Single Point Mooring FPSO Monitoring and Forecast System Design

2014 ◽  
Author(s):  
Junliang Qi ◽  
Ligong Lv ◽  
Zhiyong Su ◽  
Chao Liu ◽  
Hui Shen ◽  
...  
Keyword(s):  
System Design ◽  
Single Point ◽  
Line Tension ◽  
Green Water ◽  
Mooring Line ◽  
Bohai Bay ◽  
Forecast System ◽  
Mooring Lines ◽  
Operation Conditions ◽  
Extreme Response

The proposed paper is going to address the development of single point mooring FPSO (Floating Production, Storage and Offloading) monitoring and forecast system design. With 17 FPSOs deployed in both Bohai Bay and South China Sea, CNOOC owns one of the largest FPSO fleet in the world. Most of those FPSOs have been or will be moored to the seabed for decades. The extreme response during storm conditions could cause serious environmental problem, asset loss, personnel safety etc. In order to timely understand the tanker operation conditions and avoid potential risk of system failure when experiencing hurricanes, a monitoring and forecast system is developed for FPSO to monitor the environment conditions, tanker motions, green water, mooring tensions, FPSO heading and to predict the extreme mooring tensions and global motions before typhoon coming. The forecast system could further suggest the optimum loading condition for minimizing the extreme mooring tension and tanker motions to enhance the safe operation. In this paper, we take the Internal Turret Mooring FPSO 111 and the Submerged Soft Yoke Mooring FPSO 112 as the examples to introduce the design technology of the system. Through the integrated onboard interface information, the personnel could proactively take actions to mitigate the tensions on mooring lines and vessel motions. Furthermore, the measured mooring line tension, motion and environment history could assist the numerical studies of global performance. The details of designing or selecting the measuring and monitoring equipment, theory background of forecast system and the integrated onboard interface will be described.

scholarly journals Structural Reliability Based Dynamic Positioning of Turret-Moored FPSOs in Extreme Seas

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Yuanhui Wang ◽  
Chuntai Zou ◽  
Fuguang Ding ◽  
Xianghui Dou ◽  
Yanqin Ma ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Structural Reliability ◽  
Oil And Gas ◽  
Single Point ◽  
Line Tension ◽  
Mooring Line ◽  
Dynamic Positioning ◽  
Mooring Lines ◽  
Oil And Gas Exploration ◽  
Time Control

FPSO is widely used during the deep-sea oil and gas exploration operations, for which it is an effective way to keep their position by means of positioning mooring (PM) technology to ensure the long-term reliability of operations, even in extreme seas. Here, a kind of dynamic positioning (DP) controller in terms of structural reliability is presented for the single-point turret-moored FPSOs. Firstly, the mathematical model of the moored FPSO in terms of kinematics and dynamics is established. Secondly, the catenary method is applied to analyze the mooring line dynamics, and mathematical model of one single mooring line is set up based on the catenary equation. Thereafter, mathematical model for the whole turret mooring system is established. Thirdly, a structural reliability index is defined to evaluate the breaking strength of each mooring line. At the same time, control constraints are also considered to design a state feedback controller using the backstepping technique. Finally, a series of simulation tests are carried out for a certain turret-moored FPSO with eight mooring lines. It is shown in the simulation results that the moored FPSO can keep its position well in extreme seas. Besides, the FPSO mooring line tension is reduced effectively to ensure mooring lines safety to a large extent in harsh sea environment.

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.

FPSO Transient Responses During Cyclonic Storms

2007 ◽  
Author(s):  
Dusan Curic ◽  
Yong Luo
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Wind Waves ◽  
Rapid Change ◽  
Line Tension ◽  
Green Water ◽  
Mooring Line ◽  
Sea Waves ◽  
Transient Responses ◽  
Cyclonic Storm

This paper presents the key results and conclusions of the study of FPSO transient responses in the cyclonic storm. The measured wind, wave and current data of recent cyclonic events are utilized to simulate the FPSO responses in terms of mooring loads, vessel yaw motion and relative FPSO heading to waves as it weathervanes in the wind, waves and current, input as time series. The primary objectives are to check the FPSO responses as the cyclone (eye or fringe) passes over it, causing rapid changes in the intensity and the direction of environmental loads, and to confirm the adequacy of the present mooring system design criteria. The results of the study serve as a good benchmark of the current industry standard for mooring design and address industry’s concern of the safety of FPSO platforms in the event of cyclonic storm. This study has used the hindcast data to inspect the event of a strong cyclonic storm passing over an FPSO. Despite the fact that the wind direction changes for about 140° in only one hour in the path of the cyclone eye, higher mooring line tension has not been observed due to reduced wind speed in the eye of the storm. The extreme mooring line tension is still governed by the responses in the path of cyclone fringe due to its maximum wind speed. Note that the transient analysis has shown that, during the rapid change of wind direction, the vessel can potentially be exposed to beam sea waves. Although this does not correspond with the highest tension in mooring legs, it can lead to critical green water impact.

Sensitivity of Mooring Line Pretension in the Design Cycle for Floating Caissons

2004 ◽  
Author(s):  
Adinarayana Mukkamala ◽  
Partha Chakrabarti ◽  
Subrata K. Chakrabarti
Keyword(s):  
Reinforced Concrete ◽  
System Design ◽  
Mooring Line ◽  
Mooring System ◽  
Mooring Lines ◽  
Design Cycle ◽  
Overall Performance ◽  
The Difference ◽  
Tacoma Narrows Bridge ◽  
System Layout

The new parallel Tacoma Narrows Bridge being constructed by Tacoma Narrows Constructors will be mounted on two towers and these towers in turn will be supported by reinforced concrete caissons referred to as East Caisson (Tacoma side) and West Caisson (Gig Harbor side). Each Caisson is towed to the location and several stages of construction will take place at the actual site. During construction, the floating caissons will be moored in place to hold it against the flood and ebb currents in the Narrows. During the mooring system design, a desired pretension is established for the lines at each draft. However, due to practical limitations in the field some variations to this design pretension value may be expected. It is important to study the effect of this variation on the overall performance of the mooring system. In this paper, the sensitivity of the mooring line pretension on the overall performance of the mooring system for the above caisson is presented. During this study, all the variables that affect the mooring system design such as mooring system layout, mooring line makeup, anchor positions, fairlead departure angles, and fairlead locations are kept constant. The only variable changed is the pretension of the mooring lines. Two approaches for defining the variations in the pretension have been studied in this paper. In the first approach, the pretension is changed in a systematic way (predicted approach). In the second method the pretension is changed randomly. The latter is considered more likely to occur in the field for this type of complex mooring system. Both sets of results are presented for some selected drafts attained by the caisson during its construction. The difference in the results from the two methods is discussed.

scholarly journals The Quasi-Static Response of Moored Floating Structures Based on Minimization of Mechanical Energy

2021 ◽  
Vol 9 (9) ◽  
pp. 960
Author(s):  
Chun Bao Li ◽  
Mingsheng Chen ◽  
Joonmo Choung
Keyword(s):  
Potential Energy ◽  
Mechanical Energy ◽  
Line Tension ◽  
Line Length ◽  
Theoretical Background ◽  
Mooring Line ◽  
Floating Structure ◽  
Mooring Lines ◽  
Floating Structures ◽  
Static Responses

It is essential to design a reasonable mooring line length that ensures quasi-static responses of moored floating structures are within an acceptable level, and that reduces the cost of mooring lines in the overall project. Quasi-static responses include the equilibrium position and the line tension of a moored floating structure (also called the mean value in a dynamic response), etc. The quasi-static responses derived by the classic catenary equation cannot present mooring–seabed interaction and hydrodynamic effects on a mooring line. While a commercial program can predict reasonable quasi-static responses, costly modeling is required. This motivated us to propose a new method for predicting quasi-static responses that minimizes the mechanical energy of the whole system based on basic geometric parameters, and that is easy to implement. In this study, the mechanical energy of moored floating structures is assumed to be the sum of gravitational–buoyancy potential energy, kinetic energy induced by drag forces, and spring potential energy derived by line tension. We introduce fundamental theoretical background for the development of the proposed method. We investigate the effect of quasi-static actions on mooring response, comparing the proposed method’s results with those from the catenary equation and ABAQUS software. The study reveals the shortcomings of the catenary equation in offshore applications. We also compare quasi-static responses derived by the AQWA numerical package with the results calculated from the proposed method for an 8 MW WindFloat 2 type of platform. Good agreement was drawn between the proposed method and AQWA. The proposed method proves more timesaving than AQWA in terms of modeling of mooring lines and floaters, and more accurate than the catenary equation, and can be used effectively in the early design phase of dimension mooring lengths for moored floating structures.

scholarly journals Numerical Study on Hydrodynamic Responses of Floating Rope Enclosure in Waves and Currents

2020 ◽  
Vol 8 (2) ◽  
pp. 82
Author(s):  
Hui Yang ◽  
Yun-Peng Zhao ◽  
Chun-Wei Bi ◽  
Yong Cui
Keyword(s):  
Numerical Study ◽  
Line Tension ◽  
Wave Period ◽  
Windward Side ◽  
Mooring Line ◽  
Fish Stock ◽  
Lumped Mass ◽  
Mooring Lines ◽  
Design Factors ◽  
Volume Retention

Enclosure aquaculture is a healthy and ecological aquaculture pattern developed in recent years to relieve the pressure due to the wild fish stock decline and water pollution. The object of this paper was a floating rope enclosure, which mainly consisted of floaters, mooring lines, sinkers and a net. In order to optimize mooring design factors, the hydrodynamic responses of the floating rope enclosure with different mooring systems in combined wave-current were investigated by experimental and numerical methods. Physical model experiments with a model scale of 1:50 were performed to investigate the hydrodynamic characteristics of a floating rope enclosure with 12 mooring lines. Based on the lumped mass method, the numerical model was established to investigate the effects of mooring design factors on the mooring line tension, force acting on the bottom, and the volume retention of the floating rope enclosure. Through the analysis of numerical and experimental results, it was found that the maximum mooring line tension of the floating rope enclosure occurs on both sides of the windward. Increasing the number of mooring lines on the windward side is helpful to reduce the maximum mooring line tension. Waves and current both have an influence on the mooring line tension; in contrast, currents have a more obvious effect on the mooring line tension than waves. However, the influence of the wave period on the maximum mooring line tension is small. The force endured by the bottom of the floating rope enclosure also changes periodically with the wave period. Yet, the maximum force endured by the bottom of floating rope enclosure occurred at the windward and leeward of the structure. The volume retention of the floating rope enclosure increased with the increasing amount of mooring lines.

Performance Evaluations of Taut-Wire Mooring Systems for Deepwater Semi-Submersible Platform

2011 ◽  
Author(s):  
P. Chen ◽  
S. Chai ◽  
J. Ma
Keyword(s):  
Line Tension ◽  
Dynamic Loads ◽  
Mooring Line ◽  
Hydrodynamic Coefficients ◽  
Mooring Lines ◽  
Coupled Motion ◽  
Motion Responses ◽  
Parametric Studies ◽  
Motion Performance ◽  
Dip Angle

In order to investigate the effect of taut-wire mooring system on the motion performance of semi-submersible platforms, parametric studies of coupled motion responses are conducted using a time domain analysis in this study. The nonlinear dynamic characteristics of mooring lines and the interactions of platform and mooring lines are investigated. The parametric studies consist of investigating the effects of the hydrodynamic coefficients CA and CD of mooring line, tension dip angle, mooring line pretension, different taut-mooring arrangements and total number of mooring lines on the motion performance of a semi-submersible platform in water depth of 1500 meters, which is subjected to a 100 year return significant wave height of 13.3 meters, a peak period of 15.5 seconds, a current speed of 1.97 meters per second and wind speed of 55 meters per second. The wind and current both act in the same direction as the ocean waves in this study in order to estimate the maximum mooring line loads. The environmental load direction is varied from 0° to 90° at the interval of 15 degrees. Seven directions are calculated in total. The research results show that the different parameters, such as the hydrodynamic coefficients of the mooring line, tension dip angle, pre-tension, arrangement angle of mooring lines and total number of mooring lines, have different effects on the coupled motion responses. In particular, the arrangement angles of mooring lines have significant effect on motion responses and dynamic loads of mooring lines. The motion performance of semi-submersible platform and mooring line dynamic loads can be controlled effectively when these parameters are selected reasonably throughout parametric studies carefully designed and conducted.

scholarly journals Influence of Clumps-Weighted Moorings on a Spar Buoy Offshore Wind Turbine

Energies ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 6407
Author(s):  
Niccolo Bruschi ◽  
Giulio Ferri ◽  
Enzo Marino ◽  
Claudio Borri
Keyword(s):  
Line Tension ◽  
Optimal Choice ◽  
Offshore Wind ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
National Renewable Energy Laboratory ◽  
Mooring Lines ◽  
Offshore Wind Turbines ◽  
Open Issue ◽  
Response Amplitude Operators

The spar buoy platform for offshore wind turbines is the most utilized type and the OC3 Hywind system design is largely used in research. This system is usually moored with three catenary cables with 120° between each other. Adding clump weights to the mooring lines has an influence on the platform response and on the mooring line tension. However, the optimal choice for their position and weight is still an open issue, especially considering the multitude of sea states the platform can be exposed to. In this study, therefore, an analysis on the influence of two such variables on the platform response and on the mooring line tension is presented. FAST by the National Renewable Energy Laboratory (NREL) is used to perform time domain simulations and Response Amplitude Operators are adopted as the main indicators of the clump weights effects. Results show that the clump weight mass is not as influential as the position, which turns out to be optimal, especially for the Surge degree of freedom, when closest to the platform.

T-N Curves and Fracture Mechanics Based Mooring Fatigue Analysis for a Semi-Submersible

2017 ◽  
Author(s):  
Xutian Xue ◽  
Nian-Zhong Chen
Keyword(s):  
Fracture Mechanics ◽  
Fatigue Failure ◽  
Line Tension ◽  
Fatigue Analysis ◽  
Mooring Line ◽  
Mooring System ◽  
Bottom Line ◽  
Mooring Lines ◽  
Element Analysis ◽  
Chain Link

This paper is to perform T-N curves and fracture mechanics based fatigue analysis for mooring lines of a semi-submersible installed in Gulf of Mexico (GoM). The wave frequency (WF) and the low frequency (LF) load processes are regarded as two random processes and the load combination of the two processes is considered. Frequency-domain analysis is then conducted for calculating the tension ranges along hybrid-material mooring lines induced by motions of WF, LF and the combined WF and LF. The narrow-banded spectral method is used for calculating the mooring line tension and the fatigue damage of mooring lines is estimated by T-N curves and fracture mechanics based approaches. The fracture mechanics based analysis is combined with a finite element analysis to predict crack propagation at different locations of a studless chain link. It was found that the crown section of a mooring chain is the most critical location subjected to fatigue failure in a studless chain link. The most critical points prone to fatigue failure of the catenary and taut mooring systems designed for the semi-submersible are at the bottom end of top line and the top end of bottom line, respectively. Also, fatigue lives of mooring lines in the catenary mooring system are generally longer than those of the taut mooring system. In addition, a comparison between fatigue lives of mooring lines predicted by T-N curves and fracture mechanics based approaches shows that the results estimated by both approaches are generally comparable.

scholarly journals Fatigue Analysis of Deepwater Hybrid Mooring Line Under Corrosion Effect

2014 ◽  
Vol 21 (3) ◽  
pp. 68-76 ◽  
Author(s):  
Dongsheng Qiao ◽  
Jun Yan ◽  
Jinping Ou
Keyword(s):  
Fatigue Damage ◽  
Oil And Gas ◽  
Line Tension ◽  
Chain Structure ◽  
Mooring Line ◽  
Mooring System ◽  
Load Spectrum ◽  
Sea State ◽  
Mooring Lines

Abstract In the deepwater exploitation of oil and gas, replacing the polyester rope by a wire in the chain-wire-chain mooring line is proved to be fairly economic, but this may provoke some corresponding problems. Te aim of this paper is to compare the fatigue damage of two mooring system types, taking into account corrosion effects. Using a semi-submersible platform as the research object, two types of mooring systems of the similar static restoring stiffness were employed. Te mooring lines had the chain-wire-chain and chain-polyester-chain structure, respectively. Firstly, the numerical simulation model between the semi-submersible platform and its mooring system was built. Te time series of mooring line tension generated by each short-term sea state of South China Sea S4 area were calculated. Secondly, the rain flow counting method was employed to obtain the fatigue load spectrum. Thirdly, the Miner linear cumulative law model was used to compare the fatigue damage of the two mooring system types in long-term sea state. Finally, the corrosion effects from zero to twenty years were considered, and the comparison between the fatigue damage of the two mooring system types was recalculated.

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