Effects of Hull Flexibility on the Structural Dynamics of a Tension Leg Platform Floating Wind Turbine

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Carlos Eduardo Silva de Souza ◽  
Erin E. Bachynski
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Structural Response ◽  
Wave Excitation ◽  
Short Term ◽  
Tension Leg Platform ◽  
Flexible Beams ◽  
Fatigue Damage Accumulation ◽  
Vertical Deformations ◽  
Motion Amplitude

Abstract Dynamic analysis of floating wind turbines often considers the hull as a rigid body. This paper explores the consequences of modeling the pontoons of a tension leg platform (TLP) wind turbine as flexible beams. The analysis is based on numerical simulations of free decays, structural response to wave excitation, and short-term fatigue damage accumulation at tower base and tendons. In addition, the importance of hydroelastic effects due to the pontoons’ vertical deformations is evaluated. Pontoon flexibility changed the platform natural periods and motion amplitude significantly, and the adoption of flexible pontoons reduced the predicted fatigue damage in the tower base and tendons. On the other hand, hydroelasticity had negligible consequences for motion and load responses considered here.

Effects of Hull Flexibility on the Structural Dynamics of a TLP Floating Wind Turbine

2018 ◽  
Author(s):  
Carlos Eduardo Silva de Souza ◽  
Erin E. Bachynski
Keyword(s):  
Rigid Body ◽  
Wind Turbine ◽  
Fatigue Damage ◽  
Flexible Structures ◽  
Structural Response ◽  
Secondary Importance ◽  
Fatigue Damage Accumulation ◽  
Fatigue Damage Analysis ◽  
Order Of Magnitude ◽  
Rigid Body Motions

Structural analysis of floating wind turbines is normally carried out with the hull considered as a rigid body. This paper explores the consequences of modeling the pontoons of a tension leg platform (TLP) wind turbine as flexible structures. The analysis is based on numerical simulations of free decays, structural response to wave excitation and short-term fatigue damage accumulation at chosen points of the platform. In addition, the importance of considering hydroelasticity effects is evaluated. It is observed that pontoon flexibility can change the platform natural periods significantly, as well as the intensity and peak frequencies of internal structural loads. The adoption of a fully rigid-body is shown to be non-conservative for the fatigue damage analysis. Loads due to hydroelasticity have order of magnitude comparable to those related to rigid-body motions, but still lower enough to be considered of secondary importance.

Short-Term Fatigue Analysis of Semi-Submersible Wind Turbine Tower

2011 ◽  
Author(s):  
Marit I. Kvittem ◽  
Torgeir Moan ◽  
Zhen Gao ◽  
Chenyu Luan
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Time Domain ◽  
Narrow Band ◽  
Response Spectra ◽  
Spectral Density Function ◽  
Mean Value ◽  
Short Term ◽  
Wind Speeds ◽  
Low Wind Speeds

Coupled time domain analyses of a semi-submersible wind turbine are performed with the intention to study motions affecting fatigue damage at the base of the tower. The software applied is SIMO/RIFLEX with the extension TDHmill, which gives the wind thrust force and gyro moment on the wind turbine as point loads in the tower top. Short term environmental conditions are chosen from a joint wind and wave distribution for a site in the Northern North Sea. Variance spectra, mean value, standard deviation, kurtosis, skewness and Vanmarcke’s bandwidth parameter are calculated for stresses at the base of the tower. Damage is calculated for each short term condition by two methods; rainflow counting and narrow band approximation. The accuracy of narrow band approximation estimates for fatigue are examined for the structure in question. Time domain simulations are carried out for different sea states and fatigue damage is calculated for each case. Simulations show that turbulent wind dominates the response at low wind speeds and the response spectral density function tends to be very wide-banded. For wave dominated response, spectra have lower bandwidth, and narrow banded approximation for fatigue damage gives estimates 20–50% above rainflow counted damage.

Design and Fatigue Performance of Large Utility-Scale Wind Turbine Blades

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Peter K. Fossum ◽  
Lars Frøyd ◽  
Ole G. Dahlhaug
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Turbine Blades ◽  
Fiber Material ◽  
Fatigue Performance ◽  
Wind Turbine Blades ◽  
Additional Material ◽  
Turbulent Wind ◽  
Fatigue Damage Accumulation ◽  
Utility Scale

Aeroelastic design and fatigue analysis of large utility-scale wind turbine blades have been performed to investigate the applicability of different types of materials in a fatigue environment. The blade designs used in the study are developed according to an iterative numerical design process for realistic wind turbine blades, and the software tool FAST is used for advanced aero-servo-elastic simulations. Elementary beam theory is used to calculate strain time series from these simulations, and the material fatigue is evaluated using established methods. Following wind turbine design standards, the fatigue evaluation is based on a turbulent wind load case. Fatigue damage is estimated based on 100% availability and a site-specific annual wind distribution. Rainflow cycle counting and Miner's sum for cumulative damage prediction is used together with constant life diagrams tailored to actual material S-N data. Material properties are based on 95% survival probability, 95% confidence level, and additional material safety factors to maintain conservative results. Fatigue performance is first evaluated for a baseline blade design of the 10 MW NOWITECH reference wind turbine. Results show that blade damage is dominated by tensile stresses due to poorer tensile fatigue characteristics of the shell glass fiber material. The interaction between turbulent wind and gravitational fluctuations is demonstrated to greatly influence the damage. The need for relevant S-N data to reliably predict fatigue damage accumulation and to avoid nonconservative conclusions is demonstrated. State-of-art wind turbine blade trends are discussed and different design varieties of the baseline blade are analyzed in a parametric study focusing on fatigue performance and material costs. It is observed that higher performance material is more favorable in the spar-cap construction of large blades which are designed for lower wind speeds.

Analysis of the Fatigue Life of Offshore Wind Turbine Generators Under Combined Ice- and Aerodynamic Loading

2014 ◽  
Author(s):  
Hayo Hendrikse ◽  
Frank W. Renting ◽  
Andrei V. Metrikine
Keyword(s):  
Wind Turbine ◽  
Phenomenological Models ◽  
Fatigue Damage ◽  
Offshore Wind Turbine ◽  
Superposition Method ◽  
Design Standards ◽  
Combined Analysis ◽  
Aerodynamic Loading ◽  
Ice Load ◽  
Fatigue Damage Accumulation

A modelled wind turbine generator subjected to combined ice- and aerodynamic loading is analyzed with the focus on its fatigue lifetime. A comparison is made between the prediction of a combined analysis, taking both ice- and wind loads into account simultaneously, and a superposition analysis, computing the response of the structure as a result of ice and wind loading separately. The accumulated fatigue damage is computed considering different descriptions of the ice load. Prescribed ice load curves from current design standards, as well as phenomenological models for the prediction of dynamic ice-structure interaction are employed. Results show that the superposition method underpredicts the accumulated fatigue damage in the range of frequency lock-in, but only when phenomenological models, which are more advanced than those recommended by the design standards, are used to model the ice load. Furthermore the predicted fatigue damage computed using the design standards for the description of the ice load is found to be much larger than that resulting from the application of the phenomenological models. It is concluded that the combined analysis is desired when phenomenological models are applied. Furthermore, improvement of the predictive capabilities of such models might ultimately lead to a reduction of the predicted fatigue damage accumulation of the combined ice- and aerodynamic load case, as compared to the current prescribed methods in standards.

Long-Term Stochastic Dynamic Analysis of a Combined Floating Spar-Type Wind Turbine and Wave Energy Converter (STC) System for Mooring Fatigue Damage and Power Prediction

2014 ◽  
Author(s):  
Nianxin Ren ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Wave Energy ◽  
Wind Wave ◽  
Wave Energy Converter ◽  
Force Model ◽  
Stochastic Dynamic ◽  
Energy Converter ◽  
Short Term

In this work, a combined concept called Spar-Toru-Combination (STC) involving a spar-type floating wind turbine (FWT) and an axi-symmetric two-body wave energy converter (WEC) is considered. From the views of both long-term fatigue damage prediction of the mooring lines and the annual energy production estimation, a coupled analysis of wind-wave induced long-term stochastic responses has been performed using the SIMO-TDHMILL code in the time domain, which includes 79200 one-hour short term cases (the combination of 22 selected mean wind speeds * 15 selected significant wave heights * 12 selected spectral peak wave periods * 20 random seeds). The hydrodynamic loads on the Spar and Torus are estimated using potential theory, while the aerodynamic loads on the wind rotor are calculated by the validated simplified thrust force model in the TDHMILL code. Considering the long-term wind-wave joint distribution in the northern North Sea, the annual fatigue damage of the mooring line for the STC system is obtained by using the S-N curve approach and Palmgren-Miner’s linear damage hypothesis. In addition, the annual wind and wave power productions are also obtained by using hourly mean output power for each short-term condition and the joint wind-wave distribution.

scholarly journals Reliability Updating of Offshore Wind Substructures by Use of Digital Twin Information

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5859
Author(s):  
Dawid Augustyn ◽  
Martin D. Ulriksen ◽  
John D. Sørensen
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Damage Accumulation ◽  
Structural Reliability ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Wave Loading ◽  
Soil Stiffness ◽  
Digital Twins ◽  
Fatigue Damage Accumulation

This paper presents a probabilistic framework for updating the structural reliability of offshore wind turbine substructures based on digital twin information. In particular, the information obtained from digital twins is used to quantify and update the uncertainties associated with the structural dynamics and load modeling parameters in fatigue damage accumulation. The updated uncertainties are included in a probabilistic model for fatigue damage accumulation used to update the structural reliability. The updated reliability can be used as input to optimize decision models for operation and maintenance of existing structures and design of new structures. The framework is exemplified based on two numerical case studies with a representative offshore wind turbine and information acquired from previously established digital twins. In this context, the effect of updating soil stiffness and wave loading, which constitute two highly uncertain and sensitive parameters, is investigated. It is found that updating the soil stiffness significantly affects the reliability of the joints close to the mudline, while updating the wave loading significantly affects the reliability of the joints localized in the splash zone. The increased uncertainty related to virtual sensing, which is employed to update wave loading, reduces structural reliability.

On Short-Term Fatigue Analysis for Wind Turbine Tower of Two Semi-Submersible Wind Turbines Including Effect of Startup and Shutdown Processes

2018 ◽  
Author(s):  
Chenyu Luan ◽  
Torgeir Moan
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Wind Turbines ◽  
Limit State ◽  
Offshore Wind ◽  
Environmental Condition ◽  
Short Term ◽  
Transient Load ◽  
Sea Bed ◽  
Rule Approach

Fatigue limit state design check based on S-N curve and Palmgren-Miner rule approach is required by design standards for floating wind turbines since floating wind turbines are subjected cyclically varying environmental loads. Fatigue damage over a given period could be considered as a summation of short-term fatigue damage of each stationary environmental condition multiplying by the number of occurrence of the environmental condition during the given period. In reality, environmental condition varies continuously. While fatigue damage due to transient load processes that are induced by startup and shutdown operations cannot be captured by this conventional approach. Large data bases of real-time measurements show shutdown and startup operations may appear in any operational conditions and the number of the operations could be considerable. Analysis for startup and shutdown operations induced fatigue damage is required by standards for offshore wind turbines. However, relevant publications addressing this issue are very limited in particular for floating wind turbines. In contrast to bottom fixed wind turbines, floating wind turbines have rigid-body motions in 6 d.o.f.s, while the floating wind turbine hulls are moored by mooring lines rather than directly mounted on sea bed or land. This paper focuses on shedding light on the importance of startup and shutdown induced transient load processes on fatigue damage in the tower of two MW-level horizontal axis semi-submersible wind turbines by comparing short-term fatigue damage in several environmental conditions with and without transient load processes induced by startup and shutdown of the wind turbines. In some situations, 4,600 seconds short-term fatigue damage may be dominated by the transient load process induced fatigue damage which may make the fatigue damage be increased by up to 300%, while in many cases, the fatigue damage may be increased by 10% to 100%. The importance of the transient load processes on long-term fatigue damage is related to occurrence frequency of startup and shutdown events and needs more analysis in future.

Sign in / Sign up

Export Citation Format

Share Document