산란을 고려한 프로펠러 소음과 변동압력의 시간영역 해석 및 실선 적용 연구

Abstract

Using time domain acoustic analogy, a method to predict the sound field and hull pressure fluctuation generated by unsteady sheet cavitation on marine propeller has been developed. The Formulation 1A of Farassat is introduced to enhance theoretical understanding of this work, and it is applied to modeling scattered sound field by fuselage boundary. To express direct sound field from sheet cavitation, a new solution is studied. It could consider Dopplers effect and also express near field and far field separately. A small sphere model is used to verify the present method. Computed acoustic field pressures around the sphere are compared with the exact solution and the numerical results show good agreement. The method to obtain the pressure fluctuation is described and PFBEM (Power Flow Boundary Element Method) is introduced to interpolate pressure fluctuation over the all area of stern model. To compute vibrational response and propeller induced noise at the same time coupling method is applied to propeller noise analysis, TDFEM (Time Domain Finite Element Method) is coupled with the acoustic analogy. Absorption boundary condition is newly applied to acoustic analogy and it makes it possible to calculate interior noise of closed room like cavitation tunnel. In addition the way to consider free surface effect when the underwater noise is analyzed is introduced. Finally the software SPIN (System for Propeller Induced Noise) is developed to simulate propeller noise and pressure fluctuation.