本研究主要探討不同幾何形狀防砂壩受土石流衝擊時之受力情況，藉由改變壩體上游壩面之幾何形狀，使得土石流作用於壩體之衝擊時間增加以減少受力，並能分散部份土石流衝擊力，增加壩體之穩定性，以期提供未來土石流防砂壩設計之參考依據。
　　本研究以數值模擬之方法，利用泛用型計算流體力學軟體FLUENT進行探討，由模擬結果可得到壩體受土石流衝擊時之流況、速度場、壩面壓力分布與壩體受力(包含總力、動壓力與靜壓力)，如此可改進以往研究只能藉由壩面單點或多點得到土石流衝擊力，且無法區分出土石流動壓與靜壓效應於不同時間對壩體影響的缺點。
　　由模擬結果可清楚地發現壩體受土石流衝擊初期以動壓力為主、靜壓力為輔，之後漸漸地受到回水消能的影響，使得壩前流體流速減緩而逐漸以靜壓力為主、動壓力為輔，最後等到水面趨於平穩時，此時壩體僅受靜壓力作用。
　　總力比較方面，在低流量時，此流量對三種壩體均造成非溢流，三種壩體所受之總力幾乎相同；在中、高流量時，此流量對三種壩體均造成溢流，直立壩所受總力為最大，其次為斜面壩，最小為曲面壩，並隨著流量增加此差異越明顯。
　　由模擬結果探討可知，壩體所受土石流衝擊力之大小深受幾何形狀的影響，由於低流量對壩體的危害程度比高流量來得小，因此雖然在低流量時三種壩體受力差異性不大，但於高流量時曲面壩受力明顯小於其它壩體，此因曲面壩壩面呈弧形的特性，使得土石流流經路徑為最長且具曲率變化，因此當土石流衝擊壩體時，除使土石流作用於壩體之衝擊時間增加以減少受力，並能夠藉由曲率的變化分散部份衝擊力，因此所受之土石流衝擊力較其他兩種壩體小。

　This study primarily deals with the situation in which debris flow collides with Sabo-Dam of different geometric shapes. By changing the shape of the dam body in the upstream, we extend the time period and flow path in which debris flow impacting on the body of the dam, in order to decrease the impulsive force; moreover, these can also disperse some part of the debris-flow impulsive force and enhance stability of the dam body, with a view to providing an epitome for the design of Sabo-Dam in the future.
　The study adopts numeric simulation, using generic CFD software FLUENT, to discuss this point. From the simulation we see the fluid state of the dam body when impacted by the debris flow, the velocity field, the distribution of pressure on the surface of the dam and the forces exerted on the body of the dam (inclusive of the total force, dynamic pressure, and static pressure). In this case, we can refine the former study—in which debris flow- impacting force can be obtained only through points on the dam surface and we can distinguish between the effect of the dynamic pressure and that of the static pressure in different time duration.
　It is clear from the simulation that in the beginning the pressure on the dam body is primarily dynamic; however, as time goes by, the velocity of the fluid in the front of the dam decreases (because of backwater), which gradually render the pressure chiefly static. In the long run, when the water surface comes still, there is only static pressure
　As to the comparison of total pressure, when the discharge is low, this causes non-overflow stream to all three dam body; the total pressure on these three dam body are nearly identical; while in the medium and high discharge, these give rise to overflow stream to all three dam body; moreover, vertical dam has the maximum total pressure among the three; second largest is the slanted dam; and the smallest is the curved dam. In addition, the bigger the discharge, the clearer the difference.
From the above simulation, we know that the geometric shape of the dam bodies has acute effect on the amount of impulsive force on them. Because the low discharge is less destructive to the dam body than the high one, regardless of the minor differences of the received pressure in low discharge, its relatively small exerted force in high discharge due to the nature of its arc-shaped dam surface causes the path of the debris flow to be the longest and to meander the most. So, as the debris flow bumps into the dam body, in addition to extending the time period of impacting, the curved dam can also disperse the force by means of its changing curvature. Hence, the curved dam receives the smallest debris- flow-induced force than the other two.

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