The Effect of Mooring Line Pre-Tension on FDPSO’s Motion

2016 ◽  
Author(s):  
Yanlong Sun ◽  
Huilong Ren ◽  
Zhendong Liu ◽  
Liu Yan ◽  
Zepeng Guo
Keyword(s):  
Time Series ◽  
Model Test ◽  
Time Domain ◽  
Prediction Method ◽  
Line Tension ◽  
Mooring Line ◽  
Floating Platform ◽  
Motion Response ◽  
Drilling Unit ◽  
Environment Condition

As a multifunction floating platform, Floating Drilling, Production, Storage and Offloading (FDPSO) combining the well-known Floating Production, Storage and Offloading (FPSO) with a drilling unit. For the environment condition of deep-water oilfield is very severe, the motion response and mooring line tension of FDPSO is a worthy topic of studying. In this study, the numerical time-domain coupled prediction method for the mooring line tension and motion response of FDPSO system is constructed by ANSYS AQWA software. Furthermore, the results of a model test conducted in Harbin Engimeering University are used to investigate the feasibility and validity of the commercial simulation. The effect of mooring line pre-tension on the response of FDPSO is studied by varying the pre-tension of mooring line during the calculation. The time series curve of the mooring line tension and motion response, and the comparison of motion spectrum and mooring line tension spectrum are provided in this article.

scholarly journals Numerical Study of the Influence of Fishnet Mesh Size on a Floating Platform

2020 ◽  
Vol 8 (5) ◽  
pp. 343
Author(s):  
Hung-Jie Tang ◽  
Chai-Cheng Huang ◽  
Ray-Yeng Yang
Keyword(s):  
Resonant Frequency ◽  
Time Domain ◽  
Numerical Study ◽  
Mesh Size ◽  
Nonlinear Effects ◽  
Line Tension ◽  
Body Motion ◽  
Mooring Line ◽  
Floating Platform ◽  
The Time Domain

This study aims to investigate the influence of fishnet mesh size on a floating platform. A self-developed, time-domain numerical model was used for the evaluation. This model is based on potential flow theory, uses the boundary element method (BEM) to solve nonlinear wave-body interactions, and applies the Morison equation to calculate the hydrodynamic forces exerted on fishnets. The mooring system is treated as a linear and symmetric spring. The results near the resonant frequency of the platform indicate that the smaller the fishnet mesh size, the lower the heave, pitch, and sea-side tension response amplitude operators (RAOs), but the higher the reflection coefficient. The results in the lower frequency region reveal that the smaller the fishnet mesh size, the lower the surge and heave RAOs, but the higher the pitch and tension RAOs. Meanwhile, the time-domain results at the resonant frequency of heave motion are shown to indicate the influences of a platform with various fishnets mesh sizes on the rigid body motion, mooring line tension, and transmitted wave heights. In addition, a comparison of nonlinear effects indicates that, after reducing the fishnet mesh size, the second-order RAOs of heave, pitch, and sea-side tension decrease, but the changes are minor against the first-order results.

On the Probability Distribution of Mooring Line Tensions in a Directional Environment

2011 ◽  
Author(s):  
Jan Mathisen ◽  
Siril Okkenhaug ◽  
Kjell Larsen
Keyword(s):  
Time Series ◽  
Probability Distributions ◽  
Extreme Value Distribution ◽  
Line Tension ◽  
Extreme Value ◽  
Mooring Line ◽  
Large Set ◽  
Short Term ◽  
Reliability Method ◽  
Line Design

A joint probabilistic model of the metocean environment is assembled, taking account of wind, wave and current and their respective heading angles. Mooring line tensions are computed in the time domain, for a large set of short-term stationary conditions, intended to span the domain of metocean conditions that contribute significantly to the probabilities of high tensions. Weibull probability distributions are fitted to local tension maxima extracted from each time series. Long time series of 30 hours duration are used to reduce statistical uncertainty. Short-term, Gumbel extreme value distributions of line tension are derived from the maxima distributions. A response surface is fitted to the distribution parameters for line tension, to allow interpolation between the metocean conditions that have been explicitly analysed. A second order reliability method is applied to integrate the short-term tension distributions over the probability of the metocean conditions and obtain the annual extreme value distribution of line tension. Results are given for the most heavily loaded mooring line in two mooring systems: a mobile drilling unit and a production platform. The effects of different assumptions concerning the distribution of wave heading angles in simplified analysis for mooring line design are quantified by comparison with the detailed calculations.

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>

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.

Parameter Calculation of Viscous Damper Applied in the Truncated Model Test Design of a Deepwater Semi-Submersible Platform

2010 ◽  
Vol 168-170 ◽  
pp. 1480-1485
Author(s):  
Dong Sheng Qiao ◽  
Jin Ping Ou
Keyword(s):  
Model Test ◽  
Dissipated Energy ◽  
Mooring Line ◽  
Inertia Force ◽  
Test Design ◽  
Viscous Damper ◽  
Floating Platform ◽  
Fluid Drag ◽  
Seabed Interaction ◽  
The Time Domain

In the equivalent water depth truncated model test design of a deepwater semi-submersible platform, the viscous damper is designed to simulate the contribution of mooring damping to total damping of floating platform. The dissipated energy by a mooring line from the floating platform as a result of its oscillation is applied to calculate the mooring-induced damping. The mooring line and seabed interaction is based on the hypothesis of rigid seabed. The fluid drag force and inertia force on the mooring line are calculated according to the Morrison formula. The non-liner dynamic analysis of mooring line is executed in the time domain based on the finite element method. The mooring induced damping is obtained from the results. The value difference of mooring induced damping between the truncated and full-depth mooring line is linearized to provide parameter for the design of viscous damper.

Mooring Line Damping Estimation by a Simplified Dynamic Model

2007 ◽  
Author(s):  
Halvor Lie ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Dynamic Model ◽  
Time Domain ◽  
Low Frequency ◽  
Line Tension ◽  
Mooring Line ◽  
Short Term ◽  
Simplified Method ◽  
On Line ◽  
Simulation Results ◽  
Frequency Domain Approach

When predicting slowly varying resonant vessel motions, a realistic estimate of the motion damping is crucial. Mooring line damping, which is mainly induced by the drag force on line, can dominate the total damping of catenary moored systems and methods for predicting mooring line damping are therefore required. Based on a simplified dynamic model of mooring line tension, an approach to estimate the corresponding damping is presented in this paper. Short-term time domain simulations of dynamic line tension are carried out to verify the accuracy of the simplified frequency domain approach. Compared with the simulation results, the practical simplified method proposed herein gives a maximum 30% lower prediction of the damping coefficient of each mooring line and an about 20% smaller estimate of the total line damping and therefore yields conservative estimates of the low frequency vessel motions.

NorMoor JIP: On Safe Mooring Line Design

2012 ◽  
Author(s):  
Siril Okkenhaug ◽  
Jan Mathisen ◽  
Torfinn Hørte
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Line Tension ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Extreme Value ◽  
Mooring Line ◽  
Safety Factors ◽  
Line Design

DNV is currently running a Joint Industry Project, “NorMoor JIP”, on calibration of safety factors for mooring lines together with several oil companies, engineering companies, rig-owners, manufacturers of mooring line components and Norwegian authorities. Our motivation for initiating a study on mooring line safety factors started out with questions raised with regards to the safety level given by the Norwegian regulations. However, this is equally important for other mooring regulations like ISO, API and class-regulations. What we see is that the mooring standards are interpreted and applied in different ways. The reliability level implied by the regulations is not known, and the present safety factors were set when frequency domain analysis was prevalent while time domain analysis is often applied today. DNV carried out the DeepMoor JIP [9] during 1995–2000 using frequency domain analysis and reliability-based calibration. Now, a decade later, the increase in computing capacity makes it feasible to carry out a similar calibration for time-domain analysis of the mooring systems. The objective of the project work is to investigate and compare the characteristic line tension calculated according to design standards with the annual extreme value distribution of the line tension. Further, to calibrate safety factors for mooring line design for the ultimate limit state (ULS) as a function of the target probability of failure. The original proposal for this JIP included calculations for chain and wire rope moorings on a typical drill rig and a turret moored FPSO at three different water depths at Haltenbanken. However, since this JIP has been very well received in the industry, the scope has been extended to include calculations for a production semisubmersible, for fibre rope systems and for Gulf of Mexico environmental conditions. This paper will focus on the reasons for doing this calibration study, and the importance of seeking to agree on unified calculation recipes and requirements. Preliminary results for characteristic tension and annual extreme value distributions of tension for some designs are presented and discussed. The calibration of safety factors will be carried out later in the project when all designs are finalized.

Direct Time Domain Life Cycle Loading Analysis on a Floating Platform

2018 ◽  
Author(s):  
Ho-Joon Lim ◽  
Manoj Jegannathan ◽  
Bonjun Koo ◽  
Johyun Kyoung ◽  
Eleni Beyko
Keyword(s):  
Life Cycle ◽  
Fatigue Life ◽  
Time Domain ◽  
Simulation Analysis ◽  
Fatigue Analysis ◽  
Mooring Line ◽  
Direct Simulation ◽  
Floating Platform ◽  
Cycle Loading ◽  
Simulation Results

Time domain numerical simulations with TechnipFMC’s in-house program were performed to estimate life cycle loading on a floating platform using High Performance Computing (HPC). Direct Simulation Analysis (DSA) were conducted to estimate fatigue life of mooring lines of two Spar platforms and the results were compared with fatigue life estimated from the condensed bin approach. In the Direct Simulation Analysis, 35-year hindcast wave and wind data with 3-hour interval for Gulf of Mexico was used. The wind and wave data covers from January 1979 to December 2013 for every 3-hours. The current data was not available so associated current information was approximately estimated. The time domain direct simulation results include nonlinear loads, nonlinear responses and seasonal effects such as hurricane events. The life cycle loading analysis tool developed will reduce uncertainties and increase the accuracy and reliability of the estimation of the mooring fatigue life during the service life of platform. Fatigue life of a mooring line from condensed bin analysis is highly variable with more than 20% depending on the selected wave seed number. In addition, the fatigue life from condensed bin analysis is about 20% less than the fatigue life from the Direct Simulation Analysis. This paper presents the systematic comparisons between the conventional approach and the direct time domain simulation results and also provides some major findings. In addition to the mooring line fatigue analysis, the structural fatigue analysis is also being performed and the results will be presented in the near future.

A Conjoint Analysis of the Stability and Time-Domain Analysis on Floating Platform During Mooring Line Breaking

2019 ◽  
Author(s):  
Jiaguo Feng ◽  
Yi Yu ◽  
Yan Qu ◽  
Wenhui Xie ◽  
Min Wu ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Time Domain ◽  
Stability Problem ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Mooring Line ◽  
Floating Platform ◽  
The Stability ◽  
The Time Domain ◽  
Floating Platforms

Abstract The stability of platform is important to ensure the platforms are safe, especially during the mooring line breaking process in typhoon condition. The paper presents a stability analysis method for floating platforms of the mooring line breaking process based on the time-domain analysis. The time-domain simulation during the mooring line breaking is provided. The time of the mooring line break, the max tilt angle of platform and the amended equivalent overturning moment are calculated for the stability analysis. The results show that the platform would have a serious tilt when the mooring line breaks, this increases the overturning moments and may cause the platform not meets the stability requirements during this process. It is necessary to pay attention to the stability problem during the mooring line breaking process in typhoon condition. And properly locating the down-flooding points is recommended to avoide the stability problem.

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