for ch and xh are: „ _ 



1 + 1 L= 



(9a;^ dy^ y dy 



In the three-dimensional electrical analogue, equations analogous to [9] and [10] hold 

 in V and E. Since E no longer satisfies the Laplace equation, E and V are also not inter- 

 changeable in the electrical analogy. Hence, Analogy A in which 4) = V and ijj = E is almost 

 always used in electrolytic tank studies. If Analogy B is used, it is necessary to employ a 

 sloping tank, in which the depth of electrolyte varies as 1/r. 



No stream function exists in three-dimensional flow in which there is no axis of sym- 

 metry. Analogy A may still be applied to this case, however, since there is still a complete 

 correspondence between the hydrodynamic equipotential lines and the lines of constant elec- 

 trical potential. The velocity components are still proportional to the gradient of the electric 

 potential. 



There are a number of ways in which the electrical analogies have been realized, and 

 numerous papers have been written on special problems which have been solved with the aid 

 of an electrolytic tank and other rheoelectric methods. It is not the purpose of this report to 

 review all possible uses of an electrolytic tank but rather to describe the TMB electrolytic 

 tank and the techniques developed for obtaining pressure distributions about hydrodynamic 

 bodies. 



DESCRIPTION OF EQUIPMENT AND CIRCUIT 



Considerable care is necessary in designing and constructing an electrolytic tank. The 

 walls and bottom should be plane, and opposite walls should be parallel to each other and 

 perpendicular to the bottom and to adjacent walls. Provision should be made for leveling the 

 tank to make the bottom horizontal, levels for this purpose can be seen on the sides of the 

 steel frame in Figure 1. The conducting plates which constitute the electrodes should be 

 plane and aligned parallel to each ether and perpendicular to the bottom and adjacent walls. 

 It is equally important that the rails and cross beams for supporting the probe carriage be 

 carefully aligned with the tank walls so that the probe may be moved in true longitudinal and 

 transverse directions without canting. 



The electrolytic tank which was designed and built at the Taylor Model Basin consists 

 of a steel tank with a lining of insulating material; see Figure 1. The inside dimensions are 

 46 X 27 7/8 in. on the bottom and may be fiUed to a depth of 15 in. Two pairs of heavy copper 

 electrodes are available, one pair for the long sides of the tank and another pair for the short 

 sides. The probe for exploring the electric field may be supported either on the arm of a 



