| 摘要: | 本研究主旨在探討掉落體衝擊不同的顆粒粒徑、顆粒形狀、高剛性及顆粒密度的顆粒床之運動及力學行為。本研究設計簡單的掉落實驗裝置，採用高速攝影機拍攝掉落體衝擊過程，透過兩個視角的平面二維影像，使用改良式粒子追蹤測速技術，量測掉落體在顆粒床內的三維位置，除了求得掉落體在顆粒床內垂直方向的速度及加速度外，更增加水平面的速度及角速度量測，並藉由掉落體的加速度求得顆粒床對掉落體之阻力行為。本研究實驗項目如下: 掉落體衝擊三種粒徑(3 mm、5 mm及8 mm)的氧化鋁顆粒床、五種形狀(球形、二款橢圓形、膠囊形及雙球形)的ABS顆粒床、三種形狀(球形、碟形及圓柱形)的碳鋼顆粒床及三種密度(碳鋼、氧化鋁及ABS)的同粒徑球形顆粒床等。實驗結果顯示: (1)掉落體在粒徑較大的顆粒床的加速度、阻力、水平面速度及角速度呈現較大數值，隨著粒徑減少而降低，貫入深度則隨粒徑減少而增加；(2)在不同形狀的顆粒床，掉落體在顆粒床內的貫入深度依序為橢圓形Ⅱ、球形、橢圓形Ⅰ、膠囊形及雙球形，雙球形與膠囊形顆粒具有明顯的顆粒互鎖效應。在雙球形及膠囊形顆粒床，掉落體在水平面上呈現較大速度，而球形及二款橢圓形顆粒床因較易貫穿，造成掉落體在水平面上的速度偏低；(3)在三種形狀的碳鋼顆粒床，圓柱形顆粒具有明顯的顆粒互鎖效應，掉落體的加速度、阻力、水平面速度及角速度隨著顆粒互鎖效應增強而增加，但貫入深度則是隨顆粒互鎖效應增強而減少；(4)在三種密度的球形顆粒床，掉落體在顆粒床內的加速度、阻力、水平面速度及角速度隨著密度愈大而增加，相反地貫入深度則隨密度愈大而減少。;The aim of this study is to investigate the dynamics and mechanical behavior of a free-fall projectile impacting granular beds with different particle sizes, shapes, densities and high stiffnesses. A simple drop experimental device was designed. A high-speed camera was used to observe the impact process of the projectile, and the images from the two perpendicular directions were captured by means of the properly- orientated mirror. The 3D positions of the projectile were analyzed by using Improved Particle Tracking Velocimetry. The kinematical quantities, including the vertical velocity and acceleration of the projectile as well as the translational and angular velocities in the horizontal plane were further evaluated. The drag force on the projectile was determined by the acceleration of projectile. The main findings are summarized as follows: (1) The projectile in the granular bed with a larger particle size shows a larger vertical acceleration, drag force, and translational and angular velocities in the horizontal plane, which decreases with decreasing of the particle size. However, the penetration depth decreases with increasing of the particle size；(2) The penetration depth of the projectile was found to be in following sequence (from deep to shallow): ellipsoidal Ⅱ, spherical, ellipsoidalⅠ, capsule and paired. Paired and capsule particles have a greater interlocking effect so that the projectile has a larger translational velocity in the horizontal plane. On the other hand, the projectile easily penetrated through granular bed with spherical and ellipsoidal particles due to the shape effect, resulting in smaller translational velocity in the horizontal plane；(3) For granular beds with strong interlocking effects, the projectile has a larger value of acceleration, drag force, and translational and angular velocities in the horizontal plane. The penetration depth increases with smaller interlocking effect；(4) The results show that the acceleration, drag force, horizontal velocity and angular velocity of the projectile increases with increasing particle density. The penetration depth decreases with increasing particle density. |
