Norbert Flocke
University of Chicago
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Featured researches published by Norbert Flocke.
The Astrophysical Journal | 2013
Sean M. Couch; Carlo Alberto Graziani; Norbert Flocke
Self-gravity computation by multipole expansion is a common approach in problems such as core-collapse and Type Ia supernovae, where single large condensations of mass must be treated. The standard formulation of multipole self-gravity in arbitrary coordinate systems suffers from two significant sources of error, which we correct in the formulation presented in this article. The first source of error is due to the numerical approximation that effectively places grid cell mass at the central point of the cell, then computes the gravitational potential at that point, resulting in a convergence failure of the multipole expansion. We describe a new scheme that avoids this problem by computing gravitational potential at cell faces. The second source of error is due to sub-optimal choice of location for the expansion center, which results in angular power at high multipole l values in the gravitational field, requiring a high—and expensive—value of multipole cutoff l max. By introducing a global measure of angular power in the gravitational field, we show that the optimal coordinate for the expansion is the square-density-weighted mean location. We subject our new multipole self-gravity algorithm, implemented in the FLASH simulation framework, to two rigorous test problems: MacLaurin spheroids for which exact analytic solutions are known, and core-collapse supernovae. We show that key observables of the core-collapse simulations, particularly shock expansion, proto-neutron star motion, and momentum conservation, are extremely sensitive to the accuracy of the multipole gravity, and the accuracy of their computation is greatly improved by our reformulated solver.
Physics of Plasmas | 2017
P. Tzeferacos; A. Rigby; A. F. A. Bott; A. R. Bell; R. Bingham; A. Casner; Fausto Cattaneo; E. Churazov; J. Emig; Norbert Flocke; F. Fiuza; Cary Forest; J. Foster; Carlo Alberto Graziani; J. Katz; M. Koenig; C. K. Li; J. Meinecke; R. D. Petrasso; H.-S. Park; B. A. Remington; J. S. Ross; Dongsu Ryu; D. D. Ryutov; Klaus Weide; T. G. White; Brian Reville; Francesco Miniati; A. A. Schekochihin; D. H. Froula
The universe is permeated by magnetic fields, with strengths ranging from a femtogauss in the voids between the filaments of galaxy clusters to several teragauss in black holes and neutron stars. The standard model behind cosmological magnetic fields is the nonlinear amplification of seed fields via turbulent dynamo to the values observed. We have conceived experiments that aim to demonstrate and study the turbulent dynamo mechanism in the laboratory. Here, we describe the design of these experiments through simulation campaigns using FLASH, a highly capable radiation magnetohydrodynamics code that we have developed, and large-scale three-dimensional simulations on the Mira supercomputer at the Argonne National Laboratory. The simulation results indicate that the experimental platform may be capable of reaching a turbulent plasma state and determining the dynamo amplification. We validate and compare our numerical results with a small subset of experimental data using synthetic diagnostics.
High Energy Density Physics | 2012
P. Tzeferacos; Milad Fatenejad; Norbert Flocke; G. Gregori; D. Q. Lamb; Dongwook Lee; J. Meinecke; Anthony Scopatz; Klaus Weide
High Energy Density Physics | 2013
Milad Fatenejad; A. R. Bell; A. Benuzzi-Mounaix; R. Crowston; R. P. Drake; Norbert Flocke; G. Gregori; M. Koenig; C. M. Krauland; D. Q. Lamb; Dongwook Lee; J.R. Marques; J. Meinecke; Francesco Miniati; C. D. Murphy; H.-S. Park; A. Pelka; A. Ravasio; B. A. Remington; Brian Reville; Anthony Scopatz; P. Tzeferacos; Klaus Weide; N. Woolsey; Rachel Young; R. Yurchak
High Energy Density Physics | 2015
P. Tzeferacos; M. Fatenejad; Norbert Flocke; Carlo Alberto Graziani; G. Gregori; D. Q. Lamb; Dongwook Lee; J. Meinecke; Anthony Scopatz; Klaus Weide
Bulletin of the American Physical Society | 2016
D. Q. Lamb; Norbert Flocke; C. Graziani; P. Tzeferacos; Klaus Weide
Bulletin of the American Physical Society | 2014
P. Tzeferacos; Milad Fatenejad; Norbert Flocke; Carlo Alberto Graziani; G. Gregori; Donald Q. Lamb; Dongwook Lee; J. Meinecke; Anthony Scopatz; Klaus Weide
Bulletin of the American Physical Society | 2014
Donald Q. Lamb; Christopher S. Daley; Anshu Dubey; Milad Fatenejad; Norbert Flocke; Carlo Alberto Graziani; Dongwook Lee; P. Tzeferacos; Klaus Weide
Bulletin of the American Physical Society | 2013
P. Tzeferacos; Christopher S. Daley; Milad Fatenejad; Norbert Flocke; Carlo Alberto Graziani; Donald Q. Lamb; Dongwook Lee; Anthony Scopatz; Klaus Weide; Hugo Doyle; G. Gregori; J. Meinecke; Brian Reville; Francesco Miniati
Bulletin of the American Physical Society | 2013
Norbert Flocke; C. Daley; Milad Fatenejad; P. Tzeferacos; D. Q. Lamb