eva‎luation of Wind Turbine Offshore Structure considering pile-soil- structure interaction under breaking wave load

1/1/1900 12:00:00 AM

Dynamic behavior of wind turbine offshore platform contains some complexity due to inter-action of wave-structure and wind. Additionally, this type of structure is regularly impacted by breaking waves. Generally, breaking wave include three forces which are combination of inertia, drag and slamming forces. Drag and inertia forces show quasi static and can be esti-mated by the Morison equation. But, slamming force acts in a very short duration with high dynamic amplification and can magnify severely structural responses. The aim of this re-search is to investigate different models of pile-soil-structure interaction of jacket type wind turbine offshore structures under impact of wave breaking force. For this purpose, a finite element model of OC4 wind turbine offshore jacket with beam on nonlinear Winkler foundation is developed as a referenced model. Three other models are also developed in this research as simplified pile-soil-structure interaction. The first model is based on four effective fixity length with 2, 4, 6 and 8 times of pile diameter. The second one is based on stiffness matrix and finally the third one is constructed by uncoupled spring model. Most of methods for calculating the wave breaking slamming force are given for a single cir-cular cylinder that is appropriate for monopiles and there is no particular approach for jacket type wind turbine offshore structures. Due to the lack of information about slamming force, the result of experimental laboratory load test is taken to apply on structure as external nodal slamming forces. Structural responses such as displacement at the base of the tower, shear and internal axial forces are estimated by a transient dynamic analysis of structure and results are compared with the results estimated based on referenced model. Obtained results show that the effective fixity length model with fixity depth of 8 times the pile diameter gives natural frequency of the structure better than other simplified models but it presents two percent more than referenced model. In addition, displacement of deck for all simplified models un-der wave breaking force are less than the referenced model but effective fixity length model with fixity depth of 8 times the pile diameter shows the best association result with refer-enced model. Stiffness matrix model gives internal axial and shear forces in structural mem-bers better than other simplified models.

نيروي ضربه موج شكنا , اندركنش خاك-شمع-سازه , سازه نگهدارنده توربين بادي

breaking wave forces , pile-soil-structure interaction , support structures of wind turbines

Koorosh Khodaverdi

Dr. N. Shabakhty