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Aeolian processes and terrain characteristics that are highly localized in space and time. (A) Varied terrain of a dune and interdune at White Sands NM. (B) Dust devil in Arizona. (C) Developing soil crust at White Sands NM; car key for scale. (D) Sand accumulating downwind of a $1-m diameter shrub at White Sands, NM. (E) Aeolian sand streamers on the Tana River Delta, Norway; boot for scale. Credit: (B) NASA web page & source file, Public Domain, https://commons.wikimedia.org/w/index.php?curid= 5585657; (E) Roger Suthren., virtual-geology.info; all others from authors.
Source publication
Understanding the dynamics of sand movement on dunes and dust emissions from natural and disturbed surfaces requires measurements of boundary layer winds and rates of sediment transport and dust emissions at high temporal and spatial resolution during strong wind events. Existing instrumentation has many limitations: installing it is very labor int...
Context in source publication
Context 1
... transport, and deposition of sediment by the wind (aeolian processes) occur in a variety of environments ( Fig. 1), including the coastal zone, semi-arid and arid regions (e.g., cold and hot deserts), and agricultural fields in many climates. Aeolian processes also occur on some planetary bodies, notably Mars and Saturn's moon Titan. Common features of these environments are a sparse or non-existent vegetation cover, a supply of fine sediment ...
Citations
... The main contribution is a reactive controller for jumping on sand with a direct-drive robot which significantly reduces energetic cost of transport without reducing jump height. This controller was tested in simulation ( the literature that accompany this thesis is in Appendix A. The direct-drive Minitaur's [70] legs can be used as shear sensors to measure the erodibility of the ground -a quantity of interest to our geoscientific collaborators [97,102]. However, because of these direct-drive legs, Minitaur overheats very quickly in the desert and cannot reliably transport itself between testing locations. ...
... Mobile characterization of wind flow fields around solid and porous objects [136] Conference poster (Y) Ground robotic measurement of aeolian processes [97] Journal (Y) 2.1 Robotic measurement of aeolian processes [102] Poster (Y) 2.1 Desert RHex Technical Report: Jornada and White Sands trip [112] Tech. report (N) 2.2 ...
Most models of legged locomotion assume a rigid ground contact, but this is not a reasonable assumption for robots in unstructured, outdoor environments, and especially not for field robots in dry desert environments. Locomotion on sand, a highly dissipative substrate, presents the additional challenge of a high energetic cost of transport. Many legged robots can be adapted for desert locomotion by simple morphological changes like increasing foot size or gearing down the motors. However, the Minitaur robot has direct-drive (no gearbox) legs which are sensitive enough to measure ground properties of interest to geoscientists, and its legs would lose their sensitivity if they were geared down or the foot size increased substantially. This thesis has two main contributions. First, a controller for jumping on sand with a direct-drive robot that saves significant energy in comparison to a nominal compression-extension Raibert-style controller without sacrificing jump height. This controller was developed by examining the complex interaction between the jumping leg and the ground, and devising a force to add to the leg controller which will push the robot’s foot into a more favorable state that does not transfer as much energy to the ground. The second contribution is a ground emulator robot which can be programmed to exert ground force functions of arbitrary shape. With the ground emulator, it is possible for a robot on a linear rail to jump dozens of times per experiment, whereas traditional experiments on granular media would require the ground to be reset between individual jumps. Results from the simulation experiments used to develop the controller and the ground emulator experiments used to test it on a physical robot leg are validated with experiments on a prepared granular media bed. Finally, the contributions of this thesis are contextualized in a broader project of building explainable artificially intelligent systems by composing robust, mostly reactive controllers.
... RHex is a bio-inspired, hexapedal robot that exhibits high mobility over a variety of outdoor environments, including terrain with obstacles [Saranli et al., 2001b], inclinations from hills [Ilhan et al., 2018] and stairs [Johnson et al., 2011], and desert dunes [Qian et al., 2017;Roberts et al., 2014a, b]. The RHex robot has been employed for various aeolian research expeditions [Qian et al., 2017;Roberts et al., 2014a, b;Qian et al., 2016a;Van Pelt et al., 2016;Qian et al., 2016b], and has demonstrated its capability to perform a wide variety of measurements including wind speed, saltation grain counts, erodibility, in strong wind conditions to obtain high spatiotemporal resolution field datasets [Qian et al., 2017]. For all shear experiments at White Sands, we used a 1.5cm-wide cylindric intruder. ...
Predicting the susceptibility of soil to wind erosion is difficult because it is a multivariate function of grain size, soil moisture, compaction, and biological growth. Erosive agents like plowing and grazing also differ in mechanism from entrainment by fluid shear; it is unclear if and how erosion thresholds for each process are related. Here we demonstrate the potential to rapidly assemble empirical maps of erodibility while also examining what controls it, using a novel “plowing” test of surface‐soil shear resistance (τr) performed by a semi‐autonomous robot. Field work at White Sands National Monument, New Mexico, United States, examined gradients in erodibility at two scales: (i) soil moisture changes from dry dune crest to wet interdune (tens of meters) and (ii) downwind‐increasing dune stabilization associated with growth of plants and salt and biological crusts (kilometers). We found that soil moisture changes of a few percent corresponded to a doubling of τr, a result confirmed by laboratory experiments, and that soil crusts conferred stability that was comparable to moisture effects. We then compared different mechanisms of mechanical perturbation in a controlled laboratory setting. A new “kick‐out” test determines peak shear resistance of the surface soil as a proxy for yield strength. Kick‐out resistance exhibited a relation with soil moisture that was distinct from the plowing test and that was correlated with the independently measured threshold‐fluid stress for wind erosion. Results show that our new method maps soil erodibility in arid environments and provides an understanding of environmental controls on variations in soil erodibility.
