Wave Generating Software at the U.S. Naval Academy

Abstract

Since the 23rd ATTC in 1992, the U.S. Naval Academy Hydromechanics Laboratory (NAHL) has replaced and updated all of the computer hardware and software used to drive its three wavemakers. Until last year, some of the original equipment that was installed in the mid 1970's was still in use. The old system was cumbersome to use by today's standards, but was capable of generating very good waves. Eventually, the computer hardware became unreliable and had to be replaced. This paper describes the replacement system that was put together at NAHL. The new system is based on the old one, but wherever possible uses “off-the-shelf” components that can be easily replaced as technology advances. The paper gives an overview of the hardware and software used to drive the wavemakers and describes the types of waves that can be generated with the new system. Each time new wavemaker drive signals ar. e created, decisions must be made about digitization rates, data analysis frame lengths, etc. The paper discusses tradeoffs involved in selecting those parameters and their impact on the waves produced. Also, some of the subtleties involved in creating wavemaker drive signals are mentioned; for instance, the splicing of drive signal frames when the endpoints don't match up. Finally, details are given on a procedure used to adjust and refine drive signals so that the measured wave spectrum more closely resembles the desired spectrum.