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1
Suoja, Nicole Marie. "Directional wavenumber characteristics of short sea waves." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/88473.
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Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 2000.<br>Includes bibliographical references (leaves 134-141).<br>by Nicole Marie Suoja.<br>Ph.D.
2
Kwok, Loong-Piu. "Viscous cross-waves: Stability and bifurcation." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184441.
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In the first part of this thesis, the nonlinear Schrodinger equation for inviscid cross-waves near onset is found to be modified by viscous linear damping and detuning. The accompanying boundary condition at the wavemaker is also modified by damping from the wavemaker meniscus. The relative contributions of the free-surface, sidewalls, bottom, and wavemaker viscous boundary layers are computed. It is shown that viscous dissipation due to the wavemaker meniscus breaks the symmetry of the neutral curve. In the second part, existence and stability of steady solutions to the nonlinear Schrodinger equation are examined numerically. It is found that at forcing frequency above a critical value, f(c), only one solution exists. However, below f(c), multiple steady solutions, the number of which is determined, are possible. This multiplicity leads to hysteresis for f < f(c), in agreement with observation. A Hopf bifurcation of the steady solutions is found. This bifurcation is compared with the transition from unmodulated to periodically modulated cross-waves observed experimentally.
3
Cohen, Jennifer Esther. "Theory of turbulent wind over fast and slow waves." Thesis, University of Cambridge, 1997. https://www.repository.cam.ac.uk/handle/1810/283717.
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Sun, Haili. "Ray-tracing internal wave/wave interactions and spectral energy transfer /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/10973.
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Larsson, Ashley Ian. "Mathematical aspects of wave theory for inhomogeneous materials /." Title page, table of contents and summary only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09phl334.pdf.
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6
Dolven, Eric T. "Seaquake waves - standing wave dynamics with Faraday excitation and radiative loss /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/6785.
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7
Dally, William R. "Wave transformation in the surf zone." Gainesville, FL, 1987. http://www.archive.org/details/wavetransformati00dall.
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8
Schlottmann, Robert Brian. "A path integral formulation of elastic wave propagation /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004372.
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Decent, Stephen Paul. "Hysteresis and mode competition in Faraday waves." Thesis, University of St Andrews, 1996. http://hdl.handle.net/10023/14054.
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Faraday waves arise on the surface of a liquid in a container that is undergoing vertical periodic oscillations. We investigate two-dimensional Faraday waves in a long rectangular container, both theoretically and experimentally. Hysteresis occurs when both finite amplitude solutions and the flat surface solution are available. We derive a nonlinear model of a standing wave, extending the Lagrangian method of Miles (1976). The model is used to investigate hysteresis. It is found necessary to retain cubic damping, cubic forcing and the fifth-order conservative term in order to achieve agreement with experiments. The fifth-order conservative term was omitted from all previous studies of Faraday waves. Stable limit cycles are found to arise from this single-mode equation. We examine the structure of this new solution in detail, both analytically and numerically. We describe local bifurcations using a multiple time scales analysis and global bifurcations using Melnikov's method. The coefficients of linear and cubic damping are derived for a standing wave in a rectangular container by considering energy dissipation in the main body of the fluid (due to potential flow and streaming) and in boundary layers at the sidewalls and at the surface. Surface contamination, due to the presence of a thin viscoelastic surface film, creates a boundary layer at the surface which causes enhanced dissipation comparable to, or greater than, that caused by the boundary layers at the walls of the container. Three-mode interaction equations are used to model intermittency and complex modulations which are found to arise from a sideband instability mechanism similar to that of Eckhaus (1963) and Benjamin & Feir (1967). The role of cubic and fifth-order nonlinear terms on this instability mechanism is examined. Theoretical results are found to compare quite favourably with experimental data.
10
Podo, Smardie D. "Comparison of layering effects in the propagation of transient planar stress waves." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/18378.
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Hoseini, Sayed Mohammad. "Solitary wave interaction and evolution." Access electronically, 2007. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20080221.110619/index.html.
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Edwin, Patricia Mary. "Magnetohydrodynamic waves in structured atmospheres." Thesis, University of St Andrews, 1985. http://hdl.handle.net/10023/2701.
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The effect of structuring, in the form of magnetic or density inhomogeneities, on the magnetohydrodynamic (mhd) waves of an infinite plasma is investigated. The appropriate dispersion formulae, in both Cartesian and cylindrical polar coordinate geometries, are derived. The main properties of the allowable modes in structured plasmas are described, particularly those featuring in a slender inhomogeneity. The inclusion of non-adiabatic effects is examined, specifically for a thermally dissipative, unstratified, finite structure and for a slender inhomogeneity in a stratified medium. The dissipative time scales of slender structures are shown to have a dependence on the Peclet number. Growth factors appropriate to these time scales for the overstable motions of a thermally dissipative, Boussinesq fluid are derived. For the linear analysis of a slender structure it is shown that the dispersive nature of the waves is deducible from the simplified one-dimensional equations. The analysis is extended, for slender structures, to nonlinear motions and the governing equation representing an effective balance between nonlinear, dispersive and dissipative effects, the Benjamin-Ono-Burgers equation, is established. The solutions of this equation are considered and, for weakly-dissipative systems, are shown to be slowly decaying solitons. The importance, in the context of group velocity, of the dispersive nature of waves in ducted structures is discussed and analogies are made with other ducted waves, for example, the Love waves of seismology. It is suggested that the behaviour of such waves, following an impulse, may account for the range of oscillatory behaviour, the quasi-periodic and short time scales, observed in both the solar corona and Earth's magnetosphere. Density variations across a structure and the structure's curvature, with possible applications to coronal loops, are also considered. Further suggestions for possibly identifying some of the theoretical results with observed behaviour in sunspots, chromospheric fibrils and spicules are also made.
13
Pack, Jeong-Ki. "A wave-kinetic numerical method for the propagation of optical waves." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/104527.
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Hurlebaus, Stefan. "Laser generation and detection techniques for developing transfer functions to characterize the effect of geometry on elastic wave propagation." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/20742.
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Luker, L. Dwight. "Investigation of a cylindrical nonacoustic-wavenumber calibration array." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/15885.
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Giuliani, Chiara. "Alteration of ocean waves by periodic submerged structures for renewable energy extraction." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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Questa tesi si concentra sul comportamento di strutture immerse e sulla loro interazione con fenomeni ondosi oceanici allo scopo di modificarne l’ampiezza in superficie. Si suppone che queste strutture siano disposte sul fondale marino secondo schemi geometrici ricorrenti, per esempio lenti. Opportune disposizioni strutturali possono indurre un’interferenza costruttiva sulle onde di superficie, le quali presentano tipicamente un carattere pseudo-periodico nel tempo e nello spazio aumentandone così l’ampiezza.
Noto che l’energia delle onde di superficie è proporzionale alla loro ampiezza, i risultati proposti in questa ricerca possono essere utilizzati per migliorare, in maniera del tutto sostenibile, l’efficienza dei dispositivi che sfruttano il moto ondoso per l’estrazione di energia rinnovabile, anche noti come energy harvesters. Per questi ultimi infatti l’efficienza della conversione dell’energia dipende dalla variazione altimetrica fra la cresta e il ventre dell’onda.
Nello studio del problema, si considereranno le equazioni classiche di Navier-Stokes applicate al caso di fondali medio bassi (shallow waters). Successivamente teorie complesse per lo studio di sistemi periodici (già utilizzate in altri campi come la fisica quantistica e l’elettromagnetismo), verranno applicate per descrivere l’interazione tra le onde e il fondale periodico. Tale formulazione consentirà di progettare le strutture sul fondale capaci ottimizzare l’ampiezza dell’onda rispetto al caso di fondale indisturbato.
17
Liu, Faqi. "Surface multiple attenuation operators in the plane wave domain : theory and applications /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Guddati, Murthy Narasimha. "Efficient methods for modeling transient wave propagation in unbounded domains /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Wong, Chik Him. "A theoretical study on the static and dynamic transport properties of classical wave in 1D random media /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202007%20WONG.
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Johnson, Mark Alden Misra Anil. "The effect of normal and shear stresses on wave propagation through a fracture." Diss., UMK access, 2007.
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Thesis (Ph. D.)--School of Computing and Engineering and Dept. of Physics. University of Missouri--Kansas City, 2007.<br>"A dissertation in engineering and physics." Advisor: Anil Misra. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed July 30, 2008. Includes bibliographical references (leaf 93 ). Online version of the print edition.
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Donnelly, Cara. "Shearing waves and the MRI dynamo in stratified accretion discs." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/246452.
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Accretion discs efficiently transport angular momentum by a wide variety of as yet imperfectly understood mechanisms, with profound implications for the disc lifetime and planet formation. We discuss two different methods of angular momentum transport: first, generation of acoustic waves by mixing of inertial waves, and second, the generation of a self-sustaining magnetic field via the magnetorotational instability (MRI) which would be a source of dissipative turbulence. Previous local simulations of the MRI have shown that the dynamo changes character on addition of vertical stratification. We investigate numerically 3D hydrodynamic shearing waves with a conserved Hermitian form in an isothermal disc with vertical gravity, and describe the associated symplectic structure. We continue with a numerical investigation into the linear evolution of the MRI and the undular magnetic buoyancy instability in isolated flux regions and characterise the resultant quasi-linear EMFs as a function of height above the midplane. We combine this with an analytic description of the linear modes under an assumption of a poloidal-toroidal scale separation. Finally, we use RAMSES to perform full MHD simulations in a zero net flux shearing box, followed by spatial and a novel temporal averaging to reveal the essential structure of the dynamo. We find that inertial modes may be efficiently converted into acoustic modes for "bending waves", despite a fundamental ambiguity in the inertial mode structure. With our linear MRI and the undular magnetic buoyancy modes we find the localisation of the instability high in the atmosphere becomes determined by magnetic buoyancy rather than field strength for small enough azimuthal wavenumber, and that the critical Alfven speed below which the dynamo can operate increases with increasing distance from the midplane. We calculate analytically quasi-linear EMFs which predict both a vertical propagation of toroidal field and a method for creation of radial field. From our fully nonlinear calculations we find an electromotive force in phase with the toroidal field, which is itself 3π/2 out of phase with the radial (sheared) field at the midplane, and good agreement with our quasi-linear analytics. We have identified an efficient mechanism for generating acoustic waves in a disc. In our investigation of the accretion disc dynamo, we have reproduced analytically the EMFs calculated in our simulations, given arguments based on the phase of relevant quantities, several correlation integrals and the scalings suggested by our analytic work. Our analysis contributes significantly to an explanation for the dynamo in an accretion disc.
22
Chiu, Ching-Sang Denner Warren W. "Report on the Office of Naval Research USA-China Conference on Shallow Water Acoustics, December 18-21, 1995." Monterey, CA : Naval Postgraduate School, 1997. http://catalog.hathitrust.org/api/volumes/oclc/37486128.html.
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Chambers, Kit. "Seismological modelling of global earth structure." Thesis, University of Oxford, 2005. http://ora.ox.ac.uk/objects/uuid:68d66555-8948-404e-888e-48952ccf989d.
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<strong>Upper mantle discontinuities from PP- and SS-precursors</strong> The 410km discontinuity is examined using two global datasets of precursors to the PP and SS phases. The precursor amplitudes are used to constrain the impedance contrast, and examine lateral variations in the reflection coefficient of the discontinuity. P- and S-wave reflection amplitudes vary over different scale lengths, which could be due to the presence of melt, water or other chemical heterogeneities in the transition zone. Models for 410-topography are also derived, and the relationship between topography and transition zone seismic velocity anomalies examined. A moderate negative correlation exists between long wavelength 410-topography and transition zone velocity anomalies. However, when shorter wavelengths are included the relationship becomes more complex, and in some regions positive correlations are seen. This suggests that long wavelength variation of discontinuity topography and seismic velocity, is due to thermal effects. However, at shorter wavelengths the influence of chemical heterogeneities becomes important. Different spectra for thermal and chemical heterogeneity suggests that chemical anomalies can survive in convecting mantle. <strong>Lower mantle reflectors and S-wave scattering</strong> The lowermost mantle is investigated using a phase stripping technique and two migration methods: a backprojection, and a scheme with weights based on the Generalised Radon Transform. Resolution of the results is tested by migrating synthetic datasets. In some regions the results can be simulated using fairly simple distributions of point scatterers, but elsewhere the results require more complicated structures. The results identify several important properties of the D" region including reflectors within the D" region and a complex pattern of positive and negative scattering potentials near the core-mantle boundary. The results also show the presence of an intermittent D" discontinuity which is not a continuous, nor a global, feature. This suggests that the D" discontinuity is caused by either localised structures, such as thermal or chemical heterogeneity, or a global boundary with a variable impedance contrast.
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Yoon, Sungsoo. "Array-Based Measurements of Surface Wave Dispersion and Attenuation Using Frequency-Wavenumber Analysis." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7246.
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Surface wave methods have been used to determine dynamic properties of near-surface soils in geotechnical engineering for the past 50 years. Although the capabilities of engineering surface wave methods have improved in recent years due to several advances, several issues including (1) near-field effects, (2) combined active and passive measurements, and (3) accurate measurements of surface wave attenuation still require study to further improve the capabilities of modern surface wave methods.
Near-field effects have been studied for traditional surface wave methods with two receivers and several filtering criteria to mitigate the effects have been recommended. However, these filtering criteria are not applicable to surface wave methods with multiple receivers. Moreover, the criteria are not quantitatively based and do not account for different types of soil profiles, which strongly influence near-field effects. A new study of near-field effects on surface wave methods with multiple receivers was conducted with numerical and experimental methods. Two normalized parameters were developed to capture near-field effects. Quantitatively based near-field effect criteria for an ideal homogeneous half-space and three typical soil profiles are presented.
Combining active and passive surface wave measurements allows developing a shear wave velocity profile to greater depth without sacrificing the near-surface resolution offered by active measurements. Generally, active and passive measurements overlap in the frequency range from approximately 4 to 10 Hz, and there are often systematic differences between the two measurements. The systematic errors in active and passive surface wave methods were explored to explain and resolve the differences, allowing for a more accurate composite dispersion curve.
The accuracy of measured surface wave attenuation is improved by properly accounting for (1) geometric spreading, (2) near-field effects, and (3) ambient noise. In this study, a traditional estimation method and a frequency-wavenumber method utilizing sub-arrays were investigated using displacement data from numerical simulations, focusing on near-field and ambient noise effects. Detailed procedures for the frequency-wavenumber estimation method are developed based on a study of the primary factors affecting attenuation estimates. The two methods are also evaluated using experimental displacement data obtained from surface wave field measurements with three different arrays.
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Cardona, Orozco Yuley Mildrey. "Enhanced vertical mixing within mesoscale eddies due to high frequency winds in the south China sea." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/44917.
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The South China Sea is a marginal basin with a complex circulation influenced by the East Asian Monsoon, river discharge and intricate bathymetry. As a result, both the mesoscale eddy field and the near-inertial energy distribution display large spatial variability and they strongly influence the oceanic transport and mixing.
With an ensemble of numerical integrations using a regional ocean model, this work investigates how the temporal resolution of the atmospheric forcing fields modifies the horizontal and vertical velocity patterns and impacts the transport properties in the basin. The response of the mesoscale circulation in the South China Sea is investigated under three different forcing conditions: monthly, daily and six-hourly momentum and heat fluxes. While the horizontal circulation does not display significant differences, the representation of the vertical velocity field displays high sensitivity to the frequency of the wind forcing. If the wind field contains energy at the inertial frequency or higher (daily and six-hourly cases), then Vortex Rossby waves and near inertial waves are excited as ageostrophic expression of the vigorous eddy field. Those waves dominate the vertical velocity field in the mixed layer (vortex Rossby waves) and below the first hundred meters (near inertial waves) and they are responsible for the differences in the vertical transport properties under the various forcing fields as quantified by frequency spectra, vertical velocity profiles and vertical dispersion of Lagrangian tracers.
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Wan, Bangjun. "A numerical study of conjugate flows and flat-centred internal solitary waves in a continuously stratified fluid." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq25896.pdf.
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Afonja, Adetoso J. "Dynamics of Pitching Wave Energy Converter with Resonant U-Tank Power Extraction Device." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/98782.
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This research revolves around the concept design and theoretical validation of a new type of wave energy converter (WEC), comprising a pitching floater integrated with a resonant U-tank (RUT) and a Wells turbine as power take-off (PTO). Theoretical formulation of a fully coupled multi-body dynamic system, incorporating the thermodynamic processes of the RUT air chamber, its interaction with the PTO dynamics and their coupling with the floater is presented.
Inaccuracies of the dynamic modeling of RUT based on Lloyd's low order model, which assumes constant hydrodynamic parameters irrespective of the frequency, are demonstrated by a series of high fidelity CFD simulations. These simulations are a systematic series of fully viscous turbulent simulations, using unsteady RANSE solvers, of the water sloshing at different frequencies of oscillation. Calibration of Lloyd’s model with CFD results evidenced that the RUT hydrodynamic parameters are not invariant to frequency.
A numerical model was developed based on Simulink WEC-Sim libraries to solve the non-linear thermo-hydrodynamic equations of the device in time domain. For power assessment, parametric investigations are conducted by varying the main dimensions of the RUT and power RAOs were computed for each iteration.
Performance in irregular sea state are assessed using a statistical approach with the assumption of linear wave theory. By superimposing spectrum energy density from two resource sites with RAO, mean annual energy production (MEAP) are computed. The predicted MEAP favorably compares with other existing devices, confirming the superior efficiency of the new proposed device over a larger range of incident wave frequency.<br>M.S.<br>This study present results of an investigation into a new type of wave energy converter which can be deployed in ocean and by its pitch response motion, it can harvest wave energy and convert it to electrical energy. This device consist of a floater, a U-tank (resonant U-tank) with sloshing water free to oscillate in response to the floater motion and a pneumatic turbine which produces power as air is forced to travel across it. The pneumatic turbine is used as the power take-off (PTO) device. A medium fidelity approach was taken to carry out this study by applying Lloyd’s model which describes the motion of the sloshing water in a resonant U-tank. Computational fluid dynamics (CFD) studies were carried out to calibrate the hydrodynamic parameters of the resonant U-tank as described by Lloyd and it was discovered that these parameters are frequency dependent, therefore Lloyd’s model was modelled to be frequency dependent. The mathematical formulation coupling the thermodynamic evolution of air in the resonant U-tank chamber, modified Lloyd’s sloshing water equation, floater dynamics and PTO were presented for the integrated system. These set of thermo-hydrodynamic equations were solved with a numerical model developed using MATLAB/Simulink WEC-Sim Libraries in time domain in other to capture the non-linearity arising from the coupled dynamics. To assess the annual energy productivity of the device, wave statistical data from two resource sites, Western Hawaii and Eel River were selected and used to carrying out computations on different iterations of the device by varying the tank’s main dimensions. This results were promising with the most performing device iteration yielding mean annual energy production of 579 MWh for Western Hawaii.
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McCorkle, Tricia Dawn. "Math, music, and membranes: A historical survey of the question "can one hear the shape of a drum"?" CSUSB ScholarWorks, 2005. https://scholarworks.lib.csusb.edu/etd-project/2933.
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In 1966 Mark Kac posed an interesting question regarding vibrating membranes and the sounds they make. His article entitled "Can One Hear the Shape of a Drum?", which appeared in The American Mathematical Monthly, generated much interest and scholarly debate. The evolution of Kac's intriguing question will be the subject of this project.
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Kuechler, Sebastian. "Wave Propagation in an Elastic Half-Space with Quadratic Nonlinearity." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19823.
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This study investigates wave propagation in an elastic half-space with quadratic nonlinearity due to a line load on the surface. The consideration of this problem is one of the well known Lamb problems. Even since Lamb's original solution, numerous investigators have obtained solutions to many different variants of the Lamb problem. However, most of the solutions existing in the current literature are limited to wave propagation in a linear elastic half-space. In this work, the Lamb problem in an elastic half-space with quadratic nonlinearity is considered. For this, the problem is first formulated as a hyperbolic system of conservation laws, which is then solved numerically using a semi-discrete central scheme. The numerical method is implemented using the package CentPack. The accuracy of the numerical method is first studied by comparing the numerical solution with the analytical solution for a half-space with linear response (the original Lamb's problem). The numerical results for the half-space with quadratic nonlinearity are than studied using signal-processing tools such as the fast Fourier transform (FFT) in order to analyze and interpret any nonlinear effects. This in particular gives the possibility to evaluate the excitation of higher order harmonics whose amplitude is used to infer material properties. To quantify and compare the nonlinearity of different materials, two parameters are introduced; these parameters are similar to the acoustical nonlinearity parameter for plane waves.
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Ghazaryan, Anna R. "Nonlinear convective instability of fronts a case study /." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1117552079.
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Thesis (Ph.D.)--Ohio State University, 2005.<br>Title from first page of PDF file. Document formatted into pages; contains ix, 176 p.; also includes graphics. Includes bibliographical references (p. 172-176). Available online via OhioLINK's ETD Center
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Ardag, Dorukhan. "Examining Optimal Form of Two Scale Approximation (TSA) for Calculating Snl Source Term." UNF Digital Commons, 2014. http://digitalcommons.unf.edu/etd/483.
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Nonlinear four-wave interactions (Snl) are critical for acquiring realistic spectra needed by operational wave models. High computational demand to calculate these interactions led to an approximation method named the Discrete Interaction Approximation (DIA) to be used broadly in the major operational wave models for a long time. However, the accuracy of the DIA has been controversial since it was first introduced and more precise approximations such as the Two Scale Approximation (TSA in short) are now available. The only issue with the initial TSA`s efficiency is performing an order of a magnitude slower than the DIA in speed. This study questions the exactness of the DIA while trying to increase the competence of the TSA by making improvements on its execution time. Particularly, in this thesis, the main effort is on the local scale term of the TSA since it is the part that consumes the most time while running the code. The findings of this work imply that the TSA can improve its operation speed significantly while maintaining its accuracy with making alterations in the code. By decreasing the number of bands in the local scale it is possible to run the TSA up to 7.5 faster than its initial version.
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Benevides, Francis Leo. "Estimating ocean wave directional spectra from measurements of water particle motion by a surface buoy acoustic ranging system." Thesis, 1990. http://hdl.handle.net/10125/10001.
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Ndebele, Bright Bekithemba. "The diffraction, reflection and propagation of cylindrical shock wave segments." Thesis, 2017. http://hdl.handle.net/10539/23544.
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A thesis submitted to the Faculty of Engineering and the Built Environment, University of
the Witwatersrand, Johannesburg, in ful lment of the requirements for the degree of Doctor
of Philosophy.
Johannesburg, May 2017<br>Shock{waves (shocks) exist in various shapes; restricted to two dimensions some examples
are planar, cylindrical, parabolic and elliptical. However, most shock{wave research has
been focussed mostly on plane shocks. In this research, the scope is expanded to cylindrical
shock{wave segments where a plane shock can be viewed as a cylindrical shock segment
(referred to as a cylindrical shock) with a large radius of curvature; with this view, the
expectations are that cylindrical and plane shocks behave similarly although with
quantitative di erences.
Whereas plane shocks have constant orientation, constant strength and can be imagined to
extend unbounded, cylindrical shock segments demand that both ends be bound; this leads
to spatial constraints, shock strength varying with respect to radius and shock orientation
being non-constant. Three shock phenomena were investigated: di raction, re
ection and
propagation in converging diverging nozzles. Shock{tube experiments were run for shocks
with a radius of 165 mm and strength between Mach numbers 1.2 and 1.7. Complementing
these were Computational Fluid Dynamics (CFD) and Geometric Shock Dynamics (GSD)
simulations where GSD relies on Whitham's equations.
On shock di raction, cylindrical shocks were shown to behave qualitatively like plane
shocks. Upon encountering a sharp corner, expansion waves propagate along the shock.
However, after re
ecting o the opposite wall they become compression waves and form a
'Mach re
ection (MR)' like con guration on the shock front. A method for calculating the
locus of the expansion waves based on Whitham's theory is presented, which on comparison
with CFD simulations gives good correlation. Comparisons of shock pro les calculated
using Whitham's theory and CFD is also made; it showed good correspondence before the
formation of MR like con gurations after which the pro les di er.
The re
ection of cylindrical shocks was investigated from both an experimental and
numerical perspective. Shock{tube experiments were run for shocks propagating on concave
cylindrical walls with radii of 100 mm, 180 mm, 140 mm and 82 mm, the range was
expanded by use of CFD. An expression for calculating the locus of the MR that forms on
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the shock front was derived which generalises onto plane shocks. Two limits were
recognised, one where shock radius is much greater than wall radius and another where
shock radius is much smaller. The former corresponds to a cylindrical shock on a plane wall
while the latter a plane shock on a cylindrical wall as illustrated by the data gathered.
Cylindrical shock propagation in converging-diverging nozzles was also investigated. In this
case, the phenomena at play are di raction, re
ection and focusing, a combination which
results in a complex evolution of the shock front. Two types of channels were investigated,
one formed from a 3rd order polynomial and another from circular arcs. In both cases, wall
signal were generated on either side of the shock which split the shock{front into three
sections. The decreasing channel cross{section area causes the shock strength to increase
resulting in very weak MR formation on the shock front. Channels from circular walls
exhibit a single peak in the centre line shock strength while that from polynomial pro le
walls results in a double peak. This was then related to type of wall disturbance generated.<br>MT 2017
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"A study of non-divergent propagation of whistler waves in plasma ducts." Chinese University of Hong Kong, 1987. http://library.cuhk.edu.hk/record=b5885785.
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by Ng Chi Shing.<br>Chinese title in romanization: Shao sheng bo zai deng li zi ti guan dao nei di fei fa san zhuan bo.<br>Thesis (M.Ph.)--Chinese University of Hong Kong, 1987.<br>Bibliography: leaf 70.
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Ramberg, Andreas. "Ocean Waves Estimation : An Artificial Intelligence Approach." Thesis, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-35736.
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This thesis aims to solve the mathematical inverse problem of characterizing sea waves based on the responses obtained from a marine vessel sailing under certain sea conditions. By researching this problem the thesis contributes to the marine industry by improving products that are using ocean behavior for controlling ship's dynamics. Knowledge about the current state of the sea, such as the wave frequency and height, is important for navigation, control, and for the safety of a vessel. This information can be retrieved from specialized weather reports. However, such information is not at all time possible to obtain during a voyage, and if so usually comes with a certain delay. Therefore this thesis seeks solutions that can estimate on-line the waves' state using methods in the field of Artificial Intelligence. The specific investigation methods are Transfer Functions augmented with Genetic Algorithm, Artificial Neural Networks and Case-Based Reasoning. These methods have been configured and validated using the n-fold cross validation method. All the methods have been tested with an actual implementation. The algorithms have been trained with data acquired from a marine simulation program developed in Simulink. The methods have also been trained and tested using monitored data acquired from an actual ship sailing on the Baltic Sea as well as wave data obtained from a buoy located nearby the vessel's route. The proposed methods have been compared with state-of-the art reports in order evaluate the novelty of the research and its potential applications in industry. The results in this thesis show that the proposed methods can in fact be used for solving the inverse problem. It was also found that among the investigated methods it is the Transfer Function augmented with Genetic Algorithm which yields best results. This Master Thesis is conducted under the Master of Engineering Program in Robotics at Mälardalens högskola in Västerås, Sweden. The thesis was proposed by Q-TAGG R&D AB in Västerås, Sweden, a company which specializes in marine vessel dynamics research.
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Wang, Shih-ting, and 王世婷. "The time domain motion analysis of the Wave Piercing Catamaran ship in waves by two-dimensional theory." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/22560588282189918618.
Full textAbstract:
碩士<br>國立成功大學<br>系統及船舶機電工程學系碩博士班<br>97<br>In the paper, based on the strip theory, the time domain simulation for the motions of the wave-piercing catamaran ship in longitudinal waves is calculated by the 4th Runge- Kutta method. The nonlinear effects caused by the change of underwater hull body, the large wave amplitude and the large ship motion are considered and treated by the quasi-steady method. After comparing with the conventional catamaran, we find that the central bow hull body of wave-piercing catamaran ship works well at some specific wave frequencies, especially while pitch and heave motions are large. The present results prove that the wave-piercing catamaran ship indeed has the superior sea keeping performance at some wave conditions.
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Ikeda, Junior Isamu 1969. "Analysis of wave motion in irregular layered media using a finite-element perturbation method." 2008. http://hdl.handle.net/2152/17966.
Full textAbstract:
A technique that allows for nonparallel interfaces and lateral inhomogeneities in an irregular layered medium is described. The formulation combines a semidiscrete finite-element technique with a perturbation method, providing an approximate treatment of wave propagation in irregular layered media. The procedure treats the irregularities as perturbations with respect to a reference, horizontally-layered, laterally-homogeneous medium and produces approximations of the perturbed wave motion with little additional computation effort. Within the framework of the method, consistent transmitting boundaries and other semidiscrete hyperelements as well as Green’s functions, already available for regular layered media, can be reformulated. The method is relevant in problems of foundation dynamics, ground response to seismic waves and site characterization. Example problems are presented toward evaluation of the effectiveness of the method.<br>text
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Blackmore, Natalie Lynn. "studies on the brown alga dictyopteris longifolia (Dictyotales), with special reference to the effects of wave action." Thesis, 2016. http://hdl.handle.net/10539/20835.
Full textAbstract:
A the'.is submitted to the Faculty of Science, University
of the Witwatersrand, Johannesburg, in the fulfillment of
the requirements of the Degree of Magister Scientae.
June 1992<br>Aspects of the brown alga Pict~'ppt;eris lQ..n..qifolia at. Palm
Beach, Natal, were investigated wi\'-;.hspecial reference to
the effect of wave expozu~e~
A description of the species is giv~n and the
nomencluture discussed. D~strib1i.ltion of n. ).or~gifolia was
det~rmimad from literature and herbarium speof.mens .
various r(\~:~thodosf measuring wave exposure were assessed
and review~~d. At'!;:.emptswere made to quantify sand
abrasion and deposition in tihe scudy si.tes.
Morphological and structural aspect;s of the cha LLus were
found to vary considerably with season and wave exposure"
Light and scanning electron microscopy studie.s indicated
the relatjvely complex cell organisation of this brown
alga.
The prolific regeneration from various thallus sections
of .Q. longifolia indicate that regenerat.ion is an
important survival strate 'JY following damage.
Sexual reproduction and tetrasporogenesis were
investigated. Sex.ual reproduction was not prolific in the
field, however, tetraspores were abundant and are
believed to be particul~rly importcmt in high wave
exposure areas.
11. _j.Q.ngi;f'clige,x_periences a range of environmental
conditions and responds to these with morphological,
structural and reproductive &daptations.
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Keefer, Olivia A. "Operator splitting methods for Maxwell's equations in dispersive media." Thesis, 2012. http://hdl.handle.net/1957/30019.
Full textAbstract:
Accurate modeling and simulation of wave propagation in dispersive dielectrics such as water, human tissue and sand, among others, has a variety of applications. For example in medical imaging, electromagnetic waves are used to interrogate human tissue in a non-invasive manner to detect anomalies that could be cancerous. In non-destructive evaluation of materials, such interrogation is used to detect defects in these materials.
In this thesis we present the construction and analysis of two novel operator splitting methods for Maxwell's equations in dispersive media of Debye type which are used to model wave propagation in polar materials like water and human tissue. We construct a sequential and a symmetrized operator splitting scheme which are first order, and second order, respectively, accurate in time. Both schemes are second order accurate in space. The operator splitting methods are shown to be unconditionally stable via energy techniques. Their accuracy and stability properties are compared to established schemes like the Yee or FDTD scheme and the Crank-Nicolson scheme. Finally, results of numerical simulations are presented that confirm the theoretical analysis.<br>Graduation date: 2012<br>Access restricted to the OSU Community at author's request from June 20, 2012 - Dec. 20, 2012
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Bansal, Reeshidev 1978. "Seismic characterization of naturally fractured reservoirs." Thesis, 2007. http://hdl.handle.net/2152/3767.
Full textAbstract:
Many hydrocarbon reservoirs have sufficient porosity but low permeability (for example, tight gas sands and coal beds). However, such reservoirs are often naturally fractured. The fracture patterns in these reservoirs can control flow and transport properties, and therefore, play an important role in drilling production wells. On the scale of seismic wavelengths, closely spaced parallel fractures behave like an anisotropic media, which precludes the response of individual fractures in the seismic data. There are a number of fracture parameters which are needed to fully characterize a fractured reservoir. However, seismic data may reveal only certain fracture parameters and those are fracture orientation, crack density and fracture infill. Most of the widely used fracture characterization methods such as Swave splitting analysis or amplitude vs. offset and azimuth (AVOA) analysis fail to render desired results in laterally varying media. I have conducted a systematic study of the response of fractured reservoirs with laterally varying elastic and fracture properties, and I have developed a scheme to invert for the fracture parameters. I have implemented a 3D finite-difference method to generate multicomponent synthetic seismic data in general anisotropic media. I applied the finite-difference algorithm in both Standard and Rotated Staggered grids. Standard Staggered grid is used for media having symmetry up to orthorhombic (isotropic, transversely isotropic, and orthorhombic), whereas Rotated Staggered grid is implemented for monoclinic and triclinic media. I have also developed an efficient and accurate ray-bending algorithm to compute seismic traveltimes in 3D anisotropic media. AVOA analysis is equivalent to the first-order Born approximation. However, AVOA analysis can be applied only in a laterally uniform medium, whereas the Born-approximation does not pose any restriction on the subsurface structure. I have developed an inversion scheme based on a ray-Born approximation to invert for the fracture parameters. Best results are achieved when both vertical and horizontal components of the seismic data are inverted simultaneously. I have also developed an efficient positivity constraint which forbids the inverted fracture parameters to be negative in value. I have implemented the inversion scheme in the frequency domain and I show, using various numerical examples, that all frequency samples up to the Nyquist are not required to achieve desired inversion results.
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Kumar, Vijay. "Installation and Operation of Air-Sea Flux Measuring System on Board Indian Research Ships." Thesis, 2017. http://etd.iisc.ernet.in/2005/3778.
Full textAbstract:
Exchange of mass (water vapor), momentum, and energy between atmosphere andocean has profound influence on weather and climate. This exchange takes place at the air-sea interface, which is part of the marine atmospheric boundary layer. Various empirical relations are being used for estimating these fluxes in numericalweather and climate models but their accuracies are not sufficiently verified or tested over the Indian Ocean. The main difficulty is that vast areas of open oceans are not easily accessible. The marine environment is very corrosive and unattended long term and accurate measurements are extremely expensive. India has research ships that spend most of their time over the seas around India but that opportunity is yet to be exploited. To address this, an air-sea flux measurement system for operation on board research ships was planned. The system was tested on board Indian Research Vessels ORV SagarKanya during its cruise SK-296 in the Bay of Bengal (BoB) in July-August 2012, and NIO ship Sindhu Sadhana in June-July 2016. The complete set included instruments for measuring wind velocity, windspeed and direction, air and water temperature, humidity, pressure, all components of radiation and rainfall. In addition, ship motion was recorded at required sampling rate to correct for wind velocity. The set up facilitates the direct computation of sensible and latent heat fluxes using the eddy covariance method.
In this thesis, design and installation of meteorological and ship motion sensors onboard research ships, data collection and quality control, computation of fluxes of heat, moisture and momentum using eddy covariance method and their comparison with those derived from bulk method are described. A set of sensors (hereafter, flux measuring system) were mounted on a retractable boom, ~7 m long forward of the bow to minimize the flow disturbance caused by the ship superstructures. The wind observed in the ship frame was corrected for ship motion contaminations. During the CTCZ cruise period true mean wind speed was over 10 m/s and true wind direction was South/South-Westerly. True windspeedis computed combiningdata from the anemometer a compass connected to AWS and a GPS. Turbulent fluxes were computed from motion-corrected time-series of high frequency velocity, water vapor, and air temperature data. Covariance latent heat flux, sensible heat flux, and wind stress were obtained by cross-correlating the motion-corrected vertical velocity with fast humidity fluctuations measured with anIR hygrometer, temperate fluctuation from sonic anemometer and motion-corrected horizontal windfluctuations from sonic anemometer, respectively.
During the first attempt made in July-August 2012 as part of a cruise of CTCZ monsoonresearch program, observations were mainly taken in the North Bay of Bengal. The mean air-temperature and surface pressure were ~28 Deg C and ~998 hPa, respectively. Relative humidity was ~80%. Average wind speed varied in the range 4-12 m/s. The mean latent heat flux was 145 W/m2 , sensible heat flux was ~3 W/m2 and average sea-air temperature difference was ~ 0.7°C.
The Bay of Bengal boundary layer experiment (BoBBLE) was conducted during June-July 2016 and the NIO research ship Sindhu Sadhana was deployed. The same suite of sensors installed during CTCZ were used during BoBBLE. During daytime, peaks of hourly net heat fluxes (Qnet ) were around 600 Wm-2(positive if into the sea), whereas, night time values were around -250 W m-2. Sea surface temperature was always >28°C and maximum air temperature exceeded 29°C. During the experimental period the mean Qnet was around -24 Wm-2 from both eddy covariance and conventional bulk methods, but there are significant differences on individual days.The new flux system gives fluxes which are superior to what was available before.