MEASUREMENT OF HYDRODYNAMIC CHARACTERISTICS FROM SHIP MANEUVERING TRIALS BY SYSTEM IDENTIFICATION

The hydrodynamic coefficients are the principal terms in the mathematical model used in the simulation and prediction of ship maneuvers. The coefficients, which for a given ship are usually evaluated based on constrained tests of a model in the towing tank, may suffer from scale effects when applied to the full-size ship, especially for full forms and in shallow water. The application of system identification analysis techniques to specified ship trial maneuvers provides a way of "measuring" the hydrodynamic coefficients of the ship and helps to verify the proper form of the equations of motion used in the simulation. System identification programs using the extended Kalman filter technique were developed at M.I.T. for direct application to realistic ship maneuvers wherein the ship may suffer large speed losses and significant currents may exist. The programs identify (measure) the magnitude and direction of the current as well as the magnitude of the important linear and nonlinear hydrodynamic coefficients. Using "simulated" noisy ship motion measurements, a set of specified maneuvers was developed for the VLCC Esso Osaka which presented the best probability of identifying the hydrodynamic coefficients. Full-scale trials were carried out on the ship and the results were analysed with the identification programs developed. The proper form of the simulation equations was established and the magnitudes of the ship's coefficients were determined. When the identified values of the coefficients were used to simulate the trial maneuvers, very good agreement was obtained between the simulated motion responses and the ship trials. The identification technique also provides the possibility for the "direct" measurement of the resistance of a ship, without the necessity of propulsion trials in combination with self propelled model tests, which may suffer from scale effects. Using simulated noisy data for the simple straight-ahead maneuver in which the propeller is allowed to windmill as the ship slows down, the identification procedure indicated the potential of measuring the resistance coeffiicent to within 1 to 2 percent.

  • Corporate Authors:

    Society of Naval Architects and Marine Engineers

    601 Pavonia Avenue
    Jersey City, NJ  USA  07306-2907
  • Authors:
    • Abkowitz, M A
  • Publication Date: 1980

Media Info

  • Features: References;
  • Pagination: 27 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00323483
  • Record Type: Publication
  • Report/Paper Numbers: No. 10
  • Files: TRIS
  • Created Date: Feb 18 1981 12:00AM