The major drawback of crossflow membrane filtration is that permeate flux declines with time as a result of the increase in total membrane resistance. Pulsatile flow is well known to reduce the resistance and enhance permeate flux. This study applied pulsatile flow induced by the oscillation of a collapsible tube to microfiltration and ultrafiltration, to improve filtration performance expressed as permeate flux enhancement and backflushable resistance reduction. Three membranes (ceramic tubular microfiltration, PVDF spiral-wound microfiltration and PS hollow-fibre ultrafiltration) and two media (bentonite suspension and whey solution) were used. In bentonite pulsatile microfiltration with the tubular membrane, up to 300% of permeate flux enhancement and 90% of backflushable resistance reduction were achieved. In bentonite and whey pulsatile microfiltration with the spiral-wound membrane, moderate improvements were gained: for bentonite, the highest increase in permeate flux was 51% and decrease in backflushable resistance was 45%; for whey, the highest permeate flux enhancement and backflushable resistance reduction were 36% and 38% respectively. In ultrafiltration of both media, no significant performance improvement was found. This is thought due in the one case to the relatively minute membrane pore size, and in the other to the large irreversible resistance created by whey solution. Transmural pressure at the collapsible tube downstream end indicates the tube compression and influences the pulsation vigour. Increasing the transmural pressure was an effective way to improve filtration performance. In bentonite microfiltration with the tubular membrane, increasing crossflow velocity was also effective, but increasing transmembrane pressure was not. Analysis of pulsatility parameters showed that the pulsatile flow always resulted in enhanced wall shear, and induced pore backflush always in the tubular membrane and sometimes in the HF membrane. These mechanistic findings helped to understand the filtration performance improvements. The analysis of energy consumption in bentonite microfiltration with the tubular membrane clearly demonstrated the benefit of applying the collapsible-tube-induced pulsatile flow in energy utilisation. The system specific energy could be reduced more than 70 % relative to the equivalent steady microfiltration permeate flux. For a given specific energy, the permeate flux could be increased by a factor of nearly four.

Many complex biological systems, such as blood and polymeric materials, can be approximated as single constituent homogeneous fluids whose properties can change because of the chemical reactions that take place. For instance, the viscosity of such fluids could change because of the chemical reactions and the flow. Here, I investigate the pulsatile flow of a chemically-reacting fluid whose viscosity depends on the concentration of a species (constituent) that is governed by a convection-reaction-diffusion equation and the velocity gradient, which can thicken or thin the fluid. I study the competition between the chemical reaction and the kinematics in determining the response of the fluid. The solutions to the equations governing the steady flow of a chemicallyreacting, shear-thinning fluid are obtained analytically. The solution for the velocity exhibits a parabolic-type profile reminiscent of the Newtonian fluid profile, if the fluids are subject to the same boundary conditions. The full equations associated with the fluid undergoing a pulsatile flow are studied numerically. A comparison of the shear-thinning/chemical-thinning fluid to the shear-thinning/chemicalthickening fluid using a new non-dimensional parameter–the competition number (CN) shows that both the shear-thinning effects and the chemical-thinning/thickening effects play a vital role in determining the response of the fluid. For the parameter values chosen, the effects of chemical-thinning/thickening dominate the majority of the domain, while the effects due to shear-thinning are dominant only in a small region near the boundary.

In this research, pulsatile blood flow through a modeled arterial stenosis assuming Newtonian and non-Newtonian viscous behavior is simulated using direct numerical simulation (DNS). A serial FORTRAN code has been parallelized using OpenMP to perform DNS based on available high performance shared memory parallel computing facilities. Numerical simulations have been conducted in the context of a channel with varying the degree of stenosis ranging from 50% to 75%. For the pulsatile flow studied, the Womersley number is set to 10.5 and Reynolds number varies from 500 to 2000, which are characteristic of human arterial blood flows. In the region upstream of the stenosis, the flow pattern is primarily laminar. Immediately after the stenosis, the flow recirculates and an adverse streamwise pressure gradient exists near the walls and the flow becomes turbulent. In the region far downstream of the stenosis, the flow is re-laminarized for both Newtonian and non-Newtonian flows.

Arterial wall morphology depends strongly on the hemodynamic environment experienced in vivo. The mammalian heart pumps blood through rhythmic contractions forcing blood vessels to undergo cyclic, mechanical stimulation in the form of pulsatile blood pressure and flow. While it has been shown that stepwise, chronic increases in blood pressure and flow modify arterial wall thickness and diameter respectively, few studies on arterial remodeling have examined the influences that pulsatility (i.e., the range of cyclic stimuli) may have on biaxial wall morphology. We experimentally studied the biaxial behavior of carotid arteries from 8 control (CCA), 15 transgenic, and 21 mechanically altered mice using a custom designed mechanical testing device and correlated those results with hemodynamic measurements using pulsed Doppler. In this dissertation, we establish that increased pulsatile stimulation in the right carotid artery after banding (RCCA-B) has a strong affect on wall morphological parameters that peak at 2 weeks and include thickness (CCA=24.8±0.878, RCCA-B=99.0±8.43 μ m), inner diameter (CCA=530±7.36, RCCA-B=680±32.0μ m), and in vivo axial stretch (CCA=1.7±0.029, RCCAB= 1.19±0.067). These modifications entail stress and the change in stress across the cardiac cycle from an arterial wall macro-structural point of view (i.e., cellular and extracellular matrix) citing increases in collagen mass fraction (CCA=0.223±0.056, RCCA-B=0.314±0.011), collagen to elastin ratio (CCA=0.708±0.152, RCCA-B=1.487±0.26), and cross-sectional cellular nuclei counts (CCA=298±58.9, RCCA-B=578±28.3 cells) at 0, 7, 10, 14, and 42 post-banding surgery. Furthermore, we study the biomechanical properties of carotid arteries from a transgenic mouse of Marfan Syndrome. This arterial disease experiences increased pulse transmission and our findings indicate that alterations occur primarily in the axial direction. The above results are all applied to a predictive biaxial model of Cauchy stress vs. strain.

Turbocharging the internal combustion (IC) engine is a common technique to increase the power density. If turbocharging is used with the downsizing technique, the fuel consumption and pollution of green house gases can be decreased. In the turbocharger, the energy of the engine exhaust gas is extracted by expanding it through the turbine which drives the compressor by a shaft. If a turbocharged IC engine is compared with a natural aspirated engine, the turbocharged engine will be smaller, lighter and will also have a better efficiency, due to less pump losses, lower inertia of the system and less friction losses. To be able to further increase the efficiency of the IC engine, the understanding of the highly unsteady flow in turbochargers must be improved, which then can be used to increase the efficiency of the turbine and the compressor. The main objective with this thesis has been to enhance the understanding of the unsteady flow in turbocharger and to assess the sensitivity of inflow conditions on the turbocharger performance. The performance and the flow field in a radial turbocharger turbine working under both non-pulsatile and pulsatile flow conditions has been assessed by using Large Eddy Simulation (LES). To assess the effects of different operation conditions on the turbine performance, different cases have been considered with different perturbations and unsteadiness of the inflow conditions. Also different rotational speeds of the turbine wheel were considered. The results show that the turbine cannot be treated as being quasi-stationary; for example,the shaft power varies for different frequencies of the pulses for the same amplitude of mass flow. The results also show that perturbations and unsteadiness that are created in the geometry upstream of the turbine have substantial effects on the performance of the turbocharger. All this can be summarized as that perturbations and unsteadiness in the inflow conditions to the turbine affect the performance. The unsteady flow field in ported shroud compressor has also been assessed by using LES for two different operational points. For an operational point near surge, the flow field in the entire compressor stage is unsteady, where the driving mechanism is an unsteadiness created in the volute. For an operational point far away from surge, the flow field in the compressor is relatively much more steady as compared with the former case. Although the stable operational point exhibits back-flow from the ported shroud channels, which implies that the flow into the compressor wheel is disturbed due to the structures that are created in the shear layer between the bulk flow and the back-flow from the ported shroud channels. / QC20100622

<p>Non-pulsatile and pulsatile flow in bent pipes and radial turbine has been assessed with numerical simulations. The flow field in a single bent pipe has been computed with different turbulence modelling approaches. A comparison with measured data shows that Implicit Large Eddy Simulation (ILES) gives the best agreement in terms of mean flow quantities. All computations with the different turbulence models qualitatively capture the so called Dean vortices. The Dean vortices are a pair of counter-rotating vortices that are created in the bend, due to inertial effects in combination with a radial pressure gradient. The pulsatile flow in a double bent pipe has also been considered. In the first bend, the Dean vortices are formed and in the second bend a swirling motion is created, which will together with the Dean vortices create a complex flow field downstream of the second bend. The strength of these structures will vary with the amplitude of the axial flow. For pulsatile flow, a phase shift between the velocity and the pressure occurs and the phase shift is not constant during the pulse depending on the balance between the different terms in the Navier- Stokes equations.</p><p>The performance of a radial turbocharger turbine working under both non-pulsatile and pulsatile flow conditions has also been investigated by using ILES. To assess the effect of pulsatile inflow conditions on the turbine performance, three different cases have been considered with different frequencies and amplitude of the mass flow pulse and different rotational speeds of the turbine wheel. The results show that the turbine cannot be treated as being quasi-stationary; for example, the shaft power varies with varying frequency of the pulses for the same amplitude of mass flow. The pulsatile flow also implies that the incidence angle of the flow into the turbine wheel varies during the pulse. For the worst case, the relative incidence angle varies from approximately −80° to +60°. A phase shift between the pressure and the mass flow at the inlet and the shaft torque also occurs. This phase shift increases with increasing frequency, which affects the accuracy of the results from 1-D models based on turbine maps measured under non-pulsatile conditions.</p><p>For a turbocharger working under internal combustion engine conditions, the flow into the turbine is pulsatile and there are also unsteady secondary flow components, depending on the geometry of the exhaust manifold situated upstream of the turbine. Therefore, the effects of different perturbations at the inflow conditions on the turbine performance have been assessed. For the different cases both turbulent fluctuations and different secondary flow structures are added to the inlet velocity. The results show that a non-disturbed inlet flow gives the best performance, while an inflow condition with a certain large scale eddy in combination with turbulence has the largest negative effect on the shaft power output.</p>

Following a head concussion the intracranial pressure increases due to the impact, which cannot be adequately relieved because of the stiffness of the skull. Popular strategies aimed at decompressing the head consist in the administration of osmotic agents and skull removal. The mechanical properties of bone can be affected by the administration of different solutions. If the malleability of skull is influenced by the osmotic agents that are administered to the patient then the pressure and volume in the intracranial cavity can also be modified following the treatment. In this thesis research, we hypothesize that administered osmotic agents can influence the mechanical properties of the skull, which can also impact the volume the cavity can hold and subsequently the pressure in the head. This premise was tested by modifying existing mathematical models compiled through two general MATLAB codes that allow the computation of a non-symbolic differential-algebraic initial value problem. Three main features were changed in comparison to current models: the skull's influence on the pressure and volume modulation was tested (inputs were obtained from skull tested under different solutions); pulsatile flow was accounted for on the creation and movement of cerebrospinal fluid; and the input on the mechanical behavior of the cranial vessels was accounted for through previously published continuum-mechanics vessel-behavior models. To complete the model, materials and mechanical properties were obtained through laboratory experiments as well as data collection from existing literature. From our bone test we were able to conclude that there are different factors that affect the mechanical properties of bone in various degrees. There is a mild statistical correlation (p-value 0.05) between the mechanical properties of bone obtained from different regions of the skull samples (2-14mm) and the DPBS and hDPBS solutions. Additionally there is a strong statistical difference (p-value 0.05) between the mechanical properties obtained from cross head speed (0.02, 0.002, and 0.004 (mm/s)) and solution variation (DI, DPBS and hDPBS). Finally, we were able to see that there seems to be a correlation between the mechanical properties of bone, the solution treatments and hypertension; although more test need to be developed to affirm this premise since our results are preliminary.

Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-02-26Bitstream added on 2014-06-13T20:55:54Z : No. of bitstreams: 1 machado_da_me_ilha.pdf: 1511743 bytes, checksum: 02f8492fa42747b8dd47642f8ed0d7f9 (MD5) / Este projeto visa à análise cinemática de um arranjo experimental capaz de reproduzir o fluxo sanguíneo em artérias. O mecanismo procura realizar esse escoamento através de um sistema came-seguidor juntamente com um sistema hidráulico, utilizando êmbolo e duas válvulas controladoras de fluxo. O mecanismo came-seguidor será utilizado devido a sua versatilidade em garantir que o escoamento sanguíneo ocorra durante um ciclo cardíaco. A came será radial com seguidores de roletes. O seguidor de roletes será ligado ao cilindro hidráulico que controla o fluxo sanguíneo. Um tubo de látex foi acoplado ao sistema hidráulico representando a aorta abdominal, foi confeccionado com as dimensões reais desta artéria e o látex foi escolhido, pois possui um coeficiente de elasticidade muito próximo da artéria. Um manômetro foi acoplado ao sistema para medir a pressão no interior do tubo de látex. Na sequência um tubo de complacência simular as perdas de carga do sistema circulatório. O deslocamento radial do tubo de látex e variação de pressão do manômetro foram monitorados através de filmagem. Posteriormente, os resultados experimentais foram comparados e validados com os resultados numéricos obtidos com o programa ANSYS e com a literatura / This project aims to kinematic analysis of an experimental apparatus able to reproduce the blood flow in arteries. The mechanism cam-follower and the hydraulic system using piston and two controlling valves of flow were used to realize the fluid flow. The camfollower mechanism was used to ensure that the fluid flow occurs during the cardiac cycle. The cam is radial with roller followers. The follower roller is connected to the hydraulic cylinder which controls the fluid flow. A latex tube was attached to the hydraulic system representing the abdominal aorta. The latex tube has the same real dimensions of this artery and it was chosen due the modulus of elasticity very close to the artery. A manometer was used to measure the outlet pressure of latex tube. After latex tube there is a complacency tube to control the pressure drop of circulatory system. The radial displacement of the latex tube and pressure variation of the manometer were monitored through filming. The experimental results were compared and validated with numerical results obtained with ANSYS software and with literature

All organs, including the brain, need a pathway to remove neurotoxic extracellular proteins. In the brain this is called the glymphatic system. The glymphatic system works by exchanging proteins from interstitial fluids to cerebrospinal fluids. The extracellular proteins are then removed through the cerebrospinal fluid drains. The glymphatic system is believed to be driven by arterial pulsatility, cerebrospinal fluid production and respiration. Cerebrospinal fluids enters the brain alongside arteries. In this project, we investigate if a simulated pulsatile flow in a common carotid artery can drive cerebrospinal fluid flow running along the artery, using computational simulations of a linearly elastic and fluid-structure multiphysical model in COMSOL. Our simulations show that a heartbeat pulse increases the arterial radius of the common carotid artery by 6 %. Experimental data, assessed using 4D magnetic resonance imaging of a living human, show an increase of 13 %. Moreover, our results indicate that arterial displacement itself is not able to drive cerebrospinal fluid flow. Instead, it seems to create a back and forth flow that possibly could help with the protein exchange between the cerebrospinal and interstitial fluids. Overall, the results indicate that the COMSOL Multiphysics linearly elastic model is not ideal for approximations of soft non-linearly elastic solids, such as soft polydimethylsiloxane and artery walls work for stiffer materials. The long term aim is to simulate a part of the glymphatic system and the present work is a starting point to reach this goal. As the simulations in this work are simplified there are more things to test in the future. For example, using the same geometries a non-linear elastic model could be tested. The pulsatile waveform or the geometry could be made more complex. Furthermore the model could be scaled down to represent a penetrating artery in the brain instead of the common carotid artery.

Understanding the hemodynamics of the cardiovascular system and associated diseases is important for mitigating health risks. We applied flow diagnostic techniques to investigate pulsatile flow characteristics past sidewall cavities, which have implications to two biomedical problems in the cardiovascular system: sidewall aneurysms and the left atrial appendage. Superhydrophobically-coated mesh diverters and synthetic slippery surfaces were studied for their effects on flow diversion and cavity flow enhancements. The study of pulsatile flow over a coated mesh diverter showed that the formation of the primary vortex was prevented which prevents flow stagnation and downwash flow in the cavity. The second study indicates that the healthy heart cycle is essential to reducing flow stasis inside the left atrial appendage. After applying a synthetic slippery surface to the interior of a side wall cavity model, this surface reduced the wall shear stress and allowed vortical flow to reach deeper into the cavity.