WindCrete Fatigue Verification

Abstract WindCrete is an offshore concrete spar type platform for Wind Turbines developed at Universitat Politècnica de Catalunya – BarcelonaTech. The main characteristics of the platform are its monolithic configuration and the use of concrete as main material. The monolithic nature allows avoiding joints between the substructure and the tower increasing the service life of the structure. The use of concrete increases the resistance when exposed to an offshore environment but requires ensuring a full compression state along the structure to avoid cracking. Thus, the platform is post-tensioned by longitudinal tendons along its length. Adequate fatigue design is a key factor to ensure the reliability of offshore structures. Floating Offshore Wind Turbines are subjected to cyclic phenomena coming from waves, wind, rotor-induced vibrations and structural vibrations. These loads have to be considered in order to assess the fatigue life of offshore structures. Furthermore, pre-stressed concrete adds an internal load such that it avoids the presence of tension stresses at any given section, which has a positive influence on the fatigue response of the structure by increasing its fatigue resistance. An excess of compression can, however, also induce an adverse effect on the fatigue resistance of the concrete. In order to study the fatigue behaviour of WindCrete when fitted with a 5MW Wind Turbine, a Fatigue Limit State verification is performed according to the DNVGL-ST-0437 for load cases definition and FIB Model Code (2010) for fatigue structural verification. The location chosen to install WindCrete is the Gulf de Lion, at the west of the Mediteranian Sea off the coast of Catalunya with a mean wind speed above 9 m/s. The metocean conditions for design purpose are presented, which are obtained from available environmental data. A total of 458 simulation cases are performed using the NREL FAST software assuming wind and wave co-directionally, and quasi-static mooring response for Parked and Power-Production operational modes. Assuming an elastic response of the tower, the internal stresses at the tower base are obtained for all the simulations. Then, a fatigue analysis is performed at the tower base through a cumulative damage approach based on the Palmgren-Miner rule. The analysis accounted for the multiaxial stresses produced by the combination of axial, bending and tangential forces. The S-N material curves were defined according to the Model Code 2010 method, which accounts for the effect of the stress range as well as the average stress.

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Simulation Requirements and Relevant Load Conditions in the Design of Floating Offshore Wind Turbines

Volume 10: Ocean Renewable Energy ◽

10.1115/omae2018-78244 ◽

2018 ◽

Cited By ~ 1

Author(s):

Ricardo Faerron Guzmán ◽

Kolja Müller ◽

Luca Vita ◽

Po Wen Cheng

Keyword(s):

Wind Turbines ◽

Limit State ◽

Power Production ◽

Offshore Wind ◽

Ultimate Limit State ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Simulation Time ◽

Number Of Seeds ◽

Load Conditions

Aligned with work performed in deliverable D7.7 of the H2020 project LIFES50+, this study supports the definition of the numerical setup in the design of floating offshore wind turbines. The results of extensive simulation studies are presented, which focus particularly on determining the requirements for the load simulations in the design process. The analysis focusses on the cases of: (1) fatigue during power production and (2) ultimate loads during power production and severe sea state. For the fatigue load case, sensitivity study is performed in order to determine relevant load conditions and the expected impact of a variation in the environmental loading. Additionally, focus is put on the requirements regarding the run-in time, number of seeds and the simulation length for both fatigue and ultimate limit state (FLS, ULS) analysis. Another topic addressed is the benefit of using an increased number of seeds rather than extending the simulation time of single seeds, when a given total simulation time is required as described in the guidelines. The run-in time may be shortened when using predetermined steady states as initial conditions. Requirements for the steady state simulations are also determined and presented.

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Numerical modeling of the seismic performance of monopile supported wind turbines in sandy soils susceptible to liquefaction.

International Journal of Engineering & Technology ◽

10.14419/ijet.v7i2.13.12676 ◽

2018 ◽

Vol 7 (2.13) ◽

pp. 263

Author(s):

Mehran Tirandazian ◽

Gholamreza Nouri

Keyword(s):

Wind Turbines ◽

Computational Cost ◽

Wind Farms ◽

Bottom Layer ◽

Offshore Structures ◽

Offshore Wind ◽

Elastic Response ◽

Winkler Foundation ◽

Elastic Response Spectra ◽

Soil Layering

Since 1980, as wind farms have moved from coastal to offshore areas, the wind energy industry has been completely transformed which in turn has led to the increase in the construction of wind turbines. On the other hand, harsher offshore environmental conditions have led to larger lateral loads and anchorages applied to the wind turbines and specifically to their piles than other coastal and offshore structures. Thus, more solid piles are required to ensure proper rigidity and bearing capacity. Liquefaction is one of the most important seismic hazards through which various damages caused to different parts of wind turbines. In order to develop coastal and offshore structures in Iran, a study of liquefaction is of great importance due in part to the high risk of seismicity. In this study, the effect of liquefaction on seismic response of offshore wind turbines is examined taking advantage of a finite element model. To this end, all analyzes have been carried out in both occurrence and non-occurrence of the liquefaction, so that by comparing these two modes, the mechanisms affecting the seismic behavior of wind turbines are understood. As depth increases, the possibility of liquefaction is reduced due to higher pressure. Liquefaction is considered to a depth of 20 m and structural behavior is evaluated based on the level of seismic hazard, the thickness of the susceptible layers, soil compaction, the non-fluidizing top layer, the gradient of the earth, the thickness of the monopole, the dimensions of the wind turbine and different soil layering conditions. According to the mentioned factors, a comprehensive and parametric study of the behavior of wind turbines in seismic zones, and in different loading conditions, pile diameters and soil layering is carried out in soils prone to liquefaction. Since analyzes are performed in both occurrence and non-occurrence of the liquefaction, the number of analyzes and computational cost in this research becomes enormous. Therefore, there is a need for a highly effective software and a practical modeling method that will allow for this comprehensive study. Open Sees software and beam on nonlinear Winkler foundation approach are used to model the soil-pile-structure interaction. The minor differences observed in the laboratory values compared to the numerically calculated ones may refer to the fact that the chamber is not modeled. In the bottom layer, as the depth decreases, the elastic response spectra record larger values which are due to the resonance in the structure.

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On motion analysis and elastic response of floating offshore wind turbines

Journal of Ocean Engineering and Marine Energy ◽

10.1007/s40722-019-00159-2 ◽

2020 ◽

Vol 6 (1) ◽

pp. 71-90 ◽

Cited By ~ 3

Author(s):

Azin Lamei ◽

Masoud Hayatdavoodi

Keyword(s):

Motion Analysis ◽

Wind Turbines ◽

Offshore Wind ◽

Elastic Response ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines

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Ultimate and accidental limit state design for mooring systems of floating offshore wind turbines

Ocean Engineering ◽

10.1016/j.oceaneng.2014.09.036 ◽

2014 ◽

Vol 92 ◽

pp. 64-74 ◽

Cited By ~ 22

Author(s):

G. Benassai ◽

A. Campanile ◽

V. Piscopo ◽

A. Scamardella

Keyword(s):

Wind Turbines ◽

Limit State ◽

Offshore Wind ◽

Offshore Wind Turbines ◽

Limit State Design ◽

Floating Offshore Wind Turbines

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Study of motion of spar-type floating wind turbines in waves with effect of gyro moment at inclination

Journal of Naval Architecture and Marine Engineering ◽

10.3329/jname.v9i1.10732 ◽

2012 ◽

Vol 9 (1) ◽

pp. 67-79 ◽

Cited By ~ 8

Author(s):

N. Mostafa ◽

M. Murai ◽

R. Nishimura ◽

O. Fujita ◽

Y. Nihei

Keyword(s):

Wind Turbines ◽

Offshore Structures ◽

Moment Of Inertia ◽

Offshore Wind ◽

Irregular Waves ◽

Scale Model ◽

Water Tank ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Marine Engineering

Recently, a number of research groups have paid much attention to the study of Floating Offshore Wind Turbines (FOWTs). Similar to other offshore structures, the FOWTs are subjected to irregular waves and wind loads which cause a dynamic response in the structures. Under marine environmental conditions, they face many forces which prevent them from floating in the upright condition; they incline as a result of the winds, strong currents, typhoons, cyclones, storms etc. The motion of the FOWT might be changed by a change in gyroscopic effect which depends on the angular velocity and moment of inertia of the blade. Therefore, to investigate the effect of the gyro moment on the motion of the FOWT, two types of experiment were carried out in a water tank using a 1/360 scale model of a prototype FOWT. Firstly, the interaction between the rotary motion of the wind turbine blade and the dynamic motion of the SPAR-type FOWT was studied at small angles of inclination in regular waves. Secondly, the interaction between the change of rotational speed as well as moment of inertia of the blade and the motion of the FOWT was studied. In this paper, numerical calculations have been carried out using potential theory based on the 3D panel method. Finally, the experimental results are compared with the results of numerical simulation and findings are discussed. DOI: http://dx.doi.org/10.3329/jname.v9i1.10732 Journal of Naval Architecture and Marine Engineering 9(2012) 67-79

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Reliability Evaluation of Structural Safety Factor Using a Global Resistance Approach

IABSE Symposium, Guimarães 2019: Towards a Resilient Built Environment Risk and Asset Management ◽

10.2749/guimaraes.2019.1354 ◽

2019 ◽

Author(s):

Sergio Santos ◽

Marcio Tacques R. Monteiro Junior ◽

Luiz Fernando Martha ◽

Claudia Interlandi

Keyword(s):

Limit State ◽

Point Of View ◽

Structural Safety ◽

Structural Behaviour ◽

Limit States ◽

Average Value ◽

Model Code ◽

Resistance Approach ◽

Model Code 2010 ◽

Ultimate Limit

This paper presents a discussion on different ways of assessing the safety of concrete structures applying Reliability Analyses. The usual design approach based on the Ultimate Limit States (ULS) is confronted with the Global Resistance Format, as defined in fib Model Code 2010. The Global Format considers the several uncertainties present in the structural behaviour through a pre-defined limit state in which one or more loading variables are increased by a λ factor, until a collapse situation is attained. In this evaluation, the variables related to the actions and to the resistances are taken with their average value. The obtained values for the λ factor shall be compatible, in the safety point-of- view, with the β reliability factors corresponding to the required safety levels. A conventional building is analyzed, and the obtained reliability factors corresponding to the two approaches are presented. It is shown that the application of the Global Resistance Format can lead to more economical structures.

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Comparison of Free Vortex Wake and BEM Structural Results Against Large Eddy Simulations Results for Highly Flexible Turbines Under Challenging Inflow Conditions

10.5194/wes-2021-130 ◽

2022 ◽

Author(s):

Kelsey Shaler ◽

Benjamin Anderson ◽

Luis A. Martinez-Tossas ◽

Emmanuel Branlard ◽

Nick Johnson

Keyword(s):

Wind Turbines ◽

Economic Benefits ◽

Offshore Wind ◽

Elastic Response ◽

Vortex Wake ◽

Free Vortex ◽

Floating Offshore Wind Turbines ◽

Wind Energy Development ◽

The Many ◽

Inflow Conditions

Abstract. Throughout wind energy development, there has been a push to increase wind turbine size due to the substantial economic benefits. However, increasing turbine size presents several challenges, both physically and computationally. Modeling large, highly flexible wind turbines requires highly accurate models to capture the complicated aerodynamic response due to large deflections and nonstraight blade geometries. Additionally, development of floating offshore wind turbines requires modeling techniques that can predict large rotor and tower motion. Free vortex wake (FVW) methods model such complex physics while remaining computationally tractable to perform the many simulations necessary for the turbine design process. Recently, a FVW model—cOnvecting LAgrangian Filaments (OLAF)—was added to the National Renewable Energy Laboratory engineering tool OpenFAST to allow for the aerodynamic modeling of highly flexible turbines along with the aerohydro- servo-elastic response capabilities of OpenFAST. In this work, FVW and low-fidelity blade-element momentum (BEM) structural results are compared to high-fidelity simulation results for a highly-flexibly downwind turbine for varying TI, shear exponent, and yaw misalignment conditions. Through these comparisons, it was found that for all considered quantities of interest, SOWFA, OLAF, and BEM results compare well for steady inflow conditions with no yaw misalignment. For OLAF results, this strong agreement was consistent for all yaw misalignment values. The BEM results, however, deviated significantly more from SOWFA results with increasing absolute yaw misalignment. Differences between OLAF and BEM results were dominated by yaw misalignment angle, with varying shear exponent and TI leading to more subtle differences. Overall, OLAF results were more consistent than BEM results when compared to SOWFA results under challenging inflow conditions.

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