The present study aims to explore dynamical behavior of the fluid-elastic instability of a circular cylinder in shear flow by numerical simulations. The theoretical model comprises two groups of transient conservation equations of mass and momentum and the governing equations are solved numerically with an iterative SIMPLEC(Semi-Implicit Method for Pressure-Linked Equations Consistent) algorithm to determine the flow property and to analysis structure stress simultaneously. Additionally, the TFI (Transfinite interpolation) computation procedure is applied to characterize the behavior of fluid-structure interaction. The predictions are in reasonable agreement with literature showing the validity of the present theoretical model. The numerical results indicate that there is a transverse force acting from high velocity side toward the low velocity side in shear flow. The magnitude of this transverse force increases with the shear parameter. The Strouhal number slightly increases as the shear parameter increases for all Reynolds number. As the pattern of the approach flow changes from the uniform to shear flow, the front stagnation point shifts to high velocity side, and the base pressure increase. The magnitude of the shift of front stagnation point is linear with the shear parameter. Furthermore, this study appraises the amplitude and orbit of fluid elastic vibration of a circular cylinder in shear flow, and shows the effects of the spring constant and damping factor on fluid elastic vibration of the cylinder. In addition, various effects including shear parameter and mass ratio on the critical velocity of the fluid elastic vibration also has been examined detail.

The present study aims to explore dynamical behavior of the fluid-elastic instability of a circular cylinder in shear flow by numerical simulations. The theoretical model comprises two groups of transient conservation equations of mass and momentum and the governing equations are solved numerically with Fluent software to determine the flow property. The analysis presented that there exist both vortex-induced vibration and flow-elastic vibration for single cylinder in sear flow. The numerical results with a Harmonic Model built from Gambit indicate that there is a transverse force acting from high velocity side toward the low velocity side in shear flow. The transverse force make cylinder move periodically and thus go to a vibration. Furthermore, this study appraises the amplitude and orbit of fluid elastic vibration of a circular cylinder in shear flow and shows the effects of the shear velocity slope and damping factor on fluid elastic vibration of the cylinder. Here in the thesis, as the function applied with Fluent of displaying dynamic mesh on-time, the movement and re-mesh of cylinder could be observed. A vibration expansion diagram was presented and the pictures of flow velocity and flow pressure were retrieved from Fluent.

The aerodynamic steering forces and moments on a wind tunnel model of an axisymmetric bluff body are altered by induced segmented attachment of the separated flow over an azimuthal Coanda surface. The model is suspended in the wind tunnel by eight thin wires for minimal support interference within the wake. Each wire is instrumented with a miniature strain gage sensor for direct dynamic force measurements. Control is effected by an array of synthetic jet actuators that emanate from narrow, azimuthally-segmented slots, within a backward facing step. The aerodynamic effects are characterized using hot-wire anemometry and PIV measurements. In the first set of experiments, the array of synthetic jets is distributed around the perimeter of the circular tail end which is extended into a Coanda surface. The fluidic actuation results in segmented vectoring of the separated base flow along the rear Coanda surface and induces asymmetric aerodynamic forces and moments that can effect steering during flight. Transitory modulation of the actuation waveform of multiple actuators around the tail leads to the generation of significant dynamic side forces of controlled magnitude and direction with the potential utility for flight stabilization and fast maneuvering. In a second set of experiments the array of the synthetic jets is placed upstream of a mid-body axisymmetric cavity. A single jet induces a quasi-steady, nearly-matched force couple at the upstream and downstream ends of the cavity. Furthermore, transitory activation of multiple jets can be used to control the onset and sequencing of the couple forces and therefore the resultant force and moment.

<p>The orientation of fibres suspended in a viscous fluid, flowing over a solid surface, has been studied experimentally. A shear layer was generated, by letting the suspension flow down an inclined plate. Far upstream from the measuring section the suspension was accelerated to obtain an initial orientation of the fibres aligned with the flow direction. A CCD-camera was used to visualise the fibres. The velocity profile of the fibres coincided with the theoretical expression for fully developed flow of Newtonian liquid down an inclined wall.</p><p>The orientation of the fibres was analysed in planes parallel to the solid surface. At distances from the wall larger than one fibre length the fibres performed a tumbling motion in the flow-gradient plane in what appeared to be Jeffery-like orbits. Closer to the wall a difference was found between fibres of aspect ratio <i>r</i><i>p </i>= 10 and 40. The longer fibres of <i>r</i><i>p </i>= 40 kept their orientation, aligned with the flow, also in the near wall region. For the shorter fibres the orientation shifted gradually, to orientations closer to the vorticity axis, when the distance from the wall was decreased. In the very proximity to the wall the fibres were aligned with the vorticity, perpendicular to the direction of the flow. Another distinction, most likely related to the fibre orientation, was seen in the wall normal concentration profile. Due to sedimentation effects fibres accumulated in the near wall region. For fibres of <i>r</i><i>p </i>= 10 a peak in concentration was found at the wall, while for r=40 the maximum concentration was found approximately half a fibre length from the wall. It is previously known that a fibre can interact with the wall in what is referred to as a "pole vaulting" motion away from the wall. It is suggested, as a likely explanation to the location of the maximum concentration, that fibres of <i>r</i><i>p </i>= 40 perform this motion, while fibres of <i>rp</i>=10 do not.</p><p>In another experiment the surface of the wall was modified with ridges. For fibres of <i>r</i><i>p </i>= 10 there were no longer any fibres oriented perpendicular to the flow direction in the near wall region.</p><p>The main application in mind throughout this work is papermaking. The study is considered to be of fundamental character and is not applicable in a direct sense. The difference between the flow situation in the experiments and the paper machine is discussed further.</p>

The nano/micro particles have been widely used as a carrier of therapeutic and contrast imaging agents. The nano/micro particles have many advantages, such as, specificity, controlled release, multifunctionality and engineerability. By tuning the chemical, physical and geometrical properties, the efficacy of delivery of nano/micro particle can be improved. In this study, by analyzing the effect of physical and geometrical properties of particle, such as, size, shape, material property and flow condition, the optimal condition for particle delivery will be explored. The objectives of this study are (1) to develop predictive mathematical models and (2) experimental models for particle margination and adhesion, and (3) to find optimal particle geometry in terms of size and shape to enhance the efficiency of its delivery. The effect of particle size expressed in terms of Stokes number and shape, namely, spherical, ellipsoidal, hemispherical, discoidal and cylindrical particle on the particle trajectory is investigated. For discoidal and cylindrical particles, the effect of aspect ratio is also considered. To calculate particle trajectory in the linear shear flow near the substrate, Newton's law of motion is decomposed into hydrodynamic drag and resistance induced by particle motion. The drag and resistance is estimated through finite volume formulation using Fluent v6.3. Particle behavior in the linear shear flow does strongly depend on Stokes number. Spherical particle is transported following the streamline in the absence of external body force. However, non-spherical particles could across the streamline and marginate to the substrate. For non-spherical particles, the optimal [Stokes number] in terms of particle margination is observed; [Stokes number almost equal to] 20 for ellipsoidal, hemispherical and discoidal particle; [Stokes number almost equal to] 10 for cylindrical particle. For discoidal particle with [gamma subscript d]=0.2 shows fastest margination to the substrate. The effect of gravitational force is also considered with respect to the fluid direction. When the gravitational force is applied, mostly, gravitational force plays a dominant role for particle margination. However, using small particle aspect ratio ([gamma subscript d]=0.2 and 0.33), spontaneous drift induced by particle-fluid-substrate interaction could overcome gravitational effect in some cases ([Stokes number]=10, G=0.1). In addition the adhesion characteristic of spherical particle has been studied using in vitro micro fluidic chamber system with different particle size and flow condition. The experimental results are compared to the mathematical model developed by Decuzzi and Ferrari (Decuzzi and Ferrari, 2006) and in vivo test (Decuzzi et al., 2010). The optimal particle size for S=75 and 90 is found to be 4-5 [micrometer] through the in vitro non-specific interaction of spherical particle on the biological substrate. The suggested mathematical model has proven to be valid for current experimental condition. At the end, the mathematical model, in vitro flow chamber results and in vivo test have been compared and the scaling law for particle adhesion on the vessel wall has been confirmed. / text

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Using a two-dimensional nonlinear numerical simulation of a (viscous) stratified shear layer, strong instabilities resulted from the resonant interaction of a long linearly neutrally stable wave and the corresponding fastest growing wave. This linearly fastest growing wave, with optimal initial conditions, grows initially at a rate five times that predicted by linear theory. With other initial conditions, the linearly fastest growing wave may actually decay. The possibility of this type of interaction is suggested by the weakly nonlinear theory (cf. Maslowe, 1977). This coupled system of fourth order nonl inear partial differential equations was solved using a modified pseudospectral scheme for the spatial variables, incorporating the use of fast Fourier transforms to calculate spatial derivatives, and a second order Adams-Bashforth scheme for the temporal derivatives . / Dans cette etude, en utilisant une simulation numerique nonlineaire a deux dimensions d'une couche stratifiee, decollee et visqueuse, on obtint des resultats interessants a partir des cas correspondant a l'interaction resonnante d'une onde longue a stabilite neutre et d'une onde courte qui croit la plus rapidement selon la theorie lineaire. En utilisant certaines conditions initiales, l'onde courte croit initialement a un taux cinq fois superieur a celui predit par la theorie lineaire. Avec d'autres conditions initiales l'onde courte decroit. La possibilite de ce genre d'interaction est predite par la theorie faiblement nonlineaire (voir Maslowe, 1977). Ce systeme couple aux equations nonlineaires du quatrieme ordre aux derivees partielles, est resolu par une methode pseudo-spectrale modifiee, pour les variables spatiales, et une methode Adams-Bashforth du second ordre pour les derivees temporelles. fr