Engineering Commons^™

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 …

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 …

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 …

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 …

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 …

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 …

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 …

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 …

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 …

Long Life Electrochemical Diodes For Continuous Electrowetting, Mehdi Khodayari, Ben Hahne, Nathan B. Crane

Faculty Publications

The rate of electrochemical reactions in some systems varies with the polarity of the overpotential on the working electrode, introducing diode-like behavior at the electrode/electrolyte interface. However, with repeated bipolar cycling, the electrochemical current damages the electrodes. We have connected electrochemical diodes in series with opposing polarities to reduce the diode current while charging a capacitive circuit. We have previously used this capacitive circuit arrangement to actuate aqueous droplets continuously using the electrowetting (EW) effect. In this study, the performance of electrochemical diodes under repeated voltage cycles is investigated. Aluminum and titanium electrodes in contact with three electrolyte solutions (0.1 …

Review Of High-Temperature Central Receiver Designs For Concentrating Solar Power, Brian D. Iverson, Clifford K. Ho

Faculty Publications

This paper reviews central receiver designs for concentrating solar power applications with high-temperature power cycles. Desired features include low-cost and durable materials that can withstand high concentration ratios (~1000 suns), heat-transfer fluids that can withstand temperatures > 650°C, high solar absorptance, and low radiative and convective heat losses leading to a thermal efficiency > 90%. Different receiver designs are categorized and evaluated in this paper: (1) gas receivers, (2) liquid receivers, and (3) solid particle receivers. For each design, the following information is provided: general principle and review of previous modeling and testing activities, expected outlet temperature and thermal efficiency, benefits, perceived …