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

Abstract

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.

Response-Based Assessment of Operational Limits for Mating Blades on Monopile-Type Offshore Wind Turbines

“…Better planning strategies are therefore required which enable estimation of 'practical' operational weather limits, and thus waiting time on weather can be reduced. These limits must necessarily be methodical in nature, where emphasis must be placed on their scientific derivation by quantifying risks involved during installation, rather than relying on industrial experiences alone [8]. This is commonly referred to as response-based operational limits and these are based on explicit modelling of the installation system and process, together with assessment of dynamic motion responses (for e.g., roll motion of vessel, crane tip motions) and structural responses (for e.g., tension in the wire, contact stresses during mating) developed in the system during installation.…”

“…A generic methodology for derivation of response-based limiting sea states for installing offshore wind turbines was proposed by Acero et al [8]. A series of systematic procedures were developed, and the use of advanced numerical modelling methods was emphasized, including modelling of potential hazardous events.…”

“…A coupled heavy-lift floating vessel and monopile system were modelled in SIMO [21] and time-domain simulations were carried out. Acero et al [8] estimated the operational limiting sea states for mating task of transition piece onto monopile. The failure of mating process and structural failure of transition piece's brackets were considered to be critical events.…”

Explicit Structural Response-Based Methodology for Assessment of Operational Limits for Single Blade Installation for Offshore Wind Turbines

“…In the past, Acero, et al [10,11] has proposed a generic methodology to derive quite systematically a practical response based operational limits for any particular installation phase by measuring the responses in the system due to normal environmental loads. Li, et al [12] has successfully utilized this approach to study the operability limits for initial hammering process of the monopile using heavy lift floating vessel.…”

Numerical study on the feasibility of offshore single blade installation by floating crane vessels

“…(Zhu et al, 2017) compared the dynamic motion response of a tripod foundation for offshore wind turbines during installation by a mono-hull and a jack-up crane vessel. Acero et al (2017) studied the installation of an offshore wind turbine transition piece onto a monopile foundation by a mono-hull crane vessel. Ku and Roh (2015) studied the dynamic responses of an offshore wind turbine (tower-nacellerotor assembly) during lifting operation by a floating crane barge.…”