共查询到19条相似文献,搜索用时 125 毫秒
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锌合金用储油罐的避雷防静电接地极,不仅可以更好地改善接地条件,而且可使储油罐底板外侧仅需很小的外加电流就能得到完全保护而避免腐蚀。锌合金接地极也可以兼作牺牲阳极,提供低电阻接地和阴极保护的双重功能。 相似文献
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检查片是评价埋地管道阴极保护有效性的传统工具。近年有新的发展,如:2004年ANSI和NACE颁布改进的阴极保护检查片实施标准,增加检查片和管道间电偶电流、试片断电电位等现场测试,以提高试验的信息量。为此,开发了新的测量仪器,并在上海至银川的西气东输管道2000km沿线检查片埋设现场,进行了新仪器的测试,检测了管道和试片的直流及交流电位、试片断电电位和管道与检查片间电偶电流等大量参数。针对现场发现的电偶电流周期波动现象,经验证是环境交流干扰造成的,并讨论了交流干扰对管地电位和电偶电流的影响规律,为现场测量数据提供分析依据。 相似文献
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本文定性地分析了影响接地电阻的几个因素,全面地阐述了降阻剂的机理及施工方法;科学地论述了降低接地电阻的途径,对降低接地电阻,特别是岩石地质的接地电阻提供了理论和实践依据。 相似文献
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对深圳宝安国际机场航油输送管道及加油系统牺牲阳极保护电位的测试 ,土壤环境对阳极工作性能的影响 ,阳极静电体的接地及阳极的更换等维护管理问题进行了讨论 ,并提出了解决办法 相似文献
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Oversaturated intersection control is a long-standing problem in traffic science and engineering. The problem becomes even harder when we consider a system of oversaturated intersections. Most of the research works in this area are off-line studies that require fully knowledge of origin–destination demand, which would be difficult to obtain in reality. Although several on-line feedback control methods are proposed, they only aim at preventing queue spillover, not able to minimize vehicular delay time. Moreover, these on-line control strategies are not theoretically evaluated how optimal (or sub-optimal) they are. We propose in this paper a quasi-optimal decentralized QUEUE-based feedback (abbreviated as QUEUE) control strategy for a system of oversaturated intersections. The QUEUE strategy is applied cycle-by-cycle based on measurement of current queue sizes, but its overall result is able to approximate the optimal one derived from off-line studies. Details of the feedback control laws for upstream and downstream intersections, in the queueing period and the queue dissipation period, are discussed. Superior to the existing feedback control strategies, the upper bounds of sub-optimality of the QUEUE strategy generating from demand fluctuation and coupling of intersections are specified quantitatively. It is also theoretically proved that the queue measurement error or demand estimation error would not be amplified by the QUEUE strategy. Numerical examples show that the QUEUE strategy performs very well and is robust to errors. 相似文献
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An essential element of demand modeling in the airline industry is the representation of time of day demand—the demand for a given itinerary as a function of its departure or arrival times. It is an important datum that drives successful scheduling and fleet decisions. There are two key components to this problem: the distribution of the time of day demand and how preferred travel time influences itinerary choice. This paper focuses on estimating the time of day distribution. Our objective is to estimate it in a manner that is not confounded with air travel supply; is a function of the characteristics of the traveler, the trip, and the market; and accounts for potential measurement errors in self-reported travel time preferences. We employ a stated preference dataset collected by intercepting people who were booking continental US trips via an internet booking service. Respondents reported preferred travel times as well as choices from a hypothetical set of itineraries. We parameterize the time of day distribution as a mixture of normal distributions (due to the strong peaking nature of travel time preferences) and allow the mixing function to vary by individual characteristics and trip attributes. We estimate the time of day distribution and the itinerary choice model jointly in a manner that accounts for measurement error in the self-reported travel time preferences. We find that the mixture of normal distributions fits the time of day distribution well and is behaviorally intuitive. The strongest covariates of travel time preferences are party size and time zone change. The methodology employed to treat self-reported travel time preferences as potentially having error contributes to the broader transportation time of day demand literature, which either assumes that the desired travel times are known with certainty or that they are unknown. We find that the error in self-reported travel time preferences is statistically significant and impacts the inferred time of day demand distribution. 相似文献
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基于广泛应用的深井阳极技术,指出了研究阴极保护电位分布规律的重要性。针对以往深井阳极对储罐底板阴极保护数值模拟存在的影响(金属构件极化曲线试验限定条件不同导致电位计算系统误差;没有考虑计算区域环境介质的不连续性),提出一种根据典型电流密度分布假设求解保护电位的方法,选取2个典型的深井阳极对储罐底板阴极保护工程示例,验证了数值方法的可靠性。针对新建储罐底板阴极保护工程,该方法对于合理设计深井阳极具有借鉴意义。 相似文献
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道路交通是造成气候变化的主要碳排放来源之一。目前针对道路交通碳排放量测量和减排效果的定量评估方面仍然存在较大挑战。综述了道路交通碳排放测量方法,将道路交通碳减排措施分为经济、技术和行政三类,根据角色定位总结了影响交通碳排放的需求、供应和环境三方面的主要因素。发现不同测量方法得出的碳排放量差异较大,且各种方法的准确性和适用范围也存在较大差异。目前的碳减排措施目标针对性不够强,且缺乏对政策效果的定量研究。亟需在未来研究中规范道路交通碳排放量的统计口径和误差标准,明确各交通主体的减排责任,将更多研究工作集中在减排措施效果的量化上。 相似文献
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天然气输差是控制输气成本的一个关键指标,可分为计量输差和漏失输差两大类。在实际生产中,由于产生输差的原因非常复杂多变,往往导致天然气计量交接不能满足精度要求。因此,找出影响其计量误差和提出改进措施有着重要的意义。以塔河油田集气总站为例,从旋进旋涡流量计和超声流量计的原理特点、现场应用情况、用户负荷、外部干扰等4个主要方面对引起计量输差的因素进行了探讨,并提出了6项控制措施。其中包括通过现场流程改造,有效解决了FT301超声流量计反向计量不准确的问题,使该站的站输差从5.26%降低到了0.68%,取得了较好的效果。 相似文献
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Currently, the shipping industry is facing a great challenge of reducing emissions. Reducing ship speeds will reduce the emissions in the immediate future with no additional infrastructure. However, a detailed investigation is required to verify the claim that a 10% speed reduction would lead to 19% fuel savings (Faber et al., 2012).This paper investigates fuel savings due to speed reduction using detailed modeling of ship performance. Three container ships, two bulk carriers, and one tanker, representative of the shipping fleet, have been designed. Voyages have been simulated by modeling calm water resistance, wave resistance, propulsion efficiency, and engine limits. Six ships have been simulated in various weather conditions at different speeds. Potential fuel savings have been estimated for a range of speed reductions in realistic weather.It is concluded that the common assumption of cubic speed-power relation can cause a significant error in the estimation of bunker consumption. Simulations in different seasons have revealed that fuel savings due to speed reduction are highly weather dependent. Therefore, a simple way to include the effect of weather in shipping transport models has been proposed.Speed reduction can lead to an increase in the number of ships to fulfill the transport demand. Therefore, the emission reduction potential of speed reduction strategy, after accounting for the additional ships, has been studied. Surprisingly, when the speed is reduced by 30%, fuel savings vary from 2% to 45% depending on ship type, size and weather conditions. Fuel savings further reduce when the auxiliary engines are considered. 相似文献