Simulation of longitudinal dynamics of a freight train operating through a car dumper

A heavy haul train and car dumper model was created to analyse train longitudinal dynamics during dumping. Influence of such factors as performance curve of draft gears, total free slack in couplers, operating mode of train positioner and braking of last two cars of train on the in-train forces was considered.     

An analysis of the social context of children’s weekend discretionary activity participation

This paper examines the discretionary time-use of children, including the social context of children’s participations. Specifically, the paper examines participation and time investment in in-home leisure as well as five different types of out-of-home discretionary activities: (1) shopping, (2) social, (3) meals, (4) passive recreation (i.e., physically inactive recreation, such as going to the movies or a concert), and (5) active recreation (i.e., physically active recreation, such as playing tennis or running). The social context of children’s activity participation is also examined by focusing on the accompanying individuals in children’s activity engagement. The accompanying arrangement is classified into one of six categories: (1) alone, (2) with mother and no one else, (3) with father and no one else, (4) with both mother and father, and no one else, (5) with other individuals, but no parents, and (6) with other individuals and one or both parents. The utility-theoretic Multiple Discrete-Continuous Extreme Value (MDCEV) is employed to model time-use in one or more activity purpose–company type combinations. The data used in the analysis is drawn from the 2002 Child Development Supplement (CDS) to the U.S. Panel Study Income Dynamics (PSID). The results from the model can be used to examine the time-use choices of children, as well as to assess the potential impacts of urban and societal policies on children’s activity participation and time-use decisions. Our findings also emphasize the need to collect, in future travel surveys, more extensive and higher quality data capturing the intra- and inter-household interactions between individuals (including children). To our knowledge, the research in this paper is the first transportation-related study to rigorously and comprehensively analyze the social dimension of children’s activity participation.

Some observed details of freeway traffic evolution

Certain details of traffic evolution were studied along a 2 km, homogenous freeway segment located upstream of a bottleneck. By comparing (transformed) cumulative curves constructed from the vehicle counts measured at neighboring loop detectors, it was found that waves propagated through queued traffic like a random walk with predictable statistical variation. There was no observed dependency of wave speed on flow. As such, these waves neither focused nor fanned outward and shocks arose only at the interfaces between free-flowing traffic and the back of queues. Although these traffic features may have long been suspected, actual observations of this kind have hitherto not been documented. Also of note, the shocks separating queued and unqueued traffic sometimes exhibited unexpectedly long transitions between these two states. Finally, some observations presented here corroborate earlier reports that, in unqueued traffic, vehicle velocity is insensitive to flows and that forward-moving changes in traffic states therefore travel with vehicles. Taken together, these findings suggest that certain rather simple models suffice for describing traffic on homogeneous freeway segments; brief discussion of this is offered in Section 5.     

A structural equations analysis of commuters' activity and travel patterns

An exploratory analysis of commuters' activity and travel patterns was carried out using activity-based travel survey data collected in the Washington, DC metropolitan area to investigate and estimate relationships among socio-demographics, activity participation, and travel behavior. Structural equations modeling methodology was adopted to determine the structural relationships among commuters' demographics, activity patterns, trip generation, and trip chaining information. Three types of structural equations model systems were estimated: one that models relationships between travel and activity participation, another that captures trade-offs between in-home and out-of-home activity durations, and a third that models the generation of complex work trip chains. The model estimation results show that strong relationships do exist among commuters' socio-demographic characteristics, activity engagement information, and travel behavior. The finding that significant trade-offs exist between in-home and out-of-home activity participation is noteworthy in the context of in-home vs. out-of-home substitution effects. Virtually all of the results obtained in this paper corroborate earlier findings reported in the literature regarding relationships among time use, activity participation, and travel. This revised version was published online in June 2006 with corrections to the Cover Date.     

Integrating natural and socio-economic science in coastal management

The future more sustainable management of coastal resources is an important policy goal for all governments of countries with coastlines. Coastal areas are under intense environmental change pressure with extensive feedback effects between the natural systems and the human systems. It could be argued that there is just one jointly determined and coevolving system that needs to be studied and managed. Understanding the interactions between the coastal zone and environmental change cannot be achieved by observational studies alone. Modelling of key environmental and socio-economic processes is a vital tool, required to buttress coastal management institutions and practice. Three overlapping procedural stages can be identified in the coastal resource assessment process. The scoping and auditing stage, implemented via a ‘pressure–state–impact–response’ framework, details, among other thing, problems, system boundaries and value conflicts. The framework is itself based on a conceptual model, which lays stress on functional value diversity and the links between ecosystem processes, functions and outputs of goods and services which are deemed ‘valuable’ by society. The two subsequent stages are integrated modelling, combining natural and social science methodologies, and evaluation of management options and related gains and losses. An overview of a research project, which utilised the pressure–state–impacts–response (P–S–I–R) framework and supporting concepts and methods, is presented in the last section of the paper, together with some generic ‘lessons’ for interdisciplinary research.     

The Effectiveness of Conceptual Airport Terminal Designs

Abstract

Aviation passenger traffic is forecast to grow significantly over the next decade and beyond. To accommodate this growth will require investment in airport infrastructure, including terminals. These buildings represent large, lumpy investments, so it is important to provide the capacity to accommodate the forecast traffic. However, this depends on at least two factors: the accuracy of the forecast of future demand, and the process of translating these forecasts into designs. Error in either factor can be potentially catastrophic financially. Translating forecasts into designs depends on ‘rules of thumb’ formulae that convert design hour flows into area requirements for each terminal facility. This paper examines the process of translating demand forecasts into conceptual terminal designs. The basic methods used are outlined, and how they affect the conceptual terminal design process are revealed. A model for conceptual terminal design is derived, presented and validated based on a sample of UK airports. It is shown that even if demand forecasts can be taken to be completely accurate, there can still be errors in terminal design and size resulting from the use of these ‘rules of thumb’.     

Long marine shafting alignment and optimization considering propeller hydrodynamic force in wake field北大核心CSCD

[目的]针对计入螺旋桨水动力的舰船轴系校中计算,传统方法通常容易忽略船体伴流场的影响,使得螺旋桨水动力计算的结果与真实值之间存在较大偏差,从而导致轴系校中精度下降。[方法]以某舰船长轴系为对象,建立桨-轴-船一体化有限元模型及其伴流场流域模型,利用CFD数值仿真的叠模方法计算螺旋桨水动力;采用流固耦合法将流体计算结果作用于螺旋桨表面,进行轴系校中计算,并得到螺旋桨水动力对轴系整体挠曲线及各轴承状态参数的影响规律。在此基础上,引入多目标优化算法开展轴系多目标优化校中,来解决轴系末端四套轴承间载荷差值过大的问题。[结果]考虑螺旋桨水动力后,轴系尾部挠度变化减小,越靠近螺旋桨处的轴承其载荷所受影响越大,载荷值随进速系数的增大而减小;对比多目标优化前后的轴系校中状态,轴系各轴承之间的载荷差值明显减小,轴系运行状态得到改善。[结论]所提方法提高了计入螺旋桨水动力的轴系校中计算精度,可为轴系校中质量的提升提供参考。     

Experimental study of controlling tip clearance flow in a pump-jet propulsor北大核心CSCD

[Objective]This paper aims to suppress the adverse effects of tip clearance flow on the hydrodynamic performance and unsteady excitation force of a pump-jet propulsor. [Method]As for the pre-swirl stator pump-jet propulsor, an annular flexible seal structure closely matched with a rotor tip ring is used to study the validity of suppressing the clearance flow on the rotor tip. The rotor thrust and torque of the propulsor are measured by keeping the shroud approximately rigidly fixed, enabling the rotor open water efficiency to be obtained. In addition, the point of cavitation inception at each design condition is observed and recorded carefully with the help of a high-power stroboscope, and the cavitation inception curves of the propulsor with/without tip clearance are obtained through calculation. Finally, tests of shaft vibration acceleration on the pump-jet propulsor with/without tip clearance are conducted under conditions of cavitation and non-cavitation in order to evaluate the effects of diminishing tip clearance. [Results]The results show that the thrust and torque of the rotor of the pump-jet propulsor with a flexible seal structure are significantly increased, which in turn renders open water efficiency significantly increased at low and medium advance coefficients, unchanged near the design point and slightly decreased at the high advance coefficient. Moreover, the cavitation performance of the pump-jet propulsor without clearance is better at a wide range of advance coefficient, 0.85 相似文献