The near-field structure of strongly buoyant jet issuing from a square nozzle at low Froude and Reynolds numbers is studied by using LIF flow visualization and time-resolved scanning PIV. These experimental techniques allow the visualization of unsteady three-dimensional flow phenomenon occurring in the near-field of strongly buoyant jet. It is found that the buoyant jet is unstable to the positive buoyancy forces, which promote the inflow motion near the nozzle exit. The surrounding low temperature fluid moves into the nozzle inside along the nozzle corner and mixes with the high temperature fluid deep into the nozzle. Then, the flow pattern inside the nozzle becomes highly complex to promote the laminar to turbulent transition of the jet. The statistical flow characteristics of the strongly buoyant jet are evaluated from the scanning PIV measurement, and the result indicates the presence of axisymmetric distributions of mean flow and velocity fluctuations in the circle of diameter equal to the square side of the nozzle.

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In the present paper, simultaneous measurement of velocity and concentration field in the initial region of a buoyant jet in stagnant surrounding water was carried out using a scanning LIF and PIV technique. This technique allows the simultaneous measurement of velocity and concentration in the three-dimensional field. The result indicates that the coherent structure plays an important role in the momentum and mass transfer in the buoyant jet. It is also found that the analogy between the momentum and mass transfer does not exit in the instantaneous structure of velocity and concentration field, although the global structure is similar.

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This paper evaluates the mitigation effect of Tokai earthquake measures on housing damage using a counterfactual approach. It focuses on those measures that stimulate ex-ante investment in disaster prevention in the supposedly affected area, including earthquake-proof retrofitting and improved housing construction; the effect of the measures on housing losses is estimated monetarily. The study compares factual disaster damage computed using a real distribution of houses with counterfactual damage to a hypothetical housing distribution that would occur if the measures were not implemented. The key findings are: (i) the disaster mitigation effects of Tokai earthquake measures on housing amount to approximately JPY 18 billion (USD 0.18 billion) for Yamanashi Prefecture and JPY 0.26 trillion (USD 2.6 billion) for Shizuoka Prefecture, which would be at the centre of the event; (ii) a before-after comparison biases estimates of the mitigation effect; and (iii) statistically, the measures do not mitigate the housing damage predicted for an earthquake in Tokai.