Fraunhofer-Forschungsgruppe Hydroakustik FHAK

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  • Publication
    Finite element calculation of vibration modes of clamped propeller blades
    ( 1991)
    Homm, A.
    ;
    Bartels, F.
    The study presents results of numerical FE- calculations for modern skew propeller blades and their experimental validation. It is restricted to single clamped blades, an assumption easy to implement in the theoretical calculation but difficult to achieve in an experiment. Assumptions for the FE- calculations and the incomplete rigid clamped boundary condition in the experiment yield differences between experiment and theory, mainly in the eigenfrequencies. The fluid coupling to the structure is limited to the inviscid, incompressible case or k 1 << 1. In the limits of these assumptions the results of both, theory and experiments agree fairly.
  • Publication
    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.
  • Publication
    Richtcharakteristik einer einseitig eingespannten ebenen Platte
    ( 1991)
    Homm, A.
    ;
    Ganser, A.
    ;
    Bartels, F.
    Experiments on vibration and sound radition of a cantilever aluminium plate were carried out. For 3 eigenfrequencies the mode shapes were visualized by the Chladni method and the directivity patterns of the radiated sound were determined by the reciprocity method. The directivity patterns could be measured for nearly the whole of all directions in a 2 degree step resolution are represented in a 3-dimensional hidden line technique.
  • Publication
    Directivity pattern of a cantilever plate. Comparison of numerical results with experimental data
    ( 1991)
    Homm, A.
    ;
    Bartels, F.
    ;
    Estorff, O. von
    For a cantilever aluminium plate, the vibration modes were investigated experimentally by means of the Chladni method and numerically with the FE-method (NASTRAN). The sound radiation of three selected eigenfrequencies was determined by the reciprocity method and was calculated with a coupled FEM/BEM-approach. The comparison of the experimental and numerical results shows excellent agreement.
  • Publication
    Ergebnisse einer theoretischen und experimentellen Modalanalyse von Propellern
    ( 1988)
    Bartels, F.
    Bestimmung der Eigenmoden für Schiffspropeller. Zunächst wird die dynamische Strukturanalyse an einzelnen eingespannten Flügelblättern behandelt. Numerische FE-Rechnungen werden mit experimentellen Ergebnissen verglichen. Ergebnisse von experimentellen Untersuchungen bezüglich der Kopplung der Nabe bei mehrflügeligen Propellern werden diskutiert. (FHAK)
  • Publication
    Modulation of high-frequency propeller cavitation noise in a non-uniform wake
    ( 1987)
    Bartels, F.
    Mit dem FHAK-Propellermessfahrzeug "Vitesso" wird das visuelle und akustische Kavitationsverhalten eines 2-fluegeligen Modellpropellers im ungleichfoermigen Nachstrom untersucht. Zur Aufdeckung der Kurzzeit-Struktur des Geraeusches wurden Amplitudenmodulationsspektren sowie auf verschiedene Nachstromsektoren begrenzte Geraeuschspektren herangezogen. (IHAK)