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- R. Krasny
- 1981

The equations governing periodic vortex sheet roll-up from analytic initial data are desingularized. Linear stability analysis shows that this diminishes the vortex sheet modelâ€™s short wavelength instability. yielding a numerically more tractable set of equations. Computational evidence is presented which indicates that this approximation converges, beyondâ€¦ (More)

- R. Krasny
- 1984

The initial-value problem for perturbations of a flat, constant-strength vortex sheet is linearly ill posed in the sense of Hadamard, owing to Kelvin-Helmholtz instability. Previous numerical studies of this problem have experienced difficulty in converging when the mesh was refined. The present work examines Rosenheadâ€™s point-vortex approximation and seeksâ€¦ (More)

- R. Krasny
- 1993

An axisymmetric vortex-sheet model is applied to simulate an experiment of Didden (1979) in which a moving piston forces fluid from a circular tube, leading to the formation of a vortex ring. Comparison between simulation and experiment indicates that the model captures the basic features of the ring formation process. The computed results support theâ€¦ (More)

- Keith Lindsay, R. Krasny
- 2001

A particle method is presented for computing vortex sheet motion in three-dimensional flow. The particles representing the sheet are advected by a regularized Biotâ€“ Savart integral in which the exact singular kernel is replaced by the Rosenheadâ€“ Moore kernel. New particles are inserted to maintain resolution as the sheet rolls up. The particle velocitiesâ€¦ (More)

- ROBERT KRASNYt, R. Krasny
- 1987

Two vortex-sheet evolution problems arising in aerodynamics are studied numerically. The approach is based on desingularizing the Cauchy principal value integral which defines the sheetâ€™s velocity. Numerical evidence is presented which indicates that the approach converges with respect to refinement in the mesh-size and the smoothing parameter. For ellipticâ€¦ (More)

- R. Krasny
- 1986

In this article we shall review some recent developments for computing vortex sheet roll-up. A vortex sheet is an asymptotic model of a free shear layer in which the transition region between the two fluid streams is approximated by a surface across which the tangential velocity component is discontinuous. A common theme in fluid dynamics is that the vortexâ€¦ (More)

- R. Krasny
- 1991

Chorin's vortex blob method has been proposed as a way to extend vortex sheet motion past the singularity formation time, into the physically important roll-up regime. Basic questions are: 1. Does the vortex blob method converge to an infinite spiral as the smoothing parameter tends to zero? 2. Do vortex blob computations approximate real fluid motion? Thisâ€¦ (More)

- R. Krasny, Monika Nitsche
- 2000

Regularized point-vortex simulations are presented for vortex sheet motion in planar and axisymmetric flow. The sheet forms a vortex pair in the planar case and a vortex ring in the axisymmetric case. Initially the sheet rolls up into a smooth spiral, but irregular small-scale features develop later in time: gaps and folds appear in the spiral core and aâ€¦ (More)

- A J Christlieb, R. Krasny, J. Verboncoeur, J.W. Emhoff, I. D. Boyd
- IEEE Transactions on Plasma Science
- 2006

A common approach to modeling kinetic problems in plasma physics is to represent the plasma as a set of Lagrangian macro-particles which interact through long-range forces. In the well-known particle-in-cell (PIC) method, the particle charges are interpolated to a mesh and the fields are obtained using a fast Poisson solver. The advantage of this approachâ€¦ (More)

Thermal management is important for the efficient operation of organic light-emitting diodes (OLED, or PHOLED) at high brightness, with the device operating temperature influencing both lifetime and performance. We apply a transmission-matrix approach to analytically model the effects of thermal conduction, convection and radiation on OLED temperature. Theâ€¦ (More)