Propeller Excitation and Response of 230000 TDW Tankers 



Comparisons between the method described and several one- 

 blade dynamometer test (4 degr. of freedom) results serve to illu- 

 strate that the method in question is satisfactory for engineering pur- 

 poses unless being faced with a very sharp wake peak. 



Including successive radial displacements of wake grids we 

 have observed that a large radial velocity variation, as experienced 

 behind some ships, is accompanied by a corresponding change of hy- 

 drodynamic loading /l/. In fact no method for calculation including 

 the effect of start vortices (or not) will respond correctly to the si- 

 tuation demonstrated unless extending the boundary to positions well 

 outside the propeller disc. 



The non-linear effects referred to in the paper are produced 

 by separated flow near to the blade tip together with other tip effects 

 all related to boundary layer flow. Full scale observations have clear- 

 ly demonstrated that cavitating flows across the tips will account for 

 the main portion of the unstable cavity volume. Hence, we must draw 

 attention to the tip region - in particular - when predicting pressure 

 impulses from propeller cavities. Thus we discuss a region of the 

 blade in the present paper which cannot be considered to-day by other 

 means than experiments and corresponding emperical "separation 

 angles". 



Regarding the importance of the wake scale effect on the wake 

 distribution we will not speculate very much (the scale effect on mean 

 wake is considered when determining the values of J and a defining 

 the loading case). We will only mention that for a tanker research 

 project, now being tested in the large tunnel of SSPA, an attempt is 

 made to estimate the influence of Reynold's number by repeating the 

 tests with the same model, part of the parallel length having been cut 

 away. 



Records of blade stresses and fluctuating bearing forces on a 

 large tanker which are reported in /2/, illustrate that model and full 

 scale fluctuating stresses/forces are surprisingly similar. 



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