Model and analysis of a cylindrical in-line hydraulic suppressor with a solid compressible liner

An in-line hydraulic noise suppressor with a lossy, compressible liner made of foamed polyurethane liner is introduced which is intended to provide an alternative to current in-line silencing devices using compressed nitrogen gas volumes. The liner is engineered to be compressible at elevated pressures, such that it can provide effective noise abatement for practical hydraulic systems. In support of such work, a multimodal model is developed to characterize the device and the liner material. Because the hydraulic system is pressurized after insertion of the liner, the model must address liner compression and the corresponding small gaps introduced in the expansion volume; additionally, both compression and shear wave propagation must be considered in the liner. Several mode matching solutions are investigated, and a pseudoinverse mode matching method is found to provide good convergence characteristics. The multimodal model is validated against a finite element model, and also used in an optimization algorithm to estimate the material properties of a prototype liner using experimental transmission loss data. Experimental results show broadband transmission loss performance at 2.8 MPa system pressure; transmission loss decreases with increasing system pressure, and data at 4.1 MPa system pressure produces about 4 dB less transmission loss than a similarly sized commercial device. The multimodal model with estimated material properties at 2.8 MPa achieves a root mean squared error of 1.7 dB or less for two different length devices over a frequency range of 50–2000 Hz.