The trade-off between stability and makespan in resource-constrained project scheduling.

During the last decade a lot of research efforts in the project scheduling literature have concentrated on resource-constrained project scheduling under uncertainty. Most of this research focuses on protecting the project due date against disruptions during execution. Few efforts have been made to protect the starting times of intermediate activities. In this paper, we develop a heuristic algorithm for minimizing a stability cost function (weighted sum of deviations between planned and realized activity starting times). The algorithm basically proposes a clever way to add intermediate buffers to a minimal duration resource-constrained project schedule. We provide an extensive simulation experiment to investigate the trade-off between quality robustness (measured in terms of project duration) and solution robustness(stability). We address the issue whether to concentrate safety time in so-called project and feeding buffers in order to protect the planned project completion time or to scatter safety time throughout the baseline schedule in order to enhance stability.Stability; Project scheduling; Scheduling; Research; Uncertainty; Time; Heuristic; Simulation; Quality; Quality robustness; Robustness; Order; Scatter;

The complexity of generating robust resource-constrained baseline schedules.

Robust scheduling aims at the construction of a schedule that is protected against uncertain events. A stable schedule is a robust schedule that will change little when variations in the input parameters arise. Robustness can also be achieved by making the schedule makespan insensitive to variability. In this paper, we describe models for the generation of stable and insensitive baseline schedules for resource-constrained scheduling problems and present results on their complexity status. We start from a project scheduling viewpoint and derive results on machine scheduling sub-problems.Complexity; Information; Product scheduling; Robustness; sensitivity; stability;

The trade-off between stability and makespan in resource-constrained project scheduling.

During the last decade, considerable research efforts in the project scheduling literature have concentrated on resource-constrained project scheduling under uncertainty. Most of this research focuses on protecting the project due date against disruptions during execution. Few efforts have been made to protect the starting times of intermediate activities. In this paper, we develop a heuristic algorithm for minimizing a stability cost function (weighted sum of deviations between planned and realized activity starting times). The algorithm basically proposes a clever way to scatter time buffers throughout the baseline schedule. We provide an extensive simulation experiment to investigate the trade-off between quality robustness (measured in terms of project duration) and solution robustness (stability). We address the issue whether to concentrate safety time in so-called project and feeding buffers in order to protect the planned project completion time or to scatter safety time throughout the baseline schedule in order to enhance stability.Project management; Scheduling/sequencing; Simulation methods;

A robust solution to resource-constraint project scheduling problem

This paper aims to propose a solution to the resource-constraint project scheduling problem (RCPSP). RCPSP is a significant scheduling problem in project management. Currently, there are insufficient studies dealing with the robustness of RCPSP. This paper improves the robustness of RCPSP and develops a Robust RCPSP, namely RRCSP. RRCSP is structured with relaxing a fundamental assumption that is 'the tasks start on time as planned'. Relaxing this assumption makes the model more realistic. The proposed solution minimizes the makespan while maximizing the robustness. Maximizing the robustness requires maximizing floating time of activities (it is NP hard). This creates more stability in the project finishing time. RCPSP stands as the root cause of many other problems such as multi-mode resourceconstrained project scheduling problems (MRCPSP), multi-skill resource-constrained project scheduling problem (MSRCPSP), or similar problems and hence proposing a solution to this problem contributes to pave a new line for future research in other mentioned areas. The applicability of the proposed model is examined through a numerical example

A Simulation Based Optimization Approach for Stochastic Resource Constrained Project Management with Milestones

Project managers are challenged to continuously make decisions throughout the development of a project attempting to minimize the overall project cost and, at the same time, seeking to accomplish a pre-established deadline. These time-cost tradeoff decisions are made even more complex when resource constraints, caused by limited available resources, are added to the equation. The goal of this research is to design a simulation-based optimization approach to solve the resource constrained project scheduling problem (RCPSP) under uncertainty. Two methods are proposed: the Total Cost Resource Constrained Method (TCRCM) and the Earned Value Resource Constrained Method (EVRCM). The TCRCM seeks to minimize the total project cost, including activity and penalty costs due to lateness at project completion, while considering the RCPSP with stochastic activity times and costs in terms of resource alternatives as well as precedence relationships for activities sharing resources. The EVRCM, which is based on earned value management, not only considers penalty costs at project completion, but at several project milestones along the execution of the project. Both methods can be implemented in two phases: Phase I, and Phase II. Phase I is implemented prior the start of the project to determine the optimal resource configuration for the entire project based on the specified performance measure (e.g. total project cost). Phase II is implemented as the project progresses to determine the optimal resource configuration for the remaining activities of the project. The robustness of both methods is evaluated through a set of experiments. Lastly, the methods are integrated into Microsoft Excel

Robust Buffer Allocation for Scheduling of a Project with Predefined Milestones

The paper discusses the problem of robust buffer allocation for Resource- Constrained Project Scheduling Problem (RCPSP) with predefined milestones, for which execution deadlines have been established. To solve the problem, an algorithm is proposed supporting insertion of unit time buffers, with the simultaneous maximisation of new metrics of arrangement robustness. The presented results of experimental research speak for usability of the solutions proposed. The effectiveness is studied with use of test tasks included in the Project Scheduling Problem Library (PSPLIB) with additionally specified project milestones

The Project Scheduling Problem with Non-Deterministic Activities Duration: A Literature Review

Purpose: The goal of this article is to provide an extensive literature review of the models and solution procedures proposed by many researchers interested on the Project Scheduling Problem with nondeterministic activities duration. Design/methodology/approach: This paper presents an exhaustive literature review, identifying the existing models where the activities duration were taken as uncertain or random parameters. In order to get published articles since 1996, was employed the Scopus database. The articles were selected on the basis of reviews of abstracts, methodologies, and conclusions. The results were classified according to following characteristics: year of publication, mathematical representation of the activities duration, solution techniques applied, and type of problem solved. Findings: Genetic Algorithms (GA) was pointed out as the main solution technique employed by researchers, and the Resource-Constrained Project Scheduling Problem (RCPSP) as the most studied type of problem. On the other hand, the application of new solution techniques, and the possibility of incorporating traditional methods into new PSP variants was presented as research trends. Originality/value: This literature review contents not only a descriptive analysis of the published articles but also a statistical information section in order to examine the state of the research activity carried out in relation to the Project Scheduling Problem with non-deterministic activities duration.Peer Reviewe

A hierarchical approach to multi-project planning under uncertainty

We survey several viewpoints on the management of the planning complexity of multi-project organisations under uncertainty. A positioning framework is proposed to distinguish between different types of project-driven organisations, which is meant to aid project management in the choice between the various existing planning approaches. We discuss the current state of the art of hierarchical planning approaches both for traditional manufacturing and for project environments. We introduce a generic hierarchical project planning and control framework that serves to position planning methods for multi-project planning under uncertainty. We discuss multiple techniques for dealing with the uncertainty inherent to the different hierarchical stages in a multi-project organisation. In the last part of this paper we discuss two cases from practice and we relate these practical cases to the positioning framework that is put forward in the paper

Pre-emptive resource-constrained multimode project scheduling using genetic algorithm: a dynamic forward approach

Purpose: The issue resource over-allocating is a big concern for project engineers in the process of scheduling project activities. Resource over-allocating drawback is frequently seen after scheduling of a project in practice which causes a schedule to be useless. Modifying an over-allocated schedule is very complicated and needs a lot of efforts and time. In this paper, a new and fast tracking method is proposed to schedule large scale projects which can help project engineers to schedule the project rapidly and with more confidence. Design/methodology/approach: In this article, a forward approach for maximizing net present value (NPV) in multi-mode resource constrained project scheduling problem while assuming discounted positive cash flows (MRCPSP-DCF) is proposed. The progress payment method is used and all resources are considered as pre-emptible. The proposed approach maximizes NPV using unscheduled resources through resource calendar in forward mode. For this purpose, a Genetic Algorithm is applied to solve. Findings: The findings show that the proposed method is an effective way to maximize NPV in MRCPSP-DCF problems while activity splitting is allowed. The proposed algorithm is very fast and can schedule experimental cases with 1000 variables and 100 resources in few seconds. The results are then compared with branch and bound method and simulated annealing algorithm and it is found the proposed genetic algorithm can provide results with better quality. Then algorithm is then applied for scheduling a hospital in practice. Originality/value: The method can be used alone or as a macro in Microsoft Office Project® Software to schedule MRCPSP-DCF problems or to modify resource over-allocated activities after scheduling a project. This can help project engineers to schedule project activities rapidly with more accuracy in practice.Peer Reviewe