Structural Change in Lipid Bilayers and Water Penetration Induced by Shock Waves: Molecular Dynamics Simulations

科研費報告書収録論文(課題番号:17300168/研究代表者:小玉哲也/マイクロ気泡と超音波を用いた高効率型分子導入法の開発とがん治療法への応用

Turbulent acoustic streaming excited by resonant gas oscillation with periodic shock waves in a closed tube

Resonant gas oscillations with periodic shock waves in a closed tube are studied by executing large-scale computations of the compressible 2-D Navier–Stokes equations with a finite-difference method. In a quasisteady state of oscillation, acoustic streaming (mean mass flow) of large Rs is excited, where Rs is the streaming Reynolds number based on a characteristic streaming velocity, the tube length, and the kinematic viscosity. When Rs=560, relatively strong vortices are localized near the tube wall. The resulting streaming pattern is almost stationary but quite different from that of the Rayleigh streaming. The streaming of Rs=6200 involves unsteady vortices in a region near the center of the tube. Turbulent streaming appears in the result of Rs=56000, where vortices of various scales are irregularly generated throughout the tube. ©1999 Acoustical Society of America

The mean pressure and density in a strongly nonlinear plane acoustic wave

Exact expressions are presented for a time-averaged pressure and density at a fixed point in a strongly nonlinear plane acoustic wave radiated into an inviscid ideal gas of semi-infinite extent by a harmonic oscillation of an infinite plate. By making use of the exact solution of simple wave, the time averages of pressure and density are obtained up to the time of shock formation, in complete forms involving the hypergeometric functions. ©1996 Acoustical Society of America

Nonlinear analysis of periodic modulation in resonances of cylindrical and spherical acoustic standing waves

The nonlinear resonance of cylindrical acoustic standing waves of an ideal gas contained between two coaxial cylinders is theoretically investigated by the method of multiple scales. The wave motion concerned is excited by a small-amplitude harmonic oscillation of the radius of the outer cylinder, and the formulation of the problem includes the wave phenomenon in a hollow cylinder without the inner one as a limiting case. The spherical standing wave in two concentric spheres is also studied in parallel. The resonance occurs if the driving frequency falls in a narrow band around the linear resonance frequency, and in the weakly nonlinear regime, no shock wave is formed in contrast to the plane wave resonance. A cubic nonlinear equation for complex wave amplitude can then be derived by the method of multiple scales. Using a first integral of the cubic nonlinear equation, we shall demonstrate that the resonant oscillation is accompanied by a periodic modulation of amplitude and phase when the dissipation effect due to viscosity and thermal conductivity is negligible. The period of the modulation varies as the minus two-thirds power of the acoustic Mach number defined at the outer cylinder or sphere and decreases with an increase in the radius ratio of the inner and outer cylinders or spheres. When the dissipation effect is small but not negligible, the modulation is slowly weakened and the resonant oscillation approaches a steady state oscillation, which corresponds to the steady solution examined in earlier works. ©2006 American Institute of Physic