Tri Le

Graduation Semester and Year

2008

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Ali Abolmaali

Abstract

Long tapered poles are commonly used to support Closed Circuit Television (CCTV) Cameras for security and traffic monitoring. Images received from CCTV are normally distorted depending on the wind induced vibration characteristics of the forcing function. To reduce image distortion, three approaches are integrated to optimize the process, which are: (1) development of equations for pole's frequency of vibration in terms of its geometric variables; (2) development of a mechanical damping device to isolate the pole's vibration from that of the camera; and (3) development of an electrical image processing device for image corrections. The identification of a pole's natural frequency of long tapered hollow steel poles is the most important parameter in the design and calibration of the mechanical damping device. Thus, three-dimensional finite element model analyses, by taking into account the couplings between material, contact and geometric nonlinearities are developed to determine the natural frequency equations for poles commonly used by TxDOT in terms of their geometric variables. A sensitivity study is performed to study the effect of different geometric parameters on the overall natural frequency of the pole. Using the results from the parametric study, empirical formulae between the geometric parameters and the first, second, and third mode natural frequencies for the long tapered hollow steel poles are obtained. Cyclic loading was applied to the model to study the energy dissipation of the pole. In order to verify the Finite Element analysis, data collected from the accelerometers installed on the poles are adopted and analyzed. Natural frequency envelope obtains by varying the pole geometry provided by TxDOT for mechanical isolator device design. A biaxial mechanical isolator device is developed, specifically aimed at horizontal high-frequency motion abatement in pole-mounted camera applications and similarly conditioned supports. The device works on the principle of force and displacement transmissibility reduction via the use of a lightly damped spring interface with a tuned natural frequency. The isolator is inserted between the top of the structure (pole) and the seat of the camera, and operates by rejecting undesirable high-frequency modal vibrations experienced by the main support; this has the effect of diminishing high-acceleration ground inputs which are principally responsible for image distortion. By design, the isolator trades its high-frequency performance for a low-frequency heave, which does not induce blur but causes limited horizon shift. The developed mechanical device is designed to reduce significantly the high pole vibration frequencies experienced by the camera. Also the digital algorithm for image stabilization is developed, which is highly effective for low-frequency vibration. For this reason, the proposed mechanical solution is prescribed as an ancillary technique to image processing in installations where high-frequency or displacement conditions prevail at the camera support. Together with the mechanical approach to stabilize the images, the image processing is also performed to provide the best stabilized images. Finally, a test-bed is developed and implemented to perform experiments and analyze the speed and efficiency of different image stabilization algorithms. This algorithm is being integrated with the mechanical device to optimize the vibration reduction process.

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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