Optimal selection of suspension parameters in large scale vehicle models

Optimum values are selected for the suspension damping and stiffness parameters of complex car models, subjected to road excitation, by applying suitable numerical methodologies. These models result from a detailed finite-element discretisation and possess a relatively large number of degrees of freedom. They also involve strongly nonlinear characteristics, due mostly to large rigid body rotation of some of their components and the properties of the connection elements. First, attention is focused on gaining some insight into the dynamics of the mechanical models examined, resulting when the vehicle passes over roads involving typical geometric profiles. Then, the emphasis is shifted to presenting results obtained by applying appropriate optimisation methodologies. For this purpose, three classes of design criteria are first set up, referring to passenger ride comfort, suspension travel and car road holding and yielding the most important suspension stiffness and damping parameters. Originally, the optimisation is performed by forming a composite cost function and employing a single-objective optimisation method. Since the design criteria are conflicting, a multi-objective optimisation methodology is also set up and applied subsequently.     

A numerical investigation of the impact of turbulence on the feeding rates of Oithona davisae

Individual based numerical simulations of the copepod, Oithona davisae, feeding on motile prey, Oxyrrhis marina, under variable turbulent conditions are performed. These simulations correspond to laboratory observations conducted by Saiz et al. [Saiz, E., Calbet, A., and Broglio, E., 2003. Effects of small-scale turbulence on copepods: the case of Oithona Davisae. Limnol. Oceanogr., 48:1304–1311.].The flow field in the simulation is reconstructed by a kinematic simulation whose characteristic scales are derived from the grid mesh and the dissipation rates of the laboratory experiments. The kinematic simulation provides a simplified model, which while not fully realistic, captures the basic relevant feature of turbulence. A hop and sink swimming behaviour is prescribed for O. davisae, while O. marina moves along helical paths with random changes of directions.Three possible effects are tested: the existence of a time threshold in the duration of the contacts between predator and prey, a progressive reduction of the perceptive distance with increasing turbulence level and an abrupt reduction in feeding of O. davisae when the flow speed, in relation to the copepod position, is higher than a prescribed threshold. This last approach introduces an intermittency in the feeding which depends on the variations of velocity both in space and time within the numerical box.The introduction of the time threshold causes a dome-shaped relationship between the simulated enhancement factor and the dissipation rate, while with the other two effects, a monotonic decrease in the enhancement factor is observed, with values reasonably close to the ones observed in the laboratory experiment. In all the cases, the use of realistic values of biological parameters (e.g. swimming behaviour) reproduces response curves in the range of the observations.     

基于多目标规划的公交车调度方法研究

公交调度要考虑公司和乘客的多方利益。目标规划法是运筹学中解决多目标问题的有效方法,而优先因子的采用可以区分调度中的各方利益的主次。同一优先因子下加入了权重,可根据实际情况做出灵活有效的调度方案。     

系统效能通用评估工具研究

基于数据库和算法集成,设计了一套具有良好通用性、灵活性、可扩展性的系统效能评估工具,并以此工具为基础,针对不同的评估需求、数据量和应用环境提出对应的解决方案.     

航道货运量预测方法及其应用

为了精确预测航道未来货运量需求,克服传统预测方法无法实现复杂非线性拟合的缺点,分析了航道货运量的影响因素,探讨了遗传规划方法在航道货运量预测问题上的应用.根据遗传规划巾复制、交换、变异等进化方式,建立了基于遗传规划的航道货运量预测模型.以江苏省连申线苏北段历年货运量及区域经济发展状况为样本,采用遗传规划方法自动找出货运量随时间变化的规律,并对未来货运量进行了预测.结果表明,本箅法的计算相对误差很小,预测结果合理可信,且优于常用的回归预测,为解决航道货运量等非线性系统预测提供了一条新的途径.     

Flexible long range planning using low cost information

Contemporary transport planning requires a flexible modelling approach which can be used to monitor the implementation of a long term plan checking regularly its short term performance with easily available data; the original model is periodically updated using low cost information and this allows the evaluation of the changes to the plan which may be required. Such an approach requires models suited to regular updating and to the use of data from different sources. Models to update trip matrices from traffic counts have been available for some time; however, the estimation and/or updating of other model stages with low cost data has escaped analytical treatment. The paper discusses this idea and formulates the updating problem for an example involving a joint destination/mode choice model under various assumptions about the nature of the available data. Analytical solutions are proposed as well as some general conclusions.requests for offprints     

Alternative Modeling Approaches Used for Examining Automobile Ownership: A Comprehensive Review

Abstract

Household vehicle ownership, and the associated dimensions including fleet size, vehicle type and usage, has been one of the most researched transport topics. This paper endeavors to provide a critical overview of the wide-ranging methodological approaches employed in vehicle ownership modeling depending on the ownership representation over the past two decades. The studies in the existing literature based on the vehicle ownership representation are classified as: exogenous static, exogenous dynamic, endogenous static and endogenous dynamic models. The methodological approaches applied range from simple linear regressions to complex econometrics formulations taking into account a rich set of covariates. In spite of the steady advancement and impressive evolution in terms of methodological approaches to examine the decision process, we identify complex issues that pose a formidable challenge to address the evolution of vehicle ownership in the coming years. Specifically, we discuss challenges with data availability and methodological framework selection. In light of these discussions, we provide a decision matrix for aiding researchers/practitioners in determining appropriate model frameworks for conducting vehicle ownership analysis.     

A bi-objective dynamic programming approach for airline green fleet planning

Ensuring a fleet of green aircraft is a basic step in mitigating aviation pollution issues that are expected to be worsen in the coming years due to rapid air traffic growth. This study proposed a novel methodology in green fleet planning in which both profit and green performance of airline are considered simultaneously and explicitly. To do this, a Green Fleet Index (GFI) is derived as an indicator to quantify the green performance of airline’s fleet. It measures the degree of airline compliance with a standard requirement in terms of emission, noise, and fuel consumption. A bi-objective dynamic programming model is then formulated to find optimal aircraft acquisition (lease or purchase) decision by minimizing GFI and maximizing profit. Several interesting results are obtained: (1) considering environmental issue as secondary objective yields a greener fleet; (2) airline’s profit is affected, but could be recovered from environmental cost savings; (3) increasing load factor is an effective operational improvement strategy to enhance airline’s green performance and raise profit level. It is anticipated that the framework developed in this study could assist airlines to make a smart decision when considering the need to be green.     

Liner ship route schedule design with port time windows

This paper examines a practical tactical liner ship route schedule design problem, which is the determination of the arrival and departure time at each port of call on the ship route. When designing the schedule, the availability of each port in a week, i.e., port time window, is incorporated. As a result, the designed schedule can be applied in practice without or with only minimum revisions. This problem is formulated as a mixed-integer nonlinear nonconvex optimization model. In view of the problem structure, an efficient holistic solution approach is proposed to obtain global optimal solution. The proposed solution method is applied to a trans-Atlantic ship route. The results demonstrate that the port time windows, port handling efficiency, bunker price and unit inventory cost all affect the total cost of a ship route, the optimal number of ships to deploy, and the optimal schedule.     

二层线性规划的模糊数学解法(Ⅱ)

针对上层有约束条件、下层有Ｎ个独立的决策单元的二层线性规划问题，提出了一种模糊数学解法。首先，把这种规划分解为若干单层规划；然后引入隶属函数，用３个定理对各单层规划的解进行讨论，最终把这种二层线性规划转化为求解一个单层线必规划问题。使问题得到了简化。