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Description
In this research work, a novel control system strategy for the robust control of an unmanned ground vehicle is proposed. This strategy is motivated by efforts to mitigate the problem for scenarios in which the human operator is unable to properly communicate with the vehicle. This novel control system strategy consisted of three major components: I.) Two independent intelligent controllers, II.) An intelligent navigation system, and III.) An intelligent controller tuning unit. The inner workings of the first two components are based off the Brain Emotional Learning (BEL), which is a mathematical model of the Amygdala-Orbitofrontal, a region in mammalians brain known to be responsible for emotional learning. Simulation results demonstrated the implementation of the BEL model to be very robust, efficient, and adaptable to dynamical changes in its application as controller and as a sensor fusion filter for an unmanned ground vehicle. These results were obtained with significantly less computational cost when compared to traditional methods for control and sensor fusion. For the intelligent controller tuning unit, the implementation of a human emotion recognition system was investigated. This system was utilized for the classification of driving behavior. Results from experiments showed that the affective states of the driver are accurately captured. However, the driver's affective state is not a good indicator of the driver's driving behavior. As a result, an alternative method for classifying driving behavior from the driver's brain activity was explored. This method proved to be successful at classifying the driver's behavior. It obtained results comparable to the common approach through vehicle parameters. This alternative approach has the advantage of directly classifying driving behavior from the driver, which is of particular use in UGV domain because the operator's information is readily available. The classified driving mode was used tune the controllers' performance to a desired mode of operation. Such qualities are required for a contingency control system that would allow the vehicle to operate with no operator inputs.
ContributorsVargas-Clara, Alvaro (Author) / Redkar, Sangram (Thesis advisor) / McKenna, Anna (Committee member) / Cooke, Nancy J. (Committee member) / Arizona State University (Publisher)
Created2015
Description
Recent studies of the occurrence of post-flutter limit cycle oscillations (LCO) of the F-16 have provided good support to the long-standing hypothesis that this phenomenon involves a nonlinear structural damping. A potential mechanism for the appearance of nonlinearity in the damping are the nonlinear geometric effects that arise when the deformations become large enough to exceed the linear regime. In this light, the focus of this investigation is first on extending nonlinear reduced order modeling (ROM) methods to include viscoelasticity which is introduced here through a linear Kelvin-Voigt model in the undeformed configuration. Proceeding with a Galerkin approach, the ROM governing equations of motion are obtained and are found to be of a generalized van der Pol-Duffing form with parameters depending on the structure and the chosen basis functions. An identification approach of the nonlinear damping parameters is next proposed which is applicable to structures modeled within commercial finite element software.
The effects of this nonlinear damping mechanism on the post-flutter response is next analyzed on the Goland wing through time-marching of the aeroelastic equations comprising a rational fraction approximation of the linear aerodynamic forces. It is indeed found that the nonlinearity in the damping can stabilize the unstable aerodynamics and lead to finite amplitude limit cycle oscillations even when the stiffness related nonlinear geometric effects are neglected. The incorporation of these latter effects in the model is found to further decrease the amplitude of LCO even though the dominant bending motions do not seem to stiffen as the level of displacements is increased in static analyses.
The effects of this nonlinear damping mechanism on the post-flutter response is next analyzed on the Goland wing through time-marching of the aeroelastic equations comprising a rational fraction approximation of the linear aerodynamic forces. It is indeed found that the nonlinearity in the damping can stabilize the unstable aerodynamics and lead to finite amplitude limit cycle oscillations even when the stiffness related nonlinear geometric effects are neglected. The incorporation of these latter effects in the model is found to further decrease the amplitude of LCO even though the dominant bending motions do not seem to stiffen as the level of displacements is increased in static analyses.
ContributorsSong, Pengchao (Author) / Mignolet, Marc P (Thesis advisor) / Chattopadhyay, Aditi (Committee member) / Oswald, Jay (Committee member) / Arizona State University (Publisher)
Created2015
Description
As the robotic industry becomes increasingly present in some of the more extreme environments such as the battle field, disaster sites or extraplanetary exploration, it will be necessary to provide locomotive niche strategies that are optimal to each terrain. The hopping gait has been well studied in robotics and proven to be a potential method to fit some of these niche areas. There have been some difficulties in producing terrain following controllers that maintain robust, steady state, which are disturbance resistant.
The following thesis will discuss a controller which has shown the ability to produce these desired properties. A phase angle oscillator controller is shown to work remarkably well, both in simulation and with a one degree of freedom robotic test stand.
Work was also done with an experimental quadruped with less successful results, but which did show potential for stability. Additional work is suggested for the quadruped.
The following thesis will discuss a controller which has shown the ability to produce these desired properties. A phase angle oscillator controller is shown to work remarkably well, both in simulation and with a one degree of freedom robotic test stand.
Work was also done with an experimental quadruped with less successful results, but which did show potential for stability. Additional work is suggested for the quadruped.
ContributorsNew, Philip Wesley (Author) / Sugar, Thomas G. (Thesis advisor) / Artemiadis, Panagiotis (Committee member) / Redkar, Sangram (Committee member) / Arizona State University (Publisher)
Created2015
Description
The football helmet is a device used to help mitigate the occurrence of impact-related traumatic (TBI) and minor traumatic brain injuries (mTBI) in the game of American football. The current design methodology of using a hard shell with an energy absorbing liner may be adequate for minimizing TBI, however it has had less effect in minimizing mTBI. The latest research in brain injury mechanisms has established that the current design methodology has produced a helmet to reduce linear acceleration of the head. However, angular accelerations also have an adverse effect on the brain response, and must be investigated as a contributor of brain injury.
To help better understand how the football helmet design features effect the brain response during impact, this research develops a validated football helmet model and couples it with a full LS-DYNA human body model developed by the Global Human Body Modeling Consortium (v4.1.1). The human body model is a conglomeration of several validated models of different sections of the body. Of particular interest for this research is the Wayne State University Head Injury Model for modeling the brain. These human body models were validated using a combination of cadaveric and animal studies. In this study, the football helmet was validated by laboratory testing using drop tests on the crown of the helmet. By coupling the two models into one finite element model, the brain response to impact loads caused by helmet design features can be investigated. In the present research, LS-DYNA is used to study a helmet crown impact with a rigid steel plate so as to obtain the strain-rate, strain, and stress experienced in the corpus callosum, midbrain, and brain stem as these anatomical regions are areas of concern with respect to mTBI.
To help better understand how the football helmet design features effect the brain response during impact, this research develops a validated football helmet model and couples it with a full LS-DYNA human body model developed by the Global Human Body Modeling Consortium (v4.1.1). The human body model is a conglomeration of several validated models of different sections of the body. Of particular interest for this research is the Wayne State University Head Injury Model for modeling the brain. These human body models were validated using a combination of cadaveric and animal studies. In this study, the football helmet was validated by laboratory testing using drop tests on the crown of the helmet. By coupling the two models into one finite element model, the brain response to impact loads caused by helmet design features can be investigated. In the present research, LS-DYNA is used to study a helmet crown impact with a rigid steel plate so as to obtain the strain-rate, strain, and stress experienced in the corpus callosum, midbrain, and brain stem as these anatomical regions are areas of concern with respect to mTBI.
ContributorsDarling, Timothy (Author) / Rajan, Subramaniam D. (Thesis advisor) / Muthuswamy, Jitendran (Thesis advisor) / Oswald, Jay (Committee member) / Mignolet, Marc (Committee member) / Arizona State University (Publisher)
Created2014
Description
Monte Carlo simulations are traditionally carried out for the determination of the amplification of forced vibration response of turbomachine/jet engine blades to mistuning. However, this effort can be computationally time consuming even when using the various reduced order modeling techniques. Accordingly, some investigations in the past have focused on obtaining simple approximate estimates for this amplification. In particular, two of these have proposed the use of harmonic patterns of the blade properties around the disk as an approximate alternative to the many random patterns of Monte Carlo analyses. These investigations, while quite encouraging, have relied solely on single degree of freedom per sector models of the rotor.
In this light, the overall focus of the present effort is a revisit of harmonic
mistuning of rotors focusing first the confirmation of the previously obtained findings with a more detailed model of the blisk in both conditions of an isolated blade-dominated resonance and of a veering between blade and disk dominated modes. The latter condition cannot be simulated by a single degree of freedom per sector model. Further, the analysis will consider the distinct cases of mistuning due to variations of material properties (Young's modulus) and geometric properties (geometric mistuning). In the single degree of freedom model, both mistuning types are equivalent but they are not, as demonstrated here, in more realistic models. The difference arises because changes in geometry induce not only changes in natural frequencies of the blades alone but of their modes and the importance of these two sources of variability is discussed with both Monte Carlo simulation and harmonic mistuning results.
The present investigation focuses also on the possible extension of the harmonic mistuning concept and of its quantitative information that can be derived from such analyses. From it, a novel measure of blade-disk coupling is introduced and assessed in comparison with the coupling index introduced in the past. In conclusions, the low cost of harmonic mistuning computations in comparison with full Monte Carlo simulations is
demonstrated to be worthwhile to elucidate the basic behavior of the mistuned rotor in a random setting.
In this light, the overall focus of the present effort is a revisit of harmonic
mistuning of rotors focusing first the confirmation of the previously obtained findings with a more detailed model of the blisk in both conditions of an isolated blade-dominated resonance and of a veering between blade and disk dominated modes. The latter condition cannot be simulated by a single degree of freedom per sector model. Further, the analysis will consider the distinct cases of mistuning due to variations of material properties (Young's modulus) and geometric properties (geometric mistuning). In the single degree of freedom model, both mistuning types are equivalent but they are not, as demonstrated here, in more realistic models. The difference arises because changes in geometry induce not only changes in natural frequencies of the blades alone but of their modes and the importance of these two sources of variability is discussed with both Monte Carlo simulation and harmonic mistuning results.
The present investigation focuses also on the possible extension of the harmonic mistuning concept and of its quantitative information that can be derived from such analyses. From it, a novel measure of blade-disk coupling is introduced and assessed in comparison with the coupling index introduced in the past. In conclusions, the low cost of harmonic mistuning computations in comparison with full Monte Carlo simulations is
demonstrated to be worthwhile to elucidate the basic behavior of the mistuned rotor in a random setting.
ContributorsSahoo, Saurav (Author) / Mignolet, Marc Paul (Thesis advisor) / Chattopadhyay, Aditi (Committee member) / Oswald, Jay (Committee member) / Arizona State University (Publisher)
Created2014
Description
The Volume-of-Fluid method is a popular method for interface tracking in Multiphase applications within Computational Fluid Dynamics. To date there exists several algorithms for reconstruction of a geometric interface surface. Of these are the Finite Difference algorithm, Least Squares Volume-of-Fluid Interface Reconstruction Algorithm, LVIRA, and the Efficient Least Squares Volume-of-Fluid Interface Reconstruction Algorithm, ELVIRA. Along with these geometric interface reconstruction algorithms, there exist several volume-of-fluid transportation algorithms. This paper will discuss two operator-splitting advection algorithms and an unsplit advection algorithm. Using these three interface reconstruction algorithms, and three advection algorithms, a comparison will be drawn to see how different combinations of these algorithms perform with respect to accuracy as well as computational expense.
ContributorsKedelty, Dominic (Author) / Herrmann, Marcus (Thesis advisor) / Huang, Huei-Ping (Committee member) / Chen, Kangping (Committee member) / Arizona State University (Publisher)
Created2015
Description
In this work, the hydrodynamics of Suction Stabilization is studied. Suction stabilization was found to stabilize floating platforms/floats in a much better way as compared to the conventional methods. This was achieved by an effective increment in the metacentric height due to the Inverse Slack Tank (IST) effect. The study involves the analysis of the existing designs and optimizing its performance. This research investigates the stability of such floats and the hydrodynamic forces acting on the same for offshore applications, such as wind turbines. A simple mathematical model for the condition of parametric resonance is developed and the results are verified, both analytically and experimentally.
ContributorsCherangara Subramanian, Susheelkumar (Author) / Redkar, Sangram (Thesis advisor) / Rajadas, John (Committee member) / Rogers, Bradley (Committee member) / Arizona State University (Publisher)
Created2014
Description
The flow of liquid PDMS (10:1 v/v base to cross-linker ratio) in open, rectangular silicon micro channels, with and without a hexa-methyl-di-silazane (HMDS) or poly-tetra-fluoro-ethylene (PTFE) (120 nm) coat, was studied. Photolithographic patterning and etching of silicon wafers was used to create micro channels with a range of widths (5-50 μm) and depths (5-20 μm). The experimental PDMS flow rates were compared to an analytical model based on the work of Lucas and Washburn. The experimental flow rates closely matched the predicted flow rates for channels with an aspect ratio (width to depth), p, between one and two. Flow rates in channels with p less than one were higher than predicted whereas the opposite was true for channels with p greater than two. The divergence between the experimental and predicted flow rates steadily increased with increasing p. These findings are rationalized in terms of the effect of channel dimensions on the front and top meniscus morphology and the possible deviation from the no-slip condition at the channel walls at high shear rates.
In addition, a preliminary experimental setup for calibration tests on ultrasensitive PDMS cantilever beams is reported. One loading and unloading cycle is completed on a microcantilever PDMS beam (theoretical stiffness 0.5 pN/ µm). Beam deflections are actuated by adjusting the buoyancy force on the beam, which is submerged in water, by the addition of heat. The expected loading and unloading curve is produced, albeit with significant noise. The experimental results indicate that the beam stiffness is a factor of six larger than predicted theoretically. One probable explanation is that the beam geometry may change when it is removed from the channel after curing, making assumptions about the beam geometry used in the theoretical analysis inaccurate. This theory is bolstered by experimental data discussed in the report. Other sources of error which could partially contribute to the divergent results are discussed. Improvements to the experimental setup for future work are suggested.
In addition, a preliminary experimental setup for calibration tests on ultrasensitive PDMS cantilever beams is reported. One loading and unloading cycle is completed on a microcantilever PDMS beam (theoretical stiffness 0.5 pN/ µm). Beam deflections are actuated by adjusting the buoyancy force on the beam, which is submerged in water, by the addition of heat. The expected loading and unloading curve is produced, albeit with significant noise. The experimental results indicate that the beam stiffness is a factor of six larger than predicted theoretically. One probable explanation is that the beam geometry may change when it is removed from the channel after curing, making assumptions about the beam geometry used in the theoretical analysis inaccurate. This theory is bolstered by experimental data discussed in the report. Other sources of error which could partially contribute to the divergent results are discussed. Improvements to the experimental setup for future work are suggested.
ContributorsSowers, Timothy Wayne (Author) / Rajagopalan, Jagannathan (Thesis advisor) / Herrmann, Marcus (Committee member) / Huang, Huei-Ping (Committee member) / Arizona State University (Publisher)
Created2014
Description
In order to achieve higher gas turbine efficiency, the main gas temperature at turbine inlet has been steadily increased from approximately 900°C to about 1500°C over the last few decades. This temperature is higher than the maximum acceptable temperature for turbine internals. The hot main gas may get ingested into the space between rotor and stator, the rotor-stator disk cavity in a stage because of the pressure differential between main gas annulus and the disk cavity. To reduce this ingestion, the disk cavity is equipped with a rim seal; additionally, secondary (purge) air is supplied to the cavity. Since the purge air is typically bled off the compressor discharge, this reducing the overall gas turbine efficiency, much research has been carried out to estimate the minimum purge flow necessary (cw,min) for complete sealing of disk cavities.
In this work, experiments have been performed in a subscale single-stage axial turbine featuring vanes, blades and an axially-overlapping radial-clearance seal at the disk cavity rim. The turbine stage is also equipped with a labyrinth seal radially inboard. The stage geometry and the experimental conditions were such that the ingestion into the disk cavity was driven by the pressure asymmetry in the main gas annulus. In the experiments, time-averaged static pressure was measured at several locations in the main annulus and in the disk cavity; the pressure differential between a location on the vane platform close to lip (this being the rim seal part on the stator) and a location in the 'seal region' in the cavity is considered to be the driving potential for both ingestion and egress. Time-averaged volumetric concentration of the tracer gas (CO2) in the purge air supplied was measured at multiple radial locations on the stator surface. The pressure and ingestion data were then used to calculate the ingestion and egress discharge coefficients for a range of purge flow rates, employing a simple orifice model of the rim seal. For the experiments performed, the egress discharge coefficient increased and the ingestion discharge coefficient decreased with the purge air flow rate. A method for estimation of cw,min is also proposed.
In this work, experiments have been performed in a subscale single-stage axial turbine featuring vanes, blades and an axially-overlapping radial-clearance seal at the disk cavity rim. The turbine stage is also equipped with a labyrinth seal radially inboard. The stage geometry and the experimental conditions were such that the ingestion into the disk cavity was driven by the pressure asymmetry in the main gas annulus. In the experiments, time-averaged static pressure was measured at several locations in the main annulus and in the disk cavity; the pressure differential between a location on the vane platform close to lip (this being the rim seal part on the stator) and a location in the 'seal region' in the cavity is considered to be the driving potential for both ingestion and egress. Time-averaged volumetric concentration of the tracer gas (CO2) in the purge air supplied was measured at multiple radial locations on the stator surface. The pressure and ingestion data were then used to calculate the ingestion and egress discharge coefficients for a range of purge flow rates, employing a simple orifice model of the rim seal. For the experiments performed, the egress discharge coefficient increased and the ingestion discharge coefficient decreased with the purge air flow rate. A method for estimation of cw,min is also proposed.
ContributorsSingh, Prashant (Author) / Roy, Ramendra P (Thesis advisor) / Mignolet, Marc (Thesis advisor) / Lee, Taewoo (Committee member) / Arizona State University (Publisher)
Created2014
Description
Identification of early damage in polymer composite materials is of significant importance so that preventative measures can be taken before the materials reach catastrophic failure. Scientists have been developing damage detection technologies over many years and recently, mechanophore-based polymers, in which mechanical energy is translated to activate a chemical transformation, have received increasing attention. More specifically, the damage can be made detectable by mechanochromic polymers, which provide a visible color change upon the scission of covalent bonds under stress. This dissertation focuses on the study of a novel self-sensing framework for identifying early and in-situ damage by employing unique stress-sensing mechanophores. Two types of mechanophores, cyclobutane and cyclooctane, were utilized, and the former formed from cinnamoyl moeities and the latter formed from anthracene upon photodimerization. The effects on the thermal and mechanical properties with the addition of the cyclobutane-based polymers into epoxy matrices were investigated. The emergence of cracks was detected by fluorescent signals at a strain level right after the yield point of the polymer blends, and the fluorescence intensified with the accumulation of strain. Similar to the mechanism of fluorescence emission from the cleavage of cyclobutane, the cyclooctane moiety generated fluorescent emission with a higher quantum yield upon cleavage. The experimental results also demonstrated the success of employing the cyclooctane type mechanophore as a potential force sensor, as the fluorescence intensification was correlated with the strain increase.
ContributorsZou, Jin (Author) / Dai, Lenore L (Thesis advisor) / Chattopadhyay, Aditi (Thesis advisor) / Lind, Mary L (Committee member) / Mu, Bin (Committee member) / Yu, Hongyu (Committee member) / Arizona State University (Publisher)
Created2014