PREDICTION OF BOTH DANGER ZONE OF FLOOD AND ACCUMULATION DISTRIBUTION OF VOLCANIC ASH IN REVERE BY MEANS OF LAGRANGE METHODS

通过试验和数值研究，对洪涝危险区和火山火山灰的聚集分布进行了预测。这里使用的实验装置由一个矩形的开放通道（模拟一个在流向和法线方向上具有二维流场的revere）组成，侧壁由亚克力窗制成，用于照明和观察。特别地，利用CCD相机和图像处理观察了板周围（模拟桥墩）的流动特性。利用控制方程进行了相应的数值分析，并采用有限差分技术对控制方程进行离散，确定了流向和横向速度分量。揭示了雷诺数和狭缝宽度与狭缝厚度之比d对速度场的作用。研究发现:(i)在一个小的价值和/或d /δ,流场槽展览没有timewise变化,(2)再保险和d /δ超过一定值时,另一种穿越从板的一侧流向其他发生在槽和(iii)流体交替变化扰乱速度边界层沿板和诱发混合形成的上部和下部流板下游的槽。用离子交换树脂进行的流动显示证实了速度场的结果。

An experimental and numerical study has been performed to predict both the danger zone of flood and the accumulation distribution of volcanic ash in reveres. The experimental apparatus used here was consisted of a rectangular open channel (simulating a revere with a 2-D flow field in the streamwise and normal directions) with a side wall which Was made of acrylic windows for illumination and observation. In particular, the flow characteristics around the plate (simulating a bridge pier) is observed using a CCD camera and an image processing. The corresponding numerical analysis was carried out using the governing equations, which are discretized by means of a finite-difference technique to determine streamwise and transverse velocity components. The roles of both the Reynolds number and the ratio of the slot width, d, to its thickness, delta, on the velocity field are disclosed. It is found from the study that : (i) at a small value of Re and/or d/delta, the flow field over the slot exhibit no timewise variation, (ii) when Re and d/delta exceed certain values, an alternate crossing of flow from one side of the plate to the other occurs across the slot and (iii) the alternating change in the fluid flow disturbs the velocity boundary layer formed along the plate and induces mixing of the upper and lower streams of the plate downstream from the slot. These results in the velocity field are confirmed by the flow visualization using ion-exchange resins.