Numerical Modelling of Impact Processes

Abstract

Numerical modelling is now a well-established and important component of impact research. When used to complement small-scale impact experiments, it provides a powerful tool for exposing the physical processes in a cratering event and for investigating the effect of individual physical parameters that are not otherwise under the experimenter's control. Moreover, once adequately validated against small-scale laboratory experiments, numerical models allow us to simulate impacts much larger and more energetic than those that can be studied experimentally.The first numerical impact simulation was published in 1961 by R.L. Bjork (Fig. 17.1). That calculation of the Meteor Crater impact simulated only the first 60 ms of the collision and did not account for gravity or the strength of the target rocks (Bjork, 1961). Nevertheless, that simulation, and those that followed in the next decades, provided great insight into the physics of hypervelocity impact, including the formation and attenuation of the detached shock wave, the fate of the impactor, and the scaling of crater dimensions (e.g. Ahrens and O'Keefe, 1977;Orphal, 1977;O'Keefe and Ahrens, 1993).Nearly half a century on, and thanks to advances in numerical impact models and much improved computational resources, numerical models that include gravity and complex material models are used routinely to simulate large terrestrial impacts, aiding interpretation of geological and geophysical observations and quantifying the energy of the impact and impact-related consequences. For example, several numerical impact models of the Chicxulub impact have been performed and compared with observational data to constrain the impact energy, the fate of the projectile, the volume of climate forcing gases released into the atmosphere, the transport and re-entry of ejected material and the regional seismicity (e.g.

Exogenic Dynamics, Cratering, and Surface Ages

“…The later modification stages are crater size-dependent and need to be considered separately to define the final crater size. Instructive introductory reviews were recently published by Melosh (2013) and Collins et al (2013).…”

“…A collection of papers in the book Impact Cratering: Processes and Products (Osinski and Pierazzo, 2013) gives an extended introduction to the impact cratering topic.…”

The Steinheim Basin impact crater (SW-Germany) – Where are the ejecta?

“…In the model by Collins and Wünnemann (2009) with given parameters (basalt-basalt impact, 15 km/s impact velocity) the excavated volume of high-speed ejecta (>300 m/s) decreases by $40% in target rocks with 10% porosity, by $60% in target rocks with 20% porosity and by nearly 80% in target rocks with 40% porosity when compared to a dense target rock with a (theoretical) 0% porosity. The target rock porosity of $20% already indicates significant influence on the efficiency of the deposition of ejecta outside the forming crater.…”

Hyper-Velocity Impacts on Rubble Pile Asteroids

“…A good overview is given in Malvern (1969, Chapter 6), and a discussion of models used in recent impact simulations in Holsapple (2009) and Collins et al (2012).…”

“…Neither of these EOSs allow for the of temperature directly and therefore The Lagrangian and SPH simulations where produced using Autodyn by M. Price, the Eulerian using iSALE. Reprinted from Collins et al 2012 of State for Shock Physics Codes (ANEOS) (Thompson 1990) used analytical, thermodynamic consistent formulation to calculate the state using a computer code, including the vapor phase and melting. This approach has been extended to include multiple solid phase transitions by Melosh (2007), and is still under development (Collins and Melosh 2014).…”