Due to the nonlinearity of breathing crack, cracked structure under excitation of a single frequency always generates higher harmonic components. In this paper, operational deflection shape (ODS) at excitation frequen...Due to the nonlinearity of breathing crack, cracked structure under excitation of a single frequency always generates higher harmonic components. In this paper, operational deflection shape (ODS) at excitation frequency and its higher harmonic components are used to map the deflection pattern of cracked structure. While ODS is sensitive to local variation of structure in nature, a new concept named transmissibility of operational deflection shape (TODS) has been defined for crack localization using beam-like structure. The transmissibility indicates the energy transfer from basic frequency to higher frequency. Then, Teager energy operator (TEO) is employed as a singularity detector to reveal and characterize the features of TODS. Numerical and experimental analysis in cantilever beam show that TODS has strong sensitivity to crack and can locate the crack correctly.展开更多
To develop modal macro-strain （ MMS ） identification techniques and improve their applicability in a continuous health monitoring system for civil infrastructures, the concept of operational macro-strain shape （OMS...To develop modal macro-strain （ MMS ） identification techniques and improve their applicability in a continuous health monitoring system for civil infrastructures, the concept of operational macro-strain shape （OMSS） and the corresponding identification method are proposed under unknown ever-changing loading conditions, and the MMS is then obtained. The core of the proposed technique is mainly based on the specific property that the macro-strain transmissibility tends to be independent of external excitations at the poles of the system and converges to a unique value. The proposed method is verified using the experimental data from a three-span continuous beam excited by an impact hammer at different locations. The identified results are also compared with the commonly used methods, such as the peak- picking （PP） method, the stochastic subspace identification （SSI） method, and numerical results, in the case of unknown input forces. Results show that the proposed technique has unique merits in accuracy and robustness due to its combining multiple tests under changing loading conditions, which also reveal the promising application of the distributed strain sensing system in identifying MMS of operational structures, as well as in the structural health monitoring （SHM） field.展开更多
Full-field measurement techniques such as the scanning laser Doppler vibrometer （LDV） and the electronic speckle pattern interferometry systems can provide a dense and accurate vibration measurement on structural op...Full-field measurement techniques such as the scanning laser Doppler vibrometer （LDV） and the electronic speckle pattern interferometry systems can provide a dense and accurate vibration measurement on structural operating deflection shape （ODS） on a relatively short period of time.The possibility of structural damage detection and localization using the ODS looks likely more attractive than when using traditional measurement techniques which address only a small number of discrete points.This paper discusses the decomposition method of the structural ODSs in the time history using principal component analysis to provide a novel approach to the structural health monitoring and damage detection.The damage indicator is proposed through comparison of structural singular vectors of the ODS variation matrixes between the healthy and damaged stages.A plate piece with a fix-free configuration is used as an example to demonstrate the effectiveness of the damage detection and localization using the proposed method.The simulation results show that：（1） the dominated principal components and the corresponding singular vectors obtained from the decomposition of the structural ODSs maintain most of all vibration information of the plate,especially in the case of harmonic force excitations that the 1st principal component and its vectors mostly dominated in the system;（2） the damage indicator can apparently flag out the damage localization in the case of the different sinusoidal excitation frequencies that may not be close to any of structural natural frequencies.The successful simulation indicates that the proposed method for structural damage detection is novel and robust.It also indicates the potentially practical applications in industries.展开更多
为解决机箱振动及噪声引起的机械硬盘读写速度降低的问题,应用Abaqus软件,对某款服务器机箱分别进行模态分析、振动传递函数VTF(vibration transfer function)以及噪声传递函数NTF(noise transfer function)分析,得到机箱的动态特性、...为解决机箱振动及噪声引起的机械硬盘读写速度降低的问题,应用Abaqus软件,对某款服务器机箱分别进行模态分析、振动传递函数VTF(vibration transfer function)以及噪声传递函数NTF(noise transfer function)分析,得到机箱的动态特性、机械硬盘的振动加速度频响曲线以及机箱声腔的声压级频响曲线。通过模态贡献量、工作变形等分析手段找出机箱结构振动及结构噪声出现峰值的原因,确认机箱传递路径的优化方案并进行了验证,为研究因机箱振动及噪声引起的机械硬盘读写速度降低的问题提供参考。展开更多
文摘Due to the nonlinearity of breathing crack, cracked structure under excitation of a single frequency always generates higher harmonic components. In this paper, operational deflection shape (ODS) at excitation frequency and its higher harmonic components are used to map the deflection pattern of cracked structure. While ODS is sensitive to local variation of structure in nature, a new concept named transmissibility of operational deflection shape (TODS) has been defined for crack localization using beam-like structure. The transmissibility indicates the energy transfer from basic frequency to higher frequency. Then, Teager energy operator (TEO) is employed as a singularity detector to reveal and characterize the features of TODS. Numerical and experimental analysis in cantilever beam show that TODS has strong sensitivity to crack and can locate the crack correctly.
基金The National Natural Science Foudation of China(No.51578140)the Natural Science Foundation of Jiangsu Province(No.BK20151092)Scientific Innovation Research of College Graduates in Jiangsu Province(No.CXZZ12_0108)
文摘To develop modal macro-strain （ MMS ） identification techniques and improve their applicability in a continuous health monitoring system for civil infrastructures, the concept of operational macro-strain shape （OMSS） and the corresponding identification method are proposed under unknown ever-changing loading conditions, and the MMS is then obtained. The core of the proposed technique is mainly based on the specific property that the macro-strain transmissibility tends to be independent of external excitations at the poles of the system and converges to a unique value. The proposed method is verified using the experimental data from a three-span continuous beam excited by an impact hammer at different locations. The identified results are also compared with the commonly used methods, such as the peak- picking （PP） method, the stochastic subspace identification （SSI） method, and numerical results, in the case of unknown input forces. Results show that the proposed technique has unique merits in accuracy and robustness due to its combining multiple tests under changing loading conditions, which also reveal the promising application of the distributed strain sensing system in identifying MMS of operational structures, as well as in the structural health monitoring （SHM） field.
基金supported by Jiangsu Provincial Natural Science Foundation of China (Grant No. BK2008383)Scientific Research Foundation for the Returned Overseas Chinese Scholars,Ministry of Education of China (Grant No. M0903-021)+1 种基金Nanjing University of Aeronautics and Astronautics Grant for the Talents,China (Grant No.KT50838-021)Jiangsu Provincial Research Foundation for Talented Scholars in Six Fields of China (Grant No. P0951-021)
文摘Full-field measurement techniques such as the scanning laser Doppler vibrometer （LDV） and the electronic speckle pattern interferometry systems can provide a dense and accurate vibration measurement on structural operating deflection shape （ODS） on a relatively short period of time.The possibility of structural damage detection and localization using the ODS looks likely more attractive than when using traditional measurement techniques which address only a small number of discrete points.This paper discusses the decomposition method of the structural ODSs in the time history using principal component analysis to provide a novel approach to the structural health monitoring and damage detection.The damage indicator is proposed through comparison of structural singular vectors of the ODS variation matrixes between the healthy and damaged stages.A plate piece with a fix-free configuration is used as an example to demonstrate the effectiveness of the damage detection and localization using the proposed method.The simulation results show that：（1） the dominated principal components and the corresponding singular vectors obtained from the decomposition of the structural ODSs maintain most of all vibration information of the plate,especially in the case of harmonic force excitations that the 1st principal component and its vectors mostly dominated in the system;（2） the damage indicator can apparently flag out the damage localization in the case of the different sinusoidal excitation frequencies that may not be close to any of structural natural frequencies.The successful simulation indicates that the proposed method for structural damage detection is novel and robust.It also indicates the potentially practical applications in industries.
文摘为解决机箱振动及噪声引起的机械硬盘读写速度降低的问题,应用Abaqus软件,对某款服务器机箱分别进行模态分析、振动传递函数VTF(vibration transfer function)以及噪声传递函数NTF(noise transfer function)分析,得到机箱的动态特性、机械硬盘的振动加速度频响曲线以及机箱声腔的声压级频响曲线。通过模态贡献量、工作变形等分析手段找出机箱结构振动及结构噪声出现峰值的原因,确认机箱传递路径的优化方案并进行了验证,为研究因机箱振动及噪声引起的机械硬盘读写速度降低的问题提供参考。
