scholarly journals Proposal of Wear Estimation Method for Mooring Chain of Floating Structures

2019 ◽  
Vol 29 (0) ◽  
pp. 77-87
Author(s):  
Takaaki Takeuchi ◽  
Kimihiro Toh ◽  
Tomoaki Utsunomiya ◽  
Koji Gotoh
Keyword(s):  
Estimation Method ◽  
Floating Structures ◽  
Mooring Chain

Quantitative Wear Estimation for Floating Structures by Using 3-D Geometry of Mooring Chain

2020 ◽  
Author(s):  
Takaaki Takeuchi ◽  
Tomoaki Utsunomiya ◽  
Koji Gotoh ◽  
Iku Sato
Keyword(s):  
Estimation Method ◽  
Maintenance Cost ◽  
Offshore Wind Turbine ◽  
Response Analysis ◽  
Chain Model ◽  
Contact Method ◽  
Spring Model ◽  
Mass Spring Model ◽  
Mass Spring ◽  
Mooring Chain

Abstract For reducing the maintenance cost of floating offshore wind turbine structures, it is necessary to establish a quantitative wear estimation method for the mooring chains. In this paper, attempts have been made to improve the accuracy of the estimation method in terms of the mooring chain model. These investigations were performed about a spar-type floater moored with three catenary mooring lines at Goto, Nagasaki prefecture, Japan. Up to now, the mass-spring model had been used for the mooring chain in response analysis and the relative angle between two spring lines was considered as only a sliding angle without friction. However, there is also rolling in the motion between mooring links, which should cause less wear than by sliding. In this study, the detailed motion of the link in response analysis is calculated and applied to the wear estimation by using a 3-D model in MSC. Adams. This enables the wear estimation considering link motion closer to a real phenomenon. A Contact analysis between the 3-D chain model requires some contact properties (e.g. contact stiffness and friction). In this paper, these properties are calculated based on the Hertzian contact method and FEM analysis. As a result, the wear amounts overestimated by using the mass-spring model in the previous investigation, especially at the point located clump weight and touchdown point, decrease getting closer to the measurements. In addition, by tracking the contact points it is found that the major motion caused between links is the rolling. For future works, there remains a need for further validation and the consideration of elasticity between mooring links, impressions caused by proof load test and the effect of corrosion.

scholarly journals Estimation method of slowly varying wave drift force acting on very large floating structures

2000 ◽  
Vol 2000 (188) ◽  
pp. 287-293
Author(s):  
Yasuhiro Namba ◽  
Shunji Kato ◽  
Hiroshi Sato ◽  
Tomoki Ikoma ◽  
Katsuya Maeda
Keyword(s):  
Estimation Method ◽  
Floating Structures ◽  
Wave Drift ◽  
Drift Force ◽  
Very Large 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.

Development of Simplified Wear Estimation Method Considering Rolling Motion Between Mooring Chain Links for Floating Structures

2021 ◽  
Author(s):  
Takaaki Takeuchi ◽  
Tomoaki Utsunomiya ◽  
Koji Gotoh ◽  
Iku Sato
Keyword(s):  
Estimation Method ◽  
Irregular Waves ◽  
Rolling Motion ◽  
Spring Model ◽  
Floating Offshore Wind Turbines ◽  
Mass Spring Model ◽  
Link Model ◽  
Mass Spring ◽  
Chain Links ◽  
Mooring Chain

Abstract For the development of floating offshore wind turbines (FOWTs) in Japan, reliability assessment and cost reduction by efficient maintenance on mooring chains are part of the key issues because sites deeper than 60 m require mooring systems for station keeping. In this paper, attempts have been made to simplify the wear estimation method which was previously proposed by using a 3-D rigid-body link model for improvement of accuracy. These investigations are performed about a spar-type floating structure moored with three catenary lines at Goto, Nagasaki prefecture, Japan. In the previous study, it was confirmed that the estimation method using the 3-D link model can calculate the interlink wear amount closer to the chain diameter measurements and more reasonable than the method using the conventional mass-spring model by removing the rolling distance from the displacement of contact points. However, the estimation method has technical difficulty in terms of calculation of contact properties and analysis costs for the mooring chain design. For this reason, the wear estimation method is simplified and verified by considering the rolling motion between mooring chain links modeled by the widely employed mass-spring model based on the method proposed by Mooring Integrity JIP. Firstly, the wear due to the rolling is reproduced by a three-dimensional FE analysis to investigate the actual wear phenomenon including the effect of the proof load test as well as the idealized configuration. Secondly, the application method is proposed against the response of the mooring chain subjected to irregular waves Finally, a comparison with the measurement is conducted to verify the proposed wear estimation method.

Quantitative Wear Estimation for Mooring Chain of Floating Structures and its Validation

2019 ◽  
Author(s):  
Takaaki Takeuchi ◽  
Tomoaki Utsunomiya ◽  
Koji Gotoh ◽  
Iku Sato
Keyword(s):  
Estimation Method ◽  
Offshore Wind ◽  
Floating Body ◽  
Maintenance Cost ◽  
Offshore Wind Turbine ◽  
Lumped Mass ◽  
Sliding Angle ◽  
Mass Model ◽  
Element Analysis ◽  
Mooring Chain

Abstract For reducing maintenance cost of floating offshore wind turbine structures, it is necessary to establish quantitative wear estimation method for the mooring chains. In this paper, attempts have been made to improve the accuracy and applicability of the estimation method in the following steps. By using the wear analysis method between the links of mooring chain that Gotoh et al. investigated with the finite element analysis software (MSC. Marc), the expression of the wear amount was obtained, which was a proportional functional form associated with sliding angle and tension. The relative sliding angle and tension between links were analyzed by using a multibody dynamics software (MSC. Adams). A spar-type floater moored with three catenary mooring lines at Goto, Nagasaki prefecture, Japan was analyzed. Here, the floating body was modelled as a rigid body and mooring chains were modelled by mass-spring (lumped mass) model. From these results, the wear amounts calculated by using the estimation formula and relative sliding angle and tension between links were compared with the measured wear amounts for mooring chain of the floater which was deployed for about one-year at Goto. The cases with only waves and those with wind and waves were analyzed. From the comparison between the simulation results and the measured ones, it was found that the proposed method can fairly predict the wear amount of mooring chains. However, it was also found that the proposed method has a tendency to overestimate the measured results. These reasons were discussed in the paper.

scholarly journals Quantitative Wear Estimation for Mooring Chain of Floating Structures and Its Validation

2019 ◽  
Vol 30 (0) ◽  
pp. 131-141
Author(s):  
Takaaki Takeuchi ◽  
Tomoaki Utsunomiya ◽  
Koji Gotoh ◽  
Iku Sato
Keyword(s):  
Floating Structures ◽  
Mooring Chain
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