Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 31 for “"Linear Instability"”.
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Effect of roughness element on the stability of boundary layers
The instability of flows around hump and dip imperfections is investigated. The mean flow is calculated using interacting boundary layers, thereby accounting for viscous/inviscid interaction and separation bubbles. Then, the two-dimensional linear instability of this flow is analyzed, and the …
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Instability Waves in the Gulf Stream Front and Its Thermocline Layer
<p>Linear instability calculations were carried out on a three layer Gulf Stream front model in an attempt to elucidate the interaction of the thermocline layer with surface slopewater shoreward of the front. The basic state is geostrophic balance and constant potential vorticity in the two active …
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On the N-body Problem
… regularization of Simultaneous binary collision, linear stability of Kepler orbits, and index theory for symplectic path are studied. The history of their study is summarized in section 1. Section 2 deals with the following problem: given a collinear configuration of 4 bodies, under what …
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The Genesis and Evolution of African Easterly Waves
… of African waves is first re-examined as a linear instability problem of a general basic zonal flow with/without a parameterized latent heating. The method of eigenvalue-eigenfunction analysis is used. The analysis reveals that it is important to use a faithful representation of the …
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Development of Reduced-Order Flame Models for Prediction of Combustion Instability
… dynamics, a physically-based, reduced-order, nonlinear model was developed based on the proper orthogonal decomposition technique and generalized Galerkin method. In addition, the describing function for the flame was measured experimentally and used to identify an empirical nonlinear flame …
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Relativistic electron beam transport for fast ignition relevant scenarios
… extent of confinement along the cone surface, linear instability growth in the outer plasma corona, and the nonlinear saturated state in the inner plasma corona. Analytical and computational models were constructed to include relevant physics that had been excluded from previous models, such as …
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Dynamics of marine zooplankton : social behavior, ecological interactions, and physically-induced variability
… develop spontaneously as a result of linear instability of the uniform distribution. In this idealized ecosystem, benefits related to the local abundance of mates are offset by the cost of having to share resources with other group members. Third, I derive a weakly nonlinear …
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Nonlinear effects on interfacial wave growth into slug flow
… velocity between the two fluids, two different instability mechanisms can create initial wave disturbances on the interface: the classic Kelvin-Helmholtz instability or shear induced instability. These instability mechanisms, which affect the initial growth of the disturbances on the interface, …
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A Mathematical Analysis of Digestive Processes in a Model Stomach
… of two layers of creeping fluid through temporal instability of the perturbed fluid interface. Some attention is also paid to a more general study of the surrounding flow field. Linear, two-fluid flow next to a prescribed, sinusoidally moving wall is found to be stable in all cases. Studies of …
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Gravity Waves Studies in Mesopause Region by Using Na Wind/temperature Lidar
… wavelengths are contradicted with prediction of linear instability theory. The systematic relationships between the monochromatic gravity wave periods, wavelengths, and amplitudes agree remarkably well with predictions of diffusive filtering theory. This study suggests that the complex nonlinear …
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Generalized Navier-Stokes equations for active turbulence
… by accounting for active stresses through a linear instability mechanism, in contrast to externally driven classical turbulence. This minimal model can reproduce experimentally observed velocity statistics and is analytically tractable in planar and curved geometry. Exact stationary bulk …
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Local and Global Stability and Dynamics of a Class of Nonlinear Time-Delayed One-Degree-of-Freedom Systems
We investigate the dynamics and stability of nonlinear time-delayed one-degree-of-freedom systems possessing quadratic and cubic nonlinearities and subjected to external and parametric disturbances. Due to the time-delay terms, the trivial solution of the unforced system undergoes Hopf …
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Flow and stability studies in porous media based on some non-Darcian models.
… Rayleigh numbers, within the framework of linear theory, for both rigid and free boundaries, are calculated. The effect of considering anisotropy in the Brinkman equation is brought out. Next, an energy method is used to study the nonlinear stability of a rotating porous layer. Here the …
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The onset of gouging in high-speed sliding contacts
… explosive welding, and Kelvin-Helmholtz waves, a linear instability analysis was also performed. A total of 22 railgun experiments were performed to explore different aspects of gouging. Through these experiments, the effect of new slider materials, thin aluminum coatings, and macroscopic rail …
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Theory and Observations of Horizontal and Vertical Structure of Gravity Wave Perturbations in the Middle Atmosphere
… m-spectra contradict the predictions of the linear instability theory of Dewan and Good (1986) and the scale-dependent diffusive filtering theory of Gardner (1993) and appear to be compatible with the Doppler spreading theory of Hines (1991, 1993), the scale-dependent diffusion theory of …
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Instabilities and transport in magnetized plasmas
… collisional (fluid) magnetized magnetorotational instability (MRI) in the presence of the Braginskii viscosity. We conduct a global linear analysis of the instability in a galactic rotation profile for three magnetic field configurations: purely azimuthal, purely vertical and slightly pitched. Our …
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Wave Equations on Curved Spacetimes
… but we can gain some insight by studying linear versions of them. These simplifications give rise to wave equations on curved spacetimes. We investigate the classical stability of supersymmetric, asymptotically flat microstate geometries with 5 non-compact dimensions. These geometries …
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Dynamics of marine zooplankton : social behavior ecological interactions, and physically-induced variability
… develop spontaneously as a result of linear instability of the uniform distribution. In this idealized ecosystem, benefits related to the local abundance of mates are offset by the cost of having to share resources with other group members. Third, I derive a weakly nonlinear …
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Instability and mixing in a turbulent stratified Taylor-Couette Flow
… Oglethorpe (2014) found that, for an initially linearly stratified Taylor-Couette (STC) flow with fixed outer cylinder, the flow spontaneously forms well-mixed layers of constant height separated by sharp density gradient interfaces. She also observed a quasi-periodic mixing phenomenon across …
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Modeling wind forcing in phase resolving simulation of nonlinear wind waves
… are non-stationary, irregular and highly nonlinear, which restricts the ability of traditional phase averaged models to simulate their complex dynamics. We develop a novel phase resolving model for direct simulation of nonlinear broadband wind waves based on the High Order Spectral (HOS) …
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