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研究生: 林銘洋
Lin, Ming-Yang
論文名稱: 基於深度學習之翼型優化及流場預測
Airfoil Optimization and Flow Field Prediction Based on Deep Learning
指導教授: 闕志哲
Chueh, Chih-Che
共同指導教授: 林三益
Lin, San-Yin
學位類別: 碩士
Master
系所名稱: 工學院 - 能源工程國際碩博士學位學程
International Master/Doctoral Degree Program on Energy Engineering
論文出版年: 2023
畢業學年度: 111
語文別: 中文
論文頁數: 60
中文關鍵詞: 深度學習流場預測神經網路翼型優化計算流體力學
外文關鍵詞: Deep Learning, Flow Field Prediction, neural network, airfoil optimization, generative adversarial network, generator, discriminator, pressure flow field
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  • 基於深度學習之數值及圖像預測是近年來熱門研究之一,深度學習是透過架設所需之神經網路架構,將訓練資料作為輸入給予訓練模型來進行深度學習訓練,調整訓練參數學習率( Learning rate ) 、批量大小 ( Batch size ) 與時期 ( Epoch ) 等超參數,直到模型訓練結束,並且儲存預測模型。本研究在於探討氣動力係數預測及壓力流場圖像預測,目標為使用實驗或計算取得大量資料,利用深度學習得到預測法則,以便快速預測不同翼型攻角之氣動力係數及預測圖像。
    本研究是利用XFOIL氣動力模擬軟體得到大量氣動力係數樣本作為訓練集,透過編譯之神經網路架構進行訓練,得到預期之訓練模型,最後將氣動力係數預測模型配合基因演算法,進行外型優化。本研究優化翼型為NACA 0012外型座標,將翼型座標透過PARSEC二維參數化,並且將參數當成基因來演算得到最佳解,達到翼型優化之結果。
    在流場預測方面,本研究是利用ANSYS FLUENT商用套裝軟體進行壓力流場模擬,本研究紊流模型為SST k-ω模型,計算格點由ANSYS FLUENT內建網格生成功能,採用非結構網格,樣本圖像後處理由ANSYS ENSIGHT進行,最後將樣本圖像作為輸入套到編譯之生成對抗網路(Generative Adversarial Networks,GAN)模型架構,透過生成器(Generator)及鑑別器(Discriminator)之大小值博弈,訓練後得到生成器模型,並且以WGAN架構優化訓練穩定性,讓最後圖像誤差百分比能獲得比原本GAN架構更好的圖像質量及準確度。

    In this study, two neural network model architectures were employed to optimize airfoils and predict flow fields. The first architecture utilizes a convolutional neural network to foresee the aerodynamic coefficient. The XFOIL analysis software is employed to acquire the lift and drag coefficients of the airfoil, with collaboration of the algorithm, an airfoil optimization is achieved. The second architecture involves the use of a generative adversarial network (GAN) to predict images. Throughout the generation process, a discriminator is employed to differentiate between real and generated images. The training of the generator is adjusted by the evaluation of the discriminator to obtain the prediction model. To improve the stability of the training loss, changes were made to the neural network architecture and loss function to achieve the goal of predicting the pressure flow field image from the parameter value. Training samples are obtained by simulating the pressure flow field using ANSYS FLUENT software where k-ω SST turbulence model was utilized.

    中文摘要 i Extneded Abstract iii 致謝 vi 目錄 viii 表目錄 ix 圖目錄 x 符號說明 xii 第一章 緒論 1 1.1 前言 1 1.2 研究動機與目的 2 1.3 文獻回顧 3 1.4 內容大綱 5 第二章 理論基礎 7 2.1 多層感知器 7 2.2 卷積神經網路 7 2.3 生成對抗網路 7 2.4 Wasserstein生成對抗網路 8 2.5 PARSEC翼型參數化 9 2.6 基因演算法 10 第三章 實驗方法 11 3.1 數值方法 11 3.1.1 流場統御方程式 11 3.1.2 紊流模型 12 3.2 模型架設 13 3.3 資料前處理 13 3.4 深度學習訓練 14 3.4.1 Adam優化演算法 14 3.4.2 損失函數 15 3.4.3 激活函數 17 3.5 本實驗之神經網路架構 18 3.5.1 CAN神經網路訓練架構 18 3.5.2 GAN神經網路訓練架構 18 3.6 超參數設置 19 第四章 程式驗證與訓練參數選取優劣分析 22 4.1 XFOIL驗證 22 4.2 訓練參數選取優劣分析 23 4.2.1 CNN訓練參數分析 23 4.2.2 GAN訓練參數分析 23 4.3 訓練模型之氣動力係數預測分析 24 第五章 結果與討論 25 5.1 二維翼型優化 25 5.1.1 CFD軟體與預測模型之升阻比優化結果比較 25 5.2 GAN生成器預測壓力流場圖像結果比較 26 第六章 結論與建議 28 6.1 結論 28 6.2 未來工作與建議 30 參考文獻 31

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