scholarly journals Effects of Damaged Fiber Ropes on the Performance of a Hybrid Taut-Wire Mooring System

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Yushun Lian ◽  
Solomon C. Yim ◽  
Jinhai Zheng ◽  
Haixiao Liu ◽  
Nan Zhang
Keyword(s):  
Dynamic Stiffness ◽  
Mooring Line ◽  
Mooring System ◽  
Floating Platform ◽  
Damage Level ◽  
Maximum Tension ◽  
Tension Response ◽  
Depth Study ◽  
Rainflow Cycle Counting ◽  
The Time Domain

Abstract In this study, effects of damage levels of fiber ropes on the performance of a hybrid taut-wire mooring system are investigated. The analysis is performed using a numerical floating production storage and offloading (FPSO) model with a hybrid mooring system installed in 3000 m of water depth. An in-depth study was conducted using the numerical model, the dynamic stiffness equation of damaged fiber ropes, the time-domain dynamic theory, the rainflow cycle counting method, and the linear damage accumulation rule of Palmgren-Miner. Results indicate that, in a mooring line with an increasing damage level, the maximum tension decreases, while the offset of the FPSO increases. Particularly, when a windward mooring line failure occurs, in addition to the significant increase in the offset of the FPSO, the maximum tension, tension range, and annual fatigue damage levels of the remaining lines adjacent to the failed also increase significantly. The present work can be of great benefit to the evaluation of the offset of the floating platform, the tension response, and the service life of the hybrid mooring systems.

scholarly journals Transient Responses Evaluation of FPSO with Different Failure Scenarios of Mooring Lines

2021 ◽  
Vol 9 (2) ◽  
pp. 103
Author(s):  
Dongsheng Qiao ◽  
Binbin Li ◽  
Jun Yan ◽  
Yu Qin ◽  
Haizhi Liang ◽  
...  
Keyword(s):  
Service Condition ◽  
Mooring Line ◽  
Mooring System ◽  
Transient Effects ◽  
Floating Platform ◽  
Transient Responses ◽  
Mooring Lines ◽  
Performance Deterioration ◽  
Steady State Responses ◽  
Influence Process

During the long-term service condition, the mooring line of the deep-water floating platform may fail due to various reasons, such as overloading caused by an accidental condition or performance deterioration. Therefore, the safety performance under the transient responses process should be evaluated in advance, during the design phase. A series of time-domain numerical simulations for evaluating the performance changes of a Floating Production Storage and Offloading (FPSO) with different broken modes of mooring lines was carried out. The broken conditions include the single mooring line or two mooring lines failure under ipsilateral, opposite, and adjacent sides. The resulting transient and following steady-state responses of the vessel and the mooring line tensions were analyzed, and the corresponding influence mechanism was investigated. The accidental failure of a single or two mooring lines changes the watch circle of the vessel and the tension redistribution of the remaining mooring lines. The results indicated that the failure of mooring lines mainly influences the responses of sway, surge, and yaw, and the change rule is closely related to the stiffness and symmetry of the mooring system. The simulation results could give a profound understanding of the transient-effects influence process of mooring line failure, and the suggestions are given to account for the transient effects in the design of the mooring system.

Time-Domain Coupled Dynamic Analysis of Mooring Systems in Extreme Sea Condition

2018 ◽  
Author(s):  
Xuliang Han ◽  
ShiSheng Wang ◽  
Bin Xie ◽  
Wenhui Xie ◽  
Weiwei Zhou
Keyword(s):  
Dynamic Analysis ◽  
Body Surface ◽  
Time Domain ◽  
Mooring Line ◽  
Mooring System ◽  
Dynamic Coupling ◽  
Spar Platform ◽  
Coupled Dynamic Analysis ◽  
Motion Responses ◽  
The Time Domain

In order to predict the coupled motion and external wave load for the design of deepwater floating structure system, based on the three-dimensional time-domain potential flow theory, this paper present the indirect time-domain dynamic coupling method and the body nonlinear dynamic coupling method. The perturbation expansion theory is adopted to evaluate hydrodynamic on the fixed mean wetted body surface for the former method. The transient free surface Green function has been extended and applied to calculate the nonlinear hydrodynamic on the instantaneous wetted exact body surface for the latter method. The finite element model is employed to solve dynamic response of mooring line. Then asynchronous coupled method is adopted to achieve the coupled dynamic analysis of platform and mooring lines. The time-domain motion responses and spectrum analysis of Spar platform are verified and compared with the traditional indirect time-domain coupling dynamic method when the mooring system is completed. Also the time-domain motion responses and statistical characteristic of Spar platform are investigated with one mooring line broken in extreme sea condition. Some conclusions are obtained, that is, dynamic coupling effects are significant and transient position hydrodynamic calculation of platform has a great influence on the low frequency motion. The results also show that the influence on the global performance of mooring system is different when the broken line is in different place. A remarkable influence occurs when the broken mooring line is in the head-wave direction.

Dual Stiffness Approach for Polyester Mooring Line Analysis in Time Domain: Semisubmersible Case

2013 ◽  
Author(s):  
Arcandra Tahar ◽  
Djoni Sidarta
Keyword(s):  
Traditional Method ◽  
Dynamic Stiffness ◽  
Performance Comparison ◽  
Mooring Line ◽  
Analysis Tool ◽  
Floating Platform ◽  
Mooring Lines ◽  
Coupled Dynamic Analysis ◽  
Stiffness Method ◽  
Motion Characteristics

This paper is a continuation of a series of investigation for the dual stiffness approach for polyester mooring lines. Tahar et. al. (2012) has presented the global performance comparison between the dual stiffness method and the traditional method for the Spar platform. As shown in that study, there are appreciable differences between the former and the later methods especially in lateral motions, which, however, result in little difference in SCR strength response. Is it because the Spar has better motion characteristics than other wet tree floating platforms such as the semisubmersible and FPSO? This paper will investigate the effect of the dual stiffness method and the traditional method to SCR response for a Semisubmersible platform. The fully coupled dynamic analysis tool CHARM3D has been modified to incorporate the dual stiffness approach. Two axial stiffnesses (EA) of polyester line, post installation (static) stiffness and storm (dynamic) stiffness have been convoluted into a dual stiffness to represent the total response of the floating platform in a single run. In the traditional method, the analyses are done twice, one run for each stiffness. Then, the extremes from each run are used as governing values for design. The SCR will be modeled and analyzed using ABAQUS software.

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>

scholarly journals Dynamic Stability and Protection Design of a Submarined Floater Platform Avoiding Typhoon Wave Impact

2021 ◽  
Vol 9 (9) ◽  
pp. 977
Author(s):  
Shueei-Muh Lin ◽  
Yang-Yih Chen
Keyword(s):  
Dynamic Stability ◽  
Ocean Current ◽  
Mooring Line ◽  
Elastic Model ◽  
Mooring System ◽  
Floating Platform ◽  
Wave Impact ◽  
Diving Depth ◽  
Typhoon Wave ◽  
Typhoon Waves

This research proposes the design of a mooring system that allows the floating platform to stably dive deep enough to prevent damage induced by typhoon waves. The design principle of the mechanism is that the submarined floating platform with negative buoyancy is connected to a pontoon with positive buoyancy. The diving depth of the floating platform is determined by the rope length. If the static equilibrium of the two forces is satisfied, the diving depth will be kept. If the diving depth of the floating platform is enough, the platform will not be directly damaged by the wave impact. In reality, the system will be greatly subjected to the typhoon wave and the ocean current. The stability of the system and the dynamic tension of the rope must be significantly concerned. In this study, the linear elastic model of the mooring system composed of a floater platform, towed parachute, pontoon, traction rope, and mooring foundation is derived. The theoretical solution of the static and dynamic stability analysis of the mooring system is proposed. The dynamic behaviors of the floating platform and pontoon, and the tension of the rope under the effects of waves and ocean currents, are investigated. It is discovered that the buffer spring helps reduce the tension of the rope. The proposed protection procedure can avoid the damage of the floating platform and the mooring line, due to Typhoon wave impact.

Dual Stiffness Approach for Polyester Mooring Line Analysis in Time Domain

2012 ◽  
Author(s):  
Arcandra Tahar ◽  
Djoni Sidarta ◽  
Alex Ran
Keyword(s):  
Traditional Method ◽  
Dynamic Stiffness ◽  
Performance Comparison ◽  
Mooring Line ◽  
Axial Stiffness ◽  
Analysis Tool ◽  
Floating Platform ◽  
Mooring Lines ◽  
Nonlinear Stress ◽  
Offshore Industry

Polyester mooring lines have been used in the offshore industry since the late ’90s. With increasing oil exploration and production in deeper waters, using polyester lines provides greater benefit than using traditional steel wires and chains. Some advantages of using polyester include a reduction of mooring line weight, a reduction in vessel offset and a reduction in the dynamics of the line tensions. However, unlike steel, polyester lines exhibit axial stiffness characteristics that are nonlinear and vary with time and loading history. Tahar (2001) developed a comprehensive theory and numerical tool to capture this behavior. The formulas allow relatively large elongation and nonlinear stress-strain relationships, as typically observed in polyester fibers. The mooring line dynamics are based on a rod theory and finite element method (FEM), with the governing equations described in a generalized coordinate system. Since this theory is computationally intensive, the benefits outweigh the costs less than they do for the practical approach recommended by API. Therefore, the fully coupled dynamic analysis tool CHARM3D has been modified to incorporate the API-recommended approach. Two axial stiffnesses (EA), post installation (static) stiffness and storm (dynamic) stiffness, have been convoluted into a dual stiffness to represent the total response of the floating platform in a single run. In the traditional method, the analyses are done twice, one run for each stiffness. Then, the extremes from each run are used as governing values for design. This paper presents the global performance comparison between the dual stiffness method and the traditional method. The effect of motions on SCR strength is also investigated using ABAQUS software.

scholarly journals Alternative Mooring Systems for a Very Large Offshore Wind Turbine Supported by a Semisubmersible Floating Platform

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Jinsong Liu ◽  
Lance Manuel
Keyword(s):  
Wind Turbine ◽  
Integrated System ◽  
Offshore Wind ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
System Response ◽  
Mooring System ◽  
Floating Platform ◽  
Mooring Lines ◽  
Wind Speeds

As offshore wind turbines supported on floating platforms extend to deep waters, the various effects involved in the dynamics, especially those resulting from the influence of moorings, become significant when predicting the overall integrated system response. The combined influence of waves and wind affect motions of the structure and induce tensile forces in mooring lines. The investigation of the system response under misaligned wind-wave conditions and the selection of appropriate mooring systems to minimize the turbine, tower, and mooring system loads is the subject of this study. We estimate the 50-year return response of a semisubmersible platform supporting a 13.2 MW wind turbine as well as mooring line forces when the system is exposed to four different wave headings with various environmental conditions (wind speeds and wave heights). Three different mooring system patterns are presented that include 3 or 6 mooring lines with different interline angles. Performance comparisons of the integrated systems may be used to define an optimal system for the selected large wind turbine.

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.

Impact of Bathymetry on the Mooring Design of an Offshore Floating Unit

2016 ◽  
Author(s):  
Vivek Jaiswal ◽  
Srinivas Vishnubhotla ◽  
Sean Cole ◽  
Robert B. Gordon ◽  
Partha Sharma
Keyword(s):  
Time Domain ◽  
Previous Method ◽  
Mooring Line ◽  
Mooring System ◽  
Analysis Program ◽  
Design Assessment ◽  
True Representation ◽  
The Time Domain ◽  
Constant Slope ◽  
The Impact

Moored offshore floating units may operate in regions where the bathymetry changes significantly over the mooring spread. Traditional mooring analysis methods make the assumption that the seabed slope is constant along the azimuth direction of each mooring line. This assumption, while reasonable for a seabed with nearly constant slope, can lead to significant errors with respect to the line tensions and vessel offsets in the mooring design assessment when the seabed slope is variable. This paper demonstrates the impact of bathymetry changes on the mooring design with the help of numerical analysis examples. The floating vessel considered is a semi-submersible moored by an eight point all chain catenary mooring system. Two methods of analysis are compared. In the first method, a true representation of the seabed surface that accounts for all variations in the bathymetry is used. In the second method, the anchor depths and the seabed slopes at the anchor locations estimated in the previous method are used, however, with the assumption of constant seabed slopes along the line azimuth directions. The dynamic analysis program Orcaflex is used for performing the numerical analyses in the time domain for both the methods. Differences in the performance of the mooring system are demonstrated by comparing the static and the dynamic line tensions as well as the vessel offsets in different environmental conditions. The paper also discusses how maximum offsets and line tensions are estimated.

Hydrodynamic Behaviors of Aquaculture Net Cages After the Successive Mooring Lines Failure

2021 ◽  
Author(s):  
Hung-Jie Tang ◽  
Ray-Yeng Yang
Keyword(s):  
Mooring Line ◽  
Mooring System ◽  
Domino Effect ◽  
Lumped Mass ◽  
Mooring Lines ◽  
Upstream Side ◽  
Anchor Points ◽  
The Time Domain ◽  
Net Cages ◽  
Hydrodynamic Behaviors

Abstract This paper aims to study the successive mooring line failure (also known as the domino effect) and the collision between floating collars for aquaculture net cages subjected to currents. The numerical model of this study is developed based on the Morison equation and the lumped-mass scheme in the time domain. This model is then applied to see if the domino effect of moorings will happen after releasing the anchor point #1 on the upstream side. In this study, we adopt four different current speeds (0.5, 1.0, 1.5, 2.0 m/s) and three different safety factors (SF, 1.0, 1.5, 2.0) settings to calculate the number of mooring failures, and to see whether it will cause floating collars collision. The results show that in the case of the SF is 2.0, the domino effect will not be triggered, and the floating collar collision will not occur. When the SF is 1.5, and the current speed is up to 1.0 m/s or higher, only the two anchor points on the upstream side will fail and no collision will occur. However, if the SF is not considered (that is, 1.0), the domino effect will occur under all the four current speeds, and the floating collar collision will all occur. Therefore, we suggest that in order to avoid the domino effect of the mooring system of aquaculture net cages from currents, the SF of the mooring system design must be at least 2 times.

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