Research On Structural Optimization Design Of Vertical Axis Wind Turbine Blades With Honeycomb Core In The Main Girder

Compared with traditional materials,honeycomb structure is widely used in engineering due to its low equivalent density,convenience of manufacturing,composite effect of mechanics and designability.Therefore,filling the main beam cavity of the blade with honeycomb structure can achieve the weight reduction of the blade and maintain its mechanical properties,which is an effective means to realize the lightweight design of wind turbine blades.In this paper,based on the finite element analysis,the honeycomb structure is applied to the vertical walking wind turbine blade.The main research work and results are as follows :(1)The equivalent elastic modulus of hexagonal,quadrilateral and concave hexagonal cells in X and Y directions and the equivalent shear elastic modulus in XY plane are derived by energy method,and then the hexagonal cells of aluminum honeycomb core are calculated and compared with the experimental results and Gibson formula.The influences of the straight wall length and wall thickness of the cell and the angle between the inclined wall and the straight wall are analyzed to reveal the variation law of the equivalent elastic modulus with these structural parameters.Taking the maximum equivalent elastic modulus and the minimum relative density as design objectives,the length and thickness of straight wall and the angle between inclined wall and straight wall as design variables,the genetic algorithm is used to optimize the cell structure.The honeycomb plates were formed by the cells before and after optimization and the finite element model was established.The variation laws of stress,strain,displacement and low-order modes were studied by statics and modal analysis.The results show that after the cell structure optimization,the maximum displacement,stress and strain of the honeycomb plate are reduced,and the structural performance is improved,and the vibration frequency and maximum displacement of the first five orders are reduced.(2)Taking the volume fraction of the cell material in the closed space as the relative density,and combining the mapping between the topological unit and the cell,the density function of the topological unit with the wall thickness as the variable is constructed.The RAMP interpolation model is used to realize the expression of the design domain flexibility function based on the density of the topological unit.The minimum flexibility and material retention rate of the design domain are taken as the design objectives,and the density of the topological unit is taken as the design variable.The optimization criterion method is used for structural topology optimization to construct the two-dimensional honeycomb surface after topology optimization.The honeycomb surface was symmetrically stretched along the chordwise direction of the blade to form a three-dimensional honeycomb core layer with non-uniform variation of cell wall thickness along the blade span.The finite element model was established using ANSYS APDL language,and the volume,stress,strain,displacement,frequency and vibration mode before and after optimization were compared and analyzed.The results show that the maximum displacement,stress and strain of the honeycomb core layer are reduced after topology optimization,and the structural performance is improved.The first five order vibration frequency and the maximum displacement increase,the sixth order vibration frequency increases and the maximum displacement decreases.(3)For the external flow field of the vertical axis wind turbine blade,the aerodynamic load on the blade surface is calculated based on the FSI mapping method.Glass cloth,rubber cloth and reinforcing material were used to design the blade layer.The mass,frequency and displacement of the first mode of the blade under different layer schemes were compared and analyzed.With the maximum equivalent stress and minimum mass as the optimization objectives,the genetic algorithm is used to optimize the thickness of the airfoil layer at different sections of the blade.The maximum displacement,stress and strain of the blade before and after optimization were studied.The results show that the weight of the optimized blade is reduced by8.14%,and the displacement,stress and strain are reduced,and the structural performance is improved.