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282 H. Th. Beier et al. Maschinenhaus 100 m A 50 m Blattlagerzapfen 50 m detail A Fig. 52.1. PCGP-joint 1052 485 2840 458302 556 462 12 12 20 45 12 544 730 Maße in mm Rotorblatt 915 mm Kastenträger cracks Längsschotte Fig. 52.2. <strong>Wind</strong> energy converter GROWIAN and plate-stiffener-connection 52.2.1 Fatigue Tests The fatigue tests should give information about the location of the crack initiation and the corresponding number of cycles, the crack growth behaviour, the slope of the Wöhler-curve, the scatter of the test results and the FAT-class. The information is then used to verify the calculational fatigue resistance. Information about the scatter can be found in the literature. Because the reported scatter takes a great number of different test situations into account, the standard deviation will be generally greater than by the own tests. In this case the literature values should be used for a statistical evaluation. 52.2.2 Crack Initiation with Local Strain Approach The local strain approach relies on the assumption, that a certain cyclic stress– strain history at a local point in a structure will lead to the same damage as for
52 Fatigue Assessment of Truss Joints Based on Local Approaches 283 a standard unnotched specimen. Differences in surface, residual stresses and in size of structures and test specimens can be considered. Crack initiation is defined as a crack length of c =0.5mm, which is a crack depth a ≈ 0.25 mm. As a result the number of cycles for crack initiation is obtained (Seeger [1]). For the calculation of the local stress–strain history information must be given for: – The cyclic stress–strain law, usually as Ramberg–Osgood law ɛa = ɛa,e + ɛa,p = σa E + � σa K ′ � ′ 1/n . (52.1) – The hysteretic behaviour, usually the Masing hypothesis, which means the doubling of the cyclic stress–strain law in stresses and strains. The computation of the local stress–strain history can either be done by full elastic–plastic finite-element-calculations with true strains, or by linearelastic calculations with subsequent approximation of the plastic behaviour, e.g. by Neuber’s-rule [2] σɛE =(KtS) 2 = σ 2 lin.elast. (52.2) The strain–life curve, usually tested with polished, unnotched specimens at a given stress ratio R = −1, can be described in the form of Manson, Coffin, Morrow [3–5] ɛa = ɛa,e + ɛa,p = σ′ f E (2N)b + ɛ ′ f (2N) c . (52.3) The influence of mean stresses, i.e. the case R �= −1, can be considered by damage parameters P , e.g. in the form of Smith et al. [6] PSWT = � (σa + σm)ɛaE. (52.4) The cyclic material characteristics can be taken from the uniform material law (UML) [7]. 52.2.3 Crack Growth with Linear Elastic Fracture Mechanics The calculation of crack propagation with linear elastic fracture mechanics starts at the crack depth a =0.25 mm from local strain approach. The crack depth dependent stress–intensity-factors KI(a) can be computed with FEMsoftware, e.g. FRANC2D/L [8]. A defined fracture criterion stops the calculation resulting in the number of cycles for crack growth. Crack propagation can be calculated with the Paris-law [9] da/dN = C(∆K) m . (52.5) Both material constants C and m can be found in literature.
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Wind Energy Proceedings of the Euro
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Prof. Dr. Joachim Peinke Dr. Stepha
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VI Preface been presented, spanning
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VIII Contents 3.3 Stochastic Wind F
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X Contents 12.6 Subgrid Scale Turbu
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XII Contents 22 Stochastic Small-Sc
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XIV Contents 32 Handling Systems Dr
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XVI Contents 41 3D Numerical Simula
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XVIII Contents 51 Comparing WAsP an
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XX Contents 58.3 Ultra-High Perform
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XXII List of Contributors Lars Berg
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XXIV List of Contributors Renata Gn
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XXVI List of Contributors A. Kiss D
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XXVIII List of Contributors El˙zbi
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XXX List of Contributors Ivo Sláde
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1 Offshore Wind Power Meteorology B
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1 Offshore Wind Power Meteorology 3
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1 Offshore Wind Power Meteorology 5
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2 Wave Loads on Wind-Power Plants i
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Trubaduren 2 Wave Loads on Wind-Pow
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Base moment (10 6 Nm) 0.4 0.2 −0.
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2 Wave Loads on Wind-Power Plants i
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3 Time Domain Comparison of Simulat
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3 Time Domain Comparison Using Cons
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7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 3 T
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4 Mean Wind and Turbulence in the A
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5 Wind Speed Profiles above the Nor
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5 Wind Speed Profiles above the Nor
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Height [m] 100 90 80 70 60 50 40 30
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6 Fundamental Aspects of Fluid Flow
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f Suu(f, z) / σ 2 u(z) 10 0 10 −
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a) c) −0,375 6 Fluid Flow over Co
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7 Models for Computer Simulation of
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y/h 2.5 2 1.5 1 0.5 0 7 Models for
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8 Power Performance via Nacelle Ane
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9 Pollutant Dispersion in Flow Arou
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x1/B 0.3 0.5 0.8 1.0 9 Pollutant Di
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9 Pollutant Dispersion in Flow Arou
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10 On the Atmospheric Flow Modellin
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11 Comparison of Logarithmic Wind P
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Height above ground in m 100 90 80
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12 Turbulence Modelling and Numeric
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13 Gusts in Intermittent Wind Turbu
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Durations (s) 25 20 15 10 5 13 Gust
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14 Report on the Research Project O
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height z (m) 100 80 60 40 20 0 14 R
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14.6 Outlook 14 Report on the Resea
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15 Simulation of Turbulence, Gusts
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S(ƒ)(m/s) 2 /Hz 15 Simulation of T
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15 Simulation of Turbulence, Gusts
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16 Short Time Prediction of Wind Sp
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ms prediction error [m/s] 16 Short
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16 Short Time Prediction of Wind Sp
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17 Wind Extremes and Scales: Multif
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Log10 E(k)*k**(5/3) 6 4 2 0 5/3 cor
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17.3 Discussion and Conclusion 17 W
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18 Boundary-Layer Influence on Extr
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z/H (a) (b) 4 2 18 Boundary-Layer I
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18.6 Concluding Remarks 18 Boundary
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19 The Statistical Distribution of
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19 The Statistical Distribution of
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20 Superposition Model for Atmosphe
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h(u) 0.5 0.3 0.1 20 Superposition M
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21 Extreme Events Under Low-Frequen
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21 Extreme Events Under Low-Frequen
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22 Stochastic Small-Scale Modelling
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p(σ⏐u) 1 0.8 0.6 0.4 0.2 22 Stoc
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22 Stochastic Small-Scale Modelling
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23 Quantitative Estimation of Drift
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24 Scaling Turbulent Atmospheric St
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24 Scaling Turbulent Atmospheric St
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25 Wind Farm Power Fluctuations P.
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25 Wind Farm Power Fluctuations 141
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d rc q rc V 0 q V 25 Wind Farm Powe
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References 25 Wind Farm Power Fluct
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26 Network Perspective of Wind-Powe
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27 Phenomenological Response Theory
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28 Turbulence Correction for Power
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28 Turbulence Correction for Power
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29 Online Modeling of Wind Farm Pow
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29 Online Modeling of Wind Farm Pow
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30 Uncertainty of Wind Energy Estim
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31 Characterisation of the Power Cu
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32 Handling Systems Driven by Diffe
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32 Handling Systems Driven by Diffe
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33 Experimental Researches of Chara
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33 Experimental Researches of Chara
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34 Methodical Failure Detection in
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34 Methodical Failure Detection in
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35 Modelling of the Transition Loca
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35 Modelling an Airfoil with Surfac
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(Cl/Cd)max 120 110 100 90 80 70 60
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35 Modelling an Airfoil with Surfac
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36 Helicopter Aerodynamics with Emp
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37 Determination of Angle of Attack
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37 Determination of Angle of Attack
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Drag coefficient 0.5 0.4 0.3 0.2 0.
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38 Unsteady Characteristics of Flow
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PSD PSD 38 Unsteady Characteristics
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39 Aerodynamic Multi-Criteria Shape
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39 Multi-Criteria Shape Optimizatio
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39 Multi-Criteria Shape Optimizatio
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40 Rotation and Turbulence Effects
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Cp Xsep/c 1 0.6 0.2 −0.2 −0.6
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Standard deviation of Cp 0.7 0.6 0.
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41 3D Numerical Simulation and Eval
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41 3D-CFD-Simulation of a Wind Turb
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Page 265 and 266: 43 Aerodynamic Behaviour of a New T
Page 271 and 272: 44 Numerical Simulation of Dynamic
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Page 275 and 276: 45 Modeling of the Far Wake behind
Page 277 and 278: 8 6 uz 4 2 45 Modeling of the Far W
Page 279 and 280: 46 Stability of the Tip Vortices in
Page 281 and 282: 46 Stability of the Tip Vortices in
Page 283 and 284: 47 Modelling Turbulence Intensities
Page 289 and 290: 48 Numerical Computations of Wind T
Page 291 and 292: Z X Y 48 Numerical Computations of
Page 293 and 294: References 48 Numerical Computation
Page 295 and 296: 49 Modelling Wind Turbine Wakes wit
Page 297 and 298: U mean / U ref 1 0.9 0.8 0.7 49 Mod
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Page 301 and 302: 50 Prediction of Wind Turbine Noise
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Page 305 and 306: 51 Comparing WAsP and Fluent for Hi
Page 307 and 308: Table 51.1. Measurements and simula
Page 309 and 310: 51 Comparing WAsP and Fluent for Hi
Page 311: 52 Fatigue Assessment of Truss Join
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Page 317 and 318: 53 Advances in Offshore Wind Techno
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Page 323 and 324: 54 Benefits of Fatigue Assessment w
Page 325 and 326: ∆σN [N/mm²] 100 10 54 Benefits
Page 327 and 328: 55 Extension of Life Time of Welded
Page 329 and 330: Transverse residual stresses [N/mm
Page 331 and 332: 56 Damage Detection on Structures o
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Page 335 and 336: 57 Influence of the Type and Size o
Page 337 and 338: [W/m 2 ] q t [W/m 5000 4000 3000 20
Page 339 and 340: 58 High-cycle Fatigue of “Ultra-H
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Page 343 and 344: 59 A Modular Concept for Integrated
Page 349 and 350: 60 Solutions of Details Regarding F
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Page 355 and 356: 61 On the Influence of Low-Level Je
Page 357 and 358: Relative Power and Loading [%] 61 O
Page 359 and 360: 62 Reliability of Wind Turbines Exp
Page 361 and 362: 62 Reliability of Wind Turbines 331
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