چكيده به لاتين
Nowadays, offshore wind turbines consider as one of the clean and renewable energy production methods using wind energy in the world which are developing as time goes on. Foundation is one of the most important parts of these turbines due to the presence of this structure in specific climatic conditions and location, which should be considered. These structures foundation is selected based on water depth, distance from the coast and etc. that the gravity based foundation is one of it. Based on heavy weight property of the foundation, structural stability in various loading conditions such as vertical, horizontal and dynamic can be obtained and transfers loads from the structure to the soil. Investigation of foundations in marine and seismic zones under earthquake loading is one of the important design criteria. The occurrence of liquefaction in relatively loose sand caused by rapid earthquake loading should be also evaluated. Gravel column application is one of approach to improve the soil properties against liquefaction conventionally. In the present research, a 3D numerical study of gravity based foundation of offshore wind turbine with its structure in sandy soils are performed using OpenSees software. In this model, the gravel column has been used to reduce the liquefaction effects under foundation. Parametric studies are conducted to investigate factors such as dimensions and embedded depth of foundation, length and diameter of gravel column, relative permeability between soil and gravel column, gravel column arrangement and storm loading, on soil response at near and far from the foundation, foundation and structures performance (settlement and tilt of foundation and structure horizontal displacement). The results show that the change in permeability of soil and gravel column has the most effect on soil response, structural and foundation performance. The effect of column diameter was more than its length. Increasing the foundation dimensions decreases the settlement and tilt of foundation, but the maximum amount of Ru (ratio of increment of pore water pressure Δu to the effective stress of soil σ’) in the soil increases and the acceleration does not change. Increasing the embedded depth of foundation caused a decrease in settlement and tilt. Using more number of gravel columns under foundation in the soil, caused an increase in acceleration and the maximum amount of Ru, settlement and tilt decreased. The storm loading also had no effect on pore water pressure and acceleration in the soil. The amount of settlement and tilt due to storm loading was low in foundation and structure.
