Fraunhofer-Forschungsgruppe Hydroakustik FHAK

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  • Publication
    Hydrodynamic noise research with a planing boat under acoustical free field conditions
    ( 1991)
    Bartels, F.
    A planing boat has been designed as a tool for research of hydrodynamic noise sources under acoustical free field conditions. The facility is used primarily for investigations of propeller cavitation noise in non-uniform wake flows. The objective of these tests is to disclose the influence of propeller design and wake fields upon cavitation noise. The operational test conditions are the same as for prototype surface ships. Compared to full scale the advance speed or Mach number are the same, but the Reynolds number is lower by the scale factor. The boat is equipped with several devices for observing and recording cavitation and noise. A small acoustic range with a suspended stationary hydrophone is used for recording the radiated far field noise of the test objects.
  • 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
    Geräuschabstrahlung von Schiffspropellern im Nachstrom
    ( 1991)
    Bartels, F.
    The hydrodynamic and acoustic behavior of a ship propeller is determined by its geometry, load and speed, location and by the non-uniform wake. Acoustical predictions are based either on experience with reliable propulsion systems or with restrictions on model tests. The contribution deals with results of experimental investigations of model propellers in non-uniform wake flows, carried out with a special designed facility for propeller acoustics, which operates on an natural lake. The origins of noise with its spectral properties as tonals, frequency distributions and noise modulation by the wake are discussed. Cavitation, at higher speeds unavoidable, is the predominant underwater noise source of a ship. Types of cavitation as bubble or sheet cause very different noise levels as far as uniform flow is concerned, but in non-uniform wake flows for conditions as the same propeller load and speed, the differences in noise levels diminish. Propeller vibrations are another noise source, wh ich have special acoustical line-spectra caused by the directivity pattern of excited propeller eigenfrequencies.
  • Publication
    Geräuschabstrahlung von Schiffspropellern im Nachstrom
    ( 1991)
    Bartels, F.
    The hydrodynamic and acoustic behavior of a ship propeller is determined by its geometry, load and speed, location and by the non-uniform wake. Acoustical predictions are based either on experience with reliable propulsion systems or with restrictions on model tests. The contribution deals with results of experimental investigations of model propellers in non-uniform wake flows, carried out with a special designed facility for propeller acoustics, which operates on an natural lake. The origins of noise with its spectral properties as tonals, frequency distributions and noise modulation by the wake are discussed. Cavitation, at higher speeds unavoidable, is the predominant underwater noise source of a ship. Types of cavitation as bubble or sheet cause very different noise levels as far as uniform flow is concerned, but in non-uniform wake flows for conditions as the same propeller load and speed, the differences in noise levels diminish. Propeller vibrations are another noise source, wh ich have special acoustical line-spectra caused by the directivity pattern of excited propeller eigenfrequencies.
  • 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)
  • Publication