The authors have investigated the propulsive characteristics of a model ship with a wing that produces rotary reciprocating motions as a two-dimensional Weis-Fogh model. The authors compared the results of the investigation with those obtained using a wing that produces linear reciprocating motions. In a sailing test, the thrust of the model ship, the wing driving forces, and the wing opening angles while the wings were in motion were measured. In a towing test, the relationship between the thrust coefficient of Type B, whose opening angle is fixed with a chain, and its speed ratio, showed a correlation curve, highlighting that the law of similarity existed between the two. On the other hand, in the case of Type A, whose opening angle can be adjusted automatically with a spring, the law of similarity did not apply. This was because the angle could vary depending on wing moving speed. The loss generated by the rotary reciprocating motions was small, because the wing operated smoothly at the time of closure. However, it became greater when the wing opened, because the wing was pushed backward and the relative attack angle of the wing increased. In a self-propulsion test, which was designed to see how the ship operates at high speed, water levels at the back of the hull rose due to greater pressure applied on the wing, resulting in the lowering of the stem. Additionally, air bubbles were mixed into the channel, leading to the deterioration of performance. The investigation made clear these points, and the authors considered ways to improve these situations.
To develop a loading arm for ship-to-shore transfer of liquefied hydrogen, an emergency release system (ERS) for liquefied hydrogen has been designed and manufactured. In order to estimate its mechanical and thermal behaviors, we have developed a calculation model for temperature and stress distribution of the ERS at low temperatures during the transfer of liquefied hydrogen. The calculation has revealed that the surface temperature would exceed the boiling point of oxygen. A prototype model of the designed ERS has been manufactured and tested by filling liquid hydrogen in the model. The temperature and strain on the surface have been measured during the test and compared with the calculation results. The results have shown that the calculation can predict the temperature on the surface of ERS and that the designed ERS can avoid generating liquefied oxygen. It has also been shown that the measured strains are well consistent with the predicted strain on the surface of ERS. It has been demonstrated that the developed ERS exhibits performance good enough to be utilized for the loading arm for transfer of liquefied hydrogen.
When a manufacture error occurs, there may be a possibility of the actual size of a hydrodynamic journal bearing differing from its basic dimension. In this case, the characteristics of the hydrodynamic journal bearing can also be different from what have been expected, due to changes in oil film pressure distribution between the bearing and journal. The purpose of this study is to elucidate effects of manufacturing errors on the static characteristics of multi-lobe hydrodynamic journal bearings, whose structures are relatively simple and whose oscillation stability in the rotor shaft-bearing system is relatively strong. The study is also intended to come up with a proposal for guidelines about the optimized design for multi-lobe hydrodynamic journal bearings. This paper analyzed and examined changes in the static characteristics of a four-lobe hydrodynamic journal bearing, such as oil film pressure distribution, journal center locus, minimum oil film thickness and friction coefficient between the bearing and journal, when the position of the bottom lobe at the sliding surface is tilted from where it should be due to manufacturing errors. The results of the study showed that when the bottom lobe is tilted against the eccentric direction of the journal from the original location due to manufacturing errors, minimum oil film thickness may increase in comparison with the situation in which the lobe stays at the original location. The results also showed that friction coefficient between the journal and bearing does not change significantly in spite of manufacturing errors.