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

Abstract

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.

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