Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Numerical and Experimental Studies of Wave Slamming on Braces of Semi-submersible Platform underTowing Condition
Fali Huo a, Changdong Wei a, Jingxi Zhang a, Zhongxiang Shen b*(a. School of Naval Architecture and Ocean Engineering; b.School of Civil Engineering and Architecture, Jiangsu University of Science andTechnology, Zhenjiang, Jiangsu, China)

studies were conducted in order to investigate the wave slamming load
based on the potential flow theory and the Morison equation. Wang et al.
(2018) combined the motion response of platform with the formula ofslamming pressure coefficient, put forward the calculation method ofwave slamming load of platform based on potential flow theory andcarried out a certain study on the effect of interference effect in the nearfield. Ghamry et al. (1963) and Hayatdavoodi et al. (2015) studied thewave slamming load of marine structures by simplifying the structures
to flat and box structures. Considering the strong nonlinearity andrandomness of wave slamming and the structural complexity of marine
structures, the calculation of the load on platform was modified. Due tothe limitations of potential flow theory, the above researches did notconsider the influence of fluid viscosity, and it is difficult to simulate therun up phenomena and large-scale deformation of free surface. But CFD
method can solve these problems well.
At present, many researchers have done extensive studies on wave
slamming of floating structures based on CFD method. Numericalsimulation of waves based on the VOF (Volume of Fluid) method using
the Reynolds Averaged Navier-Stokes (RANS) equation has been
proved reliable. Wang et al. (2017) studied the wave slamming of asimple plate by using the VOF method. The characteristics of theslamming pressure and the change of free surface of the plate structureduring water entry were obtained. Abdussamie N et al. (2014, 2016, 2017)
studied the effect of wave loads on the inner deck on the motion responseof platform and slamming pressure, and found there was significant
correlation between these parameters. It can be seen that the global loadon the deck of platform will increase significantly with the decrease of
the height of the hydrostatic air gap. But the points on the deck did notquite suit these rules. Danmeier et al. (2008) discussed the importance of
nonlinearity by comparing the results of the second-order diffraction
code (WAMIT) and the fully nonlinear CFD program (Com FLOW).
The results show that the nonlinearity depends on the wave steepness
and wavelength. The run up of wave and air gap phenomena werepredicted reasonably. In addition, Iwanowski et al. (2009) set up thenumerical simulation by commercial software COM and compared withthe experimental results. The run up phenomena of wave around thevertical column of a semi-submersible platform was studied. The
climbing, rolling and deformation of the waves around the column weresimulated accurately. However, the nonlinear coupled motion between
wave and platform is not considered with this method. Bredmose et al.
(2009) and Ma et al. (2016) found that the slamming load significantly
increased when the breaking waves carried the air and slammed into thestructure. However, the above studies mainly consider the slamming

ABSTRACTThe wave slamming on a slender structure such as brace of semisubmersible platform has great influence on the safety of the structureduring the towing condition. Compared with the potential flow theory,
the unsteady computational fluid dynamics (CFD) method is moreaccurate to solve these complex nonlinear problems, such as wave
climbing, roll-over and breakage. In this paper, the model test of wave
slamming on braces of semi-submersible platform was conducted in thetowing tank. A numerical simulation using CFD method in a threedimensional numerical tank was established to investigate the wave
slamming of braces under towing conditions too. The sensitivities of thewave slamming at different wave steepness and wave direction angles
under the towing conditions were analyzed. It is found that wave
steepness and wave direction angles have significant effects on the wave
slamming pressure of the brace. The slamming pressure of the bracedecreases clearly with the decrease of the wave steepness parameter(KA). The reduction rate of peak value of wave slamming pressure in
front of the brace is obviously bigger than that of the bottom of the brace.
The wave slamming pressure on the brace is small under the oblique
waves. The superposition of waves and the increase of wave height at
the front of the brace lead to the decrease of negative pressure under
oblique wave conditions. The peak slamming pressure at all monitoring
points becomes smaller and smaller with the increasing of the wave
direction angle. Through numerical simulation, the cloud map ofpressure distribution of the transient brace was obtained, and thedistribution characteristics of the large slamming pressure at both endsof the brace were obtained. The results of this paper can provide areference for analyzing and predicting the slamming pressure on bracesof semi-submersible platform in the complex towed conditions.

KEY WORDS: wave slamming; semi-submersible platform;
towing condition; CFD method; numerical simulation.
1. Introduction
Semi-submersible platform can be used as an effective deep-water oil
and gas exploitation system with cost efficiency and structural reliability.
In harsh environmental conditions, the platform often encounters
extreme waves, which cause wave slamming pressure and threaten thestructural integrity. In general, the mechanism of wave slamming is very
complicated and some complex nonlinear problems, such as wave
climbing, roll-over and breakage must be fully considered. A lot of2241