Core value and theoretical logic of structure-borne noise .

Part 2: blocking mass and complex huge systems

WU Chongjian1，2，CAI Daming1，ZHU Yingfu1，2 1 China Ship Development and Design Center，Wuhan 430064，China 2 National Key Laboratory on Ship Vibration and Noise，Wuhan 430064，China Abstract：［Objectives］ Compared with 1-stage, 2-stage and raft vibration isolation, the attenuation of longitudinal wave and bending wave transfer for blocking mass is low，and relatively few scholars are interested in studying the application of these measures. However，with the development of submarine noise and vibration reduction，designers should survey such less effective measures as blocking mass. ［Methods］In this paper，the attenuation characteristics of blocking mass in a simple system are analyzed via the Wave Propagation Approach（WPA）. Combined with engineering practices，a "statistical concept" of blocking mass in complex huge systems is proposed.［Results］The results show that the accumulative attenuation of the structure-borne noise of blocking mass in such huge systems as submarines is no longer low，though the attenuation is low for a single blocking mass. As such low-impedance "soft measures" as vibration isolation are not applicable in many cases，the only way to improve the acoustic signature of a submarine is to apply high-impedance "hard measures" in acoustic design，forming a hypostatic union with structural and functional design. In addition，structure-borne noise with the "discontinuity point" concept and statistical ideas should be important subjects for future study.［Conclusions］ The gradual transformation and evolution from "soft measures" to "hard measures" form the core value of the leaping acoustic signature of submarines，and this is the source of innovative inspiration. Key words：structure-borne noise；wave；blocking mass；discontinuity point；complex huge system