| A computational tool has been developed by integrating National Renewable Energy Laboratory (NREL) codes, Sandia National Laboratories' NuMAD, and ANSYS to investigate a horizontal axis composite ocean current turbine. The study focused on the design, analysis, and life prediction of composite blade considering random ocean current, cyclic rotation, and hurricane-driven ocean current. A structural model for a horizontal axis FAU research OCT blade was developed. Following NREL codes were used: PreCom, BModes, ModeShape, AeroDyn and FAST. PreComp was used to compute section properties of the OCT blade. BModes and ModeShape calculated the mode shapes of the blade. Hydrodynamic loading on the OCT blade was calculated by modifying the inputs to AeroDyn and FAST. These codes were then used to obtain the dynamic response of the blade, including blade tip displacement, normal force (FN) and tangential force (FT), flap and edge bending moment distribution with respect to blade rotation. In the next step, a model was developed using NuMAD and it was used as an input file to ANSYS. Loads (FN, F T) applied to ANSYS model to perform the static and buckling analysis. It identified the regions of high stresses in the blade. Fatigue life was then predicted based on the stresses at the critical locations. Bending moment time histories were converted to stress-time histories and Goodman diagram was used to calculate life at various stress levels and ratios. Actual number of cycle was computed from the velocity-time histogram as obtained from experimental data. This allowed calculation of damage, and fatigue life of the blade was predicted using Palmgren-Miner's rule for cumulative fatigue. The OCT blade, when submerged in sea water, experiences buoyancy forces which is not accounted in NREL codes. A procedure was therefore developed to calculate buoyancy effect and adjusted the gravitational acceleration input "g" to run it on FAST. Since OCT blades rotate under water, inertia due to accelerating fluid was also considered as added mass in this investigation. This was implemented by considering an added mass coefficient. The procedures have enabled accurate determination of blade tip deflections and bending moment histories for fatigue analysis. |
