Engineering Commons^™

Hydrodynamics Of Dna Confined In Nanoslits And Nanochannels, K. D. Dorfman, D. Gupta, A. Jain, Douglas R. Tree

Faculty Publications

Modeling the dynamics of a confined, semiflexible polymer is a challenging problem, owing to the complicated interplay between the configurations of the chain, which are strongly affected by the length scale for the confinement relative to the persistence length of the chain, and the polymer-wall hydrodynamic interactions. At the same time, understanding these dynamics are crucial to the advancement of emerging genomic technologies that use confinement to stretch out DNA and “read” a genomic signature. In this mini-review, we begin by considering what is known experimentally and theoretically about the friction of a wormlike chain such as DNA confined in …

Flex-16: A Large-Displacement Monolithic Compliant Rotational Hinge, Robert Mcintyre Fowler, Alex Maselli, Peter Pluimers, Spencer P. Magleby, Larry L. Howell

Faculty Publications

This paper describes the design, analysis, and testing of a large-displacement monolithic compliant rotational hinge, called the Flex-16. The Flex-16 achieves 90 of rotation from monolithic construction and is aimed for application as a compliant satellite deployment hinge. Five prototypes were fabricated from three different materials (polypropylene, titanium, and a carbon nanotube framework) on two different size scales (macro and micro). A parametric finite element model was created to rapidly analyze a variety of design identified during a configuration study. Prototypes were tested for their ability to reach 90 of rotation without failure or self collision, and for their nonlinear …

Backfolding Of Wormlike Chains Confined In Nanochannels, Abhiram Muralidhar, Douglas R. Tree, Kevin D. Dorfman

Faculty Publications

Using pruned-enriched Rosenbluth method (PERM) simulations of a discrete wormlike chain model, we provide compelling evidence in support of Odijk’s prediction of two distinct Odijk regimes for a long wormlike chain confined in a nanochannel. In both cases, the chain of persistence length lp is renormalized into a series of deflection segments of characteristic length D2/3lp1/3, where D is the channel size. In the first (classic) Odijk regime, these deflection segments are linearly ordered. In the second Odijk regime, thin, long wormlike chains can backfold at a length scale quantified by the global persistence length. We …

Nonlinear Modeling, Estimation And Predictive Control In Apmonitor, John Hedengren, Reza Asgharzadeh Shishavan, Kody M. Powell, Thomas F. Edgar

Faculty Publications

This paper describes nonlinear methods in model building, dynamic data reconciliation, and dynamic optimization that are inspired by researchers and motivated by industrial applications. A new formulation of the ℓ₁-norm objective with a dead-band for estimation and control is presented. The dead-band in the objective is desirable for noise rejection, minimizing unnecessary parameter adjustments and movement of manipulated variables. As a motivating example, a small and well-known nonlinear multivariable level control problem is detailed that has a number of common characteristics to larger controllers seen in practice. The methods are also demonstrated on larger problems to reveal algorithmic …

A Simple Solution Method For The Blade Element Momentum Equations With Guaranteed Convergence, Andrew Ning

Faculty Publications

The blade element momentum equations, though conceptually simple, can be challenging to solve reliably and efficiently with high precision. These requirements are particularly important for efficient rotor blade optimization that utilizes gradient-based algorithms. Many solution approaches exist for numerically converging the axial and tangential induction factors. These methods all generally suffer from a lack of robustness in some regions of the rotor blade design space, or require significantly increased complexity to promote convergence. The approach described here allows for the blade element momentum equations to be parameterized by one variable: the local inflow angle. This reduction is mathematically equivalent, but …

Extended Formation Flight At Transonic Speeds, Andrew Ning, Ilan Kroo, Michael Aftosmis, Marian Nemec, James Kless

Faculty Publications

Aircraft flown in formation can realize significant reductions in induced drag by flying in regions of wake upwash. However, most transports fly at transonic speeds where the impact of compressibility on formation flight is not well understood. This study utilizes an Euler solver to analyze the inviscid aerodynamic forces and moments of transonic wing/body configurations flying in a two-aircraft formation. Formations with large streamwise separation distances (10-50 wingspans) are considered.

This work indicates that compressibility-related drag penalties in formation flight may be eliminated by slowing 2-3% below the nominal out-of-formation cruise Mach number (either at fixed lift coefficient or fixed …

Implementing Dubins Airplane Paths On Fixed-Wing Uavs, Timothy Mclain, Randall W. Beard, Mark Owen

Faculty Publications

A well-known path-planning technique for mobile robots or planar aerial vehicles is to use Dubins paths, which are minimum-distance paths between two configurations subject to the constraints of the Dubins car model. An extension of this method to a three-dimensional Dubins airplane model has recently been proposed. This chapter builds on that work showing a complete architecture for implementing Dubins airplane paths on small fixed-wing UAVs. The existing Dubins airplane model is modified to be more consistent with the kinematics of a fixed-wing aircraft. The chapter then shows how a recently proposed vector-field method can be used to design a …

A Position Analysis Of Coupled Spherical Mechanisms In Action Origami, Landen A. Bowen, L. A. Baxter, Spencer P. Magleby, Larry L. Howell

Faculty Publications

Origami has been previously utilized in design to create deployable systems. Action origami, origami designed to move, has the ability to deploy to a larger state and have motion in the deployed state. The majority of action origami achieves motion through coupled systems of spherical mechanisms. An origami vertex, the point at which folds converge, is shown to be equivalent to a spherical change-point mechanism. A position analysis of an origami vertex is presented, resulting in a relationship between input and output angles as well as the path of the coupler link. A method for analyzing coupled systems of repeated …

Are Undergraduate Gpa And General Gre Percentiles Valid Predictors Of Student Performance In An Engineering Graduate Program?, Larry L. Howell, Carl D. Sorenson, Matthew R. Jones

Faculty Publications

While both subjective measures and quantitative metrics play an important role in admissions decisions, quantitative metrics are amenable to critical analysis using the tools of academic analytics. The hypotheses that motivated this study are: 1. Can an applicant’s undergraduate grade point average (UGPA) and scores on the Graduate Records Examinations (GRE) be used to accurately predict the performance of the applicant in a graduate mechanical engineering program? 2. Is a single construct based on these quantitative predictive metrics a valuable tool in efficiently making admissions decisions? This study analyzed the relationship between quantitative predictive metrics, available at the time of …

Understanding The Benefits And Limitations Of Increasing Maximum Rotor Tip Speed For Utility-Scale Wind Turbines, Andrew Ning

Faculty Publications

For utility-scale wind turbines, the maximum rotor rotation speed is generally constrained by noise considerations. Innovations in acoustics and/or siting in remote locations may enable future wind turbine designs to operate with higher tip speeds. Wind turbines designed to take advantage of higher tip speeds are expected to be able to capture more energy and utilize lighter drivetrains because of their decreased maximum torque loads. However, the magnitude of the potential cost savings is unclear, and the potential trade-offs with rotor and tower sizing are not well understood. A multidisciplinary, system-level framework was developed to facilitate wind turbine and wind …

New Advances In Post-Installed Subsea Monitoring Systems For Structural And Flow Assurance Evaluation, Reza Asgharzadeh Shishavan, David Brower, John Hedengren, Alexis Brower

Faculty Publications

An overview of fiber optic sensors for temperature, pressure, strain, and fatigue of subsea structures is provided. Current progress details efforts to ensure proper installation and bonding to existing risers, flow-lines, mooring lines, trees, and other structures in actual subsea environments. Developments include clamp prototypes, bonding techniques, long-term fatigue analysis, sensor calibration, and temperature compensation. Fiber optic technology in subsea monitoring began over 20 years ago by migrating expertise from decommissioning of rocket motors. The first installations were on new installations of subsea pipelines, production risers, and drilling risers to measure strain and vibration for fatigue life monitoring. Of particular …

Automatic Evaluation Of Multidisciplinary Derivatives Using A Graph-Based Problem Formulation In Openmdao, Justin Gray, Tristan Hearn, Kenneth Moore, John Hwang, Joaquim Martins, Andrew Ning

Faculty Publications

The optimization of multidisciplinary systems with respect to large numbers of design variables is best pursued using a gradient-based optimization together with a method that efficiently evaluates coupled derivatives, such as the coupled adjoint method. However, implementing such a method in a problem with more than a few disciplines is time consuming and error prone. To address this issue, we develop an automated procedure for assembling and solving the coupled derivative equations that takes into account the disciplinary couplings using the interdisciplinary dependency graph of the problem. The coupled derivatives can be computed completely analytically, if analytic derivatives are available …

Quaternion Based Attitude Error For A Tailsitter In Hover Flight, Timothy Mclain, Matthew E. Argyle, Jason M. Beach, Randall W. Beard, Stephen Morris

Faculty Publications

The tailsitter is a promising airframe that can take off and land on its tail and transition to level flight. While this ability provides vertical takeoff and landing capabilities with no additional moving parts, it introduces interesting control challenges. In this paper, we look at the attitude control system of a tailsitter in hover flight and show that the behaviour of the aircraft relies on the method used to compute the attitude error. We investigate three different methods of computing the attitude error, quaternion feedback, resolved tilt twist, and the resolved Euler angles, and compare them through simulated hover flight.

Tailsitter Heading Estimation Using A Magnetometer, Timothy Mclain, Jason M. Beach, Matthew E. Argyle, Randall W. Beard, Stephen Morris

Faculty Publications

The tailsitter aircraft merges the endurance and speed of fixed-wing aircraft with the flexibility and VTOL abilities of rotorcraft. Typical control and estimation schemes make assumptions about the maximum attitude an aircraft will experience that are not valid for tailsitters. This paper discusses the limitations of a typical EKF magnetometer measurement update that uses Euler angles. It is shown how to use a second set of Euler angles to avoid gimbal lock. A method is given that bypasses the use of Euler angles altogether and directly uses the quaternion to determine heading error and update the attitude estimate. This method …

Analysis Of The Conduction-Radiation Problem In Absorbing, Emitting, Non-Gray Planar Media Using An Exact Method, Travis J. Moore, Matthew R. Jones

Faculty Publications

Systems in which both conduction and radiation are the dominant modes of heat transfer are important in many engineering applications and various numerical methods exist to analyze such systems. An exact solution to the conduction–radiation problem in a one-dimensional, planar, absorbing, emitting, non-gray medium is presented. The method uses an integrating factor to solve the radiative transfer equation and variation of parameters is used to solve the energy equation. The model is verified by comparing the temperature profiles calculated from this work to those found using numerical methods for both gray and non-gray cases.

The Odijk Regime In Slits, Douglas R. Tree, Wesley F. Reinhart, Kevin D. Dorfman

Faculty Publications

De Gennes’ blob theory has been remarkably successful at describing weakly confined polymers in both slits and channels, and comparable results surround Odijk’s theory of deflection segments for strongly confined wormlike polymers in nanochannels. However, given the success of Odijk’s theory in channels, it is remarkable that there is no comprehensive theory for the simple case of a wormlike polymer strongly confined between two parallel plates. We propose such a theory by drawing inspiration from the existing literature on ideal wormlike chains in slits and Daoud and de Gennes’ idea of mapping a slit-confined chain to a two-dimensional chain. We …

Piezoresistive Sensing Of Bistable Micro Mechanism State, Jeffrey K. Anderson, Larry L. Howell, Jonathan W. Wittwer, Timothy W. Mclain

Faculty Publications

The objective of this work is to demonstrate the feasibility of on-chip sensing of bistable mechanism state using the piezoresistive properties of polysilicon, thus eliminating the need for electrical contacts. Changes in position are detected by observing changes in resistance across the mechanism. Sensing the state of bistable mechanisms is critical for various applications, including high-acceleration sensing arrays and alternative forms of nonvolatile memory. A fully compliant bistable micro mechanism was designed, fabricated, and tested to demonstrate the feasibility of this sensing technique. Testing results from two fabrication processes, SUMMiT IV and MUMPs, are presented. The SUMMiT mechanism was then …

Tailsitter Attitude Control Using Resolved Tilt-Twist, Timothy Mclain, Jason M. Beach, Matthew E. Argyle, Randall W. Beard, Stephen Morris

Faculty Publications

The tailsitter aircraft merges the endurance and speed of fixed-wing aircraft with the flexibility and VTOL abilities of rotorcraft. Because of the requirement to be functional at a full range of attitudes, quaternions are typically employed to calculate attitude error. Attitude control is then accomplished by using the vector component of the error quaternion to drive flight control surfaces. This paper demonstrates that this method of driving the flight control surfaces can be suboptimal for tailsitter type aircraft and can lead to undesired vehicle movement. An alternate method of calculating attitude error called resolved tilt-twist is improved and validated. The …

Phase 1 Final Report: Preamble Assisted Equalization For Aeronautical Telemetry (Paq), Michael Rice, Mohammad Saquib, Arlene Cole-Rhodes, Farzad Moazzami, Erik Perrins

Faculty Publications

This is the Phase 1 report for Preamble Assisted Equalization for Aeronautical Telemetry (PAQ).

Executive Summary:

To fully leverage the benefits of a periodically inserted preamble, the preamble is used to estimate the state of the channel. To this end the following algorithms have been developed, tested in simulation, and ported to the GPU-based real-time system:

1. The preamble detector, which scans the received samples searching for the presence of the preamble. The location of the preamble in the received samples is required to use the received samples to estimate the frequency offset, channel impulse response, and noise variance. The …

Relative Navigation Approach For Vision-Based Aerial Gps-Denied Navigation, Timothy Mclain, Randal W. Beard, Robert C. Leishman

Faculty Publications

GPS-denied aerial flight is a challenging research problem and requires knowledge of complex elements from several distinct disciplines. Additionally, aerial vehicles can present challenging constraints such as stringent payload limits and fast vehicle dynamics. In this paper we propose a new architecture to simplify some of the challenges that constrain GPS-denied aerial flight. At the core, the approach combines visual graph-SLAM with a multiplicative extended Kalman filter. More importantly, for the front end we depart from the common practice of estimating global states and instead keep the position and yaw states of the MEKF relative to the current node in …

Aerial Rendezvous Of Small Unmanned Aircraft Using A Passive Towed Cable System, Timothy Mclain, Randall W. Beard, Joseph W. Nichols, Liang Sun

Faculty Publications

A method for aerial rendezvous of small unmanned aircraft systems is proposed. The system includes placing a passively towed drogue into an orbit that is suitable for a small unmanned aircraft systems to follow, and a seeker guidance method for use with a monocular camera mounted on the centerline of the unmanned aircraft systems. The principle contributions of the work include a method for controlling the drogue path in moderate winds by manipulating the mothership orbit and airspeed, and a vision-based nonlinear pursuit tracking method that uses pitch rate and roll commands to guide the unmanned aircraft systems to an …

Automated Tracking And Estimation For Control Of Non-Rigid Cloth, Marc D. Killpack

Faculty Publications

This report is a summary of research conducted on cloth tracking for automated textile manufacturing during a two semester long research course at Georgia Tech. This work was completed in 2009. Advances in current sensing technology such as the Microsoft Kinect would now allow me to relax certain assumptions and generally improve the tracking performance. This is because a major part of my approach described in this paper was to track features in a 2D image and use these to estimate the cloth deformation. Innovations such as the Kinect would improve estimation due to the automatic depth information obtained when …

Aircraft Route Optimization For Formation Flight, Jia Xu, Andrew Ning, Geoffrey Bower, Ilan Kroo

Faculty Publications

We quantify the fuel and cost benefits of applying extended formation flight to com- mercial airline operations. Central to this study is the development of a bi-level, mixed integer-real formation flight optimization framework. The framework has two main components: 1) a continuous domain aircraft mission performance optimization and 2) an integer optimization component that selects the best combination of optimized missions to form a formation flight schedule. The mission performance reflects the effects of rolled-up wakes, formation heterogeneity, and formation-induced compressibility. The results show that an airline can use formation flight to reduce fuel burn by 5.8% or direct operating …

Interplay Between Chain Stiffness And Excluded Volume Of Semiflexible Polymers Confined In Nanochannels, Abhiram Muralidhar, Douglas R. Tree, Yanwei Wang, Kevin D. Dorfman

Faculty Publications

The properties of channel-confined semiflexible polymers are determined by a complicated interplay of chain stiffness and excluded volume effects. Using Pruned-Enriched Rosenbluth Method (PERM) simulations, we study the equilibrium properties of channel-confined polymers by systematically controlling chain stiffness and excluded volume. Our calculations of chain extension and confinement free energy for freely jointed chains with and without excluded volume show excellent agreement with theoretical predictions. For ideal wormlike chains, the extension is seen to crossover from Odijk behavior in strong confinement to zero-stretching, bulk-like behavior in weak confinement. In contrast, for self-avoiding wormlike chains, we always observe that the linear …

High-Efficiency Thermodynamic Power Cycles For Concentrated Solar Power Systems, Marc T. Dunham, Brian Iverson

Faculty Publications

This paper provides a review of high-efficiency thermodynamic cycles and their applicability to concentrating solar power systems, primarily focusing on high-efficiency single and combined cycles. Novel approaches to power generation proposed in the literature are also highlighted. The review is followed by analyses of promising candidates, including regenerated He-Brayton, regenerated CO2-Brayton, CO2 recompression Brayton, steam Rankine, and CO2-ORC combined cycle. Steam Rankine is shown to offer higher thermal efficiencies at temperatures up to about 600 ˚C but requires a change in materials for components above this temperature. Above this temperature, CO2 recompression Brayton cycles are shown to have very high …

Quadrotors And Accelerometers: State Estimation With An Improved Dynamic Model, Robert C. Leishman, John Macdonald, Randal W. Beard, Timothy W. Mclain

Faculty Publications

The article examines consequences and practical aspects of using an improved dynamic model for quadrotor state estimation with only IMU measurements. The improved model correctly explains the measurements available from the accelerometers on a quadrotor. We give a brief tutorial to explain the difference between accelerometer measurements on a ground vehicle and a quadrotor. We demonstrate several observers based on the improved model to illustrate the estimation improvements available. It is shown that the parameters for this model can be estimated as elements of the state, which makes the model simple to implement and utilize. Finally, we provide hardware results …

System-Level Simulation Of A Solar Power Tower Plant With Thermocline Thermal Energy Storage, Scott M. Flueckiger, Brian D. Iverson, Suresh V. Garimella, James E. Pacheco

Faculty Publications

A thermocline tank is a low-cost thermal energy storage subsystem for concentrating solar power plants that typically utilizes molten salt and quartzite rock as storage media. Longterm thermal stability of the storage concept remains a design concern. A new model is developed to provide comprehensive simulation of thermocline tank operation at low computational cost, addressing deficiencies with previous models in the literature. The proposed model is then incorporated into a system-level model of a 100 MWe power tower plant to investigate storage performance during long-term operation. Solar irradiance data, taken from measurements for the year 1977 near Barstow, CA, are …

A Post-Installed Subsea Monitoring System For Structural And Flow Assurance Evaluation, David Brower, Alexis Brower, John Hedengren, Reza Asgharzadeh Shishavan

Faculty Publications

This paper describes major advancements for deploying sensing systems on existing subsea structures as part of the Clear Gulf study. In the past, a major shortcoming of post-installed monitoring systems has been poor coupling between the sensor and structure; this study provided methods to overcome this problem. Both subsea field testing and laboratory testing were performed to verify these advancements. The Clear Gulf study is a collaboration between the offshore energy industry and NASA with the goals of risk mitigation, safety, efficiency and environmental concerns in the offshore energy industry. The study is ongoing and has investigated new methods to …

Sensitivity Analysis Of Wind Plant Performance To Key Turbine Design Parameters: A Systems Engineering Approach, Katherine Dykes, Andrew Ning, Ryan King, Peter Graf, George Scott, Paul Veers

Faculty Publications

This paper introduces the development of a new software framework for research, design, and development of wind energy systems which is meant to 1) represent a full wind plant including all physical and nonphysical assets and associated costs up to the point of grid interconnection, 2) allow use of interchangeable models of varying fidelity for different aspects of the system, and 3) support system level multidisciplinary analyses and optimizations. This paper describes the design of the overall software capability and applies it to a global sensitivity analysis of wind turbine and plant performance and cost. The analysis was performed using …

Application Of L-Systems To Geometrical Construction Of Chamise And Juniper Shrubs, Dallan R. Prince, Marianne E. Fletcher, Chen Shen, Thomas H. Fletcher

Faculty Publications

Improved models of fire spread and fire characteristics are desired for live shrub fuels, since the majority of existing research efforts focus on either dead fuel beds or crown fires in trees. Efforts have been made to improve live fuel modeling, including detailed studies of individual leaf combustion, with results incorporated into a shrub combustion model for broadleaf species. However, this approach was not well-suited to non-broadleaf shrubs since their fuel consists of long needle-covered branches rather than easily discretized leaves. Methods were therefore developed to simulate the branching structure of chamise (Adenostoma fasciculatum) and Utah juniper (Juniperus osteosperma). The …