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Browsing by Author "Crede, Erin Dawne"

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    Aerodynamics and Acoustics of the Virginia Tech Stability Tunnel Anechoic System
    Crede, Erin Dawne (Virginia Tech, 2008-06-11)
    The acoustic treatment and calibration of a new anechoic system for the Virginia Tech Stability Wind Tunnel has been performed. This novel design utilizes Kevlar cloth to provide a stable flow boundary, which eliminates the need for a free jet and jet catcher. To test this concept a series of measurements were performed both to validate the reduction in overall test section noise levels and to ascertain the effect of these modifications on the test section aerodynamics. An extensive program of experiments has been conducted to examine the performance of this new hardware under a range of conditions. These include baseline experiments that reveal the aerodynamic and aeroacoustic performance of the tunnel in its original configuration, treatment of the tunnel circuit with validation of in-flow noise reduction, wind tunnel tests to examine the effect of the test section acoustic treatment, and measurements of the aerodynamic and aeroacoustic characteristics of a NACA 0012 airfoil model over a range of angles of attack and Reynolds numbers. These measurements show that acoustically treating the walls of the circuit both upstream and downstream of the test section, as well as the fan, result in an overall reduction of 5 dB depending on frequency, of the in-flow noise level. These measurements also show that the complete system provides a reduction of between 15 to 20dB depending on frequency, in the in-flow background noise level. Measurements taken both within the test section and in the adjacent chambers also show that large Kevlar windows can be used to quietly and stably contain the flow, eliminating the need for an open-jet and jet catcher system, as well as overall noise levels competitive with many other facilities. Measurements on several airfoils at various angles of attack and Reynolds number show that the interference correction for the fully anechoic configuration is approximately -22% for model with a chord length equal to half the test section height. Aerodynamic measurements with the NACA 0012 airfoil show its lift, drag and boundary layer characteristics at high Reynolds numbers are consistent with theoretical expectations. Measurements of the window deflection as well as examination of flow transpiration through the Kevlar windows were accomplished, both with and without the NACA 0012 model. These measurements, along with the interference correction data, confirm that the Kevlar windows are a stable flow boundary.
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    Organization and Retention in Research Groups in Graduate Engineering Departments
    Crede, Erin Dawne (Virginia Tech, 2011-09-05)
    The purpose of this research project was to better understand the experiences of graduate students in internationally diverse research groups, and how these research groups and international diversity contributes to a student's intent to complete his or her graduate degree. This exploratory mixed methods research was conducted in three phases: (1) an ethnographic study of selected research groups in two engineering graduate departments, (2) development of a survey for students in graduate engineering students, and (3) administering the survey to graduate engineering students in research groups to verify the findings. In order to address the project aims, three smaller studies were initiated that address individual elements of graduate education, including: learning in research groups and international diversity, and retention in graduate engineering programs. The focus of the first study was to understand how and under what conditions research groups foster successful learning and professional development for graduate engineering students, and how these findings can be used to inform management of engineering research groups to optimize student learning, productivity, and intent to complete the degree. Key findings from the ethnographic analysis indicate that group size directly influences the mechanisms of student learning, as well as several elements common across research groups from different universities and academic departments, including: power distance and communication, access to resources, and role of the advisor. During the (second) integration phase of this mixed methods study, the nine months of ethnographically guided observations and interviews were used to develop a survey examining graduate engineering student retention. Findings from the ethnographic fieldwork yielded several themes, including: the role of international diversity, research group organization and climate, student self efficacy, and individual and group learning experiences. Final retention themes from the ethnographic analysis are presented along with a discussion of how these data were configured into instrument questions. A discussion of the final instrument is presented, including validity and reliability analysis, and how the final questions were integrated into themes to test hypotheses for future studies. This chapter also presents implications for mixed methods researchers interested in using qualitative methods to create new instruments. In the third and final stage of the research study, the survey developed in the second phase of the research study was administered to four universities across the United States. Data analysis focused on better understanding the differences in retention constructs by student nationality. Results from more than 600 engineering PhD students from 6 international regions enrolled in U.S. engineering graduate programs were examined to characterize demographic differences in participant responses for intention to complete the degree. Six constructs were found to be significant in predicting students' responses regarding their intention to complete their degree, including: expectations, climate, organization, project ownership, perception of value, and individual preferences. Taken together these constructs were able to explain 28 percent of the variation in student responses. Additionally, all six constructs showed significant differences with respect to a respondent's country or region or origin. These results are discussed in light of the implications for faculty members advising similarly diverse groups of students. In combination, these three studies represent a sequential exploratory mixed methods approach in which ethnographically guided observations and interviews were integrated into a quantitative instrument. Results of this study can be used to inform the organization and management of internationally diverse research groups to foster student development and ultimately increase retention.