We study the time evolution of a wave packet in a rapidly varying (in time) random potential. We find that the wave function becomes "multifractal," i.e., that an infinite number of exponents is needed to describe its evolution. The width of the packet is found to increase as v7, i.e., diffusively. The evolution of the center of mass is compatible with a subdiffusive t ^^^ law.
A method to predict the nonlinear relaxation behavior from creep experiments of nonlinear viscoelastic materials is presented. It is shown that for given nonlinear creep properties, and creep compliance represented by the Prony series, the Schapery creep model can be transformed into a set of first order nonlinear equations. The solution of these equations enables the obtaining of the nonlinear stress relaxation curves. The strain-dependent constitutive equation can then be constructed for a given nonlinear viscoelastic model, as needed for engineering applications. A comparison example of the calculated stress relaxation curves, with test data for polyurethane demonstrates the very good accuracy of the proposed method.
The present paper presents a simulation of a firing process of a 7.62mm bullet and muzzle flow out of a gun barrel. The calculation is made in two stages. First, an internal ballistics (IB) simulation via the IBHVG2 software package, is performed in order to obtain bullet travel dependent breech pressure and temperature. Following this, a simulation of unsteady muzzle flow is made, beginning at the start of bullet motion and ending one meter beyond the muzzle exit point. The second stage calculation is carried out via the CFD-FASTRAN finite volume solver package. The movement of the bullet is simulated by a chimera overset meshing technique. In general, there exists very good agreement between the computed IB and the measured muzzle velocity and pressures, and between the CFD precursors flow field, main propellant flow field calculations and the experimental shadowgraph results.
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