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    Critical Speeds of an HJ364 Water Jet Assembly

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    Author
    Brittenden, Ashley Edward
    Date
    2012
    Permanent Link
    http://hdl.handle.net/10092/7551
    Thesis Discipline
    Mechanical Engineering
    Degree Grantor
    University of Canterbury
    Degree Level
    Masters
    Degree Name
    Master of Engineering

    With a new range of water jet assemblies under development, CWF Hamilton & Co. Ltd. highlighted the need to establish a validated model for predicting critical speeds. A review of the relevant literature revealed a significant lack of information concerning the operating properties of a lightly loaded, water lubricated marine bearing. Therefore, an instrumented test rig based on a CWF Hamilton & Co. Ltd. ‘HJ364’ water jet assembly was established to evaluate critical speeds and validate the predictive models.

    A number of analytical and numerical models for predicting critical speeds were investigated. Geometric modifications were made to the test rig and the changes in critical speeds were observed. The ability of the predictive models to measure these observed critical speeds was examined.

    Driveline mass and driveline overhang were found to have the most significant effects on critical speeds. Modifications to the thrust bearing housing, the impeller mass, the tailpipe stiffness and the marine bearing resulted in no significant shift in critical speeds. However, a change to the geometry of the thrust bearing resulted in a significant shift. This indicated that the thrust bearing was not performing ideally in the test rig.

    All three models predicted changes in critical speeds relatively accurately. However, the estimates of the critical speeds themselves were somewhat conservative; approximately 10 to 15 percent lower than those measured. Linearisation of the thrust bearing geometry is recommended if greater accuracy is to be achieved. Of all the predictive methods, the Myklestad-Prohl transfer-matrix and the Isolated-Mainshaft finite-element were deemed to be the most flexible and suitable for CWF Hamilton & Co. Ltd.

    Subjects
    Water Jet
     
    Critical Speeds
     
    Vibration Analysis
     
    ANSYS
     
    Marine Bearing
     
    Hydrodynamic Bearing
     
    Rayleigh
     
    Dunkerley
     
    Transfer-Matrix
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    • Engineering: Theses and Dissertations [2165]
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