scholarly journals METHOD TO PREDICT LONG TIME SPAN OF SCOUR AROUND OFFSHORE WIND TURBINE FOUNDATIONS

2012 ◽  
Vol 1 (33) ◽  
pp. 88 ◽  
Author(s):  
Martin Dixen ◽  
Iris Pernille Lohmann ◽  
Erik Damgaard Christensen
Keyword(s):  
Sediment Transport ◽  
Erosion Rate ◽  
Offshore Structures ◽  
Time Span ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Scour Hole ◽  
Long Time ◽  
Flow And Sediment Transport ◽  
Backfilling Rate

A new method to predict scour development around offshore structures has been developed. The method has been tested on a monopile. The method consists of table of scour rates, which is used to predict the scour development around the structure at different stages of the scour hole. The scour rate tables have been made based on full 3D numerical simulations of the flow and sediment transport for fixed configurations of the scour hole. When changing the governing parameters which are causing the scour development around the structure, the erosion rate or backfilling rate can be calculated from the mass balance of the sediment. This leads to the scour rates tables that are used to analyses the development of the scour hole under different current conditions. The method has been tested against experimental scour data and showed very promising results.

scholarly journals Maintenance Planning of Offshore Wind Turbine Using Condition Monitoring Information

2009 ◽  
Author(s):  
Jose´ G. Rangel-Rami´rez ◽  
John D. So̸rensen
Keyword(s):  
Condition Monitoring ◽  
Wind Turbines ◽  
Wind Farm ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Maintenance Planning ◽  
Offshore Wind Turbines ◽  
Inspection And Maintenance ◽  
Monitoring Information

Deterioration processes such as fatigue and corrosion are typically affecting offshore structures. To “control” this deterioration, inspection and maintenance activities are developed. Probabilistic methodologies represent an important tool to identify the suitable strategy to inspect and control the deterioration in structures such as offshore wind turbines (OWT). Besides these methods, the integration of condition monitoring information (CMI) can optimize the mitigation activities as an updating tool. In this paper, a framework for risk-based inspection and maintenance planning (RBI) is applied for OWT incorporating CMI, addressing this analysis to fatigue prone details in welded steel joints at jacket or tripod steel support structures for offshore wind turbines. The increase of turbulence in wind farms is taken into account by using a code-based turbulence model. Further, additional modes t integrate CMI in the RBI approach for optimal planning of inspection and maintenance. As part of the results, the life cycle reliabilities and inspection times are calculated, showing that earlier inspections are needed at in-wind farm sites. This is expected due to the wake turbulence increasing the wind load. With the integration of CMI by means Bayesian inference, a slightly change of first inspection times are coming up, influenced by the reduction of the uncertainty and harsher or milder external agents.

Experimental Investigation on the Dynamic Response of a Three Legged Articulated Type Offshore Wind Tower

2016 ◽  
Author(s):  
Chinsu Mereena Joy ◽  
Anitha Joseph ◽  
Lalu Mangal
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Renewable Energy Sources ◽  
Offshore Structures ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Experimental Investigations ◽  
Offshore Wind Turbine ◽  
Ocean Engineering ◽  
Study Results

Demand for renewable energy sources is rapidly increasing since they are able to replace depleting fossil fuels and their capacity to act as a carbon neutral energy source. A substantial amount of such clean, renewable and reliable energy potential exists in offshore winds. The major engineering challenge in establishing an offshore wind energy facility is the design of a reliable and financially viable offshore support for the wind turbine tower. An economically feasible support for an offshore wind turbine is a compliant platform since it moves with wave forces and offer less resistance to them. Amongst the several compliant type offshore structures, articulated type is an innovative one. It is flexibly linked to the seafloor and can move along with the waves and restoring is achieved by large buoyancy force. This study focuses on the experimental investigations on the dynamic response of a three-legged articulated structure supporting a 5MW wind turbine. The experimental investigations are done on a 1: 60 scaled model in a 4m wide wave flume at the Department of Ocean Engineering, Indian Institute of Technology, Madras. The tests were conducted for regular waves of various wave periods and wave heights and for various orientations of the platform. The dynamic responses are presented in the form of Response Amplitude Operators (RAO). The study results revealed that the proposed articulated structure is technically feasible in supporting an offshore wind turbine because the natural frequencies are away from ocean wave frequencies and the RAOs obtained are relatively small.

scholarly journals The advanced p-y method for analyzing the behaviour of large-diameter monopiles supporting offshore wind turbines

2020 ◽  
Vol 205 ◽  
pp. 12008
Author(s):  
William F Van Impe ◽  
Shin-Tower Wang
Keyword(s):  
Wind Turbine ◽  
Large Diameter ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Response Curves ◽  
Current Design ◽  
Jacket Structures ◽  
Load Tests ◽  
Offshore Industry

The analyses of monopile foundations have been heavily based on the p-y response curves (to represent lateral soil resistances) published by API RP 2GEO (2011) and DNV (2013), which are proven reliable and applicable for piles with smaller diameters that were normally used for jacket structures in the offshore industry. However, concerns have been raised about the validity of semi-empirical p-y criteria for large-diameter piles. Wind turbine monopiles have a significantly larger diameter and smaller length to diameter ratio than typical piles used for offshore structures. The ratio of the length to the diameter for a monopile typically is also significantly smaller than those used in the API load tests. Therefore, the response of a monopile may be more like a rigid rotation, with components of resistance mobilized at the tip and axially along the sides as it rotates. This behaviour is in contrast to long slender piles that respond to lateral loading in bending rather than rotation. The objective of this paper is to analyze the factors that may contribute to the apparent conservatism in the current design practice for large-diameter monopile foundations and to provide improved solutions on how to analyze and design the large-diameter monopiles for offshore wind turbine using the p-y method.

scholarly journals Development of Combined Load Spectra for Offshore Structures Subjected to Wind, Wave, and Ice Loading

2021 ◽  
Author(s):  
Moritz Braun ◽  
Alfons Dörner ◽  
Kane Falco ter Veer ◽  
Tom Willems ◽  
Marc Seidel ◽  
...  
Keyword(s):  
Wind Wave ◽  
Fatigue Testing ◽  
Numerical Models ◽  
Time History ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Combined Load ◽  
Load Spectra

Fixed offshore wind turbines continue to be developed for high latitude areas where not only wind and wave loads need to be considered, but also moving sea ice. Current rules and regulations for the design of fixed offshore structures in ice-covered waters do not adequately consider effects of ice loading and its stochastic nature on fatigue life of the structure. Ice crushing on such structures results in ice-induced vibrations, which can be represented by loading the structure using a variable-amplitude loading (VAL) sequence. Typical offshore load spectra are developed for wave and wind loading. Thus, a combined VAL spectrum is developed for wind, wave, and ice action. To this goal, numerical models are used to simulate the dynamic ice-, wind-, and wave-structure interaction. The stress time-history at an exemplarily selected critical point in an offshore wind energy monopile support structure is extracted from the model and translated into a VAL sequence, which can then be used as a loading sequence for the fatigue assessment or fatigue testing of welded joints of offshore wind turbine support structures. This study presents the approach to determine combined load spectra and standardized time series for wind, wave, and ice action.

Risk Assessment of Hoisting Aboard and Installation for Offshore Wind Turbine

2012 ◽  
Author(s):  
Xu Bai ◽  
Liping Sun ◽  
Hai Sun
Keyword(s):  
Risk Assessment ◽  
Wind Turbine ◽  
Failure Modes ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Main Task ◽  
Future Design ◽  
Management Measures ◽  
Operation Process

With the accidents of offshore structures occurring frequently, the significance of risk assessment in the process of transportation, installation and operation is increasing. In this paper, the risk assessment of offshore wind turbine in transportation and installation is presented. Firstly, the main task profiles are identified according to the concrete operation process, the components and risk factors related to the assessment. Secondly, FTA of hoisting aboard and FMEA of installation process are established based on RELEX Studio 2011. The failure modes of task profiles are analyzed and coefficients are assigned according to the principle of As Low As Reasonably Practicable. Finally, using Risk Priority Number method to evaluate their severity rank, and some recommended operations and management measures are given. Risk assessment is applied in offshore wind turbine transportation in this paper and the work has great significance to the evaluation and future design of offshore structures.

scholarly journals Extended Environmental Contour Methods for Long-Term Extreme Response Analysis of Offshore Wind Turbines1

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Xiaolu Chen ◽  
Zhiyu Jiang ◽  
Qinyuan Li ◽  
Ye Li ◽  
Nianxin Ren
Keyword(s):  
Turbulence Intensity ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Contour Method ◽  
Offshore Wind Turbine ◽  
Response Analysis ◽  
Modified Method ◽  
Extreme Response ◽  
Wind Turbulence

Abstract Environmental contour method is an efficient method for predicting the long-term extreme response of offshore structures. The traditional environmental contour is obtained using the joint distribution of mean wind speed, significant wave height, and spectral peak period. To improve the accuracy of traditional environmental contour method, a modified method was proposed considering the non-monotonic aerodynamic behavior of offshore wind turbines. Still, the modified method assumes constant wind turbulence intensity. In this paper, we extend the existing environmental contour methods by considering the wind turbulence intensity as a stochastic variable. The 50-year extreme responses of a monopile-based offshore wind turbine are compared using the extended environmental contour methods and the full long-term method. It is found that both the environmental contour method and the modified environmental contour method, with the wind turbulence intensity included as an individual variable, give more accurate predictions compared with those without. Using the full long-term method as a benchmark, this extended approach could reduce the nonconservatism of the environmental contour method and conservatism of the modified environmental contour method. This approach is effective under wind-dominated or combined wind-wave loading conditions, but may not be as important for wave-dominated conditions.

Numerical Study of Breaking Waves and Associated Wave Forces on a Jacket Substructure for Offshore Wind Turbines

2019 ◽  
Author(s):  
Ankit Aggarwal ◽  
Tobias Martin ◽  
Seimur Shirinov ◽  
Hans Bihs ◽  
Arun Kamath
Keyword(s):  
Numerical Study ◽  
Breaking Waves ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Forces ◽  
Intermediate Water ◽  
Offshore Wind Turbines ◽  
The Past ◽  
Jacket Structures

Abstract The interest towards offshore wind energy has grown manifolds in the last few decades. Jacket structures are one of the most widely used substructures in the offshore wind turbine installations for intermediate water depths. Offshore structures are exposed to breaking waves. The interaction of breaking waves with the jackets is quite complicated due to the multiple vertical, horizontal and diagonal members. In the present study, a numerical investigation of the wave hydrodynamics and wave forces exerted by regular breaking waves on a jacket is performed. The open-source CFD code REEF3D is used for this purpose, which raises the possibility to model the breaking process physically. The conducted model-scale laboratory experiments have been performed in the past such that a direct comparison is presented.

Numerical and Experimental Investigation Regarding the Landing Manoeuvre of a Catamaran Vessel at an Offshore Wind Turbine in Waves

2015 ◽  
Author(s):  
Daniel Ferreira González ◽  
Matthias Lemmerhirt ◽  
Moustafa Abdel-Maksoud ◽  
Marcel König ◽  
Alexander Düster
Keyword(s):  
Experimental Investigation ◽  
Time Domain ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Irregular Waves ◽  
Offshore Wind Turbine ◽  
Reaction Forces ◽  
Simulation Results ◽  
The Time Domain ◽  
Hydrodynamic Effects

In this work, the landing manoeuvre of a catamaran vessel at a monopile foundation is investigated by experiments compared with numerical simulations. Therefore, a method is presented which allows simulating the described landing manoeuvre at offshore structures. The simulation in the time domain is based on potential theory using a boundary element method (BEM) and it computes the motions of the rigid body due to the hydrodynamic loads which consist of the incoming waves and the diffraction caused by the monopile. Further, a fender model is implemented, considering the reaction forces due to the friction and the deformation of the fender. The model is further able to distinguish between slip and non-slip condition of the fender. Apart from this, model tests of the landing manoeuvre were carried out with a catamaran model. During the tests the model pushed its fender against an equally scaled monopile. The motions of the vessel and the forces at the attachment of the fender were measured in regular and irregular waves. The obtained data which leads to a better understanding of the hydrodynamic effects during a landing manoeuvre is compared with the simulation results in order to improve the numerical method. The validation with experimental results shows that the method is applicable to quantify the risk of the fender suddenly slipping.

scholarly journals Visible Light Communication System for Offshore Wind Turbine Foundation Scour Early Warning Monitoring

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1486 ◽  
Author(s):  
Yung-Bin Lin ◽  
Tzu-Kang Lin ◽  
Cheng-Chun Chang ◽  
Chang-Wei Huang ◽  
Ben-Ting Chen ◽  
...  
Keyword(s):  
Visible Light ◽  
Wind Turbine ◽  
Monitoring System ◽  
Wind Farms ◽  
Visible Light Communication ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Sea Waves ◽  
Scour Monitoring

Offshore wind farms have a superior wind source to terrestrial wind farms, but they also face more severe environmental conditions such as severe storms, typhoons, and sea waves. Scour leads to the excavation of sediments around the foundations of structures, reducing the safe capacity of the structures. The phenomenon of pier scour is extremely complex because of the combined effects of the vortex system involving time-dependent flow patterns and sediment transport mechanisms. A real-time scour monitoring system can improve the safety of structures and afford cost-effective operations by preventing premature or unnecessary maintenance. This paper proposes an on-site scour monitoring system using visible light communication (VLC) modules for offshore wind turbine installations. A flume experiment revealed that the system was highly sensitive and accurate in monitoring seabed scour processes. This arrayed-VLC sensory system, proposed in this paper, has considerable potential for safety monitoring and also can contribute to improving the accuracy of empirical scour formulas for sustainable maintenance in the life cycle of offshore structures.

scholarly journals A brief review of fatigue design criteria on offshore wind turbine support structures

2020 ◽  
Vol 15 (55) ◽  
pp. 302-315
Author(s):  
Paulo Mendes ◽  
José A.F.O. Correia ◽  
Abílio M.P. De Jesus ◽  
Bianca Ávila ◽  
Hermes Carvalho ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Wind Turbine ◽  
Influencing Factors ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Design Criteria ◽  
Design Phase ◽  
Offshore Wind Turbines ◽  
Fatigue Design

In this paper, a brief review of the main fatigue design criteria and some advanced fatigue approaches applied to offshore structures (e.g. offshore wind turbines) are presented. It is extremely important to understand the fatigue phenomenon and how it affects structures since offshore structures are constantly submitted to cyclic loading and corrosive attacks that aggravate the problem. All the influencing factors and approaches used during the design phase are also discussed.

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