TM No. 377 



CHAPTER VI 



CONCLUSIONS AND SUGGESTIONS FOR FURTHER STUDY 



The aims of this study were of a twofold nature ; (l) to design and fabri- 

 cate an instrument system to measure wind wave particle motions in situ] and 

 (2) to make subsequent exploratory measurements with emphasis on describing 

 momentum and energy transfer processes within the waves. 



The scope and the number of problems examined using the wave meter data 

 make it difficult to integrate completely all the results discussed in 

 chapter V. Hence, only highlights and conclusions are presented in this 

 summaryo The extent to which the goals were accomplished is left for the 

 reader to determine. Some of the recommended future studies are actively 

 being pursued. 



Instrumentation 



The apparent attributes and shortcomings of both the orthogonally mounted 

 wave meter ( OMDUM III) and the linearly mounted wave meter (LIMDUM I) are 

 briefly stated, along with certain recommended improvements in the hardware, 

 recording systems, calibration and measurement techniques. 



Attributes of Instrumentation Used — The ducted cylinder detectors are 

 simple in construction, inexpensive, and easy to fabricate. The impellers 

 and carborundum steel and quartz bearings are simple to replace. 



The wave meter electronics, consisting of inexpensive miniature induction 

 coils (potted in epoxy resin) that interact with tiny magnets mounted at the 

 tips of the impeller blades, were found to be satisfactory. The coils are 

 isolated from the sea water and require no power input or amplifier on the 

 output. The voltage signals are fed directly to a strip chart recorder through 

 a watertight cable. No electrical short or electrical signal interference 

 occurred during two years of measurements at BEELS. 



The individual ducted impellers are simple to calibrate for end-on or off- 

 angle, steady or accelerative, rectilinear flow. The angular velocity of the 

 impeller is directly proportional to the fluid flow through the impeller 

 (whether it be water or air). Hence, only a minimum number of points are 

 needed to establish the calibration curve. Calibration can be made in a 

 wind tunnel or a towing tank or basin. Further, the ducted meters were easily 

 fabricated to have virtually identical calibrations, including forward and 

 backward flow through the cylinders. 



The data obtained with the four different meters ( OMDUM I, II, III and 

 LIMDUM I) displayed consistently similar particle velocity characteristics and 

 produced similar auto-spectra of the motions. This fact indicates that most of 

 the meter response is caused by true motions, and that the signature of the 

 individual wave meters upon the data is minimized. Also, similar results were 

 obtained in spite of the use of different mounting or suspension methods, some 

 of which were less stable than others. 



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