Welcome

Welcome to the website for Professor Oliver M. O'Reilly's group at the University of California at Berkeley. His group's research is focused on models and analyses for the dynamics of a wide range of mechanical and manufactured systems ranging from soft robots and vehicles to plant growth and the human spine. Current research projects include:

The work uses analytical, numerical, and experimental methods to improve understanding of the engineering science underpinning these problems. You are also welcome to visit our YouTube channel or Twitter feed.

Lab News

August 2017

Welcome to the lab Nate Goldberg! Nate is an incoming M.S./Ph.D. student who just received his B.S. from UC San Diego. We wish him great success in his graduate studies at UC Berkeley!

June 2017

Welcome to the lab Daniel Kawano! Daniel is a visiting scholar who is currently on sabbatical from Rose-Hulman Institute of Technology.

May 2017

Congratulations to Hyung-Taek Kim and Evan Hemingway on passing their qualifying exams and advancing to candidacy as doctoral students!

Congratulations to Dr. Paul Drazin and Dr. Christopher Daily-Diamond who were both awarded their Ph.D. degrees in May 2017!

April 2017

A recent paper investigating the factors in a shoelace's untying has been published and we are rather excited about it! See the official press release here, an informative (slow motion!) video here, and a local news segment here.

Congratulations to Ph.D. student Evan Hemingway for receiving an Outstanding Graduate Student Instructor (OGSI) Award from U.C. Berkeley. We are also delighted to welcome him back from the International Center for Mechanical Sciences CISM-AIMETA in Udine, Italy where he presented six lectures in a mini course on "Dynamic Stability and Bifurcation in Nonconservative Mechanics."

March 2017

Congratulations to Oliver O'Reilly on the publication of his latest textbook "Modeling Nonlinear Problems in the Mechanics of Strings and Rods." The book is freely available to students.

Recent Videos, Lectures, Seminars, and Conference Presentations

Slow Motion Shoelace Untying

High-speed video capture of the shoes of a runner on a treadmill. We observed that repeated impact of the shoe on the ground produces accelerations on the knot in the range of 7gs – more than that experienced by the human body on the most extreme roller coaster in the world! – and causes the knot to loosen. As the knot loosens, a ‘whipping’ motion of the lace strands and loops help to pull apart the knot. Once this begins to happen, force imbalances develop between the bowtie loops and free strands which eventually, and suddenly, lead to runaway untying. The final failure of the knot happens in a matter of seconds, and with little visual warning. Link to publication here.

Surprising Moments in Biomechanics and the Dynamics of Rigid Bodies

Presented by Oliver O'Reilly at the Technical University of Hamburg (TUHH) on May 25 2016

Touches on topics in the following areas:

  • Euler Angle Parameterization: Euler and Dual Euler Bases
  • Conservative Moments
  • Constraint Moments
  • Lagrange's Equations of Motion
  • Joint Coordinate System in Biomechanics
Watch the Lecture...

Rotations: Perspectives on Some Old and Some New Results

Presented by Oliver O'Reilly at the Technical University of Hamburg (TUHH) on May 25 2016

Touches on topics in the following areas:

  • Attitudes with Constant Angular Velocities
  • Saccadic Motions of the Eye
  • Geodesics and Quaternions
  • SLERP Algorithm in Computer Graphics
  • Three Types of Rotations
Watch the Lecture...

Differential Geometry and Lagrange's Equations of Motion

Presented by Oliver O'Reilly at the Technical University of Hamburg (TUHH) on May 24 2016

The goal of this talk is to show how notions for differential geometry related Newton-Euler and Lagrange equations of motion, and it includes:

  • A single particle in 3-space
  • A single particle on a cone
  • A simple proof for a single particle
  • Constraints and rigid bodies
  • Lagrange's equations for a rigid body
Watch the Lecture...

Stories from Rotations: Luck, Fear, and Mystery

Presented by Oliver O'Reilly to the Department of Mechanical Engineering, University of Michigan, Ann Arbor in January 2015

This lecture discuss four stories from the rich topic of rotations:

  • Tale 1: Changing Handedness
  • Tale 2: A Hidden Basis
  • Tale 3: Hamilton and Gauss
  • Tale 4: The Human Eye
Watch the Lecture...

Recent Publications

Mass-Modulation Schemes for a Class of Wave Energy Converters: Experiments, Models, and Efficacy

In a recent series of works, mass-modulation schemes have been proposed for a class of ocean wave energy converter (WEC). The goal of the schemes is to improve the energy harvesting capabilities of these devices by taking advantage of the ambient water. However this improvement comes at the cost of increased system complexity and possible impulse loadings at the instances where the mass changes. In the present work, experimental results for a pair of these schemes are presented and one of them is shown to be effective in increasing the energy harvesting potential of a WEC. Building and testing prototype WECs are costly and challenging and so, in order to examine as wide a range of parameters and designs as possible, a detailed two degree-of-freedom model is developed for a WEC equipped with a mass-modulation scheme. Numerical analysis of the model also shows the potential benefits of the mass-modulation scheme. Read More...

C. A. Diamond, C. Q. Judge, B. Orazov, Ö. Savaş and O. M. O'Reilly, Mass-Modulation Schemes for a Class of Wave Energy Converters: Experiments, Models, and Efficacy, Ocean Engineering, Vol. 104, 452-468 (2015).

C.A. Diamond, O. M. O’Reilly, and Ö. Savaş, The Impulsive Effects of Momentum Transfer on the Dynamics of a Novel Ocean Wave Energy Converter, Journal of Sound and Vibration, Vol. 332, No. 21, 5559-5565 (2013).

On Geodesics of the Rotation Group SO(3)

Geodesics of SO(3) are characterized by constant angular velocity motions and as great circles on a three-sphere. The former interpretation is widely used in optometry and the latter features in the interpolation of rotations in computer graphics. The simplicity of these two disparate interpretations belies the complexity of the corresponding rotations. Using a quaternion representation for a rotation, we present a simple proof of the equivalence of the aforementioned characterizations and a straightforward method to establish features of the corresponding rotations. Read More...

A. Novelia and O. M. O’Reilly, On Geodesics of the Rotation Group SO(3), Regular and Chaotic Dynamics, Vol. 20, No. 6, 729–738 (2015).

A. Novelia and O. M. O’Reilly, On the Dynamics of the Eye: Geodesics on a Configuration Manifold and Motions of the Gaze Direction and Helmholtz's Theorem, Nonlinear Dyanamics, Vol. 80, No. 3, 1303-1327 (2015).

Soft Hands: An Analysis of Some Gripping Mechanisms in Soft Robot Design

In contrast to their more rigid counterparts, soft robots have the ability to gently grip and maneuver objects with open-loop kinematic control. Guided by several recent designs and implementations of soft robot hands, the present paper analyzes a rod-based model for the fingers in the hand of a soft robot. We show precisely how gripping is achieved and how the performance can be affected by varying the system’s parameters. The designs we are interested in feature pneumatic control of the soft robot and we model this actuation as a varying intrinsic curvature profile of the rod. Our work provides a framework for the theoretical analysis of the soft robot and the resulting analysis can also be used to develop some design guidelines. Read More...

X. Zhou, C. Majidi, and O. M. O’Reilly, Soft Hands: An Analysis of Some Gripping Mechanisms in Soft Robot Design, International Journal of Solids and Structures, Vol. 64-65, 155-165 (2015).

Energy Efficiency in Friction-Based Locomotion Mechanisms for Soft and Hard Robots: Slower can be Faster

Many recent designs of soft robots and nano-robots feature locomotion mechanisms that cleverly exploit slipping and sticking phenomena. These mechanisms have many features in common with peristaltic locomotion found in the animal world. The purpose of the present paper is to examine the energy efficiency of a locomotion mechanism that exploits friction. With the help of a model that captures most of the salient features of locomotion, we show how locomotion featuring stick-slip friction is more efficient than a counterpart that only features slipping. Our analysis also provides a framework to establish how optimal locomotion mechanisms can be selected. Read More...

X. Zhou, C. Majidi, and O. M. O’Reilly, Energy Efficiency in Friction-Based Locomotion Mechanisms for Soft and Hard Robots: Slower can be Faster, Nonlinear Dynamics, Vol. 78, No. 4, 2811-2821 (2014).

On the Modeling of the Intervertebral Disc in Multibody Models for the Spine

The need to develop feasible computational musculoskeletal models of the spine has led to the development of several multibody models. Central features in these works are models for the ligaments, muscles, and intervertebral joint. The purpose of the present paper is to show how experimental measurements of joint stiffnesses can be properly incorporated using a bushing element. The required refinements to existing bushing force functions in musculoskeletal software platforms are discussed and further implemented using a SpineBushing element specific to the intervertebral joint. Four simple lumbar spine models are then used to illustrate the accompanying improvements. Electronic supplemental material for this article includes a complementary review of formulations of stiffness matrices for the intervertebral joint. Read More...

M. Christophy, M. Curtin, N. A. Faruk Senan, J. C. Lotz, and O. M. O’Reilly, On the Modeling of the Intervertebral Disc in Multibody Models for the Spine, Multibody System Dynamics, Vol. 30, No. 4, 413-432 (2013).

M. Christophy, N. A. Faruk Senan, J. C. Lotz, and O. M. O’Reilly, A Muscloskeletal Model for the Lumbar Spine, Biomechanics and Modeling in Mechanobiology, Vol. 11, No. 1-2, 19-34 (2012).

Bifurcations and Instability in the Adhesion of Intrinsically Curved Rods

Motivated by applications such as gecko-inspired adhesives and microdevices featuring slender rod-like bodies, there has been an increase in interest in the deformed shapes of elastic rods adhering to rigid surfaces. A central issue in analyses of the rod-based models for these systems is the stability of the predicted equilibrium configurations. Such analyses can be complicated by the presence of intrinsic curvatures induced by fabrication processes. The results in the present paper are used to show how this curvature can lead to shear-induced bifurcations and instabilities. To characterize potential instabilities, a new set of necessary conditions for stability are employed which cater to the possible combinations of buckling and delaminating instabilities. Read More...

C. Majidi, O. M. O’Reilly and J. A. Williams, Bifurcations and Instability in the Adhesion of Intrinsically Curved Rods, Mechanics Research Communications, Vol 49, 13-16 (2013).

C. Majidi, O. M. O’Reilly and J. A. Williams, On the Stability of a Rod Adhering to a Rigid Surface: Shear-Induced Stable Adhesion and the Instability of Peeling, Journal of the Mechanics and Physics of Solids, Vol. 60, No. 5, 827-843 (2012).