Dana Grecov

Professor

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Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Lubrication performance of the cellulose nanocrystalline (CNC) aqueous suspensions as potential green lubricants (2023)

Industrial lubricants are widely introduced into mechanical systems to reduce wear and energy losses. With the increasing demand for environmental protection, developing eco-friendly lubricants becomes more crucial. Due to their abundance, biodegradability, non-toxicity, high thermal stability and low cost, cellulose nanocrystals (CNCs) may be an appropriate choice for formulating green lubricants. The wear and friction coefficient are the tribological properties that assess the effectiveness of a lubricant. Minimizing the friction coefficient and wear, using a proper lubricant, would improve lifespan of the mechanical systems in different lubrication applications. In this study, using different chemical, microstructural, rheological and tribological characterization methods, we systematically investigated the effect of particle concentration and ultrasonic treatment on the lubrication performance of CNC suspensions as potential green lubricants. It was found that the lubrication performance of liquid CNC suspensions is optimal within sonication energy of 4-50 kJ/gCNC, and the concentration regime of 1-2 wt%. The yield stress is an important rheological property for evaluating the lubrication performance of the lubricating greases. This property determines the pumpability and leakage of grease in bearing applications. In this study, we examined the effect of ultrasonic treatment and particle concentration on yield stress of highly concentrated CNC gels to evaluate their performance as potential green lubricating greases. It was found that yield stress scales linearly with CNC concentration, whereas it decreases with sonication energy through a four-step mechanism governed by microstructural transformation of the CNC agglomerates. The results confirmed that CNC aqueous suspensions may be potentially used as green lubricants. The results also suggested that by tuning ultrasonication processing and particle concentration, one may be able to optimize lubrication performance of CNC aqueous suspensions. Under the optimum CNC concentration regime (1-2 wt%), COF decreased by 50% compared to DI water. Whereas, under the optimum sonication energy regime (4-50 kJ/gCNC), COF and wear decreased by 25 and 30% compared to unsonicated CNC suspension.

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Modelling and simulation of chiral and non-chiral nematic liquid crystals between cylinders (2023)

Liquid crystallinity defines a state between a crystal solid and a liquid. Liquid Crystal (LC) molecules have the flowing properties of liquids while they keep the orientational order of solids with no positional order. To study the characteristics of disc-like LCs, initially, an analytical method to calculate the viscosity coefficients and rheological properties of discotic nematic liquid crystals (DNLCs) was proposed. The method was illustrated on nematic Graphene oxide (GO) dispersions, the most processable graphene derivative, as an example of DNLCs. GO dispersions have attracted enormous attention due to their unique liquid crystal (LC) characteristics. In the second step, the calculated Landau and Leslie viscosity coefficients were implemented in the Ericksen-Leslie (EL) theory to simulate the flow of GO dispersions. GO aqueous suspensions, with a concentration range of 15 mg/mL to 30 mg/mL, were simulated as a lubricant between two cylinders with a small gap size, which is the preliminary geometry for journal bearings. The anisotropic feature of LCs leads to a preferred direction of the molecules close to the solid surfaces, making them an outstanding candidate for the lubrication problem. Flow properties of GO dispersions at different concentrations were calculated numerically using the EL theory and compared with the respective theoretical values, which were within 1% error. Lastly, the Landau-de Gennes theory was applied to investigate the behaviour of chiral liquid crystals (CLCs) between concentric and eccentric cylinders under different flow conditions. This theory was implemented using dynamic finite element simulations (COMSOL Multiphysics) to solve the evolution of the microstructure of CLCs and coupled with a linear momentum balance equation to capture the structure of CLCs. This section focused on the microstructure formation of CLCs and their performance as lubricants under various chirality strengths (θ), Deborah numbers (De), and eccentricity of eccentric cylinders. The hexagonal structure of the CLCs at low De, where the chiral term predominates, was observed, while at higher De, the hexagonal pattern vanished. The eccentricity ratio impact on the performance of CLCs was also considered, and it was concluded that CLCs as lubricants perform well at high θ and eccentricity and low De.

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Biomechanical modeling and hemorheological assessment of ascending thoracic aortic aneurysm, aortic heart valve, and blood clot (2019)

Cardiovascular diseases account for the most cause of death over the globe annually, summarized by the World Health Organization. An aortic aneurysm is one of the cardiovascular diseases with localized abnormal growth of a blood vessel with the primary risk of aneurysm rupture or aortic dissection. The precise pathological pathway for disease progression in aneurysm formation is not completely understood; however, biomechanically, disrupted blood flow from a diseased heart valve and thrombus formation potential in the dissection could contribute to the increased risk. The current ascending thoracic aortic aneurysm (ATAA) management rely heavily on ATAA diameter and blood pressure rather than biomechanical and hemodynamical parameters including arterial wall deformation or wall shear stress (WSS). Therefore, this thesis firstly evaluated the biomechanical contributions to ATAA progression under the influence of anatomy, hypertension, and hematocrit using fully coupled fluid-structure interaction (FSI) with arterial wall anisotropy to provide additional information in patient evaluations. The investigation was then extended to study the effect of blood rheology on the hemodynamics of a bileaflet mechanical heart valve with particle image velocimetry (PIV) validation. Finally, the rheological experimentations were conducted to analyze the coagulation process and the interactions between heparinized blood and the anticoagulation reversal agents. The ATAA analysis showed significant variations in the maximum WSS despite minimal differences in flow velocity between normotension and hypertension. The three different ATAA models identified different aortic expansions that were not uniform under pulsatile pressure and a geometry depended on elevated wall stress under hypertension. The investigation on the heart valve revealed the hematocrit influenced the shear stress distributions over a cardiac cycle. The structural stresses in the mechanical valve were affected by the shear stress distributions in the blood flow. Parameter dependencies study indicated that the hematocrit is influential when conducting patient-specific modeling of prosthetic heart valves. Finally, the use of small amplitude oscillatory shear (SAOS) rheometry for studying blood coagulation provided a comprehensive assessment with the combination of multiple rheological parameters for untreated and heparin neutralized blood. The coagulation characterization could be used towards the existing FSI models to account for potential blood clot formations in future studies.

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Numerical simulation of flow and microstructure in nematic liquid crystalline materials (2013)

Liquid crystals are known for their anisotropic characteristics, which lead to a preferred orientation of their molecules in the vicinity of solid surfaces. The ability of liquid crystalline materials to form ordered boundary layers with good load-carrying capacity and outstanding lubricating properties has been widely demonstrated. In order to study the advantages of implementing liquid crystals as lubricants, the steady state/time transient isothermal flow of thermotropic/lyotropic, nematic/chiral nematic liquid crystals between two concentric/eccentric cylinders and in planar Couette geometries were studied numerically. To consider the influence of the microstructure formation/evolution on the macro-scale attributes of the flow, the Leslie-Ericksen and Landau-de Gennes theories were employed. Simplicity of the Leslie-Ericksen theory in capturing the orientational alignment angle of the molecules makes it a viable candidate for modelling the flow of flow-aligning nematic liquid crystals. On the other hand, the Landau-de Gennes nematodynamics equations are well suited for predicting texture formation since defects and disclinations are non-singular solutions of the governing equations. The Landau-de Gennes theory for the liquid crystalline microstructure along with continuity and momentum equations were solved simultaneously using General PDE and Laminar Flow modules of COMSOL Multiphysics. The investigation of flow characteristics and orientation of liquid crystalline molecules for different rotational velocities/shear rates and anchoring angles at the boundaries were presented. Furthermore, nucleation and evolution of singularities in texture of the liquid crystalline materials were tracked over the simulation time. Moreover, alterations in the macro-scale attributes of the flow such as velocity profile, pressure distribution and first normal stress difference along with the evolution of defects were studied inside the liquid crystalline domain. The implementation of Landau-de Gennes nematodynamic governing equations for LCs flow simulations offered an insight in application of these materials as lubricants. It was shown the LCs could provide protection against the wearing mechanism by forming a shielding layer in the vicinity of solid surfaces. Three-dimensional simulations of a simplified prosthetic hip joint suggested that liquid crystalline materials should be considered as potential bio-lubricants.

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Mathematical Modeling of Interaction of Wet Particles and Application to Fluidized Beds (2011)

In many industrial operations, such as fluidized bed granulators, coaters, and fluid cokers, a binding or reacting liquid is introduced into the system. Due to the effects of liquid, the multi-phase transport phenomena of these systems are more complicated compared to conventional gas-solid fluidization systems. In this thesis, mathematical modeling is used to study the interaction of wet particles. First, a coalescence model is developed to describe the binary collision of wet particles. The model is in the form of a wet coefficient of restitution and is used to determine the critical velocity—the boundary between coalescence or rebound outcomes—for a range of capillary numbers. Model predictions are compared with the available experimental data and good agreement is found. The model accounts for both liquid viscosity and surface tension effects and is used to investigate the boundary between collisions with dominant capillary and respective viscous effects. Then, by incorporating time- and temperature-dependant variations of the viscosity and thickness of the liquid coating, the model is used to determine the agglomeration tendency of bitumen-coated coke particles in fluid cokers. A simplified mathematical model and numerical solution of the Navier-Stokes equations are used to study the rupture of stretching liquid bridges between two solid spherical particles. The simplified model considers the geometry of the problem in which the gas-liquid interface is represented with a parabola. The numerical simulations of the Navier Stokes equations are performed with FLUENT and are used to investigate the viscous, surface tension, inertial, gravitational, and contact angle effects on the rupture distance and liquid distribution. Finally, the interaction of multiple wet particles is addressed by implementing the wet coefficient of restitution proposed in this thesis, using MFIX, an open-source Discrete Element Method (DEM) tool. DEM simulations of a fluidized bed consisting of mono-sized solid spherical particles pre-coated with identical liquid coatings are performed, and the effect of coating viscosity and thickness on the fluidization behaviour is investigated. Snapshots of the instantaneous particle positions are presented, and time-averaged values of the bed centroid in the y-direction, wet coefficient of restitution, and relative normal collision velocity are analyzed.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Water jet impingement in run-out table cooling (2023)

cooling process on a run-out table is a critical step that governs the final microstructure and the mechanical properties of the produced steels. In this research, we use a more recent method for obtaining the thermal history on the plate surface, which is the infrared thermal imaging technique. This technique has the advantage of capturing the surface temperature history remotely and with no contact with the plate. In this work, controlled cooling experiments under transient conditions were conducted on a hot stationary plate using an impinging top circular nozzle and a thermal camera to capture the temperature history. The measurements from the thermal camera (conducted in Abu Dhabi University) are compared with the conventional thermocouple measurements (University of British Columbia). The comparisons showed that the infrared camera gives more complete picture of the thermal history and more accurate results than thermocouple measurements. Reasons for the inaccuracy of the thermocouple (T/C) measurements include T/C response time, and distortion of the thermal field by the method of installation. These reasons are discussed in detail in the thesis. Additionally, we introduce a transient multiphase CFD numerical simulation to obtain the temperature profile on the plate surface and compare it with the experiments conducted. The numerical simulation was done using the Ansys-Fluent CFD software. A two-dimensional model was used with a highly intensive mesh near the wall region based on the wall y+ number. The surface temperature graphs for both measurements and simulation are compared at different radial locations (stagnation zone and parallel zone). Additionally, the obtained CFD results were verified and compared with the surface temperature of the experimental data.

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Lubrication performance of biolubricants (2022)

Lubrication has been used to reduce the friction and wear of the mechanical components. Friction and wear are the reason behind most of the energy and material wastage in the industry. Petroleum-based oil is primarily used as the base lubricant, which is inherently toxic and has detrimental effects on the environment. Water is also used as the base lubricant for some applications, however, water itself is a poor lubricant. Biolubricants are used as the alternative to regular lubricants and are biodegradable, environmentally friendly, and come from a variety of resources. In this research, we have studied two aqueous biolubricants. In the first study, Cellulose Nanocrystals (CNCs) were used as additives to water, due to their superior properties such as renewability, biodegradability, and mechanical strength. The lubrication performance has been investigated using tribology. Tribological tests have been performed on a pin-on-disk tribometer in order to investigate the lubrication performance of this novel lubricant and more specific to evaluate its stability. The tribological properties of the CNC Suspensions in two regimes, semi-dilute and gel (grease), have been studied. Wear, stick-slip, and visualizations results showed that the CNC suspensions in the semi-dilute regime show better tribological properties than the suspensions in the gel regime. In the second study, the lubrication performance of an aqueous fucoidan solution as a biolubricant has been characterized. Fucoidan is used in various biomedical applications and is derived from brown algae (seaweed). This biocompatible lubricant provided by ARC Medical Devices Inc was studied as part of the product development stage so that it can be applied optimally during clinical operations while retaining its lubrication characteristics. Soft tribological tests were performed for the fucoidan solution as the novel lubricant and the Lactated Ringer’s solution as the control sample. Tribological tests were also performed on pig skin. In both experiments, the efficacy and improvement in tribological properties have been shown for fucoidan solutions compared to the control sample.

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Numerical simulation of liquid crystal hydrodynamics (2022)

Liquid crystals (LCs) are a state of matter that is intermediate between crystalline solid and amorphous liquid. They are anisotropic viscoelastic materials with broad applications in science and engineering. For example, they have been traditionally used in flat panel displays and more recently, in energy conversion applications. They can also be used as lubricants or additives to lubricants to reduce wear, improve load-carrying capacity and decrease the coefficient of friction (COF) due to their anisotropic viscoelastic properties and their ability to form ordered layers in the vicinity of solid surfaces. The Landau-de Gennes (LdG) equations can model the flow of liquid crystals. The LdG equations are capable of modelling texture formation since defects in liquid crystals correspond to non-singular solutions to the governing partial differential equations (PDEs). In this research, the Landau-de Gennes equations were simplified with Reynolds scaling analysis to form the simplified LdG equations, which were then applied to the Couette geometry and the slider bearing geometry. Both the simplified LdG model and the full LdG model were numerically solved in COMSOL Multiphysics ®. The simplified LdG model was evaluated and verified by comparing simulation results with those from the full LdG model. Lubrication performance was analyzed for the slider bearing geometry with both the simplified LdG model and the full LdG model. The simplified LdG model significantly reduced simulation wall time compared to the full LdG model over the same domains. Chiral liquid crystals are a type of LCs that have a twist or helix about an axis normal to the director. They are used in thermochromic systems and flexible cholesteric displays and exist in virtually all organisms as a building block of life. The Couette flow of chiral liquid crystals was modelled, evaluated and verified in COMSOL. The 2D lid-driven cavity flow of chiral liquid crystals was simulated, evaluated and verified in COMSOL. Parametric studies investigating the effect of the chiral strength and the viscous flow effect on the microstructure of LCs were conducted.

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Numerical simulations of bifurcation cerebral aneurysm hemodynamics (2022)

A cerebral aneurysm is a dilation of a brain artery wall occurring more frequently in the circle of Willis. The cerebral aneurysm rupture is a life-threatening incident with a high mortality rate that requires emergency medical treatment. To accurately predict the growth and rupture of cerebral aneurysms, understanding the hemodynamics characteristics is of great importance.A comprehensive study regarding the combined effect of the aneurysm size and bifurcation artery angle on the aneurysm rupture risk is still missing. In patient specific geometries, the bifurcation arteries are not completely perpendicular to the parent arteries, therefore, it is essential to investigate the effect of different bifurcation artery angles on the hemodynamics of cerebral aneurysms.In the present thesis, the physiologically realistic pulsatile Newtonian and non-Newtonian blood flow conditions are numerically simulated in idealized aneurysms with different geometric features defined by the size of the aneurysm and the bifurcation artery angle to investigate the aneurysm rupture risk. The current study also considers the blood flow dynamics simulation in a patient-specific cerebral aneurysm geometry to examine the hemodynamics behavior of a real cerebral aneurysm.The results indicate that blood flow is more unstable under the Newtonian blood assumption as there are stronger viscous forces that prevent fluid flow from instabilities under non-Newtonian assumptions. Furthermore, it is seen that the aneurysm size and bifurcation artery angle have a considerable effect on aneurysmal inflow which is an important factor in cerebral aneurysm treatment. Comparison of the wall shear stress distribution in the patient-specific geometry and the idealized geometry indicates that idealized geometries can predict the real aneurysm hemodynamics characteristics with acceptable errors.

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Numerical modelling of liquid crystal flows in confined domains (2019)

Liquid crystals are anisotropic, viscoelastic materials with properties intermediate of solids and liquids. They are useful structural and functional materials and due to their ability to form ordered layers close to the bounding surfaces they are used as lubricants. Under the application of a hydrodynamic field, based on the type of velocity profile, values of non-dimensional numbers and anchoring angles, different orientation profiles are observed. Leslie-Ericksen and Landau-de Gennes theories are used to understand the evolution of the microstructure. Leslie-Ericksen theory, due to its simplicity can be used to obtain the behavior of flow aligning nematic liquid crystals. Landau-de Gennes theory is a mesoscopic model and apart from its ability to capture singular solutions can be employed in a study of lubrication using liquid crystals. This research work contains studies of liquid crystals in different flow conditions, such as the Couette flow and the Channel flow. In the study of Couette flow of Graphene oxide suspensions in water, the Leslie-Ericksen theory was used to obtain the orientation and viscosity profiles at different shear rates, up until flow alignment was observed. In the numerical study of pressure-driven channel flows, a Marker and Cell based solution methodology was implemented to solve the Leslie-Ericksen hydrodynamic theory. The expected flow alignment of liquid crystals was obtained which validated the solver. A preliminary study combining the moving wall and pressure driven flow showed that the orientation profile obtained depends on the local direction of shear and the direction of shear gradient. The scaling analysis was applied to Landau-de Gennes theory to derive the simplified equations of a planar lubrication theory. The theory was then validated by comparison with the solution obtained from numerically solving the full set of equations using the Couette flow profile. The parametric studies conducted showed that the solution was in the Elasticity-driven steady state. A discussion of the physical conditions showed its applicability for films of thickness lesser than 1 mm for a 1 m long domain.

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Rheo-PTV analysis of complex fluids (2019)

Complex fluids are ubiquitous in the everyday life. Their study enables a better perception of the surrounding environment as it can be used to model a variety of industrial, biological and geophysical applications. This study presents a novel optical capillary rheometer that benefits from the advantages of both capillary rheometry and flow visualization.The experimental setup developed in this research was applied to three different case studies, each highlighting an aspect of the rheological behavior of complex fluids. In the first case study, the slip mechanism of various concentrations of carbopol gel, as a simple yield stress fluid, was systematically investigated with respect to its material properties. Presence of a fully plugged flow and a thin layer of a Newtonian solvent, lubricating the unyielded gel at wall stresses below the yield stress was confirmed. The wall slip behavior of the carbopol gels at wall stresses above the yield stress was studied as well. It was shown that the slip velocities have a power-law correlation with the wall shear stress below the yielding point, and a linear correlation after the yielding point. Furthermore, the sliding threshold below which the gel sticks to the wall, was found to have a linear relationship with its yield stress and the fluidity of its solvent. The start-up flow of laponite as a thixotropic yield stress fluid was examined in the second case study. The time dependent behavior of the fluid was studied in terms of the variations of shear stress at a constant flow rate. Finally, the behavior of synovial fluid at high shear rates was investigated as the third case study. Synovial fluid of the knee joint undergoes extensive range of shear rates during high physical activities. Rheological behavior of synovial fluid was studied at shear rates as high as 7000 s-1, which is seven times greater than the maximum shear rate typically measurable by a rotational rheometer. The method developed in this research enables to further study the complex behavior of fluids that are challenging using the conventional rheometry methods.

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Cellulose nanocrystals aqueous suspensions as water-based lubricants (2018)

Lubrication is an effective means of controlling wear and reducing friction. Friction and wear are the major cause of material wastage and loss of mechanical performance. To reduce the friction, most of the mechanical devices are lubricated by oils or in some cases by water. To enhance the properties of lubricants a chemical component or blend is added to improve their performance. In this research, we have used Cellulose Nanocrystals (CNC) as additives in water-based lubricants. CNC is synthesized from native cellulose which is one of the most abundant biopolymer resource available. It has many advantages such as renewable, biodegradable and non-toxic.Tribological tests were performed on a pin on cylinder tribometer to investigate the application of CNC as water-based lubricants additives. The coefficient of friction and wear between a stainless-steel shaft and a chrome steel ball were measured in the presence of the CNC lubricant with different concentrations.One of the applications were water is used as a lubricant is in gland sealed slurry pumps. Gland seals prevent pumped fluid from leaking into the environment. The gland seal packing material is tested with CNC lubricant to study the behavior of the new lubricant as a possible alternative of water in industrial applications. Effect of normal force, rotational speed and shaft diameter on the coefficient of friction and wear were studied as well. It was found that adding 2 wt.% of CNC in water improved lubrication and provided a very low friction coefficient of approximately 0.09. It reduces the wear depth and width by more than 50%. The improvement of the coefficient of friction and wear is mainly due to the high strength of CNC rods and alignment of CNC nanoparticles.

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Rheological characterization of fumed silica lubricating greases (2018)

Lubricating greases have been widely used for rail lubrication systems. For an efficient grease pump design, it is important to study grease shear viscosity and it is also crucial to analyze grease yielding behavior to determine its consistency on rail surface. Among all rheological properties measured through experiments, yield stress is an ill-defined property, which investigation of a reproducible method for its determination can be invaluable. As the flow properties of a material will be usually influenced by the changes in environment temperature, studying the effects of temperature on the rheological properties of grease are important. In this study, different rheological measurements and visualization techniques, previously developed to study a wide range of materials, have been performed to characterize fumed silica based lubricating greases manufactured by L.B. Foster Rail Technologies Corp. Using commercial rheometers and different approaches to determine the yield points of these materials, it was revealed that the values obtained by curve fitting on steady-state flow curves, creep, amplitude sweep crossover and stress ramp-up were roughly similar. The microstructure of this grease was analyzed using Scanning Electron Microscope (SEM) on Cryo and non-Cryo modes. Besides visualizing a new thickener microstructure, it was shown that the heterogeneous structures developed by small fumed silica agglomerates lead to the formation of greases with higher shear viscosities. Finally, thermo-rheological analysis of these samples revealed that these materials follow neither Arrhenius equation nor time-temperature superposition principle.

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A rheological study of treatments for osteoarthritis (2016)

Osteoarthritis is a common joint disease causing pain and inflammation that limits mobility and functionality. Osteoarthritis is a widespread disease, and despite it's prevalence there is no cure. The disease progresses by degrading joint cartilage and synovial fluid. The current work aims to contribute to existing knowledge regarding osteoarthritis through three research projects including a rheological study of novel anti-inflammatory hyaluronic acid derivatives, a case study on the effects of oral glucosamine supplementation on synovial fluid viscosity, and development of a microfluidic rheometer that may be used to study low viscosity fluids such as hyaluronic acid and synovial fluid at high shear rates. The anti-inflammatory hyaluronic acid derivative demonstrated shear thinning and viscoelastic behaviour as expected. This behaviour is common among viscosupplements and is therefore promising for it's potential use as a viscosupplement, however, the viscosity and viscoelasticity were significantly lower than commercial viscosupplements. It is recommended to investigate modulating viscosity and viscoelasticity with techniques such as cross-linking and increasing hyaluronic acid concentration. In a patient discontinuing oral glucosamine supplementation the viscosity was found to be greater prior to stopping treatment at low shear rates and greater after stopping treatment at high shear rates. In a second patient no significant change was observed in viscosity. Future study should investigate the effect of glucosamine on viscoelastic behaviour, and to study the effect of glucosamine on synovial fluid viscosity over an extended period of time. A PDMS microfluidic rheometer was developed using a soft-lithography process. The rheometer was validated with water at room temperature and was found to predict fluid viscosity with a maximum of 6% error at shear rates as high as 30,000 s-¹. It is recommended to investigate possible channel deformation as a cause for decreased accuracy at higher shear rates and resultant operating pressures.

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Computational analysis of fluid structure interaction in artificial heart valves (2013)

The development of heart valve stenosis and sclerosis can lead to the development of fatal complications such as congestive heart failure. Therefore, severe valve stenosis requires a surgical operation with artificial heart valve replacement. Given that the geometrical differences between artificial valves would significantly influence hemodynamic performance around the implanted valve, additional knowledge for the interactions between blood flow and the artificial valve is necessary. Therefore, in order to proceed, this study proposes an advanced computational fluid dynamics (CFD) simulation using a fluid-structure interaction (FSI) technique to investigate artificial valve leaflet motion under different physiological conditions. Among various FSI technique, it is proposed to simulate the motion of the artificial heart valve with a fully-coupled algorithm and arbitrary Lagrangian-Eulerian formulation (ALE) using a monolithic solver. Models are constructed using a realistic aortic root for both the bileaflet and bioprosthetic valves with additional modifications and considerations for the flexible arterial wall. Normal physiological blood pressure and conditions are used to simulate healthy scenarios, which are compared with experiments. Validation is conducted by analysing particle image velocimetry (PIV) experimental data from ViVitro Lab. Hemodynamic performance analyses are conducted and found that both velocity and maximum von Mises stress are higher if calculated using a rigid wall model. The leaflet dynamics, on the other hand, is relatively the same for rigid or flexible wall model. Clinically relevant scenarios are also simulated for both mechanical and bioprosthetic valves. The clinical focus for the mechanical valve is on the malfunction of the valve due to leaflet restrictions. In addition, the clinical focus for the bioprosthetic valve is on the systolic deficiency due to different tissue properties.

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Industrial bio-lubricants performance and characterization (2013)

The general trend towards the use of high performance lubricants and environmentally friendly products supports the design of new industrial lubricants. Therefore, there are good practical reasons to extend the research related to lubrication. Bio-oils, as promising growing substitutes for mineral oils, need more research to deal with new and inherited problems. Meanwhile, there is no complete understanding of the lubrication phenomenon, nor a complete rheological characterization of oil lubricants. This research is an effort to study industrial bio-lubricants and to develop a more comprehensive approach, at the same time correlating their rheological and tribological behavior. Different commercial canola oil based lubricants were studied using different techniques. For validation and comparison, engine oil, silicone oil and mineral hydraulic oil were tested. Bio-lubricants exhibited constant viscosity at both moderate and high shear rates and shear thinning at low shear rates and temperatures below 30 degrees Celsius. Frequency sweep tests revealed a significant viscoelasticity of bio-lubricant which developed over time.Time dependence, structure recovery, gap size effect, surfactant behavior, and geometry’s material influence were all investigated. A high pressure cell and a polarized light microscope coupled with the rheometer were used to investigate the bio-lubricants. Thermal analysis was conducted using a differential scanning calorimeter. Several transition points were identified in the range of temperatures from -30 to 100 degrees Celsius, and the results have been connected to the viscoelastic behavior. Different tribological tests were used to investigate the lubricity of lubricants and bio-lubricants added by liquid crystals. The coefficient of friction, at tested temperatures, and the wear rate were observed over time. Adding two percent of ionic liquid crystals improved the wear resistance of the oil, but the bio-lubricant had the lowest coefficient of friction. This research could be considered as pioneer work. An attempt was made to achieve profound perspective matching between rheometry, tribology and thermal analysis. Some assumptions explaining the rheological and tribological behavior were hypothesized and associated with arguments and discussions. Based on, Imaginary scenario of bio-hydraulic oil behavior within a small gap was visualized.

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Osteoarthritic synovial fluid rheology and correlation with protein concentration (2013)

Synovial fluid (SF) is a lubricant for articulating joints. The study of SF rheological properties has gained significance due to SF viscoelastic properties, and SF’s ability to sustain a considerable load. The rheological performance of SF is linked to the joint’s condition. A joint disease such as osteoarthritis (OA) reduces SF rheological properties. This study is aimed at investigating the shear and extensional rheological properties of osteoarthritic synovial fluid (OA SF). Additionally, this study is aimed at correlating SF rheological properties with its protein concentration.Shear rheological properties of 35 OA SF samples were investigated at a physiological temperature (37 °C) using cone-and-plate shear rheometer. Furthermore, the effects of the temperature, the centrifugation, and the storage at -20 °C for two weeks were also studied on some samples. Additionally, the time-dependent rheological properties were investigated by rotation and oscillation tests. Extensional rheological properties were studied using a capillary breakup extensional rheometer (CaBER). First, the effects of different CaBER configurations on the extensional rheological measurements were investigated in order to determine the optimal configuration. Then, the extensional rheological properties of 21 OA SF samples were studied. The protein concentrations of SF were determined using a bicinchoninic acid (BCA) protein assay kit. I also investigate the correlations between rheological properties and protein concentration.The understanding of SF rheological properties will lead to a better understanding of its lubrication properties, and to the development of a rheological analogue to SF or to a periprosthetic fluid.

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