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Publications

Scheduling Operations and SMED: Complementary Ways to Improve Productivity

Publication . Santos, Fernando Charrua; Santos, Beatrice Paiva; Calderón-Arce, Cindy; Figueroa-Mata, Geovanni; Lima, Tânia M.

In most real cases the problem of scheduling operations are sequence de-pendent, that is, the setup time depends on the sequencing of tasks/batches in the ma-chine. Given the current industrial manufacturing trends and requirements such as high variability, customization and reduction of product life cycles, organizations seek to implement new methodologies to adapt and respond with more flexibly to new demands of the global markets. Thus, this work sought to analyse, inspired by a real case of the textile industry, how production scheduling can be understood as a complement to SMED in order to achieve productivity improvement. In the case under analysis we presented the problem of scheduling tasks in uniform parallel machines with sequence-dependent setup times. The main objective of this work was to minimize the total pro-duction time. To this goal, optimization heuristics were used, in this case, simulated annealing algorithm, that demonstrated how the use of heuristics can be an advantage to reduce setup times when associated with other methodologies such as SMED.

2019Book part

Restricted access

Parametric study by means of 3D CFD to improve the airflow pattern and temperature distribution in data center rooms

Publication . Macedo, Diogo Gonçalves Costa e Silva de; Godina, Radu; Gaspar, Pedro Dinis; Silva, Pedro Dinho da; Covas, Miguel Trigueiros

The processing efficacy and energy efficiency of data centers (DC) is directly related with the cooling performance of the air-conditioning systems. The cooling effectiveness depends on airflow pattern and temperature distribution. This paper presents the parametric study of three-dimensional (3D) computational fluid dynamics (CFD) models to improve these technical characteristics. In this case study the most suitable thermal load, as deemed by the organization, of the heat flow boundary condition is simulated and studied for maximum and minimum airflow. The analysis of the numerical results provides a prediction of the thermal performance, i.e., the lower values and spatial gradients (hot spots) of air temperature and velocity while maintaining the computational processing requirements. These results allow the development of an optimized CFD model for setting up the operational parameters of CRAC systems for DC rooms.

2019Journal article

Open access

Comparison of DBD plasma actuators flow control authority in different modes of actuation

Publication . Abdollahzadehsangroudi, M.; Páscoa, J.C.; Oliveira, P.J.

The principal mechanisms by which DBD plasma actuators influence flow characteristics, and are thus able to control that flow, depend strongly on their modes of actuation. Here two different modes based on steady and unsteady actuation are compared and investigated. A simple sinusoidal voltage distribution and a duty cycled sinusoidal voltage were considered for these purposes. Leading edge separation around a stalled NACA 0012 airfoil at Re=3 ×10^16 is considered as test case. A simplified phenomenological model which uses the correct scale of the plasma body force is considered for the modeling of the plasma actuator effects. The steady actuation results show that flow control can be effectively achieved by this mode of operation with continuous injection of momentum in the boundary layer. Unsteady actuation with an imposed frequency equal to the calculated natural frequencies of the flow gives rise to a resonance actuation effect.

2018Journal article

Open access

Optimization of FPSO Glen Lyon Mooring Lines

Publication . Figueiredo, Paulo Alexandre Rodrigues de Vasconcelos; Brojo, Francisco Miguel Ribeiro Proença

During oil and gas inspection and extraction operations both in deep and ultra-deep water, vessel mooring is a very important factor for the development of oil fields. For these depths, standard stand-alone surface facilities e.g. jack up rigs or offshore fixed platforms are not suitable due to the harsh collinear and non-collinear environment in-situ (location, waves, surface and underwater current, sea tides, ice, etc.). For deep sea wells clusters, it is usual to use floating production storage offloading (FPSO) as surface platforms for long time exploitation periods. Subsea expenditure, refers the cost of the subsea project and generally includes the capital expenditures (capex) and operational expenditures (opex). In the production of hydrocarbons capex and opex exponentially increases with increasing depth, resulting in a need for precise detailed design phase for analysis of systems to verify components strength, ductility and fatigue, stiffness, instabilities, corrosion etc. The design of oilfields is most of the times overrated (in a very conservative way) due to several requirements and complex models of costs evaluation. After detailed phase and installation of all facilities and components, as well as due to the expected life design for hydrocarbons exploitation all anchoring system shall withstand the environmental loads in order to not compromise the operation. Each oilfield has a unique development, since environmental phenomena are unique in each earth location. This work refers to the optimization process of an anchoring system for deep waters in the Schiehallion Field, or in other words, the complete development of the mooring system for a FPSO, from the positioning in-situ with environmental conditions and vessel characteristics (Orcaflex), further optimization of the mooring system for an equivalent system (Matlab), mechanical design of the mooring system (CATIA), structural detailed analysis (Altair and Nastran) as fatigue life analysis. In order to reproduce all the mooring process, it is performed and initial comparison of the former FPSO (Schiehallion FPSO) that has been working in-situ since 1993 till its replacement for the new vessel (Glen Lyon FPSO). Due to the latest discoveries in the oilfield, the project has to be redesigned alongside with former wells and having in consideration recent discovered wells. Further optimization of the complete fixation system was verified as well as finally detailed structural analysis of specific components in key locations with higher margin of failure. Within this work, all the methodology which led to the optimization of Glen Lyon mooring lines was fully detailed from vessel analysis to detailed mooring mechanical design, constraints and requirements were applied, trade-offs and assumptions made during this critical development phase are presented and discussed.

2019-06Doctoral thesis

Open access