Thesis (Ph.D.) -- University of Adelaide, Department of Mechanical Engineering, 1978.

Made available in DSpace on 2014-06-11T19:25:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-04Bitstream added on 2014-06-13T19:12:15Z : No. of bitstreams: 1 carvalho_jps_me_guara.pdf: 1120789 bytes, checksum: 42d7f707a41ef83886b116f000a33c22 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Universidade Estadual Paulista (UNESP) / Uma teoria para estudar o movimento orbital de satélites artificiais sobre efeitos do arrasto atmosférico e da pressão de radiação solar direta - considerando a sombra da Terrae alguns termos do geopotencial - é desenvolvida analiticamente. A sombra daTerra é modelada utilizando a função sombra, como introduzida por ferraz Mello: igual zero quando o satélite está na região de sombra e igual um quando é iluminado pelo sol. As componentes do arrasto são dadas por Vilhena de Moraes baseado no modelo atmosférico TD-88. O método de Hori para sistemas não canônicos é aplicado para resolver as equações de movimento. Um software para manipulação algébrica é fundamental apra fazer os cálculos necessários. Efeitos seculares e periódicos que influenciam no movimento orbital dos satélites artificiais são analisados. Expressões analíticas são apresentada explicitamente para os principais termos seculares nas variações dos elementos orbitais. É dada ênfase aos termos de acoplamento que surgem na solução do sistema de equações diferenciais. Utilizando dados orbitais do satélite CBERS-1 um estudo é feito para analisar ordens da variação do semi-eixo maior devidas as pertubações consideradas. / A theory to study the orbital motion of artificial satellites under the effects of the atmospheric drag and of the direct solar radiatin pressure - considering the Earh's shadow and some terms of the geopotential - is developed analytically. The Earth shadow is modeled using the shadow function introduced by Ferrz Mello: equal zero when the satellite is in the shadow region and equal one when it is illuminated by the Sun. The drag components are given by Vilhena of Moraes based in the TD-88 temospheric model. The Hori's method for non-canonical systems is applied to solve the motion equation. A algebric manipulator software is fundamental to do the necessary calculations. Secular and periodic effects on the orbital motion of artificial satellites are analyzed. Analytic expressions are presented explicity for the main secular terms of the variations of the orbital elements. Emphasis is given to the coupling terms that appear in the solution of the differential euqatin systems. Using orbital data of the satellite CBERS-1 a study is done to analyze the order of magnitude of the variation of the semi-major axis due to the considered pertubation.

The primary goal of this thesis is to utilize acoustical radiation from the Arctic ice cover to infer the response of sea ice to environmental forcing, and to sense remotely the mechanical properties of the ice. The work makes use of two experiments in the Canadian arctic undertaken by the Ocean Acoustics Group of the Institute of Ocean Sciences, which resulted in an extensive body of acoustical and related environmental data. Cracking sounds originating from both first and multi-year ice fracturing processes are analyzed. Data used in this thesis also include sound made by artificial sources. The survey of in situ ice conditions by air photography and synthetic radar imaging, and a crack distribution map based on observations made with a 3-D hydrophone array, reveal, for the first time, a close correlation between thermal cracking events and ice type. It is shown that most of the thermal cracks occur in irregular multi-year ice where there are exposed, snow-free surfaces. The study shows that acoustical radiation from some cracks implies a slip-stick seismic movement over the faults, and some cracks tend to radiate more high frequency sound downwards rather than sideways. This phenomenon is most clearly apparent in sounds made by artificial sources. Another interesting finding from this study is that the sound of cracking ice does not always exhibit a vertical dipole radiation pattern, and some cracks due to thermal tension on smooth first year ice radiate more energy horizontally. The observations have motivated the development of various analytical models. These models allow the observed acoustical features to be related to the length and depth of a crack, the thickness of the ice cover and its Young's modulus. The models also show that maximum sound radiation from a crack is in the direction of external forcing. Finally, it is found that noise due to rubbing between ice floes exhibits a narrow band spectrum. This phenomenon is investigated and a linear model derived shows that the observed peak frequency is that of the first mode horizontal shear wave triggered by frictional effects at the ice floe edge. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Two experiments were conducted to study the active control of acoustic radiation due to discontinuities on thin beams. One experiment investigated the radiation from a clamped end condition and the other investigated the radiation from a blocking mass. The beams were excited by subsonic flexural traveling waves which "scattered" (or produced reflected and transmitted traveling and near-field waves) when they encountered the discontinuity. This "scattering" produced supersonic wave number components in the beam vibrational response which were responsible for the acoustic radiation. The main purpose of these experiments was to control the acoustic radiation from discontinuities on beams by actively changing the characteristics of the "scattered" waves with control actuators. In each experiment the system was disturbed by a harmonic, subsonic input from a point force shaker. Control actuator( s) (in the form of shakers and piezoelectric actuators) were attached to the beam near the discontinuity. Error microphone(s) were positioned in the acoustic field which supplied an error signal to the digital controller. The digital controller employed was the filtered-x version of the adaptive LMS algorithm programmed on a dedicated signal processing board in a personal computer. An array of accelerometers was attached to the beam which were used to decompose the complex amplitudes of an assumed displacement equation. By applying a spatial Fourier transform to the displacement equation the wavenumber components present in the beam displacement were calculated. This aided in the investigation of the mechanism by which control of the acoustic field was affected. Results from these experiments showed that large attenuations at the error microphones were possible (as much as 50dB) along with global attenuation of the acoustic field. The mechanism by which the control of the acoustic far-field was achieved was demonstrated as a decrease in the supersonic wavenumber components in the beam vibrational response. / Master of Science

A double loop control scheme is developed to control broadband acoustic radiation from a cylinder. An analog feedback loop is investigated and developed to add damping to the cylinder at particular frequencies of interest. Circuitry is developed and refined to condition Polyvinylidene Fluoride Filnl (PVDF) sensor outputs as strain rate signals. The strain rate signals are used in the feedback loop to provide damping to the structure. In conjunction with the feedback loop a feedforward loop is also implemented. The feedforward loop utilizes the filtered-x LMS algorithm. The result of combining the two control laws was unknown prior to implementation.The resulting control scheme shows that the feedback control law is effective in attenuating undesirable frequency components in the feedforward error sensor. This results in an error sensor signal which is highly correlated with the disturbance. With a more correlated error signal a more effective feedforward control is achieved. The resulting control system provides acoustic control over a wide range of frequencies. The filtered-x LMS algorithm is applied to an effective acoustic radiator. The feedback loop provides for broadband control of the structure. Typical double loop controller results show power spectrum reductions of 35 dB for an effective acoustic radiator and reductions of 10 dB for other frequencies in the excitation range. In addition, the measured controlled plant transfer functions show significant reductions in the transfer of energy through the structure. Overall Sound Pressure Level (SPL) reduction in the acoustic field generated by the cylinder in response to a random excitation with a harmonic component was 4.9 dB for feedback, 18.4 dB for feedforward, and 25.2 dB for the double loop controller. / Master of Science

The concept of tailored force fields is seen as an enabler for the construction of large scale space structures. Manufacturing would take place in space using in-situ resources thereby eliminating the size and weight restriction commonly placed on space vehicles and structures. This thesis serves as the first investigation of opening the way to a generalized fabrication technology by means of force fields. Such a technology would be non-contact, flexible, and automated. The idea is based on the principle that waves carry momentum and energy with no mass transport. Scattering and gradient forces are generated from various types of wave motion. Starting from experiments on shaping walls using acoustic force fields, this thesis extends the technology to electromagnetic fields. The interaction physics of electromagnetic waves with dielectric material is studied. Electromagnetic forces on neutral dielectric material are shown to be analogous to acoustic forces on sound-scattering material. By analogy to the acoustic experiments, force fields obtained by optical tweezers are extended to longer wavelength electromagnetic waves while remaining in the Rayleigh scattering regime. Curing of the surface formed takes place by use of a higher frequency beam that scans the surface and melts a subsurface layer enabling a sintering effect to take place between the particles. The resulting capability is explored at its extremes in the context of building massive structures in Space. A unification of these areas is sought through a generalization of the various theories provided in the literature applicable for each field.

Ce travail de thèse est consacré à la manipulation et la déformation optique d'interfaces liquides molles, cela dans deux géométries fondamentales: plane et sphérique. Nous montrons alors que les déformations induites par pression de radiation optique permettent de déduire les propriétés des interfaces, comme la tension interfaciale par exemple. Dans le cadre de la déformation d'une interface liquide plane par pression de radiation, nous généralisons pour la première fois la manifestation électro-hydrodynamique des cônes de Taylor au régime optique, en montrant que des cônes liquides peuvent émerger sous fortes excitation laser. Nous avons alors caractérisé la morphologie de ces « cônes optiques » et nous montrons que l'angle de ces derniers dépend à la fois des paramètres de l'excitation laser mais aussi des caractéristiques des fluides. Une étude analytique ainsi qu'une étude numérique ont alors été menées afin de rendre compte des comportements observés.Afin d'étudier la déformation d'interfaces molles en géométrie sphérique, nous avons développé un double piège optique fibré en dispositif microfluidique dans une configuration inédite en termes de longueur d'onde excitatrice et de puissance laser. Nous avons alors appliqué notre dispositif à la déformation de vésicules en tant qu'objets modèles mous et nous montrons que notre double piège est bien adapté à la caractérisation rhéologique d'objets micrométriques déformables. Grâce à l'utilisation de faisceaux laser de forte puissance, nous mettons ici en évidence expérimentalement l'apparition d'un régime non-linéaire de déformation au sein de notre double piège optique. / This thesis work is devoted to the optical manipulation and deformation of soft liquid interfaces, in two fundamental geometries: plane and spherical. We then show that the deformations induced by optical radiation pressure allow to deduce the properties of interfaces, such as interfacial tension for example. In the framework of the deformation of a plane liquid interface by optical radiation pressure, we generalize for the first time the electro-hydrodynamic manifestation of Taylor cones to the optical regime, showing that liquid cones can emerge under intense laser excitation.We then characterized the morphology of these "optical cones" and we show that their angle depends both on the parameters of the laser excitation and on the characteristics of the fluids. An analytical study as well as a numerical investigation were then conducted to account for the observed behaviors. In order to study the deformation of soft interfaces in spherical geometry, we have developed a fiber-based dual-beam optical trap in a microfluidic device in a novel configuration in terms of excitation wavelength and laser power. We then applied our device to the deformation of vesicles as soft model objects and we show that our dual-beam trap is well adapted to the rheological characterization of deformable micron-sized objects. Thanks to the use of high laser power beams, we experimentally highlight the appearance of a non-linear deformation regime within our double optical trap.

This Ph.D. thesis is devoted to the development of a specific semi-analytical algorithm especially well-suited to derive the long-term evolution of near geosynchronous space debris and based on the concept of mean orbital motion. In a first approach, the semi-analytical theory is concerned with the singularity issues arising for circular and equatorial orbits as well as with the geostationary resonance modeling. In a second part, motivated by the discovery of high area-to-mass ratios space debris in high altitude Earth's orbit (mostly near the geosynchronous region), the direct radiation pressure models are revisited and completed. Within this context, the main effects of the direct solar radiation pressure for the mid- and long-term evolution of both the eccentricity and the inclination vectors are analyzed through a well-suited model. Moreover, by means of a smart extension, the passage in the Earth's shadow is taken into account in the computations of the orbits. Finally, a further insight into the intrinsic stability of such space debris is performed, by means of a recent numerical technique (MEGNO) which is based on the concept of ``variational chaos indicator'.

xi, 265 leaves : photos., diags ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1978

xi, 125 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / This dissertation presents experimental and theoretical studies of radiation pressure cooling in silica optomechanical microresonators where whispering gallery modes (WGMs) are coupled to thermal mechanical vibrations. In an optomechanical system, circulating optical fields couple to mechanical vibrations via radiation pressure, inducing Stokes and anti-Stokes scattering of photons. In analogy to laser cooling of trapped ions, the mechanical motion can in principle be cooled to its ground state via the anti-Stokes process in the resolved-sideband limit, in which the cavity photon lifetime far exceeds the mechanical oscillation period. Our optomechanical system is a slightly deformed silica microsphere (with a diameter 25-30 μm ), featuring extremely high Q -factors for both optical ( Q o ∼ 10 8 ) and mechanical ( Q m ∼ 10 4 ) systems. Exploiting the unique property of directional evanescent escape in the deformed resonator, we have developed a free-space configuration for the excitation of WGMs and for the interferometric detection of mechanical displacement, for which the part of input laser that is not coupled into the microsphere serves as a local oscillator. Measurement sensitivity better than 5 × 10 -18 m /[Special characters omitted.] has been achieved. The three optically active mechanical modes observed in the displacement power spectrum are well described by finite element analysis. Both radiation pressure cooling and parametric instabilities have been observed in our experiments. The dependence of the mechanical resonator frequency and linewidth on the detuning as well as the intensity of the input laser show excellent agreement with theoretical calculations with no adjustable parameters. The free-space excitation technique has enabled us to combine resolved sideband cooling with cryogenic cooling. At a cryogenic temperature of 1.4 K, the sideband cooling leads to an effective temperature as low as 210 m K for a 110 MHz mechanical oscillator, corresponding to an average phonon occupation of 37, which is one of the three lowest phonon occupations achieved thus far for optomechanical systems. The cooling process is limited by ultrasonic attenuation in fused silica, which should diminish when bath temperature is further lowered, with a 3 He cryostat, to a few hundred millikelvin. Our experimental studies thus indicate that we are tantalizingly close to realizing the ground-state cooling for the exploration of quantum effects in an otherwise macroscopic mechanical system. / Committee in charge: Michael Raymer, Chairperson, Physics; Jens Noeckel, Member, Physics; Hailin Wang, Member, Physics; Paul Csonka, Member, Physics; Jeffrey Cina, Outside Member, Chemistry