10089_001.pdf - Load set calculation - ECN

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Load set calculation DOWEC 6MW H. Efdé • tt+5-5, girders 0.5 o rotated, at root girder suction side 0.5m forward and girder pressure side 0.5 m aft. • tt-5+5, girders 0.5 o rotated, at root girder suction side 0.5m to aft and girder pressure side 0.5 m forward. The modified turbine models are tested with load cases 008, 012, 018 and 024, 231 and 234. Load case 231 is a stochastic windspeed of 12 m/s with –20 o yaw, 234 a stochastic windspeed of 25 m/s with –20 o yaw. To prevent interference of the blades with the turbine, the dynamic behaviour of the tower has been switched off. Also the baseline loadcases have been recalculated with tower dynamics off. This explains the difference in baseline loads in the table below, compared to the other variations.The results of the simulations are stored on CD C45.04/01.03/03 . The extreme and fatigue tables can be found in Appendix D as well. 5.2.1 Cost of energy. The calculation of the cost of energy can only be based on the fatigue and extreme loads of the blades. Gearbox loads, tower loads and energy production are not taken into account because the aerodynamics of the blades are not changed and the tower dynamics are off. Therefore it is assumed that these parameters have not changed. Based on the changed loads the results in relative turbine costs are as follows: Table 13: Structural pitch, cost of energy. blade parameter baseline tt-5+5 relative turbine costs tr+5-5 relative turbine costs tt+5 relative turbine costs tt+5-5 relative turbine costs kNm % % % % % % % % Myb[1]-p[01] 15535.00 0.70 0.01 3.40 0.05 0.70 0.01 3.70 0.06 1Hz-Mxb[1]-p[01] 8327.10 1.05 0.02 -0.60 -0.01 0.90 0.01 -12.00 -0.18 total 0.03 total 0.04 total 0.02 total -0.12 The influence of the design variations on the cost of energy is similar to the relative turbine costs. R45.04/01.03/03 Stentec, 3-1-03 page 16
Load set calculation DOWEC 6MW H. Efdé 5.3 Tower eigenfrequencies. The influence of the tower eigenfrequencies on the turbine behaviour is investigated by creating 8 new tower models with the following eigenfrequencies: 0.150, 0.175, 0.200, 0.225, 0.250, 0.300, 0.350 and 0.400 Hz. The clamping stiffness and material properties of the baseline tower were modified iteratively to alter the eigenfrequency. The frequencies were calculated with Phatas IV. The results of the load case calculations can be found on CD C45.04/01.03/03. The extreme and fatigue tables can be found in Appendix E as well. 5.3.1 Cost of energy. Compared to the baseline gearbox loads and annual energy production have not changed. Only blade and tower loads were used to determine the change in turbine costs. When comparing the towers the following table can be made: Table 14: Tower eigenfrequencies, cost of energy. relative relative relative relative twrfreq turbine twrfreq turbine twrfreq turbine twrfreq turbine parameter baseline 0.150 costs 0.175 costs 0.200 costs 0.225 costs blade kNm % % % % % % % % Myb[1]-p[01] 18006.00 -8.83 -0.13 -5.53 -0.08 -2.69 -0.04 -0.45 -0.01 1Hz-Mxb[2]-p[01] 6772.97 -6.11 -0.09 -4.27 -0.06 -3.37 -0.05 -1.07 -0.02 tower Myt[01] -281560.00 -21.52 -1.03 -12.35 -0.59 -4.31 -0.21 -0.62 -0.03 1Hz-Myt[02] 6424.40 -3.53 -0.11 -0.61 -0.02 -3.71 -0.12 -0.81 -0.03 total -1.37 total -0.76 total -0.42 total -0.08 relative relative relative relative twrfreq turbine twrfreq turbine twrfreq turbine twrfreq turbine parameter baseline 0.250 costs 0.300 costs 0.350 costs 0.400 costs blade kNm % % % % % % % % Myb[1]-p[01] 18006.00 0.12 0.00 -0.16 0.00 -1.26 -0.02 -1.19 -0.02 1Hz-Mxb[2]-p[01] 6772.97 -0.36 -0.01 -0.12 0.00 0.00 0.00 -0.95 -0.01 tower Myt[01] -281560.00 -1.14 -0.05 -6.89 -0.33 -28.50 -1.37 -24.63 -1.18 1Hz-Myt[02] 6424.40 -1.20 -0.04 0.00 0.00 -1.99 -0.06 -2.57 -0.08 total -0.10 total -0.33 total -1.45 total -1.30 The influence of the design variations on the cost of energy is similar to the relative turbine costs. What this table doesn’t show is a resonance of the tower with the 0.200 e.f. The 1P oscillation happens at 0.200 * 60 = 12rpm. Since this is very close to the nominal rpm of 11.844rpm, considerable fatigue damage is the result. The DOWEC wind turbine cuts out at 14rpm, so the lowest possible tower e.f. should be above 14 / 60 = 0.233Hz. R45.04/01.03/03 Stentec, 3-1-03 page 17
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