Akira Murota

Application of Turbulence Model to Stratified Shear Flow

An algebraic stress model is applied to a two-dimensional buoyant surface jet for examining applicability of the turbulence model to stably stratified shear flows. Through comparison with experimental data, it is clear that reasonable calculations can be obtained for stably stratified flows when the buoyancy term is neglected in the e-equation, although its treatment has remained unsolved and has been major weakness for using Κ-e or extending Κ-e models. The solution tested produces a good agreement with measurements on the flow development and turbulent entrainment and also the dependence of turbulence intensities and turbulence transports on the Richardson number.

MATHEMATICAL ANALYSIS ON RISK IN FLOOD CONTROL BY A STORAGE FACILITY

To drain or to reserve? That is the question discussed in this paper. The capacities of drainage and storage facilities for flood control are determined to minimize the total cost under the condition that chance of flooding is less than a tolerable level. An analytical expression of the chance constraint for a flood control system with a storage facility is presented.The capacity of a drainage facility is evaluated based on frequency analysis of “peak discharge” of floods. The capacity of a storage facility may be reasonably evaluated through frequency analysis of “total runoff” of floods. Thus, characteristics of the flood-chance constraint are analyzed in view of the joint distribution of peak discharge and total runoff. Consequently, simplified expressions of the constraint are presented for practical applications.

Interfacial seiche in composite closed water mass.

The thermocline oscillation observed in the stratified water mass, such as, deep lakes, reservoirs and land-locked bays, are sometimes generated by the resurging effects after the stop of the wind set-up motion. The oscillation characteristics of the density interface become much complex in the case of complicated geometry, e. g. reservoirs with several branches, bays composed of many inlets, etc. The authors developed the theory for the, interfacial seiche motion in the two-layered and multi-composed water mass by applying the theory of the surface seiche. Additionally, a laboratory experiment was performed by using the model tank composed of four channel elements with rectangular cross sections. Satisfactory agreements between the theory and experiment were obtained.