Fraunhofer-Forschungsgruppe Hydroakustik FHAK

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Numerical and experimental study of noise generated by a vibrating plate

1991 , Estorff, O. von , Homm, A. , Bartels, F.

Applying an indirect Boundary Element Method the sound radiation of a vibrating cantilever plate is investigated. The numerically obtained results are compared with measured data in order to show the accuracy and applicability of the numerical approach. The study clearly enhances the confidence in the computational solution of noise problems which are of particular importance in connection with the qualification of large spacecraft structures like HERMES.

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Sound radiation of a cantilever plate - comparisons of BEM results with experimental data

1991 , Estorff, O. von , Homm, A. , Bartels, F.

The sound radiation of a vibrating cantilever plate is investigated by a combined Finite Element / Boundary Element approach. First, in a FE-analysis the mode shapes of the plate are determined. Second, for three selected frequencies the acoustic pressure distribution around the plate is calculated using an indirect boundary element formulation. The results are compared with experimental data in order to show the accuracy and applicability of the numerical approach.

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Acoustical farfield directivity and vibration pattern of propeller eigenmodes in air

1991 , Blöchl, B. , Bartels, F.

The paper describes experimental results of an investigation about the propeller vibration and the directivity of sound radiation for some selected resonance frequencies. in an anechoic chamber the spatial distribution of the amplitudes and phase angles of the sound radiation has been measured by means of the reciprocity method. The results indicate that with increasing numbers of propeller blades the spatial variation of the sound amplitude decreases. The origin of the complex nature of the acoustic directivity characteristics in amplitude and phase is the vibration pattern of the propeller. The eigenvalues and the nodal lines of the eigenmodes have been evaluated by holography or by scanning the propeller surface with two acceleration pick-ups, determining the lines of phase shift. The results reveal, that for several eigenvalues the vibration amplitudes of the blades differ from each other and no vibration symmetry exist. The spatial structure of the amplitude and phase variation ca uses a very special spectral noise signature of a rotating and vibrating ship propeller.

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