As limiting values of vibration are part of the building contract, it is important for the building shipyard to receive soon substantial predictions of the vbibration level. In order to execute corresponding calculations by means of structural analysis programs (FEM), it is necessary to know as clearly as possible the forces which excite the structures. The propeller induced pressure pulses have turned out to be a main source of excitation. This paper is based on an existing vortex-lattice method and develops a prediction procedure by which it is possible to make a substantial prediction of the pressure pulses during the early design stage. Therefore the numerical characteristics and the numerical stability of the chosen method were examined in a first step. In a second step the influence of the wake was investigated. The difficulty was that the necessary wake for calculation does not exist, because in a model testing tank only the nominal model wake is measured. To handle this problem two procedures were examined within the scope of this paper. Firstly a method of Yazaki was applied to adjust the distribution of isotachyls of the wake to the conditions under full scale. Secondly a method was developed and implemented to calculate the contraction effect of the propeller on the wake. To evaluate the method a data set of 21 propellers was examined. For these propellers measurements have been done by model-testing establishments. For most of the propellers both the cavitating and the noncavitating part of pressure pulses have been measured. On the basis of this data set, it was investigated, what kind of correction method produces the best results of calculation. Further a statistical correlation method was developed in order to calibrate the calculation results by the existing empirical data.


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    Title :

    Reliable prediction of propeller-induced pressure pulses during the early design stage


    Contributors:

    Published in:

    Publication date :

    2006


    Size :

    6 Seiten, 15 Bilder, 15 Quellen



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English