subject:(Beam instability)

Delft University of Technology

1. Vicca, Elke (author). Instability of a high-speed vehicle moving through a tunnel embedded in a visco-elastic half-plane: The Hyperloop case.

Degree: 2019, Delft University of Technology

URL: http://resolver.tudelft.nl/uuid:e17786ba-54f8-44ec-9ef0-46758bb36612

► Hyperloop is a high-speed transportation mode which operates by sending magnetically levitated capsule-like vehicles through a near vacuum tunnel. Due to the reduced air resistance… (more)

▼ Hyperloop is a high-speed transportation mode which operates by sending magnetically levitated capsule-like vehicles through a near vacuum tunnel. Due to the reduced air resistance and friction, speeds exceeding those of modern aircraft should become possible. When the system is moved underground, the stability of vehicle vibrations may become problematic as, especially in soft soils, the Hyperloop pod velocities could easily surpass the propagation speeds of waves in the soil. In that case, the radiation of anomalous Doppler waves into the system may lead to instability of vehicle vibrations, which means that the amplitude of the vibrations would grow exponentially. The aim of this study is to evaluate the system’s stability and its sensitivity to changes in the model by using analytical methods. To that end, the study is motivated by two central research questions: (1) How can the system be modelled and described, taking into account the interaction between soil, tunnel and vehicle and how does the model description change when the magnetic levitation suspension system is introduced? (2) What is the influence of the model parameters on the system’s stability and what impact do modifications in the vehicle suspension have? The first research question is answered by modelling the underground Hyperloop system as a two-mass oscillator moving uniformly along an infinitely long Euler-Bernoulli beam embedded in a visco-elastic half-plane. Through definition of the governing equations of motion, boundary and interface conditions and subsequent application of Laplace and Fourier integral transforms, the model is reduced to a lumped model for which the characteristic equation has been derived. In the latter model, the reaction of the beam-half-plane system in the point of contact with the moving load is represented by an equivalent dynamic spring stiffness. The introduction of the magnetic levitation adds a magnetic spring to the lumped model. This spring is placed in series with the equivalent spring representing the beam-half-plane stiffness. The second research question is answered by first studying the velocity-dependent equivalent dynamic stiffness of the supporting structure in the point of contact with the moving oscillator as a function of the frequency of the oscillator vibrations. When the imaginary part of this stiffness is negative, instability of vertical oscillator vibrations may occur due to so-called negative radiation damping. Then, based on the D-decomposition method, the instability domain is found for the base parameters of the system, whereupon this instability zone is parametrically studied. The influence of the magnetic levitation suspension system is established by deriving the instability domain for two different models of a concrete tunnel and various magnitudes of the viscous damping in the vehicle. It is found that the model parameters significantly influence the system’s stability. The oscillator’s viscosity in particular has an important stabilizing effect. For both the non-magnetically… Advisors/Committee Members: van Dalen, Karel (mentor), Zhao, Mingjuan (mentor), Metrikine, Andrei (graduation committee), Lu, Tao (graduation committee), Delft University of Technology (degree granting institution).

Subjects/Keywords: instability; oscillator; beam; visco-elastic half-plane; Hyperloop; tunnel; vertical vibrations

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APA (6^th Edition):

Vicca, E. (. (2019). Instability of a high-speed vehicle moving through a tunnel embedded in a visco-elastic half-plane: The Hyperloop case. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:e17786ba-54f8-44ec-9ef0-46758bb36612

Chicago Manual of Style (16^th Edition):

Vicca, Elke (author). “Instability of a high-speed vehicle moving through a tunnel embedded in a visco-elastic half-plane: The Hyperloop case.” 2019. Masters Thesis, Delft University of Technology. Accessed March 07, 2021. http://resolver.tudelft.nl/uuid:e17786ba-54f8-44ec-9ef0-46758bb36612.

MLA Handbook (7^th Edition):

Vicca, Elke (author). “Instability of a high-speed vehicle moving through a tunnel embedded in a visco-elastic half-plane: The Hyperloop case.” 2019. Web. 07 Mar 2021.

Vancouver:

Vicca E(. Instability of a high-speed vehicle moving through a tunnel embedded in a visco-elastic half-plane: The Hyperloop case. [Internet] [Masters thesis]. Delft University of Technology; 2019. [cited 2021 Mar 07]. Available from: http://resolver.tudelft.nl/uuid:e17786ba-54f8-44ec-9ef0-46758bb36612.

Council of Science Editors:

Vicca E(. Instability of a high-speed vehicle moving through a tunnel embedded in a visco-elastic half-plane: The Hyperloop case. [Masters Thesis]. Delft University of Technology; 2019. Available from: http://resolver.tudelft.nl/uuid:e17786ba-54f8-44ec-9ef0-46758bb36612

University of New Mexico

2. Zhang, Yue. Experimental Investigation of Plasma Dynamics in Jets and Bubbles Using a Compact Coaxial Plasma Gun in a Background Magnetized Plasma.

Degree: Electrical and Computer Engineering, 2016, University of New Mexico

URL: https://digitalrepository.unm.edu/ece_etds/309

► Numerous solar and astrophysical observations of jet- and bubble-like plasma structures exhibit morphological similarities, suggesting that there may be common plasma physics at work… (more)

Subjects/Keywords: astrophysics; solar; plasma gun; axial sheared flow; kink instability; magnetic Rayleigh-Taylor instability; Electrical and Computer Engineering; Plasma and Beam Physics

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APA (6^th Edition):

Zhang, Y. (2016). Experimental Investigation of Plasma Dynamics in Jets and Bubbles Using a Compact Coaxial Plasma Gun in a Background Magnetized Plasma. (Doctoral Dissertation). University of New Mexico. Retrieved from https://digitalrepository.unm.edu/ece_etds/309

Chicago Manual of Style (16^th Edition):

Zhang, Yue. “Experimental Investigation of Plasma Dynamics in Jets and Bubbles Using a Compact Coaxial Plasma Gun in a Background Magnetized Plasma.” 2016. Doctoral Dissertation, University of New Mexico. Accessed March 07, 2021. https://digitalrepository.unm.edu/ece_etds/309.

MLA Handbook (7^th Edition):

Zhang, Yue. “Experimental Investigation of Plasma Dynamics in Jets and Bubbles Using a Compact Coaxial Plasma Gun in a Background Magnetized Plasma.” 2016. Web. 07 Mar 2021.

Vancouver:

Zhang Y. Experimental Investigation of Plasma Dynamics in Jets and Bubbles Using a Compact Coaxial Plasma Gun in a Background Magnetized Plasma. [Internet] [Doctoral dissertation]. University of New Mexico; 2016. [cited 2021 Mar 07]. Available from: https://digitalrepository.unm.edu/ece_etds/309.

Council of Science Editors:

Zhang Y. Experimental Investigation of Plasma Dynamics in Jets and Bubbles Using a Compact Coaxial Plasma Gun in a Background Magnetized Plasma. [Doctoral Dissertation]. University of New Mexico; 2016. Available from: https://digitalrepository.unm.edu/ece_etds/309

3. Heine, Robert Gerd. Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta.

Degree: 2006, Technische Universität Dortmund

URL: http://hdl.handle.net/2003/22989

► In einem Elektronenbeschleuniger werden Hochfrequenz-Hohlraumresonatoren zur Beschleunigung der Elektronen und zum Ausgleich des Energieverlustes der Elektronen durch Abstrahlung von Synchrotronstrahlung verwendet. Die höheren Moden dieser… (more)

Subjects/Keywords: Beam instability; Beschleuniger; Cavity resonator; Collective oscillation; Coupled-Bunch Moden; Hohlraumresonatoren; Kollektive Schwingungen; Mode damping; Modendämpfung; Particle accelerator; Strahlinstabilitäten; 530

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APA (6^th Edition):

Heine, R. G. (2006). Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta. (Thesis). Technische Universität Dortmund. Retrieved from http://hdl.handle.net/2003/22989

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Heine, Robert Gerd. “Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta.” 2006. Thesis, Technische Universität Dortmund. Accessed March 07, 2021. http://hdl.handle.net/2003/22989.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Heine, Robert Gerd. “Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta.” 2006. Web. 07 Mar 2021.

Vancouver:

Heine RG. Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta. [Internet] [Thesis]. Technische Universität Dortmund; 2006. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/2003/22989.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Heine RG. Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta. [Thesis]. Technische Universität Dortmund; 2006. Available from: http://hdl.handle.net/2003/22989

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of Colorado

4. Stawarz, Julia Elizabeth. Collisionless Plasma Turbulence: Insights from Magnetohydrodynamic and Hall Magnetohydrodynamic Simulations and Observations of the Earth's Magnetosphere.

Degree: PhD, Astrophysical & Planetary Sciences, 2016, University of Colorado

URL: https://scholar.colorado.edu/astr_gradetds/39

► Turbulence is a ubiquitous phenomenon that occurs throughout the universe, in both neutral fluids and plasmas. For collisionless plasmas, kinetic effects, which alter the… (more)

▼ Turbulence is a ubiquitous phenomenon that occurs throughout the universe, in both neutral fluids and plasmas. For collisionless plasmas, kinetic effects, which alter the nonlinear dynamics and result in small-scale dissipation, are still not well understood in the context of turbulence. This work uses direct numerical simulations (DNS) and observations of Earth's magnetosphere to study plasma turbulence. Long-time relaxation in magnetohydrodynamic (MHD) turbulence is examined using DNS with particular focus on the role of magnetic and cross helicity and symmetries of the initial con-figurations. When strong symmetries are absent or broken through perturbations, flows evolve towards states predicted by statistical mechanics with an energy minimization principle, which features two main regimes; one magnetic helicity dominated and one with quasi-equipartition of kinetic and magnetic energy. The role of the Hall effect, which contributes to the dynamics of collisionless plasmas, is also explored numerically. At scales below the ion inertial length, a transition to a magnetically dominated state, associated with advection becoming subdominant to dissipation, occurs. Real-space current, vorticity, and electric fields are examined. Strong current structures are associated with alignment between the current and magnetic field, which may be important in collisionless plasmas where field-aligned currents can be unstable. Turbulence within bursty bulk ow braking events, thought to be associated with near-Earth magnetotail reconnection, are then studied using the THEMIS spacecraft. It is proposed that strong field-aligned currents associated with turbulent intermittency destabilize into double layers, providing a collisionless dissipation mechanism for the turbulence. Plasma waves may also radiate from the region, removing energy from the turbulence and potentially depositing it in the aurora. Finally, evidence for turbulence in the Kelvin-Helmholtz instability (KHI) on the Earth's magnetopause is found using data from the Magnetospheric Multiscale (MMS) mission. With MMS, spatial properties, including spatial intermittency and anisotropy, can be examined along with temporal properties and ion and electron velocity spectra can be examined observationally into the kinetic scales. Quasi-two-dimensional anisotropy perpendicular to the magnetic field is found. Field-aligned current instabilities and wave radiation may also be relevant in the KHI. Advisors/Committee Members: Robert E. Ergun, Annick Pouquet, Mark Rast, Phil Armitage, Juri Toomre.

Subjects/Keywords: Bursty Bulk Flows; Direct Numerical Simulations; Earth's Magnetosphere; Kelvin-Helmholtz Instability; Magnetohydrodynamics; Turbulence; Astrophysics and Astronomy; Plasma and Beam Physics

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APA (6^th Edition):

Stawarz, J. E. (2016). Collisionless Plasma Turbulence: Insights from Magnetohydrodynamic and Hall Magnetohydrodynamic Simulations and Observations of the Earth's Magnetosphere. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/astr_gradetds/39

Chicago Manual of Style (16^th Edition):

Stawarz, Julia Elizabeth. “Collisionless Plasma Turbulence: Insights from Magnetohydrodynamic and Hall Magnetohydrodynamic Simulations and Observations of the Earth's Magnetosphere.” 2016. Doctoral Dissertation, University of Colorado. Accessed March 07, 2021. https://scholar.colorado.edu/astr_gradetds/39.

MLA Handbook (7^th Edition):

Stawarz, Julia Elizabeth. “Collisionless Plasma Turbulence: Insights from Magnetohydrodynamic and Hall Magnetohydrodynamic Simulations and Observations of the Earth's Magnetosphere.” 2016. Web. 07 Mar 2021.

Vancouver:

Stawarz JE. Collisionless Plasma Turbulence: Insights from Magnetohydrodynamic and Hall Magnetohydrodynamic Simulations and Observations of the Earth's Magnetosphere. [Internet] [Doctoral dissertation]. University of Colorado; 2016. [cited 2021 Mar 07]. Available from: https://scholar.colorado.edu/astr_gradetds/39.

Council of Science Editors:

Stawarz JE. Collisionless Plasma Turbulence: Insights from Magnetohydrodynamic and Hall Magnetohydrodynamic Simulations and Observations of the Earth's Magnetosphere. [Doctoral Dissertation]. University of Colorado; 2016. Available from: https://scholar.colorado.edu/astr_gradetds/39

Australian National University

5. Cox, Sebastian Penleigh. The impact of fishbones on neutron rate in beam-heated plasmas in MAST .

Degree: 2015, Australian National University

URL: http://hdl.handle.net/1885/112493

► A plasma instability has been associated with loss of fusion rate in tokamaks since the introduction of beam-heating in the 1980’s: the Fishbone. Losses of… (more)

▼ A plasma instability has been associated with loss of fusion rate in tokamaks since the introduction of beam-heating in the 1980’s: the Fishbone. Losses of fusion rate on tokamaks during the heating phase present a significant obstacle in reaching the ignition condition required to harness nuclear fusion as a power source. If the conditions exacerbating fusion rate losses during these events can be understood, they can be mitigated. We examine a wide selection of fishbone events from MAST to determine the characteristics associated with greater losses in fusion rate. Quantities for expressing the behaviour of fusion rate are discussed, and statistically significant changes in fusion rate as a function of fishbone phase are examined. Using correlation analysis and sub-classifying the dataset based on observed loss characteristics indicates that fishbone behaviour is significantly more complex than previously believed. Correlation analysis using the full dataset found no reliable quantity that relates plasma conditions during the fishbone to changes in the fusion rate. To study a fishbone undergoing loss, a reduced model of wave-particle resonant interaction between fishbone harmonics and fast ions was built. This models the physical process of fast ions losing energy to the plasma by redistributing the fast ion distribution function in velocity-space. When resonant interactions with higher fishbone harmonics are included, the reduced-model accesses regions of the fast ion distribution function at higher velocities. This results in a larger effect on the modelled fusion rate. Small changes in the fast ion distribution in these regions produces changes in fusion rate that match experimentally observed losses. These results suggest the possibility of developing inference diagnostics for the fast ion distribution function using MHD spectroscopy.

Subjects/Keywords: Plasma; Physics; Nuclear; Fusion; MAST; Spherical; Tokamak; Fishbone; Instability; Fast Ions; Beam Heating; Loss; Wave-Particle; Resonant Interaction; Redistribution; MHD

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APA (6^th Edition):

Cox, S. P. (2015). The impact of fishbones on neutron rate in beam-heated plasmas in MAST . (Thesis). Australian National University. Retrieved from http://hdl.handle.net/1885/112493

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Cox, Sebastian Penleigh. “The impact of fishbones on neutron rate in beam-heated plasmas in MAST .” 2015. Thesis, Australian National University. Accessed March 07, 2021. http://hdl.handle.net/1885/112493.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Cox, Sebastian Penleigh. “The impact of fishbones on neutron rate in beam-heated plasmas in MAST .” 2015. Web. 07 Mar 2021.

Vancouver:

Cox SP. The impact of fishbones on neutron rate in beam-heated plasmas in MAST . [Internet] [Thesis]. Australian National University; 2015. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/1885/112493.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Cox SP. The impact of fishbones on neutron rate in beam-heated plasmas in MAST . [Thesis]. Australian National University; 2015. Available from: http://hdl.handle.net/1885/112493

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of New Mexico

6. Silantyev, Denis Albertovich. Nonlinear Waves, Instabilities and Singularities in Plasma and Hydrodynamics.

Degree: Mathematics & Statistics, 2017, University of New Mexico

URL: https://digitalrepository.unm.edu/math_etds/121

► This work concentrates on Langmuir wave filamentation instability in the kinetic regime of plasma and computation of Stokes wave with high precision using conformal… (more)

▼ This work concentrates on Langmuir wave filamentation instability in the kinetic regime of plasma and computation of Stokes wave with high precision using conformal maps. Nonlinear effects are present in almost every area of science as soon as one tries to go beyond the first order approximation. In particular, nonlinear waves emerge in such areas as hydrodynamics, nonlinear optics, plasma physics, quantum physics, etc. The results of this work are related to nonlinear waves in two areas, plasma physics and hydrodynamics, united by concepts of instability, singularity and advanced numerical methods used for their investigation. The first part of this work concentrates on Langmuir wave filamentation instability in the kinetic regime of plasma. In Internal Confinement Fusion Experiments (ICF) at National Ignition Facility (NIF), where attempts are made to achieve fusion by compressing a small target by many powerful lasers to extremely high temperatures and pressures, plasma is created in the first moments of the laser reaching the target and undergoes complicated dynamics. Some of the most challenging difficulties arise from various plasma instabilities that occur due to interaction of the laser beam and a plasma surrounding the target. In this work we consider one of such instabilities that describes a decay of nonlinear plasma wave (aka Langmuir wave), initially excited due to interaction of the laser beam with the plasma, into many filaments in direction perpendicular to the laser beam, therefore named Langmuir filamentation (or transverse) instability. This instability occurs in the kinetic regime of plasma,kλ_D>0.2, where k is the wavenumber and λ_D is the Debye length. The filamentation of Langmuir waves in turn leads to the saturation of the stimulated Raman scattering (SRS) in laser-plasma interaction experiments which plays an essential role in ICF experiments. The challenging part of this work was that unlike in hydrodynamics we needed to use fully kinetic description of plasma to capture the physics in question properly, meaning that we needed to consider the distribution function of charged particles and its evolution in time not only with respect to spatial coordinates but with respect to velocities as well. To study Langmuir filamentation instability in its simplest form we performed 2D+2V numerical simulations. Taking into account that the distribution function in question was 4-dimensional function, making these simulation quite challenging, we developed an efficient numerical method making these simulations possible on modern desktop computers. Using the developed numerical method we studied how Langmuir wave filamentation instability depends on the parameters of the Langmuir wave such as wave length and amplitude that are relevant to ICF experiments. We considered several types of Langmuir waves, including nonlinear Langmuir waves exited by external electric field as well as an idealized approximation of such Langmuir waves… Advisors/Committee Members: Pavel Lushnikov, Alexander Korotkevich, Evangelos Coutsias, Jean-Claude Diels.

Subjects/Keywords: plasma; instability; filamentation; BGK; Langmuir wave; nonlinear waves; Stokes wave; singularity; Applied Mathematics; Fluid Dynamics; Plasma and Beam Physics

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APA (6^th Edition):

Silantyev, D. A. (2017). Nonlinear Waves, Instabilities and Singularities in Plasma and Hydrodynamics. (Doctoral Dissertation). University of New Mexico. Retrieved from https://digitalrepository.unm.edu/math_etds/121

Chicago Manual of Style (16^th Edition):

Silantyev, Denis Albertovich. “Nonlinear Waves, Instabilities and Singularities in Plasma and Hydrodynamics.” 2017. Doctoral Dissertation, University of New Mexico. Accessed March 07, 2021. https://digitalrepository.unm.edu/math_etds/121.

MLA Handbook (7^th Edition):

Silantyev, Denis Albertovich. “Nonlinear Waves, Instabilities and Singularities in Plasma and Hydrodynamics.” 2017. Web. 07 Mar 2021.

Vancouver:

Silantyev DA. Nonlinear Waves, Instabilities and Singularities in Plasma and Hydrodynamics. [Internet] [Doctoral dissertation]. University of New Mexico; 2017. [cited 2021 Mar 07]. Available from: https://digitalrepository.unm.edu/math_etds/121.

Council of Science Editors:

Silantyev DA. Nonlinear Waves, Instabilities and Singularities in Plasma and Hydrodynamics. [Doctoral Dissertation]. University of New Mexico; 2017. Available from: https://digitalrepository.unm.edu/math_etds/121

University of Colorado

7. Sturdevant, Benjamin. Fully Kinetic Ion Models for Magnetized Plasma Simulations.

Degree: PhD, Applied Mathematics, 2016, University of Colorado

URL: https://scholar.colorado.edu/appm_gradetds/82

► This thesis focuses on the development of simulation models, based on fully resolving the gyro-motion of ions with the Lorentz force equations of motion, for… (more)

Subjects/Keywords: gyro-motion; ion; gyrokinetic model; plasma; uniform magnetic field; ITG instability; ITG model; magnetized ion acoustic waves; Applied Mathematics; Plasma and Beam Physics

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APA (6^th Edition):

Sturdevant, B. (2016). Fully Kinetic Ion Models for Magnetized Plasma Simulations. (Doctoral Dissertation). University of Colorado. Retrieved from https://scholar.colorado.edu/appm_gradetds/82

Chicago Manual of Style (16^th Edition):

Sturdevant, Benjamin. “Fully Kinetic Ion Models for Magnetized Plasma Simulations.” 2016. Doctoral Dissertation, University of Colorado. Accessed March 07, 2021. https://scholar.colorado.edu/appm_gradetds/82.

MLA Handbook (7^th Edition):

Sturdevant, Benjamin. “Fully Kinetic Ion Models for Magnetized Plasma Simulations.” 2016. Web. 07 Mar 2021.

Vancouver:

Sturdevant B. Fully Kinetic Ion Models for Magnetized Plasma Simulations. [Internet] [Doctoral dissertation]. University of Colorado; 2016. [cited 2021 Mar 07]. Available from: https://scholar.colorado.edu/appm_gradetds/82.

Council of Science Editors:

Sturdevant B. Fully Kinetic Ion Models for Magnetized Plasma Simulations. [Doctoral Dissertation]. University of Colorado; 2016. Available from: https://scholar.colorado.edu/appm_gradetds/82

Delft University of Technology

8. Veritchev, S.N. Instability of a vehicle moving on an elastic structure.

Degree: 2002, Delft University of Technology

URL: http://resolver.tudelft.nl/uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; urn:NBN:nl:ui:24-uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; urn:NBN:nl:ui:24-uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; http://resolver.tudelft.nl/uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e

► Vibrations of a vehicle that moves on a long elastic structure can become unstable because of elastic waves that the vehicle generates in the structure.… (more)

▼ Vibrations of a vehicle that moves on a long elastic structure can become unstable because of elastic waves that the vehicle generates in the structure. A typical example of the vehicle that can experience such instability is a high-speed train. Moving with a sufficiently high speed, this train could generate in the railway track elastic waves, whose reaction might destabilise vibrations of the train. Such instability could increase the level of vibrations of both the train and the railway track, significantly worsening the comfort of passengers and increasing the probability of the track deterioration and the train derailment. Instability of a moving vehicle on an elastic structure can be classified as one of the "moving load problems". This class of problems has been drawing attention of researches for more than a century being a fundamental issue in dynamics of bridges and railway tracks. Recently, the classical "moving load problem" has attracted researches once again because of the rapid development of high-speed railways. The necessity to take a fresh look at this old problem is based on the fact that in earlier studies it was usually assumed that the load speed is much smaller than the wave velocity in the elastic structure, which the load moves on. Nowadays, this assumption is no longer acceptable, since modern high-speed trains are able to move with a speed that is comparable with the wave velocity in a railway track. The main objective of this thesis is to study the stability of the train-track system at high speeds. The practical aim behind this objective is to develop an accurate and efficient method that would allow for choosing parameters of the train-track system so that the stability is guaranteed at operational train speeds. Having such a method developed, this thesis aims to study the effect of physical parameters of a moving train bogie on stability of the train-track system; analyse the effect of periodical inhomogeneity of the track that is caused by sleepers and rail corrugation on stability of the train-track system; investigate the effect of waves in the track subsoil on stability of the train-track system; To investigate the influence of the physical parameters of a vehicle, a simplified model for a railway track, namely a one-dimensional homogeneous elastically supported Timoshenko beam is used. Since instability depends on the reaction of elastic system, a so-called equivalent stiffness of the Timoshenko beam (a complex-valued function that depends on the frequency of vibrations of the contact point, its velocity and parameters of the beam and foundation) in a moving contact point is introduced and studied. For this development, the most important is the dependence of the equivalent stiffness on the velocity of the contact point. Therefore, this dependence is investigated thoroughly and then compared to that of an Euler-Bernoulli beam. Then, a two-mass oscillator, moving uniformly along such an elastic system is considered. It has been shown that vertical vibrations of this oscillator as it… Advisors/Committee Members: Blaauwendraad, J..

Subjects/Keywords: instability; elastic structure; timoshenko beam; visco-elastic half-space; anomalous doppler waves

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APA (6^th Edition):

Veritchev, S. N. (2002). Instability of a vehicle moving on an elastic structure. (Doctoral Dissertation). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; urn:NBN:nl:ui:24-uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; urn:NBN:nl:ui:24-uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; http://resolver.tudelft.nl/uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e

Chicago Manual of Style (16^th Edition):

Veritchev, S N. “Instability of a vehicle moving on an elastic structure.” 2002. Doctoral Dissertation, Delft University of Technology. Accessed March 07, 2021. http://resolver.tudelft.nl/uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; urn:NBN:nl:ui:24-uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; urn:NBN:nl:ui:24-uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; http://resolver.tudelft.nl/uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e.

MLA Handbook (7^th Edition):

Veritchev, S N. “Instability of a vehicle moving on an elastic structure.” 2002. Web. 07 Mar 2021.

Vancouver:

Veritchev SN. Instability of a vehicle moving on an elastic structure. [Internet] [Doctoral dissertation]. Delft University of Technology; 2002. [cited 2021 Mar 07]. Available from: http://resolver.tudelft.nl/uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; urn:NBN:nl:ui:24-uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; urn:NBN:nl:ui:24-uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; http://resolver.tudelft.nl/uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e.

Council of Science Editors:

Veritchev SN. Instability of a vehicle moving on an elastic structure. [Doctoral Dissertation]. Delft University of Technology; 2002. Available from: http://resolver.tudelft.nl/uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; urn:NBN:nl:ui:24-uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; urn:NBN:nl:ui:24-uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e ; http://resolver.tudelft.nl/uuid:6b66f302-01c6-40e0-8f3d-1f1c4f3c178e

9. Wise, Matthew Geoffrey. Iceberg-keel ploughmarks on the seafloor of Antarctic continental shelves and the North Falkland Basin : implications for palaeo-glaciology.

Degree: PhD, 2018, University of Cambridge

URL: https://doi.org/10.17863/CAM.23428 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744872

► The use of iceberg-keel ploughmarks as proxy indicators of past and present iceberg morphology, keel depth and drift direction has seldom been approached in the… (more)

▼ The use of iceberg-keel ploughmarks as proxy indicators of past and present iceberg morphology, keel depth and drift direction has seldom been approached in the southern hemisphere. Using high-resolution multi-beam swath bathymetry of the mid-shelf Pine Island Trough and outermost Weddell Sea shelf regions of Antarctica, detailed analysis of >13,000 iceberg-keel ploughmarks was undertaken. By considering the draft of icebergs calved from Antarctica today, calculated from detailed satellite altimetric datasets by this work, almost all observed ploughmarks were interpreted to be relict features. In Pine Island Trough, ploughmark planform parameters and cross-sections imply calving of a large number of non-tabular icebergs with v-shaped keels from the palaeo-Pine Island-Thwaites ice stream. Geological evidence of ploughmark form and modern water depth distribution indicates calving-margin thicknesses (949 m) and subaerial ice cliff elevations (102 m) equivalent to the theoretical threshold predicted to trigger ice-cliff structural collapse and calving by marine ice-cliff instability (MICI) processes. Thus, ploughmarks provide the first observational evidence of rapid retreat of the palaeo-Pine Island-Thwaites ice stream, driven by MICI processes commencing ~12.3 cal ka BP. On the Weddell Sea shelf, ploughmark morphologies imply considerable variation in palaeo-iceberg shape and size, most likely reflecting calving from multiple source margins. In turn, an absence of grounded ice on the Weddell Sea shelf and a palaeo-oceanographic regime comparable to today are implied at the time of formation. Analysis of a 3D seismic cube of the Sea Lion Field area of the North Falkland Basin reveals iceberg-keel ploughmarks incised into the modern- and palaeo-seafloor, formed by icebergs of varying shape and size that most-likely calved from the Antarctic Ice Sheet during three past glacial periods (estimated ages ~18 - 26.5 ka BP, ~246 ka BP, ~9.8 Ma BP). Despite illustrating the possibility of iceberg drift into the North Falkland Basin today, the relict ploughmark age implies little risk to any seafloor structures in the area, which might be required for hydrocarbon production. By these analyses, the significance of iceberg-keel ploughmarks as indicators of palaeo-glaciology and palaeo-oceanography at the time of formation is emphasised.

Subjects/Keywords: 551.34; iceberg; bathymetry; marine geophysics; Antarctica; Pine Island Bay; Weddell Sea; Last Glacial Maximum; Glaciology; Oceanography; multi-beam swath bathymetry; North Falkland Basin; Marine Ice-Cliff Instability; ploughmarks

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APA (6^th Edition):

Wise, M. G. (2018). Iceberg-keel ploughmarks on the seafloor of Antarctic continental shelves and the North Falkland Basin : implications for palaeo-glaciology. (Doctoral Dissertation). University of Cambridge. Retrieved from https://doi.org/10.17863/CAM.23428 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744872

Chicago Manual of Style (16^th Edition):

Wise, Matthew Geoffrey. “Iceberg-keel ploughmarks on the seafloor of Antarctic continental shelves and the North Falkland Basin : implications for palaeo-glaciology.” 2018. Doctoral Dissertation, University of Cambridge. Accessed March 07, 2021. https://doi.org/10.17863/CAM.23428 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744872.

MLA Handbook (7^th Edition):

Wise, Matthew Geoffrey. “Iceberg-keel ploughmarks on the seafloor of Antarctic continental shelves and the North Falkland Basin : implications for palaeo-glaciology.” 2018. Web. 07 Mar 2021.

Vancouver:

Wise MG. Iceberg-keel ploughmarks on the seafloor of Antarctic continental shelves and the North Falkland Basin : implications for palaeo-glaciology. [Internet] [Doctoral dissertation]. University of Cambridge; 2018. [cited 2021 Mar 07]. Available from: https://doi.org/10.17863/CAM.23428 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744872.

Council of Science Editors:

Wise MG. Iceberg-keel ploughmarks on the seafloor of Antarctic continental shelves and the North Falkland Basin : implications for palaeo-glaciology. [Doctoral Dissertation]. University of Cambridge; 2018. Available from: https://doi.org/10.17863/CAM.23428 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744872

Université de Lorraine

10. Cavalier, Jordan. Modèles cinétiques et caractérisation expérimentale des fluctuations électrostatiques dans un propulseur à effet Hall : Kinetic modeling and experimental characterization of electrostatic fluctuations in a Hall thruster.

Degree: Docteur es, Physique, 2013, Université de Lorraine

URL: http://www.theses.fr/2013LORR0130

►

L'étude des phénomènes turbulents se développant en sortie du propulseur de Hall est nécessaire pour pouvoir modéliser le transport anormal (par opposition au transport diffusif)… (more)

▼

L'étude des phénomènes turbulents se développant en sortie du propulseur de Hall est nécessaire pour pouvoir modéliser le transport anormal (par opposition au transport diffusif) des électrons à travers les lignes de champ magnétique. Les relations de dispersion de deux instabilités pouvant être responsables de ce transport ont été mesurées à des échelles millimétriques à l'aide du diagnostic de diffusion collective de la lumière. Ce travail de thèse s'attache à en donner une description aussi bien théorique qu'expérimentale, pierre à l'édifice de la compréhension du transport dans le propulseur. Une instabilité se propageant majoritairement dans la direction azimutale du propulseur y est caractérisée comme étant l'instabilité de dérive électronique ExB et un modèle analytique décrivant la fréquence expérimentale y est dérivé et validé. De plus, le manuscrit présente une méthode de déconvolution du signal de la diffusion collective de la fonction d'appareil pour ce mode. Une fois déconvoluées, les relations de dispersion expérimentales peuvent être ajustées par la fréquence du modèle analytique, ce qui permet de mesurer expérimentalement et de manière originale la température et la densité électronique dans le jet d'ions énergétiques du plasma du propulseur. Enfin, la seconde instabilité, se développant autour de la direction axiale du propulseur, est caractérisée comme l'instabilité double faisceau entre les ions simplement et doublement chargés du plasma

The study of turbulent phenomena that grow at the exit plane of the Hall thruster is required to modelize the anomalous transport (in contrast to the diffusion transport) of electrons across the magnetic field lines. The dispersion relations of two instabilities that can be responsible for this transport have been mesured at millimetric scales by mean of the collective light scattering diagnostic. The aim of the thesis is to describe them theoretically as well as experimentally, improving the understanding of the Hall thruster transport. In the thesis, an instability that propagates principally azimuthally is caracterized as the ExB electron drift instability and an analytical model that describes the experimental frequency is derived and validated. In addition, the manuscript presents an original method to unfold the signal of the collective scattering diagnostic from the instrumental function of this mode. Once corrected, the experimental dispersion relations can be adjusted by the frequency given by the analytical model, allowing to measure experimentally and in an original way the electron temperature and density in the energetic ion jet of the Hall thruster plasma. The second instability that is mainly propagating in the axial direction is caracterized as the two-stream instability between the simply and doubly charged ions of the plasma

Advisors/Committee Members: Bonhomme, Gérard (thesis director), Lemoine, Nicolas (thesis director).

Subjects/Keywords: Plasma magnétisé; Propulseur de Hall; Turbulence; Transport électronique anormal; Diffusion collective; Modélisation cinétique; Instabilité de dérive électronique; Instabilité de faisceau; Magnetised plasma; Hall thruster; Turbulence; Anomalous electron transport; Collective scattering; Kinetic model; Electron drift instability; Beam instability; 530.41; 629.475

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APA (6^th Edition):

Cavalier, J. (2013). Modèles cinétiques et caractérisation expérimentale des fluctuations électrostatiques dans un propulseur à effet Hall : Kinetic modeling and experimental characterization of electrostatic fluctuations in a Hall thruster. (Doctoral Dissertation). Université de Lorraine. Retrieved from http://www.theses.fr/2013LORR0130

Chicago Manual of Style (16^th Edition):

Cavalier, Jordan. “Modèles cinétiques et caractérisation expérimentale des fluctuations électrostatiques dans un propulseur à effet Hall : Kinetic modeling and experimental characterization of electrostatic fluctuations in a Hall thruster.” 2013. Doctoral Dissertation, Université de Lorraine. Accessed March 07, 2021. http://www.theses.fr/2013LORR0130.

MLA Handbook (7^th Edition):

Cavalier, Jordan. “Modèles cinétiques et caractérisation expérimentale des fluctuations électrostatiques dans un propulseur à effet Hall : Kinetic modeling and experimental characterization of electrostatic fluctuations in a Hall thruster.” 2013. Web. 07 Mar 2021.

Vancouver:

Cavalier J. Modèles cinétiques et caractérisation expérimentale des fluctuations électrostatiques dans un propulseur à effet Hall : Kinetic modeling and experimental characterization of electrostatic fluctuations in a Hall thruster. [Internet] [Doctoral dissertation]. Université de Lorraine; 2013. [cited 2021 Mar 07]. Available from: http://www.theses.fr/2013LORR0130.

Council of Science Editors:

Cavalier J. Modèles cinétiques et caractérisation expérimentale des fluctuations électrostatiques dans un propulseur à effet Hall : Kinetic modeling and experimental characterization of electrostatic fluctuations in a Hall thruster. [Doctoral Dissertation]. Université de Lorraine; 2013. Available from: http://www.theses.fr/2013LORR0130

11. Heine, Robert Gerd. Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta.

Degree: 2006, Technische Universität Dortmund

URL: http://dx.doi.org/10.17877/DE290R-24

► In einem Elektronenbeschleuniger werden Hochfrequenz-Hohlraumresonatoren zur Beschleunigung der Elektronen und zum Ausgleich des Energieverlustes der Elektronen durch Abstrahlung von Synchrotronstrahlung verwendet. Die höheren Moden dieser… (more)

Subjects/Keywords: Beschleuniger; Kollektive Schwingungen; Strahlinstabilitäten; Hohlraumresonatoren; Modendämpfung; Coupled-Bunch Moden; Particle accelerator; Collective oscillation; Beam instability; Cavity resonator; Mode damping; 530

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Heine, R. G. (2006). Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta. (Doctoral Dissertation). Technische Universität Dortmund. Retrieved from http://dx.doi.org/10.17877/DE290R-24

Chicago Manual of Style (16^th Edition):

Heine, Robert Gerd. “Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta.” 2006. Doctoral Dissertation, Technische Universität Dortmund. Accessed March 07, 2021. http://dx.doi.org/10.17877/DE290R-24.

MLA Handbook (7^th Edition):

Heine, Robert Gerd. “Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta.” 2006. Web. 07 Mar 2021.

Vancouver:

Heine RG. Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta. [Internet] [Doctoral dissertation]. Technische Universität Dortmund; 2006. [cited 2021 Mar 07]. Available from: http://dx.doi.org/10.17877/DE290R-24.

Council of Science Editors:

Heine RG. Untersuchung der Wechselwirkung intensiver Elektronenstrahlen mit höheren Resonatormoden an Delta. [Doctoral Dissertation]. Technische Universität Dortmund; 2006. Available from: http://dx.doi.org/10.17877/DE290R-24

12. McNeil, Zachary. Second-order Analysis of Cable-stayed Bridge Deck Slabs.

Degree: 2013, University of Western Ontario

URL: https://ir.lib.uwo.ca/etd/1621

► Current provisions in CSA S6-06 “Canadian Highway Bridge Design Code” for computing second-order effects in slender concrete beam-columns were derived for columns in buildings, where… (more)

Subjects/Keywords: Instability; cable-stayed bridge decks; slender beam-columns; second-order analysis; flexural rigidity; reinforced concrete; Structural Engineering

…64 Figure 4.5: Deflected shape of a small segment of a beam-column… …x29; Beam elevation; b) first-order rigidity distribution; c) linear-uncracked… …axial compression loads, they must be designed as slender beam-columns since slenderness… …currently provided by Canadian standards. 1.2 SLENDER CONCRETE BEAM-COLUMNS The essential… …response of a slender beam-column can be understood by considering a simple column bent in single…

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APA (6^th Edition):

McNeil, Z. (2013). Second-order Analysis of Cable-stayed Bridge Deck Slabs. (Thesis). University of Western Ontario. Retrieved from https://ir.lib.uwo.ca/etd/1621

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

McNeil, Zachary. “Second-order Analysis of Cable-stayed Bridge Deck Slabs.” 2013. Thesis, University of Western Ontario. Accessed March 07, 2021. https://ir.lib.uwo.ca/etd/1621.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

McNeil, Zachary. “Second-order Analysis of Cable-stayed Bridge Deck Slabs.” 2013. Web. 07 Mar 2021.

Vancouver:

McNeil Z. Second-order Analysis of Cable-stayed Bridge Deck Slabs. [Internet] [Thesis]. University of Western Ontario; 2013. [cited 2021 Mar 07]. Available from: https://ir.lib.uwo.ca/etd/1621.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

McNeil Z. Second-order Analysis of Cable-stayed Bridge Deck Slabs. [Thesis]. University of Western Ontario; 2013. Available from: https://ir.lib.uwo.ca/etd/1621

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of Maryland

13. tadayyon-eslami, tabassom. TEMPERATURE DEPENDENCE OF THE GROWTH MODE DURING HOMOEPITAXY ON PATTERNED GALLIUM ARSENIDE (001); ATOMIC-SCALE MECHANISMS FOR UNSTABLE GROWTH.

Degree: Material Science and Engineering, 2006, University of Maryland

URL: http://hdl.handle.net/1903/4190

► ABSTRACT Title of Document: TEMPERATURE DEPENDENCE OF THE GROWTH MODE DURING HOMOEPITAXY ON PATTERNED GALLIUM ARSENIDE (001); ATOMIC-SCALE MECHANISMS FOR UNSTABLE GROWTH. Tabassom Tadayyon-Eslami, Doctor… (more)

▼ ABSTRACT Title of Document: TEMPERATURE DEPENDENCE OF THE GROWTH MODE DURING HOMOEPITAXY ON PATTERNED GALLIUM ARSENIDE (001); ATOMIC-SCALE MECHANISMS FOR UNSTABLE GROWTH. Tabassom Tadayyon-Eslami, Doctor of Philosophy, 2006 Directed By: Professor Raymond J. Phaneuf, Department of Materials Science and Engineering In this thesis we present an extensive investigation of instability in molecular beam epitaxial growth of GaAs(001) over a range of pattern periods, cell sizes, growth temperature and As2 flux. We find very good agreement with predictions of the continuum models of Sun, Guo and Grant [Phys. Rev. A 40, 6763(1989)] for the growth above ~540ºC and Lai and Das Sarma [Phys. Rev. Lett. 66, 2348 (1991)] for the growth below this temperature. Changing the growth temperature to lower than 540 ºC leads to the formation of ring-like protrusions in the [110] direction around pits patterned on the initial substrate, which are absent for growth at higher temperature. This change in growth mode occurs in the temperature range within in which both pre-roughening transition and surface reconstruction transition (β2(2x4) to c(4x4)) also occur. We rule out the possibility of preroughening and the change in surface reconstruction as the reason for this growth mode change, based on the As2 flux dependence of the growth mode transition temperature. Based on our atomic force microcopy characterization of the surface morphology during early the stage of growth, we propose a physically based model for the growth, which involves a competition between decreased adatom collection efficiency during growth on small terraces and a small anisotropic multiple step Ehrlich-Schwoebel barrier at the pit edge. This provides a physical basis for the nonlinear term in the continuum models proposed by Sun et. al., and Lai and Das Sarma, whose predictions qualitatively describe our experimental observations. Advisors/Committee Members: Phaneuf, Raymond j (advisor).

Subjects/Keywords: Engineering, Materials Science; Physics, Condensed Matter; Engineering, Materials Science; surface science; GaAs; Growth Instability; Patterned Surface; MBE; Molecular Beam Epitaxy; Surface Morphology

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

tadayyon-eslami, t. (2006). TEMPERATURE DEPENDENCE OF THE GROWTH MODE DURING HOMOEPITAXY ON PATTERNED GALLIUM ARSENIDE (001); ATOMIC-SCALE MECHANISMS FOR UNSTABLE GROWTH. (Thesis). University of Maryland. Retrieved from http://hdl.handle.net/1903/4190

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

tadayyon-eslami, tabassom. “TEMPERATURE DEPENDENCE OF THE GROWTH MODE DURING HOMOEPITAXY ON PATTERNED GALLIUM ARSENIDE (001); ATOMIC-SCALE MECHANISMS FOR UNSTABLE GROWTH.” 2006. Thesis, University of Maryland. Accessed March 07, 2021. http://hdl.handle.net/1903/4190.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

tadayyon-eslami, tabassom. “TEMPERATURE DEPENDENCE OF THE GROWTH MODE DURING HOMOEPITAXY ON PATTERNED GALLIUM ARSENIDE (001); ATOMIC-SCALE MECHANISMS FOR UNSTABLE GROWTH.” 2006. Web. 07 Mar 2021.

Vancouver:

tadayyon-eslami t. TEMPERATURE DEPENDENCE OF THE GROWTH MODE DURING HOMOEPITAXY ON PATTERNED GALLIUM ARSENIDE (001); ATOMIC-SCALE MECHANISMS FOR UNSTABLE GROWTH. [Internet] [Thesis]. University of Maryland; 2006. [cited 2021 Mar 07]. Available from: http://hdl.handle.net/1903/4190.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

tadayyon-eslami t. TEMPERATURE DEPENDENCE OF THE GROWTH MODE DURING HOMOEPITAXY ON PATTERNED GALLIUM ARSENIDE (001); ATOMIC-SCALE MECHANISMS FOR UNSTABLE GROWTH. [Thesis]. University of Maryland; 2006. Available from: http://hdl.handle.net/1903/4190

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of Dundee

14. Kokkalis, Efstratios. Fluid dynamic assessments of spiral flow induced by vascular grafts.

Degree: PhD, 2014, University of Dundee

URL: https://discovery.dundee.ac.uk/en/studentTheses/5b96492f-983f-4baa-8e48-20da6939e65c ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633772

► Peripheral vascular grafts are used for the treatment of peripheral arterial disease and arteriovenous grafts for vascular access in end stage renal disease. The development… (more)

▼ Peripheral vascular grafts are used for the treatment of peripheral arterial disease and arteriovenous grafts for vascular access in end stage renal disease. The development of neo-intimal hyperplasia and thrombosis in the distal anastomosis remains the main reason for occlusion in that region. The local haemodynamics produced by a graft in the host vessel is believed to significantly affect endothelial function. Single spiral flow is a normal feature in medium and large sized vessels and it is induced by the anatomical structure and physiological function of the cardiovascular system. Grafts designed to generate a single spiral flow in the distal anastomosis have been introduced in clinical practice and are known as spiral grafts. In this work, spiral peripheral vascular and arteriovenous grafts were compared with conventional grafts using ultrasound and computational methods to identify their haemodynamic differences. Vascular-graft flow phantoms were developed to house the grafts in different surgical configurations. Mimicking components, with appropriate acoustic properties, were chosen to minimise ultrasound beam refraction and distortion. A dual-beam two-dimensional vector Doppler technique was developed to visualise and quantify vortical structures downstream of each graft outflow in the cross-flow direction. Vorticity mapping and measurements of circulation were acquired based on the vector Doppler data. The flow within the vascular-graft models was simulated with computed tomography based image-guided modelling for further understanding of secondary flow motions and comparison with the experimental results. The computational assessments provided a three-dimensional velocity field in the lumen of the models allowing a range of fluid dynamic parameters to be predicted. Single- or double-spiral flow patterns consisting of a dominant and a smaller vortex were detected in the outflow of the spiral grafts. A double- triple- or tetra-spiral flow pattern was found in the outflow of the conventional graft, depending on model configuration and Reynolds number. These multiple-spiral patterns were associated with increased flow stagnation, separation and instability, which are known to be detrimental for endothelial behaviour. Increased in-plane mixing and wall shear stress, which are considered atheroprotective in normal vessels, were found in the outflow of the spiral devices. The results from the experimental approach were in agreement with those from the computational approach. This study applied ultrasound and computational methods to vascular-graft phantoms in order to characterise the flow field induced by spiral and conventional peripheral vascular and arteriovenous grafts. The results suggest that spiral grafts are associated with advanced local haemodynamics that may protect endothelial function and thereby may prevent their outflow anastomosis from neo-intimal hyperplasia and thrombosis. Consequently this work supports the hypothesis that spiral grafts may decrease outflow stenosis and hence improve patency…

Subjects/Keywords: 617.4; Spiral flow; Disturbed flow; Double spiral flow; Dean flow; Multiple spiral flow; Secondary flow motions; Flow stagnation; Flow separation; Flow instability; Peripheral arterial disease; End stage renal disease; Haemodialysis; Haemodynamics; Vascular graft; Prosthetic graft; Bypass graft; Arteriovenous graft; Peripheral vascular graft; AV graft; PV graft; Spiral flow graft; Spiral graft; Flow modification graft; Doppler ultrasound; Colour Doppler; Vector Doppler ultrasound; Flow phantom; Fluid dynamics; Fluid mechanics; Computational fluid dynamics; 31. Polyvinyl alcohol cryogel; Vessel mimic; Vessel mimicking tubing; Tissue mimic; Tissue mimicking material; Blood mimic; Blood mimicking material; Dual beam vector Doppler; Vorticity; Circulation; Velocity; Tangential velocity; Perpendicular velocity; In-plane velocity; Neo-intimal hyperplasia; Thrombosis; Vortical structures; Flow mixing; In-plane mixing; Image guided modelling; Wall shear stress; Helicity; Pressure drop

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Kokkalis, E. (2014). Fluid dynamic assessments of spiral flow induced by vascular grafts. (Doctoral Dissertation). University of Dundee. Retrieved from https://discovery.dundee.ac.uk/en/studentTheses/5b96492f-983f-4baa-8e48-20da6939e65c ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633772

Chicago Manual of Style (16^th Edition):

Kokkalis, Efstratios. “Fluid dynamic assessments of spiral flow induced by vascular grafts.” 2014. Doctoral Dissertation, University of Dundee. Accessed March 07, 2021. https://discovery.dundee.ac.uk/en/studentTheses/5b96492f-983f-4baa-8e48-20da6939e65c ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633772.

MLA Handbook (7^th Edition):

Kokkalis, Efstratios. “Fluid dynamic assessments of spiral flow induced by vascular grafts.” 2014. Web. 07 Mar 2021.

Vancouver:

Kokkalis E. Fluid dynamic assessments of spiral flow induced by vascular grafts. [Internet] [Doctoral dissertation]. University of Dundee; 2014. [cited 2021 Mar 07]. Available from: https://discovery.dundee.ac.uk/en/studentTheses/5b96492f-983f-4baa-8e48-20da6939e65c ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633772.

Council of Science Editors:

Kokkalis E. Fluid dynamic assessments of spiral flow induced by vascular grafts. [Doctoral Dissertation]. University of Dundee; 2014. Available from: https://discovery.dundee.ac.uk/en/studentTheses/5b96492f-983f-4baa-8e48-20da6939e65c ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633772

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Open Access Theses and Dissertations