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Accuracy analysis of a single-fault Markov model for FADEC system

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Journal of Systems Engineering and Electronics 2019年第5期30卷 1044-1052页

作者： CAI Jing HU Wei CAI Kunye College of Civil Aviation Nanjing University of Aeronautics and Astronautics

Time-limited dispatching(TLD)analysis of the full authority digital engine control(FADEC)systems is an important part of the aircraft system safety analysis and a necessary task for the certification of commercial aircraft and aeroengines.In the time limited dispatch guidance document ARP5107B,a single-fault Markov model(MM)approach is proposed for TLD analysis.However,ARP5107B also requires that the loss of thrust control(LOTC)rate error calculated by applying the single-fault MM must be less than 5%when performing airworthiness certification.Firstly,the sources of accuracy errors in three kinds of MM are analyzed and specified through a case study of the general FADEC system,and secondly a two-fault MM considering maintenance policy is established through analyzing and calculating the expected repair time when two related faults happen.Finally,a specific FADEC system is given to study on the influence factors of accuracy error in the single-fault MM,and the results show that the accuracy error of the single-fault MM decreases with the increase of short or long prescribed dispatch time,and the range values of short time(ST)and long time(LT)are determined to satisfy the requirement of accuracy error within 5%.

关键词： full authority digital engine control(FADEC)system Markov model(MM) accuracy analysis loss of thrust control(LOTC)

Robust LPV modeling and control of aircraft flying through wind disturbance

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Chinese Journal of Aeronautics 2019年第7期32卷 1588-1602页

作者： Zhenxing GAO Jun FU College of Civil Aviation Nanjing University of Aeronautics and Astronautics

This article deals with the disturbance attenuation control of aircraft flying through wind shear via Linear Parameter Varying(LPV) modeling and control method. A Flight Dynamics Model(FDM) with wind shear effects considered was established in wind coordinate system. An LPV FDM was built up based on function substitution whose decomposing function was optimized by Genetic Algorithm(GA). The wind disturbance was explicitly included in the system matrix of LPV FDM. Taking wind disturbance as external uncertainties, robust LPV control method with the LPV FDM was put forward. Based on ride quality and flight safety requirements in wind disturbance, longitudinal and lateral output feedback robust LPV controllers were designed respectively,in which the scheduling flight states in LPV model were actually dependent parameters in LPV control. The results indicate that LPV FDM can reflect the instantaneous dynamics of nonlinear system especially at the boundary of aerodynamic envelope. Furthermore, the LPV FDM also can approach nonlinear FDM’s response in wind disturbance special flight. Compared with a parameter-invariant LQR controller designed with a small-disturbance FDM, the LPV controllers show preferable robustness and stability for disturbance attenuation.

关键词： Function substitution Linear parameter varying LPV control Robust control Wind shear

Obstacle detection:improved YOLOX-S based on swin transformer-tiny

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Optoelectronics Letters 2023年第11期19卷 698-704页

作者： ZHANG Hongying LU Chengjian CHEN Enyao college of Electronic Information and Automation Civil Aviation University of ChinaTianjin300300China

Aiming at the accuracy challenge in obstacle detection for autonomous driving,we propose an improved you only look once X-S(YOLOX-S) model based on swin transformer-tiny YOLOX-S(ST-YOLOX-S) for obstacle detection,which could detect multiple targets,including people,cars,bicycles,motorcycles,and buses.Our method mainly comprises two aspects as follows.To improve the capability of local feature extraction and then obtain more accurate detection for obstacles under real-world vehicle conditions,the existing backbone of YOLOX-S is replaced with the swin transformer-tiny backbone.We reduced the number of channels between the swin transformer and path aggregation-feature pyramid network(PA-FPN) from [96,192,384,768] to [192,384,768],to decrease the computational cost and then make the swin transformer-tiny more compatible with the PA-FPN.Conclusively,on the popular COCO dataset,the proposed ST-YOLOX-S improves the detection mean average precision(mAP) by 6.1% when compared with YOLOX-S.Among the five types of obstacles that appear in simulated actual vehicle conditions,our ST-YOLOX-S also achieves superior performance compared to YOLOX-S.Furthermore,our method achieves significant performance over the YOLOv3 on obstacle detection,which shows the effectiveness of the proposed algorithm.

关键词： obstacle network backbone

Design and Testing of a Novel Piezoelectric-Driven Microvibration Hammerhead

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Nanomanufacturing and Metrology 2023年第1期6卷 79-87页

作者： Zhiyong Guo Zhemin Shen Weidong Liu Zhiqiang Zhang Lifeng Zhang Xuhao Wang college of Aeronautical Engineering Civil Aviation University of ChinaTianjin 300300China

A novel microvibration hammerhead consists of a piezoelectric actuator and a double cross-shape compliant mechanism(DCCM)is presented in this paper.The output force of the piezoelectric actuator can be detected in real time by an insideinstalled pressure sensor.A theoretical model including the stiffness,first natural frequency,and stress of the DCCM and the displacement output of the piezoelectric actuator are established,and then they are further analyzed using the finite element analysis method.The effects of the beam thickness on the static and dynamic properties are deeply analyzed and compared.A prototype micro hammering system is constructed by integrating the microvibration hammerhead assembly and controlling system.Various experiments are also carried out to verify the basic performance of the micro hammering system.

关键词： Piezoelectric Flexure hinge Micro hammering

Chemical Properties,Low-Temperature Performance,and Burning Performance of Bio-Jet Fuel

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China Petroleum Processing & Petrochemical Technology 2023年第4期25卷 23-30页

作者： Zhang Zongwei Wang Zihan Yang Ze Li Junqi Liu Haonan college of Aeronautical Engineering Civil Aviation University of ChinaTianjin300300China Institute for Environment and Development Civil Aviation University of ChinaTianjin300300China Transportation Science and Engineering Civil Aviation University of ChinaTianjin300300China

The effects of composition of bio-jet fuels on freezing point,smoke point,distillation range,and flash point are investigated.Performance tests using petroleum-based jet fuel with different compositions are conducted in line with standard test specifications.The results show that alkylbenzenes reduce the freezing point,with the amount of reduction becoming greater with increasing alkylbenzene content.For a 25%content of the C_8 aromatic xylene,the freezing point is in the range from-55.5℃to-60.1℃.The presence of monocyclic aromatic hydrocarbons leads to an increase in carbon deposition performance,especially when alkyl side chains are present.With cycloalkanes,carbon deposition is reduced,although alkyl side chains weaken this beneficial effect.Isomeric hydrocarbons are beneficial in reducing carbon deposition.The ASTM D7566 specifications for the distillation range are based on the average properties of petroleum-based aviation fuel,and if all the parameters governing the distillation range of an alternative jet fuel are at their lower limits,it is necessary to check whether other performance standards are met.Light components affect the flash point greatly,with 5%of benzene reducing the flash point by 17℃,whereas intermediate components(e.g.,xylene and ethylbenzene)and heavier components have less impact.Although alcohols provide better combustion performance,their content must be strictly limited owing to their effects in reducing the flash point.

关键词： sustainable aviation fuel freezing point smoke point distillation range flash point

Two constructions of LDPC codes based on pseudo-symplectic geometry over finite fields

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The Journal of China Universities of Posts and Telecommunications 2018年第2期25卷 49-59页

作者： Wang Xiuli Hao Yakun college of Science Civil Aviation University of China

F（2v＋ 1） q Based on the pseudo-symplectic space over q of characteristics 2, combining the definition of low density parity check （LDPC） codes with the knowledge of graph theory, two kinds of LDPC codes with larger girth are constructed. By the knowledge of bipartite graph and the girth properties of LDPC codes, both the girth of the code C（m1 ,2v ＋ 1 ,q） and the code C（m2 ,2v ＋ 1 ,q） are computed are 8. The girth is larger, the performance of LDPC codes is better. Finally, according to the properties of the check matrix and the linear relation between the column vectors of the check matrix, both the minimum distances of the two codes are obtained are 2q ＋ 2.

关键词： LDPC codes pseudo-symplectic geometry minimum distance girth

Generalized mixed finite element method for 3D elasticity problems

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Acta Mechanica Sinica 2018年第2期34卷 371-380页

作者： Guanghui Qing Junhui Mao Yanhong Liu college of Aeronautical Engineering Civil Aviation University of China

Without applying any stable element techniques in the mixed methods, two simple generalized mixed element(GME) formulations were derived by combining the minimum potential energy principle and Hellinger–Reissner(H–R) variational principle. The main features of the GME formulations are that the common C0-continuous polynomial shape functions for displacement methods are used to express both displacement and stress variables, and the coefficient matrix of these formulations is not only automatically symmetric but also invertible. Hence, the numerical results of the generalized mixed methods based on the GME formulations are stable. Displacement as well as stress results can be obtained directly from the algebraic system for finite element analysis after introducing stress and displacement boundary conditions simultaneously. Numerical examples show that displacement and stress results retain the same accuracy. The results of the noncompatible generalized mixed method proposed herein are more accurate than those of the standard noncompatible displacement method. The noncompatible generalized mixed element is less sensitive to element geometric distortions.

关键词： Minimum potential energy principle Hellinger–Reissner (H–R) variational principle Generalized variational principle Generalized mixed element (GME) Elasticity problem Noncompatible mode

Highly accurate symplectic element based on two variational principles

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Acta Mechanica Sinica 2018年第1期34卷 151-161页

作者： Guanghui Qing Jia Tian college of Aeronautical Engineering Civil Aviation University of China

For the stability requirement of numerical resultants, the mathematical theory of classical mixed methods are relatively complex. However, generalized mixed methods are automatically stable, and their building process is simple and straightforward. In this paper, based on the seminal idea of the generalized mixed methods, a simple, stable, and highly accurate 8-node noncompatible symplectic element(NCSE8) was developed by the combination of the modified Hellinger-Reissner mixed variational principle and the minimum energy principle. To ensure the accuracy of in-plane stress results, a simultaneous equation approach was also suggested. Numerical experimentation shows that the accuracy of stress results of NCSE8 are nearly the same as that of displacement methods, and they are in good agreement with the exact solutions when the mesh is relatively fine. NCSE8 has advantages of the clearing concept, easy calculation by a finite element computer program, higher accuracy and wide applicability for various linear elasticity compressible and nearly incompressible material problems. It is possible that NCSE8 becomes even more advantageous for the fracture problems due to its better accuracy of stresses.

关键词： Modified H-R mixed variational principle Partial-mixed element Noncompatible symplectic element Finite element method Nearly incompressible material

Topology Optimization of Self-Supporting Structures for Additive Manufacturing with Adaptive Explicit Continuous Constraint

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Computer Modeling in Engineering & Sciences 2022年第8期131卷 451-469页

作者： Jun Zou Haolei Mou college of Safety Science and Engineering Civil Aviation University of ChinaTianjin300300China

The integration of topology optimization(TO)and additive manufacturing(AM)technologies can create significant synergy benefits,while the lack of AM-friendly TO algorithms is a serious bottleneck for the application of TO in AM.In this paper,a TO method is proposed to design self-supporting structures with an explicit continuous self-supporting constraint,which can be adaptively activated and tightened during the optimization procedure.The TO procedure is suitable for various critical overhang angles(COA),which is integrated with build direction assignment to reduce performance loss.Besides,a triangular directional self-supporting constraint sensitivity filter is devised to promote the downward evolution of structures and maintain stability.Two numerical examples are presented;all the test cases have successfully converged and the optimized solutions demonstrate good manufacturability.In the meanwhile,a fully self-supporting design can be obtained with a slight cost in performance through combination with build direction assignment.

关键词： Topology optimization additive manufacturing self-supporting constraint build direction assignment gradual evolution