Speaker
Description
Super-bolides are of particular interest to planetary defense since they can release
vast amounts of energy (500 kton to >10 Mton) during atmospheric entry. Superbolides
such as Chelyabinsk (20m, 2013) and Tunguska (50m, 1908) are two
contemporary examples of the effects airburst phenomena have, ranging from minor
structural damage to prominent land devastation. Smaller scale celestial objects
responsible for airbursts exist in greater numbers in our solar system and are
significantly harder to detect. These factors underscore the necessity of developing a
robust understanding of how entry characteristics affect localities and regions on the
ground.
High-fidelity simulations of ground effects, given asteroid properties and entry
characteristics could contribute to this understanding. Unfortunately, the atmospheric
breakup and blast propagation are characterized by different length and time scales,
necessitating separate simulations and an intermediate handoff. We approached this modeling challenge by developing a hydrocode pipeline which consists of two parts,
initialized by explicitly calculating the energy deposition and momentum loss during
the bolide breakup. This deposition is then handed-off into an atmospheric blast
propagation code to estimate ground overpressures and wind speeds.
The airburst is modeled using the FSISPH package of the Smoothed Particle
Hydrodynamics (SPH) code Spheral++. Aspects of the physical problem, such as
entry angle, velocity, geometry, strength, damage, etc., are readily modeled and the
fragmentation and breakup of the asteroid is tabulated as a total energy loss of the
asteroid ‘system.’ This simulation strictly models the airburst event, which lasts several
seconds. The tabulated energy, momentum, and mass change, as a function of
altitude and time, are then utilized as input parameters in the Eulerian blast
propagation code, Miranda. In an Eulerian domain, the airburst ‘zone’ is modeled as
a moving point source with a gaussian distribution of the energy rate at each respective
time-step. This zone is then advanced along the trajectory that the asteroid takes in
space and the blast solver propagates the generated pressure wave to longer end
states.
We apply our new pipeline by utilizing the data generated from a previous SPH
simulation of the Chelyabinsk airburst case. We deposit the tabulated energy, mass,
and momentum within a 3-dimensional cartesian domain within Miranda with complex
ground geometry representative of a realistic landscape, such as an urban setting.
Simulating the Chelyabinsk event via this pipeline allows us to perform a satisfactory
comparison of the estimated to the observed ground overpressures, given some static
set of SPH input parameters based on the literature. Furthermore, informed by the
results of this specific study, we can begin an analysis of how slight variations in the
entry characteristics of a similar scenario, such as entry angle, would affect the
response on the ground.
LLNL-ABS-871533
Prepared by LLNL under Contract DE-AC52-07NA27344.