Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session Z2: Equation of State VI |
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Chair: John Aidun, Sandia National Laboratories Room: Hyatt Regency Constellation C |
Friday, August 5, 2005 10:30AM - 10:45AM |
Z2.00001: Dynamic Compaction Modeling Comparison for Porous Silica Powder John Borg, Larry Schwalbe, John Cogar, D.J. Chapman, Andrew Lloyd, Aaron Ward A computational analysis of the dynamic compaction of porous silica is presented and compared with experimental measurements. The experiments were conducted at Cambridge University's one-dimensional flyer plate facility. The experiments shock loaded samples of silica dust of various initial porous densities up to a pressure of 2.25 GPa. The computational simulations utilized porous material models, P-lambda and P-alpha, in conjunction with a linear Us-up Hugoniot. Two hydrocodes were used to simulate the compaction event: CTH and KO. CTH is a three-dimensional Eulerian hydrocode developed at Sandia National Laboratory and KO is a one-dimensional Lagrangian hydrocode developed at Lawrence Livermore National Laboratory. A comparison of the advantages and disadvantages, along with a discussion of the salient features, of the two models are presented. [Preview Abstract] |
Friday, August 5, 2005 10:45AM - 11:00AM |
Z2.00002: Thermal and mechanical dissipation associated with ramp and shock wave loading Jow-Lian Ding The entropy production mechanisms that cause the deformation process to deviate from isentrope response during ramp loading can be separated into mechanical and thermal dissipation processes. The former is due to inelasticity and rate effects inherent in deformation processes and the latter is due to irreversible heat conduction. Numerical simulations were used to gain insight into the relative importance of these two processes for ramp and shock loading. It is shown that material response for these loading conditions is essentially a manifestation of the interaction between the time scale associated with the loading process and the intrinsic time scales associated with mechanical deformation and heat transfer. The maximum ramp rate necessary to obtain quasi-isentropic compression depends on the intrinsic time scale of dissipation. Heat conduction was found to have a significant effect on the temperature history between two equilibrium states, but it contributes little to overall temperature change. However, the irreversible part of heat conduction is important to the net entropy change. [Preview Abstract] |
Friday, August 5, 2005 11:00AM - 11:15AM |
Z2.00003: Consistent thermodynamic derivative estimates for tabular equations of state. Gary Dilts A valid fluid equation of state must satisfy the thermodynamic differential conditions of consistency (derivation from a free energy) and stability (positive sound speed squared). Typical software interfaces to tabular equations of state based on polynomial or rational interpolants compute derivatives of pressure and energy and may enforce the stability conditions, but do not enforce the consistency condition and its derivatives, which is important for the computation of dimensionless quantities associated with more sensitive artificial viscosities and Riemann solvers that accurately model shock structure in regions near phase transitions. We describe a new type of table interface derived from a constrained local least squares regression technique. Application to several SESAME tables shows the consistency condition can be satisfied to round-off with third-order accuracy. An improvement of 14 orders of magnitude over conventional derivatives is demonstrated, although the new method is two orders of magnitude slower, due to solving an 11-dimensional nonlinear system. The new approach can be used to construct consistent and stable tables of derivatives, however. [Preview Abstract] |
Friday, August 5, 2005 11:15AM - 11:30AM |
Z2.00004: Modeling the Propagation of Shock Waves in Metals W. Michael Howard, John D. Molitoris We present modeling results for the propagation of strong shock waves in metals. In particular, we use an arbitrary Lagrange Eulerian (ALE3D) code to model the propagation of strong pressure waves (P $\sim $300 to 400 kbars) generated with high explosives in contact with aluminum cylinders. The aluminum cylinders are assumed to be both flat-topped and have large-amplitude curved surfaces. We use 3D Lagrange mechanics. For the aluminum we use a rate-independent Steinberg-Guinan model, where the yield strength and bulk modulus depends on pressure, density and temperature. The calculation of the melt temperature is based on the Lindermann law. At melt the yield strength and bulk modulus is set to zero. The pressure is represented as a seven-term polynomial as a function of density. For the HMX-based high explosive, we use a JWL, with a program burn model that gives the correct detonation velocity and C-J pressure (P $\sim $ 390 kbars). For the case of the large-amplitude curved surface, we discuss the evolving shock structure in terms of the early shock propagation experiments by Sakharov. We also discuss the dependence of our results upon our material model for aluminum. [Preview Abstract] |
Friday, August 5, 2005 11:30AM - 11:45AM |
Z2.00005: Hypervelocity Impact Problem Modeling Using Different Equations of State Mikhail Povarnitsyn, Pavel Levashov, Konstantin Khishchenko This study focuses on the simulation of hypervelocity impact problem with different equations of state. We have investigated effects of matter melting in strong shock waves, evaporation in rarefaction waves and spallation. We have found that a careful treatment of spalls formation mechanism is of greatest importance in obtaining accurate numerical results. Three types of wide range equations of state are discussed – caloric equation of state of condensed phase (EOS1), thermodynamically complete stable equation of state in tabular form which forbids existence of metastable states (EOS2) and thermodynamically complete metastable equation of state in tabular form which permits the existence of metastable gas, liquid or condensed phases (EOS3). We use aluminum, lead and copper in our calculations. Initial configuration consists of impactor with diameter 15 mm traveling at 6.6 km/sec and target plate 6.35 mm thickness. Comparison of experimental X-ray photographs with results of numerical simulation has demonstrated identity in shape and size of debris cloud, backsplash, flared at the edges and even rivulets of material, possibly streaming from fractures at the edges of the hole. Differences in structure of clouds were observed mainly for their inner structure. To obtain more close resemblance with experimental data a correct model of crack growing should be taken into account. [Preview Abstract] |
Friday, August 5, 2005 11:45AM - 11:59AM |
Z2.00006: Influence of Equation of State on Results of Hypervelocity Impact Modeling I.V. Lomonosov, V.E. Fortov, V.V. Kim, A.V. Matveichev, A.V. Ostrik The numerical modeling of hypervelocity impact has been done with the use of method of ``individual particles in cells.'' We carried out calculations using multi-phase and simplified caloric equations of state (EOS) in 3D setup for spherical lead impactor penetrating flat lead plate with a velocity of $6.6 $~km/s. This impact velocity correspond to melting in shock wave and to strong eveporating in release wave. Processes of crater and debris cloud formation and their dynamics have been investigated. Results of numerical modeling, such as density distribution in inner space, form and spatial size of debris cloud have been compared with experimental x-ray shots. We found that parameters of gas dynamic flow, such as pressure and density, are different for cases of multi-phase and caloric EOS. One should note that both EOS describe shock-wave data with good accuracy. The analysis proved that the quality of modeling results significantly depends on used equation of state. [Preview Abstract] |
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