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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Wind effect on super-tall buildings using computational fluid dynamics and structural dynamics

Unknown Date (has links)
Super-tall buildings located in high velocity wind regions are highly vulnerable to large lateral loads. Designing for these structures must be done with great engineering judgment by structural professionals. Present methods of evaluating these loads are typically by the use of American Society of Civil Engineers 7-10 standard, field measurements or scaled wind tunnel models. With the rise of high performance computing nodes, an emerging method based on the numerical approach of Computational Fluid Dynamics has created an additional layer of analysis and loading prediction alternative to conventional methods. The present document uses turbulence modeling and numerical algorithms by means of Reynolds-averaged Navier-Stokes and Large Eddy Simulation equations applied to a square prismatic prototype structure in which its dynamic properties have also been investigated. With proper modeling of the atmospheric boundary layer flow, these numerical techniques reveal important aerodynamic properties and enhance flow visualization to structural engineers in a virtual environment. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection
2

System modeling and modification via modal analysis

Luk, Yiu Wah January 1981 (has links)
A new method is developed for experimentally determining the system parameters of a structure that is suitable for implementation in microprocessor-based systems. It uses single degree-of-freedom models to describe a multi-degree-of-freedom system. The system is assumed to be describable by a linear, proportionally and lightly damped, lumped parameter model. Two types of damping models, viscous and structural damping, are provided. The effective mass, stiffness, and damping are obtained by fitting the experimental data in the inverse Nyquist plane. The effective mass, stiffness, and damping are convertible to global modal mass, stiffness, and damping through normal mode corrections. Then a physical space mathematical model may be assembled from the modal properties for complete and truncated modal vector system descriptions. Therefore, this method will deal with the general case where the number of degree-of-freedom exceeds the number of identified modes. After a mathematical model is developed, different ways of modifying the structure analytically are investigated. This modified model is used to predict the new dynamic characteristics of the modified structure due to changes in its mass, stiffness, or damping properties. There are three ways that modifications can be made. They are: l) modifications made in the physical coordinates model; 2) modifications made in both the physical and modal coordinates models; and 3) modifications made in the modal coordinates model. The last way is found to be the most efficient way; therefore, model modifications should be done totally in modal spaces, modal space I and II. The derivation of mass, stiffness, and damping modification matrices for general structure is also presented. The resonance specification and frequency response function synthesis are two useful techniques that aid in system modification and are, therefore, included. A resonant peak can be shifted to another frequency by making certain modifications to the structure, thus avoiding undesired vibration. The resonance specification will determine the amount of physical change needed. It is not practical to store all the frequency response function measurements of a structure during testing. Therefore, a frequency response function synthesis is needed, such that any one can be synthesized from the model developed. A theoretical three degree-of-freedom system and two experimental systems--a square plate and a C-clamp--were used to verify the techniques developed. / Ph. D.

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