Amos G. Winter

Localized fluidization burrowing mechanics of Ensis directus

SUMMARY Muscle measurements of Ensis directus, the Atlantic razor clam, indicate that the organism only has sufficient strength to burrow a few centimeters into the soil, yet razor clams burrow to over 70 cm. In this paper, we show that the animal uses the motions of its valves to locally fluidize the surrounding soil and reduce burrowing drag. Substrate deformations were measured using particle image velocimetry (PIV) in a novel visualization system that enabled us to see through the soil and watch E. directus burrow in situ. PIV data, supported by soil and fluid mechanics theory, show that contraction of the valves of E. directus locally fluidizes the surrounding soil. Particle and fluid mixtures can be modeled as a Newtonian fluid with an effective viscosity based on the local void fraction. Using these models, we demonstrate that E. directus is strong enough to reach full burrow depth in fluidized soil, but not in static soil. Furthermore, we show that the method of localized fluidization reduces the amount of energy required to reach burrow depth by an order of magnitude compared with penetrating static soil, and leads to a burrowing energy that scales linearly with depth rather than with depth squared.

Identification and Evaluation of the Atlantic Razor Clam (Ensis directus) for Biologically Inspired Subsea Burrowing Systems

In this article, we identify and analyze a subsea organism to serve as a model for biologically inspired burrowing technology to be used in applications such as anchoring, installation of cables, and recovery of oil. After inspecting myriad forms of life that live on or within ocean substrates, the Atlantic razor clam, Ensis directis, stood out as an attractive basis for new burrowing technology because of its low-energy requirements associated with digging (0.21 J/cm), its speed and depth of burrrowing (∼1 cm/s and 70 cm, respectively), and its size and simplicity relative to man-made machines. As anchoring is a prime application for the technology resulting from this work, the performance of an Ensis directus-based anchoring system was compared to existing technologies. In anchoring force per embedment energy, the E. directus-based anchor beats existing technology by at least an order of magnitude. In anchoring force per weight of device, the biologically inspired system weighs less than half that of current anchors. The article concludes with a review of E. directuss digging strategy, which involves motions of its valves to locally fluidize the substrate to reduce burrowing drag and energy, and the successful adaptation of E. directuss burrowing mechanisms into an engineering system: the RoboClam burrowing robot, which, like the animal, uses localized fluidization to achieve digging energy that scales linearly with depth, rather than depth squared, for moving through static soil.

The Effects of Prosthesis Inertial Properties on Prosthetic Knee Moment and Hip Energetics Required to Achieve Able-Bodied Kinematics

There is a major need in the developing world for a low-cost prosthetic knee that enables users to walk with able-bodied kinematics and low energy expenditure. To efficiently design such a knee, the relationship between the inertial properties of a prosthetic leg and joint kinetics and energetics must be determined. In this paper, using inverse dynamics, the theoretical effects of varying the inertial properties of an above-knee prosthesis on the prosthetic knee moment, hip power, and absolute hip work required for walking with able-bodied kinematics were quantified. The effects of independently varying mass and moment of inertia of the prosthesis, as well as independently varying the masses of each prosthesis segment, were also compared. Decreasing prosthesis mass to 25% of physiological leg mass increased peak late-stance knee moment by 43% and decreased peak swing knee moment by 76%. In addition, it reduced peak stance hip power by 26%, average swing hip power by 76%, and absolute hip work by 22%. Decreasing upper leg mass to 25% of its physiological value reduced absolute hip work by just 2%, whereas decreasing lower leg and foot mass reduced work by up to 22%, with foot mass having the greater effect. Results are reported in the form of parametric illustrations that can be utilized by researchers, designers, and prosthetists. The methods and outcomes presented have the potential to improve prosthetic knee component selection, facilitate able-bodied kinematics, and reduce energy expenditure for users of low-cost, passive knees in developing countries, as well as for users of advanced active knees in developed countries.

Critical Timescales for Burrowing in Undersea Substrates via Localized Fluidization, Demonstrated by RoboClam: A Robot Inspired by Atlantic Razor Clams

The Atlantic razor clam (Ensis directus) burrows into underwater soil by using motions of its shell to locally fluidize the surrounding substrate. The energy associated with movement through fluidized soil — characterized by a depth-independent density and viscosity — scales linearly with depth. In contrast, moving through static soil requires energy that scales with depth squared. For E. directus, this translates to a 10X reduction in the energy required to reach observed burrow depths. For engineers, localized fluidization offers a mechanically simple and purely kinematic method to dramatically reduce burrowing energy. This concept is demonstrated with RoboClam, an E. directus-inspired robot. Using a genetic algorithm to generate digging kinematics, RoboClam has achieved localized fluidization and burrowing performance comparable to that of the animal, with a linear energy-depth relationship. In this paper, we present the critical timescales and associated kinematics necessary for achieving localized fluidization, which are calculated from soil parameters and validated via RoboClam and E. directus testing.Copyright

Dynamics of digging in wet soil

Numerous animals live in, and locomote through, subsea soils. To move in a medium dominated by frictional interactions, many of these animals have adopted unique burrowing strategies. This paper presents a burrowing model inspired by the Atlantic razor clam (Ensis directus), which uses deformations of its body to cyclically loosen and re-pack the surrounding soil in order to locally manipulate burrowing drag. The model reveals how an anisotropic body ‐ composed of a cylinder and sphere varying sinusoidally in size and relative displacement ‐ achieves unidirectional motion through a medium with variable frictional properties. This net displacement is attained even though the body kinematics are reciprocal and inertia of both the model organism and the surrounding medium are negligible. Our results indicate that body aspect ratio has a strong e ect on burrowing velocity and e ciency, with a well-defined maximum for given kinematics and soil material properties.

The Design and Testing of RoboClam: A Machine Used to Investigate and Optimize Razor Clam-Inspired Burrowing Mechanisms for Engineering Applications

Razor clams (Ensis directus) are one of nature’s most adept burrowing organisms, able to dig to 70cm at nearly 1cm/s using only 0.21J/cm. Ensis reduces burrowing drag by using motions of its shell to fluidize a thin layer of substrate around its body. Although these shell motions have an energetic cost, moving through fluidized rather than packed soil results in exponentially lower overall energy consumption. This paper describes the design and testing of RoboClam, a device that mimics Ensis digging methods to understand the limits of razor clam-inspired burrowing, how they scale for different environments and conditions, and how they can be transferred into engineering applications. Using a genetic optimization solver, we found that RoboClam’s most efficient digging motion mimicked Ensis shell kinematics and yielded a power law relationship between digging energy and depth of n = 1.17, very close to the ideal value of n = 1. Pushing through static soil has a theoretical energy-depth power law of n = 2, which means that Ensis-inspired burrowing motions can provide exponentially higher energy efficiency and nearly depth-independent drag resistance.© 2009 ASME

Effects of Prosthesis Mass on Hip Energetics, Prosthetic Knee Torque, and Prosthetic Knee Stiffness and Damping Parameters Required for Transfemoral Amputees to Walk With Normative Kinematics

We quantify how the hip energetics and knee torque required for an above-knee prosthesis user to walk with the kinematics of able-bodied humans vary with the inertial properties of the prosthesis. We also select and optimize passive mechanical components for a prosthetic knee to accurately reproduce the required knee torque. Previous theoretical studies have typically investigated the effects of prosthesis inertial properties on energetic parameters by modifying both mass and mass distribution of the prosthesis and computing kinetic and energetic parameters only during swing. Using inverse dynamics, we determined the effects of independently modifying mass and mass distribution of the prosthesis, and we computed parameters during both stance and swing. Results showed that reducing prosthesis mass significantly affected hip energetics, whereas reducing mass distribution did not. Reducing prosthesis mass to 25% of the mass of a physiological leg decreased peak stance hip power by 26%, average swing hip power by 74%, and absolute hip work over the gait cycle by 22%. Previous studies have also typically optimized prosthetic knee components to reproduce the knee torque generated by able-bodied humans walking with normative kinematics. However, because the prosthetic leg of an above-knee prosthesis user weighs significantly less than a physiological leg, the knee torque required for above-knee prosthesis users to walk with these kinematics may be significantly different. Again using inverse dynamics, it was found that changes in prosthesis mass and mass distribution significantly affected this required torque. Reducing the mass of the prosthesis to 25% of the mass of the physiological leg increased peak stance torque by 43% and decreased peak swing torque by 76%. The knee power required for an above-knee prosthesis user to walk with the kinematics of able-bodied humans was analyzed to select passive mechanical components for the prosthetic knee. The coefficients of the components were then optimized to replicate the torque required to walk with the kinematics of able-bodied humans. A prosthetic knee containing a single linear spring and two constant-force dampers was found to accurately replicate the targeted torque (R 2 =0.90 for a typical prosthesis). Optimal spring coefficients were found to be relatively insensitive to mass alterations of the prosthetic leg, but optimal damping coefficients were sensitive. In particular, as the masses of the segments of the prosthetic leg were altered between 25% and 100% of ablebodied values, the optimal damping coefficient of the second damper varied by 330%, with foot mass alterations having the greatest effect on its value.

The Design, Fabrication, and Performance of the East African Trial Leveraged Freedom Chair

Massachusetts Institute of Technology. Office of the Dean for Graduate Education (Hugh Hampton Young Memorial Fellowship)

A Mathematical Model for Pressure Compensating Emitters

This paper presents a mathematical model investigating the physics behind pressure-compensating (PC) drip irrigation emitters. A network of PC emitters, commonly known as drip irrigation, is an efficient way to deliver water to crops while increasing yield. Irrigation can provide a means for farmer to grow more sensitive, and profitable crops and help billions of small-holder farmers lift themselves out of poverty. Making drip irrigation accessible and economically viable is important for developing farmers as most face the challenges of water scarcity, declining water tables and lack of access to an electrical grid. One of the main reasons for the low adoption rate of drip irrigation in the developing world is the relatively high cost of the pumping power. It is possible to reduce this cost by reducing the required activation pressure of the emitters, while maintaining the PC behavior. The work presented here provides a guide of how design changes in the emitter could allow for a reduction in the activation pressure from 1 bar to approximately 0.1 bar. This decrease in the activation pressure of each emitter in turn decreases the system driving pressure. This reduction of driving pressure will decrease the energy need of pumping, making a solar-powered system affordable for small-acreage farmers.This paper develops a mathematical model to describe the PC behavior in a commercially available emitter. It is a 2D model that explains the relationship between the pressure, structural deformation and fluid flow within a PC emitter. A parametric study has been performed to understand the effects of geometric and material parameters with regards to the activation pressure and PC behavior. This knowledge will help guide the designs and prototypes of optimized emitters with a lower activation pressure, while also providing the PC behavior.Copyright

Bio-Inspired, Low-Cost, Self-Regulating Valves for Drip Irrigation in Developing Countries

We use nonlinear behavior of thin-walled structures — an approach inspired by biological systems (the human airway, for example) — to address one of the most important problems facing subsistence farmers in developing countries: lack of access to inexpensive, water-efficient irrigation systems. An effective way of delivering water to crops is through a network of emitters, with up to 85% of the water delivered being absorbed by plants. However, of the 140 million hectares of cropped land in India alone, only 61 million are irrigated and just 5 million through drip irrigation. This is, in part, due to the relatively high cost of drip irrigation. The main cost comes from the requirement to pump the water at relatively high pressure (>1bar), to minimize the effect of uneven terrain and viscous losses in the network, and to ensure that each plant receives the same amount of water. Using a prototype, we demonstrate that the pressure required to drive the system can be reduced significantly by using thin-walled structures to design emitters with completely passive self-regulation that activates at approximately 0.1bar. This reduction in driving pressure could help bring the price of drip irrigation systems from several thousand dollars to approximately