Impact of heliostat curvature on optical performance of Linear Fresnel solar concentrators

The present paper gives a numerical investigation of the effect of mirror curvature on optical performance of a Linear Fresnel Reflector solar field installed recently in Morocco. The objective is to highlight and discuss the effect of mirror curvature on the flux density distribution over the receiver and the system optical efficiency. For this purpose, a Monte Carlo-ray tracing simulation tool is developed and used to optimize the optical design taking into account the curvature degree of the heliostat field. In order to assess the accuracy of the numerical code developed and the validity of simulation results, a set of verification tests were developed and detailed within this article. Then, the optical performance of the system is evaluated as a function of mirror curvature and receiver height. The major challenge of this study is to find a trade-off between heliostat curvature and receiver height since lower and smaller receivers may reduce the system cost. It has been found that the flux distribution over the receiver and the optical efficiency of the system are relatively sensitive to the mirror curvature. We have demonstrated quantitatively how the use of curved mirrors can enhance the optical performance and reduce the required receiver size.     

桅杆结构风振响应分析

本文根据一工程实例,建立了一个格构式桅杆的空间动力模型,利用Monte Carlo数值模拟对桅杆的非线性风振响应进行了计算。根据计算结果,对桅杆结构在风荷载作用下的响应特性进行了分析,并根据桅杆结构风振实测结果,对桅杆结构风振响应的非高斯性和宽带性进行了分析。     

基于新安江模型的降雨不确定性传播

基于模糊隶属度理论,结合蒙特卡罗方法,定量分析了降雨不确定性在新安江模型中的传播特性及其对流量过程的影响。用模糊隶属度函数表示降雨量的不确定性,用蒙特卡罗方法把3 h雨量随机解集为1 h数据,以表征降雨时程分布的不确定性影响。应用新安江模型对褒河流域进行径流模拟。结果表明,雨量量级大小的不确定性在降雨不确定性中占据主导位置,降雨时程分布的影响次之。     

Stochastic User Equilibrium Traffic Assignment with Turn-delays in Intersections

Turn-delays in intersections contribute significantly to travel times and thus route choices in urban networks. However, turns are difficult to handle in traffic assignment models due to the asymmetric Jacobian in the cost functions. The paper describes a model where turn delays have been included in the solution algorithm of Stochastic User Equilibrium (SUE) traffic assignment. When the Jacobian is symmetric, SUE minimises the road users' 'perceived travel resistances'. This is a probit-model where the links cost-functions of the links are traffic dependent. Hereby, overlapping routes are handled in a consistent way. However, no theoretical proof of convergence has been given if the Jacobian is asymmetric, although convergence can be shown probable for model data representing realistic road-networks. However, according to the authors knowledge SUE with intersection delays have not been tested earlier on a full-scale network. Therefore, an essential part of the paper presents practical tests of convergence. Both geometric delays and delays caused by other turns are considered for each turn. Signalised and non-signalised intersections are handled in different ways, as are roundabouts. In signalised intersections a separate model handles queues longer than one green-period. Green-waves can also be taken into consideration. The model has been tested on a large-scale network for Copenhagen with good results. To make it possible to establish the comprehensive data, a GIS-based 'expert system' was implemented (see Nielsen, O.A., Frederiksen, R. D. and Simonsen, N. (1997). Using expert system rules to establish data on intersections and turns in road networks. International Transactions in Operational Research , 5 , 513–529.     

考虑土体参数不确定性的供水管道地震响应分析

埋地管道周围土体性质沿管道纵向存在不确定性,直接影响到埋地管道的地震响应规律和抗震性能。为此,基于设计反应谱合成不同抗震设防烈度下的人工地震动,采用简化弹性地基梁模型,分析地震行波作用下的管道接口动力响应。考虑因安装环境差异、管道老化等因素引起的球墨铸铁管道接口强度的折减,分析土体重度、内摩擦角、黏聚力和土弹簧屈服位移4个不确定性参数对埋地球墨铸铁供水管道地震响应的影响规律,并对不同地震烈度、不同薄弱接口抗拉强度折减系数土参数不确定性规律进行总结归纳。算例分析表明:与确定性参数模型计算结果相比,4个不确定性参数对接口峰值动力响应的影响程度依次为黏聚力、内摩擦角、土体重度、土弹簧屈服位移,同时考虑4个不确定性参数的模型对结果影响最大,最大接口张开量的变异系数可高达9.54%;考虑土体参数不确定性的均值与确定性工况基本一致,最不利值为确定性工况的1.09~1.31倍;管道局部接口抗拉强度的折减对管道接口位移的响应影响显著。基于计算结果给出了不同地震动强度下接口薄弱系数与接口最大张开量的预测公式。     

A novel methodology for forecasting gas supply reliability of natural gas pipeline systems

In this paper, a novel systematic and integrated methodology to assess gas supply reliability is proposed based on the Monte Carlo method, statistical analysis, mathematical-probabilistic analysis, and hydraulic simulation. The method proposed has two stages. In the first stage, typical scenarios are determined. In the second stage, hydraulic simulation is conducted to calculate the flow rate in each typical scenario. The result of the gas pipeline system calculated is the average gas supply reliability in each typical scenario. To verify the feasibility, the method proposed is applied for a real natural gas pipelines network system. The comparison of the results calculated and the actual gas supply reliability based on the filed data in the evaluation period suggests the assessment results of the method proposed agree well with the filed data. Besides, the effect of different components on gas supply reliability is investigated, and the most critical component is identified. For example, the 48th unit is the most critical component for the SH terminal station, while the 119th typical scenario results in the most severe consequence which causes the loss of 175.61×10⁴ m³ gas when the 119th scenario happens. This paper provides a set of scientific and reasonable gas supply reliability indexes which can evaluate the gas supply reliability from two dimensions of quantity and time.     

模糊讯息分析法评估砂性土液化潜能

本文以Ｓｅｅｄ和Ｉｄｒｉｓｓ简化法为机率分析法的基础，利用模糊讯息分析的基本理论并考虑砂性土基本动态特性所建立的模糊关系，进行砂性土液化潜能评估。计算结果与机率分析及蒙地卡罗模拟法结果互相对比、验证，表明模糊讯息分析对砂性土液化潜能可提供明确评估。     

基于蒙特卡洛算法的SCR脱硝性能影响因素分析

为分析入口参数不均匀分布对选择性催化还原(Selective Catalytic Reduction, SCR)反应器脱硝性能的影响,通过MATLAB编程的方法建立了SCR脱硝反应三维数值模型。采用蒙特卡洛算法生成入口边界,以此调用模型,研究入口速度、温度及氨氮比分布不均条件下脱硝效率及氨逃逸率的变化规律。结果表明：当入口速度超过1.5 m/s,速度偏差对脱硝效率及氨逃逸率的影响较为显著,在入口速度为4 m/s时将速度偏差由0增大到80%,脱硝效率由46.77%降低到44.67%,而氨逃逸率由8.31%增加到12.57%;不同温度偏差变化区间对脱硝性能影响不同,当温度偏差小于10%时脱硝效率主要受到反应温度的影响,而当温度偏差大于10%时温度偏差成为影响脱硝效率的主要因素;氨氮比主要影响氨逃逸率,当氨氮比由0.8增大到1.2时,氨逃逸率由0.55%增大到1.02%,而脱硝效率由42.5%增大到57.23%。     

Monte Carlo simulation of the Fréedericksz transition in nematic liquid crystals

In this paper we present results of the Monte Carlo simulation of a 2D nematic liquid crystal model in the presence of an externally applied electric field. The molecular interactions were described by the Lebwohl-Lasher Hamiltonian. The boundary conditions employed in the simulations corresponded to the experimental configuration frequently used for establishing the Frank elastic constants. The results are compared with the predictions of the phenomenological Ericksen theory. Preliminary results of simulations of an experimentally important case corresponding to the nematic interacting with a spatially modulated electric fluid are presented. © 1997 John Wiley & Sons, Ltd.