W. Michael Howard

An accurate equation of state for the exponential-6 fluid applied to dense supercritical nitrogen

The exponential-6 potential model is widely used in fluid equation of state studies. We have developed an accurate and efficient complete equation of state for the exponential-6 fluid based on HMSA integral equation theory and Monte Carlo calculations. Our equation of state has average fractional error of 0.2% in pV/NkBT and 0.3% in the excess energy Uex/NkBT. This is a substantial improvement in accuracy over perturbation methods, which are typically used in treatments of dense fluid equations of state. We have applied our equation of state to the problem of dense supercritical N2. We find that we are able to accurately reproduce a wide range of material properties with our model, over a range 0.01⩽P⩽100 GPa and 298⩽T⩽15 000 K.

Ultrafast Shock Initiation of Exothermic Chemistry in Hydrogen Peroxide

We report observations of shock compressed, unreacted hydrogen peroxide at pressures up to the von Neumann pressure for a steady detonation wave, using ultrafast laser-driven shock wave methods. At higher laser drive energy we find evidence of exothermic chemical reactivity occurring in less than 100 ps after the arrival of the shock wave in the sample. The results are consistent with our MD simulations and analysis and suggest that reactivity in hydrogen peroxide is initiated on a sub-100 ps time scale under conditions found just subsequent to the lead shock in a steady detonation wave.

The equation of state of supercritical HF, HCl, and reactive supercritical mixtures containing the elements H, C, F, and Cl

We develop a model of chemical equilibrium mixtures containing the elements H, C, F, and Cl. The model is based on a recently developed equation of state for the exponential-6 fluid, combined with a simple equation of state for condensed carbon. We show that the shock response of a wide variety of molecular and polymeric fluorocarbons and chlorocarbons can be modeled as a chemical equilibrium mixture of a small number of dissociation product molecules. In particular, we predict that shocked polyvinylidine fluoride (PVF2) decomposes into a fluid phase composed mostly of HF, and a phase containing condensed carbon. HF is known to strongly associate in the supercritical fluid phase. We predict that such an association also occurs under shock conditions.

The role of viscosity in TATB hot spot ignition

The role of dissipative effects, such as viscosity, in the ignition of high explosive pores is investigated using a coupled chemical, thermal, and hydrodynamic model. Chemical reactions are tracked with the Cheetah thermochemical code coupled to the ALE3D hydrodynamic code. We perform molecular dynamics simulations to determine the viscosity of liquid TATB. We also analyze shock wave experiments to obtain an estimate for the shock viscosity of TATB. Using the lower bound liquid-like viscosities, we find that the pore collapse is hydrodynamic in nature. Using the upper bound viscosity from shock wave experiments, we find that the pore collapse is closest to the viscous limit.

Riemann solver for the Nigmatulin model of two-phase flow

The two-phase model of Nigmatulin (Dynamics of Multiphase Media, 1991) is revisited and a second order Godunov solver is constructed for the corresponding Riemann problem using a seven wave structure. This model differs from the well established Baer-Nunziato model (International J. Multiphase Flow, Vol. 12, No. 6, 1986, pp. 861-889) in that it treats the solid phase as incompressible, and also accounts for thermal as well as elastic energies for the solid phase. Numerical results are presented for three classes of Riemann problems, demonstrating the accuracy of the method. The effect of inter-granular stress on the flow physics is investigated and it is shown that this term results in faster wave speeds for higher stresses. This study confirms that the Nigmatulin model can also be useful for the study of two-phase flows.

Kinetic calculations of explosives with slow-burning constituents

The equilibrium thermochemical code CHEETAH V 1.40 has been modified to detonate part of the explosive and binder. An Einstein thermal description of the unreacted constituents is used, and the Einstein temperature may be increased to reduce heat absorption. We study the effect of the reactivity and thermal transport on the detonation velocity. Hydroxy-terminated-polybutadiene binders have low energy and density and would degrade the detonation velocity if they burned. Runs with unburned binder are closer to the measured values. Aluminum and ammonium Perchlorate are also largely unburned within the sonic reaction zone that determines the detonation velocity. All three materials appear not to fully absorb heat as well. The normal assumption of total reaction in a thermochemical code is clearly not true for these special cases, where the detonation velocities have widely different values for different combinations of processes.

Simulation of the reflected blast wave from a C-4 charge

The reflection of a blast wave from a C4 charge detonated above a planar surface is simulated with our ALE3D code. We used a finely-resolved, fixed Eulerian 2-D mesh (167 μm per cell) to capture the detonation of the charge, the blast wave propagation in nitrogen, and its reflection from the surface. The thermodynamic properties of the detonation products and nitrogen were specified by the Cheetah code. A programmed-burn model was used to detonate the charge at a rate based on measured detonation velocities. Computed pressure histories are compared with pressures measured by Kistler 603B piezoelectric gauges at 7 ranges (GR = 0, 5.08, 10.16, 15.24, 20.32, 25.4, and 30.48 cm) along the reflecting surface. Computed and measured waveforms and positive-phase impulses were similar, except at close-in ranges (GR < 5 cm), which were dominated by jetting effects.

The Equation of State and Chemistry at Extreme Conditions: Applications to Detonation Products

The chapter explains the equation of the estate and chemistry at extreme conditions as applied to detonation products. Laboratory products conducted on materials held in excess of several kbar provide insight into a realm of chemical material properties that are significantly different from those encountered under ambient conditions. Dynamical simulation based on approximate Bonn–Oppenheimer potentials plays a large and increasingly important role in chemistry and in the biological and materials sciences. The chapter reviews the recent efforts to combine experimental and theoretical efforts to refine our knowledge of interatomic potentials and chemical processes at extreme conditions of pressure and temperature. The accuracy of the equation of state of polar fluids is significantly enhanced by using multi-species or cluster representation of the fluid. The methods to measure sound velocities of various super critical fluid systems are presented. The study of chemistry and kinetics of fluid under extreme conditions is explained with the help of the diamond anvil cell and the presence of CH 2 O 2 during the detonation of some common explosion. Further resources are also provided.

The Equation of State and Chemistry at Extreme Conditions

The chapter explains the equation of the estate and chemistry at extreme conditions as applied to detonation products. Laboratory products conducted on materials held in excess of several kbar provide insight into a realm of chemical material properties that are significantly different from those encountered under ambient conditions. Dynamical simulation based on approximate Bonn–Oppenheimer potentials plays a large and increasingly important role in chemistry and in the biological and materials sciences. The chapter reviews the recent efforts to combine experimental and theoretical efforts to refine our knowledge of interatomic potentials and chemical processes at extreme conditions of pressure and temperature. The accuracy of the equation of state of polar fluids is significantly enhanced by using multi-species or cluster representation of the fluid. The methods to measure sound velocities of various super critical fluid systems are presented. The study of chemistry and kinetics of fluid under extreme conditions is explained with the help of the diamond anvil cell and the presence of CH 2 O 2 during the detonation of some common explosion. Further resources are also provided.

Chapter 14 – The Equation of State and Chemistry at Extreme Conditions: Applications to Detonation Products

The chapter explains the equation of the estate and chemistry at extreme conditions as applied to detonation products. Laboratory products conducted on materials held in excess of several kbar provide insight into a realm of chemical material properties that are significantly different from those encountered under ambient conditions. Dynamical simulation based on approximate Bonn–Oppenheimer potentials plays a large and increasingly important role in chemistry and in the biological and materials sciences. The chapter reviews the recent efforts to combine experimental and theoretical efforts to refine our knowledge of interatomic potentials and chemical processes at extreme conditions of pressure and temperature. The accuracy of the equation of state of polar fluids is significantly enhanced by using multi-species or cluster representation of the fluid. The methods to measure sound velocities of various super critical fluid systems are presented. The study of chemistry and kinetics of fluid under extreme conditions is explained with the help of the diamond anvil cell and the presence of CH 2 O 2 during the detonation of some common explosion. Further resources are also provided.