ON THE EFFECTIVENESS OF CONSTANT COEFFICIENTS ROLL MOTION EQUATION

Traditional computer codes for seakeeping calculations fail in the forecasting of large amplitude rolling. There is a great need to use semi-empirical damping models and coefficients. This stresses the importance of obtaining a deeper insight into the physical- mathematical modelling of the different contributions to the rolling equation. Experimental tests on nonlinear rolling in a regular beam sea of a ro-ro ship model have been conducted by varying both the wave steepness and the wave frequency. The use of a parameter estimation technique, based on the least squares fitting of the stationary numerical solution of the nonlinear rolling motion differential equation, allowed information on the damping and on the linear and nonlinear damping coefficients to be obtained. These exhibit a quite strong dependence on frequency that reduces the efficiency of constant coefficients rolling equation to simulate large amplitude nonlinear rolling. The results indicate that a good quality prediction model of nonlinear rolling cannot be based on constant coefficients time domain simulations. These can in fact lead to incorrect estimates of rolling amplitudes even when the parameters have been obtained through high level parameter estimation procedures based on experimental data. The analysis also indicates a marked dependence on the effective wave slope coefficient on wave amplitude. The introduction of both these dependencies on the rolling equation allows the experimental results to be reproduced with great accuracy even at large amplitudes.

• Supplemental Notes:
  • Ocean Engng, v 23 n 7, Oct 1996, p 597 [22 p, 13 ref, 3 tab, 27 fig]
• Authors:
  • Contento, G
  • Francescutto, A
  • Piciullo, M
• Publication Date: 1996

Language

• English

Subject/Index Terms

• TRT Terms: Rolling
• Uncontrolled Terms: Model tests; Parameter estimation
• Subject Areas: Marine Transportation;

Filing Info

• Accession Number: 00734166
• Record Type: Publication
• Source Agency: British Maritime Technology
• Files: TRIS
• Created Date: Mar 27 1997 12:00AM