Based on the motion differential equations of vibration and acoustic coupling system for thin elastic spherical shell with an elastic plate attached to its internal surface,in which Dirac-δ functions are employed to ...Based on the motion differential equations of vibration and acoustic coupling system for thin elastic spherical shell with an elastic plate attached to its internal surface,in which Dirac-δ functions are employed to introduce the moments and forces applied by the attachment on the surface of shell,by means of expanding field quantities as Legendre series,a semi-analytic solution is derived for the vibration and acoustic radiation from a submerged stiffened spherical shell with a deck-type internal plate,which has a satisfactory computational effectiveness and precision for an arbitrary frequency range.It is easy to analyze the effect of the internal plate on the acoustic radiation field by using the formulas obtained by the method proposed.It is concluded that the internal plate can significantly change the mechanical and acoustic characteristics of shell,and give the coupling system a very rich resonance frequency spectrum.Moreover,the method can be used to study the acoustic radiation mechanism in similar structures as the one studied here.展开更多
The impact of vibrations due to underground trains on Beijing metro line 15 on sensitive equipment in the Institute of Microelectronics of Tsinghua University was discussed to propose a viable solution to mitigate the...The impact of vibrations due to underground trains on Beijing metro line 15 on sensitive equipment in the Institute of Microelectronics of Tsinghua University was discussed to propose a viable solution to mitigate the vibrations.Using the state-of-the-art three-dimensional coupled periodic finite element-boundary element(FE-BE) method,the dynamic track-tunnel-soil interaction model for metro line 15 was used to predict vibrations in the free field at a train speed of 80 km/h.Three types of tracks(direct fixation fasteners,floating slab track and floating ladder track) on the Beijing metro network were considered in the model. For each track,the acceleration response in the free field was obtained.The numerical results show that the influence of vibrations from underground trains on sensitive equipment depends on the track types.At frequencies above 10 Hz,the floating slab track with a natural frequency of 7 Hz can be effective to attenuate the vibrations.展开更多
Circular plates with radially varying thickness, stiffness, and density are widely used for the structural optimization in engineering. The axisymmetric flexural free vibration of such plates, governed by coupled diff...Circular plates with radially varying thickness, stiffness, and density are widely used for the structural optimization in engineering. The axisymmetric flexural free vibration of such plates, governed by coupled differential equations with variable coefficients by use of the Mindlin plate theory, is very difficult to be studied analytically. In this paper, a novel analytical method is proposed to reduce such governing equations for circular plates to a pair of uncoupled and easily solvable differential equations of the Sturm-Liouville type. There are two important parameters in the reduced equations. One describes the radial variations of the translational inertia and fiexural rigidity with the consideration of the effect of Poisson＇s ratio. The other reflects the comprehensive effect of the rotatory inertia and shear deformation. The Heun-type equations, recently well-known in physics, are introduced here to solve the flexural free vibration of circular plates analytically, and two basic differential formulae for the local Heun-type functions are discovered for the first time, which will be of great value in enriching the theory of Heun-type differential equations.展开更多
为研究桥梁抗风型调谐质量阻尼器(tuned mass damper, TMD)对车辆荷载引起结构振动的减振效果,并揭示车载作用下的TMD激振机理,提出了基于模态动能演化的多自由度结构TMD控制方法,确定了安装TMD的最优设计参数和布设位置;考虑桥梁有限...为研究桥梁抗风型调谐质量阻尼器(tuned mass damper, TMD)对车辆荷载引起结构振动的减振效果,并揭示车载作用下的TMD激振机理,提出了基于模态动能演化的多自由度结构TMD控制方法,确定了安装TMD的最优设计参数和布设位置;考虑桥梁有限元模型动力求解的通用性,基于桥梁三维动力分析系统BDANS软件建立了车-桥-TMD动力耦合分析系统;以经典单自由度移动弹簧质量过简支梁模型为研究对象,分析了车-桥-TMD系统振动特性,结合某深水区非通航桥梁抗风型TMD工程实例分析了TMD对车致振动的减振效果和机理。研究结果表明:TMD行程幅值与减振效果呈现正相关特点,即行程幅值越大对车-桥动力效应引起的振动减振效果越好;安装TMD可以显著提高结构的等效阻尼比,满足等效阻尼比>1%的工程需求,提高桥梁结构振动的稳定性;TMD在一定条件下可以减小车辆通过时引发桥梁竖向位移冲击效应,最大可减少3%左右;TMD对车-桥2个子系统的加速度瞬态峰值均起到了一定的抑制效果,尤其对桥梁结构竖向振动加速度作用效果明显,安装TMD后的桥梁跨中竖向振动加速度RMS值减少约20%;对大跨钢箱桥梁而言,相比较小的车辆荷载冲击效应,一阶竖弯呈邻跨反对称特性的桥梁结构在车辆通行过程中更容易激起TMD,使桥梁结构获得更佳的减振效果。展开更多
为了解决传统式调谐质量阻尼器(tuned mass damper, TMD)在控制低频桥梁结构中弹簧静伸长过长的问题,介绍了滑轮式TMD及其用于结构振动控制时的特点,指出滑轮式TMD可以有效减小弹簧静伸长量。以一座人行景观桥为例,研究了采用气动措施...为了解决传统式调谐质量阻尼器(tuned mass damper, TMD)在控制低频桥梁结构中弹簧静伸长过长的问题,介绍了滑轮式TMD及其用于结构振动控制时的特点,指出滑轮式TMD可以有效减小弹簧静伸长量。以一座人行景观桥为例,研究了采用气动措施和滑轮式TMD对该桥的涡振控制效果。风洞试验结果显示,在最优气动措施下,主梁的涡振振幅减少了一半以上,但仍未达到行人舒适性要求。基于Scanlan线性涡激力模型进行滑轮式TMD的优化设计,在气动措施的基础上进一步辅以滑轮式TMD进行涡振控制。分析结果表明,气动措施结合滑轮式TMD进行涡振控制能够满足行人舒适性要求,并确保滑轮式TMD质量块的工作行程不超过限值。通过同时采用气动措施和滑轮式TMD,可以满足主梁涡振限值、TMD弹簧静伸长量和工作行程等多重要求,从而有效控制主梁的涡振现象。本文提出的混合控制方案为类似工程中的涡振控制提供了有益参考,可为工程实践提供指导。展开更多
基金Project supported by the National Natural Science Foundation of China(No.10172038).
文摘Based on the motion differential equations of vibration and acoustic coupling system for thin elastic spherical shell with an elastic plate attached to its internal surface,in which Dirac-δ functions are employed to introduce the moments and forces applied by the attachment on the surface of shell,by means of expanding field quantities as Legendre series,a semi-analytic solution is derived for the vibration and acoustic radiation from a submerged stiffened spherical shell with a deck-type internal plate,which has a satisfactory computational effectiveness and precision for an arbitrary frequency range.It is easy to analyze the effect of the internal plate on the acoustic radiation field by using the formulas obtained by the method proposed.It is concluded that the internal plate can significantly change the mechanical and acoustic characteristics of shell,and give the coupling system a very rich resonance frequency spectrum.Moreover,the method can be used to study the acoustic radiation mechanism in similar structures as the one studied here.
基金Projects(50538010,50848046) supported by the National Natural Science Foundation of ChinaProject(BIL07/07) supported by the Research Council of K.U.Leuven and the National Natural Science Foundation of China
文摘The impact of vibrations due to underground trains on Beijing metro line 15 on sensitive equipment in the Institute of Microelectronics of Tsinghua University was discussed to propose a viable solution to mitigate the vibrations.Using the state-of-the-art three-dimensional coupled periodic finite element-boundary element(FE-BE) method,the dynamic track-tunnel-soil interaction model for metro line 15 was used to predict vibrations in the free field at a train speed of 80 km/h.Three types of tracks(direct fixation fasteners,floating slab track and floating ladder track) on the Beijing metro network were considered in the model. For each track,the acceleration response in the free field was obtained.The numerical results show that the influence of vibrations from underground trains on sensitive equipment depends on the track types.At frequencies above 10 Hz,the floating slab track with a natural frequency of 7 Hz can be effective to attenuate the vibrations.
基金Project supported by the National Natural Science Foundation of China(Nos.11402133,11620162,11321202,and 11532001)
文摘Circular plates with radially varying thickness, stiffness, and density are widely used for the structural optimization in engineering. The axisymmetric flexural free vibration of such plates, governed by coupled differential equations with variable coefficients by use of the Mindlin plate theory, is very difficult to be studied analytically. In this paper, a novel analytical method is proposed to reduce such governing equations for circular plates to a pair of uncoupled and easily solvable differential equations of the Sturm-Liouville type. There are two important parameters in the reduced equations. One describes the radial variations of the translational inertia and fiexural rigidity with the consideration of the effect of Poisson＇s ratio. The other reflects the comprehensive effect of the rotatory inertia and shear deformation. The Heun-type equations, recently well-known in physics, are introduced here to solve the flexural free vibration of circular plates analytically, and two basic differential formulae for the local Heun-type functions are discovered for the first time, which will be of great value in enriching the theory of Heun-type differential equations.
文摘为研究桥梁抗风型调谐质量阻尼器(tuned mass damper, TMD)对车辆荷载引起结构振动的减振效果,并揭示车载作用下的TMD激振机理,提出了基于模态动能演化的多自由度结构TMD控制方法,确定了安装TMD的最优设计参数和布设位置;考虑桥梁有限元模型动力求解的通用性,基于桥梁三维动力分析系统BDANS软件建立了车-桥-TMD动力耦合分析系统;以经典单自由度移动弹簧质量过简支梁模型为研究对象,分析了车-桥-TMD系统振动特性,结合某深水区非通航桥梁抗风型TMD工程实例分析了TMD对车致振动的减振效果和机理。研究结果表明:TMD行程幅值与减振效果呈现正相关特点,即行程幅值越大对车-桥动力效应引起的振动减振效果越好;安装TMD可以显著提高结构的等效阻尼比,满足等效阻尼比>1%的工程需求,提高桥梁结构振动的稳定性;TMD在一定条件下可以减小车辆通过时引发桥梁竖向位移冲击效应,最大可减少3%左右;TMD对车-桥2个子系统的加速度瞬态峰值均起到了一定的抑制效果,尤其对桥梁结构竖向振动加速度作用效果明显,安装TMD后的桥梁跨中竖向振动加速度RMS值减少约20%;对大跨钢箱桥梁而言,相比较小的车辆荷载冲击效应,一阶竖弯呈邻跨反对称特性的桥梁结构在车辆通行过程中更容易激起TMD,使桥梁结构获得更佳的减振效果。
文摘为了解决传统式调谐质量阻尼器(tuned mass damper, TMD)在控制低频桥梁结构中弹簧静伸长过长的问题,介绍了滑轮式TMD及其用于结构振动控制时的特点,指出滑轮式TMD可以有效减小弹簧静伸长量。以一座人行景观桥为例,研究了采用气动措施和滑轮式TMD对该桥的涡振控制效果。风洞试验结果显示,在最优气动措施下,主梁的涡振振幅减少了一半以上,但仍未达到行人舒适性要求。基于Scanlan线性涡激力模型进行滑轮式TMD的优化设计,在气动措施的基础上进一步辅以滑轮式TMD进行涡振控制。分析结果表明,气动措施结合滑轮式TMD进行涡振控制能够满足行人舒适性要求,并确保滑轮式TMD质量块的工作行程不超过限值。通过同时采用气动措施和滑轮式TMD,可以满足主梁涡振限值、TMD弹簧静伸长量和工作行程等多重要求,从而有效控制主梁的涡振现象。本文提出的混合控制方案为类似工程中的涡振控制提供了有益参考,可为工程实践提供指导。
