Numerical Analysis of Floating Offshore Structures Using Overset Method

Abstract

The consciousness of global warming gradually transforms the energy dependency from fossil fuels to renewable energy resources such as waves wind solar and geothermal heat The flexible deployment range of floating offshore wind turbines makes this technology more popular in the offshore wind energy sector recently However this technique is still under development and the fluid-structure interaction (FSI) needs to be further investigated to improve the design of the floating wind turbine platform Due to the significant evolvement of computer and numerical methods in recent years computational fluid dynamics (CFD) has been widely applied to solve FSI problems Grid morphing technique is commonly used to solve FSI problems; however using this technique to deal with large body displacement problems will lead to large grid deformation and consequently induce numerical instabilities In this study overset grid was used to explore the interaction between fluid and floating structures to avoid calculation divergence due to excessive grid deformation A modified open-source CFD solver overInterFoamSponge was developed based on OpenFOAM overset grid Navier-Stokes solver overInterDyMFoam to diminish the wave reflection problem that the original solver can not handle The accuracy of the developed model was validated using a series of benchmark tests including heave decay test roll decay test and a floating structure subject to different wave conditions The influences of the overlapping zone properties on the model accuracy were discussed and the results obtained by the current study and those computed by dynamic grid solver were compared Overall the computed results presented in this study show good agreement with the results of the benchmark tests Finally this model is further used to understand the interaction between waves and three-dimensional floating submerged structures with different shapes and to analyze the dynamic motion of the structures the tension of the mooring line and the reflection and transmission of waves

Date of Award	2020
Original language	English
Supervisor	Shih-Chun Hsiao (Supervisor)