Numerical Investigation of the Flow Features Around Heave Plates Oscillating Close to a Free Surface or Seabed

Abstract

Performance of heave plates used in offshore structures is strongly influenced by their added mass and damping, which are affected by proximity to a boundary. A previous paper by the authors presented numerical simulations of the flow around a circular solid disk oscillating at varying elevations from seabed [1]. The force calculated was used to evaluate the added mass and damping coefficients for the disk. The simulations suggest that as the structure moves closer to the seabed the added mass and damping coefficients (Ca and Cb) increases continuously. In order to understand the physics behind the added mass and damping trends, when a heave plate is moving near a seabed or closer to the free surface, the flow characteristics around the heave plate are examined numerically in this paper. Flow around oscillating disks is dominated by generation and development of phase-dependent vortical structures, characterized by the KC number and the distance from the seabed or free surface to the heave plate. Numerical calculations presented in this paper have comprised the qualitative analysis of the vortex shedding and the investigation of the links between such vortex shedding and, on one hand the damping coefficient, and on the other hand, pairing mechanisms such as the shedding angle.

Hydrodynamic coefficients and pressure loads on heave plates for semi-submersible floating offshore wind turbines: A comparative analysis using large scale models

“…It would be interesting to investigate in detail, using the CFD, the dissipation mechanisms. Such an attempt is being pursued in a recent reference [12,45].…”

Wave Induced Effects on the Hydrodynamic Coefficients of an Oscillating Heave Plate in Offshore Wind Turbines

“…This reduces risks and helps to optimize the design of the prototype platform. Hydrodynamic data on heave plates are usually reported using two non-dimensional characteristic parameters (Keulegan-Carpenter number KC and frequency parameter β) that represent the amplitude and frequency of oscillation of any heave plate configuration [6][7][8][9][10]. These dimensionless parameters of relevance are defined as [11]:…”

“…When a heave plate is brought closer to a surface either by increasing the KC value or by reducing the draft of the attached column, then some changes become apparent. Numerical studies by [10] have shown that vortices shed by heave plates when executing large amplitude oscillations can disturb an otherwise quiescent free surface. They also showed that both coefficients exhibited dramatic variations with increasing KC, which depended on the distance from the free surface.…”

Hydrodynamic Coefficients of Heave Plates, With Application to Wave Energy Conversion

“…Although the true velocity field around a heave plate is rotational, the theoretical added mass does provide a reference against which the actual added mass can be normalized. This method of normalization has been used by several authors including Lake et al [6], Garrido-Mendoza et al [14], and Tao and Dray [15].…”

“…Although it is often mentioned in the heave plate literature for oil and natural gas, β is not typically used as an independent parameter. Rather, all tests are conducted at a set β to reduce the effect of frequency dependence in added mass [7], [14].…”