Chica, M.; Bautista, J.; Cordón, O.; Damas, S. Omega: the international journal of management science Vol. 58, num. January 2016, p. 55-68 DOI: 10.1016/j.omega.2015.04.003 Data de publicació: 2016-01 Article en revista
Changes in demand when manufacturing different products require an optimization model that includes robustness in its definition and methods to deal with it. In this work we propose the r-TSALBP, a multiobjective model for assembly line balancing to search for the most robust line configurations when demand changes. The robust model definition considers a set of demand scenarios and presents temporal and spatial overloads of the stations in the assembly line of the products to be assembled. We present two multiobjective evolutionary algorithms to deal with one of the r-TSALBP variants. The first algorithm uses an additional objective to evaluate the robustness of the solutions. The second algorithm employs a novel adaptive method to evolve separate populations of robust and non-robust solutions during the search. Results show the improvements of using robustness information during the search and the outstanding behavior of the adaptive evolutionary algorithm for solving the problem. Finally, we analyze the managerial impacts of considering the r-TSALBP model for the different organization departments by exploiting the values of the robustness metrics.
This paper proposes a model for dealing with the long term staff composition planning in public universities. University academic staff is organized in units (or departments) according to their field of expertise. The staff for each unit is distrib uted in a set of categories, each one characterized by their teaching hours, cost and other specificities. Besides the use for planning (and upd ating a plan), the model can be used to assess the impact that different stra tegies may have on the personnel costs and the structure of a uni versity. The proposed model is formulated generally, so it can be applied to different types of un iversities attending to their characterist ics. The model is applied to a real case and validated by means of a computational experiment considering several scenarios. The analysis is focu sed on achieving a preferable academic staff com position under service level constraints whil e also minimizing the associated economic expenditures considering a long term horiz on. The results show that the model successes in approaching the staff composition to a previously defined pattern preferable one
Roca-Riu, M.; Fernandez, E.; Estrada, M. Omega: the international journal of management science Vol. 57, num. B, p. 157-175 DOI: 10.1016/j.omega.2015.04.010 Data de publicació: 2015-05-07 Article en revista
A key element to enhance urban distribution is the adequate management of parking space, particularly for loading and unloading operations. An in-advance booking system able to be adjusted to users needs can be a very useful tool for city councils. Such a tool should be fed with criteria for allocating requests to time slots. In this paper we discuss alternative criteria for the parking slot assignment problem for urban distribution and we propose the use of mathematical programming formulations to model them. Several models are proposed, analyzed and compared among them. Extensive computational experience is presented with a detailed analysis and comparison, which provides quantitative indicators of the quality of each of the proposed models.
Fernandez, E.; Kalcsics, J.; Nickel, S. Omega: the international journal of management science Vol. 41, num. 4, p. 721-730 DOI: 10.1016/j.omega.2012.09.005 Data de publicació: 2013-08 Article en revista
Contreras, I.; Fernandez, E.; Reineltc, G. Omega: the international journal of management science Vol. 40, num. 6, p. 847-860 DOI: 10.1016/j.omega.2012.01.006 Data de publicació: 2012-12 Article en revista
This paper presents a combined Facility Location/Network Design Problem which simultaneously considers the location of facilities and the design of its underlying network so as to minimize the maximum customer-facility travel time. The model generalizes the classical p-center problem and has various applications in regional planning, distribution, telecommunications, emergency systems, and other areas. Two mixed integer programming formulations are presented and compared. Several valid inequalities are derived for the most promising of these formulations to strengthen its LP relaxation bound and to reduce the enumeration tree. Numerical results of a series of computational experiments for instances with up to 100 nodes and 500 candidate links are reported.
Kopanos, G.; Puigjaner, L.; Georgiadis, M.C. Omega: the international journal of management science Vol. 40, num. 5, p. 634-650 DOI: 10.1016/j.omega.2011.12.002 Data de publicació: 2012 Article en revista
The production and logistics operations planning in real-life single- or multi-site semicontinuous food industries is addressed in this work. A discrete/continuous-time mixed integer programming model, based on the definition of families of products, is developed for the problem in question. A remarkable feature of the proposed approach is that in the production planning problem timing and sequencing decisions are taken for product families rather than for products. However, material balances are realized for every specific product, thus permitting the detailed optimization of production, inventory, and transportation costs. Changeovers are also explicitly taken into account and optimized. Moreover, alternative transportation modes are considered for the delivery of final products from production sites to distribution centers. The efficiency and the applicability of the proposed approach is demonstrated by solving to optimality two industrial-size case studies, for an emerging real-life Greek dairy industry.
Albareda-Sambola, M.; Fernandez, E.; Saldanha da Gama, F. Omega: the international journal of management science Vol. 39, num. 3, p. 335-345 DOI: 10.1016/j.omega.2010.08.002 Data de publicació: 2011-06 Article en revista
Ribas, I.; Companys, R.; Tort-Martorell, J. Omega: the international journal of management science Vol. 39, num. 3, p. 293-301 DOI: 10.1016/j.omega.2010.07.007 Data de publicació: 2011 Article en revista