火砕流の流体力学的モデルによる解析 : 雲仙・普賢岳への適用

概要

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A fluid dynamic theory of pyroclastic flow is presented. This is based on the theory of simple inclined thermals and on the theory of powder snow avalanches. The theory of pyroclastic flow presented herein is composed of the mass conservation equations of air and pyroclastic materials, the momentum and the kinetic energy equations. In addition, the equation of temperature is included. The constitutive relations such as the air entrainment coefficient and the pyroclastic material entrainment coefficient, and the relations of shear stresses and the level of turbulence are assumed by the knowledge of powder snow avalanches. This theory is applied to the pyroclastic flow occuring at Mt. Fugen, Unzen volcano. The simulation of the dynamic behavior of pyroclastic flows is strongly dependent on the diameter of materials. If we choose the diameter as 0.075-0.1 mm, we can simulate the pyroclastic flow occurring at Mt. Fugen, Unzen Volcano, June 3, 1991. Also it becomes clear that the effect of the temperature is very important in the simulation for pyroclastic flows.
1992-10-01