Comparison of dry or wetted sand column vibrating over a clamped elastic plate: A nonlinear sand-plate-oscillator

Abstract

The sand plate oscillator apparatus uses two aluminum circular flanges sandwiching and clamping a thin circular elastic acrylic plate (density 1.21 g/cc). Dry sifted or wetted masonry sand is supported at the bottom by the clamped acrylic plate (4.5 in.) and stiff cylindrical sidewalls. Sifted masonry sand has a density of 1.55 g/cc. An accelerometer centered on the plate measures vibration response using a swept tone spectrum analyzer between 50 and 850 Hz. The plate was driven from below by a small loudspeaker. Three experiments were performed. (1) Nonlinear tuning curve response required driving the loudspeaker and incrementing the signal amplitude between sweeps. A fixed column of 354 g of dry masonry sand was used, with comparisons when 0, 11, 22, and 33 g of water were carefully sprayed on. (2) At constant drive amplitude, tuning curve response with 354 g of dry sifted sand was compared with results when 2 g of water were sprayed every 104 s. (3) Fixed drive amplitude tuning curves for incremental dry sand loading with 47 g for each layer were compared to incremental layers of 47g dry sand sprayed with 12 g water. The wetted sand had increased stiffness.