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Title: The effect of unsteady sea conditions on tidal stream turbine loads and durability
Author: Nevalainen, Thomas Mikael
ISNI:       0000 0004 6349 7018
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2016
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This thesis explores the effect that the unsteady hydrodynamics of the marine climate has on the load generation and subsequent durability of horizontal axis tidal stream turbines (TSTs). This is achieved through several campaigns of numerical modelling where the methodologies adopted were chosen on the principle of maximising the computational efficiency, allowing for time-domain durability calculations to be performed. The inflow was modelled by a variety of engineering wave models coupled with the underlying current profi€les and the rotor loads were resolved using blade element momentum theory (BEMT). The rotor loads were then fed to a six degree of freedom drive train model to analyse the stresses and the fatigue damage in the system. In order to inform on the input-output relationships of a turbine’s operating conditions and the generated loads, a sensitivity analysis was performed on the BEMT model to show each input parameter’s influence on the loading. The results showed that the rotor radius, blade pitch, signifi€cant wave height, inflow velocity and shear current steepness were the dominant factors in regards to the loading. Furthermore,an investigation on the internal contact stresses in the turbine’s main bearing found that simplifying the turbine loading problem down to a one-dimensional phenomenon gave a signi€ficant underestimation in the internal loads. It is concluded that to accurately model the internal loads on a TST, the full spatial range of the rotor loads including the o‚-axis components, must be incorporated in the structural modelling to avoid under prediction of the stresses and the related over predictions of the resulting fatigue life. The standard fatigue analysis techniques used in this work were also identifi€ed as possibly being unsuitable for the highly dynamic marine climate and suggestions on how to address this issue are provided.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral