The Dynamic Performance Study Of Composite Thin-Walled Beams Based On The Finite Element Method

Wind power as a abundant, inexhaustible, inexhaustible, non-polluting new energy has been recognized by the people, and the use of wind generators early has been carried out in many countries.Typical large composite wind turbine blades are thin-walled reinforced multi-closed cell structure, the specific airfoil cross-sectional shape to meet the aerodynamic performance.Advanced wind turbine structure’s large-scale and flexible, making large composite wind turbine blades have large bending and twisting, waving, shimmy and reverse frequency close to each other prominent modal coupling characteristics, easily induced flutter.Characteristics of large-scale wind turbine blade with composite thin-walled beams, we can optimize the ply angles, change the section size and other adjustments.In this paper, the wind turbine blades are simplified as cantilever beams,and the modal analysis of composite thin-walled beams is carried out by the finite element software AN SYS.The finite element models are established first for multi-closed cell composite box thin-walled beams and composite airfoil thin-walled beams, then the vibration modes of two box beams:Circumferentially Uniform Stiffness (CUS) and Circumferentially Antisymmetric Stiffness (CAS) are calculated and analyzed. The effects of ply angle, length-width ratio and width-height ratio on the natural frequency and the modal shape of the multi-closed cell composite thin-walled box beams (including double-cell and three-cell composite thin-walled box beams) are discussed.The conclusions are got as following:the natural frequency of the multi-cell composite box thin-walled beam decreases with the ply angle increasing,and it decreases with length-width ratios increasing,but it increases with width-height ratios increasing,while the modal shape does not change with variables. The effects of ply angle, length and layer on the natural frequency and the modal shape of the composite airfoil thin-walled beam are discussed.The conclusions are got as followingrthe modal frequency of composite airfoil thin-walled beams decrease with the ply angle increasing,and it decrease with the length increasing,but the effects of the ply layer on the natural frequency of the composite airfoil thin-walled beam is small, while the mode shapes do not change with variables.Finally, the effects of the pre-tension and compression stress on the double-cell composite thin-walled box beams are considered.The static analysis is carried out first for the double-cell composite thin-walled box beams, on this basis the natural frequency and mode shapes of the double-cell composite thin-walled box beams are got.Compared with the result of the free mode,it can see that:the pre-tensile stress has an effect on the natural frequency of the double-cell composite thin-walled box beams, while the pre-stress has no effect on the natural frequency of the double-cell composite thin-walled box beams, and the prestressed has no effect on the mode shapes of the double-cell composite thin-walled box beams.