Study on the Sound Radiation Directivity of a Railway Wheel and the Relationship between Directivity and Mode Shape
Due to the complex geometry of a railway wheel, the shape of its modes may have to be properly considered to understand and predict the sound radiation directivity around it. A straight-web metro wheel is studied in this paper with a radial excitation. First, the near-field sound radiation at the natural frequencies is measured in experiments performed in a semi-anechoic room. The natural frequencies here were determined by modal test. The corresponding mode shape is calculated from a finite element (FE) model. A good agreement is found between measurements and simulations in terms of natural frequencies. Further, the relationship between mode shape and sound field near the wheel is determined. Second, a rotating semi-circular frame of radius 2 m centered at the center of the wheel is employed to measure the directivity pattern. The directivities of A-weighted total level, one-third octave bands and modes are recorded at a total of 667 measuring points. A radial mode (r, 2) and an axial mode (1, 2) are taken as examples to derive empirical equations of directivity pattern. A model developed by the boundary element (BE) method is found to simulate the directivity pattern more precisely than the derived equations.
KeywordsFinite Element Model Mode Shape Sound Pressure Level Side Lobe Directivity Pattern
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