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1
Reasor, Daniel Archer. "Numerical simulation of cellular blood flow". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42760.
Testo completoAbstract (sommario):
In order to simulate cellular blood, a coarse-grained spectrin-link (SL) red blood cell (RBC) membrane model is coupled with a lattice-Boltzmann (LB) based suspension solver. The LB method resolves the hydrodynamics governed by the Navier--Stokes equations while the SL method accurately models the deformation of RBCs under numerous configurations. This method has been parallelized using Message Passing Interface (MPI) protocols for the simulation of dense suspensions of RBCs characteristic of whole blood on world-class computing resources.
Simulations were performed to study rheological effects in unbounded shear using the Lees-Edwards boundary condition with good agreement with rotational viscometer results from literature. The particle-phase normal-stress tensor was analyzed and demonstrated a change in sign of the particle-phase pressure from low to high shear rates due to RBCs transitioning from a compressive state to a tensile state in the flow direction. Non-Newtonian effects such as viscosity shear thinning were observed for shear rates ranging from 14-440 inverse seconds as well as the strong dependence on hematocrit at low shear rates. An increase in membrane bending energy was shown to be an important factor for determining the average orientation of RBCs, which ultimately affects the suspension viscosity. The shear stress on platelets was observed to be higher than the average shear stress in blood, which emphasizes the importance of modeling platelets as finite particles.
Hagen-Poiseuille flow simulations were performed in rigid vessels for investigating the change in cell-depleted layer thickness with shear rate, the Fåhraeus-Linqvist effect, and the process of platelet margination. The process of platelet margination was shown to be sensitive to platelet shape. Specifically, it is shown that lower aspect ratio particles migrate more rapidly than thin disks. Margination rate is shown to increase with hematocrit, due to the larger number of RBC-platelet interactions, and with the increase in suspending fluid viscosity.
2
New, David M., e Luis E. Estrada. "Computer simulations of coronary blood flow through a constriction". Thesis, Monterey, California: Naval Postgraduate School, 2014. http://hdl.handle.net/10945/41423.
Testo completoAbstract (sommario):
Approved for public release; distribution is unlimited.Stenoses (blockages) in coronary arteries cause heart attack, which the Centers for Disease Control and Prevention ranks as the leading cause of death among American adults. We have performed computer simulations in order to understand the flow patterns due to stenoses with and without a guidewire used for interventional procedures (e.g., stent deployment). Building off previous models that have been partially validated with experimental data, this thesis continues to develop the models in order to further evaluate fluid characteristics for cardiovascular applications. Reasonable agreement occurs between computational and experimental data. This work is done in preparation for future research to develop a microelectromechanical system capable of monitoring blood flow and aiding in medical diagnoses.
3
Alirezaye-Davatgar, Mohammad Taghi Graduate School of Biomedical Engineering Faculty of Engineering UNSW. "Numerical simulation of blood flow in the systemic vasculature incorporating gravitational force with application to the cerebral circulation". Awarded by:University of New South Wales. Graduate School of Biomedical Engineering, 2006. http://handle.unsw.edu.au/1959.4/26177.
Testo completoAbstract (sommario):
Background. Extensive studies have been conducted to simulate blood flow in the human vasculature using nonlinear equations of pulsatile flow in collapsible tube plus a network of vessels to represent the whole vasculature and the cerebral circulation. For non-linear models numerical solutions are obtained for the fluid flow equations. Methods. Equations of fluid motion in collapsible tubes were developed in the presence of gravitational force (Gforce). The Lax-Wendroff and MacCormack methods were used to solve the governing equations and compared both in terms of accuracy, convergence, and computer processing (CPU) time. A modified vasculature of the whole body and the cerebral circulation was developed to obtain a realistic simulation of blood flow under different conditions. The whole body vasculature was used to validate the simulation in terms of input impedance and wave transmission. The cerebral vasculature was used to simulate conditions such as presence of G-force, blockage of Internal Carotid Artery (ICA), and the effects on cerebral blood flow of changes in mean and pulse pressure. Results. The simulation results for zero G-force were in very good agreement with published experimental data as was the simulation of cerebral blood flow. Both numerical methods for solutions of governing equations gave similar results for blood flow simulations but differed in calculation performance and stability depending on levels of G-force. Simulation results for uniform and sinusoidal G-force are also in good agreement with published experimental results, Blood flow was simulated in the presence of a single (left) carotid artery obstruction with varying morphological structures of the Circle of Willis (CoW). This simulation showed significant differences in contralateral blood flow in the presence or absence of communicating arteries in the CoW. It also was able to simulate the decreases in blood flow in the cerebral circulation compartment corresponding to the visual cortex in the presence of G-force. This is consistent with the known loss of vision under increased acceleration. Conclusions. This study has shown that under conditions of gravitational forces physiological changes in blood flow in the systemic and cerebral vasculature can be simulated realistically by solving the one-dimentional fluid flow equations and non-linear vascular properties numerically. The simulation was able to predict changes in blood flow with different configurations and properties of the vascular network.
4
Rahimian, Abtin. "Parallel algorithms for direct blood flow simulations". Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43611.
Testo completoAbstract (sommario):
Fluid mechanics of blood can be well approximated by a mixture model of a Newtonian fluid and deformable particles representing the red blood cells. Experimental and theoretical evidence suggests that the deformation and rheology of red blood cells is similar to that of phospholipid vesicles. Vesicles and red blood cells are both area preserving closed membranes that resist bending. Beyond red blood cells, vesicles can be used to investigate the behavior of cell membranes, intracellular organelles, and viral particles. Given the importance of vesicle flows, in this thesis we focus in efficient numerical methods for such problems: we present computationally scalable algorithms for the simulation of dilute suspension of deformable vesicles in two and three dimensions. Our method is based on the boundary integral formulation of Stokes flow. We present new schemes for simulating the three-dimensional hydrodynamic interactions of large number of vesicles with viscosity contrast. The algorithms incorporate a stable time-stepping scheme, high-order spatiotemporal discretizations, spectral preconditioners, and a reparametrization scheme capable of resolving extreme mesh distortions in dynamic simulations. The associated linear systems are solved in optimal time using spectral preconditioners. The highlights of our numerical scheme are that (i) the physics of vesicles is faithfully represented by using nonlinear solid mechanics to capture the deformations of each cell, (ii) the long-range, N-body, hydrodynamic interactions between vesicles are accurately resolved using the fast multipole method (FMM), and (iii) our time stepping scheme is unconditionally stable for the flow of single and multiple vesicles with viscosity contrast and its computational cost-per-simulation-unit-time is comparable to or less than that of an explicit scheme. We report scaling of our algorithms to simulations with millions of vesicles on thousands of computational cores.
5
Al-Saad, Mohammed. "Blood flow simulation using smooth particle hydrodynamics". Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/105588/.
Testo completoAbstract (sommario):
Blood flow rheology is a complex phenomenon, and the study of blood flow in the human body system under normal and pathological conditions are considered to be of great importance in biomedical engineering. Consequently, it is important to identify the key parameters that influence the flow behaviour of blood. The characterisation of blood flow will also enable us to understand the flow parameters associated with physiological conditions such as atherosclerosis. Thrombosis plays a crucial role in stopping bleeding when a blood vessel is injured. Developing tools that can successfully study the influences of hemodynamics on thrombus formation in arteries and vessels are considered to be essential. This thesis describes the steps taken to develop computational tools that focus on using the meshless particle-based Lagrangian numerical technique, which is named the smoothed particle hydrodynamic (SPH) method, to study the flow behaviour of blood and to explore flow condition that induces the formation of thrombus in blood vessels. A weakly-compressible SPH method is used here to simulate blood flow inside vessels. The basic governing equations solved in the SPH are the mass and momentum conservation equations. Due its simplicity and effectiveness, the SPH method is employed here to simulate the process of thrombogenesis under the influence of various blood flow parameters. In the present SPH simulation, blood is modelled by particles that have the characteristics of plasma and platelets. To simulate a 3-dimensional coagulation of platelets which form a thrombus, the adhesion and aggregation process of platelets are modelled by an effective inter-particle force model. With these models, platelet motion in the flowing blood and platelet adhesion and aggregation are effectively coupled with viscous blood flow. In this study, the adhesion and aggregation of blood particles are performed inside vessels with various geometries and with different flow velocity scenarios. The capabilities of this strategy were evaluated by comparing the simulation results with existing numerical and experimental results. All of these cases realistically model the formation of thrombus including thrombus collapse and partial separation. This thesis is considered to be the first work that is dedicated to the SPH simulation of thrombus formation inside blood vessels with various geometries and under different flow conditions.
6
Ottosson, Johan. "Analyzing arterial blood flow by simulation of bifurcation trees". Thesis, Linköpings universitet, Matematik och tillämpad matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-154946.
Testo completoAbstract (sommario):
The flow of blood in the human body is a very important component in un-derstanding a number of different ailments such as atherosclerosis and a falseaneurysm. In this thesis, we have utilized Poiseuille’s solution to Navier-Stokesequations with a Newtonian, incompressible fluid flowing laminar with zero ac-celeration in a pipe with non-flexible walls in order to study blood flow in anarterial tree. In order to study and simulate a larger arterial tree we have uti-lized a primitive building block, a bifurcation with one inlet and two outlets,joined together forming a tree. By prescribing an inlet flow and the pressureat every outlet at the bottom of the tree we have shown that we may solvethe system by fixed-point iteration, the Matlab functionfsolve, and Newton’smethod. This way of using primitive building blocks offers a flexible way to doanalysis as it makes it possible to easily change the shape of the tree as well asadding new building blocks such as a block that represents arteriosclerosis.
7
Wishah, Mahmoud I. "Simulation of blood flow through stenotic and branched arteries". Thesis, University of Salford, 2007. http://usir.salford.ac.uk/26966/.
Testo completoAbstract (sommario):
Mathematical and physical models have been developed in order to study blood flow through arteries, numerically and experimentally. The aim of these models was to understand, apply and verify using realistic models how both flow and geometry interact through and downstream of stenosed and branched arteries. This interaction is examined in two ways; initially by investigating the influence of stenosis and branches on flow and then by examining the influence of flow haemodynamics parameters such as Reynolds number, stenosis severity, stenosis shape and bifurcation area ratio on the development of stenosis. In addition, a parametric study was performed to determine the actual influence of the geometry on flow and vice versa. The ability to describe the flow through a stenosed artery provides the possibility of developing imaging enhancement that gives medical staff the ability to diagnose the disease with high accuracy in its early stages and the opportunity of treatment before atherosclerosis becomes severe and dangerous. At the end we conclude that, sites of high wall shear stress just upstream of the stenosis throat, were factors in the process of the development of stenosis through platelet activation, as well as in the rupture of the stenosis cap triggering the process of thrombosis. Low shear stress plays a significant role in initiating the disease in the region of flow stagnation where flow cannot follow the geometry of arteries. The results presented, favour and support the theory of low wall shear stress and its important role in the initiation of atherosclerosis, and the high shear stress theory in the development of the disease. CFD in conjunction with flow visualisation and MRI can be used in the early prediction of artery stenosis and gives more accurate and reliable estimates of the stenosis severity.
8
Shojai, Leila. "Modelling of blood flow through heart valves and simulation of particle transport in blood". Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/34645.
Testo completoAbstract (sommario):
Computer modelling provides powerful and flexible methodology for the predictive simulation of complex flow systems. However, despite the versatility of this methodology quantitative modelling of blood flow through human heart presents a difficult and challenging problem. Although derivation of appropriate governing equations representing combined blood flow and soft solid deformation of the tissues of heart valves does not pose any particular theoretical problems. Accurate solution of such equations is not a trivial matter. Another source of complexity in the modelling of a biological system such as blood flow/heart valve deformation is the uncertainties associated with the available physical and rheological data that are required to obtain quantitative simulations. Variations between individual situations is usually considerable which precludes broad generalizations. In this research project an attempt has been made to identify the most important aspects of the blood flow through human heart valves. This has led to making rational approximations which render the development of a model for the described system both possible and meaningful. The main focus have been on the best use of available software and mathematical schemes. In cases where existing computational or mathematical tools were considered to be incapable of tackling realistic situations new techniques have been developed. It has been shown that using the modelling methodology which is developed in this research study a number of important and reliable conclusions about the operation of heart valves can be drawn. This information can in turn be used to design artificial heart valves.
9
Dave, Parth Pranavbhai. "Numerical simulation of blood flow in arterial stenosis under steady and pulsatile flow conditions". Thesis, Wichita State University, 2011. http://hdl.handle.net/10057/3949.
Testo completoAbstract (sommario):
Cardiovascular diseases (CVDs) are among the leading causes of death in the world. In
this study, an attempt was made to model the flow dynamics of blood in abnormally narrowed
artery. Finite volume solver FLUENT was used for the analysis with the aim of understanding
the consequences of increasing the degree of stenosis using a two-equation turbulence model.
The compliant nature of the artery was neglected, and Newtonian behavior of the blood flow was
assumed for the larger arteries. Steady-flow simulations with 75% area reductions were used to
establish the validity of the current models by employing the standard and transitional variant of
the k turbulence models. Subsequently, it was found that transitional k model was
suitable for the low Reynolds number internal flows associated with the transition to turbulence,
although only a minor departure in terms of the turbulence intensity peak was observed.
Unsteady blood flow was introduced by employing a sinusoidal pulsatile waveform at the
inlet. The pulsatile nature of the blood flow was investigated in the range of the constriction ratio
from 60% to 90%, with an inlet-specified pulse. It was hypothesized that the severity of the
stenosis played a major role in the initiation of the turbulence, since no major turbulence was
reported for the 60% and 75% area reductions, while increasing the constriction ratio of 90%
significantly altered the flow dynamics and triggered the transition to turbulence much earlier
than anticipated. The outcome of current numerical efforts was expressed in terms of wall shear
stress, a hemodynamically relevant parameter.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.
10
Healy, Timothy M. "Multi-block and overset-block domain decomposition techniques for cardiovascular flow simulation". Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/15622.
Testo completo
11
Gillespie, Jennifer L. "Modelling and computer simulation of patient flow". Thesis, Ulster University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.646847.
Testo completoAbstract (sommario):
The population of the United Kingdom is increasingly ageing and diseases, like cancer and stroke, are becoming more common in our society. This is having a detrimental affect on the performance of the National Health Service. Various schemes and services have been introduced to increase efficiency, and key performance indicators help to identify areas of best practice. By realistically modelling healthcare facilities with analytic and simulation models, based on queueing theory, we can provide detailed information to healthcare managers and clinicians. These models can help to identify issues and cost inefficiencies for early intervention. Analytic models are less data and computationally intensive, and provide results in a quick time frame compared to simulation models. However, they tend to be mathematically complex which means healthcare managers can find them difficult to understand, and are more reluctant to implement the solutions. Simulations are more data and computationally intensive compared to analytic models, but they are much easier to explain to healthcare managers when they are built in a user friendly environment. This means that managers tend to be more willing to introduce the results of the model into their department. Therefore, we use both analytic and simulation models in this work to utilise the benefits of both techniques. In this body of work a novel analytic cost model has been presented for a system which can be regarded as a network of M/M/∞ queues. The model considers the flow of patients through primary and secondary care, and is based on a mixture of Coxian phase-type models with multiple absorbing states. Costs are attached to each state of the model allowing the average cost per patient in the system to be calculated. We also provide a model which assesses whether the implementation of a new intervention is cost-effective. The model calculates the maximum cost the intervention can incur before the benefits no longer outweigh the cost of administering it. These analytic models have been applied to stroke patients deemed eligible for thrombolysis in order to assess the cost-effectiveness of thrombolytic therapy. We also present a novel simulation model for stroke patients, who are eligible for thrombolysis, in order to validate our analytic models. 'What-If' scenarios and Probabilistic Sensitivity Analysis have also been carried out to provide healthcare managers with more confidence in our models. An analytic model has been presented for a complex system of M / M / c queues in steady state. The model analyses the system to find bottlenecks and assesses whether the staff are being efficiently utilised. Two resource allocation models have then been defined: the first determines the minimum number of resources required within the department, and the second efficiently distributes the resources throughout the department. These resource allocation models have been applied to orthopaedic Integrated Clinical Assessment and Treatment Service (ICATS) data to reduce the current queues within the department. A novel simulation model has also been created for orthopaedic ICATS which includes extra variation and realistic features. This allows us to assess how robust and reliable our analytic models are, as the results are applied to our simulation model which has different assumptions. The novel analytic models provide very similar results to the simulation models built for each healthcare environment. This implies that our analytic models are robust and reliable even when applied to a department which includes different assumptions. Therefore, our analytic models will provide reliable results when healthcare managers need to make decisions in a short time frame. Simulation models have been found to be a good validation technique for analytic models, as healthcare managers understand them better. Extra components can also be easily included within a simulation model, such as complex distributions to represent the inter-arrival and service rate, and realistic features such as shift patterns.
12
Batten, Paul. "Compressible flow simulation on a parallel computer". Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358770.
Testo completo
13
Wendling, Fabrice. "Simulation of doppler ultrasound signals for a laminar, pulsatile, nonuniform flow". Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/16875.
Testo completo
14
Zhou, You. "Fast Algorithm for Simulation of Signals in Medical Ultrasound Blood Flow Imaging". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19522.
Testo completoAbstract (sommario):
The commonly used simulation method Field II, which is based on the spatial impulse response approach, has excellent accuracy in linear domain. However the computational time can be up to many days for one simulation. One of the solutions to this problem is a convolution-based methodology called COLE. It is much faster than Field II and has very good approximation. It generates the data by reducing multi-dimensional convolution model to multiple single-dimensional convolutions. This thesis is about implementing COLE on the FieldSim 3 platform and using it for blood flow imaging. This platform is written in MATLAB with object-oriented programming and it is now under development at department of circulation and medical imaging. Both Field II and real scanner have been used to compare with COLE. The simulated phantom for both simulators was a straight tube with scatterers moving inside, whereas a string phantom was used to get the data from the scanner. The computational time of COLE with 2D Doppler mode scan in FieldSim 3 achieved 85 times faster than Field II. The plotted PW Doppler spectra and the 2D power spectra showed that the velocity resolutions of both simulators were at the same level. COLE had higher noise floor than Field II and scanner in Doppler mode scan. COLE had relatively high sampling frequency requirement compared with Field II. If the sampling frequency was not high enough, COLE would produce side lobes in the PW Doppler spectra.
15
Natarajan, Sukin. "Dynamic simulation of blood flow close to vessel walls and implanted structures". Thesis, Brunel University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311659.
Testo completo
16
Hye, Md Abdul. "Simulation of transient blood flow in models of arterial stenosis and aneurysm". Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3836/.
Testo completoAbstract (sommario):
The Large Eddy Simulation (LES) technique with the Smagorinsky-Lilly dynamic subgrid model and two-equation Standard k-ω Transitional turbulence model are applied to investigate non-spiral and spiral blood flow through three dimensional models of arterial stenosis and aneurysm. A spiral pattern of blood flow is thought to have many beneficial effects on hemodynamics. Previous computational studies on spiral blood flow involve only steady spiral flow in a straight stenosed pipe without considering an upstream curved section of the artery. But a spiral pattern in the blood flow may exist due to the presence of an upstream curved section in the artery. On the other hand, pressure is generally considered a constant quantity in studies on pulsatile flow through either arterial stenosis or aneurysm; however, blood pressure is a waveform in a physiological flow. Although cosine-type or smooth regular stenoses are generally taken in investigations of blood flow in a three-dimensional model of arterial stenosis, in reality, stenoses are of irregular shape. Besides stenosis and aneurysm, another abnormal condition of the artery is the presence of stenosis with an adjacent aneurysm in the same arterial segment, especially in the posterior circulation. A study on (steady or pulsatile) flow through such arterial stenosis with an adjacent aneurysm in the same arterial segment is not available so far. Therefore, taking above things into consideration, thorough investigations of steady and unsteady pulsatile non-spiral and spiral blood flow in three-dimensional models of stenosis and aneurysm are needed to give a sound understanding of the transition-to-turbulence of blood flow due to stenosis and aneurysm and to study the the effects of spiral velocity on the transition-to-turbulence. The LES technique has mostly been used to investigate turbulent flow in engineering fields other than bio-fluid mechanics. In the last decade, LES has seen its excellent potential for studying the transition-to-turbulence of physiological flow in bio-fluid mechanics. Though the k-ω Transitional model is used in few instances, mainly LES is applied in this study. Firstly, investigations of steady non-spiral and spiral blood flow through threedimensionalmodels of cosine-type regular stenosed tube without and with upstream curved segment of varying angles of curvature are performed by using the k-ω Transitional model and LES. A fully developed Poiseuille velocity profile for blood is introduced at the inlets of the models. To introduce a spiral effect at the inlet, onesixth of the bulk velocity is taken as the tangential velocity at the inlet along with the axial velocity profile there. Secondly, physiological pulsatile non-spiral and spiral blood flow through a three-dimensional model of a straight tube having cosine-type regular stenosis are investigated by using mainly LES. A two-equation k-ω Transitional model is also used in one non-spiral flow case. The first four harmonics of the Fourier series of pressure pulse are used to generate physiological velocity profiles at the inlet. At the outlet, a pressure waveform is introduced. The effects of percentage of area reduction in the stenosis, length of the stenosis, amplitude of pulsation and Womersley number are also examined. Thirdly, transient pulsatile non-spiral and spiral blood flow through a threedimensional model of irregular stenosis are investigated by applying LES and comparison is drawn between non-spiral flow through a regular stenosis and that through an irregular stenosis. Lastly, pulsatile non-spiral and spiral blood flow through a three-dimensional model of irregular stenosis with an adjacent post-stenotic irregular aneurysm in the same arterial segment are studied by applying LES and the k-ω Transitional model. The effects of variation in spiral velocity are also examined. The results presented in this thesis are analysed with relevant pathophysioloical consequences. In steady flow through the straight stenosed tube, excellent agreement between LES results for Re = 1000 and 2000 and the corresponding experimental results are found when the appropriate inlet perturbations are introduced. In the models with an upstream curved segment, no significant effect of spiral flow on any flow property is found for the investigated Reynolds numbers; spiral pattern disappears before the stenosis – which may be due the rigid wall used in the models and/or a steady flow at the inlet. The effects of the curved upstream model can be seen mainly in the maximum turbulent kinetic energy (TKE), the maximum pressure drop and the maximum wall shear stress (WSS), which in the curved upstream models generally increase significantly compared with the corresponding results in the straight stenosed tube. The maximumcontributions of the SGS motion to the large-scale motion in both non-spiral and spiral flow through a regular stenosis, an irregular stenosis and an irregular stenosis with an adjacent post-stenotic irregular aneurysm are 50%, 55%and 25%, respectively, for the highest Reynolds number investigated in each model. Although the wall pressure and shear stress obtained from the k-ω Transitional model agree quite well with the corresponding LES results, the turbulent results obtained from the k-ω Transitional model differ significantly from the corresponding LES results – this shows unsuitability of the k-ω model for pulsatile flow simulation. Large permanent recirculation regions are observed right after the stenosis throat in both non-spiral and spiral flow, which in the model of a stenosis with an adjacent post-stenotic aneurysm are stretched beyond the aneurysm and the length of the recirculation regions increases with spiral velocity. This study shows that, in both steady and unsteady pulsatile flow through the straight tube model having either a stenosis (regular or irregular) or an irregular stenosis with an adjacent post-stenotic irregular aneurysm, the TKE rises significantly at some locations and phases if a spiral effect is introduced at the inlet of the model. However, the maximum value of the TKE in a high spiral flow drops considerably compared with that in a low spiral flow. The maximum wall pressure drop and shear stress occur around the stenosis throat during all the phases of the pulsatile cycle. In the model of a stenosis only, the wall pressure rises in the immediate post-stenotic region after its drop at the stenosis throat. However, in the model of a stenosis with an adjacent aneurysm, the wall pressure does not rise to regain its undisturbed value before the start of the last quarter of the aneurysm. The effects of the spiral flow on the wall pressure and WSS are visible only in the downstream region where they take oscillatory pattern. The break frequencies of energy spectra for velocity and pressure fluctuations from −5/3 power slope to −10/3 power slope and −7/3 power slope, respectively, are observed in the downstream transition-to-turbulence region in both the non-spiral and spiral flow. At some locations in the transition region, the velocity spectra in the spiral flow has larger inertial subrange region than that in non-spiral flow. The effects of the spiral flow on the pressure spectra is insignificant. Also, the maximum wall pressure drop, the maximum WSS and the maximum TKE in the non-spiral flow through the irregular stenosis rise significantly compared with the corresponding results in the non-spiral flow through the regular stenosis. When the area reduction in the stenosis is increased, the maximum pressure drop, the maximumWSS and the TKE rise sharply. As for the effects of the length of the stenosis, the maximum WSS falls significantly and the maximum TKE rises sharply due to the increase in the length of the stenosis; but the maximum pressure drop is almost unaffected by the increase in the stenosis length.
17
Shieh, Bernard D. "Quantitative simulation of backscatter from tissue and blood flow for ultrasonic transducers". Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53843.
Testo completoAbstract (sommario):
Ultrasound imaging is a ubiquitous part of the modern medical diagnostics toolbox. It has widespread applications to many areas of medicine, including angiology, cardiology, nephrology, urology, and obstetrics. It is often preferred over other imaging modalities, such as x-ray computed tomography (CAT) and magnetic resonance imaging (MRI) because it is non-invasive, non-ionizing, inexpensive, and has excellent penetration depth in the body.
The design, optimization, and manufacturing of ultrasound transducers used in ultrasound imaging is a challenging engineering problem. Faced with a variety of different imaging environments, ultrasound transducers must often be optimized for performance in very specific applications. This is especially true for catheter-based solutions, such as intracardiac and intravascular ultrasound, where imaging performance is strongly dependent on the strength of backscatter from tissue due to significant limitations in device size, electronics, and signal-to-noise ratio. Currently, there is a need for the accurate and fast simulation of the imaging process used in ultrasound imaging, including the ability to capture the effects of backscatter from a variety of different tissues.
This thesis discusses the development of simulation tools for the quantitative simulation of tissue backscatter and blood motion from acoustic fields coupled to spatial array transducers, based on an application of the Rayleigh speckle model to the linear systems model for acoustic diffraction from spatial array transducers. These simulation tools have potential applications in the field of medical ultrasonics, with particular attention to the areas of transducer design and optimization, beamforming and array processing, and image reconstruction. We demonstrate how the simulation tools developed here can be used to characterize array imaging performance and to investigate reconstruction performance of common flow algorithms for Doppler ultrasound imaging.
18
Li, Mingxiu. "Numerical simulation of blood flow and vessel wall stresses in stenosed arteries". Thesis, University of Edinburgh, 2006. http://hdl.handle.net/1842/12415.
Testo completoAbstract (sommario):
A flow-wall coupled model is developed by externally coupling of the CFD (Computational Fluid Dynamics) package FLUENT and the FEM (Finite Element Method) package ABAQUS using a MATLAB script. This model is used to study the flow and stress field for idealised stenosed arteries. The impedance of the stenosis is estimated by an LCR model and the boundary conditions are derived from a 1D transmission line model. Studies on localized stiffness for straight and mild stenosed arteries showed that the localized stiffness has a negligible effect on the pressure, local velocity magnitude and was wall shear stress (WSS) field, but it has a significant effect on the wall motion around the diseased part. Simulations of the blood flow and wall motion (WM) for different degrees of stenosis under physiologically realistic conditions was carried out. The results showed that maximum WSS increases substantially with the increase of stenosis severity. The maximum WSS is about 10Pa for healthy arteries, it reaches 45pa for a 30% stenosis (by diameter), at which endothelial stripping may occur, and for >=50% stenoses, the maximum WSS values were greater than 100Pa. Wall motion was increasingly constrained as the degree of stenosis increased. It was constrained at the throat by 55% for the 30% stenosis, 86% for the 50% stenosis; while for the 70% stenosis, WM at the throat is negligible through the whole cycle. With the increase of the degrees of stenosis, the maximum circumferential stress varies within 20%, which is a small variation compare with the changes in WSS as the degree of stenosis increases. However, the localized stiffness and physiological axial stretch has substantial influence on the circumferential stress distributions. Maximum circumferential stress was found at the shoulders of plaques with the presence of localized stiffness and physiological axial stretch.
19
Solomon, Luiza. "Learning and flow control in optimistic simulation". Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29475.
Testo completoAbstract (sommario):
This thesis has two main contributions. The first contribution is the development of a modular, easy-to-use Time Warp simulation engine targeted towards distributed-memory environments. The second contribution is the analysis and experimental verification of the performance of the flow control algorithm proposed by Choe in a distributed-memory environment.The Time Warp simulation engine TWSIM provides our laboratory with a research medium for Time Warp simulations in a distributed-memory environment such as a network of workstations. The modular design of TWSIM allows for easy integration of any new simulation application and for fast testing of optimizations and improvements to the Time Warp mechanism. Its compact size and object-oriented implementation using the C++ programming language result in a short learning curve for future users and developers.
The flow control algorithm proposed by Choe was implemented and analyzed with the aid of the TWSIM simulation engine. The algorithm makes use of stochastic learning automata to balance simulations loads by continuously regulating the flow of events between processors during the course of the simulation. Three different load metrics are considered: memory usage, virtual time, and a space-time product of the first two metrics. The algorithm was tested with two different simulation applications: a queuing network simulation and a Personal Communication Services (PCS) simulation. Results show that the flow control algorithm reduces the memory usage; the number of rollbacks and the number of antievents at the expense of the simulation time. As well, it becomes apparent that the behaviour of the flow control algorithm is not a consequence of learning.
Finally, we discuss a number of approaches to learning and flow control using the outlines of the flow control algorithm, and we consider the extent of the performance improvement to be expected from memory-based schemes for limiting Time Warp optimism in a distributed-memory environment.
20
Brown, David Joseph. "Computer simulation of discrete particle flow through hoppers". Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317014.
Testo completo
21
Hill, David Paul. "The computer simulation of dispersed two-phase flow". Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/8733.
Testo completo
22
Zhao, Amy (Xiaoyu Amy). "Applying video magnification techniques to the visualization of blood flow". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99799.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 85-94).
In this thesis, we investigate the use of video magnification for the visualization and assessment of blood flow. We address the challenge of low signal-to-noise ratios in video magnification by modeling the problem and developing an algorithm for measuring the SNR in the context of video magnification. We demonstrate that the algorithm can be used to estimate the SNR of a real video and predict the SNR in the magnified video. We use several techniques based on video magnification to visualize the blood flow in a healthy hand and a hand with an occluded artery, and show that these visualizations highlight differences between the hands that might be indicative of important physiological differences.
by Amy (Xiaoyu) Zhao.
S.M.
23
Su, Shen-Wei. "Modelling blood flow and oxygen transport in the human cerebral cortex". Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:cee70abb-8c36-4244-920c-71305cf97bd0.
Testo completoAbstract (sommario):
Dementia, a stepwise deterioration of cognitive function, affects over 700,000 people in the UK, resulting in over 60,000 deaths and a cost of over £1.7 billion each year. It is believed to have a combination of vascular and degenerative origins and to have correlations with localised lesions, or infarctions, in the brains of affected patients. Mini-strokes are one of the causes for this disease as the presence of ischemia is highly related to the risk factors for dysfunction of the neurovascular unit. The underlying interacting mechanisms are, however, often very complex and they remain largely poorly understood. The cerebral microvascular bed is highly irregular and localised variations in its structure are large. To capture these variations, statistical algorithms are required, rather than large volumes of expensive experimental data. Therefore, accurate modelling of blood flow and oxygen transport at the microvascular level is important in improving our understanding of the structure and function of the cerebral vasculature and hence of brain diseases. A novel algorithm is proposed here to create artificial microvascular networks that match quantitatively experimental data previously obtained in human brain tissue. Blood flow and oxygen transport in the network and the tissue are analysed through both discretised and continuum transport models. By disabling flow sources, ischemic events can be simulated. Using multiple networks, the influence of individual network structures on the response to ischemia is analysed. The relationship between the discretised and continuum formulations of the model is quantified, providing a means for scaling up the model over multi length scales. Finally, the phenomenon of microvessel collapse under ischemic conditions is examined and it is shown that this is fundamentally dependent upon the variability found at the network level, since it cannot be modelled by a continuum model. An initial infarction is also found to facilitate the occurrence of collapse events for most networks.
24
Nejadmalayeri, Alireza. "Numerical simulation of pulsatile blood flow across a tilting–disk mechanical heart valve". Thesis, Wichita State University, 2007. http://hdl.handle.net/10057/1526.
Testo completoAbstract (sommario):
To overcome several clinical challenges involving mechanical heart valves, accurate numerical simulation of blood flow through these devices has been of interest. Since heart disease is the leading cause of death around the world, the hemodynamic study of the heart is of extraordinary interest in the field of bio fluid dynamics. Recent numerical/experimental investigations have shown that mechanical heart valves inherit the “production of sufficiently large shear and turbulent stresses to cause clinical problems such as hemolysis.” Due to several parameters including the non-Newtonian behavior of blood, pulsatile waveform, strong blood and tissue interactions, clinical difficulties, etc., experimental examination of blood flow in the heart and its valves is a very difficult task. Therefore, comprehensive numerical analysis of this complex fluid-structure system is essential. However, precise experimental investigations are still imperative for developing appropriate and accurate turbulence models and for validating numerical techniques.In the current computational effort, the first set of objectives was numerical investigations of vortex shedding behind a two-dimensional tilting-disk mechanical heart valve in a straight channel, which is a simplified representation of the mitral position, using first- and several higher-order finite volume schemes as well as examination of the non-Newtonian viscosity effects on shedding frequency and amplitude. For the low Reynolds number (low inflow), both first- and higher-order schemes resulted in identical shedding frequencies; however, higher-order schemes improved the shedding amplitude. For pulsatile inflow, the first-order scheme was found to be in better qualitative and quantitative agreement with previous investigations. Careful scrutiny of the findings revealed that higher-order schemes implemented in the code produced too much dispersion error for applications in the present study. In addition, non-Newtonian viscosity did not affect the overall flow structure, although it caused significant shear-thinning for both types of inflow. Furthermore, numerical simulations of laminar Newtonian and non-Newtonian blood flow across 2D and 3D models of a Björk-Shiley tilting-disk mechanical heart valve in the aortic position with sinuses of valsalva (valve replacements are more common in the aortic position) under steady and physiological pulsatile inflows were performed to investigate the three dimensional effects as well as the influences of pulsatile waveform and non-Newtonian nature of blood on the overall flow structure. The results of grid and time-step independency tests as well as validation with previous investigations were satisfactory. Obvious differences of various flow parameters between 2D and 3D analyses clarified noticeable breakup of symmetry by the third dimension. Similar to the 2D case in a straight channel, it was observed that the non-Newtonian viscosity did not affect significantly the maximal velocity components and maximal vorticity magnitude, although it caused substantial shear-thinning and altered the overall flow structure, particularly during the regurgitation phase. It was found that three-dimensional effects were much smaller for the non-Newtonian viscosity model than the Newtonian model at all time levels. Indeed, the non-Newtonian behavior resulted in a “less complex vortical flow” and consequently “less probability of blood cell damage” compared to the Newtonian fluid. Since the longer the blood cells are trapped in the vortices, the more chance of hemodynamic damage, it is essential to consider the non-Newtonian behavior of blood in the analysis.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering
"July 2007."
25
Chan, Weng Yew, e chanwengyew@gmail com. "Simulation of arterial stenosis incorporating fluid-structural interaction and non-Newtonian blood flow". RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20070108.164458.
Testo completoAbstract (sommario):
The aim of this study is to investigate the fluid-structural response to pulsatile Newtonian and non-Newtonian blood flow through an axisymmetric stenosed vessel using FLOTRAN and ANSYS. This is to provide a basic understanding of atherosclerosis. The flow was set to be laminar and follows a sinusoidal waveform. The solid model was set to have isotropic elastic properties. The Fluid-Structural Interaction (FSI) coupling was two-way and iterative. Rigid and Newtonian cases were investigated to provide an understanding on the effects of incorporating FSI into the model. The wall expansion was found to decrease the axial velocity and increase the recirculation effects of the flow. To validate the models and methods used, the results were compared with the study by Lee and Xu [2002] and Ohja et al [1989]. Close comparisons were achieved, suggesting the models used were valid. Two non-Newtonian models were investigated with FSI: Carreau and Power Law models. The Carreau model fluid behaviour was very close to the Newtonian model. The Power Law model produced significant difference in viscosity, velocity and wall shear stress distributions. Pressure distribution for all models was similar. In order to quantify the changes, Importance Factor (IG) was introduced to determine the overall non-Newtonian effects at two regions: the entire flow model and about the vessel wall. The Carreau model showed reasonable values of IG whereas the Power Law model showed excessive values. Transient and geometrical effects were found to affect the Importance Factor. The stress distributions for all models were found to be similar. Highest stress occurred at the shoulders of the stenosis where a stress concentration occurred due to sharp corners of the geometry and large bending moments. The highest stresses were in the axial direction. Notable circumferential stress was found at the ends of the vessel. Carreau model produced slightly higher stresses than the other models. Wall stresses were found to be primarily influenced by internal pressure, rather than wall shear stresses.
26
Nejadmalayeri, Alireza Hoffmann Klaus A. "Numerical simulation of pulsatile blood flow across a tilting-disk mechanical heart valve /". Thesis, A link to full text of this thesis in SOAR, 2007. http://hdl.handle.net/10057/1526.
Testo completo
27
Bastos, Carlos Alberto da Costa. "A model for the simulation of Doppler ultrasound signal from pulsatic blood flow". Doctoral thesis, Universidade de Aveiro, 1999. http://hdl.handle.net/10773/4363.
Testo completoAbstract (sommario):
Doutoramento em Engenharia ElectrotécnicaO detector ultra-sónico de fluxo sanguíneo usa o efeito Doppler para estimar de forma não invasiva a velocidade do sangue na circulação. Tem sido bastante usado nas ultimas quatro décadas para detectar a presença de estenoses. O desenvolvimento de novas técnicas de processamento do sinal Doppler necessita de sinais de teste cujas características sejam conhecidas ou possam ser medidas com precisão. Isto é difícil de obter com sinais Doppler medidos in vivo devido à elevada variação do fluxo sanguíneo de pessoa para pessoa e também com o estado fisiológico da pessoa no momento da medida, por exemplo a tensão arterial influencia significativamente o fluxo sanguíneo. Um modelo para gerar sinais Doppler simulados cujas características sejam controláveis e/ou mensuráveis é uma ferramenta bastante útil, pois permite que as novas técnicas de processamento do sinal Doppler sejam testadas em condições controladas. Permite, também, estudar o efeito de viários factores que afectam o espectro do sinal Doppler. Habitualmente o efeito individual dos viários factores não pode ser identificado quando são usados sinais medidos in vivo. Neste trabalho foi desenvolvido um modelo para gerar sinais Doppler ultra-sónicos simulados. O modelo contêm dois sub-modelos, um para o fluxo sanguíneo nos membros inferiores de um ser humano e outro para gerar os sinais simulados a partir do campo de velocidades do sangue e das características do instrumento. O fluxo sanguíneo nos membros inferiores foi simulado com um análogo eléctrico para a rede vascular dos membros inferiores. Cada artéria foi simulada por uma linha de transmissão com perdas e as redes vasculares periféricas por um circuito Windkessel com três elementos. O circuito eléctrico foi implementado com o simulador de circuitos SPICE. Para simular a interacção entre os glóbulos vermelhos e o campo de ultra-sons o vaso sanguíneo foi dividido em pequenos volumes elementares. As contribuições dos volumes elementares foram todas somadas para gerar o sinal Doppler simulado. O modelo fez algumas aproximações como sejam, por exemplo, considerar o fluxo sanguíneo laminar e sem rotação. As características dos sinais gerados pelo modelo são bastante parecidas com as esperadas para o sinal Doppler real. O modelo desenvolvido foi usado para estudar a influencia que a aceleração sanguínea, o tamanho do volume de amostragem e a duração da janela de amostragem têm na largura de banda eficaz do espectro do sinal Doppler. Foi deduzida uma formula que estima a largura de banda eficaz a partir das contribuições individuais do alargamento espectral devido à não estacionaridade, do alargamento espectral intrínseco, do alargamento espectral devido à duração da janela de amostragem e ainda da gama das velocidades que passam pelo volume de amostragem. Foram, ainda, deduzidas expressões em forma fechada para o espectro de potência do sinal Doppler devido unicamente à gama de velocidades que atravessam um volume de amostragem com forma Gaussiana colocado num perfil de velocidades com forma exponencial. Foram, também, obtidas expressões para a largura de banda eficaz no caso especial do volume de amostragem Gaussiano ter simetria esférica e estar colocado no centro do vaso sanguíneo.
The Doppler ultrasonic blood ow detector estimates non-invasively the velocity of blood in the circulatory system. It has been extensively used in the last four decades for the detection of stenoses in the circulation. The development of new signal processing techniques for the Doppler signal requires test signals with known or measurable characteristics. This is very di cult to achieve with Doppler signals obtained in vivo because of the variability of blood ow between persons and with physiological state, for example blood pressure. A model for generating simulated Doppler signals whose characteristics are controllable and/or measurable is a useful tool because it permits the test of new processing techniques under controlled conditions. It permits also the study of the e ect of various factors on the Doppler spectrum. Usually these e ects cannot be isolated with in vivo measurements. During this work a model for the generation of simulated Doppler ultrasound signals was developed. It comprised two sub-models one for blood ow in the human lower limb and the other for generating simulated signals from the blood velocity eld and the instrument's characteristics. Blood ow in the lower limb was modelled by an electric analogue for the lower limb vascular tree. Each artery was modelled by a lossy transmission line and the peripheral vascular beds by three{element Windkessel models. The electric analogue circuit was implemented with the SPICE circuit simulator. To simulate the inter-action of the blood cells with the ultrasonic eld the vessel was divided into small elemental volumes whose contributions were added together to generate the simulated Doppler signal. The model assumed irrotational laminar ow and some other simplifying approximations. The characteristics of the signals generated by the model were similar to those expected for the Doppler signal. The model was used to study the in- uence of blood acceleration, sample volume size and data segment duration on the root mean square (rms) width of the Doppler spectrum. A simple formula was derived for estimating the Doppler rms spectral width from the individual contribution of non-stationarity broadening, intrinsic broadening, window broadening and the range of blood velocities passing through the sample volume. In addition closed form expressions were derived for the Doppler power spectrum due solely to the range of blood velocities passing through a Gaussian sample volumes placed in irrotational laminar ow with a velocity pro le obeying a simple power law. Closed form expressions were also obtained for the root mean square spectral width in the special case of a spherically symmetric Gaussian sample volume placed in the centre of the vessel.
28
Bastos, Carlos Alberto da Costa. "A model for the simulation of Doppler ultrasound signals from pulsatile blood flow". Phd thesis, Instituições portuguesas -- -Universidade de Aveiro -- -Departamento de Electrónica e Telecomunicações, 1999. http://dited.bn.pt:80/6564.
Testo completoAbstract (sommario):
The Doppler ultrasonic blood flow detector estimates
non-invasively the velocity of blood in the circulatory system. It has been
extensively used in the last four decades for the detection of stenoses in the
circulation.The development of new signal processing techniques for the Doppler
signal requires test signals with known or measurable characteristics. This is
very difficult to achieve with Doppler signals obtained in vivo because of the
variability of blood flow between persons and with physiological state, for
example blood pressure. A model for generating simulated Doppler signals whose
characteristics are controllable and/or measurable is a useful tool because it
permits the test of new processing techniques under controlled conditions. It
permits also the study of the effect of various factors on the Doppler
spectrum. Usually these effects cannot be isolated with in vivo
measurements.During this work a model for the generation of simulated Doppler
ultrasound signals was developed. It comprised two sub-models one for blood
flow in the human lower limb and the other for generating simulated signals
from the blood velocity field and the instrument's characteristics.Blood flow
in the lower limb was modelled by an electric analogue for the lower limb
vascular tree. Each artery was modelled by a lossy transmission line and the
peripheral vascular beds by three-element Windkessel models. The
electric analogue circuit was implemented with the SPICE circuit simulator. To
simulate the inter-action of the blood cells with the ultrasonic field the
vessel was divided into small elemental volumes whose contributions were added
together to generate the simulated Doppler signal. The model assumed
irrotational laminar flow and some other simplifying approximations.The
characteristics of the signals generated by the model were similar to those
expected for the Doppler signal. The model was used to study the influence of
blood acceleration, sample volume size and data segment duration on the root
mean square (rms) width of the Doppler spectrum. A simple formula was derived
for estimating the Doppler rms spectral width from the individual contribution
of non-stationarity broadening, intrinsic broadening, window broadening and the
range of blood velocities passing through the sample volume.In addition closed
form expressions were derived for the Doppler power spectrum due solely to the
range of blood velocities passing through a Gaussian sample volumes placed in
irrotational laminar flow with a velocity profile obeying a simple power law.
Closed form expressions were also obtained for the root mean square spectral
width in the special case of a spherically symmetric Gaussian sample volume
placed in the centre of the vessel.O detector ultra-sónico de fluxo sanguíneo usa o efeito Doppler para estimar de forma não invasiva a velocidade do sangue na circulação. Tem sido bastante usado nas últimas quatro décadas para detectar a presença de estenoses.O desenvolvimento de novas técnicas de processamento do sinal Doppler necessita de sinais de teste cujas características sejam conhecidas ou possam ser medidas com precisão. Isto é difícil de obter com sinais Doppler medidos in vivo devido à elevada variação do fluxo sanguíneo de pessoa para pessoa e também com o estado fisiológico da pessoa no momento da medida, por exemplo a tensão arterial influencia significativamente o fluxo sanguíneo. Um modelo para gerar sinais Doppler simulados cujas características sejam controláveis e/ou mensuráveis é uma ferramenta bastante útil, pois permite que as novas técnicas de processamento do sinal Doppler sejam testadas em condições controladas. Permite, também, estudar o efeito de vários factores que afectam o espectro do sinal Doppler. Habitualmente o efeito individual dos vários factores não pode ser identificado quando são usados sinais medidos in vivo.Neste trabalho foi desenvolvido um modelo para gerar sinais Doppler ultra-sónicos simulados. O modelo contém dois sub-modelos, um para o fluxo sanguíneo nos membros inferiores de um ser humano e outro para gerar os sinais simulados a partir do campo de velocidades do sangue e das características do instrumento.O fluxo sanguíneo nos membros inferiores foi simulado com um análogo eléctrico para a rede vascular dos membros inferiores. Cada artéria foi simulada por uma linha de transmissão com perdas e as redes vasculares periféricas por um circuito Windkessel com três elementos. O circuito eléctrico foi implementado com o simulador de circuitos SPICE.Para simular a interacção entre os glóbulos vermelhos e o campo de ultra-sons o vaso sanguíneo foi dividido em pequenos volumes elementares. As contribuições dos volumes elementares foram todas somadas para gerar o sinal Doppler simulado. O modelo fez algumas aproximações como sejam, por exemplo, considerar o fluxo sanguíneo laminar e sem rotação.As características dos sinais gerados pelo modelo são bastante parecidas com as esperadas para o sinal Doppler real. O modelo desenvolvido foi usado para estudar a influência que a aceleração sanguínea, o tamanho do volume de amostragem e a duração da janela de amostragem têm na largura de banda eficaz do espectro do sinal Doppler. Foi deduzida uma fórmula que estima a largura de banda eficaz a partir das contribuições individuais do alargamento espectral devido à não estacionaridade, do alargamento espectral intrínseco, do alargamento espectral devido à duração da janela de amostragem e ainda da gama das velocidades que passam pelo volume de amostragem. Foram, ainda, deduzidas expressões em forma fechada para o espectro de potência do sinal Doppler devido unicamente à gama de velocidades que atravessam um volume de amostragem com forma Gaussiana colocado num perfil de velocidades com forma exponêncial. Foram, também, obtidas expressões para a largura de banda eficaz no caso especial do volume de amostragem Gaussiano ter simetria esférica e estar colocado no centro do vaso sanguíneo.
29
Walton, Anthony G. "Computer simulation of liquid flow patterns on distillation trays". Thesis, Aston University, 1995. http://publications.aston.ac.uk/9586/.
Testo completoAbstract (sommario):
This thesis describes work carried out to improve the fundamental modelling of liquid flows on distillation trays. A mathematical model is presented based on the principles of computerised fluid dynamics. It models the liquid flow in the horizontal directions allowing for the effects of the vapour through the use of an increased liquid turbulence, modelled by an eddy viscosity, and a resistance to liquid flow caused by the vapour being accelerated horizontally by the liquid. The resultant equations are similar to the Navier-Stokes equations with the addition of a resistance term. A mass-transfer model is used to calculate liquid concentration profiles and tray efficiencies. A heat and mass transfer analogy is used to compare theoretical concentration profiles to experimental water-cooling data obtained from a 2.44 metre diameter air-water distillation simulation rig. The ratios of air to water flow rates are varied in order to simulate three pressures: vacuum, atmospheric pressure and moderate pressure. For simulated atmospheric and moderate pressure distillation, the fluid mechanical model constantly over-predicts tray efficiencies with an accuracy of between +1.7% and +11.3%. This compares to -1.8% to -10.9% for the stagnant regions model (Porter et al. 1972) and +12.8% to +34.7% for the plug flow plus back-mixing model (Gerster et al. 1958). The model fails to predict the flow patterns and tray efficiencies for vacuum simulation due to the change in the mechanism of liquid transport, from a liquid continuous layer to a spray as the liquid flow-rate is reduced. This spray is not taken into account in the development of the fluid mechanical model.
30
Koirala, Nischal. "Access Blood Flow Measurement Using Angiography". Cleveland State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=csu153796812445051.
Testo completo
31
Havard, Peter. "Linkflow, a linked saturated-unsaturated water flow computer model for drainage and subirrigation". Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41608.
Testo completoAbstract (sommario):
A computer simulation model, LINKFLOW, has been developed to simulate the movement of water during various water table management practices, such as subsurface drainage, controlled drainage and subirrigation. Water movement is simulated to, or from, a buried tile drainage system through a heterogeneous and anisotropic soil to a zone of water extraction by plant roots and the atmosphere. The computer package links a newly-developed one-dimensional unsaturated ground water flow model to a three-dimensional saturated water flow model that was modified for the linkage and for simulating water flow under different water table management systems and varying climatic conditions. The movement of water is determined for a region of the field and the model can show the effectiveness of a water table management scheme to meet moisture conditions for crop growth for a wide range of soil, topographical, drain layout and weather conditions. LINKFLOW was validated and verified with measurements on subsurface drainage, controlled drainage and subirrigation systems in a corn field in southwestern Quebec. The model provides a powerful tool for the design and evaluation of water table management systems, and it can assist in developing control strategies for efficient management of water resources. LINKFLOW is unique among soil water models for the following features: (1) it can be used to simulate with varying topography; (2) it determines 3-D flows from drains in a heterogeneous, anisotropic soil; (3) it presents results in tabular format, contour map format, or 3-D surface format; and (4) it contains software routines for automated control in subirrigation. The formation of the conceptual model, numerical relations, methods of solution, validation, field verification and examples are presented.
32
Doyle, Matthew Gerard. "Simulation of Myocardium Motion and Blood Flow in the Heart with Fluid-Structure Interaction". Thesis, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20166.
Testo completoAbstract (sommario):
The heart is a complex organ and much is still unknown about its mechanical function. In
order to use simulations to study heart mechanics, fluid and solid components and their
interaction should be incorporated into any numerical model. Many previous studies have
focused on myocardium motion or blood flow separately, while neglecting their interaction.
Previous fluid-structure interaction (FSI) simulations of heart mechanics have made
simplifying assumptions about their solid models, which prevented them from accurately
predicting the stress-stain behaviour of the myocardium. In this work, a numerical model
of the canine left ventricle (LV) is presented, which serves to address the limitations of previous studies. A canine LV myocardium material model was developed for use in conjunction with a commercial finite element code. The material model was modified from its original form to make it suitable for use in simulations. Further, numerical constraints were imposed when calculating the material parameter values, to ensure that the model would be strictly convex. An initial geometry and non-zero stress state are required to start cardiac cycle simulations. These were generated by the static inflation of a passive LV model to an end-diastolic pressure. Comparisons with previous measurements verified that the calculated geometry was representative of end diastole. Stresses calculated at the specified end diastolic pressure showed complex spatial variations, illustrating the superiority
of the present approach over a specification of an arbitrary stress distribution to an
end-diastolic geometry. In the third part of this study, FSI simulations of the mechanics
of the LV were performed over the cardiac cycle. Calculated LV cavity pressures agreed
well with previous measurements during most of the cardiac cycle, but deviated from them
during rapid filling, which resulted in non-physiological backflow. This study is the first one to present a detailed analysis of the temporal and spatial variations of the properties of both the solid and the fluid components of the canine LV. The observed development of non-uniform pressure distributions in the LV cavity confirms the advantage of performing FSI simulations rather than imposing a uniform fluid pressure on the inner surface of the myocardium during solid-only simulations.
33
Sun, Q. "Numerical simulation of blood flow through permeable vascular network embedded in tumour porous interstitium". Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1306876/.
Testo completoAbstract (sommario):
Tumour blood flow plays a critical role in tumour growth and cancer therapies. Computational fluid dynamics is an efficient method to study blood behaviour by modelling fluid flow through numerical simulations. A mathematical model is developed to study the blood flow through a three-dimensional permeable vascular network embedded in a solid tumour, and its transvascular movement and spread within tumour interior in context with cancer therapies. The vasculature is described by the parametric equations in terms of vessel centre lines. The flow through each tumour vessel is approximated with the leading component in the longitudinal direction of the vessel, and its governing equation becomes an ordinary differential equation based on the parameter of the parametric equation for the vessel centre line. The pressure continuity and mass conservation conditions are imposed at every junction within tumour vascular network. The interstitial flow is described by the Darcy’s law which is converted into the Laplace equation. The coupling effect between the flows through tumour vasculature and within tumour interstitial due to the vascular permeability is described by the Starling’s law. A coupling mathematical model is then developed. Based on mass conservation, a differential equation for pressures on both sides of vascular surface is obtained. Transforming the Laplace equation into the boundary-integral form by using the Green’s function offers another equation linking the pressures inside and outside vessels. The numerical procedure is developed, and the discretised differential and integral equations are solved by finite difference method and boundary element method respectively. The model is applied to investigate how different types of physical parameters and special characters of tumour vasculature affect tumour blood flow. Finally, an approximation model by ignoring the term with small value of the fully coupling model is developed, and its validity and simulation efficiency are examined.
34
Doyle, Matthew G. "Simulation of blood flow in a ventricular assist device with fluid-structure interaction effects". Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/26630.
Testo completoAbstract (sommario):
Numerical simulations combining solid and fluid models and fluid-structure interaction effects were performed for a diaphragm-type ventricular assist device (VAD). These simulations include an open loop configuration, in which the VAD inlet and outlet tubes are open to the surroundings, and a closed loop configuration, in which the VAD is connected to an idealized model of the circulatory system.
Comparisons have been made between the open loop case and previous experimental and numerical results for a similar VAD designed by a group at Brunel University. Differences between the two models can be partially accounted for by differences in flow forcing. Even with these differences, this comparison validates this method as a tool for the design and optimization of VADs.
For the closed loop case, results were limited by the required use of a slightly compressible fluid model. Further relaxation of this requirement is needed to fully explore closed loop simulations.
35
Gentile, Russell. "Adding cerebral autoregulation to a lumped parameter model of blood flow". Honors in the Major Thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/555.
Testo completoAbstract (sommario):
A mathematical model of blood flow in infants with hypoplastic left heart syndrome (HLHS) was improved by adding cerebral autoregulation. This is the process by which blood vessels constrict or dilate to keep blood flow steady in certain organs during pressure changes. The original lumped parameter model transformed the fluid flow into an electrical circuit. Its behavior is described using a system of thirty-three coupled differential equations that are solved numerically using a fourth-order Runge-Kutta method implemented in MATLAB. A literature review that includes a discussion of autoregulation mechanisms and approaches to modeling them is followed by a description of the model created for this paper. The model is based on the baroreceptor or neurogenic theory of autoregulation. According to this theory, nerves in certain places within the cardiovascular system detect changes in blood pressure. The brain then compensates by sending a signal to blood vessels to constrict or dilate. The model of the control system responded fairly well to a pressure drop with a steady state error of about two percent. Running the model with or without the control system activated had little effect on other parameters, notably cardiac output. A more complete model of blood flow control would include autonomic regulation. This would vary more parameters than local autoregulation, including heart rate and contractility. This is suggested as a topic of further research.B.S.M.E.
Bachelors
Engineering and Computer Science
Mechanical Engineering
36
Yu, Tungsheng. "Traffic flow modeling in highway networks". Master's thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-12232009-020154/.
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Wang, Xu. "Freeway exit ramp traffic flow research based on computer simulation". [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002332.
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Wang, Xu. "Freeway Exit Ramp Traffic Flow Research Based on Computer Simulation". Scholar Commons, 2007. https://scholarcommons.usf.edu/etd/554.
Testo completoAbstract (sommario):
Interstate highways are one of the most important components of the transportation infrastructure in America. Freeway ramps play an important role in the whole interstate transportation system.
This paper researches the traffic flow characteristics of four typical exit ramps in USA, which are tapered one-lane exit, tapered two-lane exit, parallel one-lane exit and parallel two-lane exit. Computer simulation software, such as CORSIM and HCS are applied as the main tools in this research. ANOVA and Tukey are used for statistical purpose.
It compares the maximum capacity, average running speed and the total lane change number of those four exit ramps. It is found that no matter in terms of traffic discharging rate or total lane charging number; the tapered two-lane exit has the best operational performance. Tapered one-lane exit ramp has the least capacity.
Parallel one-lane exit and parallel two-lane exit have very limited traffic operational difference in terms of capacity and running speed. It is recommended that parallel two-lane exit ramp should not be designed along the freeway if the right of way along arterial road is enough.
It is observed from the simulation data that the grade of freeway, truck percentage, restricted to the truck use of certain lane(s) and the location of exit sign have significant impact on the running speed and total lane change number. An uphill can decrease the running speed dramatically while more truck brings more lane change, causing safety concerns.
It is found that when trucks are restricted to the right two most lane, there will be less lane change number comparing with trucks are not restricted.
Location of exit sign operates well at the distance between 4000 ft to 5000 ft. does have a significant impact on the operational speed and total lane change number before, within or after functional area of an exit, based on the data analysis of simulation runs.
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Qin, H. Q. "Computer and water-model simulation of flow through poppet valves". Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37825.
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Sanghani, Aditya Deepak. "QUANTIFICATION OF BLOOD FLOW VELOCITY USING COLOR SENSING". DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1490.
Testo completoAbstract (sommario):
Blood flow velocity is an important parameter that can give information on several pathologies including atherosclerosis, glaucoma, Raynaud’s phenomenon, and ischemic stroke [2,5,6,10]. Present techniques of measuring blood flow velocity involve expensive procedures such as Doppler echocardiography, Doppler ultrasound, and magnetic resonance imaging [11,12]. They cost from $8500-$20000. It is desired to find a low-cost yet equally effective solution for measuring blood flow velocity. This thesis has a goal of creating a proof of concept device for measuring blood flow velocity.
Finger blood flow velocity is investigated in this project. The close proximity to the skin of the finger’s arteries makes it a practical selection. A Red Green Blue (RGB) color sensor is integrated with an Arduino Uno microcontroller to analyze color on skin. The initial analysis involved utilization of red RGB values to measure heart rate; this was performed to validate the sensor. This test achieved similar results to an experimental control as the measurements had error ranging from 0% to 6.67%.
The main analysis was to measure blood flow velocity using 2 RGB color sensors. The range of velocity found was 5.20cm/s to 12.22cm/s with an average of 7.44cm/s. This compared well with the ranges found in published data that varied from 4cm/s to 19cm/s. However, there is an error associated with the device that affects the accuracy of the results. The apparatus has the limitation of collecting data between sensors every 102-107ms, so there is a maximum error of 107ms. The average finger blood flow velocity of 7.44cm/s may actually be between 6.17cm/s and 9.39cm/s due to the sampling error. In addition, mean squared error analysis found that the most likely time difference between pulses among those found is 739ms, which corresponds to 5.21cm/s.
Although there is error in the system, the tests for heart rate along with the obtained range and average for finger blood velocity data provided a method for analyzing blood flow velocity. Finger blood velocity was examined in a much more economical manner than its traditional methods that cost between $8500-$20000. The cost for this entire thesis was $99.66, which is a maximum of 1.17% of the cost.
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Gårdhagen, Roland. "Turbulent Flow in Constricted Blood Vessels : Quantification of Wall Shear Stress Using Large Eddy Simulation". Doctoral thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-100918.
Testo completoAbstract (sommario):
The genesis of atherosclerosis has previously been shown to be affected by the frictional load from the blood on the vessel wall, called the wall shear stress (WSS). Assessment of WSS can therefore provide important information for diagnoses, intervention planning, and follow‐up. Calculation of WSS requires high‐resolved velocity data from the vessel, which in turn can be obtained using computational fluid dynamics (CFD). In this work large eddy simulation LES was successfully used to simulate transitional flow in idealized as well as subject specific vessel models. It was shown that a scale resolving technique is to prefer for this application, since much valuable information otherwise is lost. Besides, Reynolds‐Averaged Navier‐Stokes (RANS) models have generally failed to predict this type of flow. Non‐pulsating flows of Reynolds numbers up to 2 000 in a circular constricted pipe showed that turbulence is likely to occur in the post‐stenotic region, which resulted in a complex WSS pattern characterized by large spatial as well temporal fluctuations in all directions along the wall. Time averaged streamwise WSS was relatively high, while time averaged circumferential WSS was low, meaning that endothelial cells in that region would be exposed to oscillations in a stretched state in the streamwise direction and in a relaxed state in the circumferential direction. Since every vessel is unique, so is also its WSS pattern. Hence the CFD simulations must be done in subject specific vessel models. Such can be created from anatomical information acquired with magnetic resonance imaging (MRI). MRI can also be used to obtain velocity boundary conditions for the simulation. This technique was used to investigate pulsating flow in a subject specific normal human aorta. It was shown that even the flow in healthy vessels can be very disturbed and turbulence like, and even for this case large WSS variations were seen. It was also shown that regions around branches from the aorta, known to be susceptible for atherosclerosis, were characterized by high time averaged WSS and high oscillatory shear index. Finally, the predictive capability of CFD was investigated. An idealized model of a human aorta with a coarctation and post‐stenotic dilatation was studied before and after a possible repair of the constriction. The results suggested that small remaining abnormalities in the geometry may deteriorate the chances for a successful treatment. Also, high values of shear rate and Reynolds stresses were found in the dilatation after the constriction, which previous works have shown means increased risk for thrombus formation and hemolysis.
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Petersson, Sven. "Simulation of Phase Contrast MRI Measurements from Numerical Flow Data". Thesis, Linköping University, Department of Biomedical Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-14871.
Testo completoAbstract (sommario):
Phase-contrast magnetic resonance imaging (PC-MRI) is a powerful tool for measuring blood flow and has a wide range of cardiovascular applications. Simulation of PC-MRI from numerical flow data would be useful for addressing the data quality of PC-MRI measurements and to study and understand different artifacts. It would also make it possible to optimize imaging parameters prior to the PC-MRI measurements and to evaluate different methods for measuring wall shear stress.
Based on previous studies a PC-MRI simulation tool was developed. An Eulerian-Lagrangian approach was used to solve the problem. Computational fluid dynamics (CFD) data calculated on a fix structured mesh (Eulerian point of view) were used as input. From the CFD data spin particle trajectories were computed. The magnetization of the spin particle is then evaluated as the particle travels along its trajectory (Lagrangian point of view).
The simulated PC-MRI data were evaluated by comparison with PC-MRI measurements on an in vitro phantom. Results indicate that the PC-MRI simulation tool functions well. However, further development is required to include some of the artifacts. Decreasing the computation time will make more accurate and powerful simulations possible. Several suggestions for improvements are presented in this report.
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Elkanani, Hesham. "Numerical and experimental modeling of blood flow in the arteries". Thesis, Lille 1, 2018. http://www.theses.fr/2018LIL1I002/document.
Testo completoAbstract (sommario):
Le but de cette recherche consiste à la modélisation numérique et expérimentale d’écoulement sanguin dans les artères, en utilisant les nouvelles méthodes de couplage fluide structure. Plusieurs approches numériques peuvent être utilisées pour ce type de couplage, la méthode des éléments finis pour la modélisation de la structure. Pour la modélisation du domaine fluide la méthode de type éléments fnis ou méthode particulaire, Smooth Particle Hydrodynamic method, (méthode SPH) peuvent utilisées. Afin de valider ces deux méthodes numériques, Eléments Finis et SPH, une première application consiste à la modélisation numérique du gonflement d’une membrane en caoutchouc. Pour cette application des données expérimentales sont disponibles pour la validation des résultats numériques. Pour le matériau caoutchouc, une loi de comportement de type Mooney Rivlin est utilisée. Pour la structure la méthode des éléments finis, formulation coque est utilisée, pour le fluide nous avons opté pour la méthode particulaire SPH. Concernant la sensibilité par rapport au maillage, plusieurs maillages pour la modélisation des domaines fluide et structure sont testés. Une bonne corrélation en terme de déplacement et de vitesse du centre de la membrane, entre les résultats numériques et données expérimentales a été observée. Cette application est publiée dans un journal international de rang A.La seconde formulation développée dans le manuscrit consiste à la modélisation et simulation numérique du problème en vue. La méthode de couplage de type Euler Lagrange, une formulation Eulerienne à maillage fixe pour le fluide et une formulation Lagrangienne pour la structure, est utilisée pour la modélisation de l’écoulement sanguin dans les artères. Différentes méthodes de pénalisation pour le couplage fluide structure ont été testées. Pour une meilleure consistance, plusieurs types de maillages fluide et structure ont été analysés, and des pas de temps vérifiant la condition de stabilité. Comme très peu de résultats expérimentant dans le domaine biomécanique sont disponibles. Les résultats numériques sont comparés aux résultats théoriques publiés dans la littérature. Une bonne corrélation entre les résultats numériques et les données théorique a été signalée dans le manuscrit. Ces résultats sont publiés dans un Journal International de rang AThe aim of this thesis is to investigate blood flow in arteries using Fluid-Structure Interaction (FSI) numerical approach. There are different approaches which could be used, Finite Element (FE) method for modelling artery wall and either FE or Smoothed Particles Hydrodynamic (SPH) method for blood modeling. In order to investigate the appropriate numerical method to simulate the biomedical problem. both SPH and Finite Element methods were applied. Both methods were first validated for applications where experimental data are available. In order to validate the SPH and FEM method used to simulate the fluid domain and arteries, we investigate a specific problem concerning membrane inflation. Finite Element method with shell formulation was used for the membrane made of rubber material, and SPH Particle method for the fluid. This application has been selected since experimental data are available. Mooney Rivlin constitutive material law for hyper elastic incompressible material is used for the membrane and compressible air for the fluid. For mesh sensitivity and consistency, different meshes for the membrane and different particle numbers for SPH have been investigated, Good agreement with experimental data were obtained in term of displacement and velocity of the membrane center. The application is published in an international Journal with Index Citation. The second formulation developed in the manuscript concerns the fluid structure coupling problem we are interested in. Coupled Eulerian Lagrangian (CEL) approach for the modelisation of Pulse Wave Velocity (PWV) in large arteries. Different penalty methods for the fluid structure coupling have been investigated for good accuracy and consistency of the results using different fluid and structure meshes and time step satisfying stability condition. Since experimental data are not available for these approaches, numerical results were compared to the theoretical theory and previous work published in the literature. This work is published in an International Journal with Index Citation
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McCallum, Marcus Anthony. "The simulation of wet steam flow in a turbine". Thesis, University of Strathclyde, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366697.
Testo completo
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Floros, Nikolaos. "An incompressible flow simulation environment for parallel and distributed computers". Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241983.
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Deparis, Simone. "Numerical analysis of axisymmetric flows and methods for fluid-structure interaction arising in blood flow simulation /". [S.l.] : [s.n.], 2004. http://library.epfl.ch/theses/?display=detail&nr=2965.
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Ghalichi, Farzan. "Pulsatile laminar and turbulent blood flow simulation in large stenosed arteries and stenosed carotid artery bifurcation". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0013/NQ36272.pdf.
Testo completo
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Demirci, Turan. "Federated Simulation Of Network Performance Using Packet Flow Modeling". Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/2/12611704/index.pdf.
Testo completoAbstract (sommario):
Federated approach for the distributed simulation of a network, is an alternative method that aims to combine existing simulation models and software together using a Run Time Infrastructure (RTI), rather than building the whole simulation from scratch. In this study, an approach that significantly reduces the inter-federate communication load in federated simulation of communication networks is proposed. Rather than communicating packet-level information among federates, characteristics of packet flows in individual federates are dynamically identified and communicated. Flow characterization is done with the Gaussian Mixtures Algorithm (GMA) using a Self Organizing Mixture Network (SOMN) technique. In simulations of a network partitioned into eight federates in space parallel manner, it is shown that significant speedups are achieved with the proposed approach without unduly compromising accuracy.
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Zhou, Xiaowei. "Investigation of ultrasound-measured blood flow related parameters in radial and ulnar arteries". Thesis, University of Dundee, 2017. https://discovery.dundee.ac.uk/en/studentTheses/cb2a68cb-949a-413f-b561-c137b7605583.
Testo completoAbstract (sommario):
The incidence of disease of the cardiovascular system is very high and increasing worldwide, especially in the developing world. The radial and ulnar arteries are implicated in some important ailments where blood flow related parameters such as flow rate (FR), wall shear rate (WSR), arterial wall motion (AWM) and pressure, all of which can be measured using ultrasound techniques, are useful in diagnosis and patient management. However these measurements are prone to error due to the manner of image formation and the complex flow conditions within the vessels. In this thesis, the errors in ultrasound-measured parameters in the radial and ulnar arteries are investigated using experimental phantoms, computer simulation and on volunteers. Using the Womersley theory, FR and WSR were estimated using a clinical ultrasound scanner with the pulsed wave (PW) mode and B mode. Experimental flow phantoms were designed to evaluate those measurements under different circumstances. A simulation technique which combined image-based computational fluid dynamics and ultrasound simulation was also used to evaluate ultrasound estimation of these parameters. A case study was then conducted on healthy volunteers to evaluate the method of measuring FR and WSR in-vivo. For the AWM in the radial artery, an auto-correlation method was used based on the radio-frequency (RF) data and validations were done by a flow phantom, simulation, and in-vivo trial. The blood pressure waveform in a volunteer’s radial artery was derived from the ultrasound measured AWM and compared with the waveform from a tonometry. FR and WSR were both found to be overestimated by up to 50%, mainly due to the beam-vessel angle in the PW Doppler ultrasound. Measurement of the vessel diameter and assumption of the blood flow direction can also influence the estimations. Other factors, such as flow amplitude, vessel size, imaging depth and flow waveforms, do not seem to affect the estimation of these two parameters. Results taken from the flow phantoms agree with those from simulation and the estimations from the in-vivo case study also agree with the published data. The auto-correlation method for the AWM was validated from the phantom and simulation. It is able to detect motion amplitude of about tens of micrometres. The trial on volunteers proved the feasibility of this motion detection method. Blood pressure waveforms at the radial artery of a volunteer, derived from this ultrasound-measured wall motion and from the tonometry, were very similar. The Womersley-based method is able to estimate the FR and WSR in the radial and ulnar arteries with high accuracy. Sources of the error and their magnitudes in estimation of the two parameters by ultrasound pointed out in this thesis are beam-vessel angle, vessel diameter measurement and flow direction assumption. Researchers and clinicians using these measurements in practice and research should be aware. The capability of ultrasound imaging to measure arterial AWM in the radial artery is demonstrated and it is found that the blood pressure waveform can also be derived from the arterial AWM.
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薛明輝 e Ming-fai Sit. "Computation of stratified flow past three dimensional surface mounted obstacles". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1988. http://hub.hku.hk/bib/B31208897.
Testo completo