A giant earthquake of magnitude 9.0 occurred in Pacific Ocean off of Tohoku District Japan on March 11,2011. The highest seismic intensity of 7 in JMA scale was recorded in Miyagi. In the Tohoku district, around 230 b...A giant earthquake of magnitude 9.0 occurred in Pacific Ocean off of Tohoku District Japan on March 11,2011. The highest seismic intensity of 7 in JMA scale was recorded in Miyagi. In the Tohoku district, around 230 buildings are seismically isolated （hereafter, SI） mainly by elastomeric isolators （seismic rubber bearings）. According to the official survey reports by several organizations （for example）, the records of those buildings have verified the effectiveness of the seismic isolation. The response acceleration of the SI buildings was reduced by 30% to 50% of the input ground acceleration. Additionally, the difference of the conditions inside the room between SI and the fixed-base buildings was obvious as well as the damage in main structures of the buildings. The displacements of the isolators by the earthquake were around 200 mm according to the records of the instruments. As a result, the performance of SI buildings and the elastomeric isolators in the Tohoku District -- Off the Pacific Ocean Earthquake 2011 were excellent, and the efficiency of the seismic isolation was verified by the records of many buildings in wide area.展开更多
Two types of elastomeric vibration isolators used for equipment vibration isolation in aerospace vehicles are considered for the present study. These isolators are constructed using elastomers mounted in steel encasin...Two types of elastomeric vibration isolators used for equipment vibration isolation in aerospace vehicles are considered for the present study. These isolators are constructed using elastomers mounted in steel encasings. These isolators are initially deformed statically and dynamic loads are applied on the deformed configuration. To capture the static deformation, equivalent static load corresponding to its load rating and specified displacements are created. Static deformation is computed using Finite Element methods with four node axi-symmetric element which include the geometric non-linear effect for steel and with standard Yeoh hyper-elastic material model for elastomers(Muhammed and Zu, 2012) [1]. Yeoh material constants are derived from uni-axial tension test data of the elastomer specimen. These isolators are subjected to harmonic and random excitations in the pre-deformed state. For numerical analysis, elastomeric constants at dynamic conditions are obtained as complex function of frequency using Dynamic Mechanical Analyzer(DMA) for a range of frequencies. The standard material model of Yeoh is modified incorporating frequency dependant material characteristics and damping in the range of frequencies of interest. A multiplicative non-separable variables law is derived for Yeoh material model to include the effect of static pre-stress, based on the methodology given in literature(Nashif et al.,1985;Beda et al., 2014) [2,3]. The modifications of Yeoh model suitable for frequency domain analysis is the novelty in the present study. In the analysis, while dynamic loads are applied, the configuration is updated considering initial static loading. The frequency response of the isolators is computed using material properties evaluated at progressive dynamic strains until a match in natural frequency is observed. Appropriate damping corrections are then incorporated to match the test observed transmissibility. Then updated material properties are used to compute the random response which showed good agreement with results of experiments, validating the approach taken for the development of this model.展开更多
Vibration isolation is an effective method to mitigate unwanted disturbances arising from dynamic loading conditions. With smart materials as suitable substitutes, the conventional passive isolators have attained attr...Vibration isolation is an effective method to mitigate unwanted disturbances arising from dynamic loading conditions. With smart materials as suitable substitutes, the conventional passive isolators have attained attributes of semi-active as well as the active control system. In the present study, the non-homogenous field-dependent isolation capabilities of the magnetorheological elastomer are explored under torsional vibrations. Torsional natural frequency was measured using the serial arrangement of accelerometers. Novel methods are introduced to evaluate the torsional stiffness variations of the isolator for a semi-definite and a motor-coupled rotor system. For the semi-definite system, the isolation effect was studied using the frequency response functions from the modal analysis. The speed-dependent variations for motor-coupled rotor system were assessed using the shift in frequency amplitudes from torque transducers. Finite element method magnetics was used to study the variations in the non-homogenous magnetic field across the elastomer. The response functions for the semi-definite rotor system reveal a shift in the frequency in the effect of the magnetic field. Speed-dependent variations in the frequency domain indicate an increment of 9% in the resonant frequency of the system.展开更多
改进了铅芯叠层钢板橡胶垫隔震装置的 Park 模型,提出其双向弹塑性恢复力模型。建议的模型克服了 Park 模型不能从橡胶垫力学试验曲线上直观获取所需参数的缺点。采用本文建议模型的结构分析程序 HBTA2.0可以方便地用于实际隔震结构的...改进了铅芯叠层钢板橡胶垫隔震装置的 Park 模型,提出其双向弹塑性恢复力模型。建议的模型克服了 Park 模型不能从橡胶垫力学试验曲线上直观获取所需参数的缺点。采用本文建议模型的结构分析程序 HBTA2.0可以方便地用于实际隔震结构的弹塑性动力分析,计算结果也更为合理。展开更多
文摘A giant earthquake of magnitude 9.0 occurred in Pacific Ocean off of Tohoku District Japan on March 11,2011. The highest seismic intensity of 7 in JMA scale was recorded in Miyagi. In the Tohoku district, around 230 buildings are seismically isolated （hereafter, SI） mainly by elastomeric isolators （seismic rubber bearings）. According to the official survey reports by several organizations （for example）, the records of those buildings have verified the effectiveness of the seismic isolation. The response acceleration of the SI buildings was reduced by 30% to 50% of the input ground acceleration. Additionally, the difference of the conditions inside the room between SI and the fixed-base buildings was obvious as well as the damage in main structures of the buildings. The displacements of the isolators by the earthquake were around 200 mm according to the records of the instruments. As a result, the performance of SI buildings and the elastomeric isolators in the Tohoku District -- Off the Pacific Ocean Earthquake 2011 were excellent, and the efficiency of the seismic isolation was verified by the records of many buildings in wide area.
文摘Two types of elastomeric vibration isolators used for equipment vibration isolation in aerospace vehicles are considered for the present study. These isolators are constructed using elastomers mounted in steel encasings. These isolators are initially deformed statically and dynamic loads are applied on the deformed configuration. To capture the static deformation, equivalent static load corresponding to its load rating and specified displacements are created. Static deformation is computed using Finite Element methods with four node axi-symmetric element which include the geometric non-linear effect for steel and with standard Yeoh hyper-elastic material model for elastomers(Muhammed and Zu, 2012) [1]. Yeoh material constants are derived from uni-axial tension test data of the elastomer specimen. These isolators are subjected to harmonic and random excitations in the pre-deformed state. For numerical analysis, elastomeric constants at dynamic conditions are obtained as complex function of frequency using Dynamic Mechanical Analyzer(DMA) for a range of frequencies. The standard material model of Yeoh is modified incorporating frequency dependant material characteristics and damping in the range of frequencies of interest. A multiplicative non-separable variables law is derived for Yeoh material model to include the effect of static pre-stress, based on the methodology given in literature(Nashif et al.,1985;Beda et al., 2014) [2,3]. The modifications of Yeoh model suitable for frequency domain analysis is the novelty in the present study. In the analysis, while dynamic loads are applied, the configuration is updated considering initial static loading. The frequency response of the isolators is computed using material properties evaluated at progressive dynamic strains until a match in natural frequency is observed. Appropriate damping corrections are then incorporated to match the test observed transmissibility. Then updated material properties are used to compute the random response which showed good agreement with results of experiments, validating the approach taken for the development of this model.
基金the support from SOLVE: The Virtual Lab @ NITK (Grant number: No.F.16-35/2009-DL, Ministry of Human Resources Development)
文摘Vibration isolation is an effective method to mitigate unwanted disturbances arising from dynamic loading conditions. With smart materials as suitable substitutes, the conventional passive isolators have attained attributes of semi-active as well as the active control system. In the present study, the non-homogenous field-dependent isolation capabilities of the magnetorheological elastomer are explored under torsional vibrations. Torsional natural frequency was measured using the serial arrangement of accelerometers. Novel methods are introduced to evaluate the torsional stiffness variations of the isolator for a semi-definite and a motor-coupled rotor system. For the semi-definite system, the isolation effect was studied using the frequency response functions from the modal analysis. The speed-dependent variations for motor-coupled rotor system were assessed using the shift in frequency amplitudes from torque transducers. Finite element method magnetics was used to study the variations in the non-homogenous magnetic field across the elastomer. The response functions for the semi-definite rotor system reveal a shift in the frequency in the effect of the magnetic field. Speed-dependent variations in the frequency domain indicate an increment of 9% in the resonant frequency of the system.
基金Supported by National Basic Research Program of China(973 Program)(2011CB013606),(973 Program)(2012CB723304)by the National Natural Science Foundation of China(90815027)by National Science and Technology Support Projects(2009BAJ28B03,2012BAJ07B02)
