A combined distribution and assignment model for continuous facility location problem

Consider a general, heterogeneous geographical space with a set of competitive facilities, where the customers' demand locations from each of the facilities are continuously dispersed over the area. The total demand generated from a particular location in the space is fixed, but the demands from this location to the set of competitive facilities are subject to a distribution function with respect to the relative transportation costs to these facilities. Furthermore, we take into account congested transportation cost in characterizing customer choices. Congestion effect is explicitly built into our model by using a flow-dependent and location-dependent transportation cost function. The routing behavior of customers over the space and the user equilibrium choices of facilities are modeled by constructing a spatial user equilibrium flow pattern. The problem is formulated as a combined distribution and assignment model. An iterative algorithm between the distribution function for the choice of facilities and a mixed finite element method for route choices is proposed to solve the resulting continuous facility location problem. A numerical example is given to demonstrate the effectiveness of the proposed methodology. Received: May 1999/Accepted: May 2000     

Optimization of sewer networks using the mixed-integer linear programming

This paper introduces a method for optimizing sewer networks using the mixed-integer linear programming (MILP) for a given layout. The objective function is defined as the sum of the costs for pipe purchase, pipe-laying, and manhole construction expressed in linear terms and subject to minimum and maximum allowable slopes, velocities, and relative depths for both minimum and maximum sewage discharge rates in each pipe. Additionally, provisions are made as constraints or conditions to ensure that a minimum pipe cover is required, that pipe diameters do not decrease in the flow direction, and that pipes maintain a steady elevation at each manhole. All the non-linear constraints are transformed into the linear format. Pipe slope, binary variables accounting for commercial pipe diameters and average implemented depths have also been considered as decision variables. Finally, the performance of the proposed optimization method is evaluated in a benchmark sewer network from the literature.     

Constrained Ant Colony Optimisation Algorithm for the layout and size optimisation of sanitary sewer networks

The incremental solution building capability of Ant Colony Optimisation Algorithm (ACOA) is used in this paper for the efficient layout and pipe size optimisation of sanitary sewer network. Layout and pipe size optimisation of sanitary sewer networks requires optimal determination of pipe locations, pipe diameters and pipe slopes leading to a highly constrained mixed-integer nonlinear programming (MINLP) problem presenting a challenge even to the modern heuristic search methods. A constrained version of ACOA equipped with a Tree Growing Algorithm (TGA) is proposed in this paper for the simultaneous layout and pipe size determination of sewer networks. The method is based on the assumption that a base layout including all possible links of the network is available. The TGA algorithm is used in an incremental manner to construct feasible tree-like layouts out of the base layout, while the constrained ACOA is used to optimally determine the cover depths of the constructed layout. Proposed formulation is used to solve three hypothetical test examples of different scales and the results are presented and compared with those produced by a conventional application of ACOA in which an ad-hoc engineering concept is used for layout determination. The results indicate the effectiveness and efficiency of the proposed method to optimally solve the problem of layout and size determination of sewer networks.     

松软地层高压灌浆封孔浆体研制及应用论证

在松软地层进行防渗工程施工时,存在钻孔易塌孔,灌浆难起压易导致垂向挤密抬动,灌浆易漏浆串浆导致耗浆量大,灌浆过程难控制等技术难题。传统的“袖阀管灌浆法”、“预埋花管法”、“孔口封闭灌浆法”等工法在深厚松软地层的施工中很难达到设计要求。为降低成本、提高工效,研究提出一种“自下而上,浆体封闭,高压脉动灌浆”新工法,介绍其中的“浆体封闭技术”成果。针对施工工艺要求,研制出低强度快凝硬塑状封孔浆体,通过实验得到性能参数;基于浆体封闭力学机理,对封孔效果进行论证,结果表明,在灌浆过程中,封孔浆体材料具备足够的止浆、耗能作用;对灌浆所需的最低注浆压力进行了计算,为选择注浆设备提供依据;另外,对自下而上灌浆施工中,提管所需的拔管力进行了计算,为提高工效、避免灌浆管出现抱死事故,提出边灌边转工艺方法,可使灌浆管顺利提升,即使在深孔情况下也无需使用拔管机。通过在怀化托口水电站河湾地块深厚松软红层进行原型试验,验证研制的封孔浆体的应用效果,分别在浅孔全段注入、深孔（最大达 120 m ）孔底以上 20 m 深注入封孔浆体材料,实施“自下而上,浆体封闭,高压脉动灌浆”。试验中 8 m 深松软层达到 1.5 MPa 以上的灌浆压力, 120 m 深可达到近 8 MPa 的灌浆压力（均为孔口压力）,地层抬动仅为 12 mm ,灌后效果达到设计要求,表明在高压灌浆情况下,封孔浆体使用效果良好;建议在深孔注浆过程中,灌浆管边灌边转,无需使用拔管机,工艺更便捷、高效。理论研究和工程实践表明,在松软地层实施高压灌浆,采用浆体封闭技术是可行的,研制的封孔浆体性能能满足施工工艺要求。     

基于全寿命周期的供热管网管径优化设计方法

结合供热管网现代优化算法和确定管径的传统方法,提出了一种管径优化设计方法。该方法首先根据水力计算确定几种可行的管径布置方案,然后根据全寿命周期内管网成本最低确定最优方案。实例分析表明,该方法省去了编程的麻烦,克服了传统管径选取的盲目性,达到了更加节能和便于实际应用的目的。     

冰浆输冷空调系统设计方法的研究

冰浆作为载冷剂具有节能、环保、高效等优点。该文就夏季工况对某办公大楼以冰浆为载冷剂的空调系统的管道系统进行了设计计算同时对其冬季供暖时使用情况进行了校核,最终得出冬夏共用管道系统时所对应的含冰率,以期为该类空调系统的设计提供一种设计方法。     

基于枚举算法的雨水管网优化设计

考虑到雨水管网的布置和计算特点,采用枚举算法进行雨水管网的优化设计。针对雨水管网内所有的干管和支管,该算法能够遍历雨水管道可选的标准管径集,找出符合约束条件的所有管径组合,然后利用造价函数筛选出管网造价最低的一种组合,并将其作为最终优化结果。利用Visual Basic 6.0语言编程并进行了工程应用,结果表明,枚举算法可以适用于复杂地形的雨水管网优化,是非常实用的全局优化方法。     

Shortening the search time in optimization of water distribution networks

Various optimization techniques have been implemented for minimizing the costs associated with water distribution networks (WDNs). In this regard, meta-heuristic algorithms have represented the highest efficiency. One of the weaknesses of these algorithms is their high computational costs, which make their implementation sometimes impracticable for optimization of large real life WDNs. In this article an optimization model based on the ant colony optimization algorithm is presented for least cost design of WDNs. In the proposed model, ants select pipe diameters so that the energy loss per unit length of pipes will be in a specific range. In this model, the number of objective function evaluations is small. Two sample networks have been optimized using the proposed model. Obtained results show that the model presented in this article has a very low search time, which makes its implementation possible for large real-life WDNs.     

Joint power distribution and charging network design for electrified mobility with user equilibrium decisions

Rapid adoption of electric vehicles (EVs) requires the development of a highly flexible charging network. The design and management of the charging infrastructure for EV-dominated transportation systems are intertwined with power grid operations both economically and technically. High penetration of EVs in the future can increase the charging loads and cause a wide range of operational issues in power distribution networks (PDNs). This paper aims to design an EV charging network with an embedded PDN layout to account for energy dispatch and underlying traffic flows in urban transportation networks supporting electric mobility in the near future. A mixed-integer bilevel model is proposed with the EV charging facility location and PDN energy decisions in the upper level and user equilibrium traffic assignment in the lower level considering an uncertain charging demand. The objective is to minimize the cost of PDN operations, charging facility deployments, and transportation. The proposed problem is solved using a column and constraint generation (C&CG ) algorithm, while a macroscopic fundamental diagram concept is implemented to estimate the arc travel times. The methodology is applied to a hypothetical and two real-world case study networks, and the solutions are compared to a Benders decomposition benchmark. The east-coast analysis results indicate a 77.3% reduction in the computational time. Additionally, the benchmark technique obtains an optimality gap of 1.15%, while the C&CG algorithm yields a 0.61% gap. The numerical experiments show the robustness of the proposed methodology. Besides, a series of sensitivity analyses has been conducted to study the impact of input parameters on the proposed methodology and draw managerial insights.     

超细尾砂高浓度自流充填的现场试验方法

结合金鼎矿业充填法开采的现场工程,开展了对超细尾砂充填料浆短距离管道输送的研究.为达到自流、满管、通畅和高浓度等输送效果,进行实验室的扩散度测试试验,建立相对应的数学模型,得到满足现场管道输送要求的浓度,解决了工程中管道输送充填的实际问题.     

Research on probing and predicting the diameter of an underground pipeline by GPR during an operation period

It is very important that the existing networks of underground pipelines be clearly surveyed when the underground space of an old urban area is rebuilt and expanded. The GPR method is always used to locate the embedded pipes; however, it is hard to determine their diameters, especially, when the underground pipe is full of a lossy medium (i.e., water, oil, or gas) during the operation period. First, this paper proposes a new method for probing and predicting the diameter of underground pipelines filled with lossy media based on GPR using the shape of a certain circle determined by the coordinates of three points on this circle. The operational procedure of this method is listed in detail. Secondly, this method is used to detect the diameters of underground pipelines in a model experiment and the project for the detection of a sewage pipe network in Yi’xing chemical industrial park. The measurement value is approximately consistent with the real value. Lastly, some factors influencing the accuracy of this method were comprehensively analysed by applying the finite difference time domain method (FDTD). These factors are the buried depth of the pipe, the detecting frequency of the GPR, the material of the pipe and the spacing of the measured points. The results showed that the proposed method has sufficient applicability and accuracy for practical engineering. These works demonstrate that the proposed method achieves good result.     

集中式与分散式地源热泵系统的生命周期成本评价

本文首先利用生命周期成本法比较了集中式与分散式这2种不同形式的地源热泵系统的成本,包括管道系统、循环泵的初投资以及每年泵能耗的费用。而后对西安市某商场建筑进行了成本计算,结果显示集中式泵系统的生命周期成本比分散式系统高17.4%。     

基于响应面法的盾构施工膨润土改良参数优化

为确定福州地铁4号线金牛山—工业路盾构区间强风化花岗岩地层中的膨润土改良最优参数,分别选择膨润土泥浆浓度、掺入比和盾构推进速度3个影响因素,以渣土塌落度、渗透系数和改良成本为响应值。采用中心复合试验设计方法进行了20组试验,分别构建了各响应值的响应面函数。试验结果表明,膨润土泥浆浓度、掺入比和盾构推进速度对渣土改良效果均有较大影响,且各因素之间存在显著交互作用。利用响应面–满意度函数,将渣土改良的3个响应值优化问题转化为单一响应值优化,获得强风化花岗岩地层在不同盾构推进速度下的最优改良参数。该方法科学合理,为金牛山—工业路盾构区间在强风化花岗岩内的高效施工提供了技术保障。     

Evaluation of expected energy generation in multi-area interconnected systems with photo voltaic generating units

This paper presents a methodology which extends the segmentation method to evaluate the expected energy generation and the expected export/import among the electrical utilities in an interconnected system with renewable energy-based units as well as conventional thermal units. The proposed methodology is applied to the Power Grid of Bangladesh. The method helps the system planner determine the expected cost of energy generation of various sources. The randomness in the output of a renewable energy generator is appropriately modelled in the proposed methodology.     

Column Generation‐Based Approach for Solving Large‐Scale Ready Mixed Concrete Delivery Dispatching Problems

Ready mix concrete (RMC) dispatching forms a critical component of the construction supply chain. However, optimization approaches within the RMC dispatching continue to evolve due to the specific size, constraints, and objectives required of the application domain. In this article, we develop a column generation algorithm for vehicle routing problems (VRPs) with time window constraints as applied to RMC dispatching problems and examine the performance of the approach for this specific application domain. The objective of the problem is to find the minimum cost routes for a fleet of capacitated vehicles serving concrete to customers with known demand from depots within the allowable time window. The VRP is specified to cover the concrete delivery problem by adding additional constraints that reflect real situations. The introduced model is amenable to the Dantzig–Wolfe reformulation for solving pricing problems using a two‐staged methodology as proposed in this article. Further, under the mild assumption of homogeneity of the vehicles, the pricing sub‐problem can be viewed as a minimum‐cost multi‐commodity flow problem and solved in polynomial time using efficient network simplex method implementations. A large‐scale field collect data set is used for evaluating the model and the proposed solution method, with and without time window constraints. In addition, the method is compared with the exact solution found via enumeration. The results show that on average the proposed methodology attains near optimal solutions for many of the large sized models but is 10 times faster than branch‐and‐cut.     

泥浆减阻技术在粉土地层长距离曲线顶管中的应用

上海世博北京西路～华夏西路电力电缆隧道三标工程采用Ф3500F型钢筋混凝土管和大刀盘泥水平衡顶管掘进机施工。该工程分为6个区间顶程,全部是大直径长距离曲线顶管,其中11～10区间顶管穿越的地层主要为夹砂粉土层。该区间顶管实施过程中,施工技术人员对顶管触变泥浆材料、配方、搅拌方法、注浆工艺等,尤其是对触变泥浆在粉土地层中的抗渗透性能和稳定性进行了深入的研究。通过研究结果在施工中的运用,成功地将混凝土管道外壁与粉砂土之间的单位面积侧向摩阻力控制在1kPa以内,保证了顶管顺利贯通的同时,该研究与应用成果还为今后类似顶管工程的设计和施工提供了参考。     

加肋焊接空心球节点受压承载力参数分析

现行《网壳结构技术规程》在计算带加劲肋的焊接空心球时的承载力公式是由试验回归分析得出的,有关加劲提高系数方面很少有系统的研究。本文采用有限元分析的方法,对直径从300～500mm的加劲空心球,球壁厚、钢管直径、钢管壁厚不同的各种情况下的有限元分析结果与非加劲空心球的结果做一比较,得出受压承载力提高系数并非在任何情况下均为1.4,而是与钢管直径、钢管壁厚等因素有关。最后,以直径为500mm的球为例,分析了不同球壁厚、钢管直径、钢管壁厚对带加劲肋的焊接空心球受压承载力的影响,得出的结论可供实际工程或相关规程修订时参考。     

A grouting simulation method for quick-setting slurry in karst conduit: The sequential flow and solidification method

It is difficult to temporally and spatially track and characterize the slurry viscosity in flowing water during grouting simulation. In this study, a sequential flow and solidification (SFS) method considering the spatial-temporal evolution of slurry viscosity in flowing water in karst conduit is proposed. First, a time-dependent model for the threshold function of slurry viscosity is established. During the grouting process, the spatial-temporal evolution of slurry viscosity is revealed by tracking the diffusion behavior of the slurry injected at different times. This method is capable of describing the gradual solidification process of the slurry during grouting. Furthermore, a physical model of grouting in a karst conduit is developed. Second, the effectiveness of the SFS method in grouting simulation is verified by the experiment of grouting conduit in flowing water. The SFS method enables real-time monitoring of fluid velocity and pressure during grouting in flowing water and provides a feasible calculation method for revealing the grouting plugging mechanism in complex karst conduits at different engineering scales. In addition, it can be used to guide the design of grouting tests in flowing water, improve cost efficiency, and provide theoretical basis for optimizing grouting design and slurry selection.     

Cost functions for multiple transportation modes in the presence of congestion

This paper introduces an alternative way of specifying the social cost function for transportation services. This paper formulates the transportation cost function as a social cost minimization problem in the presence of congestion phenomena. This social cost function has an advantage in terms of assessing the cost structure of various transportation modes in a unified manner. In addition, the social cost function has a structure that can yield precise information about the structures of other cost functions such as a marginal social cost function and a marginal supplier cost function. This paper illustrates those advantages with the analysis to derive the specific expressions of the various cost functions for highway uses, and for public transit services. Especially, this analysis pinpoints on identifying the difference in the structures of cost functions for the two modes. Received: February 2001/Accepted: December 2001     

Resilience-based post-disaster recovery strategies for road-bridge networks

This paper presents a novel resilience-based framework to optimise the scheduling of the post-disaster recovery actions for road-bridge transportation networks. The methodology systematically incorporates network topology, redundancy, traffic flow, damage level and available resources into the stochastic processes of network post-hazard recovery strategy optimisation. Two metrics are proposed for measuring rapidity and efficiency of the network recovery: total recovery time (TRT) and the skew of the recovery trajectory (SRT). The TRT is the time required for the network to be restored to its pre-hazard functionality level, while the SRT is a metric defined for the first time in this study to capture the characteristics of the recovery trajectory that relates to the efficiency of those restoration strategies considered. Based on this two-dimensional metric, a restoration scheduling method is proposed for optimal post-disaster recovery planning for bridge-road transportation networks. To illustrate the proposed methodology, a genetic algorithm is used to solve the restoration schedule optimisation problem for a hypothetical bridge network with 30 nodes and 37 bridges subjected to a scenario seismic event. A sensitivity study using this network illustrates the impact of the resourcefulness of a community and its time-dependent commitment of resources on the network recovery time and trajectory.