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 Time and Frequency Domain Dynamic Analysis of Offshore Mooring

2021 ◽  
Vol 9 (7) ◽  
pp. 781
Author(s):  
Shi He ◽  
Aijun Wang
Keyword(s):  
Dynamic Analysis ◽  
Frequency Domain ◽  
Time Domain ◽  
Linearization Method ◽  
Euler Method ◽  
Single Component ◽  
Hydrodynamic Drag ◽  
Lumped Mass ◽  
Mooring Lines ◽  
The Time Domain

The numerical procedures for dynamic analysis of mooring lines in the time domain and frequency domain were developed in this work. The lumped mass method was used to model the mooring lines. In the time domain dynamic analysis, the modified Euler method was used to solve the motion equation of mooring lines. The dynamic analyses of mooring lines under horizontal, vertical, and combined harmonic excitations were carried out. The cases of single-component and multicomponent mooring lines under these excitations were studied, respectively. The case considering the seabed contact was also included. The program was validated by comparing with the results from commercial software, Orcaflex. For the frequency domain dynamic analysis, an improved frame invariant stochastic linearization method was applied to the nonlinear hydrodynamic drag term. The cases of single-component and multicomponent mooring lines were studied. The comparison of results shows that frequency domain results agree well with nonlinear time domain results.

The Anchor-Last Deployment Problem for Inextensible Mooring Lines

1975 ◽  
Vol 97 (3) ◽  
pp. 1046-1052 ◽  
Author(s):  
Robert C. Rupe ◽  
Robert W. Thresher
Keyword(s):  
Numerical Model ◽  
Equations Of Motion ◽  
Simultaneous Equations ◽  
Mooring Line ◽  
Integration Scheme ◽  
Lumped Mass ◽  
Mooring Lines ◽  
Concentrated Masses ◽  
Predictor Corrector ◽  
Lagrange’S Method

A lumped mass numerical model was developed which predicts the dynamic response of an inextensible mooring line during anchor-last deployment. The mooring line was modeled as a series of concentrated masses connected by massless inextensible links. A set of angles was used for displacement coordinates, and Lagrange’s Method was used to derive the equations of motion. The resulting formulation exhibited inertia coupling, which, for the predictor-corrector integration scheme used, required the solution of a set of linear simultaneous equations to determine the acceleration of each lumped mass. For the selected cases studied the results show that the maximum tension in the cable during deployment will not exceed twice the weight of the cable and anchor in water.

scholarly journals Dynamic Response of Floating Wind Turbine Under Consideration of Dynamic Behavior of Catenary Mooring-Lines

2017 ◽  
Author(s):  
Shuangxi Guo ◽  
Yilun Li ◽  
Min Li ◽  
Weimin Chen ◽  
Yiqin Fu
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Nonlinear Dynamic ◽  
Ocean Waves ◽  
Wave Frequency ◽  
Mooring Line ◽  
Mooring Lines ◽  
Restoring Force ◽  
Dynamic Behaviors ◽  
Floating Wind Turbine

Recently, wind turbine has been developed from onshore area to offshore area because of more powerful available wind energy in ocean area and more distant and less harmful noise coming from turbine. As it is approaching toward deeper water depth, the dynamic response of the large floating wind turbine experiencing various environmental loads becomes more challenge. For examples, as the structural size gets larger, the dynamic interaction between the flexible bodies such as blades, tower and catenary mooring-lines become more profound, and the dynamic behaviors such as structural inertia and hydrodynamic force of the mooring-line get more obvious. In this paper, the dynamic response of a 5MW floating wind turbine undergoing different ocean waves is examined by our FEM approach in which the dynamic behaviors of the catenary mooring-line are involved and the integrated system including flexible multi-bodies such as blades, tower, spar platform and catenaries can be considered. Firstly, the nonlinear dynamic model of the integrated wind turbine is developed. Different from the traditional static restoring force, the dynamic restoring force is analyzed based on our 3d curved flexible beam approach where the structural curvature changes with its spatial position and the time in terms of vector equations. And, the modified finite element simulation is used to model a flexible and moving catenary of which the hydrodynamic load depending on the mooring-line’s motion is considered. Then, the nonlinear dynamic governing equations is numerically solved by using Newmark-Beta method. Based on our numerical simulations, the influences of the dynamic behaviors of the catenary mooring-line on its restoring performance are presented. The dynamic responses of the floating wind turbine, e.g. the displacement of the spar and top tower and the dynamic tension of the catenary, undergoing various ocean waves, are examined. The dynamic coupling between different spar motions, i.e. surge and pitch, are discussed too. Our numerical results show: the dynamic behaviors of mooring-line may significantly increase the top tension, particularly, the peak-trough tension gap of snap tension may be more than 9 times larger than the quasi-static result. When the wave frequency is much higher than the system, the dynamic effects of the mooring system will accelerate the decay of transient items of the dynamic response; when the wave frequency and the system frequency are close to each other, the displacement of the spar significantly reduces by around 26%. Under regular wave condition, the coupling between the surge and pitch motions are not obvious; but under extreme condition, pitch motion may get about 20% smaller than that without consideration of the coupling between the surge and pitch motions.

Effects of Mooring Line Design Parameters on the Line Dynamics and Fatigue Response of Subsea Mooring Lines

2018 ◽  
Author(s):  
Hamid Sedghi ◽  
Mehrdad Kimiaei
Keyword(s):  
Dynamic Analysis ◽  
Fatigue Damage ◽  
Dynamic Responses ◽  
Statistical Characteristics ◽  
Design Parameters ◽  
Mooring Line ◽  
Engineering Practice ◽  
Mooring Lines ◽  
Fatigue Design ◽  
Line Design

Dynamic characteristics of mooring lines play an important role in overall structural response and fatigue design of mooring systems. Full dynamic analysis including line dynamics is a vital part of fatigue design process although in time domain it needs excessive computational efforts. For fatigue analysis of mooring lines where hundreds of different environmental loads have to be checked, alternative analysis approach such as quasi-dynamic analysis with implicit inclusion of the line dynamic effects are used widely in engineering practice. This paper presents the results of series of case studies on the effects of various mooring line design parameters on the line dynamics as well as the mooring line dynamic fatigue response. Various mooring line composition types (all chain and chain-polyester-chain) used in different mooring configurations (catenary, semi-taut and taut) with variable range of mooring line pretensions connected to a floater in shallow and deep water depths are studied. Ratios of fatigue damage results between dynamic and quasi-dynamic results as well as the relation between fatigue damage and statistical characteristics of the line dynamic responses for different line configurations and load cases are investigated in detail.

scholarly journals Numerical Study on Hydrodynamic Responses of Floating Rope Enclosure in Waves and Currents

2020 ◽  
Vol 8 (2) ◽  
pp. 82
Author(s):  
Hui Yang ◽  
Yun-Peng Zhao ◽  
Chun-Wei Bi ◽  
Yong Cui
Keyword(s):  
Numerical Study ◽  
Line Tension ◽  
Wave Period ◽  
Windward Side ◽  
Mooring Line ◽  
Fish Stock ◽  
Lumped Mass ◽  
Mooring Lines ◽  
Design Factors ◽  
Volume Retention

Enclosure aquaculture is a healthy and ecological aquaculture pattern developed in recent years to relieve the pressure due to the wild fish stock decline and water pollution. The object of this paper was a floating rope enclosure, which mainly consisted of floaters, mooring lines, sinkers and a net. In order to optimize mooring design factors, the hydrodynamic responses of the floating rope enclosure with different mooring systems in combined wave-current were investigated by experimental and numerical methods. Physical model experiments with a model scale of 1:50 were performed to investigate the hydrodynamic characteristics of a floating rope enclosure with 12 mooring lines. Based on the lumped mass method, the numerical model was established to investigate the effects of mooring design factors on the mooring line tension, force acting on the bottom, and the volume retention of the floating rope enclosure. Through the analysis of numerical and experimental results, it was found that the maximum mooring line tension of the floating rope enclosure occurs on both sides of the windward. Increasing the number of mooring lines on the windward side is helpful to reduce the maximum mooring line tension. Waves and current both have an influence on the mooring line tension; in contrast, currents have a more obvious effect on the mooring line tension than waves. However, the influence of the wave period on the maximum mooring line tension is small. The force endured by the bottom of the floating rope enclosure also changes periodically with the wave period. Yet, the maximum force endured by the bottom of floating rope enclosure occurred at the windward and leeward of the structure. The volume retention of the floating rope enclosure increased with the increasing amount of mooring lines.

Research on Influence of Horizontal Offsets of Underwater Equipment Based on Pendulous Installation Method

2018 ◽  
Author(s):  
Jingqian Wang ◽  
Liping Sun ◽  
Zhongchao Deng ◽  
Gang Ma ◽  
Xiaomeng Zhu ◽  
...  
Keyword(s):  
Deep Water ◽  
Water Environment ◽  
Three Dimensional ◽  
Mooring Line ◽  
Analysis Model ◽  
Lumped Mass ◽  
Lumped Mass Method ◽  
Traction Fluid ◽  
Simulation Problem ◽  
Domain Coupling

Large underwater equipment used in deep-sea engineering, which needs mooring line in order to hang down while using pendulous installation method in 1500m deep-water installation. During the procession, the mooring line will suffer the vessel’s pull, large equipment’s traction, fluid force leading to elongation, bending and other deformation, so need to analyze its motion. Aiming at the numerical simulation problem of underwater equipment installed by pendulous installation method in deep-water environment, this paper combines lumped mass method, three-dimensional potential theory and Morison equation to establish the analysis model of the whole installation system. Under the different horizontal dropping offsets of the equipment, this paper computes not only tension of mooring line, but motion performance of underwater equipment and working vessel during the pendulous lowering phase. The Pendulous Installation Method (PIM) puts a working vessel, a mooring line and a underwater equipment installed in succession, and there is a coupling interaction among them, so it is essential to do time-domain coupling analysis. So the Orcaflex Software is used to simulate the entire deep-water installation system. Using different horizontal dropping position as a variable, we can get the contrast about the different movement states of the mooring line and underwater equipment, and finally we will get the conclusion.

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.

scholarly journals Coupled Mooring Analyses for the WEC-Sim Wave Energy Converter Design Tool

2016 ◽  
Author(s):  
Senu Sirnivas ◽  
Yi-Hsiang Yu ◽  
Matthew Hall ◽  
Bret Bosma
Keyword(s):  
Numerical Method ◽  
Wave Energy ◽  
Coupled Model ◽  
The Body ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Lumped Mass ◽  
Energy Converter ◽  
Mooring Lines ◽  
Point Absorber

A wave-energy-converter-specific time-domain modeling method (WEC-Sim) was coupled with a lumped-mass-based mooring model (MoorDyn) to improve its mooring dynamics modeling capability. This paper presents a verification and validation study on the coupled numerical method. First, a coupled model was built to simulate a 1/25 model scale floating power system connected to a traditional three-point catenary mooring with an angle of 120 between the lines. The body response and the tension force on the mooring lines at the fairlead in decay tests and under regular and irregular waves were examined. To validate and verify the coupled numerical method, the simulation results were compared to the measurements from a wave tank test and a commercial code (OrcaFlex). Second, a coupled model was built to simulate a two-body point absorber system with a chain-connected catenary system. The influence of the mooring connection on the point absorber was investigated. Overall, the study showed that the coupling of WEC-Sim and the MoorDyn model works reasonably well for simulating a floating system with practical mooring designs and predicting the corresponding dynamic loads on the mooring lines. Further analyses on improving coupling efficiency and the feasibility of applying the numerical method to simulate WEC systems with more complex mooring configuration are still needed.

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