Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014
When there is a family of graphics, a law by which the first graphic is transformed into the last one can also be determined by some parameter. When the law of change is known, the inter-values of graphics can also be determined, i.e. the interpolation of graphics can be done, as shown in Figures 9, 10 and 11.
The examples with the families of graphics and the interpolation demonstrate how, on the basis of test results of the model propeller series, we can obtain the curves of the coefficients KT and KQ of any model which is not a model of the series, i.e. a model with any geometric quantities Ae and P within the range of the series, and any value of the cavitation number within the range of the tests. The procedure is carried out in three steps.
In the first step, the results of testing of all models of the series are brought down to the required cavitation number, i.e. a new family of twelve graphics with the same
cavitation number is obtained. Then, these
graphics are brought down to the required value of P/D. Again, a new family of four graphics with the same value of P/D is obtained. In the third step, these
graphics are brought down to the required value of Ae /A0, i.e. only one graphic with the required values of quantities Ae /A0, P/D and is obtained. In this way an interpolation of a new propeller into the propellers of the series is done, as shown in Figure 2 (the propeller with bold
outline). Its curves of the
coefficients KT and KQ are obtained for a certain value of the cavitation number. The result of the interpolation is showed in Figure 12. In practice, the
required values of , P/D and Ae /A0 are determined from the conditions of the project. In this example
they are arbitrarily determined.
The curves of the coefficients KT and KQ are obtained through interpolation procedures, and these procedures are described by procedures of the computer program which directly use the results of the experiments as basic data. Consequently, mathematical expressions with coefficients are replaced by program procedures that use more memory and computer time, but produce more accurate and more reliable results than mathematical functions.
for all values of Ae /A0
10KQ
KT
Figure 8: Model propellers with: P/D=1.66, =0.50
B-52
©2014: The Royal Institution of Naval Architects
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