Low Noise Mechanical Drive Propulsion System Alternatives
For more than 80 years, mechanical drive propulsion systems consisting of reduction gears and various prime movers have proven their reliability and performance onboard numerous commercial and navy ships. GE has more than 40 years of continuous experience in the design, manufacture and performance/noise testing of SSN, SSBN, CVN and DDG main propulsion reduction gears, and has reportedly accumulated the largest industrial database of Naval propulsion system noise performance. This database was used extensively in the development of the DDG 51 main reduction gears (MRGs), and yielded a system with noise performance at least 18 dB below specification. Based on this extensive experience, GE believes that mechanical drive propulsion systems can deliver the low noise, high power density, operational flexibility, reliability and performance needed to satisfy 21th century Naval ship mission requirements. Currently, GE has approximately 240 MRGs in service on over 170 U.S. Navy surface ships and submarines. These MRGs combine high reliability with high availability (approx. 99 percent), high efficiency (greater than 98 percent), high power density (generally less than 0.1 lb./ft.-lb. output torque), and very low maintenance designs. GE's low noise propulsion gearing satisfies the operational and noise requirements of these ships.
Propulsion System Noise Sources The first step in developing a low noise propulsion system is to identify and characterize the noise sources. In general, a propulsion system consists of one or more prime movers (gas turbines, steam turbines, electric motors, diesel engines), reduction gears, and isolation systems; a ship foundation; and various auxiliary systems. The noise generated by the propulsion system includes contributions from all of these components. Table 1 (page 40) presents a list of the typical noise sources associated with the principle propulsion system components and identifies general approaches to control these sources. Note that the mounting system (isolation system plus ship foundation) is a control mechanism for all propulsion system noise sources.