CONCLUSIONS 



1. The acoustic flowmeters, for several reasons, are not suitable for 

 measurement of steady-state currents in shallow water. 



2. The nonlinear outputs and the noncosine response of impellor 

 flowmeters give rise to false dc levels when filtered. 



3. The inherent hydrodynamic problems of the drag force method are too 

 great. 



4. The necessary support effort required for the Lagrangian method makes 

 its employment impractical. Nonlinear forces produce false dc levels. 



5. The electromagnetic flowmeter is inherently capable of measuring 

 direction of current; the output is linear. Direction response is unknown for the 

 tube configuration. 



RECOMMENDATIONS 



The electromagnetic method is recommended for the intended use. 

 Specific recommendations are as follows: 



1. Investigate new configurations using ac fields that will provide 

 minimum hydrodynamic interference and possibly measure flow over large dis- 

 tances. 



2. AC Magnetic Field Tube Configuration (fig. 8): Experimentally deter- 

 mine the directional response of this type. Investigate effects of different 

 length-to-diameter pipe ratios and pipe fairing shapes in order to obtain a nearly 

 cosine response. By using the best response curve obtained, calculate the 

 expected errors (similar to example on p. 25). Determine if these errors are 

 acceptable. 



3. Earth's Field Type: Use of this method is recommended only if a 

 feature for zeroing the meter is employed (similar to description by Mangelsdorf'^'^). 



41 



