Thesis (M.S.)--Rochester Institute of Technology, 2006. / Typescript. Includes bibliographical references (leaves 171-181).

This study investigates the accuracy of the wave products retrieved by a 12-MHz high-frequency (HF) phased-array radar, and establishes their potential to characterise wave-current interactions. The two stations composing the system were deployed in 2011 to overlook the Wave Hub, a test site for marine renewable energy devices located on the south-western coast of the United Kingdom. The system was conceived and configured to reduce the inaccuracies introduced by short time averaging and minimal overlap between stations, both associated with the most traditional HF radar deployments, whose primary activity is current measurement. Wave spectra were retrieved by two independent inversion algorithms, which were evaluated both independently and relative to each other. This process helped determining the errors associated to the algorithm used, and differentiated them from those inherent to the radar technology itself. The first method investigated was a semi-empirical algorithm distributed with Wellen Radars (WERA), which was calibrated using in situ measurements collected within the radar footprint. Evaluated through comparison against measurements acquired by three in situ devices, the results revealed estimates of significant wave height with biases below 9 cm, Pearson correlations higher than 0.9, and RMS errors that range from 29 to 44 cm. The relative error of wave energy period comparisons was within 10% for periods between 8 and 13 s, while both under- and overestimations were observed above and below that range, respectively. The validation demonstrated that when locally calibrated, the algorithm performs better than in its original form in all metrics considered. Observed discrepancies were mainly attributable to single-site estimations, antenna sidelobes, and the effect of the second-harmonic peaks of the Doppler spectrum. As opposed to the semi-empirical inversion, the second method evaluated in this work provides estimates of the full directional spectrum. Compared against the in situ measurements, the radar spectra were more spread over frequencies and directions, and had a lower energy content at the peak of the spectrum. In terms of parameter estimation, this was generally translated in a slight underestimation of wave periods, but accurate estimates of significant wave heights. Pearson correlations between these parameters and the in situ measurements for the bulk of the spectrum were higher than 0.9, and both types of measurements resulted in similar standard deviations. The inversion algorithm showed a high skill estimating mean wave directions, which revealed linear correlations higher than 0.8, when compared to the in situ devices. Overall, the inversion algorithm has shown to be capable of providing accurate estimates of directional spectra and the parameters derived from them, and at present the main drawback of the method is the data return, which due to the high data quality requirements of the algorithm, did not exceed 55% over the 8-month period studied here. In the second part of this work, the validated measurements were examined to determine their ability to reproduce the effects of wave-current interactions. The fine structure of the surface current was first evaluated, and revealed a circulation dominated by tides. The residual flow was seen to respond to the wind, as well as to the stratification present in the area during the spring and summer months. These data were then used to assess their contribution to wave refraction over the radar domain. The results show modulations in the wave phase parameters, which resulted from both the temporal and spatial derivatives of the surface current velocities. The evaluation of HF radar wave measurements provided in this work has shown that, properly configured, this technology can produce accurate estimates of several statistical descriptors of the wave field. Together with the highly accurate surface currents also measured by this device, the spatial wave data obtained has proved to have great potential for studying wave-current interactions; a skill that can be of support to coastal wave modelling.

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.

Wave dissipation was previously investigated intensively in the frequency domain, in which the dissipation of waves is described as attenuation of pressure pulse decay with respect to the frequency or harmonics. In this thesis, wave dissipation, including decay of pressure pulse, peak of wave intensity and wave energy, is investigated in the time domain using wave intensity analysis (WIA). Wave intensity analysis benefits to this research in several aspects including: 1) WIA allows for wave dissipation investigated in the time domain; 2) WIA does not make any assumptions about the tube's wall non-linearity and the analysis takes into account the effects of the vessel's wall viscoelastic properties, convective, frictional effects and fluid viscosity; 3) WIA offers a technique (separation) to study wave dissipation in one direction whilst taking into account the effect of reflections from the opposite direction; 4) The physical meaning of wave intensity provides a convenient method to study the dissipation of energy carried by the waves along flexible tubes. In this research, it is found that the degree of dissipation in flexible tube were not only affected by the mechanical properties of the wall property and viscosity of liquid but also by the other factors including initial pressure and pumping speed of piston as well as direction of wave in relation to direction of flow. Also an new technique to separate waves into forward and backward directions only using diameter and velocity might potentially be used to separate the waves in both directions non-invasively based on the non-invasive measurement of diameter (wall movement) available.

A set of closely-spaced tide-gauge records of the 1960 Chilean tsunami was obtained on the Pacific Coast of Canada. The object of this study was to glean as much as possible of the information contained in these records. The investigation was carried on by power spectrum analysis, cross-spectrum analysis and visual inspection of the tide-gauge records. An interpretation is offered which invokes the mechanisms of wave buildup due to shoaling, clapotis effect, resonance, viscous dissipation, and shift of energy between wave and current by Reynolds stresses to explain the form of the power spectra. In the appendices are given a formula for the response characteristics of stilling wells, an application of an electrical engineering result for the response characteristics of pressure gauges, an elucidation of the conversion of power estimates to the positive frequency range, an interpretation of the phase difference from cross-spectra, and a formula for prewhitening the covariances before performing the Fourier transform in the spectral analysis. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A 30.5 cm diameter, detonation driven shock tube facility has been designed, constructed and tested. The design goals of the shock tube were to reproduce free field blast wave profiles on a laboratory scale using atmospheric gaseous detonation as the energy source. Numerical simulations were utilized to explore the gas dynamic evolution inside detonation driven shock tubes and to select the optimal design parameters for the shock tube.The Friedlander profile was used to evaluate the generated pressure profiles as an approximation of free field blast waves. It has been found that the detonation driver length should be kept below 20% of the total length of the tube in order to produce Friedlander waves. Additionally, it has been found that an annular vent can be added to the shock tube to enhance the negative phase of the blast profile, more accurately reproducing real free field blast waves. The shock tube has been constructed in a modular fashion from 2.54 cm thick steel tubing. An adjustable bag type diaphragm has been employed to allow for a variable driver size and a high voltage ignition system is used to initiate detonation in the driver section. Due to the available location for the shock tube, tests using the vented configuration could not be accomplished for safety reasons. Conducted experiments produced results that agree well with corresponding numerical simulations. Overall, the shock tube design was successful in creating Friedlander blast waves. At the time of writing, a manufacturer error in correctly reporting the specifications of the clamps used on the shock tube resulted in a lower maximum pressure of operation.

Four different heat wave definitions (as outlined by Hajat et al, 2006; D’lppoliti et al, 2010; Anderson and Bell, 2011; Nairn and Fawcett, 2013) were used to characterize heat wave mortality across the United States. The goal was to identify if certain definitions perform better or worse than others. Overall every definition performed poorly, resulting in high False-Alarm Ratios and low Heidke Skill Scores. However, the Nairn and Fawcett (2013) and Anderson and Bell (2011) definitions performed consistently better than the other definitions. Despite several limitations, the results of this study indicate that the heat wave definitions need refinement. Additionally, the Nairn and Fawcett (2013) definition could be one of the best definitions for assessing heat waves and heat-related mortality.

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No description available.

Wave energy is a major driver for many coastal processes and influences wetland vegetation and shoreline stability. Coastal conservation and restoration projects often include wave climate estimations in the decision-making process for project design. The current method primarily used to estimate a project area's wave climate is the use of wind-wave models. These models use wind speed, wind direction, bathymetry, and fetch to estimate site-specific wave activity. However, these models neglect boat wake which is an important contributor to wave energy in fetch-limited environments. This study used site-specific wave measurements to compare wind-protected and open sites in Back Bay, Mississippi. Study results demonstrated that some protected sites experienced similar or even higher wave activity when compared to the open sites. These findings indicate that excluding boat activity from wave climate estimations could lead to an under-estimation of site-specific wave activity.