Very Low Structure Borne Noise Unit Enclosures for COTS Modules

Structure borne noise generated by cooling fans and other moving components in COTS can be transmitted to the ship's structure in a hard deck environment. The research proposed here is to evaluate the feasibility of using low-density granular fill (LDGF) for the purpose of reducing this structure borne noise to a level that is considered innocuous. LDGF, a passive damping treatment, has been shown to be effective in significantly reducing structure borne sound in truss like structures used in the Navy cradle program. In lightly damped structures subject to broadband excitation, it is not uncommon to achieve greater than 20 dB reduction in bending wave resonances, even at frequencies as low as 150 Hz. For compressional and torsional resonances the reduction is commonly greater than 10 dB. The fundamental technology is patent pending with several application patents in draft. The technical approach proposed herein is to evaluate the feasibility of constructing unit enclosures employing low-density granular fill in which COTS equipment may be mounted. The advantages of this approach are great in terms of cost, weight, simplicity, ease of maintenance, and reliability.