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Output only modal identification and structural damage detection using time frequency & wavelet techniques

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Earthquake eng.neering and eng.neering Vibration 2009年第4期8卷 583-605页

作者： S.Nagarajaiah B.Basu dept.of Civil & Environmental eng.and dept.of Mechanical eng.& Material Sc. Rice University dept.of Civil Structural& Environmental Eng.Trinity College Dublin

The primary objective of this paper is to develop output only modal identification and structural damage detection. Identification of multi-degree of freedom （MDOF） linear time invariant （LTI） and linear time variant （LTV--due to damage） systems based on Time-frequency （TF） techniques--such as short-time Fourier transform （STFT）, empirical mode decomposition （EMD）, and wavelets--is proposed. STFT, EMD, and wavelet methods developed to date are reviewed in detail. In addition a Hilbert transform （HT） approach to determine frequency and damping is also presented. In this paper, STFT, EMD, HT and wavelet techniques are developed for decomposition of free vibration response of MDOF systems into their modal components. Once the modal components are obtained, each one is processed using Hilbert transform to obtain the modal frequency and damping ratios. In addition, the ratio of modal components at different degrees of freedom facilitate determination of mode shape. In cases with output only modal identification using ambient/random response, the random decrement technique is used to obtain free vibration response. The advantage of TF techniques is that they arc signal based; hence, can be used for output only modal identification. A three degree of freedom 1：10 scale model test structure is used to validate the proposed output only modal identification techniques based on STFT, EMD, HT, wavelets. Both measured free vibration and forced vibration （white noise） response are considered. The secondary objective of this paper is to show the relative ease with which the TF techniques can be used for modal identification and their potential for real world applications where output only identification is essential. Recorded ambient vibration data processed using techniques such as the random decrement technique can be used to obtain the free vibration response, so that further processing using TF based modal identification can be performed.

关键词： Time-frequency methods short time Fourier transform Hilbert transform wavelets modal identification:output only structural health monitoring damage detection

Slope Stability Analyses of Outang Landslide Based on the Peak and Residual Shear Streng.h Behavior

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工程科学与技术 2019年第4期51卷 55-68页

作者： YANG Xiuhan VANAPALLI Sai dept.of Civil eng. Univ.of Ottawa

Most of the natural and compacted fine-grained soil slopes that are in saturated or unsaturated condition undergo a large deformation prior to reaching failure *** slopes should be designed taking account of their strain-softening behavior using the residual shear streng.h (RSS) *** this paper,the slope stability of a recently reactivated Outang landslide near the Three Gorges Dam in China is analyzed based on the RSS parameters of unsaturated *** addition,comparisons are provided in the FOS values of slope using both the peak shear streng.h (PSS) and RSS ***,a series of site investigations of the hydrologic and geologic conditions,ground surface displacements and cracks were *** PSS and RSS behaviors of the sliding soils derived from a series of direct shear test results performed on saturated and unsaturated soil specimens are ***,a series of slope stability analysis were conducted considering the precipitation and Yangtze River water level variation within a representative period of 7 months,based on the PSS and the RSS *** this study,three different scenarios were considered,which include: i) considering only the precipitation with a constant water level;ii) considering only the decrease in water level without rainfall;iii) considering the combination of precipitation and decrease in water *** each scenario,four steps were included to calculate the values of factor of safety (FOS) at different times.1) A steady-state seepage analysis was conducted with a constant total head at 525 m on the left boundary and 175 m on the slope surface below the Yangtze River water *** initial pore water pressures were simulated in the slope under no precipitation and variation of water level.2) A specific boundary condition was applied on the slope surface to model the precipitation and Yangtze River water level variation.A transient seepage analysis was conducted to calculate pore water pres

关键词： unsaturated soil landslide reactivation residual shear streng.h slope stability analysis

Ultrasonic Approach of Rayleigh Pitch-Catch Contact Ultrasound Waves on CFRP Laminated Composites

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Journal of Materials Science & Technology 2008年第3期24卷 407-409页

作者： In-Young Yang Kwang-Hee Im Uk Heo David K Hsu Je-Woong Park Hak-Joon Kim Sung-Jin Song School of Mechanical eng. Chosun Univ Department of automotive eng. Woosuk Univers-ity Center for Nondestructive Evaluation Iowa State University dept.of Naval Arch.and Ocean eng. Chosun Univ School of Mechanical eng. Sungkyunkwan University

CFRP （carbon fiber reinforced plastics） composite materials have wide applicability because of their inherent design flexibility and improved material properties. However, impacted composite structures have 50%-75% less streng.h than undamaged structures. In this work, a CFRP composite material was nondestructively characterized in order to ensure product quality and structural integrity of CFRP and one-sided pitch-catch technique was developed to measure impacted-damaged area by using an automated-data acquisition system in an immersion tank. A pitch-catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave under defect conditions in the composite.

关键词： Impact damages C-scanner Carbon fiber reinforced plastics (CFRP) Pitchcatch mode

Pattern Recognition of Thermal Analysis Cooling Curves and Quality Evaluation of Melt Cast Alloys

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Journal of Materials Science & Technology 2001年第1期17卷 73-74页

作者： Yanxiang LI Xiao HU Xuerong XU dept.of Mechanical eng. Tsinghua UniversityBeijing 100084China

The development of thermal analysis techniques for evaluation of cast alloy melt quality and its current applications in the foundry were reviewed. The characteristics of the current thermal analysis techniques were analyzed. A new comprehensive method for cooling curve recognition has been proposed. The evaluation of cast alloy melt quality was realized.

关键词： Quality Evaluation Cooling Curves thermal analysis cooling curve recognition comprehensive method alloy melt

An Adaptive Joint Source/Channel Coding Using Error Correcting Arithmetic Codes

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Journal of Shanghai Jiaotong university(Science) 2007年第4期12卷 448-453页

作者：刘军清逄玉叶孙军 dept.of Electronic eng. China Three Gorges Univ. dept.of Electronic eng. Shanghai Jiaotong Univ.

An approximately optimal adaptive arithmetic coding (AC) system using a forbidden symbol (FS) over noisy channels was proposed which allows one to jointly and adaptively design the source decoding and channel correcting in a single process, with superior performance compared with traditional separated techniques. The concept of adaptiveness is applied not only to the source model but also to the amount of coding redundancy. In addition, an improved branch metric computing algorithm and a faster sequential searching algorithm compared with the system proposed by Grangetto were proposed. The proposed system is tested in the case of image transmission over the AWGN channel, and compared with traditional separated system in terms of packet error rate and complexity. Both hard and soft decoding were taken into account.

关键词： arithmetic coding joint source channel coding maximum a posteriori (MAP) forbidden symbol

Adaptive Synchronization in Small-World Dynamical Networks

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Journal of Shanghai Jiaotong university(Science) 2007年第2期12卷 211-215页

作者：邹艳丽朱杰罗晓曙 dept.of Electronic eng. Shanghai Jiaotong Univ. dept.of Physics and Electronic eng. Guangxi Normal Univ.

Adaptive synchronization in NW small-world dynamical networks was studied. Firstly, an adaptive synchronization method is presented and explained. Then, it is applied to two different classes of dynamical networks, one is a class-B network, small-world connected R6 ssler oscillators, the other is a class-A network, small-world connected Chua＇s circuits. The simulation verifies the validity of the presented method. It also shows that the adaptive synchronization method is robust to the variations of the node systems parameters. So the presented method can be used in networks whose node systems have unknown or time-varying parameters.

关键词： NW small-world network master stability function adaptive synchronization

A New Arithmetic Coding System Combining Source Channel Coding and MAP Decoding

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Journal of Shanghai Jiaotong university(Science) 2007年第4期12卷 442-447页

作者：逄玉叶孙军王嘉 dept.of Electronic eng. Shanghai Jiaotong Univ.

A new arithmetic coding system combining source channel coding and maximum a posteriori decoding were proposed. It combines source coding and error correction tasks into one unified process by introducing an adaptive forbidden symbol. The proposed system achieves fixed leng.h code words by adaptively adjusting the probability of the forbidden symbol and adding tail digits of variable leng.h. The corresponding improved MAP decoding metric was derived. The proposed system can improve the performance. Simulations were performed on AWGN channels with various noise levels by using both hard and soft decision with BPSK *** results show its performance is slightly better than that of our adaptive arithmetic error correcting coding system using a forbidden symbol.

关键词： arithmetic code (AC) forbidden symbol joint source channel coding (JSCC) maximum a posteriori (MAP) decoding

Bedload resistance in supercritical flow

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International Journal of Sediment Research 2009年第4期24卷 400-409页

作者： Alireza HABIBZADEH Mohammad Hossein OMID dept.of Irrigation and Reclamation eng. University of Tehran dept. of Irrigation and Reclamation eng. University of Tehran

The movement of bedload in subcritical flow produces additional roughness as compared to flow in a rigid bed. The magnitude of this bed load roughness is proportional to the thickness of the sediment layer moving along the bed, the particle size and the sediment concentration. In a supercritical flow, however, further resistance is expected due to the momentum absorption by the high flow velocity. In this study the effect of sediment movement on the flow resistance in supercritical flow was experimentally investigated. The experiments included flows over smooth and rough beds carrying sediment of mean diameters D 50 =2.80, 5.42 and 7.06 mm in a rigid rectangular channel. The results show that the sediment transport may increase the friction factor by up to 90% and 60% in smooth and rough beds, respectively. Bedload extracts its momentum from the flow, which causes a reduction of near bed flow velocity and steeper velocity gradient near the bed resulting in an increase in shear velocity as well as in roughness height. The increase in friction factor is directly related to bedload concentration and particle size.

关键词： Hydraulic resistance Friction factor Bedload transport Supercritical flow

Efficient Accurate Context-Sensitive Anomaly Detection

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Journal of Shanghai Jiaotong university(Science) 2007年第5期12卷 639-644,650页

作者：李红娇李建华 dept.of Electronic eng. Shanghai Jiaotong Univ.

For program behavior-based anomaly detection, the only way to ensure accurate monitoring is to construct an efficient and precise program behavior model. A new program behavior-based anomaly detection model, called combined pushdown automaton (CPDA) model was proposed, which is based on static binary executable analysis. The CPDA model incorporates the optimized call stack walk and code instrumentation technique to gain complete context information. Thereby the proposed method can detect more attacks, while retaining good performance.

关键词： program behavior-based anomaly detection system call combined pushdown automaton (CPDA) model