A simheuristic algorithm for solving an integrated resource allocation and scheduling problem

Modern companies have to face challenging configuration issues in their manufacturing chains. One of these challenges is related to the integrated allocation and scheduling of resources such as machines, workers, energy, etc. These integrated optimization problems are difficult to solve, but they can be even more challenging when real-life uncertainty is considered. In this paper, we study an integrated allocation and scheduling optimization problem with stochastic processing times. A simheuristic algorithm is proposed in order to effectively solve this integrated and stochastic problem. Our approach relies on the hybridization of simulation with a metaheuristic to deal with the stochastic version of the allocation-scheduling problem. A series of numerical experiments contribute to illustrate the efficiency of our methodology as well as their potential applications in real-life enterprise settings

Biomaterials for cartilage tissue engineering under mechanical stimulus

Tese de doutoramento em Ciências (ramo do conhecimento em Física)Tissue engineering is being explored as a suitable strategy to repair tissues that have no capability of regenerating by themselves, such as articular hyaline cartilage in the knee. This strategy involves the combination of cells and scaffold biomaterials, able to support the adhesion of cells and their guidance into differentiation. In the knee, the scaffolds have to bear cyclical stress and compressive loading. Therefore, the mechanical properties of the scaffolds are a key component to understand their performance in animal models and clinical trials. In this work, a new methodology has been developed to analyze the mechanical properties of scaffolds for cartilage tissue engineering by studying the fatigue behavior of macroporous poly-ε-caprolactone PCL scaffolds under cyclic loading in different conditions. The PCL scaffolds in dry state were compared with scaffolds under immersion in water, in order to determine the hydrodynamic effects in resistance to fatigue by analyzing the evolution of the dissipated energy with the help of the Morrow’s model. Moreover, the effect of fibrin hydrogel inside the pores was determined. This has been performed due to the fact that fibrin is a component in chirurgical interventions and can be a suitable matrix for cell differentiation in tissue engineering. It was found that water inside the pores plays a critical effect improving resistance to fatigue. On the other hand, the fibrin clot does not represent a relevant factor in determining the mechanical properties, when compared with water. The same analysis was carried out in PCL scaffold combined with poly(vynil-alcohol) PVA hydrogel, an in vitro model of growing tissue inside the pores, in order to study how the addition of a third material resembling some aspects of tissue, can affect the mechanical response. It was concluded that the resistance to fatigue improved when the PVA hydrogel increased in stiffness. Further, the experimental data deviated from the model after few cycles, meaning that unknown effects were taking place inside the pores. This methodology was also implemented in scaffolds with chondrogenic precursors seeded inside the pores in order to study the variations in the fatigue behavior due to the produced extracellular matrix. To simulate some mechanical conditions during cell culture, a bioreactor was designed, capable of applying mechanical compression in multiple samples at the same time. The fabrication of the bioreactor implied the development of the corresponding electronics and mechanics suited to cell incubator environment, as well as sterility tests. Thus, PCL scaffolds were seeded with chondrogenic precursor cells and fibrin and some of them were submitted to free swelling and others to cyclic loading in the bioreactor. All the samples were analyzed for fatigue. Moreover, some components of the extracellular matrix were identified. No differences were observed between samples undergoing free swelling or loading conditions, neither respect to matrix components nor to mechanical performance to fatigue. The extracellular matrix did not achieve in any case all the desired chondrogenic traits. However, an interesting fact was found: when compared with PCL and PCL with PVA under immersion, the extracellular matrix properties improved fatigue resistance, despite the fact that the measured elastic modulus at the first cycle was similar in all the cases. This is interesting as it corroborates the hypothesis that fatigue analysis in tissue engineering constructs can provide additional information missed with traditional measurements. Different factors in these constructs, from the porosity – that influences, among others, water uptake - , to the characteristics of the hydrogel or cellular matrix within them, determine the evolution of fatigue resistance to specific cyclic loading. These effects should be considered for developing predictive models that provide information beyond the traditional mechanical measurements in cartilage tissue engineering.A engenharia de tecidos está a ser explorada como uma estratégia adequada para a reparação de tecidos que não possuem a capacidade de regenerarem-se, como por exemplo, a cartilagem hialina do joelho. Esta estratégia combina células e biomateriais (scaffolds), com a capacidade de suportar a adesão das células e a sua diferenciação. No joelho, os scaffolds têm de suportar tensões e cargas de compressão cíclica. Desta forma, as propriedades mecânicas dos scaffolds são um fator chave para perceber o seu desempenho em modelos animais e ensaios clínicos. Neste trabalho, foi desenvolvida uma nova metodologia para analisar as propriedades mecânicas dos scaffolds para engenharia de tecidos de cartilagem, através do estudo do comportamento de fadiga dos scaffolds macroporosos de poli-ε-caprolactona (PCL) sob cargas cíclicas em diferentes condições. Os scaffolds de PCL secos foram comparados com scaffolds imersos em água para determinar os efeitos hidrodinâmicos na resistência à fadiga, analisando a evolução da energia dissipada com ajuda do modelo de Morrow. Além disso, o efeito de um hidrogel de fibrina no interior dos poros também foi determinado. A utilização da fibrina prende-se com o facto de esta ser um compoente usado em intervenções cirúrgicas, sendo também uma matriz adequada para a diferenciação celular em engenharia de tecidos. Verificou-se ainda que a água no interior dos poros possui um efeito crítico na melhoria da resistência à fadiga. Por outro lado, o coágulo de fibrina não representa um fator determinante nas propriedades mecânicas, quando comparado com a água. A mesma análise foi realizada em scaffolds de PCL combinados com um hidrogel de poli(vinil-álcool) – PVA, um material que serve como modelo in vitro de tecido em crescimento dentro dos poros, de forma a estudar como a adição de um terceiro material, semelhante ao tecido, pode afetar a resposta mecânica. Assim, foi possível concluir que a resistência à fadiga melhora com o aumento da rigidez do hidrogel de PVA. Além disso, verificou-se que os dados experimentais sofreram um desvio relativamente aos dados do modelo teórico após poucos ciclos, o que significa que sucederam efeitos indeterminados no interior dos poros. Esta metodologia foi também aplicada em scaffolds com precursores condrogênicos colocados no interior dos poros, com o objetivo de estudar as variações no comportamento de fadiga causado pela matriz extracelular produzida. Para simular algumas das condições mecânicas durante o cultivo celular foi desenvolvido um bioreactor com a capacidade de aplicar uma compressão mecânica a múltiplas amostras ao mesmo tempo. O fabrico do bioreactor implicou o desenvolvimento das correspondentes partes eletrónica e mecânica, adequadas ao ambiente da incubadora de células, assim como aos testes de esterilização. As células precursoras condrogênicas foram introduzidas nos scaffolds de PCL com fibrina, sendo parte deles submetidos a condições estáticas sem carga e outros com cargas cíclicas através da utilização do bioreactor. O comportamento de fadiga foi analisado para todas as amostras. Alguns componentes da matriz extracelular foram identificados. Verificou-se que comparando as amostras obtidas em condições estáticas e dinâmicas, nenhuma diferença foi encontrada quer para as propriedades mecânicas quer nas componentes da matriz. Além disso, constatou-se que a matriz extracelular não chegou a obter as características condrogênicas desejadas em nenhuma dessas amostras. Contudo, um facto interessante foi observado: aquando a comparação com as amostras de PCL em imersão com PVA, as propriedades da matriz extracelular melhoram a resistência à fadiga, apesar do módulo elástico medido no primeiro ciclo ser semelhante em todas as amostras. Isto é interessante uma vez que reforça a hipótese de que a análise da fadiga em engenharia de tecidos pode fornecer informações adicionais relativamente às medições tradicionais. Os diferentes fatores nestas amostras, desde a porosidade – que influência, entre outros, o movimento da água no interior do scaffold – até às características do hidrogel ou da matriz no seu interior, determinam a evolução da resistência à fadiga para uma carga cíclica específica. Estes efeitos devem ser considerados para o desenvolvimento de modelos de previsão que forneçam informação para além das medições mecânicas tradicionais em engenharia de tecidos da cartilagem.To the FCT for the SFRH/BD/64586/2009 grant. Part of the experimental work was performed in the Center for Biomaterials and Tissue Engineering of the Universitat Politècnica de València, supported by national projects MAT2010-21611-C03-01 and MAT2013-46467-C4-1-R

A strategic oscillation simheuristic for the Time Capacitated Arc Routing Problem with stochastic demands

[EN] The Time Capacitated Arc Routing Problem (TCARP) extends the classical Capacitated Arc Routing Problem by considering time-based capacities instead of traditional loading capacities. In the TCARP, the costs associated with traversing and servicing arcs, as well as the vehicle's capacity, are measured in time units. The increasing use of electric vehicles and unmanned aerial vehicles, which use batteries of limited duration, illustrates the importance of time-capacitated routing problems. In this paper, we consider the TCARP with stochastic demands, i.e.: the actual demands on each edge are random variables which specific values are only revealed once the vehicle traverses the arc. This variability affects the service times, which also become random variables. The main goal then is to find a routing plan that minimizes the expected total time required to service all customers. Since a maximum time capacity applies on each route, a penalty time-based cost arises whenever a route cannot be completed within that limit. In this paper, a strategic oscillation simheuristic algorithm is proposed to solve this stochastic problem. The performance of our algorithm is tested in a series of numerical experiments that extend the classical deterministic instances into stochastic ones.This work has been partially supported by the Spanish Ministry of Science (PID2019-111100RB-C21/AEI/10.13039/501100011033, RED2018102642T, PGC2018-0953322-B-C21/MCIU/AEI/FEDERUE) . The authors are also grateful to the Michael Smurfit Graduate Business School at University College Dublin, Ireland for supporting research stays that contributed to the development of this work.Keenan, P.; Panadero, J.; Juan, AA.; Martí, R.; Mcgarraghy, S. (2021). A strategic oscillation simheuristic for the Time Capacitated Arc Routing Problem with stochastic demands. Computers & Operations Research. 133:1-12. https://doi.org/10.1016/j.cor.2021.10537711213

Optimizing transport logistics under uncertainty with simheuristics: concepts, review and trends

Background: Uncertainty conditions have been increasingly considered in optimization problems arising in real-life transportation and logistics activities. Generally, the analysis of complex systems in these non-deterministic environments is approached with simulation techniques. However, simulation is not an optimization tool. Hence, it must be combined with optimization methods when our goal is to: (i) minimize operating costs while guaranteeing a given quality of service; or (ii) maximize system performance using limited resources. When solving NP-hard optimization problems, the use of metaheuristics allows us to deal with large-scale instances in reasonable computation times. By adding a simulation layer to the metaheuristics, the methodology becomes a simheuristic, which allows the optimization element to solve scenarios under uncertainty. Methods: This paper reviews the indexed documents in Elsevier Scopus database of both initial as well as recent applications of simheuristics in the logistics and transportation field. The paper also discusses open research lines in this knowledge area. Results: The simheuristics approaches to solving NP-hard and large-scale combinatorial optimization problems under uncertainty scenarios are discussed, as they frequently appear in real-life applications in logistics and transportation activities. Conclusions: The way in which the different simheuristic components interact puts a special emphasis in the different stages that can contribute to make the approach more efficient from a computational perspective. There are several lines of research that are still open in the field of simheuristics.Peer ReviewedPostprint (published version

A Fuzzy Simheuristic for the Permutation Flow Shop Problem under Stochastic and Fuzzy Uncertainty

[EN] Stochastic, as well as fuzzy uncertainty, can be found in most real-world systems. Considering both types of uncertainties simultaneously makes optimization problems incredibly challenging. In this paper, we analyze the permutation flow shop problem (PFSP) with both stochastic and fuzzy processing times. The main goal is to find the solution (permutation of jobs) that minimizes the expected makespan. However, due to the existence of uncertainty, other characteristics of the solution are also taken into account. In particular, we illustrate how survival analysis can be employed to enrich the probabilistic information given to decision-makers. To solve the aforementioned optimization problem, we extend the concept of a simheuristic framework so it can also include fuzzy elements. Hence, both stochastic and fuzzy uncertainty are simultaneously incorporated in the PFSP. In order to test our approach, classical PFSP instances have been adapted and extended, so that processing times become either stochastic or fuzzy. The experimental results show the effectiveness of the proposed approach when compared with more traditional ones.This work has been partially supported by the Spanish Ministry of Science (PID2019111100RB-C21/AEI/10.13039/501100011033), as well as by the Barcelona Council and the "la Caixa" Foundation under the framework of the Barcelona Science Plan 2020-2023 (grant 21S09355-001).Castaneda, J.; Martín, XA.; Ammouriova, M.; Panadero, J.; Juan-Pérez, ÁA. (2022). A Fuzzy Simheuristic for the Permutation Flow Shop Problem under Stochastic and Fuzzy Uncertainty. Mathematics. 10(10):1-17. https://doi.org/10.3390/math10101760117101

Applying simheuristics to minimize overall costs of an MRP planned production system

Looking at current enterprise resource planning systems shows that material requirements planning (MRP) is one of the main production planning approaches implemented there. The MRP planning parameters lot size, safety stock, and planned lead time, have to be identified for each MRP planned material. With increasing production system complexity, more planning parameters have to be defined. Simulation-based optimization is known as a valuable tool for optimizing these MRP planning parameters for the underlying production system. In this article, a fast and easy-to-apply simheuristic was developed with the objective to minimize overall costs. The simheuristic sets the planning parameters lot size, safety stock, and planned lead time for the simulated stochastic production systems. The developed simheuristic applies aspects of simulation annealing (SA) for an efficient metaheuristic-based solution parameter sampling. Additionally, an intelligent simulation budget management (SBM) concept is introduced, which skips replications of not promising iterations. A comprehensive simulation study for a multi-item and multi-staged production system structure is conducted to evaluate its performance. Different simheuristic combinations and parameters are tested, with the result that the combination of SA and SBM led to the lowest overall costs. The contributions of this article are an easy implementable simheuristic for MRP parameter optimization and a promising concept to intelligently manage simulation budget.Peer ReviewedPostprint (published version

Solving the time capacitated arc routing problem under fuzzy and stochastic travel and service times

[EN] Stochastic, as well as fuzzy uncertainty, can be found in most real-world systems. Considering both types of uncertainties simultaneously makes optimization problems incredibly challenging. In this paper we propose a fuzzy simheuristic to solve the Time Capacitated Arc Routing Problem (TCARP) when the nature of the travel time can either be deterministic, stochastic or fuzzy. The main goal is to find a solution (vehicle routes) that minimizes the total time spent in servicing the required arcs. However, due to uncertainty, other characteristics of the solution are also considered. In particular, we illustrate how reliability concepts can enrich the probabilistic information given to decision-makers. In order to solve the aforementioned optimization problem, we extend the concept of simheuristic framework so it can also include fuzzy elements. Hence, both stochastic and fuzzy uncertainty are simultaneously incorporated into the CARP. In order to test our approach, classical CARP instances have been adapted and extended so that customers' demands become either stochastic or fuzzy. The experimental results show the effectiveness of the proposed approach when compared with more traditional ones. In particular, our fuzzy simheuristic is capable of generating new best-known solutions for the stochastic versions of some instances belonging to the tegl, tcarp, val, and rural benchmarks.Spanish Ministry of Science, Grant/Award Number: PID2019-111100RB-C21/AEI/10.13039/501100011033; Barcelona Council and the "la Caixa" Foundation under the framework of the Barcelona Science Plan 2020-2023, Grant/Award Number: 21S09355-001; Generalitat Valenciana,Grant/Award Number: PROMETEO/2021/065Martín, XA.; Panadero, J.; Peidro Payá, D.; Pérez Bernabeu, E.; Juan-Pérez, ÁA. (2023). Solving the time capacitated arc routing problem under fuzzy and stochastic travel and service times. Networks. 82(4):318-335. https://doi.org/10.1002/net.2215931833582

Battery sharing: a feasibility analysis through simulation

Nowadays, several alternatives to internal combustion engines are being proposed in order to reduce CO2 emissions in freight transportation and citizen mobility. According to many experts, the use of electric vehicles constitutes one of the most promising alternatives for achieving the desirable reductions in emissions. However, popularization of these vehicles is being slowed by long recharging times and the low availability of recharging stations. One possible solution to this issue is to employ the concept of battery sharing or battery swapping. This concept is supported by important industrial partners, such as Eni in Italy, Ample in the US, and Shell in the UK. This paper supports the introduction of battery swapping practices by analyzing their effects. A discrete-event simulation model is employed for this study. The obtained results show that battery sharing practices are not just a more environmentally and socially friendly solution, but also one that can be highly beneficial for reducing traffic congestion.Postprint (published version