We have studied the analysis method of interior noise in railway cars by means of a ray tracing method. Firstly, by using a point source as input, sound distribution inside a car was analysed and compared with the measurement result obtained by a loud speaker test. It was found that the analysis result of sound decay along the longitudinal direction of the car did not always match the measurement result. It is possibly because the wave character of the sound cannot be strictly simulated by the ray tracing method. However, for the purpose of analysing the sound distribution while the train is running, it may not be necessary to accurately simulate the sound decay in the longitudinal direction, because the sound sources are distributed everywhere inside the running car and therefore the importance of the sound decay along the longitudinal direction may be low. Based on this perspective, we have proposed the interior noise analysis method for the running condition by applying multiple sources inside the car. The amplitude of each source was estimated from the measured vibration of the interior panels as well as from the estimated radiation efficiency of each panel. Validation of the analysis was conducted by comparison with the measured data of the interior noise inside the running train, and it was confirmed that the level of interior noise reduction by the installation of passenger seats matched well between the analysis and the measurement.
This paper presents the numerical simulation methods used to reproduce droplet retention and sliding on an inclined surface by using the Moving Particle Semi-implicit (MPS) method. The MPS method is useful for simulating free surface flows with highly deformed gas–liquid interfaces, such as the behavior of condensed water in an evaporator. However, the existing MPS method cannot correctly reproduce the behavior of a droplet retention and droplet sliding on an inclined surface. In the simulation of a droplet on a wall using the existing MPS method, the simulated droplet starts sliding as soon as the wall is inclined even slightly and falls down at a very high speed. In this study, the details of the forces acting from the wall to a droplet are considered, and the boundary condition models that contain the resistance forces acting on the contact line of a droplet are proposed. Droplet retention and droplet sliding on an inclined plate are successfully simulated by using the proposed models. Furthermore, the simulation results are compared with the experimental results reported in literature. The relationship between the droplet volume and critical sliding angle and that between the inclination angle of a slope and droplet sliding velocity are each compared using the experimental results and evaluated both qualitatively and quantitatively; they show good agreement with the experimental results.