Various technologies are being developed for noise prediction at the design stage of vessels. However, research on noise level prediction technologies for air conditioners and each section connected to these systems has not been actively pursued up until now. This results in low prediction accuracy of air conditioning noise at the design stage, causing some ship designers have no choice but to introduce excessive noise control measures. To address this issue, we have developed a new air conditioning noise calculation method after conducting various experiments. This method allows appropriate noise insulation measures to be adopted at the design stage of a new vessel. In this paper, we describe the outline and results of the above-mentioned experiments.
IMO sulfur regulations are expected to increase the blending ratio of catalytic cracking fuels, such as LCO (Light Cycle Oil) and CLO (Clarified Oil), with marine fuels. The aim of this paper is to investigate whether blending those fuels can cause any specific problems.
The authors prepared test fuels blended with LCO and ones without it based on the cetane index. The effects of these fuels on the ignition, combustion and exhaust characteristics of diesel spray were investigated by combusting it. We found that delayed ignition of the test fuels showed close association with the cetane index even when pilot injection was performed following ambient temperature changes. It was also learned that the emission characteristics of diesel spray were correlated with delayed ignition, and that an increase in NOx emissions was prevented at high temperature because of a reduction in the burnt volume caused by restricted air entrainment. In our experiments using a series of test fuels, the blending of LCO has not presented any specific problems that affect the ignitability and emission characteristics of diesel spray.
Loosening of threaded fasteners is one of the most fundamental causes leading to serious accidents of various machines, structures and electronic devices. There are two types of loosening mechanism, i.e., loosening with/without rotation of threaded fasteners. Loosening with rotation frequently causes such issues as bolt force reduction, falling of threaded fasteners and fatigue failure of bolted joints. In this paper, loosening mechanism with rotation is analyzed in detail by FEM using helical thread models with accurate geometry. The target joint is subjected to shear loads perpendicular to the bolt axis. It shows quantitatively how the bolt force decreases due to alternating shear loads. The numerical results have also clarified that the loosening of bolt-nut connections progresses when a slip occurs in the order of the plate interface, the thread surface and the nut bearing surface, and the contact conditions at each surface behave in an irreversible manner.