1 / 23

Pencil Code: multi-purpose and multi-user maintained

Pencil Code: multi-purpose and multi-user maintained. Axel Brandenburg (Nordita, Stockholm) Wolfgang Dobler (Univ. Calgary) and now many more…. (...just google for Pencil Code ). Pencil Code. Started in Sept. 2001 with Wolfgang Dobler High order (6 th order in space, 3 rd order in time)

havily
Download Presentation

Pencil Code: multi-purpose and multi-user maintained

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Pencil Code: multi-purpose and multi-user maintained Axel Brandenburg (Nordita, Stockholm) Wolfgang Dobler (Univ. Calgary) and now many more…. (...just google for Pencil Code)

  2. PencilCode • Started in Sept. 2001 with Wolfgang Dobler • High order (6th order in space, 3rd order in time) • Cache & memory efficient • MPI, can run PacxMPI (across countries!) • Maintained/developed by ~40 people (SVN) • Automatic validation (over night or any time) • Max resolution so far 10243 , 4096 procs • Isotropic turbulence • MHD, passive scl, CR • Stratified layers • Convection, radiation • Shearing box • MRI, dust, interstellar • Self-gravity • Sphere embedded in box • Fully convective stars • geodynamo • Other applications • Homochirality • Spherical coordinates

  3. Pencil formulation • In CRAY days: worked with full chunks f(nx,ny,nz,nvar) • Now, on SGI, nearly 100% cache misses • Instead work with f(nx,nvar), i.e. one nx-pencil • No cache misses, negligible work space, just 2N • Can keep all components of derivative tensors • Communication before sub-timestep • Then evaluate all derivatives, e.g. call curl(f,iA,B) • Vector potential A=f(:,:,:,iAx:iAz), B=B(nx,3)

  4. Switch modules • magnetic or nomagnetic (e.g. just hydro) • hydro or nohydro (e.g. kinematic dynamo) • density or nodensity (burgulence) • entropy or noentropy (e.g. isothermal) • radiation or noradiation (solar convection, discs) • dustvelocity or nodustvelocity (planetesimals) • Coagulation, reaction equations • Chemistry (reaction-diffusion-advection equations) Other physics modules: MHD, radiation, partial ionization, chemical reactions, selfgravity

  5. High-order schemes • Alternative to spectral or compact schemes • Efficiently parallelized, no transpose necessary • No restriction on boundary conditions • Curvilinear coordinates possible (except for singularities) • 6th order central differences in space • Non-conservative scheme • Allows use of logarithmic density and entropy • Copes well with strong stratification and temperature contrasts

  6. (i) High-order spatial schemes Main advantage: low phase errors Near boundaries: x x x x x x x x x ghost zones interior points

  7. Wavenumber characteristics

  8. Higher order – less viscosity

  9. Less viscosity – also in shocks

  10. (ii) High-order temporal schemes Main advantage: low amplitude errors 2N-RK3 scheme (Williamson 1980) 2nd order 3rd order 1st order

  11. Shock tube test

  12. Increase in # of auto tests

  13. Evolution of code size User meetings: 2005 Copenhagen 2006 Copenhagen 2007 Stockholm 2008 Leiden 2009 Heidelberg

  14. Pencil Code check-ins

  15. Vector potential • B=curlA, advantage: divB=0 • J=curlB=curl(curlA) =curl2A • Not a disadvantage: consider Alfven waves B-formulation A-formulation 2nd der once is better than 1st der twice!

  16. Comparison of A and B methods

  17. Faster and bigger machines

  18. 256 processor run at 10243

  19. Hyperviscous, Smagorinsky, normal height of bottleneck increased Haugen & Brandenburg (PRE, astro-ph/0402301) onset of bottleneck at same position Inertial range unaffected by artificial diffusion

  20. Online data reduction and visualization non-helically forced turbulence

  21. Scalars on periphery of the box

  22. MRI turbulenceMRI = magnetorotational instability 2563 w/o hypervisc. t = 600 = 20 orbits 5123 w/o hypervisc. Dt = 60 = 2 orbits

  23. Vorticity and Density See poster by Tobi Heinemann on density wave excitation!

More Related