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Publicações

Publicações por CESE

2013

Flexible and Reconfigurable Layouts in Complex Manufacturing Systems

Autores
Azevedo, MM; Crispim, JA; de Sousa, JP;

Publicação
ADVANCES IN PRODUCTION MANAGEMENT SYSTEMS: COMPETITIVE MANUFACTURING FOR INNOVATIVE PRODUCTS AND SERVICES, AMPS 2012, PT I

Abstract
This paper studies the Facility Layout Problem (FLP) of a first tier supplier in the automotive industry. This complex manufacturing system involves multiple facilities, complex products, and layout reconfiguration constraints. One of the key requirements of this particular system is the need for high levels of flexibility in the reconfiguration of the layouts. This problem is formulated as a mixed-integer programming (MIP), based on a FLP model with multiple objectives and unequal areas. The model allows for two reconfiguration types: small and large changes. We explore the application of optimization methodologies to produce efficient and flexible layouts.

2013

New General Discrete-Time Scheduling Model for Multipurpose Batch Plants

Autores
Moniz, S; Barbosa Povoa, AP; de Sousa, JP;

Publicação
INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH

Abstract
This work deals with the optimal short-term scheduling of general multipurpose batch plants, considering multiple operational characteristics such as sequence-dependent changeovers, temporary storage in the processing units, lots blending, and material flows traceability. A novel Mixed Integer Linear Programming (MILP) discrete-time formulation based on the State-Task Network (STN) is proposed, with new types of constraints for modeling changeovers and storage. We also propose some model extensions for addressing changeovers start; nonpreemptive lots; lots start and sizes; alternative task-unit and task-unit-layout assignments. Computational tests have shown that the proposed model is more effective than a similar model based on the Resource-Task Network (RTN).

2013

An approach for integrated design of flexible production systems

Autores
Marques, AF; Alves, AC; Sousa, JP;

Publicação
FORTY SIXTH CIRP CONFERENCE ON MANUFACTURING SYSTEMS 2013

Abstract
The paper presents a holistic methodological approach for designing flexible production systems, integrating the management of the production resources, operations planning, internal logistics and quality. The proposed methodology relies on lean principles and encompasses a series of stages and tools that may be used to design and to assess the robustness of the production system for tackling small series and frequent changes in the productive processes due to customized production. This approach has been applied to the redesign of the production system of a Portuguese machinery manufacturing industrial company. Results show that it effectively led to a new flexible production system and a new industrial layout capable of responding to diverse future scenarios of products demand. (C) 2013 The Authors. Published by Elsevier B.V.

2013

The airport business in a competitive environment

Autores
Jimenez, E; Claro, J; de Sousa, JP;

Publicação
EUROPEAN JOURNAL OF TRANSPORT AND INFRASTRUCTURE RESEARCH

Abstract
The liberalisation of the European air transport market has introduced new dynamics in the airport industry. In recent decades, airports evolved from infrastructure providers in a monopolistic context, to commercially orientated enterprises in a competitive environment. Current studies of airport strategic management lack a comprehensive perspective that enables airport operators to best identify the opportunities created by such dynamics. This paper analyses an airport as a multi-service firm that interacts with a network of stakeholders - the airport business network - to deliver several service packages to different groups of customers. An integrated conceptual framework was developed to aid academics and practitioners in the appraisal and design of competitive strategies for airports. Such framework covers a clear gap in existing literature, partly due to the fact that current perspectives on airport management fail to address the complexity of the industry in the present competitive environment.

2013

Combining optimization and simulation tools for short-term planning of forest operations

Autores
Marques, AF; de Sousa, JP; Ronnqvist, M; Jafe, R;

Publicação
Scandinavian Journal of Forest Research

Abstract
The use of optimization techniques is well established in forest short-term planning and decision-making. Yet, existing techniques may pose some limitations for tackling with stochastic factors impacting in the execution of forest operations, such as delays, equipment breakdowns and other unexpected events. This paper explores the potential of using optimization techniques in combination with discrete-event simulation (DES) models for planning harvesting and logistics operations acknowledging uncertainty. DES models may be useful for assessing the performance and identifying bottlenecks associated with the execution of the deterministic plans retrieved with optimization techniques, when such stochastic events occur. This paper further presents an approach for the combination of a heuristic and a DES model developed in SIMIO. This approach was used to solve the raw material reception problem (RMRP) at a Portuguese pulp mill. This paper concludes with the analysis of the performance of deterministic schedules for the wood trucks considering uncertainty in their arrival at the mill. © 2013 © 2013 Taylor & Francis.

2013

Circle covering using medial axis

Autores
Rocha, P; Rodrigues, R; Toledo, FMB; Gomes, AM;

Publicação
IFAC Proceedings Volumes (IFAC-PapersOnline)

Abstract
A good representation of a simple polygon, with a desired degree of approximation and complexity, is critical in many applications. This paper presents a method to achieve a complete Circle Covering Representation of a simple polygon, through a topological skeleton, the Medial Axis. The aim is to produce an efficient circle representation of irregular pieces, while considering the approximation error and the resulting complexity, i.e. the number of circles. This will help to address limitations of current approaches to some problems, such as Irregular Placement problems, which will, in turn, provide a positive economic and environmental impact where similar problems arise. © 2013 IFAC.

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