15 Finite Element Modeling of a 40 m Space Frame Wind Turbine Tower 165 Table 15.7 MAC for the no bolt model vs original model Original bold model No bold model Mode 1 2 3 4 5 6 7 8 91011121314 15 2 44:9 52:6 0:2 0 0 0 0:1 0:1 0 0:5 2:8 0:2 0:1 0:1 0:5 2 54:8 46 0 0:2 0:3 0 0 0 0:1 4:9 0:7 0 0 0 0:1 3 0:1 0 70:727:7 0 0 0:2 0 0 0 1:9 0 0 0 0:2 4 0:8 1:1 27:8 71:7 0 0:4 0:6 0 0 0:5 0:1 0 0 0 0 5 0:1 0 0 0 99:2 0 0:1 0:1 6:2 0:7 0:1 0 0:1 0:1 0 6 0 0:1 0:4 0 0:255:642:7 0 0 0 0 0 0 0:10 7 0 0:3 0 1:5 0 42:856:8 0 0 0 0 0:1 0 0:10 8 0:1 0:1 0:1 0 1:5 0:1 0 99:1 0 0 0 0:1 0 3:7 0 9 0:5 0 0:2 0 2:5 0:1 0 0 57:1 9:4 9:5 14 4:1 0:6 0 10 0:4 0:7 0:2 0:1 0:5 0:3 0 0:1 16:9 33:3 30 42:5 3:8 0:5 1:6 11 1:6 0 0:1 0 2 0 0 0:1 23:8 45:6 0:2 0:1 27:7 0:7 0:4 12 0 3:9 0:6 0:5 0:3 0:1 0 0 0:3 4:3 50 41:7 4:2 0 1:3 13 2:7 0 0:6 0 0:5 0 0 0 0:4 33:2 2:9 4:3 58:4 0:1 0:3 14 0:1 0 0 0 0:3 0:1 0 4:1 0:4 0 0 0:3 0 91:1 0:5 15 0:3 0 0 0 0 0 0 0 0:1 3:4 0:6 0 0:1 2:73:9 Fig. 15.14 Mode shapes of Mode 1, 3, and 9 for the (left to right) original model, no-bolt model, and all regular bolt model 15.3.5 Modeling of the Ground Surrounding the Tower Since the simplifications have been proven on complex structures the boundary is tested. In modal analysis frequencies are dependent on the mass and stiffness of the structure and boundaries. Modeling the boundary as fixed or flexible will result in different dynamic responses [28]. The tower is located in an area that the soil is largely “hard” clay which has a much lower stiffness than that of the tower; this results in the boundary being flexible. Many researchers have studied the effects of soil
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