Approved for public release; distribution is unlimited. / Swell propagates across thousands of kilometers of ocean in almost unchanged parallel wave fronts. Within the nearshore region however, refraction causes wave fronts to turn toward shallow depths transforming the wave field. The Nearshore Canyon Experiment (NCEX) Pilot, conducted from October 10 to October 17, 2002, observed wave transformation across the Scripps and La Jolla canyon system near San Diego, CA. Four Datawell Directional Waverider Buoys, three Nortek Vector PUV recorders, and two pressure sensors were deployed in depths ranging from 10 to 300 m. Observed energy density spectra and mean propagation directions were examined for three case studies representative of the range of observed swell conditions. Observations were compared to predictions of a back-refraction model provided by Dr. William O'Reilly. Observations indicate that refraction causes the waves to propagate along the deep axes of the Scripps and La Jolla canyons. At the shallow canyon heads, the convergence and divergence of ray trajectories cause extreme (2-3 orders of magnitude!) spatial variations in wave energy. Considering the complexity of the canyon environment, predictions of wave transformation agree surprisingly well with observations. / Ensign, United States Naval Reserve

This thesis sets out to explore the effects on the dynamic response of a hybrid trolley system employed in ship to shore cargo transfer operating in a realistic short crested irregular seaway. Compared to the uni-directional long crested waves, the multi-directional nature of short crested waves enhances the realism of the modeling. A standard cosine-squared spreading law was added to the two-parameter Bretschneider spectrum. The results provide added data on the coupled system response in all directions and moderate any overestimation that may be derived from simply using long crested waves. / Republic of Singapore Navy author.

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Thesis advisor: Willie J. Padilla / The field of metamaterials (MMs) has garnered a great deal of attention ever since the experimental demonstration of negative refractive indexes. Such an exotic response stemmed from the engineering capability of MMs, as they can obtain almost any optical responses at any given frequency by carefully structuring the geometries. There are countless examples where MMs have posed promising results in tailoring free space radiation. However, their usage beyond this common platform is far less explored. For examples, surface electromagnetic waves, which offer great potentials for future device applications, could be an intriguing place for the further development of metamateirals. In this dissertation, we study various MM configurations where the interplay between surface waves and metamaterials has a significant impact on the device performance. Firstly, Chapter 1 introduces some fundamental concepts of metamaterials and surface electromagnetic waves, and outline the fabrication, experiments, and characterization details. In Chapter 2, we investigate whether the effective optical parameters of MMs have the exact physical meaning as those of natural substances. Two types of MM resonators are studied, and we found the thickness of the host matrix plays a crucial role in such a homogenization process. Next, we present a computational and experimental study of MMs in conjunction with a novel gigahertz/terahertz transmission line, in Chapter 3. By optimizing the coupling between the MMs and the signal, information can be encoded. Chapter 4 presents a study of designing an extremely subwavelength magnetic MM. By maximizing the effective inductance and capacitance of the structure, the final geometry obtains a strong magnetic resonance with the size of merely λₒ/2000, where λₒ is the resonant wavelength. A novel time-domain spectroscopic method is also proposed to determine the frequency-dependent permeability of the samples. In Chapter 5, we characterize two hidden channels of MM perfect absorbers : scattering and generation of surface electromagnetic waves. In particular, we unveil lossy surface waves are generated during the process resulting in an enhancement of angular absorbance. The study provides a new insight to the working principle of MMAs. In Chapter 6, we investigate complementary MM structures that exhibit strong extraordinary optical transmission with higher transmission efficiency. We discover the origin of the fundamental mode is irrelevant to the Bloch modes. Lastly, we summarize all achievements and give an outlook in Chapter 7. / Thesis (PhD) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johanneaburg, in fulfilment of the requirerments for the degree of Doctor of Philosophy. / In this work a new high speed metal forming process is experimentally and theoretically investigated and discussed. The high speed metal forming is carried out in a liquid shock tube. The pressure energy of a liquid shock wave, which is generated non-explosively is used to form the metal workpiece.(abbreviation abstract) / Andrew Chakane 2019

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2017. / The cardinal aspects of supersonic and hypersonic propulsion intake design involve understanding the internal shock wave structures forming therein. A study was conducted to explore the effects of internal surface curvature and entry deflection angle on steady axisymmetric shock waves. Very little is known about these influences with only Curved Shock Theory, produced by M¨ older, providing analytical insight directly after a curved shock wave. The shock waves and accompanying flow fields which were generated were studied via experimental and numerical means. Radius normalised internal radii of curvature of 1, 1.5 and 2 with entry deflection angles of 0◦, 4◦ and 8◦ were investigated between a Mach number range of Mach 2.4 and 3.6. Experimental results were produced using a blow down supersonic wind tunnel facility and were captured via shadowgraph and schlieren flow visualisation techniques. The numerical simulations were validated using the experimental results. A self similar curved shock wave shape equation was presented with an empirical model which uses flow Mach number and internal radius of curvature in order to produce the resulting curved shock shape. Curved Shock Theory streamlines were used to try predict the internal surfaces that produced the curved shocks but results did not correlate. This was due to extreme streamline curvature curving the streamlines when the shock angle approached the Mach angle. Very good agreement was however found between the theoretical and numerical streamlines at lower curvatures. The higher the internal surface curvature and entry deflection angle, the greater the flow fields were impacted. Steeper characteristics formed as a result, curving the shock wave more noticeably. Both the internal surface curvature and entry deflection angle were found to have an effect on the trailing edge expansion fans which then altered the shape of downstream shock wave structures. The highest curvature models produced steady double reflection patterns due the flow being turned in onto itself by the imposed internal surface curvature. The effects of conical and curved internal surfaces were explored for additional insight into the presence of flow-normal curvature and the curving of the attached shock waves. / XL2018

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2017. / In traditional two-dimensional shock wave theory the reflection of a shock wave off a surface is treated as an adiabatic process and that the reflection surface is perfectly rigid and smooth with an inviscid flow of the fluid. In reality it has been found that these assumptions are not entirely accurate, and that although they are a good indication in the regular and irregular reflection domains of shock waves over the surface, viscous and thermal effects are present within the flow field. It has been experimentally shown that the transition of regular reflection to irregular reflection exceeds the theoretical limit, which is known as the von Neumann paradox. This paradox has largely been accounted for in the formation of a viscous boundary layer behind the reflected shock wave, based on numerous experimental and computational studies. However, the thermal effects in the reflection process have largely been neglected as the assumption of heat transfer between the post-shock wave gas and the reflection surfaces is assumed to be invalid. These thermal effects were investigated by testing materials with a varying range of thermal conductivities (1.13 to 401 W/mK) and similar surface roughness’s below the suggested limit for hydraulic smoothness. Each experiment placed two test pieces at the same incidence angle, symmetrically in the shock tube. This allowed flow properties to be exactly the same for the two materials being tested with a single plane shock wave. Test Mach numbers ranged from 1.2790 to 1.3986, with tests conducted at shock wave incidence angles of 36◦, 40◦, 60◦ and 70◦. This allowed both the regular and irregular reflection domains to be tested. Shadowgraph images were created using a z-configuration optical set up. These shadowgraph images were analysed quantitatively based on the angles measured as well as qualitatively based on flow features and symmetry. Both the quantitative and qualitative tests indicated that there was a difference in the angles between the reflected shock waves and surfaces based on the material thermal conductivity. In the quantitative tests the value of this angle was larger for materials with a lower thermal conductivity, and smaller for ones with a higher thermal conductivity for the regular reflection cases. In the irregular reflection cases the angle between the reflected and incident shock waves was larger for materials with a higher thermal conductivity. The materials with midrange thermal conductivities had reflection angles that lay within the bounds of the glass and copper angle values. The qualitative images supported these findings showing asymmetry in materials with different thermal conductivities with the intersection of reflected shock waves lying closer to the material with a higher thermal conductivity. Control experiments using test pieces made from an identical material showed no bias due to the location of the test piece in the shock tube / XL2018

Soft gamma repeaters (SGRs) and anomalous X-ray pulsars are thought to be neutron stars with strong magnetic fields, called magnetars, which emit intermittent bursts of hard X-rays and soft gamma rays. Three highly energetic bursts, known as giant flares, have been observed originating from three different SGRs, the latest and most energetic of which occurred on December 27, 2004, from the SGR with the largest estimated magnetic field, SGR 1806-20. Modulations in the X-ray tails of giant flares may be caused by global seismic oscillations. Non-radial oscillations of the dense neutron star matter could emit gravitational waves powered by the magnetar's magnetic energy reservoir. This analysis searched for long-duration transient gravitational waves associated with three magnetar bursts that occurred during LIGO's sixth science run, from July 7, 2009 to October 20, 2010. The search results were consistent with the calculated background, and 90% confidence upper limits on the possible undetected gravitational wave energy were found.

Two aspects of detonation dynamics are addressed in this thesis by articles. The first part of the thesis investigates shock reflection phenomena believed to be responsible for enhancing reaction rates in detonations, namely Kelvin-Helmholtz instability and Mach stem bifurcation caused by forward jetting. Three papers are presented. The first numerically investigates shock reflections from a wedge under detonation-like conditions. A state of the art solver of the Euler equations is used. The shock reflection configuration is shown to depend on solver type, wedge implementation, and resolution. The type of reflection (i.e. regular or irregular) is found to depend on corner geometry, even far from the corner, showing initial conditions can play important roles in shock reflections. These complications are addressed with shock-resolved viscous simulations and a new initial condition: the triple point reflection. The numerical method is demonstrated in the second paper, and the presence of Kelvin-Helmholtz instability is investigated. Viscosity is found to play an important role in delaying the instability, which is found not to be a likely source of reaction acceleration on time scales commensurate with autoignition behind the Mach stem, but may become important on scales associated with the detonation cell. Mach stem bifurcations are investigated experimentally and numerically in the third paper. Experimental shock reflections are performed from a free-slip boundary in gases with differing isentropic exponents. Bifurcations are found in experiments, viscous and inviscid simulations. Viscosity is found to delay bifurcations. Inviscid simulations are used to approximate the limits of Mach stem bifurcation in the phase space of Mach number, isentropic exponent, and reflection angle. A maximum isentropic exponent is found beyond which bifurcations do not occur, matching the irregular/regular boundary of the detonation cellular structure. Flow field instability is found in experiments at high Mach number and low isentropic exponent. The second part of the thesis, comprised of one paper, investigates the dynamics of detonations with multiple thermicity peaks using Fickett's detonation analogue. Steady state analysis predicts multiple possible steady states, but only the fastest is singularity-free. Simulations show other solutions develop shock waves that eventually establish a detonation travelling at the fastest velocity allowed by the generalized Chapman-Jouguet criterion. Characteristic and linear stability analysis shows these shocks are found to arise due to instability at the sonic points.

Travelling waves of activity have been experimentally observed in many neural systems. The functional significance of such travelling waves is not always clear. Elucidating the mechanisms of wave initiation, propagation and bifurcation may therefore have a role to play in ascertaining the function of such waves. Previous treatments of travelling waves of neural activity have focussed on the mathematical analysis of travelling pulses and numerical studies of travelling waves. it is the aim of this thesis to provide insight into the propagation and bifurcation of travelling waveforms in biologically realistic systems. There is a great deal of experimental evidence which suggests that the response of a neuron is strongly dependent upon its previous activity. A simple model of this synaptic adaptation is incorporated into an existing theory of strongly coupled discrete integrate-and-fire (IF) networks. Stability boundaries for synchronous firing shift in parameter space according to the level of adaptation, but the qualitative nature of solutions is unaffected. The level of synaptic adaptation is found to cause a switch between bursting states and those which display temporal coherence.