Numerical Simulation Model On Irreversibility Of Shock Wave Process

The objective of this research is to develop a better understanding of the irreversibilities associated with the shock compaction of matter, especially as a result of impact. Due to complex shock processes, experimentation alone cannot fix the material state, since properties such as internal energy, entropy as well as the shock process are not measurable. Thus, in addition to experimentation, analytical and numerical methods are also used to completely characterize the shock process, although they are restricted by underlying constitutive assumptions. Instead of using artificial irreversibility, such as artificial viscosity to simplify and stabilize the numeric shock model, this work will directly incorporate and solve the correct constitutive relations that describe the sources of irreversibility. Shock wave processes in gas and water are simulated and two equations of state (EOS) are discussed. For a one-dimensional shock wave in gas, results from simulations at two different non-dimensional scales utilizing two different EOS are comparable to the idealized analytical solution and experimental data. Besides, the Mie-Grüneisen (M-G) equation of state, which has been used for solids, is extended to study gas and liquid. The value of Mie-Grüneisen constant, which is a function of atom oscillator frequency and specific volume, is hard to detect from experiment. Based on statistical mechanics, a relationship between the gas Mie-Grüneisen constant and specific heat ratio is derived analytically, which makes Mie-Grüneisen EOS available for gas. The M-G constant is also derived from shock jump condition and Mie-Grüneisen EOS for water and a sensitivity analysis is done based on the simulation result.

The purpose of this work is to directly simulate shock wave structures without the use of artificial viscosity. The commonly used artificial viscosity model is replaced with an irreversibility model. Irreversibilities are not typically taken into account when modeling the shock processes because shocks are resolved in a large domain where the thickness of the shock is thin compared to the numeric grid resolution. The result is the shock is poorly resolved. In addition processes other than shock processes are adiabatic and reversible. The result is artificial viscosity, a form of irreversibility, is added to the numeric cells near the shock in order to account for the irreversibilities generated within the shock structure. In this work the shocks are resolved and the physical sources of irreversibilities, namely viscous dissipation and localized heat transfer, are directly incorporated within the shock process. The resulting simulations yield a more realistic shock structure, the shape of which can be integrated to determine the resulting increase in entropy of the shocked material. Metrics such as shock thickness and wave structure compare favorably to experimental results. Irreversibility is traditionally accounted for by inserting artificial viscosity into the energy balance. Artificial viscosity reduces numerical overshoot, diminishes the total energy, and smears out the shock front over several cells thereby eliminating the need for nanoscale grid resolution necessary to resolve the shock front and numerically resolve the gradients. This approach fails to correctly model the shock wave structure of distended materials because their dynamic loading is a highly dissipative process and completely irreversible. Thus, the work described herein models on a bulk scale a thermodynamically consistent representation of the irreversibilities associated with shock wave formation such as viscous dissipation and heat conduction and seeks to determine if these sources of irreversibility are comparable to artificial viscosity.

CFD numerical simulations of low-density shock-wave interactions for an incident shock impinging on a cylinder have been performed. Flow-field density gradient and surface pressure and heating define the type of interference pattern and corresponding perturbations. The maximum pressure and heat transfer level and location of various interaction types are presented. A time-accurate solution of the Type IV interference is employed to demonstrate the establishment and the steadiness of the low-density flow interaction.

The 26th International Symposium on Shock Waves in Göttingen, Germany was jointly organised by the German Aerospace Centre DLR and the French-German Research Institute of Saint Louis ISL. The year 2007 marked the 50th anniversary of the Symposium, which first took place in 1957 in Boston and has since become an internationally acclaimed series of meetings for the wider Shock Wave Community. The ISSW26 focused on the following areas: Shock Propagation and Reflection, Detonation and Combustion, Hypersonic Flow, Shock Boundary Layer Interaction, Numerical Methods, Medical, Biological and Industrial Applications, Richtmyer Meshkov Instability, Blast Waves, Chemically Reacting Flows, Diagnostics, Facilities, Flow Visualisation, Ignition, Impact and Compaction, Multiphase Flow, Nozzles Flows, Plasmas and Propulsion. The two Volumes contain the papers presented at the symposium and serve as a reference for the participants of the ISSW 26 and individuals interested in these fields.

Recently, there have been significant advances in the fields of high-enthalpy hypersonic flows, high-temperature gas physics, and chemistry shock propagation in various media, industrial and medical applications of shock waves, and shock-tube technology. This series contains all the papers and lectures of the 19th International Symposium on Shock Waves held in Marseille in 1993. They are published in four topical volumes, each containing papers on related topics, and preceded by an overview written by a leading international expert. The volumes may be purchased independently.

The book contains 12 chapters written by well-known shock wave researchers from seven different countries. Each researcher provides a brief description of his main research interests and results, thereby providing the readers with an excellent view of shock wave research conducted in the past fifty years. It also provides hints as to what still needs further investigation. It will be an excellent guide for young researchers entering the field of shock wave phenomena. Among the described investigations are the following topics: Blast wave interaction with a body when the body is in the area of interference of two blast waves moving in different directions; equation of state for water based on the shock Hugoniot data; Mach waves occurring over a backward facing edge in supersonic flow; shock waves in dusty gas; shock wave interaction with various bodies; three shock interactions.

The present paper focuses on numerical simulation of wave processes observed in near-wall fluidized layer under action of normal shock wave. The unsteady process of interaction is described for various shock wave intensities and layer densities. It is shown that shock wave intensity increases significantly in the dense layer and the gain factor does not depend on the shock wave Mach number and defined only by the density ratio. Two different schemes (regular and Mach) of shock reflections are observed in computations that lead to a principally distinguished scenarios of instability development in a dusty layer.

This book offers an interdisciplinary theoretical approach based on non-equilibrium statistical thermodynamics and control theory for mathematically modeling shock-induced out-of-equilibrium processes in condensed matter. The book comprises two parts. The first half of the book establishes the theoretical approach, reviewing fundamentals of non-equilibrium statistical thermodynamics and control theory of adaptive systems. The latter half applies the presented approach to a problem on shock-induced plane wave propagation in condensed matter. The result successfully reproduces the observed feature of waveform propagation in experiments, which conventional continuous mechanics cannot access. Further, the consequent stress–strain relationships derived with relaxation and inertia effect in elastic–plastic transition determines material properties in transient regimes.

Computational Fluid Dynamics (CFD) numerical simulations of low-density shock-wave interactions for an incident shock impinging on a cylinder have been performed. Flow-field density gradient and surface pressure and heating define the type of interference pattern and corresponding perturbations. The maximum pressure and heat transfer level and location for various interaction types (i.e., shock-wave incidence with respect to the cylinder) are presented. A time-accurate solution of the Type IV interference is employed to demonstrate the establishment and the steadiness of the low-density flow interaction. Glass, Christopher E. Langley Research Center NASA/TM-1999-209358, NAS 1.15:209358, L-17878