基于LS-DYNA公路桥梁车桥耦合振动模型

基于LS-DYNA程序,采用线弹性的橡胶及钢材模拟车轮并定义轮胎内气压,运用转动约束关节和圆柱形约束关节实现车轮转动特性;结合车辆悬架系统动力特性,运用弹簧阻尼单元及梁单元仿真实现悬架动力特性;调整质量单元的大小及分布,实现车体质量分布与实际一致.以某三轴重型车辆为例,建立了用于研究车桥耦合振动响应的精细车辆模型.对比车辆有限元模型的轴载、自振频率理论值与实测值,验证车辆模型的有效性.以某一简支梁桥为例,采用LS-DYNA有限元模拟和MATLAB数值分析移动弹簧-质量-阻尼振动系统,对比研究车辆匀速通过简支梁桥时,各片梁的振动响应.研究结果表明,运用LS-DYNA精细有限元模型能准确分析车桥耦合振动响应,但计算工作量大.     

中高水头船闸三角门流固耦合动力特性分析

船闸三角门考虑流固耦合作用下的自振特性是分析闸门流激振动的关键因素。采用空间有限元数值模拟,分析得到了三角闸门在不同水位条件下的自振频率和振型模态。计算表明,流固耦合作用对闸门自振特性的影响,总是使闸门的自振频率下降,振型模态也相应发生转变。在计算分析的基础上,对船闸三角门的安全运行操作提出了合理化建议。     

海港进港航道设计辅助分析系统设计与实现*

为合理确定海港进港航道设计的基本尺度,建立海港进港航道设计辅助分析系统,为设计人员提供港口服务水平、船舶等待时间等信息。充分利用网络、计算机仿真等技术,实现船舶航行作业系统仿真、影响因素分析等功能,并给出系统总体结构及类结构。应用实例表明该系统能模拟船舶航行作业过程,可有效协助设计人员优化航道设计方案。     

Modelling trip distribution with fuzzy and genetic fuzzy systems

This paper explores the potential capabilities of fuzzy and genetic fuzzy system approaches in urban trip distribution modelling with some new features. First, a simple fuzzy rule-based system (FRBS) and a novel genetic fuzzy rule-based system [GFRBS: a fuzzy system improved by a knowledge base learning process with genetic algorithms (GAs)] are designed to model intra-city passenger flows for Istanbul. Subsequently, their accuracy, applicability and generalizability characteristics are evaluated against the well-known gravity- and neural network (NN)-based trip distribution models. The overall results show that: traditional doubly constrained gravity models are still simple and efficient; NNs may not show expected performance when they are forced to satisfy trip constraints; simply-designed FRBSs, learning from observations and expertise, are both efficient and interpretable even if the data are large and noisy; and use of GAs in fuzzy rule-based learning considerably increases modelling performance, although it brings additional computation cost.     

基于相互积分的应力强度因子数值分析

应力强度因子可反映裂纹尖端弹性应力场的强弱,是解决结构疲劳断裂问题的重要参数。工程上常采用有限元分析软件对各种复杂裂纹体进行数值模拟进而求解断裂问题。有限元分析软件ANSYS提供后处理功能可直接计算各种断裂参数。借助ANASYS计算平台,分别采用传统的位移插值法和基于相互积分的数值方法可求得张开型二维及三维裂纹应力强度因子。将数值分析结果与二维裂纹的解析解和三维裂纹扩展实验的测量结果进行对比分析后发现,基于相互积分理论求得的应力强度因子更为精确,这种优势在三维裂纹数值分析中更为显著。     

桩基础桥梁的土—结构动力相互作用

首先以加权残差公式为基础，采用积分方程方法推导与桩基础对应的层状场地动力刚度矩阿公式，并用解析解验证了数值分析的计算结果。然后用子结构法联合积分方程方法和有限元法的计算结果，求解土-结构动力相互作用的地震响应；最后以芜湖长江大桥主跨斜拉桥长塔墩的地震响应为例，将本文的计算结果与Penzien模型的计算结果作了比较。     

Convection and the seeding of the North Atlantic bloom

Observations of vertical velocities in deep wintertime mixed layers using neutrally buoyant floats show that the convectively driven vertical velocities, roughly 1000 m per day, greatly exceed the sinking velocities of phytoplankton, 10 m or less per day. These velocities mix plankton effectively and uniformly across the convective layer and are therefore capable of returning those that have sunk to depth back into the euphotic zone. This mechanism cycles cells through the surface layer during the winter and provides a seed population for the spring bloom. A simple model of this mechanism applied to immortal phytoplankton in the subpolar Labrador Sea predicts that the seed population in early spring will be a few percent of the fall concentration if the plankton sink more slowly than the mean rate at which the surface well-mixed layer grows over the winter. Plankton that sink faster than this will mostly sink into the abyss with only a minute fraction remaining by spring. The shallower mixed layers of mid-latitudes are predicted to be much less effective at maintaining a seed population over the winter, limiting the ability of rapidly sinking cells to survive the winter.     

土层液化过程中桩土相互作用的动力p-y曲线研究

依据加权余量法原理,推导了确定桩与液化土层相互作用振动台模型试验动力p-y曲线的方法。分析了具有不同初始相对密度的土层在液化过程中动力p-y曲线的弱化以及桩土相互作用阻尼的变化,对动力p-y曲线和拟静力弱化p-y曲线进行了比较。结果表明,依据静力p-y曲线、按折减系数法确定拟静力弱化p-y曲线时,折减系数的取值不仅取决于土层初始相对密度,还与土层的埋深有关。     

大跨度铁路桥梁刚度统一描述方法探讨

研究目的:本文在已建成的桥梁基础上,进一步开展了大跨度铁路桥梁刚度描述方法和预应力混凝土连续梁(刚构)桥刚度的限值研究,以提出一种大跨度铁路桥梁刚度问题的统一描述方法。研究结论:采用设计荷载下的梁端横向、竖向、扭转角及非梁端处横向、竖向、扭转角的变化率(即曲率)描述桥梁刚度,推导了大跨度铁路预应力混凝土连续梁(刚构)桥刚度设计参考限值。该方法不但能方便地描述简支梁的刚度问题,与现有规范相衔接,而且在描述规范所不能涵盖的大跨度桥梁、特殊桥梁结构刚度问题时也非常方便。研究方法和研究成果有利于提高桥梁刚度研究和设计水平,为发展更大跨度桥梁提供技术支撑。     

粤北山区高速公路煤系地层滑坡机理分析

以京珠高速粤境北段k18 170～k18 225滑坡为例,研究了煤系地层滑坡机理,通过对滑动带土的矿物组成及其物理力学性质分析,发现该类边坡滑坡的主要原因是煤系地层中的泥炭土含有一定比例的亲水矿物,在水的作用下力学性质发生大幅度降低.有限差分法分析结果表明:在边坡滑动带的泥炭层存在剪应力集中区,与滑动带的地质和物理力学滑坡分析结果相吻合.