Abstract
The performance of a polyester mooring line is non-linear and its elongation plays a significant role in the dynamic response of an offshore moored structure. However, unlike chain, the tension-elongation relationship and the overall behavior of elastic polyester ropes are complex. In this paper, by applying an enhanced stiffness model of the mooring line, the traditional elastic rod theory has been extended to allow for large elongations. One beneficial feature of the present method is that the tangent stiffness matrix is symmetric; in non-linear formulations the tangent stiffness matrix is often non-symmetric. The static problem was solved by Newton-Raphson iteration, whereas a direct integration method was used for the dynamic problem. The computed mooring line tension was validated against the proprietary OrcaFlex software. Results of mooring line top tension predicated by different elongations are compared and discussed. The present method was then used for a simulation of an offshore floating wind turbine moored with taut lines. From a comparison between linear and non-linear formulations, it is seen that a linear spring model under-estimates the mean position when the turbine is operating, but over-estimates the amplitude of the platform response at low frequencies when the turbine has shut down.
| Language | English |
|---|---|
| Pages | 444-453 |
| Number of pages | 10 |
| Journal | Ocean Engineering |
| Volume | 109 |
| Early online date | 8 Oct 2015 |
| DOIs | |
| Publication status | Published - 15 Nov 2015 |
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Keywords
- dynamic response
- elastic rod theory
- finite element method
- large extension
- mooring system
- motion response
Cite this
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An enhanced stiffness model for elastic lines and its application to the analysis of a moored floating offshore wind turbine. / Lin, Zi; Sayer, P.
In: Ocean Engineering, Vol. 109, 15.11.2015, p. 444-453.Research output: Contribution to journal › Article
TY - JOUR
T1 - An enhanced stiffness model for elastic lines and its application to the analysis of a moored floating offshore wind turbine
AU - Lin, Zi
AU - Sayer, P.
PY - 2015/11/15
Y1 - 2015/11/15
N2 - The performance of a polyester mooring line is non-linear and its elongation plays a significant role in the dynamic response of an offshore moored structure. However, unlike chain, the tension-elongation relationship and the overall behavior of elastic polyester ropes are complex. In this paper, by applying an enhanced stiffness model of the mooring line, the traditional elastic rod theory has been extended to allow for large elongations. One beneficial feature of the present method is that the tangent stiffness matrix is symmetric; in non-linear formulations the tangent stiffness matrix is often non-symmetric. The static problem was solved by Newton-Raphson iteration, whereas a direct integration method was used for the dynamic problem. The computed mooring line tension was validated against the proprietary OrcaFlex software. Results of mooring line top tension predicated by different elongations are compared and discussed. The present method was then used for a simulation of an offshore floating wind turbine moored with taut lines. From a comparison between linear and non-linear formulations, it is seen that a linear spring model under-estimates the mean position when the turbine is operating, but over-estimates the amplitude of the platform response at low frequencies when the turbine has shut down.
AB - The performance of a polyester mooring line is non-linear and its elongation plays a significant role in the dynamic response of an offshore moored structure. However, unlike chain, the tension-elongation relationship and the overall behavior of elastic polyester ropes are complex. In this paper, by applying an enhanced stiffness model of the mooring line, the traditional elastic rod theory has been extended to allow for large elongations. One beneficial feature of the present method is that the tangent stiffness matrix is symmetric; in non-linear formulations the tangent stiffness matrix is often non-symmetric. The static problem was solved by Newton-Raphson iteration, whereas a direct integration method was used for the dynamic problem. The computed mooring line tension was validated against the proprietary OrcaFlex software. Results of mooring line top tension predicated by different elongations are compared and discussed. The present method was then used for a simulation of an offshore floating wind turbine moored with taut lines. From a comparison between linear and non-linear formulations, it is seen that a linear spring model under-estimates the mean position when the turbine is operating, but over-estimates the amplitude of the platform response at low frequencies when the turbine has shut down.
KW - dynamic response
KW - elastic rod theory
KW - finite element method
KW - large extension
KW - mooring system
KW - motion response
UR - http://www.scopus.com/inward/record.url?scp=84943552003&partnerID=8YFLogxK
U2 - 10.1016/j.oceaneng.2015.09.002
DO - 10.1016/j.oceaneng.2015.09.002
M3 - Article
VL - 109
SP - 444
EP - 453
JO - Ocean Engineering
T2 - Ocean Engineering
JF - Ocean Engineering
SN - 0029-8018
ER -