The value of travel time savings in freight transport: a meta-analysis

Transportation - The value of freight travel time savings (VFTTS) is a monetary value that is considered an important input into cost–benefit analysis and traffic forecasting. The VFTTS is...     

Do frequent satisfying trips by public transport impact its intended use in later life?

Transportation - Previous studies have indicated that factors such as the built environment, attitudes and past behaviour can influence travel behaviour. However, the possible effect of travel...     

20000吨级自航半潜船冷却水系统故障诊断与排除

随着技术发展,越来越多的船舶采用电力推进装置.同常规推进相比,更多的设备比如变频器、变压器,需要采用淡水冷却,而且它们往往布置在机舱外,增加了中央冷却水系统调试的难度.介绍了采用电力推进的自航半潜船,中央冷却水系统调试中暴露出的问题,并针对其中的主要矛盾,提出了解决方案.     

Characteristics of bubble plumes, bubble-plume bubbles and waves from wind-steepened wave breaking

Observations of breaking waves, associated bubble plumes and bubble-plume size distributions were used to explore the coupled evolution of wave-breaking, wave properties and bubble-plume characteristics. Experiments were made in a large, freshwater, wind-wave channel with mechanical wind-steepened waves and a wind speed of 13 m s^− 1. Bubble plumes exhibited a wide range of bubble distributions, physical extent and dynamics. A classification scheme was developed based on plume extent and “optical density” which is the ability of a plume to optically obscure the image of the background until maximum penetration of the plume. Plumes were classified as either dense (obscure) or diffuse (no-obscure). For each class, the plume bubble population size distribution, Φ(r,t), where r is the bubble radius and t the time, was determined. Dense plumes have a large radius peak in Φ and thus are enhanced in large bubbles. Diffuse plumes are well-described by a weakly size decreasing Φ(r,t) for r < 1000 μm and a more strongly size decreasing Φ(r,t) for r > 1000 μm.The bubble-plume formation rate, P, for each class, wave-breaking rate and wave characteristics were measured with respect to fetch. Wave-breaking rate and intensity are strongly fetch-dependent. In general, the trends in P and wave breaking are similar, reaching a maximum at the fetch of maximum wave breaking. The ratio of P for dense to diffuse plumes is even more sensitive to the occurrence of the most intense wave breaking, where dense plume formation is the greatest.Using P and the bubble size population distributions for each plume class, the global bubble-plume, injection size distribution, Ψ_i(r), was calculated. The volume injection rate for the study area was 640 cm³ s^− 1 divided approximately equally between bubbles smaller and larger than r  1700 μm.     

3 600 t不锈钢化学品船轴系校中问题处理

介绍了对3600t不锈钢化学品船轴系校中问题的处理过程。     

船体纵骨典型节点疲劳裂纹扩展寿命评估

基于有限元软件ABAQUS,结合虚拟裂纹闭合法、裂纹扩展判据及子结构技术,应用脚本语言Python开发出模拟疲劳裂纹扩展的程序(FCG-System)。对含初始裂纹的油船纵骨典型节点在侧面压力作用下进行疲劳裂纹扩展数值模拟,并探讨了软趾、背肘板及防倾肘板对疲劳裂纹扩展路径和寿命的影响。结果表明,增设软趾、背肘板或防倾肘板都会使裂纹扩展路径曲率增大,且软趾、防倾肘板可使裂纹扩展寿命增大,背肘板可使裂纹扩展寿命减小。     

民营科技企业融资困难的原因和对策探讨

从企业内部和外部两个方面分析了民营科技企业融资困难的原因，在此基础上提出解决融资问题的对策建议：（1）在思想认识上，应坚持“三要三不要”原则和制定“有所为，有所不为”的重点资助计划；（2）在融资体系的建设上，应从企业、政府和国际三个层次来建设“多层次、多渠道、全方位”的融资体系。     

低温送风系统散流器的性能评价

通过实验和数值模拟计算，对风车－风扇诱导型散流器的性能进行分析，表明该型散流器具有高诱导比，并且在一次风量变化范围很大时均能正常工作，因而能在空调房间的工作区内形成较为均匀的气流分布和温度分布。由此可见，在冰蓄冷低温送风系统中，采用该型散流器可获得舒适的室内热环境。     

A NEW ESTIMATION METHOD OF SPATIAL PEAK TEMPORAL AVERAGE INTENSITY AND SPATIAL PEAK PULSE AVERAGE INTENSITY IN HIFU FIELD

High intensity focused ultrasound( HIFU) inmedicine has been developed rapidly for more thanten years.It changes the situation of slowly ad-vancing in ultrasonic therapy. HIFU has become anew character of ultrasound in medicine.The ex-tracorporal lithotriptor,the pyrothrapy,the HIFUsurgery,the HIFU hemostasis,and the HIFUabortion are the most important progresses.Theyshow that the applications of ultrasound in therapywill have greater project than that in diagnosis[1] .China has made m…     

敷设粘弹性阻尼的加筋板振动和阻尼分析

对敷设粘弹性阻尼的加筋板的固有频率和模态损耗因子进行了分析。考察了在加筋板结构上加自由阻尼层和加粘弹性筋梁的两种情况，分析了粘弹性阻尼材料模量、损耗因子、阻尼层厚度以及粘弹性梁剖面尺寸的影响。对粘弹性筋梁的讨论，拓宽了加筋板的粘弹性阻尼的敷设形式。