Abstract
This paper presents a numerical and experimental investigation of the second-order steady horizontal and vertical drift forces acting on cylindrical bodies in regular waves. The examined bodies are either kept restrained in front of a vertical breakwater or are considered free- floating when alone in the wave field. Two principally different approaches for mean drift forces determination are described: the momentum conservation principle and the direct integration of all pressure contributions upon the instantaneous wetted surface of the bodies, whereas, for the solution of the associated diffraction and motion radiation problems, analytical and panel methodologies are applied. The hydrodynamic interaction phenomenon between the bodies and the adjacent breakwater are taken into account by using the method of images. Theoretical and numerical results, concerning the horizontal and the vertical drift forces, are presented and compared with each other. Furthermore, additional comparisons are made with experimental data obtained during an experimental campaign at French research institute for exploitation of the sea (IFREMER), in France.
Highlights
The numerical and theoretical prediction of drift forces upon floating bodies in regular and random waves is not a recent concept
Several efforts related its importance and the determination methods have been presented in the literature since the first theoretical approach was presented in Reference [1], where the steady drift force acting on a fixed vertical circular cylinder in waves was calculated
Despite the increased interest in mean drift forces, only a few studies scaled down the experimental tests that are available in the literature
Summary
The numerical and theoretical prediction of drift forces upon floating bodies in regular and random waves is not a recent concept. The previous examples demonstrate that the mean and slowly-varying second-order wave excitations may induce significant dynamic responses on floating structures, and it is important to understand them and to develop and validate numerical and theoretical prediction methods for their accurate prediction. In order to avoid the time consuming calculation of the second-order velocity potential, a usual procedure for calculating the second-order difference-frequency excitations, introduced in Reference [7], is to simplify the QTF by representing the difference–frequency terms by means of the zero difference results, i.e., by the mean drift forces, provided that the natural frequency associated with slow-drift motions is sufficiently small In this way, the second-order problem is simplified, along with minimizing the computational effort. Indicative reviews on drift forces on several examined floating bodies or structures, using the aforementioned calculation methods, were shown in References [25,26,27]
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