Oleg Vorobiev

A strength and damage model for rock under dynamic loading

A thermodynamically consistent strength and failure model for granite under dynamic loading has been developed and evaluated. The model agrees with static strength measurements and describes the effects of pressure hardening, bulking, shear-enhanced compaction, porous dilation, tensile failure, and failure under compression due to distortional deformations. This paper briefly describes the model and the sensitivity of the simulated response to variations in the model parameters and in the inelastic deformation processes used in different simulations. Numerical simulations of an underground explosion in granite are used in the sensitivity study.

Simulations of an underground explosion in granite

This paper describes the results of a computational study performed to investigate the behavior of granite under shock wave loading conditions. A thermomechanically consistent constitutive model that includes the effects of bulking, yielding, material damage, and porous compaction on the material response was used in the simulations. The model parameters were determined based on experimental data, and the model was then used in a series of one-dimensional simulations of PILE DRIVER, a deeply-buried explosion in a granite formation at the Nevada Test Site. Particle velocity histories, peak velocity and peak displacement as a function of slant range, and the cavity radius obtained from the code simulations compared favorably with PILE DRIVER data.

A continuum model for concrete informed by mesoscale studies

The paper describes a novel computational approach to refine continuum models for penetration calculations which involves two stages. At the first stage, a trial continuum model is used to model penetration into a concrete target. Model parameters are chosen to match experimental data on penetration depth. Deformation histories are recorded at few locations in the target around the penetrator. In the second stage, these histories are applied to the boundaries of a representative volume comparable to the element size in large scale penetration simulation. Discrete-continuum approach is used to model the deformation and failure of the material within the representative volume. The same deformation histories are applied to a single element which uses the model to be improved. Continuum model may include multiple parameters or functions which cannot be easily found using experimental data. We propose using mesoscale response to constrain such parameters and functions. Such tuning of the continuum model using typical deformation histories experienced by the target material during the penetration allows us to minimize the parameter space and build better models for penetration problems which are based on physics of penetration rather than intuition and ad hoc assumptions.

Simulation of Explosion Ground Motions Using a Hydrodynamic‐to‐Elastic Coupling Approach in Three Dimensions

Abstract Near‐field ground motions from explosions are governed by hydrodynamics and nonlinear material response. However, the calculation of the response using hydrodynamic solvers to observational distances, where motions are elastic, is computationally challenging. In order to propagate explosion ground motions from the near‐source region to the far field, we developed a hybrid modeling approach with a hydrodynamic‐to‐elastic coupling in three dimensions. Near‐source motions are computed with a Eulerian hydrodynamics code with adaptive mesh refinement. Motions on a dense grid of points are saved, resampled, and then passed to an elastic finite‐difference code for seismic‐wave modeling. Our coupling strategy is based on the uniqueness theorem, where motions are introduced into the elastic code as time‐dependent boundary sources and propagate as elastic waves at much lower computational cost than with the hydrodynamics code. We developed and verified the methodology to compute the hydrodynamic responses in either 2D or 3D into the elastic region and pass these to the elastic solver as 3D boundary motions. The accuracy of the numerical calculations and the coupling strategy is demonstrated in cases with a purely elastic medium as well as a nonlinear medium. Importantly, we show that our hydrodynamics code can accurately model motions for shallow sources in an elastic medium including surface waves, which is essential to insure that near‐source motions are correct. An application of our hybrid modeling approach is shown for a problem with scattering by 3D heterogeneity. Our strategy is capable of incorporating complex nonlinear effects near the source as well as volumetric and topographic material heterogeneity along the propagation path to receiver, making it very powerful for modeling a wide variety of effects and providing new prospects for modeling and understanding explosion‐generated seismic waveforms.

Spall effects on infrasound generation from explosions at the Nevada National Security Site

We apply two methods to evaluating the spall signature from underground chemical explosions such as those at the Source Physics Experiment (SPE) at the Nevada National Security Site (NNSS). The first approach uses the Rayleigh integral to compute overpressures for buried explosions from synthetic vertical acceleration data at surface ground zero. To obtain the acceleration data, we systematically vary parameters such as the spall duration, depth of burial and magnitude and observe the effect on the resulting acoustic waveform shape. The second method uses a hydrodynamic approach to more fully characterize the varied parameters to produce the acoustic waveforms. As the spall decreases we find that the acoustic waveform shape changes dramatically. This waveform signature may provide diagnostics on the explosive source and may be a useful metric for underground explosion monitoring. [This work was done under award number DE-AC52-06NA25946. Sandia National Laboratories is a multi-program laboratory managed an...

EQUIVALENT CONTINUUM MODELING FOR WAVE PROPAGATION IN DISCONTINUOUS MEDIA

This study presents numeric simulations of nonlinear wave propagating through jointed rock masses. The simulations were performed using the Lagrangian hydrocode GEODYN-L with joints treated explicitly using an advanced contact algorithm.