Shock wave simulation

Oran et al. [218,219] developed a global parameterized model which describes the chemical induction time as a function of temperature and pressure. Parameters of the induction time function were determined for stoichiometric hydrogen and methane in air mixtures. The parameters were fitted to numerical results obtained from the simulations based on detailed reaction mechanisms. This technique allowed a 22-times faster calculation of the induction time and reduced the simulation time in a onedimensional model by a factor of 7.5. The fitted model was used in two-dimensional shock-wave simulations. 

Figure 8 shows the volume as a function of time for four overdriven single shock wave simulations in the [110] direction of a 25688 atom perfect Lennard-Jones face centered cubic crystal. Elastic compression is characterized by VjV 0.9 and plastic compression occurs for smaller volumes. As the shock speed decreases, the amount of time the molecular dynamics system spends in the elastically compressed state increases. This plot illustrates how the final thermodynamic state in the shock is a function of the simulation duration when slow chemical reactions or phase transitions occur. For example, on the 10-20 ps timescale, the 2.8 km/sec shock has an elastically compressed final state on the 100 ps timescale, this simulation has a plastically compressed final state. 

Each of the single wave simulations performed to construct a plot like in Figure 7 has physical validity regardless of the presence or lack of regions on the Hugoniot where a double shock wave can form. For this reason, it is possible to perform a physically valid single shock wave simulation without any knowledge of the existence of double shock waves. This... 

Figure 1 Sideways view of a fluid-carbon nanotube system. The solid lines represent the nanotube. The dashedlines represent either minimum image boundaries (shock wave simulations) or initial locations of driving and driven membranes (pressure wave simulations). Fluid atoms are enclosed within...

Two types of simulations, namely shock and pressure wave, are reported. In the shock wave simulations, Zi and Zj are fixed at the tenth and tenth to last rings of the nanotube and represent locations of minimum image boundaries described previously. A 10 A plug of fluid is given an initial z velocity. Subsequent fluid motion is tracked very carefully through visualization and through extensive analysis. 

Figure 2 Typical shock wave simulation results (fraction of kinetic energy in the direction of flow) for helium within a 19.9 A diameter nanotube Solid line central region atoms. Dashed line adjacent region atoms. 

Equation-of-state measurements add to the scientific database, and contribute toward an understanding of the dynamic phenomena which control the outcome of shock events. Computer calculations simulating shock events are extremely important because many events of interest cannot be subjected to test in the laboratory. Computer solutions are based largely on equation-of-state models obtained from shock-wave experiments which can be done in the laboratory. Thus, one of the main practical purposes of prompt instrumentation is to provide experimental information for the construction of accurate equation-of-state models for computer calculations. 

D.C. Wallace, Computer Simulation of Non-Equilibrium Processes, in Shock Waves in Condensed Matter (edited by Y.M. Gupta), Plenum, New York, 1986, pp. 37-49. 

Computational methods have played an exceedingly important role in understanding the fundamental aspects of shock compression and in solving complex shock-wave problems. Major advances in the numerical algorithms used for solving dynamic problems, coupled with the tremendous increase in computational capabilities, have made many problems tractable that only a few years ago could not have been solved. It is now possible to perform two-dimensional molecular dynamics simulations with a high degree of accuracy, and three-dimensional problems can also be solved with moderate accuracy. 

More than 40 years ago, Hochstim (1963) showed that organic products are formed in simulation experiments using shock waves. However, no information on yields is available. Using shock wave heating of a reducing gas mixture, Bar-Nun et al. (1970) were able to obtain relatively high yields of amino acids. However, when the work was later repeated, it turned out that the authors had been too optimistic the yields were lower by a factor of 30 (Bar-Nun and Shaviv, 1975). 

Sklavounos, S. and Rigas, F., Computer simulation of shock waves transmission in obstructed terrains, /. Loss Prevent. Process Ind., 17,407,2004. 

Three types of combushon test facility are used to evaluate the combushon efficiencies of ducted rockets direct-connect flow (DCF) test, semi-freejet (SFJ) test, and freejet (FJ) test, as shown in Fig. 15.13. Pressurized heated air or cooled air is supplied to the DCF, SFJ, and FJ test facilihes. The pressure and temperature of the airflow are adjusted by means of an air control system to simulate the air condihons during flight of the ducted rocket projechle. In the case of the DCF test, the airflow is supplied to the ramburner from a pressurized air tank through a directly connected pipe. No air-intakes are used in the DCF test. Thus, the pressure and temperature of the air in the ramburner are as directly supplied from the pressurized air tank. No supersonic flow or shock waves are formed during the supply of air to the ramburner. In the DCF test, the combustion efficiency in the ramburner is measured as a function of the air-to-fuel flow ratio, s. The combustion charac-... 

Hydrodynamic simulations of non-linear pulsation for less-massive cooler supergiants have been perfoemed by several authors (Tuchman, Sack and Barkat, 1979 Fadeyev and Tutukov, 1981 Fadeyev, 1982, 1984 Nakata, 1987 Buchler et al., 1987). The outburst of large amplitude pulsation at times is one of common features of these models, and renders mass-loss from the atmosphere of pulsating stars by generating strong shock waves. 

Under high vacuum conditions, i.e., pressure p < 10 2 mbar, the material transfer can be described using Monte Carlo simulations. Usually, inelastic collisions and collective phenomena as shock waves cannot be considered here. The so called Direct Simulation Monte Carlo method allows extension to slightly higher gas pressures. 

The model is currently being refined to better allow for concentration related changes in the velocity of the shock waves, as well as improvements in modeling the density dependent parameters of the simulation. Work continues on the determination of adsorption and desorption isotherms for several ternary systems, as well as the thermal and mass transfer characteristics for the column and media being employed. Accurate determination of the model parameters will be required for optimization of the of the operational regime. 

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