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Lagrangian Averaging, Nonlinear Waves, and Shock Regularization


Bhat, Harish Subrahmanya (2005) Lagrangian Averaging, Nonlinear Waves, and Shock Regularization. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/8DJ2-F672.


In this thesis, we explore various models for the flow of a compressible fluid as well as model equations for shock formation, one of the main features of compressible fluid flows.

We begin by reviewing the variational structure of compressible fluid mechanics. We derive the barotropic compressible Euler equations from a variational principle in both material and spatial frames. Writing the resulting equations of motion requires certain Lie-algebraic calculations that we carry out in detail for expository purposes.

Next, we extend the derivation of the Lagrangian averaged Euler (LAE-alpha) equations to the case of barotropic compressible flows. The derivation in this thesis involves averaging over a tube of trajectories centered around a given Lagrangian flow. With this tube framework, the LAE-alpha equations are derived by following a simple procedure: start with a given action, expand via Taylor series in terms of small-scale fluid fluctuations, truncate, average, and then model those terms that are nonlinear functions of the fluctuations.

We then analyze a one-dimensional subcase of the general models derived above. We prove the existence of a large family of traveling wave solutions. Computing the dispersion relation for this model, we find it is nonlinear, implying that the equation is dispersive. We carry out numerical experiments that show that the model possesses smooth, bounded solutions that display interesting pattern formation.

Finally, we examine a Hamiltonian partial differential equation (PDE) that regularizes the inviscid Burgers equation without the addition of standard viscosity. Here alpha is a small parameter that controls a nonlinear smoothing term that we have added to the inviscid Burgers equation. We show the existence of a large family of traveling front solutions. We analyze the initial-value problem and prove well-posedness for a certain class of initial data. We prove that in the zero-alpha limit, without any standard viscosity, solutions of the PDE converge strongly to weak solutions of the inviscid Burgers equation. We provide numerical evidence that this limit satisfies an entropy inequality for the inviscid Burgers equation. We demonstrate a Hamiltonian structure for the PDE.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Burgers equation; Hamiltonian partial differential equations; Lagrangian averaging; nonlinear waves; shock waves
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Control and Dynamical Systems
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Marsden, Jerrold E.
Thesis Committee:
  • Marsden, Jerrold E. (chair)
  • Hajimiri, Ali
  • Fetecau, Razvan Constantin
  • Murray, Richard M.
  • Schneider, Tapio
Defense Date:6 May 2005
Non-Caltech Author Email:harish.bhat (AT)
Record Number:CaltechETD:etd-05262005-100534
Persistent URL:
Bhat, Harish Subrahmanya0000-0001-7631-1831
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2089
Deposited By: Imported from ETD-db
Deposited On:26 May 2005
Last Modified:12 Aug 2020 22:55

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