Experimental Investigation of the Performance of a Tuned Heave Plate Energy Harvesting System for a Semi-Submersible Platform

Heave plates are widely used for improving the sea keeping performance of ocean structures. In this paper, a novel tuned heave plate energy harvesting system (THPEH) is presented for the motion suppression and energy harvesting of a semi-submersible platform. The heave plates are connected to the platform though a power take-off system (PTO) and spring supports. The performance of the THPEH was investigated through forced oscillation tests of a 1:20 scale model. Firstly, the hydrodynamic parameters of the heave plate were experimentally studied under different excitation motion conditions, and a force model of the power take-off system was also established through a calibration test. Then, the motion performance, control performance, and energy harvesting performance of the THPEH subsystem were systematically studied. The effects of the tuned period and PTO damping on the performance of the THPEH were analyzed. Finally, a comparison between the conventional fixed heave plate system and THPEH was carried out. The results show that a properly designed THPEH could consume up to 2.5 times the energy from the platform motion compared to the fixed heave plate system, and up to 80% of the consumed energy could be captured by the PTO system. This indicates that the THPEH could significantly reduce the motion of the platform and simultaneously provide considerable renewable energy to the platform.

Hydrodynamic Response of Buoy Form Spar With Heave Plate Near Free Surface

Hydrodynamic response of spar with appendages such as heave plate has been investigated in the past, mostly attached at the bottom of the spar. The effect of geometry and appendages on the hydrodynamic response of spar has been investigated in this article. A curved neck form with a heave plate near the free surface is proposed as an energy dissipation device for both heave and pitch responses. Numerical simulation using Computational Fluid Dynamics (CFD) is used for capturing the flow around the curved neck with heave plate and corresponding damping characteristics. CFD free decay simulations have been carried out to obtain heave and pitch damping and were noted to be higher than the conventional spar with heave plate at the bottom. Comparison of the proposed geometry and heave plate at the free surface with a conventional heave plate at the bottom of the spar has been made, and significant changes to the response and hydrodynamic characteristics have been noted. It is observed that the buoy form spar combined with the heave plate located near the surface (within 10% of the draft) helps dissipate energy and thus reduce the heave response.

Influence of an Integral Heave Plate on the Dynamic Response of Floating Offshore Wind Turbine Under Operational and Storm Conditions

The hydrodynamic performance of the floating foundation for offshore wind turbines is essential to its stability and energy harvesting. A semi-submersible platform with an integral heave plate is proposed in order to reduce the vertical motion responses. In this study, we compare the heave, pitch, and roll free decay motions of the new platform with a WindFloat-type platform based on Reynolds-Averaged Navier-Stokes simulations. The differences of the linear and quadratic damping properties between these platforms are revealed. Then, a FAST (Fatigue, Aerodynamics, Structures, and Turbulence) model with the consideration of fluid viscosity effects is set up to investigate the performance of the new platform under storm and operational conditions. The time-domain responses, motion spectra, and the mooring-tension statistics of these two platforms are evaluated. It is found that the integral heave plate can increase the viscous hydrodynamic damping, significantly decrease the heave and pitch motion responses, and increase the safety of the mooring cables, especially for the storm condition.

Hydrodynamic Study on the Damping Characteristics of Cylindrical FPSO With the Heave Plate

The heave plate setting up on the hull can effectively improve the movement performance of the cylindrical FPSO. In the research process of its damping effect, a reliable model is also needed to do the further study besides the physical model test. The objective of the present work is to establish a reasonable hydrodynamic model to investigate the damping behavior of the cylindrical FPSO with the heave plate. Based on the k-ε turbulence model and the VOF method, a three-dimensional hydrodynamic model are established to simulate the movement of the cylindrical FPSO in the offshore environment. A typical annular thin plate is set up on the bottom side of the hull as the damping structure. The available experimental data are adopted to preliminarily verify the established model. The structural pattern of the damping plate is optimized considering different widths of the plate and excitation modes. The motion amplitude, natural period and damping coefficient can be extracted from the computation and be analyzed to obtain the hydrodynamic performance of the cylindrical FPSO. From the simulation and verification, the numerical results are agreed quite well with the measured values in the model test, which proves that the model is reliable. When the cylindrical FPSO oscillates in the water body, the vortexes are generated around the heave plate and shed from it, which are the primary reason for the increase of the viscous damping. As the width of the heave plate increases, the damping coefficient and ratio increase gradually, but the natural period of the structure is basically unchanged. As for the amplitude of the motion, the variation of the damping coefficient is not obvious, and the natural period of the structure is also basically unchanged. When the motion amplitude is relatively small, the damping ratio increases gradually with the increase of the motion amplitude; while the motion amplitude is large, the amplitude increment of damping ratio tends to be flat, or even decreases. This hydrodynamic study is meaningful for the researcher and engineer to further understand the damping characteristics of the cylindrical FPSO. It can also provide some technical supports for the structural optimization design of the heave plate.