复杂环境下钢筋混凝土简支梁式桥爆破拆除

介绍了城市复杂环境下钢筋混凝土简支梁式桥梁爆破拆除实例。根据待爆破桥梁自身结构特点及周围环境要求,采用浅孔爆破和深孔爆破相结合的爆破拆除施工方案。桥墩、台帽、联系梁采用浅孔爆破,南北两端承台基础采用中深孔爆破技术一次性爆破拆除。在保证桥梁结构安全的条件下,对桥梁南北两跨及部分桥面进行了预处理。为了增加桥梁构件部分空中解体效果及减少爆破后二次破碎量,起爆网路采用由北向南逐跨逐段延时起爆技术。在施工过程中进行精细化管理,对爆破参数进行优化,严格控制钻孔质量,采取有效的安全防护措施,对重点对象景观"中隔墙"采取缓冲垫层进行防护。爆破达到了预期的爆破效果,桥体空中解体较为充分,爆破有害效应没有对周边建构筑物造成影响,重点保护对象"中隔墙"完好无损。     

The Stable Levitation of an Iron Ball over a Ring Magnet

An iron ball floats in midair in a plastic tube when the plastic tube is coaxially inserted in a ring-shaped permanent magnet. A ring permanent magnet has a special paraboloidal interface around its axis, the magnetic field Bz is of negative value, and points down in the range Zlow. But it is of positive value and points up in the range Zup; it is 0 at Z0 position. The iron ball cannot be stable levitated over the ring magnet no matter it is in the Zlow or Zup regions; it is only possible to realize the stable levitation of the iron ball at Z0 position. Theoretical calculation and experiment have been done and identified the stable levitation of an iron ball over a ring magnet. It is helpful to design and develop new magnetic levitation system for practical applications.     

船-桥梁浮式钢套箱碰撞数值模拟中的流场处理方法对比研究

本文采用Ansys/Ls-dyna对1000吨级船舶与浮式桥梁钢套箱的碰撞过程进行了数值仿真,为了较精确地分析流场处理方法对于数值计算结果的影响,分别采用了流固耦合方法和附加质量系数法来模拟碰撞过程中流场的作用,并对比分析了两种方法下浮式钢套箱的碰撞力、撞深、竖向位移、内能变化等计算结果。研究结果表明,与采用附加质量系数法的结果相比,考虑流固耦合时防撞钢套箱的最大撞深较小而最大撞击力较大,且随着碰撞能量的增加,最大撞击力明显大于采用附加质量系数法的结果。因此对于桥梁的防撞钢套箱设计,常规附加质量系数法偏于危险,有必要用流固耦合方法来考虑流场的作用。另外,船体的撞击能量越大时,浮式钢套箱的竖向位移约束也越重要,可以通过设计浮式钢套箱的压载水,减小钢套箱在碰撞过程中的竖向位移,以提高其吸能效果。     

汽车-自行车碰撞事故三维仿真再现研究

针对一起实际的汽车与自行车碰撞事故，运用多刚体动力学方法建立事故小客车与自行车及骑车人碰撞的三维多刚体动力学仿真模型，利用MADYMO对事故碰撞过程进行了直观的三维仿真再现，分析研究它们在碰撞后的动力学行为特性，计算得出碰撞时刻小客车车速为正确鉴定事故提供了科学的参考依据。仿真再现结果与实际事故情况能较好吻合，初步验证了仿真方法和模型的可行性。     

两类船-桥碰撞力差异及桥梁结构响应分析

 船桥碰撞是跨航道桥梁需考虑的重要问题。本文以美国AAHSTO规范推荐两类船舶为例,研究了驳船和散装货轮撞击桥梁后碰撞力、船艏刚度和碰撞能量的变化过程,讨论了导致两类船舶碰撞力、船艏刚度和碰撞能量变化差异的原因,分析了两类船桥碰撞桥梁结构的主要响应,并将本文动力模型计算响应与已有规范计算得到响应进行了对比。结果表明,两类船舶不同的船艏外形及内部构造会对碰撞力造成较大影响;同等吨位和碰撞速度下,驳船碰撞峰值荷载比散装货轮大,驳船碰撞的墩顶位移比散装货轮小,基底剪力和弯矩比散装货轮大,驳船与散装货轮作用下桥梁结构响应的动力反应系数存在较大差异;不同规范对于碰撞荷载规定差异较大,欧洲规范计算得到响应总体较大,中国公路规范荷载对于内河船舶撞击计算得到的响应最小,中国铁路规范计算得到的响应与其他规范海轮撞击响应进行对比最小。     

构件跌落碰撞的数值模拟研究

针对构件跌落碰撞问题,将Hertz-damp模型与有限元方法结合,给出了结构碰撞位移突加约束条件,建立了碰撞结构体系的动力方程。该方法能考虑碰撞体质量分布对碰撞过程的影响,同时可描述结构碰撞过程中的刚度非线性和能量损失。建立了构件跌落碰撞模型,初步分析了跌落构件质量、质量分布以及跌落高度等参数对碰撞过程的影响。研究表明:结构碰撞模拟中碰撞体质量沿接触面法线轴向不对称时应考虑其质量分布,否则会高估碰撞反应;碰撞荷载峰值和单次碰撞持续时间与跌落构件质量和跌落高度均成指数关系,碰撞荷载峰值随跌落构件质量和跌落高度增大而增大,而单次碰撞持续时间则随跌落构件质量增大而增大,随跌落高度增大而减小。这些规律能为减轻结构碰撞破坏研究提供参考。     

Mechanics of minor ship collisions

A structural method is presented by which the critical velocity for a minor collision of a ship striking another ship midships at right angles can be determined rather realistically with a minimum of computational effort. The velocity of the striking ship is defined as critical for a minor collision when the side wall of the struck ship just ruptures. This means the possibility of an oil spill in an oil tanker.The proposed method takes into account the deformability of both collision opponents. The energies absorbed in both ships, up to rupture of the struck ship hull, are computed using internal collision mechanics. The critical velocity can then be determined using external collision mechanics.The method is used for the collision of two equal oil tankers of 141,000 TDW with bulbous bows. The critical velocity was found to be 6.8 knots.     

Examining driver injury severity in two vehicle crashes – A copula based approach

A most commonly identified exogenous factor that significantly affects traffic crash injury severity sustained is the collision type variable. Most studies consider collision type only as an explanatory variable in modeling injury. However, it is possible that each collision type has a fundamentally distinct effect on injury severity sustained in the crash. In this paper, we examine the hypothesis that collision type fundamentally alters the injury severity pattern under consideration. Toward this end, we propose a joint modeling framework to study collision type and injury severity sustained as two dimensions of the severity process. We employ a copula based joint framework that ties the collision type (represented as a multinomial logit model) and injury severity (represented as an ordered logit model) through a closed form flexible dependency structure to study the injury severity process. The proposed approach also accommodates the potential heterogeneity (across drivers) in the dependency structure. Further, the study incorporates collision type as a vehicle-level, as opposed to a crash-level variable as hitherto assumed in earlier research, while also examining the impact of a comprehensive set of exogenous factors on driver injury severity. The proposed modeling system is estimated using collision data from the province of Victoria, Australia for the years 2006 through 2010.     

船舶撞击作用下车桥系统动力响应及高速列车运行安全分析

将船舶撞击力时程作为系统的外部激励,建立了撞击荷载作用下的车桥系统动力分析模型。以一座 (32+48+32) m双线预应力混凝土连续梁桥和国产CRH2高速列车为例,模拟船舶撞击力作用于桥墩时列车过桥的全过程,分析了桥梁和车辆的动力响应。结果表明：船舶撞击作用大幅度增大了桥梁的横向位移和加速度响应,显著影响了桥上高速列车的运行安全。探讨了船舶撞击荷载作用下的桥上高速列车走行安全评价方法,综合分析了列车速度和荷载撞击强度对列车运行安全的影响,在此基础上给出了列车速度－撞击力强度安全阈值曲线。     

基于非线性数值模拟的船桥碰撞力快速估算

船舶对桥墩的最大撞击载荷是桥梁设计的重要依据之一。通过有限元仿真技术模拟了5000、10000、50000、60000吨4种不同载重吨位的船舶正撞刚性桥墩时的碰撞载荷,归纳出船桥碰撞力-撞深、能量-撞深等曲线和最大碰撞力数据。并在此基础上,得到最大碰撞力-船舶吨位曲线,可用于近似估算各种吨位船舶在不同航速时的最大撞击桥梁力。     

The effect of Operation 24 Hours on reducing collision in the City of Edmonton

In the City of Edmonton, in order to reduce the prevalence of collisions, the Operation 24 Hours program (OPS24) was developed by using existing police and transportation services resources. The program uses traditional manned police speed enforcement method, which are supplemented by traffic safety messages displayed on permanent and mobile dynamic messaging signs (DMS). In this paper, collision data analysis was performed by looking at the daily number of collisions from 2008 to 2011 that covers 28 Operation 24 Hours (OPS24) events. The objective of the collision data analysis is to analyze if there is a reduction in collision frequencies after OPS24 was held and examined how long the collision reduction effect last. Weather factors such as temperature, thickness of snow, and wind gust have been considered by many as a great influence on collision occurrences, especially in a city with long and cold winter such as Edmonton. Therefore, collision modeling was performed by considering these external weather factors. To analyze the linear and periodic trend of different collision types (injury, fatal, and property damage only (PDO)) and examine the influence of weather factors on collisions, negative binomial time series model that accounts for seasonality and weather factors was used to model daily collision data. The modeling also considered collision proportion to account for missing traffic volume data; the Gaussian time series model that accounts for seasonality and weather factors was used to model collision proportion. To estimate the collision trend and test for changes in collision levels before/after OPS24, interrupted time series model with segmented regression was used. While for estimating how long the effect of the OPS24 last, change point method was applied.     

局部集中质量接触单元法在梁式桥梁体与桥台碰撞问题模拟中的应用

近年来,模拟碰撞问题的接触单元法已经广泛运用于桥梁碰撞问题当中。其中集中参数接触单元法把碰撞两物体各自简化成质点,无法表达出碰撞应力波的传播现象;另一类Watanabe和Kawashima接触单元法,其碰撞单元的刚度是一种仅为满足精确模拟碰撞过程而采用的虚拟刚度,并无物理意义。针对梁式桥梁体与桥台的碰撞问题,该文首先提出一种新的碰撞问题模拟方法—局部集中质量接触单元法,然后详细地介绍了其在梁式桥梁体与桥台碰撞问题模拟中的应用,并通过试验验证了该方法模拟梁体与桥台碰撞的合理性。最后将该方法与两种接触单元法进行了比较,说明了该方法在模拟梁体与桥台碰撞问题中的优势。     

桥墩在船舶撞击作用下的损伤仿真研究

评述了考虑应变率效应和材料损伤的HJC混凝土模型,就材料参数的取值进行了讨论。通过刚性球撞击混凝土板的例子,讨论了HJC模型中损伤参数的敏感性,并据此确定了计算中采用的HJC模型参数。对一艘万吨级的散货船与桥墩的碰撞过程进行了仿真,给出了船舶与桥墩的碰撞力时程以及桥墩损伤形态。结果表明,由于混凝土的破损,船舶对桥墩的撞击力峰值显著降低。为获得真实的结果,在船舶与薄壁桥墩碰撞的仿真分析中应考虑混凝土的动态损伤特征。     

纳米团簇碰撞合并过程的分子动力学模拟

一直以来,金属纳米材料有着非常重要的应用价值且受到广泛关注,金属团簇碰撞合并过程的研究成果对认清团簇的沉积和纳米金属膜及块体材料的形成有重要的意义。采用Johnson的嵌入原子势(Embeded atom method,EAM)模型并结合分子动力学模拟方法,模拟金原子团簇在不同的碰撞平动速度作用下的碰撞合并过程,仅给弹团簇一定大小的碰撞动能,迫使两个团簇产生相对速度并发生相互碰撞合并,研究在不同的碰撞平动速度下和不同的团簇大小下对团簇碰撞合并过程产生的影响及对碰撞合并之后新团簇的性质产生的影响。在进行模拟碰撞之前,先对团簇进行了"退火"处理,只模拟了同等尺度大小的两个金原子团簇之间的碰撞合并过程。     

船舶-自升式海洋平台碰撞相似率研究

海洋平台作为海洋能源勘探开发的主要组成部分,是海洋油气探井、钻井、开采的主要作业基地。船舶碰撞致使平台结构损伤破坏一直是威胁海洋平台安全的主要因素之一,开展海洋平台碰撞性能研究,揭示平台结构在碰撞过程中的损伤变形机理,对提升平台安全性具有重要意义。评估平台结构耐撞性能最可靠的方法是实船碰撞试验,然而因其耗资巨大而不易开展。按一定相似关系进行比例模型试验成为现实条件下的首选。本文基于相似第二定理,运用量纲分析法推导船舶-自升式海洋平台碰撞过程中各物理量的相似关系,为平台碰撞模型试验的开展及试验参数的确定提供重要依据。结合有限元仿真技术,以平台典型的T型和K型管节点为研究对象,建立不同缩尺比下的简化碰撞模型,比较验证相似理论的可靠性。研究结果表明,缩尺模型在碰撞冲击载荷下的结构损伤变形、碰撞力和能量吸收等动态响应与实尺度模型结果一致性较好。本文研究成果可以为大型平台结构碰撞模型试验设计提供技术支撑。     

基于整船整桥模型的船桥碰撞数值仿真

桥梁在船舶碰撞时受到的动力载荷和响应是复杂的动力非线性问题。近代非线性有限元技术为该问题的求解提供了有效的工具。简述了该技术的基本原理,并基于整船整桥模型对一艘4万吨实船与桥梁的碰撞过程进行了计算。仿真结果显示了船艏结构损坏、碰撞力演变、能量传递和桥墩内部应力变化的详细情景,讨论了船-桥碰撞的力学特征。演示的方法比传统的经验公式和简化解析法提供更为精确的结果。所提供的桥墩应力状态对桥梁的设计与碰撞后的损伤评估有重要参数价值。     

Collision avoidance timing analysis of DSRC-based vehicles

Dedicated short-range communication (DSRC) has been used in prototyped vehicles to test vehicle-to-vehicle communication for collision avoidance. However, there is little study on how collision avoidance software should behave to best mitigate accident collisions. In this paper, we analyse the timing of events and how they influence software-based collision avoidance strategies. We have found that the warning strategies for collision avoidance are constrained by the timing of events such as DSRC communication latency, detection range, road condition, driver reaction and deceleration rate. With these events, we define two collision avoidance timings: critical time to avoid collision and preferred time to avoid collision, and they dictate the design of software-based collision avoidance systems.     

滚动碰撞式调制质量阻尼器力学模型及参数分析

滚动碰撞式调制质量阻尼器(PTRMD)由调谐质量阻尼器及颗粒阻尼器发展而来,其在土木工程减振控制领域中的研究仍处于初步分析与探索阶段,阻尼器自身参数及外部激励条件对其减振性能的影响尚不明确。在考虑颗粒与主体结构碰撞和摩擦效应的基础上,建立PTRMD力学模型,并将颗粒和结构的振动过程划分为非碰撞过程、碰撞过程及黏滞振动过程;建立PTRMD-单自由度结构运动微分方程并分别对其进行求解;基于数值仿真分析方法,分别对碰撞间隙比、颗粒运动频率比、滚动摩擦因数、碰撞恢复系数、颗粒质量与简谐激励强度及频率等参数对PTRMD减振性能的影响进行研究。结果表明:颗粒运动频率比较小时,PTRMD减振效果随碰撞间隙比的增加而基本成线性增加,且受激励幅值的影响较小;当颗粒运动频率比较大时,其减振效果随碰撞间距比的增加先增大后减小,且受激励幅值影响较大。     

Nucleation and Growth Kinetics of MgO in Molten Steel

The size,number,morphology and type of inclusion particles are the key factors to estimate the quality of steel product.Although considerable efforts have been made in the mathematical modeling of inclusion growth,few papers were involved in inclusion s nucleation and collision-growth,and all the existing researches about the behaviors of magnesia inclusion were based on the experiments.Thus,a mathematical model was developed to investigate the nucleation,Ostwald ripening and collision-growth of magnesia inclusion in the molten steel.Numerical results showed that the predicted particle size distributions are consistent with the previous experimental data.For the magnesia inclusions smaller than 100 nm,Brownian collision is the main collision modes.For the inclusions ranging from 0.1 to 10 μm,Brownian collision and turbulent collision are the main collision modes.For the inclusions ranging from 10 to 100 μm,turbulent collision and Stokes collision are the main collision modes.Thus,the strong turbulent flow can decrease the peak-value diameter of the magnesia inclusion effectively.