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.

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.

A Comparison of Time Domain Seismic Analysis Methods for Offshore Wind Turbine Structures: Using a Superelement Approach

2019 ◽  
Author(s):  
Laurens Alblas ◽  
Corine de Winter
Keyword(s):  
Rigid Body ◽  
Wind Turbine ◽  
Time Domain ◽  
Wind Farm ◽  
Assessment Tool ◽  
Seismic Analysis ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Rigid Body Motions ◽  
Seismic Accelerations

Abstract Recently, wind farm development has gained more traction in Asian countries such as Taiwan, which are seismically active. Compared to Europe, the offshore wind structures need to be designed for these additional extreme environmental conditions. For monopiles, these calculations can typically be performed in an integrated way in the wind turbine load calculation, but for jackets the superelement (SE) approach remains preferred. At the time of writing different approaches are being applied in the industry to apply the SE approach for seismic time domain analysis. This work explains and compares three different methods, based on calculations performed in offshore strength assessment tool Sesam and aeroelastic tool BHawC. When including additional interface nodes at the foundation model bottom into the SE to which the seismic accelerations can be applied in BHawC similarly as in the re-tracking run in Sesam, the results between BHawC and Sesam are nearidentical. Using a normal SE, which only includes an interface node for the connection to the wind turbine tower bottom, and including the response due to seismic displacements into the SE load file gives a match between BHawC and Sesam, and closely matches the results of the case with additional interface nodes. Doing the same but only including the dynamic response of the interface point relative to a frame of reference moving with the rigid body motions as caused by the seismic accelerations into the SE load file, significant differences occur. This is due to the lack of the loading effect of rigid body motions. The same conclusions on how these methods compare can be drawn when using different wind and wave cases. The presented results give insights into the differences between the methods and how the choice of method may influence the results.

Experimenal analysis of in-plane strain on curved surfaces using transferring techniques

1978 ◽  
Vol 13 (2) ◽  
pp. 121-128 ◽  
Author(s):  
J Buitrago ◽  
A J Durelli ◽  
V J Parks
Keyword(s):  
Rigid Body ◽  
Finite Deformation ◽  
Flat Surface ◽  
Flexible Structures ◽  
Strain Analysis ◽  
Curved Surfaces ◽  
Double Curvature ◽  
Threshold Strain ◽  
Rigid Body Motions ◽  
Inside Out

A new grid-transferring technique is introduced that allows the strain analysis of flat or curved surfaces of single or double curvature. The technique consists of transferring a grid from the structure to a flat surface by means of a thin, adhesive, transparent ribbon. Information is obtained along a strip, or point-by-point when circles or rosettes are used. The technique is specially suitable for the solution of problems of finite deformation of flexible structures, and its threshold strain is about 0.004. As a verification of the new method, strains obtained on a disc under diametral compression are compared with results already given in the literature. As a general example of application, strains on the anticlastic surface of tubes with and without perforation, and turned inside out, are determined. The method is not influenced by rigid-body motions.

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.

Nonlinear Effects in Dynamic Analysis of Flexible Multibody Systems

2001 ◽  
Author(s):  
Y. C. Mbono Samba ◽  
M. Pascal
Keyword(s):  
Rigid Body ◽  
Standard Method ◽  
Multibody Systems ◽  
Nonlinear Effects ◽  
Elastic Deformations ◽  
Dynamics Of Multibody Systems ◽  
Flexible Parts ◽  
Order Of Magnitude ◽  
Rigid Body Motions ◽  
Crank Mechanism

Abstract The work is concerned with the dynamics of multibody systems with flexible parts undergoing large rigid body motions and small elastic deformations. The standard method used in most cases leads to keep only linear terms with respect to the deformations. However, for large rates or large accelerations, this linearisation is sometimes too premature. In this work, a non dimensional analysis of the system is performed, with some estimate about the order of magnitude of the different parameters occuring in the dynamical model obtained by Kane’s method [1]. A flexible slider crank mechanism is used as a test example, together with AUTOLEV [2] software for numerical results.

Influence of Rigid Body Motions on Rotor Induced Velocities and Aerodynamic Loads of a Floating Horizontal Axis Wind Turbine

2014 ◽  
Author(s):  
Jacobus B. de Vaal ◽  
Martin O. L. Hansen ◽  
Torgeir Moan
Keyword(s):  
Rigid Body ◽  
Wind Turbine ◽  
Horizontal Axis ◽  
Simplified Model ◽  
Wake Vortex ◽  
Horizontal Axis Wind Turbine ◽  
Aerodynamic Loads ◽  
Vortex Model ◽  
Rigid Body Motions ◽  
Free Wake

This paper discusses the influence of rigid body motions on rotor induced velocities and aerodynamic loads of a floating horizontal axis wind turbine. Analyses are performed with a simplified free wake vortex model specifically aimed at capturing the unsteady and non-uniform inflow typically experienced by a floating wind turbine. After discussing the simplified model in detail, comparisons are made to a state of the art free wake vortex code, using test cases with prescribed platform motion. It is found that the simplified model compares favourably with a more advanced numerical model, and captures the essential influences of rigid body motions on the rotor loads, induced velocities and wake influence.

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.

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