Statistics – Computation
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.2419k&link_type=abstract
American Astronomical Society, DPS meeting #39, #24.19; Bulletin of the American Astronomical Society, Vol. 39, p.457
Statistics
Computation
Scientific paper
I report on three-dimensional simulations of the impacts of ice and rock bolides into simple model atmospheres. The calculations were performed using the ZEUSMP hydrocode v. 2 with a Tillotson equation of state for the impactors. The emphasis in these simulations is on the basic processes the bolides undergo during an impact: flattening and compression due to pressure gradients, ablation, and fragmentation. Depending on the material properties and degree of cohesion, material strength may also play a role in controlling the breakup of the object. For these calculations, I concentrate on large bodies with negligible material strength. In that case, a hydrodynamical approach to the problem is appropriate.
The deformation of an impactor of radius R, velocity V, and density rho proceeds on the same timescale [ (ρ/ρa)(1/2)(R/V)] as the growth of hydrodynamical instabilities. We expect that impactors penetrate to depths and corresponding column masses that are independent of V and proportional to impactor mass and scale as the square root of the ratio of impactor to atmospheric density. Previous studies have found weak departures from these scalings.
Detailed results such as energy deposition profiles are strongly (and unpredictably) sensitive to very small changes in initial conditions such as the exact placement of the impactor on the computational grid. Multiple runs of given parameter sets must be made to sample the distribution of results and statistical measures must be developed. In particular, an "overlap integral", that measures the degree of divergence between two functions, serves as a basis for statistical comparisons of sets of calculations and models.
This work is supported by the National Science Foundation under Grant AST 0406841 and a grant of computer time on the Discover cluster at the NASA Center for Computational Sciences.
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