Új projekt ütemezési módszerek a termelés-tervezés támogatására = New project scheduling approaches for production planning

Munkákat az motiválta, hogy az általános erőforrás-korlátos projekt ütemezési probléma olyan új modelljeit és megoldási módszereit dolgozzuk ki, melyek megfelelnek a termelés-tervezés és -ütemezés aktuális, ipari gyakorlat által is támasztott követelményeinek. A kutatás során a következő fő eredményeket értük el: 1. Új modelleket és megoldó algoritmusokat dolgoztunk ki a változó intenzitású tevékenységekkel történő erőforrás-korlátos projekt ütemezés témájában. 2. Nagyméretű korlátozás programozási és korlátozás-alapú ütemezési feladatok megoldására dolgoztunk ki olyan általános módszereket, melyek kihasználva a gyakorlati feladatokra jellemző strukturális sajátosságokat jelentősen növelik a megoldó hatékonyságát. 3. A fenti modellek és megoldó módszerek alkalmazásával megvalósítottunk egy közös modellen alapuló, ám a részletezettség (ún. aggregáltság) eltérő szintjein működő hierarchikus termeléstervező és -ütemező rendszert. 4. A termeléstervezés és -ütemezés terén elért eredményeket termelési hálózatokra is kiterjesztettük: autonóm gyártó és beszállító felek közt működő kooperatív tervezési modellt dolgoztunk ki, amely biztosítja a gyártó anyagellátását. | Our research was focused on advanced production planning and scheduling models and methods that were able to meet real industrial requirements. This called for generic resource-constrained project scheduling models with strong representative power on the hand, and efficient solution techniques on the other hand. 1. We have developed a novel approach to modeling and solving production planning problems that unifies the capacity and the material flow oriented aspects of planning. Orders are modeled as projects comprising of networks of variable-intensity activities that compete for limited resources. 2. For solving detailed production scheduling problems we have taken a constraint programming approach and developed new methods that exploit the hidden structural properties of large, real-life job-shop scheduling problems. It was proven that these methods reduced the search space drastically and improved the performance of constraint solvers. 3. Based on the above results, we developed a pilot production planner and scheduler system. The planning and scheduling levels are integrated by a new aggregation method that warrants for the executability of high-level production plans on the detailed level of scheduling. 4. The results in production planning and scheduling were extended to the management of production networks, where a cooperative customer-supplier planning model has been elaborated for supporting material supply at the lowest possible costs

Beyond C<i>max</i>: an optimization-oriented framework for constraint-based scheduling

This paper presents a framework taking advantage of both the flexibility of constraint programming and the efficiency of operations research algorithms for solving scheduling problems under various objectives and constraints. Built upon a constraint programming engine, the framework allows the use of scheduling global constraints, and it offers, in addition, a modular and simplified way to perform optimality reasoning based on well-known scheduling relaxations. We present a first instantiation on the single machine problem with release dates and lateness minimization. Beyond the simplicity of use, the ptimizationoriented framework appears to be, from the experiments, effective for dealing with such a pure problem even without any ad-hoc heuristics

Beyond C<i>max</i>: an optimization-oriented framework for constraint-based scheduling

This paper presents a framework taking advantage of both the flexibility of constraint programming and the efficiency of operations research algorithms for solving scheduling problems under various objectives and constraints. Built upon a constraint programming engine, the framework allows the use of scheduling global constraints, and it offers, in addition, a modular and simplified way to perform optimality reasoning based on well-known scheduling relaxations. We present a first instantiation on the single machine problem with release dates and lateness minimization. Beyond the simplicity of use, the ptimizationoriented framework appears to be, from the experiments, effective for dealing with such a pure problem even without any ad-hoc heuristics

Heuristic procedures for reactive project scheduling.

This paper describes new heuristic reactive project scheduling procedures that may be used to repair resource-constrained roject baseline schedules that suer from multiple activity duration disruptions during project execution.The objective is to minimize the deviations between the baseline schedule and the schedule that is actually realized.We discuss computational results obtained with priority-rule based schedule generation schemes, a sampling approach and a weighted-earliness tardiness heuristic on a set of randomly generated project instances.Project scheduling; Scheduling; Reactive scheduling; Research; Uncertainty; Stability;

A linear programming based method for the resource constrained multiproject scheduling problem with weighted earliness/tardiness costs

This study addresses the Resource Constrained Multi Project Scheduling Problem with Weighted Earliness Tardiness Costs (RCMPSPWET). In multi-project environments, the project portfolio of a company does often change dramatically in time. In this dynamic context, the arrival of a new project requires quoting a due date while keeping the disruptions to the existing plans and schedules to a minimum. The suggested solution method is an adaptation of the well known shifting bottleneck (SB) heuristic in the job shop literature. Initially, a base schedule is obtained by relaxing all resource capacities and solving the resulting model as a linear program (LP). The SB heuristic then resolves the resource conflicts present in the optimal solution of this resource relaxation iteratively by solving a set of single-resource weighted earliness tardiness scheduling subproblems with precedence constraints. The unit earliness and tardiness costs in the subproblems are estimated by drawing upon tools from LP sensitivity analysis recently proposed by Bülbül and Kaminsky [1] for a general job shop scheduling problem. The subproblems in the SB heuristic are a generalization of the NP-hard single machine weighted earliness tardiness problem, and a neighborhood search based algorithm is applied to these for the efficiency of the overall SB algorithm. The solution of a subproblem introduces new precedence relationships based on the concept of resource ows. These new precedence constraints are incorporated into the LP mentioned above and ensure that the capacity of the resource under consideration is observed. These steps are repeated until all resource conflicts are removed. The order in which the resource conflicts are resolved is a major determinant of the final solution quality, and therefore, a systematic tree search strategy is implemented for resolving the resource conflicts in different orders. A local search algorithm for the original problem is also adopted to benchmark the results

Proactive-reactive procedures for robust project scheduling.

The vast majority of research efforts in project scheduling concentrates on developing procedures to generate workable baseline schedules that minimize the project makespan in a deterministic environment. However, a real-life project is inevitably subject to uncertainty during execution. This dissertation aims at introducing procedures that cope with disruptions during execution. We limit ourselves to the treatment of time uncertainties caused by the fact that actually realized activity durations during project execution may deviate from the expected activity durations. When dealing with uncertainty in a scheduling environment, there are, generally spoken, two main approaches. Proactive scheduling focuses at incorporating safety in the schedule to absorb future disruptions, while reactive scheduling denotes how to react when a disruption occurs. Both approaches are inescapably related. We will investigate in how several proactive-reactive scheduling decisions can help a project manager to increase the quality of a project. The text of this dissertation is organized as follows. Chapter 1 introduces the problem of proactive-reactive project scheduling and situates it in the extensive project scheduling literature. Chapter 2 formulates the problem at hand and defines the concepts required in the remainder of the thesis. The trade-off between makespan and stability in project scheduling of Chapter 3 justifies the research efforts made in Chapters 4, 5 and 6 to add safety to the baseline schedule. Mainly two approaches to add safety are discussed in this thesis. First, a schedule is made proactive in Chapter 4 by deciding how the resources flow throughout the project. Next in Chapter 5, we develop efficient and effective procedures to add idle time (buffers) into a schedule to anticipate unforeseen events. Chapter 6 contains an extension of Chapters 4 and 5 by merging scheduling, resource allocation and buffer allocation decisions into an integrated approach. The reactive procedures that are required to decide how to react on disruptions that cannot be absorbed by the baseline schedule are introduced in Chapter 7. In Chapter 8 an extensive simulation-based experiment is set-up to evaluate several predictive-reactive resource-constrained project scheduling procedures proposed in the previous chapters. Chapter 9 applies the proactive-reactive project scheduling methodology on a real-life project that stems from our experience in the Belgian construction industry. Accordingly, a risk management framework is introduced to detect and analyze the risks that constitute the uncertainty implied in the project. In a last chapter, some overall conclusions and recommendations are provided.