A simplified method to predict grounding damage of double bottom tankers

This paper presents a set of analytical expressions for the calculation of damage opening sizes in tanker groundings. The simplified formulas were given for the grounding force, longitudinal structural damage and the opening width in the inner and outer plating of a tanker's double bottom. The simplified formulas derived are based on a set of numerical simulations conducted with tankers of different dimensions- 120, 190 and 260 m in length. The simulations were performed for five penetration depths and for several rock/ground topologies.The formula for the horizontal grounding force was derived provided the grounding force is proportional to the contact area and the contact pressure. By use of regression analysis it was shown that the contact pressure for any combination of ship and rock size can be expressed with a single normalized polynomial. The actual contact pressure was found by scaling the normalized pressure with the structural resistance coefficient. Given the formulation for the normalized contact pressure, the actual contact force for a ship can be found as a product of average contact pressure and the contact area.The longitudinal length of the damage was evaluated based on the average contact force and the kinetic energy of the ship. The damage opening widths in the outer and inner bottom of the ship were derived separately for two ranges of relative rock sizes as they have strong influence on the deformation mode. The damage widths were given as a function of rock size, penetration depth and double bottom height. To improve the prediction of the onset of the inner bottom failure, a critical relative penetration depth as a function of the ratio of the rock size and the ship breadth was established.Comparison to the numerical simulations showed that the derived simplified approach describes the horizontal grounding force and the damage length well for the penetration depths above 0.5 m. For the range of specified relative rock sizes, the damage width in the inner and outer bottom deviates from numerical simulations approximately up to 25%, which was considered sufficient for the analyses where rapid damage assessment is needed. Comparison was also made to real accidental damage data and to the results of several simplified formulas.     

校企协同模式下开放性双师型教师队伍建设机制探讨

高等职业教育的发展和改革正在步入深水区,校企协同的深入推进,为"四位一体"的校企合作模式提出了更多实质性的要求,为具有开放性特征的现代职业教育体系建设搭建了平台。本文分析了现代职业教育体系构建背景下对教师队伍建设的新要求和校企协同育人模式的主要内容,探讨了校企协同模式下开放性双师型教师队伍的建设机制。     

铁路救援基地层级规划选址模型

基于中国铁路组织机构的特点和应急救援现状,提出了铁路救援基地的层级网络建设理念。分析了现有铁路救援基地多目标规划选址模型的不足,将铁路救援基地分为枢纽救援基地和快速救援基地。以最小救援基地总成本和最短救援响应时间为双目标函数,以最大服务距离为约束条件,建立了铁路救援基地多目标层级规划选址模型。采用层次分析法、灰色关联分析与线性参考技术等方法抽象模型参数,采用蚁群算法求解模型,并将计算结果与现有的救援决策方案进行对比。研究结果表明:应用提出的模型,通过抽象模型参数,可得到26个救援基地备选点、61个服务需求点与188条路径;在完全覆盖事故风险的情况下,救援基地数量减少3个,节约成本约240万元,总救援响应时间、最大平均救援响应时间和最小平均救援响应时间分别降低0.04、0.46、0.29h。     

包西铁路GSM-R数字光纤直放站方案研究

通过传输损耗、上行噪声叠加、传输时延和组网等方面来比较模拟光纤直放站和数字光纤直放站的优缺点,试验利用数字光纤直放站在既有包西线GSM-R系统中替代模拟光纤直放站进行弱场覆盖,发现数字光纤直放站近、远端机之间的光纤传输链路不受光功率衰减的影响,并能通过调整远端机时延可以良好解决实际应用中多个远端单元RRU之间重叠覆盖区域的时延色散问题,对数字光纤直放站今后在铁路推广应用具有参考价值。     

多孔双曲拱桥加固加宽典型案例研究

早期修建的双曲拱桥运行多年,大部分已不能满足道路交通的要求,需要拆除重建或加宽加固。文章结合福建省将乐县三华大桥桥梁实际情况,提出了一系列加固加宽措施及交通工程保障措施,提高了桥梁的结构安全和道路通行能力。     

关于地铁中漏泄同轴电缆的选择、配置和建议

简要介绍了漏泄同轴电缆的原理和基本性能,提出了以提高接收电平作勾选择和配置漏泄同轴电缆基本要求的计算方法,并举出了实例,还提出了建议。     

再论悬挂索的重力刚度——双索、多跨

按双悬挂索的受力特性，应用悬挂索重力刚度解析双悬挂索结构的经济效果和修建多跨悬索桥的可行性，并以示例予以说明。     

基于双面双弧焊接工艺的焊接接头残余应力及变形分析

本文采用数值模拟手段和小孔法测试试验,对新型双面双弧焊接工艺和现行单弧焊接工艺下船体高强度钢对接接头焊接过程及焊后残余应力、变形进行对比分析,为双面双弧焊接的实际应用及大面积推广奠定工艺基础。     

大面积随机无线传感器网络的覆盖问题研究

为解决大面积随机无线传感器网络覆盖的测量问题，根据大面积随机布放WSNs探测系统的特点，定义区域覆盖率、节点覆盖率和通路覆盖率三种测量来描述覆盖问题。利用节点密度、探测半径和通路距离等基本网络参数，研究了随机分布的大面积WSNs覆盖属性的渐近特征。最后通过仿真实验分析网络参数对各覆盖测量的影响。     

ZPW-2000A无绝缘移频轨道电路监测系统

针对ZPW-2000A无绝缘移频轨道电路的系统结构和技术特点,提出一套切实可行的监测与维护解决方案.