| Summary: | 碩士 === 長庚大學 === 機械工程學系 === 105 === Recently, developing renewable energy has drawn great attention of many countries in the world. Capital and manpower are invested in the study of renewable energies, especially wind power. Due to Taiwan's geological position, there are northeast monsoons in the winter and typhoons in the summer. A mechanism is required for small horizontal wind turbines to protect them from damages due to strong winds. Therefore, the purpose of this study is to investigate the effect of the pitching moment of the blades on the mechanism that varies the blade pitch with swing bars. Firstly, a computer code is developed that takes into account the pitching moment of the blades as well as the moment generated by the swing bars to find the relation between the blade pitch variation with respect to wind speed and rotational speed of the rotor. The analysis shows that shortening the swing bar can delay the mechanism's activating rotational speed but cannot increase the blade pitch further with the rotational speed. However, if the length of the balancing bar becomes 7.2 cm instead of the original 6.2 cm and the spring constant changes to 11,200 N/m instead of the original 3,900 N/m without changing the swing bar, the activating rotational speed becomes 800 rpm. Using the results of the analysis, an existed mechanism is adjusted accordingly and put to test on a vehicle mounted test bench. The experimental result shows that the mechanism activates when the rotor’s speed exceeds 800 rpm but blade pitch does not increase as expected when the rotor's speed reaches 1000 rpm. It is possible that at high rotating speed and high blade pitch the angle of attack may be more negative than the data range that are used to train the Artificial Neural Network (ANN) for predicting blade pitching moment rapidly. This may cause the inaccurate prediction of blade pitch variation under such circumstance. Even though the blade pitch does not vary as predicted at 1000 rpm rotor speed, the rotor speed has reached the upper limit due to the blade pitch variation no matter how high the wind speed is. This has already reached the goal of the study. We also found that changing the pointing direction and the length of the swing bar to 15.5and 8 cm respectively from the original 24 and 800 rpm and remove the balancing bar all together may give the same result of the above mentioned blade design. That is the mechanism activates at 800 rpm rotor speed and varies the blade pitch to 25 at 1000 rpm rotor speed. The blade pitch variation is 5less than expected but the upper limit of the rotor speed has reached the goal of this study.
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