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Publications

Publications by Bernardo Almada-Lobo

2024

Matheuristic for the lot-sizing and scheduling problem in integrated pulp and paper production

Authors
Furlan, M; Almada Lobo, B; Santos, M; Morabito, R;

Publication
COMPUTERS & INDUSTRIAL ENGINEERING

Abstract
Vertical pulp and paper production is challenging from a process point of view. Managers must deal with floating bottlenecks, intermediate storage levels, and by-product production to control the whole process while reducing unexpected downtimes. Thus, this paper aims to address the integrated lot sizing and scheduling problem considering continuous digester production, multiple paper machines, and a chemical recovery line to treat by-products. The aim is to minimize the total production cost to meet customer demands, considering all productive resources and encouraging steam production (which can be used in power generation). Production planning should define the sizes of production lots, the sequence of paper types produced in each machine, and the digester working speed throughout the planning horizon. Furthermore, it should indicate the rate of byproduct treatment at each stage of the recovery line and ensure the minimum and maximum storage limits. Due to the difficulty of exactly solving the mixed integer programming model representing this problem for realworld instances, mainly with planning horizons of over two weeks, constructive and improvement heuristics are proposed in this work. Different heuristic combinations are tested on hundreds of instances generated from data collected from the industry. Comparisons are made with a commercial Mixed-Integer and Linear Programming solver and a hybrid metaheuristic. The results show that combining the greedy constructive heuristic with the new variation of a fix-and-optimize improvement method delivers the best performance in both solution quality and computational time and effectively solves realistic size problems in practice. The proposed method achieved 69.41% of the best solutions for the generated set and 55.40% and 64.00% for the literature set for 1 and 2 machines, respectively, compared with the best solution method from the literature and a commercial solver.

2014

An Optimization based on Simulation Approach to the Patient Admission Scheduling Problem: Diagnostic Imaging Department Case Study

Authors
Granja, C; Almada Lobo, B; Janela, F; Seabra, J; Mendes, A;

Publication
JOURNAL OF DIGITAL IMAGING

Abstract
The growing influx of patients in healthcare providers is the result of an aging population and emerging self-consciousness about health. In order to guarantee the welfare of all the healthcare stakeholders, it is mandatory to implement methodologies that optimize the healthcare providers' efficiency while increasing patient throughput and reducing patient's total waiting time. This paper presents a case study of a conventional radiology workflow analysis in a Portuguese healthcare provider. Modeling tools were applied to define the existing workflow. Re-engineered workflows were analyzed using the developed simulation tool. The integration of modeling and simulation tools allowed the identification of system bottlenecks. The new workflow of an imaging department entails a reduction of 41 % of the total completion time.

2023

A Memetic Algorithm for the multi-product Production Routing Problem

Authors
Rodrigues, LF; Dos Santos, MO; Almada-Lobo, B;

Publication
COMPUTERS & INDUSTRIAL ENGINEERING

Abstract
This article addresses the Production Routing Problem (PRP), which consists of determining, in an integrated way, production and inventory planning, and vehicle routing to minimize the costs involved. In the problem, a plant is responsible for producing several types of products to meet the known demand of a set of customers using a homogeneous fleet of vehicles over the planning horizon. In the literature, evolutionary approaches have not been explored in depth for the PRP, specifically for the problem with multiple products. Thus, this work mitigates this gap, presenting a novel Memetic Algorithm and testing its effectiveness on randomly generated sets of instances, comparing the results obtained with a commercial optimization solver. In our solution approach, several classic operators from the literature were implemented. Furthermore, we propose four novel genetic operators. In addition, we evaluated the proposed method's performance in classical instances of literature considering a single item. The computational experiments were carried out to assess the impact of the numerous parameter combinations involving the metaheuristic, and, from statistical analyses, we evidence the proposed technique's robustness. Computational experiments showed that our proposed method outperforms the commercial solver Gurobi in determining feasibly high-quality solutions, mainly on large instances for the PRP with multiple items.

2006

IMAGE - students' leadership in a project development

Authors
Estima, M; Mendes, D; Almada Lobo, B; Magalhaes, B;

Publication
SEFI 2006 - 34th Annual Conference: Engineering Education and Active Students

Abstract
Several discussions concerning the improvement of engineering students' learning process take place. The use of Active Learning tools is grabbing the attention of the pedagogical community as an answer to the recent education process requirements for the new century. A debut-mother project named PESC (To Project, To Undertake, To Know How to Achieve) aimed to fulfil these needs by involving students in a hands-on experience. Within this framework, the development of an industrial engineering and management game (IMAGE) was conducted. PESC initiative shows some similarities with CDIO (Conceiving-Designing-Implementing-Operating). However, the authors consider that this framework needs to be improved addressing other important attributes such as the capacity of identifying, evaluating and formulating problems beforehand. The argument is that PESC fulfils these requirements, based on the creation of multidisciplinary working teams under the students' leadership. Work organization and control were vital to the accomplishment of the proposed task. The project key success factors were the establishment of a direct communication and of ambitious assignments that would challenge the whole group. Moreover, detailed task scheduling, weekly meetings and weekly progress reports were implemented by the leaders. These steps induced team work, dynamism, competition and responsibility on the students, enabling the fulfilment of the ambitious deadlines.

2011

Scheduling wafer slicing by multi-wire saw manufacturing in photovoltaic industry: a case study

Authors
Guimaraes, L; Santos, R; Almada Lobo, B;

Publication
INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY

Abstract
Wafer slicing in photovoltaic industry is mainly done using multi-wire saw machines. The selection of set of bricks (parallelepiped block of crystalline silicon) to be sawn together poses difficult production scheduling decisions. The objective is to maximize the utilization of the available cutting length to improve the process throughput. We address the problem presenting a mathematical formulation and an algorithm that aims to solve it in very short running times while delivering superior solutions. The algorithm employs a reactive greedy randomized adaptive search procedure with some enhancements. Computational experiments proved its effectiveness and efficiency to solve real-world based problems and randomly generated instances. Implementation of an on-line decision system based on this algorithm can help photovoltaic industry to reduce slicing costs making a contribution for its competitiveness against other sources of energy.

2012

Annual production budget in the beverage industry

Authors
Guimaraes, L; Klabjan, D; Almada Lobo, B;

Publication
ENGINEERING APPLICATIONS OF ARTIFICIAL INTELLIGENCE

Abstract
Driven by a real-world application in the beverage industry, this paper provides a design of a new VNS variant to tackle the annual production budget problem. The problem consists of assigning and scheduling production lots in a multi-plant environment, where each plant has a set of filling lines that bottle and pack drinks. Plans also consider final product transfers between the plants. Our algorithm fixes setup variables for family of products and determines production, inventory and transfer decisions by solving a linear programming (LP) model. As we are dealing with very large problem instances, it is inefficient and unpractical to search the entire neighborhood of the incumbent solution at each iteration of the algorithm. We explore the sensitivity analysis of the LP to guide the partial neighborhood search. Dual-reoptimization is also used to speed-up the solution procedure. Tests with instances from our case study have shown that the algorithm can substantially improve the current business practice, and it is more competitive than state-of-the-art commercial solvers and other VNS variants.

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