Stability of Offshore Barge Subjected to Parametrric Rolling in Waves

Abstract

This paper deals with the stability of an offshore barge when subjected to parametric rolling in longitudinal waves. The main aim of this paper is to understand the roll behaviour of an offshore barge under longitudinal waves, to predict the susceptibility of parametric rolling in longitudinal waves and to identify the region of instability when subjected to parametric rolling. The primary objective is to find the roll response of a geometrically modeled offshore barge in ANSYS AQWA for regular sea conditions followed by the calculation of roll response in a conservative way by the Linear Strip theory to validate with the results obtained from ANSYS AQWA. Two major cases were studied; once when the length of the waves is equal to the length of the barge and the other when the length of the encountering waves is four times the length of the barge The severity of the parametric rolling for the offshore barge is calculated by the mathematical modeling for solution of Mathieu's Differential equation using Matlab programming, taking in account the stability parameters for the offshore barge for which stability curves are plotted. This Graphical Ince-Strutt diagram was then verified by numerical modeling to illustrate the instability of barge. The boundary approximations for the instability zone for which frequencies prone to parametric roll resonance were identified and their threshold damping coefficient was then calculated.

Boundary Approximations, Effect of Forward Speed and Implementation of Genetic Algorithm in Parametric Rolling

“…Initially an offshore barge was modeled in ANSYS AQWA ( Fig. 1) and the response [1] in the six degree of freedom was validated with a Journal Paper (Seung-Chul Lee et al, Analysis of motion response of barges in regular waves, 2012).…”

“…Four cases [1] were studied to find out the stability using the graphical Ince-Strutt diagram. Table I and Table II represents stability of ship for different relationship between length of the wave and length of the ship respectively.…”

“…In the cases [1] that have been considered before for finding the susceptibility of parametric rolling, we have considered the initial angle of roll as 0.01degrees or 0.1degrees, and the rolling of the barge was seen to be predominantly dependent on the initial angle of roll. So it can be further easily said that the rolling of the barge depends on the initial angle of roll considered and the plot of rolling versus time also manifests itself as the initial angle of rolling is chosen.…”