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The influence of monochromatic waves interacting with a submerged bar structure is investigated through laboratory experiments in a wave flume. Wave profiles for a range of non-breaking, spilling, and plunging waves were analyzed for three offshore water depths through the interpretation of wave gauge and video imagery data. Evolution of propagating waves was reflected in data which showed increased amplitudes due to shoaling with subsequent breaking, transfer of single frequency spectrum from lower to higher frequency harmonics, and dissipation of energy after breaking onset. Comparisons of collected experimental data with previous theory developed by Yao et al (2013), Smith & Kraus (1991), Galvin (1968) for wave classification showed to be relatively accurate for both relative submergence and surf similarity methods. Wave breaking onset identified by instability in the wave crests allowed for measurements of breaking wave height and depth at breaking. Theory by Johnson (2006) and Goda (1974) compared to experimental data showed little agreement for predicting breaking wave heights. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xiv, 215 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 107-113).

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: George C. Hsiao, Dept. of Mathematical Sciences. Includes bibliographical references.

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Typescript, etc. / Digitized by Kansas State University Libraries

published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

The formulation and calculation of the electromagnetic fields scattered from, and the natural resonances of, a thin, perfectly conducting circular strip mounted on a perfectly conducting ground plane is presented. The fields are excited by an axial electric dipole, oriented normal to the surface of the ground plane. An electric field integral equation is formulated in terms of the induced surface current and solved in closed form in the quasi-static limit as an expansion of Chebyshev polynomials. In addition, the integral equation is solved for the general case by the method of moments (MOM). Numerical results are given which show the excellent agreement between the quasi-static and method of moments solutions. The MOM currents are used to determine the field scattered from the circular strip, in both the frequency and time domains. The frequency domain analysis is applied to the problem of fencing small vertical broadcast antennas. We find that appropriately designed fencing can enhance the ground wave of the antenna, while decreasing the sky wave. In addition, we determine that the radiation efficiency of the dipole is sensitive to the size of the circular strip, and that the radiation efficiency displays resonant behavior when the frequency of operation is near a natural resonance of the circular strip. We, also, calculate the time domain transient scattered fields for different circular strip geometries, using the MOM currents and GTD. By deemphasizing the low frequencies in the transient pulse spectrum, we obtain good agreement between the GTD early time scattering and the transient scattering determined from the MOM formulation. Using the MOM formulation, we determine the natural resonances of the circular strip. These resonances are divided into two classes: the exterior resonances and interior resonances. We show the pole trajectories for the first layer of exterior resonances for a wide range of strip height-to-radius ratios. In addition, we locate strong interior resonances which correspond to TM₀(pq) circular cavity modes. Included in these interior resonances are weakly damped resonances which correspond to the TM₀(p)₀ cavity modes. This is the first known report of these TM₀(p)₀ interior resonances for the circular strip geometry. We find that these resonances dominate the scattering in our problem. Using the transient scattered fields calculated from the MOM formulation as input and output data for a single input, single output identification algorithm, we identify the dominant poles in the scattered fields. We show that these dominant poles are those associated with the TM₀(p)₀ interior resonances of the circular strip. In addition, we show that by using intelligent filtering and source selection, a few resonances with higher damping can also be identified.

The generation and evolution of cross-waves in a channel are investigated analytically, numerically and experimentally. The derivation of the modulation equation governing the inviscid cross-wave amplitude yields the nonlinear Schrodinger equation with a homogeneous Robin boundary condition at the wavemaker. Either of two uniformly valid scalings--cross-wave amplitude of the same order as or much larger than the wavemaker amplitude--may be used in the derivations. The differences between the two scalings are discussed. The inviscid modulation equation is augmented by a linear damping term, the coefficient of which is determined empirically from the measured neutral stability curve. The viscous modulation equation is solved numerically. The theory is compared to experiments in a channel 30.9 cm wide, for mode n = 6, for frequencies close to the cutoff frequency 7.82 Hz. Measurements include the neutral stability curve, the onset of modulation, cross-wave phase along the channel, and cross-wave amplitude as functions of wavemaker amplitude, forcing frequency and distance from the wavemaker. These measurements are in good agreement with the numerical results. The results are also observed to be sensitive to viscous effects. Additionally, both numerical calculations and experiment reveal trapped and propagating modes. The trapped mode is most easily observed at positive detuning.

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