臺灣博碩士論文加值系統

本論文利用實驗及電腦模擬方法驗證125 c.c機車引擎曲軸總成模態特性，並利用兩種實驗方法探討及比較曲軸的自然頻率、模態振型及應力分佈。模態分析實驗中以移動激振點與移動感測點兩種方式，量測激發響應所得之頻率響應函數（FRF），再輸入模態分析軟體STAR內處理，求得曲軸之自然頻率與對應之模態振型。在模擬分析上，係利用SOLID WORK軟體建立實體模型，再使用ANSYS有限元素分析軟體內之Block Lanczos 與Subspace 模態求解方法，於不同轉速下分析受力分布、自然頻率及模態振型。
研究結果顯示於轉速6000 RPM時產生最大應力值，並於X-Z平面上產生最大剪應力。有限元素求解方法中Subspace method之自然頻率精確度較Block Lanczos method佳。若以模態實驗與有限元素法所求自然頻率相較，除第一、二模態誤差較大外，第三、四、五、六模態之自然頻率皆很吻合。

In this investigation, the modal characteristics of the crankshaft assembly of the 125c.c. motorcycle are verified by the methods of the experiment and the computer simulation. The natural frequencies, mode shapes, and stress distribution of the crankshaft are examined and compared with the solutions from two methods. In the experiment of modal analyses, the frequency response functions of the crankshaft are measured by using the methods of moving exciters and moving sensors. The mode shapes related to the natural frequencies of the crankshaft can be constructed by using the modal analysis software “STAR”. In the analysis of the computer simulation, the model of the crankshaft is generated by the software “SOLID WORK”. Then the stress distributions, the natural frequency, and the related mode shapes are analyzed by using the software of the finite element method “ANSYS”. The accuracy of the computation in the method of the finite element is examined by using the Lanczos method and the subspace method
The results show that the maximum stress and the shear stress in the plane were occurred when the angular velocity of the crankshaft is around 6000 RPM. The natural frequencies obtained from the subspace method are more accurate than that obtained from the Block Lanczos method. It is also shown that the third, fourth, fifth, and sixth natural frequencies obtained from the methods of the experiment and the computer simulation are closer than the first and the second natural frequencies.

誌謝……………………………………………………….…………Ⅰ
摘要…………………………………………………………II
Abstract………………………………………………… III
目錄……………………………………………………………....IV
表錄…………………………………………………………….…VII
圖錄………………………………………………………………VIII
符號說明……………………………………………………….…XI
第一章 緒論……………………………………………………..1
1-1 前言……………………………………………………….1
1-2 模態分析方法簡介…………………………………………2
1-3 文獻探討…………………………………………4
1-4 研究動機…………………………………………7
第二章 模態分析理論………………………………………9
2-1 模態特性…………………………………………9
2-2 FFT轉換原理.…………...……………..….……….…….10
2-3 訊號處理………………….…………………………..13
2-3-1取樣與頻率混疊原理……………………….. …… ..13
2-3-2訊號處理與檢驗…………………………….. …… ..15
2-4模態實驗理論…………….………………………….. … ..16
第三有限元素模擬分析………………………………………..22
3-1 應力場分析………………………………………..22
3-1-1 力矩負荷…………………………………….. …… ..24
3-1-2 重力負荷…………………………………….. …… ..26
3-2 振動分析……………………………………………..26
3-2-1 Reduced method………………………………………27
3-2-2 Block Lanczos method……………………….………28
3-2-3 Subspace method ……………………………………..29
第四章 模態實驗分析………………………………………..45
4-1 模態實驗目的……………………………………………45
4-2 實驗儀器設備與架構………………………………45
4-3 實驗方法與步驟…………………………………………49
4-3-1 衝擊鎚法………………...…………………………..50
4-3-2 激振器法…………………………………………….53
第五章 結果與討論……………….……………………….68
5-1 靜力場比較…………………………………………68
5-2 自然頻率與收斂時間比較…………………………69
5-3 模擬與實驗之模態振型比較………………………..70
5-4 實驗激振方法與阻尼比討論………………………..71
5-5 結論與未來展望……..…………………….…..72
參考文獻…………………………………………………………76
附錄一………………………………………………………………80
附錄二………………………………………………………………84

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