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研究生: Abdul Qadir
Abdul Qadir
論文名稱: 應用梯度照明與機器學習減噪演算法之二維微粒紋痕測速儀於微流道內之聲射流之研究
Study of Acoustic Streaming in Microchannel using 2-D Particle Streak Velocimetry with Graded Illumination and Machine-Learning Based Noise Reduction Scheme
指導教授: 田維欣
Wei-Hsin Tien
口試委員: 田維欣
Wei-Hsin Tien
劉孟昆
Meng-Kun Liu
林怡均
Yi-Jiun Lin
學位類別: 碩士
Master
系所名稱: 工程學院 - 機械工程系
Department of Mechanical Engineering
論文出版年: 2023
畢業學年度: 112
語文別: 英文
論文頁數: 126
中文關鍵詞: 微粒紋痕影像測速儀 (PSV)聲射流聲射阻抗流場可視化
外文關鍵詞: Particle Streak Velocimetry, Acoustic Streaming, Acoustic impedance, Flow Visualization
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  • 微粒紋痕影像測速儀 (Particle Streak Velocimetry, PSV) 為受廣泛使用的微粒影像測速儀 (Particle Image Velocimetry, PIV) 和微粒循跡測速儀 (Particle Tracking Velocimetry, PTV) 技術之延伸,常應用於流場分析。在 PSV 技術中,微粒的軌跡是透過攝影機以長曝光時間下記錄影像所獲得的。在實際流場可視化應用中,經常受到硬體的限制而需要以更長的曝光時間成像,導致拍攝移動微粒的影像拉伸為微粒紋痕影像。在Qureshi & Tien (2022) 研發的PSV技術可以提供實驗流體力學有價值的觀察結果,但其性能表現受到影像雜訊和流動方向模糊的困擾而限制了其準確性和適用性。首先發展了一種基於深度學習特別為 PSV 影像所設計的去雜訊方法,藉由結合卷積神經網路 (Convolutional Neural Networks, CNNs) 與特製的之影像處理技術,我們的方法能有效地處理各種類型的 PSV 影像雜訊。對比分析證實其性能優越,增加流體速度量測的準確性且提高計算效率。其次,實驗設置採用了一個梯度變化照明的發光二極體光源來解決實驗量測時單幀影像含多條紋痕的實驗流場方向。這種新的實驗技術將光源照明強度從全亮度的100% 線性變化至50% 。紋痕解析的演算法亦根據此改善方案進行調整,以便以最小平方擬合法決定流動的方向。為了評估驗證此法的概念可行性,將此技術應用於恆定平行流。平行流進一步分為恆定照明和梯度照明,也就是變化照明光強度,並進行測試比較。結果顯示所提出的方法改善了PSV的精確度與有效性,讓結果改善了96%。這些改善隨後被應用於研究微流道內以三角形微結構誘發的聲射流 (Acoustic Streaming) 現象,其中振盪透過電壓20V、頻率12kHz的壓電轉換器傳遞至流體。透過PSV 技術研究微結構周圍所產生的穩定聲射渦旋,分別採用三種不同頂角 (α=20°, 35°, 70°) 以及傾斜角 (β=30°, 45°, 60°) 的非對稱三角形微結構進行速度場分析。實驗結果顯示聲射渦旋的流動模式會隨著非對稱三角形微結構的傾斜角度變化,且與過往的研究比較顯示了合理的一致性。這些結果顯示,本研究所提出的方法可以在無需昂貴的高速成像硬體之下解析速度場,因此適用於各種應用。


    Particle streak velocimetry (PSV) is an extension of widely used methods, particle image velocimetry (PIV), and particle tracking velocimetry (PTV), to resolve flow fields experimentally. The particle's trajectory is obtained by using a long exposure time of the camera in PSV. Practical applications often encounter hardware limitations, necessitating longer exposure times that cause captured images of moving particles to elongate into particle streak images. The currently developed PSV technique by Qureshi & Tien (2022) provides valuable insights for experimental fluid mechanics; however, its performance is plagued by image noise and direction ambiguity in the flow, limiting its accuracy and applicability. Two major modifications are proposed in this study to denoise the images and resolve the direction ambiguity problem. Firstly, a deep-learning-based denoising scheme specifically designed for PSV images is developed. By combining Conventional Neuro Network (CNNs) and custom image processing, our approach effectively handles various types of PSV image noise. Comparative analysis demonstrates its superior performance, enhancing the accuracy of fluid velocity measurements and computational efficiency. Secondly, in this study, a graded illumination LED light source is used for the experimental setup to determine the experimental flow field direction for a single image frame containing multiple streaks. The new experimental approach involves varying the illumination intensity of each exposure from 100% to 50% linearly of the full intensity of the light source. The streak-resolving algorithm is modified accordingly so the flow direction can be found through the least-square fitting process. To assess the validity of the concept, we applied this technique to a constant parallel flow. The Parallel flows were tested and compared with constant illumination and graded illumination, in which the intensity is varied. The results show that the proposed approach enhances the accuracy and reliability of PSV, by 95% in the tested flow cases. The modifications were then applied to the study of acoustic streaming phenomenon induced by triangular microstructures in the microchannels, in which the oscillation is transmitted to the fluid through the piezoelectric transducer at 20V and 12kHz. The asymmetrical triangular structure of three different tip angles (α=20°, 35°, 70°) and inclined angles (β=30°, 45°, 60°) is used for velocity field analysis. The results show that flow pattern of the acoustic streaming vortex changes with the inclined angle of the asymmetric triangular microstructure, and the results were compared to the previous study and showed reasonable agreements. These results suggest that the proposed approach can be used to resolve velocity fields without expensive hardware for high-speed imaging and is thus suitable for diverse applications.

    Table of Content 摘要 ii Abstract iii Acknowledgment vii Nomenclature x Greek Symbols xii Chapter 1 Introduction 1 1.1 MOTIVATION 1 1.1.1 Non-Intrusive Flow Measurement Techniques 1 1.1.2 Psv Direction Ambiguity 2 1.2 LITERATURE REVIEW 3 1.2.1 Acoustic Streaming Technique 3 1.2.2 Psv Optical System 9 1.2.3 Psv Particle Information 14 1.2.4 Psv Various Flow Speed And Applications 17 1.2.5 Image Noise Reduction 25 1.3 SUMMERY 28 1.4 OBJECTIVES 29 1.8 ORGANIZATION OF THESIS 30 Chapter 2 Methods And Experimental Principles 31 2.1 EXPERIMENTAL SETUP 31 2.1.1 Optical Setup 31 2.1.2 Microcofluidic Devises 33 2.1.3 Acoustic Appliances 41 2.1.4 Parallel Flow Experimental Measurement System Setup 44 2.1.5 Acoustic Streaming Experimental Measurement Setup 46 2.2 DATA PROCESSING 48 2.2.1 Psv Image Preprocessing 48 2.2.1.2 Deep Learning Process For Psv Image 50 2.2.1.3 Deep Learning Model Training And Validation Process 54 2.2.1.4 Deep Learning Model Testing Phase 56 2.2.1.5 Real Scenarios Application 58 2.2.2 The Principle Of The Streak-Resolving Algorithm 60 2.2.2.1 Streak Resolved By Least Square Curve-Fitting 62 2.2.2.2 Velocity Measurement 63 2.2.2.3 Graded Illumination And The Determination Of The Direction Of Streak Velocity Vector 65 2.2.2.4 Algorithm Key Features 65 2.3 GEOMETRICAL DESIGN OF THE ACOUSTIC STREAMING MICROCHANNELS 69 Chapter 3 Results & Discussion 71 3.1 SECTION A: THE MACHINE-LEARNING BASED DENOISING SCHEME 71 3.1.1 Parallel Flow Psv Image Denoising 71 3.1.2 Resolving Direction Ambiguity 76 3.3 SECTION B: APPLICATION TO ACOUSTIC STREAMING FLOW IN MICROCHANNEL 80 3.3.1 Case 1 (?=20°, ?=30°) Acoustic Streaming Observation Results 81 3.3.2 Case 2 (?=35°, ?=30°) Acoustic Streaming Observation Results 88 3.3.3 Case 3 (?=35°, ?=45°) Acoustic Streaming Observation Results 97 3.3.4 Case 4 (?=35°, ?=60°) Acoustic Streaming Observation Results 105 3.3.5 Case 5 (?=70°, ?=30°) Acoustic Streaming Observation Results 111 3.4 DISCUSSION 117 Chapter 4 Conclusions And Future Work 122 References 124

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