本研究提出離散元素模型探討掉落體衝擊顆粒床的力學與運動行為，並以粒子影像測速技術 (PIV) 量測實驗中顆粒床的表面速度，並連同文獻的衝擊實驗結果，進行離散元素模型的驗證，驗證的物理量包含顆粒床表面速度場和掉落體的位置、速度、加速度、角速度與角加速度。本研究進一步透過驗證合理的離散元素模型，探討衝擊時顆粒床內部的物理性質。顆粒床的材質為三氧化二鋁，且分別使用三種不同的粒徑 (3mm、5mm及8mm)。研究結果顯示 : (1)顆粒床粒子體積佔有率受到衝擊的影響範圍僅限於掉落體周圍，但整個顆粒床的配位數與摩擦啟動因子皆有明顯的變化； (2)衝擊過程中，垂直方向應力的上升最為明顯； (3)接觸力的水平分佈為均向性，而垂直分佈為異向性； (4)衝擊時顆粒床內的摩擦啟動因子明顯上升； (5)衝擊時顆粒間的正向與切向接觸力分佈皆快速上升，但顆粒與牆壁間接觸力分佈無明顯變化； (6)衝擊時引發的縱波與橫波波速與顆粒床粒徑有關，且顆粒床的孔隙率也會影響縱波波速，而縱波與橫波間波速變化呈一線性比例。;The aim of the study is to investigate the mechanical and motion behavior of a projectile vertically impacting into a cylindrical granular bed experimentally and numerically. The surface velocity distribution of granular bed was measured by particle image velocimetry technique (PIV). This study proposed a discrete element model to simulate this granular system and this DEM model was validated against the experimental data in the literature. The compared physical quantities include the penetration depth, translational and angular velocities, and translational and angular acceleration of the projectile as well as the surface velocity distribution of granular bed. The validated DEM model is then used to explore the internal physical properties of the granular system. The main research findings are as follows : (1) The solid fraction of the granular bed is partially influenced during the impacting process, especially in the region around the projectile, but the coordination number and the mobilized friction are influenced in the whole granular bed; (2) The vertical normal stress is dominated during the impacting process; (3) The contact force shows isotropic distribution in the horizontal plane, while the contact force distribution in the vertical plane was anisotropic; (4) The impact of a projectile on the granular bed greatly makes friction factor mobilized; (5) Normal and tangential contact force distributions for the inter-particle contact greatly change during the impact process, but those for particle-wall has no significant change; (6) The velocity of pressure wave depends upon the particle size and granular porosity, whereas the shear wave is related to only the particle size. The ratio of the pressure wave velocity to the shear wave velocity is found to be constant.
