The critical hitch angle for jackknife avoidance during slow backing up of vehicle–trailer systems

We set out to answer the question: At what hitch angle does it become impossible for a vehicle and trailer to continue to backing up without getting into a jackknife? Jackknifing during backing up of trailers occurs when the hitch angle increases to a point such that the vehicle and trailer fold together about the hitch point like a jackknife. If the backward motion is continued, the jackknife effect progressively worsens, until the vehicle and trailer are in physical contact with each other. Jackknifing can result in traffic disruptions and wasted time, and can potentially cause damage or personal injury. Our goal is to analytically determine the ‘critical hitch angle’ (θ_cr), the hitch angle threshold beyond which a continued reverse motion causes an inescapable jackknifing. In this paper, we provide a formal definition of θ_cr for slow backing up of vehicle–trailer systems on a level solid surface, beyond which the vehicle must stop backing up and revert to forward motion in order to escape from jackknifing. The critical hitch angle is sub-categorised into Absolute (θ_cr, a) and Directional (θ_cr, d) critical hitch angles depending on the operating constraints and vehicle steering objectives. One solution for θ_cr is posed as a numerical solution to the steady-state conditions of the dynamic equations. The effects of such hitch angle limitations are demonstrated through simulation. Also, a warning system making use of the θ_cr is proposed. Such warning systems can assist drivers in avoiding jackknifing while backing up a vehicle–trailer system.     

利用高压喷射注浆法处理桩底夹层缺陷

某工程嵌岩桩桩底存在强风化夹层,经方案比选后确定采用高压喷射注浆法予以处理。该文介绍了其处理技术难点。合理设计喷嘴的类型、压力、喷嘴直径、喷嘴数量等技术参数是决定对夹层置换程度的关键因素,也是该方案的技术难点。夹层全置换完成后高压注入水泥浆填充空洞并与上下微风化层胶结,确保桩端持力层的完整性。     

隧道内拆解盾构机主轴承的要点作业

就狮子洋海底隧道2台盾构机主轴承在隧道内拆解过程中的吊点分布、吊点受力及吊点依附结构局部应力进行分析,确定主轴承在隧道内拆解的方法,并对本次主轴承的实际拆解进行了总结,以期对类似作业提供一定的借鉴。     

电子海图的显示精度分析

综合考虑了影响海图信息显示精度的主要误差源，对电子海图的显示精度进行分析和估算，并指出提高精度的方法和途径。     

一维单峰幅度非对称映象的标度因子

计算了z=4,6时的一维单峰幅度非对称映象的两个标度因子δ和a值。结果表明,它们都具有振荡行为,即交替地收敛到各自的两个常数c_1、c_2和d_1、d_2。对于固定的z值,c_1·c_2=δ~2,d_1·d_2=a~2。在聚点a~*处有c_1=c_2=δ,d_1=d_2=a。这里δ,a及a~*是一维单峰对称映象中相同z值下的标度因子值和聚点值。     

大秦线重点隧道病害调查情况及建议

20 0 2年 1月 ,由铁道部运输局组织 ,北京铁路局、大同铁路分局等单位参加 ,对大秦铁路隧道的衬砌渗漏水及路基翻浆冒泥等病害进行调研。通过对重点隧道的实地考查 ,召开现场座谈会 ,广泛听取基层管理及养护部门的情况汇报 ,结合隧道设计、施工、运营等各方面的资料进行全面的分析和论证 ,初步提出对病害进行综合整治的有关建议和措施     

实时悬点高度测量与放样研究

研究悬点高度测量与放样的原理、精度分析及其观测方法。     

邮轮结构表面缺陷处理等级表示方法

考虑到邮轮结构复杂,舱室及功能多样,结构表面缺陷处理等级较一般民船更为复杂,对大型邮轮等级设置和表达方式进行分析,提出大型邮轮特有的结构表面缺陷处理等级表示方法,供解决现场区域难以识别问题和质量过剩问题参考.     

橡胶粉掺量对沥青技术指标的影响

为了研究橡胶粉在沥青中的作用机理,通过室内试验分析了橡胶粉掺量对沥青软化点、针入度和低温延度的影响。试验结果表明:软化点和延度都随橡胶粉掺量的增大先增大后减小,当橡胶粉掺量为15%时,软化点和延度都达到最大值,表明此时橡胶沥青的高低温性能最好;针入度随橡胶粉掺量的增大逐渐降低,但与基质沥青的针入度相差不大。     

缺陷汽车召回管理条例解读

简要地介绍了缺陷汽车产品召回管理条例的核心内容及召回条例发布后汽车企业和消费者应该注意的事项,重点对企业合理规避召回风险进行了解读与分析。