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Investigation of Bilge Keel Influence on Nonlinear Roll Motion of a Small Cargo Carrier

Dehestani Esfandabadi, Hamid | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49728 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Seif, Mohammad Saeed
  7. Abstract:
  8. Generally, Vessels at sea are exposed to water waves. Large displacement of the vessel affects its performance, passengers’ and crews’ activities or duties. Based on the type of the displacement (translational/rotational) and the orientation about the reference axes, floating vessels are collapse onto 6 distinct categories. One of the above-mentioned displacements about the reference axis is rolling motion. Rolling motion is the rotation of the vessel about its longitudinal axis. This displacement may lead the commuters or crews to seasickness. Furthermore, greatness of this displacement increases the probability of damage to the goods. Moreover, performance of the propulsion systems grows less than the optimum value. Therefore, adequate measures should be performed to reduce these movements. In the present thesis, the effect of bilge on the nonlinear rolling motion of a vessel is investigated. One of the disadvantages of the foregoing vessels is the lack of achievements of reducing its rolling motion. The equation of motion is assumed to be nonlinear, then the nonlinear terms of the equation is studied. The experimental tests are conducted in two distinct situations, with and without bilge, and then the effect of bilge on hydrodynamic coefficients is observed. The coefficients of rolling equation of motion are calibrated by means of experimental tests. The restoring coefficient is computed to obtain the GZ curve. To draw the foregoing curve the inclining test or available marine engineering software such Auto Ship, Max Surf etc. can be utilized. To calculate the damping coefficient (reduced damping) and rolling moment, the free decay rolling test is utilized, and then the damping coefficient (reduced damping) is computed. Indeed, scale coefficient affects the damping coefficient; in this regard, scale coefficient effects are well scrutinized to generalize about the other models. The nonlinear rolling equation of motion are solved in both time and frequency domain to assess bilge impact. Fourth-order Runge-Kutta method, accurate numerical method, and duffing oscillator are employed to obtain the time domain solution of the nonlinear rolling equation of motion and frequency domain solution, respectively. Next, the bilge is design and the free decay test is repeated to investigate the subsequent effects and compute the hydrodynamics coefficients
  9. Keywords:
  10. Dhow ; Nonlinear Rolling ; Free Roll Test ; Small Cargo Carrier ; Bilge Kell

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