11 



bulkhead vas operated in such manner that its forward motion displaced 

 water from the basin into the model, thus reproducing the rising phase 

 of the hurricane tide, while its backward motion permitted water to flow 

 from the model into the basin, thus producing the falling phase of the 

 tide. The drive motor was of the three-phase type to permit the neces- 

 sary reversal in direction of movement of the bulkhead, and a PIV (posi- 

 tive, infinitely variable) speed control lonit was installed in the drive 

 mechanism to permit a highly accurate control over the speed of the bulk- 

 head. This system was found very satisfactory for generation of hurri- 

 cane tides, in that the apparatus could be quickly adjusted to reproduce 

 any desired ocean tide with a minimum of effort, and that tide could then 

 be duplicated accurately as many times as necessary. The hurricane tide 

 generator system is shown on fig. 6. 



18. Because of the very rapid rate of rise and fall of hvirricane 

 tides, recording tide gages were utilized to measure and record these 

 tides at various locations throughout the model. The gages consisted of 

 a roll of recording paper moving on a drum which was revolved at a known 

 and constant speed by a small synchronuous motor, and a float- supported 

 pen which inked a continuous record of water- surface elevation on the 



'»8*^ES^g.,° 



Fig. 6. Hurricane tide generator 



