Design loads and long term distribution of mooring line response of a large weathervaning vessel in a tropical cyclone environment

Stanisic, Dunja; Efthymiou, Mike; Kimiaei, Mehrdad; Zhao, Wenhua

doi:10.1016/j.marstruc.2018.06.004

Cited by 43 publications

(9 citation statements)

References 9 publications

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“…Note that the most suitable quantity of maxima values to describe the short-term extreme distribution is sealed. Although this problem was involved in some studies, 11,22 no guidance was provided on its execution. In this study, we adopted Q = 100 to obtain an exact distribution of the short-term extreme response as much as possible because the long-term response was a short-term iteration result.…”

Section: Assessment Of Short-term Performanceof Mooring Systemsmentioning

confidence: 99%

“…The extreme response can be regarded as the N -year response using the peak over threshold (POT) method. 10,11 The short-term analysis, in which the design characteristic values are used as input, is simple and rapid, but the results may deviate from the actual situation. It does not consider the correlation between environmental parameters; in addition, the smaller environmental parameters with higher occurrence frequencies are ignored, which may contribute significantly to the extreme response.…”

Section: Introductionmentioning

confidence: 99%

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Long-term extreme response analysis for semi-submersible platform mooring systems

Zhao

Dong

2020

Proceedings of the Institution of Mechanical Engineers, Part M:

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The accurate assessment of long-term extreme responses of floating-structure mooring system designs is important because of small failure probabilities caused by long-term and complex ocean conditions. The most accurate assessment would involve considering all conceivable sea states in which each sea state is regarded as a stochastic process and performing nonlinear time-domain numerical simulations of mooring systems to estimate the extreme response from a long-term analysis. This procedure would be computationally intensive because of the numerous short-term sea states involved. Here, a more feasible approach to evaluate the long-term extreme response is presented through immediate integration combined with Monte Carlo simulations. A parameter fitting procedure of the short-term extreme response distribution under irregular wave conditions is employed to solve the long-term response integration. Case studies were conducted on a semi-submersible platform using environmental data measurements of the Gulf of Mexico and a joint distribution model of the environmental parameters was considered. This approach was observed to be effective and the results were compared with those of traditional methodologies (univariate extreme value design and environmental contour methods). The differences were reflected using a reliability analysis of mooring lines, which indicated that the design standards must be stricter when using long-term analysis.

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Section: Assessment Of Short-term Performanceof Mooring Systemsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Long-term extreme response analysis for semi-submersible platform mooring systems

Zhao

Dong

2020

Proceedings of the Institution of Mechanical Engineers, Part M:

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“…The long term distribution for the mooring line response was developed for both the mooring chain and the pile. The method of obtaining the long term distribution accounts for short term variability and is presented in detail in [16] but a summary is provided in this paper, with a focus on the new distributions for the NS environment. The method is presented in terms of the mooring line response, but the same approach is applicable for the pile.…”

Section: Long Term Mooring Responsementioning

confidence: 99%

Mooring system reliability in tropical cyclone and North Sea winter storm environments

Stanisic

Efthymiou

White

et al. 2019

Applied Ocean Research

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The characteristics of waves, winds and currents in a tropical cyclone environment differ significantly from those in a winter storm environment, like the North Sea. This can have a significant effect on the reliability of a mooring system that is designed to satisfy 100yr conditions with specified Factors of Safety in accordance with ISO19901-7 or API RP 2SK. This paper presents reliability analysis of the mooring system of a permanently connected Floating LNG vessel, placed at two locations: (a) a tropical cyclone environment of the North West Shelf of Australia and (b) a winter storm environment of the North Sea. It is demonstrated that as a result of differences in the long term distribution of environmental parameters (waves, winds) between a North Sea environment and a tropical cyclone environment, the long term distribution of the mooring line response differs significantly in these two locations. This paper shows that a mooring system which is designed in accordance with ISO (or API), in these two environments, will achieve very different reliability levels because of the significant differences in environmental characteristics. In order to achieve the same reliability for the mooring system at these two geographical locations, Factors of Safety for use with 100yr environmental conditions (Ultimate Limit State) were derived to achieve the same target probability of failure of 10-4 /annum. It was found that for the North Sea environment, a factor of 1.5 is required for both the mooring chain and the pile, while for the tropical cyclone environment the required Factor of Safety has to be increased to 2.1. These differences are very significant and design standards need to be revised to reflect these findings.

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“…In order to restrict the movement of the object, the mooring chains are connected to the fixed anchor and moving object in the model [27]. In the simulation, three-dimensional dynamics of the mooring chain and the interaction with the tethered moving object are calculated.…”

Section: Cylinder Motion and Wavementioning

confidence: 99%

Numerical Study on the Hydrodynamic Characteristics and Responses of Moored Floating Marine Cylinders Under Real-World Tsunami-Like Waves

et al. 2019

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In recent tsunami events like those happened in the Indian Ocean in 2004 and 2018 and in Japan in 2011, many ocean and coastal infrastructures have been damaged tremendously, revealing the need of the work to study the hydrodynamic interaction between real-world tsunami waves and offshore structures. Besides, the destructive energy of tsunami wave on the offshore structures should also be assessed. However, to study the impact of tsunami waves on offshore structures, solitary waves are used generally instead of real-world tsunami waves despite the vast differences in hydrodynamic characteristics. Using Computational Fluid Dynamics (CFD) approach, this paper investigates the hydrodynamic characteristics of the floating cylinders moored by chains, under the real-world tsunami-like waves (2011 Japan Tohoku tsunami). Comparisons of hydrodynamic characteristics between real-world tsunami-like wave and solitary wave propagating over the moored cylinders are analyzed and discussed, indicating that the flow fields, the tension forces of mooring chains, the impinging forces and the movement trajectories of the cylinder caused by the two types of waves are greatly different from each other. Moreover, the influences of single cylinder diameter and tandem cylinder spacing on the interaction between real-world tsunami-like waves and cylinders are considered through a series of simulation tests, while meaningful conclusions are drawn. INDEX TERMS Hydrodynamic characteristics, moored cylinder, real-world tsunami-like wave, solitary wave, hydrodynamic forces.

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Design loads and long term distribution of mooring line response of a large weathervaning vessel in a tropical cyclone environment

Cited by 43 publications

References 9 publications

Long-term extreme response analysis for semi-submersible platform mooring systems

Long-term extreme response analysis for semi-submersible platform mooring systems

Mooring system reliability in tropical cyclone and North Sea winter storm environments

Numerical Study on the Hydrodynamic Characteristics and Responses of Moored Floating Marine Cylinders Under Real-World Tsunami-Like Waves

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