Field surveys were performed in the southwest of Bangladesh to learn lessons out of severe disasters due to Cyclone Sidr. Spatial distributions of inundation heights were measured around the most damaged area. Inundation heights along the Baleshwar river and the Burishwar river were relatively high compared to those observed on the coast of Kuakata although these sites are far from the coast. Detailed surveys were thus performed in these three areas and there found several residents who witnessed bore-like waves hitting on the damaged area. Embankments along the river had been eroded before the storm while dikes on the coast significantly functioned to reduce the damages of the coastal area behind.
A gyroscopic power generator that generates a power of 1.8 W is developed with a rotor of 100 mm diameter and 500 rpm spin speed. In conventional vibration generators, which use simple vibrations of an inner pendulum, the output power has been less than 60 mW. Gyroscopic generators increase the inertial force by rotating the pendulum at a high speed and generate about 50 times greater power than the conventional ones. However, wearable gyro generators that operate under arbitrary vibrations have not been realized because the gyro torque and the electromechanical transformation efficiency are greatly reduced by miniaturization. In this study, first, a theoretical model is developed to clarify the basic characteristics of the generator. Next, a desktop-sized generator that works under any vibration is developed using highly precise motors and gears determined by the theory; the optimum rotor, motor, and gear parameters are decided according to the approximate solution of the mathematical model. Next, mechanical and electrical characteristics are measured to show the validity of the theory. Finally, a wearable test device is produced by modifying a 2.52" hard disk drive (HDD) to show the possibility of obtaining a practical generator.
Field observations were conducted on the morphology and hydrodynamics around the Tenryu River mouth. The sand bar was eroded by storm waves followed by flood due to the typhoon in September, 2013, which significantly changed the water level variations inside the river mouth. The large friction at the narrow opening of the river mouth was found to raise the daily-averaged river water level by 0.2 m. The presence of sand bar appeared to decrease the intrusion of tides and waves into the river. The transmission coefficient of waves increased from 0.2-2 % to 2-5 % as the cross-sectional area at the river mouth was increased. The water level variation due to tides and wave setup was found even at 3 km upstream from the river mouth.
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