Nonlinear Dynamic Response of Spars

David Weggel (PhD student), Iftekhar Anam, F. Hardjanto, F. Morera (MS students), Mona Hossain (UG student)

Nonlinear response of spar buoys;
Relative importance of various nonlinear effects;
Evaluation of methods for nonlinear analysis of spars.
Part of overall effort on spars.

Coordinated through J.M. Niedzwecki with work by M.H. Kim using second order diffraction and C.P. Johnson and J. Zhang using Morison's equation. A number of parametric studies were being conducted to obtain first order diffraction forces and radiation coefficients as well as second order diffraction forces for solid and hollow truncated cylinders. These results were then used to modify Morison's equation type solutions. A number of parametric studies were conducted to obtain first order diffraction forces and radiation coefficients as well as second order diffraction forces for solid and hollow truncated cylinders. These results were then used to modify Morison's equation type solutions. Nonlinear diffraction analyses using WAMZT and TFPOP and including or neglecting various nonlinear effects have also been completed. We are now in the process of combining the conclusions of both approaches (slender body theory and nonlinear diffraction). Some statistical analyses have been conducted to assess variability of results.

Work on TLP's of similar nature by Eatock Taylor et al at Cambridge University, McNamara in Ireland, Natvig with Norwegian Contractors.

To obtain a better understanding of nonlinear effects, their potential importance and the best way to reproduce them is essential for reliable designs of spars.

October 1994 to September 1997

The main expected accomplishments are a better understanding of the nonlinear dynamic behavior of spar buoys under wave and current action, the identification of the key parameters controlling their response and the selection of the most adequate analysis model.

Guidance for some aspects of this study have been provided by Tim Finnigan (Chevron) and Rick Mercier (Shell). Technology transfer is primarily through publication of findings and a planned thrust area workshop.