Scholars Hangar (United States Air Force Academy)
Not a member yet
204 research outputs found
Sort by
Finger Strengthening Device and Method
No full textA finger strengthening device (FSD) includes a plurality of finger strengthening elements formed therewith. The FSD is attachable to a structure in a plurality of different orientations to permit a variation in finger exercise techniques
Remembering the Past with Today’s Technology: A Scoping Review of Reminiscence-Based Digital Storytelling with Older Adults
Full text linkNumerical Heat Transfer Simulations for Laser-Scanned Ice Shapes
No full textIce accretions on aircraft flight surfaces can degrade lift, increase drag, and reduce controllability. Anti-icing systems can remove or prevent ice growth. To predict the ice shrinkage or accretion using models such as LEWICE, the convective heat transfer behavior at the ice surface must be quantified. The work here is focused on understanding the convective heat transfer for several laser-scanned ice shapes by using commercial computational fluid dynamics (CFD) heat transfer simulations. The leading edge ice shape from a NACA 0012 airfoil and its geometrically unwrapped simplification are studied. Limitations encountered with a semi-automated unstructured mesh generation tool are presented. Thin boundary layer mesh thicknesses (i.e. much thinner than the flow’s viscous or thermal boundary layers) are found to be necessary in order to capture the surface curvature features and preserve good mesh quality near the geometric surface. To better model a prior experiment, the unwrapped geometry uses a conjugate heat transfer model which includes a thickness to the unwrapped ice shape to allow the modeling of its internal conductive heat transfer. The unwrapped geometry CFD heat transfer results are compared to prior experimental results for an identical shape in a similar heat transfer setup. Also, heat transfer results for the original airfoil ice shape are presented for constant surface temperature, and compared to the unwrapped iced plate. The CFD results predict higher Stanton numbers for turbulent flows as compared to laminar flows, but overall underpredict the Stanton numbers when compared to experiments, particularly in the iced bumpy region. Additional work is needed to study alternative meshing strategies and various turbulence model settings. The results are useful for advancing the understanding of convective heat transfer from ice shapes and conductive heat transfer in ice layers
The Hydrostatic Vacuum Tube: a Low-Cost Thermal Fluid Science Laboratory
Full text linkStudents often comment that they benefit from exposure to both analytical and experimental results of concepts discussed in class, especially in the abstract thermal-fluid sciences emphasis area of a Mechanical Engineering curriculum. As educators, we sought to address this deficiency by developing a new test apparatus, the Hydrostatic Vacuum Tube (HVT). In short, a HVT is a vertical tube partially filled with water and a trapped air pocket at the top, initially at atmospheric pressure. One experiment involves opening a valve at the bottom to expose an exit port of sufficiently small exit diameter to prevent backflow of air. Water is collected and measured until the flow stops due to the hydrostatic vacuum created as the air pocket expands. A second experiment (the Draining Tank) can be conducted without trapping the air, by exposing/venting the liquid surface to ambient pressure. The height of the water is measured versus time as the tank drains, driven by a hydrostatic head. Predictive theory is developed and results compared with experiment, with excellent agreement. Key thermodynamics concepts involved are expansion of an ideal gas, hydrostatic pressure, and mass conservation in a control volume. The device could be used in other courses, such as Fluid Mechanics, Engineering System Dynamics, Heat Transfer and Experimental Mechanics. Using the same lab equipment in several courses iteratively will make connections between subject areas. The construction and use of the lab hardware and relevant theory is discussed in this paper. Plans are outlined for assessment of the effectiveness of the lab in improving conceptual understanding of the technical content, broadening the experimental experience, and enhancing the ability to use appropriate technical language when comparing test data and theoretical predictions
The Ground Reaction Curve and Mobilization of Soil Arching in Geosynthetic-Reinforced Column-Supported Embankments
No full textThis paper presents a method to develop a Simplified Ground Reaction Curve (SGRC) for 3D vertical load transfer associated with soil arching in column supported embankments (CSEs). The SGRC is comprised of three piecewise linear relationships for the normalized differential settlement between columns and the normalized vertical stress between the columns. The differential base settlement is normalized by the column diameter to establish a percent relative displacement as opposed to plane strain trapdoor tests which use the clear span. Peak arching is modeled using approximations of the Concentric Arches (CA) or Hewlett and Randolph (HR) models, while terminal arching is modeled using the Adapted Terzaghi (AT) model. The Approximate Concentric Arches (ACA) and Approximate Hewlett and Randolph (AHR) models were developed herein using fitted relationships between the AT model for arching and the CA and HR models. The ACA and AHR models are assumed to be applicable to triangular as well as rectangular column arrangements. Measurements of the load transfer due to soil arching in full-scale CSEs were used to compare the predictions using the SGRC to those using the AT, ACA, and AHR models alone. Based on the results of the comparison with 13 measurements from five case histories, the authors do not see a compelling reason to use an GRC due to the added complexity and lack of performance gains over simpler options such as the Bilinear Adapted Terzaghi (BAT) method used in Load-Displacement Compatibility Analysis
Probabilistic Assessment of Stability of Sloped Pavement Shoulders Subjected to Super Heavy Load (SHL) Vehicles
No full textConference: Geo-Congress 2022Super Heavy Load (SHL) vehicles typically carry heavy loads that exceed the permissible truck weight/size limits set forth by state highway agencies. Operation of wide SHL trailers with heavy wheel loads and non-conventional axle arrangements can potentially jeopardize the stability of pavement shoulders. This study presents a methodology for assessment of the stability of sloped pavement shoulders under SHL vehicle operations. The proposed approach extends the conventional Limit Equilibrium Method (LEM) to a probabilistic methodology that accounts for the uncertainties associated with shear strength properties of pavement unbound layers. Another major point of departure of the proposed methodology from the traditional LEM pertains to its capability for handling the demanding loading conditions imposed by SHL vehicles. To accomplish the research objective, initially, the authors devised a plan of field testing to collect relevant information on traffic loading conditions, pavement layer properties, and shoulder characteristics in ten representative sites in overload corridors in Texas. Subsequently, this information was incorporated into a 3D finite-element system to calculate the horizontal driving forces applied to the pavement shoulder due to SHL vehicle movement. A Monte Carlo Simulation (MCS) was then used to randomly generate the shear strength parameters of the base and subgrade layers. Ultimately, the resisting shear forces were compared with the sliding forces along the trial slip surfaces to determine the probability of failure for the sloped shoulders, with consideration of the SHL-induced surcharge loads, weight of the sliding block, and lateral earth pressure from the adjacent soil. The results underscored the significance of the wheel load and shoulder slope in stability analysis procedure, as operation of SHL vehicles with higher load magnitude on tires resulted in a substantial increase in the probability of failure for pavement shoulders with steep side slopes. The proposed approach can provide means to assess the potential risk against failure of sloped shoulders subjected to SHL vehicles, considering the non-conventional axle assembly of SHLs, and unique characteristics of pavement shoulders in the network
ATTITUDES TOWARD AGING AMONG COLLEGE STUDENTS: RESULTS FROM THE INTERGENERATIONAL CONNECTIONS PROJECT
Full text linkIntegrating Technical Communication Block in a Civil Engineering Computer Applications Course: Lessons Learned
No full textThis paper describes the addition of a four-lesson block on technical writing in a recently redesigned computer applications course for civil engineering majors in a constrained program at the United States Air Force Academy. The new technical communication block focused on students’ ability to effectively communicate ideas for both diverse technical and non-technical audiences by adapting their content and rhetorical strategies according to the audience and purpose. The technical communication principles of user-centeredness, accessibility, usability, and accuracy guided course instruction as well as served as the grading criteria throughout the semester. The instructors also provided students with a self-assessment tool (knowledge survey) to help guide their writing and as a final check of their written submissions. Advice on how to weave writing into technical assignments and how to set realistic expectations for incremental improvements is offered
REMINISCENCE AND DIGITAL STORYTELLING TO IMPROVE WELL-BEING OF OLDER ADULTS WITH COGNITIVE IMPAIRMENT
No full textStudent Self-Assessment: Relationships between Accuracy, Engagement, Perceived Value, and Performance
Full text linkThe final published version of this paper is located on the ASCE Journal of Civil Engineering 1 Education website at: 2 https://ascelibrary.org/doi/full/10.1061/%28ASCE%29EI.2643-9115.0000063The ability to self-assess is a key component of learning and particularly of life-long learning. Knowledge surveys (KS) are a self-assessment tool where respondents rate their ability to answer a question or perform a skill rather than answer directly with knowledge content or by solving a problem as they would on an exam. KS were implemented in a junior level hydraulics class in three successive semesters, with a total of 64 students, in order to evaluate the accuracy of student self-assessments compared to instructor assessments (exams). Students’ self-reported behaviors and attitudes towards KS were assessed via qualitative feedback surveys. Results of this study show that 1) students are reasonably accurate self-assessors, 2) accuracy improves with feedback and practice during the semester, and 3) higher exam scores are correlated with both earlier and more engaged use of KS, and with more positive self-reported attitudes. Given the successful use of KS in this study, civil engineering faculty should be encouraged to use KS in their courses to stimulate metacognitive reflection and learning. Further, KS and self-assessment have the potential to be a significant tool for achieving the ABET student outcome for acquiring and applying new knowledge, both in academic and professional settings as civil engineers adapt to an ever-changing world