An experimental study of ultrasonic vibration and the penetration of granular material

Abstract

This work investigates the potential use of direct ultrasonic vibration as an aid to penetration of granular material. Compared with non-ultrasonic penetration, required forces have been observed to reduce by an order of magnitude. Similarly, total consumed power can be reduced by up to 27%, depending on the substrate and ultrasonic amplitude used. Tests were also carried out in high-gravity conditions, displaying a trend that suggests these benefits could be leveraged in lower gravity regimes.

Keywords: granular; penetration; rheology; ultrasonic.

Figure 1.

Size and shape of the ultrasonic penetrator used. Dimensions are given in millimetres. The transducer attaches at the right. (Online version in colour.)

Figure 2.

The force/power rig. (Online version in colour.)

Figure 3.

The gravity rig. (Online version in colour.)

Figure 4.

Sand particle size distributions: (a) by cumulative percentage weight passing, (b) by percentage of total mass. (Online version in colour.)

Figure 5.

Effects of consecutive penetrations into low density ES-3 without sample reset. Each test densifies the deep sand, causing subsequent penetrations to experience a larger force. (Online version in colour.)

Figure 6.

Maximum encountered penetration force as a function of ultrasonic amplitude used [7]. (Online version in colour.)

Figure 7.

Peak power consumption during penetration through regoliths: (a) SSC-3 and (b) BP. (Online version in colour.)

Figure 8.

Peak penetration forces in various levels of gravity. The circled data points are estimated values. (Online version in colour.)

Figure 9.

Peak penetration forces normalized to the non-ultrasonic force. The data plots for 7g and 10g are dotted to illustrate the 0 µm values (on which the normalisation is based) are estimates. (Online version in colour.)

Figure 10.

Normalized peak penetration forces at 1.6 µm with respect to gravity. Lower gravities show proportionally less force required than higher gravities, using the same vibration amplitude. (Online version in colour.)

Figure 11.

Illustrated example of using a controllable anchor. (a) The penetrator is inserted with ultrasonics on, creating a region of fluidized sand and reducing the required force for penetration. (b) The ultrasonics is switched off, returning the sand to its motionless state, and allowing the anchor to function normally. (c) When anchoring is no longer needed, the ultrasonics is switched back on, fluidizing the sand and reducing the required force for withdrawal. (Online version in colour.)