Controlling subterranean forces enables a fast, steerable, burrowing soft robot

2021 ◽  
Vol 6 (55) ◽  
pp. eabe2922
Author(s):  
Nicholas D. Naclerio ◽  
Andras Karsai ◽  
Mason Murray-Cooper ◽  
Yasemin Ozkan-Aydin ◽  
Enes Aydin ◽  
...  
Keyword(s):  
Granular Media ◽  
The Body ◽  
Nonlinear Dependence ◽  
Soft Robot ◽  
Flow Angle ◽  
Drag Forces ◽  
Tip Extension ◽  
Order Of Magnitude ◽  
Lift And Drag ◽  
And Control

Robotic navigation on land, through air, and in water is well researched; numerous robots have successfully demonstrated motion in these environments. However, one frontier for robotic locomotion remains largely unexplored—below ground. Subterranean navigation is simply hard to do, in part because the interaction forces of underground motion are higher than in air or water by orders of magnitude and because we lack for these interactions a robust fundamental physics understanding. We present and test three hypotheses, derived from biological observation and the physics of granular intrusion, and use the results to inform the design of our burrowing robot. These results reveal that (i) tip extension reduces total drag by an amount equal to the skin drag of the body, (ii) granular aeration via tip-based airflow reduces drag with a nonlinear dependence on depth and flow angle, and (iii) variation of the angle of the tip-based flow has a nonmonotonic effect on lift in granular media. Informed by these results, we realize a steerable, root-like soft robot that controls subterranean lift and drag forces to burrow faster than previous approaches by over an order of magnitude and does so through real sand. We also demonstrate that the robot can modulate its pullout force by an order of magnitude and control its direction of motion in both the horizontal and vertical planes to navigate around subterranean obstacles. Our results advance the understanding and capabilities of robotic subterranean locomotion.

Computational Aerodynamics of a Winston-Cup-Series Race Car

2002 ◽  
Author(s):  
Oktay Baysal ◽  
Terry L. Meek
Keyword(s):  
Present Model ◽  
Pressure Coefficient ◽  
The Body ◽  
Race Car ◽  
Drag Forces ◽  
Surface Pressure Distribution ◽  
Computational Aerodynamics ◽  
Baseline Case ◽  
Quantitative Results ◽  
Lift And Drag

Since the goal of racing is to win and since drag is a force that the vehicle must overcome, a thorough understanding of the drag generating airflow around and through a race car is greatly desired. The external airflow contributes to most of the drag that a car experiences and most of the downforce the vehicle produces. Therefore, an estimate of the vehicle’s performance may be evaluated using a computational fluid dynamics model. First, a computer model of the race car was created from the measurements of the car obtained by using a laser triangulation system. After a computer-aided drafting model of the actual car was developed, the model was simplified by removing the tires, roof strakes, and modification of the spoiler. A mesh refinement study was performed by exploring five cases with different mesh densities. By monitoring the convergence of the computed drag coefficient, the case with 2 million elements was selected as being the baseline case. Results included flow visualization of the pressure and velocity fields and the wake in the form of streamlines and vector plots. Quantitative results included lift and drag, and the body surface pressure distribution to determine the centerline pressure coefficient. When compared with the experimental results, the computed drag forces were comparable but expectedly lower than the experimental data mainly attributable to the differences between the present model and the actual car.

scholarly journals Mechanical models of sandfish locomotion reveal principles of high performance subsurface sand-swimming

2011 ◽  
Vol 8 (62) ◽  
pp. 1332-1345 ◽  
Author(s):  
Ryan D. Maladen ◽  
Yang Ding ◽  
Paul B. Umbanhowar ◽  
Adam Kamor ◽  
Daniel I. Goldman
Keyword(s):  
High Speed ◽  
High Performance ◽  
Granular Media ◽  
The Body ◽  
Physical Models ◽  
Particle Simulation ◽  
Sinusoidal Wave ◽  
Drag Forces ◽  
Single Period ◽  
Discrete Particle Simulation

We integrate biological experiment, empirical theory, numerical simulation and a physical model to reveal principles of undulatory locomotion in granular media. High-speed X-ray imaging of the sandfish lizard, Scincus scincus , in 3 mm glass particles shows that it swims within the medium without using its limbs by propagating a single-period travelling sinusoidal wave down its body, resulting in a wave efficiency, η , the ratio of its average forward speed to the wave speed, of approximately 0.5. A resistive force theory (RFT) that balances granular thrust and drag forces along the body predicts η close to the observed value. We test this prediction against two other more detailed modelling approaches: a numerical model of the sandfish coupled to a discrete particle simulation of the granular medium, and an undulatory robot that swims within granular media. Using these models and analytical solutions of the RFT, we vary the ratio of undulation amplitude to wavelength ( A / λ ) and demonstrate an optimal condition for sand-swimming, which for a given A results from the competition between η and λ . The RFT, in agreement with the simulated and physical models, predicts that for a single-period sinusoidal wave, maximal speed occurs for A / λ ≈ 0.2, the same kinematics used by the sandfish.

Dragonfly flight. I. Gliding flight and steady-state aerodynamic forces.

1997 ◽  
Vol 200 (3) ◽  
pp. 543-556 ◽  
Author(s):  
JM Wakeling ◽  
CP Ellington
Keyword(s):  
Steady State ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
The Body ◽  
Flat Plates ◽  
Viscous Forces ◽  
Drag Forces ◽  
Aerodynamic Properties ◽  
Gliding Flight ◽  
Lift And Drag

The free gliding flight of the dragonfly Sympetrum sanguineum was filmed in a large flight enclosure. Reconstruction of the glide paths showed the flights to involve accelerations. Where the acceleration could be considered constant, the lift and drag forces acting on the dragonfly were calculated. The maximum lift coefficient (CL) recorded from these glides was 0.93; however, this is not necessarily the maximum possible from the wings. Lift and drag forces were additionally measured from isolated wings and bodies of S. sanguineum and the damselfly Calopteryx splendens in a steady air flow at Reynolds numbers of 700-2400 for the wings and 2500-15 000 for the bodies. The maximum lift coefficients (CL,max) were 1.07 for S. sanguineum and 1.15 for C. splendens, which are greater than those recorded for all other insects except the locust. The drag coefficient at zero angle of attack ranged between 0.07 and 0.14, being little more than the Blassius value predicted for flat plates. Dragonfly wings thus show exceptional steady-state aerodynamic properties in comparison with the wings of other insects. A resolved-flow model was tested on the body drag data. The parasite drag is significantly affected by viscous forces normal to the longitudinal body axis. The linear dependence of drag on velocity must thus be included in models to predict the parasite drag on dragonflies at non-zero body angles.

Numerical Prediction of 3-D Vortex-Induced Vibration of Catenary Riser In Planar and Non-Planar Flows

2021 ◽  
Author(s):  
Bowen Ma ◽  
Narakorn Srinil
Keyword(s):  
Flow Direction ◽  
Cross Flow ◽  
Travelling Wave ◽  
Flow Angle ◽  
Fluid Structure ◽  
Vortex Induced Vibration ◽  
Drag Forces ◽  
Wake Oscillators ◽  
Lift And Drag ◽  
Planar Flows

Abstract Vortex-induced vibration (VIV) is one of the most critical issues in deepwater developments due to its resultant fatigue damage to subsea structures such as risers, pipelines and jumpers. Although VIV effects on slender bodies have been comprehensively studied over decades, very few studies have dealt with VIV modelling and prediction of catenary risers in current flows with varying directions leading to complex fluid-structure interactions. This study advances a numerical model to simulate and predict 3-D VIV responses of a catenary riser in three flow orientations, relative to the riser curvature plane, including concave/convex (planar) and perpendicular (non-planar) flows. The model is described by equations of cross-flow and in-line responses of the catenary riser coupled with the hydrodynamic forces modelled by the distributed nonlinear wake oscillators. A finite difference method is applied to solve the coupled fluid-structure dynamic system. To consider the approaching flow in different directions, the vortex-induced lift and drag forces are formulated by accounting for the effect of flow angle of attack and the riser-flow relative velocities. Results show VIV features of a long catenary riser exhibiting a standing and travelling wave response pattern. VIV response amplitudes and oscillation frequencies are predicted and compared with experimental results in the literature for both straight and catenary risers. Overall results highlight the model capability in capturing the effect of approaching flow direction on 3-D VIV of the curved inclined flexible riser.

scholarly journals Unsteady dynamics of rapid perching manoeuvres

2015 ◽  
Vol 767 ◽  
pp. 323-341 ◽  
Author(s):  
Delyle T. Polet ◽  
David E. Rival ◽  
Gabriel D. Weymouth
Keyword(s):  
Unsteady Aerodynamics ◽  
Boundary Layer Separation ◽  
Added Mass ◽  
High Lift ◽  
Drag Forces ◽  
Image Velocimetry ◽  
Trailing Edges ◽  
Series Of Experiments ◽  
Lift And Drag ◽  
And Control

AbstractA perching bird is able to rapidly decelerate while maintaining lift and control, but the underlying aerodynamic mechanism is poorly understood. In this work we perform a study on a simultaneously decelerating and pitching aerofoil section to increase our understanding of the unsteady aerodynamics of perching. We first explore the problem analytically, developing expressions for the added-mass and circulatory forces arising from boundary-layer separation on a flat-plate aerofoil. Next, we study the model problem through a detailed series of experiments at $\mathit{Re}=22\,000$ and two-dimensional simulations at $\mathit{Re}=2000$. Simulated vorticity fields agree with particle image velocimetry measurements, showing the same wake features and vorticity magnitudes. Peak lift and drag forces during rapid perching are measured to be more than 10 times the quasi-steady values. The majority of these forces can be attributed to added-mass energy transfer between the fluid and aerofoil, and to energy lost to the fluid by flow separation at the leading and trailing edges. Thus, despite the large angles of attack and decreasing flow velocity, this simple pitch-up manoeuvre provides a means through which a perching bird can maintain high lift and drag simultaneously while slowing to a controlled stop.

Vortex force map method for viscous flows of general airfoils

2017 ◽  
Vol 836 ◽  
pp. 145-166 ◽  
Author(s):  
Juan Li ◽  
Zi-Niu Wu
Keyword(s):  
Flat Plate ◽  
Normal Force ◽  
Viscous Flows ◽  
Reynolds Numbers ◽  
The Body ◽  
Drag Forces ◽  
Edge Force ◽  
Lift And Drag ◽  
Critical Regions ◽  
Map Approach

In a previous paper, an inviscid vortex force map approach was developed for the normal force of a flat plate at arbitrarily high angle of attack and leading/trailing edge force-producing critical regions were identified. In this paper, this vortex force map approach is extended to viscous flows and general airfoils, for both lift and drag forces due to vortices. The vortex force factors for the vortex force map are obtained here by using Howe’s integral force formula. A decomposed form of the force formula, ensuring vortices far away from the body have negligible effect on the force, is also derived. Using Joukowsky and NACA0012 airfoils for illustration, it is found that the vortex force map for general airfoils is similar to that of a flat plate, meaning that force-producing critical regions similar to those of a flat plate also exist for more general airfoils and for viscous flow. The vortex force approach is validated against NACA0012 at several angles of attack and Reynolds numbers, by using computational fluid dynamics.

Fluid forces on a body in shear-flow; experimental use of ‘stationary flow'

1974 ◽  
Vol 340 (1621) ◽  
pp. 147-171 ◽  
Keyword(s):  
Shear Flow ◽  
Lift Force ◽  
Force Measurement ◽  
Fluid Velocity ◽  
Stationary Flow ◽  
The Body ◽  
Fluid Forces ◽  
Drag Forces ◽  
Lift And Drag ◽  
Repulsive Forces

The lift and drag forces have been measured on a sphere and a transverse cylinder immersed in an open liquid shear-flow and situated close to the lower, frictional, boundary (the bed). Two conditions were investigated: ( a ) that of zero drag, when the body was drifting with the flow, and ( b ) that when it was held against the flow. In condition ( a ) the body could be either allowed to rotate about a transverse axis subject to unavoidable pivot friction, or prevented from rotating. Marked difference was found in the magnitude of the lift force according to the applied resistance to rotation. The lift force was a maximum when rotation was prevented and small or undetectable when free rotation was allowed. In the conditions ( a ) and ( b ) the lift force decreased with increasing clearance between body and boundary, to zero when the clearance exceeded approximately one body diameter. In condition ( b ) lift, i. e. normally repulsive, forces of approximately equal magnitudes to those below were exerted as the body approached the upper free liquid surface. In the drifting condition ( a ) the considerable difficulties of observation and force measurement when a body is moving with the flow were removed by the use of a backward-moving bed boundary. By thus superimposing a reverse velocity on the whole system, the mean fluid velocity at any desired distance from the boundary can be made zero relative to the observer without appreciably affecting the internal dynamics of the flow. This device also permitted the repetition of the measurements made by using liquids of greater viscosity than water available in limited quantities. The results are interpreted with an explanation in mind of certain aspects of the motions of unsuspended solids in saltation over a stream bed.

scholarly journals Cavities at atmospheric pressure behind two-dimensional bodies at an angle of attack

2005 ◽  
Vol 47 (1) ◽  
pp. 103-119
Author(s):  
P. M. Haese
Keyword(s):  
Atmospheric Pressure ◽  
Angle Of Attack ◽  
The Body ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Physical Conditions ◽  
Drag Forces ◽  
Lift And Drag ◽  
Drag Ratio ◽  
Lift To Drag Ratio

AbstractThis paper presents an interior source method for the calculation of semi-infinite cavities behind two-dimensional bluff bodies placed at an angle of attack in a uniform stream. Aspects under consideration include the pressure distribution along the body, especially just ahead of the separation point, lift and drag forces, and how these quantities vary with the angle of attack. We include discussion of the physical conditions of separation, and identify critical angles of attack for which the cavitating flow past an airfoil may (a) become unstable, or (b) yield the greatest lift to drag ratio.

scholarly journals A Perturbation Method to Analyze the Effect of Cross Section and Angle of Attack for Some Conical Bodies in Hypersonic Flow

2010 ◽  
Vol 3 (1) ◽  
pp. 52-58
Author(s):  
N. Talebanfard ◽  
A. B. Rahimi
Keyword(s):  
Perturbation Method ◽  
Cross Section ◽  
Cross Sections ◽  
Angle Of Attack ◽  
The Body ◽  
Drag Forces ◽  
Lift And Drag ◽  
Flow Variables ◽  
Drag Ratio ◽  
Lift To Drag Ratio

An analysis is performed to study the supersonic flow over conical bodies of three different cross sections circular, elliptic and squircle (square with rounded corners) shaped. Perturbation method is applied to find flow variables analytically. In order to find lift and drag forces the pressure force on the body is found, the component along x is drag and the component along z is lift. Three equations are obtained for lift to drag ratio of each cross section. The graphs for L/D show that for a particular cross section an increase in angle of attack, increases L/D. Comparing L/D in the three mentioned cross sections it is obtained that L/D is the greatest in squircle then in ellipse and the least in circle. The results have applications in design of flying objects such as airplanes where many more seats can be arranged in ellipse and or squircle cross section compared to regular circular case.

Magnetohydrodynamic wakes

1963 ◽  
Vol 15 (1) ◽  
pp. 1-12 ◽  
Author(s):  
M. B. Glauert
Keyword(s):  
Velocity Field ◽  
Electric Current ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Effective Diffusivity ◽  
The Body ◽  
Flow Perturbation ◽  
Drag Forces ◽  
Lift And Drag ◽  
Three Degrees Of Freedom

The most notable feature of the magnetohydrodynamic flow at large distances from a three-dimensional body is the formation of two wakes, within which vorticity and electric current are confined. In this paper results are obtained for the effective diffusivity and the relation between current and vorticity in each wake, for the balance between the strengths of the disturbances in the wakes and in the irrotational current-free flow outside, and for the lift and drag forces acting on the body. The final answers take the form of remarkably simple extensions of the corresponding formulae for non-conducting flow. In spite of the extra wake and the presence of a magnetic as well as a velocity field, the flow perturbation at large distances still has only three degrees of freedom.

Sign in / Sign up

Export Citation Format

Share Document