Design of Wind Turbine Tower
The tower of wind turbine is not only a constructional member which is there to endure the static and dynamic load of wind turbine system. Keeping in view the high weight of nacelle and heavy operational load of the turbine, turbine tower designing is given a special importance in the designing stage of whole system [N. Bazeos, 2002]. The tower for a small scale wind turbine is given a simple cylindrical shape whereas for medium and large scale turbines, the shape of tower becomes complex i.e. conical [Gwon, 2011]. Complexion in the making of tower for medium and large scale turbines arises due to large height and high weight. Due to large weight the tower is made in multiple sections which are later assembled in the factory or on site [Guo, 2011]. Thickness of the wall and diameter of the tower vary along its length. The diameter of tower and wall thickness decreases from bottom to top section of the tower [Yang, 2014]. The process of designing any wind turbine consists of estimating different parameters of the tower such as material, length, diameter, and wall thickness. Height of tower is usually fixed with the locality and power requirement whereas wall thickness and diameter can vary depending upon the material selected.
According to Satish (2017) work the analytical and theoretical deflection of a wind turbine tower with no joints was about 232.8 mm which is less than 1% of the towers height. However, the Finite element analysis report generated after conducting the static structural analysis of the tower model in Ansys Workbench showed that the deflection in the tower to be 253.69 mm under wind load. The deviation in the theoretical and Ansys workbench deflection of the tower is 15.5%. In the second case when the tower was modeled with a finite number of joints, then the theoretical and analytical deflection was observed to be 232.8 mm. Whereas the deflection of towers reported in Ansys workbench analysis is to be 274.09 mm. Resulting in a variation of 17.7% in tower deflection from the calculated data.
It is observed that in both the cases the deflection in wind turbine tower under wind flow load has a variation of 17.7% in the case of tower model with the finite number of joints and 15.5% in case of tower model without any joint from their theoretically calculated value to finite element analysis value. This kind of variation is observed due to the assumptions made while doing the theoretical calculations. The assumptions made were that the whole tower is a single entity in the case of the tower without joints and a finite number of joints in the case of the tower with joints. This resulted in the assumption that the tower is stiff in both the cases yielded the same theoretical deflection of 232.8 mm in both the cases. Whereas the FEA showed that the tower is not stiff as assumed and the result showed the real variation in the tower under the wind load.
FEM of Wind Turbine Tower
According to Satish (2017) work which was carried out on the wind turbine tower of two structural variances It was observed that the theoretical deflection in the tower was identical in both the tower models that are 232.8 mm under the given wind load and conditions. However, when the tower models were subjected to finite element analysis in Ansys workbench, the result showed that the variation in tower model without any joint to be minimum 253.69 mm and maximum deflection to be 253.75 mm. In the case of a tower model with a finite number of joints, the analysis reported that the minimum variation in the tower to be 260.22 mm and maximum deflection to be 260.25 mm after that the wind turbine tower doesn't deflect in both the cases.
Deflection of the wind Turbine tower with joints in the direction of wind
The variation in deflection of the tower from FEA data to the theoretical data for the tower without any joint is 15.5 % due to the assumptions made during the calculation. These assumptions made the tower to be stiff theoretically and the deflection calculated was less from that of FEA. Similarly in the case of a tower model with a finite number of joints the deflection of the tower from FEA data to the theoretical data for the tower without any joint is 17.7 % due to the assumptions made during the calculation. These assumptions made the tower to be stiff theoretically and the deflection calculated was less from that of FEA.
Deflection of wind Turbine tower without joints
The tower under finite element analysis is modeled as a single entity without any joint. The analysis is carried out in Ansys workbench for a different number of elements. It was observed that the number of elements that is mesh increased on the tower the deflection value increased. The increase in deflection was observed to be to a certain value after which the graph of deflection in the tower became constant and didn't increase. The result revealed that for 1000 mesh the deflection in the tower was observed to be 253.69 mm and for 2000 mesh it was 253.7 mm and for 3000 mesh it was reported as 253.75 mm and after which the deflection didn’t change, stating that the maximum deflection of the modeled monopole tower is 253.75 mm under the wind load. The tower under finite element analysis is modeled with a finite number of joints. The analysis is carried out in Ansys workbench for a different number of elements. It was observed that as the number of elements that is mesh increased on the tower the deflection value increased. The increase in deflection was observed to be till a certain value after which the graph of deflection in the tower became constant and didn't increase. The result revealed that for 1000 mesh the deflection in the tower was observed to be 260.22mm and for 2000 mesh it was 260.25mm and after which the deflection didn’t change, stating that the maximum deflection of the modeled tower is 260.22 mm under the wind load. These results suggest that when we construct a wind turbine tower, the theoretical deflection will be less due to the constrains in the assumptions. Hence we need to do a proper FEA analysis before physical construction and determining the materials to be used. The slight variation in the tower determination of the maximum deflection a tower will show under the given wind load can affect the efficiency and life of the tower. From the above analysis, we find that the tower model with a finite number of joints will undergo minimum deflection even if we increase the mesh amount.
It was reported that as the tower have joints it will show less deflection because the joints will absorb and discontinue the deflection from migrating and accumulating from one part to another, because of the joints the deflection from the previous part will end at the joint and the deflection has to again start from next part resulting in less deflection. Also, the mesh amount should be maximum because as the mesh density increased the point of analysis increases resulting in a better analysis report. Hence it is reported that in order to obtain better efficiency and life of the wind turbine tower, we need to conduct an in-depth finite element analysis, where the number of mesh is kept to be maximum and the proper details such as wind load conditions, materials to be used in the construction of tower should be fed properly and based on the result from the analysis a proper material to be used, to minimize the cost of construction and future maintained and produce maximum efficiency with the prolonged life cycle.