Adaptive locomotion of artificial microswimmers

Bacteria can exploit mechanics to display remarkable plasticity in response to locally changing physical and chemical conditions. Compliant structures play a striking role in their taxis behavior, specifically for navigation inside complex and structured environments. Bioinspired mechanisms with rationally designed architectures capable of large, nonlinear deformation present opportunities for introducing autonomy into engineered small-scale devices. This work analyzes the effect of hydrodynamic forces and rheology of local surroundings on swimming at low Reynolds number, identifies the challenges and benefits of utilizing elastohydrodynamic coupling in locomotion, and further develops a suite of machinery for building untethered microrobots with self-regulated mobility. We demonstrate that coupling the structural and magnetic properties of artificial microswimmers with the dynamic properties of the fluid leads to adaptive locomotion in the absence of on-board sensors

Morphing of Geometric Composites via Residual Swelling

Understanding and controlling the shape of thin, soft objects has been the focus of significant research efforts among physicists, biologists, and engineers in the last decade. These studies aim to utilize advanced materials in novel, adaptive ways such as fabricating smart actuators or mimicking living tissues. Here, we present the controlled growth--like morphing of 2D sheets into 3D shapes by preparing geometric composite structures that deform by residual swelling. The morphing of these geometric composites is dictated by both swelling and geometry, with diffusion controlling the swelling-induced actuation, and geometric confinement dictating the structure's deformed shape. Building on a simple mechanical analog, we present an analytical model that quantitatively describes how the Gaussian and mean curvatures of a thin disk are affected by the interplay among geometry, mechanics, and swelling. This model is in excellent agreement with our experiments and numerics. We show that the dynamics of residual swelling is dictated by a competition between two characteristic diffusive length scales governed by geometry. Our results provide the first 2D analog of Timoshenko's classical formula for the thermal bending of bimetallic beams - our generalization explains how the Gaussian curvature of a 2D geometric composite is affected by geometry and elasticity. The understanding conferred by these results suggests that the controlled shaping of geometric composites may provide a simple complement to traditional manufacturing techniques

Experimental and numerical investigation of bulging behaviour of hyperelastic textured tubes

The inflation and propagation of a localized instability in elastic tubes shares the same mathematical features with a range of other localization problems, including buckling propagation in long metal tubes under external pressure. Recent research into origami-inspired tubular geometries has suggested that geometric texturing is able to significantly improve metal pipe resistance to propagation buckling failures, with an increase in critical and propagation pressures. This paper aims to investigate whether texturing generates a similar improvement in hyperelastic tubes under axial loading and internal pressure, with elastomer origami structures of recent interest for use as soft actuators and robots. A new fabrication method with 3D printed moulds in a dip process was first developed to enable fabrication of textured tube samples. An experimental study was then conducted on inflated smooth and textured latex tubes, with instability formation observed at a 1 ms resolution. Comparative numerical models with a Mooney–Rivlin material were able to provide a good prediction of experimentally-observed behaviours up to and slightly past the critical pressure and bulge formation. A parametric numerical study is then conducted to show that the number of divisions in the axial direction and circumferential direction have no and modest effects on critical pressure, respectively. The experimental and numerical investigations both showed that the critical pressure of the textured tube was increased compared to the smooth tube, however the degree of increase was a modest 8% and so unlikely to be of significant practical benefit. This work can provide reference and guidelines for future investigations of tubular inflatable origami structures

Assessment of solar energy potential in Johor, Malaysia

Solar energy is one of the well-known renewable energy sources from sunlight that convert to free-pollution energy. One of the major development problems for developing countries is the energy dilemma. The energy problem is considered a significant obstacle to economic development. In the current situation, solar energy can be considered one of the safest options. This paper presents the assessment of solar energy potentials at nine stations in Johor, Malaysia for a five-year period stretching between 2015 and 2020. The assessment data for all stations were obtained from the Malaysian meteorological department. The meteorological parameters involved include temperature, extraterrestrial solar radiation and clearness index. The assessment technique involved the use of the Angstrom-Prescott (A-P) model to estimate the solar energy potentials at the sites. From the results obtained from the A-P model, it is apparent that Station Segamat has the highest average monthly global solar radiation on the horizontal surface with 6.7921 kWh/m2 monthly solar radiation, while Pontian station has the lowest with 6.7893 kWh/m2 monthly solar radiation. The monthly clearness index throughout the year in each station varies between 0.65 to 0.7 and the maximum temperature ranges from 22.71°C at Pontian station to 32.42°C at station Kota Tinggi. Based on the comparison and analysis of the results, it is clear that each station at Johor has an excellent solar energy potential and is suitable for photovoltaic module system application

VORTEX DYNAMICS: GEOMETRIC INFLUENCES ON MILLIROBOT MOBILITY IN FLUIDS

The Immersed Boundary Lattice Green Function (IBLGF) is a computational method for simulating fluid dynamics around complex boundaries. It combines the immersed boundary method, which enables fluid flow simulations around non-conforming geometries, with lattice Green's functions for efficient computation on a fixed Cartesian grid. We use IBLGF to analyze the propulsion mechanism of a magnetically actuated swimming millirobot developed by the Zhao Lab at Stanford. The primary feature of interest is its unique Kresling origami design, characterized by a hollow hexagonal body with radial cuts along tilted triangular panels. A rotating magnetic field spins the body, inducing an internal flow through cutouts. The mechanisms by which this propulsive flow is created are not well understood. To investigate, we first test a non-rotating millirobot in a steady flow to establish a baseline drag force. Next, we examine how the drag force is reduced, and eventually, thrust is generated as a function of the spin rate. Understanding the fluid dynamics around such a geometry will provide insights into fully optimizing the Kresling pattern —or similar tessellations— for a broader range of applications

Localized Structures in Indented Shells: A Numerical Investigation

We present results from a numerical investigation of the localization of deformation in thin elastomeric spherical shells loaded by differently shaped indenters. Beyond a critical indentation, the deformation of the shell ceases to be axisymmetric and sharp structures of localized curvature form, referred to as “s-cones,” for “shell-cones.” We perform a series of numerical experiments to systematically explore the parameter space. We find that the localization process is independent of the radius of the shell. The ratio of the radius of the shell to its thickness, however, is an important parameter in the localization process. Throughout, we find that the maximum principal strains remain below 6%, even at the s-cones. As a result, using either a linear elastic (LE) or hyperelastic constitutive description yields nearly indistinguishable results. Friction between the indenter and the shell is also shown to play an important role in localization. Tuning this frictional contact can suppress localization and increase the load-bearing capacity of the shell under indentation.National Science Foundation (U.S.) (1122374)National Science Foundation (U.S.) (CMMI-1351449