Risk-based optimization of the debt service schedule in renewable energy project finance

Project finance is used in capital intensive renewable energy projects worldwide. Financial entities such as large banks and institutional investors are active in providing syndicated loans for infrastructure projects and compete to offer better terms to the sponsors of these projects. The literature is full of research on capital structure optimization. We propose a novel stochastic framework for optimizing the debt service schedule with due regard to the probability of default of the project company. The applicability of the proposed method is demonstrated for a 10 MW solar photovoltaic project employing a genetic algorithm (GA) as the optimization tool. The NASA SSE dataset is used to collect irradiation data, and PVsyst software is employed to simulate the performance of the project. The uncertainties are accounted for using Monte Carlo simulation, and the revenue generated, its corresponding free cash flow and the debt service coverage ratio are simulated as random variables. The proposed optimization framework enables lenders to offer an optimized debt service that maximizes the shareholder's profitability index. A particle swarm optimization is also employed to validate the stability and usefulness of GA optimization.     

A simulation-based method for effective workface planning of industrial construction projects

The generation of well-defined and moderately sized field installation work packages for the construction workforce, referred to as workface planning, has been recently employed to plan large-scale industrial construction projects under tight schedules. However, traditional CPM-based scheduling of several thousand work packages (e.g. 5000 activities multiply by 10 work packages per activity on average) is a tedious, error prone process. Defining proper logics and controlling congestion among work packages crossing several work areas, and also effective resource allocation over time are other major challenges in workface planning. This paper presents a novel simulation-based framework to implement workface planning for large-scale industrial construction projects. This framework proposes a time-stepped discrete event simulation-based modelling for dynamic resource allocation based on congestion and other constraints on the job site. The proposed method is demonstrated and tested against traditional CPM-based solutions based on an actual case study.     

Optimal probabilistic design of seismic dampers for the protection of isolated bridges against near-fault seismic excitations

A probabilistic, simulation-based framework is presented in this paper for risk assessment and optimal design of supplemental dampers for multi-span bridge systems supported on abutments and intermediate piers through isolation bearings. The adopted bridge model explicitly addresses nonlinear characteristics of the isolators and the dampers, the dynamic behavior of the abutments, and the effect of pounding between the neighboring spans against each other as well as against the abutments. Nonlinear dynamic analysis is used to evaluate the bridge performance, and a realistic stochastic ground motion model is presented for describing the time history of future near-fault ground motions and relating their characteristics to the seismic hazard for the structural site. A probabilistic foundation is used to address the various sources of structural and excitation uncertainties and ultimately characterize the seismic risk for the bridge. This risk is given by the expected value of the system response over the adopted probability models. Stochastic simulation is used for evaluating the multi-dimensional integral representing this expected value and for performing the associated optimization when searching for the most favorable damper characteristics. An efficient probabilistic sensitivity analysis is also established for identifying the importance of each of the uncertain model parameters in affecting the overall risk. An illustrative example is presented that considers the design of nonlinear viscous dampers for the protection of a two-span bridge.     

关键绩效指标KPI——国际最新的工程项目绩效评价体系

本文详细介绍了国际上最新的工程项目绩效评价体系KPI,该评价体系全面考虑了进度、成本、质量、安全、生产率、利润率、客户满意度等关键绩效指标,对于我国建筑业开展相关领域的研究和实践具有重要的借鉴和指导作用.     

A stochastic model of cash flow forecasting considering delays in owners’ payments

Delays in progress payments have always been one of the most aggravating difficulties, threatening the desired profit margin and should be considered based on the owners’ financial records at the bidding stage. However, previous models have often ignored the probabilistic nature of cash inflow. The conducted research endeavours to develop a new stochastic simulation-based framework for forecasting the cash flow of the construction projects considering the owners’ payment history in previous projects and intertemporal correlation between successive progress payments. This process involves introducing the Budget Realization Index, with probabilistic nature, whose underlying distribution is determined based on the owners’ behaviour. The model was applied to four real projects in Iran. The financing costs inflicted on the contractors stood in the range of the simulation results in the uncertainty level of 50–80%. Therefore, the proposed systematic framework would appropriately perform for forecasting contractors’ financial status through the project.     

Overlapping design and construction activities and an optimization approach to minimize rework

Construction industry often faces challenge to complete project in minimum possible time. Overlapping design and construction activities with early information from the precedent activities shortens project completion with the expense of rework in downstream design and construction activities. However, the expected amount of rework must be properly quantified to decide on the overlapping strategy. This study presents an integrated framework to overlap design and construction activities using the concepts of upstream evaluation and downstream sensitivity characteristics and develops a simulation model in order to ascertain project performance in terms of total project duration and expected amount of rework. The results indicate that reduction in project duration and expected rework amount vary based on the accuracy of upstream early information and sensitivity of downstream activities. Moreover, unplanned overlapping may not necessarily reduce project duration but may result in excessive design and construction rework which can be very costly. This study also describes a decision-making framework to optimize project schedule with minimal rework. The search for an optimal overlapping strategy is carried out using an Overlapping Strategy Matrix (OSM) with the genetic algorithm (GA) to eliminate unnecessary rework. The proposed optimization method minimizes the expected amount of rework while maintaining the project completion contract date and provides an effective means to decide on the overlapping strategy.     

基于BIM的桥梁工程设计与施工优化研究

为了提高桥梁工程的设计和施工效率,将建筑信息模型（BIM）引入到桥梁工程中来。通过分析桥梁工程设计和施工的特点及其存在问题,提出了基于BIM的桥梁工程设计和施工优化解决方案,包括初步设计优化、施工设计优化、施工工序优化、施工进度优化和施工管理优化等,并结合实际工程项目进行了适用性和成效分析。案例应用表明,BIM在桥梁工程项目中是适用的,可以为桥梁工程设计和施工提供有效的支持,进而减少返工、提高效率。该研究可为大型或复杂桥梁工程应用BIM提高设计与施工的效率和效益提供参考。     

Decision support for tower crane selection with building information models and genetic algorithms

Tower cranes are major construction equipment that is highly demanded in construction projects. The planning process for tower cranes utilization starts in early stages of the construction projects. Poor selection could incur extra costs on the construction projects or cause delays in project duration. The planning procedures for tower cranes include selection, allocation and operation. This paper presents a framework for the selection of tower cranes types and locations at construction sites. The framework considers three main models: 1) decision making model to select the tower crane type, 2) optimization model for the selection of the ideal number and location of tower cranes, and 3) 4D simulation model to simulate tower crane operations. Several clash detection scenarios are presented to assure the safety operation of the tower crane group. A case study is shown herein to demonstrate the capabilities of the developed framework.     

Optimization of ventilation systems in office environment,Part II: Results and discussions

Whether one considers the issues related to office workers' well-being and productivity or the issues from an energy and environmental perspective, there are clear evidences in favor of improving the quality of office environment. Part I of this paper proposed a simulation-based optimization approach by using computational fluid dynamics (CFD) techniques in conjunction with genetic algorithm (GA), with the integration of an artificial neural network (ANN) for response surface approximation (RSA) and for speeding up fitness evaluations inside GA loop. In this part, the results from data preparation for ANN model construction, ANN training and testing, and sensitivity analysis (regarding the impact of weighting factors in the objective function on the optimization results) are presented. Final optimization results indicate that the present choices of objective function and optimization approach are able to result in great improvement in the design and operation of ventilation systems in an office environment, with the goal of enhancing the thermal comfort and indoor air quality (IAQ) without sacrificing the energy costs of ventilation.     

超高层建筑顶升模板体系设计及模态分析

在超高层建筑施工中,顶升模板技术是一种新工艺。由于高强度混凝土的终凝时间较长,运用需要周转的模板模式施工是不利的。以实际工程为例,对顶升模板体系进行设计,借助SAP 2000对系统进行数值模拟和模态分析,进而对整个顶升模板体系进行优化设计,得出最优的设计方案。     

大型洞室群稳定性与优化的并行进化神经网络有限元方法研究--第一部分:理论模型

提出并行进化神经网络有限元方法，通过有限元计算构造样本，用并行进化搜索到的神经网络学习并建立计算方案与地下洞室关键点最大位移和破损区体积之间的映射关系；随机产生一组初始方案，以关键点最大位移和破损区体积大小与参考值的差值比加权和作为评价指标，对该组方案进行遗传操作，产生下一代可行方案，由此进行下一步操作直至找到最优方案。利用自主开发的基于WINDOWS平台的并行计算环境(RsmVPC)来实现并行计算，该方法使得大规模优化问题在PC机群上实现了并行求解，提高了计算速度、规模与精度。     

基于BIM的桥梁全生命周期管理研究初探

基于BIM的桥梁全生命周期管理,从规划设计到施工再到运维,这样全生命周期的数据和模型传递以及过程中的管理已经成为桥梁建设的一种趋势。然而,目前基本上所有没有对桥梁的设计和施工过程和运维等整个生命周期做到快速精确建模,管理进度,实时计算和仿真,以及根据需要动态显示施工设备的行为等一系列过程的集成。本文就是基于一种集成理念的通过产品生命周期管理(PLM)的方法,在一个一体化的体验仿真平台上,对桥梁的全生命周期管理进行初步探索,同时也对比其他可能的技术路径。这个平台集成了协同设计和建模、施工管理、施工过程分析、施工动画、施工进度生成、运行维护等等。     

A framework for Virtual Interactive Construction Education (VICE)

Training and process analysis in the construction industry has not taken full advantage of new technologies in simulation, modeling, and semantic web and software engineering. The purpose of this research is to develop a framework for a virtual interactive construction education system taking full advantage of these technologies. The modules will simulate the construction process for a facility from start to finish using information drawn from domain experts using real projects in the built environment. These modules can be used as training tools for new employees where they attempt to optimize time and cost in a virtual environment given a limited number of equipment, time and employee options. They can also be used as a process analysis tool before, during and after construction where a number of situational variables could be analyzed for exposure of potential risk. These modules would be particularly useful for repetitive construction where the initial project or task is analyzed for optimization and risk mitigation. This paper describes the framework using a residential construction example that is a 900 square foot (about 85 m²) wood frame single family house designed for the United States.     

基于受力性能优化的大型钢筋混凝土拱桥设计实践

结合包头市北梁腾空区外环路东河大桥工程设计实践,为优化桥体受力性能,有效提升上、下部结构经济合理性,对多跨不对称钢筋混凝土连拱桥主要设计要点进行研究。主要包括拱上建筑造型优化设计、拱轴线形式优化设计、拱脚构造优化设计、拱上建筑变形缝设计等拱桥构造优化设计和拱桥安全施工流程设计。为同类工程提供参考、借鉴。     

Handling construction pollutions using multi‐objective optimization

Quantitative assessment of emissions associated with construction projects should be carried out during the planning phase of the projects. This is important to detect and highlight any excesses of residuals during the construction phase. A newly developed framework is proposed to handle construction pollution using multi‐objective optimization. The approach, utilized by the proposed framework, is based on calculating the generated pollution for each activity involved in the project, as a result of dust, harmful gases and noise. The results of the quantitative assessment are integrated in a utility function that expresses the amount of total pollution. Then, evolutionary genetic algorithms (GAs) are used to carry multi‐objective optimization, considering three objective functions (project duration, project cost and total pollution). The proposed application considers the dynamic nature of construction activities including different types of relationships and the change of activities' criticality. An actual case study is worked out to demonstrate the practical use of the proposed framework and to investigate the sensitivity of its parameters.     

Towards an agent-based construction supply network modelling and simulation platform

The construction industry is being asked by more progressive clients to change its crude ways of working and to adopt more efficient business processes to improve its performance by adopting supply chain management (SCM) practices that have evolved in more advanced industries. This represents a major risk for many companies given the “one off” and complex nature of construction projects. The long-term aim of the work presented in this paper is to develop a modelling and simulation platform, which will provide an inexpensive and risk-free environment for organisations to experiment with emerging SCM practices prior to implementation. The wider adoption of such best practices has the potential to save the industry large sums of money. The case for the use of a multiagent systems framework for developing the platform is presented. A prototype system developed to explore the potential for the use of such an approach to model and simulate collaborative project supply network preplanning is presented. Future research work required to achieve the long-term aim is then presented.     

A framework for an automated and integrated project monitoring and control system for steel fabrication projects

This paper presents an automated and integrated project monitoring and control framework that facilitates decision making by enabling project managers to take corrective actions immediately after deviations occur and to mitigate potential damage to ongoing steel fabrication projects. An automated data acquisition system integrated with computer simulation provides a reliable platform for the proposed framework, as the former reduces the time required to obtain as-built data while the latter simulates different scenarios for possible corrective actions in advance. The framework employs High Level Architecture (HLA) as its infrastructure and is composed of several individual monitoring and control components which cooperate and interact with each other in real-time within a unified environment. To verify the concept and test the feasibility of this framework, a model consisting of several components, including automated data capturing, simulation, and visualization, was developed and implemented in the fabrication phase of steel construction.     

地下工程并行优化反演分析及算例验证

 通过重构非线性惯性权重函数和引入“加速因子”,对传统粒子群优化算法的收敛性进行改进。同时基于消息传递平台对算法进行主从式并行改进,编程实现基于普通计算机机群系统分布式存储并行模式的大型地下工程并行优化反演分析。算例分析表明,改进的粒子群优化算法其收敛性能得到显著改善,并行改进策略可显著加快反演速度和提高计算效率。探讨围岩松动损伤劣化、监测数据可靠性、并行粒度和负载均衡等并行优化反演分析中所面临的主要问题及其对计算精度和效率的影响,并提出有效解决方案,为大型地下工程的参数反演和动态优化设计提供一种新思路。     

Bidding strategy to support decision-making by integrating fuzzy AHP and regression-based simulation

This study proposes a new bidding strategy to support decision-making that is based on a combined framework of the Fuzzy Analytical Hierarchy Process (FAHP) and regression-based simulation. First, the FAHP method integrates the AHP with fuzzy set theory to determine the weights of factors that influence the cost of a project. Second, the integration of the cumulative distribution functions that are generated by the Monte Carlo simulation with a regression model yields bid amounts that correspond to various confidence levels. The proposed approach is used to analyze data on bridge construction projects that are taken from a database of the Taiwan Public Construction Commission. The systematic bid assessment model and the cost-probability curve can be used as strategic tools for quantifying project risks and calculating bids for construction projects.     

公路中小桥涵水文分析计算

中小桥涵是公路工程的重要组成部分,水文分析计算关系到中小桥涵跨径及总体方案的拟定,对保障公路安全、节省公路造价具有重要意义。文章介绍了公路中小桥涵水文分析计算的内容和方法,并通过介绍具体的工程实例,对公路中小桥涵水文分析计算起到一定的借鉴作用。