Nonlinear dynamic modeling of an electro-pneumatic pressure converter for VGT pneumatic actuator

This paper presents a detailed physical model of an electro-pneumatic system, used to control Variable Geometry Turbochargers (VGT). The VGT actuator system consists of two parts, a diaphragm based pneumatic actuator and a solenoid based Electro-pneumatic Pressure Converter (EPC). The proposed model copes with the pressure dynamics inside the pneumatic actuator, with special focus on the EPC. The dynamics of both parts have been modeled separately and combined into one model by parameterizing the effective flow area and the air mass flow through the pneumatic actuator. The variations in volume, temperature and air mass flow rate have been taken into account. The model so obtained serves mainly for studying the effect of actuator dynamics on the global engine system. For control purposes, the detailed model is simplified to reduce the calculation load. Both models are validated using experimental data obtained from an engine test bench.     

Cooling performance of 25 kW in-wheel motor for electric vehicles

The in-wheel motor used in electric vehicles was designed and constructed for an electric direct-drive traction system. It is difficult to connect cooling water piping to the in-wheel motor because the in-wheel motor is located within the wheel structure. In the air cooling structure for the in-wheel motor, an outer surface on the housing is provided with cooling grooves to increase the heat transfer area. In this study, we carried out the analysis on the fluid flow and thermal characteristics of the in-wheel motor for various motor speeds and heat generations. In order to resolve heat release, the analysis has been performed using conjugate heat transfer (conduction and convection). As a result, flow fields and temperature distribution inside the in-wheel motor were obtained for base speed condition (1250 rpm) and maximum speed condition (5000 rpm). The thermo-flow analysis of the in-wheel motor for vehicles was performed in consideration of ram air effect. Also, in order to improve cooling effect of the motor, we variously changed geometries of housing. Therefore, we confirmed the feasibility of the air cooling for the motors of 25 kW capacity with housing geometry having cooling grooves and investigated the cooling performance enhancement. We found that the cooling effect was most excellent, in case that cooling groove direction was same with air flow direction and arranged densely.     

Development trend and key technologies of autonomous underwater vehicles北大核心CSCD

为推进和引导我国自主水下航行器(AUV)的发展,总结国内外AUV的研究现状,提出其系列化、集群化、体系化、大型化的发展趋势。重点探讨AUV总体多学科优化设计、结构与材料设计、动力与推进、导航与控制、探测与通信等关键技术,为更好地利用AUV经略海洋,从而实现“进入海洋、探测海洋、利用海洋”的战略目标提出发展意见。     

Design and development of a stated choice experiment for interdependent agents: accounting for interactions between buyers and sellers of urban freight services

Stated choice experiments have proven to be a powerful tool in eliciting preferences across a broad range of choice settings. This paper outlines the elements of a group-based experiment designed for interdependent urban freight stakeholders, along with the procedure to administer the questionnaire sequentially. The focus is on the design of a computer-assisted personal survey instrument and the value in disseminating the details of a new approach to design and collect stated choice data for interacting agents. The paper also discusses how to specify a reference alternative, and then how to recruit appropriate real-market or representative decision-making group members to participate in a subsequent phase of the survey, which incorporates the reference alternative and contextual information from an initial phase. The empirical strategy, set out in some detail, provides a new framework within which to understand more fully the role that specific attributes, such as variable user charges, influencing freight distribution chains might play, and who in the supply chain is affected by specific attributes in terms of willingness to pay for the gains in distribution efficiency.

尾涡/固体边界交互作用下表面压力的数值模拟

当强劲的尾涡撞击到结构时,其表面压力将呈现大幅的变化.这种大幅变化的脉动压力是引起结构震动以及水动力噪声的主要原因之一.许多相关的工程领域都希望使用相对经济的方法对此压力脉动进行有效地预报.本文介绍一种已经嵌入一面元法程序(PROPELLA)的尾涡砰击模型,及其在一吊舱桨尾涡撞击支柱诱导表面压力模拟中的应用.由模拟的时均表面压力分布和相均压力的时序变化与对应的实验数据的比较来看,数值模拟与试验结果吻合较好.     

Entry barriers in seaports

The different types of entry barrier in seaports are analysed and the policies and practices to reduce them are discussed in this paper. In most seaports, economic, regulatory, and geographical entry barriers are substantial and increasing in complexity as ports become embedded in supply chains and multilayered networks with multiple entry-levels. Various entry barriers in seaports are identified through an overview of the relevant literature and their presence is confirmed by empirical data describing them. The case is then made for lowering these barriers. This would be desirable from an economic point of view, since lower barriers strengthen the contestability of markets and increase the level of intra-port competition. The latter might yield substantial benefits, such as fostering specialization and preventing the abuse of market power. Finally, low entry barriers would facilitate the faster implementation of new technologies and business models. In the third part of the analysis, policies and practices designed to reduce entry barriers are examined. The implications are discussed of current national and supranational (EU) policy initiatives aimed to liberalize service provision in seaports. Other (de)regulatory policies that could contribute to the reduction of entry barriers are analysed.     

High-Speed Generators for Power-Dense, Medium-Power, Gas Turbine Generator Sets

Concepts to improve turbine generator (TG) set power density (PD) are identified, developed, and evaluated. The evaluation focuses on the TG set as a part of overall system optimization, with weight and volume penalties for special auxiliaries. PD is given priority, while other attributes such as efficiency, acoustics, and total system cost are also assessed. The strengths and weaknesses of each concept are assessed based on technical viability, potential for PD improvement, and risk. Sixty-one generator concepts over four generator types—air-cooled wound field, water-cooled wound field, permanent magnet (PM), and high-temperature superconducting (HTS)—are evaluated with three ship-level electrical distribution architectures—high-frequency AC and active- and passive-rectified DC. A prime mover of 14 MW at 7,000 r.p.m. is assumed. The study assesses generator size enabled by directly coupling the generator to the prime mover, eliminating the typical gear required in TG sets with engine speeds greater than 3,600 r.p.m. Technology approaches are described and trends in the design data are identified. Advanced PM and superconducting rotor technologies are evaluated. For the power, speed, and system requirements studied, these technologies do not differ significantly from water-cooled designs in size and weight. A water-cooled generator would be compatible with a range of future power distribution systems such as high-frequency AC, rectified DC, or 60 Hz AC (using a rectifier and an inverter).     

Effect of fuel choice on nanoparticle emission factors in LPG-gasoline bi-fuel vehicles

Nanoparticle and gas-phase emission factors are presented for a liquefied petroleum gas (LPG) passenger vehicle and are compared to gasoline operation. A bi-fuel LPG-gasoline vehicle certified for use on either fuel was used as the test vehicle so that a direct comparison of the emissions could be made based on fuel choice. These values were considered along with previous studies to determine the relative change in particulate emissions due to fuel choice over a wide range of vehicles and operating conditions. The vehicle examined in this study was tested on a chassis dynamometer for both steadystate and transient conditions. Transient test cycles included the US FTP72 driving cycle, Japanese driving cycle and modified Indian driving cycle while steady-state tests were done at vehicle speeds ranging from 10–90 km/hr in various transmission gears. Exhaust particle size distributions were measured in real-time using a differential mobility spectrometer (DMS50), and particle number and particle mass emission factors were calculated. For both fuels, the majority of the particles ranged from 5 to 160 nm in terms of particle diameter, with typically more than 85% of the particles in the nucleation mode (between 5–50 nm). In most cases, the vehicle produced a greater fraction of larger (accumulation mode) particles when fuelled on LPG. Using the data in the literature as well as the data in the current study, gasoline fuel produces 4.6 times more particles in terms of number and 2.1 times more particles in terms of mass.     

Changing ownership structures in the Dutch fleet

The new Dutch shipping policy has given rise to high expectation and curiosity in the world of shipping. This, together with the obvious difficulties of an ex-post study of the effectiveness of such innovative policy, has prompted the authors to take an interest in attempting to investigate changes in ownership of the Dutch fleet 2 years after the new policy has been introduced. To do this, a rather new concept of 'flagging out' has been adopted, which is interpreted as a process leading to different degrees of 'foreignness' in a shipping operation. In this paper, a method to structure is presented, and ownership information, and changes in it are presented, that are essentially based on the theory of stochastic processes. The data used is the Dutch fleet data, which includes information on the nationality of the flag, parent ownership and management over the period 1994-1998. The results yield interesting insights in the shifts in the ownership and operational structure of shipping companies induced by the new policy. In particular, they allow one to establish the origin of new vessels, in which stage of ownership/operation it is most likely that shifts occur, and to determine the relationship between the different stages of the 'flagging out' process. These results, thus, enable an evaluation of the areas in which the policy can be expected to yield results.