP algorithm, performance indexes of the sensor with and without branch fault are analyzed respectively. The experimental results show that the spoke piezoelectric six-dimensional force/torque sensor with the eight-point support structure has good accuracy and reliability. Meanwhile, it has strong decoupling characteristic that can effectively shield the coupling between dimensions. The nonlinear errors and maximum interference errors of decoupled data with and without branch faults are less than 1% and 2%, respectively. The natural frequency of the six-dimensional force sensor can reach 2856.45 Hz and has good dynamic characteristics. The research content lays a theoretical and experimental foundation for the design, development and application of the new six-dimensional force/torque sensors with redundancy. Meanwhile, it will significantly improve the research level in this field, and provide a strong guarantee for the smooth implementation of force feedback control of the space station manipulator project.

During the whole service lifetime of aircraft structures with composite materials, impacts are inevitable and can usually cause severe but barely visible damages. Since the occurrences of impact are random and unpredictable, it is a hotspot direction to develop an online impact monitoring system that can meet strict limitations of aerospace applications including small size, light weight, and low power consumption. Piezoelectric (PZT) sensor, being able to generate impact response signals with no external power and cover a large-scale structure with only a small amount of them, is a promising choice. Meanwhile, for real systems, networks with multiple nodes are normally required to monitor large-scale structures in a global way to identify any impact localization confliction, yet the existing studies are mostly evaluated with single nodes instead of networks. Therefore, in this paper, based on a new low-power node designed, a Bluetooth-based digital impact monitoring PZT sensor network is proposed for the first time with its global confliction-solving impact localization method. Evaluations of the system as a network are researched and analyzed on a complex real aircraft wing box for a global confliction-solving impact localization, showing a satisfying high accuracy.

Digital twin is currently undergoing a significant transformation from the conceptual and theoretical research phase to the implementation and application phase. However, a universally adaptable research and development platform for digital twin is critically needed to meet the development requirements. Specifically, a publicly accessible simulation, testing, and validation platform which can support digital twin model building, data processing, algorithm design, configuration, etc., is urgently required for researchers. Furthermore, for developers from the industry, a low-code development platform that can offer a customizable suite of functions such as model creation, data management, protocol configuration, and visualization is urgently needed. Meanwhile, for enterprise users, there is a lack of an application management platform that can be configured and migrated for various application scenarios, functions, and modes. Therefore, based on the system research of digital twin theories and key technologies by the authors (such as the five-dimension digital twin model, digital twin modeling and digital twin data theory, digital twin standards, and so on), a digital twin software platform reference architecture, namely makeTwin, is proposed and designed, as well as its ten core functions. The workflow of the makeTwin and the interaction mechanisms among its core functions are described. Finally, a digital twin application system for a chemical fiber textile shop floor (CFTS) which was developed according to makeTwin, is introduced, which validates the proposed reference architecture.

Heterogeneous pressure-carrying medium was employed to establish a differentiated pressure field on sheet metal in flexible die forming process in this work, which aimed at matching the non-symmetric shape of target component and improving metal inflow to avoid local tensile instability. Specifically, metal inflow corresponding to the differentiated pressure field was analytically evaluated. Forming of a typical non-symmetric shell component was experimentally and numerically studied based on the proposed method. Compared with forming processes based on the uniform pressure, difference of metal inflow in two sides of the non-symmetric component increased from 2.16 mm to 3.36 mm and metal inflow in critical region increased by 11.9% when differentiated pressure field (taking heterogeneous elastomer #4–3 for example) was employed. The resultant maximum thinning ratio decreased by 4.2% and the uniformity of shell thickness increased by 16.9%. With the decrease of Shore hardness of elastomer in the formed region, stress path in the ready-to-form region transferred towards the bi-axial tension stress state, i.e., stress ratio (α) increased. And, stress triaxiality (η) in characteristic regions were regulated appropriately, which decreased the risk of tensile instability. It was attributed to the decreased normal pressure and frictional resistance at sheet/elastomer interface in the formed region.

During long-term service in space, Gallium Arsenide (GaAs) solar cells are directly exposed to electron irradiation which usually causes a dramatic decrease in their performance. In the multilayer structure of solar cells, the germanium (Ge) layer occupies the majority of the thickness as the substrate. Due to the intrinsic brittleness of semiconductor material, there exist various defects during the preparation and assembly of solar cells, the influences of which tend to be intensified by the irradiation effect. In this work, first, Ge specimens for mechanical tests were prepared at scales from microscopic to macroscopic. Then, after different doses of electron irradiation, the mechanical properties of the Ge specimens were investigated. The experimental results demonstrate that electron irradiation has an obvious effect on the mechanical property variation of Ge in diverse scales. The four-point bending test indicates that the elastic modulus, fracture strength, and maximum displacement of the Ge specimens all increase, and reach the maximum value at the irradiation dose of 1 × 10¹⁵ e/cm². The micrometer scale cantilever and nanoindentation tests present similar trends for Ge specimens after irradiation. Atomic Force Microscope (AFM) also observed the change in surface roughness. Finally, a fitting model was established to characterize the relation between modulus change and electron irradiation dose.

A multi-body dynamic rigid-flexible coupling model of landing gear is established to study the gear walk instability caused by the friction characteristics of the brake disc. After validating the model with the experimental results, the influence of the landing gear structure and braking system parameters on gear walk is further investigated. Among the above factors, the slope of the graph for the friction coefficient of the brake disc and the relative velocity of brake stators and rotors is the most influential factor on gear walk instability. Phase trajectory analysis verifies that gear walk occurs when the coupling of multiple factors causes the system to exhibit an equivalent negative damping trend. To consider a more realistic braking case, a back propagation neural network method is employed to describe the nonlinear behavior of the friction coefficient of the brake disc. With the realistic nonlinear model of the friction coefficient, the maximum error in predicting the braking torque is less than 10% and the effect of the brake disc temperature on gear walk is performed. The results reveal that a more negative friction slope may contribute to a more severe unstable gear walk, and reducing the braking pressure is an effective approach to avoid gear walk, which provides help for future braking system design.

Deep learning significantly improves the accuracy of remote sensing image scene classification, benefiting from the large-scale datasets. However, annotating the remote sensing images is time-consuming and even tough for experts. Deep neural networks trained using a few labeled samples usually generalize less to new unseen images. In this paper, we propose a semi-supervised approach for remote sensing image scene classification based on the prototype-based consistency, by exploring massive unlabeled images. To this end, we, first, propose a feature enhancement module to extract discriminative features. This is achieved by focusing the model on the foreground areas. Then, the prototype-based classifier is introduced to the framework, which is used to acquire consistent feature representations. We conduct a series of experiments on NWPU-RESISC45 and Aerial Image Dataset (AID). Our method improves the State-Of-The-Art (SOTA) method on NWPU-RESISC45 from 92.03% to 93.08% and on AID from 94.25% to 95.24% in terms of accuracy.

Small and micro unmanned aircraft are the focus of scientific interest due to their wide range of applications. They often operate in a highly unstable flight environment where the application of new morphing wing technologies offers the opportunity to improve flight characteristics. The investigated concept comprises port and starboard adjustable wings, and an adaptive elasto-flexible membrane serves as the lifting surface. The focus is on the benefits of the deforming membrane during the impact of a one-minus-cosine type gust. At a low Reynolds number of Re = 264000, the morphing wing model is investigated numerically by unsteady fluid–structure interaction simulations. First, the numerical results are validated by experimental data from force and moment, flow field, and deformation measurements. Second, with the rigid wing as the baseline, the flexible case is investigated, focusing on the advantages of the elastic membrane. For all configurations studied, the maximum amplitude of the lift coefficient under gust load shows good agreement between the experimental and numerical results. During the decay of the gust, they differ more the higher the aspect ratio of the wing. When considering the flow field, the main differences are due to the separation behavior on the upper side of the wing. The flow reattaches earlier in the experiments than in the simulations, which explains the higher lift values observed in the former. Only at one intermediate configuration does the lift amplitude of the rigid configuration exceeds that of the flexible by about 12%, with the elastic membrane resulting in a smaller and more uniform peak load, which is also evident in the wing loading and hence in the root bending moment.