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 124 for “"Coherent Structures"”.
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Coherent structures in incompressible fluid flows
… and includes a discussion of two classes of structures observed during the transition to turbulence: numerically-extracted solutions of the Navier-Stokes equations (the "exact'') and localized/patterned turbulent spots that are not themselves solutions of the Navier-Stokes equation but are …
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Coherent structures in a baroclinic atmosphere
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985.
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Numerical and Theoretical Developments for Coherent Structures
… development of Lagrangian and objective Eulerian coherent structures. This theory extends notions developed for autonomous systems to those that may have arbitrary dependence on time and whose flow data may not be known or available for all time. The structures obtained from this theory are …
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Active Control of Coherent Structures in an Axisymmetric Jet
<p>The primary objective of this work is to develop high-fidelity simulation model for jet noise control predictions and quantify the sound reduction when an external source frequency mode excitation is imposed on the jet flow. Whereas passive approaches using mixing devices, such as chevrons, have …
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Mixing layers and coherent structures in vegetated aquatic flows
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2000.
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Characteristics of Coherent Structures in Marine Atmospheric Surface Layer
… the spatial and temporal characteristics of coherent structures in the near neutral marine atmospheric surface layer. With Taylor's hypothesis, the temporal velocity signals have been transformed to spatial fluctuations and then visualize these spatial velocity fluctuations to identify the …
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Quasi-coherent structures in the marine atmospheric boundary layer
… decades has confirmed the existence of quasi-coherent structures amidst the chaos of a turbulent boundary layer. It has been observed that a quasi-periodic phenomena called "bursting" accounts for a major contribution to the turbulent Reynolds stress and the production of turbulent kinetic …
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Detecting and analyzing coherent structures in two-dimensional dynamical systems
The identification of coherent structures enhances the understanding of transport by complex flows such as those found at the ocean surface. The rapidly developing approach of Lagrangian Coherent Structures (LCSs) is based on the identification of codimension-1 structures that are locally the …
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On Turbulent Swirling Jets: Vortex Breakdown, Coherent Structures, and their Control
Diese Arbeit umfasst die experimentelle und theoretische Untersuchung der Entstehung großskaliger kohärenter Strukturen in turbulenten Drallstrahlen. Die untersuchte Strö-mungskonfiguration zeichnet sich durch eine hohe Komplexität aufgrund gleichzeitig auftretender axialer und azimutaler …
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LAMINAR TURBULENT TRANSITION - SPECTRAL ANALYSIS AND COHERENT STRUCTURES OF DNS WAVEPACKETS
… of subsets of the 3D spectrum result in coherent structures of the flow. These are compared with the results of proper orthogonal decomposition (POD). A hybrid POD-FFT approach is also pioneered to synergize the strengths of both methods, taking advantage of the optimal basis constructed …
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Towards Detecting Atmospheric Coherent Structures using Small Fixed-Wing Unmanned Aircraft
The theory of Lagrangian Coherent Structures (LCS) enables prediction of material transport by turbulent winds, such as those observed in the Earth's Atmospheric Boundary Layer. In this dissertation, both theory and experimental methods are developed for utilizing small fixed-wing unmanned aircraft …
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Identifying dynamical boundaries and phase space transport using Lagrangian coherent structures
In many problems in dynamical systems one is interested in the identification of sets which have qualitatively different fates. The finite-time Lyapunov exponent (FTLE) method is a general and equation-free method that identifies codimension-one sets which have a locally high rate of stretching …
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Exact coherent structures in spatiotemporal chaos: From qualitative description to quantitative predictions
… us to find their invariant solutions (exact coherent structures) numerically. In this thesis, we try to elucidate the chaotic dynamics of nonlinear partial differential equations by studying their exact coherent structures and invariant manifolds. Specifically, we investigate the …
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Detection and Analysis of Coherent Structures within and above Tall-vegetated Canopies
Coherent structures are an inherent phenomenon of the atmospheric turbulent flow in the proximity to tall-vegetated canopies. Although coherent structures have called increasing attention of the turbulence community during the past decades, the basic mechanisms of their emergence, their …
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Lagrangian coherent structures and trajectory similarity: two important tools for scientific visualization
… the computation and visualization of Lagrangian coherent structures (LCS), an emerging technique for analyzing time-varying velocity fields (e.g. blood vessels and airflows), and the measure of similarity for trajectories (e.g. hurricane paths). LCS surfaces and trajectory-based techniques (e.g. …
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Modifications of Coherent Structures in Fan Blade Wakes for Broadband Noise Reduction
… control strategies on the organization of the coherent structures of the wakes and their potential to generate noise. A baseline flow was established by measuring the wake downstream of unmodified GE-Rotor-B blades. Four sets of serrated trailing edge blades (with two different serration sizes …
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Momentum and mass transport by coherent structures in a shallow vegetated shear flow
… of a shear layer with nearly periodic vortex structures. The vortices are documented with respect to their physical characteristics and their effect on mass and momentum exchange. Distributions of mean velocity and turbulent Reynolds stress show a two layer structure in the shear flow. An …
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An experimental study of coherent structures in a three-dimensional turbulent boundary layer
… for some time now that organized motions or coherent structures in the flow play a large part in determining the flow characteristics, and there is now a large body of literature dealing with various aspects of coherent structures. However, almost all of the existing literature deal with mean …
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The Effect of Thermal Non-Uniformity on Coherent Structures in Supersonic Free Jets
… in the exhaust plume. Large-scale turbulent structures have been shown to be the dominant source of noise in heated supersonic jets, especially over long, streamwise distances. Therefore, a large field-of-view measurement is desirable for studying these structures. Time-Resolved Doppler …
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