Development of an analytical solution of modified Biot's equations for the optimization of lightweight acoustic protection.

During lift-off, space launchers are submitted to high-level of acoustic loads, which may damage sensitive equipments. A special acoustic absorber has been previously integrated inside the fairing of space launchers to protect the payload. A new research project has been launched to develop a low cost fairing acoustic protection system using optimized layers of porous materials covered by a thin layer of fabric. An analytical model is used for the analysis of acoustic wave propagation within the multilayer porous media. Results have been validated by impedance tube measurements. A parametric study has been conducted to determine optimal mechanical and acoustical properties of the acoustic protection under dimensional thickness constraints. The effect of the mounting conditions has been studied. Results reveal the importance of the lateral constraints on the absorption coefficient particularly in the low frequency range. A transmission study has been carried out, where the fairing structure has been simulated by a limp mass layer. The transmission loss and noise reduction factors have been computed using Biot's theory and the local acoustic impedance approximation to represent the porous layer effect. Comparisons between the two models show the frequency domains for which the local impedance model is valid.

[1]  J. Bolton,et al.  Oblique incidence sound transmission through multi-panel structures lined with elastic porous materials , 1987 .

[2]  Guy Bonnet,et al.  Basic singular solutions for a poroelastic medium in the dynamic range , 1987 .

[3]  Raymond Panneton,et al.  Numerical prediction of sound transmission through finite multilayer systems with poroelastic materials , 1996 .

[4]  A. Cummings,et al.  Impedance tube measurements on porous media: The effects of air-gaps around the sample , 1991 .

[5]  Raymond Panneton,et al.  Enhanced weak integral formulation for the mixed (u_,p_) poroelastic equations , 2001 .

[6]  Franck Sgard,et al.  Behavioral criterion quantifying the effects of circumferential air gaps on porous materials in the standing wave tube , 2004 .

[7]  J. Allard.  Propagation of Sound in Porous Media: Modelling Sound Absorbing Materials , 1994 .

[8]  Raymond Panneton,et al.  BOUNDARY CONDITIONS FOR THE WEAK FORMULATION OF THE MIXED (U, P) POROELASTICITY PROBLEM , 1999 .

[9]  J. S. Bolton,et al.  Normal incidence sound transmission through double-panel systems lined with relatively stiff, partially reticulated polyurethane foam , 1993 .

[10]  J. S. Bolton,et al.  SOUND TRANSMISSION THROUGH MULTI-PANEL STRUCTURES LINED WITH ELASTIC POROUS MATERIALS , 1996 .

[11]  M. Biot.  Theory of Propagation of Elastic Waves in a Fluid‐Saturated Porous Solid. I. Low‐Frequency Range , 1956 .

[12]  Yeon June Kang,et al.  Effect of circumferential edge constraint on the acoustical properties of glass fiber materials , 2001 .

[13]  Franck Sgard,et al.  On the modeling of sound radiation from poroelastic materials , 2006 .

[14]  Raymond Panneton,et al.  A mixed displacement-pressure formulation for poroelastic materials , 1998 .

[15]  Franck Sgard,et al.  On the use of poroelastic materials for the control of the sound radiated by a cavity backed plate , 2006 .