Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session L6: Ballistics I: Heterogeneous Media |
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Chair: David Lambert, Air Force Research Laboratory Room: Grand Ballroom VI |
Wednesday, June 29, 2011 9:15AM - 9:45AM |
L6.00001: Verification and Validation of computational models for shaped charge jet completion of well bores in fluid saturated sandstone Invited Speaker: Completion of cased and cemented wells by shaped charge perforation is a now standard method to establish a pathway liberating oil entrained in reservoir sandstone. However, the penetration event causes its own damage to the formation, potentially reducing well productivity by lodging fragmentation fines in pore throats. To simulate the perforation and penetration process, a computational framework must accommodate massive deformations (usually necessitating an Eulerian solver) while at the same time preserving the integrity of highly history-dependent internal state variables in constitutive models for inelastic flow, damage, and fracture. Results from a three year effort to improve predictive capability of numerical models of well bore completion are summarized. A hierarchical approach to verification and validation (V\&V) is underway that begins with numerous straightforward verification tests, then introduces simple partial constitutive validation tests for simple loading (such as demonstrations that the constitutive models can reproduce observed unconfined and confined uniaxial stress data for drained and undrained sandstone), partial validation of the solvers for penetration of aluminium plates, and culminating in a full-scale simulation of the entire completion process consisting of: manufacture of the shaped charge jet liners, explosive formation of the jet, perforation of the metal well bore casing and cement, penetration of the compressed saturated sandstone, and subsequent flow of water and oil from the formation. The parts of this V\&V effort to be discussed include: qualitative trend testing of the manufacturing process for power-compacted liners, trend testing (with some quantitative verification against idealized models) of the new effective-stress component of the sandstone constitutive model, convergence testing for benchmark tests of localization and fracture, massive deformation kinematics trend testing in a converging plate problem (which emulates shaped charge jet formation without having to worry about the explosives model), incorporation of aleatory uncertainty, and quantitatively assessing accuracy and convergence of the particle-based momentum solver via new manufactured solutions (\textit{cf.}\footnote{P. Knupp and K. Salari, \textit{Verification of Computer Codes in Computational Science and Engineering}, Chapman and Hall/CRC, (2003).}). These new manufactured solutions allow quantifying accuracy of the host code's solver when it is used with history-dependent plasticity and damage constitutive models (these tests also assess basis and frame indifference of the constitutive model). Benefits of hierarchical approaches to V\&V include catching anomalous behaviours, such as under-integration of the Jacobian in large shear time steps, that would not have been otherwise detected in ``reasonable looking'' simulation results.\footnote{A. Sadeghirad, R. Brannon and J. Burghardt, ``A convected particle domain interpolation technique to extend applicability of the material point method for problems involving massive deformations,'' \textit{Int. J. Num. Meth. Engng}, (2011) accepted for publication.} These verification tests are illustrated in an example that quantitatively reveals advantages of a particular enhancement of the material point method\footnote{D. Sulsky, A. Chen and H. Schreyer, ``A particle method for history-dependent materials", \textit{Comput. Meth. Appl. Mech. Eng,} \textbf{118}, 179-196 (1994).} over other large-deformation solvers. [Preview Abstract] |
Wednesday, June 29, 2011 9:45AM - 10:00AM |
L6.00002: Deceleration of Projectiles in Sand Stephan Bless, William Cooper, Zach Stone, Keiko Watanabe, Robert Peden Deceleration of projectiles has been measured for hemispherical and conical nose shapes penetrating granular media. Targets were beds of~Ottawa sand and Eglin sand.~The velocity range extended up to 600 m/s. Projectiles were rigid metals. Deceleration was measured by conventional time-of-arrival screens plus several innovative techniques: embedded EM coils, embedded optical fibers, and a photonic Doppler velocimeter (PDV), which observed the rear surface of the penetrator. Experimental parameters that were varied included velocity (from 300 to 600 m/s), sand density, and scale (from 5 mm to 25 mm). In this paper we will compare these various measurement techniques and we will show how the cavity geometry (cavitation and crushed veins of sand) and retarding stress $(MdV/dt)/A$vary with velocity, scale, and density. [Preview Abstract] |
Wednesday, June 29, 2011 10:00AM - 10:15AM |
L6.00003: Ballistic Penetration of Sand With Small Caliber Projectiles John Borg, Andrew Fraser In this work a series of experiments were carried out in which right-circular cylinders were launched into sand targets at velocities ranging from 70 to 150 m/s. The projectiles were launched along a view window in order to record the penetration event with high-speed photography. Stress measurements of the transmitted wave forms were simultaniouly collected from a piezoelectric load cells buried in the sand at various locations relative to the shot line. A particle image velocimetry (PIV) technique, which extracted information from the photographic images, was used to resoved both the penetration and transmitted wave profiles. Two proment waves are observed in these experiments. The first wave is a propagating compaction wave which moves at the bulk sound speed of the sand. The second is an attached bow shock fracture wave which is stationary relative to the projectile. Together these experiments further our understanding of high speed granular penetration events. [Preview Abstract] |
Wednesday, June 29, 2011 10:15AM - 10:30AM |
L6.00004: Hign-speed penetration of projectile with cavitator into sand Anna Daurskikh, Vladislav Veldanov Cavitators are used in underwater projectiles design to form a cavern in which projectile could move with no or significantly reduced drag. An investigation of possible application of this structural element for penetration into porous media was conducted. High-speed impact of a conical-shaped head projectile with cavitator was studied in terms of its influence on penetration capacity and projectile stability in sand for impact velocity about 1500 m/s. Cavitators were manufactured of steel with different strength moduli, and thus two penetration regimes (with eroding/non-eroding cavitator) were compared. Numerical simulations showing wave propagation in target and projectile were performed in AUTODYN with Johnson-Cook model for projectile and granular model for sand. [Preview Abstract] |
Wednesday, June 29, 2011 10:30AM - 10:45AM |
L6.00005: Impact effects of explosively formed projectiles on normal strength concrete Laurin Bookout, Jason Baird This paper will address the experimental results of the impact of four-inch explosively formed projectiles on normal strength concrete targets. Five projectiles will be recovered using a soft recovery system to determine the average mass and nose shape of the projectiles. Velocity data for each test will be measured with a high speed camera. The average projectile nose shape and mass plus the striking velocity, and the penetration depths from ten tests will then be compared to existing penetration equations to see if one or more of the equations are applicable for this type of projectile impact. The coarse aggregate gradation used in the concrete mix has Hugoniot data available. If spalling occurs on any of the targets, the Hugoniot data will allow comparison of the observed spalling with the theoretical predictions. [Preview Abstract] |
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