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Damage Detection of Offshore Jacket Structures Using Frequency Response Measurements

Kianian, Morteza | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40115 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Golafshani, Ali Akbar
  7. Abstract:
  8. Structures face various loadings and confront different circumstances as they are built and used. This situation causes the aging structures to deteriorate, which would lead to a decrease in reliability and safety. In the recent decades, the need for systems to assure the integrity of structures in terms of their age, usage and level of safety when experiencing infrequent and extreme forces such as earthquakes, tornados, hurricanes, large waves has deeply been recognized. These systems are often referred to as structural health monitoring (SHM) in the literature. The main objective of such system is to increase reliable operating lifetime. In the case of offshore structures, utilizing such systems is not only necessary but also inevitable due to some of its exclusive characteristics, which can be summarized as: (1) offshore structures are so important, expensive and huge that their failure or collapse would be a catastrophic event. (2) Poor visibility and concealment of damage by marine growth cause other techniques to be accompanied with prohibitive cost. (3) Cyclic wave loading, severe storms, sea quakes and hostile environment could harshly affect the integrity of the structure. This project applies a frequency response based method for the purpose of structural health monitoring. In this approach the concept of minimum rank perturbation theory is used. The feasibility of using finite number of sensors and its effect on damage detection capabilities is investigated. This thesis introduces a promising methodology to select frequency points effectively using element modal starin energy ratio. The proposed methodology opens up the possibility of much greater detection accuracy. In addition the performance of the proposed method is evaluated in the case of multiple damages. The aforementioned points are illustrated using the numerical study of API jacket platform, and the results of the proposed methodology were acceptable.

  9. Keywords:
  10. Damage Identification ; Fixed Offshore Platform ; Frequency Response ; Structural Health Monitoring ; Minimum Rank Perturbation Theory ; Element Modal Strain Energy Ratio

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