Examinando por Autor "Linfati, Rodrigo"
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Ítem A mathematical model for scheduling and assignment of customers in hospital waste collection routes(MDPI, 2021-11) Linfati, Rodrigo; Gatica, Gustavo; Escobar, John WillmerThe collection, transport, and final disposal of hospital waste may cause contamination and disease if improperly handled. Therefore, such residues are hazardous to the health of waste collectors. These wastes are generated by public agencies, such as hospitals, family health centers, dialysis centers, and private healthcare providers. In this study, a mixed-integer linear programming model is proposed for monthly customer scheduling and route assignment. The proposed approach was fulfilled according to customers’ collection frequency, truck capacity, and customer geographical location. The proposed mathematical model successfully balanced the number of customers and the workload during each day. The effectiveness of the proposed model was tested on data obtained from a waste collection company. The model has been implemented in AMPL language, and the performance of commercial solvers, GUROBI and CPLEX, to obtain an optimal solution were tested. The results show the efficiency of the proposed approach to balance the workload concerning previous scheduling is done ad hoc at the company. The use of the formulated model provides an automatic procedure that was previously performed manually. The methodology can be adapted to other companies with similar requirements.Ítem A new genotype-phenotype genetic algorithm for the two-dimensional strip packing problem with rotation of 90°(Pontificia Universidad Javeriana, 2016-01) Gatica, Gustavo; Villagrán, Gonzalo; Contreras-Bolton, Carlos; Linfati, Rodrigo; Escobar, John WillmerGiven a set of rectangular pieces and a fixed width with infinite length, the strip-packing problem (SPP) of two dimensions (2D), with a rotation of pieces in 90° consists of orthogonally placing all the pieces on the strip, without overlapping them, minimizing the height of the strip used. Several algorithms have been proposed to solve this problem, being Genetic Algorithms one of the most popular approach due to it effectiveness solving NP-Hard problems. In this paper, three binary representations, and classic crossover and mutation operators are introduced. A comparison of the three binary representations on a subset of benchmarking instances is performed. The representation R2 outperforms the results obtained by representation R1 and R3. Indeed, some of the bestknown results found by previous published approaches are improved. © 2015, Pontificia Universidad Javeriana. All rights reserved.Ítem Un algoritmo metaheurístico para el problema de localización y ruteo con flota heterogénea(Escuela de Ciencias y Humanidades y Escuela de Ingeniería de la Universidad EAFIT, 2014) Linfati, Rodrigo; Willmer Escobar, John; Gatica, GustavoEste artículo considera el problema de localización y ruteo con flota heterogénea (LRPH, por sus siglas en inglés), en el cual se busca determinar los depósitos a ser abiertos, los clientes a ser asignados a cada depósito, y las rutas a ser construidas para satisfacer las demandas de los clientes, considerando una flota de vehículos con capacidad diversa y costos de utilización asociados. El objetivo es minimizar la suma de los costos asociados con la apertura de depósitos, los costos de los vehículos utilizados, y los costos variables directamente relacionados con las distancias recorridas. En este artículo, se propone un algoritmo metaheurístico basado en una búsqueda tabú granular para la resolución del problema. Experimentos computacionales en instancias adaptadas de la literatura, muestran que el algoritmo propuesto es capaz de obtener, en tiempos computacionales razonables, soluciones de alta calidad demostrando su efectividad.Ítem An Implicit Formulation for Calculating Final Conditions in Drainage Maneuvers in Pressurized Water Installations(MDPI, 2022-11) Coronado Hernández, Oscar E.; Bonilla Correa, Dalia M.; Lovo, Aldo; Fuertes Miquel, Vicente S.; Gatica, Gustavo; Linfati, Rodrigo; Coronado Hernández, Jairo R.Emptying processes are typical maneuvers that should be performed by water distribution companies for operation purposes. These processes involve a complex numerical analysis, since a set of algebraic and ordinary differential equations needs to be solved for the intricacy of hydraulic and thermodynamic formulations for two analyzed phases (liquid and gas). This research provides an implicit equation to compute exactly the final conditions in water emptying operations in single pipelines without an air valve (or admitted air). The implicit expression was developed by considering that for all final conditions, the water velocity is null, and thus, the water column length and air pocket pressure can be computed. The friction factor, internal pipe diameter, and opening maneuvers of drain valves do not disturb the final conditions in draining processes. The developed implicit formulation was validated using experimental measurements in a pipeline with a total length of 4.36 m. The equation is of utmost importance, since it can be utilized for engineers to easily plan for future conditions in water distribution networks. © 2022 by the authors.Ítem Multimodal Capacitated Hub Location Problems with Multi-Commodities: An Application in Freight Transport(Hindawi Limited, 2020) Osorio-Mora, Alan; Núñez-Cerda, Francisco; Gatica, Gustavo; Linfati, RodrigoHub location problems (HLPs) support decision making on multimodal transport strategic planning. It is related to the location of hubs and the allocation of origin/destination (O/D) flow in a system. Classical formulations assume that these flows are predefined paths and direct delivery is not available. This applied research presents a mixed integer linear programming (MILP) model for a capacitated multimodal, multi-commodity HLP. Furthermore, an application on the export process in a Latin American country is detailed. The new proposed model, unlike the traditional HLP, allows direct shipment, and its O/D flows are part of the decision model. Situations with up to 100 nodes, six products, and two transport modes are used, working with initial and projected flows. All instances can be solved optimally using the commercial solver, Gurobi 7.5.0, in computational times less than a minute. Results indicate that only one hub is profitable for the case study, both for the initial and projected scenarios. The installation of a hub generates transport savings over 1% per year. Two factors affect the location decision: low concentration and distance between the hubs and destinations. Long distances involve an exhaustive use of trains instead of trucks, which leads to lower transport cost per unit. © 2020 Alan Osorio-Mora et al.Ítem Probabilistic Approach to Determine the Spatial Distribution of the Antecedent Moisture Conditions for Different Return Periods in the Atlántico Region, Colombia(MDPI, 2022-04-02) Salgado-Cassiani, Julio Jose; Coronado-Hernández, Oscar E.; Gatica, Gustavo; Linfati, Rodrigo; Coronado-Hernández, Jairo R.Previous soil moisture conditions play an important role in the design of hydraulic structures because they are directly related to the runoff threshold associated with a return period. These represent one of the main determinants of the runoff response of a drainage basin. One of the main difficulties facing hydrologists in Colombia lies in the time spent gathering and analyzing information related to the selection of antecedent moisture conditions. In this study, complete records from 19 rainfall stations located in the Atlántico region, Colombia, were used to analyze the cumulative precipitation during the 5 days prior to the annual maximum daily precipitation associated with different return periods using the Gev, Gumbel, Pearson Type III and Log Pearson Type III probability distributions. Different interpolation methods (IDW, kriging and spline) were applied to evaluate the spatial distribution of the antecedent moisture conditions. The main contribution of this research is establishing, using a probabilistic approach, the behavior of antecedent moisture conditions in a particular region, which can be used by engineers and designers to plan water infrastructure. This probabilistic approach was applied to a case study of the Atlántico region, Colombia, where the spatial distribution of antecedent moisture conditions was calculated for several return periods. The results indicate that the better results were obtained with the IDW interpolation method, and the Pearson Type III and Gumbel distributions also showed the best fits based on the Akaike criterion.Ítem Sensitivity of Empirical Equation Parameters for the Calculation of Time of Concentration in Urbanized Watersheds(MDPI, 2022-09) Echeverri Díaz, Jamilton; Coronado Hernández, Óscar E.; Gatica, Gustavo; Linfati, Rodrigo; Méndez Anillo, Rafael D.; Coronado Hernández, Jairo R.The time of concentration is the time it takes a drop of water in a basin to travel from the most distant point to the outlet, and is one of the most important parameters, along with the morphometric characteristics, for determining the design flow rate in rainfall-runoff models. This study aims to determine the sensitivity of the parameters included in different equations for the calculation of the time of concentration. A case study was conducted on small, urbanized watersheds in the city of Montería, Colombia. The study uses information obtained through field work using GPS equipment and electronic total station, supplemented by geographic information contained in the city drawings of the local sewage company, which includes data on elevations above sea level with sub-metric precision. The time of concentration determined by the 12 empirical equations was compared to the results obtained from the equation proposed by the Natural Resources Conservation Service (NRCS), which was considered as a baseline formulation for the intricacy of calculation. Based on this comparison, it was found that the Carter equation is the one that best fits the results obtained from the NRCS equation because it displayed highly significant goodness of fit values. Even though the equations by Kirpich, Ventura, California Culvert Practice, Simas-Hawkins and TxDOT provide a relatively good fit compared to other empirical equations, they tend to over-estimate time of concentration values, which could lead to the under-estimation of the design flow rates. For this reason, sensitivity analysis of the parameters of these equations represents an alternative for improving the calculation of the time of concentration. The current research analyses deepen the influence of some parameters in the estimation of time of concentration. The research can also be used by designers and engineers in the city of Montería, Colombia, as an important reference to compute time of concentrations in urbanized watersheds. © 2022 by the authors.