A technique to extract real modes from the identified complex modes is presented in this paper, which enables the normalized real mode shapes, modal masses, and full or reduced mass and stiffness matrices to be obtain...A technique to extract real modes from the identified complex modes is presented in this paper, which enables the normalized real mode shapes, modal masses, and full or reduced mass and stiffness matrices to be obtained. The theoretical derivation of the method is provided in detail. An 11-DOF vibration system is used to validate the algorithm, and to analyze the effects of the number of modes utilized and measurement DOFs on the extraction results. Finally, the method is used to extract real modes from both experimental modal analysis and operational modal analysis.展开更多
Modal strain energy based methods for damage detection have received much attention. However, most of published articles use numerical methods and some studies conduct modal tests with simple 1D or 2D structures to ve...Modal strain energy based methods for damage detection have received much attention. However, most of published articles use numerical methods and some studies conduct modal tests with simple 1D or 2D structures to verify the damage detection algorithms. Only a few studies utilize modal testing data from 3D frame structures. Few studies conduct performance comparisons between two different modal strain energy based methods. The objective of this paper is to investigate and compare the effectiveness of a traditional modal strain energy method(Stubbs index) and a recently developed modal strain energy decomposition(MSED) method for damage localization, for such a purpose both simulated and measured data from an offshore platform model being used. Particularly, the mode shapes used in the damage localization are identified and synthesized from only two measurements of one damage scenario because of the limited number of sensors. The two methods were first briefly reviewed. Next, using a 3D offshore platform model, the damage detection algorithms were implemented with different levels of damage severities for both single damage and multiple damage cases. Finally, a physical model of an offshore steel platform was constructed for modal testing and for validating the applicability. Results indicate that the MSED method outperforms the Stubbs index method for structural damage detection.展开更多
The aim of this paper is to conduct experimental modal analysis and numerical simulation to verify the structural characteristics of a deployable-retractable wing for aircraft and spacecraft. A modal impact test was c...The aim of this paper is to conduct experimental modal analysis and numerical simulation to verify the structural characteristics of a deployable-retractable wing for aircraft and spacecraft. A modal impact test was conducted in order to determine the free vibration characteristics. Natural frequencies and vibration mode shapes were obtained via measurement in LMS Test. Lab. The frequency response functions were identified and computed by force and acceleration signals, and then mode shapes of this morphing wing structure were subsequently identified by PolyMAX modal parameter estimation method. FEM modal analysis was also implemented and its numerical results convincingly presented the mode shape and natural frequency characteristics were in good agreement with those obtained from experimental modal analysis. Experimental study in this paper focuses on the transverse response of morphing wing as its moveable part is deploying or retreating. Vibration response to different rotation speeds have been collected, managed and analyzed through the use of comparison methodology with each other. Evident phenomena have been discovered including the resonance on which most analysis is focused because of its potential use to generate large amplitude vibration of specific frequency or to avoid such resonant frequencies from a wide spectrum of response. Manufactured deployable-retractable wings are studied in stage of experimental modal analysis, in which some nonlinear vibration resulted should be particularly noted because such wing structure displays a low resonant frequency which is always optimal to be avoided for structural safety and stability.展开更多
Mode shape has become a hotspot of vibration-based damage detection in plates.Two-dimensional(2D)modal curvature(MC2D),derived from mode shapes,is a prevailing physical quantity used to indicate damage.Unfortunately,t...Mode shape has become a hotspot of vibration-based damage detection in plates.Two-dimensional(2D)modal curvature(MC2D),derived from mode shapes,is a prevailing physical quantity used to indicate damage.Unfortunately,the physical mechanism of MC2 Dfor characterizing damage in plates has not been clarified to date.In contrast,one-dimensional(1D)modal curvature(MC1D)has explicit physical mechanism to portray damage in beams.Unresolved physical mechanism of MC2 Dseverely hampers its applications for damage identification in plates.To address this deficiency,the clarification mechanism of MC2 Dis investigated to identify damage.With the clarified mechanism,numerical and experimental cases are used to demonstrate the effectiveness of MC2 Din detecting damage in plates.展开更多
文摘A technique to extract real modes from the identified complex modes is presented in this paper, which enables the normalized real mode shapes, modal masses, and full or reduced mass and stiffness matrices to be obtained. The theoretical derivation of the method is provided in detail. An 11-DOF vibration system is used to validate the algorithm, and to analyze the effects of the number of modes utilized and measurement DOFs on the extraction results. Finally, the method is used to extract real modes from both experimental modal analysis and operational modal analysis.
基金Supported by the National Natural Science Foundation of China （51209189, 51379196）, and the Natural Science Foundation of Shandong Province （ZR2013 EEQ006, ZR2011 EL049）
基金supported by the National Basic Research Program of China (2011CB013704)863 project (2008AA092701-5)+1 种基金the National Natural Science Foundation of China (50909088, 51010009, 51379196)the Program for New Century Excellent Talents in University (NCET-10-0762)
文摘Modal strain energy based methods for damage detection have received much attention. However, most of published articles use numerical methods and some studies conduct modal tests with simple 1D or 2D structures to verify the damage detection algorithms. Only a few studies utilize modal testing data from 3D frame structures. Few studies conduct performance comparisons between two different modal strain energy based methods. The objective of this paper is to investigate and compare the effectiveness of a traditional modal strain energy method(Stubbs index) and a recently developed modal strain energy decomposition(MSED) method for damage localization, for such a purpose both simulated and measured data from an offshore platform model being used. Particularly, the mode shapes used in the damage localization are identified and synthesized from only two measurements of one damage scenario because of the limited number of sensors. The two methods were first briefly reviewed. Next, using a 3D offshore platform model, the damage detection algorithms were implemented with different levels of damage severities for both single damage and multiple damage cases. Finally, a physical model of an offshore steel platform was constructed for modal testing and for validating the applicability. Results indicate that the MSED method outperforms the Stubbs index method for structural damage detection.
文摘The aim of this paper is to conduct experimental modal analysis and numerical simulation to verify the structural characteristics of a deployable-retractable wing for aircraft and spacecraft. A modal impact test was conducted in order to determine the free vibration characteristics. Natural frequencies and vibration mode shapes were obtained via measurement in LMS Test. Lab. The frequency response functions were identified and computed by force and acceleration signals, and then mode shapes of this morphing wing structure were subsequently identified by PolyMAX modal parameter estimation method. FEM modal analysis was also implemented and its numerical results convincingly presented the mode shape and natural frequency characteristics were in good agreement with those obtained from experimental modal analysis. Experimental study in this paper focuses on the transverse response of morphing wing as its moveable part is deploying or retreating. Vibration response to different rotation speeds have been collected, managed and analyzed through the use of comparison methodology with each other. Evident phenomena have been discovered including the resonance on which most analysis is focused because of its potential use to generate large amplitude vibration of specific frequency or to avoid such resonant frequencies from a wide spectrum of response. Manufactured deployable-retractable wings are studied in stage of experimental modal analysis, in which some nonlinear vibration resulted should be particularly noted because such wing structure displays a low resonant frequency which is always optimal to be avoided for structural safety and stability.
基金supported by the Key Program of the National Natural Science Foundation of China (No. 11132003)the Qing Lan Projectthe Fundamental Research Funds for the Central Universities (Nos. 2012B05814,2014B03914)
文摘Mode shape has become a hotspot of vibration-based damage detection in plates.Two-dimensional(2D)modal curvature(MC2D),derived from mode shapes,is a prevailing physical quantity used to indicate damage.Unfortunately,the physical mechanism of MC2 Dfor characterizing damage in plates has not been clarified to date.In contrast,one-dimensional(1D)modal curvature(MC1D)has explicit physical mechanism to portray damage in beams.Unresolved physical mechanism of MC2 Dseverely hampers its applications for damage identification in plates.To address this deficiency,the clarification mechanism of MC2 Dis investigated to identify damage.With the clarified mechanism,numerical and experimental cases are used to demonstrate the effectiveness of MC2 Din detecting damage in plates.
