Tunable Vibration Absorber System

In Phase I a system for structural hull vibration reduction using tunable vibration absorbers will be developed which can reduce the radiated noise of small underwater vehicles using minimum weight, volume and energy. This system will use minimal power for tuning control and monitoring in comparison to the use of active noise control. This is especially important for electrically powered UUVs which carry a limited energy supply. The basic concepts to be used for adaptively controlled frequency tunable resonators were demonstrated in part in an earlier program. This program will extend tunable vibration absorber capabilities to multi modal structures such as those in torpedo hulls. Practical tunable vibration absorber devices, sized for minimum volume and weight and capable of providing specified noise reduction performance will be designed and analyzed. We will evaluate and develop additions to current tuning strategies that assure that the absorber is tuned only to frequencies related to modes which radiate well. These will range from simple lookup tables based on reciprocity radiation efficiency tests, to onboard sensors including accelerometers and hull mounted acoustic intensity probes. Associated signal processing methods capable of determining the hull mode shapes and possibly their radiation efficiency will be developed as needed. Ultimately the use of towed arrays will be available for determining real time radiated noise. The benefits of the adaptive tunable absorber system to be developed will be the capability to reduce low frequency range vibration and noise with minimum weight, small, low average power consumption devices. These devices will provide much better performance per unit weight for reducing tonal vibration than passive broadband treatments usually applied over extended areas. When combined with broad band treatments, total noise control system treatment weight can be reduced by tailoring the design of the broad band treatment to absorb the higher frequency vibration while using the tuned absorber to reduce low frequency noise. These devices will be used in applications which are sensitive to noise weight and power requirements including torpedos UUVs and advanced marine vehicles, amphibious and automotive vehicles, and manned and unmanned aircraft, particularly when variable speed operation is involved.