scholarly journals Platform Motions and Mooring System Coupled Solver for a Moored Floating Platform in a Wave

Processes ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 1393
Author(s):  
Sang Chul Lee ◽  
Seongjin Song ◽  
Sunho Park
Keyword(s):  
System Analysis ◽  
Mooring Line ◽  
Mooring System ◽  
Offshore Platforms ◽  
Floating Platform ◽  
Lumped Mass ◽  
Time Step ◽  
Restoring Force ◽  
Line Model ◽  
Platform Motions

In advance of building moored floating offshore platforms, in recent years, there has been a greater demand for two-way coupled simulations between a motion solver based on the viscous flow theory and a mooring line model, including cable dynamics. This paper introduces open-source libraries such as MoorDyn (the lumped-mass mooring line model) and OpenFOAM (the computational fluid dynamics libraries). It describes the methods by which they can be coupled bi-directionally. In each time step, the platform motions calculated by OpenFOAM are transferred to MoorDyn as the boundary conditions for the mooring system analysis. In contrast, MoorDyn calculates the restoring force and moment due to the mooring system and transfers them to OpenFOAM. The restoring force and moment act on the platform as the external force and moment for the platform motions in the next time step. The static tension and profile of the mooring system, dynamic tension of the mooring system, and free decay motions of the floating buoy in the still water were simulated to check the accuracy of OpenFOAM and MoorDyn. The coupled solver was used to produce simulations of the moored decay motions of the floating buoy in the still water and the moored motions with the Stokes 5th order wave. All simulation results were compared and showed good agreement with the numerical solution and experiment results. In addition, the characteristics of each solver were investigated.

Optimal Design Methodology for Multi-Component Mooring Systems in Deep Water

2010 ◽  
Author(s):  
Long Yu ◽  
Jiahua Tan
Keyword(s):  
Optimal Design ◽  
Deep Water ◽  
Design Methodology ◽  
Element Model ◽  
Gas Production ◽  
Mooring Line ◽  
Mooring System ◽  
Offshore Platforms ◽  
Mooring Lines ◽  
Restoring Force

Multi-component mooring systems, one of the crucial equipments of offshore platforms, play an important role in deep water oil&gas production because of relative low cost and light weight. A single mooring line can be constructed by combination of wire ropes, chains, fiber ropes, buoys and connectors etc. and provide adequate restoring force at fairlead point of platforms. Although the static and dynamic analyzing approaches for a determined multi-component system have been studied already, it is still hard to design and predetermine an appropriate mooring system that can satisfy the codes with multi-component lines. Referred to the conventional mooring system design method, this paper brings out an optimal design methodology for multi-component mooring systems. According to quasi-static method, at extreme offset position of the platform, an optimization model for designing the multi-component mooring line with biggest tension in deep water has been provided. Then, with the aid of design wave method and morison equation, a finite element model has been used to calculate mooring line dynamics at each fairlead point in time domain. The nonlinear interaction of mooring lines and seabed has also been investigated. Heave and surge of the platform have also been considered. Both 2D and 3D mooring system models have been built to search the interference of the lines and directional influence of environment loads like current and wave. The paper applied this set of analyzing methods and processes into a deep water semisubmersible serving at South China Sea. Compared with the results calculated by other software, the methodology mentioned in the paper got similar result with less weight and bigger restoring force.

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.

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.

Development of a Numerical Dynamic Mooring Model for Visco-Elastic and Visco-Plastic Deformation of Synthetic Ropes

2020 ◽  
Author(s):  
Nhu Nguyen ◽  
Krish Thiagarajan Sharman
Keyword(s):  
System Analysis ◽  
Dynamic Environment ◽  
Offshore Wind ◽  
Mooring Line ◽  
Published Data ◽  
Mooring System ◽  
Fibrous Materials ◽  
Stress Strain ◽  
Nonlinear Properties ◽  
Nonlinear Stress

Abstract Synthetic ropes are increasingly being considered for various offshore and marine applications, including for mooring offshore wind turbines and for aquaculture cages. Studies have shown that nonlinear behaviors of a synthetic rope in a dynamic environment can complicate the mooring system analysis. Nonlinear stiffness coupled with time- and load history-dependent characteristics of fibrous materials can allow for over or under estimation of the mooring forces. It is critical that these nonlinear properties are incorporated correctly into a mooring model, especially for studies of structures’ performances in extreme events. The study aims at developing a simulation tool capable of predicting the dynamic behavior of highly extensible synthetic mooring system used in coastal and offshore floating structures. The program employs an implicit finite-difference approach to model the dynamic behaviors of the mooring line subjected to user-defined motions of the fairlead. As opposed to a linear stress-strain relationship typically incorporated in other mooring models, the current program is built with constitutive model of fibrous materials to account for the nonlinearity time- and load-dependent characteristics of synthetic lines. As part of the program, an inverted constitutive stress-strain model, in which stresses are calculated from given strains in stress-based formulas, were presented. Comparisons with published data indicates that the proposed inverted nonlinear stress-strain formulas were successfully integrated with the mooring solver. The coupled nonlinear mooring program predicts accurately both nonlinear reversible and irreversible deformations of synthetic cables.

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.

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.

“ASEMOS”—Advanced Semisubmersible Mooring System

1985 ◽  
Vol 22 (01) ◽  
pp. 36-49
Author(s):  
Christian V. Wolff
Keyword(s):  
Heavy Chain ◽  
Load Capacity ◽  
Wire Rope ◽  
Center Of Gravity ◽  
Mooring Line ◽  
Lower Grade ◽  
Mooring System ◽  
Restoring Force ◽  
Improved Stability ◽  
Drilling Rigs

The least efficient, yet most popular mooring system on semisubmersibles is the conventional chain-only type. These perform well in shallow to moderate depths, but as water depth increases, so do horizontal excursions of the rig. System efficiency also decreases because more and more of the strength of the chain is required to support its own weight and less is available to provide horizontal restoring forces. This paper describes an advanced mooring system that offers several distinct advantages over the usual alternatives: more elasticity in the mooring line at shallow depths; maximum strength and restoring force at the vessel; lower center of gravity and improved stability; increased variable deck-load capacity; and protection of the winches from wind and sea. One feature that makes the "ASEMOS" system unique is the placement of the mooring winches within the pontoons (Figs. 1 and 2). This location not only protects the winches from the elements, but results in a much lower center of gravity than that of other comparably sized semisubmersible drilling rigs. Another key feature is the use of oversized very heavy chain between the end of the wire rope mooring line and the anchors. This heavy chain provides extra elasticity in the mooring line catenary in shallow depths, and shortens the length of wire rope required to achieve maximum anchor-holding power in deep water. The greater breaking strength of the oversized chain permits the use of a lower-grade steel and avoids the high cost and fatigue problems commonly encountered in other systems.

Numerical Simulation of the Domino Effect of Mooring System Failure for an Aquaculture Net Cage Under Waves and Currents

2020 ◽  
Author(s):  
Hung-Jie Tang ◽  
Ray-Yeng Yang ◽  
Tzu-Chieh Wen ◽  
Po-Hung Yeh ◽  
Chai-Cheng Huang
Keyword(s):  
Line Tension ◽  
Body Motion ◽  
Economic Losses ◽  
Mooring Line ◽  
Mooring System ◽  
System Failure ◽  
Domino Effect ◽  
Lumped Mass ◽  
Waves And Currents ◽  
Net Cage

Abstract Up to date, the mooring system failure of aquaculture net cage remains a continuing problem, especially the domino effect, which often leads to huge economic losses. Thus, this study aims to investigate the domino effect of a mooring system of a net cage under waves and currents. In this study, a time-domain numerical model based on the Morison equation and the lumped mass method is applied. A full-scale net cage system widely used in a local sea area is adopted. A 50 years return period waves with a strong following current is considered to be the design condition. It can be expected that the tension on the remaining upstream anchor increases dramatically when an upstream anchor is lost. Then, the domino effect occurs if the maximum tension on the remaining anchor exceeds its design condition. Therefore, in this simulation, the initial failure is considered to be a man-made event at a preset time, but the rest failures are resulted from exceeding the breaking strength of a rope. Both the current-only condition and the wave-current condition have been examined. The results including mooring line tension, volume reduction coefficient and rigid body motion are discussed. In addition, the results show that the failure sequence of anchor is different between the current-only condition and the wave-current condition.

Sign in / Sign up

Export Citation Format

Share Document