Savitsky 



The envelope of wave height at the moving probes is given in 

 Figs, 16 and 17 for wave lengths of 2 ft and 6 ft respectively. The 

 wave probe positions are at distances of 1 ft and 6 ft aft of the grid 

 and just off its centerline. The grid was 3 ft wide, had a draft of 

 1 . 7 f t and a mesh size of 2. 7 inches. Figure 16 presents results 

 for grid speeds of 1 . and 1.6 ft /sec, while Fig. 17 is for speeds of 

 1,0 and 2.6 ft/sec. It is seen that there is a continuous reduction in 

 wave height with time. For the 2 ft long wave and a grid speed of 

 1.0 ft/sec, the amplitude is reduced to nearly 10 per cent of its 

 initial value after approximately 20 ft of grid travel. It remains 

 essentially at this value for the length of the test record which ex- 

 tended for 30 seconds after the grid was stopped. The effect of 

 increasing the speed of the grid from 1 . to 1.6 ft /sec reduced the 

 wave height to nearly 8% of its initial value. It is to be noted that 

 there is a distinct absence of oscillations in these time histories. 



The results for the 6 ft long wave (Fig. 17) are essentially 

 similar to those for the 2 ft long wave. At a grid speed of 1 ft/sec, 

 the wave height is reduced to approximately 35 per cent of its initial 

 value. When the grid speed was increased to 2.6 ft/sec, the wave 

 height was reduced to 1 2 per cent of its initial value. 



An overwater photograph of the wave deformation for a typical 

 two-dimensional test is shown in Fig. 18. The reduction in wave 

 height along the centerline wake area and the amplification outside 

 this area are clearly visible in this photograph. 



Fig. 18 Typical wave deformation for two-dimensional grid 



418 



