Marine turbines -- Mathematical models

Several modifications have been implemented to numerical simulation codes based on
blade element momentum theory (BEMT), for application to the design of ocean current
turbine (OCT) blades. The modifications were applied in terms of section modulus and
include adjustments due to core inclusion, buoyancy, and added mass. Hydrodynamic loads
and mode shapes were calculated using the modified BEMT based analysis tools. A 3D
model of the blade was developed using SolidWorks. The model was integrated with
ANSYS and several loading scenarios, calculated from the modified simulation tools, were
applied. A complete stress and failure analysis was then performed. Additionally, the
rainflow counting method was used on ocean current velocity data to determine the loading
histogram for fatigue analysis. A constant life diagram and cumulative fatigue damage
model were used to predict the OCT blade life. Due to a critical area of fatigue failure being
found in the blade adhesive joint, a statistical analysis was performed on experimental
adhesive joint data.

The research presented in this thesis utilizes Blade Element Momentum (BEM) theory with a
dynamic wake model to customize the OrcaFlex numeric simulation platform in order to allow
modeling of moored Ocean Current Turbines (OCTs). This work merges the advanced cable modeling
tools available within OrcaFlex with well documented BEM rotor modeling approach creating a
combined tool that was not previously available for predicting the performance of moored ocean
current turbines. This tool allows ocean current turbine developers to predict and optimize the
performance of their devices and mooring systems before deploying these systems at sea. The BEM
rotor model was written in C++ to create a back-end tool that is fed continuously updated data on the
OCT’s orientation and velocities as the simulation is running. The custom designed code was written
specifically so that it could operate within the OrcaFlex environment. An approach for numerically
modeling the entire OCT system is presented, which accounts for the additional degree of freedom
(rotor rotational velocity) that is not accounted for in the OrcaFlex equations of motion. The properties
of the numerically modeled OCT were then set to match those of a previously numerically modeled
Southeast National Marine Renewable Energy Center (SNMREC) OCT system and comparisons were
made. Evaluated conditions include: uniform axial and off axis currents, as well as axial and off axis wave fields. For comparison purposes these conditions were applied to a geodetically fixed rotor, showing nearly identical results for the steady conditions but varied, in most cases still acceptable accuracy, for the wave environment. Finally, this entire moored OCT system was evaluated in a dynamic environment to help quantify the expected behavioral response of SNMREC’s turbine under uniform current.