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322 J. Bergers et al. Fig. 60.3. Hot-spot stresses for cylindrical and conical connections at the upper central joint One result of the detail analysis is shown in Fig. 60.3. For tubular connections hot-spot stresses at the transition between brace and chord cannot be avoided. The knowledge about stress distribution enables the localization of critical areas for partial damage calculation. The size of hot-spot stresses is depending on loading and tubular geometry. The hot-spot stresses can be calculated by use of stress concentration factors (SCF) or by finite-element methods. To increase the fatigue resistance of the upper central joint the hot-spot stresses has to be reduced. One possible solution is shown in the right part of Fig. 60.3. Here a stress reduction is achieved by conical widening of the braces at transition. Another possibility for a construction with high fatigue resistance is worked out together with crane constructors which have many experiences in fatigue design. An analogous connection to the upper central joint is solved in conveyor technique with a ring insert. In this construction the shear forces are carried off by internal stiffeners and not by plate bending, which reduce hot-spot stresses. Another effect is that the central shaft below the upper central joint is no longer needed, which also leads to an omission of the lower central joint and the lower braces. This idea of an innovative construction without lower central joint is transferred to a tripod foundation structure for offshore wind turbines. At first a global and a detailed model of the upper central joint without ring insert was developed, see Fig. 60.4. The braces of this structure have the bearing behaviour of bending beams. Typical for tubular connections is that hot-spot stresses appear at tubular intersections. Figure 60.5 shows the results of the stress calculation for the same load case as before for a tripod structure with ring insert. Here one can see that the hot-spot stresses are enormously reduced, which will lead to an efficient solution regarding fatigue design.
60 Solutions of Details Regarding Fatigue 323 Fig. 60.4. Hot-spot stresses for tripod design without lower central joint Fig. 60.5. Hot-spot stresses for tripod design without lower central joint and ring insert Fig. 60.6. Examples for FE-analyses on cut-outs of the tripod for finding a suitable test-setup This specified innovative construction for the foundation structure of OWEC builds the basis for all further investigations in the new research project, which is now continued by material testing. Structures with large wall thicknesses cause problems for the execution of the tests, so that simplified test specimens are investigated at first. In the second step, further tests on sections of the tripod joint are to be carried out. To determine the complex stress distribution in the tripod joint and to consider the surrounding conditions for the test setup, further comprehensive finite-element analyses are performed, as is illustrated in Fig. 60.3. In parallel, practical parameter studies are supported by extensive numerical work.
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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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42 Performance of the Risø-B1 Airf
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42 Performance of the Risø-B1 Airf
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43 Aerodynamic Behaviour of a New T
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44 Numerical Simulation of Dynamic
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44 Numerical Simulation of Dynamic
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45 Modeling of the Far Wake behind
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8 6 uz 4 2 45 Modeling of the Far W
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46 Stability of the Tip Vortices in
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46 Stability of the Tip Vortices in
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47 Modelling Turbulence Intensities
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48 Numerical Computations of Wind T
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Z X Y 48 Numerical Computations of
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References 48 Numerical Computation
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49 Modelling Wind Turbine Wakes wit
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U mean / U ref 1 0.9 0.8 0.7 49 Mod
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49.5 Conclusion 49 Modelling Wind T
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Page 305 and 306: 51 Comparing WAsP and Fluent for Hi
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Page 311 and 312: 52 Fatigue Assessment of Truss Join
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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
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Page 359 and 360: 62 Reliability of Wind Turbines Exp
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