MATHIEU INSTABLITY STUDY OF A DEEPWATER SEMI-SUBMERSIBLE PLATFORM

The heave response of a semi-submersible platform is relatively significant than other floaters. While a certain ratio of heave natural period and pitch/roll natural period is reached, the pitch/roll motions of the platform will fall into a Mathieu instability zone. In the paper, a damped Mathieu equation for the semi-submersible platform was derived and the formulae of the control parameters were obtained to determine the stability of its pith/roll motion according to the parameter diagram of Mathieu instability or via numerical simulations. A semi-submersible platform was analyzed to investigate the Mathieu instability conditions. Furthermore, engineering measures on avoiding possible Mathieu instability are proposed and they may be some references for the design of semi-submersible platforms.