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Theses and Dissertations

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Browsing Theses and Dissertations by Subject "aeroelastic"

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    ItemOpen Access
    Correlated wind turbulence and aeroelastic instability modeling for 3-D time-domain analysis of slender structural systems
    (Colorado State University. Libraries, 2007) Goode, Jonathan S., author; Van de Lindt, John W., advisor
    Slender structural systems, such as high-mast lighting structural supports, are known to be sensitive to natural wind fluctuations. In particular, these systems are also prone to produce aeroelastic instabilities as a result of the structural motion and wind flow. This in turn can result in poor fatigue performance for these structures. In order to accurately estimate this fatigue performance, numerical time-domain solution techniques are needed. Time-domain solutions, however, require accurate modeling of the fluid/structure interaction and the structural system. Because these systems interact with the wind flow, this modeling problem is only exacerbated due to the modeling complexities associated with the wind flow and corresponding aeroelastic instabilities. This study seeks to incorporate existing models for wind flow and vortex shedding into a numerical time-domain analysis solution procedure. The objectives and contributions of this study are focused on three modeling techniques. First, the modeling of the approach wind flows to generate a simulated wind speed time history for use in the time-domain structural analysis algorithm is considered. The approach makes use of random field theory to model the spatial correlation of the approach flow based on an empirical relationship. The effects of varying the spatial correlation of the wind flow on the response of the slender structural system are determined. Second, the modeling of vortex shedding phenomenon into the time-domain structural analysis routine is implemented. Again, the model considered is empirical in nature and a numerical investigation is similarly conducted to determine the effects of varying parameters of the model on the response of the structure. Finally, the fatigue performance of a structural system with respect to a statistically described lifetime wind speed distribution that describes the natural wind fluctuations over the lifetime of the structure is modeled. The spatially correlated wind flow and vortex shedding models are subsequently included to determine their effects on the fatigue performance of the system. Recommendations for future study and improvement are made so that other studies can extend the work contained herein to obtain further understanding and potential improvements in design standards and mitigation techniques to improve performance.
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    ItemOpen Access
    Experimental investigation of wind effects on long-span slender bridges with stochastic traffic flow
    (Colorado State University. Libraries, 2011) Nelson, Ryan Scott, author; Chen, Suren, 1973-, advisor; Bienkiewicz, Bogusz, committee member; Sakurai, Hiroshi, committee member
    The aeroelastic and aerodynamic effects on long-span slender bridges due to traffic has traditionally been neglected as it is assumed that the bridges will be closed to traffic under strong winds. However, with ever changing weather, natural disasters, and important roles of many long-span bridges throughout the United States, the reality is that these long-span bridges are often not closed and there are still many vehicles on the bridges even when considerably strong winds exist. Therefore, to rationally evaluate the aerodynamic performance of a bridge deck, the impacts from stochastic traffic should be appropriately considered as a key part toward any safety or serviceability study. The present study discusses the wind tunnel experimental tests of a long-span bridge section with stochastic traffic. The details of the experimental investigations are reported, including the design and construction of a bridge section model, two-degree-of-freedom testing frame and vehicle models representing stochastic traffic. Several tests were performed to determine a baseline for the bridge section without traffic, under different wind speeds and attack angles. The bridge section was then re-tested with many scenarios representing stochastic and extreme traffic conditions. The aeroelastic flutter derivative coefficients were extracted using the iterative mean square method and the values plotted and compared with the baseline results. Under the given reduced velocity range being tested, it is observed that several traffic scenarios increase the aeroelastic and aerodynamic effects as the bridge section becomes more susceptible to flutter and vortex shedding. Finally, the statistical descriptions of the flutter derivatives with the presence of traffic on the bridge section model are also made.