TM No. 377 



Figure 11-17 shows a second system configuration, in which the wave 

 meters are spatially separated. The cylinders are mounted linearly so that 

 their axes are either collinear in the vertical (as in figure 11-17 ) or 

 parallel in the horizontal. The spatial separation permits simultaneous 

 measurement of the vertical or horizontal velocity component of flow at 

 two different vertical levels. Mounted on a rigid brass rod 2 cm in 

 diameter by means of stainless steel hose clamps, the cylinders can he 

 separated up to 3 meters when the rod is suspended vertically. This con- 

 figuration is termed the Linearly Mounted Ducted Meter System (LMDUM i) 

 because of the straight shaft suspension of the cylinders. 



Since the modified smaller-scale ducted meters were, in a sense, an end 

 product of the instrument development and of the knowledge gained in the 

 study and use of the previous instruments, a very complete examination of the 

 dynamic characteristics of the new meters is requisite. 



Calibration — The first calibration of the GMDUM II model was, at most, 

 a rough estimation of the characteristic response. As noted earlier, the 

 rotating arm system had certain limitations that prohibited precise deter- 

 mination of the reaction of the orthogonally mounted meters to the off- 

 angle flow. The calibration data, however, did permit a fair interpreta- 

 tion of these preliminary measurements of wave motions (listed as BBELS 

 5 and 7 in appendix B). 



For the OMDUM III system, which is a more precise instrument for 

 measuring wave particle motions in the XZ plane, a more exacting calibra- 

 tion was required. System calibrations were made in the orthogonal con- 

 figuration ( OMDUM III) and also with the cylinders individually mounted 

 in the linear configuration (klMDUM I). 



Towing Tank and Associated Equipment. The new wave meters were calibra- 

 ted in the Capt. Mary B. Converse Towing Tank in Marion, Mass. These experi- 

 ments were made to determine system response to steady and accelerated recti- 

 linear flow, both end-on and at various angles between the cylinder axis and 

 the relative direction of towing. 



The Converse Towing Tank is a privately owned installation. Calibration 

 was therefore accomplished with the assistance of the Braincon Corporation 

 of Marion, Mass, The tank is about 21 meters long, with a rectangular cross- 

 section 71 cm wide and 66 cm deep. The towing carriage support for the 

 individual and the coupled meters is shown in figures II-18 and 11-19 respec- 

 tively. The carriage is supported by a center beam upon which rubber caster 

 wheels move. The carriage is towed by a 3/32-inch-diameter st ainl ess steel 

 aircraft cable, which is run through a shieve at each end of the tank. Thus, 

 the carriage can be moved freely between the two shieves. The tight clearance 

 of the wheel and shieve drive permits a minimum amount of free play in the 

 track mount. 



The power drive of the system is a 10 hp electro-hydraulic motor. A 

 small pulley (10 cm diameter) on the motor shaft is connected by a rubber 



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