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Master's Projects

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Parametric Analysis and Targeting Capabilities for the Planetary Entry Systems Synthesis Tool

2008-12-05 , Smith, Patrick J.

Modeling and simulation has led to major advances in the design of complex systems largely because it provides designers with an affordable method of testing new ideas. This report describes recent improvements to a modeling and simulation tool, known as the Planetary Entry Systems and Synthesis Tool or PESST, that allow a designer to quickly conduct parametric and targeting studies. PESST has been used in several conceptual design studies and the improvements to this tool allow a user to complete several cases quickly and gain valuable insight to a larger region of the design space. It would be impossible for designers to create truly robust systems without the ability to fully grasp the design space. By testing the effect of many different input variable values, the designer gains valuable insight to overall system response. As an example of the improvements added to PESST, hypothetical parametric and targeting studies have been completed for the Orion Crew Entry Vehicle.

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Corridor Possibilities: Governor's Drive in Huntsville, Alabama

2008-05 , Hsu, Jerry Shiuan-hua

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Natural Progression of Non-Synostotic Plagiocephaly

2008-04-23 , Spragg, Rebecca

Background. Despite having a good understanding of the causes and treatment for deformational plagiocephaly, the need for treatment has yet to be determined conclusively. The purpose of this study was to determine the natural progression of non-synostotic plagiocephaly in children between the ages of 18 and 48 months. The study also aimed to determine parent impressions about the current head shape of children with untreated deformational plagiocephaly. Methods. A survey and follow-up scan were completed for twenty-two children diagnosed with deformational plagiocephaly of severity level 3 or higher who declined orthotic treatment. Subjects were between the ages of 18 and 48 months at the time of the study. Cranial vault asymmetry index (CVAI), cephalic ratio (CR), and severity level were compared from the initial diagnosis scan and the current scan. Results. Of the 22 subjects, 17 showed an improvement in CVAI, with an average decrease of 1.6%. CR had an average decrease of 4%. Parents perceived the head shape to have "improved" in 14, "stayed the same" in 6, and were unsure of any change in 4 subjects. Parents were "very satisfied" in 11, "somewhat satisfied" in 6, and "not very" satisfied in 5 subjects. Conclusions. Although there was a decrease in CVAI, it was not large enough to move subjects into a non-treatment severity level. 77% of subjects would still be recommended for orthotic treatment based on their current head shape. Parents are satisfied with the current shape of their children's heads despite any asymmetry that may still be present.

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Lower Limb Joint Forces in Transtibial Amputees during Cycling

2008-04-16 , Jones, Laura

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Friendship Village Final Studio Presentation

2008-12-03 , Anderson, Claudius , Arkin, Chelsea , Blaiklock, Philip , Branum, Cassie , Caimbeul, David , Drake, Thomas , Collums, Joe , Conville, Lane , Dagenhart, Richard , Doyle, Jessica , Drake, Thomas , Duong, Binh , Leigh, Nancey Greene , Kovacheva, Maria , Lawrence, Nathan , Finkelstein, Aria Ritz , Skach, John , Tucker, Tasheika

The Friendship Village group had the charge of advising a large-scale land developer on directions for promoting sustainability in the plans for a 210 acre multi-use project in south Fulton County, Georgia. Their work included site design recommendations modeled after traditional town centers in ten case studies but also included innovative open space and stormwater management proposals and ideas about educational and health care facilities. The diverse professional audience expressed admiration and the developer’s lead representative indicated that results exceeded her expectations.

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Supersonic Retropropulsion Technology for Application to High Mass Mars Entry, Descent, and Landing

2008-04-30 , Korzun, Ashley M.

As vehicle masses continue to increase for missions involving atmospheric entry, supersonic deceleration is challenging the qualifications and capabilities of Viking-heritage entry, descent, and landing (EDL) technology. At Mars, high entry masses and insufficient atmospheric density often result in unacceptable parachute deployment and operating conditions, requiring the exploration of alternative approaches to supersonic deceleration. Supersonic retropropulsion, the initiation of a retropropulsion phase while the vehicle is still traveling supersonically, may be an enabling technology for systems with high ballistic coefficients operating in thin atmospheres such as at Mars. The relevance of this technology to the feasibility of Mars EDL has been shown to increase with ballistic coefficient to the point that it is likely required for human Mars exploration. In conjunction with a literature review of supersonic retropropulsion technology as it applies to blunt body entry vehicles, a systems study was performed to assess the impact of supersonic retropropulsion on high mass Mars EDL. This investigation addresses the applicability, limitations, and performance implications of supersonic retropropulsion technology in the context of future human and robotic Mars exploration missions.

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The Effect Of Prosthesis Suspension On Residual Limb Pistoning

2008-04-23 , Balogh, Austin

The main goal of transtibial prosthesis suspension is to minimize residual limb motion within the prosthesis. Poor suspension can lead to negative outcomes in prosthetic treatment, and may have a great impact on the mobility of an amputee. Prior research on this topic has focused on measuring pistoning by radiographic imaging of the residual limb in positions of simulated gait. Several suspension methods have previously been compared, but there is limited research on elevated vacuum suspension method. The purpose of this study is to investigate the effect of elevated vacuum suspension, standard suction with an expulsion valve, and knee sleeve suspension on residual limb pistoning. Five persons with unilateral transtibial amputations were recruited to participate in this study. Each subject was fit with a custom prosthesis that was easily converted between suspension methods. Dual energy x-ray absorptiometry DEXA scans were taken of the subjects' limb in the prosthesis under three different loading conditions to determine the amount of pistoning. Pistoning was measured as the difference between the half body weight loaded condition and the 44.5 N distraction force condition for each suspension. There was no statistical significance between the suspension methods determined using a repeated measures within subjects ANOVA. Future research should include addition of more subjects to increase the power and significance of this work. Another logical step would focus on measuring pistoning during dynamic activity.

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Guidance, Navigation, and Control Technology System Trades for Mars Pinpoint Landing

2008-05-01 , Steinfeldt, Bradley A.

Landing site selection is a compromise between safety concerns associated with the site’s terrain and scientific interest. Therefore, technologies enabling pinpoint landing (sub-100 m accuracies) on the surface of Mars are of interest to increase the number of accessible sites for in-situ research as well as allow placement of vehicles nearby prepositioned assets. A survey of various guidance, navigation, and control technologies that could allow pinpoint landing to occur at Mars has shown that negligible propellant mass fraction benefits are seen for reducing the three-sigma position dispersion at parachute deployment below approximately 3 km. Four different propulsive terminal descent guidance algorithms were analyzed with varying applicability to flight. Of these four, a near propellant optimal, analytic guidance law showed promise for the conceptual design of pinpoint landing vehicles. In addition, subsonic guided parachutes are shown to provide marginal performance benefits due to the timeline associated with Martian entries, and a low computational-cost, yet near fuel optimal propulsive terminal descent algorithm is identified. This investigation also demonstrates that navigation is a limiting technology for Mars pinpoint landing, with landed performance being largely affected by sensor accuracy.

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Frontal Plane Characteristics of Multi-Axis Feet: A Test Method for Evaluation and Effect of Shoes on Foot Performance

2008-04-23 , Gaw, Stephen

Introduction: The purpose of this project is to analyze the stiffness properties of multiaxis prosthetic feet in the frontal plane, and analyze the influence on mechanical testing of those feet when a shoe is worn. We hypothesize: (1) Stiffness properties of multiaxis feet in the frontal plane will vary significantly, and the feet will naturally divide into subcategories based on stiffness properties, and (2) Testing with shoes will influence the stiffness properties in the frontal plane of the multiaxis prosthetic foot. Methods: 6 multiaxis prosthetic feet (including dynamic response/multiaxis feet) were tested on an Instron materials testing machine. The feet underwent cyclic loading to simulate midstance phase of gait, and were loaded onto a range of inclines from 0° to 20°. The tests were repeated with a shoe added to the feet. A SACH foot was also tested for comparison purposes. Results: There was significant variability among the feet when tested barefoot. The SACH foot displayed a lower stiffness than 3 of the multiaxis feet at all inclines. Statistical analysis showed there were natural divisions among the feet according to stiffness data. When the feet were tested with a shoe, the stiffness decreased for all feet in all conditions, although the magnitude of the change varied by foot. Natural divisions among feet were also present when tested with a shoe, but the divisions were different than when tested barefoot. Discussion: The results showed that stiffness properties among multiaxis feet did vary, and the feet did divide themselves naturally. When tested with a shoe, stiffness decreased for all feet in all conditions. Limitations of this study include anonymity of feet, variability of shoes, and small aspect of gait cycle.

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Evaluation of Alignment Methods for Transtibial Prostheses

2008-04-16 , Malkush, Missy

There are an estimated 3-4 million amputees in need of a prosthesis in developing countries. These people are unlikely to receive prosthetic limbs due to remote living conditions, finances, and few providers of care. The monolimb is considered appropriate prosthetic technology for developing countries. The monolimb is made of fewer components, more affordable, durable, and appropriate for prosthetic outreach missions because it can be delivered on an initial fit. Appropriate alignment of the monolimb must be captured prior to fabrication because the prosthesis is not modular. Objective- To determine if an alignment method based on patient measurements produces a more appropriately aligned prosthesis than traditional bench alignment (TRAD). The alternative alignment methods included the vertical alignment axis (VAA) and anatomical based alignment (ABA). Methods- 8 transtibial amputees, 8 students of prosthetics, and 2 prosthetists per amputee-student pair participated in the study. The student bench aligned 3 sets of endo components for the amputee according to each alignment method. The prosthetists dynamically aligned the 3 prostheses for each amputee. The magnitude of change from bench to dynamic alignment was determined by quantifying 6 alignment parameters. Results- No significant differences were found between the 3 different alignment methods. Future Directions- Control the student variable to test the accuracy of the alignment methods. Control the amputee variable to test how little training is necessary to appropriately align a prosthesis with the 3 alignment methods.

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