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Assessment of Marine Operations for Offshore Wind Turbine Installation with Emphasis on Response-Based Operational Limits

Acero, Wilson Ivan Guachamin
Doctoral thesis
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URI
http://hdl.handle.net/11250/2432746
Date
2016
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  • Institutt for marin teknikk [2357]
Abstract
This thesis addresses methodologies for assessment of response-based operational

limits in terms of allowable vessel responses or sea state parameters,

and numerical analyses of current and novel o_shore wind turbine (OWT)

installation activities.

A generic and systematic approach that allows for identi_cation of critical

events, limiting (response) parameters and assessment of response-based

operational limits of marine operations was developed. The approach is

based on numerical simulations of the actual operations. Frequency and

time domain techniques or operation-speci_c numerical analysis methods

may be applied. An e_cient method for assessment of the operational limits

of mating operations has been proposed. The method relies on a number

of crossings that a mating pin is allowed to perform out of a circular boundary

(docking cone circular perimeter) in a given period of time. By carrying

out a quantitative assessment of the system dynamic responses, the critical

events and corresponding limiting parameters are identi_ed. A characteristic

value of a limiting parameter needs to be determined based on extreme

value distributions for a target exceedance probability. This depends on

the type of operation and consequences of failure events. The characteristic

value is compared with the allowable limit of the limiting parameter, so the

environmental conditions can be identi_ed. The limits of these environmental

parameters represent the operational limits of an installation activity.

In this thesis only the e_ect of wave actions are considered, while current

and wind actions are not included.

The OWT installation activities studied in this thesis are executed with

a oating heavy lift vessel (HLV). Three main activities were considered:

the monopile (MP) initial hammering process, the transition piece (TP)

mating operation, and the entire installation of the tower and rotor nacelle

assembly (RNA). For the installation of the MP and TP, standard operational

procedures were employed, while for the tower and RNA, a novel and

e_cient single lift installation concept was developed. This novel concept is

based on the principle of the inverted pendulum and requires a cargo barge,

a medium-size HLV and a specially designed upending frame. The need

for huge (in terms of lifting height and capacity) o_shore crane vessels is

eliminated. Moreover, it has been shown that the novel concept is a feasible

and valid alternative for current installation procedures. The current procedures

employ jack-up vessels for sequential installation of wind turbine

components; however, these activities are not studied in this thesis.

The generic approach was applied to the MP, TP and tower and RNA installation activities. For the MP initial hammering process, it was found

that the critical events are failure of the hydraulic system and out-oftolerance

inclination of the MP. For the TP mating operation, the critical

events are the failure of the bracket supports and the failed mating attempt

between the TP bottom tip and the MP. During the tower and RNA installation,

structural failure of the hoist wire, structural damage of the hinged

supports, and a failed mating attempt of the upending frame are identi_ed

to be critical events. For various limiting parameters, the operational limits

were established in terms of allowable limits of sea states, which are a basis

for assessment of the operatiblity.

A methodology for weather window analysis and assessment of operability

of marine operations was also developed. This methodology includes

the response-based operational limits and accounts for sequence, continuity

and duration of the activities, which are shown to be important in the

analyses. The operational limits of the MP and TP installation were used

for weather window analysis and assessment of the operability during the

planning phase. Moreover, it is shown that weather forecasts can be used to

identify workable weather windows and support on-board decision making

during the execution phase.

The methodologies provided in this thesis are systematic and e_cient

for modeling of current and novel OWT installation activities with the aim

of establishing response-based operational limits. These are necessary for

planning and safe execution of OWT installation activities.
Publisher
NTNU
Series
Doctoral theses at NTNU;2016:336

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