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Research Papers: Ocean Renewable Energy

Methodology for Assessment of the Allowable Sea States During Installation of an Offshore Wind Turbine Transition Piece Structure Onto a Monopile Foundation

[+] Author and Article Information
Wilson Guachamin Acero

Department of Marine Technology,
Centre for Ships and Ocean Structures (CeSOS),
Centre for Autonomous Marine Operations
and Systems (AMOS),
Norwegian University of Science
and Technology (NTNU),
Trondheim NO-7491, Norway;
Departamento de Ingeniería Mecánica,
Escuela Politécnica Nacional (EPN),
Quito 17-01-2759, Ecuador
e-mails: wilson.i.g.acero@ntnu.no,
wilson.guachamin@epn.edu.ec

Zhen Gao

Department of Marine Technology,
Centre for Ships and Ocean Structures (CeSOS),
Centre for Autonomous Marine Operations
and Systems (AMOS),
Norwegian University of Science
and Technology (NTNU),
Trondheim NO-7491, Norway

Torgeir Moan

Department of Marine Technology,
Centre for Ships and Ocean Structures (CeSOS),
Centre for Autonomous Marine Operations
and Systems (AMOS),
Norwegian University of Science and
Technology (NTNU),
Trondheim NO-7491, Norway

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received April 9, 2016; final manuscript received June 21, 2017; published online August 8, 2017. Assoc. Editor: Qing Xiao.

J. Offshore Mech. Arct. Eng 139(6), 061901 (Aug 08, 2017) (16 pages) Paper No: OMAE-16-1039; doi: 10.1115/1.4037174 History: Received April 09, 2016; Revised June 21, 2017

In this paper, a methodology suitable for assessing the allowable sea states for installation of a transition piece (TP) onto a monopile (MP) foundation with focus on the docking operation is proposed. The TP installation procedure together with numerical analyses is used to identify critical and restricting events and their corresponding limiting parameters. For critical installation phases, existing numerical solutions based on frequency and time domain (TD) analyses of stationary processes are combined to quickly assess characteristic values of dynamic responses of limiting parameters for any given sea state. These results are compared against (nonlinear and nonstationary) time domain simulations of the actual docking operations. It is found that a critical event is the structural damage of the TP's bracket supports due to the potential large impact forces or velocities, and a restricting installation event (not critical) is the unsuccessful mating operation due to large horizontal motions of the TP bottom. By comparing characteristic values of dynamic responses with their allowable limits, the allowable sea states are established. Contact–impact problems are addressed in terms of assumed allowable impact velocities of the colliding objects. A possible automatic motion compensation system and human actions are not modeled. This methodology can also be used in connection with other mating operations such as float-over and topside installation.

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References

Figures

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Fig. 1

Monopile and transition piece structures in the motion monitoring phase prior to mating [14]

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Fig. 2

Models for TP-MP axial contact–impact prior to mating: (a) physical model, (b) contact scenarios, and (c) spring–damper model

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Fig. 3

Lateral contact during TP mating operation: (a) physical model and (b) spring–damper model

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Fig. 4

Contact–impact during TP landing: (a) physical model and (b) spring–damper model

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Fig. 5

Potential critical events, limiting parameters, and allowable limits for the docking operation of a TP onto a MP foundation (refer to Fig. 1)

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Fig. 6

Dynamic coupled model for TP docking operation in the motion monitoring phase prior to mating

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Fig. 7

Methodology for assessment of the allowable sea states for the docking operation of a TP onto a MP foundation: (a) screening of limiting parameter and (b) assessment of allowable sea states

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Fig. 8

Numerical methods for assessment of dynamic responses

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Fig. 9

Determination of impact and snap velocities based on TP's bottom tip displacement and velocity TD histories: (a) TP's bottom tip relative heave displacements (with respect to the crane tip) for constant lowering speed and (b) possible impact and snap velocities (no winch speed included)

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Fig. 10

Allowable limits of sea states for the monitoring phase of the TP's bottom tip. Limiting parameter: TP's bottom tip motions, allowable crossing rate limit: νallow+=0.0167 Hz, and mating gap: r = 0.3 m. Wave direction measured counter clockwise from the HLV's stern.

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Fig. 11

Average number of crossings per minute based on stationary process TD simulations for various mating gaps

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Fig. 12

Statistical parameters of the axial impact velocities prior to the mating phase, based on the collision approach method

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Fig. 13

Dynamic responses as consequence of axial impact events vdyn = 0.10 m/s, vwinch = 0.033 m/s, ξa = 1.0 m, T = 7.0 s, and α = 135 deg. For the contact points, refer to Fig. 4(b).

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Fig. 14

Crossing rates and statistical parameters of radial impact velocities for r = 0.3 m, α = 135 deg: (a) number of crossing per minute and (b)–(d) statistical parameters averaged from several 5 min interval TD simulations

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Fig. 15

Statistical parameters for snap velocities during landing and lift-off, α = 135 deg. Statistical parameters averaged over several 5 min TD history intervals.

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Fig. 16

Allowable limits of sea states for TP-MP mating. Limiting parameter for the motion monitoring phase: crossing rate νallow+=0.0167 Hz for r = (0.3, 0.5) m, limiting parameter for the landing phase: vimp = (0.10, 0.18) m/s.

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Fig. 17

Statistical parameters of dynamic responses obtained from nonstationary process TD simulations of the TP lowering and landing operations for various sea states, 36 seeds, α = 135 deg

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Fig. 18

Example of dynamic responses from TD simulations of the lowering and landing phases. Hs = 1.60 m, Tp = 6 s, α = 135 deg.

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Fig. 19

Typical dynamic responses following impact events. ξa = 0.5 m, T = 7 s, α = 135 deg.

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