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Modelling of the viscosity effect of heave plates for floating wind turbines by hydrodynamic coefficients

Ciba Ewelina, Dymarski Paweł

Acta Mechanica et Automatica

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2023

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Vol. 17, no. 3

469--476

EN

One of the methods of modelling the movement of floating wind turbines is the use of the diffraction method. However, this method does not take into account the influence of viscosity; therefore, in many cases, it needs to be extended with a matrix of appropriate coefficients. The effect of viscosity causes both the added mass coefficient and the damping coefficient to increase. The determined coefficients were entered into the ANSYS AQWA program, and the calculation results of the transfer function determined with the use of linear and quadratic damping were presented. The results were compared with the results of the experiment, indicating greater convergence for the quadratic model.

2

Heave plates with holes for floating offshore wind turbines

Ciba Ewelina, Dymarski Paweł, Grygorowicz Mirosław

Polish Maritime Research

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2022

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nr 1

26--33

EN

The paper presents an innovative solution which is heave plates with holes. The long-known heave plates are designed to damp the heave motion of platforms. They are most often used for Spar platforms. The growing interest in this type of platform as supporting structures for offshore wind turbines makes it necessary to look for new solutions. Based on the available literature and the authors’ own research, it was concluded that the main element responsible for the damping of heave plates is not so much the surface of the plate, but its edge. Therefore, it was decided to investigate the effect of the holes in heave plates on their damping coefficient. Model tests and CFD calculations were performed for three different structures: a smooth cylinder, a cylinder with heave plates with a diameter of 1.4 times the diameter of the cylinder, and a cylinder with the same plate, in which 24 holes were cut (Fig. 1). Free Decay Tests (FDT) were used to determine the damping coefficient and the natural period of heave, and then the values obtained were compared. The full and punched heave-plate designs were also tested with regular waves of different periods to obtain amplitude characteristics. The results obtained are not unequivocal, as a complex motion appears here; however, it is possible to clearly define the area in which the damping of a plate with holes is greater than that of a full plate.

3

Heave motion of a vertical cylinder with heave plates

Ciba Ewelina

Polish Maritime Research

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2021

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nr 1

42--47

EN

The shape of a vertical cylinder resembles the classic form of a spar platform. Spar platforms are floating platforms that are successfully used in waters of great depths and have several advantages that mean they are readily used in the oil industry. Many of these advantages are also relevant to their application for offshore wind turbines, which is currently being considered. In the hydrodynamic analysis of spar platforms, the determination of their hydrodynamic coefficients plays an important role. They can be determined based on the free decay test. The study presents a method for determining the hydrodynamic coefficients of an object based on the free decay test. The results of free oscillation calculations with the help of numerical fluid mechanics tools are presented and compared with the results of the experiment and analytical solution. The application of determined coefficients and their significance for floating platforms are discussed. The influence of change in the form of an additional damping element on the behaviour of spar structures is shown.