Large part of country in Japan is mountainous area. Many villages and large structures have the potential of damage by pyroclastic flow associated with volcano eruption. In order to prevent these disaster, the understandings on characteristic of pyroclastic flow is necessary. A hazard map can be made based on such knowledge. Also, the constructions of facilities preventing these disasters are possible. The flow mechanisms of pyroclastic flow are similar to the thermal flow on the inclined boundaries. The models and the numerical simulator on such flows are developed considering the three dimensional topography. Such a model was originally proposed by Fukushima and Kagiyama(1992). This numerical simulator can analyze the route of flow and lateral spreads of pyroclastic flow in addition to the velocity, the concentration of pyroclastic materials, the kinetic energy of turbulence. The simulator for the pyroclastic flow on the three dimensional topography can estimate the actual behaviors of these flows.
An experimental investigation was performed to clarify the effect of addition of surfactant on the reduction in pressure drop for solid-liquid mixtures flowing through a vertical pipe. Initially, the pressure drops were measured under various operating conditions for the surfactant-added single phase water flowing through a vertical pipe. In the region of high Reynolds number, the pressure drops were much smaller than those of the flow without the surfactant. The surfactant in water was considered to form many rod-like micelles which tend to stand in each stream line, and accordingly to keep the flow against the transition to turbulent flow. Secondly, the similar examination was carried out for solid-water two phase flows. It was consequently concluded that the addition of the surfactant was also useful enough to reduce the pressure drops of the two-phase flows while the effect was not so remarkable compared with the case of single phase flow.