The behavior of subsea equipment has been widely studied by companies to minimize risks during subsea installation, which brings huge costs to the operation. The prediction of equipment motions typically is accomplished by utilizing either commercial software or recommended practices from Classification Societies to comply with the minimum requirements for launching operations. This paper analyzes subsea installation in time and frequency domains using experimental, numerical, and analytical approaches. Experiments have been carried out at Instituto de Pesquisas Tecnológicas (IPT) to investigate the dependency of drag and added mass coefficients on Keulegan-Carpenter number and at Laboratory of Waves and Currents (LOC-COPPE/UFRJ) to study equipment and cable responses on the installation. A numerical model is made in OrcaFlex^® for determining the transmissibility of displacement and force in function of frequency ratio, and the time series of manifold responses. Linearized models from DNV [1] and the so-called natural KC (proposed in the present paper) are taken in the investigation and compared to previous methodologies. The natural KC approach arises as an innovative way of investigating subsea equipment as the literature only provides parametric analysis considering an arbitrary KC value (i.e., Pestana et al. [2]). The analyses notice a good agreement among experiments, OrcaFlex^® model and natural KC model whereas the curves found by the DNV method usually overpredict the response of subsea equipment, especially around resonance region.

This study presents a comprehensive parametric optimization of the blade geometry for the so-called Vertical Axis Autorotation Current Turbine (VAACT) using Computational Fluid Dynamics (CFD) simulations at high-blockage conditions. The optimization process aimed to minimize the resisting torque produced by the returning blade, the major contributor to performance loss in drag-type vertical axis turbines. The investigation was first conducted to assess the effects of maximum camber and its position on turbine efficiency. A response surface relating the power coefficient ($C_P$) to maximum camber (M), camber position (P), and tip-speed ratio ($TSR$) was then generated and used as input for the optimization routine. The optimal configuration was M = 40%, P = 65%, and $TSR$ = 1.06, achieving an efficiency of 40.68% at 21.4% blockage ratio. The enhanced blade demonstrated a 21% improvement in performance compared to the conventional S-shaped profile, primarily due to the reduction in resisting torque during the returning phase. The intracycle analysis showed that the optimized turbine allowed a better distribution of hydrodynamic effects along the cycle, improving efficiency. Flow field analysis confirmed that the optimized geometry delays vortex shedding and reduces pressure gradients along the returning blade, leading to improved hydrodynamic behavior. The results demonstrate this procedure offers an effective way for the design of vertical axis hydrokinetic turbines.

This study presents a comprehensive parametric optimization of the blade geometry for the so-called Vertical Axis Autorotation Current Turbine (VAACT) using Computational Fluid Dynamics (CFD) simulations at high-blockage conditions. The optimization process aimed to minimize the resisting torque produced by the returning blade, the major contributor to performance loss in drag-type vertical axis turbines. The investigation was first conducted to assess the effects of maximum camber and its position on turbine efficiency. A response surface relating the power coefficient (C_P) to maximum camber (M), camber position (P), and tip speed ratio (TSR) was then generated and used as input for the optimization routine. The optimal configuration was M = 40%, P = 65%, and TSR = 1.06, achieving an efficiency of 40.68% at 21.4% blockage ratio. The enhanced blade demonstrated a 21% improvement in performance compared to the conventional S-shaped profile, primarily due to the reduction of resisting torque during the returning phase. The intra-cycle analysis showed that the optimized turbine allowed a better distribution of hydrodynamic effects along the cycle, improving efficiency. Flow field analysis confirmed that the optimized geometry delays vortex shedding and reduces pressure gradients along the returning blade, leading to improved hydrodynamic behavior. The results demonstrate this procedure offers an effective way for the design of vertical axis hydrokinetic turbines.