21,483 research outputs found
Point absorber wave energy converters in regular and irregular waves with time domain analysis
A discrete control of latching is used to increase the bandwidth of the efficiency of the Wave Energy Converters (WEC) in regular and irregular seas. When latching control applied to WEC it increases the amplitude of the motion as well as absorbed power. It is assumed that the exciting force is known in the close future and that body is hold in position during the latching time. A heaving vertical-cylinder as a point-absorber WEC is used for the numerical prediction of the different parameters. The absorbed maximum power from the sea is achieved with a three-dimensional panel method using Neumann-Kelvin approximation in which the exact initial-boundary-value problem is linearized about a uniform flow, and recast as an integral equation using the transient free-surface Green function.The calculated response amplitude operator, absorbed power, relative capture width, and efficiency of vertical-cylinder compared with analytical results
Control of Wave Energy Converters for Maximum Power Absorption with Time Domain Analysis
A discrete control of latching is used to increase the bandwidth of the efficiency of the Wave Energy Converters (WEC) in regular and irregular seas. When latching control applied to WEC it increases the amplitude of the motion as well as absorbed power. It is assumed that the exciting force is known in the close future and that body is hold in position during the latching time. A heaving vertical-cylinder as a point-absorber WEC is used for the numerical prediction of the different parameters. The absorbed maximum power from the sea is achieved with a three-dimensional panel method using Neumann-Kelvin approximation in which the exact initial-boundary-value problem is linearized about a uniform flow, and recast as an integral equation using the transient free-surface Green function. The calculated response amplitude operator, absorbed power, relative capture width, and efficiency of vertical-cylinder compared with analytical results
Cable Robot Performance Evaluation by Wrench Exertion Capability
Although cable driven robots are a type of parallel manipulators, the evaluation of their performances cannot be carried out using the performance indices already developed for parallel robots with rigid links. This is an obvious consequence of the peculiar features of flexible cables-a cable can only exert a tensile and limited force in the direction of the cable itself. A comprehensive performance evaluation can certainly be attained by computing the maximum force (or torque) that can be exerted by the cables on the moving platform along a specific (or any) direction within the whole workspace. This is the idea behind the index-called the Wrench Exertion Capability (WEC)-which can be employed to evaluate the performance of any cable robot topology and is characterized by an efficient and simple formulation based on linear programming. By significantly improving a preliminary computation method for the WEC, this paper proposes an ultimate formulation suitable for any cable robot topology. Several numerical investigations on planar and spatial cable robots are presented to give evidence of the WEC usefulness, comparisons with popular performance indices are also provided
Scale Factor Duality and the Energy Condition Inequalities
We demonstrate, by a simple analysis, that cosmological line elements related
by scale factor duality also exhibit a duality with respect to the
conservation/violation of the Weak Energy Condition (WEC) by the matter that
acts as the source in the one-loop beta function equations for the metric
coupling written explicitly in the form of the Einstein equations. Furthermore,
a study of specific pairs of line elements (obtained via O(d,d)
transformations) hints at a possible generalisation of the above duality w.r.t.
WEC for the case of O(d,d) related spacetimes. Consequences and extensions
thereof are also pointed out.Comment: 16 pages, RevTex, no figure
Towards the numerical simulation of 5 Floating Point Absorber Wave Energy Converters installed in a line array using OpenFOAM
In this paper we use the CFD toolbox OpenFOAM to
perform numerical simulations of multiple floating point
absorber Wave Energy Converters (WECs) in a numerical wave
basin. The two-phase Navier-Stokes fluid solver is coupled with a
motion solver to simulate the wave-induced rigid body heave
motion. The purpose of this paper is twofold. The first objective
is to extend numerical simulations of a single WEC unit to
multiple WECs and to tackle the issues of modelling individual
floating objects close to each other in an array layout. The second
objective aims to include all the physical processes (e.g. friction
forces) observed during experimental model tests in the
numerical simulations. The achievements are verified by
validating the numerical model with laboratory experiments for
free decay and regular wave tests using a line array of two and
five WECs. For all the simulations presented, a good agreement
is found between the numerical and experimental results for the
WECs’ heave motions, the surge forces on the WECs and the
perturbed wave field. As a result, our coupled CFD–motion
solver proves to be a suitable and accurate toolbox for the study
of wave-structure interaction problems of WEC arrays.location: Cork, Irelandstatus: publishe
Evolving Lorentzian Wormholes
Evolving Lorentzian wormholes with the required matter satisfying the Energy
conditions are discussed. Several different scale factors are used and the
corresponding consequences derived. The effect of extra, decaying (in time)
compact dimensions present in the wormhole metric is also explored and certain
interesting conclusions are derived for the cases of exponential and
Kaluza--Klein inflation.Comment: 10 pages( RevTex, Twocolumn format), Two figures available on request
from the first author. transmission errors corrected
Cosmological reconstruction and energy bounds in gravity
We discuss the cosmological reconstruction of
(where ,
and represents the Ricci scalar, Ricci
invariant and scalar field) corresponding to power law and de Sitter evolution
in the framework of FRW universe model. We derive the energy conditions for
this modified theory which seem to be more general and can be reduced to some
known forms of these conditions in general relativity, and
theories. We have presented the general constraints in terms of recent values
of snap, jerk, deceleration and Hubble parameters. The energy bounds are
analyzed for reconstructed as well as known models in this theory. Finally, the
free parameters are analyzed comprehensively.Comment: 27 pages, 3 figure
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