Equivalent bending stiffness of simply supported preflex beam bridge with variable cross-section

In order to understand mechanical characters and find out a calculating method for preflex beams used in particular bridge engineering projects, two types of simply supported preflex beams with variable cross-section, preflex beam with alterative web depth and preflex beam with alterative steel flange thickness, are discussed on how to achieve the equivalent moment of inertia and Young’s modulus. Additionally, methods of calculating the equivalent bending stiffness and post-cracking deflection are proposed. Results of the experiments on 6 beams agree well with the theoretical analysis, which proves the correctness of the proposed formulas.

THE GENERAL SOLUTION FOR DYNAMIC RESPONSE OF NONHOMOGENEOUS BEAM WITH VARIABLECROSSSECTION

In this paper by means of the exact analytic method [1], the general solution fordynamic response of nonhomogeneous beam with variable cross section is obtained un-der arbitrary resonant load and boundary conditions. The problem is reduced to solvea non-positive differential equation. Generally, it is not solved by variational method.By the present method, the general solution for this problem may be written as an ana-lytic form. Hence, it is convenient for structure optimizing problem. In this paper, itsconvergence is proved. Numerical examples are given at the end of the paper. which in-dicates satisfactory results can be obtained.

High Resolution Crossed Beams Scattering Study of the F＋HD→DF＋H Reaction

散布学习的穿过的横梁用标注 time-of-flight 技术的高分辨率的 H 原子 Rydberg 在 F+HDDF+H 反应上被执行。震动的解决状态的微分生气的节被测量，与部分旋转州的分辨率，在在 2.515.60 kJ/mol 的范围的八个碰撞精力。试验性的结果显示产品尖分布向后主要被散布。作为碰撞精力增加，向后散布的山峰逐渐地变得更宽广。精力也是的碰撞上的分叉的比率决定了的产品颤动的依赖。试验性的结果证明 DF 产品高度在震动的州的分发和 DF 被转换(v “ = 3 ) 产品是大多数占据状态。而且， DF (v “ = 1 ) 产品也在 3.97 kJ/mol 上面在碰撞精力被观察了。

A crossed focused vortex beam with application to cold molecules

We report the generation of a crossed,focused,optical vortex beam by using a pair of hybrid holograms,which combine the vortex phase and lens phase onto a spatial light modulator.We study the intensity distributions of the vortex beam in free propagation space,and the relationship of its dark spot size with the incident Gaussian beam’s waist,the lens’s focal length,and its orbital angular momentum.Our results show that the crossed,focused,vortex beam’s dark spot size can be as small as 16.3μm and adjustable by the quantum number of the orbital angular momentum,and can be used to increase the density of trapped molecules.Furthermore,we calculate the optical potential of the blue-detuned,crossed vortex beam for MgF molecules.It is applicable to cool and trap neutral molecules by intensity-gradient-induced Sisyphus cooling,as the intensity gradient of such vortex beam is extremely high near the focal point.

Direct acceleration of electrons using two crossed Laguerre-Gaussian laser beams in vacuum

The basic physical characteristics of electrons accelerated by two linearly polarized and circularly symmetric crossed Laguerre-Gaussian （LG） laser beams with equal frequency and amplitude in vacuum are studied in detail. The condition, under which electrons can be accelerated effectively, and the energy gain are discussed.

Electron acceleration by two crossed Bessel-Gaussian beams in vacuum

The direct acceleration of electrons by using two linearly polarized crossed Bessel-Gaussian （BG） beams with equal frequency and amplitude in vacuum is proposed and studied. It is shown that two linearly polarized BG beams of the same order （0 or 1） with a π-rad phase difference have a resultant non-zero longitudinal electric field on the z-axis and can be used, in principle, to accelerate electrons.

Modeling and analysis of piezoelectric beam with periodically variable cross-sections for vibration energy harvesting

A bimorph piezoelectric beam with periodically variable cross-sections is used for the vibration energy harvesting. The effects of two geometrical parameters on the first band gap of this periodic beam are investigated by the generalized differential quadrature rule （GDQR） method. The GDQR method is also used to calculate the forced vibration response of the beam and voltage of each piezoelectric layer when the beam is subject to a sinusoidal base excitation. Results obtained from the analytical method are compared with those obtained from the finite element simulation with ANSYS, and good agreement is found. The voltage output of this periodic beam over its first band gap is calculated and compared with the voltage output of the uniform piezoelectric beam. It is concluded that this periodic beam has three advantages over the uniform piezoelectric beam, i.e., generating more voltage outputs over a wide frequency range, absorbing vibration, and being less weight.

SHEAR STRESS ANALYSIS OF TIMOSHENKO'S BEAM WITH MULTIPLY CONNECTED CROSS SECTION

In this paper, a finite element method is developed to numericallyevaluate the shear coefficient of Timoshenko's beam with multiplyconnected cross section. With focus on analyzing shear stressesdistributed at the neutral axis of the beam, an improved definitionof the shear coeffi- cient is presented. Based on this definition, aGalerkin-type finite element formulation is proposed to analyze theshear stresses and shear deflections. Numerical solutions of theexamples for some typical cross-sections are compared with thetheoretical results. The shear coefficient of tower sections of theTsing Ma Bridge is calculated by use of the proposed approach, sothat the finite element modeling of The bridge can be developed withthe accurate values of the sectional properties.

类氦C离子诱发不同金属厚靶原子的K-X射线

利用中国原子能科学研究院HI-13MV串列加速器上提供的动能为15—55 MeV的类氦C离子分别轰击Fe,Ni,Nb和Mo金属厚靶,采用HpGe探测器测量了K-X射线,获得了相应的K-X射线的发射截面.本文中由于各个靶原子外壳层电离度的不同,类氦C离子与Fe,Ni靶原子相互作用发射的K_(β)与K_(α)X射线的分支强度比随入射离子动能增加而减小,而Nb,Mo靶原子发射的K-X射线分支强度比变化不明显.利用厚靶截面公式计算了靶原子K-X射线的发射截面,并与不同的理论模型及质子的结果进行了对比.结果表明随类氦C离子动能的增大,Fe,Ni靶原子发射的K_(β)与K_(α)X射线的总产生截面与考虑多电离的两体碰撞近似修正模型最为符合Nb,Mo靶原子发射的K_(β)与K_(α)X射线的总产生截面与平面波恩近似模型的理论值最为接近.质子与单核子C离子能量相同时,质子比类氦C离子激发不同靶的K-X射线产生截面约小3个数量级.

Digital Cross-Correlation Detection of Multi-Laser Beams Measuring System for Wind Field Detection

A cross-correlation detection method to process backscatter signals of multi-laser beams measuring （MLBM） is presented, which can be firstly filtered by the digital filter composed of average median filter and finite impulse response （FIR） digital filter. The processing of backscatter signals using single-pulse and three-pulse cross-correlation detection methods is depicted in detail. From calculation results, the multi-pulse cross-correlation detection could effectively improve signal-to-noise ratio （SNR）. Finally, both wind velocity and direction are determined by the peak-delay method based on the correlation function which shows high measuring precision and high SNR of the MLBM system with the assistance of the digital cross- correlation detection.

基于PIN管的1-bit波束可重构反射阵

针对传统反射阵列天线不能灵活地进行波束转向,无法满足部分应用场景需求这一问题,文中设计、制作并测试了一种具有12×12个反射单元的1-bit波束可重构反射阵列。通过在两个尺寸相同的L形结构中间加载PIN二极管实现1位可重构单元,采用Ansys HFSS 15对该单元进行建模和仿真,在4.36 GHz~5.06 GHz频率范围内,单元在PIN二极管导通和断开两种状态下的相位差在180°±25°范围内,并在4.46 GHz和4.96 GHz两个频率下,具有180°相位差。对4.96 GHz进行验证,通过数字控制板独立调节每个PIN二极管,从而实现所需的相位分布。仿真和测试结果表明反射阵可以在4.96 GHz的中心频率下实现±50°范围内的波束扫描,并且在4.76 GHz~5.46 GHz频率范围内,具有相对良好的波束扫描性能。此外,反射阵采用镜面对称排布方式以改善交叉极化,实测交叉极化为-26.7 dB,相比较传统排布方式,交叉极化峰值降低了15.2 dB。

基于等效刚度法优化的风力机叶片刚度计算

风力机叶片刚度由于非线性且截面变化程度大的特点,针对叶片建模初期刚度的评估问题通常采用刚度展项分布图体现叶片刚度,存在评估叶片刚度的参考参数不够直接、宏观的问题。基于变刚度梁挠度计算的等效刚度法,将叶片等效成变截面悬臂梁,根据叶片特征合理选取边界条件,以叶片建模的截面数据特点为基础,优化原始等效刚度法的计算方式,使该方法更加贴合叶片模型,从而适用于叶片,达到方法优化的目的。利用ANSYS有限元软件进行叶片的预应力模拟实验,得出叶片的挠度模拟数值,以该模拟计算的挠度值为参考,验证优化后方法的有效性。结果表明:优化后的等效刚度法得到的刚度值,在低均布载荷值22.5 Pa下理论计算的挠度值与试验挠度值的误差达到9.68%,减小原始方法计算的误差贴近叶片模型,可用于叶片刚度估算,为叶片的刚度计算提供新方法。

基于渐近分析法的复杂截面梁振动分析

梁结构在工程工业中发挥着重要的作用,梁的自振问题能够体现其本征动力学特性,是梁动力学分析中的基本问题.经典梁理论的提出往往基于不同的假设,文章采用渐近分析的方法,以梁的截面尺寸与长度之比为特征参数,严格地推导了三维梁结构的一维等效振动分析模型.基于梁结构几何特征的参数的引入,有助于确定梁结构应力场和位移场等物理量之间的真实量级关系.渐近分析结果表明,纯弯曲变形只是细长梁振动分析中的首阶项,对于复杂截面梁结构仍然可以使用与欧拉梁模型复杂度相似的一维等效梁模型进行振动分析.以精细三维有限元的计算结果为基准,验证了所提出的一维等效梁模型用于振动分析的准确性和有效性.一维等效梁模型可以在商业有限元软件中通过自定义截面等内嵌模块便捷地实现.对比有限元软件中多种梁单元的计算结果发现,在相似的模型复杂度下,等效模型对细长梁自振频率的分析精度与稳定性显著优于在商业有限元软件中直接选择复杂梁截面使用梁单元计算的结果.

小角度斜交上跨铁路异型T构桥受力分析研究

随着铁路大规模的建设,线路间的小角度斜交交叉穿越不可避免。当桥下净空受限时,常用的门式刚构方案存在不适用性。本文结合西十高铁西安东站动走线上跨西十正线工程,将门式墩与小T构梁结合,采用空间异型框架T构梁桥满足净空受限情况下的线路间小角度斜交跨越。建立了全桥三维整体模型、纵向计算模型、横梁局部模型等有限元模型,通过不同模型间的比较,分析了异型框架T构梁桥的纵、横向受力计算方法,对纵向模型、局部横梁模型的适用性进行了论证,并对常用的局部横梁模型进行刚度修正,提出了修正刚度后的局部横梁模型。修正后的横梁局部模型受力明确,计算结果与三维空间模型一致,可满足设计计算要求。

连续梁桥跳车冲击下车桥耦合振动响应分析

为研究车辆在不同工况下发生跳车对变截面连续梁桥动力响应的影响,文章选用1/4车辆模型,采用D’Alembert原理建立车辆振动平衡方程;基于Euler-Bernoulli梁理论将变截面连续梁划分成多个微段并进行受力分析,建立桥梁振动平衡方程,采用模态坐标法考虑振型的正交性对方程进行简化,与车辆振动方程联立得到车桥耦合振动方程,最终理论推导出跳车冲击过程中的车桥耦合振动平衡方程;利用MATLAB自编程序求解车桥耦合振动方程,得出车桥耦合动力响应。研究表明:当跳车高度不断增加时,桥梁动力响应持续加重,位移最大值逐渐增加;当不同桥跨跨中发生跳车时,跳车跨位移响应最大,距离跳车跨越远,位移响应越小。

基于Dynamo模式+Revit二次开发的变截面连续梁桥初步设计研究

针对变截梁桥建模困难、效率低下、精确度不足等问题,以鄂州市东沟大桥为工程背景,基于Revit+Dynamo模式提出一套搭建变截面梁桥参数化模型方案,成功搭建全桥三维模型,验证了该参数化模型方案具有可行性。并在此模型基础上,通过Revit API程序接口进行二次开发创建0#节段箱梁钢筋参数化模型,实现了桥梁工程参数化、自动化建模效果,期望能为同类型和其他类型桥梁参数化设计提供一些思路和参考。

基于离散Beam梁法的变截面钢板弹簧建模及仿真

采用离散Beam梁法在多体动力学软件ADAMS中建立变截面钢板弹簧的动力学模型。以某轻型客车的后悬架变截面钢板弹簧为例,仿真计算其刚度,并与试验测试结果进行对比。结果表明,该方法用于变截面钢板弹簧的建模具有有效性。

不同布置形式钢横梁门式墩对比研究

以一座新建铁路上跨既有铁路钢横梁门式墩为背景,建立有限元模型,从受力和经济方面对正交布置、斜交布置两种形式钢横梁门式墩进行分析。结果表明:采用斜交布置虽然能够减小钢横梁跨度,但是需要增加横梁宽度来满足相关规范的构造要求;斜交布置的钢横梁截面强度较大,安全储备高,但是纵向及横向刚度较低;斜交布置钢横梁框架墩的每延米费用高,正交布置的综合概算高。门式墩布置形式选型中应结合新建线路与既有线路的交角大小、场地情况等,选择合理的布置形式,在满足结构安全的前提下达到经济效益最大化。

考虑衬砌截面协调变形约束的既有隧道受盾构下穿施工影响的Fourier能量变分解

目前关于新建盾构开挖诱发既有地铁隧道变形的理论研究,大多将既有隧道简化为不含接头的Euler-Bernoulli梁,而忽视了衬砌截面的剪切变形与管片接头的局部刚度削弱。此外,既有地基模型理论较少考虑衬砌管片与接触土体的协调变形约束。首先,采用Loganathan-Polous公式计算盾构开挖诱发的土体自由位移场,并将既有隧道视为考虑剪切变形的Timoshenko梁,基于沿轴线变化的抗弯与剪切刚度函数来描述管片接头的局部削弱作用;然后,结合能量变分原理与连续弹性体Mindlin解,建立考虑衬砌截面协同变形约束的隧道位移控制方程,将盾构开挖诱发的附加荷载施加于既有隧道,并使用Fourier级数方法求解既有隧道纵向变形;最后,将Fourier能量变分解与3组工程实测数据进行对比验证,取得了较好的一致性。此外,考虑隧道抗弯刚度、剪切刚度、接头刚度削弱作用、土体参数与隧道空间位置等因素的共同影响,使用抗弯系数、剪切系数及接头系数进行敏感性分析。结果表明,考虑截面变形协调约束的理论解更为符合实际,不考虑变形协调约束所得隧道位移结果偏大;衬砌接头局部刚度的削弱作用将造成隧道弯矩沿轴线在接头处发生明显锯齿状突变;抗弯系数与剪切系数的增长均导致隧道结构所受弯矩降低;剪切系数由低到高的增长将导致隧道变形模式发生“弯曲控制-弯剪混合-剪切控制”三阶段变化;隧道变形模式进入“剪切控制”阶段的过程中,抗弯刚度的变化对隧道内力影响逐渐降低;接头系数的增长将造成隧道所受弯矩降低,但隧道抗弯刚度较大时其影响逐渐减弱。

斜拉加固技术在栈桥抢险工程中的应用

斜拉加固技术研究基于盐城港大丰港区栈桥抢险加固工程,原有栈桥桩基被船舶撞击后出现断裂,导致上部横梁失稳,出现不同程度开裂及梁端沉降现象,严重影响上部设备安全。该项目处于外海无掩护开敞海域,栈桥横梁除后方引桥以外无任何可支撑依靠构件,在不拆除原有横梁及空心板条件下,采用一种斜拉加固技术,对栈桥横梁进行加固,从而快速解除现有危险状态,为后期桩基及横梁修复提供施工平台,有助于降低施工成本、加快施工进度和提高施工安全系数,可为类似工程施工提供参考。