Browsing by Subject "wind turbine blade"
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Item Stress and Fracture Analysis of a Class of Bonded Joints in Wind Turbine Blades(2013-05-08) Chen, ChangA simplified model is proposed to investigate the stress fields and the strain energy release rate (SERR) associated with cracks in bonded joints in wind turbine blades. The proposed two-dimensional model consists of nonparallel upper and lower shells with adhesive between the shells at the tapered end. Nonlinear finite element analysis (FEA) is performed in a systematic parametric study of material and geo- metric properties. Two failure modes and their locations are predicted at different combinations of parameters: yielding at the outside end of the adhesive and interface cracking at the inside end of the bondline. Effect of the shell curvature on the stress fields is also considered. Based on the classic beam theory and the beam-on-elastic-foundation (BOEF) assumption, stress and displacement fields of the adhesively-bonded joint were determined by a new theoretical model to support the results from the numerical computation. The failure analysis is continued by studying the effects of manufacturing defects in the adhesive bond. Single and multiple voids are embedded to simulate air bubble trapped in the interface. The numerical and analytical studies are conducted to investigate SERR associated with the voids and results are provided to illustrate the effects of void position and void size.Item Vibration and Structural Response of Hybrid Wind Turbine Blades(2011-02-22) Nanami, NorimichiRenewable energy is a serious alternative to deliver the energy needs of an increasing world population and improve economic activity. Wind energy provides better environmental and economic benefits in comparison with the other renewable energy sources. Wind energy is capable of providing 72 TW (TW = 10^12 W) of electric power, which is approximately four and half times the world energy consumption of 15.8 TW as reported in 2006. Since power output extracted from wind turbines is proportional to the square of the blade length and the cube of the wind speed, wind turbine size has grown rapidly in the last two decades to match the increase in power output. As the blade length increases, so does its weight opening up design possibilities to introduce hybrid glass and carbon fiber composite materials as lightweight structural load bearing alternatives. Herein, we investigate the feasibility of introducing modular composite tubulars as well as hybrid sandwich composite skins in the next generation blades. After selecting a target energy output, 8 MW with 80 m blade, airfoil geometry and the layup for the skin as well as internal reinforcements are proposed. They are incorporated into the computational blade via linear shell elements for the skin, and linear beam elements for the composite tubulars to assess the relationship between weight reduction and structural performance. Computational simulations are undertaken to understand the static and dynamic regimes; specifically, displacements, stresses, and vibration modes. The results showed that the composite layers did not exhibit any damage. However, in the balsa core of the sandwich skin, the von Mises stress exceeded its allowable at wind speeds ranging from 11.0 m/sec to 12.6 m/sec. In the blades with composite tubular reinforcement, two different types of damage are observed: a. Stress concentrations at the tubular-skin attachments, and b. Highest von Mises stress caused by the flapping bending moment. The vibration studies revealed a strong coupling mode, bending and twist, at the higher natural frequencies of the blade with tubular truss configuration. The weight saving measures in developing lighter blades in this study did not detract from the blades structural response for the selected load cases.