台灣因地理位置、氣候、降雨等因素，自然災害發生的頻率較高，如山崩、土石流等這些快速移動的質量體，基本上皆可歸類於顆粒流的運動，為了解顆粒流的運動行為及機制，速度場的量測扮演重要關鍵性的角色。由於這些觀測的流體是顆粒體亦是複合流體，並非單一物質所構成，是顆粒和空氣或顆粒和液體的混合體，加上速度場變化非常劇烈，而且有部份是沒有速度場，造成粒子影像測速法(Particle Image Velocimetry，PIV )運用上的困難。隨著數位化的影響，從過去使用膠片拍攝到現今以數位的方式進行拍攝和影像的存取，亦把PIV以Digital Particle Image Velocimetry(DPIV)來稱呼。本研究目的就是針對這樣的問題找出最佳的解決方案，因此採用PIVlab進行速度場分析，來彌補PIV不足之處，並透過乾顆粒實驗、水中滑塊實驗、水砂混合實驗來呈現改善後的結果。於三種不同實驗分別驗證整合後的成果，分別是顆粒崩塌剖面速度趨勢類似線性，邊界mask影響範圍為2~4 mm；水中滑塊實驗的散射等問題大多可以克服及改善；水砂混合實驗於穩態的狀況下，可以多張照片平均彌補少數速度場缺失的情形，提高速度場的準確度。並從三個實驗結果提供實驗拍攝張數設定和影像顆粒對應之關係，提高速度場分析結果的準確度。

Due to the specific location and geological conditions, Taiwan is suffering from the high frequency of natural disasters, such as earthquakes, heavy rainfalls and the induced landslides, debris flow, etc. These destructive flows can be roughly classified as granular flow movement, although they are generally composed of grains of different size and the interstitial void is sometimes filled with water. From the viewpoint of disaster mitigation and risk management, it is of significant importance to investigate the dynamics of these flows, where the velocity measurement of the moving mass plays a crucial role. Because of the complexity of the fluid composition, it is dramatic to measure the velocity fields, not only of the fluid but also of the particle/sediment. It thus enhances the difficulty of velocity analysis by particle image velocimetry (Particle Image Velocimetry, PIV). The present study aims at the optimal solutions of velocity measurement, for which an open-source software, PIVlab, was chosen to analyze the high-speed camera captured images. Three experiments were performed to illustrate the achievements. They are a) dry granular collapsed experiment; b) the block sliding into water experiment; and c) water mixing sand experiments. The results also provide the indications for relationships between the number of shots and images particles, to improve the accuracy as well as the efficiency by velocity analysis in experiments.

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