Numerical and experimental assessment of steering forces during horizontal penetration in sand – a validation of a bio-inspired optimal tip shape
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The exploration, characterisation, and monitoring of the subsurface are relevant to a wide range of applications, from environmental monitoring and in-situ characterisation to infrastructure construction (e.g., directional drilling and tunnelling) and resource withdrawal. Bio-inspiration offers promising solutions to overcome two of the most important challenges in the development of autonomous subsurface exploration probes: exploration range (related to drag forces) and steerability (i.e., ability to control the direction of movement). The work uses a previously proposed bio-inspired intruder shape to study the relationship between tip orientation and the resulting forces (lateral and vertical); and explores the idea that these forces can be used to steer the probe, i.e., control the direction of motion of the probe as it advances. Numerical results with the discrete element method and experimental results with a large-scale testbed show a direct relation between tip orientation and the steering forces – supporting the case for steering systems based on intruder tip rotation. Lateral forces increase with tip orientation, validating the potential use of rotations as a method of horizontal re-orientation of the intruder. Vertical forces also show a strong relation with tip orientation, however, for the tip shape tested, the range of steering is limited to neutral to upward direction (i.e., towards the free surface). Experimental results evidence the effect of intruder deformation (bending) and/or path deviation in the penetration forces acting on the intruder.