乾沙穩流產生之不連續崩塌與動床作用之研究

Intermittent Avalanching of Dry Sand in Loose Boundary Channels

洪嘉駿(Jia-Jun Hung)

指導教授 ： 卡艾瑋

國立臺灣大學/工學院/土木工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202001535

摘要

受到位於支流上游集水區崩塌地的豐富材料，本論文主要以實驗探討上游顆粒流對動床渠道之影響。實驗的設計將以最簡單化的現象來進行，以一個長形渠道鋪滿乾砂至安息角，渠道保持接近安息角的角度，以免侵蝕至底床。上游及下游分別有一提供穩定流量的源頭以及三角形的出口。
實驗在上游穩定供砂，但卻出現了不連續崩塌的現象。此外，在實驗中也同時發現了不規律以及規律的的動床變化。為了測量這些變化以及各項數值，於出口處設置了一電子天平，可測得出流量；於渠道的中線處，以雷射光照射，並以相機紀錄影像，隨後利用影像分析得到表面高度的變化。
實驗分析採循序漸進的幾個步驟。首先，將影像分析得到的高度變化繪製成時間、位置與高程的三維圖片。以此表達方式可以初步且快速的辨認在實驗中所觀察到的波動現象。隨後，波經過時的波峰、在崩塌事件之間渠道的底床以及波的週期以分析方式挑出。藉由頻率分析，可得知在渠道各處的分布狀態以及該處之標準差。在此分析中也得到了波峰以及穩定時底床的標準差隨著渠道距離出口長度增長而增加，同時渠道的長度也會使其增加；週期的標準差，只會隨著渠道的長度而增加。在此過程中得到的所有結果及現象，包含標準差、包裹不規則高程變化的規則循環等，都將用於建立預測高程變化的模型。
在分析出流量時，以逐步方式進行分析，獲得之無因次參數呈現正比關係。
在比較實驗與現地的過程中，發現現地得到標準差與實驗峰值的標準差呈現高度相關，有機會以實驗分析結果套入OU過程，模擬現地狀況。

關鍵字

土石流 ； 顆粒流 ； 不連續崩塌 ； 空間-時間之三維繪圖 ； 頻率分析 ； OU過程

並列摘要

Motivated by landslide-supplied debris flows in headwater catchments, this thesis investigates loose boundary granular flows in steep channels. A simple geometry is adopted, an inclined rectangular sand box filled with a uniform layer of sand is supplied by a constant upstream silo inflow, and discharges through a downstream triangular notch.
Despite these simple conditions, the channel experiences intermittent avalanching, with waves of dry sand propagating down, either regularly or irregularly. To measure the weight of these intermittent flows, an electronic scale is placed downstream and an imaging system composed of a laser stripe and camera is used to measure the evolving elevation profile of the channel centerline.
The analysis is gradually and orderly approached . First of all, the space-time plots are made to observe the roughly motion of collapse. Then the elevation of motion and outflow are divided into peak data, low data and the period. After that, the frequency analysis have been done to have the distribution. By analyzing the frequency, the relation between standard deviation, the distance from the exit and the length of channel are revealed. The standard deviation of peaks increase as the distance and the length, the standard deviation of period increase as the length. In the process of analysis, the phenomenon of envelope, the regular cycle, is also revealed. From the result, a preliminary model can be build.
The outflow is also been analyzed. By comparing with frequency of collapse and steady inflow, the relation between two dimensionless parameters have been revealed as proportional
Comparison between experiment and field indicates that the standard deviation has highly correlated tendency. Thus, it seems possible to connect the experiment to the field by OU process.

並列關鍵字

debris flow ； granular flow ； intermittent avalanching ； space-time plot ； frequency analysis ； OU process

參考文獻

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