Numerical Simulation of a Spar Interacting With a Polyester Mooring System

2004 ◽  
Author(s):  
Minsuk Kim ◽  
Yu Ding ◽  
Jun Zhang
Keyword(s):  
Energy Dissipation ◽  
Cyclic Loads ◽  
Mooring System ◽  
Floating Structure ◽  
Mooring Lines ◽  
Floating Structures ◽  
System A ◽  
Large Elongation ◽  
The Mean ◽  
Offset Curve

A numerical scheme, known as CABLE3D, originally developed for the simulation of dynamics of steel mooring lines is extended to allow for special properties pertaining to polyester ropes, such as relatively large elongation under tension, dependence of the modulus on loads, and energy dissipation under cyclic loads. The modified CABLE3D is then integrated into a numerical package, known as COUPLE6D, for computing the interaction between a floating structure and its polyester mooring system. A classical SPAR is chosen in this study as a representative of deepwater floating structures. By considering large elongation in polyester ropes, the static offset curve of a polyester mooring system is softer than that calculated under the assumption of small elongation. The effects of the mean loads on the modulus of polyester ropes are much greater than those of the dynamic loads. The energy dissipation in polyester ropes under cyclic loading does not play a significant role in the responses of the SPAR and tensions in a polyester mooring system. The above observations though made based on a classical SPAR may still have important implications to other floating structures moored by a polyester mooring system.

Numerical Investigation on Interaction Between a Semi-Submersible Platform and its Mooring System

2015 ◽  
Author(s):  
Yuanchuan Liu ◽  
Yao Peng ◽  
Decheng Wan
Keyword(s):  
Mooring Line ◽  
Mooring System ◽  
Floating Structure ◽  
Mooring Lines ◽  
Flow Solver ◽  
Floating Structures ◽  
Marine Renewable Energy ◽  
Motion Responses ◽  
Increasing Demand ◽  
Energy Engineering

With the increasing demand of floating structures in offshore, coastal and marine renewable energy engineering, the interaction between the mooring system and floating structure becomes more and more important. In this paper, motion responses of a semi-submersible platform with mooring system under regular wave conditions are investigated numerically by a viscous flow solver naoe-FOAM-SJTU based on the open source toolbox OpenFOAM. Influence of the mooring system on the platform motion responses is evaluated in two different ways. Investigations are covered for analysis methods adopted for solving mooring lines and the length of each part of a multi-component mooring line. Several important conclusions are drawn.

Optimization of Mooring System for Multi-Arrayed Tidal Turbines in a Strong Current Area

2014 ◽  
Author(s):  
Yu-ho Rho ◽  
Chul-hee Jo ◽  
Do-youb Kim
Keyword(s):  
Power Systems ◽  
Tidal Current ◽  
Mooring Line ◽  
Limited Area ◽  
Mooring System ◽  
Ocean Energy ◽  
Floating Structure ◽  
Energy Potential ◽  
Mooring Lines ◽  
Floating Structures

Recently, focus has been placed on ocean energy resources as environmental concerns regarding the exploitation of hydrocarbons are increasing. The enormous energy potential in tidal current power fields has been exploited by installing floating tidal current power turbines. Due to other floating structures operating within a limited area, stationkeeping is needed in order to keep the motions of the floating structures within permissible limits. In this study, methods for selecting and optimizing the mooring system for floating tidal current power systems in shallow water are investigated. The mooring system provides restoring forces and moments on a floating structure, pulling the structure back toward its equilibrium position. Typically, the mooring lines are segmented in order to optimize the force and displacement characteristics known as the mooring line characteristics. The mooring system concepts investigated in this study include the distributed mass, clump weight, and buoyancy element mooring systems.

Influence of Nonlinear Mooring Stiffness on Hydrodynamic Performance of Floating Bodies

2009 ◽  
Author(s):  
Huilong Ren ◽  
Jian Zhang ◽  
Guoqing Feng ◽  
Hui Li ◽  
Chenfeng Li
Keyword(s):  
Equilibrium Position ◽  
Equations Of Motion ◽  
Offshore Structures ◽  
Hydrodynamic Performance ◽  
Coupled Analysis ◽  
Mooring System ◽  
Main Function ◽  
Ocean Engineering ◽  
Mooring Lines ◽  
Floating Structures

Coupled dynamic analysis between floating marine structures and flexible members such as mooring lines and risers, is a challenging work in the ocean engineering field. Coupled analysis on mooring-buoy interactions has been paid more and more concern for recent years. For floating offshore structures at sea, the motions driven by environmental loads are inevitable. The movement of mooring lines occurs due to the excitation on the top by floating structures. Meanwhile the lines restrict the buoy’s motion by forces acting on the fareleads. Positioning is the main function of mooring system, its orientation effects can’t be ignored for floating structures such as semi-submersible, FPS, and TLP, especially when the buoy’s equilibrium position shifting to another place. Similar as hydrostatic restoring forces, mooring force related with the buoy’s displacement can be transformed into mooring stiffness and can be added in the differential equations of motion, which is calculated at its equilibrium point. For linear hydrodynamic analysis in frequency domain, any physical quantity should be linear or be linearized, however mooring stiffness is nonlinear in essence, so the tangent or differential stiffness is used. Steel chains are widely used in catenary mooring system. An explicit formulation of catenary mooring stiffness is derived in this article, which consists of coupled relations between horizontal and vertical mooring forces. The effects of changing stiffness due to the shift of equilibrium position on the buoy’s hydrodynamic performance are investigated.

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.

VIM Model Test and Assessment on a Semi-Submersible Type Floater With Different Column Intervals

2016 ◽  
Author(s):  
Toshifumi Fujiwara ◽  
Tadashi Nimura ◽  
Kohei Shimozato ◽  
Ryosuke Matsui
Keyword(s):  
Estimation Method ◽  
Assessment Method ◽  
Design Stage ◽  
Resource Exploitation ◽  
Floating Structure ◽  
Mooring Lines ◽  
Floating Structures ◽  
Reynolds Number Flow ◽  
Number Flow ◽  
High Reynolds

Semi-submersible type offshore floating structures are expected to be used in the Japanese coastal area and at sea off Japan for promoting resource exploitation and development in near future. As a moored offshore floating structure may be suffered from current, Vortex-induced Motion (VIM) effect should be assessed in an appropriate manner since the VIM may cause fatigue damage of the floating structure’s mooring lines. VIM phenomenon on semi-submersible type floating structures, however, is not clear, and its comprehension is insufficient since there are only small number of open research papers with lack specifications of the structures. Moreover, a standardized assessment method for the VIM on them has not ever been proposed. At first in this paper, the results of VIM measurement test using some large semi-submersible floating structure models in relatively high Reynolds number flow are presented, and afterwards simplified estimation method, that is useful in the design stage for a semi-submersible type offshore floating structure, is introduced as one trial.

Remote Connection and Disconnection Device for Mooring Lines KSDIN32, KS40 and KS50 Hook and Its Modelling for Structural Finite Elements

2005 ◽  
Author(s):  
Jose Carlos Lima de Almeida ◽  
Ricardo Sobral
Keyword(s):  
Mooring System ◽  
Fundamental Characteristic ◽  
Environmental Condition ◽  
Mooring Lines ◽  
System A ◽  
Deep Waters ◽  
Campos Basin ◽  
The World ◽  
Adverse Environmental Condition ◽  
Technological Challenge

With the new sceneries of oil exploration in ultra deep waters that move forward to 3000 m, it has been putting for the companies that accepted this technological challenge significant border of the techno-scientific knowledge. Therefore, in this cases of ultra deep waters, where the use of the polyester synthetic rope in the Petrobras Floating Production Units, is present, it can appears the need replace. THE NEED TO LOOK FOR A SOLUTION FOR THE RELATIVE PROBLEMS THE CHANGES OF THE POLYESTER ROPE IN THE PRODUCTION PLATFORMS WITHOUT THE CHANGE OF THE EXTENSION OF BOTTOM AND OF ITS FUNDATION (FIXED POINT). THEREFORE, APPEARS THE KS HOOK AND ITS OTIMIZATION UNDER THE OPTICS OF THE CONCEPTS OF THE MECHANICS OF THE FRACTURE AND OF THE TOOLS EXISTENT COMPUTACIONAIS (MEF AND MOORING SOFTWARE). This way it was needed to make available for the Mooring System a connection Device and remote disconnection for permanent use in production and drilling units. This device, already approved for the classifying society, it is the hook KS32/40/50, one of the first open device used in permanent mooring systems in the world. This device presents as fundamental characteristic, the easy installation for at adverse environmental condition in Campos’ Basin, where the sea is Bimodal and Bi-directional (sea in development).

Motion Responses of a Catenary-Taut-Hybrid Moored Single Module of a Semisubmersible Very Large Floating Structure in Multisloped Seabed

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Yiting Wang ◽  
Xuefeng Wang ◽  
Shengwen Xu ◽  
Lei Wang
Keyword(s):  
Shallow Water ◽  
Time Domain ◽  
Large Scale ◽  
Bottom Topography ◽  
Three Dimensional ◽  
Low Frequency ◽  
Mooring System ◽  
Floating Structure ◽  
Mooring Lines ◽  
Motion Responses

Motion responses of moored very large floating structures (VLFSs) in coastal regions are remarkably influenced by shallow water, seabed topography, and mooring system, which were given particular focus in this paper. A three-dimensional (3D) numerical model of a moored semisubmersible single module (SMOD) was described, and time domain simulated and experimentally validated. A catenary-taut-hybrid mooring system was adopted considering coastal space limitations. Large-scale catenary mooring lines were deployed on the deep water side, while taut chains were used on the shore side to decrease the anchor radius. Although the mooring system may induce a stiffness difference between the two sides, the effectiveness of the mooring system was demonstrated by time-domain simulation and model tests. The moored semisubmersible SMOD in shallow water exhibits significant low frequency characteristics. Water depth, asymmetric stiffness, and bottom topography effects were investigated by a series of sensitivity studies. The results show that these factors play an important role in motion responses of the moored SMOD, which can further conduce to better understandings on the hydrodynamic of the semisubmersible-type VLFSs.

The Influence of the Mooring System on the Motions and Stability of a Semi-Submersible Floating Wind Turbine

2015 ◽  
Author(s):  
Fons Huijs
Keyword(s):  
Wind Turbine ◽  
Low Frequency ◽  
Considerable Effect ◽  
Offshore Wind ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Mooring System ◽  
Mooring Lines ◽  
System A ◽  
Turbine Design

One of the main aspects of a floating offshore wind turbine design is its mooring system, which can strongly influence the floater stability and motions. This is illustrated by considering two catenary mooring systems for the same semi-submersible. The main difference between the two systems is the position of the connection points of the mooring lines on the floater, the so-called fairleads. The philosophy is that the design can be improved by shifting the fairleads to the highest feasible level. For both mooring systems, the floater motions and stability are assessed. Stability curves are derived, taking both the effect of hydrostatics and the mooring system into account. Floater motions are analyzed using both uncoupled frequency domain calculations and coupled aero-hydro-servo-elastic time domain simulations. The mooring system is found to have a considerable effect on the floating stability. The effect on the motions is less profound for the considered mooring systems and limited to the low frequency range. Mooring line tensions are however significantly affected by the fairlead position. It is concluded that, with a well-designed mooring system, a smaller and thus less expensive floater can be used while still meeting the requirements in terms of stability and maximum motions. In addition, the mooring lines may be lighter as well.

Oscillating Wave Surge Converter-Type Attachment for Extracting Wave Energy While Reducing Hydroelastic Responses of Very Large Floating Structures

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
H. P. Nguyen ◽  
C. M. Wang
Keyword(s):  
Wave Energy ◽  
Wave Force ◽  
Mooring System ◽  
Energy Converter ◽  
Floating Structure ◽  
Incident Wavelength ◽  
Floating Structures ◽  
Horizontal Wave ◽  
Horizontal Wave Force ◽  
Better Than

Abstract This paper presents an oscillating wave surge converter (OWSC)-type attachment, comprising a submerged vertical flap connected to the fore edge of a very large floating structure (VLFS) with hinges and linear power take-off (PTO) systems, for extracting wave energy while reducing hydroelastic responses of VLFS. In terms of reductions in hydroelastic responses of VLFS, the OWSC-type attachment is better than the recently proposed raft wave energy converter (WEC)-type attachment for relatively short waves (T < 7 s) and better than the conventional anti-motion device comprising a submerged vertical flap rigidly connected to the fore edge of VLFS for all wave periods. Importantly, the horizontal wave force acting on the submerged flap for the OWSC-type attachment is smaller than that for the conventional anti-motion device, leading to a more economical mooring system. In terms of wave energy extraction, the OWSC-type attachment is better than the raft WEC-type attachment for intermediate and long waves (T ≥ 7 s). In addition, for maximizing power production, the required flap length for the OWSC-type attachment is much smaller than the required pontoon length for the raft WEC-type attachment (about λ/10 as compared to about λ/3, where λ is the incident wavelength).

scholarly journals Experimental Data of a Hexagonal Floating Structure under Waves

Data ◽  
2021 ◽  
Vol 6 (10) ◽  
pp. 105
Author(s):  
Roman Gabl ◽  
Robert Klar ◽  
Thomas Davey ◽  
David M. Ingram
Keyword(s):  
Irregular Waves ◽  
Experimental Investigations ◽  
Mooring System ◽  
Floating Structure ◽  
Floating Structures ◽  
Validation Experiment ◽  
Wide Range ◽  
Wave Heights ◽  
The Individual ◽  
Six Degree Of Freedom

Floating structures have a wide range of application and shapes. This experimental investigations observes a hexagonal floating structure under wave conditions for three different draft configurations. Regular waves as well as a range of white noise tests were conducted to quantify the response amplitude operator (RAO). Further irregular waves focused on the survivability of the floating structure. The presented dataset includes wave gauge data as well as a six degree of freedom motion measurement to quantify the response only restricted by a soft mooring system. Additional analysis include the measurement of the mass properties of the individual configuration, natural frequency of the mooring system as well as the comparison between requested and measured wave heights. This allows us to use the provided dataset as a validation experiment.

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