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Experimental and Numerical Investigation on the Hydrodynamic Properties of Heave Plates in Translational and Rotational Oscillations

Abazari, Abuzar | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 52161 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Behzad, Mehdi
  7. Abstract:
  8. Many offshore platforms as TLP, Semi-submersible and Spar are used for oil extraction and energy harvesting. One of the challenges of these structures is related to vibrations due to the environmental sea waves and wind loads. The optimal way for the response reduction of an offshore structure in heave direction is the installing of thin heave plate. The heave plate induces vortex shedding and pressure drop on fluid flow downstream. Diameter difference of heave plates in an array can improve the obtained damping and added mass for a given small spacing between plates, which has not been studied up to now. Hence, in the present thesis it was observed that converting of the uniform to non-uniform configuration improves the hydrodynamic properties for a given vibration amplitude and spacing through an experimental and CFD simulation tests. In the following the new proposed combined rigid-elastic disk was studied which improves damping compared to a fully rigid disk while its added mass is lower than the fully rigid disk. However, this trend occurs when the axisymmetric mode is excited. This design can be used for structures in which the increasing of the equal mass may increase the dynamic response. Moreover, the tests showed that the boundary proximity increases the damping and added mass coefficients. It should be noted that there is a drawback for investigating the dependency of the angular hydrodynamic coefficients on vibration amplitude and frequency. First, tests on disks with different size on oscillating shaft determined that both of the rotational hydrodynamic coefficients have linear increasing trend against vibration amplitude. The increasing of the frequency can increase the damping while the added mass decreases. Second, the experimental tests on disks, which rotate in a distance from the shaft, showed that the added moment of inertia has a decreasing trend versus vibration amplitude at high frequencies and large distances form the shaft
  9. Keywords:
  10. Heave Plate ; Hydrodynamic Coefficients ; Non-Uniform Arrangement ; Combined Rigid-elastic Disk ; Translational Oscillation ; Rotational Oscillation

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