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80 years education of aerospace science and technology in Tsinghua University

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Chinese Journal of Aeronautics 2018年第9期31卷 1797-1804页

作者： Jie LU Yongli GAO Xiaojing WANG Chenyuan BAI Bing WANG Ziniu WU school of aerospace Engineering Tsinghua University

The development of aerospace science and technology largely relies on the education and academic contribution of students in universities covering aerospace science and technology. The school of aerospace Engineering of Tsinghua University, with a history of eighty years since the set-up of its Department of Aeronautical Engineering in 1938, graduated 5273 undergraduate students, 1939 master students and 931 Ph.D. students. This paper provides an overview and analysis of the data related to undergraduate, master and Ph.D. students of this school. These data include the historical evolution of number of students and the actual status of students like their various interests and academic performance. The data and information shared in this paper may be useful for comparative study and for those who need primitive data to study relevant issues such as mental health of students, promotion of gender balance and educational improvement.

关键词： Academic output aerospace Education Favorite activity Students

Characteristics of the electromagnetic wave propagation in magnetized plasma sheath and practical method for blackout mitigation

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Chinese Physics B 2024年第5期33卷 489-499页

作者：吴翔张珈珲董果香石磊 School of Aerospace Science and Technology Xidian UniversityXi'an 710071China

“Magnetic window”is considered as an effective method to solve the communication blackout issue.COMSOL software package based on the finite element method is utilized to simulate the propagation of right-handed circularly polarized wave in the magnetized plasma sheath.We assume a double Gaussian model of electron density and an exponential attenuation model of magnetic field.The propagation characteristics of right-handed circularly polarized wave are analyzed by the observation of the reflected,transmitted and loss coefficient.The numerical results show that the propagation of right-handed circularly polarized wave in the magnetized plasma sheath varies for different incident angles,collision frequencies,non-uniform magnetic fields and non-uniform plasma densities.We notice that reducing the wave frequency can meet the propagation conditions of whistle mode in the weak magnetized plasma sheath.And the transmittance of whistle mode is less affected by the variation of the electron density and the collision frequency.It can be used as a communication window.

关键词： magnetized plasma sheath communication blackout finite element incident angle whistler wave

Numerical and experimental investigation of aerodynamic heat control of leading edge of hypersonic vehicle's flexible skin

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science China(Information sciences) 2022年第10期65卷 211-224页

作者： Xiaozhou Lü Chao YUAN Weimin BAO Guanghui BAI Fancheng MENG School of Aerospace Science and Technology Xidian University science and technology on Space Physics Laboratory College of Materials science and Engineering Chongqing University of Technology

In this paper, a flexible skin inspired by the sudoriferous gland structure of human skin is developed for ultra-thermal protection of hypersonic morphing vehicles. The effect of different coolants and cooling flow rates on the cooling performance of the leading edge is studied using finite element analysis.A wind tunnel experiment is conducted at high temperatures with the heat flux Q = 700 k W/m2, and the results indicate the following:(1) the flexible skin can effectively reduce the surface temperature of hypersonic vehicles;(2) when using liquid water instead of argon as the cooling medium, the cooling efficiency of flexible skin performs better;(3) when liquid water is used as the cooling medium, the cooling effect peaks at a flow rate of 0.01 m/s, and further increasing the flow rate will not benefit cooling efficiency significantly;(4) the flexible skin can withstand extreme thermal environments, demonstrating its feasibility in applications of over-limit thermal protection for hypersonic morphing vehicles. This study aims at optimizing the cooling performance of the flexible skin for ultra-thermal protection. The proposed skin can overcome the heat-resistance limit of flexible materials with morphing properties, laying a theoretical and experimental foundation for its future applications in hypersonic morphing vehicles.

关键词： hypersonic vehicle flexible skin ultra-thermal protection micro-channel transpiration cooling

Exponentially weighted proportional fair scheduling algorithm for the OFDMA system

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science China(Information sciences) 2019年第4期62卷 177-186页

作者： Siyu LIANG Weisheng CHEN Yake LI Xinpeng FANG School of Aerospace Science and Technology Xidian University

This study aims to propose an exponentially weighted proportional fair(EWPF) scheduling algorithm for orthogonal frequency division multiple access(OFDMA) system for long-term evolution downlink transmission. The proposed algorithm improves the system performance in the user-perceived throughput(UPT) by adding exponential weights to different types of services. The UPT employed to measure the system capability is novel and customer oriented; it reflects the experiences of users in an efficient manner and determines whether the user’s scheduling is reasonable. The EWPF algorithm is compared with two other schedulers, and our simulation results showed that the EWPF can increase the overall UPT and can maintain the fairness for prioritizing the transmission of some types of traffic.

关键词： exponentially weighted proportional fair user perceived throughput downlink scheduling algorithm scheduled IP throughput

Lock threshold deterioration induced by antenna vibration and signal coupling effects in hypersonic vehicle carrier tracking system of Ka band

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Chinese Journal of Aeronautics 2018年第4期31卷 776-781页

作者： Congying ZHU Lei SHI Xiaoping LI Yanming LIU Wei AI School of Aerospace Science and Technology Xidian University

The envelope of a hypersonic vehicle is affected by severe fluctuating pressure, which causes the airborne antenna to vibrate slightly. This vibration mixes with the transmitted signals and thus introduces additional multiplicative phase noise. Antenna vibration and signal coupling effects as well as their influence on the lock threshold of the hypersonic vehicle carrier tracking system of the Ka band are investigated in this study. A vibration model is initially established to obtain phase noise in consideration of the inherent relationship between vibration displacement and electromagnetic wavelength. An analytical model of the Phase-Locked Loop（PLL）, which is widely used in carrier tracking systems, is established. The coupling effects on carrier tracking performance are investigated and quantitatively analyzed by imposing the multiplicative phase noise on the PLL model. Simulation results show that the phase noise presents a Gaussian distribution and is similar to vibration displacement variation. A large standard deviation in vibration displacement exerts a significant effect on the lock threshold. A critical standard deviation is observed in the PLL of Binary Phase Shift Keying（BPSK） and Quadrature Phase Shift Keying（QPSK） signals. The effect on QPSK signals is more severe than that on BPSK signals. The maximum tolerable standard deviations normalized by the wavelength of the carrier are 0.04 and 0.02 for BPSK and QPSK signals,respectively. With these critical standard deviations, lock thresholds are increased from à12 andà4 d B to 3 and à2 d B, respectively.

关键词： Antenna vibration Carrier tracking performance Lock threshold Phase locked loop Tracking Telemetry and Command（TT＆C） signals

Unique sandwich design of high-efficiency heat-conducting phosphor-in-glass film for high-quality laser-driven white lighting

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Journal of Advanced Ceramics 2022年第12期11卷 1889-1900页

作者： Yang PENG Zikang YU Jiuzhou ZHAO Qing WANG Jiaxin LIU Bo SUN Yun MOU Mingxiang CHEN school of aerospace Engineering Huazhong University of Science and TechnologyWuhan 430074China school of Mechanical science and Engineering Huazhong University of Science and TechnologyWuhan 430074China

Multi-color phosphor-in-glass(PiG)film has been considered as a promising color converter in high-quality laser lighting owing to its outstanding merits of phosphor versatility,tunable luminescence,and simple preparation.However,the opto-thermal properties of PiG film are severely affected by the photon reabsorption and backward scattering of phosphor structure and the heat conduction of substrate.Herein,a unique sandwich design of phosphor structure was introduced in the multi-color PiG film for high-quality laser lighting.By elaborately synthesizing the borosilicate glass with low glass transition temperature(T_(g)),similar expansion coefficient,and high refractive index(RI),the sandwiched PiGs were prepared by sintering(~600℃)broadband green and red phosphor glass films on the double sides of sapphire.The green and red PiG films were tightly coated on the sapphire with no delamination and maintained higher luminescence intensity than raw phosphors at high temperatures.By simultaneously coupling photon reabsorption and backward scattering,the sandwiched green PiG film-sapphire-red PiG film(G-S-R PiG)yields a high-quality white light with a high luminous efficacy of 163 lm/W and an excellent color rendering index(CRI)of 85.4 under a laser power of 2.4 W,which are the best comprehensive results yet reported.Benefiting from the ingenious sandwich design with heat-conducting sapphire and thin PiG films,the G-S-R PiG displays low working temperatures(<200℃)under high-power laser excitation.This work reveals the role of sandwiched phosphor structure in photon loss and heat dissipation,which provides a new strategy to design PiG films for high-quality laser lighting.

关键词： laser-driven lighting phosphor-in-glass(PiG)film sandwich structure color quality heat dissipation

Orbit determination using incremental phase and TDOA of X-ray pulsar

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Frontiers of Information technology & Electronic Engineering 2016年第6期17卷 543-552页

作者： Rong JIAO Lu-ping XU Hua ZHANG Cong LI School of Aerospace Science and Technology Xidian University

X-ray pulsars offer stable, periodic X-ray pulse sequences that can be used in spacecraft positioning systems. A method using X-ray pulsars to determine the initial orbit of a satellite is presented in this paper. This method suggests only one detector to be equipped on the satellite and assumes that the detector observes three pulsars in turn. To improve the performance, the use of incremental phase in one observation duration is proposed, and the incremental phase is combined with the time difference of arrival(TDOA). Then, a weighted least squares(WLS) algorithm is formulated to calculate the initial orbit. Numerical simulations are performed to assess the proposed orbit determination method.

关键词： X射线脉冲星卫星定位系统增量到达时间差定轨加权最小二乘初始轨道脉冲序列

Denoising of X-ray pulsar observed profile using biorthogonal lifting wavelet transform

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Journal of Systems Engineering and Electronics 2016年第3期27卷 514-523页

作者： Mengfan Xue Xiaoping Li Yanming Liu Haiyan Fang Haifeng Sun Lirong Shen School of Aerospace Science and Technology Xidian University

In X-ray pulsar-based navigation, strong X-ray background noise leads to a low signal-to-noise ratio（SNR） of the observed profile, which consequently makes it very difficult to obtain an accurate pulse phase that directly determines the navigation precision. This signifies the necessity of denoising of the observed profile. Considering that the ultimate goal of denoising is to enhance the pulse phase estimation, a profile denoising algorithm is proposed by fusing the biorthogonal lifting wavelet transform of the linear phase characteristic with the thresholding technique. The statistical properties of X-ray background noise after epoch folding are studied. Then a wavelet-scale dependent threshold is introduced to overcome correlations between wavelet coefficients. Moreover, a modified hyperbola shrinking function is presented to remove the impulsive oscillations of the observed profile. The results of numerical simulations and real data experiments indicate that the proposed method can effectively improve SNR of the observed profile and pulse phase estimation accuracy, especially in short observation durations. And it also outperforms the Donoho thresholding strategy normally used in combination with the orthogonal discrete wavelet transform.

关键词： X-ray pulsar denoising linear phase wavelet-scale dependent threshold

A fast pulse phase estimation method for X-ray pulsar signals based on epoch folding

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Chinese Journal of Aeronautics 2016年第3期29卷 746-753页

作者： Xue Mengfan Li Xiaoping Sun Haifeng Fang Haiyan School of Aerospace Science and Technology Xidian University

X-ray pulsar-based navigation （XPNAV） is an attractive method for autonomous deep- space navigation in the future. The pulse phase estimation is a key task in XPNAV and its accuracy directly determines the navigation accuracy. State-of-the-art pulse phase estimation techniques either suffer from poor estimation accuracy, or involve tile maximization of generally non- convex object function, thus resulting in a large computational cost. In this paper, a fasl pulse phase estimation method based on epoch folding is presented. The statistical properties of the observed profle obtained through epoch folding are developed. Based on this, we recognize the joint prob- ability distribution of the observed profile as the likelihood function and utilize a fast Fourier transform-based procedure to estimate the pulse phase. Computational complexity of the proposed estimator is analyzed as well. Experimental results show that the proposed estimator significantly outperforms the currently used cross-correlation （CC） and nonlinear least squares （NLS） estima- tors, while significantly reduces the computational complexity compared with NLS and maxinmm likelihood （ML） estimators.

关键词： Epoch folding Maximum likelihoodPhase estimation X-ray pulsar X-ray pulsar-basednavigation （XPNAV）