A research note on a study of motion characteristics of tension leg spar

Abstract

The present research note, reports a study on the dynamic motion analysis of a tension leg spar (TLS). In the research note the time domain analysis is done using USFOS^*TM software for a tension leg spar supporting a ‘National Renewable Research Laboratory (NREL)’ 5MW wind turbine at an operating depth of 320m to determine the dynamic responses of tension leg spar subjected to sea state 11 (=15m and =16sec). Motion characteristics such as surge, pitch and heave as well as the combined effect of the above are discussed at length. Non-linear effect is introduced in the spar due to the tension leg. The nonlinear effects include combined-frequency effect such as double natural pitch and surge frequencies as well as sum of frequencies. The reported study is only limited to wave induced motions and no aerodynamic forces are taken into account. Hydrodynamic loads are based on a combination of the Morison formula and the pressure integration method. The response for the base case is compared with available result from the literature. Furthermore, to achieve a proper understanding of the response of the floating concept, parametric studies are carried out by varying parameters such as draft, pretension and position of ‘center of gravity (COG)’. The results highlight the variation in platform responses caused by changing these parameters. The analyses are carried out for combination of parameters in order to find a configuration having the least response for the above sea state.

Keywords: Tension leg spar, Coupled motion characteristics, Time domain analysis, Dynamic response, Parametric study.

Cite this Article

Yadav K, Vamshikrishna Domala, Sharma R. A Research Note on a Study of Motion Characteristics of Tension Leg Spar. Journal of Offshore Structure and Technology. 2017; 4(3): 1–20p.