An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> This paper is concerned with establishing the mathematical basis of the Critical-Path Method---a new tool for planning, scheduling, and coordinating complex engineering-type projects. The essential ingredient of the technique is a mathematical model that incorporates sequence information, durations, and costs for each component of the project. It is a special parametric linear program that, via the primal-dual algorithm, may be solved efficiently by network flow methods. Analysis of the solutions of the model enables operating personnel to answer questions concerning labor needs, budget requirements, procurement and design limitations, the effects of delays, and communication difficulties. <s> BIB001 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Although literature on the achievement of monetary objectives in a resource-constrained project environment is limited, the maximization of project net present value (NPV) is an important criterion of project success. This paper presents a procedure for developing a late-start resource-constrained project schedule using the critical path method-material requirements planning. Using an extensive set of problems from the literature, we show that this procedure yields a higher NPV and lower average duration than schedules derived with heuristics that schedule each activity as early as possible. In addition, while the late-start schedule on average was significantly longer than the optimal-duration resource-constrained schedule, no significant difference occurred in the average NPVs of the two scheduling methods. <s> BIB002 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> A survey of project scheduling problems since 1973 limited to work done specifically in the project scheduling area (although several techniques developed for assembly line balancing and job‐shop scheduling can be applicable to project scheduling): the survey includes the work done on fundamental problems such as the resource‐constrained project scheduling problem (RCPSP); time/cost trade‐off problem (TCTP); and payment scheduling problem (PSP). Also discusses some recent research that integrates RCPSP with either TCTP or PSP, and PSP with TCTP. In spite of their practical relevance, very little work has been done on these combined problems to date. The future of the project scheduling literature appears to be developing in the direction of combining the fundamental problems and developing efficient exact and heuristic methods for the resulting problems. <s> BIB003 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Abstract A recurring problem in managing project activities is to minimize the deviation between the resource requirements and stated desirable levels. This paper presents a new optimizing approach for resource leveling based on non-serial dynamic programming. This approach permits a marked reduction of the complexity of the problem as it checks for only the feasible time subsets which are far less numerous than feasible sequences. The model, which is applied to an activity-on-node network, requires as input the scheduling results provided by the critical path method (CPM). Applications of the model to two opposite cases are also described and the solutions compared with the ones achieved by the Burges and Killebrew heuristic. Computational results indicate that the procedure provides exact solutions for small to medium size problems, requiring only modest computing facilities. <s> BIB004 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> In this paper, research on the resource-constrained project scheduling problem is classified according to specified objectives and constraints. Each classified area is extensively surveyed, and special emphasis is given to trends in recent research. Specific papers involving nonrenewable resource constraints and time/cost-based objectives are discussed in detail because they present models that are close representations of real-world problems. The difficulty of solving such complex models by optimization techniques is noted. For the purposes of this survey, a set of 78 optimally solved test problems from the literature and a second set of 110 benchmark problems have been subjected to analysis with some well-known dispatching rules and a scheduling algorithm that consists of a decision-making process utilizing the problem constraints as a base of selection. The computational results are reported and discussed in the text. Constructive scheduling algorithms that are directly based on the problem constraints... <s> BIB005 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> We consider the problem of minimizing renewable resource availability costs in an activity-on-the-node project network subject to a project due date. Project activities have fixed durations and may require the use of multiple renewable resources in constant amounts throughout their duration. Various assumptions may be made about the type of precedence relations, ready times, due dates, and task interruptability. Given a discrete, non-decreasing cost function of the constant resource availability for every resource type, the objective is to determine the resource availability levels in order to minimize the sum of the availability costs over all resource types. An effective optimal algorithm is described and extensive computational experience is reported. <s> BIB006 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Department of Applied Economics, Katholieke Universiteit Leuven Naamsestraat 69, B-3000 Leuven (Belgium) The great variety of project scheduling problems motivates the introduction of a systematic notation that could serve as the basis for a classification scheme. The extensive classification scheme introduced in this paper is similar to the standard classification scheme used in the machine scheduling literature. It is composed of three fields· a 1 /31 y. The field a describes the resource characteristics of the problem. The field /3 describes the characteristics of the project activities and the third field r denotes the performance measure(s). The composition of the various fields and the precise meaning of the parameters are specific to the field of project scheduling. We illustrate the potential use of the classification scheme by applying it to the characterization of the most important project scheduling problems which have been introduced in the growing literature. We discuss the close relationships between the various scheduling problems by offering graphs which show the various interrelations among the different values of the particular classification parameters. <s> BIB007 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Repetitive activities are found commonly in the construction of high-rise buildings, pipeline networks and highway and housing projects. Construction crews assigned to these activities often perform the work sequentially, moving from one repetitive unit in the project to the next. Because of this frequent crew movement, construction of repetitive activities should be scheduled in such a way as to enable prompt movement of crews among the repetitive units so as to minimize idle crew time. In order to maximize the efficiency of crew utilization, the schedule of repetitive activities should be resource driven, and should satisfy the crew work continuity constraint in addition to precedence relationships and crew availability constraints. This paper presents a flexible algorithm for resource-driven scheduling of repetitive activities that satisfies the three constraints, and considers the impact of a number of practical factors encountered commonly during the construction of this class of projects. The algori... <s> BIB008 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Abstract Project scheduling is concerned with single-item or small batch production where scarce resources have to be allocated to dependent activities over time. Applications can be found in diverse industries such as construction engineering, software development, etc. Also, project scheduling is increasingly important for make-to-order companies where the capacities have been cut down in order to meet lean management concepts. Likewise, project scheduling is very attractive for researchers, because the models in this area are rich and, hence, difficult to solve. For instance, the resource-constrained project scheduling problem contains the job shop scheduling problem as a special case. So far, no classification scheme exists which is compatible with what is commonly accepted in machine scheduling. Also, a variety of symbols are used by project scheduling researchers in order to denote one and the same subject. Hence, there is a gap between machine scheduling on the one hand and project scheduling on the other with respect to both, viz. a common notation and a classification scheme. As a matter of fact, in project scheduling, an ever growing number of papers is going to be published and it becomes more and more difficult for the scientific community to keep track of what is really new and relevant. One purpose of our paper is to close this gap. That is, we provide a classification scheme, i.e. a description of the resource environment, the activity characteristics, and the objective function, respectively, which is compatible with machine scheduling and which allows to classify the most important models dealt with so far. Also, we propose a unifying notation. The second purpose of this paper is to review some of the recent developments. More specifically, we review exact and heuristic algorithms for the single-mode and the multi-mode case, for the time–cost tradeoff problem, for problems with minimum and maximum time lags, for problems with other objectives than makespan minimization and, last but not least, for problems with stochastic activity durations. <s> BIB009 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> The paper presents polynomial heuristic procedures for different types of resource levelling problems for projects with minimum and maximum time lags between project activities. Both problems without and with explicit resource constraints are treated. Thus far, only pseudopolynomial heuristics for special resource levelling problems without maximum time lags and resource constraints have been proposed. An experimental performance analysis shows that the new heuristics approximately solve problem instances with up to 500 activities and five resources within reasonable computing time. <s> BIB010 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Abstract This paper deals with resource-constrained project scheduling problems with nonregular objective functions where general temporal constraints given by minimum and maximum time lags between activities are prescribed. In particular, resource leveling and net present value problems are studied. We present different heuristic and exact procedures for (approximately) solving those problems. A detailed experimental performance analysis shows that these procedures also solve large problem instances in reasonable computing time. <s> BIB011 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> We consider the scheduling of interdependent subprojects incurring costs for early or tardy completion w.r.t. given milestones. Each subproject consists of several activities between which minimum and maximum start-to-start time lags have to be observed. In addition, the processing of activities takes up scarce shared resources. The problem is to determine an activity schedule complying with the temporal constraints such that the resource requirements can be matched by the capacities at any point in time and the earliness-tardiness costs of the project are minimized. For solving the resource-unconstrained version of this problem, we propose a primal and a dual algorithm which are based on the iterative calculation of locally optimal descent and ascent directions, respectively. An initial (generally resource-infeasible) schedule for the problem with resource constraints is determined by applying the primal method to the resource relaxation. Within a branch-and-bound algorithm, resource conflicts are resolved by enumerating sets of precedence constraints between activities which are executed simultaneously and whose requirements exceed the capacity of at least one resource. At each enumeration node, the corresponding relaxation is solved by the dual algorithm starting with the schedule of the father node. <s> BIB012 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> The resource investment problem deals with the issue of providing resources to a project such that a given deadline can be met. The objective is to make the resources available in the cheapest possible way. For each resource, expenses depend on the maximum amount required during the course of the project. In this paper we develop two lower bounds for this NP-hard problem using Lagrangean relaxation and column generation techniques, respectively. Both procedures are capable of yielding feasible solutions as well. Hence, we also have two optimization guided heuristics. A computational study consisting of a set of 3210 instances compares both approaches and allows insight into the performance. <s> BIB013 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> We introduce a project scheduling problem subject to temporal constraints where the resource availability costs have to be minimized. As an extension of known project scheduling problems which consider only time-independent costs, this problem includes both time-independent procurement costs and time-dependent renting costs for the resources. Consequently, in addition to projects where all resources are bought, we can deal with projects where resources are rented. Based on the enumeration of a finite set of schedules which is proved to contain an optimal schedule, we develop a depth-first branch-and-bound procedure. Computational experience with a randomly generated test set containing 10800 problem instances is reported. <s> BIB014 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> In this paper we study the resource-constrained project scheduling problem with weighted earliness–tardinesss penalty costs. Project activities are assumed to have a known deterministic due date, a unit earliness as well as a unit tardiness penalty cost and constant renewable resource requirements. The objective is to schedule the activities in order to minimize the total weighted earliness–tardinesss penalty cost of the project subject to the finish–start precedence constraints and the constant renewable resource availability constraints. With these features the problem becomes highly attractive in just-in-time environments.We introduce a depth-first branch-and-bound algorithm which makes use of extra precedence relations to resolve resource conflicts and relies on a fast recursive search algorithm for the unconstrained weighted earliness–tardinesss problem to compute lower bounds. The procedure has been coded in Visual C++, version 4.0 under Windows NT. Both the recursive search algorithm and the branch-and-bound procedure have been validated on a randomly generated problem set. <s> BIB015 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Scope and Relevance of Project Scheduling.- The Project Scheduling Process.- Classification of Project Scheduling Problems.- Temporal Analysis: The Basic Deterministic Case.- Temporal Analysis: Advanced Topics.- The Resource-Constrained Project Scheduling Problem.- Resource-Constrained Scheduling: Advanced Topics.- Project Scheduling with Multiple Activity Execution Modes.- Stochastic Project Scheduling.- Robust and Reactive Scheduling. <s> BIB016 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Abstract In this paper we study the unconstrained project scheduling problem with discounted cash flows where the net cash flows are assumed to be dependent on the completion times of the corresponding activities. Cash outflows occur when an activity is completed whereas cash inflows are incurred as progress payments at the end of some time period. The objective is to schedule the activities in order to maximize the net present value of the project subject to the precedence constraints and a fixed deadline. This paper extends the ever-growing amount of research concerning the financial aspects in project scheduling in which cash flows are time-dependent. We introduce a branch-and-bound algorithm which computes upper bounds by making piecewise linear overestimations. In doing so, the algorithm transforms the problem into a weighted earliness–tardiness project scheduling problem. The algorithm is extended with two new rules in order to reduce the size of the branch-and-bound tree. Computational results are reported. <s> BIB017 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> The scheduling of activities over time has gained increasing attention with the development of the critical path method (CPM) and the program evaluation and review technique (PERT). Since then, a large amount of solution procedures for a wide range of problem types have been proposed in the literature. Many of these procedures, however, are not able to solve real-life problems. In this paper we describe a capacity expansion project at a water production center (WPC) of the Vlaamse Maatschappij voor Watervoorziening VMW) in Belgium. This project aims at expanding the production capacity of pure water. We show that scheduling the project with certain techniques will improve the financial status of the project. We illustrate this statement with different schedules. <s> BIB018 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Abstract The bodies of knowledge that serve project management as a practice and academic discipline provide a potentially useful organizational resource. However, coordinating bodies of knowledge and keeping pace with changing concepts create a challenge. Overall, many believe that we have a generally accepted body of knowledge for use in managing projects. However, practitioners filter and critically interpret information that in turn shapes their perceptions and generates knowledge to either support or challenge what seems to be “true” from book learning or practical experience. This paper purposely questions whether project-based terminology and definitions are actually as widely accepted as believed. The scope limits the presentation to a summary of two exploratory pieces of scholarly work. The initial literature review from the first source [C. Delisle, Success and communication in virtual project teams, Unpublished Doctoral Dissertation, Dept. of Civil Engineering. Project Management Specialization, The University of Calgary, Calgary, Alberta, July 2001, pp. 1–442], follow up literature review, web-based search and in-class experiment from the second source [D. Olson, Is a common vocabulary lacking in project management? Final assignment for Information Technology Project Management, Athabasca University, 2001] provide key information on where we are in terms of investigating assumptions around project management language use. The authors conclude that coordination of glossaries and dissemination of information about project management terms and definitions lack coordination on a broad scale. <s> BIB019 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> This paper considers the problem of minimizing resource investment required to execute the tasks in a project network by a given project due date. A project consists of non-pre-emptive tasks executed in a known and required precedence order. Each task is completed in one of its feasible modes, which may differ not only in task duration but also in consumption of renewable resources. A priority rule heuristic with polynomial computational complexity is presented for this computationally intractable problem. This heuristic simultaneously considers due date constraints and resource usage to select and schedule tasks with one decision rule. This differs from prior multi-mode priority rule scheduling heuristics that apply two consecutive decision rules to schedule tasks. Extensive computational testing indicates promising results. <s> BIB020 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> In this paper the multi-mode resource-constrained project scheduling problem with discounted cash flows is considered. A project is represented by an activity-on-node (AoN) network. A positive cash flow is associated with each activity. Four different payment models are considered: lump-sum payment at the completion of the project, payments at activities' completion times, payments at equal time intervals and progress payments. The objective is to maximize the net present value of all cash flows of the project. Local search metaheuristics: simulated annealing and tabu search are proposed to solve this strongly NP-hard problem. A comprehensive computational experiment is described, performed on a set of instances based on standard test problems constructed by the ProGen project generator, where, additionally, the activities' cash flows are generated randomly with the uniform distribution. The metaheuristics are computationally compared, the results are analyzed and discussed and some conclusions are given. <s> BIB021 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> This paper considers heuristics for the well‐known resource‐constrained project scheduling problem (RCPSP). It provides an update of our survey which was published in 2000. We summarize and categorize a large number of heuristics that have recently been proposed in the literature. Most of these heuristics are then evaluated in a computational study and compared on the basis of our standardized experimental design. Based on the computational results we discuss features of good heuristics. The paper closes with some remarks on our test design and a summary of the recent developments in research on heuristics for the RCPSP. <s> BIB022 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> This paper considers a project scheduling problem with the objective of minimizing resource availability costs, taking into account a deadline for the project and precedence relations among the activities. Exact methods have been proposed for solving this problem, but we are not aware of existing heuristic methods. Scatter search is used to tackle this problem, and our implementation incorporates advanced strategies such as dynamic updating of the reference set, the use of frequency-based memory within the diversification generator, and a combination method based on path relinking. We also analyze the merit of employing a subset of different types when combining solutions. Extensive computational experiments involving more than 2400 instances are performed. For small instances, the performance of the proposed procedure is compared to optimal solutions generated by an exact cutting plane algorithm and upper and lower bounds from the literature. For medium and larger size instances, we developed simple multi-start heuristics and comparative results are reported. <s> BIB023 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> The execution of project activities generally requires the use of (renewable) resources like machines, equipment or manpower. The resource allocation problem consists in assigning time intervals to the execution of the project activities while taking into account temporal constraints between activities emanating from technological or organizational requirements and costs incurred by the resource allocation. If the total procurement cost of the different renewable resources has to be minimized we speak of a resource investment problem. If the cost depends on the smoothness of the resource utilization over time the underlying problem is called a resource levelling problem. In this paper we consider a new tree-based enumeration method for solving resource investment and resource levelling problems exploiting some fundamental properties of spanning trees. The enumeration scheme is embedded in a branch-and-bound procedure using a workload-based lower bound and a depth first search. Preliminary computational results show that the proposed procedure is promising for instances with up to 30 activities. <s> BIB024 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Repetitive projects involve the repetition of activities along the stages of the project. Since the resources required to perform these activities move from one stage to the other, a main objective of scheduling these projects is to maintain the continuity of work of these resources so as to minimize the idle time of resources. This requirement, often referred to as work continuity constraints, involves a tradeoff between total project duration and the resource idle time. The contribution of this paper is threefold. First, we provide an extensive literature summary of the topic under study. Although most research papers deal with the scheduling of construction projects, we show that this can be extended to many other environments. Second, we propose an exact search procedure for scheduling repetitive projects with work continuity constraints. This algorithm iteratively shifts repeating activities further in time in order to decrease the resource idle time. We have embedded this recursive search procedure in a horizon-varying algorithm in order to detect the complete tradeoff profile between resource idle time and project duration. The procedure has been coded in Visual C++ and has been validated on a randomly generated problem set. Finally, we illustrate the concepts on three examples. First, the use of our new algorithm is illustrated on a small fictive problem example from literature. In a second example, we show that work continuity constraints involve a tradeoff between total project duration and the resource idle time. A last example describes the scheduling of a well-known real-life project that aims at the construction of a tunnel at the Westerschelde in The Netherlands. <s> BIB025 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Abstract In this paper a genetic algorithm for solving a class of project scheduling problems, called Resource Investment Problem, is presented. Tardiness of project is permitted with defined penalty. Elements of algorithm such as chromosome structure, unfitness function, crossover, mutation, immigration and local search operations are explained. The performance of this genetic algorithm is compared with the performance of other published algorithms for Resource Investment Problem. Also 690 problems are solved and their optimal solutions are used for the performance tests of the genetic algorithm. The tests results are quite satisfactory. <s> BIB026 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> The scheduling of projects has gained increasing attention since the introduction of PERT and CPM. Both the scheduling literature and the software scheduling packages rely on (meta-)heuristic and exact procedures to schedule projects under various assumptions. However, there is still room for improvement by incorporating specific characteristics into the scheduling procedures. In this paper we describe the scheduling of a real-life project that aims at the construction of a tunnel at the Westerschelde in the Netherlands. In doing so, we show that so-called work continuity is the main issue during the scheduling phase. No software package, however, is able to incorporate this requirement in an exact way. We compare different possible schedules under various assumptions and prove the necessity of this new feature. <s> BIB027 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> We work with a project scheduling problem subject to temporal constraints where the resource availability costs have to be minimised. As an extension of the more well known Resource Investment Problem, which considers only time-independent costs, this problem includes both time-independent fixed costs and time-dependent variable renting costs for the resources. Consequently, in addition to projects where all resources are bought, we can deal with projects where resources are rented. Based on a new codification of a solution for project scheduling, we develop a Genetic Algorithm capable of outperforming a branch-and-bound procedure that exists for the problem. <s> BIB028 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Most work in project scheduling problems has been done with so-called regular objective functions, where a solution S never dominates another solution S’ if no activity is scheduled earlier in S than in S’. This has provided with techniques and metaheuristic frameworks to create heuristic algorithms for these kinds of problems, something which does not exist in the nonregular case. One of these problems is the Resource Renting Problem, which models the renting of resources. In this paper we compare the quality of three algorithms for this problem, one adapted from the regular case, another specially designed for the problem and a third that might be adapted for other problems. We will also show that two of these algorithms are capable of outperforming a branch-and-bound procedure that exists for the problem. <s> BIB029 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> In this paper, we present a new genetic algorithm for the resource-constrained project scheduling problem with discounted cash flows and investigate the trade-off between a project’s net present value and its corresponding makespan. We consider a problem formulation where the pre-specified project deadline is not set as a hard constraint, but rather as a soft constraint that can be violated against a certain penalty cost. the genetic algorithm creates children from parents taken from three different populations, each containing relevant information about the (positive or negative) activity cash flows. We have tested various parent selection methods based on four crossover operators taken from literature and present extensive computational results. <s> BIB030 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> In order to develop a more realistic resource-constrained project-scheduling model that is applicable to real-world projects, in this paper, the resource investment problem with discounted cash flows and generalized precedence relations is investigated under inflation factor such that a bonus-penalty structure at the deadline of the project is imposed to force the project not to be finished beyond the deadline. The goal is to find activity schedules and resource requirement levels that maximize the net present value of the project cash flows. The problem is first mathematically modeled. Then, a genetic algorithm (GA) is designed using a new three-stage process that utilizes design of experiments and response surface methodology. The results of the performance analysis of the proposed methodology show an effective solution approach to the problem. <s> BIB031 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> In this paper, we present a meta-heuristic algorithm for the resource-constrained project scheduling problem with discounted cash flows. We assume fixed payments associated with the execution of project activities and develop a heuristic optimisation procedure to maximise the net present value of a project subject to the precedence and renewable resource constraints. We investigate the use of a bi-directional generation scheme and a recursive forward/backward improvement method from literature and embed them in a meta-heuristic scatter search framework. We generate a large dataset of project instances under a controlled design and report detailed computational results. The solutions and project instances can be downloaded from a website in order to facilitate comparison with future research attempts. <s> BIB032 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> The resource-constrained project scheduling problem (RCPSP) consists of activities that must be scheduled subject to precedence and resource constraints such that the makespan is minimized. It has become a well-known standard problem in the context of project scheduling which has attracted numerous researchers who developed both exact and heuristic scheduling procedures. However, it is a rather basic model with assumptions that are too restrictive for many practical applications. Consequently, various extensions of the basic RCPSP have been developed. This paper gives an overview over these extensions. The extensions are classified according to the structure of the RCPSP. We summarize generalizations of the activity concept, of the precedence relations and of the resource constraints. Alternative objectives and approaches for scheduling multiple projects are discussed as well. In addition to popular variants and extensions such as multiple modes, minimal and maximal time lags, and net present value-based objectives, the paper also provides a survey of many less known concepts. <s> BIB033 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> Meant to complement rather than compete with the existing books on the subject, this book deals with the project performance and control phases of the project life cycle to present a detailed investigation of the project’s time performance measurement methods and risk analysis techniques in order to evaluate existing and newly developed methods in terms of their abilities to improve the corrective actions decision-making process during project tracking. As readers apply what is learned from the book, EVM practices will become even more effective in project management and cost engineering. Individual chapters look at simulation studies in forecast accuracy, schedule adherence, time sensitivity, activity sensitivity and using top-down or bottom-up project tracking. The book also offers an actual real-life case study, a short tutorial on the EVM use in ProTrack, and conclusions on the relative effectiveness for each technique presented. <s> BIB034 </s> An Overview of Recent Research Results and Future Research Avenues Using Simulation Studies in Project Management <s> Baseline Scheduling. <s> We present a project scheduling problem subject to general temporal constraints where the utilization of a set of renewable resources has to be smoothed over time. For solving the NP-hard optimization problem, we point out some important structural properties and introduce a new enumeration scheme. Combining this enumeration scheme with some branch-and-bound techniques, we propose an appropriate solution procedure for the project scheduling problem at hand. To outline the practical importance of resource levelling, we sketch exemplary the optimization of mid-term planning schedules with regard to the resource requirements of IT projects. Finally, we present results from a comprehensive computational study on problem instances of the well-known rlp_j10 and rlp_j20 test sets devised by Kolisch et al. (Benchmark Instances for Project Scheduling Problems, Kluwer, Boston, 1999). <s> BIB035
The project baseline schedule plays a central role in any project control simulation study since it acts as a point of reference for all calculations done during the simulation runs of Step 3. Constructing a baseline schedule is necessary to have an idea about the expected time and cost of a project. Indeed, by determining an activity timetable, a prediction can be made about the expected time and cost of each individual activity and the complete project. This timetable will be used throughout all simulation studies as the point of reference from which every deviation will be monitored and saved. These deviations will then be used to calculate the output metrics of Step 4 and to draw general conclusions as will be illustrated in later sections of this paper. Project baseline scheduling can be defined as a mathematical approach to determine start and finish times for all activities of the project, taking into account precedence relations between these activities as well as a limited availability of resources, while optimising a certain project objective, such as lead-time minimisation, cash-flow optimisation, levelling of resource use, and many more. The early research endeavours on baseline scheduling stem from the late 1950s resulting in the two well-known scheduling techniques known as the critical path method (CPM) and the program evaluation and review technique (PERT)   BIB001 . These methods make use of activity networks with precedence relations between the activities and the primary project objective to optimise the minimisation of the total project time. Due to the limited computer power at this time, incorporating resource constraints has been largely ignored. However, these methods are still widely recognised as important project management tools and techniques and are often used as basic tools in more advanced baseline scheduling methods. Since the development of the PERT/CPM methods, a substantial amount of research has been carried out covering various areas of project baseline scheduling. The most important extensions of these basic scheduling methods are the incorporation of resource constraints, the extension to other scheduling objectives, and the development of new and more powerful solution methods to construct these baseline schedules, as summarised along the following lines. (i) Adding Resources. Resource-constrained project scheduling is a widely discussed project management topic which has roots in and relevance for both academic and practical oriented environments. Due to its inherent problem complexity, it has been the subject of numerous research projects leading to a wide and diverse set of procedures and algorithms to construct resource feasible project schedules. Thanks to its practical relevance, many of the research results have found their way into practical project management applications. Somewhat more than a decade ago, this overwhelming amount of extensions has inspired authors to bring structure in the chaos by writing overview papers BIB003  BIB005  BIB009 , summary books  BIB016 and by developing two different classification schemes BIB009 BIB007 on resource-constrained project scheduling. (ii) Changing Objectives. The PERT/CPM methods mainly focused on constructing baseline schedules aiming at minimising the total lead-time of the project. However, many other scheduling objectives can be taken into account and the choice of an objective to optimise can vary between projects, sectors, countries, and so forth. Some of these scheduling objectives take the cost of resources into account. The so-called resource availability cost project (RACP) aims at minimising the total cost of the resource availability within a predefined project deadline, and references can be found in Demeulemeester BIB006 , Drexl and Kimms BIB013 , Hsu and Kim BIB020 , Shadrokh and Kianfar BIB026 , Yamashita et al. BIB023 , Drexl and Kimms BIB013 , Gather et al. BIB024 , and Shahsavar et al. BIB031 . The resource leveling project (RLP) aims at the construction of a precedence and resource feasible schedule within a predefined deadline with a resource use that is as level as possible within the project horizon. Various procedures have been described in papers written by Bandelloni et al. BIB004 , Gather et al. BIB024 , Neumann and Zimmermann BIB010 BIB011 , Coughlan et al.  , Shahsavar et al. BIB031 , and Gather et al. BIB035 . The resource-constrained project with work continuity constraints (RCP-WC) takes the so-called work continuity constraints BIB008 into account during the construction of a project schedule. The objective is to minimise the total idle time of bottleneck resources used in the project, and it has been used by Vanhoucke BIB025 BIB027 . The resource renting problem (RRP) aims at minimising the total resource cost, consisting of time-dependent, and time-independent costs. Time-dependent costs are encountered each time unit a renewable resource is in the resource set while timeindependent costs are costs made every time a resource is added to the existing resource set. References to solution procedures for this problem can be found at Nübel BIB014 , Ballestín BIB028 BIB029 , and Vandenheede and Vanhoucke  . Other scheduling objectives take the cost of activities into account to determine the optimal baseline schedule. The resource-constrained project with discounted cash fows (RCP-DCF) optimises the timing of cash flows in projects by maximising the net present value. The basic idea boils down to shifting activities with a negative cash flow further in time while positive cash flow activities should be scheduled as soon as possible, respecting the precedence relations and limited resource availabilities. Algorithms have been developed by Smith-Daniels and Aquilano BIB002 BIB017 , and Vanhoucke BIB030 BIB032 . An overview is given by Mika et al. BIB021 . Vanhoucke and Demeulemeester BIB018 have illustrated the use and relevance of net present value optimisation in project scheduling for a water company in Flanders, Belgium. When activities have a preferred time slot to start and/or end and penalties have been defined to avoid that these activities start/end earlier or later than this preferred time slot, the problem is known as the Resource-Constrained Project with weighted earliness/tardiness (RCP-WET) problem. This baseline scheduling problem is inspired by the just-in-time philosophy from production environments and can be used in a wide variety of practical settings. Algorithmic procedures have been developed by Schwindt BIB012 and Vanhoucke et al. BIB015 . The Resource-Constrained Project with quality time slots (RCP-QTSs) is an extension of this RCP-WET problem. Quality-dependent time slots can be considered as an extension of the RCP-WET scheduling objective. In this scheduling objective, multiple time slots are defined rather than a single preferred start time and earliness/tardiness penalties must be paid when activities are scheduled outside one of these time slots. To the best of our knowledge, the problem has only been studied by Vanhoucke  . (iii) New Solution Methods. The vast majority of solution methods to construct resource-constrained baseline schedules can be classified in two categories. The exact procedures aim at finding the best possible solution for the scheduling problem type and are therefore often restricted to small projects under strict assumptions. This class of optimisation procedures is widely available in the literature but can often not be used in real settings due to the high computation times needed to solve the problems. Heuristic procedures aim at finding good, but not guaranteed to be optimal schedules for more realistic projects (i.e., under different assumptions and for larger sizes) in a reasonable (computational) time. Although these procedures do not guarantee an optimal solution for the project, they can be easily embedded in any scheduling software tool due to their simplicity and generality to a broad range of different projects. An extensive discussion of the different algorithms is not within the scope of this paper. For a review of exact problem formulations, the reader is referred to Demeulemeester and Herroelen BIB016 . The use of heuristic procedures consists of single pass and multipass algorithms as well as the use of metaheuristics and their extensions, and the number of published papers has exploded through the last years. An experimental investigation of heuristic search methods to construct a project schedule with resources can be found in Kolisch and Hartmann BIB022 . Today, project baseline scheduling research continues to grow in the variety of its theoretical models, in its magnitude, and in its applications. Despite this ever growing amount of research on project scheduling, it has been shown in the literature that there is a wide gap between the project management discipline and the research on project management, as illustrated by Delisle and Olson BIB019 , among many others. However, research efforts of the recent years show a shift towards more realistic extensions trying to add real needs to the state-of-the-art algorithms and procedures. Quite recently, a paper has been written in which a survey of variants and extensions of the resource-constrained project scheduling problem have been described BIB033 . This paper clearly illustrates that the list of extensions to the basic resource-constrained project scheduling problem is long and could possibly lead to continuous improvements in the realism of the state-of-the-art literature, bringing researchers closer to project management professionals. Moreover, while the focus of decennia of research was mainly on the static development of algorithms to deal with the complex baseline scheduling problems, the recent research activities gradually started to focus on the development of dynamic scheduling tools that make use of the baseline schedule as a prediction for future project progress in which monitoring and controlling the project performance relative to the baseline schedule should lead to warning signals when the project tends to move into the danger zone BIB034 .