dc.contributor.advisor | Venugopal, Vengatesan | en |
dc.contributor.advisor | Ingram, David | en |
dc.contributor.author | McNatt, James Cameron | en |
dc.date.accessioned | 2017-02-20T10:24:07Z | |
dc.date.available | 2017-02-20T10:24:07Z | |
dc.date.issued | 2016-06-27 | |
dc.identifier.uri | http://hdl.handle.net/1842/20378 | |
dc.description.abstract | The interaction between water waves and a floating or fixed body is bi-directional: wave
forces act on and cause motion in the body, and the body alters the wave field. The
impact of the body on its wave field is important to understand because: 1) it may
have positive or negative consequences on the natural or built environment; 2) multiple
bodies in proximity interact via the waves that are scattered and radiated by them;
and 3) in ocean wave energy conversion, by conservation of energy, as a device absorbs
energy, so too must the energy be removed from the wave field.
Herein, the cylindrical solutions to the linear wave boundary-value problem are used
to analyze the floating body wave field. These solutions describe small-amplitude,
harmonic, potential-flow waves in the form of a Fourier summation of incoming and
outgoing, partial, cylindrical, wave components. For a given geometry and mode of
motion, the scattered or radiated waves are characterized by a particular set of complex
cylindrical coefficients.
A novel method is developed for finding the cylindrical coefficients of a scattered or
radiated wave field by making measurements, either computationally or experimentally,
over a circular-cylindrical surface that circumscribes the body and taking a Fourier
transform as a function of spatial direction. To isolate evanescent modes, measurements
are made on the free-surface and as a function of depth. The technique is demonstrated
computationally with the boundary-element method software, WAMIT. The resulting
analytical wave fields are compared with those computed directly by WAMIT and the
match is found to be within 0.1%.
A similar measurement and comparisons are made with experimental results. Because
of the difficulty in making depth-dependent measurements, only free-surface measurements were made with a circular wave gauge array, where the gauges were positioned far
from the body in order to neglect evanescent modes. The experimental results are also
very good. However, both high-order harmonics and wave reflections led to difficulties.
To compute efficiently the wave interactions between multiple bodies, a well-known
multiple-scattering theory is employed, in which waves that are scattered and radiated
by one body are considered incident to another body, which in turn radiates and scatters
waves, sending energy back to the first. Wave fields are given by their cylindrical
representations and unknown scattered wave amplitudes are formulated into a linear
system to solve the problem. Critical to the approach is the characterization of, for
each unique geometry, the cylindrical forces, the radiated wave coefficients, and the
scattered waves in the form of the diffraction transfer matrix.
The method developed herein for determining cylindrical coefficients is extended to
new methods for finding the quantities necessary to solve the interaction problem. The
approach is demonstrated computationally with WAMIT for a simple cylinder and
a more complex wave energy converter (WEC). Multiple-scattering computations are
verified against direct computations from WAMIT and are performed for spectral seas
and a very large array of 101 WECs. The multiple-scattering computation is 1,000-
10,000 times faster than a direct computation because each body is represented by 10s
of wave coefficients, rather than 100s to 1,000s of panels.
A new expression for wave energy absorption using cylindrical coefficients is derived,
leading to a formulation of wave energy absorption efficiency, which is extended to a
nondimensional parameter that relates to efficiency, capture width and gain. Cylindrical
wave energy absorption analysis allows classical results of heaving and surging point
absorbers to be easily reproduced and enables interesting computations of a WEC in
three-dimensions. A Bristol Cylinder type WEC is examined and it is found that its
performance can be improved by flaring its ends to reduce "end effects". Finally, a
computation of 100% wave absorption is demonstrated using a generalized incident
wave.
Cylindrical representations of linear water waves are shown to be effective for the
computations of wave-body wave fields, multi-body interactions, and wave power absorption, and novel methods are presented for determining cylindrical quantities. One
of the approach's greatest attributes is that once the cylindrical coefficients are found,
complex representations of waves in three dimensions are stored in vectors and matrices
and are manipulated with linear algebra. Further research in cylindrical water waves
will likely yield useful applications such as: efficient computations of bodies interacting
with short-crested seas, and continued progress in the understanding of wave energy
absorption efficiency. | en |
dc.contributor.sponsor | other | en |
dc.language.iso | en | |
dc.publisher | The University of Edinburgh | en |
dc.relation.hasversion | J. C. McNatt, V. Venugopal, and D. Forehand. The Cylindrical Wave Field of Wave Energy Converters. In Proc. of the 10th European Wave and Tidal Energy Conf., Aalborg, Denmark, Aalborg, Denmark, 2013 | en |
dc.relation.hasversion | J. C. McNatt, V. Venugopal, and D. Forehand. The cylindrical wave field of wave energy converters. International Journal of Marine Energy, 3-4:e26-e39, December 2013 | en |
dc.relation.hasversion | J. C. McNatt, V. Venugopal, and D. Forehand. A novel method for deriving the diffraction transfer matrix and its application to multi-body interactions in water waves. Ocean Engineering, 94:173-185, January 201 | en |
dc.relation.hasversion | J. C. McNatt, V. Venugopal, D. Forehand, and G. S. Payne. Experimental Analysis of Cylindrical Wave Fields. In Proc. of the 11th European Wave and Tidal Energy Conf., Nantes, France, 2015 | en |
dc.relation.hasversion | J. C. McNatt, M. Hall, J. Davidson, A. de Andres, and S. Hamawi. Innovation in Offshore Renewable Energy: International Collaboration and INORE. In Proc. of the 5th International Conf. on Ocean Energy, Halifax, Canada, 2014. | en |
dc.rights | Attribution-NonCommercial-ShareAlike 4.0 International | en |
dc.rights.uri | http://creativecommons.org/licenses/by-nc-sa/4.0/ | |
dc.subject | linear wave theory | en |
dc.subject | cylindrical waves | en |
dc.subject | wave energy converter | en |
dc.subject | WEC | en |
dc.title | Cylindrical linear water waves and their application to the wave-body problem | en |
dc.type | Thesis or Dissertation | en |
dc.relation.references | J. C. McNatt, V. Venugopal, and D. Forehand. The Cylindrical Wave Field of Wave Energy Converters. In Proc. of the 10th European Wave and Tidal Energy Conf., Aalborg, Denmark, Aalborg, Denmark, 2013 | en |
dc.type.qualificationlevel | Doctoral | en |
dc.type.qualificationname | PhD Doctor of Philosophy | en |