EOC - Artigos em revistas internacionais
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- The spatial dynamics of niche trajectory: the case of wave energyPublication . Fontes, Margarida; Sousa, Cristina; Ferreira, J.This paper proposes that niches, as protected spaces where technologies are developed and articulated with societal needs, transcend territorial boundaries, encompassing communities and actions that span several spatial levels. To support this assertion, the paper builds on the socio-cognitive perspective to niche development and extends it, introducing a new dimension – space – thus broadening and “spatializing” the concept of technological niche. This framework is applied to the case of wave energy. Empirical research combines a generic analysis of the construction of an “overall niche space” with a detailed analysis of the processes taking place in Portugal, which was one of the pioneers in the emerging field. The results confirm the niche multi-spatial dynamics, showing that it is shaped by the interplay between a niche relational space constructed by actors’ actions and interactions, and the territorial effects introduced by their embeddedness in particular geographical and institutional settings.
- The Levelized Cost of Energy (LCOE) of wave energy using GIS based analysis: the case study of PortugalPublication . Castro-Santos, Laura; Garcia, Geuffer; Estanqueiro, Ana; Justino, Paulo AlexandreThe main objective of this paper is to establish an economic modelling of wave energy through a Geographical Information System (GIS). Furthermore, this method has been tested for the particular case of the Portuguese coast. It determines the best sea areas to install wave energy converters in this region, using spatial analysis of the Levelized Cost of Energy (LCOE). Several economic parameters, as capital or O&M costs, have been considered. In addition, a sensitivity analysis has been performed by varying the discount rate in three different scenarios. Several types of physical restrictions have been taken into account: bathymetry, submarine electrical cables, seabed geology, environmental conditions, protected areas in terms of heritage, navigation areas, seismic fault lines, etc. Spatial operations have been carried out to complete the procedure, using Model Builder of GIS software. Results indicate the most suitable areas in economic terms in Portugal to install wave energy devices.
- Nonlinear dynamics of a tightly moored point-absorber wave energy converterPublication . Vicente, Pedro C.; Falcão, António F. de O.; Justino, Paulo AlexandreTightly moored single-body floating devices are an important class of offshore wave energy converters. Examples are the devices under development at the University of Uppsala, Sweden, and Oregon State University, USA, prototypes of which were recently tested. These devices are equipped with a linear electrical generator. The mooring system consists of a cable that is kept tight by a spring or equivalent device. This cable also prevents the buoy from drifting away by providing a horizontal restoring force. The horizontal and (to a lesser extent) the vertical restoring forces are nonlinear functions of the horizontal and vertical displacements of the buoy, which makes the system a nonlinear one (even if the spring and damper are linear), whose modelling requires a time-domain analysis. Such an analysis is presented, preceded, for comparison purposes, by a simpler frequency-domain approach. Numerical results (motions and absorbed power) are shown for a system consisting of a hemispherical buoy in regular and irregular waves and a tight mooring cable. The power take-off is modelled by a simplified system of a linear spring and a linear damper and also by a system formed by a hydraulic piston and spring. Different scenarios are analysed.
- Modelling, control and Pontryagin Maximum Principle for a two-body wave energy devicePublication . Justino, Paulo Alexandre; Cândido, J.Frequency domain analysis is applied to a wave energy device composed by two coaxial axisymmetric bodies. For each frequency optimal damping coefficient values which maximize absorbed power are obtained. Several displacement amplitude restriction scenarios are considered. A stochastic model to describe the device’s behaviour in irregular waves is developed. Optimal mechanical damping and spring coefficients are computed. Considering different sea state conditions, probability density functions are defined for relevant parameters and time averaged absorbed power values are obtained.A time domain model is also developed for the device. A non-linear power take-off mechanism configuration, consisting in a hydraulic circuit with low-pressure and high-pressure gas accumulators, is devised. Time averaged absorbed power is maximized in terms of characteristic mechanism parameter. A sub-optimal method of phase control by latching is applied to the device in order to improve its performance. Analytical development of Pontryagin Maximum Principle is used to establish an algorithm for device’s control.