Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 2003. / Thesis advisor(s): Fotis Papoulias. Includes bibliographical references (p. 73). Also available online.

Thesis (M.S. in Mechanical Engineering)--University of Michigan, 2001. / Includes bibliographical references (p. 49). Also available online.

Thesis (Ph. D.)--University of Hong Kong, 1987.

Thesis (Ph. D.)--University of Hong Kong, 1988. / Also availalbe in microfilm.

Thesis (M. Phil.)--University of Hong Kong, 1987.

We present the results from a series of experimental investigations into the hydrodynamic instabilities that occur in radiative blast waves. In particular, we examine the Vishniac instability in which the perturbation modes oscillate in time and, for certain mode numbers and polytropic index of the medium, can exhibit a growth in their amplitudes. Experiments were conducted on the GHOST laser laboratory in which a source of atomic clusters was irradiated by a 1J-2J, 115fs laser pulse to produce cylindrical blast waves. The thrust of this thesis falls into two categories. First, we analyze the effects radiative cooling has on the evolution of blast waves such as the lowering of the effective polytropic index and consequently the lowering of their deceleration parameter. Radiation from the blast wave surface results in a preheated ionization precursor in the upstream material and is indicated by a gradual decline in the electron density profile of the blast wave rather than a sharp jump. This mechanism, if strong enough, can also create a secondary shock wave to form ahead of the main blast wave. The second set of experiments investigates the temporal evolution of longitudinal perturbations induced on the blast waves by use of a transverse interferometric beam that modifies the cluster medium prior to the onset of the main pump beam. These perturbations are analyzed and compared to theory set forth in Vishniac's mechanism for oscillatory instabilities and their growth rate. / text

Several significant wave propagation problems in the fields of nonlinear optics and hydrodynamics are studied in this thesis. In optics, the physical model considered is the two-core optical fiber (TCF), which is an essential component of lightwave technology. In hydrodynamics, the motion of a wave packet on the free surface of water of finite depth allowing modulations from two mutually perpendicular and horizontal directions, governed by the famous Davey-Stewartson (DS) equations, is taken into account. The main contributions of this thesis are: In optics, the effects of the intermodal dispersion (IMD) and the birefringence induced effects, both of which always exist in the TCFs, have been ignored in the previous studies of the modulation instability (MI) of continuous waves (CWs) in the TCFs. In this thesis, a detailed analysis of these effects on the MI spectra has been done. It is found that IMD does not seriously affect the MI spectra of the symmetric/antisymmetric CW states, but can significantly modify the MI spectra of the asymmetric CW states. In exploring the birefringence induced effects, a particular class of asymmetric CW states, which admits analytical solutions and has no counterpart in the single-core fibers, is focused on. It is found that the MI spectra of a birefringent TCF in the normal dispersion regime can be distinctively different from those of a zero-birefringence TCF especially for the circular-birefringence TCF. All the findings of MI analysis can be well verified by the wave propagation dynamics. Another contribution of this thesis is that we find the dramatic pulse distortion and even pulse splitting phenomenon due to IMD in TCFs, which is unexpected in many situations, can be effectively suppressed and even avoided by Kerr nonlinearity, which has never been reported in the literatures in the studies of TCFs. In hydrodynamics, DS equations describe the evolution of weakly nonlinear, weakly dispersive wavepackets with slow spanwise dependences on a fluid of finite depth. Generally, DS equations are divided into two types e, i.e. DSI and DSII equations, depending on the specific fluid configurations (fluid depth, wavelength of the water wave, surface tension etc). Due to the importance of DS equations, many exact solutions have been derived by different nonlinear wave methods over the years in the literature. In this thesis, two new exact doubly periodic wave patterns of DS equations are derived by the use of properties of the theta functions, or equivalently, the Jacobi elliptic functions, and the corresponding solitary waves are also deduced in the long wave limits. The new feature of the two wave patterns found is that they can be applied to both DSI and DSII systems at the same time. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Not available / text

We present a series of numerical galaxy formation studies which apply new numerical methods to produce increasingly realistic galaxy formation models. We first investigate the metallicity evolution of a large set of idealized hydrodynamical galaxy merger simulations of colliding galaxies. We find that inflows of metal--poor interstellar gas triggered by galaxy tidal interactions can account for the systematically lower central oxygen abundances observed in local interacting galaxies. We show the central metallicity evolution during merger events is determined by a competition between the inflow of low--metallicity gas and enrichment from star formation. We find a time-averaged depression in the galactic nuclear metallicity of ~0.07 dex for gas--poor disk--disk interactions, which explains the observed close pair mass-metallicity and separation-metallicity relationships. / Astronomy

published_or_final_version / abstract / toc / Mechanical Engineering / Doctoral / Doctor of Philosophy