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Feasibility and Efficiency of Vibration Control Algorithms on Offshore Platforms

Gholizadeh, Amin | 2008

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 39432 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Golafshani, Ali Akbar
  7. Abstract:
  8. Offshore platforms are of the economic life lines of oil rich countries. These infrastructures are located at severe environmental conditions, their construction and installation involves expense and these justify utilization of these structures with novel auxiliary vibration control device. Two passive vibration control systems have been evaluated in this study aiming to fatigue damage mitigation in offshore steel jacket platforms. Performances of tuned mass damper and friction damper to suppression of wave induced vibrations in fixed offshore platforms have been investigated in this study. Due to the random nature of ocean waves, a fully stochastic analysis method has been used to evaluate the response of the structures equipped with these devices. A stochastic linearization technique has been used to take the nonlinear behavior of friction dampers into account. The developed mathematical formulation has been applied to evaluate the response of realistic models, and to find out the optimal values for the adjustable parameters of friction damper. The results have been verified in comparison with time domain nonlinear analyses results. Also a computer utility has been provided in FORTRAN to perform the spectral fatigue analysis of platforms. Prepared program takes the nonclassical damping into account in the modal analyses and it has been used together with a Genetic Algorithm utility to find out the optimal parameters of tuned mass damper to dissipate the wave induced vibrations of the platforms. Considering the dependency of TMD optimality on exciting waves dominant frequency on each sea-state, a semi active variable mass TMD system has been proposed to supply its optimality for all sea-states. Although the efficiency of both dissipative systems increases for more flexible platforms due to the dominancy of the dynamic response, functionality of TMD devices is more dependent to dynamic characteristics of the platform and friction dampers seems to be more efficient for fixed steel jacket platforms
  9. Keywords:
  10. Vibration Control ; Friction Damper ; Genetic Algorithm ; Tuned Mass Damper (TMD) ; Steel Jacket Platform ; Power Spectral Analysis ; Stochastic Linearzation

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