This paper is a report on the highlights of aeroacoustics research and development in Europe in 1999, compiled from the information provided to the Aeroacoustics Specialists Committee (ASC) of the Confederation of European Aerospace Societies (CEAS). CEAS presently comprises the national Aerospace Societies of France (AAAF), Germany (DGLR), Italy (AIDAA), The Netherlands (NVvL), Spain (AIAE), Sweden (FTEF), Switzerland (SVFW) and the United Kingdom (RaeS).
We predict scattering cancellation in diffusive transport of acoustics waves propagating through multiple scattering media in the stationary limit. This would enable sensing of diffusive sound without disrupting the exterior acoustic field. We present design schemes for making spherical or cylindrical core-shell structures with multiple layers, characterized by homogenous and isotropic diffusion coefficients, neutral to an arbitrary applied multipole field. The double-layered sphere is found to support transparency to two concurrent multipole fields and unique cloaking solutions of arbitrary multipole order. One extra degree of freedom is provided by every layer added to the core-shell structure which may be exploited with our iterative formula for effective diffusivity for cloaking of additional field terms. From this we pass over to the long wavelength limit of ballistic sound and provide formulas for effective mass densities of multi-layered structures in spherical and cylindrical geometries with respect to multipole pressure fields. (C) 2017 Elsevier Ltd. All rights reserved.
In the present paper, a large rotational approach for dynamic contact problems with friction is proposed. The approach is used for modelling a spur gear pair with shafts and bearings. The model is obtained by superposing small displacement elasticity on rigid-body motions, and postulating tribological laws on the gear flanks. The finite element method is used to model the elastic properties of the gear pair. Shafts and bearings are represented by linear springs. The tribological laws of the contact interface are Signorini's contact law and Coulomb's law of friction. An important feature of the approach is that the difficulties of impacting mass nodes are avoided. The governing equations of the model are numerically treated by use of the augmented Lagrangian approach. In such manner the geometry of the gear flanks are well represented in the numerical simulations. It is possible to study accurately the consequences of different types of profile modifications as well as flank errors. In this work, the dynamic transmission error is studied. For instance, it turns out that the effect from profile modification is less significant for the transmission error when frictional effects are included.
Reflection, transmission and dissipation of the energy of an incident extensional wave at a linearly viscoelastic junction between two uniform and collinear linearly elastic bars are considered. The junction consists of a finite number of uniform segments of the same material and length. The optimum shape of a junction with given material, length and number of segments which maximizes the energy transmission for given input and output bars and a given incident wave of finite duration is determined numerically with the use of a quasi-Newton method. Results are presented for rectangular incident waves of different durations and 40-segment junctions of standard linear solid material. In the special case of linearly elastic material, the optimum junctions have piece-wise constant characteristic impedances with a certain number of plateaux of equal lengths. These plateaux are independent of the number of segments provided that this number is an integral multiple of the number of plateaux. The optimum viscoelastic junctions have the appearance of deformed and displaced versions of their elastic counterparts. Thus, the plateaux of the elastic junctions are increasingly deformed and displaced with increased damping and, less markedly, with decreased response time of the material. The transitions between these plateaux of a junction appear to be discontinuous, similarly as in the case of elastic material. The apparent discontinuities become less notable with increased damping of the material.