No abstract

No abstract

No abstract

The objective of this study is to investigate the influence of damping from the PTO device on the cumulative output of the oscillating water column wave energy converter under real sea conditions which encompasses wide range of wave period and height. In this presentation, a time domain dynamic simulation model of OWC motion is developed and validated with water tank test results. Then the model is used to calculate a wide range of wave period and height. Finally, annual cumulative air power output of OWC is calculated with different damping values. In the water tank experiment, a cylindrical oscillating water column with a diameter of 0.3 m and submerged depth of 0.2 m is tested. PTO damping was emulated by using several orifice plates. Since the orifice pressure is proportional to square of flow-rate of the orifice, In the simulation, a model was constructed to solve the dynamic equation of motion assuming water column as a rigid equivalent floating body. Validation showed the model captures the influence of PTO damping as observed in the water tank testing. Using simulation, output air power from real scale OWC was evaluated under wide range of inlet wave period and height. With the output power database from dynamic simulation and frequency of wave height and period at specific sites in Japan (Fukui and Kamaishi), annual cumulative output power is calculated. From the results, it was confirmed that a higher output can be obtained with higher energy in high waves by adopting a damping characteristic that increases the efficiency under a wide wave condition rather than a nozzle characteristic that achieves maximum efficiency in the resonance period. Furthermore, it became clear that the damping that increases the maximum efficiency does not necessarily increase the accumulated energy. When considering operation in real sea condition in the future, it is not always effective to select PTO damping that maximizes the output at specific wave height or period. And it is important to adopt a method that can estimate wide range of wave condition and evaluate the cumulative output power.

The temperature calculation of a practical hydrogen storage tank filled with a metal hydride under development was carried out. The metal hydride was a nano-stractured FeTi (n-FeTi) by mechanical alloying, which has low particle decay and low price.The governing equations used in the calculation were the unsteady two-dimensional heat conduction equations. Expansion and contraction of metal hydride due to hydrogen storage and release were considered as changes in porosity and changes in thermal properties. The change in porosity was treated as the change in energy generated per unit volume. For changes in thermal properties, the empirical formulas based on our experiments were used for the changes in effective thermal conductivity and effective thermal diffusivity due to hydrogenation. A hydrogen storage tank was actually manufactured, and the experimental and calculated results were compared. From the results, it is considered that the use of empirical formulas is important for improving the reliability of calculation results because the change in thermal properties of the packed bed of hydrogen storage alloy due to hydrogenation affects the temperature distribution. In addition, the effect of the presence or absence of heat transfer enhancement fins was evaluated by the calculation. As a result, this calculation can be used to design the heat transfer enhancement fins for hydrogen storage tanks.