ABSTRACT The focus of this article is the evaluation of the traditional method of time domain analysis regarding its assumption that the maximum stresses of the structural members appear at the same time and specifically, at the time of the base shear maximization. Two procedures are followed for the analysis of identical offshore jacket type models in order to gain adequate data for performing comparisons between them. The first, is the generally used method mentioned above, while the second examines every member independently during time domain simulation and reveals the maximum values of their internal forces and moments whenever they appear. Various comparisons between the two groups of results are performed, and the final conclusions are presented.
INTRODUCTION The society's needs for energy often leads to the construction of offshore structures; traditionally for oil exploration and production, and for most recently for wind energy exploitation. According to EWEA (European Wind Energy Association, 2012), 235 new Offshore Wind Turbines in nine wind farms were fully grid connected in the year 2011. Offshore structures are subjected to the wave load, which is dynamic and thus, a need for dynamic analysis arise for their safe design. For the dynamic analysis two main approaches are used, frequency domain analysis and time domain analysis. In the case of Offshore Wind Turbines, a time domain approach is preferable primarily due to the nature of the wind load. Several investigators have dealt with time domain simulation. Kurian et al. (2010) worked on the dynamic behavior of semi submergible platforms. Pollio et al. (2006) investigated the non linear dynamic behavior of risers in the time domain, using an implementation of the Runge-Kutta algorithm. Morooka et al. (2006) demonstrated that time domain can address better riser nonlinearities, while frequency domain analysis makes easier the handling of the solution obtained and requires less computational efforts, in general.