Conditional Reliability Analysis of a Semi-Submersible Mooring Line With Random Hydrodynamic Coefficients

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Sheng Xu ◽  
A. P. Teixeira ◽  
C. Guedes Soares
Keyword(s):  
Reliability Analysis ◽  
Line Tension ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Global Maximum ◽  
Hydrodynamic Drag ◽  
Dynamic Simulations ◽  
Wave Condition ◽  
Drag Coefficients ◽  
Fully Coupled

Abstract In this paper, a detailed procedure to study the mooring line conditional strength reliability of a semi-submersible platform in a 100-year sea state is presented. A fully coupled analysis is conducted to calculate the mooring line tension of a deepwater semi-submersible floating system operated in the 100-year wave condition in South China Sea. 3-h extreme mooring line tensions are estimated by the average conditional exceedance rate (ACER) method from the data obtained by 10 and 20 min fully coupled dynamic simulations, and the results are validated by the global maximum method. A kriging metamodel is trained to predict the 3-h mooring line extreme tension taking into account the effect of random hydrodynamic drag coefficients. The hydrodynamic sampling points are generated by Latin hypercube sampling technique. A reliability analysis is carried out by Monte Carlo simulation considering the random hydrodynamic drag coefficients and mooring line breaking strength.

Reliability Analysis of Short Term Mooring Tension of a Semi-Submersible System

2018 ◽  
Author(s):  
Sheng Xu ◽  
C. Guedes Soares ◽  
Ângelo P. Teixeira
Keyword(s):  
Reliability Analysis ◽  
Line Strength ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Global Maximum ◽  
Hydrodynamic Drag ◽  
Sampling Point ◽  
Wave Condition ◽  
Drag Coefficients ◽  
Fully Coupled

A detail procedure to study mooring line strength reliability is presented. A fully coupled analysis is carried out to get the mooring tensions of a deep water semi-submersible floating systems operated in 100 year wave condition in South China Sea. The ACER method is applied to predict the 3h extreme mooring tension, and the results are validated by global maximum method. The hydrodynamic sampling points are generated by Latin Hypercube Sampling technique. The 3h extreme mooring tension is calculated by the ACER method with 10 minutes fully coupled dynamic simulation for each sampling point. The Kriging meta model method is trained to predict 3h mooring extreme tension under the effects of random hydrodynamic drag coefficients. A reliability analysis is carried out by implementing Monte Carlo simulation with the random hydrodynamic drag coefficients and mooring breaking strength considered.

The Dynamic Motion of the OC4 Floating Turbine with Different Incident Wave and Wind Directions in a Mooring System Failure Condition in Numerical Model

2020 ◽  
Author(s):  
Tzu-Ching Chuang ◽  
Wen-Hsuan Yang ◽  
Yi-Hong Chen ◽  
Ray-Yeng Yang
Keyword(s):  
Steady State ◽  
Line Tension ◽  
Time Domain Analysis ◽  
Mooring Line ◽  
Second Phase ◽  
Mooring System ◽  
System Failure ◽  
Floating Platform ◽  
Initial Tension ◽  
Wave Condition

<p><span>In this paper, the commercial software Orcaflex is used to simulate the motion behavior of the OC4 floating platform, and the floater stability and mooring line tension after the mooring system failure. In the time domain analysis, the discussion is divided into three phases—the first phase (before the tether failure), the second phase (before the tether failure, before reaching the new steady-state), and the third phase (after reaching the new steady-state). The motion characteristics and tension values at different stages were observed. In this study, only a 50-year return period wave condition is used as an input condition and simulating 11 different incident wind and wave directions. The numerical results are presented in the trajectory map and the table. About the tension of the mooring line, after the mooring system fails, it is notable that the mooring line tension will first decrease and then increase slightly above the initial tension value. In other words, the mooring system may survive after the failure of one mooring line and got a new balance of it. However, the tension amplitude will be higher than the first stage in the new balance and it will likely increase the risk of mooring line fatigue.</span></p>

Towards the Integration of Analysis and Design of Mooring Systems and Risers: Part I — Studies on a Semisubmersible Platform

2002 ◽  
Author(s):  
Stael Ferreira Senra ◽  
Fabricio Nogueira Correa ◽  
Breno Pinheiro Jacob ◽  
Ma´rcio Martins Mourelle ◽  
Isai´as Quaresma Masetti
Keyword(s):  
Motion Analysis ◽  
Production Systems ◽  
Companion Paper ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Mooring System ◽  
Analysis And Design ◽  
Design Methodologies ◽  
Campos Basin ◽  
Fully Coupled

The objective of this paper is to study different analysis methodologies for the design of floating production systems. The main issues are the use of uncoupled and coupled analysis methods, and the integration in the analysis and design of the mooring system and the risers. This paper is a companion to another paper also presented in the OMAE2002 Conference [1] The present paper begins describing a “basic” classic, uncoupled methodology, and proceeds with comments on some refinements in the representation of the behavior of the lines in the motion analysis of the vessel. Comments regarding the introduction of some level of integration between mooring line and riser behavior are also presented. These issues are illustrated with studies applying some of the considered design methodologies to the P-18 semi-submersible platform in Campos basin. The companion paper [1] proceeds describing a fully coupled methodology, and some hybrid methodologies that combine coupled and uncoupled analysis tools, and illustrates their application to a DICAS system for deepwater applications in Campos basin.

Fully Coupled Analysis of Ship Motion and Sloshing Tanks in Regular and Irregular Waves

2018 ◽  
Author(s):  
Yuan Zhuang ◽  
Decheng Wan
Keyword(s):  
Open Source ◽  
Ship Motion ◽  
Irregular Waves ◽  
Coupled Analysis ◽  
Regular Waves ◽  
Wave Condition ◽  
Sloshing Phenomenon ◽  
Fully Coupled ◽  
Fully Coupled Analysis ◽  
External Wave

Fully coupled analysis of ship motion and sloshing tank in waves is essential for floating structures which store and transports natural gas. For partially filled tanks would generate violent sloshing due to external wave excitation, and the sloshing flow can consequently affect ship motion. Therefore, how to evaluate ship motion and sloshing phenomenon in tank is of great importance, especially under real sea state, when wave induced sloshing would be more complex than that under linear wave condition. In the present work, a CFD-based method is applied to simulate both external wave field and inner sloshing tank field in regular waves and irregular waves. The ship is a simplified FPSO, with two LNG tanks. All the numerical simulations are carried out by the in-house CFD code naoe-FOAM-SJTU, which is developed on the open source platform OpenFOAM. The regular and irregular wave condition is simulated based on open source toolbox waves2Foam. The main parameters of coupling effect of ship motion and sloshing tank, such as the time history of ship motion, sloshing phenomenon in tanks are obtained by our computations. The predicted results for the coupling effects of ship motion and sloshing tank in regular waves are compared with the corresponding experimental data. The comparison is satisfactory and shows that the CFD method has the ability to simulate coupling effects of ship motion and sloshing tank in waves.

Study on Weight Control Methods of Single Point Mooring System of FPSO in Deepwater

2015 ◽  
Author(s):  
Yuan Hongtao ◽  
Zeng Ji ◽  
Chen Gang ◽  
Mo Jian ◽  
Zhao Nan
Keyword(s):  
Weight Control ◽  
Linear Time ◽  
Single Point ◽  
Line Tension ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Mooring System ◽  
Control Methods ◽  
Analysis Method ◽  
Mooring Lines

This paper applies 3D potential theory and non-linear time domain coupled analysis method to analyze motion response of FPSO and dynamic response of mooring line of single mooring system. In addition, respectively to calculate mooring line tension of tension type and composite mooring line type and added buoy in mooring line. There the paper analyze different mooring lines to affect on the weight of single point mooring system of deepwater FPSO. Which expects to provide a theoretical basis for single point mooring system design and weight control.

Experimental Study on Mooring Manner and Safety Operation for 450,000DWT Supertanker

2014 ◽  
Vol 580-583 ◽  
pp. 2124-2128
Author(s):  
Bing Jiang ◽  
Xuan Jun Huang ◽  
Ying Xue Lv ◽  
Xian Bo Zhang
Keyword(s):  
Experimental Study ◽  
Model Test ◽  
Line Tension ◽  
Mooring Line ◽  
Physical Model Test ◽  
Working Ability ◽  
Steel Cable ◽  
Wave Condition ◽  
Oil Tank ◽  
Safety Operation

At present, many oil tank wharfs of 300,000DWT which taken the maximum of 450,000DWT supertanker into account had been built in our country. In this paper, through the physical model test on 450,000DWT supertanker, the mooring line tension with different mooring arrangements, cable diameters and cable materials were studied and the wave condition for the supertanker safety operation was given. The results showed that: on the same wave condition, to increase the steel cable’s diameter could reduce the ship’s movements, which could enhance the ability to operation. In addition, using the combination cable on the same diameter instead of the steel cable could reduce the tension of mooring line and increase the working ability effectively. The research results can provide reference and guidance for the future of supertankers mooring operation.

Numerical Analysis of Submersible Mussel Raft for Exposed Marine Environment

2017 ◽  
Author(s):  
Xinxin Wang ◽  
Fenfang Zhao ◽  
Yanli Tang ◽  
Liuyi Huang ◽  
Rong Wan ◽  
...  
Keyword(s):  
Finite Element ◽  
Marine Environment ◽  
Line Tension ◽  
Hydrodynamic Characteristics ◽  
Mooring Line ◽  
Mooring Lines ◽  
Finite Element Program ◽  
Wave Condition ◽  
Waves And Currents ◽  
Submergence Depth

To study the hydrodynamic characteristics of the submersible mussel raft in waves and currents, the numerical model of the submersible raft was established based on the finite element method and kinematics theory. The finite element program Aqua-FE™ was applied to simulate the impacts of waves and currents on the hydrodynamic responses of the surface and submerged rafts, respectively. Morison Equation was applied to compute the tension of the mooring lines. Apart from the wave condition, the flow has a significant effect on the mooring line tension of the submersible raft. The submerged raft is useful for reducing the mooring loads. The submergence depth of the mussel raft can be adjusted depending on the marine environment. The results show that the submerged raft wave response was found to be reduced relative to the surface raft. The vertical motion of mussel rope connection points was significantly reduced by submergence, resulting in reduced potential for mussel drop-off. Compared the performance of the submerged raft in the same condition, the motion amplitude of the framework of the raft decreased significantly while increasing the submergence depth. At the same period, the trend of the decrease followed by levelling off with an increasing wave height. However, the submergence depth had no significant effect on the mooring line tension.

The Effect on Hydrodynamic Performance of Multi-Point Moored FPSO in Swell Condition of West Africa

2014 ◽  
Author(s):  
Chen Gang ◽  
Yuan Hongtao ◽  
Dou Peilin ◽  
Zeng Ji ◽  
Zhu Jian ◽  
...  
Keyword(s):  
West Africa ◽  
Frequency Response ◽  
Linear Time ◽  
Incident Angle ◽  
Low Frequency ◽  
Line Tension ◽  
Hydrodynamic Performance ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Wind Sea

The paper respectively study the effect on hydrodynamic performances of FPSO under only swell and only wind-sea based on 3D potential theory and non-linear time domain coupled analysis method. The analysis results indicated that swell and wind-sea act as the same role in low frequency response. Swell is key factor in wave frequency response. Incident angle of swell evidently effects on mooring line tension. So it is necessary that we should consider swell and wind-sea at the same time in studying the hydrodynamic performances of FPSO in West Africa. The study offered an important reference on FPSO hydrodynamic performances analysis in West Africa.

Less=Moor: A Time-Efficient Computational Tool to Assess the Behavior of Moored Ships in Waves

2017 ◽  
Author(s):  
Yijun Wang ◽  
Alex van Deyzen ◽  
Benno Beimers
Keyword(s):  
Dynamic Response ◽  
Research Effort ◽  
Equations Of Motion ◽  
Line Tension ◽  
Mooring Line ◽  
Induced Response ◽  
Wave Forces ◽  
Computational Tool ◽  
The Time Domain ◽  
Nonlinear Equations Of Motion

In the field of port design there is a need for a reliable but time-efficient method to assess the behavior of moored ships in order to determine if further detailed analysis of the behavior is required. The response of moored ships induced by gusting wind and/or waves is dynamic. Excessive motion response may cause interruption of the (un)loading operation. High line tension may cause lines to snap, introducing dangerous situations. A (detailed) Dynamic Mooring Analysis (DMA), however, is often a time-consuming and expensive exercise, especially when responses in many different environmental conditions need to be assessed. Royal HaskoningDHV has developed a time-efficient computational tool in-house to assess the wave (sea or swell) induced dynamic response of ships moored to exposed berths. The mooring line characteristics are linearized and the equations of motion are solved in the frequency domain with both the 1st and 2nd wave forces taken into account. This tool has been termed Less=Moor. The accuracy and reliability of the computational tool has been illustrated by comparing motions and mooring line forces to results obtained with software that solves the nonlinear equations of motion in the time domain (aNySIM). The calculated response of a Floating Storage and Regasification Unit (FSRU) moored to dolphins located offshore has been presented. The results show a good comparison. The computational tool can therefore be used to indicate whether the wave induced response of ships moored at exposed berths proves to be critical. The next step is to make this tool suitable to assess the dynamic response of moored ships with large wind areas, e.g. container ships, cruise vessels, RoRo or car carriers, to gusting wind. In addition, assessment of ship responses in a complicated wave field (e.g. with reflected infra-gravity waves) also requires more research effort.

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