Romero-Silva, Rodrigo
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Romero-Silva, Rodrigo
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Romero Silva, Rodrigo
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rromeros
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The effects of supply variability on the performance of assembly systems

2022 , Romero-Silva, Rodrigo , Hurtado-Hernandez, Margarita

Assembly processes play a big role in the current business context as global supply chains depend on many subcomponents to produce a single finished product. Previous studies have shown contrasting results regarding the effect that supply variability (the variability of feeding stations) has on the performance of assembly systems, as opposed to the variability of the station matching and assembling the components. This paper aims to close this gap by studying the behaviour of simple assembly systems with differing degrees of variability allocation among the stations through an experimental simulation study. Results suggest that a reduction in feeding station variability results in higher throughput, even in systems where the variability of one of the feeding stations increases while the other decreases. Furthermore, in scenarios with high total variance, the highest throughput is reached by transferring both variance and work from one of the feeding stations to any other station, whereas in low variance systems symmetrical work transfer to the feeding stations results in the highest throughput, as previously shown. Finally, reducing feeding station variability decreased the time spent in the assembly station (waiting time for component matching plus time for the assembly operation) only in experiments with high total variance. © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.

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Reducing the variability of inter-departure times of a single-server queueing system : the effects of skewness

2019 , Romero-Silva, Rodrigo , Marsillac, Erika , Shaaban, Sabry , Hurtado-Hernandez, Margarita

A critical performance measure in serial production lines is the variability of inter-departure times of a single-server queue. Increasing upstream inter-departure time variability generates greater downstream variability, diminishing overall line performance. Theory suggests that the variability of inter-departure times of a single-server queue is reduced by decreasing the variance of inter-arrival and service times. This study investigates the effects of the skewness of inter-arrival and service time distributions on the variability of inter-departure times. Contrary to previous results suggesting that mean waiting times of a GI/G/1 queue can be reduced by increasing inter-arrival time skewness, this experimental study of a GI/G/1 queue with triangular inter-arrival and service times shows that the inter-departure time coefficient of variation is reduced through a combination of negative inter-arrival time skewness and positive service time skewness. These results also suggest that the absolute value of the negative autocorrelation between consecutive departures is reduced by the same combination of negative inter-arrival time skewness and positive service time skewness for low values of server's utilization, while positive skewness for both inter-arrival and service times reduces this value for high values of server's utilization. Finally, it was found that queue capacity constraints increase the coefficient of variation of inter-departure times, as has been previously suggested, as well as the skewness and the absolute correlation values of the inter-departure time distribution. © 2019 Elsevier Ltd

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Shop-floor scheduling as a competitive advantage: A study on the relevance of cyber-physical systems in different manufacturing contexts

2020 , Romero-Silva, Rodrigo , Hernández-López, Gabriel

The aim of this paper is to analyse the relevance of cyber-physical systems (CPS) in different manufacturing contexts and to study whether CPS could provide companies with competitive advantage by carrying out a better scheduling task. This paper is developed under the umbrella of contingency theory which states that certain technologies and practices are not universally applicable or relevant in every context; thus, only certain companies will benefit from using particular technologies or practices. The conclusion of this paper, developed through deductive reasoning and supported by preliminary simulation experiments and statistical tests, is that factories with an uncertain and demanding market environment as well as a complex production process could benefit the most from implementing a CPS at shop-floor level since a cyber-physical shop-floor will provide all the capabilities needed to carry out the complex scheduling task associated with this type of context. On the other hand, an increase in scheduling performance due to a CPS implementation in factories with simple production flows and stable demand could not be substantial enough to overcome the high cost of installing a fully operational CPS.

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Learning from the past to shape the future: A comprehensive text mining analysis of OR/MS reviews

2021 , Romero-Silva, Rodrigo , Leeuw, Sander de

This paper provides an overview of the evolution and state-of-the-art of the Operations Research and Management Science (OR/MS) subject area from 1956 to 2019. Using text mining techniques on the content of the title, abstract, and author keywords of papers classified by the Web of Science as literature review studies in OR/MS, we found that there are 76 topical consolidated clusters in the field covering a wide range of reviewed topics. Since 2015, reviews on supply chain risk management and big data analytics have had the highest impact in the field, whereas topics such as Industry 4.0, socio-technical systems, social networks, green supply, sustainable supply chain, and resilience engineering have all received significant attention from researchers. Reviews on analytic hierarchy process were found to be the most impactful overall, showing the high relevance of multi-criteria decision making in the current research and practice contexts. Furthermore, a text mining analysis of the papers citing OR/MS literature reviews showed that optimization continues to be one of the most highly influential methodological contributions of OR/MS to other research areas and that topics such as circular economy, carbon emissions, and social commerce have yet to find some traction in OR/MS research, suggesting future research and multidisciplinary opportunities for the field. Results also show that the research area of Public Administration has been greatly influenced by OR/MS reviews as 16% of all the papers published in that field have cited at least one of the 1744 review papers included in this study. Finally, a summary table of published structured literature reviews per topic (benchmarks, classifications, taxonomies) is presented as a short bibliography of OR/MS review papers.

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Mapping operations research in project management: a bibliometric analysis

2021 , Muñoz Villamizar, Andrés , Solano Charris, Elyn L. , Romero-Silva, Rodrigo

Successful project management can help organisations in reducing costs and increasing its efficiency. Likewise, operations research has contributed significantly to improve project management performance with phase-project-planning methodologies. However, as far as we know, there is no literature review that compiles operations research in project management (OR+PM). Thus, this paper aims to present a bibliometric analysis of OR+PM using 1,254 research papers retrieved from ISI Web of Science. This final dataset is composed of articles from scientific journals published between 2001-2018. The results indicate that project scheduling, project management and resource-constrained project scheduling have been the backbone concepts of OR+PM; while terms, such as sustainability, earned value management, multi-objective optimisation, and multi-mode resource-constrained project scheduling problem have been gaining relevance in recent years. Results also show who have been the most influential authors, institutions and countries in the development of this field. Finally, future research opportunities for OR+PM are identified.

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Performance of merging lines with uneven buffer capacity allocation: the effects of unreliability under different inventory-related costs

2020 , Shaaban, Sabry , Romero-Silva, Rodrigo

This simulation study investigates whether machine efficiency, mean time to failure (MTTF) and mean time to repair (MTTR) significantly affect the performance of uneven buffer capacity allocation patterns for merging lines. Also studied is the trade-off between increasing throughput via bigger buffers and their associated inventory-related costs, since previous studies have shown that higher overall buffer capacity and higher average inventory content result in higher throughput. Results suggest that an ascending buffer allocation pattern (concentrating buffer capacity towards the end of the line) produces higher throughput in shorter, more unreliable lines; whereas the balanced pattern shows better performance in longer, more reliable lines. Increasing average buffer capacity per station and/or having higher average buffer content was found to be more cost-effective in lines with lower machine inefficiency, shorter MTTF and MTTR, and longer lines. Results differed between reliable and unreliable lines since reliable lines were particularly penalised by buffer capacity investiment/maintenance costs due to a relatively low increase in throughput resulting from the addition of extra buffer capacity.

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Estimation of Quantile Confidence Intervals for Queueing Systems Based on the Bootstrap Methodology

2017 , Romero-Silva, Rodrigo , Hurtado-Hernandez, Margarita

This paper presents a simple methodology for estimating confidence intervals of quantiles in queueing systems. The paper investigates the actual probability density function of quantile estimators resulting of independent replications. Furthermore, we present a methodology, based on the concepts of bootstrapping, i.e., re-sampling and sub-sampling, to calculate the variability of an estimator without running different independent replications. Contrary to what overlapping and non-overlapping batching procedures suggest, we propose to randomly select data points to form a sub-sample, instead of selecting time-consecutive data points. The results of this study suggest that this proposal reduces the correlation between sub-samples (or batches) and overcomes the issue of normality. © 2017, Springer International Publishing AG.

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Is the scheduling task context-dependent? A survey investigating the presence of constraints in different manufacturing contexts

2016 , Romero-Silva, Rodrigo , Hurtado-Hernandez, Margarita , Santos, Javier

Most studies regarding real scheduling constraints only consider the constraints related to the specific manufacturing environment studied, limiting the possibility of drawing general conclusions. A survey of 50 companies was conducted in order to discover which constraints were present and what their relationship was with the scheduling context. This paper investigates which practical scheduling constraints are present in the manufacturing industry and whether the scheduling task is context-dependent. Results of this study show that some practical production constraints are context-dependent. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

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A framework for studying practical production scheduling

2014 , Romero-Silva, Rodrigo , Santos, Javier , Hurtado-Hernandez, Margarita

The aim of this paper is to present what we believe are the most relevant findings and results regarding practical scheduling in order to define practical production scheduling and create a framework that helps researchers to study the various topics that fall under the umbrella of practical production scheduling and to identify the current state of knowledge for each topic. Studies from different fields were analysed and included in this paper, contributing significant knowledge to build a definition of practical production scheduling. Finally, we discuss the applicability that scheduling, as a task, could have in real companies.

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Studying the effects of the skewness of inter-arrival and service times on the probability distribution of waiting times

2020 , Romero-Silva, Rodrigo , Shaaban, Sabry , Marsillac, Erika , Hurtado-Hernandez, Margarita

Previous studies have shown that the mean queue length of a GI/G/1 system is significantly influenced by the skewness of inter-arrival times, but not by the skewness of service times. These results are limited because all the distributions considered in previous studies were positively skewed. To address this limitation, this paper investigates the effects of the skewness of inter-arrival and service times on the probability distribution of waiting times, when a negatively skewed distribution is used to model inter-arrival and service times. Subsequent to a series of experiments on a GI/G/1 queue using discrete-event simulation, results have shown that the lowest mean waiting time and the lowest variance of waiting times can be attained with a combination of positive inter-arrival skewness and negative service skewness. Results also show an interesting effect of the skewness of service times in the probability of no-delay in environments with a higher utilization factor. © 2020 Brazilian Operations Research Society.

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