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Coarse analysis of multiscale systems: diffuser flows, charged particle motion, and connections to averaging theory

Citation

Fung, Jimmy (2005) Coarse analysis of multiscale systems: diffuser flows, charged particle motion, and connections to averaging theory. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-05272005-165938

Abstract

We describe a technique for the efficient computation of the dominant-scale dynamics of a fluid system when only a high-fidelity simulation is available. Such a technique is desirable when governing equations for the dominant scales are unavailable, when model reduction is impractical, or when the original high-fidelity computation is expensive. We adopt the coarse analysis framework proposed by I. G. Kevrekidis (Comm. Math. Sci. 2003), where a computational superstructure is designed to use short-time, high-fidelity simulations to extract the dominant features for a multiscale system. We apply this technique to compute the dominant features of the compressible flow through a planar diffuser. We apply the proper orthogonal decomposition to classify the dominant and subdominant scales of diffuser flows. We derive a suitable coarse projective Adams-Bashforth time integration routine and apply it to compute averaged diffuser flows. The results include accurate tracking of the dominant-scale dynamics for a range of parameter values for the computational superstructure. These results demonstrate that coarse analysis methods are useful for solving fluid flow problems of a multiscale nature.

In order to elucidate the behavior of coarse analysis techniques, we make comparisons to averaging theory. To this end, we derive governing equations for the average motion of charged particles in a magnetic field in a number of different settings. First, we apply a novel procedure, inspired by WKB theory and Whitham averaging, to average the variational principle. The resulting equations are equivalent to the guiding center equations for charged particle motion; this marks an instance where averaging and variational principles commute. Secondly, we apply Lagrangian averaging techniques, previously applied in fluid mechanics, to derive averaged equations. Making comparisons to the WKB/Whitham-style derivation allows for the necessary closure of the Lagrangian averaging formulation. We also discuss the Hamiltonian setting and show that averaged Hamiltonian systems may be derivable using concepts from coarse analysis. Finally, we apply a prototypical coarse analysis procedure to the system of charged particles and generate trajectories that resemble guiding center trajectories. We make connections to perturbation theory to derive guidelines for the design of coarse analysis techniques and comment on the prototypical coarse analysis application.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:charged particle motion; coarse analysis; computational fluid dynamics; diffuser flows; equation-free; guiding center theory; Lagrangian averaging; proper orthogonal decomposition; variational averaging; Whitham averaging; WKB
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Murray, Richard M. (advisor)
  • Marsden, Jerrold E. (advisor)
Thesis Committee:
  • Murray, Richard M. (chair)
  • Marsden, Jerrold E.
  • Ortiz, Michael
  • Gharib, Morteza
  • Colonius, Timothy E.
Defense Date:10 May 2005
Record Number:CaltechETD:etd-05272005-165938
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-05272005-165938
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2163
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:31 May 2005
Last Modified:26 Dec 2012 02:47

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