風吹落的物體，譬如樹枝、招牌、屋頂的瓦片被強風吹落後，往往會對下風處的建築物、行人或車輛造成極大的危險。尤其是在風災頻繁的台灣，這一類的災害時有所聞，值得深入的研究。本研究擬以風洞實驗加上數位攝影機，在不同流況下，例如穩態流以及陣風流場下實際量測各種形狀的物體，例如球體、正方塊體和長方塊體等被風吹落的軌跡。本研究並建立一個數值模式以二維的四階Runge-Kutta法來求取每個時間的水平和垂直速度，再進而推求物體水平和垂直方向之位置，模擬物體在風中飛行的軌跡，以實驗結果比較及驗證模式。比較發現，本研究之模式預測物體墜落的落點，誤差皆在10%以內，得以證明本模式之適用性。再更進一步發展模式，以模擬紊流流況下之物體受風吹落的軌跡。研究結果將可增進吾人對風吹落物體行為的瞭解，並可降低風災所帶來的危害。

Impacts by wind-borne debris are a major source of damage in severe wind storms such as typhoons. Debris that can be projected as missiles include branches from tree, roof tiling, as well as items removed by strong wind from building cladding and structure. These items could penetrate the walls and windows of downwind buildings and cause human life. This study used wind tunnel experiment and numerical simulation to study the trajectory and velocity of wind-borne objects, such as sphere, cube and rectangular plate, in uniform flow and gusty flow. The numerical model used a two-dimensional fourth-order Runge-Kutta scheme to solve the horizontal and vertical velocities. The results of numerical simulation and wind tunnel experiment show good agreement. The numerical model was then used to simulate the trajectory and impact velocity of wind-borne objects in turbulent flow.

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