d94e71a63ff4c3d19e2d1fba15bb4af5.ppt

- Количество слайдов: 27

Computational Astrophysics: Research to Teaching and Beyond Adam Frank University of Rochester

A Cast of Many Astro. BEAR MHD / Clumpy Flows Sorin Mitran UNC *Andrew Cunningham (UR, UC Berkeley, LLNL) Alexei Poludnenko (UR, NRL) Kris Yirak (UR Grad Student) Jonathan Carroll (UR Grad Student) Thanks to: NSF, DOE, NASA, UR Laboratory for Laser Energetics

space Simulations: Numerical Experiments with Diff. Eq & PDEs Initial conditions Boundary conditions space tim e

3 rd Age of Simulations: n 1 st Age: 1 -D calculations with computers – CDC 7600, etc n 2 nd Age: Moderate rez 2 -D calculations – Supercomputers: Cray, etc n 3 rd Age: High rez Multi-D, Multi-physics calc. – Grid Computing, Massively Parallel, Clusters n n We are talking about “Virtual Reality” on a scientific level. Sim. data sets now as “rich” as real data sets – Petabytes/flops 1015 = one quadrillion bytes. n Not just simulation but “Cyberscience” – Integrate IT on all levels of science practice

History: Research Simulation Shocked Clumps Woodward 1976 • Astrophysical environments very heterogeneous. • Winds, Blastwaves & ISM are all “clumpy” • Interaction of 1 -clump with passing wind is a well studied problem. Critical Parameter tcc: Cloud Crushing Time

Frontiers of Algorithm Development n Adaptive Mesh Refinement – code automatically places grid cells where needed. n Multi-physics – code simulates many physical processes simultaneously – Magnetic Fields, gravity, radiation transport, chemistry, ionization dynamics.

UR Computational Group: Astro. BEAR Multiyear, Multi grad-student effort Began 2002 Now on 4 th generation of student

Simulation in Age of Cyber. Science How to maintain 106 line code base across N years M revisions K Student Generations Static documentation doesn’t work. Our solution: Wiki, selfcompiling documentation

Adaptive Mesh Refinement AMR • Different AMR Methods: Grid based regridding Cell based regridding • University of Rochester Code Astro. BEAR: grid • Hierarchy of Grids • Require Prolongation/Restriction Operators Carry data from one grid level to another • Prolongation (Corse to Fine) • Restriction (Fine to Corse) R. Deiterding

Pre-Planetary Nebula: CRL 618 “Explosion” from dying Solar-type star Mach 10 radiatively cooled bullet AMR grid generation in the system

AMR MHD Div B = 0 n n Hydro: Need conservative prolongation/ restriction operators. MHD: Maintain solenoidal condition. Need divergence free operators on “staggered mesh”. Cunningham et al 2007

Results I MHD Shocked Clump “Standard” Test M = 10 h= nc/nw = 10 b=4

Many Clumps: Radiative MHD Shocks in Heterogeneous Media Cunningham et al 2007 M = 10 h= nc/nw = 10 b = 10

How AMR Changes Game: Resolution and Convergence formally defined as approach to known analytic solution. For complex non-linear problem these rarely exist Define convergence as change relative to highest resolution simulation possible. • For adiabatic shock clump convergence appears at N = 120 cells/Rc

Resolution and Convergence Radiative Clumps Radiative cooling allows post shock flows to collapse – but how far? AMR allows us to run highest resolution radiative clump simulations to date: N = 1500/Rc Highest resolution radiative clump simulations to date: N ~ 1500/R c

Resolution and Convergence Radiative Clumps Radiative cooling allows post shock flows to collapse – but how far? Increases in resolution show qualitatively new behaviors as Dx < lcrit

Resolution and Convergence Radiative Clumps What measures, metrics can we trust at given resolution? http: //www. pas. roch ester. edu/~yirak/for adam/vorticities. png

Radiative MHD Clumps with Self-consistent Fields

How many MHD-AMR Codes ØNot many ØAstro. BEAR ØFlash ØENZO ØOrion ØAMR VAC ØAthena

Computation in Teaching My adventure in E-ed-biz 2000 NSF Career Award Astro. Flow – Simulation outreach tool Planetarium asks to buy copy (? !? ) Create Truth-N-Beauty LLC with UR E-education digital media company Produce simulation based modules for: Mc. Graw-Hill, Prentice Hall etc

Second Avenue Software The e-biz goes it alone 2006 Truth-N-Beauty becomes 2 nd Ave

What we built Celestial Sphere Phases of Moon Seasons Solar System Builder Planetary Atmospheres

Going Beyond Teaching Outreach: Use partners in new media to create interactives for websites. Discover/Astronomy/Sci. American “Serious Games” – twitch games with a science theme.

Going Beyond Teaching

Star Formation

Conclusions n Computation n Teaching by Simulation – Advanced AMR/multi-physics codes allow new era of simulation – “Weather vs. Climate”: what to do with Petaflops/bytes – New opportunities if done well (graphics, pedagogy) – New opportunities outside of classroom.