scholarly journals Influence of motion coupling and nonlinear effects on parametric roll for a floating production storage and offloading platform

2015 ◽  
Vol 373 (2033) ◽  
pp. 20140110 ◽  
Author(s):  
M. Greco ◽  
C. Lugni ◽  
O. M. Faltinsen
Keyword(s):  
Stability Analysis ◽  
Single Point ◽  
Three Dimensional ◽  
Nonlinear Effects ◽  
Mooring Line ◽  
Mooring Lines ◽  
Parametric Roll ◽  
Line System ◽  
Dynamic Positioning System ◽  
Existence Region

Occurrence and features of parametric roll (PR) on a weather-vaning floating production storage and offloading (FPSO) platform with a turret single-point mooring-line system are examined. The main focus is on the relevance of motions coupling and nonlinear effects on this phenomenon and on more general unstable conditions as well as on the occurrence and severity of water on deck. This work was motivated by recent experiments on an FPSO model without mooring systems highlighting the occurrence of parametric resonance owing to roll–yaw coupling. A three-dimensional numerical hybrid potential-flow seakeeping solver was able to capture this behaviour. The same method, extended to include the mooring lines, is adopted here to investigate the platform behaviour for different incident wavelengths, steepnesses, headings, locations of the turret and pretensions. From the results, sway and yaw tend to destabilize the system, also bringing chaotic features. The sway–roll–yaw coupling widens the existence region of PR resonance and increases PR severity; it also results in a larger amount of shipped water, especially at smaller wavelength-to-ship length ratio and larger steepness. The chaotic features are excited when a sufficiently large yaw amplitude is reached. Consistently, a simplified stability analysis showed the relevance of nonlinear-restoring coefficients, first those connected with the sway–yaw coupling then those associated with the roll–yaw coupling, both destabilizing. From the stability analysis, the system is unstable for all longitudinal locations of the turret and pre-tensions examined, but the instability weakens as the turret is moved forward, and the pre-tension is increased. The use of a suitable dynamic-positioning system can control the horizontal motions, avoiding the instability.

Research on the Arrangement of the Mooring Lines of the Thruster Assisted Mooring System

2013 ◽  
Author(s):  
Gang Zou ◽  
Lei Wang ◽  
Feng Zhang
Keyword(s):  
Mooring Line ◽  
Mooring System ◽  
Main Function ◽  
Time Domain Simulation ◽  
Mooring Lines ◽  
Dynamic Positioning System ◽  
Optimum Arrangement ◽  
Line Angle ◽  
Mooring Forces ◽  
Offshore Industry

As the offshore industry is developing into deeper and deeper water, station keeping technics are becoming more and more important to the industry. Based on the dynamic positioning system, the thruster assisted mooring system (TAMS) is developed, which consisted of mooring lines and thrusters. The main function of the TAMS is to hold a structure against wind wave and current loads with its thruster and cables, which is mainly evaluated by the holding capacity of the system. The arrangement of the mooring lines (location of anchor or the mooring line angle relative to platform) will directly affect the TAMS holding capacity because of the influence of the directions of the mooring forces. So finding out an optimum arrangement of the mooring lines is essential since the performance of the TAMS depends greatly on the arrangement of the mooring lines. The TAMS of a semi-submersible platform, which is studied in this paper, consisted of eight mooring lines. By fixing the layout of the thrusters and changing the location of each mooring line for every case, the performances of the TAMS are analyzed. The platform motions, mooring line tensions and power consumptions are compared to obtain the optimum arrangement of mooring lines, and thus a thruster assisted mooring system with a better performance can be achieved. Time domain simulation is carried out in this paper to obtain the results.

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.

Linear and Nonlinear PSE for Stability Analysis of the Blasius Boundary Layer Using Compact Scheme

2001 ◽  
Vol 123 (3) ◽  
pp. 545-550 ◽  
Author(s):  
V. Esfahanian ◽  
K. Hejranfar ◽  
F. Sabetghadam
Keyword(s):  
Stability Analysis ◽  
Three Dimensional ◽  
Nonlinear Effects ◽  
Numerical Investigations ◽  
Blasius Boundary Layer ◽  
Incompressible Boundary ◽  
Linear And Nonlinear ◽  
Tollmien Schlichting ◽  
The Stability ◽  
Good Agreement

A highly accurate finite-difference PSE code has been developed to investigate the stability analysis of incompressible boundary layers over a flat plate. The PSE equations are derived in terms of primitive variables and are solved numerically by using compact method. In these formulations, both nonparallel as well as nonlinear effects are accounted for. The validity of present numerical scheme is demonstrated using spatial simulations of two cases; two-dimensional (linear and nonlinear) Tollmien-Schlichting wave propagation and three-dimensional subharmonic instability breakdown. The PSE solutions have been compared with previous numerical investigations and experimental results and show good agreement.

An Experimental Study of Snap Loads on a Vertical Hanging Cable System

2019 ◽  
Author(s):  
Wei-Ting Hsu ◽  
Tzu-Ching Chuang ◽  
Wen-Yang Hsu ◽  
Krish Sharman ◽  
Ray-Yeng Yang
Keyword(s):  
Drag Force ◽  
Excitation Amplitude ◽  
Offshore Wind ◽  
Theoretical Development ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Hydrodynamic Drag ◽  
Cable Model ◽  
Mooring Lines ◽  
Line System

Abstract Sudden snap events on mooring lines and hanging cables can cause spikes in tension, resulting in reduced safety factors during extreme events. For example, the mooring system of a floating offshore wind turbine (FOWT) can be exposed to wave-induced motions making the former vulnerable to snap type impact. Suitable criteria to define snap events are still largely unclear, making current design practices overly conservative. To understand the underlying physics of snap loads on a mooring line system, this paper presents a theoretical development and an experimental parametric study of snap events. The effects of the nonlinearity of bilinear line stiffness and hydrodynamic drag force, as well as the weight of payload on snap events are investigated using the vertical hanging cable model. This cable model includes two springs in series and a payload. The bilinear spring model is designed to create nonlinear dynamic tension. A total of 108 tests were conducted in the wave tank of Tainan Hydraulic Laboratory. The excitation amplitude ranges from 0.01 to 0.04m; excitation time period ranges from 0.5 to 2s; the weight of payload ranges from 6.13 to 18.95N. The tests carried out in water are compared to those conducted in air. It is seen that the hydrodynamic drag force together with the small pretension could result in larger normalized tension ranges.

Three-Dimensional Dynamic Analysis Method of Multi-Component Mooring Lines

2019 ◽  
Author(s):  
Yuda Apri Hermawan ◽  
Yoshitaka Furukawa
Keyword(s):  
Dynamic Analysis ◽  
Numerical Method ◽  
Three Dimensional ◽  
Experimental Results ◽  
Mooring Line ◽  
Lumped Mass ◽  
Mooring Lines ◽  
Dynamic Behaviors ◽  
Component Object ◽  
Deep Depth

Abstract Complicated mooring system well-known as a multi-component mooring line is highly required owing to the deep depth of water and severe sea conditions. Since the dynamic behaviors of such mooring line are quite complex, proper numerical method is indispensable to predict the dynamic behaviors of a multi-component mooring line efficiently and precisely. In this paper, a numerical method improving the lumped mass method is proposed to introduce the three-dimensional dynamic analysis of multi-component mooring line with the motion of an anchor and clump weights. The mooring line is regarded as a multi-component object which has nonuniform segment line characteristics. In this method, lumped mass technique is developed to represent the three-dimensional dynamic behavior of each segment individually, allowing the motion of bottom-end segment as well as the anchor. Then, the motion of the end-segment is regarded as the motion of the upper-end of lower segment. Meanwhile, calculation method of initial condition for dynamic calculation is developed by adopting the basic principle of multi-component mooring line catenary equations. The results of time histories representing the three-dimensional dynamic analysis of mooring line are obtained and compared with other numerical and experimental results presented in published papers. The results show good agreement with both numerical and experimental results.

scholarly journals Effect of Water Depths on the Hydrodynamic Responses of an FPSO Platform

2018 ◽  
Vol 203 ◽  
pp. 01022
Author(s):  
Matthew Guan ◽  
Montasir Osman Ahmed Ali ◽  
Cheng Yee Ng
Keyword(s):  
Oil And Gas ◽  
Response Spectrum ◽  
Low Frequency ◽  
Mooring Line ◽  
Random Wave ◽  
Statistical Parameters ◽  
Mooring Lines ◽  
Line System ◽  
Wave Condition ◽  
Water Depths

Ship-shaped Floating Production Storage Offloading platforms (FPSO) are commonly used in the production of oil and gas in offshore deepwater regions. The vessel is held in place by mooring lines anchored to the seabed during operation, either in spread or turret mooring arrangement. When designing such systems, water depth is a main factor that needs to be considered. At greater depths, the hydrodynamic properties of mooring lines become important and may not be accurately predicted through traditional experiments or numerical quasi-static models. Numerical simulation using coupled dynamic analysis is thus recommended, as the hull-mooring behaviour is analysed simultaneously, and the damping and added mass properties of the entire mooring line system is taken into account. This paper investigates the motions and mooring line tensions of a turret-moored FPSO at various water depths ranging from 1000 m to 2000 m. The analysis focuses on numerical simulations in the fully coupled dynamic time domain. The study utilizes the commercial software AQWA, with the FPSO model subjected to a unidirectional random wave condition. The hull hydrodynamics is first solved using the 3D radiation/diffraction panel method, and the hull response equation is then coupled with the mooring line equation. The dynamic motions and mooring line tensions results are presented in terms of statistical parameters as well as response spectrum. The results highlight the significance of greater water depths on low frequency responses in surge motions and mooring line tensions, and provides insight on the increasing and decreasing trend of these responses.

Quasi-Static Analysis of the Multicomponent Mooring Line for Deeply Embedded Anchors

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Zhen Guo ◽  
Lizhong Wang ◽  
Feng Yuan
Keyword(s):  
Soil Column ◽  
Realistic Model ◽  
Static Model ◽  
Original Position ◽  
Mooring Line ◽  
Special Focus ◽  
Mooring System ◽  
Mooring Lines ◽  
Line System ◽  
Service Conditions

Multicomponent taut mooring lines are widely used to secure floating facilities to anchors embedded in the seabed to restrict motions. Optimal design of the mooring line system requires a realistic model of the combined performance of all segments of the mooring line, including the separate segments contained within both the water column and the soil column. This paper presents a two-dimensional quasi-static model, which can analyze mooring lines comprising multiple types of mooring lines or chains, taking into account the effects of ocean currents, soil resistance, and elastic elongation of mooring line. An example analysis is carried out to predict the responses of multicomponent mooring line during pretension and under service conditions. The example analysis puts special focus on conditions where the floating facility undergoes a series of motion away from its original position to assess the effect of the vertical offset is studied in detail. Finally, based on the presented model, the performances of different components of the mooring system are thoroughly investigated and some useful conclusions are drawn.

Dynamics of Spread Mooring Systems With Hybrid Mooring Lines

2000 ◽  
Vol 122 (4) ◽  
pp. 274-281 ◽  
Author(s):  
Luis O. Garza-Rios ◽  
Michael M. Bernitsas ◽  
Kazuo Nishimoto ◽  
Joa˜o Paulo J. Matsuura
Keyword(s):  
Stability Analysis ◽  
Deep Water ◽  
Parametric Design ◽  
Line Tension ◽  
Slow Motion ◽  
Synthetic Fiber ◽  
Mooring Line ◽  
Vertical Force ◽  
Mooring Lines ◽  
Steady Current

The weight of a chain mooring line in deep water is the main source of mooring line tension. Chain weight also induces a vertical force on the moored vessel. To achieve the desired tension without excessive weight, hybrid mooring lines, such as lighter synthetic fiber ropes with chains, have been proposed. In this paper, the University of Michigan methodology for design of mooring systems is developed to study hybrid line mooring. The effects of hybrid lines on the slow-motion nonlinear dynamics of spread mooring systems (SMS) are revealed. Stability analysis and bifurcation theory are used to determine the changes in SMS dynamics in deep water based on pretension and angle of inclination of the mooring lines for different water depths and synthetic rope materials. Catastrophe sets in two-dimensional parametric design spaces are developed from bifurcation boundaries, which delineate regions of qualitatively different dynamics. Stability analysis defines the morphogeneses occurring as bifurcation boundaries are crossed. The mathematical model of the moored vessel consists of the horizontal plane—surge, sway, and yaw—fifth-order, large drift angle, low-speed maneuvering equations. Mooring lines are modeled quasistatically as nonlinear elastic strings for synthetic ropes and as catenaries for chains, and include nonlinear drag and touchdown. Excitation consists of steady current, wind, and mean wave drift. Numerical applications are limited to steady current, which is adequate for revealing the SMS design depending on the selected parameters. [S0892-7219(00)00804-9]

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