<p> The space industry is dominated by chemical propulsion systems that increase the cost of space travel. The dependence of these conventional methods of propulsion on propellants is overcome by using a solar sail that works on the principle of production of thrust based on the solar radiation pressure from the Sun. Solar sails, being a low thrust form of propulsion, need to be optimized to produce reasonable time trajectories. This paper presents the minimum time transfer for a solar sail interplanetary trajectory between Earth and Mars. Therefore, an optimization tool is introduced that can ensure minimum time trajectories for the sail. A hybrid optimization tool is developed between two direct methods, one that uses a global optimization technique and another one that uses a local optimization technique for the problem. Global optimization is carried out using Genetic Algorithm (GA), and local optimization is carried out using a Sparse Nonlinear Optimizer (SNOPT). The GA is run for 300 generations with a population size of 2000, and the SNOPT continues from the point where the GA is terminated using the results from the GA as the initial start point for the optimization. The steering angles of the sail are used as the control parameters. To minimize time, the problem is implemented as a parameter optimization method and the trajectory is discretized into multiple segments. The control angles are defined for each segment of the transfer. The transfer time was optimized to 331 days and on comparing the solution with earlier studies this method provides a better optimal solution. </p><p>

<p> The TNO model, a trailing edge noise prediction method, is validated, modified, and analyzed for various input formats. Two different methods are used to calculate the flow field for this model: Reynolds averaged Navier-Stokes (RANS) and a viscous panel method, XFOIL. It is found that the RANS-based TNO model show good agreement with the experiments but the XFOIL-based TNO was found to overpredict the turbulence kinetic energy and, consequently, the sound pressure level. A modification is made in the XFOIL-based TNO model by substituting Prandtl's mixing length hypothesis from the original model with a new blended model consisting of the mixing length hypothesis and the Cebeci-Smith eddy viscosity model. Twenty-six different test cases are tested with airfoils: NACA 0012, NACA 0015, NACA 64-618, NACA 64₃-418, and DU 96-w-180. RANS input to the TNO model is able to predict the sound pressure spectrum to within 3 dB for the frequency range of 800Hz to 2000Hz in 16 of the 26 cases. The new blended model is found to show clear improvements to the prediction for 14 out of the 26 cases when compared to the original XFOIL input. Moreover, the new XFOIL input was able to predict sound pressure level to within 3 dB for 14 of the 26 cases. Overall, the new proposed model improves the prediction for the XFOIL-based TNO model.</p><p>

<p> Due to millions of years of evolution, sharks have evolved to become quick and efficient ocean apex predators. Shark skin is made up of millions of microscopic scales, or denticles, that are approximately 0.2 mm in size. Scales located on the shark&rsquo;s body where separation control is paramount (such as behind the gills or the trailing edge of the pectoral fin) are capable of bristling. These scales are hypothesized to act as a flow control mechanism capable of being passively actuated by reversed flow. It is believed that shark scales are strategically sized to interact with the lower 5% of a boundary layer, where reversed flow occurs at the onset of boundary layer separation. Previous research has shown shark skin to be capable of controlling separation in water. This thesis aims to investigate the same passive flow control techniques in air. </p><p> To investigate this phenomenon, several sets of microflaps were designed and manufactured with a 3D printer. The microflaps were designed in both 2D (rectangular) and 3D (mirroring shark scale geometry) variants. These microflaps were placed in a low-speed wind tunnel in the lower 5% of the boundary layer. Solid fences and a flat plate diffuser with suction were placed in the tunnel to create different separated flow regions. A hot film probe was used to measure velocity magnitude in the streamwise plane of the separated regions. The results showed that low-speed airflow is capable of bristling objects in the boundary layer. When placed in a region of reverse flow, the microflaps were passively actuated. Microflaps fluctuated between bristled and flat states in reverse flow regions located close to the reattachment zone.</p><p>

<p> As aircraft are designed to a greater extent on computers, the need for accurate and fast CFD algorithms has never been greater. The development of CFD algorithms requires experimental data against which CFD output can be validated and from which insight about flow physics can be acquired. Skin friction, in particular, is an important quantity to predict with CFD, and experimental skin friction data sets aid not only with the validation of the CFD predictions, but also in tuning the CFD models to predict specific flow fields. However, a practical experimental technique for collecting spatially and temporally resolved skin friction data on complex models does not yet exist. This dissertation develops and demonstrates a new luminescent oil film skin friction meter which can produce spatially-resolved quantitative steady and unsteady skin friction data on models with complex curvature. </p><p> The skin friction acting on the surface of a thin film of oil can be approximated by the expression &tau;<i>_w</i> =&mu;<i>_o</i><i>u_h/h</i>, where &mu;<i>_o</i> is the dynamic viscosity of the oil, <i>u_h</i> is the velocity of the surface of the oil film, and <i>h</i> is the thickness of the oil film. The new skin friction meter determines skin friction by measuring <i>h</i> and <i>u_h</i>. The oil film thickness <i>h</i> is determined by ratioing the intensity of the fluorescent emissions from the oil film with the intensity of the incident light which is scattered from the surface of the model. When properly calibrated, that ratio provides an absolute oil film thickness value. This oil film thickness meter is therefore referred as the Ratioed-Image Film-Thickness (RIFT) Meter. The oil film velocity <i>u_h</i> is determined by monitoring the evolution of tagged molecules within the oil film: Photochromic molecules are dissolved into the fluorescent oil and a pattern is written into the oil film using an ultraviolet laser. The evolution of the pattern is recorded, and standard cross-correlation techniques are applied to the resulting sequence of images. This newly developed skin friction meter is therefore called the Luminescent Oil Film Flow-Tagging skin friction meter, or the LOFFT skin friction meter. The LOFFT skin friction meter is demonstrated by collecting time-averaged skin friction measurements on NASA's FAITH model and by collecting unsteady skin friction measurements with a frequency response of 600Hz. Higher frequency response is possible and is dependent on the experimental setup. </p><p> This dissertation also contributes to the work done on the Global Luminescent Oil Film Skin Friction Meter (GLOFSFM) by noting that the technique could be influenced by ripples at the oil-air interface. An experiment studying the evolution of ripples at the oil-air interface was conducted to determine under what oil film conditions the GLOFSFM can be appropriately applied. The RIFT meter was crucial for this experiment, as it facilitated quantitative distributed oil film thickness measurements during the wind-tunnel run. The resulting data set is rich in content, permitting the computation of mean wavelengths, peak-to-trough ripple heights, wave speeds, and mean thicknesses. In addition to determining under what oil film conditions the GLOFSFM may be applied, this experiment directly determined the oil film conditions under which the velocity of the ripples may be used to proxy the velocity of the oil film surface. The RIFT meter and the ability to determine oil film surface velocity by monitoring ripple velocities admit yet another time-averaged skin friction meter, the Fluorescent-Oil Ripple-Velocity (FORV) skin friction meter. The FORV skin friction meter recovers skin friction as &tau;<i>_w</i> = &mu;<i>_ov_rip/H</i>, where <i> v_rip</i> is the velocity of the ripples, and <i>H</i> is the oil film thickness averaged over the thickness fluctuations due to the ripples. The FORV skin friction meter is demonstrated on NASA's FAITH model.</p><p>

As it stands, there are currently no means to wash clothing aboard the International Space Station (ISS). Astronauts are forced to re-wear their soiled clothes, despite having to exercise over two hours per day. Instead of cleaning their clothing using a formal laundry machine, astronauts simply discard fouled articles after extensive use. This method of wear-and-tear has worked thus far, as the ISS has remained in an orbit reachable by resupply capsules. However, with agencies aiming to travel farther and longer than ever before, this practice seems both wasteful and costly. To address this problem, a terrestrial pedal-powered washing machine has been developed to provide proof-of-concept data for a microgravity iteration. The machine consists of a horizontal drum unit linked to the drivetrain of a bicycle, which has been modified to replicate the ISS CEVIS exercise bike. Using computer simulations, the concept of an axial-running agitator to induce mechanical agitation in space was explored and verified. This project served as the first step towards making clean clothes a reality for astronauts. / Mechanical Engineering

Flying insects exhibit a remarkable ability to fly in environments that are small, cluttered and highly dynamic. Inspired by these animals, scientist have made great strides in understanding the aerodynamic mechanisms behind insect-scale flapping-wing flight. By applying these mechanisms together with recent advances in meso-scale fabrication techniques, engineers built an insect-scale flapping-wing robot and demonstrated hover by actively controlling the robot about its roll and pitch axes. The robot, however, lacked control over its yaw axis preventing control over its heading angle. In this thesis, we show that the roll and pitch axes of a single actuator insect-scale flapping-wing robot can also be passively stabilized by the addition of a pair of aerodynamic dampers. We develop design guidelines for these dampers, showing that the previously unstable robot with the addition of the dampers is able to perform stable vertical flights and altitude control. To address the lack of yaw control, we develop a yaw torque generating mechanism inspired by the fruit fly wing hinge. We present the development of this mechanism in three stages: from the conceptual stage, to the torque measurement stage and finally to a hover capable stage. We show that the robot is able to generate sufficient yaw torque enabling the robot to transition from hover to heading control maneuvers. / Engineering and Applied Sciences - Engineering Sciences

<p> With the growing threat of orbital debris impacts to space structures, the development of space shielding concepts has been a critical research topic. In this study, numerical simulations of the hypervelocity impact response of stacked aluminum 6061-T6 sheets were performed to assess the effects of layering on penetration resistance. This work was initially motivated by set of experimental tests where a stack of four aluminum sheets of equal thickness was observed to have a higher hypervelocity ballistic resistance than a monolithic aluminum sheet with the same total thickness. A set of smoothed particle hydrodynamic simulations predicted a 40% increase in the ballistic limit for a 6-layer target compared to a monolithic sheet. In addition, the effect of variable sheet thickness and sheet ordering on the impact resistance was investigated, while still maintaining a constant overall thickness. A set of thin layers in front of a thick layer generally lead to a higher predicted ballistic limit than the inverse configuration. This work demonstrates an increase in the performance of advanced space shielding structures associated with multi-layering. This suggests that it may be possible to dramatically improve the performance of such structures by tailoring the material properties, interfaces, and layering concepts.</p><p>

Unmanned Aerial Vehicles (UAVs) have attracted considerable interest in the commercial markets for the military and civilian uses, such as surveillance and reconnaissance, aerial surveys for natural sources, traffic monitoring, and early forest fire detection, etc. Presently, UAVs are being proven as a cost-effective platform for the military and civilian applications because they gather information without endangering the lives of the pilots, increase maneuverability without limitations from human abilities, cost much less than the traditional aircrafts and do not need human-pilot interfaces. Although UAVs present numerous advantages over the manned aircrafts, they face challenges in achieving autonomous control. Model Predictive Control (MPC) is an interesting solution for UAV control to improve the level of autonomous control, but is mostly applicable to a linear or linearized system at this time. In this thesis, first is presented a complete kinematics and dynamic model of Unmanned Aerial Vehicles which is programmed in Simulink. Second, a control scheme based on a proportional controller for the inner loop and a proportional-integral controller for the outer loop is investigated. Model predictive control is applied to a linearized UAV using dynamic inversion, and simulation results obtained using a nonlinear UAV model are presented and analyzed in view of the suitability for UAV autonomous control.

A new instrument system for the non-invasive assessment of biological systems has been designed, built and validated. This system utilizes the optical characteristics of a biological system to assess both its static and dynamic response over time. The changes in the optical properties can then be used to quantify the response of the biological system to external or internal stimuli. This new system incorporates an efficient light delivery system, as well as a novel light collection system to provide high repeatability, reproducibility, sensitivity, and detection thresholds. The system incorporates simultaneous measurement of transmitted light, forward scattered light, specularly reflected light, and non-specularly reflected light in across the visible spectrum, to provide flexibility in the biological systems that can be measured. It is shown that typical values are 0.02% for repeatability and 0.15% for reproducibility. Sensitivity in transmission and backscatter measurements was improved by a factor of 20 compared to a previously built instrument, which was the basis for the new design. The system is capable of detecting light attenuated down to 0.0063% of the maximum intensity, resulting in a superior threshold. The system was then validated by measuring the optical properties of various biological samples, both natural and engineered. These samples include bovine, porcine, and human corneas and lenses, as well as synthetic materials. Biological sample testing were consistent with published results on the back vertex distance (BVD) test (bovine lenses), the bovine corneal opacity test (BCOP, bovine corneas), and published results obtained with the precursor to the new device.

A multibody model is presented which simulates the conversion process associated with tilt-wing aircraft. A multibody dynamics approach is used to derive the equations of motion for a tilting articulated rotor with flap-pitch-lag root geometry. An enhanced model is used for the near-wake aerodynamics and uniform dynamic-inflow is used for the far-wake aerodynamics. A thrust control system computes the required trim settings. It is found that the controller can "fly" the model to a hover condition at a desired altitude, and can be used to achieve desired thrust levels during conversion. It is noted that conventional blade twist is inadequate during conversion. It is observed that unsteady aerodynamics are important during conversion. Also nonlinear effects on the tilt-wing cause large variations in tilt-torque during conversion.