30 Modal Parameter Identification of New Design of Vertical Axis Wind Turbine 291 Fig. 30.3 Finite-element mesh. (a) Mesh at rotor shaft. (b) Mesh at blade connection 30.2.2 FEM Model The commercial finite-element method (FEM) package Abaqus cae is used to model the VAWT using solid continuum finite elements. eight-node brick elements with quadratic spatial interpolation of the displacement are adopted with global mesh size of 5 mm. The mesh size is chosen based on the geometrical size of smallest part of rotor structure. The global mesh is created in such a way that the changes in the geometry is approximately aligned since it lowest fundamental frequencies are focus of this study. Figure 30.3 shows the mesh of the VAWT All structural elements are merged by retaining the geometry of each structural element and then global mesh is created. Later on properties are assigned to the each structural element. The bottom of the end plate is constrained in all degrees of freedom. The proposed VAWT consists of a steel structure to hold the blades made up of fiber glass reinforced plastic. In reality blades are fiber composites having two directional lay-up to provide structural strength. In this study it is focused on overall structural modes of the proposed VAWT therefore blades are assigned with solid element with a homogeneous and isotropic properties. The structure of proposed VAWT is made from square sections and pipes and also assigned with a homogeneous and isotropic properties to avoid complicities in FE model and perform quick analysis. The material is regarded as a linear elastic with a Young’s modulus Es D2GPa, a Poisson ratio of s D0:30and amass density s D7;800kg/m3. The blades are assigned with linear elastic fiber reinforced plastic material with Young’s modulus Eb D1:81GPa, a poisson ratio b D0:50and a mass density b D1;800kg/m3.Subscripts s andb represents steel structure and blade structure respectively. 30.3 Modal Analysis The fundamental Eigen frequencies and the corresponding Eigen modes are determined for proposed VAWT model as described in Chap. 30.2. The subspace solver implemented in Abaqus cae is applied for the structural analysis and 100 modes below 20 Hz frequency are requested with 300 maximum integrations to avoid computational errors. In this study lowest fundamental modes are of interest hence the modes are examined one by one in order to identify the required modes. The Eigen modes and the corresponding Eigen frequencies of the proposed wind turbine are extracted. Figure 30.4 shows the accumulated number of modes appearing below a given frequency in the interval from 0 to 20 Hz. Figure 30.4 shows the first three independent modes of the slat blade. It is to be noted that in Figs. 30.4 and 30.5 the blue color represents the main blade and red color represents a slat blade. Figure 30.5 shows the first three independent modes of the main blade
RkJQdWJsaXNoZXIy MTMzNzEzMQ==