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Influences on the fatigue of offshore structures at the example of the FINO 1 research platform Cord Böker Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Agenda • Introduction • Influence of wave directions • Structural modeling Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Introduction • Joint research project GIGAWINDplus: Validation and improvement of design methods and tools for support structures of Offshore Wind turbines • Focusing on fatigue • Measurement data from the research platform FINO 1 strain gages at 11 locations • Enhanced structural model Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark FINO Scatter diagram 2.75 18 8 3.25 28 58 3 3.75 19 90 55 1 4.25 10 59 85 35 1 4.75 5 29 51 73 17 1 1 26 89 165 190 176 Hs [m] 0.25 0.75 1.25 1.75 2.25 2.75 3.25 3.75 4.25 4.75 5.25 5.75 6.25 6.75 Sum 2.25 1 (Quelle: Google Earth) Tz [s] h=1m h=2m h=3m h=4m h=5m h=6m h=7m 8.25 8.75 Sum 7.25 7.75 6.75 of 6.25 number 5.25 5.75Relative N 83 1 occurrences 1 266 2 4 18 NE NW 240 1 1 1 1 5 13 25 183 1 7 20 46 97 1 6 28 43 54 3 12 26 12 38 1 8 15 12 2 E W 15 2 7 5 1 9 4 4 1 6 2 2 1 5 1 2 1 1SE 2 1 SW 2 1 1 1 1 S 1000 3 4 6 12 26 54 146 104 Long-term directional spread Based on 12896 30-minute-intervalls Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Influence of wave / sea state direction • Damage Equivalent Load (axial force) in the diagonal bracing 60,0 DNBDSW,DEL [kN] 50,0 40,0 315° BDSW 225° BDSW What is the reason for this 30,0 discrepancy? 20,0 Wave Spreading? 10,0 0,0 Database: Simulation: 5 realizations per sea state Measurements: mean values of 8 to 38 10-minute-intervalls, neqv = 2·108 Simulation Simulation Measurement Messung Simulation Simulation Measurement Messung Seegangzustand Seastate 1: 1: Hs =1m, Tz =4s Seegangzustand Seastate 2: 2: Hs =3m, Tz =6s Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Wave Spreading • Linear, regular waves: Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Wave Spreading • Irregular sea state without wave spreading: Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Wave Spreading • Irregular sea state with wave spreading: Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Simulation of sea states considering spreading • Mittendorf, Zielke (GIGAWIND Symposium ´03): Aij 2Si Dj DD 60.0 Seastate 2: Hs = 3m; Tz = 8s Seastate 1: Hs = 1m; Tz =4s 2 ; cos with, e.g.: D 2 2 2 50,0 315° 40.0 DNBDSW,DEL [kN] DNBDSW,DEL [kN] 50.0 60,0 BDSW 40,0 30.0 30,0 20.0 20,0 225°calculation expensive BDSW nJonswap x nspreading partial waves! 10,0 10.0 0,0 0.0 Simulation Messung Simulation Messung Simu Meas1: Simulation SimuSeegangzustand Simu 2:Messung Meas Simulation Simu Simulation Messung Simulation Seegangzustand w/o w/w/spread w/o spread w/ w/o spread spread w/o w/ spread spread Hspread Hs=3m, Tspread s=1m, Tz=4s z=6s Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Application to a Monopile 4 possible cases: (with increasing calculation cost) Long-term distribution Short-term distribution 0,3 NW N 0,25 NE 0,2 0,15 0,1 0,05 W 0 E SW SE S Case #1 Case #2 Case #3 Case #4 Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Application to a Monopile (2) Relative Damage: N N NW 0,3 NW NE N 0,25 NE 0,2 0,15 0,1 0,05 W NW NE 0 E W E W 0,3 E NW N 0,25 NE 0,2 0,15 0,1 0,05 W SW 0 E SE S SW SE S SW Dmax = 100 % SE 0,3 SE S S N N NW NW SW NW NE Dmax = 46 % NE N 0,25 0,3 NE 0,2 NW 0,15 0,1 N 0,25 NE 0,2 0,15 0,05 W 0 E SW W E 0,1 W E 0,05 W 0 E SE SW SE S S Dmax = 37 % SW SE S SW SE Dmax = 35 % S Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Application to a Monopile (2) Relative Damage: Dmax = 100 % Dmax = 37 % Spreading should be considered, at least for monopiles Long-term distribution strongly sitedependant For jacket or tripod structures more investigations necessary Dmax = 46 % Dmax = 35 % Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Structural modeling EF 1: 0.616 Hz EF 2: 0.635 Hz EF 3: 1.452 Hz EF 4: 1.746 Hz EF 5: 1.825 Hz Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Local Joint Flexibilities • In the FE model it is assumed that chords and braces are connected by rigid joints over-estimation of system stiffness! • This has an influence on: – Structural dynamics – Fatigue (due to the distribution of member forces) Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Local Joint Flexibilities • • Parameterized formulae acc. Buitrago et al. (e.g. in DNV OS-J101) Modeling of LJF using flex-elements: Beam Elements “Rigid link” “Flex Element” Stiffness properties determined by parameterized formulae Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Local Joint Flexibilities – first results • LJF included in structural model 0.57 0.62 1.23 1.45 1.68 1.75 w/ LJF FFT of the global bending moment at mudline Hs = 3m, Tz = 6s, dir = 290 deg 10000 Statical excitation due to wave loading w/o LJF Global Moment at mudline [kN²m²] ) 100000 1000 100 10 1 0 0.5 1 1.5 Frequency [Hz] Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark 2 Local Joint Flexibilities - Outlook Sub-structuring approach: • Use detailed models needed for fatigue analysis Beam Elements Superelement: K, M, C 18 DOF in the example (6 per masternode) • • • Advantage: use of existing detail models allows integrated workflow in the design More accurate than simplified approach Arbitrary joint geometries possible (e.g. Tripod) Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark Thanks for your attention! Institute for Steel Construction – Leibniz University of Hannover 2. PhD Seminar on Wind Energy in Europe October 4th and 5th 2006 at Risø National Laboratory, Roskilde, Denmark