Browsing by Subject "Structural analysis"
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Item Cenozoic structural evolution of the eastern margin of the Middle Magdalena Valley basin, Colombia : integration of structural restorations, low-temperature thermochronology, and sandstone petrography(2011-08) Sánchez, Carlos Javier, M.S. in geological Sciences; Horton, Brian K., 1970-; Mann, Paul; Ketcham, RichardStructural analysis of surface and subsurface data from the Middle Magdalena Valley basin and Eastern Cordillera fold-thrust belt to construct a kinematic model for its Cenozoic structural and stratigraphic evolution. The La Salina west-vergent thrust system marks the boundary between the Paleogene foreland basin of the Middle Magdalena basin and the Eastern Cordillera fold-thrust belt. New low-temperature thermochonological and sandstone petrographic analyses provide constraints on ages of thrust deformation and sediment dispersal. Apatite fission track (AFT) and U-Th/He thermochronological results show the timing of three structural events along the La Salina fault system: (1) late Eocene-early Oligocene (~43–35 Ma) initial hanging wall exhumation; (2) continued middle Miocene (~15 Ma) exhumation; and (3) continued but more rapid late Miocene (~12–3 Ma) hanging wall exhumation. Vitrinite reflectance results provide estimates of maximum burial depths for the hanging wall of the La Salina fault ranging from 4 to 6 km., this depth of burial estimates constrain the basin geometry during its late Eocene to late Miocene evolution. The eastern hanging wall of the La Salina fault displays a broad anticline-syncline pair affecting Cretaceous to Eocene strata with no significant faulting, whereas the western footwall contains a complex series of tight, thrust-related folds in Eocene-Quaternary strata. For foreland basin province, a proposed triangle zone accommodates a small amount of east-west shortening (< 1000 m) along the frontal thrust system by east-vergent backthrusting within a broader passive-roof duplex. East-west shortening in the Cenozoic stratigraphic section was also accommodated by detachment folding, which produced localized areas of steep dips. In the proposed kinematic restoration, the most recent phase of deformation represents out-of-sequence reactivation of the La Salina fault that is consistent with irregular crosscutting relationships of some footwall structures. Earliest exhumation by ~45–30 Ma in the Eastern Cordillera fold-thrust belt province matches (1) an increased proportion of sedimentary lithic fragments; and (2) a high degree of compositional maturity (Q88F4Lf8). Exhumation since ~15 Ma in the foreland province coincides with (1) the highest accumulation rates observed for the upper Miocene Real Group; and (2) a decrease in compositional maturity (Q55F8Lf36).Item Flow around a rotating short cylinder: a computational study(Texas Tech University, 1996-08) Rahman, Abu Sadek SaifurDespite wide spread interest in the aerodynamics of cars in recent years, the flow field associated with the wheels has received relatively little attention, mainly due to difficulties in obtaining an adequate simulation of the flow. Yet in many cases where aerodynamic designs are important, flow around the wheels can play a major role in the behavior of the vehicle. The obvious example is racing cars, which travel at high speeds with totally exposed wheels. A detailed understanding of the flow should also help in dealing with the hazard formed by entrainment and dispersal of spray from a wet road caused by trucks. In the present study, AIRFL03D~a multi-grid based finite-volume code has been used to predict numerically the flow around a short cylinder which resembles the flow around a wheel. Comparisons are made for the flow around a stationary cylinder with that around the same cylinder when rotating in order to highlight the specific effects of rotation. Lift and drag are also calculated from pressure distributions. Standard k-e model was used in the AIRFL03D code. Although it has been reported that the standard k-s model cannot accurately predict rotational flow, reasonable results have been obtained for a certain range of wheel rotation. ICEM^^ CFD/CAE a commercial preprocessing software has been used for model generation as well as generation of the grid. EnSight^^ another commercial postprocessing software has been used for the visualization of the analysis. The computational results obtained show very good trends in the prediction of the flow field compared with previous experimental results.Item A multifocal analysis of Korean educational policies on the teaching profession(2011-05) Kim, Kyu Tae; Reyes, Pedro, 1954-; Sharpe, Edwin R.; Young, Michelle D.; Holme, Jennifer J.; Sakamoto, ArthurKorean education policies were derived from the 5.31 Education Reform oriented to the increase of autonomy and accountability for school effectiveness and the quality instruction through teacher professionalism enhancement. The policies are related to the influences of historical events and contexts embedded in the interactions of policy players who have their own arguments, particularly professionalism versus managerialism. The policies have been driven by right-wing perspectives. As a result, the roles, powers, functions, and structures of teaching profession have gradually changed. From the structural analysts, Basil Bernstein and Michel Foucault, teaching profession has become a system of supervision, compliance, normalization, isomorphism related to the collection code. The dynamic, complex and multilevel policy implementation need to be analyzed from a multifocal approach coupled with historical institutional, political, and structural analysis. This analysis contributes to understanding the changes of teaching profession resulted from intricate and dynamic interactions embedded in policy environments causing or influencing policy implementation directly and indirectly. Korean educational policy analysts, generally, tend to use one of the institutional, the political, and the structural perspective. Most policy analyses are concerned with the political analysis focused on exploring the political interaction between policy players, presenting policy issues and alternatives, analyzing the new institutionalism of education policy formation and implementation process, and influencing of policies on school organization and teachers apart from the political environment and the political interactions. In this respect, the multifocal policy analysis will be beneficial to shed light on a multifocal analysis of Korean educational policies.Item Simplified modeling of shear tab connections in progressive collapse analysis of steel structures(2010-05) Heumann, Eric Michael, 1985-; Williamson, Eric B., 1968-; Engelhardt, Michael D.Recent tragedies involving the collapse of several large and prominent buildings have brought international attention to the subject of progressive collapse, and the field of structural engineering is actively investigating ways to better protect structures from such catastrophic failures. One focus of these investigations is the behavior and performance of shear tab connections in steel structures during progressive collapse events. The shear tab, a simple connection, is typically modeled as a perfect pin in standard design, but in progressive collapse analysis, a much more accurate model of its true behavior and limits is required. This report documents the development of a simple yet accurate shear tab model and its use in understanding the behavior and limits of shear tab connections in column removal scenarios. Particular attention is paid to the connections’ axial force limit state, an aspect of behavior that is typically unimportant in standard design.Item Solar concentrator wind loadings(Texas Tech University, 1996-12) Wagner, Geoffrey L.The objective of this project was to determine the maximum wind loadings on a notched parabohc solar concentrator. To accomplish this objective, a test program was conducted using the Texas Tech tow tank. The results from testing a one-tenth scale model were put into nondimensional force and moment coefficients. The maximum coefficients are as follows: hft,0.92; drag, 1.42; side force, 1.05; yaw moment, -0.23; roll moment, 0.72; and pitch moment, 1.28. These results shovdd be used as a starting estimate for the beginning stages of the structural design of the solar concentrator support structure.Item Structural and electrochemical characterization of high-energy oxide cathodes for lithium ion batteries(2012-12) Lee, Eun Sung; Manthiram, ArumugamLithium-ion batteries are the most promising rechargeable battery system for both vehicle applications and stationary storage of electricity produced from renewable sources such as solar and wind energies. However, the current lithium ion technology does not fully meet the requirements of these applications in terms of energy and power density. One approach to realizing a combination of high energy and power density is to use a composite cathode that consists of the high-capacity lithium-rich layered oxide Li[Li,Mn,Ni,Co]O2 and the high-voltage spinel oxide LiMn1.5Ni0.5O4. This dissertation explores the unique structural characteristics and their effect on the electrochemical performance of the layered-spinel composite oxide cathodes along with individual layered and spinel oxides over a wide voltage range (5.0 – 2.0 V). Initially, the effect of cation ordering on the electrochemical and structural characteristics of LiMn1.5Ni0.5O4 during cycling between 5.0 and 2.0 V were investigated by an analysis of the X-ray diffraction (XRD) and electrochemical data. Structural studies revealed that the cation ordering affects the size of the empty-octahedral sites in the spinel lattice. The differences in the size of the empty-octahedral sites affect the discharge profile below 3 V due to the variation in lattice distortion during lithium ion insertion into 16c octahedral sites. With the doped LiMn1.5Ni0.5-xMxO4 (M = Cr, Fe, Co, and Ga) spinels, different dopant ions have different effects on the degree of cation ordering due to the differences in ionic radii and surface-segregation characteristics. The compositional and wt.% variations of the layered and spinel phases from the nominal values in the layered-spinel composites were obtained by employing a joint XRD and neutron diffraction (ND) Rietveld refinement method. With the obtained composition and ex-situ XRD data, the mechanism for the increase in capacity and the facile phase transformation of the layered phase in the composite cathodes to a 3 V spinel-like phase during cycling was proposed. Investigations focused on synthesis temperature revealed that the electrochemical characteristics of the composites are highly affected by the synthesis temperature due to the change in the surface area of the sample and cation ordering of the spinel phase. In addition, the electrochemical performance of the lithium-rich layered oxide Li[Li,Mn,Ni,Co]O2 could be improved by blending it with a lithium-free insertion host VO2(B) and by controlling the amount of lithium ions extracted from the layered lattice during the first charge process.Item Structural optimization for a photovoltaic vehicle(2011-05) Ford, Bennett Alan 1984-; O'Connor, James ThomasPhotovoltaic vehicles are designed to harness solar energy and use it for self-propulsion. In order to collect sufficient energy to propel a passenger, a relatively large photovoltaic array is required. Controlling the loads imparted by the array and the body that supports it, while protecting the passenger and minimizing vehicle weight, presents a unique set of design challenges. Weight considerations and geometric constraints often lead system designers toward unconventional structural solutions. This report details analytical and experimental processes aimed at proving the concept of integrating aluminum space-frame elements with composite panels. Finite element analysis is used to simulate load conditions, and results are compared with empirical test data.Item Wavelet-based acoustic emission analysis of composite materials(Texas Tech University, 1996-08) Qi, GangIn this dissertation, a methodology for time-frequency analysis of acoustic emission (AE) signals generated due to static loading of composite specimen is presented. The tool is based on a recently developed mathematical transform called the wavelet transform. Two aspects of AE-based nondestructive evaluation (NDE) are failure mode identification and residual strength prediction. In this work, the wavelet-based AE method is applied to these two aspects of AE-based NDE. Presently, the public literature review indicates that AE techniques are dominated by time domain analysis methods. It can be seen that these methods have matured into tools which provide satisfactory results. There are limited results available that use frequency domain techniques, however, there is valuable information available in the frequency domain. Thus, it is evident that there is a need for an AE analysis technique that simultaneously utilizes both the time and frequency domains. In this dissertation, a hybrid technique is developed. With the application of wavelet transforms to the failure mode identification, the AE signals are decomposed into different wavelet levels. A general trend is observed by investigating the energy-frequency distribution of the decomposed AE signals. This trend indicates that the energy in the AE signals is essentially concentrated in three levels (seven, eight, and nine), representing frequency rages of 50-150 kHz, 150-250 kHz, and 250-310 kHz. Furthermore, the energy percentages in levels seven, eight, and nine are determined to be 8%, 15%, and 75%, respectively. The analysis indicates that the three dominant wavelet levels may be related to different failure modes associated with the fracture of CFR composites. In the prediction of residual strength, the ability of the wavelet transform to enhance the signal to noise ratio is employed. The exponential constant in value used to determine the relationship between stress and stress intensity factor are compared relative to classical fracture mechanics and AE techniques. In the comparison study, the conventional and wavelet-based AE techniques are presented side-by-side to show the advantage of wavelet-based methods. The results verify that the wavelet-based method improves on the results relative to classical fracture mechanics methods.