scholarly journals STRUCTURAL ANALYSIS OF JACKET FOUNDATIONS FOR OFFSHORE WIND TURBINES IN TRANSITIONAL WATER

Brodogradnja ◽  
2021 ◽  
Vol 72 (1) ◽  
pp. 109-124
Author(s):  
Issa Fowai ◽  
◽  
Zhang Jianhua ◽  
Ke Sun ◽  
Bin Wang ◽  
...  
Keyword(s):  
Dynamic Analysis ◽  
Modal Analysis ◽  
Static Analysis ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Von Mises Stress ◽  
Mode Shapes ◽  
Offshore Wind Turbines ◽  
Static And Dynamic Analysis ◽  
Von Mises

Most of the offshore wind turbines (OWT) recently installed in Europe, China and North America are in shallow water. However, unlocking the full potential of OWT lies in deeper waters. Jacket substructures have presented themselves as a reliable foundation concept for transitional water depth. This study focuses on the structural static and dynamic analysis of the traditional jacket substructures (with X and K bracing) and the recently patented three-legged twisted jackets (with a twisted angle of 30 and 60 degrees) for deployment in transitional water (beyond 60 m). To facilitate comparison, the dimensions of all the jackets remain the same, while, the geometric configurations are distinct. Static analysis was implemented to better understand the global load bearing behaviour of the jackets. First, the global displacement patterns at the tower top are compared. The individual reactions at mud-line were investigated, followed by the evaluation of the maximum von Mises stress. Subsequently, this research went on to investigate the effect of dynamic loading. In this dynamic analysis, three main critical points were considered, including the wave point (67 m), the platform and the tower top. A modal analysis was performed to compute the mode shapes and natural frequencies for all the jackets. The first five modes of all the jackets were also checked against the results available for the OC4 project. A similar analytical approach was adopted for the structural design of monopile or tripod foundations for offshore wind turbines. The results showed that in the static analysis both the traditional jackets and the twisted jackets were safe under the provided load combination. The twisted jacket proved to possess excellent structural behaviour compared to the traditional four-legged jackets, while maintaining the merits of lower material usage with fewer nodes. Analysing the von Mises stress revealed that the maximum stress occurred at the transition piece and close to the working platform. The modal analysis results of the jackets demonstrated that the twisted jackets (30 and 60 degrees) with the first natural frequency of 0.29 and 0.31 Hz fell under the soft-stiff design category whereas the traditional four-legged jackets were classified as stiff-stiff designs. The discovered structural performance of OWTs equipped with various jacket foundations contributes to the preliminary structural selection and optimal design of foundations of OWTs to be installed in transitional water.

scholarly journals Structural health monitoring of offshore wind turbines using automated operational modal analysis

2014 ◽  
Vol 13 (6) ◽  
pp. 644-659 ◽  
Author(s):  
Christof Devriendt ◽  
Filipe Magalhães ◽  
Wout Weijtjens ◽  
Gert De Sitter ◽  
Álvaro Cunha ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Modal Analysis ◽  
Wind Turbines ◽  
Operational Modal Analysis ◽  
Offshore Wind ◽  
Dynamic Monitoring ◽  
Mode Shapes ◽  
Offshore Wind Turbine ◽  
Complex Frequency ◽  
Offshore Wind Turbines

This article will present and discuss the approach and the first results of a long-term dynamic monitoring campaign on an offshore wind turbine in the Belgian North Sea. It focuses on the vibration levels and modal parameters of the fundamental modes of the support structure. These parameters are crucial to minimize the operation and maintenance costs and to extend the lifetime of offshore wind turbine structure and mechanical systems. In order to perform a proper continuous monitoring during operation, a fast and reliable solution, applicable on an industrial scale, has been developed. It will be shown that the use of appropriate vibration measurement equipment together with state-of-the art operational modal analysis techniques can provide accurate estimates of natural frequencies, damping ratios, and mode shapes of offshore wind turbines. The identification methods have been automated and their reliability has been improved, so that the system can track small changes in the dynamic behavior of offshore wind turbines. The advanced modal analysis tools used in this application include the poly-reference least squares complex frequency-domain estimator, commercially known as PolyMAX, and the covariance-driven stochastic subspace identification method. The implemented processing strategy will be demonstrated on data continuously collected during 2 weeks, while the wind turbine was idling or parked.

scholarly journals Dynamic Analysis of Mooring Cables with Application to Floating Offshore Wind Turbines

2016 ◽  
Vol 142 (3) ◽  
pp. 04015101 ◽  
Author(s):  
Crescenzo Petrone ◽  
Nicholas D. Oliveto ◽  
Mettupalayam V. Sivaselvan
Keyword(s):  
Dynamic Analysis ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

scholarly journals Damping Identification of Offshore Wind Turbines using Operational Modal Analysis: A Review

2021 ◽  
Author(s):  
Mees van Vondelen ◽  
Sachin T. Navalkar ◽  
Alexandros Iliopoulos ◽  
Daan van der Hoek ◽  
Jan-Willem van Wingerden
Keyword(s):  
Modal Analysis ◽  
Wind Turbines ◽  
Measurement Data ◽  
High Energy ◽  
Operational Modal Analysis ◽  
Offshore Wind ◽  
Vibration Measurement ◽  
Research Attention ◽  
Offshore Wind Turbines ◽  
Vibration Data

Abstract. To increase the contribution of offshore wind energy to the global energy mix in an economically sustainable manner, it is required to reduce the costs associated with the production and operation of offshore wind turbines (OWTs). One of the largest uncertainties and sources of design conservatism for OWTs is the determination of the global damping level of the OWT. Estimation of OWT damping based on field measurement data has hence been subject to considerable research attention and is based on the use of (preferably operational) vibration data obtained from sensors mounted on the structure. As such, it is an output-only problem and can be addressed using state-of-the-art Operational Modal Analysis (OMA) techniques, reviewed in this paper. The evolution of classical time- and frequency-domain OMA techniques has been reviewed; however, literature shows that the OWT vibration data is often contaminated by rotor speed harmonics of significantly high energy located close to structural modes, which impede classical damping identification. Recent advances in OMA algorithms for known or unknown harmonic frequencies can be used to improve identification in such cases. Further, the transmissibility family of OMA algorithms is purported to be insensitive to harmonics. Based on this review, a classification of OMA algorithms is made according to a set of novel suitability criteria, such that the OMA technique appropriate to the specific OWT vibration measurement setup may be selected. Finally, based on this literature review, it has been identified that the most attractive future path for OWT damping estimation lies in the combination of uncertain non-stationary harmonic frequency measurements with statistical harmonic isolation to enhance classical OMA techniques, orthogonal removal of harmonics from measured vibration signals, and in the robustification of transmissibility-based techniques.

A two-step approach to damage localization at supporting structures of offshore wind turbines

2017 ◽  
Vol 17 (5) ◽  
pp. 1313-1330 ◽  
Author(s):  
Karsten Schröder ◽  
Cristian Guillermo Gebhardt ◽  
Raimund Rolfes
Keyword(s):  
Numerical Model ◽  
Objective Function ◽  
Wind Turbines ◽  
Optimization Algorithm ◽  
Measurement Data ◽  
Offshore Wind ◽  
Mode Shapes ◽  
Damage Localization ◽  
Offshore Wind Turbines ◽  
Supporting Structures

This article introduces a new adaptive two-step optimization algorithm for finite element model updating with special emphasis on damage localization at supporting structures of offshore wind turbines. The algorithm comprises an enhanced version of the global optimization algorithm simulated annealing, the simulated quenching method that approximates an initial guess of damage localization. Subsequently, sequential quadratic programming is used to compute the final solution adaptively. For the correlation of numerical model and measurement data, both a measure based on eigenfrequencies and mode shapes and a measure employing time series are implemented and compared with respect to their performance for damage localization. Phase balance of the time signals is achieved using cross-correlation. The localization problem is stated as a minimization problem in which the measures are used in time and modal domain as the objective function subject to constraints. Furthermore, the objective function value of the adjusted model is used to distinguish correct from wrong solutions. The functionality is proven using a numerical model of a monopile structure with simulated damage and a lab-scaled model of a tripile structure with real damage.

Supporting the Engineering Analysis of Offshore Wind Turbines Through Advanced Soil-Structure 3D Modelling

2017 ◽  
Author(s):  
Simone Corciulo ◽  
Omar Zanoli ◽  
Federico Pisanò
Keyword(s):  
Dynamic Analysis ◽  
Wind Turbines ◽  
Soil Structure ◽  
Current Trend ◽  
Offshore Wind ◽  
Fe Modelling ◽  
Offshore Wind Turbines ◽  
Geotechnical Design ◽  
Foundation Type ◽  
Increasing Load

Monopiles are at present the most widespread foundation type for offshore wind turbines (OWTs), due to their simplicity and economic convenience. The current trend towards increasingly powerful OWTs in deeper waters is challenging the existing procedures for geotechnical design, requiring accurate assessment of transient soil-monopile interaction and, specifically, of the associated modal frequencies. In this work, advanced 3D finite element (FE) modelling is applied to the dynamic analysis of soil-monopile-OWT systems under environmental service loads. Numerical results are presented to point out the interplay of soil non-linearity and cyclic hydro-mechanical (HM) coupling, and its impact on transient response of the system at increasing load magnitude. It is shown how the lesson learned from advanced modelling may directly inspire simplified, yet effective, spring models for the engineering dynamic analysis of OWTs.

Sign in / Sign up

Export Citation Format

Share Document