PSI - Issue 64

Serdar Soyoz et al. / Procedia Structural Integrity 64 (2024) 484–491 Soyoz et al. / Structural Integrity Procedia 00 (2024) 000 – 000

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Table 2. Details of tower. Parts Length (m)

Bottom dia. (m)

Top dia. (m)

1 2 3

17 17 20

3.3 2.4 1.8

2.4 1.8 1.3

3.2. FEM updating Initial FEM of the wind turbine was developed in SAP2000 software. The steel tower of the wind turbine was modeled with shell elements. Since the wind turbine has varying diameter and thickness values, tower diameter at 40 different elevations were calculated and the steel tower was created by assigning shell elements between these defined coordinates. Soil flexibility was represented by soil springs recommended in API guideline (2002). Three types of soil springs exist in this guideline which are p – y, t – z and Q – z springs. Fig. 6 shows the finite element model including foundation and soil springs.

Fig. 6. Finite Element Model of the turbine.

FEM updating parameters were chosen as steel Young’s modulus and soil spring coefficients. Steel Young’s modulus was considered to vary between 180 and 220 MPa, while soil spring coefficients were considered to vary between 20 and 200% of the first calculated coefficients. 399 analyses are performed for each combination of these updating parameters (21 cases for Young ’s modulus and 19 cases for soil springs) and natural frequencies and mode shape results were recorded. In the updating process of the finite element model, the first three modes in each direction were considered. Results show that minimum error occurs when soil spring coefficients are 50% of the calculated values and steel Young’s modulus is 192 MPa. So, the final version of the finite element model was developed with these parameters. Table 3 shows the comparison of identified natural frequencies and the ones before and after the updating process.

Table 3. Natural frequency comparison. Natural frequencies (Hz) Initial FEM

Updated FEM

Identified

1 2 3

0.48 3.48 9.72

0.47 3.26 9.40

0.46 3.31 9.37