不同供油规律下的燃气轮机加速过程仿真

供油规律决定着燃气轮机的机动性,不同的供油规律对燃气轮机的性能有重大影响。为研究不同供油规律对燃气轮机加速过程的影响,本文首先采用面向对象的方法和非线性化建模方法建立了三轴燃气轮机的动态仿真模型,并通过稳态计算检验了模型的精确性;然后选取不同的供油规律,对燃气轮机的加速过程进行了仿真,得到了不同供油规律下转子转速的变化规律;最后对仿真结果进行了分析,比较了各种供油规律的优劣。     

龙门吊“油改电”的供电线路谐波危害及抑制

龙门吊"油改电"后,供电线路都有谐波产生。抑制谐波是改善供电品质的重要手段。分析了"油改电"供电线路的电流、电压谐波产生的原因,陈述了谐波造成的危害。介绍了3种抑制交流供电线路电流、电压谐波影响的方法。     

重庆市县际联网公路建设中招标办法的探讨

本文通过分析和比较近年来重庆市县际联网公路建设中所采用的招标办法的优缺点,提出采用有标底低标法,可以有效地控制建设投资,遏制一些小单位借资质投标的现象,在工程施工中掌握主动权.为工程建设的招标工作提供了一定的借鉴经验.     

Changes in transaction costs over time - The case of franchised train operating firms in Britain

The significant effects of competition, franchising and vertical separation of rail infrastructure from train operation on the level of transaction costs are often anecdotally described in the literature. Although it has been shown that franchising has an effect on total costs, there is very little empirical evidence on whether franchising has an impact on the level of transaction costs over time. One reason for this is, of course, the limited systematic work on the measurement of transaction costs in railways. This paper builds on recent work that applied a top-down approach to transaction cost measurement to identify the size of the transaction sector within rail firms in different EU countries. In cross-country comparison particularly, British train operators turned out to be associated with high levels of transaction costs. However, since the previous work focused on a single fiscal year it did not show any longitudinal effects within one institutional environment or country. Therefore, this paper focuses on British franchised passenger train operating firms and aims to reveal how the transaction sector within those firms has changed over the period 1996/1997-2007/2008 and whether the franchise contract details, such as contract length or the franchising regime, matter. It also aims to estimate the resulting changes in the level of transaction costs and their share in total operating costs for the first time.     

The cost of second best pricing and the value of risk premium

Private provision of public infrastructure (PPP) is meant to give incentives to increased efficiency in construction as well in operation and maintenance of the infrastructure e.g. within the transport sector. Efficiency is not only (private) economic efficiency, but also social efficiency e.g. social marginal cost pricing of use of the infrastructure.Is it possible to design contracts concerning payment mechanisms and financial instruments for transport infrastructure that will stimulate social efficiency and optimal allocation of risks between parties? The paper discusses whether different targets can be met and whether compromises may lead to acceptable second best solutions.PPP implies an opportunity to let the user-payment give desired incentives in the form of Social Marginal Cost Pricing (SMCP). A PPP project is a set of contracts and agreements between several parties, including the Government, the private contractor, subcontractors, banks and infrastructure users. These contracts should be designed to give the right incentives to the parties to achieve optimal risk allocation and utilising of resources.Long contract-periods are a common feature of PPPs. The paper examines the way that financial solutions should be designed to achieve the goals for the PPP-projects concerning economic and social efficiency. The expected size and variation of the income stream from the project will influence the loan conditions offered by banks concerning interest rates, guarantees and repayment and also the ability to attract investors. The balance between equity and loans again influences the conditions of the loans. An additional problem is asymmetric information between parties. The private contractor usually knows more about the task than the Government (hidden knowledge), and the Government cannot have full knowledge of the efforts of the contractor (hidden actions).     

浅谈工程项目的投资监理

进入“十五”计划以后,工程项目固定资产投资进入新一轮发展高潮,几乎每一个领域都有大量基本建设项目,给工程造价咨询业带来了“如何最有效控制项目投资”的课题。该文着重从现场投资监理的角度,讨论从招标到竣工结算等重要环节的工程投资监理方法。     

直线电机在轨道交通系统中的应用

介绍了直线电机的基本原理、不同的应用方式及其在城市轨道交通中的应用情况;并就供电系统中存在的变电所较多、能耗较高等问题,提出了如何设法减少线路总阻抗、如何回收利用迷流等初步解决方案。     

深水大跨码头结构研究

通过对我国港口现状的分析,对高桩码头上部结构改革状况的研究,提出了适应深水大跨要求的悬链线拱式纵梁码头结构型式。该结构能充分利用拱结构的跨越能力和钢筋混凝土的抗压性能,大幅度增加码头的排架间距,减少水下工程量,进而降低工程造价。与上海港洋山港区三期工程的普通纵梁结构相比,该结构排架间距可增大到28 m,基桩数量和水下施工工程量明显减少,工程造价降低23%。     

工程项目施工成本风险分析及建议

伴随着建筑行业总产值的逐年大幅攀升，建筑行业的利润却呈下滑趋势。笔者从人为因素、材料成本因素、施工机械水平因素、政策法规因素和环境风险因素5个方面分析了出现这种背离现象的原因，认为只有从施工企业内外部环境两方面着手，分别加大市场规范监督力度和提高施工企业自身管理水平，才能从根本上解决建筑行业利润和产值背离的问题。     

南京地铁大胜关桥与国铁交流系统共地方案分析

国铁和地铁同桥水平近距离敷设,在国内尚属首次,并且无经验可参考.由于地铁和国铁两个供电系统的接地及连接方法有着本质的不同,因此必需考虑接地问题.通过对地铁、国铁供电系统与地关系的说明,从杂散电流防护、绝缘、轨电位等角度,对南京大胜关桥地铁和国铁采用绝缘地还是共地方案分别进行了分析.基于人身设备安全,推荐采用共地方案.