Comfort plays an increasingly important role in the interior design of airplanes. In general, comfort is defined as ‘freedom from pain, well-being’; in scientific literature, indeed, it is defined as a pleasant state of physiological, psychological and physical harmony between a human being and the environment or a sense of subjective well-being. Cabin noise in passenger aircraft is one of the comfort parameter, which creates straightaway discomfort when exceeding personal thresholds. In general the cabin noise varies by the seat position and changes with flight condition. It is driven by several source types, which are transmitted through different transfer paths into the cabin. In the forward area the noise is mainly dominated by the turbulent boundary layer described by pressure vortexes traveling along the fuselage surface.

In this paper evaluation of the Sound Pressure level, for the medium-high frequency range, of an aircraft fuselage section at different stations and locations inside the cabin has been performed numerically by using Statistical Energy Analysis (SEA) method. Different configurations have been considered for the analysis: from the “naked” cabin (only primary structure) up to “fully furnished” (primary structure with interiors and noise control treatments) one. These results are essential to understand which are the main parameters affecting the noise insulation. Furthermore, the Power Inputs evaluation has been determined to see the contribution of each considered aeronautic component on the acoustic insulation. Finally, the effect of a viscoelastic damping layer embedded in the glass window has been evaluated.

To know more: https://www.sciencedirect.com/science/article/pii/S1270963818315372

The sound field in train compartments, treated as a series of connected air cavities, is modelled using statistical energy analysis, SEA. For the case under study, with five cavities in series and the source in the second cavity, a closed-form solution is obtained. An adjusted SEA model is used to predict the rate of spatial decay within a cavity. The SEA model is validated using results from a ray tracing method and from scale model measurements. For the octave bands 500–4000 Hz, good agreement is shown between the results from measurements, the ray tracing and the SEA model, for the two saloons closest to the source cavity (a vestibule).

The SEA model was shown to slightly underestimate the rate of spatial decay within a cavity. It is concluded that a reasonable cause is the additional diffusion due to the seating.

To know more: https://www.sciencedirect.com/science/article/pii/S0003682X11002696

The 12th chapter introduces the basic principle of statistical energy analysis (SEA) and the application of SEA method in analyzing the tire/road noise.

First, the basic theory of SEA method is introduced, including basic equation, energy description of subsystem, damping loss factor, and coupling loss factor. And the partition of subsystems and the calculation methods of damping/coupling loss factors are also discussed.

Second, the construction methods of two kinds of tire SEA models with/without cavity are described, and the identification methods of parameters in the models are introduced and analyzed. And the simulation results are discussed.

At last, the application of SEA method on the tire/road noise modeling and simulation of a passenger car is shown, and the simulation results are analyzed.

To know more: https://www.sciencedirect.com/science/article/pii/B978012818409700012X

In a thesis at LTDS in 2005, a new method is proposed to predict the noise radiated in the high frequency range by a structure vibrating in the low frequency range. This method is called hybrid as it couples two methods valid on different frequency ranges.

The application proposed is concerned with the noise radiated by the casing of a gearbox inside an engine compartment. The vibratory behavior of the casing is induced by the excitation produced by meshing process, the static transmission error. It is computed with an original method allowing the solving of parametrically excited systems. Equivalent energy sources are introduced to reproduce the noise radiated in the free field by the casing of the gearbox. Each source is the sum of three contributions due to a pressure source, a velocity source and an intensity source. Analytical formulations for the amplitudes and directivity diagrams of these sources are proposed. They are then used in the radiative transfer method based on the radiative transfer exchanges in thermics which estimates the acoustical field inside the engine compartment. This method is generalized in this work to account for acoustical diffraction.

The hybrid method has been applied to a baffled plate, and to a ribbed plate whose surface vibratory and pressure fields are previously measured, and results have been compared to those given by the boundary element methods. Finally, the case of a gearbox inside the engine compartment of a truck is solved. The main interest of the hybrid method is to couple a low frequency vibratory method to a high frequency acoustical method which leads to reduced computational times compared to the boundary element methods.

To know more (French): https://www.theses.fr/2005ECDL0034

The City Lightweight and Innovative Cab (CLIC) project was a scientific collaboration gathering public and private organizations. The aim was to propose an innovative lighten truck cab, where a high strength steel was used. As long as it could affect directly the acoustic environment of the cab, it was necessary to be able to simulate the vibroacoustic behavior of the truck cab in the mid frequency range. The dissipative treatments used for noise and vibration control such as viscoelastic patches and acoustic absorbing materials must then be taken into account in the problem.

A process based on the SmEdA (Statistical modal Energy distribution Analysis) method was developed and is presented in this paper. SmEdA allows us substructuring the global problem, to study the interaction between the floor and the interior cavity. The process consists in building finite element models FEM) of each subsystem (floor, internal cavity), including the dissipative material (damping layer, poroelastic material). Standard modal FEM calculations are then performed for each uncoupled subsystem. From the spatial mode shapes, and the modal strain-kinetic energies, the modal loss factors of both subsystems are estimated. Finally, the pressure levels inside the cavity are deduced from the resolution of the SmEdA equations.

To validate this process, a truck cabin has been excited mechanically on a rail of the floor and the pressure levels at different positions inside the cabin were measured for different configurations of dissipative treatment. Comparisons between SmEdA and experimental results allows us to assess the accuracy of the proposed method.

To know more: https://saemobilus.sae.org/content/2018-01-1506/