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.

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.

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.

High-resolution seismic processing technique with broadband,wide-azimuth, and high-density seismic data - A case study of thin-sand reservoir in eastern China

2021 ◽  
pp. 1-45
Author(s):  
Qin Su ◽  
Huahui Zeng ◽  
Yancan Tian ◽  
HaiLiang Li ◽  
Lei Lyu ◽  
...  
Keyword(s):  
Seismic Data ◽  
Oil And Gas ◽  
Single Point ◽  
Eastern China ◽  
High Density ◽  
Songliao Basin ◽  
Seismic Processing ◽  
Oil And Gas Exploration ◽  
Sand Body

Seismic processing and interpretation techniques provide important tools for the oil and gas exploration of the Songliao Basin in eastern China, which is dominated by terrestrial facies. In the Songliao Basin, a large number of thin-sand reservoirs are widely distributed, which are the primary targets of potential oil and gas exploration and exploitation. An important job of the exploration in the Songliao Basin is to accurately describe the distribution of these thin-sand belts and the sand-body shapes. However, the thickness of these thin-sand reservoirs are generally below the resolution of the conventional seismic processing. Most of the reservoirs are thin-interbeds of sand and mudstones with strong vertical and lateral variations. This makes it difficult to accurately predict the vertical and horizontal distribution of the thin-sand bodies using the conventional seismic processing and interpretation methods. Additionally, these lithologic traps are difficult to identify due to the complex controlling factor and distribution characteristics, and strong concealment. These challenges motivate us to improve the seismic data quality to help delineate the thin-sand reservoirs. In this paper, we use the broadband, wide-azimuth, and high-density integrated seismic exploration technique to help delineate the thin-reservoirs. We first use field single-point excitation and single-point receiver acquisition to obtain seismic data with wide frequency-bands, wide-azimuth angles, and high folds, which contain rich geological information. Next, we perform the near-surface Q-compensation, viscoelastic prestack time migration, seismic attributes, and seismic waveform indication inversion on the new acquired seismic data. The 3D case study indicates the benefits of improving the imaging of thin-sand body and the accuracy of inversion and reservoir characterization using the method in this paper.

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.

Influence of Heave Plate on Hydrodynamic Response of Spar

2011 ◽  
Author(s):  
S. Sudhakar ◽  
S. Nallayarasu
Keyword(s):  
Oil And Gas ◽  
Scale Model ◽  
Mooring Line ◽  
Floating Structures ◽  
Oil And Gas Exploration ◽  
Numerical Studies ◽  
Heave Plate ◽  
Offshore Oil And Gas ◽  
Experimental Values ◽  
Offshore Oil

Spar technology has been used in offshore oil and gas exploration successfully for number of years for drilling, production and storage in deepwater. The motion response of floating structures especially the heave response in particular, is very important to the selection of suitable drilling and production equipments. Reduction of heave response can be achieved by attaching a heave damping plate to the keel of a Spar. This has been used in the past. Experimental and numerical studies on such devices of various diameters under regular waves has been carried out and presented. The experiments were conducted on a 1: 100 scale model of Spar designed for a water depth of 245m with a payload of 10000 tonnes and the numerical analysis was carried out using ANSYS AQWA software. Numerical and experimental values of RAOs for surge, pitch and heave compares reasonably well. Measured and numerical results of RAOs for surge, pitch and heave and the effect of diameter ratio, wave steepness, and mooring line pretension were presented and discussed. An optimum heave response is achieved when the heave plate diameter is 20% to 30% larger than the diameter of the spar.

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.

Structural Reliability-Based Control for Moored Vessels: Experimental Results

2007 ◽  
Author(s):  
Per I. B. Berntsen ◽  
Ole M. Aamo ◽  
Bernt J. Leira
Keyword(s):  
Structural Properties ◽  
Reliability Index ◽  
Laboratory Experiments ◽  
Structural Reliability ◽  
Weather Conditions ◽  
Dynamic Positioning ◽  
Mooring System ◽  
Reliability Measures ◽  
Mooring Lines ◽  
Surface Vessels

This paper addresses dynamic positioning of surface vessels moored to the seabed via a turret based spread mooring system, referred to as position mooring. The controller utilize a reliability index to determine the actuator force needed to operate safely. The structural reliability measures become an intrinsic part of the controller, automatically adjusting the allowed geographical region based on current weather conditions and structural properties of the mooring lines. The performance of the controller is demonstrated through laboratory experiments on a model vessel named CyberShip III.

Experimental and Numerical Investigation on Planar Motion Responses of a Single Point Moored Shuttle Tanker in Waves

2019 ◽  
Author(s):  
Ning He ◽  
Cheng Zhang ◽  
Zhuang Kang ◽  
Youwei Kang ◽  
Changhong Wang
Keyword(s):  
Model Test ◽  
Deep Water ◽  
Oil And Gas ◽  
Single Point ◽  
Diffraction Theory ◽  
Line Length ◽  
Plane Motion ◽  
Mooring Line ◽  
Motion Responses ◽  
Motion Characteristics

Abstract In order to ensure the safety of the single point moored shuttle tanker in waves, the numerical model of a shuttle tanker moored with a fixed point was established on the basis of radiation / diffraction theory and pressure integral method in this paper, which was further checked by a series of model tests. Then the plane motion characteristics of the tanker like fishtailing oscillation were analyzed by applying the combined approach of numerical simulation and model test. On this basis, the effects of wave and ballast conditions as well as mooring line length and stiffness on the plane motion of the single point moored tanker were investigated by means of model test. Overall, the research can provide a reference for the design and safety assessment of deep-water offloading system, and give the technical support for the engineering development of deep-water oil and gas projects.

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