R-3 Repository :: Browsing by Author "Dick, Andrew J."

Browsing by Author "Dick, Andrew J."

Now showing 1 - 20 of 26

Analysis of human movement for a complex dynamic task: What predicts success?
(2013-09-16) Purkayastha, Sagar; O'Malley, Marcia K.; Byrne, Michael D.; Dick, Andrew J.
This thesis identiﬁes and analyzes successful movement strategies for the completion of a complex dynamic task. In the past it has been shown that movement strategies correlate well to performance for simple tasks. Therefore, in this thesis I was motivated to ﬁnd out if motion based metrics correlated well to performance for more complicated motor tasks. First, the Nintendo Wiimote was veriﬁed as a suitable gaming interface enabling gross human motion capture through experimental comparisons with other gaming interfaces and precision sensors. Then, a complex motor task was rendered in an open-source gaming environment. This environment enabled the design of a rhythmic task that could be controlled with the Wiimote while data were simultaneously recorded for later analysis. For the task, success and failure could be explained by high correlation between two motion based performance metrics, mean absolute jerk (MAJ) and average frequency (AVF) per trial. A logistic regression analysis revealed that each subject had a range of MAJ and AVF values for being successful, outside of which they were unsuccessful. Therefore, this thesis identiﬁes motion based performance metrics for a novel motor control task that is signiﬁcantly diﬃcult to master and the techniques used to identify successful movement strategies can be used for predicting success for other such complex dynamic tasks.
Characterizing Effective d31 Values for PZT from the Nonlinear Oscillations of Clamped-Clamped Micro- Resonators
(Journal of Mechanical Engineering, 2013) Dick, Andrew J.; Nonlinear Phenomena Laboratory
In order to accurately predict the performance of micro-electromechanical systems which use piezoelectric material, precise knowledge of the piezoelectric coefficients is critical. Current material characterization methods rely on either simple structures restricted to small amplitude, linear oscillations or consider the piezoelectric material separate from the specific micro-scale device. A method is proposed for the characterization of the effective transverse piezoelectric coefficient d31 of lead zirconate titanate in a clamped-clamped micro-beam resonator experiencing nonlinear oscillations. Parameter trends identified by using a parametric identification scheme are analyzed and an approach is presented to calculate the linear piezoelectric coefficient. This method utilizes the relationship between a DC bias added to the excitation signal and the frequency shift experienced by the nonlinear response behavior. Through an additional numerical study, the sensitivity of the results to changes in the device length is identified and all data sets provide the same coefficient value when a length variation of less than 2% is allowed.
Design of vibration inspired bi-orthogonal wavelets for signal analysis
(2013-07-24) Phan, Quan; Dick, Andrew J.; Spanos, Pol D.; Stanciulescu, Ilinca
In this thesis, a method to calculate scaling function coefficients for a new bi-orthogonal wavelet family derived directly from an impulse response waveform is presented. In literature, the Daubechies wavelets (DB wavelet) and the Morlet wavelet are the most commonly used wavelets for the dyadic wavelet transform (DWT) and the continuous wavelet transform (CWT), respectively. For a specific vibration signal processing application, a wavelet basis that is similar or is derived directly from the signal being studied proves to be superior to the commonly used wavelet basis. To assure a wavelet basis has a direct relationship to the signal being studied, a new formula is proposed to calculate coefficients which capture the characteristics of an impulse response waveform. The calculated coefficients are then used to develop a new bi-orthogonal wavelet family.
Developing Innovative Designs with Manufacturing Capability Using the Level Set Method
(2012-09-05) Baradaran Nakhjavani, Omid; Meade, Andrew J., Jr.; Akin, John Edward.; Padgett, Jamie E.; Dick, Andrew J.
This thesis discusses how to use topology and shape optimization, specifically the level set method, for innovative design. The level set method is a numerical algorithm that simulates the expansion of dynamic implicit surfaces. In this research, the equations for manufacturability are generated and solved through use of the level set method joined with the COMSOL multi-physics package. Specific constraints are added to make the optimization practical for engineering design. The resulting method was applied to design the best underlying support structure, conforming to both curvature and manufacturability constraints, for the longerons used with the International Space Station solar panels.
Dynamic stability of elastomeric seismic isolation bearings and seismic protection using enhanced adaptive negative stiffness system
(2013-09-16) Vemuru, Venkata; Nagarajaiah, Satish; Padgett, Jamie E.; Dick, Andrew J.
In this study the issue of stability of elastomeric bearings subjected to extreme dynamic loading is studied in detail and response reduction strategies in structures both fixed base and base-isolated structures using a negative stiffness device (NSD) are evaluated. For response reduction, the composite response spectrum approach is utilized to provide a comprehensive representation of the trade-offs associated with each choice of design strategies. A comprehensive database of strong ground motion is used to study the suitability of NSD for seismic protection. The spectral characteristics of all the ground motions selected are identified using a mathematical model and the characteristics of the ground motion that affect the structural assembly and the response reduction strategies considered are evaluated. The results of the study are organized based on the identified characteristics of ground motion to demonstrate the effectiveness of the negative stiffness device for response reduction. The analytical study takes into account both linear fixed base structures as well as base-isolated structures equipped with linear and nonlinear dampers. For stability of elastomeric bearings, detailed analytical models that capture the nonlinear behavior of the bearings under extreme axial loads and horizontal displacements are developed, calibrated and verified using experimental data. A new analytical model is developed to capture the highly nonlinear horizontal behavior of the bearings under dynamic loading. This includes both the response under normal operating conditions as well as the instability experienced by the bearings under large axial loads and extreme horizontal displacements. The analytical model developed for the horizontal behavior of bearings is enhanced to include the coupled horizontal-vertical behavior of the bearings with the main objective of understanding the actual behavior of the bearings at the instant it experiences loss of stability. An important distinction is made between the geometrical effects and deformation of the bearing that contributes to its vertical response at this instant. The important effect the increased vertical reaction has on the bearing stability is demonstrated and an empirical analytical model is developed to capture this effect. By using the analytical models developed above for elastomeric bearings the response of a six storeyed structure isolated using elastomeric bearings is studied for different ground motions. The effectiveness of the NSD in reducing the response of the structure for different ground motions is demonstrated based on this study and the findings are organized using the identified characteristics of the ground motion. By identifying completely the limitations of the isolation system and subjecting it to actual ground motions the behavior of the system under extreme ground motions is studied. For instances where the bearings fail due to severe ground motions, addition of an NSD not only reduces the response of the superstructure but also protects the bearings by retaining their stability. Stability retention is mainly achieved due to a decrease in the imposed axial loads in the system with an NSD. A fail-safe NSD with mechanical displacement feedback is proposed to prevent accidental failure of isolation systems and its effectiveness is demonstrated for severe ground motion using analytical study.
Frequency domain analysis of linear and nonlinear structures with applications to impact force identification and micro-resonator design
(2013-12-06) Ghaderi, Pooya; Akin, John Edward.; Stanciulescu, Ilinca; Dick, Andrew J.
The modeling and analysis of structures using frequency-domain methods simplify the procedure of the modeling and analysis and provides better understanding of the response of the structures. There are different applications in frequency-domain structural modeling and analysis such as modeling and analysis in impact engineering, wave propagation in structures, and micro-resonators. The identification of the impact force and the impact location in structures are important for monitoring the condition of the structures and also for the design of the future structures. The complexity and nonlinearity of the impact incident makes it impractical to measure the impact force directly. In this study, a new method that uses the spectral finite element method (SFEM) is introduced in order to identify and locate the applied impact force. Using SFEM facilitates for the successfully identification of the high frequency content in the impact forces. Also, using SFEM allows for the identification of the impact force independent of the location of the impact force. The impact force identification and localization method is verified by experimental results. For designing and analyzing micro-resonators, it is required to do the frequency-analysis of these structures which provide the frequency characteristics and the frequency-response of the structures. In this study, a novel class of parametrically excited micro-resonators is introduced. The micro-resonator takes advantage of piezo-electric excitation which improves the performance of the micro-resonator over that of the micro-resonators with electrostatic excitation for certain applications.
High amplitude response behavior of a linear oscillator-nonlinear absorber system: Identification, analysis, and attenuation by using a semi-active absorber in series
(2013-09-16) Eason, Richard; Dick, Andrew J.; O'Malley, Marcia K.; Nagarajaiah, Satish
Auxiliary absorbers provide an effective means to attenuate the vibrations of a structural or mechanical system (the "primary structure"). The simplest auxiliary absorber, a tuned mass damper (TMD), provides reliable narrow-band attenuation but is not robust to the effects of detuning. Strongly nonlinear tuned mass dampers (NTMDs) are capable of wide-band, irreversible energy transfer known as "energy pumping" but can also exhibit high amplitude solutions which significantly amplify the response of the primary structure. Semi-active tuned mass dampers (STMDs) incorporate an actuating element in order to achieve real-time tuning adjustment capability. This thesis presents a global dynamic analysis of the response of a primary structure with an NTMD and then explores the performance of a novel absorber configuration consisting of an NTMD and STMD attached to the primary structure in series. The global dynamic analysis is conducted using a new cell mapping method developed by the author and introduced within the thesis: the parallelized multi-degrees-of-freedom cell mapping (PMDCM) method. The benefits of the additional STMD component are explored for two distinct applications: (1) restoring the performance of a linear TMD which develops a weak nonlinearity due to operation outside of the intended range or other means, and (2) acting as a safety device to eliminate or minimize convergence to the detached high-amplitude response. In the weakly nonlinear case, the STMD is shown to reduce the effects of the nonlinearity and improve attenuation capability by constraining the motion of the NTMD. In the strongly nonlinear case, the STMD effectively eliminates the complex response behavior and high amplitude solutions which were present in the original system, resulting in a single low amplitude response. Experimental tests using an adjustable-length pendulum STMD verify the numerical results.
Influence of Effective Modulus on Period-Doubling Bifurcation in Atomic Force Microscopy: Investigation and Implementation for Sample Characterization
(2011) Huang, Wei; Dick, Andrew J.
Atomic force microscope (AFM) is an important tool for measuring the topographical and other properties of a sample with nanometer resolution. The cantilever probe of the AFM is influenced by nonlinear interaction forces which act between the probe and the sample. For certain non-standard excitation conditions, this can result in bifurcations in the probe's response. This work numerically examines a period-doubling bifurcation observed to occur for interactions with soft materials. The influence of the sample properties and other conditions on the bifurcation is studied and a method is proposed for sample material characterization. The identified values from simulated 1-D and 2-D scans agree well with the true values. The proposed method does not require the use of special probes and it uses the control algorithm for traditional tapping mode AFM with minor modification. This proposed method could also achieve high scan speeds and prevent strong, destructive interaction forces.
Magnetic Flux Leakage System for External Robotic Inspection of Oil and Gas Pipelines
(2015-04-24) Ben Moallem, Issam; Ghorbel, Fathi Hassan; Dick, Andrew J.; Stanciulescu, Ilinca
Pipelines transport invaluable energy resources such as crude oil and natural gas over long distances. The integrity of the piping system in terms of safety of the process is then of high importance. However, pipes are prone by time to defects that may degrade their properties and lead to failures. Particularly, wall thinning is a serious anomaly that threatens aging pipelines. Therefore, their inspection plays a critical role to prevent the collapse of the system. Magnetic Flux Leakage (MFL) is by far the most effective technique of nondestructive evaluation for robotic diagnosis of ferromagnetic pipes. This work follows a novel approach to control such problem and assess the condition of the pipe by measuring with a good precision the wall radial thickness based on calibrated curves of reference and using an MFL diagnostic system tool. The proposed technique is generic and can be applied systematically for pipes with different sizes and material properties. It represents an advancement over the current conventional practices which require multiple physical experiments to generate empirical reference curves. Such procedures are cumbersome, time consuming and in consequence costly. The MFL sensing tool will be placed at the end-effector of a mobile robot platform devoted for external pipe inspection in a desert environment. It is based on permanent magnets producing a strong magnetic field that locally magnetizes and saturates the sample in question. At areas where there is metal loss, the magnetic flux flowing in the pipe leaks from the wall, which is detected by a Hall effect sensor and compared to the reference curve to estimate the wall thickness.
Multiphysics model of a cardiac myocyte: A voltage-clamp study
(2013-07-24) Krishna, Abhilash; Clark, John W., Jr.; Cavallaro, Joseph R.; Dick, Andrew J.
We develop a composite multiphysics model of excitation-contraction coupling for a rat ventricular myocyte under voltage clamp (VC) conditions to: (1) probe mechanisms underlying the response to Ca2+-perturbation; (2) investigate the factors influencing its electromechanical response; and (3) examine its rate-dependent behavior (particularly the force-frequency response (FFR)). Motivation for the study was to pinpoint key control variables influencing calcium-induced calcium-release (CICR) and examine its role in the context of a physiological control system regulating cytosolic Ca2+ concentration and hence the cardiac contractile response. Our cell model consists of an electrical-equivalent model for the cell membrane and a fluid-compartment model describing the flux of ionic species between the extracellular and several intracellular compartments. The model incorporates frequency-dependent calmodulin (CaM) mediated spatially heterogenous interaction of calcineurin (CaN) and Ca2+/calmodulin-dependent protein kinase-II (CaMKII) with their principal targets and accounts for rate-dependent, cyclic adenosine monophosphate (cAMP)-mediated up-regulation. We also incorporate a biophysical model for cardiac contractile mechanics to study the factors influencing force response. The model reproduces measured VC data published by several laboratories, and generates graded Ca2+-release with high Ca2+ gain by achieving negative feedback control and Ca2+-homeostasis. We examine the dependence of cellular contractile response on: (1) the amount of activator Ca2+ available; (2) the type of mechanical load applied; (3) temperature (22 to 38ºC); and (4) myofilament Ca2+ sensitivity. We demonstrate contraction-relaxation coupling over a wide range of physiological perturbations. Our model reproduces positive peak FFR observed in rat ventricular myocytes and provides quantitative insight into the underlying rate-dependence of CICR. The role of Ca2+ regulating mechanisms are examined in handling induced Ca2+-perturbations using a rigorous cellular Ca2+ balance. Extensive testing of the composite model elucidates the importance of various direct and indirect modulatory influences on the cellular twitch-response with wide agreement with measured data on all accounts. We identify cAMP-mediated stimulation, and rate-dependent CaMKII-mediated up-regulation of Ca2+-trigger current (ICaL) as the key mechanisms underlying the aforementioned positive FFR. Our model provides biophysically-based explanations of phenomena associated with CICR and provides mechanistic insights into whole-cell responses to a wide variety of testing approaches used in studies of cardiac myofilament contractility.
Nanomechanical and Electro-mechanical Characterization of Materials for Flexible Electrodes Applications
(2013-09-16) Peng, Cheng; Lou, Jun; Dick, Andrew J.; Xu, Qianfan
Flexible electronics attract research and commercial interests in last 2 decades for its flexibility, low cost, light weight and etc. To develop and improve the electro-mechanical properties of flexible electrodes is the most critical and important step. In this work, we have performed nanomechanical and electro-mechanical characterization of materials for flexible electrode applications, including metallic nanowires (NWs), indium tin oxide (ITO)-based and carbon nanotube (CNT)-based electrodes. First, we designed and developed four different testing platforms for nanomechanical and electro-mechanical characterization purpose. For the nano/sub-micro size samples, the micro mechanical devices can be used for uni-axial and bi-axial loading tests. For the macro size samples, the micro tester will be used for in situ monotonic tensile test, while the fatigue tester can be used for in situ cyclic tensile or bending testing purpose. Secondly, we have investigated mechanical behaviors of single crystalline Ni nanowires and single crystalline Cu nanowires under uni-axial tensile loading inside a scanning electron microscope (SEM) chamber. We demonstrated both size and strain-rate dependence on yield stress of single-crystalline Ni NWs with varying diameters (from 100 nm to 300 nm), and themolecular dynamics (MD) simulation helped to confirm and understand the experimental phenomena. Also, two different fracture modes, namely ductile and brittle-like fractures, were found in the same batch of Cu nanowire samples. Finally, we studied the electro-mechanical behaviors of flexible electrodes in macro scale. We reported a coherent study integrating in situ electro-mechanical experiments and mechanics modeling to decipher the failure mechanics of ITO-based and CNT-based electrodes under tension. It is believed that our combined experimental and simulation results provide some further insights into the important yet complicated deformation mechanisms for nanoscale metals and fracture mechanism for flexible electrodes applications.
Nonlinear Aeroelastic Analysis of UAVs: Deterministic and Stochastic Approaches
(2012-09-05) Sukut, Thomas; Spanos, Pol D.; Meade, Andrew J., Jr.; Dick, Andrew J.
Aeroelastic aspects of unmanned aerial vehicles (UAVs) is analyzed by treatment of a typical section containing geometrical nonlinearities. Equations of motion are derived and numerical integration of these equations subject to quasi-steady aerodynamic forcing is performed. Model properties are tailored to a high-altitude long-endurance unmanned aircraft. Harmonic balance approximation is employed based on the steady-state oscillatory response of the aerodynamic forcing. Comparisons are made between time integration results and harmonic balance approximation. Close agreement between forcing and displacement oscillatory frequencies is found. Amplitude agreement is off by a considerable margin. Additionally, stochastic forcing effects are examined. Turbulent flow velocities generated from the von Karman spectrum are applied to the same nonlinear structural model. Similar qualitative behavior is found between quasi-steady and stochastic forcing models illustrating the importance of considering the non-steady nature of atmospheric turbulence when operating near critical flutter velocity.
Nonlinear Dynamics in Atomic Force Microscopy for Various Excitation Conditions
(2015-05-11) Huang, Wei; Dick, Andrew J.; O' Malley, Marcia K.; Clark, John W.
The atomic force microscopy (AFM) is a high-resolution measurement tool for measuring sample topography and material properties in micro-scale and nano-scale research. The dynamics of the cantilever probe in AFM is influenced by the intrinsically nonlinear interaction between the probe tip and the surface of the sample. Previous work has shown that in off-resonance excited intermittent-contact AFM, a period-doubling bifurcation can occur as a result of the nonlinearity. The amplitude of the resulting sub-harmonic frequency component of the response has been identified as a source of contrast to measure the Young's modulus of the sample. This dissertation details the continued work in this area and includes three parts. In the first part, the focus is to investigate the performance of a material characterization method, proposed to use the relationship between the sample modulus and the sub-harmonic frequency component, to study material property transitions for one-dimensional samples. In the second part, the focus is on the effect of the inclusion of the explicit dissipative interaction force in the system model on the numerical simulation on the AFM. Both resonant and off-resonant excitation conditions are discussed. In the third part, the focus is on the generation of the sub-harmonic amplitude for an unique dual-frequency excitation condition. The influence of this excitation condition is numerically investigated and experimental studies are conducted with a macro-scale constrained cantilevered beam system to qualitatively verify the numerically predicted behavior. The work in this dissertation brings a wider understanding for these nonstandard excitation methods and their applications in AFM.
Nonlinear Stochastic Analysis of Motorcycle Dynamics
(2013-09-16) Robledo Ricardo, Luis; Spanos, Pol D.; Barrera, Enrique V.; Dick, Andrew J.; Duenas-Osorio, Leonardo
Off-road and racing motorcycles require a particular setup of the suspension to improve the comfort and the safety of the rider. Further, due to ground unevenness, off-road motorcycle suspensions usually experience extreme and erratic excursions in performing their function. In this regard, the adoption of nonlinear devices, such as progressive springs and hydro pneumatic shock absorbers, can help limiting both the acceleration experienced by the sprung mass and the excursions of the suspensions. For dynamic analysis purposes, this option involves the solution of the nonlinear differential equations that govern the motion of the motorcycle, which is excited by the stochastic road ground profile. In this study a 4 degrees-of-freedom (4-DOF) nonlinear motorcycle model is considered. The model involves suspension elements with asymmetric behaviour. Further, it is assumed that the motorcycle is exposed to loading of a stochastic nature as it moves with a specified speed over a road profile defined by a particular power spectrum. It is shown that a meaningful analysis of the motorcycle response can be conducted by using the technique of statistical linearization. The validity of the proposed approach is established by comparison with results from pertinent Monte Carlo studies. In this context the applicability of auto-regressive (AR) filters for efficient implementation of the Monte Carlo simulation is pointed out. The advantages of these methods for the synthesis of excitation signals from a given power spectrum, are shown by comparison with other methods. It is shown that the statistical linearization method allows the analysis of multi-degree-of-freedom (M-DOF) systems that present strong nonlinearities, exceeding other nonlinear analysis methods in both accuracy and applicability. It is expected that the proposed approaches, can be used for a variety of parameter/ride quality studies and as preliminary design tool by the motorcycle industry.
On stability and performance characteristics in control of haptic interfaces and bilateral teleoperation systems
(2013-11-27) Chawda, Vinay; O'Malley, Marcia K.; Dick, Andrew J.; Clark, John W., Jr.
Stability and performance are the two conflicting goals in control of force reflecting robotic systems, such as haptic interfaces and bilateral teleoperation systems. Both the uncertainty attributed to inclusion of a human user in the control loop, and stringent robust stability requirements typically result in very conservative performance. Furthermore, time-varying delays inherent in commercial communication lines compound the already difficult nonlinear control problem of stabilizing bilateral teleoperation systems, and subsequently affect performance. In the first part of this thesis, factors affecting the range of achievable performance in haptic interfaces are analyzed, and accurate real-time velocity estimation from position encoder data is identified as a limiting factor. The efficacy of Levant's differentiator as a velocity estimator, to allow passive implementation of higher stiffness virtual walls, as compared to some of the commonly used velocity estimators in the field of haptics, is studied. A novel performance descriptor, combining passivity and fidelity of haptic rendering, is proposed and used to compare the haptic device performance obtained with Levant's differentiator, to other methods using simulations and experiments. In the second part of this thesis, the effect of time-varying delays on the stability and performance of bilateral teleoperation systems is considered. A framework for increasing performance in Time Domain Passivity Approach (TDPA) based bilateral teleoperation is developed, while preserving robust stability characteristics against time-varying communication delays and remote environment conditions. Several performance compensation schemes are developed within the proposed framework that ensure position tracking between master and slave robot trajectories, and improve force reflection during hard contact interactions. The proposed performance compensation schemes are compared experimentally for their effectiveness in position tracking and force reflection capabilities. In addition, a feedback passivity control based scheme to achieve position synchronization in bilateral teleoperation with power-based TDPA is developed and implemented in simulations and experiments. The proposed method encodes position information with velocity to construct a composite signal, which is transmitted across the communication channel to attain position tracking. Results demonstrate robust position tracking performance with the proposed approach under variable communication delays and remote environment conditions. Combined, these analyses, simulations, and experiments extend the limits of performance in haptic interfaces and bilateral teleoperation systems, while preserving robust stability characteristics.
Optical biopsy systems using ultra-slim objectives for the diagnosis of breast cancer
(2013-09-16) Kyrish, Matthew; Tkaczyk, Tomasz S.; Richards-Kortum, Rebecca Rae; Dick, Andrew J.; Huang, Huey W.
One in eight women in America will develop breast cancer at some point in their lives. Breast cancer is the second deadliest form of cancer for women in the United States. When a suspicious region of the breast is detected, the tissue is diagnosed by remo
Optical Lever Measurement Accuracy for Off-Resonance Atomic Force Microscopy
(2011) Eason, Richard Parker; Dick, Andrew J.
This research evaluates measurement accuracy in optical lever-based atomic force microscopy (AFM) for off-resonance conditions and parameter variations. Under controlled conditions and correct calibration, AFM provides researchers with the ability to accurately observe and manipulate matter on the micro- and nano-scale. Accuracy of imaging and nano-manipulation operations are directly correlated to the accuracy with which the displacement of the probe is measured. The optical lever method, a common displacement measurement technique employed in AFM, calculates probe displacement based on a calibration that assumes a consistent response profile throughout operation. Off-resonance excitation and tip-sample interaction forces during intermittent contact mode AFM can alter this response profile. Standard tapping-mode operation at the fundamental frequency is observed to be robust to changes in effective stiffness, maintaining accurate measurements for all laser spot positions considered. A nominal laser spot position between Xp = 0.5 and 0.6 is determined to most accurately predict displacement for off-resonance excitation during both free response and intermittent contact condit ions. Measurement accuracy for off-resonance tapping- mode is more directly correlated to changes introduced to the interaction force profile than choice of spot position.
Practical high-fidelity frequency-domain force and location identification
(Elsevier, 2015) Ghaderi, Pooya; Dick, Andrew J.; Foley, Jason R.; Falbo, Gregory
Identifying the force information and location of an impact event is important for predicting and/or monitoring potential damage to the structures. Directly measuring the impact event and/or locating the impact force is not always possible due to the nature of the impact or the structure. In this work, a new force and location identification method is introduced which utilizes a spectral finite element method (SFEM) model of the structure. The identification technique is demonstrated and studied through its application to beam structures in order to identify impulsive loads. Wave propagation data collected with accelerometers placed on the structure are used in order to determine the impact information. When the impact force is applied between the accelerometers, the calculated force is distributed over the two accelerometer positions on either side of the impact location. The location identification process uses the distribution of the identified force information in order to locate the impact position. This method is performed by matching simulated data to the identified force data by tuning the impact location within the numerical model. When a sufficient level of agreement is achieved, the impact location is determined. In order to validate the results of the numerical studies, identified impact forces and locations are calculated for experimental data and good agreement is observed with the measured force information and impact locations.
Solution of the Fokker-Planck Equation by Sequentially Optimized Meshfree Approximation
(2014-02-20) Mokhtarzadeh, Arya; Meade, Andrew J., Jr.; Dick, Andrew J.; Nagarajaiah, Satish
This thesis presents a technique to solve the Fokker-Planck equation by applica- tion of the Sequentially Optimized Meshfree Approximation (SOMA) method. It is well known that numerical solution of the Fokker-Planck equation is made di cult by the challenges of positivity enforcement, in nite domain, and high dimensionality. Through the use of optimization, radial basis functions, and its mesh-free architecture, respectively, the SOMA method attempts to address these challenges and sidestep the exponential growth of dimensionality, which hinders traditional numerical methods. Results are presented for one, two, and four-dimensional Fokker-Planck equations. This work will show that SOMA allows for enforcement of a positivity condition that removes the need for log-transforms, produces a solution domain that does not re- quire arti cial boundary condition enforcement, and provides the capability of solving higher dimensional forms of the Fokker-Planck equation.
Spacecraft Attitude Estimation Integrating the Q-Method into an Extended Kalman Filter
(2013-09-16) Ainscough, Thomas; Spanos, Pol D.; Dick, Andrew J.; Shahsavari, Rouzbeh; Zanetti, Renato
A new algorithm is proposed that smoothly integrates the nonlinear estimation of the attitude quaternion using Davenport's q-method and the estimation of non-attitude states within the framework of an extended Kalman filter. A modification to the q-method and associated covariance analysis is derived with the inclusion of an a priori attitude estimate. The non-attitude states are updated from the nonlinear attitude estimate based on linear optimal Kalman filter techniques. The proposed filter is compared to existing methods and is shown to be equivalent to second-order in the attitude update and exactly equivalent in the non-attitude state update with the Sequential Optimal Attitude Recursion filter. Monte Carlo analysis is used in numerical simulations to demonstrate the validity of the proposed approach. This filter successfully estimates the nonlinear attitude and non-attitude states in a single Kalman filter without the need for iterations.

Browsing by Author "Dick, Andrew J."

Results Per Page

Sort Options