Recent flood hazards occurring in mountainous areas are often characterized by numerous amounts of sediment and large wood supplied from upstream, which often exacerbate flood disasters in downstream areas. This paper proposes a method for describing large-wood behavior in terms of the convection and storage equations, together with the governing equations for describing flood flows and channel changes associated with active sediment erosion and deposition. The proposed method is tested for its validity by simulating the phenomena occurring in an open channel with an erodible bed and flood flow with numerous amounts of sediment and large wood in the Akatani River flood disaster. As a result of calculations reproducing the open channel experiment, the applicability of the method is indicated as the percentage of wood pieces captured in the sediment deposition areas in the channel is within the range of the experimental results. The results of 2-D flood flow calculations with sediment and large wood in the Akatani River flood disaster suggested that large-wood deposition is reproduced where bed deformation is well reproduced. Overall, since the proposed method makes it possible to simulate the behavior of various amounts of large wood, it can be applied to the management of hazards in mountainous rivers such as the Akatani River.

Shot peening is a method widely used to improve the fatigue strength of materials, through the creation of a compressive residual stress field (CRSF) in their surface layers. In the present research the gain in fatigue life of AISI 4340 steel, obtained by shot peening treatment, is evaluated under the three different hardnesses used in landing gear. Rotating bending fatigue tests and alternating tension tests were conducted and the CRSF was measured by x-ray tensometry prior and after interrupted fatigue tests. The evaluation of fatigue life after shot peening in relation to the relaxation of CRSF, of the crack initiation sites and surface roughness is done.

This study aims to clarify the characteristics of the riverbed deformation, bank erosion, and channel changes in the lower Sangu River basin using a depth-averaged 2-D flow model where suspended sediment transport is dominant and its flow characteristics are influenced by active tides. A 45 km long area including the river mouth is computed using the 2-D model, and the results are compared with the observed channel changes. The computation results show that bed deformation and channel change are mainly caused during the ebb tide period of the spring tide particularly in an area of about 10 km from the river mouth. The detail study domain calculation results show that the flow concentration at the bend area causes the bed erosion there, and the eddy separated from the main stream causes the sediment deposition at the inner bank, while this eddy is not developed at the outer bank, resulting in the bank erosion there. Through these investigations, the characteristics and mechanisms of the morphodynamics in the lower Sangu River reach, particularly the potential of the combination of tides and floods to enhance riverbed deformations and the associated bank shifts, have been clarified.

This study investigates the basin scale sediment transport processes in the Sangu river in Bangladesh by using a rainfall-sediment runoff (RSR) model. One year numerical simulations are conducted with two different sediment transport formulas and the results were compared with observed sediment size distribution and suspended sediment discharge. As a result of computation, a clear longitudinal sediment sorting is shown in one case, while that is not shown in the other case, and the difference between two cases is explained by the difference in the erosion rate of suspended sediment formula. The sediment sorting significantly affects the results of the basin scale sediment transport analysis. Thus, we conclude that in a river dominated by suspended sediment such as the Sangu River, it is very important whether the erosion rate of suspended sediment and associated transport processes can evaluate the sorting process.

In recent years, the need for piping inspection has been increasing, and various in-pipe inspection robots have been studied and developed by several research and educational institutes and companies so far. However, there are few verification examples of moving mechanisms considering the run-through performance of pipe fitting (bent pipes and branch pipes). We have proposed an omnidirectional mobile mechanism for pipe-inspection robot in small diameter pipes. A movement control method in the pipe by omnidirectional movement mechanism equipped with four independent rotary wheels has been discussed. It was shown that the approach of movement control of vehicles was applicable. The straight, spiral and rotary movements can be confirmed by modeling of the omnidirectional mechanism and simulation using proposed method.