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Publications

Publications by Bernardo Almada-Lobo

2021

Integrating supplier selection with inventory management under supply disruptions

Authors
Saputro, TE; Figueira, G; Almada Lobo, B;

Publication
INTERNATIONAL JOURNAL OF PRODUCTION RESEARCH

Abstract
In the current global market, managing supply is not a straightforward process and it becomes even more complex as uncertainty and disruptions occur. In order to mitigate their impact, the selection of suppliers of strategic items should have a more holistic view of the operations in the supply chain. We propose an integrated model for supplier selection, considering inventory management and inbound transportation. We approach this problem, incorporating stochastic demand and suppliers' imperfect quality. Imperfect quality triggers additional costs, including external failure and holding costs. Supply disruptions also affect the suppliers' lead time, resulting in delivery delays. We develop a methodology to address this challenge with simulation-optimisation. A genetic algorithm determines supplier selection decisions, while inventory decisions are computed analytically. Discrete-event simulation is used to evaluate the overall performance, as well as to update the lead time dynamically, according to the disruptions. Finally, sensitivity analysis providing managerial insights reveals that criteria in supplier selection should be given a different priority depending on the characteristics of the items, and the effectiveness of disruption mitigation strategies depends on the disruption characteristics.

2023

Hybrid MCDM and simulation-optimization for strategic supplier selection

Authors
Saputro, TE; Figueira, G; Almada-Lobo, B;

Publication
EXPERT SYSTEMS WITH APPLICATIONS

Abstract
Supplier selection for strategic items requires a comprehensive framework dealing with qualitative and quantitative aspects of a company's competitive priorities and supply risk, decision scope, and uncertainty. In order to address these aspects, this study aims to tackle supplier selection for strategic items with a multi-sourcing, taking into account multi-criteria, incorporating uncertainty of decision-makers judgment and supplier-buyer parameters, and integrating with inventory management which the past studies have not addressed well. We develop a novel two-phase solution approach based on integrated multi-criteria decision -making (MCDM) and multi-objective simulation-optimization (S-O). First, MCDM methods, including fuzzy AHP and interval TOPSIS, are applied to calculate suppliers' scores, incorporating uncertain decision makers' judgment. S-O then combines the (quantitative) cost-related criteria and considers supply disruptions and uncertain supplier-buyer parameters. By running this approach on data generated based on previous studies, we evaluate the impact of the decision maker's and the objective's weight, which are considered important in supplier selection.

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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