Assessment of Allowable Sea States During Installation of Offshore Wind Turbine Monopiles With Shallow Penetration in the Seabed

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Lin Li ◽  
Wilson Guachamin Acero ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Time Domain ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Offshore Wind Turbines ◽  
Heavy Lift ◽  
Characteristic Values ◽  
Limiting Parameters ◽  
The Time Domain ◽  
Penetration Depths

Installation of offshore wind turbines (OWTs) requires careful planning to reduce costs and minimize associated risks. The purpose of this paper is to present a method for assessing the allowable sea states for the initial hammering process (shallow penetrations in the seabed) of a monopile (MP) using a heavy lift floating vessel (HLV) for use in the planning of the operation. This method combines the commonly used installation procedure and the time-domain simulations of the sequential installation activities. The purpose of the time-domain simulation is to quantitatively study the system dynamic responses to identify critical events that may jeopardize the installation and the corresponding limiting response parameters. Based on the allowable limits and the characteristic values of the limiting response parameters, a methodology to find the allowable sea states is proposed. Case studies are presented to show the application of the methodology. The numerical model of the dynamic HLV–MP system includes the coupling between HLV and MP via a gripper device, and soil–MP interaction at different MP penetration depths. It is found that the limiting parameters are the gripper force and the inclination of the MP. The systematic approach proposed herein is general and applies to other marine operations.

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

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Wilson Guachamin Acero ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Time Domain ◽  
Structural Damage ◽  
Numerical Solutions ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Critical Event ◽  
Offshore Wind Turbine ◽  
Characteristic Values ◽  
Transition Piece ◽  
Limiting Parameters

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.

scholarly journals Numerical Simulations for Installation of Offshore Wind Turbine Monopiles Using Floating Vessels

2013 ◽  
Author(s):  
Lin Li ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Time Domain ◽  
Coupled System ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Support Structures ◽  
Offshore Wind Turbines ◽  
Motion Responses ◽  
Sensitivity Studies ◽  
Jack Up

Monopiles are the most commonly used support structures for offshore wind turbines with up to 40m water depth due to the simplicity of the structure. The installation of turbine support structures can be carried out by a jack-up vessel which provides a stable working platform. However, the operational weather window using jack-up vessels is very limited due to the low sea states required for jacking up and down. Compared to jack-up installation vessels, floating vessels have more flexibility due to fast transportations between foundations. However, the vessel motions will affect the motion responses of the lifting objects, which might bring installation difficulties. Therefore, it is necessary to examine the dynamic responses of the coupled system to ensure safe offshore operations. In this paper, the installation operation of a monopile using a floating installation vessel is studied by a numerical model. Time domain simulations were carried out to study the installation process of a monopile, including lowering phase, landing phase and steady states after landing. Sensitivity studies were performed focusing on the effects by the gripper device stiffness and landing device stiffness. Comparisons of critical responses by using floating vessel and a jack-up vessel were also studied in the paper.

PyraWind™: An Innovative Floating Offshore Wind Turbine (FOWT) Global Performance Analysis

2021 ◽  
Author(s):  
Zhiyong Yang ◽  
Xiaoqiang Bian ◽  
Yu Shi
Keyword(s):  
Wind Turbine ◽  
Hydrodynamic Model ◽  
Coupled System ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Floating Offshore Wind Turbine ◽  
Offshore Wind Turbines ◽  
Ongoing Work ◽  
Heavy Lift ◽  
Solid Foundation

Abstract In the near future, the offshore wind industry will experience a significant increase of turbine size and of floating wind development activities. A floating offshore wind turbine foundation offers many advantages, such as flexibility in site selection, access to better offshore wind resources, and quayside integration to avoid a costly heavy lift vessel offshore campaign. PyraWind™ is a patented three canted column semisubmersible floating foundation for ultra large offshore wind turbines. It is designed to accommodate a wind turbine, 14 MW or larger, in the center of the interconnected columns of the hull with minimal modifications to the tower, nacelle and turbine. The pyramid-shaped hull provides a stable, solid foundation for the large wind turbine under development. This paper summarizes the feasibility study conducted for the PyraWind™ concept. The design basis for wind turbine floating foundations is described and the regulatory requirements are discussed. Also included are the hydrodynamic analysis of the hull and ongoing work consisting of coupling hull hydrodynamics with wind-turbine aerodynamic loads. The fully coupled system was analyzed using OpenFAST, an aerodynamic software package for wind turbine analysis with the ability to be coupled with the hydrodynamic model. Due to the canted columns, a nonlinear analysis was performed using the coupled numerical hydrodynamic model of the platform with mooring system in extreme sea states.

Dynamic Responses of a Spar Type Floating Offshore Wind Turbine With Failed Moorings

2020 ◽  
Author(s):  
Yajun Ren ◽  
Vengatesan Venugopal
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Mooring System ◽  
Floating Offshore Wind Turbine ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Platform Motions

Abstract The complex dynamic characteristics of Floating Offshore Wind Turbines (FOWTs) have raised wider consideration, as they are likely to experience harsher environments and higher instabilities than the bottom fixed offshore wind turbines. Safer design of a mooring system is critical for floating offshore wind turbine structures for station keeping. Failure of mooring lines may lead to further destruction, such as significant changes to the platform’s location and possible collisions with a neighbouring platform and eventually complete loss of the turbine structure may occur. The present study focuses on the dynamic responses of the National Renewable Energy Laboratory (NREL)’s OC3-Hywind spar type floating platform with a NREL offshore 5-MW baseline wind turbine under failed mooring conditions using the fully coupled numerical simulation tool FAST. The platform motions in surge, heave and pitch under multiple scenarios are calculated in time-domain. The results describing the FOWT motions in the form of response amplitude operators (RAOs) and spectral densities are presented and discussed in detail. The results indicate that the loss of the mooring system firstly leads to longdistance drift and changes in platform motions. The natural frequencies and the energy contents of the platform motion, the RAOs of the floating structures are affected by the mooring failure to different degrees.

Challenges in the Design of an Offshore Wind Turbine Foundation for Arctic Conditions

2002 ◽  
Author(s):  
Alistair E. Gill ◽  
Ramsay Fraser
Keyword(s):  
Fatigue Life ◽  
Sea Ice ◽  
Time Domain ◽  
Deep Layer ◽  
Life Time ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Offshore Wind Turbines ◽  
Arctic Conditions ◽  
Ice Loads

NEG Micon’s Yttre Stengrund Offshore Wind Turbines in the Kalmarsund, Sweden, are supported on unique foundations designed by AMEC. The chosen foundation comprised a steel monopile secured into a rock socket drilled out beneath a deep layer of overlying soil. Sea-ice loading and fatigue governed the design. To minimise the sea-ice loads the foundation was fitted with an ice protection shield. In order to achieve the required fatigue life, time domain simulations were conducted to determine the response of the turbine to combined wind and wave action. Details of the fatigue analyses and methods used to calculate the sea-ice loading are presented herein.

Comparing Frequency and Time Domain Simulations for Geometry Optimization of a Floating Offshore Wind Turbine Mooring System

2018 ◽  
Author(s):  
Ajit C. Pillai ◽  
Philipp R. Thies ◽  
Lars Johanning
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Pareto Front ◽  
Geometry Optimization ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Mooring System ◽  
Efficient Design ◽  
Frequency Domain Methods ◽  
The Time Domain

This paper explores geometry optimization of an offshore wind turbine’s mooring system considering the minimization of the material cost and the cumulative fatigue damage. A comparison of time domain simulations against frequency domain simulations is made to explore the suitability of these methods to the design process. The efficient design options, the Pareto front, from the frequency domain study are also re-evaluated using time domain simulations and compared against the time domain Pareto front. Both the time and frequency domain results show optimal results utilizing similar design philosophies, however, the frequency domain methods severely under predict the fatigue loads in the mooring system and incorrectly class infeasible solutions as feasible. The frequency domain is therefore not suitable for optimization use without some external means of applying engineering constraints. Furthermore, re-evaluation of the frequency domain solutions provides guidance to the uncertainty and the necessary design fatigue factors required if implementing frequency domain methods in design.

Response Analysis of a Nonstationary Lowering Operation for an Offshore Wind Turbine Monopile Substructure

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Lin Li ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Wind Turbine ◽  
Time Domain ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Offshore Wind Turbine ◽  
Response Analysis ◽  
Steady State Condition ◽  
Strip Theory ◽  
Lifting System

This study addresses numerical modeling and time-domain simulations of the lowering operation for installation of an offshore wind turbine monopile (MP) with a diameter of 5.7 m and examines the nonstationary dynamic responses of the lifting system in irregular waves. Due to the time-varying properties of the system and the resulting nonstationary dynamic responses, numerical simulation of the entire lowering process is challenging to model. For slender structures, strip theory is usually applied to calculate the excitation forces based on Morison's formula with changing draft. However, this method neglects the potential damping of the structure and may overestimate the responses even in relatively long waves. Correct damping is particularly important for the resonance motions of the lifting system. On the other hand, although the traditional panel method takes care of the diffraction and radiation, it is based on steady-state condition and is not valid in the nonstationary situation, as in this case in which the monopile is lowered continuously. Therefore, this paper has two objectives. The first objective is to examine the importance of the diffraction and radiation of the monopile in the current lifting model. The second objective is to develop a new approach to address this behavior more accurately. Based on the strip theory and Morison's formula, the proposed method accounts for the radiation damping of the structure during the lowering process in the time-domain. Comparative studies between different methods are presented, and the differences in response using two types of installation vessel in the numerical model are also investigated.

scholarly journals Transient Response Estimation of an Offshore Wind Turbine Support System

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 891 ◽  
Author(s):  
Fushun Liu ◽  
Xingguo Li ◽  
Zhe Tian ◽  
Jianhua Zhang ◽  
Bin Wang
Keyword(s):  
Wind Turbine ◽  
Frequency Domain ◽  
Transient Response ◽  
Time Domain ◽  
Initial Conditions ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Domain Method ◽  
The Time Domain ◽  
External Loads

To obtain reliable estimations of the dynamic responses of high-rising marine structures such as offshore wind turbines with obvious nonzero initial conditions, traditional frequency-domain methods cannot be employed because they provide only steady-state results. A novel frequency-domain transient response estimation method for offshore wind turbines is presented in this paper. This method builds upon a recent, significant theoretical development, which found that expressions of external loads in the frequency domain can be obtained by discretizing their eigenvalues and corresponding complex coefficients rather than directly by discrete Fourier transform (DFT) analysis, which makes it possible to deal with nonzero conditions in the frequency domain. One engineering advantage of this approach is its computational efficiency, as the motion equations of the system can be solved in the frequency domain. In order to demonstrate this approach, a case of a monopile-supported wind turbine with nonzero initial conditions was investigated. The numerical results indicate that the approach matches well with the time-domain method, except for a small, earlier portion of the estimated responses. A second case study of a sophisticated, jacket support wind turbine, involving practical issues such as complex external loads and computation efficiency, is also discussed, and comparisons of the results with the time-domain method and traditional frequency-domain method using the commercial software ANSYS are included here.

scholarly journals Dynamic Response of Articulated Offshore Wind Turbines under Different Water Depths

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2784
Author(s):  
Pei Zhang ◽  
Shugeng Yang ◽  
Yan Li ◽  
Jiayang Gu ◽  
Zhiqiang Hu ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Dynamic Responses ◽  
Wind Pressure ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Offshore Area ◽  
Offshore Wind Turbines ◽  
Water Depths

Focusing on the transitional depth offshore area from 50 m to 75 m, types of articulated foundations are proposed for supporting the NREL 5 MW offshore wind turbine. To investigate the dynamic behaviors under various water depths, three articulated foundations were adopted and numerical simulations were conducted in the time domain. An in-house code was chosen to simulate the dynamic response of the articulated offshore wind turbine. The aerodynamic load on rotating blades and the wind pressure load on tower are calculated based on the blade element momentum theory and the empirical formula, respectively. The hydrodynamic load is simulated by 3D potential flow theory. The motions of foundation, the aerodynamic performance of the wind turbine, and the loads on the articulated joint are documented and compared in different cases. According to the simulation, all three articulated offshore wind turbines show great dynamic performance and totally meet the requirement of power generation under the rated operational condition. Moreover, the comparison is based on time histories and spectra among these responses. The result shows that dynamic responses of the shallower one oscillate more severely compared to the other designs.

Radiative Damping of Offshore Wind Turbine Gravity Base Foundations at Low Frequencies

2016 ◽  
Author(s):  
Rui He ◽  
Ting Huang
Keyword(s):  
Wind Turbines ◽  
Clean Energy ◽  
The Other ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Low Frequencies ◽  
Offshore Wind Turbines ◽  
Dynamic Loadings ◽  
Radiative Damping

With the fast increasing need of clean energy, more and more offshore wind turbines (OWTs) are being planned or constructed. Some offshore wind turbines are supported on Gravity Base Foundations (GBFs). As tall and slender offshore wind turbines are very sensitivity to the dynamic loadings at low frequencies, if designed improperly, it is likely to cause resonances. On the other hand, most of the designs ignore the radiative damping of GBFs, which will lead to a conservative solution and a cost of more money. In this paper, by referring to three different models, the corresponding vertical, horizontal and rocking damping ratios for a typical GBF at low frequencies are obtained and compared, respectively. With these damping ratios obtained, one can develop a more realistic and economic model to calculate the dynamic responses of offshore wind turbines on GBFs under both vertical and horizontal forces at low frequencies.

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