Numerical Analysis of Stress Distribution in Offshore Wind Turbine M72 Bolted Connections

The use of bolted joints to connect the transition piece and monopile is nowadays widely applied in the offshore wind industry. Traditionally, grouted connections were used in the early generation of offshore wind turbines, but the experienced failures in such connections led to an increased tendency towards bolted flange connections to join the transition piece and monopile in the new generation of offshore wind turbines. The bolts used for this purpose have high strength and huge sizes, and are subjected to a preload that is applied during the tightening process. The present study is focused on the analysis of preload effects on stress distribution in M72 bolted connections by considering different friction coefficients between the bolt and nut threads. The bolt is considered to be made of grade 10.9 steel, whereas the nut is assumed to be made of grade 8.8 steel, which is a softer material. Using the finite element commercial software package Abaqus, numerical models were developed and analysed to establish trends for stress distribution and plastic strains during the bolt tightening process, and to quantify stress concentration factors in individual engaged threads.

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Analysis of Tightening Sequence Effects on Preload Behaviour of Offshore Wind Turbine M72 Bolted Connections

Energies ◽

10.3390/en12234406 ◽

2019 ◽

Vol 12 (23) ◽

pp. 4406 ◽

Cited By ~ 4

Author(s):

Braithwaite ◽

Mehmanparast

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Fe Model ◽

Bolted Connections ◽

Minimum Requirement ◽

Offshore Wind Turbines ◽

Sequence Effects ◽

Transition Piece

Offshore wind turbines in shallow waters are predominantly installed using a monopile foundation, onto which a transition piece and wind turbine are attached. Previously, the monopile to transition piece (MP-TP) connection was made using a grouted connection, however, cases of grout failure causing turbine slippage, among other issues, were reported. One solution is to use bolted ring flange connections, which involve using a large number of M72 bolts to provide a firm fixing between the MP-TP. It is in the interest of offshore wind operators to reduce the number of maintenance visits to these wind turbines by maintaining a preload (Fp) level above the minimum requirement for bolted MP-TP connections. The present study focuses on the effect of the tightening sequence on the Fp behaviour of M72 bolted connections. A detailed finite element (FE) model of a seven-bolt, representative segment of a monopile flange was developed with material properties obtained from the available literature. Three analyses were made to examine the effect on Fp after tightening, including the initial Fp level applied to the bolts, the tightening sequence and the effect of an additional tightening pass.

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Experimental Validation of Aero-Hydro-Servo-Elastic Models of a Scaled Floating Offshore Wind Turbine

Applied Sciences ◽

10.3390/app9061244 ◽

2019 ◽

Vol 9 (6) ◽

pp. 1244 ◽

Cited By ~ 3

Author(s):

Kasper Jessen ◽

Kasper Laugesen ◽

Signe M. Mortensen ◽

Jesper K. Jensen ◽

Mohsen N. Soltani

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Experimental Validation ◽

Numerical Models ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Scaled Model ◽

Floating Offshore Wind Turbine ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines

Floating offshore wind turbines are complex dynamical systems. The use of numerical models is an essential tool for the prediction of the fatigue life, ultimate loads and controller design. The simultaneous wind and wave loading on a non-stationary foundation with a flexible tower makes the development of numerical models difficult, the validation of these numerical models is a challenging task as the floating offshore wind turbine system is expensive and the testing of these may cause loss of the system. The validation of these numerical models is often made on scaled models of the floating offshore wind turbines, which are tested in scaled environmental conditions. In this study, an experimental validation of two numerical models for a floating offshore wind turbines will be conducted. The scaled model is a 1:35 Froude scaled 5 MW offshore wind turbine mounted on a tension-leg platform. The two numerical models are aero-hydro-servo-elastic models. The numerical models are a theoretical model developed in a MATLAB/Simulink environment by the authors, while the other model is developed in the turbine simulation tool FAST. A comparison between the numerical models and the experimental dynamics shows good agreement. Though some effects such as the periodic loading from rotor show a complexity, which is difficult to capture.

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Maintenance Planning of Offshore Wind Turbine Using Condition Monitoring Information

Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B ◽

10.1115/omae2009-79159 ◽

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.

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

Applied Sciences ◽

10.3390/app11020574 ◽

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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Impact of Typhoons on Floating Offshore Wind Turbines: A Case Study of Typhoon Mangkhut

Journal of Marine Science and Engineering ◽

10.3390/jmse9050543 ◽

2021 ◽

Vol 9 (5) ◽

pp. 543

Author(s):

Jiawen Li ◽

Jingyu Bian ◽

Yuxiang Ma ◽

Yichen Jiang

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Safety Evaluation ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Motion Response ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Coupling Motion

A typhoon is a restrictive factor in the development of floating wind power in China. However, the influences of multistage typhoon wind and waves on offshore wind turbines have not yet been studied. Based on Typhoon Mangkhut, in this study, the characteristics of the motion response and structural loads of an offshore wind turbine are investigated during the travel process. For this purpose, a framework is established and verified for investigating the typhoon-induced effects of offshore wind turbines, including a multistage typhoon wave field and a coupled dynamic model of offshore wind turbines. On this basis, the motion response and structural loads of different stages are calculated and analyzed systematically. The results show that the maximum response does not exactly correspond to the maximum wave or wind stage. Considering only the maximum wave height or wind speed may underestimate the motion response during the traveling process of the typhoon, which has problems in guiding the anti-typhoon design of offshore wind turbines. In addition, the coupling motion between the floating foundation and turbine should be considered in the safety evaluation of the floating offshore wind turbine under typhoon conditions.

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Physical Modelling of Offshore Wind Turbine Foundations for TRL (Technology Readiness Level) Studies

Journal of Marine Science and Engineering ◽

10.3390/jmse9060589 ◽

2021 ◽

Vol 9 (6) ◽

pp. 589

Author(s):

Subhamoy Bhattacharya ◽

Domenico Lombardi ◽

Sadra Amani ◽

Muhammad Aleem ◽

Ganga Prakhya ◽

...

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Prior Experience ◽

Physical Modelling ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Foundation Design ◽

Offshore Wind Turbines ◽

Sea Bed ◽

Geological Conditions

Offshore wind turbines are a complex, dynamically sensitive structure due to their irregular mass and stiffness distribution, and complexity of the loading conditions they need to withstand. There are other challenges in particular locations such as typhoons, hurricanes, earthquakes, sea-bed currents, and tsunami. Because offshore wind turbines have stringent Serviceability Limit State (SLS) requirements and need to be installed in variable and often complex ground conditions, their foundation design is challenging. Foundation design must be robust due to the enormous cost of retrofitting in a challenging environment should any problem occur during the design lifetime. Traditionally, engineers use conventional types of foundation systems, such as shallow gravity-based foundations (GBF), suction caissons, or slender piles or monopiles, based on prior experience with designing such foundations for the oil and gas industry. For offshore wind turbines, however, new types of foundations are being considered for which neither prior experience nor guidelines exist. One of the major challenges is to develop a method to de-risk the life cycle of offshore wind turbines in diverse metocean and geological conditions. The paper, therefore, has the following aims: (a) provide an overview of the complexities and the common SLS performance requirements for offshore wind turbine; (b) discuss the use of physical modelling for verification and validation of innovative design concepts, taking into account all possible angles to de-risk the project; and (c) provide examples of applications in scaled model tests.

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A Review of Recent Advancements in Offshore Wind Turbine Technology

Energies ◽

10.3390/en15020579 ◽

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.

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Proposal and Performance Study of a Novel Mooring System with Six Mooring Lines for Spar-Type Offshore Wind Turbines

Applied Sciences ◽

10.3390/app112411665 ◽

2021 ◽

Vol 11 (24) ◽

pp. 11665

Author(s):

Shi Liu ◽

Yi Yang ◽

Chao Wang ◽

Yuangang Tu

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Offshore Wind ◽

Irregular Waves ◽

Offshore Wind Turbine ◽

Mooring System ◽

Mooring Lines ◽

Included Angle ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines

Spar-type floating offshore wind turbines commonly vibrate excessively when under the coupling impact of wind and wave. The wind turbine vibration can be controlled by developing its mooring system. Thus, this study proposes a novel mooring system for the spar-type floating offshore wind turbine. The proposed mooring system has six mooring lines, which are divided into three groups, with two mooring lines in the same group being connected to the same fairlead. Subsequently, the effects of the included angle between the two mooring lines on the mooring-system’s performance are investigated. Then, these six mooring lines are connected to six independent fairleads for comparison. FAST is utilized to calculate wind turbine dynamic response. Wind turbine surge, pitch, and yaw movements are presented and analyzed in time and frequency domains to quantitatively evaluate the performances of the proposed mooring systems. Compared with the mooring system with six fairleads, the mooring system with three fairleads performed better. When the included angle was 40°, surge, pitch, and yaw movement amplitudes of the wind turbine reduced by 39.51%, 6.8%, and 12.34%, respectively, when under regular waves; they reduced by 56.08%, 25.00%, and 47.5%, respectively, when under irregular waves. Thus, the mooring system with three fairleads and 40° included angle is recommended.

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Development of a CFD-CSD Coupling Technique for Large Scale Offshore Wind Turbines

Volume 12: Wind Energy ◽

10.1115/gt2020-16281 ◽

2020 ◽

Author(s):

Auraluck Pichitkul ◽

Lakshmi N. Sankar

Keyword(s):

Fluid Dynamics ◽

Renewable Energy ◽

Wind Turbines ◽

Large Scale ◽

Time History ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Renewable Energy Resources ◽

Aerodynamic Loads ◽

Offshore Wind Turbines

Abstract Wind engineering technology has been continuously investigated and developed over the past several decades in response to steadily growing demand for renewable energy resources, in order to meet the increased demand for power production, fixed and floating platforms with different mooring configurations have been fielded, accommodating large-scale offshore wind turbines in deep water areas. In this study, the aerodynamic loads on such systems are modeled using a computational structural dynamics solver called OpenFAST developed by National Renewable Energy Laboratory, coupled to an in-house computational fluid dynamics solver called GT-Hybrid. Coupling of the structural/aerodynamic motion time history with the CFD analysis is done using an open File I/O process. At this writing, only a one-way coupling has been attempted, feeding the blade motion and structural deformations from OpenFAST into the fluid dynamics analysis. The sectional aerodynamic loads for a large scale 5 MW offshore wind turbine are presented, and compared against the baseline OpenFAST simulations with classical blade element-momentum theory. Encouraging agreement has been observed.

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Support condition monitoring of offshore wind turbines using model updating techniques

Structural Health Monitoring ◽

10.1177/1475921719875628 ◽

2019 ◽

Vol 19 (4) ◽

pp. 1017-1031 ◽

Cited By ~ 3

Author(s):

Ying Xu ◽

George Nikitas ◽

Tong Zhang ◽

Qinghua Han ◽

Marios Chryssanthopoulos ◽

...

Keyword(s):

Finite Element ◽

Wind Turbine ◽

Wind Turbines ◽

Model Updating ◽

Element Model ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Support Condition ◽

Offshore Wind Turbines ◽

Wind Turbine System

The offshore wind turbines are dynamically sensitive, whose fundamental frequency can be very close to the forcing frequencies activated by the environmental and turbine loads. Minor changes of support conditions may lead to the shift of natural frequencies, and this could be disastrous if resonance happens. To monitor the support conditions and thus to enhance the safety of offshore wind turbines, a model updating method is developed in this study. A hybrid sensing system was fabricated and set up in the laboratory to investigate the long-term dynamic behaviour of the offshore wind turbine system with monopile foundation in sandy deposits. A finite element model was constructed to simulate structural behaviours of the offshore wind turbine system. Distributed nonlinear springs and a roller boundary condition are used to model the soil–structure interaction properties. The finite element model and the test results were used to analyse the variation of the support condition of the monopile, through an finite element model updating process using estimation of distribution algorithms. The results show that the fundamental frequency of the test model increases after a period under cyclic loading, which is attributed to the compaction of the surrounding sand instead of local damage of the structure. The hybrid sensing system is reliable to detect both the acceleration and strain responses of the offshore wind turbine model and can be potentially applied to the remote monitoring of real offshore wind turbines. The estimation of distribution algorithm–based model updating technique is demonstrated to be successful for the support condition monitoring of the offshore wind turbine system, which is potentially useful for other model updating and condition monitoring applications.

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