Dissertations and Theses - Aerospace Engineering
http://hdl.handle.net/2142/14800
Sun, 29 Nov 2015 12:55:00 GMT2015-11-29T12:55:00ZMethodology for nonlinear quantification of a cantilever beam with local nonlinearities
http://hdl.handle.net/2142/88099
Methodology for nonlinear quantification of a cantilever beam with local nonlinearities
Herrera, Christopher Angelo
This study presents a methodology for the identification of linear and nonlinear regions of operation for a system that behaves almost linearly in the limit of extreme values of (a) certain parameter(s). An Euler-Bernoulli cantilever beam with two nonlinear configurations is used to develop and validate the methodology. One configuration consists of a cantilever beam with a cubic spring attached at a specific distance from the beam root to achieve a smooth nonlinear effect. The other configuration is a cantilever beam undergoing vibro-impact between symmetrically-spaced stops. Both systems have the property that, in the limit of small and large values of a parameter, the system is almost linear and can be modeled with negligible error as fixed-free or fixed-pinned, depending on the configuration. For the beam with a cubic spring attachment, the forcing amplitude is the varied parameter. For the vibro-impact beam, the parameter is the clearance between the stops and the beam at static equilibrium. Proper orthogonal decomposition is employed to obtain an optimal basis used to describe the systems with varying parameter values. The frequencies of the modes that comprise the basis are estimated using the Rayleigh quotient. The variations of these frequencies are studied to successfully identify parameter values for which the system is approximately linear and those for which it is highly nonlinear. A criterion based on the Betti-Maxwell reciprocity theorem is used to validate the existence of nonlinear behavior for the set of parameter values suggested by the described methodology.
It was found that transition regions in which the dynamics of the system shifted from one linear system to the other exist and that these regions occur for different sets of parameter values for each mode. The effect of heavy damping on proper orthogonal decomposition is found to be important, particularly for the vibro-impact beam, due the method's dependence on the system response. An attempt is also made to isolate parameter values for which transient resonance capture occurs and prove its existence through use of empirical mode decomposition and the Hilbert transform.
Nonlinear Dynamics; Proper Orthogonal Decomposition (POD); Empirical Mode Decomposition (EMD); Vibro-impact; Nonlinear Quantification
Tue, 21 Jul 2015 00:00:00 GMThttp://hdl.handle.net/2142/880992015-07-21T00:00:00ZHerrera, Christopher AngeloCharacterization of electrical conductivity of carbon fiber/epoxy composites with conductive AFM and scanning microwave impedance microscopy
http://hdl.handle.net/2142/88098
Characterization of electrical conductivity of carbon fiber/epoxy composites with conductive AFM and scanning microwave impedance microscopy
McKenzie, Andrew B.
This thesis investigates the electrical conductivity of IM7 carbon fibers using two Atomic Force Microscope (AFM) –based techniques: Conductive AFM (C-AFM) and Scanning Microwave Impedance Microscopy (sMIM). Unidirectional IM7/977-3 carbon fiber/epoxy laminates were manufactured and examined with these two techniques. C-AFM was used to measure the bulk resistivity of IM7 fibers at (1.9 ± 1.1) x 10-3 Ω∗cm. Given that the uncertainty of these measurements is rather large, implementation of calibration experiments is needed. sMIM experiments revealed large nano-scale spatial variations in the axial and transverse conductances of IM7 fibers. Attempts were made to quantify sMIM results through construction of experimental and computational calibration curves, but neither of these efforts was successful in yielding conductivity measurements that agreed with the measurements made with C-AFM or the manufacturer specification. Refinements to the computational methodology such as improved material property inputs and better isolation of the sMIM signal could yield promising future results for sMIM characterization of conductivity.
Carbon fibers; Composites; Electrical conductivity; Atomic Force Microscopy; Conductive AFM; Scanning Microwave Impedance Microscopy
Tue, 21 Jul 2015 00:00:00 GMThttp://hdl.handle.net/2142/880982015-07-21T00:00:00ZMcKenzie, Andrew B.Nonlinear control strategies for quadrotors and CubeSats
http://hdl.handle.net/2142/88078
Nonlinear control strategies for quadrotors and CubeSats
Subramanian, Giri Prashanth
This thesis is presented in two parts. In the first part, a fully nonlinear controller is developed for controlling the position and attitude of the Crazyflie quadrotor. In order to use this controller, a system identification is first performed in order to completely model the dynamics of the Crazyflie quadrotor. A proof of convergence is also given for this controller to show that the developed controller is globally exponentially stable. The controller is then implemented on hardware and a quadrotor testbed capable of flying 10-15 quadrotors simultaneously, is developed. In the second part of the thesis, a Systems Engineering study for formation flying CubeSats has been undertaken. Two different kinds of formation flying missions using 4-6 CubeSats have been developed, one with an actively controlled formation and the other with a passively controlled formation. Different controllers have been developed for these missions and the current technological bottlenecks in realizing these missions have been identified.
Quadrotors; Controls; Nonlinear controls; Quadrotor testbed; Swarms; CubeSat System Engineering; CubeSat Reconfiguration; J2-invariant relative orbits; Formation flight
Mon, 20 Jul 2015 00:00:00 GMThttp://hdl.handle.net/2142/880782015-07-20T00:00:00ZSubramanian, Giri PrashanthAn improved model-based observer for inertial navigation for quadrotors with low cost IMUs
http://hdl.handle.net/2142/88007
An improved model-based observer for inertial navigation for quadrotors with low cost IMUs
Hanley, David John
In this thesis, we present a model-based observer for inertial navigation of quadrotors and other multirotor aircraft. We include in our model a Coriolis term that has been neglected in prior work. Doing so allows us to estimate the entire velocity vector in the quadrotor's frame of reference---including along the z-axis of this frame---with data only from a low-cost inertial measurement unit (IMU), something that has not been demonstrated previously. An observability analysis predicts that our proposed observer will perform well. Experimental results over 110 flight trials verify this prediction, showing that our proposed observer achieves lower root mean square error than three other state-of-the-art model-based observers.
Inertial Navigation; Unmanned Aircraft; Quadrotors; Observer; Estimator
Wed, 15 Jul 2015 00:00:00 GMThttp://hdl.handle.net/2142/880072015-07-15T00:00:00ZHanley, David JohnCharacterization of local strain fields in cross-ply composites under transverse loading
http://hdl.handle.net/2142/87966
Characterization of local strain fields in cross-ply composites under transverse loading
Wilhelmsen, Ariel
Transverse matrix cracks often occur in fiber-reinforced cross-ply polymer matrix composites subjected to tensile loads. Experimental visualizations of strain fields are necessary to calibrate and validate computational models that predict strain development and transverse crack initiation. In this study, fluorescent digital image correlation (DIC) measurements are used to study the evolution of highly localized displacements and strains under transverse tension. Composite coupons and Aluminum 6061-T6 control samples, both with dimensions of 50 mm in length, 2 mm in width, and 1.25 mm in height, were prepared with one polished surface spincast with a solution of fluorescent nanoparticles to produce a DIC speckle pattern. Specimens were tested in a miniature load frame in an optical microscope. Using a long working distance objective lens and a monochrome camera with a 668.4 by 534.7 μm resolution, fluorescent images of the polished surface were captured periodically to track the developing strains in the specimen. Strains were successfully measured using DIC for composite specimens. Bands of strain were observed to form perpendicular to 0° plies and often traced along pockets of resin. Additionally, strain concentrations formed between tow borders and pockets of resin and were nearly twice the value of the average strain for the area of interest. These results were consistent qualitatively with a photoelastic study shown in literature.
DIC (Digital Image Correlation); carbon fiber; composites; transverse tension; cross-ply; composite laminates
Thu, 18 Jun 2015 00:00:00 GMThttp://hdl.handle.net/2142/879662015-06-18T00:00:00ZWilhelmsen, ArielBifurcations of Parametrically Excited Gyroscopic Systems Near a 0 : 1 Resonance
http://hdl.handle.net/2142/85134
Bifurcations of Parametrically Excited Gyroscopic Systems Near a 0 : 1 Resonance
McDonald, Robert Joseph
The final part of this research involves study of the global bifurcations of the two gyroscopic systems. Using recently developed bifurcation methods, we detect the presence of multi-pulse orbits homoclinic to a slow manifold. In certain parameter regions, we can prove that multi-pulse orbits exist which are homoclinic to fixed points on the slow manifold, leading to chaotic dynamics in the system. These multi-pulse orbits provide the mechanism by which energy transfer between modes may occur.
Engineering, Mechanical
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/2142/851342000-01-01T00:00:00ZMcDonald, Robert JosephInvestigation of Residual Stresses in Shape Memory Alloy (Sma) Composites
http://hdl.handle.net/2142/85136
Investigation of Residual Stresses in Shape Memory Alloy (Sma) Composites
Berman, Justin Bradley
A three-phase concentric cylinder micromechanics model and an SMA composite thermoelastic beam theory were developed to analyze the micromechanical and structural-level thermal and transformational stresses for nitinol composites induced by nitinol wires embedded in a host matrix. A series of warpage experiments were conducted on nitinol composite beams during heating cycles to provide experimental validation of model predictions and to assess their thermoelastic structural behavior under non-mechanical loading. Micromechanical model results indicate that excessive residual hoop stresses in nitino/graphite/epoxy composites leads to radial cracking around the embedded nitinol wires. Based on modeling results, the most important factor in reducing residual stresses (and thereby preventing radial cracking) is increasing the level of recovery strain for the nitinol wire. The SMA composite beam model agrees well with experimental data captured for the nitinol/epoxy beam series. Warpage experiments on nitinol/glass/epoxy beams showed a large increase in the effective austenitic start temperature (As) of 9.3°C. The elevation of the effective As together with other observations of warpage development indicates that plastic flow may have occurred in nitinol wires when embedded in glass/epoxy. These observations reinforce the need to train nitinol wires at modest recovery levels when embedding in relatively stiff materials.
Engineering, Materials Science
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/2142/851362001-01-01T00:00:00ZBerman, Justin BradleyContributions to the Computational Analysis of Multi-Dimensional Stochastic Dynamical Systems
http://hdl.handle.net/2142/85135
Contributions to the Computational Analysis of Multi-Dimensional Stochastic Dynamical Systems
Wojtkiewicz, Steven F., Jr
Classical covariance control theory is extended to the case of nonlinear systems using the method of statistical linearization. The design procedure is applied to several nonlinear systems of civil engineering interest including hysteretic oscillators. The idea of covariance control is then generalized to the problem of response moment specification where higher order response moments are prescribed with the hope of having more authority over response extremes. The algorithm is then demonstrated by application to a Duffing oscillator.
Engineering, Civil
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/2142/851352000-01-01T00:00:00ZWojtkiewicz, Steven F., JrSwing-Up and Balancing Control of Underactuated Robotic Systems
http://hdl.handle.net/2142/85130
Swing-Up and Balancing Control of Underactuated Robotic Systems
Lee, Kangsik
To validate the control algorithms experimentally, a complete controller for swing-up and balancing has been designed and implemented on the Pendubot, a two-link underactuated robot. The parameters of the Pendubot were varied by up to 50% in order to test robustness to parameter errors. The robust control scheme using sliding mode concepts successfully compensated for modeling imprecision and disturbances inherent in the experimental demonstration.
Engineering, Electronics and Electrical
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/2142/851301998-01-01T00:00:00ZLee, KangsikHydrodynamic Instability of Fluid Flow Through Homogeneous Porous Media
http://hdl.handle.net/2142/85133
Hydrodynamic Instability of Fluid Flow Through Homogeneous Porous Media
Low, Corwyn Eng Kong
To examine mechanisms for the production of large-amplitude, steady disturbances at elevated Reynolds number, the effective porosity of the medium is reconsidered. Experimental results and detailed microscale flow simulations indicate that significant regions of flow separation exist around and downstream of the contact points of the particles in the porous medium. This results in a decrease in the effective porosity of the medium as Reynolds number is increased, insofar as transport of mass and momentum are concerned, and this phenomenon has not been addressed in prior experimental or computational studies. A new porosity-based streamfunction transformation is introduced, similar in aspects to the density-based transformations used in compressible flows. The porosity is then assumed to be a function of flow Reynolds number. The equation for the linearized disturbance streamfunction then depends on the derivative of porosity with respect to pore Reynolds number evaluated at the mean flow conditions. Flow in the porous media system is found to be spatially unstable for relatively small negative values of the porosity derivative, thus providing a new potential mechanism for observed instabilities.
Physics, Fluid and Plasma
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/2142/851332000-01-01T00:00:00ZLow, Corwyn Eng Kong