A module-oriented tool for optimum design of stiffened structures—Part I

The development of the LBR-5 “Stiffened Panels Software” is included in the development of a new design methodology to ease and to improve preliminary studies of naval structures and floating hydraulic structures. The ultimate target is to link standard design tools (steel structure CAD, hull form, hydrostatic curves, floating stability, weight estimation, etc.) with a rational optimization design module and a minimum construction cost (or minimum weight) objective function. This paper is the first part of a series of two articles. It focuses on the ‘Module-Oriented Optimization’ methodology and on the rational constraints. The second paper presents the optimization technique using convex linearization and a dual approach, and the optimization of an FSO unit as an example (Rigo and Fleury, Marine Stuructures, 2001). LBR-5 allows, as of the first draft, an optimization of the scantling of the structure's constituent elements. Relevant limit states of the structure are taken into account thanks to a 3D rational analysis of the structure based on the general rules of solid-mechanics and structure behaviour. The optimization module is composed of 3 basic modules (OPTI, CONSTRAINT and COST) and a group of sub-modules (in external databases). Among these the user selects a set of relevant sub-modules (i.e. geometrical and structural constraints). Since the present optimization deals with least construction costs (as objective function), and uses an explicit objective function (not empirical), the user must specify labor costs (unitary material costs, welding, cutting, etc.).     

面向计算的船体曲面NURBS造型

该文介绍了NURBS曲面的数学模型,提出用NURBS方法构造船体曲面的主要步骤,讨论了边界条件对曲线曲面形状的影响,给出一船体曲面,结果表明该方法的可行性,为基于曲面的船体几何特性计算奠定了基础。     

时空紧约束的大都市圈轨道交通规划研究

进入大都市圈快速发展阶段后,中国大城市交通发展普遍面临空间和时间紧约束。轨道交通由此成为大都市圈时空组织的战略选择,构建以轨道交通为主体、多层次中低运量公共交通为基础的公共交通体系成为共识。面对大都市圈集聚发展、近中期通勤圈可能继续外扩等发展前景,提出轨道交通线网规划应重点围绕缩短出行时间和提高覆盖率等时空组织要求。进而通过差别化的空间政策和交通政策,耦合轨道交通枢纽与城市中心体系,促进轨道交通轴带功能集聚。最后,强调以轨道交通为核心,加强一体化衔接规划和城市交通综合治理,主动引导城市空间有序拓展,实现轨道交通与大都市圈协同发展。     

具有时空约束的无人车集群构型变换方法

针对具有时空约束的无人车集群构型变换问题,采用图论方法描述集群协同关系,将集群构型变换问题分解为最小变换单元的队形变换问题. 为满足队形变换的空间约束,运用基于模型的轨迹预测方法为无人车规划提供满足起点和目标点约束的行驶路径,运用曲线插值方法规划平滑且满足时间约束的速度曲线,根据碰撞检测结果提出速度规划的边界条件. 仿真和实车实验证明了构型变换方法的有效性.     

基于遗传算法的飞行器航迹规划研究

针对飞行器航迹规划问题展开研究,提出了一种基于遗传算法的飞行器航迹规划方法.该算法采用一种变长实值基因编码方式和一组重新设计的与之对应的进化算子.仿真实验结果表明,该算法能够快速有效地完成航迹规划任务,获得较为满意的航迹,同时也能满足在线实时规划的要求.     

三塔悬索桥中塔弹性纵向约束对结构设计的影响

以泰州大桥为例,用有限元法分析了三塔悬索桥中塔弹性纵向约束的合理弹性刚度,研究了弹性纵向约束对主塔、加劲梁、主缆以及结构动力特性的影响,研究结果表明,设置弹性索能有效改善三塔悬索桥的受力性能。     

集合规划方法在航线网络枢纽选址上的应用

研究带有容量限制的单分配多枢纽网络选址问题,将问题简化为带有容量限制的聚类问题。通过节点之间的距离以及各个节点的需求量,根据聚类分析原理,采用集合规划的方法对问题进行建模,运用自然约束语言NCL,在POEM平台上对模型进行编程求解,并通过实例将计算结果在地图中可视化。运用模糊聚类方法对多枢纽选址位置进行分析。     

半潜平台动力定位系统模型预测控制器设计(英文)

This paper researches how to apply the advanced control technology of model predictive control(MPC) to the design of the dynamic positioning system(DPS) of a semi-submersible platform.First,a linear low-frequency motion model with three degrees of freedom was established in the context of a semi-submersible platform.Second,a model predictive controller was designed based on a model which took the constraints of the system into account.Third,simulation was carried out to demonstrate the feasibility of the controller.The results show that the model predictive controller has good performance and good at dealing with the constraints of the system.     

Cash flow sensitivities during normal and crisis times: Evidence from shipping

Using a system of equations model, we analyze how cash flow shocks influence the investment and financing decisions of shipping firms in different economic environments. Even financially healthy shipping firms felt strong negative effects on their financing activities during the recent crisis. These firms were nevertheless able to increase long-term debt. Banks internalized the impact of foreclosure decisions on vessel prices and avoided an industry-wide collateral channel effect. Even during benign economic conditions, financially weak shipping firms underinvest because of their inability to raise sufficient external capital. The substitution between long- and short-term debt during the pre-2008 crisis periods shows that the composition of financing sources is more indicative of whether firms face financial constraints than the pure size of the financing-cash flow sensitivities. An analysis of firms’ excess cash holdings confirms the importance of financial flexibility.     

How flexible is flexible? Accounting for the effect of rescheduling possibilities in choice of departure time for work trips

In departure time studies it is crucial to ascertain whether or not individuals are flexible in their choices. Previous studies have found that individuals with flexible work times have a lower value of time for late arrivals. Flexibility is usually measured in terms of flexible work start time or in terms of constraints in arrival time at work. Although used for the same purpose, these two questions can convey different types of information. Moreover, constraints in departure time are often related not only to the main work activity, but to all daily activities. The objective of this paper is to investigate the effect of constraints in work and in other daily trips/activities on the willingness to shift departure time and the willingness to pay for reducing travel time and travel delay. We set up a survey to collect detailed data on the full 24-hour out-of-home activities and on the constraints for each of these activities. We then built a stated preference experiment to infer preferences on departure time choice, and estimated a mixed logit model, based on the scheduling model, to account for the effects of daily activity schedules and their constraints. Our results show that measuring flexibility in terms of work start time or constraints at work does not provide exactly the same information. Since one-third of the workers with flexible working hours in the survey indicated that they have restrictions on late work-arrival times, their willingness to pay will be overestimated (almost doubled) if flexibility information is asked only in terms of fixed/flexible working hours. This clearly leads to different conclusion in terms of demand sensitivity to reschedule to a later departure time. We also found that having other activities and constraints during the day increases the individuals’ willingness to pay to avoid being late at work, where the presence of constraints on daily activities other than work is particularly relevant for individuals with no constraints at work. The important impact of these findings is that if we neglect the presence of constraints, as is common practise in transport models, it will generally lead to biased value-of-time estimates. Results clearly show that the shift in the departure time, especially towards a late departure time, is strongly overestimated (the predicted shift is more than double) when the effect of non-work activities and their constraints is not accounted for.