The validity of any mathematical analysis of ship-hull vibration depends on the idealization of the ship's structure that is used. The authors believe that an oversimplified idealization of the structure has been largely responsible for past failures to accurately predict ship vibration characteristics. In a previous investigation, the authors used a ship idealization in which double-bottom degrees of freedom were added to a single-elastic-axis idealization of the hull to improve the accuracy of the predicted hull-bending-moment response to slam forces. For the present investigation, the previous idealization was extended to include (1) a propulsion-system idealization consisting of a propeller, propeller shaft, thrust bearing, and thrust-bearing foundation, and (2) an idealization of a deckhouse elastically connected to the main hull and free to deform by shear and bending in a fore and aft direction. As in the previous work, the MARINER-class ship was used as a guide in assigning mass and stiffness properties to various components of the idealization. Also, as before, the approximations of neglecting shear lag and rotary inertia in the main hull, of assuming constant damping and added mass in all vibratory modes, and of lumping the mass at discrete points were incorporated in the analysis. The vibratory-response calculations that were performed with the improved idealization indicate that the addition of the deckhouse and propulsion system did not significantly alter the natural mode shapes and frequencies predicted by the previous idealizations; however, the additional component of propeller excitation (the fluctuating thrust in the propeller shaft) significantly changed the predicted vibratory response of the main hull. The most important aspects of the added excitation were its magnitude and its phase with respect to the vertical excitation force at the propeller. The location of the thrust-bearing foundation also had an important influence on the amplitude of main-hull response, whereas the stiffness of the foundation and the mass of machinery effectively attached to the forward end of the shaft had only a minor influence.

  • Supplemental Notes:
    • Paper presented at Northern California Section of the Society of Naval Architects and Marine Engineers, March 1971
  • Corporate Authors:

    Society of Naval Architects and Marine Engineers

    601 Pavonia Avenue
    Jersey City, NJ  United States  07306-2907
  • Authors:
    • Kline, R G
    • Clough, R W
    • Kavlie, D
  • Publication Date: 1971-3

Media Info

  • Features: Figures; References; Tables;
  • Pagination: 62 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00019558
  • Record Type: Publication
  • Source Agency: Society of Naval Architects and Marine Engineers
  • Files: TRIS
  • Created Date: Nov 25 1971 12:00AM