A variable ballast module has been developed for a NUWC UUV using the conventional concept of pumping seawater into and out of a ballast tank. The module design priorities were affordability, reliability, quiet operation and compactness. Affordability was addressed by using only commercial-off-the-shelf (COTS) hardware. Reliability was addressed by making the entire system seawater compatible, and capable of withstanding full pressure depth. Ballast weight was determined by directly measuring the tank water level.
The entire system was built with proven COTS technology. Using COTS isolation mounts a 40 dB reduction in tonals and a 30 dB reduction in broadband vibrations between the pump source and the shell were realized. Compactness was addressed by selecting the smallest available components and using computer aided design (CAD) tools to package the system.
The control philosophy was to have two independent modules, one forward and one aft, each slaved to the vehicle controller. The VC using the CTD sensor suite to determine vehicle buoyancy, would control the amount of ballast to be added or subtracted from each module to maintain vehicle trim. Each module has a local controller which response to VC commands. The module controller returns module status (net weight, tank pressure, pump and valve status, etc.) to the vehicle controller.
More information: NUWC