Day11-slides - Why are we nesting To minimize errors - Atms...

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1 Atms 502 Numerical Fluid Dynamics Thu., Sep. 28, 2006 9/29/06 Atms 502 - Fall 2006 - Jewett 2 Why are we nesting To minimize errors - Amplitude Phase speed Group velocity Truncation error To better resolve small-scale features … which are damped out if represented by too few grid points (e.g. 4-6 x) To save computation time Nested grids allow higher resolution only where needed 9/29/06 Atms 502 - Fall 2006 - Jewett 3 shaded Why are we nesting 9/29/06 Atms 502 - Fall 2006 - Jewett 4 Irregular grids Instead of regular, structured grids - Grid distortion in response to evolving solution “Dynamic grid adaptation for computational magnetohydrodynamics” - Keppens et al., 2000
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2 Problem 3: nested grid BCs Nested grid : Shown below: grid-1 time step, u1 to u2 Added: nested grid step, refinement factor Grid 1 nest Coarse grid time step t Grid 2 Nested grid step #1 BC t t+ t t t+ t/2 2 t/2 Problem 3: nested grid BCs Nested grid : Shown below: grid-1 time step, u1 to u2 Added: nested grid step, refinement factor Coarse grid time step t t t+ t t t+ t 2 t+ t/2 Nested grid steps: requires time-dependent BC from grid 1 Nested grid step #1 t+ t/2 Nested grid step #2 I n t e r p o l a t e d t/2 t/2 Problem 3: interpolation Interpolation: coarse nested J=4 5 6 7 8 9 10 11 12 36 37 J=1 5 9 13 17 21 25 121 // Nested grid size … nx=121 (both coarse and nested grids) nested grid is 121 nest points wide, and nested grid is (121-1)/4=30 coarse points wide
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This note was uploaded on 10/06/2009 for the course ATMOSPHERI 502 taught by Professor Jewett during the Spring '09 term at University of Illinois at Urbana–Champaign.

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Day11-slides - Why are we nesting To minimize errors - Atms...

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