Research on the Water Ridge and Slamming Characteristics of a Semisubmersible Platform under Towing Conditions

Fali Huo,Changdong Wei,Zhaojun Yuan,Chenyang Zhu,Sheng Xu

doi:10.3390/jmse10010116

Fali Huo, Changdong Wei + Show 3 more

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https://doi.org/10.3390/jmse10010116

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Abstract

During the towing of semisubmersible platforms, waves impact and superpose in front of the platform to form a ridge shaped “water ridge”, which protrudes near the platform and produces a large slamming pressure. The water ridges occur frequently in the towing conditions of semisubmersible platforms. The wave–slamming on the braces and columns of platform is aggravated due to the water ridges, particularly in rough sea conditions. The effect of water ridges is usually ignored in slamming pressure analysis, which is used to check the structural strengths of the braces and columns. In this paper, the characteristics of the water ridge at the braces of a semisubmersible platform are studied by experimental tests and numerical simulations. In addition, the sensitivity of the water ridge to the wave height and period is studied. The numerical simulations are conducted by a Computational Fluid Dynamics (CFD) method, and their accuracy is validated based on experimental tests. The characteristics of the water ridge and slamming pressure on the braces and columns are studied in different wave conditions based on the validated numerical model. It is found that the wave extrusion is the main reason of water ridge. The wave–slamming pressure caused by the water ridge has an approximately linear increase with the wave height and is sensitive to the wave period. With the increase of the wave period, the wave–slamming pressure on the brace and column of the platform increases first and then decreases. The maximum wave–slamming pressure is found when the wave period is 10 s and the slamming pressure reduces rapidly with an increase of wave period.

Highlights

With the rapid exploitation of marine resources, semisubmersible platforms have attracted more and more attention in the past decades
It is very important to analyze wave–slamming created by wave climbing under the towing condition of semisubmersible platforms in order to improve the safety and stability of the platforms
The results showed that the air has a complex effect on the uplift demand in offshore bearings and columns, which can decrease or increase even more than the total deck uplift, and an inconsistent effect on the uplift force of different structural components introduced by the same wave

Summary

Introduction

With the rapid exploitation of marine resources, semisubmersible platforms have attracted more and more attention in the past decades. Semisubmersible platforms are vulnerable to damage under extreme ocean conditions during the towing process, especially when the platform is towed in the deep sea. The waves run–up to the braces and columns, and these structures collide violently with the wave surface instantly, which give rise to a very large wave–slamming pressure. It is very important to analyze wave–slamming created by wave climbing under the towing condition of semisubmersible platforms in order to improve the safety and stability of the platforms. With the development of a numerical computation methods and computer technology, many scholars have used numerical methods to study the wave run–up and wave–slamming load suffered by marine structures. Based on the finite volume method, Pakozdi et al [1] used the commercial CFD tool Star–CCM+ to simulate a long crested breaking wave and its impact on an idealised model test setup of a rectangular cylinder and deck structure in order to test the feasibility of a numerical reconstruction of such events

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