A statistical investigation of time-variant hull girder strength of aging ships and coating life

Risk- and reliability-based approaches are increasingly being applied in assisting inspection and maintenance planning. One of the keys to such approaches is properly predicting the hull girder strength (HG) of gradually degradated hull structures. The development has been limited by the lack of data on aging ships—validation of the developed methods has not been possible. To fill the gap of knowledge on hull strength of ships in service, this paper presents a database of as-gauged hull structures and a statistical study of the time-variant HG of tankers. The expanded data set was collected from 2195 as-gauged girth belts (transverse sections) of 211 single-hull tankers that were 12–32 years old. It was intended to (1) provide actual data on hull girder section modulus (HGSM) of tankers, (2) investigate the general trends of the change in the HG over ships’ service life, and (3) propose formulations for presenting time-variant HGSM and coating life.

The data set demonstrated a high variation of HGSM that changed over time. The mean value and standard deviation of HGSM loss were derived as functions of time. The probability density function (pdf) of coating life was also derived. Comparisons were made between previous studies on HG and the current data set. It was found that almost all previous studies showed much greater HG loss than what this database revealed. The refinement of existing calculations appears to be needed. The data set and statistical study were expected to form the basis for validating formulations of HG that are key components in risk- and reliability-based approaches.     

休闲交通：公共交通公司的发展良机

瑞士的休闲交通量已达到650亿乘客／km,这意味着瑞士交通里程中有60％是属 于休闲交通范围内的。所以,未来的公共交通需要对这一巨大的潜能倾注更多的注意。　　公共交通公司在它们的主要市场 上班族和长期车票使用者 的交通中正面临着扩大经 营的极限。虽然采取适当的调整措施可以增加一定程度的班次,拓宽一些供需渠道,但要实现运输 量的飞跃,只有在特殊情况下才有可能（例如当一个地区的服务业或经济水平迅猛发展时）。 除了山区旅游线路以外,很显然,交通公司的服务重点主要是那些长期乘车的顾客。而与此形成鲜明对 照的,是休闲交通可能提供的其它服务项目,但至少在目前,人们对休闲交通的充分开发还没有足 够的认识。　　休闲交通的特征　　休闲交通与日常交通在各方面都有很大的区别。在闲暇时,人们有了更多选择的自由。 人们在闲暇时间里是否有外出的希望,想去干什么和如何去干,都不会受到外界的干预,而在很大 程度上取决于自己。然而,在休闲旅行中经常发生的一窝蜂现象和休闲娱乐基础设施方面的种种缺 陷,却经常使休闲成为一种相似的、团体的行为方式,我们对此需要预先进行仔细的分析。　　对现代休闲交通的要求     

全轮驱动车辆传动系统的养护

多年的工作经验表明,熟悉全轮驱动车辆(AWD)传动系统的一些技术细节,将十分有助于增强在四轮驱动车辆(4WD)传动系统的保养与维修方面的业务竞争力。 当我们嘟嘟囔囔发着牢骚,一肚子怨气地看着运货卡车停在皮卡车的后面时,当然也会看到了红色的4x4平头驾驶室连同两个车轮悬在半空中。但悬置在     

Coordinating buses and rapid rail in the San Francisco Bay Area: The case of Bay Area Rapid Transit

This paper examines attempts by planners and policy makers to analyze and bring about the coordination of rail and bus transit in the San Francisco Bay Area. Drawing on studies and plans before and after the creation of the rapid rail system BART (Bay Area Rapid Transit), the author points to technical, analytical and political problems in attempts to link BART and buses. Some options and cautions are presented for planners considering route coordination, feeder buses, transfers and institutional arrangements to manage bus and rail services.     

Signalized intersections with variable flow rates: II A model for delay estimation

This second part of our work develops a model for delay estimation at intersections whose traffic signal controls are continuously being updated. Generally, these traffic signals are centrally controlled. The foundation for the delay estimation model is based on a queuing theory model called “Preemptive resume discipline for M/G/1 with two priority levels.” This queuing model assumes that two customers arrive at acertain point by a Poisson arrival process, and that one customer has service priority over the second customer. The analogy for the case of intersection control is that the preferred customers are the red lights and the secondary customers are the vehicles. In order to adapt the model to the realistic behavior of vehicle traffic at continuously adjusted signals, components are derived to modify the model. The simulation results of the first part of this work are used to calculate adjustment factors that fairly accurately reproduce the simulated delays. This gives rise to the advantage of using in practice a closed mathematical model, in particular when trying to optimize the operation of signalized intersections at the network level.     

Moving between mobility cultures: what affects the travel behavior of new residents?

This paper analyzes the complex interdependencies between residential relocation and daily travel behavior by focusing on modal change. To help explain changes in daily travel patterns after a long distance move between cities the concept of urban mobility cultures is introduced. This comprehensive approach integrates objective and subjective elements of urban mobility, such as urban form and socio-economics on the one hand, and lifestyle orientations and mode preferences on the other, within one socio-technical framework. Empirically, the study is based on a survey conducted among people who recently moved between the German cities Bremen, Hamburg and the Ruhr area. Bivariate analyses and linear multiple regression models are applied to analyze changes in car, rail-based and bicycle travel. This is done by integrating variables that account for urban mobility cultures and controlling for urban form, residential preferences and socio-demographics. A central finding of this study is, that changes in the use of the car and rail-based travel are much more dependent on local scale, such as neighborhood type and residential preferences, whereas cycling is more affected by city-wide attributes, which we addressed as mobility culture elements.     

Addressing endogeneity in strategic urban mode choice models

Transportation - Endogeneity is a potential anomaly in econometric models, which may cause inconsistent parameter estimates. Transport models are prone to this problem and applications that...     

Perception bias in route choice

Travel time is probably one of the most studied attributes in route choice. Recently, perception of travel time received more attention as several studies have shown its importance in explaining route choice behavior. In particular, travel time estimates by travelers appear to be biased against non-chosen options even if these are faster. In this paper, we study travel time perception and route choice of routes with different degrees of road hierarchy and directness. In the Dutch city of Enschede, respondents were asked to choose a route and provide their estimated travel times for both the preferred and alternative routes. These travel times were then compared with actual travel times. Results from previous studies were confirmed and expanded. The shortest time route was chosen in 41 % of the cases while the perceived shortest time route was chosen by almost 80 % of the respondents. Respondents overestimated travel time in general but overestimated the travel time of non-chosen routes more than the travel time of chosen routes. Perception of travel time depends on road hierarchy and route directness, as more direct routes and routes higher up in the hierarchy were perceived as being relatively fast. In addition, there is evidence that these attributes also influence route choice independently of perceived travel time. Finally, travel time perceptions appear to be most strongly biased against non-chosen options when respondents were familiar with the route or indicated a clear preference for the chosen routes. This result indicates that behavior will be more difficult to change for the regular travelers.     

Flexible parking requirements for office developments: New support for public parking and ridesharing

The author examines new, flexible parking requirements in several U.S. cities and Canada. Flexible requirements provide relaxations in zoning code specifications for off-street parking in return for developer commitments to ridesharing measures, support of transit or in-lieu fees for public parking. Issues examined include whether developers take advantage of flexible requirements, whether agreements with developers lead to agreed-upon action, and whether actions lead to desired results. Based on experiences of several cities, implications and cautions are drawn for local planners. The first caution relates to cities using flexible requirements to collect in-lieu fees in support of public parking. Where cities delay providing parking, inflation may make it difficult to provide the desired parking supply. Or, developers may not choose to pay the fee, such as in the case where cities grant relaxations for other measures more attractive than paying the fees.Other implications relate to flexible requirements in support of ridesharing or transit. Developers will not necessarily take advantage of relaxations tied to support of these modes. Generally, developers will take the least-cost ways to gain relaxations. They may choose to provide the parking where transit or ridesharing measures are too costly or complex. Or, they may take relaxations easier to obtain than those for ridesharing and transit. Finally, even where developers do agree to ridesharing measures, the measures may not be effective. On the other hand, developer-sponsored actions have proven effective in some cities where tight or expensive parking prevails, or where neighborhood residents have organized against office commuters parking on neighborhood streets, or where other economic or community variables favor ridesharing and transit.