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Effect of Auxiliary Gas Flow Parameters on Microstructure and Properties of Ta Coatings Prepared by Three-Cathode Atmosphere Plasma Spraying

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Journal of Beijing Institute of Technology 2022年第3期31卷 302-316页

作者： Jing Cui Haiyang Xia Lang Cui Guang Liu college of Aeronautical Engineering Civil Aviation University of ChinaTianjin 300300China China civil aviation Ground Special Equipment Research Base Tianjin 300300China Ningbo Branch of Chinese Academy of Ordnance Science Ningbo 315103ZhejiangChina

Based on the three-cathode plasma spraying system,tantalum(Ta)coatings were pre-pared on the substrate of CuCrZr alloy.The effects of different auxiliary gas(helium)flow rates on the microstructure,phase composition,mechanical and wear resistance properties of Ta coatings were studied.The results showed that the oxidation degree of the coatings decreases first and then increases with the increase of the auxiliary gas flow.When the auxiliary gas flow rate is 70 L·min-1,the oxidation degree of the coating is the lowest,minimum value of the porosity is 0.21%,and the bonding strength reaches the maximum,59.3 MPa.At this time,the coating wear rate is 0.0012 mm^(3)·N^(-1)·m^(-1)with the best wear resistance.This indicates that the auxiliary gas flow has an important influence on the quality and surface mechanical properties of tantalum coating.

关键词： plasma spraying tantalum(Ta)coating auxiliary gas flow rate bonding strength tri-bological property

Analysis on Potential Conflict Frequency of Intersected Air Routes in Terminal Airspace Design

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Transactions of Nanjing University of Aeronautics and Astronautics 2014年第5期31卷 580-588页

作者：王超韩邦村刘菲 college of Air Traffic Management Civil Aviation University of China

In order to obtain accurate conflict risks in terminal airspace design,the concept and calculation model of potential conflict frequency for intersected routes are proposed.Conflict frequency is represented by the product of horizontal conflict frequency and vertical conflict probability.The horizontal conflict frequency is derived from the probability density distribution of conflicts in a period of time.Based on the recorded radar trajectory data,the concept and model of ROUTE distance are proposed,and the probability density function of aircraft height at a specified ROUTE distance is deduced by kernel density estimation.Furthermore,vertical conflict probability and its horizontal distribution are achieved.Examples of three intersected arrival and departure route design schemes are studied.Compared with scheme 1,the conflict frequency values of the other two improved schemes decrease to53% and 24%,respectively.The results show that the model can quantify potential conflict frequency of intersected routes.

关键词： air traffic management terminal airspace design horizontal conflict frequency vertical conflict proba-bility kernel density estimation(KDE)

Loading Localization by Small-Diameter Optical Fiber Sensors

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Transactions of Nanjing University of Aeronautics and Astronautics 2018年第2期35卷 275-281页

作者： Liu Rongmei Zhu Lujia Lu Jiyun Liang Dakai college of Aerospace Engineering Nanjing University of Aeronautics and Astronautics College of Civil Aviation Nanjing University of Aeronautics and Astronautics

Structural health monitoring(SHM)in service has attracted increasing attention for years.Load localization on a structure is studied hereby.Two algorithms,i.e.,support vector machine(SVM)method and back propagation neural network(BPNN)algorithm,are proposed to identify the loading positions individually.The feasibility of the suggested methods is evaluated through an experimental program on a carbon fiber reinforced plastic laminate.The experimental tests involve in application of four optical fiber-based sensors for strain measurement at discrete points.The sensors are specially designed fiber Bragg grating(FBG)in small diameter.The small-diameter FBG sensors are arrayed in 2-D on the laminate surface.The testing results indicate that the loading position could be detected by the proposed method.Using SVM method,the 2-D FBG sensors can approximate the loading location with maximum error less than 14 mm.However,the maximum localization error could be limited to about 1 mm by applying the BPNN algorithm.It is mainly because the convergence conditions(mean square error)can be set in advance,while SVM cannot.

关键词： small diameter optical fiber sensor structural health monitoring loading localization back propagation neural network support vector machine

An Improved Enthalpy-Based Lattice Boltzmann 3D Model with Added Probability Function for the Growth Characteristics of Frost Layer

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Journal of Thermal Science 2019年第2期28卷 378-392页

作者： CUI Jing YANG Tinghao YANG Fan YANG Guangfeng Airport college Civil Aviation University of China

In this paper, the effects of different surface properties on the growth of frost layer were numerically studied from the mesoscopic scale using the lattice Boltzmann method. The improved enthalpy method and nucleation probability model were combined to establish a three-dimensional lattice Boltzmann model based on nucleation probability theory. The model was used to carry out numerical research on frost layer formation and growth process on cold wall surface. The model could not only simulate the gradual densification and thickening process of frost layer growth from the macro scale, but also describe the change process of the frost layer structure caused by ice branch growth on the micro scale. The average thickness, average density and the amount of the frost layer could be obtained. Through this model, the temporal and spatial evolution characteristics of the topography of the frost layer were obtained. The model was used to analyze the effects of cold wall surface temperature, relative humidity and cold surface wettability on the frosting characteristics. The average thickness, frost average density, frost quality and average solid volume fraction of frost at different times were obtained by calculation.

关键词： lattice Boltzmann model improved enthalpy model nucleation probability model three-dimensional frost surface wettability

Global bifurcations and multi-pulse chaotic dynamics of rectangular thin plate with one-to-one internal resonance

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Applied Mathematics and Mechanics(English Edition) 2012年第9期33卷 1115-1128页

作者：李双宝张伟 college of Science Civil Aviation University of China college of Mechanical Engineering Beijing University of Technology

Global bifurcations and multi-pulse chaotic dynamics for a simply supported rectangular thin plate are studied by the extended Melnikov method. The rectangular thin plate is subject to transversal and in-plane excitation. A two-degree-of-freedom nonlinear nonautonomous system governing equations of motion for the rectangular thin plate is derived by the von Karman type equation and the Galerkin approach. A one-to- one internal resonance is considered. An averaged equation is obtained with a multi-scale method. After transforming the averaged equation into a standard form, the extended Melnikov method is used to show the existence of multi-pulse chaotic dynamics, which can be used to explain the mechanism of modal interactions of thin plates. A method for calculating the Melnikov function is given without an explicit analytical expression of homoclinic orbits. Furthermore, restrictions on the damping, excitation, and detuning parameters are obtained, under which the multi-pulse chaotic dynamics is expected. The results of numerical simulations are also given to indicate the existence of small amplitude multi-pulse chaotic responses for the rectangular thin plate.

关键词： rectangular thin plate global bifurcation multi-pulse chaotic dynamics extended Melnikov method

Optimization of Aeroengine Shop Visit Cost in its Service Life Cycle

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International Journal of Plant Engineering and Management 2018年第2期23卷 79-88页

作者： ZHAO Hongli CHEN Duowen GAO Jingdong college of aviation Engineering Civil Aviation University of China

It is an important task for airlines to make a reasonable workscope for their engines, which has effects not only on engine performance and reliability, but also on airlines operating cost. Based on the recommendations given in the engine maintenance management manual, and taking the repair levels adopted in the previous shop visits into account, a series of module repair level optimization rules were set up, and a shop visit cost optimization model was also created for engine service life cycle. The particle swarm method was used to optimize the engine workscope and overhaul cost. The method proposed in this paper will be a reference for airlines to make engine workscope and to do engine maintenance management.

关键词： engine workscope maintenance cost optimization soft time engine overhaul

GAS PATH ELECTROSTATIC SENSOR MONITORING AND COMPARISON EXPERIMENT ON TURBOJET ENGINE

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Transactions of Nanjing University of Aeronautics and Astronautics 2013年第4期30卷 361-365页

作者：付宇左洪福刘鹏鹏蔡景刘君强 College of Civil Aviation Nanjing University of Aeronautics and Astronautics

A monitoring and comparison experiment with two types of sensors on a turbojet engine is carried out. Compared with a probe-typed sensor,which is designed successfully before,signals are collected to verify the validity and better feasibility of the circular sensor.According to the signals monitored over 131h,the typical signals of 125—129 phases are analyzed.The results show that the unusual exhaust particles are carbon depositions from fuel spray nozzle.Therefore,with the electrostatic sensor,early warning can be provided for initial fault condition, as well as real-time reference for the condition-based maintenance.

关键词：航空空气动力学类型直升飞机

An adaptive and robust strategy for GPS/IMU/VO integrated navigation

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An adaptive and robust strategy for GPS/IMU/VO integrated na...

Low-Rate DoS Attack Flows Filtering Based on Frequency Spectral Analysis

第十四届中国卫星导航年会

作者： Yeying Dai Rui Sun College of Civil Aviation Nanjing University of Aeronautics and Astronautics

The multi-sensor integrated navigation is critical for improving the continuity and accuracy of positioning for intelligent transport system(ITS) applications. Global Positioning System(GPS)、inertial measurement unit(IMU) and visual odometry(VO) are commonly used sensors due to their complementarity. In complex urban environments, multipath interference(MI),non-line of sight(NLOS) and insufficient satellites degrade the positioning performance. Therefore, VO is required to correct the accumulated IMU errors and unreliable GPS positioning. Filter algorithms are commonly used in multi-sensor fusion. In the traditional Kalman filter, the measurement noise matrix and the fusion strategy of multi-sensors are usually fixed, which cannot adapt to the surrounding environment and the measurement quality of different sensors. To address this issue, we propose an adaptive and robust strategy for GPS/IMU/VO integrated navigation system. For the construction of the measurement vector, a dual GPS quality check method is proposed to realize adaptive switch of the filter. We also construct the robust factor weight matrix, so as to reduce the interference of gross errors on filter estimation. The field test in urban environment shows that the horizontal and 3D positioning accuracy of the proposed algorithm is 5.45m and 5.83m. Compared with the traditional GPS/IMU and GPS/IMU/VO fusion algorithm without adaptive and robust strategies, the 3D positioning accuracy has improvement of 69.49% and 44.64%, respectively.

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China Communications 2017年第6期14卷 98-112页

作者： Zhijun Wu Minxiao Wang Changcan Yan Meng Yue The college of Electronic Information & Automation Civil Aviation University of China Tianjin 300300China

In frequency domain,the power spectrum of Low-rate denial of service(LDoS) attacks is totally spread into the spectrum of normal traffic.It is a challenging task to detect and filter LDoS attack flows from the normal traffic.Based on the analysis of LDoS attack flows and legitimate TCP traffic in time and frequency domains,the periodicity of the TCP traffic and LDoS attack flows is explored to facilitate the research of network traffic processing.Hence,an approach of LDoS attack flow filtering based on frequency spectrum analysis is proposed.In this approach,the TCP traffic and LDoS attack flows are transformed from the time domain into the frequency domain.Then the round-trip time(RTT) is estimated by using frequency domain search method.Analysis of amplitude spectrum shows that TCP traffic energy is mainly concentrated on the points of n/RTT.Therefore,a comb filter using infinite impulse response(IIR) filter is designed to filter out the LDoS attack flows in frequency domain,while most legitimate TCP traffic energy at the points of n/RTT are pass through.Experimental results show that the maximum pass rate for legitimate TCP traffic reaches 92.55%,while the maximum filtration rate of LDoS attack flows reaches 81.36%.The proposed approach can effectively filter the LDoS attack flows while less impact on the legitimate TCP traffic.

关键词： DoS攻击频谱分析流过滤低速率无限脉冲响应滤波器 TCP流量拒绝服务攻击频率域