Ocean currents--Mathematical models.

A comprehensive study was performed to overcome the design issues related to
Ocean Current Turbine (OCT) blades. Statistical ocean current models were developed in
terms of the probability density function, the vertical profile of mean velocity, and the
power spectral density. The models accounted for randomness in ocean currents, tidal
effect, and ocean depth. The proposed models gave a good prediction of the velocity
variations at the Florida Straits of the Gulf Stream.
A novel procedure was developed to couple Fluid-Structure Interaction (FSI) with
blade element momentum theory. The FSI effect was included by considering changes in
inflow velocity, lift and drag coefficients of blade elements. Geometric non-linearity was
also considered to account for large deflection. The proposed FSI analysis predicted a
power loss of 3.1 % due to large deflection of the OCT blade. The method contributed to
saving extensive computational cost and time compared to a CFD-based FSI analysis. The random ocean current loadings were calculated by considering the ocean
current turbulence, the wake flow behind the support structure, and the velocity shear. The
random ocean current loadings had large probability of high stress ratio. Fatigue tests of
GFRP coupons and composite sandwich panels under such random loading were
performed. Fatigue life increased by a power function for GFRP coupons and by a linearlog
function for composite sandwich panels as the mean velocity decreased. To accurately
predict the fatigue life, a new fatigue model based on the stiffness degradation was
proposed. Fatigue life of GFRP coupons was predicted using the proposed model, and a
comparison was made with experimental results.
As a summary, a set of new design procedures for OCT blades has been introduced
and verified with various case studies of experimental turbines.

Mangrove trees play a prominent role in coastal tropic and subtropical regions, providing habitat for many organisms and protecting shorelines against storm surges, high winds, erosion, and tsunamis. The motivation of this proposal is to understand the complex interaction of mangrove roots during tidal flow conditions using simplified physical models. In this dissertation, the mangrove roots were modeled with a circular array of cylinders with different porosities and spacing ratios. In addition, we modeled the flexibility of the roots by attaching rigid cylinders to hinge connectors. The models were tested in a water tunnel for a range of Reynolds number from 2200 to 11000. Additionally, we performed 2D flow visualization for different root models in a flowing soap film setup. We measured drag force and the instantanous streamwise velocity downstream of the models. Furthermore, we investigated the fluid dynamics downstream of the models using a 2-D time-resolved particle image velocimetry (PIV), and flow visualization. The result was analyzed to present time-averaged and time-resolved flow parameters including the velocity distribution, vorticity, streamline, Reynolds shear stress and turbulent kinetic energy. We found that the frequency of the vortex shedding increases as the diameter of the small cylinders decreases while the patch diameter is constant, therefore increasing the Strouhal number, St=fD/U By comparing the change of Strouhal numbers with a single solid cylinder, we introduced a new length scale, the “effective diameter”. In addition, the effective diameter of the patch decreases as the porosity increases. In addition, patch drag decreases linearly as the spacing ratio increases. For flexible cylinders, we found that a decrease in stiffness increases both patch drag and the wake deficit behind the patch in a similar fashion as increasing the blockage of the patch. The average drag coefficient decreased with increasing Reynolds number and with increasing porosity. We found that the Reynolds stress (−u′v′) peak is not only shifted in the vortex structure because of shear layer interference, but also the intensity was weakened by increasing the porosity, which causes a weakening of the buckling of vorticity layers leading to a decline in vortex strength as well as increase in wake elongation.