8/10/2019 Coupled Analysis of a Semisubmersible Platform With Two Types of Mooring Systems

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Coupled Analysis of a Semisubmersible Platform with Two Types of Mooring Systems

Dongsheng Qiao1, Fei Wu

2, Jinping Ou

1

1. Deepwater Engineering Research Center, Dalian University of Technology, Dalian, China2. Luxun Academy of Fine Arts, Shenyang, China

.

ABSTRACT

Mooring system design selection of a semi-submersible platform whichworks in 1500m water depth of South China Sea was carried out. The

3-dimension hydrodynamic finite element model of the semi-

submersible platform is built firstly. The nonlinear time domain

coupled analysis between the semi-submersible platform and itsmooring system is calculated through numerical simulation. The wave

forces are calculated under diffraction theory by boundary element

method, and the wind forces are obtained from the wind tunnel test

with the model scale 1:100, and the current forces are considered assteady. Two types of mooring system have the similar static restoring

force characteristics, the same mooring line number and angle

arrangement. The single mooring line is respectively consisting ofchain-wire-chain and chain-polyester-chain. The polyester rope is

adopted as the substitute for the wire while other conditions are keptunchanged. The mooring system is considered under intact and

damaged conditions. The influences of different mooring models on the

motions of the semi-submersible platform and mooring line tension areinvestigated. The specific numerical simulation results would behelpful for the preliminary design of semi-submersible platform.

KEY WORDS: mooring system; semi-submersible platform; timedomain; coupled analysis.

INTRODUCTION

Semi-submersible platform has been successfully installed and operatedin many practical projects for oil and gas production. Comparing with

other floating platforms, semi-submersible has little water plane whichcould suffer small wave force. So far, the semi-submersible platform

has developed six generation since 1961, and now it is still the mostused type of floating platform in the world, especially when it is

worked as drilling platform. In 2012, the HYSY981 semi-submersible

platform, which represents the substantial development to deepwater

offshore oil industry for China, has worked in service.

Station keeping system design plays an important role in the whole

design of the floating platform. Due to the relative expensive price, the

mooring system is still widely applied within the water depth of 1500m.In the preliminary design stage, the choices of different types of

mooring systems, as well as the materials used for the mooring line,

need investigating through comparative analysis. Tong et al. (2009)

compared the responses of a semi-submersible platform respectivelyusing catenary and taut mooring system. Sun and Wang (2010) studied

on the responses of a spar platform under equally distributed mooring

method and grouped mooring method. Qiao et al. (2012) compared the

global responses of a semi-submersible platform using three types ofmooring systems, which are catenary, semi-taut, and taut. These

researches mainly focus on the choices of different mooring types, and

give some suggestions for the preliminary design selection for themooring system of floating platform.

In recent years, the common used materials for mooring line are chain,wire, synthetic fiber, and the traditional catenary mooring system is still

widely used (Mohanraj et al. 2011, Beck and Vandenworm 2011).

Mooring lines are usually made up of different materials, such as thecombination of chain-wire-chain or chain-polyester-chain. Because of

the lightweight and high strength to weight ratios, the polyester ropeshave significant advantages over wires. Meanwhile, the corresponding

other problems may be introduced, due to the complex dynamiccharacteristics of polyester.

The coupling effects between a floating platform and its mooring

system has been investigated by many scholars, and the couplingeffects should be considered in the responses predicting of floating

platform (Paulling and Webster 1986, Kim et al. 2001a, Kim et al.

2001b, Kim et al. 2001c,). The coupled dynamic analysis has beendeveloped to the fully-coupled time domain approach (Chakrabarti et al.

1996, Senra et al. 2002, Garrett 2005, Li et al. 2010, Yang et al. 2012).

In this work, globalresponses analysis of a semi-submersible platformrespectively using chain-wire-chain and chain-polyester-chain mooring

system are calculated. Two types of hybrid mooring systems have thesimilar static restoring force characteristics, the same mooring line

number and angle arrangement. The dynamic coupling effects between

the semi-submersible platform and its mooring lines are investigated

through numerical simulation method which has been validated through

993

Proceedings of the Twenty-fourth (2014) I nternational Ocean and Polar Engineeri ng Conference

Busan, Korea, June 15-20, 2014

Copyri ght 2014 by the International Society of Of fshore and Polar Engineers (I SOPE)

I SBN 978-1 880653 91-3 (Set); I SSN 1098-6189 (Set)

www.isope.org