铁路路基病害类型、机理及检测与整治技术

针对既有铁路的特点,分析了常见铁路路基病害的类型、机理;提出路基病害的检测应运用现代化检测工具,采用原位和区段测试相结合的方法;针对路基病害整治技术的复杂多样,整治具体路基病害的困难性,指出了铁路路基病害智能管理系统能较好地解决此问题。     

青藏铁路路基加宽的变形特征研究

通过青藏铁路清水河冻土站场路基试验段冻土路堤、地基的沉降变形、水平位移、地温及路堤温度等进行较全面的试验和监测,分析了路基加宽对冻土路基温度场及变形产生的影响。     

基于可靠度的多年冻土区路基稳定性评价及应用分析

通过对多年冻土区道路路基稳定性的分析和研究,从冻土类型、温度、厚度、地质地貌单元以及工程条件5个方面选取了12项对多年冻土区路基稳定影响较大的因素作为评价指标,建立了冻土路基稳定性评价指标体系。基于安全可靠度并考虑各个影响因素之间的关系,运用层次分析法和模糊数学理论确定冻土区路基稳定状况的模糊综合评价模型,提出了基于安全可靠度的用于评价多年冻土区路基稳定的模糊综合评价方法,并结合青藏公路清水河段进行实例分析,结果表明,在该段公路实施热棒处理措施前后,其路基稳定性评价系统可靠度分别为0.48和0.55,与该段公路实际运营过程中路基稳定状态相一致,即由不稳定到稳定,进一步对布设热棒后路基稳定性进行二级模糊综合评价,其评价系统得分为63.74分。     

青藏高原清水河多年冻土区铁路路基沉降变形特征研究

通过埋设在青藏铁路路基中两个断面内的6条沉降观测管3 a来的地基沉降变形资料,研究了高原多年冻土区铁路路基的沉降变形特征,分析了填筑铁路路基对下伏多年冻土融化变形的影响。研究表明,由于受到填筑路基时赋存在路基填料内的热量的影响,铁路路基下伏多年冻土上限在施工初期会有一个明显的下移沉降,铁路路基也随之有一个较大幅度的工后下沉变动,随着时间的推移,路基下降速率会逐渐下降,但在短时间内不会停止下来,而且由于太阳辐射和路基边坡形状的影响,路基向阳面与背阴面的变形有较大的差别,且在近南北向展布的路基上表现最为明显。     

路基不均匀沉降的解析解

如何准确地计算路基的不均匀沉降是铁道工程中急待解决的重要问题.本文用应力扩散法和等效截面法的思想建立了在路堤荷载作用下分析路基不均匀沉降的平面应变模型,它由两段不同土质的路基组成,土的力学参数沿深度按指数规律变化.建立了广问题的基本方程和边界条件.对问题的解进行了拆分,一部分是猜测的解,另一部分用Fourier变换方法...     

青藏铁路冻土区遮挡式路基结构安全可靠性预测分析

冻土区路基的安全可靠性取决于路基地温场特征和路基面抗自然侵蚀特征。在路基基床上部修筑遮阳棚和在边坡上修筑遮阳板既可阻挡太阳对路基面和路基边坡的直接辐射,改变路基地温场形态,降低土层温度,又可防止降水渗入路基或降雪覆盖路面。这对防止冻土退化,提高冻土区铁路路基安全可靠性是一种非常有效而又简单易行的工程措施。本文以青藏铁路冻土区遮挡式路基结构路基表面温度数据和该地段气象资料为基础,运用带有相变的一维热传导方程模拟分析了青藏铁路长期运营过程中遮挡式路基结构对冻土区路基人为上限的抬升效果及对路基稳定性的影响,认为遮挡式路基结构是一种安全可靠的冻土区路基工程结构形式,同时也是未来铁路运营过程整治路基病害的一种有效工程措施。     

青藏铁路冻土区路基工程安全可靠性监测技术研究

通过对冻土区路基工程和冻土之间相互作用过程的分析,提出冻土区路基工程的安全可靠性监测关键技术一是监测方法,二是监测手段,三是数据分析。冻土区路基工程的安全可靠性首先取决于工程周围和工程基底多年冻土的热稳定性,其次取决于发生变形的路基填土厚度及其基底融化层厚度。因此,路基顶面以下不同深度地温监测和年际冻融季节时段路基土层变形监测是冻土区工程长期可靠性监测的主要指标。青藏铁路自然条件的严酷性,要求监测手段具有可靠性和耐久性以及对复杂自然条件变化的适应性。文章提出一种自动观测多年冻土地温和路基变形,并能够实现数据无线传输的现场监测系统设计方案,通过现场试验,证明这种监测系统能够适应青藏高原恶劣的自然条件,减轻了人工监测的劳苦,具有可靠性和耐久性。作者还提出了能够简便判断冻土区工程安全可靠性的监测数据分析方法,对目前冻土区工程安全可靠性分析具有一定的理论指导作用。     

公路路基黄土湿陷性评价问题

公路工程对湿陷性黄土的研究基本上是采用房建建筑的规范和试验规程进行勘察和设计,由于公路路基的工作环境和受力状态与房建工程地基差异很大,将房建建筑的规范直接应用于黄土地区高等级公路的湿陷性评价与计算存在着盲目性、不合理性,更为重要的是缺乏针对性。本文通过对现有规范在路基黄土湿陷性方面的合理性与实用性研究,结合降雨入渗的分布规律,提出了适合黄土地区高速公路的路基黄土湿陷性评价方法与模型。     

青藏铁路冻土路基温度场随机有限元分析

从一阶Taylor展开式入手,结合冻土温度场计算有限元法,推导了冻土路基温度场随机有限元方程及有关计算公式,并对青藏铁路北麓河试验段冻土路基温度场进行了随机有限元分析,结果表明温度标准差与温度场的分布趋势大致相同,在垂直方向上,最大值都出现在路基上部,向下逐渐减小,但两者分布范围略有不同,路基内部标准差的分布范围明显较大,在一定深度处达到均化。     

高速公路路基性态反分析及沉降预报

本文用三元件粘弹性流变模型模拟路基土体的流变特性, 根据施工期实测资料, 采用粘弹性有限元和非线性二乘法阻尼优化方法, 反演路基土体的地质力学参数, 然后计算路面铺筑后的工后沉降, 编制了土体粘弹性有限元正反分析程序, 并对沪宁高速公路某路段进行了反分析计算, 得到了满意的结果。     

Influences of large deformation and rotary inertia on wave propagation in piezoelectric cylindrically laminated shells in thermal environment

Influences of large deformation (geometrical non-linear) and rotary inertia on wave propagation in a long, piezoelectric cylindrically laminated shell in thermal environment is presented in this paper. Nonlinear dynamic governing equations of piezoelectric cylindrically laminated shells are derived by means of Hamilton’s principle. The wave propagation modes are obtained by solving an eigenvalue problem. Numerical examples show that the characteristics of wave propagation in piezoelectric cylindrically laminated shells are relates to the large deformation, rotary inertia and thermal environment of the piezoelectric cylindrically laminated shells. The effect of large deformation, rotary inertia and thermal load on wave propagation in the piezoelectric cylindrically laminated shells is discussed by comparing with the result from the small deformation (geometrical linear shell theory). This method may be used to investigate wave propagation in various laminated material, layers numbers and thickness of piezoelectric cylindrically laminated shells under large deformation. The results carried out can be used in the ultrasonic inspection techniques and structural health monitoring.     

工程爆破问题数值模拟研究

工程爆破方法在开矿、筑坝、修路和凿洞中得到了广泛使用,经验和分析表明,当炸药埋深超过40米时,重力对爆破抛掷现象有明显影响,但目前缺乏系境研究。本文提出了一个用于爆破作用下的岩体本构数学模型,并用二维轴对称数值计算方法对有重力影响的工程爆破问题初始阶段进行了详细研究,计算结果包括爆炸应力波的传播规律,岩体的加速与破坏过程,空腔与地表面的运动规律,抛掷区的形成与划定,能量分配关系等,结果表明:重力对爆炸波的传播基本无影响,重力仅影响抛掷区的大小和抛掷区动能占总爆炸能的比例。     

Influence of partial constrained layer damping on the bending wave propagation in an impacted viscoelastic sandwich

This paper presents a parametric model to study the transient bending wave propagation in a viscoelastic sandwich plate due to impact loading. The effect of partial constrained layer damping (PCLD) geometry on wave propagation is investigated by comparing with propagation in single layer elastic plate. Several boundary conditions are also considered, and their effect on wave propagation is highlighted.The equation of motion is obtained from Lagrange’s equations. For the single layer plate, the governing equation is solved in time domain using Newman and Wilson method. For the plate with PCLD, the frequency dependant viscoelastic behavior of the core is represented by Prony series; the equation of motion is converted into frequency domain using Fourier transform the displacement is obtained in the frequency domain and is converted into time domain with the Inverse Fast Fourier Transform.The model was validated in our previous paper (Khalfi and Ross (2013)) with experimental results, additional validation is carried in this paper with literature, and good agreement is recorded. The results show that the plate covered with PCLD remains a dispersive medium. The shape of the wave is mainly related to the sandwich stiffness while the viscoelastic layer contributes in reducing the amplitude and speed of propagation. The particularity of this transient model lies in its ability to follow the shape of the bending wave at all times to observe formation, propagation and disappearance. With this model, the influence of any structural input parameters on the bending wave can be studied. The findings presented will also serve as a research base for more advanced horizons.     

刚架结构中瞬态波的传播

在改进回传矩阵法的基础上 ,引入节点质量阻尼模型 ,结合射线展开技术 ,研究刚架结构中的弹性瞬态波的传播。根据分析结果可以看出 ,节点质量对弹性波的传播影响不大 ,节点阻尼对弹性波的传播影响很大。如果选取合适的节点 ,就可以阻碍波在结构局部中的传播 ,达到结构局部控制的目的。刚架结构中的弹性瞬态波的传播 ,可以对大型刚架结构的无损检测提供一定的帮助。     

Laplace变换法及其在粘弹性波中传播的应用

针对波传播分析理论的发展历程进行了简要的综述，详细介绍了几种处理粘弹性波传播问题的分析方法，重点讲解Laplace变换法以及Laplace变换在粘弹性波中的应用，对比分析几种方法在各自应用上的优劣，由于Laplace变换法能准确地描述应力波在任意时刻、任意点的波动情况，在处理大尺寸混凝土类构件中应力波传播问题时具有其独特的优势。     

近场动力学系统中波传播特性的探究

近场动力学是一类基于非局部思想的新固体力学方法,其采用积分形式的控制方程,自然地适用于极端载荷下材料破碎和裂纹发展的模拟,被广泛用于国防安全等领域的研究.但是,非局部性会引入色散效应,对波的传播产生不利影响,制约其对断裂等固体行为的捕捉能力.为此,采用谱分析方法,对近场动力学系统的色散行为进行了全面的研究.发现相比于低频成分,高频成分的色散关系呈现出振荡趋势和零能模式,色散问题更为严重.高频域的色散行为还随波的传播方向发生改变,呈现出沿45°的对称性.而近场动力学系统本身缺乏数值耗散,无法抑制色散问题带来的不利影响.因此,从引入数值耗散的角度出发,在合理保留传统近场动力学理论框架的基础上,建立了黏性引入的控制方程.并考虑固体中常见的体积变形和对高频成分的选择性抑制,构造了相应的黏性力态.最后,在数值研究中模拟了极端载荷下激波的产生,以探究波的间断性对色散行为的影响.发现间断性强的波表现出更为显著的色散行为,呈现出Gibbs不稳定性.这些均能有效地被黏性力态所抑制,验证了所提方法的正确性.这为在近场动力学系统中实现对波传播过程的正确捕捉,获得正确的固体行为提供了重要参考,从而为国防安全领...     

Numerical modeling of PZT-induced Lamb wave-based crack detection in plate-like structures

This paper presents the numerical modeling and simulations of PZT-induced Lamb wave propagation in plate-like structures by using the spectral finite element method. A novel spectral plate finite element, which can efficiently model the three-dimensional (3D) behavior of Lamb waves, is proposed. In the formulation, linear displacement distributions in the thickness direction are assumed for both the PZT layer and the base plate. A way to avoid the thickness locking is proposed and used in the formulations. Two examples, one for the validation of the proposed two-dimensional (2D) spectral finite element and the other for the demonstration of crack detection in plates, are presented and discussed. The contact between the two faces of crack is considered. Numerical results show that (1) only the anti-symmetric mode is prone to thickness locking thus remedy should be made only on this part, (2) the proposed 2D spectral finite element can adequately model the Lamb wave propagation in plate-like structures and the complex scattering for the crack, and (3) crack location can be well determined by a PZT-induced Lamb wave-based diagnosis algorithm.     

Propagation of guided waves in pressure vessel

Pressure vessels usually operate under extremes of high/low temperatures and high pressures. Defect, such as crack and corrosion, can result in leakage or rupture failures, even catastrophic incidents. Guided wave-based structural health monitoring (SHM) technology is one of the most prominent options in non-destructive evaluation and testing (NDE/NDT) techniques. Propagation of guided waves in a typical pressure vessel is systematically investigated in this study for the application of guided wave-based SHM. Shape of the pressure vessel is a cylinder with two end caps. Because of geometric similarity, theory of guided wave propagation in the cylinderical structure is analyzed to study dispersive features of guided waves in the pressure vessel. Dispersion curves of three different types of guided wave modes, viz. the longitudinal, torsional and flexural modes, are calculated using theoretical method. Based on the analyses and experimental wave signals, central frequency and wave parameters of incident wave are optimized. Effect of contained liquid on propagation of guided waves, especially the L(0, 2) mode, in the pressure vessel is further investigated to minimize energy leakage of the wave to the contained liquid. The analytical method, finite element analysis (FEA) and experiments are applied to study propagation characteristics of guided waves in the pressure vessel, so as to demonstrate the feasibility of guided wave-based non-destructive evaluation and testing (NDE/NDT) for such kind of complex structures.     

Synthesis of highly convergent 2D and 3D finite elements for short acoustic wave simulation

New higher-order finite elements of enhanced convergence properties for acoustic wave simulation are presented in the paper. The element matrices are obtained by combining modal synthesis and optimization techniques in order to achieve minimum errors of higher modes of the computational domain. As a result, simulation models of propagating wave pulses require a smaller number of finite element divisions per wavelength compared to the conventional element model thus significantly reducing computational costs. Though finite element matrices are obtained in optimization, the resulting patterns of the matrices are versatile and further can be used in any wave propagation model. The mass matrices of the elements are diagonal, so explicit time integration schemes are applicable. The usage of new elements is especially efficient in situations where wavelengths of the simulated signal are much shorter than the dimensions of the computational domain. This is referred to as short wave propagation analysis. The results of wave propagation simulation for ultrasonic measurements are presented as application examples. The B-scans and computed dispersion curves are provided for visual interpretation of the results.