Read Books Online and Download eBooks, EPub, PDF, Mobi, Kindle, Text Full Free.
Advances In Quasilinear Gyrokinetic Modeling Of Turbulent Transport
Download Advances In Quasilinear Gyrokinetic Modeling Of Turbulent Transport full books in PDF, epub, and Kindle. Read online Advances In Quasilinear Gyrokinetic Modeling Of Turbulent Transport ebook anywhere anytime directly on your device. Fast Download speed and no annoying ads. We cannot guarantee that every ebooks is available!
Book Synopsis Advances in Quasilinear Gyrokinetic Modeling of Turbulent Transport by : Cole Darin Stephens
Download or read book Advances in Quasilinear Gyrokinetic Modeling of Turbulent Transport written by Cole Darin Stephens and published by . This book was released on 2021 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt: The quest to harness fusion energy requires the successful modeling of plasma turbulence and transport in magnetic confinement devices. For such modeling, the requisite length and time scales span many orders of magnitude. Integrated modeling approaches are constructed to account for the wide range of physics involved in turbulent transport by coupling separate physical models together. The primary physical models used in this work are kinetic and designed to simulate microturbulence on the smallest scales associated with turbulent transport. However, high precision nonlinear kinetic simulations often cannot be easily coupled to integrated modeling suites due to the extreme computational costs that would be involved. Model reduction which drastically reduces the computational complexity of the problem is therefore necessary. One must of course ensure that the reduced model does not severely diminish the accuracy of the calculation; the model reduction itself must be founded on more exact computational approaches as well as fundamental theoretical principles. One of the most successful approaches in model reduction is quasilinear gyrokinetics. There are two fundamental assumptions for the quasilinear model examined in this work. First, the three adiabatic invariants (the magnetic moment, the longitudinal invariant, and the poloidal flux) must be appropriately conserved and their associated single charged particle motions (the gyromotion, the bounce-transit motion, and the toroidal drift motion) must be characterized accurately. Second, the quasilinear approximation must hold such that the coherent linear response is adequate enough to compute the quasilinear fluxes without full calculation of the nonlinear physics. The particular model used, QuaLiKiz, has been proven successful in reproducing local gyrokinetic fluxes in the tokamak core while remaining computationally tractable. There are three primary goals of this dissertation project. The first is to examine the fundamental physics underlying gyrokinetic and reduced model approaches at the single charged particle scale. To achieve this goal, we examine the assumption of magnetic moment invariance in a wide variety of electromagnetic fields. We successfully identify the dimensionless parameters that determine magnetic moment conservation in each scenario and then proceed to quantify the degree to which magnetic moment conservation is broken. In doing so, we confirm that the magnetic moment is sufficiently conserved for a wide range of regimes relevant to tokamak plasmas. In addition, we derive new analytic formulas for quantities associated with bounce-transit motion in circular tokamak fields. We compare these new, more exact calculations to approximations commonly used in reduced models (including QuaLiKiz) and determine the conditions such that the approximations break down. We then also confirm that the approximations are valid in the tokamak core for conventional, large aspect ratio devices. The second goal of this dissertation project is to rederive and compile the model equations for QuaLiKiz from first principles. Over the years of QuaLiKiz's development, there has never been a complete manuscript that sketches the derivation of QuaLiKiz from start to finish. The lack of such a document makes it difficult to extend the physics of QuaLiKiz to new parameter regimes of interest. Various possible extensions such as including electromagnetic effects or more realistic tokamak geometries require the adjustment of several different assumptions that would affect the derivation in key ways. As such, correct implementations of new physics would require an existing derivation as a reference point lest the implementation be handled in an incoherent fashion. In addition, a step-by-step outline of how each assumption of QuaLiKiz affects the derivation can be helpful in determining which assumptions can be relaxed for a more accurate model. The successful completion of this derivation, included in this dissertation, will be immensely useful for future QuaLiKiz improvement and validation. With the derivation in hand, we proceed to the third goal of this project: improving the collisional model of QuaLiKiz. Collisions play an essential role in characterizing the transport associated with trapped electron modes. It has become evident in recent studies that the collisional model in QuaLiKiz requires improvement; in integrated modeling, the imprecise treatment of collisional trapped electron modes leads to incorrect density profile predictions near the tokamak core for highly collisional regimes. We revisit the collision model implemented in QuaLiKiz and use the more exact gyrokinetic code GENE (Gyrokinetic Electromagnetic Numerical Experiment) to make improvements to QuaLiKiz's collision operator. We then use the new version of QuaLiKiz in integrated modeling to compare density profiles predicted by the old and new collision operators. We confirm that the new collision operator leads to density profiles that more accurately match the experimental profiles.
Book Synopsis Modeling the Turbulent Momentum Transport in Tokamak Plasmas by : Pierre Cottier
Download or read book Modeling the Turbulent Momentum Transport in Tokamak Plasmas written by Pierre Cottier and published by LAP Lambert Academic Publishing. This book was released on 2014-04-01 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt: The magnetic confinement in tokamaks is for now the most advanced way towards energy production by nuclear fusion. Both theoretical and experimental studies showed that rotation generation can increase its performance by reducing the turbulent transport in tokamak plasmas. The rotation influence on the heat and particle fluxes is studied along with the angular momentum transport with the quasi-linear gyro-kinetic eigenvalue code QuaLiKiz. For this purpose, the QuaLiKiz code is modified in order to take the plasma rotation into account and compute the angular momentum flux. It is shown that QuaLiKiz framework is able to correctly predict the angular momentum flux including the ExB shear induced residual stress as well as the influence of rotation on the heat and particle fluxes. The different contributions to the turbulent momentum flux are studied and successfully compared against both non-linear gyro-kinetic simulations and experimental data.
Book Synopsis Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas by :
Download or read book Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas written by and published by . This book was released on 2011 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt: The three-year project GPS-TTBP resulted in over 152 publications and 135 presentations. This summary focuses on the scientific progress made by the project team. A major focus of the project was on the physics intrinsic rotation in tokamaks. Progress included the first ever flux driven study of net intrinsic spin-up, mediated by boundary effects (in collaboration with CPES), detailed studies of the microphysics origins of the Rice scaling, comparative studies of symmetry breaking mechanisms, a pioneering study of intrinsic torque driven by trapped electron modes, and studies of intrinsic rotation generation as a thermodynamic engine. Validation studies were performed with C-Mod, DIII-D and CSDX. This work resulted in very successful completion of the FY2010 Theory Milestone Activity for OFES, and several prominent papers of the 2008 and 2010 IAEA Conferences. A second major focus was on the relation between zonal flow formation and transport non-locality. This culminated in the discovery of the ExB staircase - a conceptually new phenomenon. This also makes useful interdisciplinary contact with the physics of the PV staircase, well-known in oceans and atmospheres. A third topic where progress was made was in the simulation and theory of turbulence spreading. This work, now well cited, is important for understanding the dynamics of non-locality in turbulent transport. Progress was made in studies of conjectured non-diffusive transport in trapped electron turbulence. Pioneering studies of ITB formation, coupling to intrinsic rotation and hysteresis were completed. These results may be especially significant for future ITER operation. All told, the physics per dollar performance of this project was quite good. The intense focus was beneficial and SciDAC resources were essential to its success.
Book Synopsis Advances In Turbulence by : Stanley Corrsin
Download or read book Advances In Turbulence written by Stanley Corrsin and published by CRC Press. This book was released on 1988-10-01 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt: Based on a symposium held in June 1986 in Minneapolis, USA, this volume surveys current information on turbulence measurement and modelling, computational fluid mechanics, vortex flow and physical modelling, cavitation and two-phase flow, bluff body flow and fluid structure interaction.
Book Synopsis Modeling of Turbulent Transport in the Surface Layer by : George Louis Smith
Download or read book Modeling of Turbulent Transport in the Surface Layer written by George Louis Smith and published by . This book was released on 1973 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Advances in the Simulation of Toroidal Gyro Landau Fluid Model Turbulence by :
Download or read book Advances in the Simulation of Toroidal Gyro Landau Fluid Model Turbulence written by and published by . This book was released on 1994 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: The gyro-Landau fluid (GLF) model equations for toroidal geometry have been recently applied to the study ion temperature gradient (ITG) mode turbulence using the 3D nonlinear ballooning mode representation (BMR). The present paper extends this work by treating some unresolved issues conceming ITG turbulence with adiabatic electrons. Although eddies are highly elongated in the radial direction long time radial correlation lengths are short and comparable to poloidal lengths. Although transport at vanishing shear is not particularly large, transport at reverse global shear, is significantly less. Electrostatic transport at moderate shear is not much effected by inclusion of local shear and average favorable curvature. Transport is suppressed when critical E x B rotational shear is comparable to the maximum linear growth rate with only a weak dependence on magnetic shear. Self consistent turbulent transport of toroidal momentum can result in a transport bifurcation at suffciently large r/(Rq). However the main thrust of the new formulation in the paper deals with advances in the development of finite beta GLF models with trapped electron and BMR numerical methods for treating the fast parallel field motion of the untrapped electrons.
Book Synopsis Measurements and Modeling of Turbulent Transport in the HSX Stellarator by : Walter Allen Guttenfelder
Download or read book Measurements and Modeling of Turbulent Transport in the HSX Stellarator written by Walter Allen Guttenfelder and published by . This book was released on 2008 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Advanced Approaches in Turbulence by : Paul Durbin
Download or read book Advanced Approaches in Turbulence written by Paul Durbin and published by Elsevier. This book was released on 2021-07-30 with total page 552 pages. Available in PDF, EPUB and Kindle. Book excerpt: Front Cover -- Advanced Approaches in Turbulence -- Copyright -- Contents -- Contributors -- Preface -- 1 Basics of turbulence -- 1.1 Introduction -- 1.2 Eddy diffusion -- 1.3 Scales of turbulence -- 1.3.1 Isotropic decay -- 1.3.2 Stretching and diffusion of vorticity -- 1.4 Spectral equations -- 1.4.1 Isotropic turbulence -- 1.4.2 Shear and streaks -- 1.5 Averaged equations -- 1.5.1 Jets -- 1.5.2 Boundary layer -- 1.6 The form of turbulence models -- 1.6.1 Two equation models -- 1.6.2 Reynolds stress transport -- 1.7 Conclusion -- References -- 2 Direct numerical and large-eddy simulation of complex turbulent flows -- 2.1 Introduction -- 2.2 Error as a function of scale -- 2.2.1 Modified wavenumber -- 2.2.2 Nonlinear sources of error -- 2.2.3 Time advancement error as a function of scale -- 2.3 Analysis of numerical errors in large-eddy simulation using statistical closure theory -- 2.3.1 EDQNM closure -- 2.3.2 EDQNM-LES and the inclusion of numerical error -- 2.3.3 EDQNM model -- 2.3.4 Relative magnitudes of error -- 2.4 Simulations in complex geometries -- 2.4.1 Decay of isotropic turbulence -- 2.4.2 Gas turbine combustor -- 2.5 Simulating the flow around moving bodies -- 2.5.1 Fluid phase -- 2.5.2 Solid phase -- 2.5.3 The effects of interpolation -- 2.5.4 Particles in a turbulent channel -- 2.6 What is a 'canonical' flow? -- 2.6.1 Jets in crossflow -- 2.6.2 DNS of turbulent channel flow over random rough surfaces -- 2.7 The analysis of 'big data' -- 2.7.1 DMD of large datasets and numerical error -- 2.7.2 Analysis of wall-pressure fluctuation sources in turbulent channel flow -- 2.8 Bridging the Reynolds number divide -- 2.9 Concluding remarks -- Acknowledgments -- References -- 3 Large-eddy simulations -- 3.1 Introduction -- 3.1.1 Motivation -- 3.2 Governing equations -- 3.2.1 Filtering.
Book Synopsis Gyrokinetic Simulation of Pedestal Turbulence Using GENE by : Xing Liu (Ph. D. in physics)
Download or read book Gyrokinetic Simulation of Pedestal Turbulence Using GENE written by Xing Liu (Ph. D. in physics) and published by . This book was released on 2018 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present here a study based on gyrokinetic simulations (using GENE) to model turbulence in the pedestals on several well-diagnosed shots: two H-modes on DIII-D and one I-mode on Alcator C-Mod. We match frequencies, power balance, and other transport characteristics in multiple channels with the observations. The observed quasi-coherent fluctuations on the DIII-D shots are identified as Micro Tearing Modes (MTM). The MTMs match frequency and power balance (together with heat loss from Electron Temperature Gradient (ETG) driven turbulence), and cause low transport in the particle, ion heat and impurity particle transport channels – consistent with observed inter-ELM evolution of ion and electron temperature, electron and impurity density or transport analysis of those channels. We find the Weakly Coherent Mode on C-Mod I-mode to be an electrostatic Ion Temperature Gradient/Impurity density gradient (ITG/Impurity) driven mode. The ITG/Impurity mode match frequency and the impurity confinement time observed on the I-mode. Electron scale turbulence, ETG, provides energy transport to match power balance. A novel concept called the transport fingerprints is used throughout this work, which greatly assists in identifying the instabilities. This work shows that the concept should be very valuable in many future investigations of pedestal turbulence.
Book Synopsis Progress in Gyrokinetic Simulations of Toroidal ITG Turbulence by :
Download or read book Progress in Gyrokinetic Simulations of Toroidal ITG Turbulence written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The 3-D nonlinear toroidal gyrokinetic simulation code PG3EQ is used to study toroidal ion temperature gradient (ITG) driven turbulence--a key cause of the anomalous transport that limits tokamak plasma performance. Systematic studies of the dependence of ion thermal transport on various parameters and effects are presented, including dependence on {rvec E} x {rvec B} and toroidal velocity shear, sensitivity to the force balance in simulations with radial temperature gradient variation, and the dependences on magnetic shear and ion temperature gradient.
Book Synopsis New Developments in Nuclear Fusion Research by : Y. Nakamura
Download or read book New Developments in Nuclear Fusion Research written by Y. Nakamura and published by Nova Publishers. This book was released on 2006 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nuclear fusion is a process in which two nuclei join, forming a larger nucleus and releasing or absorbing energy. With some exceptions, nuclei lighter than iron release energy when they fuse, while heavier nuclei absorb energy; this is because iron has the largest binding energy. Nuclear fusion of light elements is the energy source which causes stars to shine and hydrogen bombs to explode. Nuclear fusion of heavy elements is part of the process that triggers supernovae. Nuclear fusion as an energy source has several advantages: It is vast, new source of energy; Fuels are plentiful; Inherently safe since any malfunction results in a rapid shutdown; No atmospheric pollution leading to acid rain or "greenhouse" effect; Radioactivity of the reactor structure, caused by the neutrons, decays rapidly and can be minimised by careful selection of low-activation materials. Provision for geological time-span disposal is not needed. This book brings together leading research in this field which will play a major role in the 21st century.
Book Synopsis Progress in the Modelling of Turbulent Transport by : Brian Edward Launder
Download or read book Progress in the Modelling of Turbulent Transport written by Brian Edward Launder and published by . This book was released on 1975 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Gyrokinetic Studies of Turbulence in Steep Gradient Region by : Taik Soo Hahm
Download or read book Gyrokinetic Studies of Turbulence in Steep Gradient Region written by Taik Soo Hahm and published by . This book was released on 2004 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Gyrokinetic Simulations of ETG and ITG Turbulence by : D. Shumaker
Download or read book Gyrokinetic Simulations of ETG and ITG Turbulence written by D. Shumaker and published by . This book was released on 2006 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: Published gyrokinetic continuum-code simulations indicated levels of the electron thermal conductivity {chi}{sub e} due to electron-temperature-gradient (ETG) turbulence large enough to be significant in some tokamaks, while subsequent global particle-in-cell (PIC) simulations gave significantly lower values. We have carried out an investigation of this discrepancy. We have reproduced the key features of the aforementioned PIC simulations using the flux-tube gyrokinetic PIC code, PG3EQ, thereby eliminating global effects and as the cause of the discrepancy. We show that the late-time low-transport state in both of these sets of PIC simulations is a result of discrete particle noise, which is a numerical artifact. Thus, the low value of {chi}{sub e} along with conclusions about anomalous transport drawn from these particular PIC simulations are unjustified. In our attempts to benchmark PIC and continuum codes for ETG turbulence at the plasma parameters used above, both produce very large intermittent transport. We have therefore undertaken benchmarks at an alternate reference point, magnetic shear s=0.1 instead of s=0.796, and have found that PIC and continuum codes reproduce the same transport levels. Scans in the magnetic shear show an abrupt transition to a high-{chi}{sub e} state as the shear is increased above s=0.4. When nonadiabatic ions are used, this abrupt transition is absent, and {chi}{sub e} increases gradually reaching values consistent with transport analyses of DIII-D, JET, and JT60-U discharges. New results on the balances of zonal-flow driving and damping terms in late-time quasi-steady ITG turbulence and on real-geometry gyrokinetic simulations of shaped DIII-D discharges are also reported.
Book Synopsis Gyrokinetics Simulation of Energetic Particle Turbulence and Transport by :
Download or read book Gyrokinetics Simulation of Energetic Particle Turbulence and Transport written by and published by . This book was released on 2011 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: Progress in research during this year elucidated the physics of precession resonance and its interaction with radial scattering to form phase space density granulations. Momentum theorems for drift wave-zonal flow systems involving precession resonance were derived. These are directly generalizable to energetic particle modes. A novel nonlinear, subcritical growth mechanism was identified, which has now been verified by simulation. These results strengthen the foundation of our understanding of transport in burning plasmas.
Book Synopsis Unified Framework for Development of Pressure-Strain Correlation Turbulent Transport and Sub-Grid Stress Closure Models for Turbulence Simulation by :
Download or read book Unified Framework for Development of Pressure-Strain Correlation Turbulent Transport and Sub-Grid Stress Closure Models for Turbulence Simulation written by and published by . This book was released on 2003 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Study of turbulence is of vital scientific, military and economic interest. Advances in several areas of external aerodynamics and internal combustor flows of interest to Air Force hinge on our ability to clearly understand and adequately predict the effects of turbulence. At the current time, however, there exists a substantial gap between our knowledge of the physics of turbulence phenomenon and the physics that is incorporated into turbulence models, especially subgrid closures. The disciplines of turbulence theory/analysis (e.g., rapid distortion theory, spectral closure models), high-order turbulence modeling (e.g., second-moment closures, structure-based models and realizability constraints) and turbulence simulation (DNS- direct numerical simulations, and LES- large eddy simulations) are evolving independently with very little cross fertilization of ideas. For example, the currently popular LES subgrid closures (e.g., Smagorinsky, dynamic Smagorinsky) are algebraic in nature; completely insensitive to extra rates of strain such as rotation, curvature, and buoyancy and, further, may not even be realizable. These major deficiencies in the LES-SGS modeling are tolerated despite the fact that, in higher order closures, these physical effects and mathematical constraints have long been represented adequately. Further, we would like to point out that the very premise of detached-eddy simulation (DES) approach - that is seen as the practical computational tool for turbulence - is erroneous. This is due to the fact that inhomogeneous spatial filtering is inevitable in this method, and yet the governing equations ignore the effects that necessarily arise with inhomogeneous filtering of the velocity field.
Book Synopsis Improved Modeling of Turbulent Transport by : Debasmita Samaddar
Download or read book Improved Modeling of Turbulent Transport written by Debasmita Samaddar and published by . This book was released on 2010 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Turbulence and turbulent transport are ubiquitous in nature and are of fundamental importance in everything from the spread of pollution to confinement in fusion plasmas. In order to study this, turbulence models need to be as realistic as possible and one must also be able to evolve the turbulence and the profiles of the quantities of interest on transport (long) time scales. Improving turbulence simulations by the introduction of new techniques forms the basis of this research. One part of this work involved improving the performance of a ID transport model by the addition of noise. On a more fundamental level, studying long time dynamics for turbulence simulations is very difficult even with the fastest computers available now or in the near future. To help overcome this difficulty, a new way of simulating turbulence has been presented, namely parallelizing in time. Time parallelization of a fully developed turbulent system is a new application. parallelizing the space domain to computationally solve partial differential equations has been extensively used and is one of the most common forms of parallelization. In contrast, the Parareal Algorithm parallelizes the time domain and has been found to significantly reduce the computational wall time in many simpler systems. Despite its success in other less complex problems, it has not yet been successfully applied to a turbulent system (to the best of our knowledge). If efficiently applied, this algorithm will allow study of the turbulent transport dynamics on transport time scales - something that has heretofore been very difficult. In this work, the results of applying the Parareal Algorithm to simulations of drift wave turbulence in slab geometry in which the relative dominance of the polarization and E x B nonlinearities are tuned artificially, are presented. These turbulent systems are in many ways similar to neutral fluid turbulence models, so success of the Parareal scheme in them expands the prospect of a broader range of application to many other turbulent problems. This thesis also presents the results of a modification to the algorithm. A model to study and predict the parameters governing the convergence of the scheme is also explored"--Leaf iii.
