Winkler地基梁在温度场中受简谐激励3次超谐共振分析

本文研究W inkler地基梁在温度场中受简谐激励作用的3次超谐共振问题,应用弹性理论和Galerk in方法建立W inkler地基梁在温度场中受简谐激励作用的非线性动力方程,根据非线性振动的多尺度法求得系统满足3次超谐共振情况的一次近似解,分析了温度、阻尼、激励幅值、地基刚度等参数对系统的影响。     

Winkler地基梁在温度场中受简谐激励的主共振分析

研究W inkler地基梁在温度场中受简谐激励作用的主共振问题。应用弹性理论和Galerk in方法建立W inkler地基梁在温度场中受简谐激励作用的非线性动力方程。应用非线性振动的多尺度法,求得系统主共振的近似解。分析不同参数对主共振响应曲线的影响。     

简谐横向荷载作用下弹性地基上不可伸长梁的1/2次亚谐共振响应分析

基于已建立的弹性地基上不可伸长梁的非线性动力学模型,本文针对简谐横向荷载作用下梁的1/2次亚谐共振响应进行研究。利用弹性地基梁的非线性运动方程和多尺度方法,求得梁1/2次亚谐共振响应的二次近似解。进而,运用幅频响应曲线对梁的亚谐共振响应进行研究,并分析了边界条件、地基模型、Winkler参数等对梁非线性共振响应的影响。结果表明:三参数地基模型中弹性层的引入对其支承梁的亚谐共振响应影响显著;临界激励幅值决定了弹性地基梁1/2次亚谐共振响应非平凡解的存在性;梁端约束条件在一定程上改变了Winkler参数对梁非线性动力响应的作用效应。     

非线性弹性地基上圆形薄板三次超谐共振

本文研究非线性地基上圆形薄板受简谐激励的次谐波共振问题。按照弹性力学理论建立非线性地基上圆形薄板受简谐激励的动力学方程。利用Galerk in方法将其转化为非线性振动方程。应用非线性振动的多尺度法求得系统满足3次超谐共振条件的一次近似解,并进行数值计算。分析阻尼、地基系数、调谐值、激励等参数对共振响应曲线的影响。     

简谐横荷载作用下Winkler地基上有限长梁1/3次亚谐共振分析

基于Winkler地基模型及Euler - Bernoulli梁理论,建立了Winkler地基上有限长梁的非线性运动方程.运用Galerkin方法对运动方程进行一阶模态截断,得到离散的非线性振动方程,利用多尺度法求得该系统1/3次亚谐共振的一阶近似解.分析了长细比、弹性模量、地基刚度、阻尼、密度等参数对其亚谐共振幅频响...     

地基-非线性结构相互作用体系的 超谐和亚谐振动

本文对上部结构的以线型恢复力进行最小二乘法拟合，得到类似于Duffing振子的恢复力曲线模型，地基上简化为集中参数模型，运用多尺度法研究地基－结构相互作用体系在强激励下当频率接近结构的三分之一固有频率（超谐共振），三倍固有频率（亚谐共振）时的非线性动力行为，并通过算例得到了异频振动时一些有益的结论。     

地基-非线性结构相互作用空间效应的超谐和亚谐共振研究

建立了考虑空间效应的无质量基础-地基-结构相互作用模型,将模型简化为三个自由度体系,得到了考虑结构水平侧移和扭转位移相耦合的振动方程,用多尺度法研究了体系在强激励下的超谐共振和亚谐共振行为,通过算例分析得到了一些不同于线性体系的结论,为结构非线性分析提供了更深刻的理论依据。     

考虑非对称效应的非线性结构超谐共振与亚谐共振

本文将考虑空间效应非对称刚度的单层结构简化为三个自由度体系，用多尺度法研究了体系在强激励下的超谐共振与亚谐共振时的动力行为，通过算例分析得到一些不同于线性结构的结论，为结构非线性抗震分析提供了途径。     

Winkler地基上有限长梁联合共振分析

为进一步完善弹性地基上梁的非线性振动理论以及满足实际工程的需要,本文对三种联合共振情况进行了研究。文中基于已建立的Winkler地基上有限长梁的非线性振动方程,运用Galerkin离散法以及多尺度法推导其稳态运动方程组,分析了主/次联合共振时,结构参数及初始条件对系统幅频响应曲线、调谐-相位曲线的影响,初步探讨了主/超联合共振、次/超联合共振的基本性质。研究结果表明:当且仅当两个激励频率是可公度关系时,联合共振才存在稳态响应;对于一个给定的调谐参数,系统最多存在七个解,而解的最终形式是由初始条件决定;系统参数及初始条件的微小变动,可能会激烈地改变系统的响应;工程中为了较好地抑制结构的振动,必须选择合适的方法提高系统的刚度。     

Winkler地基上有限长梁的组合共振响应分析

基于Winkler地基模型及Euler-Bernoulli梁理论,建立了两个横向激励共同作用下Winkler地基上有限长梁的组合共振模型,运用Galerkin方法和多尺度方法求得组合共振幅频响应方程,进而研究地基刚度、弹性模量、黏滞阻尼、外激励幅值等主要参数对其幅频响应曲线的影响。研究结果表明:增大地基刚度、弹性模量、黏滞阻尼或减小外激励幅值均可减小梁的响应幅值。黏滞阻尼的变化对影响的共振区域并无影响。     

Steady state rocking response of rigid blocks part 2: Experiment

The results of an experimental investigation on the rocking response of rigid blocks subjected to sinusoidal base motion is presented. It is shown that two common types of steady state response are harmonic and 1/3 subharmonic response. The measured steady state response amplitudes correlate well with theoretical predictions for both harmonic and 1/3 subharmonic responses. Within each type of steady state response, theoretical studies show that the system may respond in either a symmetric or an unsymmetric mode. A symmetric mode denotes that the block oscillates about a mean zero position while an unsymmetric mode implies the mean position of oscillation is at an inclined position. One form of unsymmetric response was observed in the experiment. In addition, almost periodic responses were also observed in the experiment, although their existence has not been reported in theoretical studies.     

Effective elimination of subharmonic ghost events from vibroseis data

Harmonic or subharmonic noise is often present in vibroseis data as reverberation‐like, laterally coherent bands occurring parallel to and before or after, the main events. Such periodic noise is typically generated during the standard correlation process when the actual source signal travelling through the subsurface is, for whatever reason, different from the desired source signal, i.e., the pilot‐sweep controlling the baseplate and used for correlation. A typical cause can be that harmonic or subharmonic frequency partials are generated in addition to the vibroseis sweep's desired fundamental frequencies. These harmonics produce strong ‘ghost events’ during correlation of the geophone trace with the pilot‐sweep, originating from additional correlations between the fundamental and harmonic frequencies. Especially subharmonic ‘ghosts’ will overlap with ‘good’ fundamental signals, since for typically used up‐sweeps they are folded to later traveltimes, where the signal/noise‐ratio is already lower, thus aggravating or preventing a reliable interpretation of possible later reflections. Here, a method is introduced to remove these unwanted noise trains (with only negligible impact on the fundamental signal) by transforming the seismogram traces into a so‐called ‘(sub)harmonic domain’. In this domain, the respective harmonic noise portions are focused and separated from the fundamental signals, enabling easier detection and appropriate suppression. After back‐transformation to the x‐T domain, the records are free from the corresponding harmonic contamination and can then be processed as usual. The method operates in a data‐driven fashion, i.e., the traces are not uniformly processed but are processed depending upon their actual (sub)harmonic content. The decontamination procedure can be applied universally, i.e., to uncorrelated/correlated and/or vertically unstacked/stacked data either in a manual, semiautomated or fully automated manner. The method works perfectly for synthetic vibroseis traces with or without harmonic/subharmonic portions. The application to real, crustal‐scale vibroseis records that were acquired in 2006 in the Dead Sea region, Israel and that were severely contaminated by subharmonic ground‐roll ghosts covering reflectivity from the basement to the Moho, shows the robustness and success of the presented method.     

DYNAMIC RESPONSE OF EQUIPMENT IN STRUCTURES WITH SLIDING SUPPORT

The dynamic behaviour of a single degree-of-freedom (DOF) equipment mounted on a sliding primary structures subjected to harmonic and earthquake ground motions is studied numerically. To deal with the discontinuity nature of sliding structural systems, in this work the fictitious spring model is adopted. With the problem formulated in a state space form, an incremental numerical scheme capable of dealing with multi-DOF sliding structural systems is proposed for solving the time history responses. Numerical examples excited by harmonic and real earthquake ground motions are considered in order to study the following three effects: (1)the variation of the frictional coefficient of the sliding support, (2)subharmonic resonance and (3)effect of tuning (i.e. when the frequency of the equipment is coincident with or close to the fundamental frequency of the primary structure) on the mounted equipment. The dynamic characteristics of the mounted equipment are highlighted in the analysis of the numerical examples. © 1997 by John Wiley & Sons, Ltd.     

Seismic response of tall building considering soil-pile-structure interaction

The seismic behavior of tall buildings can be greatly affected by non-linear soil-pile interaction during strong earthquakes. In this study a 20-storey building is examined as a typical structure supported on a pile foundation for different conditions: (1) rigid base, i.e. no deformation in the foundation: (2) linear soil-pile system; and (3) nonlinear soil-pile system. The effects of pile foundation displacements on the behavior of tall building are investigated, and compared with the behavior of buildings supported on shallow foundation. With a model of non-reflective boundary between the near field and far field, Novak’s method of soil-pile interaction is improved. The computation method for vibration of pile foundations and DYNAN computer program are introduced comprehensively. A series of dynamic experiments have been done on full-scale piles, including single pile and group, linear vibration and nonlinear vibration, to verify the validity of boundary zone model.