长输在役修复管道热力允许开挖长度的计算方法

开挖长度是热油管道修复过程中的重要参数之一,其值的合理确定对管道开挖修复方案及油田节能起到重要作用.文中从热力学角度,建立运行开挖不停输工况一次性最大允许开挖长度的热力数学模型,并以林源站至太阳升站的输油管道为例,进行了模拟计算,研究了维修季节、计划维修时间及油品出站温度对热力允许开挖长度的影响.结合油田节能降耗要求,给出热油管道开挖维修建议.     

热油管道输送含蜡原油的轴向温降计算

在含蜡原油热油管道输送工艺计算中,根据比热容随温度变化的趋势,得出3个不同温度区域内的比热容表达式,分别将其代入能量平衡方程中,推导出热油管道输送含蜡原油的轴向温降公式,将其与苏霍夫温降公式进行对比。结果表明:应用该公式能更精确的计算出热站间距、出站温度,减少不必要的损失。     

含蜡热油管道站间摩阻损失的计算

在含蜡热油管道的实际运行过程中，油品的一些物性参数，如比热容、黏度、密度等均随油温的变化而变化。在加热站间管道沿线，流态和流型随着温度的变化也会发生转变。综合考虑以上因素，采用数值积分方法，对加热站间管路划分了区间，各自应用不同的摩阻特性公式进行摩阻损失计算，提高了计算精度。     

热油管道的程序设计

针对热油管道输送过程中的计算问题,应用计算机技术实现复杂计算,使用VB编程,用计算机实现热油管道的加热站数目、油输量、站间摩阻、泵站数等的计算.通过和实际数值的对比,编制的程序可以进行长输管道工艺计算,为以后相关软件的研制奠定了基础.     

用预测-校正法计算埋地热油管道停输时的轴向温降

在充分考虑影响热油管道轴向温降的各个因素的基础上,并考虑油品物性(密度、比热容、黏度)和总传热系数随温度变化而变化,建立了热油管道停输时轴向温降的数学模型,模型还适用于有进分油点的管道,并用预测-校正法求解数学模型,最后进行了实例计算.该方法已应用在新疆油田的几条热油管道轴向温降的计算中,计算结果令人满意.     

埋地热油管道沿程温降的数值模拟

运用fluent软件在三维笛卡尔直角坐标系下建立埋地热油管道的物理模型,分别对不同传热系数和不同流速的热油管道以及非稳态环境下的热油管道进行数值模拟,得到热油管道轴向温度的分布图,通过改变管道总传热系数和流速分析其温度的变化规律并对其进行比较分析。计算结果很好地反映出埋地热油管道沿程温降的基本特征,可为实际生产管理提供科学的依据,对于指导油田的输油生产、管道安全运行和节能降耗具有重要意义。     

海底单层保温管线总传热系数分析

总传热系数K是海底热油管道的运行管理中的一个非常关键的参数.文中通过对中海油涠洲11 -1油田至涠洲12 -1油田之间的海底管道总传热系数进行理论计算,并与投产前根据实际预热数据反算的总传热系数进行对比,得出理论计算的总传热系数与实际预热反算得到的总传热系数相近,同时指出海管接口的散热损失较大,海底管线应对接口部分进行...     

含蜡热油管道结蜡厚度计算

结蜡是影响热油管道安全、经济运行的重要因素。管线结蜡厚度可以根据管道的运行参数反算,文中为此设计了计算模型,可以准确快捷地计算出管道的结蜡厚度,为管道的安全、经济运行提供了依据。     

对原油管道最低出站油温的控制分析

对原油管道最低出站油温的控制进行分析，通过全面考虑原油管道正常运行、停输和再启动情况下管道系统的散热和流动特性，对建立的数学模型利用数值解法的预测一校正法和有限元法联立求解，并在此基础上编制了模拟软件，可对实际生产提供科学依据。通过对实际管道进行分析，得出原油管道最低出站油温的控制由季节、管道的允许停输时间、要求恢复正常运行的时间以及出站最高可加热油温等因素而决定。     

流动保障技术在海底热油管道上的应用

为保障海上终端装卸船海底热油管道安全经济运行,引入了国外始于深海油气田开发的流动保障的概念,建立了海底热油管道的水力、热力模型.为了提高计算的准确性,在建立热力模型时,采用变化的比热容进行计算,考虑了含蜡原油结晶潜热的影响;建立水力模型时,考虑了含蜡原油在管内流动的温降过程是蜡结晶的相变过程,采用了分段计算方法.同时,...     

On the fundamental diagram and supply curves for congested urban networks

Macroscopic fundamental diagrams (MFD) of traffic for some networks have been shown to have similar shape to those for single links. They have erroneously been used to help estimate the level of travel in congested networks. We argue that supply curves, which track vehicles in their passage through congested networks, are needed for this purpose, and that they differ from the performance curves generated from MFD. We use a microsimulation model, DRACULA and two networks, one synthesizing the network for Cambridge, England, and one of the city of York, England, to explore the nature of performance curves and supply curves under differing patterns of demand.We show that supply curves differ from performance curves once the onset of congestion is reached, and that the incorrect use of performance curves to estimate demand can thus seriously underestimate traffic levels, the costs of congestion, and the value of congestion relief measures. We also show that network aggregated supply curves are sensitive to the temporal distribution of demand and, potentially, to the spatial distribution of demand. The shape of the supply curve also differs between origin–destination movements within a given network.We argue that supply curves for higher levels of demand cannot be observed in normal traffic conditions, and specify ways in which they can be determined from microsimulation and, potentially, by extrapolating observed data. We discuss the implications of these findings for conventional modelling of network management policies, and for these policies themselves.     

广域网的建设及应用

文章从企业网络建设实际出发,分析了租用专用线路建设企业广域网时存在的问题,指出运用VPN技术建设企业广域网具有成本低、安全性好、扩展性强、可以满足用户随时随地接入要求等优点,为企业的信息化建设提供借鉴。     

Development of transitioned vertical curve I Properties

Introducing spiral curves before and after horizontal circular curves has been widely accepted to enhance traffic safety, highway esthetics, sight distance, and driver comfort. Though, vertical curves are still designed as parabolic curves that are connected directly to the tangent (without transitions). In this paper, a cubic polynomial is used to develop a vertical transition curve before and after the parabolic vertical curve. The resulting curve, called transitioned vertical curve, consists of transition-parabolic-transition segments. Detailed mathematical formulation and derivation of the instantaneous elevation, grade, rate of curvature, and offset from the first tangent at any point are presented. The highest (or lowest) point on a transitioned crest (or sag) vertical curve, where the instantaneous grade equals 0, is determined as it is of particular importance in highway drainage design. The minimum length of a transition curve is derived based on the criterion of driver comfort. In addition, guidelines are provided to identify the conditions where the drainage of surface water on transitioned curves can be a concern. Finally, the layout of the transitioned vertical curve is described and illustrated using two numerical examples. The new transitioned vertical curve, which exhibits striking similarities to the spiraled horizontal curve, should enhance the design of highway vertical alignments.     

全球民航事故调查数据统计与分析

为探索全球民航事故的发生及调查规律,从航空安全网(ASN)采集626起事故调查数据,对事故发生季度、类型、机型等特征进行统计分析,同时对事故调查的实施机构、调查时长、各类事故调查时长等特征展开分析。结果发现:全球民航事故随运行时间的增加呈现波浪形缓慢下降;事故数量最多的前两位为冲偏出跑道和飞机失去控制,并多集中在第三季度(7-9月);波音公司各机型事故曲线整体类似,同时与空客公司各机型飞机事故曲线存在差异。民航事故调查从开始到发布报告的平均周期为26.1个月;各调查机构针对冲偏出跑道、失去控制、可控飞行撞地事故的平均调查周期分别为22.2、40.4、12.4个月。研究结果为民航事故预防政策制定及事故调查提供参考依据。     

X52焊缝失效评定曲线

失效评定曲线被广泛应用于管道的断裂评定,针对严重影响国内在役老管道安全运行的焊缝问题,建立焊缝失效评定曲线.以在役老管道常用管材X52为例,采用R6方法建立焊缝失效评定曲线(选择3曲线),并与R6选择1曲线和选择2曲线比较,表明选择3曲线的精确性对于在役管道焊缝失效精确评估的重要性.给出了3种焊缝材料特性的失效评定曲线...     

煤矿采空区管道监测方法的应用

煤矿采空塌陷对埋地管道长期安全运营造成严重威胁。介绍了煤矿采空区管道的受力特点,提出了管道安全监测的必要性。结合长距离输油气管道在煤矿采空区的实际情况,提出可行的监测方法,并在鄯乌线芦草沟段进行了实际应用。通过监测得到管体在采空塌陷过程中应力的变化特征和变化量,为长输管道沿线采空区的安全维护提供了经济可行的解决方案,并为处于其他地质灾害区的管道维护提供参考。     

Hysteresis phenomena of a Macroscopic Fundamental Diagram in freeway networks

Observations of traffic pairs of flow vs. density or occupancy for individual locations in freeways or arterials are usually scattered about an underlying curve. Recent observations from empirical data in arterial networks showed that in some cases by aggregating the highly scattered plots of flow vs. density from individual loop detectors, the scatter almost disappears and well-defined macroscopic relations exist between space-mean network flow and network density. Despite these findings for the existence of well-defined relations with low scatter, these curves should not be universal. In this paper we investigate if well-defined macroscopic relations exist for freeway network systems, by analyzing real data from Minnesota’s freeways. We show that freeway network systems not only have curves with high scatter, but they also exhibit hysteresis phenomena, where higher network flows are observed for the same average network density in the onset and lower in the offset of congestion. The mechanisms of traffic hysteresis phenomena at the network level are analyzed in this paper and they have dissimilarities to the causes of the hysteresis phenomena at the micro/meso level. The explanation of the phenomenon is dual. The first reason is that there are different spatial and temporal distributions of congestion for the same level of average density. Another reason is the synchronized occurrence of transitions from individual detectors during the offset of the peak period, with points remain beneath the equilibrium curve. Both the hysteresis phenomenon and its causes are consistently observed for different spatial aggregations of the network.     

A reverse causal-effect modeling approach for signal control of an oversaturated intersection

A novel approach is presented in which signalized intersections are treated as normal highway bottlenecks for improved computational efficiency. It is unique in two ways. First, it treats the signalized intersections as common freeway bottlenecks by a reversed cause and effect modeling approach. Both traffic arrivals and departures are modeled by smooth continuous functions of time as if there were no interruptions to traffic flows from signals. The use of smooth continuous functions for departure curves instead of commonly used step functions makes it easy to apply differential calculus in optimization and future extension to a system of intersections. Second, a dynamic linear programming (LP) model is then developed to maximize the total vehicular output from the intersection during the entire period of congestion subject to prevailing capacity and other operational constraints. The continuous optimal departure flow rate (the effect) is then converted to signal timing parameters (the cause) that can be readily implemented. Two numerical examples are presented to demonstrate the properties of the proposed algorithm and examine its performance.     

氮气清扫技术在管道封存中的应用

废弃原油管道的扫线封存是防止管道发生泄漏和次生灾害的重要手段。利用氮气吹扫技术实现废弃原油管道的扫线封存,目前国内在这方面的实际案例还非常少,可供参考的技术规范还不健全。文中通过对原油管道的氮气扫线的方案编制,着重总结了原油管道的氮气扫线过程的施工经验和主要技术要点,分析和推荐了氮气扫线过程的风险管控措施,为相关的工程实践提供技术参考。     

Effects of local roads and car traffic on the occurrence pattern and foraging behaviour of bats

The most negative impacts of roads on bats are increased mortality caused by collisions with vehicles, noise pollution reducing both communication and foraging, and barriers to movement. To test the effect of roads and traffic on the occurrence and foraging habits of bats in forested landscapes in western Poland we compared 53 sites located along local asphalt roads of low to medium traffic volume with paired reference sites on unsurfaced forest roads. Acoustical monitoring systems with Anabat detectors were used at night to detect bats at all sites. Overall, we found a strongly significant preference of bats for local asphalt roads; 640 bat passes were recorded at asphalt roads but only 271 at reference sites. Furthermore, significantly more bat taxa, longer activity and a greater frequency of feeding buzzes (calls used during foraging) were also recorded at asphalt roads. However, significant benefits were not shown for all species. This study clearly shows that local asphalt roads in forested landscapes are important foraging areas for several bat species.