PERT技术在电子信息工程项目进度评估和预测中的应用

工程实践中,电子信息工程项目进度计划和工期经常难以准确的预估.介绍了通过PERT计划评审技术对项目工期进行预估的计算方法,并能评估项目在给定工期内完工的概率.     

基于活动工期风险和资源约束风险的缓冲大小计算方法

提出一种不确定情况下考虑活动工期风险和多资源约束风险的缓冲大小计算方法. 首先, 运用贝叶斯网络技术分析关键风险因素, 评估其造成的活动工期风险; 其次, 通过资源流网络方法衡量资源约束风险, 进而提出合理的缓冲配置方法以构建稳定的关键链调度计划. 通过算例分析和比较研究, 验证了所提出方法兼具有效性和实用性, 能够在保证较高按时完工率的同时, 有效缩短项目工期并保持进度计划稳定.

     

工程项目未按期完工概率估算的新型数值模拟算法

考虑到生产力波动、现场条件改变等不确定性因素的影响,工程项目的进度管理一般采用计划评审技术(program evaluation and review technique,PERT)网络模型,并以未按期完工概率作为重要的进度风险分析指标.针对工程项目的未按期完工概率估算,基于区域分解法,提出一种新型的数值模拟算法.针对PERT网络中的任一路径,将该路径的工期超出目标工期的事件定义为基本事件,从而将项目的未按期完工事件表示为所有基本事件的并集.所提出算法通过估计基本事件间的交集程度,对基本事件的概率求和进行折减,从而估算项目的未按期完工概率.通过算例验证,所提出模拟算法具有较好的估算准确度,且与蒙特卡罗方法相比有明显的计算效率提升.     

基于仿真的费用优化与风险分析软件系统

Arena仿真软件环境和Excel2000统计软件环境下,设计开发了一个针对特定随机型活动网络计划的进度／费用风险分析以及费用分析、均衡优化的集成化软件系统。该系统能实现特定随机型网络计划模型中各个活动时问和费用及其概率分布参数的输入和修改、仿真建模及运行、仿真结果动态可视化输出、网络计划的进度／费用仿真及其风险概率估计、代表性样本点的选择、网络计划各活动Weibull分布的参数估计、整个工期多峰Welbull分布的生成及投资强度分布的均衡优化,可埔于辅助武器装备系统研制项目及其他大型工程项目的风险分析与投资管理。     

一种求双代号网络图关键线路的简便矩阵算法

关键线路的总持续时间决定了项目的工期，因此关键线路的求解是网络计划分析的目标。以往求解双代号网络图关键线路的计算方法都不够简洁。在分析双代号网络图的结构矩阵和邻接矩阵的基础上，提出了一种求解双代号网络图关键线路的简便矩阵算法，最后结合实例验证了该算法的简便性。     

矿井网络计划技术优化设计的电算化

１　概述网络技术是一项科学的管理方法，已在国内外多种工业企业中应用，如基本建设工程，开发性研究项目，新产品的测试等。大到长远规划，大型项目的开发顺序，小到一个具体计划的落实。网络技术适合于大型和小型、简单和极端复杂的项目及管理活动。但中型以上复杂网络用手工计算，不但复杂、耗费时间，而且还容易出错，因此提出用计算机解决。２　网络计划技术优化设计所谓网络计划技术优化设计，就是对任何一项具体工作，都可以用时间参数标出工序时间（即工期），开始和结束的时间，及各项工序前后之间的相关作用，有的工序必须在另一…     

基于Stateflow的设备维修过程仿真研究

设备维修是工业企业的一项复杂工作,提高设备维修的效率对减少维修周期、节省企业成本具有重要意义。针对传统计划评审技术（PERT）在设备维修过程工期计算和关键路线分析等方面的局限,提出了基于Stateflow的设备维修过程仿真方法,进行了实例分析。仿真结果表明,基于Stateflow的仿真分析方法能够有效评估设备维修过程的完工时间和关键线路的分布情况,具有可视化、流程化和层次化的特点。     

基于时延Petri网的肯定型工程关键工序的求解

针对工程施工安排问题中关键工序的求解,传统的通过时延Petri网确定肯定型工程关键工序的算法既要正向计算每个工序的最早开工时间,也要逆向计算每个工序的最晚开工时间,然后进行比较,计算量比较大。本文对传统的通过时延Petri网确定肯定型工程关键工序的算法进行改进。只需正向计算各工序的最早开工时间和进行简单的比较,对于比较大型、工序比较繁多的工程项目。计算变得更加简单容易。     

考虑“时间-资源”的大型客机协同研制GERT网络优化

研究大型客机协同研制过程中项目活动时间和投入资源具有不确定性的图示评审技术(GERT)网络优化问题.采用GERT网络表征复杂项目研制过程,给出基于GERT的项目完成费用计算方法,提出项目时间与资源投入数量影响下的完工实现概率表征方式;为实现对复杂产品研制项目中时间-费用-资源优化调整,针对项目各活动和整体完工时间的不确定性,建立总完工时间、资源、实现概率受限情况下的时间规划与资源调度优化模型,并给出问题求解的差分进化启发式算法;考虑到大型客机全面试制过程是衡量能否按期完工的关键,以此过程为例进行案例分析,从而表明所提出方法的可行性和有效性.     

含风险时差的工序可间断多资源均衡分析

针对网络计划资源均衡问题,已经提出过一种工序可间断的单资源均衡模型。通过引入多资源的条件和风险时差的概念,对该模型加以改进。改进后的模型在求解多资源均衡问题的同时,可以为某些选定的工序预留出一定的时差,从而避免因资源均衡过程对这些时差的过度利用而增加工期风险。通过采用遗传算法对模型进行求解,验证了模型的有效性。     

Applying fuzzy method for measuring criticality in project network

Program evaluation and review technique (PERT) is widely used as a tool for managing large-scale projects. In the traditional PERT model, the durations of activities (tasks) are either represented as crisp numbers or drawn from the beta distribution to estimate the task durations such as pessimistic, most likely and optimistic times. However, the operation time for each activity is usually difficult to define and estimate precisely in a real situation. The aim of this paper is to present an analytical method for measuring the criticality in a project network with fuzzy activity times. Triangular fuzzy numbers are used to express the operation times for all activities in a project network. A new model that combines fuzzy set theory with the PERT technique is proposed to determine the critical degrees of activities (tasks) and paths. In the proposed model, a possibility index is defined to identify the likelihood of meeting a specified required time for a project network. At the end of the paper, an example is presented to compare with those obtained using the proposed method as well as other methods. The comparisons reveal that the method proposed in this paper is more effective in determining the activity criticalities and finding the critical path.     

软件项目进度跟踪方法的综合研究

进度是软件项目的第一大风险，受到顾客和承制方的高度关注。该文概述了软件项目的进度管理机制，对历史上主要的6种软件项目进度跟踪方法：里程碑进度，人为设定活动进度，工作单元进展，挣值法，甘特图和网络图进行了比较说明，从计算公式、使用时机、使用性能和发展进化等方面指出了它们各自的特点，推荐了最佳软件进度跟踪方案。     

GENRES: An extension of Brooks Algorithm for project scheduling with resource constraints

In project scheduling by network analysis, traditional critical path methods fail to include resource considerations. Other methods must be used to allow for resource considerations. This article explores one area of resource considerations: project scheduling under resource constraints. The specific case investigated is the single resource, single project schedule. A model, entitled the GENRES search model, is developed. The model utilizes Brooks Algorithm (BAG) to generate the project schedule. The criteria used are various weighted combinations of ACTIM and ACTRES (Bedworth, Industrial Systems). The best project schedule is that which gives the least project duration.The GENRES model was found effective in finding project durations equal to or less than that of ACTIM, ACTRES or TIMRES (the combination of ACTIM and ACTRES with each given equal weight). The research also found that when the project completion time found by the algorithm approaches the critical path duration, resource leveling may be preferred.     

IT项目进度计划风险量化预测方法

针对IT项目进度基线定义质量普遍偏低的问题,提出了一种资源约束条件下基于蒙特卡洛模拟的进度风险量化评估方法．首先,考虑资源对进度的限制问题,提出资源约束条件下的活动历时抽样方法;其次,提出在活动历时随机变化情况下,项目关键路径动态识别方法,研究项目工期概率分布问题．最后,通过实例表明,资源约束条件下的蒙特卡洛模拟方法,能够有效地评估IT项目中的进度风险,辅助项目决策．     

Improving system performance for stochastic activity network: A simulation approach

An activity network with returning loop activities has a wide variety of applications, but can cause a heavy computational burden for large networks. Moreover, if an activity processing time and/or the probability of taking a particular activity changes when the number of activity visits is added, the computation is very complicated and difficult. We propose a simulation approach to deal with stochastic activity networks consisting of multiple terminal nodes, no limit on looping activities, non-constant activity selection probabilities, and non-deterministic activity times following arbitrary distributions. Probability and time control functions are introduced to reflect the acceleration, or learning effect, of repeated activities. Performance measures such as system success/failure probabilities, time to completion/success/failure times, time between success/failure, and the pth percentile times of a project are obtained. A series of sensitivity analysis was performed to understand the trend and behavior of system performance. A cost function is developed to find an optimal strategy by manipulating control factors. To illustrate the efficacy of this simulation approach a new drug discovery and development project was analyzed. The Promodel simulation language was used for performance evaluations, and the SimRunner optimization tool for obtaining the optimal solution.     

Algorithms of Optimal Supply of Resources to a Group of Projects (Stochastic Networks)

Several concurrently realized PERT-like network projects with random lengths of the their activities were considered. Each activity consumes several kinds of resources of fixed powers, all resources being reproducible in the course of their service. For each project, the schedule date and the admissible confidence probability of timely completion of the project were defined. The initial instants of realization of all projects, the required total power of each of the reproducible resources (for each project), the delivery schedule of rare reproducible resources that are not at the disposal of the project management system, and the schedule of beginning all activities (for each project) were determined. The minimal nonoperational costs (penalty provisions for failure to execute the project in time, fines for idling of the rare external resources, costs of resource lease, et al.,) were used as the target function.     

A solution approach to find the critical path in a time-constrained activity network

Finding the longest path in an activity network, where time constraints are attached to activities, is generalized from the traditional critical path problem. Time constraints have attracted much research interest in recent years, because they can be used to represent a large set of real situations, arising not only in the field of the project management.In this paper, we propose a general approach for finding the critical path in a deterministic activity-on-the-arc network, considering three different types of time constraints. The first one is the time-window constraint, which imposes that an activity can start only in a predefined time interval, whereas no constraints are imposed on the activity completion time. The second one is the time-schedule constraint, which assumes that an activity can start its execution at one of the pre-specified instants of time. The third one is the time-switch constraint, which imposes a specified starting time on the project activities and forces them to be inactive during specified time periods.The algorithm introduced in this paper has been developed by redefining and combining together two procedures well-known in the scientific literature. The former, proposed by Chen, Rinks and Tang in 1997, can be used for finding the critical path in an activity network where time-schedule and time-window constraints are considered. The latter, proposed by Yang and Chen in 2000, can be applied in activity networks with only time-switch constraints.The method, developed in this paper, can be used to find the critical path in all the practical situations, in which the aforementioned time constraints are taken into account simultaneously. The proposed approach has been coded in Java and has been validated by considering two sets of instances: the former has been taken from the public domain project scheduling problem library, developed by Kolisch and Sprecher in 1997, whereas the latter consists of randomly generated activity networks.The computational results collected are very promising, showing that the solution process for the considered instances required at most few seconds, using a commercial Pentium class PC.