水中顆粒體崩塌分析與電腦模擬比對

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姓名

林傳遠(LIN-CHUAN-YUAN) 查詢紙本館藏

畢業系所

機械工程學系

論文名稱

水中顆粒體崩塌分析與電腦模擬比對

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摘要(中)

土石流、水災和山崩等天災在地球已經造成許多人死亡，所以能夠深入探討顆粒內部的流動行為的話有助於了解土石流的崩塌機制。本論文主要是在狹窄流道內進行乾顆粒崩塌與水中顆粒崩塌實驗，並且針對水中顆粒崩塌實驗的結果與DEM模擬結果進行比對。此外我們將會比對不同顆粒堆高寬比和不同粒徑大小的顆粒在崩塌過程中的流動行為。為了要能夠分析顆粒流的流動行為，我們藉由Voronoi影像處理技術來得到顆粒流的速度。
本論文主要觀察顆粒流在崩塌過程中的速度分佈，沿深度方向速度剖面，流動層厚度與出口流量變化。結果顯示流動層的速度分佈在大的高寬比下會比小的高寬比的情況還劇烈。同樣的，使用大顆粒產生的速度分佈會比小顆粒的還強烈。出口流量與流動層厚度在初期會增加至一極值，然後隨時間逐漸遞減。在大的高寬比下，出口流量初期會比小的高寬比有較大的出口流量，遞減程度也比較劇烈。使用大顆粒的情況下初期也是有較大的流量，但是流量的遞減程度明顯比小顆粒還緩慢。水中顆粒崩塌實驗與模擬比對的結果顯示表面的速度分佈與出口流量在崩塌初期模擬比實驗還劇烈些。但是其餘時段的兩者的結果是相近的。從模擬結果還可發現沉積顆粒堆底部的壓力在崩塌初期有明顯下降的現象。

摘要(英)

The disasters like debris flows, flooding and avalanches have caused many deaths and injuries on the earth, and it is important to understand the inner behavior of debris flows. In this thesis, we will investigate the collapse of rectangular granular piles in the narrow channel for both dry and wet conditions, and validate the DEM simulation with the corresponding experimental results in wet condition. The effects of different aspect ratios and particle diameters on the behavior of granular flows during collapse are also analyzed. We use the Voronoi imaging method to measure the velocity of granular flow.
Some characteristics such as distribution of velocity, velocity profile, thickness of flowing layer and flow rate at the outlet are analyzed in this thesis. Results show that greater velocity on the flowing layer occurs in the high aspect ratio. Likewise, larger particle tend to have greater velocity on the flowing layer during collapse. The flow rate and flowing layer at the outlet reach a maximum initially and decline with time. As the aspect ratio increases, the greater flow rate occurs at the initial period, and declines sharply with time. In the comparison of different particle diameters, the flow rate declines more slowly for large particles than for small particles. By comparison with experimental data, the simulation results show greater flow rate at the outlet and the great velocity in the free surface at initial collapse. However, both results between experiment and simulation show good agreement at later period. The pressure dip is obvious in the formation of the granular pile at initial collapse.

關鍵字(中)

★ 顆粒流

關鍵字(英)

★ granular flows

論文目次

1. INTRODUCTION....................1
1.1 Granular materials..............1
1.2 Literatures review..............2
1.2.1 Granular flow collapsing experiment in dry condition............................2
1.2.2 Granular flow collapsing experiment in wet condition.....................3
1.2.3 Granular flow simulation in wet condition....... 4
1.3 Motivation of research.......5
2. EXPERIMENTAL SETUP AND DISCRETE ELEMENT METHOD.......6
2.1 Experimental setup.......6
2.1.1 Experimental setup and procedure.......6
2.1.2 Digital imaging technique.......7
2.1.3 Measurement of DEM input parameters.......7
2.1.3.1 Measure particle’s size.......8
2.1.3.2 Response angle test.......8
2.1.3.3 Friction coefficient test.......8
2.1.3.4 Restitution coefficient test.......9
2.2 Discrete element method.......9
2.2.1 Introduction to discrete element method.......9
2.2.2 Particle motion.......10
2.2.3 Fluid flow motion.......10
2.2.4 DEM frame work.......12
2.2.5 Contact force model.......12
2.2.6 Critical time step.......14
2.3 Analysis of velocity profile.......15
2.4 Analysis of Flow rate.......15
3. RESULT AND DUSCUSSION.......17
3.1 Effect of aspect ratio.......18
3.1.1 Surface profile.......18
3.1.2 Distribution of velocity vector.......18
3.1.3 Thickness of flowing layer.......19
3.1.4 Velocity profile.......19
3.1.5 Flow rate.......21
3.1.6 Flow rate versus scaled flowing depth.......21
3.2 Effect of particle size.......22
3.2.1 Surface profile.......22
3.2.2 Distribution of velocity vector.......23
3.2.3 Thickness of flowing layer.......23
3.2.3 Velocity profile.......23
3.2.4 Flow rate.......24
3.2.5 Flow rate versus scaled flowing depth.......24
3.3 DEM result compared with experimental result .......24
4. CONCLUSION.......27
REFERENCES.......29
TABLES.......31
FIGURES.......37

參考文獻

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指導教授

鍾雲吉(Chung, Yun-Chi)

審核日期

2015-10-12

推文