289 



larger regular waves bbs.erved at a given fetch. In general, smaller ripples are 

 superimposed on the larger disturbances. 



In this paper, a number of experimental results are discussed which 

 refer to the mean air and water motion as indicated in Figure 1. Measure- 

 ments of the statistical properties of the wind generated waves, including 

 the autocorrelation and spectral density functions, are examined in the light 

 of other properties of the fluid motion. There has been no attempt to model 

 the ocean-atmosphere interaction with the laboratory equipment. However, it 

 will be seen that a niimber of experiments for fluid flow in the channel are 

 at least qualitatively related to the observed small scale interaction between 

 the sea and the atmosphere . 



II. EXPERIMENTAL EQUIPMENT AND PROCEDURE 



The experiments were conducted in the wind- water tunnel at Colorado 

 State University. This facility, shown schematically in Figure 2 consists 

 of a tunnel or a closed channel 0.6l m wide by 0.j6 m high whose plexiglass 

 test section has a length of about 12 m. During operation, the maximum depth 

 of water is approximately 15 cm. Air is sucked through the tunnel at 

 velocities up to l8 mps by a large axial fan at the outlet. The inlet cone 

 is designed to give a k/l contraction ratio. Two fine mesh screens are 

 placed in the inlet cone . Honeycombs are placed just upstream of the outlet 

 diffuser to minimize the axial rotation in the air induced by the fan. 

 Sloping beaches are placed at the inlet and the outlet to prevent the reflec- 

 tion of waves. The "beaches" are constructed of aluminum honeycomb. The 

 inclines are shaped in such a way that as smooth as possible a transition can 

 be effected in the air- water flow. In this study, the bottom of the tunnel 

 was smooth. 



The air flow through the tunnel was measured by a pitot-static tube 

 placed on a carriage in conjunction with a capacitative pressure transducer. 

 The probe could be positioned anywhere in the section of the tunnel from the 

 bottom to a level about 10 cm from the top. 



The pressure gradient of the air and the depth of the water were measured 

 every h feet down the tunnel with piezometer taps connected to a set of 

 manometers . 



Phase speeds and lengths of waves were determined from photographs taken 

 with a movie camera. The length for successive waves was measured from the 

 movies by comparing the distance between crests with a ruler in the picture. 

 The phase velocities of waves referred to a fixed point were estimated by 

 measuring from adjacent frames the distance traveled by a given crest during 

 the time between successive frames. Time intervals between frames were read 

 off a timer that was shown in the film. 



To measure the change in the height of the water, a capacitance probe 

 was used which is similar to Tucker and Chamock's (1955)- This probe con- 

 sisted of a 3k gauge magnet wire stretched vertically along the center 



