1,720,974 research outputs found
Applying non-hertzian wheel-rail contact models in dynamic railway vehicle-track calculations
No full textAcoustic behaviour of elliptical mufflers with single-inlet and double-outlet
No full textExpansion chambers with single-inlet and double-outlet are used in the exhaust system of internal combustion engines since they provide noise attenuation similar to simple chambers (single inlet/outlet), and reduce the flow noise and back pressure. This work presents a detailed analysis of the acoustic attenuation performance of elliptical expansion chambers with single-inlet and double-outlet. First, the finite element method (FEM) is considered in order to obtain a reference solution. Then, the mode-matching method (MMM) is applied at the area discontinuities of the muffler, considering a circular inlet pipe, a central elliptical chamber and two circular outlet pipes. This method reduces the computational requirements and enables to couple the acoustic fields within each region, described by means of Mathieu functions in the elliptical chamber and Bessel functions in the circular pipes. The solution given by this analytical approach is compared with finite element results and experimental measurements for a selected configuration, showing a good agreement. The acoustic behaviour is then analysed in detail as a function of the chamber length, the . eccentricity of the elliptical cross-section and the position of the inlet and outlet pipes. Some potential means to improve the acoustic performance are proposed
Comparison of numerical approaches for the acoustic modelling of dissipative silencers with temperature gradients and mean flow
No full textNumerical approach for the acoustic connection of nonconforming meshes by transfer matrices
No full textAn Eulerian coordinate-based method for analysing the structural vibrations of a solid of revolution rotating about its main axis
No full textA multidimensional analytical study of sound attenuation in catalytic converters
No full textIn this work, a multidimensional analytical model is presented for the sound attenuation assessment of axisymmetric catalytic converters. Bessel functions are considered for the circular ducts, while spherical Hankel and Legendre functions are used for the expansion/contraction tapered ducts. Two alternative modelling techniques are implemented and compared for the monolith: (1) An equivalent bulk reacting absorbent material, in which the wave propagation is determined by the effective complex and frequency dependent density and speed of sound; (2) A coupling approach between both sides of the ceramic monolith in which a plane wave transfer matrix is considered, therefore retaining only onedimensional propagation within the capillary ducts. Benchmarking of the developed analytical techniques with finite element calculations shows good agreement. The influence of several parameters on the sound attenuation of the catalyst is investigated
Numerical mode matching in dissipative silencers with temperature gradients and mean flow
Full text linkThis work presents a mathematical approach based on the mode matching method to compute the transmission loss of perforated dissipative silencers with temperature gradients and mean flow. Three-dimensional wave propagation is considered in silencer geometries with arbitrary, but axially uniform, cross section. To reduce the computational requirements of a full multidimensional finite element calculation, a method is developed combining axial and transversal solutions of the wave equation. First, the finite element method is employed in a twodimensional problem to extract the eigenvalues and associated eigenvectors for the silencer cross section. Mean flow as well as radial temperature gradients and the corresponding thermal-induced material heterogeneities are included in the model. Assuming a low acoustic influence of axial gradients (compared to radial variations), an axially uniform temperature field is taken into account, its value being the inlet/outlet average. A weighted residual approach is then used to match the acoustic fields (pressure and axial acoustic velocity) at the geometric discontinuities between the silencer chamber and the inlet and outlet pipes. Transmission loss predictions are compared favourably with a general three-dimensional finite element approach, offering a reduction in the computational effort
A model of the rotating rigid wheelset and its influence on the wheel and track rolling noise
No full textThe dynamic and acoustic behaviour of the railway wheel is defined by its numerous vibration modes and natural frequencies. The modes whose contribution to the rolling noise radiation are predominant generally have 2 or more nodal diameters and appear above 2 kHz. The vibration due to these modes is decoupled from the rest of the wheelset, allowing the wheel to be treated separately. The error produced in the wheel noise prediction by this treatment appears at the low and medium frequencies and is negligible since the wheel emission occurs mainly at the high frequency range. However, given the dynamic coupling between the wheel and track, the changes in the dynamics ofthe former affect the latter, whose radiation is predominantly in the low and medium frequency range. Therefore, in order to correctly study both elements, it is necessary to include the contribution of the rest of the wheelset in the wheel response. In this work, this contribution is introduced through an analytical approach considering the rigid body motion of the wheelset and a benchmarking against an equivalent numerical formulation is carried out for validation purposes. In addition, the inertial effects associated with the rotation under straight circulation conditions are considered.<br/
Acoustic modelling of exhaust devices with nonconforming finite element meshes and transfer matrices
Full text link[EN] Transfer matrices are commonly considered in the numerical modelling of the acoustic behaviour associated with exhaust devices in the breathing system of internal combustion engines, such as catalytic converters, particulate filters, perforated mufflers and charge air coolers. In a multidimensional finite element approach, a transfer matrix provides a relationship between the acoustic fields of the nodes located at both sides of a particular region. This approach can be useful, for example, when one-dimensional propagation takes place within the region substituted by the transfer matrix. As shown in recent investigations, the sound attenuation of catalytic converters can be properly predicted if the monolith is replaced by a plane wave four-pole matrix. The finite element discretization is retained for the inlet/outlet and tapered ducts, where multidimensional acoustic fields can exist. In this case, only plane waves are present within the capillary ducts, and three-dimensional propagation is possible in the rest of the catalyst subcomponents. Also, in the acoustic modelling of perforated mufflers using the finite element method, the central passage can be replaced by a transfer matrix relating the pressure difference between both sides of the perforated surface with the acoustic velocity through the perforations. The approaches in the literature that accommodate transfer matrices and finite element models consider conforming meshes at connecting interfaces, therefore leading to a straightforward evaluation of the coupling integrals. With a view to gaining flexibility during the mesh generation process, it is worth developing a more general procedure. This has to be valid for the connection of acoustic subdomains by transfer matrices when the discretizations are nonconforming at the connecting interfaces. In this work, an integration algorithm similar to those considered in the mortar finite element method, is implemented for nonmatching grids in combination with acoustic transfer matrices. A number of numerical test problems related to some relevant exhaust devices are then presented to assess the accuracy and convergence performance of the proposed procedure.Authors gratefully acknowledge the financial support of Ministerio de Ciencia e Innovacion and the European Regional Development Fund by means of the Projects DPI2007-62635 and DPI2010-15412.Denia, F.; Martínez-Casas, J.; Baeza, L.; Fuenmayor, F. (2012). Acoustic modelling of exhaust devices with nonconforming finite element meshes and transfer matrices. Applied Acoustics. 73(8):713-722. https://doi.org/10.1016/j.apacoust.2012.02.003S71372273
A model of the rotating rigid wheelset and its influence on the wheel and track rolling noise
No full textThe dynamic and acoustic behaviour of the railway wheel is defined by its numerous vibration modes and natural frequencies. The modes whose contribution to the rolling noise radiation are predominant generally have 2 or more nodal diameters and appear above 2 kHz. The vibration due to these modes is decoupled from the rest of the wheelset, allowing the wheel to be treated separately. The error produced in the wheel noise prediction by this treatment appears at the low and medium frequencies and is negligible since the wheel emission occurs mainly at the high frequency range. However, given the dynamic coupling between the wheel and track, the changes in the dynamics of the former affect the latter, whose radiation is predominantly in the low and medium frequency range. Therefore, in order to correctly study both elements, it is necessary to include the contribution of the rest of the wheelset in the wheel response. In this work, this contribution is introduced through an analytical approach considering the rigid body motion of the wheelset and a benchmarking against an equivalent numerical formulation is carried out for validation purposes. In addition, the inertial effects associated with the rotation under straight circulation conditions are considered
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