This review summarized recent experimental studies by the hydraulic observations and measurements in small natural channel streams, such as tiny rivers, irrigation and drainage canals. Three modern topics were selected in river hydraulic engineering: (1) gravel-cobble bed flows, (2) flows with vegetation zones, and (3) flows around spur dyke visualizations and measurements: flow velocity, flow lateral spreading, and water-surface and bed-surface levels. In conclusion, it was suggested that hydraulic experiments in small natural channel streams have a possibility to provide This review summarized recent experimental studies by the hydraulic observations and measurements in small series. Discussion was extensively developed from various viewpoints, using many field data obtained by flow effective information in future river hydraulic engineering research.

Birds foraging under water are collectively called diving birds. For example, the brown dipper, little grebe, common cormorant, tufted duck seen in rivers, ponds and lakes are classified into this category. Of course, penguins and shearwaters are typical of diving birds very familiar with us. High diving performance of the diving birds is expected to be useful for improving the performance of the current ships and developing new underwater vehicles. In this review article, the drag coefficient of the diving birds is introduced because it is one of key parameters for designing ships and underwater vehicles.

In order to improve the effects of an energy-saving duct installed in front of a propeller of a ship, a measurement system of the flow inside the duct is to be developed. For that purpose in a ship model basin the transparent material close to the refractive index of water is required. In this study, a measurement of a flow field behind a model made by a transparent material, CYTOP, has been carried out by PIV system. From the test in a small circulating water tank, it is found that the flow field measured by the model of CYTOP can be measured for the mainstream velocity with difference of 2.5% or less. From the study CYTOP is one of the promising materials for using the flow field measurement by the refractive index matching method in a ship model basin.

Dandelion is a classic example of a wind-dispersed plant and enabling long-distance seed dispersal. In 2018, Cummins et al. reported their results of freely flying tests and fixed tests on both real dandelion seeds and a separated vortex ring was found above the pappus of the dandelion using flow visualization techniques. The separated vortex ring is the main aerodynamic feature of the dandelion seed which enables its flight. However, the effect of the gap structure of the pappus on the vortex generation has not been fully understood. In the present study, in order to investigate the effect of the pappus’s porosity on flow structure in the wake of pappus, drop tests and flow visualization experiments were conducted using a vertical airflow pipe for the pappus with different porosity. The experimental samples are artificially changed porosity of pappus by partially removing filaments for the real (inhabit in nature) dandelion pappus. The pappus’s porosity affects the strength of vortices generated in the wake of the pappus and the vortex growth during posture changes in free-fall motion. This vortex behavior is strongly related to the aerodynamic forces acting on the pappus.

Magatama type blade configuration, which has been exclusively designed for vertical axis wind turbine (VAWT), is improved by Reinforcement Learning (RL). In this RL, VAWT blade configuration that generates larger aerodynamic force in direction of rotor rotation is developed. Power performances of the VAWT with the improved new Magatama type blades are tested by wind tunnel experiments. Results show the power from the VAWT rotor with the new Magatama blades is increased. Flow structure around the new Magatama blades in the VAWT rotor and aerodynamic forces generated by the blades are investigated by unsteady numerical simulation. Results show the new blades increase rotational force in downwind zone. In this downwind zone, direction of aerodynamic force is close to that of rotor rotation.

A circular water-channel experiment was carried out to study suppression of the local scour around outer-banks in curved-rivers through the use of a series of simple rectangular spur dykes, under the condition of ‘major bed-load and minor suspended-load’. Bed variations were intensively measured around the spur dykes in the wide range of their aspect ratio Ar, defined by the super dyke interval / spur dyke length. In the range of Ar≦1, the spur dykes negatively worked and made a large scour hole in their neighboring region. On the other hand, the scour area decreased due to their effective operation in the range of Ar≧3. In particular, at Ar = 5, it would be less than a half of that in the absence of spur dykes. In conclusion, it has been verified that a series of spur dykes with the suitable values of Ar have the potential to protect outer-banks in curved-rivers.