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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2.3. Operational and environmental effects Supervisory control and data acquisition (SCADA) is a fundamental system to monitor and control several parameters about operational and environmental conditions. In this study, wind speed, rotor speed, temperature and nacelle position were obtained from SCADA system. Temperature and wind speed were measured at 55 m height. The effects of wind speed, rotor speed, temperature, and nacelle position on the frequencies of the wind turbine were obtained for the first three modes in both directions. To eliminate effects of environmental and operating conditions on identified modal values, multiple linear regression analysis was performed. Firstly, regression models were created for the first three bending modes in both wind directions. These models consist of all predictors which represent environmental and operational conditions for different modes and wind directions. After creating regression models, relations between frequencies and conditions can be predicted. Regression analysis showed that the analysis was not appropriate for the first mode in both wind directions because these values are almost constant and do not change with environmental and operational conditions. Fig. 5 shows the second mode frequency with and without environmental and operational conditions. It is obvious that operational and environmental conditions change the modal properties of the turbine to some extent and removing the effects of these parameters on the turbine results in more consistent frequency values. The mean frequency values after removing the effects in the first, second and third mode frequencies were 0.47 Hz, 3.30 Hz, 9.29 Hz in the first wind direction and 0.46 Hz, 3.30 Hz, 9.36 Hz in the second wind direction.

Fig. 5. The second mode frequencies with and without effects.

3. Finite element model 3.1. Tower, foundation and soil properties

The steel tower of the wind turbine consists of three thin-walled tubular parts which have varying diameter and thickness values through height. The height of the steel tower is 54 m. Details of the steel tower parts are given in Table 2. The material of the tower is S355 steel. The total weight of the wind turbine is 860 kN. The weight of the nacelle and rotor parts is 332 kN. The center of mass of the nacelle + rotor is located 1.52 m away from the center of the tower section in the horizontal direction causing eccentricity. The wind turbine foundation includes a pile cap and 26 piles. The top diameter of the pile cap is 5 m, while the bottom diameter is 13.5 m. The total depth of the pile cap is 1.6 m. Distribution of piles are in circular form with 2 layers. The inner layer has 8 piles, while the outer layer has 18 piles having a constant angle between all adjacent piles. All piles are identical having a circular cross-section with 0.4 diameter and 18 m depth from the bottom of the pile cap. The upper layer of the soil deposit is a sand layer which has 10.5 m depth. Below this depth, soil deposit around piles is a clay layer.