When preliminarily investigating offshore wind turbine tower concepts it is common to develop optimization software for determining the best possible structural layout. This type of optimization procedure requires a large number of iterations to determine the best possible design and can be quite time consuming, particularly if the dynamic performance of each structure is to be investigated using an aero-hydro-servo-elastic type solver. When performing this type of “dynamic optimization” it is convenient to simply assume fixed boundary conditions at the soil-structure interface and ignore the dynamic properties of the foundation. Using fixed conditions allows for each of the layouts to be compared quickly and makes the computer models simple to create and more efficient in computation than if the foundation is included. Alternatively, the foundations of offshore wind turbine support structures can be represented with several different methods of varying complexity and detail. The most widely used method is the use of a distributed spring model commonly known as the p-y method. This approach is the primary method in most offshore wind turbine design standards for determining the static and cyclic reaction of offshore piles. In this work, two offshore wind support structure layouts are modeled and analyzed in the wind turbine analysis program HAWC2. Dynamic time series analyses under operating conditions are carried out for each tower with fixed conditions and with foundation models based on the p-y method in order to determine the appropriateness of utilizing fixed foundation conditions for optimization procedures.

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