Repositório Comunidade:
http://hdl.handle.net/10400.9/93
Mon, 22 Jan 2018 23:46:36 GMT2018-01-22T23:46:36ZOptimization of mooring configuration parameters of floating wave energy converts
http://hdl.handle.net/10400.9/1436
Título: Optimization of mooring configuration parameters of floating wave energy converts
Autor: Vicente, Pedro C.; Falcão, António de O.; Justino, Paulo Alexandre
Resumo: Floating point absorbers devices are a large class of wave energy converters for deployment offshore, typically in water
depths between 40 and 100m. As floating oil and gas platforms,the devices are subject to drift forces due to waves, currents and
wind, and therefore have to be kept in place by a proper mooring system.
Although similarities can be found between the energy converting systems and floating platforms, the mooring design requirements will have some important differences between
them, one of them associated to the fact that, in the case of a wave energy converter, the mooring connections may
significantly modify its energy absorption properties by interacting with its oscillations. It is therefore important to
examine what might be the more suitable mooring design for wave energy devices, according to the converters
specifications.
When defining a mooring system for a device, several initial parameters have to be established, such as cable material and thickness, distance to the mooring point on the bottom, and which can influence the device performance in terms of motion,power output and survivability.
Different parameters, for which acceptable intervals can be established, will represent different power absorptions,displacements from equilibrium position, load demands on the moorings and of course also different costs.
The work presented here analyzes what might be, for wave energy converter floating point absorber, the optimal mooring configuration parameters, respecting certain pre-established acceptable intervals and using a time-domain model that takes into account the non-linearities introduced by the mooring
system.
Numerical results for the mooring forces demands and also motions and absorbed power, are presented for two different mooring configurations for a system consisting of a
hemispherical buoy in regular waves and assuming a liner PTO.Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10400.9/14362011-01-01T00:00:00ZModelling of the IPS buoy wave energy converter including the effect of non-uniform tube cross-section
http://hdl.handle.net/10400.9/1434
Título: Modelling of the IPS buoy wave energy converter including the effect of non-uniform tube cross-section
Autor: Falcão, António F. de O.; Cândido, José J.; Justino, Paulo Alexandre; Henriques, João C. C.
Resumo: An important class of floating wave energy converters (that includes the IPS buoy, the Wavebob and the PowerBuoy) comprehends devices in which the energy is converted from the relative (essentially heaving) motion between two bodies oscillating differently. The paper considers the case of the IPS buoy, consisting of a floater rigidly connected to a fully submerged vertical (acceleration) tube open at both ends. The tube contains a piston whose motion relative to the floater-tube system (motion originated by wave action on the floater and by the inertia of the water enclosed in the tube) drives a power take-off mechanism (PTO) (assumed to be a linear damper). To solve the problem of the end-stops, the central part of the tube, along which the piston slides, bells out at either end to limit the stroke of the piston. The use of a hydraulic turbine inside the tube is examined as an alternative to the piston. A frequency domain analysis of the device in regular waves is developed, combined with a one-dimensional unsteady flow model inside the tube (whose cross-section is in general nonuniform). Numerical results are presented for a cylindrical buoy in regular waves, including the optimization of the acceleration tube geometry and PTO damping coefficient for several wave periods.Sun, 19 Jun 2011 00:00:00 GMThttp://hdl.handle.net/10400.9/14342011-06-19T00:00:00ZFrequency and Stochastic Domain Models for Two Geometries of the IPS Wave Power Buoy
http://hdl.handle.net/10400.9/1357
Título: Frequency and Stochastic Domain Models for Two Geometries of the IPS Wave Power Buoy
Autor: Cândido, J.; Justino, Paulo Alexandre; Henriques, J.C.C.
Resumo: Frequency-domain analysis is applied to a geometry of the original IPS buoy device concept. The analysis is particularly useful in the early development stages to establish
the response of power take-off mechanism characteristic parameters to different frequencies of the wave spectrum.
Optimal mechanical damping and spring coefficients are computed for some parameters restrictions. Absorbed power,
capture width and other variables, such as relative displacement,are computed for regular waves and these optimal mechanical
coefficients. A stochastic model is developed in order to evaluate the IPS buoy
behaviour for irregular waves’ conditions. This allows defining probability density functions for parameters that characterize
the device’s behaviour. Assuming that the overall system behaviour is linear and that the surface elevation for irregular waves may be regarded as a stochastic process with a Gaussian probability density function, the variables that define the system behaviour, such as bodies’ displacements and velocities, will also hold a Gaussian probability density function. The average power extraction is computed for different sea state conditions.Aiming to enhance the device’s hydrodynamic performance, a new non-axisymmetric IPS geometry is conceived. Using the stochastic modelling approach, the device’s behaviour is studied for several wave directions and compared to the axisymmetric configuration’s behaviour.Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10400.9/13572011-01-01T00:00:00ZNon-linear Slack-Mooring Modelling of a Floating Two-Body Wave Energy Converter
http://hdl.handle.net/10400.9/1356
Título: Non-linear Slack-Mooring Modelling of a Floating Two-Body Wave Energy Converter
Autor: Vicente, Pedro C.; Falcão, António de O.; Justino, Paulo Alexandre
Resumo: Most floating oscillating-body wave energy
converters that have been proposed and developed so far are two-body systems where the power is extracted from the relative
translational motion between the two bodies. As any floating device, floating point absorbers are subject to drift forces due to
waves, currents and wind, and therefore need to be kept in place by a proper mooring system. The mooring cables can be approximately modelled as catenary lines in a quasi-static analysis. The use of a time-domain analysis allows for nonlinear mooring forces of slack chain cables to be considered. Numerical results for motion, mooring tensions and absorbed power are
presented for a two body system consisting of a hemispherical floater and a submerged body and slack bottom moorings, for regular and irregular waves. Comparisons are given with the unmoored two-body heaving system, the moored heaving twobody system and with the simplified one body linear PTO model.
Results show the possibility of occurrence of low-frequency horizontal oscillations of large amplitude, and non linear motions, even for regular waves. Some differences are seen in comparison with the simplified one body model and with the heave two-body system. The moorings were found not to affect
very significantly the power absorbed.Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10400.9/13562011-01-01T00:00:00Z