Pencil Code User Meeting 2011

24-28 October 2011

Observatoire Midi-Pyrénées, Toulouse (France)


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Meeting program

Day Morning session 10:00-12:30 Afternoon session 14:00-18:00
Monday 24 09:30-10:30 Welcome coffee
10:30-11:00 Practical informations
11:00-12:00 Boris Dintrans
14:00-15:00 Axel Brandenburg
15:00-16:00 Michiel Lambrechts
16:00-16:30 Coffee break
16:30-18:00 Code technical discussions
Tuesday 25 09:30-10:00 Welcome coffee
10:00-12:00 Code technical discussions
14:00-16:00 Code technical discussions
16:00-16:30 Coffee break
16:30-18:00 Code technical discussions
Wednesday 26 09:30-10:00 Welcome coffee
10:00-11:00 Chi-kwan Chan
11:00-12:00 Wladimir Lyra
13:00-14:00 Colin McNally
14:30-18:00 Visit to Cité de l'Espace
19:30-22:00 Dinner at Aux saveurs des Paradoux
Thursday 27 09:30-10:00 Welcome coffee
10:00-11:00 Karsten Dittrich
11:00-12:00 Julien Morin
13:00-14:00 Nils Erland L. Haugen
14:00-15:00 Alexander Hubbard
15:00-16:00 Chunlin Tian
16:00-16:30 Coffee break
16:30-18:00 Code technical discussions
Friday 28 09:30-10:00 Welcome coffee
10:00-11:00 Nils Erland L. Haugen
11:00-12:00 Code technical discussions
14:00-16:00 Code technical discussions
16:00-16:30 Coffee break
16:30-18:00 Code technical discussions

Agenda topics

Topics are given in the agenda file: agenda.txt

Talk abstracts

  • Axel Brandenburg (Nordita, Stockholm): Detection of negative effective magnetic pressure instability in turbulence simulations
    We present the first numerical demonstration of the negative effective magnetic pressure instability in direct numerical simulations of stably-stratified, externally-forced, isothermal hydromagnetic turbulence. By the action of this instability, initially uniform horizontal magnetic field forms flux concentrations whose scale is large compared to the turbulent scale. We further show that the magnetic energy of these large-scale structures is only weakly dependent on the magnetic Reynolds number. Our results supports earlier mean-field calculations and analytic work which identified this instability. Applications to the formation of active regions in the Sun are discussed.
    [PDF of the talk]
  • Chi-kwan Chan (Nordita, Stockolm): Making the Pencil Code Run on GPUs: The Rolling Cache Algorithm
    Abstract: The architecture of GPUs is significantly different from CPUs. The pencil code needs to be rewritten from a very fundamental level in order to take advantage of these massive parallel processors. In this talk, I will report the status of rewriting the pencil code from scratch using CUDA C. I will give a basic introduction to GPU programming and describe the (very important) rolling cache algorithm. I will then show some benchmark of the new code.
    [PDF of the talk]
  • Michiel Lambrechts (Lund Observatory, Lund): Pebble Interaction with Gas Giant Cores
    Abstract: The core accretion scenario is the most successful theoretical model for gas-giant formation. However, the initial growth of the core depends on arbitrary assumptions on planetesimal sizes. Growing the solid core with larger-than-km-sized planetesimals, before the gas in the protoplanetary disc is accreted or photo-evaporated away, is problematic due to the long time-scale for run-away accretion, especially in the outer distant regions of the disc. We have studied the dynamics of gas-coupled cm-sized pebbles, gravitationally interacting with larger than km-sized embryo cores. The presence of these pebbles in the gaseous disc influences the growth rate of the gas-giant core. Under favourable conditions, i.e. unity mid-plane dust-to-gas ratio and particle growth to mm and cm sizes, pebble accretion turns out to be significantly faster than run-away accretion of planetesimals. The Pencil Code is used to correctly model the gas drag hydrodynamics.
    [PDF of the talk]
  • Karsten Dittrich (MPIA, Heidelberg): Gravoturbulent Planetesimal Formation with P3M in the Pencil Code
    Abstract: A very attractive way to form the kilometer sized planetesimals in the early solar system is the 'Gravoturbulent Fragmentation' of a cloud of relatively small icy and dusty objects. Using the Pencil Code, Anders Johansen et al. (see papers 2007 (Nature) and 2010 (A&A)) did not reach convergence in the size of the planetesimals. In trying to overcome this resolution problem, we intend to implement another selfgravity solution into the Pencil Code. It should solve the short-range forces in a direct particle-particle calculation.
    [PDF of the talk, movie1.mpg and movie2.avi]
  • Julien Morin (Institut für Astrophysik, University of Göttingen): Star-in-a-box simulations of fully-convective stars
    Abstract: Important observational progress has been made on fully convective stars -- either main sequence M dwarfs or young T Tauri stars -- during the past decade. Further theoretical work is required to model these observational results, in particular differential rotation and dynamo action. I will present star-in-a-box numerical simulations of fully-convective stars carried out with the Pencil Code. The setup and the main differences with the work by Dobler, Stix & Brandenburg (2006) are first detailed. Then the first results obtained on differential rotation and dynamo action will be described.
    [PDF of the talk]
  • Alexander Hubbard (MPIA, Heidelberg): An investigation into turbulence induced dust collisional velocities
    Abstract: Turbulence induced dust collisional velocities are a key piece to understanding dust grain growth in protoplanetary disks. I have inserted inertial dust grains into an artificial cascade, and found an interesting collisional velocity probability distribution.
    [PDF of the talk]
  • Boris Dintrans (IRAP, Toulouse): Thermal excitation of sound in stars
    Abstract: Pulsations are usually excited in stars through two main mechanisms: (i) the kappa-mechanism based on opacity bumps; (ii) the small-scale fluctuations induced by turbulent convection. I will present a new original excitation mechanism based on the interplay between gravity and thermal diffusion at the star surface. The associated instability strips have been computed by the means of a linear stability analysis and growning rates as well as the long-term nonlinear saturation have been confirmed by 1-D and 2-D direct simulations done with the Pencil Code.
    [PDF of the talk]
  • Chunlin Tian (University of Helsinki): Numerical simulations of turbulent magneto-convection in the Star
    Abstract: Based on recently developed gas kinetic BGK-MHD scheme, the interaction between vertical magnetic fields and stellar-type of turbulent convection is parametrically studied. Besides reproduced numerically three types of magneto-convection: ie., intermittent field, flux separation and small scale convection, which have been reported by the other authors, we find the intermediate cases between flux separation and small scale convection are very interesting and can be used to interpret the umbral dots.
    [PDF of the talk]
  • Wladimir Lyra (American Museum of Natural History, New-York): The gas-rich phase: dynamics of the turbulent Solar Nebula
    Abstract: During the first million years of evolution, the forming solar system was embedded in a dense disk-shaped cloud of gas, the Solar Nebula. Due to the presence of magnetization, the disk is susceptible to the magneto-rotational instability (MRI), which brings about turbulence and enables accretion of the gas onto the proto-sun. Turbulence also has a positive effect on the small solids, concentrating them into transient pressure maxima for long enough to achieve gravitational collapse into km-sized bodies. Vortices may exist in the resistive dead zone, which are even more prone to collecting solid material, producing the first cores of giant planets. The architecture of the planetary system formed comes about through migration in the gas disk, N-body interactions, and random walks owing to torques from the turbulent gas, scattering small bodies in their wake. In this talk, I will review the current state of the art on the dynamics of small bodies in the Solar Nebula, including yet unpublished work.
    [PDF of the talk]
  • Colin McNally (American Museum of Natural History, New-York): Getting Pedantic about Kelvin-Helmholtz Instability
    Abstract: We used the Pencil Code to generate a verifiable reference solution to a well posed Kelvin-Helmholtz test problem. As the flow is smooth and subsonic, the Pencil Code is well suited to producing a high accuracy result. We preformed a convergence study from 128^2 to 4096^2, while configuring Pencil Code to so that outputs were made at exact time intervals and so that the grids at successive resolutions overlap on every second point. This allows us to compute a Richardson extrapolation based Grid Convergence Index, and hence rigorously state an uncertainty on the highest resolution result. This result lets us demonstrate the convergence behaviour of other codes to the correct solution to the test problem.
    [PDF of the talk]
  • Nils Erland L. Haugen (SINTEF Energy Research, Trondheim): Development of an incompressible module for the Pencil Code
    Abstract: current state of the incompressible module.
    [PDF of the talk]