Compliant (flexible) structures play an important role in several biofluid problems including flow in the lungs, heart and arteries. Atherosclerosis is a vascular disease which causes a remodelling of the arterial wall causing a restriction (stenosis) by thickening the intima and the formation of vascular plaque by the deposit of fatty materials. This remodelling alters the compliance of the artery stiffening the arterial wall locally. A common location for this to occur is in the carotid artery which supplies blood to both the brain and the face. It can lead to complete occlusion of the artery in the extreme case and is a major cause of stroke and ischemic infarction. Stroke is the third largest cause of death in the U.S.A., but even if not fatal it can cause coma, paralysis, speech problems and dementia. Atherosclerosis causes a change in the local hemodynamics. It can produce areas of flow separation and low wall shear stress, which can lead to endothelial dysfunction and to promotion of plaque growth. In-vitro modelling with artificial flow phantoms allows the fluid mechanics of the circulatory system to be studied without the ethical and safety issues associated with animal and human experiments. Extensive work has been performed using both experimental and computational techniques to study rigid models representing the arterial system. Computational methods, in which the equations governing the flow and the elastic walls are coupled, are maturing. There is a lack of experimental data in compliant arterial systems to validate the numerical predictions. This thesis sets out to address the problems associated with the in vitro experimental analysis of compliant structures representing the human vasculature. A novel construction technique that produced idealised compliant geometries representing both a healthy and stenosed carotid artery from transparent silicone material was developed. A complete analysis was performed of the circumferential and longitudinal response of the geometry, which allowed for dynamic similarity between in vitro and in vivo conditions to be achieved. Inherent difficulties associated with thin walled phantom construction were overcome, which included the design of a novel endplate that allowed for a smooth transition from the flow system to the flow phantom and a bottom up silicone injection system that ensured the phantom was free of bubbles. The final phantom evolution had a wall thickness that could be produced to within a tolerance of 5%. The constructed flow phantom was ported to a flow system producing a physiological inlet flow waveform scaled to in vitro conditions via Reynolds and Womersley number matching. Experimental analysis was performed using a laser based optical technique, particle image velocimetry (PIV). A novel Light Emitting Diode (LED) illumination system was also implemented to obtain to obtain high speed planar PIV measurements. The combined set up of the LED light source, driver unit components and fibre optics for high speed imaging costs in the region of $US 650 which provides a far cheaper option in comparison to the pulse laser system (In the region of $US 50,000). Results obtained in the healthy geometry were compared to a rigid geometry with the same dimensions. It was found that compliance reduced the peak velocity experienced. It also caused a reduction in wall shear stress (WSS) observed and acted to ameliorate the magnitude of the WSS. This is physiologically significant as high WSS can promote atherosclerosis. The introduction of a stenosis caused an increase in the peak velocity observed over the cardiac cycle. A large increase in WSS can be seen to occur in the stenosis throat in both a symmetric and asymmetric stenosed geometry. It is also evident that stenosis eccentricity is important, with asymmetry (where the centre of the stenosis does not coincide with the centre of the artery) producing a major change in WSS and flow field. The study of the flow field downstream of a symmetric stenosis exit showed a Kelvin-Helmholtz vortex ring system to occur between the jet exiting the stenosis throat and the low velocity reverse flow region that surrounded it. The strength of these vortices varied between the acceleration and deceleration phase, demonstrating the failings of a quasi-steady assumption. It was shown that varying the external pressure applied to the flow phantom, along with stenosis eccentricity, affected the inlet flow and pressure waveform and the failings of the common assumption to idealise the physiological flow wave with a sinusoidal input was presented.

Rail and bridge infrastructure assets are critical elements of Canada’s transportation network and their continued efficient and safe operation is necessary to ensure the nation’s economic livelihood. Monitoring technologies that can detect changes in performance as well as precursors to failure are an important element of ensuring this efficient and safe operation. Digital Image Correlation (DIC) is a monitoring technology that has the potential to provide critical data for infrastructure assessment and to replace various conventional sensors with one integrated monitoring solution. In this research, the accuracy of DIC is evaluated using numerical, laboratory and field-based experiments. The sources of error of particular relevance to dynamic measurement using DIC are identified as (i) bias error in the sub-pixel interpolation scheme, (ii) the ratio of sample rate to the frequency of the signal being monitoring and (iii) the signal to noise ratio. It is also shown that the chosen sub-pixel interpolation scheme can greatly affect the accuracy of dynamic measurements. The use of DIC was investigated for field monitoring of both horizontal and vertical railway displacements at sites with good and poor subgrade conditions under dynamic train loading. It is shown that there is a significant benefit to using an absolute displacement measurement system rather than a relative displacement measurement system as the former can capture irrecoverable rail displacements in both the vertical and horizontal directions. Finally, DIC was also used for field monitoring of a very stiff reinforced concrete bridge during static and dynamic load tests. It is shown that when using DIC for deflection monitoring, corrections may have to be made to compensate for errors such as camera jitter and drift to acquire the most accurate results. Two potential correction methods were the use of a fixed reference point and generating composite images using average pixel intensity values from multiple images. It was found that using a fixed reference point was the optimal choice in this bridge test. It is concluded that DIC can be used as an effective displacement measurement tool for bridge assessment because it shows excellent correlation with linear potentiometer results and it can allow measurements to be taken without having to close the bridge. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-09-26 15:40:16.744

The Richtmyer-Meshkov Instability (RMI) (Commun. Pure Appl. Math 23, 297-319, 1960; Izv. Akad. Nauk. SSSR Maekh. Zhidk. Gaza. 4, 151-157, 1969) occurs due to an impulsive acceleration acting on a perturbed interface between two fluids of different densities. In the experiments presented in this thesis, single mode 3D RMI experiments are performed. An oscillating speaker generates a single mode sinusoidal initial perturbation at an interface of two gases, air and SF6. A Mach 1.19 shock wave accelerates the interface and generates the Richtmyer-Meshkov Instability. Both gases are seeded with propylene glycol particles which are illuminated by an Nd: YLF pulsed laser. Three high-speed video cameras record image sequences of the experiment. Particle Image Velocimetry (PIV) is applied to measure the velocity field. Measurements of the amplitude for both spike and bubble are obtained, from which the growth rate is measured. For both spike and bubble experiments, amplitude and growth rate match the linear stability theory at early time, but fall into a non-linear region with amplitude measurements lying between the modified 3D Sadot et al. model (Phys. Rev. Lett. 80, 1654-1657, 1998) and the Zhang & Sohn model (Phys. Fluids 9. 1106-1124, 1997; Z. Angew. Math Phys 50. 1-46, 1990) at late time. Amplitude and growth rate curves are found to lie above the modified 3D Sadot et al. model and below Zhang & Sohn model for the spike experiments. Conversely, for the bubble experiments, both amplitude and growth rate curves lie above the Zhang & Sohn model, and below the modified 3D Sadot et al. model. Circulation is also calculated using the vorticity and velocity fields from the PIV measurements. The calculated circulation are approximately equal and found to grow with time, a result that differs from the modified Jacobs and Sheeley's circulation model (Phys. Fluids 8, 405-415, 1996).

Approved for public release, distribution unlimited / The flow around second generation controlled-diffusion compressor blades in cascade at stall was examined through the use of a Particle Image Velocimeter (PIV). This examination was conducted from the trailing edge of the blade well into the wake region. Flow visualization techniques were used to observe and record the behavior of the region of flow separation. The PIV data showed that the separated regions continued to grow up to approximately 10% of blade chord length past the trailing edge. Past this point, these areas began to show signs of becoming entrained in the free stream. The flow visualization highlighted the extent of the backflow. The PIV measurements documented the velocity profiles within the wake region.

The very first study of the development of the turbulent isothermal and incompressible air jet which issues at a constant velocity from a slender annular slot, circumnavigating an open core, into an otherwise quiescent and unbounded environment of the same density, is presented. The geometry of this source is defined by three diameters: the outer diameter of the slot $D_o$; the inner diameter of the slot $D_i$; and the diameter of the (circular) open core $D_v$. `Slender' refers to a slot for which the inner and outer diameters are approximately equal, i.e. $D_i/D_o\approx 1$. Our focus lies in understanding the development of the time-averaged flow with distance downstream and the influence of the source geometry on the development of the jet. Given the absence of information on jets issuing from the sources of interest, the investigation follows an approach reminiscent of the classic investigations into round jets. That is, it begins with the development of a nozzle and experimental set-up which are suitable for studying the slender open-core annular jet. In addition to the experimental measurements, a complementary mathematical model was developed to describe the unique near-field behaviour of the open-core jet. Measurements were acquired using flow visualisation and Particle Image Velocimetry. On examining the streamwise development of the flow, the slender almost fully open-core jet was delineated into four key regions and the characteristic scalings identified. The regions were as follows: a bounded induced-flow region; a near-source planar-jet region; a transitional region; and a far-field round-jet region. Fluid induced through the open core of the nozzle and subsequently entrained into the jet significantly enhanced the near-field dilution of the jet. Following on from this, the influence of the diameter ratio $D_i/D_o$ and ventilation ratio $D_v/D_i$ on jet coalescence was examined. Over the range of diameter ratios examined ($0.845 \leq D_i/D_o\leq 0.981$), experimental measurements and the predictions from mathematical modelling indicated that $D_i/D_o$ significantly influenced the volume flux induced through the core while the coalescing behaviour of the jet and the far-field region remained largely unchanged. Over the range of ventilation ratios examined ($0 \leq D_v/D_i\leq 0.90$), experimental measurements demonstrated that $D_v/D_i$ controlled the restriction experienced by fluid induced through the open core and significantly influenced the far-field behaviour of the jet. Our findings suggest that jet of interest is then uniquely characterised by the momentum flux $M_0$, the diameter ratio $D_i/D_o$, and the ventilation ratio $D_v/D_i$.

Planar and stereo particle image velocimetry measurements were conducted of a wing-tip vortex decaying in free-stream turbulence in order to understand the evolution of a vortex and its decay mechanism. The vortex decayed faster in the presence of turbulence. The decay of the circulation was found to be almost entirely due to a decrease in circulation of the vortex core, caused by the relative decrease in peak tangential velocity without a corresponding increase in core radius. These events were found to be connected with the stripping of core fluid from the vortex core. The increased rate of decay of the vortex in turbulence coincided with the formation of secondary vortical structures which wrapped azimuthally around the primary vortex. It was also found that regardless of the free-stream condition, the core scaled by peak tangential velocity and core radius.

This dissertation describes the development of a device capable of suspending a microscale object in a controlled flow. The uPIVOT is a system integrating two laser-based techniques: micron particle image velocimetry (uPIV) and optical tweezers (OT). The OT allows the suspension and manipulation of micron-sized objects such as microspheres or biological cells. uPIV provides imaging of the suspended object and velocity measurements from which fluid induced stresses can be determined. Using this device, we measured fluid velocities around an optically suspended polystyrene microsphere (an experimental first) and studied the interaction between two particles suspended in a uniform flow. The results were consistent with theoretical low Reynolds number, Newtonian flow predictions. Additionally, we analyzed a single cell's mechanical response to a controlled and measurable multiaxial external force (fluid flow) without the cell being physically attached to a surface. The cell's mechanical response was monitored by observing its morphology and measuring its deformation. The results show significant deformations of optically suspended cells at substantially smaller stresses than previously reported and demonstrate the opportunity to optically distinguish a cell by its trapping efficiency. These initial applications of the uPIVOT demonstrate the potential of this unique device as a research tool for novel studies in the fields of fluid/particle(s) interactions, non-Newtonian fluid mechanics, and single cell biomechanics.

In Particle Image Velocimetry (PIV), the number of particle images per interrogation region, or particle image density, impacts the strength of the correlation and, as a result, the number of valid vectors and the measurement uncertainty. Therefore, any a-priori estimate of the accuracy and uncertainty of PIV requires knowledge of the particle image density. An autocorrelation-based method for estimating the local, instantaneous, particle image density is presented. Synthetic images were used to develop an empirical relationship based on how the autocorrelation peak magnitude varies with particle image density, particle image diameter, illumination intensity, interrogation region size, and background noise. This relationship was then tested using images from two experimental setups with different seeding densities and flow media. The experimental results were compared to image densities obtained through using a local maximum method as well as manual particle counts and are found to be robust. The effect of varying particle image intensities was also investigated and is found to affect the particle image density.

Thesis (M.S.)--University of Delaware, 2007. / Principal faculty advisor: Fabrice Veron, College of Marine and Earth Studies. Includes bibliographical references.

According to the American Heart Association about 795,000 people suffer a stroke each year. Of those strokes almost 140,000 are fatal; this makes Stroke the third leading cause of death in the United States behind coronary heart disease and cancer. Hemorrhagic strokes are caused when an artery in the brain ruptures, such as a ruptured aneurysm. One possible treatment for cerebral aneurysm is a porous tubular structure, similar to a stent, called a flow diverter. A flow diverter can be placed across the neck of a cerebral aneurysm to induce the cessation of flow and initiate the formation of an intra-aneurysmal thrombosis. This excludes the aneurysm from the parent artery and returns the flow of blood to normal. The process of flow diversion alone has been shown to take months to fully exclude the aneurysm. It is possible however with an adjuvant therapy called photothrombosis to accelerate this process so that the aneurysm is excluded within minutes. Previous flow diverting devices have been analyzed to determine optimal characteristics, such as braiding angle and wire diameter. From this information a new optimized device was designed and is now in the process of being tested. In order to evaluate the effect of the device, a model must be created. One such model is the rabbit elastase induced aneurysm, which was characterized so that elastomer models could be created for in vitro studies. Particle Image Velocimetry (PIV) is a method of analysis that utilizes very small glass spheres (between 8 mu m and 12 mu m in diameter) to determine the velocity vectors of fluid flow in an in vitro model. These velocities can be used to calculate hydrodynamic circulation and kinetic energy inside an elastomer model of the elastase induced aneurysm. By comparing these values inside the aneurysm with values for previously developed diverters and a control without a diverter, it can be shown that despite changes in the braiding angle and individual wire thickness that the behavior of the devices is not significantly different (P > 0.05). Flow diversion is also being used in concert with photothrombosis. A flow diverter is used to exclude the neck remnant from the parent vessel and to provide a scaffold for the remodeling of the neck. This combination of techniques allows for very fast and near complete occlusion of the aneurysm thereby excluding the aneurysm from the parent vessel and eliminating the risk of a rupture.