271 



13 



1.0 

 0.8 

 0.6 

 0.4 

 0.2 

 



1.0 

 0.8 

 0.6 

 0.4 

 0.2 

 



"KRYM"-Type Tanker 



' o o o — Model, Experiment 



- Correlation 



2.4 



LWL 



Taniguchi and Fujita 

 Experiment, 1969 

 o o o — Model, Experiment 

 Ship, Experiment 



0.8 1.6 



(Y/L) X 10^ 



2.4 



FIGURE 8. Comparison of velocity distributions for 

 model and ship wake. 



3. PROPELLER EFFECT UPON THE WAKE DISTRIBUTION 



Consideration of the wake scale effect when using 

 the nominal velocity field as initial data will not 

 always improve the agreement between the calcula- 

 tions and full-scale measurements of nonstationary 

 loads acting on the shafting and, particularly, of 

 the constant bending moment component defined by 

 the analysis of the first harmonic. Systematic 

 model basin test results indicate that signigicant 

 variations of the velocity distribution at the stern 

 may be due to the propeller performance. Several 

 factors are to be taken into account when analysing 

 the causes of this phenomenon. The most important 

 among these are the propeller- induced acceleration 

 of flow and, hence, the decrease of the layer thick- 

 ness upstream, and the effect of propeller- induced 

 radial velocity in the immediate vicinity of the 

 propeller. 



Thus it becomes necessary to investigate the 

 ship-hull boundary layer and the wake taking into 

 account the transverse pressure gradient. Semi- 

 empirical theories do not permit this problem to 

 be solved and are adequate only for the most ap- 

 proximate estimations of the flow history. There- 

 fore, just as in studying some features of the 

 nominal wake flow mentioned above, preliminary 

 theoretical investigations of the velocity field 

 under simplified conditions are of great importance 

 here. Although these results are not directly 

 applicable to the ship, they may be useful for a 

 better understanding of the main relationships of 

 the phenomena under study and for the devleopment 

 of practical methods to obtain the effective wake. 

 In this connection one cannot but mention the 

 important contribution of American scientists to 

 the investigation of the axisyrametrical problem, 

 particularly, the latest works by Huang and Cox 

 (1977) . 



To obtain approximate estimates of the effective 



relation reveals the characteristic features of 

 variation in the velocity field and its harmonic 

 spectrum. However, these conclusions cannot be 

 considered reliable enough; they need further veri- 

 fication. 



Model "d" 



Several years ago, simulation of the velocity field 

 in the case of afterbody boundary layer separation 

 attracted the special attention of researchers in 

 connection with the development of very large tankers 

 with high block coefficients and a tendency to de- 

 crease the length-to-breadth ratio. Although this 

 problem has lost its vitality by now, studies in 

 this field are being continued. The attempts in 

 Japan and in the Soviet Union to theoretically and 

 experimentally evaluate the scale effect of separa- 

 tion of three-dimensional and even two-dimensional 

 boundary layers do not yet allow any definite con- 

 clusions to be made, even regarding the qualitative 

 aspect of the phenomenon, or the development of the 

 most approximate scheme of variation with Rn number, 

 not only in the velocity distribution, but also in 

 the mean value of the wake . Thus the problem of 

 simulating the characteristics of flow at the stern 

 with the boundary layer separation remains one of 

 the unsolved problems in ship hydrodynamics . 



Tanker, Taniguchi and Fujita 

 Experiment, 1969 



3 0.5 



FIGURE 9. Circumferential velocity distribution and 

 harmonic spectrum for model and ship. 



