Browsing by Subject "Aerospace engineering and mechanics"

Now showing 1 - 17 of 17
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    Commercial aircraft trajectory optimization and efficiencyf air traffic control procedures.
    (2011-11) Howe-Veenstra, Ryan
    The Next Generation Air Traffic System (NextGen) offers a historical opportunity to re-examine the assumptions and constraints in the current Air Traffic Control (ATC) system and their effects on ight efficiency and safety. Modern day commercial air- craft are fully capable of ying continuously varying smooth trajectories. However in the current air traffic control ATC system, commercial ight trajectories consist of a series of segments due to historical development of navigation and surveillance systems. Segments are defined by one or more constant parameters such as Mach number or altitude. In this paper, characteristics and efficiencies of optimal free ights when ATC constraints are absent and optimal segmented ights in the current ATC system are compared. In this paper, aircraft ights are modeled as a point-mass. Both horizontal and vertical ight profiles are considered. Results of this paper seek to determine the potential benefit of supporting continuous trajectories in future ATC systems.
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    Copepod response behavior in turbulence
    (2014-09) Krizan, Daniel
    The objective of this thesis is to determine copepod response to turbulence generated by obstacles in cross flow. Mainly, flow and copepod response downstream a square fractal grid is examined but experiments downstream a cylinder provides comparison. This is done by simultaneously measuring the copepods position and velocity using 3D-PTV in a measurement volume and measuring the two dimensional three component velocity vectors of the flow using stereo PIV. These measurements are done in a way that does not elicit copepod response. Tomographic PIV is done downstream the square fractal grid without copepods to gain volumetric velocity knowledge of the flow in the measurement volume. Copepods are known to execute sudden high speed jumps (or escapes) in response to sensed hydrodynamic signals. The fractal grid was shown to elicit copepod escape, specifically directly downstream with escape frequency decreasing further downstream where turbulence levels were much lower. It was found that at a slower freestream speed copepods exhibited jumps not in reaction to flow disturbances but to reorient themselves (cruise swimming). There was almost no copepod response in the wake of a cylinder, but copepods again exhibited cruise swimming behavior at a slower freestream speed. In regions with high maximum principal strain rate (MPSR) downstream of the fractal grid, copepods were observed to exhibit multiple escapes. Moreover, copepods were observed to jump towards regions of lower turbulence and against the freestream direction. From stereo PIV, instantaneous 2D MPSR values of less than 3s^(-1) were shown to create escape in 60% of copepod escapes analyzed. Finally, it was found that on average larger MPSR resulted in larger jumps from copepods.
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    Density functional methods for objective structures: theory and simulation schemes
    (2013-12) Banerjee, Amartya Sankar
    Objective structures are atomic/molecular configurations which generalize the notion of crystals and are such that all the constituent atoms/molecules of the structure see the same environment up to orthogonal transformations and translations. Objective structures are ubiquitously present in all of materials science, biology and nanotechnology and examples of these structures include nanotubes, buckyballs, tail sheaths and capsids of viruses, graphene sheets and molecular bilayers. Due to their association with large degrees of symmetry, objective structures are likely to be a fertile source of materials with remarkable material properties: particularly, collective material properties such as ferromagnetism and ferroelectricity. A systematic study of objective structures therefore, is likely to lead to the discovery of novel materials. At the same time, formulation of computational methods specifically designed for studying objective structures, is likely to lead to the development of novel nanomechanics simulations methodologies. Following this line of thought, this thesis deals with the development of Objective Density Functional Theory: a suite of rigorously formulated Density Functional methods and numerical algorithms for carrying out abinitio simulation studies of objective structures. Drawing analogies from the classical planewave density functional method of solid state physics, our focus has been on the development of novel spectral schemes for studying objective structures using Kohn Sham Density Functional Theory. In this work, we demon strate how the equations of Kohn Sham Density Functional Theory for objective structures admit interpretation in terms of symmetry adapted cell problems. We propose complete orthonormal basis sets for discretizing these cell problems. Next, we discuss the significant challenges associated with the efficient solution of the discretized cell problems and our progress in addressing these challenges through a variety of numerical and algorithmic strategies. Many of these strategies and methods have been implemented within the framework of a powerful first principles simulation package called ClusterES (Cluster Electronic Structure) that we designed and developed as part of this work. We end with some examples highlighting the efficiency and accuracy of our numerical methods as well as a brief discussion of ongoing applications of our spectral schemes to the study of some problems in nanomechanics.
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    Discrete roughness effects on high-speed boundary layers
    (2015-01) Iyer, Prahladh Satyanarayanan
    This dissertation studies the effects of a discrete roughness element on a high-speed boundary layer using Direct Numerical Simulations (DNS) on unstructured grids. Flow past a cylindrical roughness element placed perpendicular to the flow and a hemispherical bump is studied. A compressible linear stability theory (LST) solver for parallel flows is developed based on the algorithm by Malik [33] and validated for a range of Mach numbers ranging from incompressible to Mach 10. The evolution of the perturbations from DNS is validated with the linear stability solver making the DNS algorithm suitable to study transition problems. Flow past a cylindrical roughness element at Mach 8.12 is simulated using DNS and the velocity profiles in the symmetry and wall--parallel planes are compared to the experiments of Bathel et al. [7]. The flow remains steady and laminar, and does not transition. Overall, good agreement is observed between DNS and experiments, thus validating our algorithm to study effect of roughness on high-speed flows. However, differences are observed in the separation region upstream and recirculation region downstream of the roughness. The DNS results are used to quantify possible uncertainties in the measurement technique as suggested by Danehy [20]. The effect of upstream injection (5% of the free-stream velocity) is also simulated to quantify its effects on the velocity profiles to mimic the injection of NO into air in the experiment. While the boundary layer thickness of the flow increases downstream of the injection location, its effect on the velocity profiles is small when the profiles are scaled with the boundary layer thickness.Flow past a hemispherical bump at Mach 3.37, 5.26 and 8.23 are simulated using DNS with the flow conditions matching the experiments of Danehy et al. [19] to understand the different flow features associated with the flow and the physical mechanism that causes the flow to transition to turbulence. It is observed that the Mach 3.37 and 5.26 flows transition to turbulence while the Mach 8.23 flow remains laminar downstream of the roughness element. The roughness element used in this study is large since the boundary layer thickness of the laminar boundary layer at the location of the roughness is smaller than the roughness height.The Mach 3.37 flow undergoes transition closer to the bump when compared to Mach 5.26, in agreement with experimental observations. Transition is accompanied by an increase in C_f and C_h (Stanton number). Even for the case that did not undergo transition (Mach 8.23), streamwise vortices induced by the roughness cause a significant rise in C_f until 20D downstream. Mean Van-Driest transformed velocity and Reynolds stress for Mach 3.37 and 5.26 shows good agreement with available data. The transition process involves the following key elements - Upon interaction with the roughness element, the boundary layer separates to form a series of spanwise vortices upstream of the roughness, and a separation shear layer. The system of spanwise vortices wrap around the roughness element in the form of horseshoe/necklace vortices to yield a system of counter-rotating streamwise vortices downstream of the element. These vortices are located beneath the separation shear layer and perturb it, which results in the formation of trains of hairpin-shaped vortices further downstream of the roughness for the cases that undergo transition. These hairpins spread in the span with increasing downstream distance and the flow increasingly resembles a fully developed turbulent boundary layer. A local Reynolds number based on the wall properties is seen to correlate the onset of transition for the cases considered.To assess the effect of roughness height on transition, a Mach 3.37 flow past a hemispherical bump is studied by varying the boundary layer thickness (k/delta = 2.54, 1.0, 0.25 & 0.125) where k is the roughness height and delta is the laminar boundary layer thickness at the location of the roughness. Transition occurs in all cases, and the essential mechanism of transition appears to be similar. At smaller boundary layer thickness, multiple trains of hairpin vortices are observed immediately downstream of the roughness, while a single train of hairpin vortices is observed at larger delta. This behavior is explained by the influence of the boundary layer thickness on the separation vortices upstream of the roughness element. Also, hairpin vortices that form downstream of the roughness initially scale with the height of the roughness element and further downstream, begin to scale with the boundary layer thickness, thus causing the entire boundary layer to transition. Dynamic Mode Decomposition of the pressure field for k/delta= 1 and 0.125 is used to obtain the frequency of shedding of hairpin vortices.
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    Flow characterization on a thin film spinning apparatus
    (2014-09) Alvarado, Alonso Antonio
    In industrial milling operations that use comminution and wet-comminution techniques, the reduction of the particle size is usually achieved through crushing the sample with a material harder than the product. These methods are convenient when the required median particle size is above 400 um. However, to obtain post-milling particle distributions with 85% sub-micron particles (in number) is both energy intensive, and time consuming. For conventional milling machines, to have the required output in several ton/hr of a product, having a large number of particles in the micron or sub-micron sizes at an affordable rate is cumbersome.Here, a wet-comminution machine that has shown to achieve the aforementioned milestones in the laboratory scale is studied. However, when the machine is scaled to industrial processes, it was recorded that some of the product variables are difficult to scale. In these studies, we attempt to understand the mechanisms by which this machine operates in order to achieve successful scaling. The apparatus operates completely on fluid mechanics principles, it consists of two concentric cylinders, the inner cylinder that has a smaller radius than the outer, rotates while the larger is held stationary. The inner cylinder is also shorter in length than outer, hollow in the inside and has transversal holes where the shaft attaches to the apparatus. The apparatus can operate in batch condition, where the liquid volume is much less than the volume of the apparatus, typically 0.3Vt, 0.42Vt and 0.54Vt. In addition, the apparatus can operate with throughflow, which the upper plate covering the apparatus is reduced in radius.Two component Laser Doppler Velocimetry (LDV) was used to obtain even-time averaged statistics of the azimuthal and axial velocities, in the gap and underneath the impeller. Also, Flow Visualization using Kalliroscopic particles was performed as means of observing large scale structures in the gap. Moreover, single plane Particle Image Velocimetry (PIV) was used to acquire statistics of the axial and radial velocities in the gap, and both underneath as well as above the inner cylinder.It was found that at both throughflow conditions, the topology of the apparatus creates a free spinning boundary both at the bottom and above the inner cylinder. Near the bottom, the thickness of the boundary was found to decrease with Reynolds number to a limiting value, where Re; is based on gap thickness and inner cylinder tip speed. For Re > 2546, the liquid/air interface thickness is constant for a given holding volume. In the regions above and underneath the inner cylinder, corner vortices were detected; if viewing the left-hand-side, the lower one rotating counter clockwise, while the upper rotates clockwise. The thickness of these vortices was found to be constant for various axial flows at Re = 1110 and 2230. The radial length scale of the stationary vortices was found to be ~2.5d;.The flow generated inside of the gap was characterized to have Taylor vortex signatures. It was found that the length scale of the Taylor vortices in the gap is rather insensitive to Reynolds number or holding volume ratio. The average vortex pair wavelength; was found to be 3.6d. Average flow statistics in batch condition indicate that in the gap, at Re = 1110 and 2230, the azimuthal velocity is 0.5U over much of the length. Similarly, it was found that the net axial flow through the gap is close to zero.
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    Fluid mechanic phenomena relating to flow control in conduits and pumps
    (2014-08) Bayazit, Yilmaz
    The attainment of controlled homogenized fluid flow is a major issue in the efficient utilization of internal flows for applications as diverse as heat exchange, electrostatic filtration, water purification, particle conveyance, swirl control, and waste disposal. Among the candidate methodologies for accomplishing the homogenization task, perforated plates provide exceptional versatility and adaptability. The principle that underlies perforated plate flow control is the tendency of a flowing fluid to seek the path of least resistance. This tendency is coupled with the capability of the fluid to "see" what lies ahead, enabling it to adjust its trajectory. That capability is due to streamwise diffusion, which transfers information both upstream and downstream. In contrast, advection is a one-way information transfer mechanism, the direction of transfer coinciding with the direction of fluid motion.The degree of homogenization afforded by perforated plates depends on several geometrical and operating parameters. The geometrical parameters include: (a) plate porosity, (b) plate thickness, (c) aperture diameter, (d) pattern of aperture deployment, and (e) distance between apertures. With respect to operating parameters, those investigated here encompass (f) fluid velocity, (g) flow regime, and (h) angle of attack. Nondimensionalization diminished the total number of parameters to five. Numerical simulation was employed to solve the three-dimensional flow covering a Reynolds number range from 0.01 to 25,000. Results extracted from the solutions included dimensionless pressure drop, downstream distance for disturbance decay, vector diagrams and streamlines, and flow regime boundaries. A paradox where the pressure drop for a thin plate exceeded that for a thick plate was rationalized.The pressure drop characteristics of a perforated plate are akin to those for a porous medium. The Darcy-Forchheimer pressure drop model was extended into the turbulent flow regime for the first time, thereby contradicting the prior limitation to inertial laminar flow.The Taguchi method was applied to pinpoint the most important among the independent variables with respect to the dimensionless pressure drop, highlighting the importance of the porosity.Control of the liquid flow produced by a pump was analyzed as a problem of fluid-structural interaction.
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    Gain scheduling of an extended Kalman Filter for use in an attitude/heading estimation system.
    (2012-03) Horkheimer, Donald Patrick
    Even with recent advances in computing power the development of smaller Unmanned Aerial Vehicles (UAVs) and sophisticated sensor payloads with high data rates can still challenge on-board computer resources. In response to this challenge, gain scheduling is investigated as a means to reduce the computational burden associated with a nonlinear attitude estimator. The attitude/heading filter used to validate the gain scheduling approach is based on an Euler angle parameterization. Its process dynamics and measurement updates are provided by nonlinear rate kinematic equations and absolute attitude measurement updates, respectively. The gain scheduling approach is intended to be instrumentation independent for the attitude parameterization used. Validation of the gain scheduling attitude/heading estimation filter utilized process dynamics driven by a low-cost Micro-Electromechanical System (MEMS) based Inertial Measurement Unit (IMU). Measurement updates are provided by an external machine-vision infrared tracking system. The gain scheduling approach should be applicable to other sensor types such as GPS, magnetometers, and other aides. Gain scheduling filter development has been tested using simulated trajectories and real data collected from a remote control helicopter own indoors and processed off-line.
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    Harmonic analysis on isometry groups of objective structures and its applications to objective density functional theory.
    (2011-11) Banerjee, Amartya Sankar
    Objective structures (defined in James [2006]) generalize the notion of crystals and are atomic/molecular structures in which all the constituent atoms/molecules of the structure “see” the same environment up to orthogonal transformations and translations. It has been conjectured [James, 2006] that the high degree of symmetry associated with these structures can lead to interesting material properties such as ferromagnetism, ferroelectricity and superconductivity. This provides a motivation to systematically study the electronic properties of these structures and to formulate Density Functional Theory methods specifically designed for objective structures. We term density functional methods/algorithms designed for studying Objective Structures as Objective Density Functional Theory. The purpose of this work is to serve as the first important step toward the formulation and implementation of objective density functional theory. Keeping in mind, that density functional theory methods designed for studying crystals obtain leverage out of the translational symmetry of the underlying periodic system, the primary theoretical issue in formulating objective density functional theory methods, becomes quantifying the effects of (non-translational) symmetry on electronic structure computation. In this work, we borrow ideas from abstract harmonic analysis/group representation theory, in order to understand how the symmetry of objective structures generated by finite groups of isometries interacts with the boundary value problems of Kohn-Sham density functional theory. To achieve our goal, we first work through the formulation of a suitable group representation theory. We then apply this representation theory to simplified versions of the boundary value problems associated with electronic structure calculation and we demonstrate how this results in simplifications of those problems. Finally, we formulate symmetry adapted finite difference and spectral schemes for numerical solution of the boundary value problems.
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    Model and Control validation of a high speed supercavitating vehicle
    (2012-08) Escobar Sanabria, David
    Underwater, supercavitating vehicles can achieve higher speeds than conventional submarine vehicles due to the drag reduction result of the vehicle-fluid isolation. Re- search on the control of high speed supercavitating vehicles has led to theoretical so- lutions; however, validation and testing of control laws to drive the vehicle motion are expensive, complex and have not been presented in the open literature. This thesis presents an approach to the experimental validation of control systems for a supercavitating test vehicle in the longitudinal plane. The supercavitating vehi- cle considered in this thesis consists of a cylindrical body with a disk cavitator and two lateral, sweptback, wedge fins. The control validation platform enables the use of the high speed water tunnel located at the Saint Anthony Falls Laboratory to recre- ate realistic flight scenarios including the effect of ocean waves on the vehicle. The test platform uses the hydrodynamic forces produced by the fluid-vehicle interaction, embedded flight computer, and analytical equations of motion to test the closed-loop system performance in real time. The equations of motion for the test vehicle are de- rived based on experiments in which the effect of perturbed flow on the vehicle motion is also considered. A controller for the test vehicle is synthesized using H-infinity op- timization. Water tunnel tests successfully validated the supercavitating vehicle model and controller. The objectives were tracking of pitch angle reference commands and rejection of disturbances produced by an oscillating foil gust generator. The experimental results show the accuracy of the vehicle modeling and control design as well as the effect of the perturbed flow on the closed-loop system performance. The experience gained from this work enabled the introduction of the next generation test platform capable to capture planing phenomena.
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    Molecular dynamics modeling of normal shock waves in monatomic and polyatomic gas mixtures.
    (2011-09) Tump, Patrick Alan
    Large-scale molecular dynamics (MD) simulations using the Lennard-Jones potential are performed to study the structure of normal shock waves in dilute Nitrogen and mixtures of Helium-Argon and Helium-Xenon. The use of realistic MD simulations of normal shock waves promises to provide a more detailed solution than can be provided experimentally, providing a means to validate and create better DSMC models. MD simulations of Nitrogen and Helium-Argon mixtures show promising comparisons to experimental results, with near perfect agreement between MD and DSMC using Generalized Hard Sphere (GHS).
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    Reliability assessment for low-cost unmanned aerial vehicles
    (2014-11) Freeman, Paul Michael
    Existing low-cost unmanned aerospace systems are unreliable, and engineers must blend reliability analysis with fault-tolerant control in novel ways. This dissertation introduces the University of Minnesota unmanned aerial vehicle flight research platform, a comprehensive simulation and flight test facility for reliability and fault-tolerance research. An industry-standard reliability assessment technique, the failure modes and effects analysis, is performed for an unmanned aircraft. Particular attention is afforded to the control surface and servo-actuation subsystem. Maintaining effector health is essential for safe flight; failures may lead to loss of control incidents. Failure likelihood, severity, and risk are qualitatively assessed for several effector failure modes. Design changes are recommended to improve aircraft reliability based on this analysis. Most notably, the control surfaces are split, providing independent actuation and dual-redundancy. The simulation models for control surface aerodynamic effects are updated to reflect the split surfaces using a first-principles geometric analysis.The failure modes and effects analysis is extended by using a high-fidelity nonlinear aircraft simulation. A trim state discovery is performed to identify the achievable steady, wings-level flight envelope of the healthy and damaged vehicle. Tolerance of elevator actuator failures is studied using familiar tools from linear systems analysis. This analysis reveals significant inherent performance limitations for candidate adaptive/reconfigurable control algorithms used for the vehicle. Moreover, it demonstrates how these tools can be applied in a design feedback loop to make safety-critical unmanned systems more reliable.Control surface impairments that do occur must be quickly and accurately detected. This dissertation also considers fault detection and identification for an unmanned aerial vehicle using model-based and model-free approaches and applies those algorithms to experimental faulted and unfaulted flight test data. Flight tests are conducted with actuator faults that affect the plant input and sensor faults that affect the vehicle state measurements. A model-based detection strategy is designed and uses robust linear filtering methods to reject exogenous disturbances, e.g. wind, while providing robustness to model variation. A data-driven algorithm is developed to operate exclusively on raw flight test data without physical model knowledge. The fault detection and identification performance of these complementary but different methods is compared. Together, enhanced reliability assessment and multi-pronged fault detection and identification techniques can help to bring about the next generation of reliable low-cost unmanned aircraft.
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    Results on the interaction between atomistic and continuum models
    (2014-08) Admal, Nikhil Chandra
    In this thesis, we develop continuum notions for atomistic systems which play an important role in developing accurate constitutive relations for continuum models, and robust multiscale methods for studying systems with multiple length and time scales. We use a unified framework to study the Irving--Kirkwood and Murdoch--Hardy procedures used to obtain definitions for continuum fields in atomistic systems. We identify and investigate the following three problems. 1. Continuum fields derived for atomistic systems using the Irving--Kirkwood or the Murdoch--Hardy procedures correspond to a spatial description. Due to the absence of a deformation mapping field in atomistic simulations, it is uncommon to define atomistic fields in the reference configuration. We show that the Murdoch--Hardy procedure can be modified to obtain pointwise continuum fields in the reference configuration using the motion of particles as a surrogate for the deformation mapping. In particular, we obtain definitions for the first and second atomistic Piola--Kirchhoff stress tensors. An interesting feature of the atomistic first Piola--Kirchhoff stress tensor is the absence of a kinetic contribution, which in the atomistic Cauchy stress tensor accounts for thermal fluctuations. We show that this effect is also included in the atomistic first Piola--Kirchhoff stress tensor through the motion of the particles. 2. We investigate the non-uniqueness of the atomistic stress tensor stemming from the non-uniqueness of the potential energy representation. In particular, we show using rigidity theory that the distribution associated with the potential part of the atomistic stress tensor can be decomposed into an irrotational part that is independent of the potential energy representation, and a traction-free solenoidal part. Therefore, we have identified for the atomistic stress tensor a discrete analog of the continuum generalized Beltrami representation (a version of the vector Helmholtz decomposition for symmetric tensors). 3. We show that an ambiguity in the original Irving--Kirkwood procedure resulting due to the non-uniqueness of the energy decomposition between particles can be completely avoided through an alternate derivation for the energy balance. It is found that the expressions for the specific internal energy and the heat flux obtained through the alternate derivation are quite different from the original Irving--Kirkwood procedure and appear to be more physically reasonable. Next, we apply spatial averaging to the pointwise field to obtain the corresponding macroscopic quantities. These lead to expressions suitable for computation in molecular dynamics simulations.
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    Robust, model-based fault detection for commercial transport air data probes.
    (2011-11) Freeman, Paul
    Air data probes provide essential sensing capabilities to aircraft. The loss or corruption of air data measurements due to sensor faults jeopardizes an aircraft and its passengers. To address such faults, sensor hardware redundancy is typically combined with a voting system to detect and discard erroneous measurements. This approach relies on redundancy, which may lead to unacceptable increases in system weight and cost. This thesis presents an alternative, model-based approach to fault detection for a non-redundant air data system. The model-based fault detection strategy uses robust linear filtering methods to reject exogenous disturbances, e.g. wind, and provide robustness to model errors. The proposed algorithm is applied to NASA's Generic Transport Model aircraft with an air data system modeled based on manufacturer data provided by Goodrich Sensors and Integrated Systems. The fault detection filter is designed using linearized models at one flight condition. The detection performance is evaluated at a particular reference flight condition using linear analysis and nonlinear simulations. Detection performance across the flight envelope is examined, and scheduling and blending techniques used to improve detection robustness across an expanded flight regime are explored.
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    Synthetic air data estimation: a case study of model-aided estimation
    (2014-09) Lie, F. Adhika Pradipta
    A method for estimating airspeed, angle of attack, and sideslip without using conventional, pitot-static airdata system is presented. The method relies on measurements from GPS, an inertial measurement unit (IMU) and a low-fidelity model of the aircraft's dynamics which are fused using two, cascaded Extended Kalman Filters. In the cascaded architecture, the first filter uses information from the IMU and GPS to estimate the aircraft's absolute velocity and attitude. These estimates are used as the measurement updates for the second filter where they are fused with the aircraft dynamics model to generate estimates of airspeed, angle of attack and sideslip. Methods for dealing with the time and inter-state correlation in the measurements coming from the first filter are discussed. Simulation and flight test results of the method are presented. Simulation results using high fidelity nonlinear model show that airspeed, angle of attack, and sideslip angle estimation errors are less than 0.5 m/s, 0.1 deg, and 0.2 deg RMS, respectively.Factors that affect the accuracy including the implication and impact of using a low fidelity aircraft model are discussed. It is shown using flight tests that a single linearized aircraft model can be used in lieu of a high-fidelity, non-linear model to provide reasonably accurate estimates of airspeed (less than 2 m/s error), angle of attack (less than 3 deg error), and sideslip angle (less than 5 deg error). This performance is shown to be relatively insensitive to off-trim attitudes but very sensitive to off-trim velocity.
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    System identification for the Clipper Liberty C96 wind turbine
    (2014-06) Showers, Daniel
    System identification techniques are powerful tools that help improve modeling capabilities of real world dynamic systems. These techniques are well established and have been successfully used on countless systems in many areas. However, wind turbines provide a unique challenge for system identification because of the difficulty in measuring its primary input: wind. This thesis first motivates the problem by demonstrating the challenges with wind turbine system identification using both simulations and real data. It then suggests techniques toward successfully identifying a dynamic wind turbine model including the notion of an effective wind speed and how it might be measured. Various levels of simulation complexity are explored for insights into calculating an effective wind speed. In addition, measurements taken from the University of Minnesota's Clipper Liberty C96 research wind turbine are used for a preliminary investigation into the effective wind speed calculation and system identification of a real world wind turbine.
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    System identification of the Brompton bicycle
    (2015-01) Hladun, Monique Victoria Teresa
    The Brompton (a European folding design) bicycle was instrumented with a variety of sensors including acceleration, angular rate, speed, and steering sensors. A bicycle state estimator was designed to obtain additional information from this data including heading, turn rate, lean angle, steer rate, and positions of the wheels during a trajectory. The first part of the thesis describes the model setup for system identification including the Steer-to-Lean dynamics and Lean-to-Steer dynamics reduced models. CIFER software was used in the system identification process of these models. The second part describes the validation of the Empirical model by using the Rider Control model ([1]) and the Complete Rider/Vehicle model ([1]) to determine the feedback gains. The Theoretical model feedback gains were also determined by using the Rider Control model ([1]) and the Complete Rider/Vehicle model ([1]).
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    Time delay margin analysis for adaptive flight control laws.
    (2010-12) Dorobantu, Andrei
    Adaptive control algorithms have the potential to improve performance and reliability in flight control systems. Implementation of adaptive control on commercial and military aircraft requires validation and verification of the control system's robustness to modeling error and uncertainty. Currently, there is a lack of tools available to rigorously analyze the robustness of adaptive systems due to their inherently nonlinear dynamics. This thesis addresses the use of nonlinear robustness analysis for adaptive flight control systems. First, a model reference adaptive controller is derived for an aircraft short period model. It is noted that the controller is governed by polynomial dynamics. Polynomial optimization tools are then applied to the closed-loop model to assess its robustness to time delays. Time delay margins are computed for various tuning of design parameters in the adaptive law, as well as in the presence of model uncertainty.