基于直线型滑移索单元的输电线路结构张力分析

为了研究高压架空输电线索结构与塔架等其他杆件连接处的滑移特性,定义了一组滑移索单元,由一个通过滑动节点连接的三节点活动滑移索单元和多个两节点非活动滑移索单元组成．基于更新拉格朗日格式推导了三节点直线型滑索单元几何非线性刚度矩阵,并通过两跨和三跨等高连续索结构的有限元数值算例验证了空间直线型滑移索单元的有效性．研究结果表明,推导的直线型滑移索单元张力与已有计算结果相比,误差在1％以内．考虑滑移的索结构初始平衡状态内力与不考虑滑移的情况比较相差较大,因而在实际工程中应该考虑索的滑移．     

一种非等阶积分的求积元孔压单元（英文）

目的:在对土体固结问题进行求解时,如果对孔压和位移采用等阶积分,当时间步长取值很小时,得到的孔压结果会出现数值振荡,导致精度降低。本文提出一种非等阶积分的求积元孔压单元,致力于减小孔压振荡,提高单元稳定性和计算精度。创新点:1.建立了一种对于孔压和位移采用不同阶积分的求积元复合单元;2.有效降低了小时间步长引起的孔压振荡。方法:1.通过求积元法对弱形式控制方程进行数值积分,并对比奥固结方程中的位移项和孔压项采用不等阶积分;2.通过拉格朗日插值获得位移点上的孔压和孔压点上的位移值;3.通过一维及二维问题的数值算例,验证所建立方法的有效性。结论:1.通过采用复合求积元单元,大大降低了孔压的数值振荡;2.应用复合求积单元时,采用二阶精度的Crank-Nicolson积分格式不会产生随时间的孔压振荡;3.本文所建立的单元可以大大提高固结问题求解的数值计算精度和计算效率。     

修正的增广拉格朗日算法的收敛性

考虑了四种不同的算法策略来修正增广拉格朗日算法,表明不要求乘子有界就能收敛到原问题的全局最优解.     

三等跨曲线连续梁模态分析试验

为了得到三等跨曲线连续梁(曲梁)的固有频率和振型,利用Midas有限元分析软件计算了曲梁的固有频率和振型,并对其进行了振动试验。试验结果采用DASP模态分析软件处理,得到曲梁的前3阶频率及振型,将试验结果与计算结果进行对比,证实振型变化的真实性,并对其冲击系数的取值进行了探讨。结果表明:曲梁前3阶频率的相对误差均不超过4%,振型基本吻合;曲梁的有限元计算频率均小于试验实测频率,且曲梁的前3阶频率均小于等跨直梁,刚度是影响同等跨径直梁和曲梁自振频率不同的主要因素。     

欧拉—拉格朗日方程的推广

变分法是处理泛函极值的一种数学方法,欧拉—拉格朗日方程是基于变分法得到的,该方程在除数学外的很多其他领域有着广泛的运用.如果能将欧拉—拉格朗日方程的应用范围进一步扩大,即条件减弱或者放松限制条件,就可以使已有的结论更完善.本文运用变分法,得到更普遍适用的欧拉—拉格朗日方程.     

混凝土框格梁加固填筑边坡的数值分析

采用FLAC3D三维快速拉格朗日分析程序,对混凝土框格梁加固填筑边坡进行数值分析。选取安全系数、剪应变位移增量、坡体表面监测点的侧向位移和竖向沉降作为评价指标,对框格梁加固边坡稳定性效果进行了分析,并对不同框格梁加筋方案对边坡稳定性的影响进行了初步探讨。     

两等跨曲线连续梁模态试验及有限元分析

为了得到曲线连续梁的固有频率和振型,以便为桥梁检测提供校核依据;有机地结合了有限元模态分析方法和试验模态分析方法,对某两等跨曲线连续梁进行了模态分析,得到曲梁的前4阶频率及振型,并将试验结果与有限元计算结果进行对比。结果表明:除去一阶频率误差较大外,第2~4阶相对误差均小于4%,振型基本吻合;一阶固有频率受扭转影响较大,第2~4阶频率受扭转影响依次减小;曲梁前4阶频率均小于等跨直梁。     

基于MLP法的磁浮列车非线性系统的稳定性分析

以磁浮列车的垂向运动为研究对象,研究其非线性系统的稳定性。选取气隙值、电流值为磁浮列车悬浮系统的广义坐标,依据拉格朗日-麦克斯韦方程建立磁浮列车非线性悬浮系统的动力学模型,得到的振动方程是三阶的强非线性负刚度微分方程。应用MLP法求得系统的共振永年项条件,并对初始方程进行了数值计算,得到了磁浮列车在空载、满载、过载情况下的悬浮系统振动时间响应曲线和相图,结果表明:随着列车质量的增加,列车初始位移增加,但列车启动后50 s的时间内,系统振动趋于稳定。     

圆弧形曲梁的传递函数方法

应用传递函数方法求解圆弧曲梁,将复杂的曲梁分成若干一维子系统,轴力作为子系统的参数,通过引入状态变量,将曲梁的控制方程及边界条件改写成状态空间形式,再借鉴有限元的拼接方法,得到梁的变形解.文中的数值算例显示了此方法的可行性.     

编织型食管支架结构及其丝线的力学性能分析(英文)

旨在找出支架结构参数与支架径向刚度之间的关系并了解支架变形及丝线上的应力分布规律.按照空间螺旋曲线方程创建几何模型,用梁-梁接触单元和三维梁单元建立有限元模型,并定义丝线为线弹性材料.有限元分析结果显示支架结构径向刚度及丝线上的应力分布与支架的各个结构参数都相关,其中丝线螺距对其影响最大.在相同载荷作用下,当丝线头数是24且支架的其他结构参数都不变时,丝线横截面上的应力最小.最后,将体外实验结果与分析结果进行比较,数据规律具有一致性,可以证明该有限元模型能够用于近似预测编织型食管支架的相关力学性能.     

A co-rotational updated Lagrangian formulation for a 2D beam element with consideration of the deformed curvature

A tensor-based updated Lagrangian （UL） formulation for the geometrically nonlinear analysis of 2D beam-column structures is developed by using curvilinear coordinates, which has considered the effects of the deformed curvature. Between the known configuration C1 and the desired configuration C2, a configuration C2^＊ derived by rigid-body motion of C1 is introduced to eliminate the element-end transverse displacements between C2^＊ and C2. A stiffness matrix is obtained in C2^＊; and then by a transformation defined by the element-end displacements, the stiffness matrix in C2^＊ is transformed into that in CI. Comparing the stiffness matrix with that in the conventional UL formulation for a 2D beam element, the initial displacement stiffness matrix emerges, which results from the deformed curvature within the element. Numerical examples have verified the accuracy and efficiency of the present formulation, and the results show that the deformed curvatures have significant effects when deformations are large.     

Analytical study on the dynamic displacement response of a curved track subjected to moving loads

A closed-form out-of-plane dynamic displacement response of a curved track subjected to moving loads was pro- posed. The track structure was modeled as a planar curved Timoshenko beam periodically supported by the double-layer spring-damping elements. The general dynamic displacement response induced by the moving loads along the curve on the elastic semi-infinite space was firstly obtained in the frequency domain, according to the Duhamel integral and the dynamic reciprocity theorem. In the case of the periodic curved track structure subjected to moving loads, the dynamic displacement equation was simplified into a form of summation within the basic track cell instead of the integral. The transfer function for the curved track was expressed in the form of a transfer matrix. Single and series moving loads were involved in the calculation program. For the verification of the analytical model, the mid-span vertical deflection of a simply support curved beam subjected to moving load was recalculated and compared with the same case in the reference. The research results indicate that： under the same moving loads, the displacement response of the curved track decreases slightly with the increasing track radius, and the displacement response of the curved track with the radius greater than or equal to 600 m is almost equivalent to the displacement response of the straight track; the frequency spectrum of the curved track is more abundant than that of the straight track, which may result in more wheel-rail resonance and rail corrugation in the curved lines.     

Improved simulation method for soil-geogrid interaction of reinforced earth structure in FEM

The interaction between geogrid and soil is crucial for the stability of geogrid-reinforced earth structure. In finite element (FE) analysis, geogrids are usually assumed as beam or truss elements, and the interaction between geogrid and soil is considered as Coulomb friction resistance, which cannot reflect the true stress and displacement developed in the reinforcement. And the traditional Lagrangian elements used to simulate soil always become highly distorted and lose accuracy in high-stress blocks. An improved geogrid model that can produce shear resistance and passive resistance and a soil model using the Eulerian technique, in combination with the coupled Eulerian-Lagrangian (CEL) method, are used to analyze the interaction between geogrid and soil of reinforced foundation test in ABAQUS. The stress in the backfill, resistance of geogrid, and settlement of foundation were computed and the results of analysis agree well with the experimental results. This simulation method is of referential value for FE analysis of reinforced earth structure.     

Dynamic stiffness for thin-walled structures by power series

INTRODUCTION Thin-walled structures have considerable tech-nological importance in many situations of engi-neering practice. The rotary and warping inertia terms should be considered in the analyses of thin-walled structures (Alwis and Wang, 1996), although it is difficult to obtain the analytical solutions of govern-ing differential equations, especially of thin-walled frame and spatial twisted structure. The finite element method (FEM) is widely used for vibration and sta-bility analy…     

Infant responsivity to curvature.

The reactions of 112 10-month-old male infants to the property of curvature were examined using a habituation paradigm with lever pressing as an instrumental response. 4 levels of curvature (straightt line, minimal curve, moderate curve, large curve) each served as a standard (habituation) stimulus and as a transformation stimulus in 9 separate experimental conditions. Results revealed a greater initial dishabituation of reinforced instrumental responding in those conditions crossing the curved/straight boundary; furthermore, this initial dishabituation was sustained throughout the transformation phase of the experiment in those conditions which involved changes from straight to curved, but not curved to straight. Results are interpreted as implying a special attention-recruiting value for curvature in 10-month old infants.     

Multi-scaled simulation of latticed frames considering bending collapse of pipes

To consider the bending collapse of the pipes in the latticed frames, based on the multi-scale simulation, the collapsed parts of the pipe are meshed by the shell elements as micro-scaled models, and the other parts are meshed by beam elements macro-models. The incremental displacement constraint equations for the nodes on the section between the two models are established based on the plane section premise of classical beam theory. The method to introduce the constraint equations is derived based on the Updated Largrangian method. The location of the micro-model is predicted by the stress field of the beam element, and the length of the collapsed part is adjusted by the plastic energy in the micro model. Several examples are included to illustrate the efficiency and accuracy of this method.     

基于Matlab的菲涅尔直边衍射仿真与GUI设计

利用Matlab软件进行了菲涅尔直边衍射实验的模拟仿真,给出了对应的光强分布曲线和仿真图像．利用Matlab的图形用户界面（GUI）建立动态的实验仿真界面．仿真结果图形细致逼真,使该过程的物理规律直观形象,有助于学生理解菲涅尔直边衍射现象中的物理规律．     

基于位移型Gurtin变分原理的非时间步参数时间有限元法

本文基于位移型Gurtin变分原理,对时间域进行离散时,采用具有非时间步参数的插值函数逼近广义节点位移,给出了一种新的计算弹性动力学初值问题的非时间步参数时间有限元法,这是一种无条件稳定的计算格式,通过算例,可知本文方法具有计算方法简便、实用和精度较高的特点。     

非时间步参数时间有限元法

本文基于位移型Gurtin变分原理,对时间域进行离散时,采用具有非时间步参数的话值函数逼近广义节点位移,给出了一种新的计算弹性动力学初值问题的非时间步参数时间有限元法这是一种无条件稳定的计算格式算例表明,本文方法具有计算方法简便、实用以及精度较高的特点