Hydrodynamic scaling and wave force estimation of offshore structures
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RESEARCH PAPER
Hydrodynamic scaling and wave force estimation of offshore structures Jifu Zhou1,2 · Ling Chen1,2 · Xu Wang1 Received: 9 June 2020 / Revised: 13 August 2020 / Accepted: 8 September 2020 © The Chinese Society of Theoretical and Applied Mechanics and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Offshore structures are generally classified as small-scale structures or large-scale structures. Their wave forces are then estimated by Morison equation and diffraction/radiation theories, respectively. However, the classification criterion is not well quantified. In the present paper, a numerical wave flume is established to simulate the wave forces acting on a fixed and vertical surface-piercing circular cylinder under linear waves. By solving Navier–Stokes equation and Euler equation with free surface involved, respectively, the viscous force and inertia force are separated accurately. The variation of viscous force and inertia force with the cylinder diameter to wave length ratio is discussed in detail. The scale intervals for significant viscous and diffraction effects are given. The error caused by neglecting viscous and diffraction forces is quantitatively analyzed. Based on these analysis, the concept of medium-scale structure is proposed and the classification criteria for small-, mediumand large-scale structures are given. In the meantime, the estimation methods of wave forces for different scales of structures are suggested. Keyword Wave force · Viscous effect · Diffraction effect · Medium-scale structure · Numerical wave flume
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1 Introduction How to accurately estimate wave loads of an offshore structure is of primary importance in offshore engineering design. The components of wave loads are very complex. They are significantly influenced by viscous, diffraction, radiation and nonlinear effects, etc. These effects have important impact on the accurate estimation of wave loads on offshore structures. In order to clarify the composition and mechanism of wave loads, hydrodynamic and structural parameters have to be considered carefully. A typical example of investigating wave loads on a structure is to consider a fixed and vertical surface-piercing circular cylinder in the flow field of a regular wave.
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Jifu Zhou [email protected] CAS Key Laboratory for Mechanics in Fluid Solid Coupling Systems, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China School of Engineering Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
A simple dimensional analysis shows that any timeinvariant force F on a fixed body may be written as follows [1] F f ρg H D 2
d H D , , , Re , L L L
(1)
where Re is a characteristic Reynolds number, D the diameter of the cylinder, L the wavelength, H the wave height, d the water depth under still water level, ρ the density of water, g the acceleration due to gravitation. The wave depth parameter d/L and the wave steepness H/L can determine the incident wave. The di
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