Three dimensional computation scheme for groundwater flows by Integral Equation Method has been developed. A validity of the computaion scheme was confirmed through the comparison between theoretical and numerical results on a duct flow and fresh-salt water flow in an unconfined aquifer. The integral equation of three dimension Laplacian equation was integrated analytically by using the local coordinate systems. The proposed computation method was applied to the fresh-salt groundwater flow around an underground dam. The time change of velocity profiles and shapes of the groundwater table and interface between fresh and salt groundwater were computed and three dimensional characteristics of groundwater flows around an underground dam became clear.

View full abstract

Conditions for a vortex to form in front of an inlet located near a solid wall have been examined. The correlation for the critical inlet mass flux required to form a vortex has been obtained from existing experimental data. The stagnation-point criteria based on the potential-flow theory are found to fail in reproducing the experimental correlation. Improved calculations with an imbedded line vortex have been carried out but they are still inadequate to explain the experimental results, indicating a need for a more realistic model.

View full abstract

River courses supply good environment for vegetation growth. Vegetation is an essential element composing river landscape and river environment, but it is also roughness element for making the resistance to flow increase. In this paper, the lateral distribution of depth-averaged velocity is firstly obtained from equations of motion within a cross-section and continuity equation in which we consider the flow resistance in compound cross-section and resistance due to interaction between distributed vegetation and flood stream. Secondly, longitudinal water level is calculated from one-dimensional momentum equation taking account of distributed vegetation and the lateral velocity distribution.
The applicability of the basic equations determining velocity distribution and longitudinal water level is assured by two sets of data of large floods in the Ishikari River.

View full abstract

A formula was developed for lateral eddy viscosity in flows with bank vegetation. Based on the formula the lateral shear stress has been calculated, which reveals that the lateral shear stress at the boundary of vegetated area has a maximum when the depth-averaged flow velocity in the vegetation area is one-third of that in non-vegetated area. Deposition rate of suspended sediment in the vegetated area was derived using the result of the lateral eddy diffusivity. Vegetation between dikes is commonly seen in natural rivers, and the present laboratory test indicates that the dikes amplify the strength of horizontal eddies generated at the boundary of vegetation, resulting in the increase of lateral mass conveyance such as sediment.

View full abstract

Open channel flow over rigid vegetation is analyzed numerically by horizontaly averaged Reynolds equations based on k-ε turbulence model. Not only uniform flow over vegetated bed but also a transitional flow from area over a smooth bed to area over vegetated bed is studied. The experiments were previously conducted for the former case. For the latter case, the flow experiments are conducted. The experimental data are well described by the numerical model. Furthermore, the effect of the vegetation density on the turbulent structure is investigated with numerical prediction of flow by the present model.

View full abstract

The flow field and transverse bed profile in vane-installed curved channel are investigated analytically and experimentally to establish a rational vane design method. Distributions of secondary currents supplied by vanes are derived from the vorticity equation for a vane-installed flow, then the transverse bed profile is obtained using the secondary current distributions.
The theoretical results are found in good coincidence with experimental results.

View full abstract

This paper elucidates that the modification of the motion of closure of gates from constant speed closure to dual speed closure makes the maximum pressure rise smaller for the same time of total closure of gates. The change of closing speed of gates adjusted to take place at the instant of the end of the first phase of water hammer in pressure conduits has been dealt with. The form of dual speed gate closure which makes the maximum rise of pressure as small as possible is named as “optimal dual speed gate closure, ” and the water hammer for this form of closure has been studied in detail. A chart for the determination of the maximum pressure rise for that optimal gate closure has been shown and compared with the Allievi chart for constant speed closure. Also, a chart for the determination of increase of speed of rotation of water-turbines in the same optimal gate closure has been presented. This study has been made theoretically and by the vast use of numerical computer.

View full abstract

This paper discusses the motion of a floating power plant joined to a dolphin-link mooring system in short-crested waves through simulation and physical model tests with a multi-directional wave maker. Numerical models based on the boundary element method are developed by means of the inverse fourier transformation of the plant barge responses to component waves in short-crested seas. Model tests of a plant barge are performed to compare the computation results. The numerical models and the experimental results show close agreement. The in-line motion components of the plant to the principal wave direction of short-crested waves are less than the corresponding values in long-crested waves. Transverse motion components in short-crested waves however, are greater than those in long-crested waves. On the other hand, the difference between heaves caused by short-and long-crested waves is small. These trends increase as the directional spreading of incident waves increases.

View full abstract