天线选择性幅值扰动形成阵列零陷的技术

首先提出了一种在阵元关于阵列中心对称的线阵中利用幅值扰动形成零陷的新方法,该方法克服了传统幅值扰动方法零陷深度不足、旁瓣水平高的缺陷,且能够在多个强干扰源方向或在较宽的范围形成深度零陷而不影响主瓣。为了减少每次需要控制的阵元数,提高系统鲁棒性,在此基础上进一步提出了利用天线选择性幅值扰动形成零陷的方法。仿真结果表明,其性能可与基于全部天线进行幅值扰动的算法相比,甚至可与复权值控制方法的性能相比。     

Hierarchical global search for fuel-optimal impulsive transfers between lunar libration orbits

The attention to the periodic orbit in the Earth-Moon restricted three-body system continues to grow due to its special environment and locations. This research investigates the feasibility of constructing fuel-optimal single and multiple impulse transfers between unstable periodic orbits at L₁ and L₂ points. Invariant manifolds, which could provide the appropriate initial trajectories for optimization, are analyzed deeply to enable previously unknown orbit options and potentially to reduce mission cost. A global search strategy based on comparing the orbital state of the unstable and stable manifolds, incorporated with low-thrust techniques, is performed to seek a suitable matching point for maneuver application. Then the sequential quadratic programming (SQP) is adopted to further optimize the velocity increment and obtain the single/multiple impulse optimal transfers. The associated constraint gradients are derived to achieve higher accuracy and rapidity of the algorithm. To highlight the effectivity of the transfer scheme, three-dimensional low-energy transfers between different types and spatial regions of performing single and multiple impulses are explored. The total Delta-V required varies between a few meters per second and tens of meters per second, and the related flight time is about several weeks, mainly depending on the energy of periodic orbits and the invariant manifold structure. The results obtained in this paper can provide a useful reference for the selection of escape and capture site along the manifolds, maneuver magnitude and transfer time.     

Experiment on a Double-Foot Stepping Piezoelectric Linear Motor

A novel double-foot piezoelectric linear motor is proposed.The kinematic model of the motor under stepping motion is presented.The motor mainly consists of a stator with four piezoelectric stacks,a mover,a holding mechanism,and a preloading mechanism to achieve large stroke with high resolution.Finite element simulations are carried out to analyze the motion characteristics of the motor.A prototype is fabricated and a serial experiments are conducted to validate the feasibility of the motor principle.Experimental results indicate that the motor can move at a speed of 670.22μm/s with a driving frequency of 120 Hz and a voltage of 120 V.The resolution of the proposed motor is 3.6μm while the resolution of the single-step motion is 0.1μm.     

An optimal beam alignment method for large-scale distributed space surveillance radar system

Large-scale distributed space surveillance radar is a very important ground-based equipment to maintain a complete catalogue for Low Earth Orbit (LEO) space debris. However, due to the thousands of kilometers distance between each sites of the distributed radar system, how to optimally implement the Transmitting/Receiving (T/R) beams alignment in a great space using the narrow beam, which proposed a special and considerable technical challenge in the space surveillance area. According to the common coordinate transformation model and the radar beam space model, we presented a two dimensional projection algorithm for T/R beam using the direction angles, which could visually describe and assess the beam alignment performance. Subsequently, the optimal mathematical models for the orientation angle of the antenna array, the site location and the T/R beam coverage are constructed, and also the beam alignment parameters are precisely solved. At last, we conducted the optimal beam alignment experiments base on the site parameters of Air Force Space Surveillance System (AFSSS). The simulation results demonstrate the correctness and effectiveness of our novel method, which can significantly stimulate the construction for the LEO space debris surveillance equipment.     

Strength design model for thin-walled structures

In this paper, the finite element analysis of the stress-strain state for cylindrical structures is discussed. In this case, various fundamental hypotheses can be used in the framework of a model that is of interest for design and optimization. Numerical examples are presented to evaluate the possibilities of this model.     

EBAA：An efficient broadcast authentication scheme for ADS-B communication based on IBS-MR

Automatic dependent surveillance-broadcast （ADS-B） systems can broadcast satellitebased aircraft position, identification, etc., periodically, and are now on track to replace radar to become the backbone of next-generation air traffic management （ATM） systems. However, ADS-B systems suffer severe cyber-security problems due to the broadcast-type data link and the lack of designed-in security measures. Especially, since ADS-B messages are unauthenticated, it is easy to insert fake aircraft into a system via spoofing or insertion of false messages. Unfortu- nately, the authentication for ADS-B messages has not yet been well studied. In this paper, based on identity-based signature with message recovery （IBS-MR）, an efficient broadcast authentication scheme for ADS-B messages is proposed. The security analysis demonstrates that the scheme can achieve authenticity and integrity of ADS-B broadcast messages, as well as adaptive evolution of broadcasters＇ private keys. The performance evaluation shows that the scheme is computationally efficient for typical avionics devices with limited resources. Furthermore, the scheme achieves low communication overhead since broadcast messages can be recovered from signatures, and thus it is suitable for low-bandwidth ADS-B data link.     

美军军事训练/教学系统开发模型综述及特点分析

通过对美军军事训练教学系统采办指导手册(MIL-HDBK-1379)的分析,介绍了美军军事训练系统采办方法ISD/SAT的概念及其运作模型,并对ISD/SAT的工作过程及其特点作了简要分析.     

FERA in parameter identification with application in low speed wind tunnel test

This paper presents a new approach which consists of a fuzzified eigensystem realization algorithm (FERA) to identify the parameters of the designed mini-UAV model performance in the low speed wind tunnel (LSWT) power on testing system. On the basis of the identification scheme, it is able to reduce system operational cost of wind tunnel tests and provide a tool for predicting results without resorting to on-site experiments. A variety of variables in model types and testing environment such as model profile, angle of attack, elevator, tunnel wind speed and power system (motor and propeller) are considered. The method based on logic devices is simple yet effective. The results obtained are compared to those obtained by the conventional wind-tunnel testing method. To verify effectiveness of the proposed methodology, both of simulations and real-world experiments are conducted. The results show that the working performance of the proposed method correlates well with expectation.     

飞机后缘襟翼运动同步性设计和计算

在飞机的起飞、降落、巡航飞行中,襟翼运动起着重要的作用.全机有多块内、外襟翼,当分别绕各自不同的转轴运动时,会产生不同的圆锥运动.为实现所有的内、外襟翼同步运动,需对每块襟翼上的不同作动器进行精心设计、布局,及对作动器运动参数进行计算.这既非常关键,又相当复杂,一直是设计中的难题.介绍了现代客机襟翼作动器运动学计算方法...     

高校“双困”毕业生就业难点及就业对策探析

高校"双困"毕业生是就业的特殊群体,要实现"双困"毕业生的充分就业,国家应该从政策上加大扶持力度;高校要有针对性地进行专业技能拓展、心理健康教育和就业指导,提高学生的综合素质能力;"双困"生也应认清就业形势,转变观念,培养自身能力,提升就业竞争力。只有从多方面入手,才能最终达到充分就业的目的。