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Roadrunner Open Science: important strides taken

Open Science (unclassified work) on Roadrunner, the world's first petaflop/s computer, resulted in significant breakthroughs in materials, astronomy, and laser plasma science. Presented here are images, movies, and brief explanations of the exciting new work done on Roadrunner by seven Principal Investigators (P.I.s):

 

Laser Plasma Interaction using the VPIC (particle-in-cell) code, Lin Yin, P.I.

Fusion experiments in the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory are scheduled to begin in 2010. In these, over a million joules of laser energy are focused within a gas-filled hohlraum (a container for radiation experiments). We are studying the physics of onset and saturation of stimulated Raman scattering (SRS) in the fundamental building block of a NIF laser beam, a single laser speckle. Unlike the linear growth of SRS, the nonlinear physics was not well understood. This simulation shows isosurfaces of the electrostatic fields associated with RS bursts; the wave fronts exhibit bending or “bowing,” arising from nonlinear electron trapping, as well as self-focusing, which breaks up the phase fronts. This study is only possible on Roadrunner, where at-scale kinetic simulations of laser-plasma interaction in 3D at realistic laser speckle and multispeckle scales can be done at unprecedented size, speed, and fidelity.

Additional resources: Advances in Kinetic Plasma Simulation with VPIC and Roadrunner SciDAC Conference, 2009

Parallel Replica Nanowires using the ParRep-AMD code, Arthur Voter, P.I.

 

We can now begin to understand how materials behave down to the nanometer scale, where the motion of even a single atom can sometimes change mechanical or electrical properties. We are simulating the stretching process of metallic nanowires. Using Roadrunner, we can slow down the simulation to see exactly what is happening during the stretching, many times more than previously possible, to observe the formation of networks of stacking faults (highlighted in red) between atoms.

 

 

Magnetic Reconnection using the VPIC (particle-in-cell) code, Bill Daughton, P.I.

 

Magnetic reconnection is a basic plasma process involving the rapid conversion of magnetic field energy into various forms of plasma kinetic energy. These types of dynamical changes are conveniently viewed in terms of the breaking and reconnection of magnetic field lines, thus explaining the origin of the term magnetic reconnection. The process is thought to play an important role in solar ares (a source of solar energetic particles), geomagnetic substorms, magnetic fusion devices, and a wide variety of astrophysical problems. This simulation features highly elongated electron current layers that are unstable to flux rope formation over a wide range of angles. These plasma instabilities cause the sheets to break into filaments as illustrated by an isosurface of the current density colored by the plasma density.

 

HIV phylogenetics using the ML code, Tanmoy Bhattcharya P.I.

movie (.mov)

This colored tree is a large set of HIV sequences collected to find properties of HIV right after transmission. The underlying computational problem is to take all of this sequence data (here 10442 strings of ~3873 nucleotides) and find a model of how the virus evolved over time. When a node on the tree is near another node, that means that one virus is similar to another virus. When nodes are separated by a number of intermediate nodes (white), that means that the model would estimate there were parent, grandparent, etc. viruses that lived (and possibly died) along the way to those two forms. Roadrunner found an evolutionary model where the sequences of one patient rarely overlap with sequences of another patient. One important goal is to identify possible vaccine target areas.

Roadrunner Universe using the MC3 code, Salman Habib, P.I.

Roadrunner Universe simulation

Dark matter and dark energy are the dominant components of the Universe. From modern sky surveys we have a comprehensive picture of the evolution history of the Universe and its fundamental make-up: 23% dark matter (a large fraction of which is in localized clumps called halos), and 73% in a smooth “dark energy” component. The Roadrunner Universe project is creating the largest-ever high-resolution simulations of the distribution of matter in the Universe. A comprehensive database of all the Roadrunner Universe simulations will become an essential component of Dark Universe science for years to come. Shown is the velocity field of the dark matter halos from one of the Roadrunner cosmology simulations. The simulation tracked almost 70 billion particles. Due to gravity, the particles form bound structures, the halos. Each halo in this graph consists of at least 10 particles and is shown as an arrow, colored by its velocity. This is a time snapshot of 1/64 of the full simulation volume, which was (750Mpc/h)3.

see also Abstract of Hybrid petacomputing meets cosmology: The Roadrunner Universe project, Salman Habib et al., 2009 J. Phys.: Conf. Ser. 180 012019 (10pp)

Ejecta and Spall using the SPaSM code, Tim Germann, P.I.

Ejecta and Spall Open Science

We studied how copper reacts when shocked, using SPaSM (scalable parallel short-range molecular dynamics), a computer code that simulates processes such as shock waves in solids at nanosecond time scales. We use SPaSM to understand how materials deform and fail at the molecular level, allowing better materials design and prediction of their lifetime at full strength. Many fundamental materials phenomena take place at length and time scales just beyond those presently accessible by molecular dynamics (MD) simulations. Roadrunner, along with improvements in methodology, makes simulations of more realistic spatial and temporal scales possible. SPaSM was successfully used to perform the fastest MD simulation to date, reaching ~369 TFlop/s on the full Roadrunner machine.

Direct Numerical Simulation of Reacting Turbulence, Daniel Livescu, P.I.

Direct numerical simulation of reacting turbulence

In the field of fluid dynamics, understanding turbulence, the behavior of fluids under stress, remains one of the unsolved problems in physics. This study focuses on the interactions of flame and turbulence, under complex conditions, as those encountered in the early stages of a type 1a supernova. There is a complicated phenomenology associated with these interactions, from the suppression of the smallest vortex tubes due to the flame “fire polishing,” enhancement of intermediate turbulent scales, to the rapid acceleration of the flame itself to large velocities, which is one of the important open questions related to the supernova modeling. The Roadrunner architecture was instrumental in showing excellent performance using large structured fluid dynamics codes and the possibility of tackling complex turbulence problems.

 

 

   

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