Crab Nebula

The supernova explosion that created the Crab was seen on about July 4 1054 AD. This image is a combination of x-ray optical and radio images.At the center is a rapidly spinning pulsar with a disc and jets.

Tube Fracture

Result of a fluid/solid AMR coupled simulation, by Fehmi Cirak and Ralf Deiterding. The Virtual Test Facility (VTF) developed by the ASC Alliance Center for the Simulation of Dynamic\ Response of Materials at the California Institute of Technology is an integrated software environment for computing the dynamic response of solid materials due to impinging high energetic gaseous shock and combustion waves.

The fluid flow is simulated with Eulerian finite volume methods considering the solid as a moving rigid body while Lagrangian finite element methods advance the solid with respect to the current hydrodynamic pressure load. A temporal splitting approach is applied to exchange fluid-solid interface data between sub-steps. In order to allow for an almost arbitrary motion through the Eulerian fluid mesh without tedious remeshing, especially for fracture and fragmentation, we employ an implicit representation of the solid geometry in a level-set function. The level-set stores the point-wise distance to the solid surface and is then used to construct internal boundary conditions for a Cartesian finite volume scheme supplemented with highly efficient blockstructured dynamic mesh adaption.

As an example, we show preliminary computational results for one of the key validation experiments for the VTF: the dynamic response of thin aluminum tubes subjected to detonation induced loading in three space dimensions. These calculations couple Riemann solvers of Roe-type for solving the Euler equations with detailed and one-step reaction terms to a thin-shell solver for simulating the elastic tube deformation. Cohesive interface elements located at the shell element edges allow for crack propagation and branching. We sketch briefly the software layout, parallelization strategy and current computational performance for this VTF application.

Making the Sumatra Movies

Snapshot from a spectral-element simulation of the Great 2004 Sumatra- Andaman earthquake. Shown is the vertical component of velocity 15.8 minutes after the initiation of the rupture. Red colors denote upward motion and blue colors denote downward motion. Stations in the Global Seismographic Network are denoted by the yellow triangles. The yellow seismogram shows the actual-size vertical component of displacement at GSN station PALK (more information)