الفهرس 
The Development of ZAFARANA Wind FarmOnly 14 pages are availabe for public view
 |  | from | 151 |  |  |
| | | from | 151 | | |
Abstract
This study is performed as part of a major Egyptian-USA research project funded by STDF investigating the structural performance of full-scale wind turbine towers under seismic loading. The project entitled ‘Seismic risk assessment of wind turbine towers in Zafarana Wind Farm’. The dynamic parameters (frequencies, mode shapes and damping) of wind turbine towers were obtained by performing an Ambient Vibration Test (AVT). The test performed on two types of wind turbine towers. The first one is 40 m Nordex N43 tower while the other one of height 45 m Vestas V47 tower. For a half an hour, the vibration accelerations of the tower were recorded in WAV format using data recorder. By using ARTeMIS extractor program, the modal identification was performed using two techniques, the Enhanced Frequency Domain Decomposition (EFDD) and the Stochastic Subspace Identification (SSI). The modal assurance criterion (MAC) values were computed to study the correlation between the mode shapes obtained for the Nordex wind turbine tower using EFDD and SSI methods. The final modal parameters were taken from EFDD technique. In this stage, the actual dynamic parameters (frequencies, mode shapes and damping) were obtained for both Nordex N43 and Vestas V47 tower. A finite element model (FEM) was developed by the use of ANSYS software V.12. The tubular wind tower was simulated as a shell element with variable thickness and door opening. The complete nacelle (including hub and rotor) was simplified by a combination of mass element representing the weight and beam element consists of twelve beams connected to the top of the tower. An initial FEM was created by simulating the complete nacelle as mass at the top of the tower. The dynamic parameters obtained from the initial FEM were compared with the AVT ones and gave a good agreement in the first two modes but the higher modes gave a high difference ratio up to 63.18% with AVT ones. Then the FEM was updated by simulating the nacelle with twelve beams connected to the top of the tower, the hub was presented with a beam connected to the Nacelle, the nacelle weight with masses at the top of the tower and the rotor and hub weight with a concentrated mass at the end of the hub beam. The updated FEM results were obtained and compared with the AVT ones and gave a good agreement with a maximum difference of 9%. The seismic behavior of wind turbine tower was studied by two different techniques. The first technique applied a response spectrum from the Egyptian code for loads (2012). Since the code did not have a case to represent the wind turbine tower, the wind turbine parameters were approximated to chimney ones. In the second technique, an actual time history from a 300 m circle around the site was collected in order to obtain another seismic behavior. The seismic loads were applied to the updated FEM for both Nordex and Vestas towers. The results were taken for several nodes and elements. It was found that the maximum drift of the wind turbine tower at the hub level whereas the maximum stress located at the door section 4 m from the base. The Egyptian code for loads (2012) gave almost good simulation for the seismic loads that could be applied to wind turbine tower considering the approximation of wind tower parameters to chimney ones. More researches are recommended in the field of applying response spectrum from Egyptian code for loads in order to consider wind turbine tower as structural case with specified parameters.