Matching Items (404)
- Creators: Mechanical and Aerospace Engineering Program
- Member of: Barrett, The Honors College Thesis/Creative Project Collection
- Resource Type: Text
The purpose of this investigation is to computationally investigate instabilities appearing in the wake of a simulated helicopter rotor. Existing data suggests further understanding of these instabilities may yield design changes to the rotor blades to reduce the acoustic signature and improve the aerodynamic efficiencies of the aircraft. Test cases of a double-bladed and single-bladed rotor have been run to investigate the causes and types of wake instabilities, as well as compare them to the short wave, long wave, and mutual inductance modes proposed by Widnall. Evaluation of results revealed several perturbations appearing in both single and double-bladed wakes, the origin of which was unknown and difficult to trace. This made the computations not directly comparable to theoretical results, and drawing into question the physical flight conditions being modeled. Nonetheless, they displayed a wake structure highly sensitive to both computational and physical disturbances; thus extreme care must be taken in constructing grids and applying boundary conditions when doing wake computations to ensure results relevant to the complex and dynamic flight conditions of physical aircraft are generated.
Measuring the dynamic strength of a material based on stress and strain data is challenging due to the diculty in recording strain and stress under the short times and large loads typical of dynamic events, such as impact and shock loading. The research involved in this study aims to perform nite element simulations for a new experimental method that can provide information on material dynamic strength, which is crucial for many engineering applications. In this method, a shock wave is applied to a metallic sample with a perturbed surface, i.e, one with periodic ripples machined or etched on the surface. The speed and magnitude of the change of am- plitude of the ripples are recorded. It is known that these parameters are functions of both geometry and material strength. The experimental data are compared with the simulation results produced. The dynamic yield strength of a material is taken to be the same as the strength used in simulations when a close match is found. The simulations have produced results that closely matched the experimental data and predicted the dynamic yield strength of metallic samples and have led to the discov- ery of a new experimental technique to lower the impact velocity required to induce amplitude changes in surface perturbations under shock loading. Thus, shock experi- ments to measure strength using surface perturbations will become easier to conduct and span a wider range of conditions. However, the existing simulation models are not adequate to examine the relations among hardening behavior and the change of amplitude and velocity on the sample surface. Thus, the models should be further modied to study dierent material hardening behaviors under dynamic loadings.
Understanding damage evolution, particularly as it relates to local nucleation and growth kinetics of spall failure in metallic materials subjected to shock loading, is critical to national security. This work uses computational modeling to elucidate what characteristics have the highest impact on damage localization at the microstructural level in metallic materials, since knowledge of these characteristics is critical to improve these materials. The numerical framework consists of a user-defined material model implemented in a user subroutine run in ABAQUS/Explicit that takes into account crystal plasticity, grain boundary effects, void nucleation and initial growth, and both isotropic and kinematic hardening to model incipient spall. Finite element simulations were performed on copper bicrystal models to isolate the boundary effects between two grains. Two types of simulations were performed in this work: experimentally verified cases in order to validate the constitutive model as well as idealized cases in an attempt to determine the microstructural characteristic that define weakest links in terms of spall damage. Grain boundary effects on damage localization were studied by varying grain boundary orientation in respect to the shock direction and the crystallographic properties of each grain in the bicrystal. Varying these parameters resulted in a mismatch in Taylor factor across the grain boundary and along the shock direction. The experimentally verified cases are models of specific damage sites found from flyer plate impact tests on copper multicrystals in which the Taylor factor mismatch across the grain boundary and along the shock direction are both high or both low. For the idealized cases, grain boundary orientation and crystallography of the grains are chosen such that the Taylor factor mismatch in the grain boundary normal and along the shock direction are maximized or minimized. A perpendicular grain boundary orientation in respect to the shock direction maximizes Taylor factor mismatch, while a parallel grain boundary minimizes the mismatch. Furthermore, it is known that <1 1 1> crystals have the highest Taylor factor, while <0 0 1> has nearly the lowest Taylor factor. The permutation of these extremes for mismatch in the grain boundary normal and along the shock direction results in four idealized cases that were studied for this work. Results of the simulations demonstrate that the material model is capable of predicting damage localization, as it has been able to reproduce damage sites found experimentally. However, these results are qualitative since further calibration is still required to produce quantitatively accurate results. Moreover, comparisons of results for void nucleation rate and void growth rate suggests that void nucleation is more influential in the total void volume fraction for bicrystals with high property mismatch across the interface, suggesting that nucleation is the dominant characteristic in the propagation of damage in the material. Further work in recalibrating the simulation parameters and modeling different bicrystal orientations must be done to verify these results.
This study was designed to create a more user-friendly experience in utilizing the M-Sorter package for spike sorting and detection. This was achieved through the creation of a Graphical User Interface or GUI. The GUI was created for the spike detection portion of sorting. Through the creation of the M-Sorter detection GUI, now novice programmers can run the detector process. Additionally, the parameters are easily altered which will greatly decrease the time it takes to enter data and eliminate mistakes users may make in data entry.
This paper summarizes the  ideas behind,  needs,  development, and  testing of 3D-printed sensor-stents known as Stentzors. This sensor was successfully developed entirely from scratch, tested, and was found to have an output of 3.2*10-6 volts per RMS pressure in pascals. This paper also recommends further work to render the Stentzor deployable in live subjects, including  further design optimization,  electrical isolation,  wireless data transmission, and  testing for aneurysm prevention.
The global energy demand is expected to grow significantly in the next several decades and support for energy generation with high carbon emissions is continuing to decline. Alternative methods have gained interest, and wind energy has established itself as a viable source. Standard wind farms have limited room for growth and improvement, so wind energy has started to explore different directions. The urban environment is a potential direction for wind energy due to its proximity to the bulk of energy demand. CFD analysis has demonstrated that the presence of buildings can accelerate wind speeds between buildings and on rooftops. However, buildings generate areas of increased turbulence at their surface. The turbulence thickness and intensity vary with roof shape, building height, and building orientation. The analysis has concluded that good wind resource is possible in the urban environment in specific locations. With that, turbine selection becomes very important. A comparison has concluded that vertical axis wind turbines are more useful in the urban environment than horizontal axis wind turbines. Furthermore, building-augmented wind turbines are recommended because they are architecturally integrated into a building for the specific purpose of generating more energy. The research has concluded that large-scale generation in the urban environment is unlikely to be successful, but small-scale generation is quite viable. Continued research and investigation on urban wind energy is recommended.
The goal of this project was to use the sense of touch to investigate tactile cues during multidigit rotational manipulations of objects. A robotic arm and hand equipped with three multimodal tactile sensors were used to gather data about skin deformation during rotation of a haptic knob. Three different rotation speeds and two levels of rotation resistance were used to investigate tactile cues during knob rotation. In the future, this multidigit task can be generalized to similar rotational tasks, such as opening a bottle or turning a doorknob.
3D printing has recently become a popular manufacturing process and the goal of the project was to take that process to the kitchen. This was done by utilizing existing knowledge of the culinary process of "spherification", by which a liquid is encapsulated in an edible shell, and combining it with the hydrogel research advancements in tissue engineering to make robust fibers. A co-flow nozzle was constructed and the two fluids needed for spherification were flowed in various configurations to create different fibers. By outlining a stability regime and measuring the outer diameters for both regular and reverse spherification, the optimal method of production and fibers that would be suitable for 3D printing were discovered. The results of the experiments can be used to begin 3D printing edible 2D patterns and eventually 3D structures.
The purpose of my Honors Thesis was to generate a tool that could be implemented by Aerospace students at Arizona State University. This tool was created using MatLab which is the current program students are using. The modeling system that was generated goes step-by-step through the flow of a two spool gas turbine engine. The code was then compared to an ideal case engine with predictable values. It was found to have less than a 3 percent error for these parameters, which included optimal net work produced, optimal overall pressure ratio, and maximum pressure ratio. The modeling system was then run through a parametric analysis. In the first case, the bypass ratio was set to 0 and the freestream Mach number was set to 0. The second case was with a bypass ratio of 0 and fresstream Mach number of 0.85. The third case was with a bypass ratio of 5 and freestream Mach number of 0. The fourth case was with a bypass ratio of 5 and fresstream Mach number of 0.85. Each of these cases was run at various overall pressure ratios and maximum Temperatures of 1500 K, 1600 K and 1700 K. The results modeled the behavior that was expected. As the freestream Mach number was increased, the thrust decreased and the thrust specific fuel consumption increased, corresponding to an increase in total pressure at the combustor inlet. It was also found that the thrust was increased and the thrust specific fuel consumption decreased as the bypass ratio was increased. These results also make sense as there is less airflow passing through the engine core. Finally the engine was compared to two real engines. Both of which are General Electric G6 series engines. For the 80C2A3 engine, the percent difference between thrust and thrust specific fuel consumption was less than five percent. For the 50B, the thrust was below a two percent difference, but the thrust specific fuel consumption clearly provided inaccurate results. This could be caused by the lack of inputs provided by General Electric. The amount of fuel injected is largely dependent on the maximum temperature which is not available to the public. Overall, the code produces comparable results to real engines and can display how isolating and modifying a certain parameter effects engine performance.
The generation of walking motion is one of the most vital functions of the human body because it allows us to be mobile in our environment. Unfortunately, numerous individuals suffer from gait impairment as a result of debilitating conditions like stroke, resulting in a serious loss of mobility. Our understanding of human gait is limited by the amount of research we conduct in relation to human walking mechanisms and their characteristics. In order to better understand these characteristics and the systems involved in the generation of human gait, it is necessary to increase the depth and range of research pertaining to walking motion. Specifically, there has been a lack of investigation into a particular area of human gait research that could potentially yield interesting conclusions about gait rehabilitation, which is the effect of surface stiffness on human gait. In order to investigate this idea, a number of studies have been conducted using experimental devices that focus on changing surface stiffness; however, these systems lack certain functionality that would be useful in an experimental scenario. To solve this problem and to investigate the effect of surface stiffness further, a system has been developed called the Variable Stiffness Treadmill system (VST). This treadmill system is a unique investigative tool that allows for the active control of surface stiffness. What is novel about this system is its ability to change the stiffness of the surface quickly, accurately, during the gait cycle, and throughout a large range of possible stiffness values. This type of functionality in an experimental system has never been implemented and constitutes a tremendous opportunity for valuable gait research in regard to the influence of surface stiffness. In this work, the design, development, and implementation of the Variable Stiffness Treadmill system is presented and discussed along with preliminary experimentation. The results from characterization testing demonstrate highly accurate stiffness control and excellent response characteristics for specific configurations. Initial indications from human experimental trials in relation to quantifiable effects from surface stiffness variation using the Variable Stiffness Treadmill system are encouraging.