Structural integrity assessment of fixed support structures for offshore wind turbines: A review

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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Tripod-Supported Offshore Wind Turbines: Modal and Coupled Analysis and a Parametric Study Using X-SEA and FAST

Journal of Marine Science and Engineering ◽

10.3390/jmse7060181 ◽

2019 ◽

Vol 7 (6) ◽

pp. 181 ◽

Cited By ~ 3

Author(s):

Pasin Plodpradit ◽

Van Nguyen Dinh ◽

Ki-Du Kim

Keyword(s):

Wind Turbines ◽

Natural Frequencies ◽

Offshore Wind ◽

Computational Time ◽

Coupled Analysis ◽

Physical Interaction ◽

Support Structures ◽

Coupled Models ◽

Support Structure ◽

Offshore Wind Turbines

This paper presents theoretical aspects and an extensive numerical study of the coupled analysis of tripod support structures for offshore wind turbines (OWTs) by using X-SEA and FAST v8 programs. In a number of site conditions such as extreme and longer period waves, fast installation, and lighter foundations, tripod structures are more advantageous than monopile and jacket structures. In the implemented dynamic coupled analysis, the sub-structural module in FAST was replaced by the X-SEA offshore substructure analysis component. The time-histories of the reaction forces and the turbine loads were then calculated. The results obtained from X-SEA and from FAST were in good agreement. The pile-soil-structure interaction (PSSI) was included for reliable evaluation of OWT structural systems. The superelement concept was introduced to reduce the computational time. Modal, coupled and uncoupled analyses of the NREL 5MW OWT-tripod support structure including PSSI were carried out and the discussions on the natural frequencies, mode shapes and resulted displacements are presented. Compared to the uncoupled models, the physical interaction between the tower and the support structure in the coupled models resulted in smaller responses. Compared to the fixed support structures, i.e., when PSSI is not included, the piled-support structure has lower natural frequencies and larger responses attributed to its actual flexibility. The models using pile superelements are computationally efficient and give results that are identical to the common finite element models.

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On the fatigue behavior of support structures for offshore wind turbines

Wind and Structures ◽

10.12989/was.2014.18.2.117 ◽

2014 ◽

Vol 18 (2) ◽

pp. 117-134 ◽

Cited By ~ 8

Author(s):

N. Alati ◽

V. Nava ◽

G. Failla ◽

F. Arena ◽

A. Santini

Keyword(s):

Wind Turbines ◽

Fatigue Behavior ◽

Offshore Wind ◽

Support Structures ◽

Offshore Wind Turbines

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Two-stage local optimization of lattice type support structures for offshore wind turbines

Ocean Engineering ◽

10.1016/j.oceaneng.2016.03.035 ◽

2016 ◽

Vol 117 ◽

pp. 163-173 ◽

Cited By ~ 8

Author(s):

S. Schafhirt ◽

D. Zwick ◽

M. Muskulus

Keyword(s):

Wind Turbines ◽

Local Optimization ◽

Offshore Wind ◽

Support Structures ◽

Two Stage ◽

Offshore Wind Turbines ◽

Lattice Type

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How to Detect Local Out-of-Plane Vibrations in Jacket Support Structures for Offshore Wind Turbines

Volume 9B: Ocean Renewable Energy ◽

10.1115/omae2014-24245 ◽

2014 ◽

Cited By ~ 1

Author(s):

Sebastian Schafhirt ◽

John M. Hembre ◽

Michael Muskulus

Keyword(s):

Fatigue Damage ◽

Wind Turbines ◽

Sequential Analysis ◽

Offshore Wind ◽

Support Structures ◽

Local Vibration ◽

Offshore Wind Turbines ◽

Simulation Based ◽

Out Of Plane ◽

The Impact

There has been an ongoing debate whether local out-of-plane vibrations of braces exist in jacket support structures for wind turbines. The issue has been raised with the sequential analysis of offshore wind turbines, where increased fatigue damage for bracings was observed. Local vibration modes, excited by rotor harmonics, were detected as a reason for it. A methodology to remove global motion of the jacket from the displacements of the central joint in a brace is presented and the amplitude of local out-of-plane displacements is analyzed, using an integrated wind turbine simulation based on a flexible multibody solver. Finally, the impact on fatigue damage is calculated. Results indicate that the extent of local vibrations is much less than previously thought or predicted in other studies.

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