scholarly journals A Summary of the Recent Work at NTNU on Marine Operations Related to Installation of Offshore Wind Turbines

2018 ◽  
Author(s):  
Zhen Gao ◽  
Amrit Verma ◽  
Yuna Zhao ◽  
Zhiyu Jiang ◽  
Zhengru Ren
Keyword(s):  
Wind Turbine ◽  
Recent Work ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Structural Safety ◽  
Offshore Wind Turbines ◽  
Global Dynamic ◽  
Contact Impact

In this paper, a summary of the recent work at NTNU on the installation of offshore wind turbines using jack-up and floating vessels will be reported. The wind turbine components considered here are the monopile foundations and the blades. The detailed discussions are given to the crane operations for installing wind turbine blades as well as novel installation methods for pre-assembled rotor-nacelle-tower. It includes numerical modelling and analysis for global dynamic responses of the installation system (installation vessels plus wind turbines) and for local structural responses of the blades in case of contact/impact. In particular, the stochastic nature of the environmental conditions (mainly wind and waves) and their influence on the global dynamic responses of the installation system will be assessed based on time-domain simulations. In addition, tugger line tension control is introduced for the final connection to the hub in order to reduce the motions of the blade and therefore the potential damages to the blades. It is then followed by a discussion about nonlinear structural analysis of the blade in contact with tower or surrounding structures using ABAQUS. Damages in the composite plies and sandwich core materials of the blade due to contact/impact for a given initial velocity are then estimated. The obtained damage distribution formulates the basis for a probabilistic assessment of structural safety during installation. Novel installation methods in which the rotor-nacelle-tower structure is pre-assembled onshore and installed on top of the foundation offshore, and the corresponding installation vessels are discussed at the end of the paper. Finally, the main conclusions and the recommendations for future work are drawn.

scholarly journals A Review of Recent Advancements in Offshore Wind Turbine Technology

Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 579
Author(s):  
Taimoor Asim ◽  
Sheikh Zahidul Islam ◽  
Arman Hemmati ◽  
Muhammad Saif Ullah Khalid
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Structural Integrity ◽  
Turbine Blades ◽  
Offshore Wind ◽  
System Level ◽  
Offshore Wind Turbine ◽  
Component Level ◽  
Foundation Design ◽  
Offshore Wind Turbines

Offshore wind turbines are becoming increasingly popular due to their higher wind energy harnessing capabilities and lower visual pollution. Researchers around the globe have been reporting significant scientific advancements in offshore wind turbines technology, addressing key issues, such as aerodynamic characteristics of turbine blades, dynamic response of the turbine, structural integrity of the turbine foundation, design of the mooring cables, ground scouring and cost modelling for commercial viability. These investigations range from component-level design and analysis to system-level response and optimization using a multitude of analytical, empirical and numerical techniques. With such wide-ranging studies available in the public domain, there is a need to carry out an extensive yet critical literature review on the recent advancements in offshore wind turbine technology. Offshore wind turbine blades’ aerodynamics and the structural integrity of offshore wind turbines are of particular importance, which can lead towards system’s optimal design and operation, leading to reduced maintenance costs. Thus, in this study, our focus is to highlight key knowledge gaps in the scientific investigations on offshore wind turbines’ aerodynamic and structural response. It is envisaged that this study will pave the way for future concentrated efforts in better understanding the complex behavior of these machines.

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.

Resonance Avoidance of Offshore Wind Turbines

2010 ◽  
Author(s):  
Martin L. Pollack ◽  
Brian J. Petersen ◽  
Benjamin S. H. Connell ◽  
David S. Greeley ◽  
Dwight E. Davis
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Structural Response ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Support Structure ◽  
Offshore Wind Turbines ◽  
Wind Turbine System ◽  
Dynamic Forces ◽  
Technical Basis

Coincidence of structural resonances with wind turbine dynamic forces can lead to large amplitude stresses and subsequent accelerated fatigue. For this reason, the wind turbine system is designed to avoid resonance coincidence. In particular, the current practice is to design the wind turbine support structure such that its fundamental resonance does not coincide with the fundamental rotational and blade passing frequencies of the rotor. For offshore wind turbines, resonance avoidance is achieved by ensuring that the support structure fundamental resonant frequency lies in the frequency band between the rotor and blade passing frequencies over the operating range of the turbine. This strategy is referred to as “soft-stiff” and has major implications for the structural design of the wind turbine. This paper details the technical basis for the “soft-stiff” resonance avoidance design methodology, investigates potential vulnerabilities in this approach, and explores the sensitivity of the wind turbine structural response to different aspects of the system’s design. The assessment addresses the wind turbine forcing functions, the coupled dynamic responses and resonance characteristics of the wind turbine’s structural components, and the system’s susceptibility to fatigue failure. It is demonstrated that the design practices for offshore wind turbines should reflect the importance of aerodynamic damping for the suppression of deleterious vibrations, consider the possibility of foundation degradation and its influence on the support structure’s fatigue life, and include proper treatment of important ambient sources such as wave and gust loading. These insights inform potential vibration mitigation and resonance avoidance strategies, which are briefly discussed.

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

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1867 ◽  
Author(s):  
Amrit Shankar Verma ◽  
Zhiyu Jiang ◽  
Zhengru Ren ◽  
Zhen Gao ◽  
Nils Petter Vedvik
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Wind Wave ◽  
Turbine Blades ◽  
Offshore Wind ◽  
Extreme Value Analysis ◽  
Wind Turbine Blades ◽  
Value Analysis ◽  
Offshore Wind Turbines ◽  
Blade Root

Installation of wind-turbine blades on monopile-type offshore wind turbines is a demanding task. Typically, a jack-up crane vessel is used, and blades are individually lifted from the vessel deck and docked with the preinstalled hub. During the process of mating, large relative motions are developed between the hub and root due to combined effects of wind-generated blade-root responses and wave-generated monopile vibrations. This can cause impact loads at the blade root and induce severe damages at the blade-root connection. Such events are highly likely to cause the failure of the mating task, while affecting the subsequent activities, and thus require competent planning. The purpose of this paper is to present a probabilistic response-based methodology for estimating the allowable sea states for planning a wind-turbine blade-mating task, considering impact risks with the hub as the hazardous event. A case study is presented where the installation system consisting of blade-lift and monopile system are modelled using multibody formulations. Time-domain analyses are carried out for various sea states, and impact velocities between root and hub are analyzed. Finally, an extreme value analysis using the Gumbel fitting of response parameters is performed and limiting sea state curves are obtained by comparing characteristic extreme responses with allowable values. It is found that the limiting sea states for blade-root mating tasks are low for aligned wind–wave conditions, and further increase with increased wind–wave misalignment. The results of the study also show that the parameter T p is essential for estimating limiting sea states given that this parameter significantly influences monopile vibrations during the blade-root mating task. Overall, the findings of the study can be used for a safer and more cost-effective mating of wind-turbine blades.

Numerical Analysis of a Gravity Substructure for 5MW Offshore Wind Turbines due to Soil Conditions

2015 ◽  
Author(s):  
Min-Su Park ◽  
Youn-Ju Jeong ◽  
Young-Jun You ◽  
Du-Ho Lee ◽  
Byeong-Cheol Kim
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Soil Structure ◽  
Offshore Wind ◽  
Soil Structure Interaction ◽  
Structural Safety ◽  
Soil Conditions ◽  
Wave Forces ◽  
Offshore Wind Turbines ◽  
Structure Interaction

In order to increase the gross generation of wind turbines, the size of a tower and a rotor-nacelle becomes larger. In other words, the substructure for offshore wind turbines is strongly influenced by the effect of wave forces as the size of substructure increases. In addition, since a large offshore wind turbine has a heavy dead load, the reaction forces on the substructure become severe, thus very firm foundations should be required. Therefore, the dynamic soil-structure interaction has to be fully considered and the wave acting on substructure accurately calculated. In the present study ANSYS AQWA is used to evaluate the wave forces. The wave forces and wave run up on the substructure are presented for various wave conditions. Moreover, the substructure method is applied to evaluate the effect of soil-structure interaction. Using the wave forces and stiffness and damping matrices obtained from this study, the structural analysis of the gravity substructure is carried out through ANSYS mechanical. The structural behaviors of the strength and deformation are evaluated to investigate an ultimate structural safety and serviceability of gravity substructure for various soil conditions. Also, the modal analysis is carried out to investigate the resonance between the wind turbine and the gravity substructure.

scholarly journals A Coupled CFD/Multibody Dynamics Analysis Tool for Offshore Wind Turbines With Aeroelastic Blades

2017 ◽  
Author(s):  
Yuanchuan Liu ◽  
Qing Xiao ◽  
Atilla Incecik
Keyword(s):  
Wind Turbine ◽  
Multibody Dynamics ◽  
Wind Turbines ◽  
Large Scale ◽  
Turbine Blades ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Analysis Tool ◽  
Dynamics Analysis ◽  
Offshore Wind Turbines

Aero-elasticity is an important issue for modern large scale offshore wind turbines with long slender blades. The behaviour of deformable turbine blades influences the structure stress and thus the sustainability of blades under large unsteady wind loads. In this paper, we present a fully coupled CFD/MultiBody Dynamics analysis tool to examine this problem. The fluid flow around the turbine is solved using a high-fidelity CFD method while the structural dynamics of flexible blades is predicted using an open source code MBDyn, in which the flexible blades are modelled via a series of beam elements. Firstly, a flexible cantilever beam is simulated to verify the developed tool. The NREL 5 MW offshore wind turbine is then studied with both rigid and flexible blades to analyse the aero-elastic influence on the wind turbine structural response and aerodynamic performance. Comparison is also made against the publicly available data.

Structural damping sensitivity affecting the flutter performance of a 10-MW offshore wind turbine

2020 ◽  
Vol 23 (14) ◽  
pp. 3037-3047
Author(s):  
Xugang Hua ◽  
Qingshen Meng ◽  
Bei Chen ◽  
Zili Zhang
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Delay Model ◽  
Structural Damping ◽  
Torsional Mode ◽  
Offshore Wind Turbines

Classical flutter of wind turbine blades is one of the most destructive instability phenomena of wind turbines especially for several-MW-scale turbines. In the present work, flutter performance of the DTU 10-MW offshore wind turbine is investigated using a 907-degree-of-freedom aero-hydro-servo-elastic wind turbine model. This model involves the couplings between tower, blades and drivetrain vibrations. Furthermore, the three-dimensional aerodynamic effects on wind turbine blade tip have also been considered through the blade element momentum theory with Bak’s stall delay model and Shen’s tip loss correction model. Numerical simulations have been carried out using data calibrated to the referential DTU 10-MW offshore wind turbine. Comparison of the aeroelastic responses between the onshore and offshore wind turbines is made. Effect of structural damping on the flutter speed of this 10-MW offshore wind turbine is investigated. Results show that the damping in the torsional mode has predominant impact on the flutter limits in comparison with that in the bending mode. Furthermore, for shallow water offshore wind turbines, hydrodynamic loads have small effects on its aeroelastic response.

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.

scholarly journals Improving the Strategy of Maintaining Offshore Wind Turbines through Petri Net Modelling

2021 ◽  
Vol 11 (2) ◽  
pp. 574
Author(s):  
Rundong Yan ◽  
Sarah Dunnett
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Petri Net ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Maintenance Costs ◽  
Offshore Wind Turbines ◽  
Major Repair ◽  
Wind Turbine System ◽  
Periodic Maintenance

In order to improve the operation and maintenance (O&M) of offshore wind turbines, a new Petri net (PN)-based offshore wind turbine maintenance model is developed in this paper to simulate the O&M activities in an offshore wind farm. With the aid of the PN model developed, three new potential wind turbine maintenance strategies are studied. They are (1) carrying out periodic maintenance of the wind turbine components at different frequencies according to their specific reliability features; (2) conducting a full inspection of the entire wind turbine system following a major repair; and (3) equipping the wind turbine with a condition monitoring system (CMS) that has powerful fault detection capability. From the research results, it is found that periodic maintenance is essential, but in order to ensure that the turbine is operated economically, this maintenance needs to be carried out at an optimal frequency. Conducting a full inspection of the entire wind turbine system following a major repair enables efficient utilisation of the maintenance resources. If periodic maintenance is performed infrequently, this measure leads to less unexpected shutdowns, lower downtime, and lower maintenance costs. It has been shown that to install the wind turbine with a CMS is helpful to relieve the burden of periodic maintenance. Moreover, the higher the quality of the CMS, the more the downtime and maintenance costs can be reduced. However, the cost of the CMS needs to be considered, as a high cost may make the operation of the offshore wind turbine uneconomical.

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