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Multiobjective fault detection and isolation for flexible air-breathing hypersonic vehicle

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Journal of Systems Engineering and Electronics 2011年第1期22卷 52-62页

作者： Xuejing cai Fen wu Department of Mechanical and Aerospace Engineering North Carolina State University Raleigh NC 27695 USA

An application of the multiobjective fault detection and isolation（FDI） approach to an air-breathing hypersonic vehicle（HSV） longitudinal dynamics subject to disturbances is *** sustainable and safe flight of HSV is a challenging task due to its strong coupling effects,variable operating conditions and possible failures of system components.A common type of system faults for aircraft including HSV is the loss of effectiveness of its actuators and *** detect and isolate multiple actuator/sensor failures,a faulty linear parameter-varying（LPV） model of HSV is derived by converting actuator/system component faults into equivalent sensor *** a bank of LPV FDI observers is designed to track individual fault with minimum error and suppress the effects of disturbances and other fault *** simulation results based on the nonlinear flexible HSV model and a nominal LPV controller demonstrate the effectiveness of the fault estimation technique for HSV.

关键词： fault detection and isolation(FDI) hypersonic vehicle(HSV) actuator and sensor faults multiobjective optimization.

A new nonparametric stability test with an application to major Chinese macroeconomic time series

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Applied Mathematics(A Journal of Chinese Universities) 2013年第1期28卷 1-16页

作者： cai Nan cai Zong-wu FANG Ying The Wang Yanan Institute for Studies in Economics MOE Key Laboratory of Econometrics (Xia- men University) Fujian Provincial Key Laboratory of Statistical Science Xiamen University Department of Mathematics and Statistics University of North Carolina at Charlotte

In this paper, we propose a new test for testing the stability in macroeconomic time series, based on the LASSO variable selection approach and nonparametric estimation of a time-varying model. The wild bootstrap is employed to obtain its data-dependent critical values. We apply the new method to test the stability of bivariate relations among 92 major Chinese macroeconomic time series. We find that more than 70% bivariate relations are significantly unstable.

关键词： LASSO stability test time-varying coefficients model wild bootstrap.

Precipitation and stability of reversed austenite in 9Ni steel

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International Journal of Minerals,Metallurgy and Materials 2010年第5期17卷 587-595页

作者： Yue-hui Yang Qing-wu cai Di Tang Hui-bin wu Research Institute of Metallurgical Engineering University of Science and Technology Beijing Beijing 100083 China

A new method was used to analyze the factors affecting the precipitation of reversed austenite during tempering. The samples were kept at various tempering temperatures for 10 min and their length changes were recorded. Then, the precipitation of reversed austenite which led to the length reduction was shown by thermal expansion curves. The results show that the effects of process parameters on the precipitation of reversed austenite can be determined more accurately by this method than by X-ray diffraction. When the quenching and tempering process is adopted, both the lower quenching temperature and higher tempering temperature can promote the precipitation of reversed austenite during tempering; and when the quenching, lamellarizing, and tempering process is used, intercritical quenching is considered beneficial to the precipitation of reversed austenite in the subsequent tempering because of Ni segregation during holding at the intercritical temperature.

关键词： cryogenic equipment low carbon steel reversed austenite precipitation stability thermal expansion measurement

Effects of Si on the stability of retained austenite and temper embrittlement of ultrahigh strength steels

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International Journal of Minerals,Metallurgy and Materials 2011年第5期18卷 543-550页

作者： Li-jun Wang Qing-wu cai Hui-bin wu Wei Yu National Engineering Research Center for Advanced Rolling Technology University of Science and Technology Beijing Beijing 100083 China

Effects of silicon （Si） content on the stability of retained austenite and temper embrittlement of ultrahigh strength steels were investigated using X-ray diffraction （XRD）,transmission electron microscopy （TEM）,and other experimental *** results show that Si can suppress temper embrittlement,improve temper resistance,and hinder the decomposition of retained *** austenite appears gradually with the increase of Si content during *** has a significant effect on enhancing carbon （C） partitioning and improving the stability of retained *** and C atoms are mutually exclusive in lath bainite,while they attract each other in austenite.ε-carbides are found in 1.8wt% Si steel tempered at 250℃,and they get coarsened obviously when tempered at 400℃,leading to temper *** ε-carbides but acicular or lath carbides lead to temper embrittlement in 0.4wt% Si steel,which can be inferred as cementites and composite *** embrittlement is closely related to the decomposition of retained austenite and the formation of reversed austenite.

关键词： silicon ultrahigh strength steel retained austenite temper embrittlement reversed austenite

Influence of Mo on Growth and Coarsening of Nanometer-sized Carbides in Low-alloy Ferritic Steels Containing Ti

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Journal of Iron and Steel Research International 2014年第9期21卷 878-885页

作者： Bin-hao HU Qing-wu cai Hui-bin wu Engineering Research Institute University of Science and Technology Beijing

By optical microscopy, transmission electron microscopy and energy dispersive spectroscopy, the changes with aging time in size, composition and distribution of nanometer-sized （Ti, Mo）C precipitated in Ti-Mo low-alloy ferritc steel have been studied in comparison with that of nanometer-sized TiC precipitated in Ti low-alloy ferritc steel. It was found that the growth rate of （Ti,Mo）C in Ti-Mo steel was less than that of TiC in Ti steel. Nanometer- sized carbides formed at 650 ~C （or 550 ~C） for 55 h were at transitional stage from growth to coarsening. When aging time reaches 55 h, the coarsening rates of nanometer-sized carbides in Ti and Ti-Mo steel tend to be the same and in- variable. The influence of Mo on growth and coarsening of nanometer-sized carbides tends to decrease with increasing aging time, and Mo contents in nanometer-sized carbides with the same size at different aging time were different.

关键词： Ti-Mo low alloy ferritic steel nanometer-sized carbide precipitation strengthening Ostwald coarsening

Kinetics of Precipitation Behavior of Second Phase Particles in Ferritic Ti-Mo Microalloyed Steel

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Journal of Iron and Steel Research International 2013年第7期20卷 69-77页

作者： HU Bin-hao cai Qing-wu wu Hui-bin Engineering Research Institute University of Science and Technology Beijing

Two types of stress relaxation tests were carried out to investigate the incubation time for incipient precipi-tation of Ti（C,N） in deformed austenite and （Ti,Mo）C in ferrite of ferritic Ti-Mo microalloyed steel The size dis-tribution, amount and chemical composition of precipitates were obtained by using physicochemical phase analysis, and calculated according to thermodynamics and kinetics. The experimental results demonstrated that the incubation time was reduced with increasing Ti content, and prolonged with the addition of Mo. After 30 % deformation at 850 ℃, the nucleation of strain-induced Ti（C,N） was a relatively slow process. On the other hand, the temperature where the nucleation rate of （Ti, Mo）C in ferrite was the highest descended first and then ascended with increasing Ti content, and so did the temperature where the incubation time was the shortest. The key point is that the tempera-ture of steel containing about 0.09 % Ti is the lowest. The mass fraction of MC-type particles with size smaller than 10 nm in steel containing 0.09% Ti and 0.2% Mo reached 73.7%. The size distributions of precipitates in steel containing 0.09% Ti were relatively concentrated compared with that in steel containing 0.07% Ti.

关键词： ferritic Ti-Mo microalloyed steel precipitation behavior second phase particle stress relaxation parti-cle size distribution

Comprehensive early warning of rock burst utilizing microseismic multi-parameter indices

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International Journal of Mining Science and Technology 2018年第5期28卷 767-774页

作者： Linming Dou wu cai Anye Cao Wenhao Guo Key Laboratory of Deep Coal Resource Mining (Ministry of Education of China) School of Mines China University of Mining & Technology

Rock bursts have become one of the most severe risks in underground coal mining and its early warning is an important component in the safety management. Microseismic(MS) monitoring is considered potentially as a powerful tool for the early warning of rock burst. In this study, an MS multi-parameter index system was established and the critical values of each index were estimated based on the normalized multi-information warning model of coal-rock dynamic failure. This index system includes bursting strain energy(BSE) index, time-space-magnitude independent information(TSMII) indices and timespace-magnitude compound information(TSMCI) indices. On the basis of this multi-parameter index system, a comprehensive analysis was conducted via introducing the R-value scoring method to calculate the weights of each index. To calibrate the multi-parameter index system and the associated comprehensive analysis, the weights of each index were first confirmed using historical MS data occurred in LW402102 of Hujiahe Coal Mine(China) over a period of four months. This calibrated comprehensive analysis of MS multi-parameter index system was then applied to pre-warn the occurrence of a subsequent rock burst incident in LW 402103. The results demonstrate that this multi-parameter index system combined with the comprehensive analysis are capable of quantitatively pre-warning rock burst risk.

关键词： Rock burst Microseismic(MS)monitoring Multi-parameter indices Comprehensive early warning

Novel implementation of homogenization method to predict effective properties of periodic materials

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Acta Mechanica Sinica 2013年第4期29卷 550-556页

作者： Geng-Dong Cheng Yuan-wu cai Liang Xu Dept. of Engineering Mechanics Dalian University of Technology

Representative volume element （RVE） method and asymptotic homogenization （AH） method are two widely used methods in predicting effective properties of pe- riodic materials. This paper develops a novel implementa- tion of the AH method, which has rigorous mathematical foundation of the AH method, and also simplicity as the RVE method. This implementation can be easily realized using commercial software as a black box, and can use all kinds of elements available in commercial software to model unit cells with rather complicated microstructures, so the model may remain a fairly small scale. Several examples were car- fled out to demonstrate the simplicity and effectiveness of the new implementation.

关键词： Effective property ~ Periodic material - Homog-enization ~ RVE method

Fault-Induced Coal Burst Mechanism under Mining-Induced Static and Dynamic Stresses

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Engineering 2021年第5期7卷 687-700页

作者： wu cai Linming Dou Guangyao Si Yawei Hu State Key Laboratory of Coal Resources and Safe Mining School of MinesChina University of Mining and TechnologyXuzhou 221116China Department of Earth Science and Engineering Royal School of MinesImperial College LondonLondon SW72AZUK School of Minerals and Energy Resources Engineering University of New South WalesSydneyNSW 2052Australia

Fault is a common geological structure that has been revealed in the process of underground coal excavation and *** nature of its discontinuous structure controls the deformation,damage,and mechanics of the coal or rock *** interaction between this discontinuous structure and mining activities is a key factor that dominates fault reactivation and the coal burst it can *** paper first summarizes investigations into the relationships between coal mining layouts and fault occurrences,along with relevant conceptual models for fault ***,it proposes mechanisms of fault reactivation and its induced coal burst based on the superposition of static and dynamic stresses,which include two kinds of fault reactivations from:mining-induced quasi-static stress(FRMSS)-dominated and seismic-based dynamic stress(FRSDS)-*** two kinds of fault reactivations are then validated by the results of experimental investigations,numerical modeling,and in situ microseismic *** this basis,monitoring methods and prevention strategies for fault-induced coal burst are discussed and *** results show that fault-induced coal burst is triggered by the superposition of high static stress in the fault pillar and dynamic stress from fault *** static stress comes from the interaction of the fault and the roof structure,and dynamic stress can be ascribed to FRMSS and *** results in this paper could be of great significance in guiding the monitoring and prevention of fault-induced coal bursts.

关键词： Coal burst Fault reactivation Mining-induced stress Seismic-based dynamic stress Fault pillar