Breaking wave loads on truss support structures for offshore wind turbines

2014 ◽  
pp. 1219-1226
Keyword(s):  
Wind Turbines ◽  
Offshore Wind ◽  
Breaking Wave ◽  
Wave Loads ◽  
Support Structures ◽  
Offshore Wind Turbines

Implied Reliability Levels in Different Load Models for Offshore Wind Turbines

2014 ◽  
Author(s):  
P. Agarwal ◽  
L. Manuel
Keyword(s):  
Wind Turbines ◽  
Large Diameter ◽  
Offshore Wind ◽  
International Electrotechnical Commission ◽  
Wave Loads ◽  
Support Structures ◽  
Wave Load ◽  
Load Effect ◽  
Offshore Wind Turbines ◽  
Inertia Forces

Assuring uniform reliability levels across various system configurations is the intent of design standards based on the Load and Resistance Factor Design (LRFD) methodology. One such design standard for offshore wind turbines developed by the International Electrotechnical Commission was based on the European experience and may not necessarily represent conditions suited for U.S. waters where several offshore wind energy projects are being planned. It is, hence, of interest to investigate how uniform is the reliability of offshore wind turbines under various levels of wind and wave loads. We assess the reliability of bottom-supported offshore wind turbines in ultimate limit states associated with the fore-aft tower bending moment at the mudline. We compare reliability index estimates for different characteristic load definitions and assumed coefficients of variation for wind and wave loads, as well as for various hydrodynamic to aerodynamic load influences. Effectively, such variations serve to describe different sites and turbine designs. Since large-diameter monopile support structures are dominated by inertia forces, while jacket or tripod support structures with smaller diameter members are dominated by drag forces, we extend an available combined wind-wave load effect model for offshore wind turbines, to include both drag and inertia forces. We show that reasonably uniform reliability levels may be achieved for various combinations of wind and wave loads. Results suggest that drag-dominated wave load cases result in smaller and less uniform reliability estimates than is the case for inertia-dominated wave load cases.

Detailed Study on Breaking Wave Interactions With a Jacket Structure Based on Experimental Investigations

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Jithin Jose ◽  
Olga Podrażka ◽  
Ove Tobias Gudmestad ◽  
Witold Cieślikiewicz
Keyword(s):  
Wind Turbines ◽  
Wave Breaking ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Wave Forces ◽  
Breaking Wave ◽  
Offshore Wind Turbines ◽  
Wave Parameters ◽  
Wave Slamming ◽  
Breaking Wave Forces

Wave breaking is one of the major concerns for offshore structures installed in shallow waters. Impulsive breaking wave forces sometimes govern the design of such structures, particularly in areas with a sloping sea bottom. Most of the existing offshore wind turbines were installed in shallow water regions. Among fixed-type support structures for offshore wind turbines, jacket structures have become popular in recent times as the water depth for fixed offshore wind structures increases. However, there are many uncertainties in estimating breaking wave forces on a jacket structure, as only a limited number of past studies have estimated these forces. Present study is based on the WaveSlam experiment carried out in 2013, in which a jacket structure of 1:8 scale was tested for several breaking wave conditions. The total and local wave slamming forces are obtained from the experimental measured forces, using two different filtering methods. The total wave slamming forces are filtered from the measured forces using the empirical mode decomposition (EMD) method, and local slamming forces are obtained by the frequency response function (FRF) method. From these results, the peak slamming forces and slamming coefficients on the jacket members are estimated. The breaking wave forces are found to be dependent on various breaking wave parameters such as breaking wave height, wave period, wave front asymmetry, and wave-breaking positions. These wave parameters are estimated from the wave gauge measurements taken during the experiment. The dependency of the wave slamming forces on these estimated wave parameters is also investigated.

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

2019 ◽  
Vol 7 (6) ◽  
pp. 181 ◽  
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.

scholarly journals The Effect of the Second-Order Wave Loads on Drift Motion of a Semi-Submersible Floating Offshore Wind Turbine

2020 ◽  
Vol 8 (11) ◽  
pp. 859
Author(s):  
Thanh-Dam Pham ◽  
Hyunkyoung Shin
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Second Order ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Hydrodynamic Loads ◽  
Drift Motion ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

Floating offshore wind turbines (FOWTs) have been installed in Europe and Japan with relatively modern technology. The installation of floating wind farms in deep water is recommended because the wind speed is stronger and more stable. The design of the FOWT must ensure it is able to withstand complex environmental conditions including wind, wave, current, and performance of the wind turbine. It needs simulation tools with fully integrated hydrodynamic-servo-elastic modeling capabilities for the floating offshore wind turbines. Most of the numerical simulation approaches consider only first-order hydrodynamic loads; however, the second-order hydrodynamic loads have an effect on a floating platform which is moored by a catenary mooring system. At the difference-frequencies of the incident wave components, the drift motion of a FOWT system is able to have large oscillation around its natural frequency. This paper presents the effects of second-order wave loads to the drift motion of a semi-submersible type. This work also aimed to validate the hydrodynamic model of Ulsan University (UOU) in-house codes through numerical simulations and model tests. The NREL FAST code was used for the fully coupled simulation, and in-house codes of UOU generates hydrodynamic coefficients as the input for the FAST code. The model test was performed in the water tank of UOU.

On the fatigue behavior of support structures for offshore wind turbines

2014 ◽  
Vol 18 (2) ◽  
pp. 117-134 ◽  
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

Analysis of the Fatigue Damage on the Offshore Wind Turbines Exposed to Wind and Wave Loads Within the Typhoon Area

2004 ◽  
Author(s):  
Atsushi Yamashita ◽  
Kinji Sekita
Keyword(s):  
Fatigue Damage ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Wave Loads ◽  
Wave Load ◽  
Offshore Wind Turbines ◽  
Simple Addition ◽  
Recorded Data ◽  
Term Data

For the design of offshore wind turbines exposed to wind and wave loads, the method of combining the wind load and the wave load is significantly important to properly calculate the maximum stresses and deflections of the towers and the foundations1). Similarly, for the analysis of the fatigue damage critical to the structural life, the influences of combined wind and wave loads have not been clearly verified. In this paper fatigue damage at the time of typhoon passing is analyzed using actually recorded data, though intrinsically long-term data more than 10years should be used to properly evaluate the fatigue damage. This paper concludes that the fatigue damage of the tower caused by the wave load is not substantial and, thus, the fatigue damage by the combined wind and wave load is only 2–3% larger than the simple addition of the independent fatigue damages by the wind and the wave loads. The fatigue damage of the tower top, which is required to reduce the diameter in order to minimize the aerodynamic confliction with blades, is larger than that of the tower bottom. The fatigue damage at the foundation by the combined wind and wave load is 25% larger than the simple addition of the wind and wave damages, as the foundation is directly exposed to the wave load. For the foundation, the proper structural section can be designed in order to improve the structural performance against fatigue.

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