Final report for WP4.3: Enhancement of design methods ... - Upwind

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UPWIND WP4: Offshore Support Structures and Foundations L (|F |) ∞ X1 L (|F |) ∞ X3 L (|F |) ∞ X5 10 0 10 -5 10 -2 10 -3 10 -4 10 0 10 -2 10 -4 10 2 Number of unknowns 10 2 Number of unknowns 10 2 Number of unknowns 98 10 4 10 4 10 4 L (|F |) ∞ X2 L (|F |) ∞ X4 L (|F |) ∞ X6 10 -2 10 -3 10 -4 10 -5 10 -10 10 -15 10 -12 10 -14 10 -16 10 2 Number of unknowns 10 2 Number of unknowns 10 2 Number of unknowns Figure 8.5: Evolution of the convergence in terms of the error norm for the linear excitation force associated with the OC3-Hywind. Convergence studies for the semi-submersible platform To simplify the model used to compute the hydrodynamic loads of the semi-submersible platform it was assumed that the major contributions of the hydrodynamic interaction are due only to the three cylindrical columns and horizontal damping plates. The influence of the submerged braces which interconnect the three columns was considered negligible with regard to the hydrodynamic loads (see Figure 8.3 b). The geometry of this structure was discretised for three grid sizes with the panel size parameter equal to 10.0 m, 5.0 m and 2.5 m. The hydrodynamic quantities were computed for five wave periods selected randomly between 5 s to 16 s. The three discretisations considered for the convergence analysis are shown in Figure 8.6. Figure 8.6: Three discretisations of the geometry of the semi-submersible platform used in the convergence tests. The panel size parameter equal to (a) 10.0 m (b) 5.0 m and (c) 2.5m. The convergence ratio (R) associated with the excitation forces obtained for the discretisation triplet used in this study is shown in Table 8.8. As with the previous geometry, most of the values are between -1 and 1 and the solution for these quantities can be classified as convergent. The estimation of the exact solution for the linear excitation force at the incident wave periods considered in this study is presented in Table 8.9 and the uncertainty associated with the finer mesh is presented in Table 8.10. The evolution of the convergence for four different discretisations presented in terms of the error norm for the linear excitation forces is presented in Figure 8.7. Once again the uncertainty estimates are several orders of magnitude smaller than the excitation force values, which is reassuring of the quality of the numerical solutions. The relation between the panel size parameter and the number of equations (N) in the linear system to be solved by WAMIT which is used as a measure of the total number of panels is shown in Table 8.11. 10 4 10 4 10 4
UPWIND WP4: Offshore Support Structures and Foundations A panel size equal to 5.0 m was chosen for the computations of the hydrodynamic quantities associated with the semi-submersible structure. Table 8.8: Convergence ratio (R) associated with the absolute value of the linear excitation force for a discretisation triplet with panel sizes equal to 10.0 m, 5.0 m and 2.5 m for the semi-submersible platform geometry. T (s) | FX1 | | FX2 | | FX3 | | FX4 | | FX5 | | FX6 | 7.4 0.294 1.092 0.792 0.611 0.612 -0.675 8.4 -0.031 -0.532 0.601 0.613 0.616 -1.042 9.5 -0.212 -1.190 0.601 0.579 0.613 -1.864 10.3 -0.314 0.121 0.611 0.626 0.610 -1.512 11.7 -0.338 0.303 0.600 0.667 0.606 0.073 Table 8.9: Estimations of the exact value of the linear excitation force at five wave periods associated with the semisubmersible platform. T (s) | FX1 | | FX2 | | FX3 | | FX4 | | FX5 | | FX6 | 7.4 1.80E+002 4.50E+001 1.80E+001 1.40E+003 5.90E+002 1.10E+004 8.4 1.70E+002 4.30E+001 1.80E+001 1.60E+003 1.10E+003 1.10E+004 9.5 1.60E+001 2.30E+001 5.40E+000 1.40E+003 1.50E+003 7.90E+003 10.3 1.30E+002 1.20E+001 2.60E+001 1.10E+003 1.60E+003 4.80E+003 11.7 1.90E+002 6.00E+000 4.90E+001 6.50E+002 1.40E+003 2.70E+003 Table 8.10: Uncertainty of the linear excitation force computations with the finer mesh (panel size 2.5 m) at five wave periods for the WindFloat platform. T (s) | FX1 | | FX2 | | FX3 | | FX4 | | FX5 | | FX6 | 7.4 6.00E-3 1.77E-3 2.19E+0 2.46E+2 2.07E+1 9.30E-1 8.4 8.10E-1 4.80E-3 2.16E+0 1.98E+2 3.60E+1 2.55E+0 9.5 4.20E-2 1.14E+0 1.62E+0 1.68E+2 1.71E+2 3.30E+0 10.3 7.20E-4 1.89E-2 3.30E+0 1.44E+2 2.52E+2 2.49E+0 11.7 2.64E-2 1.17E-2 7.20E+0 9.00E+1 2.70E+2 1.59E+0 Table 8.11: Relation between the panel size parameter and the number of unknowns which is used as measure of the number of panels in WAMIT for the semi-submersible platform. Panel Size (m) 2.5 5.0 7.5 10 Number of Unknowns 2976 1287 981 792 99
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Project UpWind Contract No.: 019945
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Acknowledgement The presented work
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Summary The overall aim of the UpWi
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Table of Contents Acknowledgement..
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Task 4.1 Integration of support str
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Sequential coupling The sequential
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analysis. In the new multibody code
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Figure 2.4: 2nd global bending mode
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3.2 Comparison of deterministic loa
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Figure 3.5: Time series of axial fo
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• Time domain simulation in ADCoS
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• A supplementary load vector for
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The following results are found: Fi
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Figure 4.5: Output positions in the
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It is directly visible that there i
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ated eigenfrequency is shifted into
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Water levels For the calculation of
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guidelines for the inclusion of cli
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damaging if the frequency of the ex
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uncertain parameters carefully. Thr
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Table 5.3 shows annual reliability
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Steel substructure for offshore win
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Table 5.16 shows the required FDF v
Page 48 and 49: A Fracture Mechanical (FM) modellin
Page 50 and 51: Figure 5.4: Annual reliability indi
Page 52 and 53: Further, the effect of possible ins
Page 54 and 55: Rainflow evaluation The load cases
Page 56 and 57: For DLC 7.2 it has to be considered
Page 58 and 59: Guideline, DLC 1.5). Furthermore, t
Page 60 and 61: Table 5.28: Output locations for da
Page 62 and 63: From these results it can be clearl
Page 64 and 65: Figure 5.11: Normalised DELs with v
Page 66 and 67: Figure 5.14 presents normalized DEL
Page 68 and 69: Figure 5.16: Output locations for e
Page 70 and 71: UPWIND WP4: Offshore Support Struct
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Final report for WP4.3: Enhancement of design methods ... - Upwind

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