Most components or structures experience in service a variety of cyclic stresses. In the case of cyclic constant amplitude loading the fatigue crack growth depends only on the crack, the component geometry and the applied loading. In the case of variable amplitude loading it also depends on the preceding cyclic loading history. Various types of load sequence (overloads, under-loads, or combination of them) may induce different load-interaction effects which can cause either acceleration or reduction of the fatigue crack growth rate. The previously developed UniGrow fatigue crack growth model for constant amplitude loading histories which was based on the analysis of the local stress-strain material behaviour at the crack tip has been improved, modified and extended to such a level of sophistication that it can be used for fatigue crack growth analyses of cracked bodies subjected to arbitrary variable amplitude loading spectra. It was shown that the UniGrow model enables to correctly predict the effect of the applied compressive stress and tensile overloads by accounting for the existence of the internal (residual) stresses induced by the reversed cyclic plasticity around the crack tip. This idea together with additional structural memory effect model has been formalized mathematically and coded into computer program convenient for predicting fatigue crack growth under arbitrary variable amplitude loading spectra. The experimental verification of the proposed model was performed using 7075-T6, 2024-T3, 2324-T7, 7010-T7, 7050-T7 aluminium alloys, Ti-17 titanium alloy, and 350WT steel. The good agreement between theoretical and experimental data proved the ability of the UniGrow model to predict fatigue crack growth and fatigue crack propagation life under a wide variety of real variable amplitude loading spectra.

Most components or structures experience in service a variety of cyclic stresses. In the case of cyclic constant amplitude loading the fatigue crack growth depends only on the crack, the component geometry and the applied loading. In the case of variable amplitude loading it also depends on the preceding cyclic loading history. Various types of load sequence (overloads, under-loads, or combination of them) may induce different load-interaction effects which can cause either acceleration or reduction of the fatigue crack growth rate. The previously developed UniGrow fatigue crack growth model for constant amplitude loading histories which was based on the analysis of the local stress-strain material behaviour at the crack tip has been improved, modified and extended to such a level of sophistication that it can be used for fatigue crack growth analyses of cracked bodies subjected to arbitrary variable amplitude loading spectra. It was shown that the UniGrow model enables to correctly predict the effect of the applied compressive stress and tensile overloads by accounting for the existence of the internal (residual) stresses induced by the reversed cyclic plasticity around the crack tip. This idea together with additional structural memory effect model has been formalized mathematically and coded into computer program convenient for predicting fatigue crack growth under arbitrary variable amplitude loading spectra. The experimental verification of the proposed model was performed using 7075-T6, 2024-T3, 2324-T7, 7010-T7, 7050-T7 aluminium alloys, Ti-17 titanium alloy, and 350WT steel. The good agreement between theoretical and experimental data proved the ability of the UniGrow model to predict fatigue crack growth and fatigue crack propagation life under a wide variety of real variable amplitude loading spectra.

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Thesis (M.S.)--Oregon State University, 2004. / Typescript (photocopy). Includes bibliographical references (leaves 43-44). Also available on the World Wide Web.

Thesis (Ph. D.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2005. / Includes bibliographical references (p. 137-141).

The majority of fundamental research on wave-driven sediment transport has been based on regular waves and regular oscillatory flows. Systematic research into isolating the effect of irregularity on oscillatory boundary layer hydrodynamics and sand transport are not presently available. This research reports on large-scale oscillatory flow tunnel experiments designed to isolate the effect of flow irregularity (specifically amplitude-modulated flows) on oscillatory flow boundary layer hydrodynamics and net sand transport rates. Two main series of experiments - one focussing on the hydrodynamics of amplitude-modulated flows over a fixed (immobile) bed and a second focussing on the sediment transport over mobile sand beds – were conducted. Detailed boundary layer velocity measurements are presented for regular and amplitude-modulated oscillatory flows over two fixed rough beds, coarse sand and gravel. The results show that amplitude-modulation of the flow has a variable effect on the hydrodynamic behaviour of the oscillatory boundary layer: the broad conclusion is that time-history effects are not significant near the bed but become more significant higher in the flow. Net transport rate measurements are presented for regular and amplitudemodulated flows for two mobile sand beds, medium and fine sand. The mobile bed experiments show that: for medium sand, net transport rates are similar for the amplitude-modulated and equivalent regular; for fine sand, net transport rates are very different for the amplitude-modulated and equivalent regular flows. The SANTOSS model-predicted sand transport rates shows that the model correctly predicts the net transport for the present experimental conditions, indicating that the major unsteady transport processes are captured in the model. The SANTOSS model is used to compare net transport rates for equivalent regular and amplitude-modulated flows across a wide range of flow conditions and two sand sizes. The results show good agreement in net transport rate between equivalent regular and amplitude-modulated flows, for conditions in which phase lag effects are weak and poor agreement when phase lags effects are strong.

Made available in DSpace on 2014-06-12T23:16:29Z (GMT). No. of bitstreams: 2 arquivo8985_1.pdf: 6256902 bytes, checksum: bf1bb2fb349ad80458b99abb9d0c8eea (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2002 / Universidade Federal de Pernambuco / A existência de temperaturas compreendidas entre valores médios e elevados e pequena amplitude térmica, combinadas com valores elevados de umidade relativa e radiação solar, tornam a cidade do Recife uma região considerada como de escassas possibilidades em termos de oportunidades de climatização através de métodos passivos ou de baixo consumo de energia. Levando em conta essas características, as cartas bioclimáticas sugerem, como alternativa principal para a climatização local, a circulação natural de ar, recurso muitas vezes insuficiente. No intuito de identificar oportunidades de obtenção de conforto térmico, foi realizado um estudo teórico-experimental sobre a interação entre fatores ambientais e um recinto localizado na cidade do Recife. O comportamento térmico de um dos laboratórios do Grupo de Pesquisas em Fontes Alternativas de Energia (Grupo FAE DEN/UFPE) foi utilizado como referência experimental. Com tal fim, foram monitoradas, ao longo de vários meses, a temperatura interna desse laboratório, a radiação solar, a temperatura ambiente, a velocidade e direção do vento e a umidade relativa. A interação entre os fatores climáticos e o recinto foi estudada através da correlação entre sua temperatura interna e os parâmetros meteorológicos observados. Modelos disponíveis na literatura para representar analiticamente os valores de temperatura ambiente, umidade relativa e radiação solar xix incidente nas paredes e teto do recinto, são fornecidos como uma proposta para generalizar os resultados obtidos para outras localidades e períodos do ano. Os resultados dos modelos de cálculo de umidade relativa e temperatura ambiente, baseados em valores médios, máximos e mínimos históricos dessas variáveis, são apresentados. A análise da carga térmica do laboratório nos meses de junho e novembro mostra que entre 76 a 78 % da mesma é devida a incidência de radiação solar no teto. Sua temperatura interna encontra-se em torno de 3 oC acima da temperatura média ambiente, com uma amplitude térmica entre 2,5 e 3,6 oC, enquanto que a amplitude térmica ambiente apresenta valores entre 5,9 e 8,2 oC. O conjunto de observações realizadas permite discutir as oportunidades que o clima de Recife oferece para a realização de projetos residenciais que forneçam condições térmicas confortáveis e com baixo consumo de energia. Por conseguinte, foram identificadas estratégias tais quais: a injeção de ar frio proporcionada pela ventilação noturna, durante o período em que o ar ambiente atinge temperaturas em torno de 230C, promoção de transferência de calor através do piso da residência, mediante tratamento adequado de sua estrutura assim como do entorno da habitação, criação de micro-clima através do resfriamento evaporativo nos horários de maiores valores de temperaturas ambientes e menores de umidade relativa, além dos procedimentos habituais de isolamento térmico e radiante do telhado e ou uso de tintas seletivas, bloqueio da radiação incidente nas paredes mais atingidas e ventilação cruzada. Espera-se que este estudo possa contribuir no processo de planejamento e concepção de projetos bioclimáticos localizados em Recife, propiciados pela utilização de meios passivos e sustentáveis do ponto de vista energético e de conforto

<p> Using a Q-spoiled Nd-glass laser, an experimental investigation of frequency doubling in NiSO4•6 H2O was carried out. The frequency doubling was observed to occur at a phase matching angle of 56° ± 1°. Experimentally, it is shown that the fundamental frequency at λ = 1.06 μm is an O-ray while the doubled frequency at λ = .53μm is an E-ray. Since the amplitude for electric dipole frequency doubling in NiSO4•6 H2O is zero, these observations are unusual. The observations are attributed to magnetic dipole and/or electric quadrupole frequency doubling. Evidence to support this view comes from the magnitude of the effect and from its azimuthal dependence. The electric quadrupole type frequency doubling is consistent with the data only if the susceptibility coefficients satisfy the relation QאEE =1/2 (QאEE - QאEE ) 1212 1111 1122 </p> / Thesis / Doctor of Philosophy (PhD)

The world is filled with richly diverse sounds which we are able to perceptually distinguish using a variety of properties. One of these properties is the amplitude envelope, or the intensity of a sound over time. While it is common in the real world for sounds to have time-varying amplitude envelopes, the majority of sounds used in perceptual research have time-invariant or unspecified amplitude envelopes. The aim of the present thesis is twofold. Because many of the studies using time-invariant or undefined envelopes make use of very short sounds (below 100 msec), the first experiment aimed to determine the duration required for discriminating among three different envelopes: flat (invariant), ramped (increasing in intensity over time), and damped (decreasing in intensity over time). In Experiment 1, participants took part in a 2-alternative forced choice, psychophysical staircase paradigm in which they indicated which of two envelopes they thought they were listening to. Results showed that, when telling ramped tones apart from either flat or damped tones, participants showed discrimination thresholds below 50 msec, while they had thresholds of approximately 75-80 msec when differentiating flat from damped tones. Because amplitude envelope has been shown to impact audiovisual integration and the perceptual system is sensitive to interaural envelope differences when localizing sounds, the second experiment aimed to determine whether amplitude envelope could modulate the visual bias present in spatial ventriloquism, an audiovisual illusion where the perceived location of a sound is influenced by the location of a visual stimulus. In Experiment 2, participants performed a psychophysical staircase task which measured their accuracy in localizing sounds with flat and damped envelopes, with or without a simultaneous flash on the screen in front of them. Results showed that, at durations above the envelope discrimination thresholds found in Experiment 1 (83 msec), there was no visual bias on perceived location of the sound, while the bias was present at a duration below this threshold (16 msec). Together, these results add to the mounting evidence suggesting that amplitude envelope has profound and varied effects on our perception of sounds, and is an important property to consider when designing experiments. / Thesis / Master of Science (MSc)