DYNAMIC RESPONSE OF SHALLOW WATER MONOPOD PLATFORMS

摘要

This paper describes a systematic desktop study of the non-linear dynamic behavior of monopod platforms. The aim of this work is to highlight some important factors in the dynamics of minimum structures in shallow water. The analysis is performed in the time domain with regular wave loading. The non-linearities are due to the wave theory (Stream function of 8th order), to the shallow water environment and to the drag-dominated situation. Idealizations of two braced monopod configurations are compared with the simpler and more commonly studied unbraced monopod. Aspects highlighted for each configuration include the effect of wave period and top mass on the dynamic amplification factor. In particular, the analysis focuses on the highly non-linear behavior in the wave zone. The results show that braced monopods are dynamically more sensitive than unbraced monopods. In particular, braced monopods exhibit more energy at higher harmonics in the quasi-static response. This yields a consistently stronger dynamic response even if the wave period and the natural period of the structure are very different. The importance of the mass at the top of the structure in the dynamic response and in particular its role in increasing the dynamic amplification factor up the water column are highlighted.