Earthquake is a kind of sudden and destructive random excitation in nature.It is significant to determine the probability distribution characteristics of the corresponding dynamic indicators to ensure the safety and t...Earthquake is a kind of sudden and destructive random excitation in nature.It is significant to determine the probability distribution characteristics of the corresponding dynamic indicators to ensure the safety and the stability of structures when the intensive seismic excitation,the intensity of which is larger than 7,acts in train-bridge system.Firstly,the motion equations of a two-dimensional train-bridge system under the vertical random excitation of track irregularity and the vertical seismic acceleration are established,where the train subsystem is composed of 8 mutually independent vehicle elements with 48 degrees of freedom,while the single-span simple supported bridge subsystem is composed of 102D beam elements with 20 degrees of freedom on beam and 2 large mass degrees of freedom at the support.Secondly,Monte Carlo method and pseudo excitation method are adopted to analyze the statistical parameters of the system.The power spectrum density of random excitation is used to define a series of non-stationary pseudo excitation in pseudo excitation method and the trigonometric series of random vibration history samples in Monte Carlo method,respectively solved by precise integral method and Newmark-βmethod through the inter-system iterative procedure.Finally,the results are compared with the case under the weak seismic excitation,and show that the samples of vertical acceleration response of bridge and the offload factor of train obeys the normal distribution.In a high probability,the intensive earthquakes pose a greater threat to the safety and stability of bridges and trains than the weak ones.展开更多
To study the stiffness distribution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the gird...To study the stiffness distribution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the girder with double ribs. Based on the simplified model four stiffness formulae were deduced according to Hamilton principle. These formulae reflect well the contribution of the flexural, shearing, free torsion and restricted torsion deformation, respectively. An identification method about modal parameters was put forward by combining method of peak value and power spectral density according to modal test under ambient excitation. The dynamic finite element method analysis and modal test were carried out in a long-span concrete cable-stayed bridge. The results show that the errors of frequencies between theoretical analysis and test results are less than 10% mostly, and the most important modal parameters for cable-stayed bridge are determined to be the longitudinal floating mode, the first vertical flexural mode and the first torsional mode, which demonstrate that the method of stiffness distribution for three beams model is accurate and method to identify modal parameters is effective under ambient excitation modal test.展开更多
The understanding of the excitation mechanism of ultra high frequency (UHF) electromagnetic waves (EW) is essential for ap- plying UHF method to partial discharge (PD) detection. Since the EW induced by PD in gas insu...The understanding of the excitation mechanism of ultra high frequency (UHF) electromagnetic waves (EW) is essential for ap- plying UHF method to partial discharge (PD) detection. Since the EW induced by PD in gas insulated switchgear (GIS) contains not only transverse electromagnetic (TEM) wave, but also high-order transverse electric (TE) and high-order transverse magnetic (TM) waves, we analyzed the proportions between the TEM wave and the high order waves, as well as the influence of the PD position on this proportion, using the finite different time domain (FDTD) method. According to the unique characteristics of the waves, they are separated only ap- proximately. It is found that the high-order mode is the main component, more than 70%, of the electric field around the enclosure of GIS, and that with the increasing distance between PD source and inner conductors, the low frequency ( below about 800 MHz) component of EW decreases, but the high frequency component (above 1 GHz) increases, meanwhile the proportion of high-order components in EW could reach 77% from 70%. It concluded that the closer the PD source to the enclosure is, the easier high order EW may be excited.展开更多
针对海上浮式风机复杂的受荷环境,特别是持续、周期性的海浪作用带来的疲劳损伤隐患,对其在波浪耦合作用下的疲劳性能展开了研究,给出了一种浮式风机长期视角下的疲劳损伤评估方法。以Spar型海上浮式风机为对象,基于拉格朗日方程建立了...针对海上浮式风机复杂的受荷环境,特别是持续、周期性的海浪作用带来的疲劳损伤隐患,对其在波浪耦合作用下的疲劳性能展开了研究,给出了一种浮式风机长期视角下的疲劳损伤评估方法。以Spar型海上浮式风机为对象,基于拉格朗日方程建立了其8-DOF(dgree of freedom)的波浪耦合作用非线性模型,并验证了所建模型的准确性,随后在所建模型基础上根据所提方法对其疲劳性能进行了探讨。结果表明,浮式风机的疲劳损伤与波浪载荷特性关系很大,不同工况下表现出不同的损伤性能,由于海况条件的随机性,仅按传统方法对风机进行疲劳估计不足以准确了解其疲劳性能,还需进行长期视角下的疲劳分析。而且风机塔架根部疲劳损伤的峰值出现在塔架自振周期附近,而长期疲劳损伤的峰值则出现在海域高概率海况周期范围,因此应尽量使风机的自振周期避开其峰值周期,从而避免风机损伤的高位叠加,减小疲劳损伤。分析还表明了所提基于蒙特卡洛法的浮式风机长期疲劳计算方法的有效性,精度高且耗时少,提出的改进算法能使输出结果波动变小、稳定性增强,结果也更为精确。展开更多
对含有分数阶微分项和参数激励的Duffing⁃van der Pol振子的动力学行为进行了研究,分析了在黏惯性(1≤p≤2)和参数激励共同作用下系统的各项参数对系统幅频曲线的影响。采用平均法分析此系统,用等效线性阻尼和等效质量的概念处理分数阶...对含有分数阶微分项和参数激励的Duffing⁃van der Pol振子的动力学行为进行了研究,分析了在黏惯性(1≤p≤2)和参数激励共同作用下系统的各项参数对系统幅频曲线的影响。采用平均法分析此系统,用等效线性阻尼和等效质量的概念处理分数阶微分项,得到系统的近似解析解。将所得近似解析解与数值解进行比较,二者具有较高的吻合度,证明了解析解的正确性。分析了系统参数对幅频响应曲线的影响,发现共振峰值、共振频率、共振区域、多值解的范围和解的数量都会受到系统参数的影响。经过分析发现,外激励幅值和分数阶微分项系数在一定程度上会抑制参数激励的效果。展开更多
基金Project(52178101) supported by the National Natural Science Foundation of China。
文摘Earthquake is a kind of sudden and destructive random excitation in nature.It is significant to determine the probability distribution characteristics of the corresponding dynamic indicators to ensure the safety and the stability of structures when the intensive seismic excitation,the intensity of which is larger than 7,acts in train-bridge system.Firstly,the motion equations of a two-dimensional train-bridge system under the vertical random excitation of track irregularity and the vertical seismic acceleration are established,where the train subsystem is composed of 8 mutually independent vehicle elements with 48 degrees of freedom,while the single-span simple supported bridge subsystem is composed of 102D beam elements with 20 degrees of freedom on beam and 2 large mass degrees of freedom at the support.Secondly,Monte Carlo method and pseudo excitation method are adopted to analyze the statistical parameters of the system.The power spectrum density of random excitation is used to define a series of non-stationary pseudo excitation in pseudo excitation method and the trigonometric series of random vibration history samples in Monte Carlo method,respectively solved by precise integral method and Newmark-βmethod through the inter-system iterative procedure.Finally,the results are compared with the case under the weak seismic excitation,and show that the samples of vertical acceleration response of bridge and the offload factor of train obeys the normal distribution.In a high probability,the intensive earthquakes pose a greater threat to the safety and stability of bridges and trains than the weak ones.
基金Project(50608008) supported by the National Natural Science Foundation of Chinaproject(20050536002) supported by the Specialized Research Fund for the Doctoral Program of Higher Education
文摘To study the stiffness distribution of girder and the method to identify modal parameters of cable-stayed bridge, a simplified dynamical finite element method model named three beams model was established for the girder with double ribs. Based on the simplified model four stiffness formulae were deduced according to Hamilton principle. These formulae reflect well the contribution of the flexural, shearing, free torsion and restricted torsion deformation, respectively. An identification method about modal parameters was put forward by combining method of peak value and power spectral density according to modal test under ambient excitation. The dynamic finite element method analysis and modal test were carried out in a long-span concrete cable-stayed bridge. The results show that the errors of frequencies between theoretical analysis and test results are less than 10% mostly, and the most important modal parameters for cable-stayed bridge are determined to be the longitudinal floating mode, the first vertical flexural mode and the first torsional mode, which demonstrate that the method of stiffness distribution for three beams model is accurate and method to identify modal parameters is effective under ambient excitation modal test.
基金Project supported by National High-tech Research and Development Program of China (863 Program) (2011AA05A121)
文摘The understanding of the excitation mechanism of ultra high frequency (UHF) electromagnetic waves (EW) is essential for ap- plying UHF method to partial discharge (PD) detection. Since the EW induced by PD in gas insulated switchgear (GIS) contains not only transverse electromagnetic (TEM) wave, but also high-order transverse electric (TE) and high-order transverse magnetic (TM) waves, we analyzed the proportions between the TEM wave and the high order waves, as well as the influence of the PD position on this proportion, using the finite different time domain (FDTD) method. According to the unique characteristics of the waves, they are separated only ap- proximately. It is found that the high-order mode is the main component, more than 70%, of the electric field around the enclosure of GIS, and that with the increasing distance between PD source and inner conductors, the low frequency ( below about 800 MHz) component of EW decreases, but the high frequency component (above 1 GHz) increases, meanwhile the proportion of high-order components in EW could reach 77% from 70%. It concluded that the closer the PD source to the enclosure is, the easier high order EW may be excited.
文摘针对海上浮式风机复杂的受荷环境,特别是持续、周期性的海浪作用带来的疲劳损伤隐患,对其在波浪耦合作用下的疲劳性能展开了研究,给出了一种浮式风机长期视角下的疲劳损伤评估方法。以Spar型海上浮式风机为对象,基于拉格朗日方程建立了其8-DOF(dgree of freedom)的波浪耦合作用非线性模型,并验证了所建模型的准确性,随后在所建模型基础上根据所提方法对其疲劳性能进行了探讨。结果表明,浮式风机的疲劳损伤与波浪载荷特性关系很大,不同工况下表现出不同的损伤性能,由于海况条件的随机性,仅按传统方法对风机进行疲劳估计不足以准确了解其疲劳性能,还需进行长期视角下的疲劳分析。而且风机塔架根部疲劳损伤的峰值出现在塔架自振周期附近,而长期疲劳损伤的峰值则出现在海域高概率海况周期范围,因此应尽量使风机的自振周期避开其峰值周期,从而避免风机损伤的高位叠加,减小疲劳损伤。分析还表明了所提基于蒙特卡洛法的浮式风机长期疲劳计算方法的有效性,精度高且耗时少,提出的改进算法能使输出结果波动变小、稳定性增强,结果也更为精确。
文摘对含有分数阶微分项和参数激励的Duffing⁃van der Pol振子的动力学行为进行了研究,分析了在黏惯性(1≤p≤2)和参数激励共同作用下系统的各项参数对系统幅频曲线的影响。采用平均法分析此系统,用等效线性阻尼和等效质量的概念处理分数阶微分项,得到系统的近似解析解。将所得近似解析解与数值解进行比较,二者具有较高的吻合度,证明了解析解的正确性。分析了系统参数对幅频响应曲线的影响,发现共振峰值、共振频率、共振区域、多值解的范围和解的数量都会受到系统参数的影响。经过分析发现,外激励幅值和分数阶微分项系数在一定程度上会抑制参数激励的效果。
