Shock wave propagation in vibrofluidized granular materials.

Shock wave formation and propagation in vertically vibrated quasi-two-dimensional granular materials are studied by digital high speed photography. Steep density and temperature wave fronts form at the bottom of the granular layer when the layer collides with vibrating plate. Then the fronts propagate upwards through the layer. The temperature front is always in the transition region between the upward and downward granular flows. The effects of driving parameters and particle number on the shock are also explored.

Formation and transport of a sand heap in an inclined and vertically vibrated container.

We investigate experimentally the formation and the transportation of a heap formed by granular materials in an inclined and vertically vibrated container. We observe how the transport velocity of heap up the container is related to the driving acceleration, the driving frequency, and the inclination of the container. An empirical law which governs the transport velocity of the heap is presented. An analogous experiment was performed with a heap-shaped Plexiglas block. We propose that the compressive force resulted from pressure gradient in ambient gas plays a crucial role in enhancing and maintaining a heap, and the ratchet effect causes the movement of the heap.

Dynamic behaviors of supersonic granular media under vertical vibration.

We present experimental study of vibrofluidized granular materials by high speed photography. Statistical results present the averaged dynamic behaviors of granular materials in one cycle, including the variations of height, velocity and mechanical energy of the center of mass. Furthermore, time-space distribution of granular temperature which corresponds to the random kinetic energy shows that a temperature peak forms in the compression period and propagates upward with a steepened front. The Mach number in the steepened front is found to be greater than unity, indicating a shock propagating in the supersonic granular media.

Interior dynamics of subharmonious surface wave in an idealized bidimensional granular layer.

In this paper, high-speed photography was used to investigate the intrinsic dynamics of subharmonious surface wave in a vertical vibrated and idealized bidimensional granular layer. Using the high-speed photography, velocity fields of the granular layer at different stages through two cycles were obtained, which show the continuous particle motions during a cycle. From the velocity fields, a crystal structure in the wave-hollow was observed, which is reported for the first time. Furthermore, quantitative results of kinetic energy distribution in the layer were calculated, which shows temporal correspondence with the evolution of the wave pattern.

Bubble oscillations driven by aspherical ultrasound in liquid.

In this paper we study the bubble dynamics driven by an aspherical acoustic field, based on the theory of hydrodynamics. Evolution equations for an aspherical bubble are derived under the aspherical acoustic driving. The numerical calculations show that the aspherical bubble can oscillate stably and periodically under suitable conditions, which is out of the explanation of spherical perturbation theory. Furthermore, under some controlling parameters, the aspherical distortion can either grow rapidly, leading to the bubble's breakdown, or decay gradually making the bubble spherical, which is similar to the result of the perturbation theory driven by a spherical ultrasound.

Single bubble sonoluminescence driven by non-simple-harmonic ultrasounds.

The dependence of the single bubble sonoluminescence (SBSL) on the waveforms of the driving ultrasound has been investigated by both experiment and numerical calculation. Three types of non-simple-harmonic waves, the rectangular, triangular and as well as the sinusoidal wave with a pulse, are used to drive the SBSL in our research. The triangular wave is the most effective, while the rectangular wave is the worst and the sinusoidal wave in the middle. However, the rectangular wave drives the brightest SBSL among those waves if the sound pressure amplitude keeps constant. When we use a simple-harmonic wave with a pulse as the driving sound, stable and periodic SBSL flashes have been observed. An increase in the flash intensity can be observed as the pulse is put at a suitable phase related to the sinusoidal wave. All of the observations are investigated numerically. Well qualitative agreements between the numerical simulations and the experimental measurements have been achieved.