Introduction to fMRI: experimental design and data analysis

This provides an introduction to functional MRI, experimental design and data analysis procedures using statistical parametric mapping approach

Transient Performance Simulation of Aircraft Engine Integrated with Fuel and Control Systems

A new method for the simulation of gas turbine fuel systems based on an inter-component volume method has been developed. It is able to simulate the performance of each of the hydraulic components of a fuel system using physics-based models, which potentially offers more accurate results compared with those using transfer functions. A transient performance simulation system has been set up for gas turbine engines based on an inter-component volume (ICV) method. A proportional-integral (PI) control strategy is used for the simulation of engine controller. An integrated engine and its control and hydraulic fuel systems has been set up to investigate their coupling effect during engine transient processes. The developed simulation system has been applied to a model aero engine. The results show that the delay of the engine transient response due to the inclusion of the fuel system model is noticeable although relatively small. The developed method is generic and can be applied to any other gas turbines and their control and fuel systems

Surface decorated silicon nanowires: a route to high-ZT thermoelectrics

Based on atomistic calculations of electron and phonon transport, we propose to use surface decorated Silicon nanowires (SiNWs) for thermoelectric applications. Two examples of surface decorations are studied to illustrate the underlying deas: Nanotrees and alkyl functionalized SiNWs. For both systems we find, (i) that the phonon conductance is significantly reduced compared to the electronic conductance leading to high thermoelectric figure of merit, $ZT$, and (ii) for ultra-thin wires surface decoration leads to significantly better performance than surface disorder.Comment: Accepted for PR

Large Eddy Simulations of gaseous flames in gas turbine combustion chambers

Recent developments in numerical schemes, turbulent combustion models and the regular increase of computing power allow Large Eddy Simulation (LES) to be applied to real industrial burners. In this paper, two types of LES in complex geometry combustors and of specific interest for aeronautical gas turbine burners are reviewed: (1) laboratory-scale combustors, without compressor or turbine, in which advanced measurements are possible and (2) combustion chambers of existing engines operated in realistic operating conditions. Laboratory-scale burners are designed to assess modeling and funda- mental flow aspects in controlled configurations. They are necessary to gauge LES strategies and identify potential limitations. In specific circumstances, they even offer near model-free or DNS-like LES computations. LES in real engines illustrate the potential of the approach in the context of industrial burners but are more difficult to validate due to the limited set of available measurements. Usual approaches for turbulence and combustion sub-grid models including chemistry modeling are first recalled. Limiting cases and range of validity of the models are specifically recalled before a discussion on the numerical breakthrough which have allowed LES to be applied to these complex cases. Specific issues linked to real gas turbine chambers are discussed: multi-perforation, complex acoustic impedances at inlet and outlet, annular chambers.. Examples are provided for mean flow predictions (velocity, temperature and species) as well as unsteady mechanisms (quenching, ignition, combustion instabil- ities). Finally, potential perspectives are proposed to further improve the use of LES for real gas turbine combustor designs

The Role of Active Flow-Control Devices in the Dynamic Aeroelastic Response of Wind Turbine Rotors

The significance of wind as a renewable source of power is growing with the increasing capacity of individual utility-scale wind turbines. Contemporary wind turbines are capable of producing up to 8 MW and consequently, their rotor sizes are rapidly growing in size. This has led to an increased emphasis on studies related to improvements and innovations in load-control methodologies. Most often than not, controlling the loads on an operational turbine is a precarious scenario, especially under high wind loading. The up-scaling of turbine rotors would thus benefit from a rationale change in load control through methodologies such as variable-speed stall, flexo-torsional adaptive blades, and active flow-control devices. This thesis work extends the capabilities of an aeroelastic code to provide a platform to analyze wind turbines with flow-control devices as active load control techniques. It also explores the effectiveness of such devices under rapid load-control scenarios relevant to benchmark turbines. Pre-determined rapid control actions such as pitching and trailing-edge flap actuation are implemented under nominal operating conditions. The benchmark turbine designed by National Renewable Energy Laboratory (NREL), which is an upwind three-bladed rotor rated at 5 MW forms the test bed for the current thesis study. The goal is to obtain an overall understanding of the aeroelastic rotor response of utility-scale wind turbines under rapid control actions, paying special attention to the power of actuation

Ankle-Foot Orthosis Stiffness: Biomechanical Effects, Measurement and Emulation

Ankle-foot orthoses (AFOs) are braces worn by individuals with gait impairments to provide support about the ankle. AFOs come in a variety of designs for clinicians to choose from. However, as the effects of different design parameters on AFO properties and AFO users have not been adequately quantified, it is not clear which design choices are most likely to improve patient outcomes. Recent advances in manufacturing have further expanded the design space, adding urgency and complexity to the challenge of selecting optimal designs. A key AFO property affected by design decisions is sagittal-plane rotational stiffness. To evaluate the effectiveness of different AFO designs, we need: 1) a better understanding of the biomechanical effects of AFO stiffness and 2) more precise and repeatable stiffness measurement methods. This dissertation addresses these needs by accomplishing four aims. First, we conducted a systematic literature review on the influence of AFO stiffness on gait biomechanics. We found that ankle and knee kinematics are affected by increasing stiffness, with minimal effects on hip kinematics and kinetics. However, the lack of effective stiffness measurement techniques made it difficult to determine which specific values or ranges of stiffness influence biomechanics. Therefore, in Aim2, we developed an AFO stiffness measurement apparatus (SMApp). The SMApp is an automated device that non-destructively flexes an AFO to acquire operator- and trial-independent measurements of its torque-angle dynamics. The SMApp was designed to test a variety of AFO types and sizes across a wide range of flexion angles and speeds exceeding current alternatives. Common models of AFO torque-angle dynamics in literature have simplified the relationship to a linear fit whose slope represents stiffness. This linear approximation ignores damping parameters. However, as previous studies were unable to precisely control AFO flexion speed, the presence of speed effects has not been adequately investigated. Thus, in Aim3, we used the SMApp to test whether AFOs exhibit viscoelastic behaviors over the range of speeds typically achieved during walking. This study revealed small but statistically significant effects of flexion speed on AFO stiffness for samples of both traditional AFOs and novel 3-D printed AFOs, suggesting that more complex models that include damping parameters could be more suitable for modeling AFO dynamics. Finally, in Aim 4, we investigated the use of an active exoskeleton, that can haptically-emulate different AFOs, as a potential test bed for studying the effects of AFO parameters on human movement. Prior work has used emulation for rapid prototyping of candidate assistive devices. While emulators can mimic a physical device's torque-angle profile, the physical and emulated devices may have other differences that influence user biomechanics. Current studies have not investigated these differences, which limits translation of findings from emulated to physical devices. To evaluate the efficacy of AFO emulation as a research tool, we conducted a single-subject pilot study with a custom-built AFO emulator device. We compared user kinematics while walking with a physical AFO against those with an emulated AFO and found they elicited similar ankle trajectories. This dissertation resulted in the successful development and evaluation of a framework consisting of two test beds, one to assess AFO mechanical properties and another to assess the effects of these properties on the AFO user. These tools enable innovations in AFO design that can translate to measurable improvements in patient outcomes.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163219/1/deema_1.pd

Optimal face-to-face coupling for fast self-folding kirigami

Kirigami-inspired designs can enable self-folding three-dimensional materials from flat, two-dimensional sheets. Hierarchical designs of connected levels increase the diversity of possible target structures, yet they can lead to longer folding times in the presence of fluctuations. Here, we study the effect of rotational coupling between levels on the self-folding of two-level kirigami designs driven by thermal noise in a fluid. Naturally present due to hydrodynamic resistance, we find that optimization of this coupling as control parameter can significantly improve a structure's self-folding rate and yield

Small Internal Combustion Engine Testing for a Hybrid-Electric Remotely-Piloted Aircraft

Efficient operation of a hybrid-electric propulsion system (HEPS) powering a small remotely-piloted aircraft (RPA) requires that a controller have accurate and detailed engine and electric motor performance data. Many small internal combustion engines (ICEs) currently used on various small RPA were designed for use by the recreational hobbyist radio-control (R/C) aircraft market. Often, the manufacturers of these engines do not make accurate and reliable detailed engine performance data available for their engines. A dynamometer testing stand was assembled to test various small ICEs. These engines were tested with automotive unleaded gasoline (the manufacturer\u27s recommended fuel) using the dynamometer setup. Torque, engine speed and fuel flow measurements were taken at varying load and throttle settings. Power and specific fuel consumption (SFC) data were calculated from these measurements. Engine performance maps were generated in which contours of SFC were mapped on a mean effective pressure (MEP) versus engine speed plot. These performance maps are to be utilized for performance testing of the controller and integrated HEPS in further research. Further follow-on research and development will be done to complete the goal of building a prototype hybrid-electric remotely piloted aircraft (HE-RPA) for flight testing. Minimum BSFC for the Honda GX35 engine was found to be 383.6 g/kW hr (0.6307 lbm/hp hr) at 4500 RPM and 60% throttle. The Honda GX35 was overall the better fit for incorporation into the HE-RPA

Fullwave Maxwell inverse design of axisymmetric, tunable, and multi-scale multi-wavelength metalenses

We demonstrate new axisymmetric inverse-design techniques that can solve problems radically different from traditional lenses, including \emph{reconfigurable} lenses (that shift a multi-frequency focal spot in response to refractive-index changes) and {\emph{widely separated}} multi-wavelength lenses ($\lambda = 1\,\mu$m and $10\,\mu$m). We also present experimental validation for an axisymmetric inverse-designed monochrome lens in the near-infrared fabricated via two-photon polymerization. Axisymmetry allows fullwave Maxwell solvers to be scaled up to structures hundreds or even thousands of wavelengths in diameter before requiring domain-decomposition approximations, while multilayer topology optimization with $\sim 10^5$ degrees of freedom can tackle challenging design problems even when restricted to axisymmetric structures.Comment: 13 pages, 6 figure