钢夹层板数值模拟技术(英文)

Sandwich plate systems (SPS) are advanced materials that have begun to receive extensive attention in naval architecture and ocean engineering. At present, according to the rules of classification societies, a mixture of shell and solid elements are required to simulate an SPS. Based on the principle of stiffness decomposition, a new numerical simulation method for shell elements was proposed. In accordance with the principle of stiffness decomposition, the total stiffness can be decomposed into the bending stiffness and shear stiffness. Displacement and stress response related to bending stiffness was calculated with the laminated shell element. Displacement and stress response due to shear was calculated by use of a computational code write by FORTRAN language. Then the total displacement and stress response for the SPS was obtained by adding together these two parts of total displacement and stress. Finally, a rectangular SPS plate and a double-bottom structure were used for a simulation. The results show that the deflection simulated by the elements proposed in the paper is larger than the same simulated by solid elements and the analytical solution according to Hoff theory and approximate to the same simulated by the mixture of shell-solid elements, and the stress simulated by the elements proposed in the paper is approximate to the other simulating methods. So compared with calculations based on a mixture of shell and solid elements, the numerical simulation method given in the paper is more efficient and easier to do.     

深水SPAR平台截断技术研究(英文)

To solve the dimensional limitations of physical models in tests, an equivalent water depth truncated design for a classical SPAR working in 913 m water was investigated. The water depth was reduced to 736m and then to 552m. As this was done, the mooring line lengths, EA value, and mass per meter were adjusted. Truncation rules and formulas for parameters and truncation factors were proposed. SPAR static characteristics were made to be consistent with those at full water depth. Then further time-domain coupled analysis was carried out for the SPAR when the mooring system experienced waves. The mooring lines were simulated by quasi-static method. Global responses and mooring line forces were found to agree well with test results for a prototype at that water depth. The truncation method proved to be robust and reliable.     

非结构化网格浸入边界法的流固耦合数值模拟(英文)

This paper presents an improved unstructured grid immersed boundary method. The advantages of both immersed boundary method and body fitted grids which are generated by unstructured grid technology are used to enhance the computation efficiency of fluid structure interaction in complex domain. The Navier-Stokes equation was discretized spacially with collocated finite volume method and Euler implicit method in time domain. The rigid body motion was simulated by immersed boundary method in which the fluid and rigid body interface interaction was dealt with VOS (volume of solid) method. A new VOS calculation method based on graph was presented in which both immersed boundary points and cross points were collected in arbitrary order to form a graph. The method is verified with flow past oscillating cylinder.     

周期性波动管流的压降研究

Experiments were conducted to study characteristics of flow when flow is fluctuating. The experimental results showed a phase difference between the flow rate and the pressure drop fluctuations. This phase difference between the fluctuating flow rate and pressure drop was analyzed for laminar flow. Analysis showed that the phase difference changes with the period of the flow fluctuation, the pipe radius, the density and the dynamic viscosity of the liquid. Fluctuating pipe flow was then numerically simulated. Results of the numerical simulation were compared with theoretical values and experimental results. It was shown that, when the flow rate fluctuates with time as a sine wave, the pressure drop fluctuates with the same periodicity, and there is a phase difference between them.     

Analysis of the economic and social parameters of the Three-Wheeler Taxi service in Sri Lanka

Sri Lanka has an extensive Three-Wheeler Taxi service comprised of around 300,000 vehicles. These vehicles, which first made an entry to Sri Lanka’s roads in the early 1980s, account for around 15% of the active motor vehicle fleet at present. Three-Wheelers Taxis also account for around 6% of the passenger kilometres. These vehicles are mostly individually operated with some owned by the operator and others hired on a monthly or daily basis. The industry is unregulated with vehicle registration and driving licenses being the only instruments of regulation. Fares are unregulated. However, most operators belong to associations which are loose collections of operators found in a given locality. These associations impose a degree of self regulation with respect to fares. They also tend to demonstrate oligapolistic behaviour.The paper is based on a survey of 200 operators and 100 passengers from a Divisional Secretariat area in Colombo District. The survey covered a number of details pertaining to ownership, management and fare structures, as well as opinions on the service attributes by users. The survey also covered perceptions of operators to determine the social, economic and transport implications of the services provided. Details were also obtained on the profiles of the operators and their expectations.The paper provides the results of the analysis of this data and draws a number of conclusions on the economics of the industry as well as the social aspects associated with it. It also discusses the characteristics of the users of these three wheelers as well as their typical use. The analysis also investigates complementarily of service provision between three wheelers as an access mode to buses and railways. This analysis has been used to develop an understanding of the manner in which the industry has grown over the last two decades and how it is being operated today. It also identifies areas wherein the industry has become inefficient and assesses the degree of over pricing that exists due to this. The data also helps to determine the relationship between unemployment and provision of self-employed transport services.The paper concludes with a synopsis of the profile of the industry and its role within the wider transport sector and with respect to ownership. It also discusses the positive and negative impacts of the lack of regulation on the industry.     

Extending stated choice analysis to recognise agent-specific attribute endogeneity in bilateral group negotiation and choice: a think piece

This paper is a think piece on variations in the structure of stated preference studies when modelling the joint preferences of interacting agents who have the power to influence the attribute levels on offer. The approach proposed is an extension of standard stated choice methods, known as ‘stated endogenous attribute level’ (SEAL) analysis. It allows for interactive agents to adjust attribute levels off a base stated choice specification that are within their control, in an effort to reach agreement in an experimental setting. This accomplishes three goals: (1) the ability to place respondents in an environment that more closely matches interactive settings in which some attribute levels are endogenous to a specific agent, should the modeller wish to capture such behaviour; (2) the improved ability of the modeller to capture the behaviour in such settings, including a greater wealth of information on the related interaction processes, rather than simply outcomes; and (3) the expansion of the set of situations that the modeller can investigate using experimental data.

Mass transit systems of Beijing: governance evolution and analysis

Developing a more efficient mass transit system, in highly populated cities, improves the mobility, decreases the dependency of private cars, alleviates traffic congestion, and provides a more environmentally friendly means of travel. Recently, the city of Beijing decided to have a target of becoming as a ‘public-transport city’ with a fascinating mass transit system within a larger plan, of building humanistic, scientific and technological, and green public-transport systems. This work discusses the governance evolution of the mass transit system of Beijing between 1949–2008, comprised of two groups of transit systems, the road surface public-transport system (bus, tram, trolley, etc.), and the subway public-transport system. In addition, a time-series analysis is introduced in an attempt to examine the effect of governance evolution on the two transit systems, and of the impacts of the governance structural changes on the mass transit system. The time-series model is introduced using the annual statistics data of the period 1949–2008. The outcome of the analysis is viewed with precaution because of the incompleteness of the many endogenous and exogenous factors to affect the public-transport demand. Generally speaking it is concluded that the governance evolution provides beneficial effect of the Beijing mass transit activity; however, for satisfying the significant increase of the Beijing city’s travel demand and maintaining sustainable development, the governance-involvement pattern needs to be reformed.     

Exploring public transport usage trends in an ageing population

An ageing population remains one of the most significant challenges for Western society in the 21st century. Whilst public transport use has attractive sustainability features for older generations there is mixed evidence with regard to trends in travel and public transport use in ageing societies. This paper explores public transport trip rates amongst older age groups using travel survey evidence collected from a household travel survey in Melbourne, Australia for the period 1994 to 1999. A particular aim of the research was to establish trends in trip rates so as to explore the impact of the ageing Baby Boomer generation on travel by public transport. The results suggested that compared to those aged below 60, those aged over 60 years demonstrated 30% lower trip making overall and 16% lower public transport trip rates. Longitudinal trends in trip rates showed those aged over 60 had a very small decline in trip rates by public transport (−0.004 average daily trips per annum) but increasing rates for car trips. A further analysis showed a small but significant increase in longitudinal trip rates of public transport use amongst Baby Boomers (0.004 daily trips p.a., p < .05) while car usage for Baby Boomers was steady. The implication of these findings is that trends in the existing over 60s population are not necessarily going to flow through to behaviour patterns in the Baby Boomer generations. The Baby Boomer age group showed longitudinal trends in travel behaviour which contrasted with those of the existing over 60s generation notably with a trend towards increased public transport usage.