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.

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 A Study on a Floating Solar Energy System Applied in an Intertidal Zone

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7789
Author(s):  
Ray-Yeng Yang ◽  
Sheng-Hung Yu
Keyword(s):  
Energy System ◽  
Mooring Line ◽  
Solar Photovoltaic ◽  
Solar Panels ◽  
Floating Platform ◽  
Mooring Lines ◽  
Ansys Fluent ◽  
Wave Condition ◽  
Scale Ratio ◽  
Motion Characteristics

This study was aimed at investigating a floating solar photovoltaic (FPV) system by numerical and experimental simulations under wave and wind loads to analyze the motion characteristics of the platform, the tension of the mooring line, and the pressure and uplift coefficient of panels at 2.5 m/5 m water depth conditions. The floating platform was installed with four rows of solar panels, each row with five panels, attached with four catenary types of mooring lines at the corner of the platform. The numerical model was based on ANSYS AQWA and ANSYS FLUENT (ANSYS Inc., Canonsburg, PA, USA). The experiment model was a scaled FPV platform with four rows of panels scaled in the 1:4 scale ratio. The results obtained from the experiment and numerical simulation achieved a good agreement. The results show that under normal sea conditions, the FPV system may resonate in a high frequency of wave condition, and a larger lift force occurred at the windward surface. Under extreme sea conditions, the pitch motion of the floating platform changed about ±6° without overturning; however, the wind will cause a large drift of the floating platform and the vortex area formed, which will cause damage to the solar panel.

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.

A New Nonlinear Coupled Analysis Tool for Floating Structures

2012 ◽  
Author(s):  
Zhiling Li ◽  
Carlos Llorente ◽  
Cheng-Yo Chen ◽  
Chang Ho Kang ◽  
Edmund Muehlner ◽  
...  
Keyword(s):  
Performance Analysis ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Analysis Tool ◽  
Wave Load ◽  
Mooring Lines ◽  
Dynamic Interactions ◽  
Floating Structures ◽  
Coupled Method ◽  
Global Performance

For the global performance analysis of a floater, the traditional semi-coupled method models mooring lines/risers as nonlinear massless springs and ignores 1) the inertial effects from mooring lines/risers, 2) the current and wave load effects on mooring lines/risers, and 3) the dynamic interaction between mooring lines/risers and the floater. However, these effects are deemed critical for deepwater and ultra deepwater floating structures as they may have a significant impact on the floaters’ motions and mooring line/riser tensions. This paper presents the development and verification of a time-domain nonlinear coupled analysis tool, MLTSIM-ROD, which is an integration of a recently developed 3D rod dynamic program, ROD3D, with the well-calibrated floater global performance analysis program, MULTISIM (Ref [9]). The ROD3D was developed based on a nonlinear finite element method and merged with MULTISIM by matching the forces and displacements of mooring lines/risers with the floater at their connections. MLTSIM-ROD can thus predict the floater’s large displacement/rotation motions and mooring line/riser tensions including all the coupled effects between the floater and mooring lines/risers. In this paper, global performance predictions for a SPAR in the Gulf of Mexico in deepwater were carried out using MLTSIM-ROD. The results were then verified with those from other coupled analysis programs. The paper also presents the results of motions and mooring line/riser tensions of the SPAR using both the coupled and semi-coupled methods. The results from the coupled and semi-coupled analyses indicate that the floater’s motions and mooring line/riser tensions could be significantly influenced by the dynamic interactions between the floater and mooring lines/risers. Hence, the coupled method needs to be considered for deepwater floating structures.

Mooring- and Riser-Induced Damping in Fatigue Seastates

2002 ◽  
Author(s):  
D. L. Garrett ◽  
R. B. Gordon ◽  
J. F. Chappell
Keyword(s):  
Coupled Model ◽  
Rational Approach ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Floating Platform ◽  
Mooring Lines ◽  
Equivalent Linear ◽  
Floating System ◽  
Linear Damping ◽  
Stiffness And Damping

Viscous damping due to drag on mooring lines and risers is seastate dependent and significantly affects the motion of a floating platform in deep water, particularly in everyday seastates. This in turn impacts design of the risers, which are typically controlled by fatigue. The dynamic interaction between the platform, mooring and risers cannot be evaluated using conventional uncoupled analysis tools, where each is analyzed separately. Rather, coupled analysis is required to provide a consistent way to model the drag-induced damping from mooring lines and risers. We describe a coupled, frequency domain approach (RAMS – Rational Approach to Marine Systems) for calculating the dynamic response of vessel, mooring and risers. In coupled analysis, the risers and mooring lines are included in the model along with the floater. In this way, damping of the floater motion due to drag on the mooring lines and risers is incorporated directly. It is also valuable to estimate the linear damping factors from the full, coupled analysis results. These damping factors may then, for example, be used in an equivalent linear model of the floating system in which the stiffness and damping effects of the mooring and risers are represented as additions to the floater stiffness and damping matrices. Such a model could be used to efficiently design a subsystem (e.g.; an export riser). We describe a technique to determine the equivalent linear damping factors from the coupled analysis results. This paper also illustrates the use of these methods for a West Africa FPSO. The need for coupled analysis is shown by comparing results from the fully coupled model with those obtained using an uncoupled method in which the mooring line damping is approximated.

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.

scholarly journals Proposal of a Novel Semi-Submersible Floating Wind Turbine Platform Composed of Inclined Columns and Multi-Segmented Mooring Lines

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1809 ◽  
Author(s):  
Zhenqing Liu ◽  
Qingsong Zhou ◽  
Yuangang Tu ◽  
Wei Wang ◽  
Xugang Hua
Keyword(s):  
Wind Turbine ◽  
Offshore Wind ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Analysis Tool ◽  
Mooring Lines ◽  
Offshore Area ◽  
Floating Wind Turbine ◽  
Inclined Angle ◽  
Heave Motion

The semi-submersible floating offshore wind turbine has been studied in detail due to its good stability. However, the occurrence of typhoons are very frequent in China’s offshore area, putting forward a higher requirement for the stability of the floating wind turbine system. By changing the connection mode of the mooring line as well as the structural form of the platform based on the original OC4 model, two groups of models were examined by an in-house developed code named as the Analysis Tool of Floating Wind Turbine (AFWT). The influence of the arrangement of the mooring lines and the inclination angle of the upper columns on the motion response were clarified. It was found that the surge motion of the platform would be obviously decreased by decreasing the length of the upper segments of the mooring lines, while the heave motion of the platform would be significantly decreased as increasing the inclined angle of the columns. Therefore, a new model integrating the optimized multi-segmented mooring lines and the optimized inclined columns was proposed. The examinations showed that compared with the response motions of the original OC4 semi-submersible model, the proposed model could reduce both the surge and heave motions of the platform effectively.

Reliability Analysis of Mooring Lines for Deep Water Floating Systems

2012 ◽  
Author(s):  
K. Gurumurthy ◽  
Suhail Ahmad ◽  
A. S. Chitrapu
Keyword(s):  
Dynamic Analysis ◽  
Reliability Analysis ◽  
Deep Water ◽  
Reliability Assessment ◽  
Mooring Line ◽  
Analysis Method ◽  
Mooring Lines ◽  
Line Load ◽  
Coupled Dynamic Analysis ◽  
Floating Systems

Reliability analysis of mooring lines requires an accurate prediction of extreme responses for large number of sea states even for a short-term based approach. In deep water, the interactions between the floater motions and the large number of risers and mooring lines become significant and must be considered for accurate prediction of floater motions as well as line dynamics. Time-domain coupled dynamic analysis procedures have been shown to give more accurate results but at a higher computational expense. Therefore, efficient computational tools are required for reliability analysis of mooring lines for deep water floating systems. Enhanced decoupled dynamic analysis method, in which the floater motions are computed by coupled analysis considering a coarse finite element model of the mooring line, is an efficient method and provides results comparable in accuracy with the fully coupled dynamic analysis procedures. This paper presents the application of enhanced de-coupled dynamic analysis method for reliability assessment of mooring lines for deep water floating systems. For reliability analysis of mooring lines, the methodology presented in Ding et al. [5] is adopted. Reliability analysis of a critically loaded mooring line for a deep water classical spar floater under extreme environmental loads is performed using environmental contour approach. Mooring line tension time histories under various storm conditions are calculated using enhanced de-coupled dynamic analysis. The uncertainty in the predicted maximum mooring line load due to different storm events, variability in met-ocean conditions and numerical models is considered. Probability of failure and the corresponding reliability index of the mooring line are calculated. The impact of variability in predicted mooring line load, line capacities and factors of safety on mooring line reliability are studied. It is seen that enhanced de-coupled dynamic analysis, which predicts the mooring line loads as accurately as coupled dynamic analysis with lesser CPU time, can be used more efficiently for reliability assessment of mooring lines for deep water floating systems.

Hull-Mooring Coupled Dynamic Analysis of Two Side-by-Side Operating Vessels

2010 ◽  
Author(s):  
Mahdi Mirzaei ◽  
Mehdi Shafieefar ◽  
Mohammad Reza Moharrami
Keyword(s):  
The Other ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Mooring Lines ◽  
Gas Field ◽  
Finite Element Program ◽  
Coupled Dynamic Analysis ◽  
Element Program ◽  
The Mean ◽  
The Persian Gulf

This paper contains the results of mooring analyses of two side-by-side operating crane barges in the installation procedure of a jacket type platform in an oil-gas field in the Persian Gulf. Since the vessels are proposed to operate next to a fixed structure, making sure about their displacements and a convenient clearance between them and the jacket is a highly important aspect of the design process. In essence, the analyses consist of setting an appropriate configuration and positioning of the vessels relative to each other, considering a reasonable gap between vessels and the jacket, connecting the vessels together, and studding the behavior of the moored system when it is subjected to a set of environments. In particular, an equilibrium configuration is found when the system is subjected to the mean force of the environment which consists of waves, wind gusts and currents. Then the dynamics of the system about the mean position is investigated. In order to study the influence of a dynamic mooring analysis, two cases are compared; one considering weight and buoyancy as the only forces acting on the lines and carrying out a quasi-static mooring analysis, and the other taking into account the hydrodynamic forces from the mooring lines. An accurate and efficient finite element program for the coupled analysis of the hull-mooring system is used and two types of modeling the connected vessels are compared; one using joints with restraints for all relative motions but in relative roll, and the other using slings and fenders. In all cases, the results of time domain analyses consisting of mooring line loads and motion responses of the vessels are presented in time histories and the statistics are studied.

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