Dissertations / Theses on the topic 'Nonlinear internal waves'
To see the other types of publications on this topic, follow the link: Nonlinear internal waves.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 33 dissertations / theses for your research on the topic 'Nonlinear internal waves.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Fedorov, Alexey V. "Nonlinear effects in surface and internal waves /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9737309.
2
Dobra, Tom. "Nonlinear interactions of internal gravity waves." Thesis, University of Bristol, 2019. http://hdl.handle.net/1983/4a3f99e2-5e73-4c7c-8d3d-e1141fb23dda.
Abstract:
Internal waves carry more available energy than any other transmission system on Earth: lunar diurnal excitation drives 1 TW of wave power inside the world's oceans. Energy is transmitted over thousands of kilometres and individual waves may be hundreds of metres high. Where they break, they deposit their energy, and, in such regions, they greatly enhance the vertical transport of carbon dioxide, oxygen and heat. Despite their significance, much remains to be understood about internal waves, and this thesis explores some of these questions using a combination of experiments and theory. One way to generate internal waves is by sinusoidally oscillating the boundary of the fluid. A full spectrum of harmonics is generated, whose phases and amplitudes are predicted by perturbation theory. Their origin is identified solely as nonlinear geometric excitation at the boundary; no interactions between the harmonics of the same infinitely wide, monochromatic input are possible within the fluid. However, for narrow wave beams, resonant triadic wave-wave interactions are predicted using a novel numerical implementation of the singular two-dimensional Green's function. To verify the predictions, a new experiment was designed, consisting of an electronically actuated "magic carpet" inserted into the base of a tank. It perturbs the fluid lying above its surface to generate internal waves of almost any shape and size. The carpet is actuated by an array of 100 stepper motors, which are controlled by bespoke software that manages the timing in increments of 30 ns; this ensures precise spatiotemporal control of the waveform. The carpet itself is made of a neoprene-nylon composite, and its bending behaviour is modelled in detail to characterise the waveform imparted on the fluid. The experiments support the theoretical predictions, but also permit strongly nonlinear regimes, such as wave breaking, at amplitudes above the applicable domain of the theory.
3
Zhao, Zhongxiang. "A study of nonlinear internal waves in the northeastern South China Sea." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 11.38Mb, 181 p, 2005. http://wwwlib.umi.com/dissertations/fullcit/3157312.
4
Yuan, Chunxin. "The evolution of oceanic nonlinear internal waves over variable topography." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10053741/.
Abstract:
This thesis is concerned with the evolution of oceanic nonlinear internal waves over variable one-dimensional and two-dimensional topography. The methodology is based on a variable-coefficient Korteweg-de Vries (vKdV) equation and its vari- ants, including the Ostrovsky equation which takes rotation into account and a Kadomtsev-Petviashvili (KP) equation which extends these one-dimensional models to two space dimensions. In addition, a fully nonlinear and non-hydrostatic three- dimensional primitive equation model, MIT general circulation model (MITgcm), is invoked to provide supplementary analyses. First, the long-time combined effect of rotation and variable topography on the evolution of internal undular bore is stud- ied; then an initial mode-2 internal solitary wave propagating onto the continental shelf-slope in a three-layer fluid is investigated. After that, the research is extended to two-dimensional space in which submarine canyon and plateau topography are implemented to examine a mode-1 internal solitary wave propagating over these topographic features. Finally, the topographic effect on internal wave-wave interac- tions is examined using an initial ‘V-shape’ wave representing two interacting waves in the framework of the KP equation.
5
Alias, Azwani B. "Mathematical modelling of nonlinear internal waves in a rotating fluid." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/15861.
Abstract:
Large amplitude internal solitary waves in the coastal ocean are commonly modelled with the Korteweg-de Vries (KdV) equation or a closely related evolution equation. The characteristic feature of these models is the solitary wave solution, and it is well documented that these provide the basic paradigm for the interpretation of oceanic observations. However, often internal waves in the ocean survive for several inertial periods, and in that case, the KdV equation is supplemented with a linear non-local term representing the effects of background rotation, commonly called the Ostrovsky equation. This equation does not support solitary wave solutions, and instead a solitary-like initial condition collapses due to radiation of inertia-gravity waves, with instead the long-time outcome typically being an unsteady nonlinear wave packet. The KdV equation and the Ostrovsky equation are formulated on the assumption that only a single vertical mode is used. In this thesis we consider the situation when two vertical modes are used, due to a near-resonance between their respective linear long wave phase speeds. This phenomenon can be described by a pair of coupled Ostrovsky equations, which is derived asymptotically from the full set of Euler equations and solved numerically using a pseudo-spectral method. The derivation of a system of coupled Ostrovsky equations is an important extension of coupled KdV equations on the one hand, and a single Ostrovsky equation on the other hand. The analytic structure and dynamical behaviour of the system have been elucidated in two main cases. The first case is when there is no background shear flow, while the second case is when the background state contains current shear, and both cases lead to new solution types with rich dynamical behaviour. We demonstrate that solitary-like initial conditions typically collapse into two unsteady nonlinear wave packets, propagating with distinct speeds corresponding to the extremum value in the group velocities. However, a background shear flow allows for several types of dynamical behaviour, supporting both unsteady and steady nonlinear wave packets, propagating with the speeds which can be predicted from the linear dispersion relation. In addition, in some cases secondary wave packets are formed associated with certain resonances which also can be identified from the linear dispersion relation. Finally, as a by-product of this study it was shown that a background shear flow can lead to the anomalous version of the single Ostrovsky equation, which supports a steady wave packet.
6
Smith, Sean Paul. "Laboratory Experiments on Colliding Nonresonant Internal Wave Beams." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3300.
Abstract:
Internal waves are prominent fluid phenomena in both the atmosphere and ocean. Because internal waves have the ability to transfer a large amount of energy, they contribute to the global distribution of energy. This causes internal waves to influence global climate patterns and critical ocean mixing. Therefore, studying internal waves provides additional insight in how to model geophysical phenomena that directly impact our lives. There is a myriad of fluid phenomena with which internal waves can interact, including other internal waves. Equipment and processes are developed to perform laboratory experiments analyzing the interaction of two colliding nonresonant internal waves. Nonresonant interactions have not been a major focus in previous research. The goal of this study is to visualize the flow field, compare qualitative results to Tabaei et al., and determine the energy partition to the second-harmonic for eight unique interaction configurations. When two non-resonant internal waves collide, harmonics are formed at the sum and difference of multiples of the colliding waves' frequencies. In order to create the wave-wave interaction, two identical wave generators were designed and manufactured. The interaction flow field is visualized using synthetic schlieren and the energy entering and leaving the interaction region is analyzed. It is found that the energy partitioned to the harmonics is much more dependent on the general direction the colliding waves approach each other than on the angle. Depending on the configurations, between 0.5 and 7 percent of the energy within the colliding waves is partitioned to the second-harmonics. Interactions in which the colliding waves have opposite signed vertical wavenumber partition much more energy to the harmonics. Most of the energy entering the interaction is dissipated by viscous forces or leaves the interaction within the colliding waves. For all eight configurations studied, 5 to 8 percent of the energy entering the interaction has an unknown fate.
7
Stastna, Marek. "Large fully nonlinear solitary and solitary-like internal waves in the ocean." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ65262.pdf.
8
Lin, Duo-min Wu Theodore Y. T. Wu Theodore Y. T. "Run-up and nonlinear propagation of oceanic internal waves and their interactions /." Diss., Pasadena, Calif. : California Institute of Technology, 1996. http://resolver.caltech.edu/CaltechETD:etd-12192007-084353.
9
Kim, Won-Gyu 1962. "A Study of Nonlinear Dynamics in an Internal Water Wave Field in a Deep Ocean." Thesis, University of North Texas, 1996. https://digital.library.unt.edu/ark:/67531/metadc278092/.
Abstract:
The Hamiltonian of a stably stratified incompressible fluid in an internal water wave in a deep ocean is constructed. Studying the ocean internal wave field with its full dynamics is formidable (or unsolvable) so we consider a test-wave Hamiltonian to study the dynamical and statistical properties of the internal water wave field in a deep ocean. Chaos is present in the internal test-wave dynamics using actual coupling coefficients. Moreover, there exists a certain separatrix net that fills the phase space and is covered by a thin stochastic layer for a two-triad pure resonant interaction. The stochastic web implies the existence of diffusion of the Arnold type for the minimum dimension of a non-integrable autonomous system. For non-resonant case, stochastic layer is formed where the separatrix from KAM theory is disrupted. However, the stochasticity does not increase monotonically with increasing energy. Also, the problem of relaxation process is studied via microscopic Hamiltonian model of the test-wave interacting nonlinearly with ambient waves. Using the Mori projection technique, the projected trajectory of the test-wave is transformed to a form which corresponds to a generalized Langevin equation. The mean action of the test-wave grows ballistically for a short time regime, and quenches back to the normal diffusion for a intermediate time regime and regresses linearly to a state of statistical equilibrium. Applying the Nakajima-Zwanzig technique on the test-wave system, we get the generalized master equation on the test-wave system which is non-Markovian in nature. From our numerical study, the distribution of the test-wave has non-Gaussian statistics.
10
Wang, Caixia. "Geophysical observations of nonlinear internal solitary-like waves in the Strait of Georgia." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/17468.
Abstract:
A novel observational method for studying internal features in the coastal ocean is devel-
oped and tested in a study of large nonlinear internal solitary-like waves. Observations were
carried out in the southern Strait of Georgia in the summers of 2001 and 2002. By quantitatively combining photogrammetrically rectified oblique photo images from a circling aircraft
with water column data we track a number of internal wave packets for periods of up to one
hour and obtain a more complete view of internal waves, including propagation, oblique
interaction, and generation. First, the applicability of various weakly nonlinear theories in
modeling propagation of these large waves is tested. Both two-layer and continuous linear,
KdV (Korteweg-de Vries), and BO (Benjamin-Ono) models are applied with and without
background shear currents. After background shear currents are included, it is found that
a continuously stratified BO equation can be used to model propagation speeds within ob-
servational error, and that this is not true for other theories. Second, four observed oblique
wave-wave interactions including two Mach interactions, one interaction which varied from
known interaction patterns, and one very shallow angle regular interaction are analyzed.
An existing small-amplitude theory is applied but is found to overestimate the likelihood of
Mach interaction at large amplitude. Finally, large-scale aerial surveys are mapped. Using
speeds typical of observed waves, their time and place of origin are predicted. It is found
that the observed waves are generated at the passes to the south of the Strait of Georgia
and are released into the Strait after ebb tides.
11
Ceschini, Joseph J. "Modeling the effects of transbasin nonlinear internal waves through the South China Sea basin." Monterey, California: Naval Postgraduate School, 2013. http://hdl.handle.net/10945/34641.
Abstract:
Approved for public release; distribution is unlimitedThe objective of this research is to model and study the effects of transbasin internal waves on low-frequency signal transmission through the South China Sea (SCS) basin. Specifically, the fluctuations in the multipath arrival structure of a 400-Hz acoustic pulse transmitted through a distance of 167-km in the SCS basin in the presence of an internal ocean soliton was modeled and examined. The modeling entailed the integration of a raytracing program with an eigenray search and arrival-structure calculation program, and the use of measured bathymetry and inferred bottom-loss characteristics from previous research. A range-dependent perturbation was added to a range-independent background sound-speed profile to model the varying sound-speed field as the nonlinear ocean internal soliton propagates along the transmission path. All cases studied, each simulating a soliton at a different location, had six distinct acoustic arrivals that suffered from large-amplitude fluctuations (~ 10 dB). The factors that affect the amplitude of the arrivals are changes: in the number of bottom interaction, in ray tube spreading, phase interference and in the number of eigenrays making up an arrival. The results also show that the closer the soliton to the receiver, the less impact the soliton has on the arrival structure.
12
Mueller, Martin Fritz. "Analytical investigation of internally resonant second harmonic lamb waves in nonlinear elastic isotropic plates." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31827.
Abstract:
Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010.Committee Chair: Laurence J. Jacobs; Committee Member: Jianmin Qu; Committee Member: Jin-Yeon Kim. Part of the SMARTech Electronic Thesis and Dissertation Collection.
13
Tiron, Roxana Camassa Roberto. "Strongly nonlinear internal waves in near two-layer stratifications generation, propagation and self-induced shear instabilities /." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2009. http://dc.lib.unc.edu/u?/etd,2527.
Abstract:
Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2009.Title from electronic title page (viewed Oct. 5, 2009). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Mathematics." Discipline: Mathematics; Department/School: Mathematics.
14
Moncuquet, Adèle. "Coastal internal waves on the Bay of Biscay shelf and their impact on cross-shelf transport." Electronic Thesis or Diss., Brest, 2024. http://www.theses.fr/2024BRES0010.
Abstract:
Les ondes internes (OI) se propagent dans des milieux stratifiés où elles déforment le gradient de densité et génèrent des courants horizontaux et verticaux. Dans l’océan côtier, différentes formes d’OI peuvent être observées en fonction du profil vertical de densité et des courants avec lesquels les ondes interagissent. Sur les plateaux continentaux les OI génèrent du mélange et du transport qui dépend des caractéristiques des ondes. Dans certaines régions du monde, les OI génèrent du transport comparable au mouvement d’upwelling. Le Golfe de Gascogne est un haut lieu de génération de marées internes et d'ondes internes non linéaires (ONLI). Dans le GdG les OI ont été uniquement caractérisées au large et leurs capacités de transport est inconnue. La première partie de la thèse présente la marée et des ONLI observée pendant 1 mois sur le plateau Aquitain du GdG dans ~60 et 150m de fond. La marée interne et les ONLI de mode 1 ont générés des courants plus de trois fois supérieurs aux courants de marée barotrope. Sous deux pycnoclines, nous avons observé la coexistence et l'interaction d'ONLI de polarités opposées. Dans une seconde partie, nous quantifions le transport côte large sur le plateau Aquitain (62 m de fond) et le plateau Armoricain (48 m de fond) en utilisant les isothermes comme coordonnées verticales d'intégration. Sur le plateau Armoricain, le transport total est dominé par le pompage par les ondes internes. Sur le plateau Aquitain, le transport par les ondes internes domine proche du fondThe Bay of Biscay (BoB) is a hot spot for the generation of internal tides and nonlinear internal waves (NLIW). Previous studies have focused mainly on the seaward propagation of internal waves, and less on the shoreward propagation. The shelf region can be affected by internal tides and NLIW transport. The shelf is a complex hydrodynamical region and processes of different scales modify the background stratification and currents. Therefore, internal waves transform as they propagate across the shelf. Internal wave transformation on the shelf and the induced transport remain poorly described worldwide, especially on the BoB shelves. In this thesis, we describe the internal tide and NLIW from mooring observations on the BoB shelf and the induced cross-shelf transport. First, we describe the internal tide and NLIW on the Aquitaine shelf using 22 days of measurements (at 62 and 153 m depth). The results highlight the unexpected importance of the internal tide and NLIW during summer-time stratified conditions. NLIW of depression and elevation, with amplitude reaching up to 1/4th of the water depth and propagating shoreward with different speeds were observed. We observed conditions in which depression and elevation waves coexisted within the same internal tide phase, and could potentially interact. The second part of the work is dedicated to crossshelf net transport, associated with internal waves, or internal waves pumping (IWP) on both the Aquitaine and the Armorican shelf. On the Armorican shelf, IWP was the main driver of total transport near the boundaries and counterbalanced the subtidal dynamics in the middle of the water column. On the Aquitaine shelf, the total cross-shelf transport was a combination of subtidal transport and IWP
15
Renaud, Antoine. "On wave-mean flow interactions in stratified fluid." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN059/document.
Abstract:
La dynamique des écoulements géophysiques planétaires est fortement influencée par des processus physiques souvent non résolus par les modèles numériques de circulation générale. Il est essentiel de comprendre les mécanismes physiques sous-jacents pour paramétrer l’effet des petites échelles sur les grandes. Dans cette thèse, nous étudions un problème emblématique d’interactions entre ondes et écoulements moyens : la dynamique des écoulements zonaux forces par des ondes internes de gravite. Une manifestation remarquable de ces interactions est l’oscillation quasi-biennale (QBO) des vents équatoriaux dans l’atmosphère terrestre. Dans un premier temps, nous décrivons une transition vers le chaos dans un modèle quasi-linéaire classique du QBO. Nous montrons que ces bifurcations persistent dans des simulations numériques directes. A l’aune de ces résultats, nous proposons une interprétation de l’observation d’une rupture inattendue de la périodicité du QBO en 2016. Le mécanisme de génération d’écoulements moyens par les ondes dans les fluides stratifies nécessite la prise en compte d’effets dissipatifs. Il s’agit d’un phénomène analogue au "streaming" acoustique. Dans un second temps nous exploitons cette analogie en étudiant la génération d’écoulements moyens par les ondes internes proche d’une paroi, a l’aide d’approches asymptotiques multi échelles. Finalement, nous proposons une approche inertielle pour décrire l’émergence spontanée d’écoulements vorticaux en présence d’ondes : nous appliquons les outils de mécanique statistique pour calculer la partition d’énergie entre petites et grandes échelles dans le modèle d’eau peu profondeThe dynamics of planetary-scale geophysical flows is strongly influenced by physicalprocesses, mostly unresolved by general circulation numerical models. To parametrisethe coupling between small and large scales, it is essential to understand the underlying physical mechanisms. In this thesis, we study an emblematic problem of interactions between waves and mean flows: the dynamics of zonal flows forced by internal gravity waves. A striking manifestation of these interactions is the quasi-biennial oscillation (QBO) of equatorial winds in the Earth’s atmosphere. First, we describe a transition to chaos in a classical quasilinear model of the QBO and show that these bifurcations persist in direct numerical simulations. Based on these results, we suggest an interpretation for the observation of the unexpected periodicity disruption of the QBO in 2016. The mechanism by which mean flows are generated by waves in stratified fluids requires the consideration of dissipative effects. This phenomenon is analogous to acoustic "streaming". In a second time, we exploit this analogy to study the generation of mean flows by internal gravity waves close to a wall, using multi-scale asymptotic approaches. Finally, we propose an inertial approach to describe the spontaneous emergence of vortical flows in the presence of waves: we apply the tools of statistical mechanics to calculate the partition of energy between small and large scales in the shallow-water model
16
Girard, Réjean. "Relativistic nonlinear wave equations with groups of internal symmetry." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75688.
Abstract:
A nonlinear wave equation invariant with respect to unitary representations of the Lorentz group is considered in an attempt to describe extended particles with spin and positive definite energy by means of a self-confined classical field. The wave function has an infinite number of components and, in the specific representations used, the corresponding internal degree of freedom is identified with the spin. A fractional power of the scalar bilinear invariant appears as an appropriate choice for the nonlinearity in order that all the stationary states be localized. Two approximation methods are proposed and both lead to results that bear a resemblance to the results of the MIT bag model.
17
Tabaei, Befrouei Ali 1974. "Theoretical and experimental study of nonlinear internal gravity wave beams." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/30193.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2005.Includes bibliographical references (leaves 121-124).
Continuously stratified fluids, like the atmosphere and the oceans, support internal gravity waves due to the effect of buoyancy. This type of wave motion is anisotropic since gravity provides a preferred direction. As a result, a localized source oscillating at a frequency below the buoyancy frequency in a uniformly stratified Boussinesq fluid, rather than cylindrical wavefronts, gives rise to elongated disturbances propagating along specific directions depending on the driving frequency. Such wave beams can be readily generated in the laboratory by oscillating a cylinder in a stratified fluid tank, and, according to recent numerical simulations and field observations, often arise in the atmosphere due to thunderstorms and may also be generated in the oceans by tidal flow over sea-floor topography. So far, internal wave beams have been studied mostly using the linearized equations of motion valid for small-amplitude disturbances. The present thesis examines theoretically and experimentally some aspects of non-linearity in the propagation, reflection and collision of internal gravity wave beams. An asymptotic theory is developed for the propagation of isolated two-dimensional or axisymmetric nonlinear beams, that also takes into account viscous as well as re- fraction effects due to the presence of a mean flow and non-uniform buoyancy frequency. In this instance, it turns out that non-linearity plays a secondary role even for a finite-amplitude beam, which explains why a linear approach has been useful in interpreting observations of isolated beams in the atmosphere. On the other hand, nonlinear effects play an important part in the reflection of wave beams from a sloping wall.
(cont.) Using small-amplitude expansions, it is shown that nonlinear interactions are confined solely in the vicinity of the sloping wall where the incident and reflected beams meet, and this overlap region acts as a source of additional reflected beams with higher-harmonic frequencies. In some flow geometries, higher-harmonic reflected beams are found on the opposite side to the vertical than the primary reflected beam. Similarly, when two obliquely propagating beams collide, nonlinear interactions in the overlap region induce secondary beams with frequencies equal to the sum and difference of those of the colliding beams, consistent with recent numerical simulations of oscillatory stratified flow of finite depth over a ridge. A singularity arises in the reflection of linear wave beams when the angle of incidence is close to the wall slope and the reflected beam propagates nearly parallel to the sloping wall. The near-critical reflection of weakly nonlinear wave beams is studied separately by a matched-asymptotics approach. Non-linearity alone is not capable of healing the singularity of linear theory, as the inviscid nonlinear response at the critical angle grows with time and most likely eventually overturns. Laboratory experiments are also performed for the reflection of two-dimensional wave beams from a sloping wall. Internal-wave disturbances are generated by oscillating a circular cylinder in salt-stratified water and visualized using the synthetic schlieren non-intrusive technique. Secondary reflected beams due to nonlinear effects can be quite strong under certain flow conditions, and are in excellent agreement with the theoretical predictions in regards to their propagation characteristics.
by Ali Tabaei Befrouei.
Ph.D.
18
Harris, Victoria Siân. "Creation of nonlinear density gradients for use in internal wave research." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40437.
Abstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007."June 2007."
Includes bibliographical references.
A method was developed to create a nonlinear density gradient in a tank of water. Such gradients are useful for studying internal waves, an ocean phenomenon that plays an important role in climate and ocean circulation. The method was developed by expanding on the two-tank system currently used to create linear density gradients. A mathematical model of the two-tank system was used and a Matlab script was written to solve the model for the required flow rates in the system given a desired density gradient. The method was tested by creating three different density gradients: a linear gradient, a hyperbolic gradient, and a two-layer gradient. It was discovered that for a two-layer gradient the flow rates for each layer must be calculated independently of each other, because of problems integrating over a density gradient with a non-continuous slope. It was also discovered that the system failed at very low flow rates; insufficient mixing in the two-tank system led to gradients weaker than expected. Overall, the measured gradients matched up well with the expected gradients, and it was concluded that the system can successfully produce nonlinear density gradients.
by Victoria Siân Harris.
S.B.
19
Patel, Rupa Ashyinkumar. "Theory and computation on nonlinear vortex/wave interactions in internal and external flows." Thesis, Imperial College London, 1997. http://hdl.handle.net/10044/1/8597.
20
Dosser, Hayley V. "Propagation and breaking of nonlinear internal gravity waves." Master's thesis, 2010. http://hdl.handle.net/10048/878.
Abstract:
Thesis (M. Sc.)--University of Alberta, 2010.Title from pdf file main screen (viewed on April 20, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science, Department of Physics, University of Alberta. Includes bibliographical references.
21
Dorostkar, ABBAS. "Three-Dimensional Dynamics of Nonlinear Internal Waves." Thesis, 2012. http://hdl.handle.net/1974/7693.
Abstract:
The three-dimensional (3D) baroclinic response of Cayuga Lake to surface wind forcing was investigated using the fully nonhydrostatic MITgcm. The model was validated against observed temperature data using a hydrostatic 450 m (horizontal) grid and both qualitative and quantitative methods. The model correctly reproduces the basin-scale dynamics (e.g., seiche with horizontal mode-one period T1 = 80 h) with a basin-wide root-mean-square error of 1.9 C. Nonlinear internal surges were visualized to evolve due to (i) a wind-induced locally downwelled thermocline (wind duration Twind < T1/4), (ii) a basin-scale wind-induced upwelled thermocline (Twind > T1/4), (iii) internal hydraulic jumps (IHJs).
Results from a 113 m grid and field observations were used to characterize the basin-scale internal wave field according to composite Froude number (G2), Wedderburn number (WN), and Lake number (LN). The typical Cayuga Lake response is a surge when ~ 1 < WN (LN) < ~ 2-12 and a surge with emergent nonlinear internal waves (NLIWs) when WN or LN < ~ 2, in agreement with published laboratory studies. An observed shock front was simulated to be an IHJ, occurring at mid-basin during strong winds when WN < 0.8. This is the first simulation of a mid-basin seiche-induced IHJ due to super critical conditions (G2 > 1) in a lake. The topographic-induced IHJs were also shown to form when the surges interact with a sill-contraction topographic feature.
Both high-resolution hydrostatic and nonhydrostatic models were used to investigate the evolution, propagation and shoaling of NLIWs at medium lake-scale. A nonhydrostatic 22 m grid with lepticity λ ~ 1 ensures minimal numerical relative to physical dispersion, qualitatively reproducing observed dispersive NLIWs using ~ 2.3E+8 grid cells. Solitary waves evolve with almost unchanged wavelengths upon grid refinement from 40 m (λ ~ 2) to 22 m; suggesting model convergence to the correct solution. Corresponding hydrostatic grids were shown to produce a packet of narrower spurious solitary-like motions with different wavelengths, representing a balance between nonlinear steepening and numerical dispersion. Local gyre-like patterns and secondary transverse NLIW packets were visualized to result from wave-topography interaction, suggesting that NLIW propagation in long narrow lakes, where the bottom topography has irregularities is fundamentally 3D.Thesis (Ph.D, Civil Engineering) -- Queen's University, 2012-12-14 12:45:21.727
22
Kiss, Andrew Elek. "Nonlinear interactions of internal gravity waves in a continuously stratified fluid." Thesis, 1995. http://hdl.handle.net/1885/240918.
Abstract:
Internal gravity waves are buoyancy-driven oscillations which can arise in a density-stratified fluid. They exist throughout the oceans and atmosphere, the oceanic internal wavefield being sufficiently energetic for nonlinear effects to play an important role in the internal wave dynamics. Numerical studies of oceanic internal waves (such as Broutman & Young, 1986) have suggested that under the right conditions a weak internal gravity wave can be strongly refracted and frequency-shifted by the time-varying shear of a large-amplitude internal wave. My project aimed to experimentally observe this type of strongly nonlinear interaction by generating the required internal gravity waves in a continuously stratified aqueous solution. The waves were observed using a colour schlieren system, and power spectra of the internal wavefield were obtained using conductivity probes and polarimetry. Several nonlinear phenomena were observed, including anharmonic waves and forced sum and difference frequencies, as well as second-harmonic generation from the wave sources. However a combination of wavelength limitations imposed by viscosity, inescapable restrictions on the strong wave amplitude and severe observational difficulties all conspired to prevent detection of the particular nonlinear interaction of interest. A proposed apparatus could overcome these difficulties, but its construction would be quite beyond the scope of an Honours project.
23
Chang, Ming-Huei, and 張明輝. "Study of Large-Amplitude Nonlinear Internal Waves in the South China Sea." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/86114265552616480614.
Abstract:
博士國立臺灣大學
海洋研究所
96
The study is focused on the large-amplitude nonlinear internal waves (NLIW) in the South China Sea (SCS): the propagation characteristics, the energy, energy flux and dissipation, and the relationship between the interior properties of NLIW and its surface scattering strength. Three sets of long-term ADCP measurements taken on the Dongsha plateau, integrating with both the shipboard measurement and the remote sensing data, are used to study the propagation characteristics of the NLIWs. The moorings were aligned along 21o05’N near the eastern edge of the Dongsha plateau. From east to west, the distances between the two successive moorings are ~8.5’ and ~17’, respectively. The NLIW propagating directions and speeds were computed by NLIW-induced current velocity and NLIW arrival time between two successive mooring stations, respectively. The averaged propagating direction of NLIW is 165o, which is northwestward. The averaged propagating speeds between two successive mooring stations are 1.83±0.38 m/s and 1.61±0.20 m/s from east to west. The above estimations are further verified by the observations of both shipboard marine radar and satellite images. The propagating directions reveal irregular variation. Nonetheless, the propagating speeds, which are higher in Aug.-Oct. and are slower in Jan.-Mar, reveal apparently seasonal variation. Such seasonal variation could relate with the typically seasonal stratification in the SCS, strong stratification in Aug.-Oct and weak stratification in Jan.-Mar. The linear phase speed, which is calculated using the climatological density profiles of Generalized Digital Environmental Model (GDEM) output, has good correlation with the measured NLIW propagating speed. Both the propagation direction and speed reveal daily inequality. Two types of NLIW appear reciprocally around the spring tide. One of them propagates faster and mainly northwestward and the other propagates slower and more northward than the previous one. It could be associated with the tidal current in the Luzon Strait. Three sets of ADCP measurements taken on the Dongsha plateau, on the shallow continental shelf, and on the steep continental slope in the northern South China Sea are analyzed. The data show strong divergences of energy and energy flux of nonlinear internal waves along and across waves’ prevailing westward propagation path. The NLIW energy flux is 8.5 kW m-1 on the plateau, only 0.25 kW m-1 on the continental shelf 220 km westward along the propagation path, and only 1 kW m-1 on the continental slope 120 km northward across the propagation path. Along the wave path on the plateau, the average energy flux divergence of NLIW is ~0.04 W m-2, which corresponds to a dissipation rate of O(10-7-10-6)Wkg-1. Combining the present with previous observations and model results, a scenario of NLIW energy flux in the SCS emerges. NLIWs are generated east of the plateau, propagate predominantly westward across the plateau along a beam of ~100 km width that is centered at ~210N, and dissipate nearly all their energy before reaching the continental shelf. Surface signatures and interior properties of NLIWs were measured during a period of weak northeast wind (~2 m s-1) using shipboard marine radar, ADCP, CTD, and echo sounder. The surface scattering strength measured by the marine radar is positively correlated with the local wind speed when NLIWs are absent. When NLIWs approach, the surface scattering strength within the convergence zone is enhanced. The sea surface scattering induced by NLIWs is equivalent to that of a ~6 m s-1 surface wind speed, i.e., three times greater than the actual surface wind speed. The horizontal spatial structure of the enhanced sea surface scattering strength predicts the horizontal spatial structure of the NLIW. The observed average half-amplitude full width of NLIWs is 1.09±0.2 km; the average half-amplitude full width of the enhanced scattering strength is ~0.57 . The average half-amplitude full width of the enhanced horizontal velocity convergence of NLIWs is approximately equal to . The peak of the enhanced surface scattering leads the center of NLIWs by ~0.46 . NLIW horizontal velocity convergence is positively correlated with the enhancement of the surface scattering strength. NLIW amplitude is positively correlated with the spatial integration of the enhancement of the surface scattering strength within the convergence zone of NLIWs. The analysis concludes that in low-wind conditions remote sensing measurements may provide useful predictions of horizontal velocity convergences, amplitudes, and spatial structures of NLIWs. Further applications and modification of our empirical formulas in different conditions of wind speed, surface waves, and NLIWs, or with other remote sensing methods are encouraged.
24
Lin, Duo-min. "Run-up and nonlinear propagation of oceanic internal waves and their interactions." Thesis, 1996. https://thesis.library.caltech.edu/5066/1/Lin_dm_1996.pdf.
Abstract:
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
A weakly nonlinear and weakly dispersive oceanic internal long wave (ILW) model, in analogy with the generalized Boussinesq's (gB) model, is developed to investigate generation and propagation of internal waves (IWs) in a system of two-layer fluids. The ILW model can be further derived to give a bidirectional ILW model for facilitating calculations of head-on collisions of nonlinear internal solitary waves (ISWs). The important nonlinear features, such as phase shift of ISWs resulting from nonlinear collision encounters, are presented. The nonlinear processes of reflection and transmission of waves in channels with a slowly varying bottom are studied.
The terminal effects of IWs running up submerged sloping seabed are studied by the ILW model in considerable detail. Explicit solution of the nonlinear equations are obtained for several classes of wave forms, which are taken as the inner solutions and matched, when necessary for achieving uniformly valid results, with the outer solution based on linear theory for the outer region with waves in deep water. Based on the nonlinear analytic solution, two kinds of initial run-up problems can be solved analytically, and the breaking criteria and run-up law for IWs are obtained. The run-up of ISWs along the uniform beach is simulated by numerical computations using a moving boundary technique. The numerical results based on the ILW model are found in good agreement with the run-up law of ISWs when the amplitudes of the ISWs are small.
The ILW model differs from the corresponding KdV model in admitting bidirectional waves simultaneously and conserving mass. This model is applied to analyze the so-called critical depth problem of ISWs propagating across a critical station at which the depths of the two fluid layers are about equal so as to give rise to a critical point of the KdV equation. As the critical point is passed, the KdV model may predict a new upward facing ISW relative to a local mean interface is about to emerge from the effects of disintegrating original downward ISW. This phenomenon has never been observed in our laboratory. Numerical results are presented based on the present ILW model for ISWs climbing up a curved shelf and a sloping plane seabed. It is shown that in the transcritical region, the behaviour of the ISWs predicted by the ILW model depends on the relative importance of two dimensionless parameters, [...], the order of ISW wave slope, and s, the beach slope. For s >> [...], the wave profile of ISWs exhibits a smooth transition across the transcritical region; for s << [...], ISWs emerge with an oscillatory tail after passing across the critical point. Numerical simulations based on the ILW model are found in good agreement with laboratary observations.
Finally, conclusions are drawn from the results obtained in the present study based on the ILW model.
25
CAVALIERE, DAVIDE. "Investigation on internal solitary waves breaking for geophysical applications." Doctoral thesis, 2020. http://hdl.handle.net/11573/1434133.
Abstract:
Nonlinear internal waves are a spectacular phenomenon taking place in many parts
of the world ocean. They consist in oscillations that travel along the pycnocline, i.e.,
the portion of the water column separating the surface layer from relatively more
dense underlying fluid. They are mostly generated by the interaction between tidal
flow and bottom topography features, such as underwater sills and the continental
shelf. Nonlinear internal waves can take the shape of a special waveform called
internal solitary wave (ISW), a class of nonsinusoidal waves that has the ability to
retain its form over long distances and extended periods of time.
In the present work, we investigate the propagation, shoaling and breaking of ISWs
in a two–layer stratified fluid system through analytical and numerical methods.
We study the propagation of ISWs over a varying bathymetry through variable
coefficients KdV–type equations, which are widely used to model weakly–nonlinear
waves in the oceanic context. We study the shoaling and breaking of ISWs along a
sloping bathymetry, and we build an anaytical model to derive the ISWs breaking
location. Theoretical results are validated by laboratory experiments performed in a
wave tank. We then apply KdV–type equations to describe both numerically and
analitically the evolution of ISWs generated in the Messina Strait (Mediterranean
Sea) propagating northward, towards the frontal slope of a headland, i.e., Capo
Vaticano. Finally, we apply our wave–breaking model to predict breaking location
of ISWs along this frontal slope. We also focus on the mixing process induced by
the ISWs breaking, defining the potential energy, the background potential energy
and the available potential energy (APE) of an ISW in a two–layer fluid. Through
the Thorpe and Ozmidov length scales we build a theoretical model to predict the
values of mixing efficiency involved in ISWs breaking and we validate the model
through laboratory experiments.
26
Hu, Youna. "The Effects of the Earth's Rotation on Internal Wave Near-resonant Triads and Weakly Nonlinear Models." Thesis, 2007. http://hdl.handle.net/10012/3180.
Abstract:
This thesis investigates the effects of the earth's rotation on internal waves from two perspectives of nonlinear internal wave theory: near-resonant triads and weakly nonlinear models.
We apply perturbation theory (multiple scale analysis) to the governing equations of internal waves and develop a near-resonant internal wave triad theory. This theory explains a resonant-like phenomenon in the numerical results obtained from simulating internal waves generated by tide topography interaction. Furthermore, we find that the inclusion of the earth's rotation (nonzero $f$) in the numerical runs leads to a very special type of resonance: parametric subharmonic instability.
Through using perturbation expansion to solve separable solutions to the governing equations of internal waves, we derive a new rotation modified KdV equation (RMKdV). Of particular interest, the dispersion relation of the new equation obeys the exact dispersion relation for internal waves for both small and moderate wavenumbers ($k$). Thus this new RMKdV is able to model wea
kly nonlinear internal waves with various wavenumbers ($k$), better than the Ostrovsky equation which fails at describing waves of small $k$.
27
Sagers, Jason Derek. "Predicting acoustic intensity fluctuations induced by nonlinear internal waves in a shallow water waveguide." Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-08-6025.
Abstract:
Many problems in shallow water acoustics require accurate predictions of the acoustic field in space and time. The accuracy of the predicted acoustic field depends heavily on the accuracy of the inputs to the propagation model. Oceanographic internal waves are known to introduce considerable temporo-spatial variability to the water column, subsequently affecting the propagation of acoustic waves. As a result, when internal waves are present, errors in model inputs can significantly degrade the accuracy of the predicted acoustic field. Accurate temporo-spatial predictions of the acoustic field in the presence of internal waves therefore depend largely on one's ability to accurately prescribe the water column properties for the acoustic model. This work introduces a data-driven oceanographic model, named the evolutionary propagated thermistor string (EPTS) model, that captures the temporo-spatial evolution of the internal wave field along a fixed track, thereby permitting prediction of temporal fluctuations in the acoustic field. Simultaneously-measured oceanographic and acoustic data from the Office of Naval Research Shallow Water 2006 experiment are utilized in this work. Thermistor measurements, recorded on four oceanographic moorings spaced along the continental shelf, provide the data from which the EPTS model constructs the internal wave field over a 30 km track. The acoustic data were acquired from propagation measurements over a co-located path between a moored source and a vertical line array. Acoustic quantities computed in the model space, such as received level, depth-integrated intensity, and scintillation index are directly compared to measured acoustic quantities to evaluate the fidelity of the oceanographic model. In addition, a strong correlation is observed between the amplitude of the internal wave field and acoustic intensity statistics at a distant receiving array. It is found that the EPTS model possessed sufficient fidelity to permit the prediction of acoustic intensity distributions in the presence of nonlinear internal waves.text
28
Fu, Ke-Shian, and 傅科憲. "The effect of nonlinearity and mixed layer thickness on the propagation of nonlinear internal waves." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/z78s3z.
Abstract:
碩士國立中山大學
海洋物理研究所
95
This thesis applies a numerical model to study the propagation of internal solitary wave based on a two-dimensional model developed by Lynett and Liu (2002) and modified by Cheng et al. (2005).The numerical model derived assumes weak nonlinearity and weak dispersion in a two-layer inviscid fluid system. The governing continuity and momentum equations are solved and the real topography is included in the wave model. In order to improve the accuracy of simulation, mixed-layer thickness is allowed to change from place to place. Initial conditions are modified so that wave forms of non-hyperbolic -secant functions and wave fronts taken by satellite can be used. The diffraction near the island of Dongsha is simulated, and results of both fixed and variable mixed-layer thickness are compared. Simulated waveform in MODIS images after 24 hours are compared with other wave fronts of the same image. Laterally, internal waves can become very wide when it is far away from its origin. The extra energy can be explained by nonlinear wave-wave interaction because the energy of large amplitude internal wave increases after interacting with smaller internal waves.
29
Soontiens, Nancy. "Stratified Flow Over Topography: Steady Nonlinear Waves, Boundary Layer Instabilities, and Crater Topography." Thesis, 2013. http://hdl.handle.net/10012/8049.
Abstract:
This thesis investigates several aspects of stratified flow over isolated topography in ocean, lake, and atmospheric settings. Three major sub-topics are addressed: steady, inviscid internal waves trapped over topography in a pycnocline stratification, topographically generated internal waves and their interaction with the viscous bottom boundary layer, and flow over large-scale crater topography in the atmosphere.
The first topic examines the conditions that lead to very large internal waves trapped over topography in a fluid with a pycnocline stratification. This type of stratification is connected to ocean or lake settings. The steady-state Euler equations of motion are used to derive a single partial differential equation for the isopycnal displacement in supercritical flows under two conditions: a vertically varying background current under the Boussinesq approximation and a constant background current under non-Boussinesq conditions. A numerical method is developed to solve these equations for an efficient exploration of parameter space. Very large waves are found over depression topography when the background flow speed is close to a limiting value. Variations in the background current are examined, as well as comparisons between Boussinesq and non-Boussinesq results.
The second topic aims to extend the above subject by considering unsteady, viscous flows. Once again, supercritical flow over topography in a pycnocline stratification generates internal waves. These internal waves interact with the viscous bottom boundary layer to produce bottom boundary instabilities. The three-dimensional aspects of these instabilities are studied under changes in viscosity. The boundary layer instabilities have important implications for sediment transport in the coastal oceans or lakes.
Lastly, the final topic is motivated by the connection between dust streaks on the Martian surface and crater topography. Flow over a large 100-km diameter crater is examined with numerical simulations conducted using the Weather Research and Forecasting model. Modifications to the stratification and topography are applied. It is found that a large hydraulic structure of amplitude comparable to the crater depth forms in many cases. This structure may have important implications for dust transport in the atmosphere. In addition, Martian atmospheric parameters are used to study the flow properties under Mars-like conditions.
30
Shieh, Jih-hong, and 謝志宏. "A study of generation and evolution of nonlinear internal waves in the andaman sea by using SAR and MODIS images." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/81664695225580457037.
Abstract:
碩士國立臺灣海洋大學
海洋科學系
92
The main research domain in the earlier articles about internal wave phenomenon in the Andaman Sea, like Osborne (1980) and Alpers (1997). From CRISP and MODIS websites, we searched more than 5000 SAR images during 1995 and 2003 that acquired by ERS-1/2 satellite, and some MODIS images acquired by Terra and Aqua satellite over the Andaman Sea. In order to study the generation and revolution of nonlinear internal wave in the Andaman Sea, we had composed some figures including SAR images and sea bottom topography. We had found another four generation areas of internal wave, one origin of reflection. Since the internal wave was produced, generally spread to the direction of the Malay Peninsula eastwards. The interaction of internal waves was obvious. While the wave packets were propagated onto to the continental shelf, such that the shoaling effect include refraction and breaking was obvious, too.
31
Wu, Chung-lin, and 吳承霖. "Simulation of nonlinear internal wave based on two-layer fluid model." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/83111631729069116253.
Abstract:
碩士國立中山大學
海下科技暨應用海洋物理研究所
99
The main topic of this research is the simulation of internal wave interaction by a two-dimensional numerical model developed by Lynett & Liu (2002) of Cornell University, then modified by Cheng et al. (2005). The governing equation includes two-dimensional momentum and continuity equation. The model uses constant upper and lower layer densities; hence, these factors as well as the upper layer thickness. Should be determined before the simulation. This study discusses the interface depth and the density according to the buoyancy frequency distribution, the EOF, and the eigen-value based on the measured density profile. Besides, a method based on the two-layer KdV equation and the KdV of continuously-stratified fluid. By minimize the difference of linear celeriy, nonlinear and dispersion terms, the upper layer thicknes can also be determined. However, the interface will be much deeper than the depth of max temperature drop in the KdV method if the total water depth is bigger than 500 meters. Thus, the idealization buoyancy frequency formula proposed by Vlasenko et al. (2005) or Xie et al. (2010) are used to modify the buoyancy frequency. The internal wave in the Luzon Strait and the South China Sea are famous and deserves detailed study. We use the KdV method to find the parameters in the two fluid model to speed up the simulation of internal wave phenomena found in the satellite image.
32
Zhang, Zh-Wei, and 張志瑋. "Three Dimensional Variation of Underwater Acoustic Propagation due to Nonlinear Internal Wave." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/55924144831209462384.
Abstract:
碩士國立臺灣大學
工程科學及海洋工程學研究所
99
There is a biggest internal wave in the South China Sea. The amplitude can more than one hundred meter and the vertical current velocity can large then 2.5 meters per second. The internal wave perturbs the water column dramatically which affect sound propagation greatly. This thesis is about the sound propagation’s variation in three dimensions due to internal waves. The acoustic and environment data are from the 2007 NLIWI experiment. We study both depression and elevation internal waves simulates KdV formula analysis the 3D effect on acoustic propagation using FOR3D model.
33
Lee, Chou-Heng, and 李周衡. "A Study of Generation and Evolution of Nonlinear Internal Wave in the Sulu Sea Using SAR." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/41353851416819992372.
Abstract:
碩士國立海洋大學
海洋科學系
89
The large-scaled internal wave phenomenon in the Sulu Sea in Philippine is prominent. In the early research, only Apel et al. (1985) acquired numerous in-situ data in the Sulu Sea, analyzed less low-resolution visible-wavelength imagery and applied the KdV equation to carry out the numerical simulation. However, few papers had been published since then. Recently the spatial and temporal resolution of the spaceborn Synthetic Aperture Radar (SAR) have largely promoted. From Centre for Remote Imaging, Sensing and Processing (CRISP) web site, http://crisp.nus.edu.sg , we first searched about four hundred SAR images captured during 1996 and 2001 by the ERS-1/2 satellite over the Sulu Sea. In order to investigate the generation and evolution of nonlinear internal wave in the Sulu Sea in Philippine, we have plot some multi-layer synthetic figures including SAR images and sea bottom topography by seasons and months, so they are easy to study and reveal some features. It is found that most of the internal waves are generated from the Sulu archipelago in southeast of the Sulu Sea and travels toward the Palawan Island. Some sources are near the Pearl Bank and Doc Can Island instead of the underwater shallow sill between the two islands. Another source also have been found near the Pandu Can Island about sixty five kilometers northeast from the Doc Can Island. When the water depth becomes shallow to about two hundred meters, the refraction effect is significant.