拱坝-地基动力体系的简化计算模型及其在地震作用下的动力反应分析

通过对拱坝地基的半无限空间动力体系的分析,提出了拱坝－地基动力相互作用问题的简化求解途径,并结合小湾拱坝进行了实际分析。结果表明,这种直接应用于时域求解的简化模型,既反映了影响相互作用的主要因素,又使计算工作量大大减少,结果可靠合理,便于工程上的推广应用,同时为进一步进行非线性体系在时域中的简化计算打下了基础。     

拱坝—地基动力体系的简化计算模型及其在地震作用上的动力反应分析

通过对拱坝地基的半夫限空间动力体系的分析,提出了拱坝－地基动力相互作用问题的简化求解途径,并结合小湾拱坝进行了实验分析。结果表明,这种直接应用于时域求解的简化模型,既反映了影响相互作用的主要因素,又使计算工作量大大减少,结果可靠合理,便于工程上的推广应用,同时为进一步进行非线性体系在时域中的简化计算打下了基础。     

考虑混凝土应变率变化的高拱坝非线性动力响应研究

提出一种新的应变率相关的混凝土非线性弹塑性损伤模型。采用此模型对混凝土拱坝的非线性地震响应作了分析。在综合考虑坝-地基-库水动力相互作用和坝缝非线性接触的基础上，着重研究了混凝土应交率相关效应及加载历史对混凝土极限强度等重要参数及拱坝响应的影响，并与采用不考虑应交率影响的混凝土损伤模型计算结果进行了对比分析。结果表明，拱坝考虑横缝作用后的坝面应变率分布不同于整体拱坝。应交率分布形态不仅可以很好地表征拱坝的振动形态，而且对于高拱坝的动力响应的影响也不可忽略。     

土-基础相互作用隔震体系地震随机响应分析

视地基土为各向同性的弹性半空间,用弹簧-粘性阻尼器模拟土对结构的影响,将地震激励模拟为平稳随机过程,对基础隔震体系的随机响应进行了分析。分析结果表明,地基土的性质对隔震结构有直接影响,但其影响比非隔震结构小得多。     

地基土—多自由度非线性结构相互作用体系的非平稳随机动力响应分析

本文应用一个改进的等效线性化方法探讨了地基土——多自由度非线性结构相互作用体系在随机地震荷载作用下的非平稳动力响应问题。对非线性恢复力模型采用一个具有三线性滞回特性的非线性系统。最后将在平稳Gauss过滤白噪声激励下的非平稳随机响应与Monte-carlo法的统计结果进行了比较,得出了较为满意的结果。     

双参数地基上环板的非线性动力响应

研究双参数地基上环板的大挠度动力响应问题，给出了求解该问题的一种有效方法，即在空间域上运用摄动微分求积法处理非线性边值问题，在时间域上则以三点递推格式的Ｎｅｗｍａｒｋ－β法计算其动力响应。文中同时讨论了不同形式地基对环板在均布阶跃载荷作用下动力响应的影响。     

混凝土大坝抗震中的力学问题

论述了我国混凝土大坝抗震安全性评价的工程背景和指导思想,着重于简介高拱坝体系特点的线性和非线性地震响应分析方法．讨论了混凝土大坝随机地震响应及其抗震可靠度评估方法．此外,还基于大坝混凝土全级配试件动力试验成果,通过三维细观力学分析,探讨了其动态破坏过程和机理及应用CT技术的验证。     

大跨度空间网格结构多点输入反应谱计算方法的研究

根据大跨度空间网格结构的特点,忽略拟静力反应项与动力反应项的耦合项,提出了多点输入反应谱计算的简化方法.该方法所表示的结构地震动反应主要由拟静力响应和动力响应两部分组成,其中拟静力响应是由地面各点输入位移不一致引起的;动力响应部分主要是由结构在地面加速度作用下引起的,它在形式上与传统的一致输入反应谱保持一致,但考虑了多点输入的影响.结果表明,简化方法是可行的,它一方面减少了计算工作量,另一方面又保证了计算精度.     

老山奥运会自行车馆在多维多点输入下的响应分析和可靠度分析

考虑地震动两个水平分量和一个竖向分量,同时考虑了地震动场的空间相关性,用时程分析法对老山奥运会自行车场馆进行了多维多点输入和多维一致输入下的动力响应分析,考查了两种输入方法下结构响应的差异以及视波速对这种差异的影响.另一方面,本文在快速多点输入反应谱法的基础上,对老山奥运会自行车场馆进行了多维多点输入和多维一致输入下的构件层面上的抗震可靠度分析,考查了两种输入方法下危险杆件在结构分布、数量等方面的差异以及危险杆件随视波速的变化关系.得出以下结论:采用地震动的多点输入法,导致整个结构的内力分布更加均匀;两种输入方法下,杆件内力可靠指标明显降低的杆件有相当一部分位于支承附近区域;会产生一定数量的"一致输入下安全而多点输入下危险"的杆件,且它们大多分布于支承区域附近.     

地震作用下高拱坝损伤开裂分析

采用应变率相关的砼非线性损伤模型模拟拱坝横缝,研究了砼非线性本构情况下整体拱坝与考虑分缝拱坝的应力响应和损伤开裂的特点与差别。对实际拱坝的地震响应分析表明,基于非线性砼模型的整体拱坝动力响应模型可以基本反映拱坝的实际应力分布情况。     

Multiple Non-Smooth Events in Multi-Degree-of-Freedom Vibro-Impact Systems

The behaviour of a multi-degree-of-freedom vibro-impact system is studied using a 2 degree-of-freedom impact oscillator as a motivating example. A multi-modal model is used to simulate the behaviour of the system, and examine the complex dynamics which occurs when both degrees of freedom are subjected to a motion limiting constraint. In particular, the chattering and sticking behaviour which occurs for low forcing frequencies is discussed. In this region, a variety of non-smooth events can occur, including newly studied phenomena such as sliding bifurcations. In this paper, the multiple non-smooth events which can occur in the 2 degree-of-freedom system are categorised, and demonstrated using numerical simulations.     

Conservation laws of dynamical systems via d'alembert's principle

In this note we study a method for finding the conserved quantities of nonconservative holonomic dynamical systems. In contrast to the classical Noetherian approach, which is based upon the variational principle of Hamilton, the starting point in this note is based on the differential principle of D'Alembert which is equally valid for conservative and nonconservative systems. In the second part of this note, an attempt is made to employ symmetry properties as a vehicle for obtaining approximate solutions of linear and non-linear dynamical systems.     

A mesh-free radial basis function–based semi-Lagrangian lattice Boltzmann method for incompressible flows

In this paper, a local radial basis function–based semi-Lagrangian lattice Boltzmann method (RBF-SL-LBM) is proposed. This is a mesh-free method that can be used for the simulation of incompressible flows. In this method, the collision step is performed locally, which is the same as in the standard LBM. In the meanwhile, the steaming step is solved in a semi-Lagrangian framework. The distribution functions at the departure points, which may be not the grid points in general, are computed by the local radial basis function interpolation. Several numerical tests are conducted to validate the present method, including the lid-driven cavity flow, the steady and unsteady flow past a circular cylinder, and the flow past an NACA0012 airfoil. The present results are in good agreement with those published in the previous literature, which demonstrates the capability of RBF-SL-LBM for the simulation of incompressible flows.     

弹性接触过程分析的有限元数值模拟

本文针对机械行业中的弹性接触问题，在有限元分析中，引主接触面单元和预留单元。以滚针轴承为例，对接触问题进行了深入的探讨，为准确地描述两接触体之间相互作用及变形协调的接触过程，提供了一种新方法。     

Soliton-like solutions based on geometrically nonlinear Cosserat micropolar elasticity

The Cosserat model generalises an elastic material taking into account the possible microstructure of the elements of the material continuum. In particular, within the Cosserat model the structured material point is rigid and can only experience microrotations, which is also known as micropolar elasticity. We present the geometrically nonlinear theory taking into account all possible interaction terms between the elastic and microelastic structures. This is achieved by considering the irreducible pieces of the deformation gradient and of the dislocation curvature tensor. In addition we also consider the so-called Cosserat coupling term. In this setting we seek soliton type solutions assuming small elastic displacements, however, we allow the material points to experience full rotations which are not assumed to be small. By choosing a particular ansatz we are able to reduce the system of equations to a sine–Gordon type equation which is known to have soliton solutions.     

A three-party password-based authenticated key exchange protocol with user anonymity using extended chaotic maps

In this paper, we propose a scheme utilizing three-party password-based authenticated key exchange protocol with user anonymity using extended chaotic maps, which is more efficient and secure than previously proposed schemes. In order to enhance the efficiency and security, we use the extended chaotic maps to encrypt and decrypt the information transmitted by the user or the server. In addition, the proposed protocol provides user anonymity to guarantee the identity of users, which is transmitted in the insecure public network.     

A Nonlinear Temporal Headway Model of Traffic Dynamics

In order to describe the dynamics of a group of road vehicles travelling in a single lane, car-following models attempt to mimic the interactions between individual vehicles where the behaviour of each vehicle is dependent upon the motion of the vehicle immediately ahead. In this paper we investigate a modified car-following model which features a new nonlinear term which attempts to adjust the inter-vehicle spacing to a certain desired value. In contrast to our earlier work, a desired time separation between vehicles is used rather than simply being a constant desired distance. In addition, we extend our previous work to include a non-zero driver vehicle reaction time, thus producing a more realistic mathematical model of congested road traffic. Numerical solution of the resulting coupled system of nonlinear delay differential equations is used to analyse the stability of the equilibrium solution to a periodic perturbation. For certain parameter values the post-transient response is a chaotic (non-periodic) oscillations consisting of a broad spectrum of frequency components. Such chaotic motion leads to highly complex dynamical behaviour which is inherently unpredictable. The model is analysed over a range of parameter values and, in each case, the nature of the response is indicated. In the case of a chaotic solution, the degree of chaos is estimated.     

A nonlocal diffuse interface model for microstructure evolution of tin-lead solder

Microstructural length scales are relatively large in typical soldered connections. A microstructure which is continuously evolving is known to have a strong influence on damage initiation and propagation in solder materials. In order to make accurate lifetime predictions by numerical simulations, it is therefore necessary to take the microstructural evolution into account. In this work this is accomplished by using a diffuse interface model incorporating a strongly nonlocal variable. It is presented as an extension of the Cahn-Hilliard model, which is weakly nonlocal since it depends on higher order gradients which are by definition confined to the infinitesimal neighbourhood of the considered material point. Next to introducing a truly nonlocal measure in the free energy, this nonlocal formulation has the advantage that it is numerically more efficient. Additionally, the model is extended to include the elastically stored energy as a driving force for diffusion after which the entire system is solved using the finite element approach. The model results in a computational efficient algorithm which is capable of simulating the phase separation and coarsening of a solder material caused by combined thermal and mechanical loading.     

Acoustic stop bands in almost-periodic and weakly randomized stratified media： perturbation analysis

In this paper, we analyze the effect of both deter- ministic and random perturbations of a regular multi-layered elastic structure on its stop band properties. The tool of choice is the transfer matrix method, which is both versatile and easy to implement. In both cases, we find that the stop-bands widen. We observe the appearance of very narrow pass-bands within the stop-bands, which can be observed in other instances in optics.     

Guided electromagnetic waves in anisotropic media

Summary The propagation of guided waves in anisotropic media has recently become of interest in two fields, viz. in the interpretation of ferromagnetic resonance experiments and in the construction of microwave fourpoles which violate the reciprocity relation. In both cases we are faced with the solution of Maxwell's equations in a volume which is enclosed by perfectly conducting walls and which is completely or partially filled with a medium whose magnetic permeability is described by a second order tensor. An account is given here of some work, both theoretical and experimental, on this subject. Chapter I is an introduction, containing a short survey of the theory of guided waves in isotropic media and of the problems arising in anisotropic media, together with a historical synopsis. Chapter II gives a general formulation of the theory of guided waves in anisotropic media, comprising the existing theories, and also deals with some new applications. In Chapter III a cavity technique for measuring Faraday rotations is described which has several advantages over older techniques. In Chapter IV experimental results obtained for the series of Ferroxcubes IVA, B, C, D, E are collected. Chapter V finally deals with the physical interpretation of these results. In particular the experimental data are compared with Rado's theory of the permeability tensor in non-saturated ferromagnetics.