圆柱壳结构输入功率流主动控制研究

利用导纳函数表示圆柱壳体在激励力与控制力同时作用下的响应,将输入壳体的总功率流表示为哈密顿二次型函数的形式,并以此为目标函数对壳体振动进行主动控制研究.另外,在目标函数中添加控制力幅值二次项以便用较小的控制力取得较为理想的控制效果.利用前馈二次型最优控制理论得到最优控制力并讨论了几个重要参数对控制效果的影响.     

商用车冷却模块匹配设计方法研究

分析车辆的冷却系统流动传热规律,提高冷却系统在车辆部件设计过程中的准确性。文章主要针对商用车的冷却模块作为主要的研究,从流体力学及传热学理论基础上,通过试验分析进行了车辆冷却的传热问题分析和数据测试,希望能够为实际应用提供冷却系统性能的改善指导。     

Transaction costs and tradable mobility credits

Artificial markets for mobility credits have been proposed as an alternative to conventional congestion pricing schemes. This paper examines the effects of transaction costs on two types of markets: an auction market and a negotiated market. In an auction market, users purchase all of the needed mobility credits through a competitive bidding process. In a negotiated market, the users initially receive certain amount of mobility credits from the government and trade with each other through negotiation to fulfill their needs. We assume that a brokerage service is built in both markets to facilitate transactions and accordingly, the users have to pay a commission fee proportional to the value of trade. The users are also given the option to purchase credits from the government if for some reasons they cannot use or wish to avoid the markets. Our analyses suggest that the auction market can achieve the desired equilibrium allocation of mobility credits as long as the government sets its price properly and the unit transaction cost is lower than the price that the market would reach in absence of transaction costs. However, in the negotiated market, transaction costs could divert the system from the desired equilibrium regardless of their magnitude. More importantly, the initial allocation of mobility credits may affect the final equilibrium even when marginal transaction costs are constant.     

Parking management for promoting sustainable transport in urban neighbourhoods. A review of existing policies and challenges from a German perspective

ABSTRACT

The organisation of parking is a key challenge to more sustainable mobility in urban areas, as its pricing and availability affect the rates of private car ownership and use. However, changing parking policies is a challenging issue for local politicians and planners because residents frequently oppose changes or restrictions to conditions they have taken for granted such as on-street parking in a public space. The aim of this paper is firstly to assess how the parking policy of an urban neighbourhood can be structured to contribute to more sustainable mobility and to increase liveability in the neighbourhood. The second aim is to apply the policies reviewed to an example neighbourhood. For this purpose, we systematically reviewed academic literature and identified five types of relevant parking policies: (i) maximum parking requirements, (ii) physical detachment of residence and parking space, (iii) residential parking permits and the limitation of available parking space, (iv) performance-based pricing and (v) parking as a demand management strategy. We discovered that most research focuses on econometric models about parking and that studies rarely address the effects of parking on the quality of life in neighbourhoods. Therefore, we need further research regarding the relationship of parking and liveability. We conclude that for the implementation of such parking policies in an example neighbourhood, the municipality needs to develop a mobility vision for its city. It has to understand parking as a tool for transportation demand management to increase the acceptance of parking policy concepts and to avoid spillover problems. Finally, in the German case, as in most other countries, states and municipalities need to redesign their legal frameworks to be able to manage parking supply better and to react to changes related to digital developments and parking. The findings have implications for other European neighbourhoods regarding the transfer from research to local circumstances and applications for the whole city.     

迁居对家庭日常活动—出行行为交互机理的影响

居住地是家庭成员日常活动的主要起讫点,迁居会导致家庭日常生活空间重组,进而成为影响成员活动安排和出行模式的关键因素.本文以迁居家庭为研究对象,分别从个体和家庭两个层面分析迁居前后日常活动—出行行为的调整变化,以揭示家庭成员间的交互模式及其内在机理.研究表明:迁居对成员活动—出行行为的影响首先体现在通勤模式调整上,其次是在家务分担上.具体来说,当两个成员均受到职住错位影响时,双方在家务活动安排上交互强烈,家庭内部会通过替代或互助等互动模式来平衡通勤活动所受到的时空制约;当只有一方受到职住错位制约时,双方交互程度进一步降低,家务活动安排上表现出显著性别差异,男方较容易受通勤活动的影响而放弃承担家务活动;当双方均处于职住邻近状态时,双方交互程度最弱,家务活动常采用陪伴或联合等协作方式来完成.     

Constructal design of tree-shaped microchannel disc heat sink with wavy walls北大核心CSCD

［Objective］To meet the efficient thermal management needs of electronic devices such as ships and underwater vehicles, this study focuses on the constructal design of a tree-shaped microchannel disc heat sink with wavy walls. ［Method］A design prototype of the heat sink with wavy walls is first proposed. Based on constructal theory, the amplitude and wavelength of the wavy walls are designed under the constraints of fixed heat sink volume and fixed microchannel volume by maximizing the comprehensive performance evaluation criteria (PEC) while considering both heat transfer and flow pressure drop. ［Results］The results show that the wavy walls increase the heat transfer surface areas and generate vortices in their cavities, effectively reducing the maximum temperature. When the inlet Reynolds number is fixed at 700, 900 or 1100 respectively, the maximum temperature is reduced by 13.5 K by increasing the amplitude of the wavy walls, while the pressure drop increases significantly; and the maximum temperature is reduced by 4.7 K by reducing the wavelength of the wavy walls, while the pressure drop increases slightly. There are optimal amplitudes that raise the comprehensive performance evaluation criteria to extreme values for given larger wavelengths, while the comprehensive performance evaluation criteria increase monotonously as the amplitude increases for given smaller wavelengths. ［Conclusion］Wavy walls can significantly improve the thermal performance of tree-shaped microchannel disc heat sinks, and the use of constructal design can realize optimal geometric constructs with optimal comprehensive performance evaluation criteria. © 2023 Authors. All rights reserved.