Here we report a novel twin polarization angle （TPA） approach in the quantitative chirality detection with the surface sum-frequency generation vibrational spectroscopy （SFG-VS）. Generally, the achiral contributio...Here we report a novel twin polarization angle （TPA） approach in the quantitative chirality detection with the surface sum-frequency generation vibrational spectroscopy （SFG-VS）. Generally, the achiral contribution dominates the surface SFG-VS signal, and the pure chiral signal is usually two or three orders of magnitude smaller. Therefore, it has been difficult to make quantitative detection and analysis of the chiral contributions to the surface SFG- VS signal. In the TPA method, by varying together the polarization angles of the incoming visible light and the sum frequency signal at fixed s or p polarization of the incoming infrared beam, the polarization dependent SFG signal can give not only direct signature of the chiral contribution in the total SFG-VS signal, but also the accurate measurement of the chiral and achiral components in the surface SFG signal. The general description of the TPA method is presented and the experiment test of the TPA approach is also presented for the SFG-VS from the S- and R-limonene chiral liquid surfaces. The most accurate degree of chiral excess values thus obtained for the 2878 cm^-1 spectral peak of the S- and R-limonene liquid surfaces are （23.7±0.4）% and （-25.4±1.3）%, respectively.展开更多
This paper concentrates on investigating the mechanical stability of a Beam Position Monitor (BMP)support prototype of the Shanghai Synchrotron Radiation Facility(SSRF)project.Both finite element analysis and vibratio...This paper concentrates on investigating the mechanical stability of a Beam Position Monitor (BMP)support prototype of the Shanghai Synchrotron Radiation Facility(SSRF)project.Both finite element analysis and vibration measurements have been performed.Inconsistent results between the simulations and experiments motivate us to study three connections between the support and the ground:ground bolt(used in the initial design),part grout and full grout(proposed in the later research).After changing the connection, the first eigenfrequency is increased from 20.2Hz to 50.2Hz,and the ratio of the integrated RMS displacement (4—50Hz)is decreased from 4.36 to 1.23 in the lateral direction.The mechanical stability is improved greatly.展开更多
This paper presents an effective approach for updating finite element dynamic model from incomplete modal data identified from ambient vibration measurements.The proposed method is based on the relationship between th...This paper presents an effective approach for updating finite element dynamic model from incomplete modal data identified from ambient vibration measurements.The proposed method is based on the relationship between the perturbation of structural parameters such as stiffness and mass changes and the modal data measurements of the tested structure such as measured mode shape readings.Structural updating parameters including both stiffness and mass parameters are employed to represent the differences in structural parameters between the finite element model and the associated tested structure.These updating parameters are then evaluated by an iterative solution procedure,giving optimised solutions in the least squares sense without requiring an optimisation technique.In order to reduce the influence of modal measurement uncertainty,the truncated singular value decomposition regularization method incorporating the quasi-optimality criterion is employed to produce reliable solutions for the structural updating parameters.Finally,the numerical investigations of a space frame structure and the practical applications to the Canton Tower benchmark problem demonstrate that the proposed method can correctly update the given finite element model using the incomplete modal data identified from the recorded ambient vibration measurements.展开更多
Structural health monitoring (SHM) is a relevant topic for civil systems and involves the monitoring, data processing and interpretation to evaluate the condition of a structure, in order to detect damage. In real str...Structural health monitoring (SHM) is a relevant topic for civil systems and involves the monitoring, data processing and interpretation to evaluate the condition of a structure, in order to detect damage. In real structures, two or more sites or types of damage can be present at the same time. It has been shown that one kind of damaged condition can interfere with the detection of another kind of damage, leading to an incorrect assessment about the structure condition. Identifying combined damage on structures still represents a challenge for condition monitoring, because the reliable identification of a combined damaged condition is a difficult task. Thus, this work presents a fusion of methodologies, where a single wavelet-packet and the empirical mode decomposition (EMD) method are combined with artificial neural networks (ANNs) for the automated and online identification-location of single or multiple-combined damage in a scaled model of a five-bay truss-type structure. Results showed that the proposed methodology is very efficient and reliable for identifying and locating the three kinds of damage, as well as their combinations. Therefore, this methodology could be applied to detection-location of damage in real truss-type structures, which would help to improve the characteristics and life span of real structures.展开更多
In summary,the interval uncertainty is introduced to the acoustic metamaterial with Helmholtz resonators.And then,new descriptions(the conservative approximation,the unsafe approximation and the approximation precisio...In summary,the interval uncertainty is introduced to the acoustic metamaterial with Helmholtz resonators.And then,new descriptions(the conservative approximation,the unsafe approximation and the approximation precision)on uncertainties of physical properties of this interval acoustic metamaterial are defined.Lastly,an optimization model for this interval acoustic metamaterial is proposed.The organization of this paper is listed as follows.The acoustic transmission line method(ATLM)for an acoustic metamaterial with Helmholtz resonators is described in Section 2.In Section3,uncertain analysis of the interval acoustic metamaterial is presented.In Section 4,optimization model of the interval acoustic metamaterial is proposed.The discussion on optimization results is shown in Section 5.In section 6,some conclusions are given.展开更多
文摘Here we report a novel twin polarization angle （TPA） approach in the quantitative chirality detection with the surface sum-frequency generation vibrational spectroscopy （SFG-VS）. Generally, the achiral contribution dominates the surface SFG-VS signal, and the pure chiral signal is usually two or three orders of magnitude smaller. Therefore, it has been difficult to make quantitative detection and analysis of the chiral contributions to the surface SFG- VS signal. In the TPA method, by varying together the polarization angles of the incoming visible light and the sum frequency signal at fixed s or p polarization of the incoming infrared beam, the polarization dependent SFG signal can give not only direct signature of the chiral contribution in the total SFG-VS signal, but also the accurate measurement of the chiral and achiral components in the surface SFG signal. The general description of the TPA method is presented and the experiment test of the TPA approach is also presented for the SFG-VS from the S- and R-limonene chiral liquid surfaces. The most accurate degree of chiral excess values thus obtained for the 2878 cm^-1 spectral peak of the S- and R-limonene liquid surfaces are （23.7±0.4）% and （-25.4±1.3）%, respectively.
文摘This paper concentrates on investigating the mechanical stability of a Beam Position Monitor (BMP)support prototype of the Shanghai Synchrotron Radiation Facility(SSRF)project.Both finite element analysis and vibration measurements have been performed.Inconsistent results between the simulations and experiments motivate us to study three connections between the support and the ground:ground bolt(used in the initial design),part grout and full grout(proposed in the later research).After changing the connection, the first eigenfrequency is increased from 20.2Hz to 50.2Hz,and the ratio of the integrated RMS displacement (4—50Hz)is decreased from 4.36 to 1.23 in the lateral direction.The mechanical stability is improved greatly.
文摘This paper presents an effective approach for updating finite element dynamic model from incomplete modal data identified from ambient vibration measurements.The proposed method is based on the relationship between the perturbation of structural parameters such as stiffness and mass changes and the modal data measurements of the tested structure such as measured mode shape readings.Structural updating parameters including both stiffness and mass parameters are employed to represent the differences in structural parameters between the finite element model and the associated tested structure.These updating parameters are then evaluated by an iterative solution procedure,giving optimised solutions in the least squares sense without requiring an optimisation technique.In order to reduce the influence of modal measurement uncertainty,the truncated singular value decomposition regularization method incorporating the quasi-optimality criterion is employed to produce reliable solutions for the structural updating parameters.Finally,the numerical investigations of a space frame structure and the practical applications to the Canton Tower benchmark problem demonstrate that the proposed method can correctly update the given finite element model using the incomplete modal data identified from the recorded ambient vibration measurements.
基金Project (No. PIFI-2012 U. de Gto.) supported by the Secretariat of Public Education (SEP), Mexico
文摘Structural health monitoring (SHM) is a relevant topic for civil systems and involves the monitoring, data processing and interpretation to evaluate the condition of a structure, in order to detect damage. In real structures, two or more sites or types of damage can be present at the same time. It has been shown that one kind of damaged condition can interfere with the detection of another kind of damage, leading to an incorrect assessment about the structure condition. Identifying combined damage on structures still represents a challenge for condition monitoring, because the reliable identification of a combined damaged condition is a difficult task. Thus, this work presents a fusion of methodologies, where a single wavelet-packet and the empirical mode decomposition (EMD) method are combined with artificial neural networks (ANNs) for the automated and online identification-location of single or multiple-combined damage in a scaled model of a five-bay truss-type structure. Results showed that the proposed methodology is very efficient and reliable for identifying and locating the three kinds of damage, as well as their combinations. Therefore, this methodology could be applied to detection-location of damage in real truss-type structures, which would help to improve the characteristics and life span of real structures.
基金supported by National Natural Science Foundation of China(Grant Nos.11402083&11572121)Independent Research Project of State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body in Hunan University(Grant No.51375002)Fundamental Research Funds for the Central Universities,Collaborative Innovation Center of Intelligent New Energy Vehicle,and the Hunan Collaborative Innovation Center of Green Automobile
文摘In summary,the interval uncertainty is introduced to the acoustic metamaterial with Helmholtz resonators.And then,new descriptions(the conservative approximation,the unsafe approximation and the approximation precision)on uncertainties of physical properties of this interval acoustic metamaterial are defined.Lastly,an optimization model for this interval acoustic metamaterial is proposed.The organization of this paper is listed as follows.The acoustic transmission line method(ATLM)for an acoustic metamaterial with Helmholtz resonators is described in Section 2.In Section3,uncertain analysis of the interval acoustic metamaterial is presented.In Section 4,optimization model of the interval acoustic metamaterial is proposed.The discussion on optimization results is shown in Section 5.In section 6,some conclusions are given.
