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An Influence of the Wall Acoustic Impedance on the Room Acoustics. The Exact Solution

Brański A., Kocan-Krawczyk A., Prędka E.

Archives of Acoustics

2017

Vol. 42, No. 4

677--687

The Fourier method is applied to the description of the room acoustics field with the combination of uniform impedance boundary conditions imposed on some walls. These acoustic boundary conditions are expressed by absorption coefficient values In this problem, the Fourier method is derived as the combination of three one-dimensional Sturm-Liouville (S-L) problems with Robin-Robin boundary conditions at the first and second dimension and Robin-Neumann ones at the third dimension. The Fourier method requires an evaluation of eigenvalues and eigenfunctions of the Helmholtz equation, via the solution of the eigenvalue equation, in all directions. The graphic-analytical method is adopted to solve it It is assumed that the acoustic force constitutes a monopole source and finally the forced acoustic field is calculated. As a novelty, it is demonstrated that the Fourier method provides a useful and efficient approach for a room acoustics with different values of wall impedances. Theoretical considerations are illustrated for rectangular cross-section of the room with particular ratio. Results obtained in the paper will be a point of reference to the numerical calculations.

A thermomechanical aspect of the ceramic-capped piston of hypothetical adiabatic diesel engine

Jaskólski J., Krzyżak R.

Journal of KONES

2006

Vol. 13, No. 2

169-177

The paper concerns a hypothetical Al.-alloy piston coated (capped) first by labradore and then capped by YSZ. The labradore, a member of the feldspar group is deemed thermal-shock resistant, the YSZ(PSZ) can be shock-resistant, but the outcome of the two with the Al.-alloy is not known. The analysis were made in two ways by ANSYS 10.0, as wholly isotropic materials and (second) labradore treated as wholly orthotropic one as basing on a designed texture. The above programme was fed up by the FORTRAN95-outcome of temperatures and the other B.C.’s.The temperatures between the ceramics and the alloy (except one node!!, the FORTRAN) are ( from the above two procedures), 222.63 to 270-300 graduate C, at the first groove are about 290 graduate C, and, surely lower (orthotropic). The relatively low (to ceramic) inner tensile stresses are embraced by the compressive ones from all the sides. The only problem is the-alloy bearing capacity at some sections at the ceramic boundary (and only there). But, it was the aim of the work to stick ceramics there.The dangerous stresses can occur at the pin .The ‘orthotropic ‘ results are better than the ‘iso’-ones and more true.. Taking into account that the real loading will be lower (porosity of the ceramics, the mass and the possible subtraction of stresses, i.e. those ceramic-production-confined ones) , the laboratory production of the piston appears worth.