Abstract
Wind turbine technology has developed tremendously over the past years. In Egypt, the Zafarana wind farm is currently generating at a capacity of 517 MW, making it one of the largest onshore wind farms in the world. It is located in an active seismic zone along the west side of the Gulf of Suez. Accordingly, seismic risk assessment is demanded for studying the structural integrity of wind towers under expected seismic hazard events. In the context of ongoing joint Egypt–US research project “Seismic Risk Assessment of Wind Turbine Towers in Zafarana wind Farm Egypt” (Project ID: 4588), this paper describes the dynamic performance investigation of an existing Nordex N43 wind turbine tower. Both experimental and numerical work are illustrated explaining the methodology adopted to investigate the dynamic behavior of the tower under seismic load. Field dynamic testing of the full-scale tower was performed using ambient vibration techniques (AVT). Both frequency domain and time domain methods were utilized to identify the actual dynamic properties of the tower as built in the site. Mainly, the natural frequencies, their corresponding mode shapes and damping ratios of the tower were successfully identified using AVT. A vibration-based finite element model (FEM) was constructed using ANSYS V.12 software. The numerical and experimental results of modal analysis were both compared for matching purpose. Using different simulation considerations, the initial FEM was updated to finally match the experimental results with good agreement. Using the final updated FEM, the response of the tower under the AQABA earthquake excitation was investigated. Time history analysis was conducted to define the seismic response of the tower in terms of the structural stresses and displacements. This work is considered as one of the pioneer structural studies of the wind turbine towers in Egypt. Identification of the actual dynamic properties of the existing tower was successfully performed based on AVT. Using advanced techniques in both the field testing and the numerical investigations produced reliable FEM specific for the tested tower, which can be further used in more advanced structural investigations for improving the design of such special structures.
Highlights
In 2003, a detailed wind atlas was published for Egypt’s Gulf of Suez coast, concluding that the region has an excellent wind regime with wind speeds of 10 m/s and the potential to host several large-scale wind farms
In the context of ongoing joint Egypt–US research project ‘‘Seismic Risk Assessment of Wind Turbine Towers in Zafarana wind Farm Egypt’’ (Project ID: 4588), this paper describes the dynamic performance investigation of an existing Nordex N43 wind turbine tower
This work presented was one of the pioneer studies concerning the investigation of the structural dynamic performance of a full-scale wind turbine tower under seismic load in Egypt
Summary
In 2003, a detailed wind atlas was published for Egypt’s Gulf of Suez coast, concluding that the region has an excellent wind regime with wind speeds of 10 m/s and the potential to host several large-scale wind farms. The actual dynamic parameters (frequencies, mode shapes and damping) of wind turbine were obtained from ambient vibration test and FE models were developed to simulate the tested tower. The last few decades have witnessed an exceptional interest in a better understanding of the structural dynamic behavior and identifying the modal parameters, namely the natural frequencies, damping ratios and mode shapes This field of research is referred to as experimental modal analysis.
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