The objective of this study is to investigate and characterize the mechanism of the island wake behind an island called Liu Chiu Yu off the southwestern Taiwan coast based on the in-situ data of Sb-ADCP, CTD and satellite images. The findings suggest that a counter-clockwise eddy and a clockwise eddy both are with 0.01 S vortice appears in the wake of Liu Chiu Yu when the background flows are toward the northwest. The system of two eddies with opposite rotation and a central return flow develops an unsteady eddy shedding. On the other hand, when the background flows are toward the southeast, island wake generated in the lee of Liu Chiu Yu is attached system of two eddies with opposite rotation and a central return flow. The Sb-ADCP data shows that the flow pattern in the northeastern coast of Liu Chiu Yu is mainly semidiurnal. The major axis of the ellipse of the semidiurnal current is parallel to the orientation of the coast line (northeast to southwest) and the shape of the ellipse is quite long and narrow. The amplitude of the semidiurnal current is approximately two times that of the diurnal current. Generally, the currents are stronger and the occurring probability of the island wake is higher during spring tide. The CTD data shows that the eddy center appears to be divergent and upwelling occurs in the areas under the influence of island wakes. The upwelling pumps deep seawater to the surface and results in low temperature, high salinity, high oxygen concentration and low chlorophyll concentration. On the other hand, in the eddy edges, downwelling occur causing high temperature, low salinity, low oxygen concentration and high chlorophyll concentration. Strong shear was formed at the depth of 60m inside the island wake which generates thermocline so that the mixing phenomenon is quite obvious there. Moreover, in the regions without the influence of island wakes, the stratifying effect is clear and the horizontal variation of temperature, salinity and oxygen concentration is small. Therefore, neither upwelling nor downwelling occurs there. Furthermore, along the edge between blocking and free-stream areas, the shear stress increases and the mixing phenomenon arises to a certain degree. The satellite images show that an island wake appears in the southeastern Liu Chiu Yu during spring tide. The island wake develops a phenomenon called von Karman vortex street. At the same time, a counter-clockwise eddy with heavy suspensions appears in the northern Liu Chiu Yu. The radius of the eddy is around 4 Km. The area of the lowest chlorophyll concentration is located at the center of the eddy. By analyzing all these data, it is concluded that the island wake in Liu Chiu Yu usually appears during spring tide.

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This experiment is to investigate the effects of fluid with and without mass injection through a slit on the vortex shedding from a single cylinder. We research Reynolds Numbers on ranges from 800 to 4000. We used four kinds of ways which contain no mass injection, steady blowing, steady suction and oscillatory jet to study of the wake behind a circular cylinder under excitation in this experiment. No mass injection is measured for the sake of its reliability and comparability of experiment. Steady blowing and suction are applied to influence the wake flow. An oscillatory jet is used to influence the wake flow with varying frequencies and amplitudes. The experiment looks forward to use the results of this experiment so as to research into the effects on the wake flow, including the velocity values of fluctuation and turbulence intensity of the vortices structure, the dominant frequency in the flow pattern on a single cylinder. The main parameters in the study are the frequency, momentum and the location of the blowing and suction jet, which are a steady jet or unsteady oscillatory jet. Flow visualization has been carried out to investigate the interaction of steady or unsteady fluid perturbation and the vortex shedding of a cylinder.

<p>Wind tunnel studies of the wake behind model wind turbines with one, two and three blades have been made in order to get a better understanding of wake development as well as the possibility to predict the power output from downstream turbines working in the wake of an upstream one. Both two-component hot-wire anemometry and particle image velocimetry (PIV) have been used to map the flow field downstream as well as upstream the turbine. All three velocity components were measured both for the turbine rotor normal to the oncoming flow as well as with the turbine inclined to the free stream direction (the yaw angle was varied from 0 to 30 degrees). The measurements showed, as expected, a wake rotation in the opposite direction to that of the turbine. A yawed turbine is found to clearly deflect the wake flow to the side showing the potential of controlling the wake position by yawing the turbine. The power output of a yawed turbine was found to depend strongly on the rotor. The possibility to use active wake control by yawing an upstream turbine was evaluated and was shown to have a potential to increase the power output significantly for certain configurations. An unexpected feature of the flow was that spectra from the time signals showed the appearance of a low frequency fluctuation both in the wake and in the flow outside. This fluctuation was found both with and without free stream turbulence and also with a yawed turbine. The non-dimensional frequency (Strouhal number) was independent of the freestream velocity and turbulence level but increases with the yaw angle. However the low frequency fluctuations were only observed when the tip speed ratio was high. Porous discs have been used to compare the meandering frequencies and the cause in wind turbines seems to be related to the blade rotational frequency. It is hypothesized that the observed meandering of wakes in field measurements is due to this shedding.</p>

Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Howard, Richard M. Second Reader: Healey, J. Val. "September 1990." Description based on title screen as viewed on December 15, 2009. DTIC Identifier(s): Strakes, Yaw, Aerodynamic Forces, Surface To Air Missiles, Angle Of Attack, High Angles, Sides, Side Forces, Wind Tunnel Models, Guided Missile Models, Vortex Shedding, High Angle Of Attack, Turbulence, Forebody Strakes, Ogives, Computer Programs, Theses, Vertical Launch. Author(s) subject terms: Vortex, Vertical Launch, Surface to Air Missile, High Angle of Attack, Turbulence, Strakes, Forebody, Ogive. Includes bibliographical references (p. 154-157). Also available in print.

No description available.

Antibiotics are important to equine medicine, but can cause detrimental side-effects including reduced feed intake, allergic reactions, and diarrhea. Antibiotic-associated diarrhea (AAD) is attributed to disruption of the hindgut microflora, permitting proliferation of pathogenic microbes. The objectives were to evaluate the effects of antibiotics on beneficial fecal bacteria, AAD-associated pathogens, microbial species richness and fermentation. Horses were assigned to treatment groups: control (no antibiotics, n=6), trimethoprim-sulfadiazine (oral, n=6), or sodium ceftiofur (IM, n=6). Fecal samples were taken during adaptation (3 wk), antibiotic challenge (1 wk), and withdrawal (1 wk). Fecal cellulolytics decreased by >99% during challenge and did not recover during withdrawal (P < 0.0001). Lactobacilli decreased by >60% during challenge (P = 0.0453). Salmonella spp. increased 94% with trimethoprim-sulfadiazine challenge (P = 0.0115). There was no detectable Clostridium difficile during adaptation or in any control horse. C. difficile increased (P < 0.0001) when horses were challenged, and remained elevated 7 d after withdrawal. There was no effect of challenge on in vitro digestibility or microbial species richness as evaluated by denaturing gradient gel electrophoresis (P > 0.05). These results indicate that antibiotics can disrupt the normal flora and allow proliferation of pathogens, even without affecting digestibility and causing AAD.

[Truncated abstract] The subject of fan noise generating mechanisms and its control has been studied intensively over the past few decades as a result of the ever-increasing demand for more powerful fans. A unique feature of fan noise is that it consists of high-level discrete frequency noise related to the blade passing frequency, and low-level broadband noise due mostly to turbulent airflow around the fan. Of the two types of fan noise, the discrete frequency noise is the more psychologically annoying component. Past research into fan noise has shown that the discrete frequency fan noise are dipole in nature and are caused predominantly by the fluctuating lift acting on the surfaces of the fan blades. Based on this, several theoretical models have been established to correlate these fluctuating lift forces to the far-field sound pressure. However, one general assumption in these models is that the fan blades are assumed rigid, and the consequence of such an assumption is that it is unclear if the far-field sound pressure is caused solely by the aerodynamic lift force, or whether the blade vibration also plays a substantial role in the generation of the far-field fan noise. One of the goal of this thesis was thus to experimentally quantify the contribution of blade vibration to far-field fan noise and it was found that blade vibration, whilst coherent with the far-field fan noise, did not contribute significantly. Aside of this, several experiments aimed at filling knowledge gaps in the understanding of fan noise characteristics were also be conducted, in particular, to understand the relationship between far-field sound pressure level to blade lengths as well as the number of blades on the fan. The experiments showed that for fans with many blades, the dependency of the far-field sound pressure on blade length is stronger than fans with less blades. Furthermore, dipole measurements showed that the dipole characteristics of fan noise does not occur only at the discrete frequencies, but also within a range of broadband frequencies, implying that the source for both discrete and broadband is the same. The second section of this thesis deals with the study of vortex shedding and its active control. When a circular cylinder (or any object) is placed in a flow within a specified Reynolds number range, flow separation and periodical wake motion is formed behind the cylinder, which is known as vortex shedding. It has been found in previous research that this wake motion is affected by acoustic field imposed on it via loudspeakers. This suggests that there is a strong acoustic-vortex relationship. However, little of this relationship is understood as conventional methods of studying vortex centre around the use of hot-wire anemometry, which effectively measures the velocity fluctuation in the flow. This thesis is the first in using a microphone to study the acoustic characteristic of the vortex wake, and experimental results shows that the two parallel shear layers of the wake carry the strongest pressure signals at the vortex shedding frequency, whilst the entrapped region between the layers carries the strongest pressure signals at the first harmonic.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 101-121).

O conhecimento do comportamento aerodinâmico do tabuleiro de uma ponte é um fator determinante em projetos de pontes e na resolução de problemas práticos de engenharia associados. No Brasil ainda são poucas, mas crescentes, as construções de pontes com cabos, sejam elas pênseis ou estaiadas. Estas fazem parte do foco do estudo desta tese de doutorado que visa à obtenção de contribuições para ampliar a base de dados referentes aos parâmetros que influenciam o comportamento aerodinâmico de pontes. Busca-se investigar e quantificar os efeitos de interferência devidos à ação do vento em tabuleiros paralelos (próximos) de pontes, frente à resposta induzida pelo desprendimento de vórtices, gerando subsídios para a elaboração de projetos e solução de problemas da prática da Engenharia Civil. O programa experimental foi realizado nas instalações do Túnel de Vento Prof. Joaquim Blessmann da Universidade Federal do Rio Grande do Sul. Foram realizadas medidas em modelos seccionais reduzidos de um tabuleiro de ponte. Um modelo teve sua secção transversal média instrumentada com tomadas de pressão para determinação do campo de pressões. Foram obtidos campos de pressões para o modelo isolado e para distintas configurações de vizinhança (posicionamento de outro tabuleiro idêntico paralelo ao instrumentado) O outro modelo seccional foi ensaiado com o auxílio de um dispositivo que permite a simulação de dois graus de liberdade, vertical e torcional, utilizado para a determinação do comportamento dinâmico do tabuleiro frente ao desprendimento de vórtices. Nestes testes foram investigadas as condições de vizinhança, de dispositivos aerodinâmicos (nariz de vento) além da variação do nível de amortecimento em relação ao crítico, sendo a seguir realizadas medidas do campo de velocidades no entorno do modelo do tabuleiro. Os efeitos de interferência observados, a partir dos testes com modelos estáticos, variaram de acordo com cada uma das disposições geométricas estudadas. Em determinadas situações foram observados efeitos benéficos de proteção, entretanto, aumentos nos coeficientes também ocorreram. Os resultados obtidos com os modelos dinâmicos indicaram, de uma forma geral, melhora na estabilidade aerodinâmica em relação à situação com modelo isolado. Foi observada a ocorrência de mais de um pico na resposta vertical por desprendimento de vórtices o que ocasionou estudos adicionais aos inicialmente propostos. A partir da verificação da real possibilidade de ocorrência de mais de um pico na resposta, propõe-se a inclusão de novas orientações para o projeto de estruturas suscetíveis a vibrações verticais por desprendimento de vórtices em texto de normas ou recomendações de projeto. / The knowledge of the aerodynamic behavior of a bridge deck is a major factor in the design of bridges and in the solving of related engineering problems. There are still not many suspension or cable stayed bridges in Brazil, although the construction of these kind of structures has been increasing in the last years. This Thesis has the aim of contributing with the broadening of the state of the art in the aerodynamics of cable stayed bridges. The objective is to investigate the effects of aerodynamic interference in closely spaced bridge decks due to vortex shedding. The experimental program was performed in the boundary layer wind tunnel Prof. Joaquim Blessmann of the Universidade Federal do Rio Grande do Sul. The measurements were obtained through sectional models of bridge decks. One of the models was instrumented with pressure taps for the measurement of the individual pressure field (isolated model) as well as for several vicinity configurations (two closely spaced parallel models). The other sectional model was tested through an experimental device which allows the simulation of two degrees of freedom, vertical and torsional, used for the investigation of the bridge deck behavior under vortex shedding excitation. Several vicinity configurations, aerodynamic devices, damping levels and measurement points around the models were investigated in the wind tunnel tests. The interference effects observed from the static models vary according to each one of the geometric positions studied. For some situations there were beneficial protection effects, although an increase in the value of the coefficients also occurred. The results from the dynamic model have generally indicated an improvement in the aerodynamic stability in relation to the isolated model. It was also observed that more than one peak occurred for the vertical response due to vortex shedding, which lead to additional studies to the initial planned. From these observations, the inclusion of new guidelines for the design of structures susceptible to vertical vibrations due to vortex shedding, in the specific codes, are recommended.