Figure 13-5. The filling port 



depth of 18 ft (5.49 m). The board is a flat aluminum plate on the seaward 

 side with webbed reinforcement welded to the back side of the structure. A 

 hydraulic actuator is attached to the back side of the wave board via a clevis 

 at an elevation of 10 ft (3.9 m) above the bottom of the channel. The actuator 

 is an 8-in.- (20.3-cm-) diam hydraulic ram with a stroke of ±30 in. (±76 cm) 

 (Figure 13-6). 



The wave board operates with water on one side. With no water on the 

 back side, waves are generated only on the seaward side, requiring half the 

 power of a wave generator with water on both sides. Polyethylene wiping 

 seals attached to the vertical edges of the wave board slide along stainless steel 

 cladding on the sides of the concrete wave channel. A pivoting knife-edge 

 seal minimizes seepage at the bottom of the wave board. The total leakage 

 rate for 15 ft (4.6 m) of head on the wave board is in the range of 5 to 

 10 gal/min (0.3 to 0.6 I /sec). A sump pump returns this water to the seaward 

 side of the board. 



Fifteen feet of head provide a hydrostatic pressure force of approximately 

 84,000 lb (374,000 N) on the wave board. This head is overcome by apply- 

 ing nitrogen gas pressure to the back face of the hydraulic ram. The ram 

 places the hydrostatic force in equilibrium with a gas spring, requiring no 

 additional power from the hydraulic power supply. Oil hydraulic pressure is 

 applied to a piston ring at the center of the ram, isolated from the ambient 

 pressure by fore and aft ring seals set in the walls of the ram cylinder. Oil 



262 



Chapter 13 Wave Generation and Data Collection Systems 



