Figure 13-6. Back side of the wave board 



hydraulic pressure on the back side of the piston ring pushes the ram and the 

 attached wave board forward. Oil hydraulic pressure on the front side of the 

 piston ring pushes the ram and the attached wave board back. A servo-valve 

 on top of the cylinder gates the oil flow from one side of the piston ring to the 

 other to control the wave board motion. 



The hydraulic actuator is powered by a 76-gal/min (4.8-^/sec), 3,000-psi 

 (21,000-kPa) positive displacement pump. The pump is driven by a 150-hp 

 (112-kW) a-c electric motor. The hydraulic power supply is water cooled and 

 located in a covered enclosure adjacent to the actuator, as shown in Fig- 

 ure 13-7. 



Direct digital control of the wave generator is provided by a two-loop feed- 

 back system. The primary loop computes the error between the wave board 

 displacement, measured by a linearly variable displacement transducer, and 

 the computed displacement, calculated from linear-wavemaker theory 

 (Hudspeth and Chen 1981). This error is minimized by changing the input 

 displacement of the wave board. The secondary loop computes the error 



Chapter 13 Wave Generation and Data Collection Systems 



263 



