京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第14135号 / 工博第2969号 / 新制||工||1441(附属図書館) / 26441 / UT51-2008-N452 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 杉浦 邦征, 准教授 白土 博通, 准教授 宇都宮 智昭 / 学位規則第4条第1項該当 / Doctor of Engineering / Kyoto University / DFAM

On étudie le transport et la dispersion hydrodynamique d’un traceur passif et/ou d’une suspension de particules dans deux fractures modèles avec deux parois lisses ou avec une distribution aléatoire d’obstacles dans l’ouverture. On utilise un écoulement oscillant d’un fluide newtonien afin d’observer les effets sur la dispersion de la réversibilité du déplacement. On caractérise de manière quantitative l’influence des paramètres caractéristiques de l’écoulement: période T et amplitude A des oscillations et temps caractéristique τ_m de diffusion moléculaire sur l’épaisseur.Dans le cas de parois lisses, on montre que les régimes de dispersion sont déterminés par le rapport τ_m/T . Pour τ_m/T≤2, le régime de dispersion de Taylor est dominant et irréversible à l’échelle globale. Pour τ_m/T≥20, on a un régime partiellement réversible pour lequel le mélange reste diffusif à l’échelle globale mais où, localement, la distribution des particules de traceur dans l’épaisseur suit les oscillations de la vitesse locale v_x (z,t) . Dans ce cas, il existe une composante purement convective et réversible de la dispersion.Dans le cas d’une cellule rugueuse, le désordre induit par les obstacles fait apparaitre une composante de dispersion géométrique quand τ_m/T≤0,6, pour laquelle la dispersivité normalisée par l’amplitude l_d/A ne dépend pas de la période T. On observe le régime de dispersion de Taylor dans une gamme 〖0,8≤τ〗_m/T≤1 dépendant de l’amplitude de l’oscillation. Lorsque τ_m/T≥20, on observe le régime de dispersion partiellement réversible déjà observé précédemment dans la cellule lisse. En comparant ces mesures avec celles obtenues par des techniques complémentaires (écho et transmission), on a pu séparer la composante irréversible de la dispersion de la composante réversible associée à des chenaux macroscopiques d’écoulement préférentiel dus à la géométrie de la fracture. L’influence sur la dispersion de particules de 40 µm de diamètre en suspension dans l’écoulement oscillant a été ensuite étudiée dans la cellule lisse. La mesure globale de dispersion a mis en évidence les mêmes régimes d’écoulement qu’en l’absence de particules avec des domaines d’existence déterminés, comme dans ce cas, par la valeur du rapport τ_m/T.Pour mieux comprendre l’origine microscopique des résultats, nous avons suivi les trajectoires individuelles des particules dans un écoulement oscillant. Leur mouvement et la distribution de leurs vitesses ont été mesurés dans plusieurs couches à différentes distances dans l’épaisseur. On observe que les particules suivent les lignes de courant et que le profil de leurs vitesses dans l’épaisseur a la forme parabolique d’un profil de Poiseuille. Par ailleurs, nous avons comparé les distributions des particules après un certain nombre d’oscillations à celles au temps initial et observé, pour de longues périodes T, une migration des particules vers les parois de la cellule. Enfin, certaines particules présentant une réversibilité cinématique de leur mouvement, avec des allers retours suivant la même trajectoire, même en présence d’interactions entre elles.Enfin, en augmentant la concentration des particules, on observe une structuration de la suspension en bandes perpendiculaires à l’écoulement. On a étudié la longueur d’onde λ de cette instabilité en fonction de paramètres géométriques (épaisseur H et largeur de la cellule, diamètre des particules), physiques (viscosité et densité du fluide, densité des particules) et de l’écoulement (variation sinusoïdale ou carrée du débit, amplitude A et période T). La longueur d’onde normalisée λ/H augmente linéairement avec l’amplitude normalisée A/H mais est constante avec T et H et avec le diamètre des particules. Au niveau local, l’instabilité correspond à des variations périodiques de concentration suivant la largeur de la cellule et présentes dans toute l’épaisseur. / We study the transport and the hydrodynamical dispersion of a passive tracer and/or a suspension of non-Brownian particles in two model fractures with smooth walls or a random distribution of obstacles in the aperture. We use an oscillating flow of a Newtonian fluid in order to study the effects of the reversibility of the displacement on dispersion. We characterize quantitatively the effects of the characteristic parameters of the flow: period T and amplitude A of the oscillations, and characteristic time τ_m of molecular diffusion across the thickness of the cell.In the case of smooth walls, we show that the dispersion regimes are determined by the value of the ratio τ_m/T. For τ_m/T≤2, the Taylor dispersion mechanism is dominant and irreversible at the global scale. For τ_m/T≥20, one has a partly reversible regime in which mixing remains diffusive at the global scale but, locally, the distribution of the particles in the thickness of the cell follows the oscillations v_x (z,t) of the local velocity. In this case, there exists a purely convective and reversible dispersion component.In the case of a cell with rough walls, flow disorder due to the obstacles results in a geometrical dispersion component when τ_m/T≤0,6, for which the dispersivity normalized by the amplitude l_d/A does not depend on the period T. The Taylor dispersion regime is observed in a range 0,8≤τ_m/T≤1 depending on the amplitude of the oscillation. When τ_m/T≥20, one obtains the partly reversible dispersion regime already observed previously for the smooth cell. Comparing these results to those obtained by complementary techniques (echo and transmission) allows us to separate the irreversible component of dispersion from the reversible one associated to macroscopic preferential flow channels due to the fracture geometry.The influence on dispersion of a suspension of 40 µm diameter non Brownian particles in the oscillating flow has then be studied in the cell with smooth walls. The global tracer dispersion measurements have shown the same dispersion regimes than without particles with domains of existence determined, like in this latter case, by the value of the ratio τ_m/T.In order to understand better the origin of these results at the microscopic scale, we tracked the individual trajectories of the particles in an oscillating flow. Their motion and the distribution of their velocities have been measured in several layers at different distances from the walls in the cell thickness. The particles are observed to follow the flow liens; the profile of their velocities in the thickness displays the parabolic shape of a Posieuille profile. Moreover, we compared the distribution of the particles after a certain number of oscillations to those at the initial time and observed, for long periods T, a migration of the particles towards the vicinity of the cell walls. Moreover, the motion of some particles display a kinematic reversibility and follow the same trajectory for both directions of the flow, even when there are interactions with the others.Finally, when the concentration of the particles is increased, one observes a structuration of the suspension into bands perpendicular to the flow. The wavelength λ of this instability has been studied as a function of geometrical (thickness H and width of the cell, particle diameter) and physical parameters (viscosity and density of the fluid, particle density) and of the characteristics of the flow (sine or square wave variation of the flow, amplitude A et period T). The normalized wavelength λ/H increases linearly with the normalized amplitude A/H but is constant with T and H and with the particle diameter. At the local level, the instability corresponds to periodic variations of the particle concentration along the length of the cell which extend across its whole thickness H. / Se estudió el transporte y dispersión hidrodinámica de un trazador pasivo y/o de una suspensión de partículas en una fractura de paredes lisas y en otra, con una distribución aleatoria de obstáculos en su espesor. Se utiliza un flujo oscilante de un fluido newtoniano, permitiéndonos observar los efectos de la reversibilidad del desplazamiento sobre el fenómeno. En todos los casos se buscó cuantificar la influencia de los parámetros característicos del flujo: el período T y la amplitud A de las oscilaciones, el tiempo característico de difusión molecular sobre el espesor τ_m, la concentración y el tamaño de las partículas. En el caso de paredes lisas, se puso en evidencia que los regímenes de dispersión están gobernados por la relación τ_m /T. Se encontró que, a bajos τ_m /T ≤ 2, el régimen de dispersión de Taylor es dominante y, a escala global, es irreversible. Para τ_m /T ≥ 20 encontramos un régimen parcialmente reversible donde la mezcla continúa siendo difusiva a escala global; sin embargo, localmente, las simulaciones numéricas de tipo Monte Carlo mostraron que la distribución de partículas de trazador en el espesor sigue las oscilaciones de la velocidad local v_x (z, t). En este caso, el coeficiente de dispersión tiene una componente puramente convectiva, que es reversible. En el caso de una celda rugosa, el desorden introducido por los obstáculos hizo aparecer la dispersión geométrica a τ_m /T ≤ 0,6, donde la dispersividad ldg varía con la amplitud y no depende del período de la oscilación del flujo. El régimen de dispersión de Taylor se detectó en un intervalo de la relación entre los tiempos característicos más estrecho que en el caso de celda lisa, 〖0,8≤τ〗_m/T≤1, este rango depende de la amplitud de la oscilación. También se encontró el régimen de dispersión parcialmente reversible, para τ_m /T ≥ 20, correspondiendo con lo visto previamente en la celda de paredes lisas. Con técnicas complementarias (eco y transmisión), se aisló la componente de la dispersión irreversible de la reversible indicando la existencia de canales de flujo macroscópicos generados por la geometría de la fractura. Luego, se estudió el efecto sobre la dispersión por la presencia de una suspensión de partículas de poliestireno de 40 μm de diámetro, en la celda de Hele-Shaw lisa, con un flujo oscilante. En la medida global de la dispersión, se encontraron básicamente los mismos regímenes que en la celda lisa. Luego, en una escala microscópica, para terminar de comprender lo que sucede en el fenómeno de dispersión, se realizó el seguimiento de las trayectorias individuales de las partículas dentro de la celda sometidas a un flujo oscilante. Se analizó el movimiento en diferentes capas del espesor y se obtuvieron las distribuciones de velocidades. Se pudo observar que, las partículas se mueven siguiendo las diferentes líneas de corriente y su perfil de velocidades mantiene la forma parabólica característica de Poiseuille. Por otro lado, se aislaron las trayectorias que presentan reversibilidad cinemática, comprobando que hay partículas que van y vienen por el mismo camino, aún en presencia de interacciones débiles entre ellas. Por último, se aumentó la concentración de partículas presentes en la suspensión y se observó que, con un flujo oscilante, la suspensión dentro de la celda se estructura formando bandas periódicas transversales al flujo. Se caracterizó la dependencia de la longitud de onda λ de esta inestabilidad en función de parámetros geométricos (apertura y ancho de la celda, diámetro de partículas); físicos (viscosidad del fluido, densidad de las partículas) y geometría de flujo (sinusoidal, onda cuadrada, T y A). Se encontró que: para cada espesor de la celda, diferente diámetro y densidad de las partículas, viscosidades del fluido, λ resulta constante con T y aumenta linealmente con A. Localmente, se observó que la inestabilidad corresponde a variaciones de la concentración de las partículas en el espesor de la celda.

Interaction of fluctuating vortex shedding with blade vibration can lead to a new class of aeromechanical instability referred as Non-synchronous vibrations. Investigating a well-known case that shows similar NSV features such as a circular cylinder can develop the understanding of physics behind NSV. A common approach to further investigating the vortex induced vibration is to control the motion of the cylinder and allowing the response of the wake to the motion to be studied in isolation. It has been found very important to carefully match the experimental conditions between free and controlled vibration. Many of research in the field of vortex induced vibration apply a rigid cylinder mounted horizontally and moving transversely to the flow stream as a paradigm for understanding the physics behind this phenomenon. Regarding the difficulties of implementation of vertically moving cylinder in experimental study, vortex dynamic and lock-in behavior of eccentrically rotating cylinder is studied in this M.Sc. Thesis. The main focus of this research is to understand to what extend a general feature of free vortex-induced vibration can be observed in the case of eccentrically rotating cylinder. If the present case captures the essential characteristics of freely oscillating cylinder the results of the forced motion via eccentrically rotating cylinder can be applied to predict the motion of an elastically mounted body. To do so a CFD model is established to predict the response, vorticity structure in near wake, timing of vortex shedding and the range of lock-in region over specific parameter space of the introduced alternative case. A commercial CFD code, Ansys/CFX, was implemented to perform this numerical study. Existences of synchronization region, striking similarity in lift force coefficient and wake mode have been observed in the current study.

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<p>The objectives of this investigation were to experimentally and analytically evaluate the  performance of a valve train cam and oscillating roller follower mechanism. Of particular interest  was the effect of operating conditions on the slide-to-roll ratio (SRR) of the roller follower. In order to experimentally measure the SRR at the cam-roller contact, a valve train test rig  (VTTR) was utilized. The VTTR contained a section of a heavy-duty diesel engine valve train that  was instrumented with encoders and Hall effect sensors to measure the camshaft and roller  follower angular velocities as a function of operating parameters.  To corroborate the experimental with analytical results, a numerical model for the cam and  oscillating roller follower was developed. In this modeling approach, the roller angular velocity  was determined via a torque balance between the frictional torque of the pin-roller follower and  cam-roller follower interfaces. The pin-roller friction was obtained by developing a time-dependent hydrodynamic journal bearing model with variable speed and load. Friction maps were  developed for the cam-roller follower interface using a ball-on-disk EHD2 rig to capture the  friction behavior across a range of entraining velocities, contact pressures, and SRRs. Additional  areas of investigation included thermal effects and wear in the pin-roller contact. Overall, good agreement was obtained between the experimental and analytical roller  follower angular velocity, with the normalized RMS errors less than 7%, across all operating  conditions investigated. The analytical investigation determined that thermal effects in the pin-roller contact are insignificant for the typical operating conditions. However, it was shown that the  pin-roller friction torque is critical in causing roller follower slip, as the SRR greatly increases  once the pin-roller friction torque is greater than the cam-roller friction torque. Finally, pin-roller  local wear was demonstrated to have detrimental effects on the SRR of the roller follower once a  critical wear depth was reached. </p>

The development and implementation of technologies that improves Heating Ventilation & Air Conditioning (HVAC) system efficiency, including unique waste heat recovery methods, are sought while considering financial constraints and benefits. Recent studies have found that through the use of advanced waste heat recovery systems, it is possible to reduce building’s energy consumption by 30%. Oscillating heat pipes (OHP) exists as a serpentine-arranged capillary tube, possesses a desirable aerodynamic form factor, and provides for relatively high heat transfer rates via cyclic evaporation and condensation of an encapsulated working fluid with no internal wicking structure required. In last two decade, it has been extensively investigated for its potential application in thermal management of electronic devices. This dissertation focuses on the application of OHP in waste heat recovery systems. To achieve the goal, first a feasibility study is conducted by experimentally assessing a nine turn copper-made bare tube OHP in a typical HVAC ducting system with adjacent air streams at different temperatures. Second, for a prescribed temperature difference and volumetric flow rate of air, a multi-row finned OHP based Heat Recovery Ventilator (OHP-HRV) is designed and analyzed for the task of pre-conditioning the intake air. Additionally, the energy and cost savings analysis is performed specifically for the designed OHP-HRV system and potential cost benefits are demonstrated for various geographical regions within the United States. Finally, an atypically long finned OHP is experimentally investigated (F-OHP) under above prescribed operating condition. Helical fins are added to capillary size OHP tubes at a rate of 12 fins per inch (12 FPI), thereby increasing the heat transfer area by 433%. The coupled effect of fins and oscillation on the thermal performance of F-OHP is examined. Also, F-OHP’s thermal performance is compared with that of bare tube OHP of similar dimension and operating under similar condition. It was determined that OHP can be an effective waste heat recovery device in terms of operational cost, manufacturability, thermal and aerodynamic performance. Moreover, it was also determined that OHP-HRV can significantly reduce energy consumption of a commercial building, especially in the winter operation.

This thesis describes the analytical study of a structural system under the combined action of noncirculatory or circulatory loading and oscillating base motion. The model is a double inverted pendulum composed of two rigid weightless bars of equal length with two concentrated masses at the ends of each bar, on an oscillating base. Noncirculatory or circulatory loading is applied at the free end. At the hinges restoring moments are produced by spring and damping forces. Damping coefficients are taken as positive, and gravitational effects are considered. The stability of the system under the combined action of the noncirculatory or circulatory loading and the parametric excitation can be investigated by Hsu's method. This method is applied to solve the coupled Mathieu equations by the given system and determine the unstable resonance, a nonlinear analysis is used to find the steady state response. / Thesis / Master of Engineering (MEngr)

Piezoelectricity crystal is used in different area in industry, such as downhole oil, gas industry, and ballistics. The piezoelectricity crystals are able to create electric fields due to mechanical deformation called the direct piezoelectric effect, or create mechanical deformation due to the effect of electric field called the indirect piezoelectric effect. In this thesis, piezoelectricity effect is the core part. There are 4 parts in the frequency output pressure transducer: two crystal oscillators, phase-locked loop (PLL), mixer, frequency counter. Crystal oscillator is used to activate the piezoelectricity crystal which is made from quartz. The resonance frequency of the piezoelectricity crystal will be increased with the higher pressure applied. The signal of the resonance frequency will be transmitted to the PLL. The function of the PLL is detect the frequency change in the input signal and makes the output of the PLL has the same frequency and same phase with the input signal. The output of the PLL will be transmitted to a Mixer. The mixer has two inputs and one output. One input signal is from the pressure crystal oscillator and another one is from the reference crystal oscillator. The frequency difference of the two signal will transmitted to the frequency counter from the output of the mixer. Thus, the frequency output pressure transducer with a frequency counter is a portable device which is able to measure the pressure without oscilloscope or computer.

This thesis introduces the Deterministic Disturbance Generator (DDG) and its development process. The DDG performs two motions and five pitch rates. The flap motion, which rotates the airfoil from 0◦ to 20◦ and back, and the ramp motion, which rotates it from 0◦ to 20◦ with a dwell of 1s before returning to 0◦. To determine the angle of attack, a Matlab function converted thrust rod displacement into the assumed angle, validated against true angle of attack measurements on the DDG. Mean angular displacements were plotted, and standard deviations of the 95% confidence intervals were calculated within ±1.3◦ for all motions. The mechanical force on the actuator was computed to be 77N. Aerodynamic forces on the DDG were determined to be 15N and 19N for flap and ramp motions respectively. The total force on the system did not exceed 100N in any case, staying below the peak force capacity, while acceleration reached its limit. Flow velocimetry in the Virginia Tech Stability Wind Tunnel (VTSWT) employed a time-resolved Particle Image Velocimetry (PIV) to study the effects of 20◦ flap and ramp motions, with mean actuation times of 63ms and 37ms. Flap motion showed a significant deficit in mean streamwise velocities, and the ramp motion exhibited similar behavior until its dwell position, generating a large wake region due to airfoil stall after its peak. Comparison of data from the Goodwin Hall Subsonic Tunnel (GHST) with VTSWT data for overlapping domains revealed similar flow field features when normalized based on the boundary layer velocity (43mm plane from wall) of the latter. Considering actuation time differences, the freestream normalized GHST data was combined with VTSWT data. The cohesive PIV domain offered a broader perspective on the missing flow features. / Master of Science / A Deterministic Disturbance Generator (DDG) was designed to generate consistent largescale transversal transient disturbances in the wall boundary layer of the Virginia Tech Stability Wind Tunnel. It comprises an airfoil connected to an actuator through a rotating mechanism. The rotating mechanism can be controlled by manipulating the actuator to induce motion. The rotational speed of the airfoil is regulated by a program provided to the actuator. The DDG motions were validated to achieve nearly identical motion profiles to ensure it produced consistent turbulence wakes. The linear displacement of the actuator and airfoil was measured using a laser sensor, and a code was developed to convert this data into the observed angle of attack. Tests were conducted to verify repeatability and fine-tune the system's motions. A comprehensive description of the fabrication process, hardware and software setup, and calibration procedures involved in developing the DDG are provided. Using aerodynamic models, a computational study is performed to determine the forces associated with the airfoil and actuator. Subsequently, the DDG was subjected to testing in two wind tunnels: the Goodwin Hall Subsonic Tunnel for preliminary characterization and error mitigation and the Virginia Tech Stability Wind Tunnel for final assessment of the DDG's performance. Flow velocimetry data obtained from both tests are analyzed, revealing similarities in the induced motions. Mean flow fields and turbulence values are determined, and the effects of different pitch rates are also assessed. Finally, the mean flow fields corresponding to identical motion types from both datasets were integrated into a cohesive plot. This resulted in a comprehensive understanding of the flow field.

Our oceans contain tremendous resource potential in the form of mechanical energy. With the ability to capture and convert the energy carried in surface waves into usable electricity, wave energy converters (WECs) have been a long-held aspiration in ocean renewable energy. One of the most popular wave energy design concepts is the Oscillating Surge Wave Energy Converter (OSWEC). True to their namesake, OSWECs extract energy from the surge force induced by incident waves. In their most basic form, OSWECs are analogous to a bottom-hinged paddle which pitches fore and aft in the direction of wave motion. Most commonly, OSWECs are designed for nearshore use in water depths of less than 20 m where they are mounted to the seafloor at their point of rotation. This work seeks to explore the response and design loads of foundation raised OSWECs for use in deeper waters, unlocking new and greater areas of wave energy resource. A foundation raised OSWEC was designed, built, and tested in a laboratory wave tank. The scale OSWEC was modeled using two methods and compared to data from the experiments. The first of these methods is a highly efficient, analytical approach which derives from the solution to the boundary value problem transformed into elliptical coordinates. Previous validation results demonstrate the analytical model is capable of reproducing results from higher fidelity numerical simulations with computation times on the order of seconds. The second approach combines hydrodynamic coefficients evaluated in WAMIT with the open-source time domain solver WEC-Sim. Two model configurations were observed: the scale OSWEC with no external attachments, and the OSWEC with external torsion springs, as to excite the model at its natural period. The pitch displacement, surge and heave forces, and pitch moment were recorded at the base of the model foundation in response to regular waves with periods ranging from 0.8 s to 2.8 s and heights from 1.5 mm to 14.3 mm. The experimental results show the surge force and pitch moment increase drastically across the observed period range from the addition of external springs. The increase is 20–30 times greater in the most extreme cases. Little to no change in heave forcing was observed between the configurations. The analytical and numerical models capture the natural period of the two configurations well, but the pitch displacement responses of both models fall short of the observations by as much as 60-80% at some periods. Excellent agreement in surge, heave, and pitch loading was obtained between the experimental data and both models. The models were used to simulate a simple power takeoff (PTO) system to approximate the additional PTO torque on the OSWEC. This torque was found to be substantial in magnitude relative to the pitch foundation moment over much of the observed period range.