Fumiyasu Kuratani

On Scale Effect of the Resistance due to Stern Waves Including Forward-oriented Wave Breaking just behind a Transom Stern

This paper describes how when a ship with a wide immersed transom stern operates on a deeper draft, forward-oriented wave breaking often occurs just behind the transom stern. Stern waves in such conditions consist of two main components: the forward-oriented wave breaking and remained following waves. The purpose of this paper is to develop a method to treat the remained following waves and to clarify scale effect of such stern waves. Methods have been developed to estimate resistance. Most of the recent container ships have wide immersed transom sterns to keep necessary stability with much more containers on deck as compared with ships of two decades ago. When such a ship runs on a deeper draft than its design draft, forward-oriented wave breaking with high turbulence intensity occurs just behind the transom stern. The phenomenon accompanies large momentum loss and accordingly generates large hull resistance. Research is important for energy saving for such ships.

How the sound adjustment process of cymbals affects their vibration and sound radiation characteristics

Cymbals are percussion instruments. They vibrate and radiate sounds when hit with a drumstick or when used in pairs and the sounds depend on the vibration characteristics. Cymbals are made through spin forming, hammering and lathing. The spin forming creates the domed shape of the cymbal, determining its basic vibration characteristics. The hammering and lathing produce specific sound adjustments by changing the vibration characteristics. In this study, we focus on how the hammering affects the vibration and sound radiation characteristics. The hammering produces many shallow dents over the cymbal’s surface, generating residual stresses in it. These residual stresses change the vibration characteristics. We perform finite element analysis of the hammered cymbal to obtain its vibration and sound radiation characteristics. In the analysis, we use thermal stress analysis to reproduce the stress distribution and then with this stress distribution we perform vibration analysis. The results show that the effect...

Estimation of rotational degrees‐of‐freedom components of experimental mode shapes using an analytical model

Rotational degrees of freedom (RDOFs) have difficulty with measurement, although structural modifications with beam and plate elements require mode shapes including RDOFs. This paper presents a method to estimate RDOF components as a linear combination of mode shapes of the finite‐element (FE) model of a test structure. Since the estimation accuracy depends on a set of combined modes, an effective technique for selecting modes to be combined is proposed. This technique is based on the modal assurance criterion (MAC) value which indicates the degree of correlation between experimental mode shapes having only translational degrees of freedom and analytical mode shapes of the FE model. To demonstrate the applicability of the proposed technique, a frame model which has simulated experimental mode shapes with added measurement noise is analyzed. It is confirmed that the optimal set of combined modes can be predicted from the MAC values, although the set differs with each mode number to be estimated.