Revistas
Revista:
VEHICLE SYSTEM DYNAMICS
ISSN 0042-3114
Vol. 60
N° 3
Año 2022
Págs.835 - 864
The air spring is the main part of the secondary suspension of passenger railway vehicles. The aim of this paper is to review existing modelling techniques for air springs in order to check if challenges set in the past decade for available models have been met. The advantages and disadvantages of different air spring models (phenomenological/mechanical, thermodynamic, analytic, FEM) are summarised and discussed from the point of view of: model accuracy, multiphysics interaction, influence of structural and material non-linearities, obtention of parameters, frequency range and the balance between accuracy and computational effort. The first conclusion is that current research is mainly focused on the vertical behaviour with less attention paid to the lateral performance. Moreover, it is concluded that further research is needed to include non-linearities of the bellow and to consider fluid-structural interaction; this would allow improving the model of vertical behaviour and evaluating better the lateral performance of the pneumatic system. FEM models might be an interesting tool that allows performing a more complete analysis of air springs (combining different physics, including material non-linearities, considering the real shape of the bellow and reinforcing fibres, etc) favouring the comfort analysis and including the lateral dynamics of the air spring.
Revista:
POLYMER TESTING
ISSN 0142-9418
Vol. 111
Año 2022
Págs.107617
The effect of the lubrication on the mechanical behavior of magnetorheological elastomers (MREs) in compression mode is experimentally studied. According to ISO 7743, there are two procedures to characterize specimens in compression mode. Differences in the properties of these materials between lubricated and nonlubricated conditions must be considered if devices such as vibration absorbers and isolators are to be developed. With lubrication, compression is said to be uniaxial and homogeneous, thus material properties can be obtained. Without lubrication, tests are easier to perform but results are strongly dependent on the piece shape. In this study isotropic and anisotropic MREs with iron particle volume concentrations of 10, 20, 30 and 40% are tested under different strain amplitudes, prestrain and magnetic fields for a frequency range up to 300 Hz, with and without lubrication. Important design parameters like amplitude, frequency and magnetic field dependency are showed to be dependent on lubrication.
Revista:
VEHICLE SYSTEM DYNAMICS
ISSN 0042-3114
Vol. 60
N° 6
Año 2022
Págs.1993 - 2017
Rail accelerations can be used on the defect detection and health monitoring of railway vehicle and track components; therefore, mathematical models that predict this response are of interest for reproducing its behaviour in a wide range of situations. The numerical track models based on the Timoshenko beam theory introduce a non-physical response, which is especially noticeable in the rail accelerations. It is due to the lack of dynamic convergence of the Timoshenko finite element (FE). This paper addresses this phenomenon employing an enhanced formulation of the Timoshenko FE that includes internal degrees of freedom (iDoF). The iDoF shape functions are derived from the Timoshenko beam dynamic governing equations. Firstly, the formulation is presented, and its performance is compared with a similar Timoshenko FE formulation. Secondly, the proposal is assessed in the dynamic modelling of railway track structures. The use of iDoF efficiently corrects the non-physical response of rail accelerations by improving the FE dynamic convergence. Subsequently, a filtering criterion for accelerations is proposed, which removes the remaining non-physical response while guaranteeing the conservation of coherent frequency content. Finally, practical cases are simulated for which the proposed methodology is proved to be more efficient and reliable than the standard approach.
Revista:
SMART MATERIALS AND STRUCTURES
ISSN 0964-1726
Vol. 31
N° 9
Año 2022
Págs.95005
In this article, the compression characterization of silicon-based magnetorheological elastomers is addressed, emphasizing the difficulties associated to the test set-up in order to obtain accurate results of the behaviour of the material. Measurement errors associated to friction and vibration coupling due to design flaws in the electromagnet are solved by providing guidelines on an adequate electromagnet layout. The designed electromagnet allows conducting compression dynamic tests up to 300 Hz in specimens of dimensions 40 x 40 x 8 mm(3), reaching magnetic flux densities in the order of 1000 mT and showing the expected increase in the dynamic stiffness. Additionally, the electromagnet might be used in the manufacturing and curing of anisotropic magnetorheological compression specimens.
Revista:
IET ELECTRIC POWER APPLICATIONS
ISSN 1751-8660
Vol. 14
N° 10
Año 2020
Págs.1974 - 1983
This study presents the electromagnetic, thermal and mechanical analysis of a 750 kW, 1200 rpm, 690 V surface permanent magnet motor aimed at marine propulsion (azimuth thruster). Based on a preliminary machine design, key electromagnetic design aspects including magnet demagnetisation and magnet loss reduction by tangential and axial segmentation are assessed. Then, three different cooling solutions are evaluated via computational fluid dynamics simulations combining the use of a water-jacket surrounding the stator, wafters attached to the rotor structure and the addition of an inner fan. Subsequently, the dynamic design analysis method is applied in order to check the machine's response to shock loadings due to underwater explosions. Finally, a machine prototype is successfully manufactured and tested, showing the proper fulfilment of the design requirements.
Revista:
VEHICLE SYSTEM DYNAMICS
ISSN 0042-3114
Vol. 57
N° 10
Año 2019
A vertical track model suitable for the study of the dynamic response and the interaction between wheel and rail in the time domain is developed by using Timoshenko beam elements, and its performance is optimised by accounting for the local deflection of these type of elements. Implementation of the local system enables one to obtain an accurate description of the contact force in a more computationally efficient way than other numerical methods, and it leads to an almost total elimination of the discontinuities caused by the local displacement underestimation and the shear incompatibilities introduced by the conventional formulation with Timoshenko beam elements. The work presented here describes both static and dynamic approaches of the local system directly obtained through the resolution of the beam governing equations. The dynamic approach guarantees the shear rotation continuity and describes accurately the track frequency content. The method is tested for parametric excitation, in which it ensures the smoothness of the response. Secondly, it is tested for short-pitch corrugated rails, where overestimation of the contact force is avoided with a reduced model size when compared with conventional Timoshenko element formulation. The results are validated by comparison with those from previous studies
Revista:
VEHICLE SYSTEM DYNAMICS
ISSN 0042-3114
Vol. 56
N° 4
Año 2018
Págs.529 - 552
The finite length nature of rail-pad supports is characterised by a Timoshenko beam element formulation over an elastic foundation, giving rise to the distributed support element. The new element is integrated into a vertical track model, which is solved in frequency and time domain. The developed formulation is obtained by solving the governing equations of a Timoshenko beam for this particular case. The interaction between sleeper and rail via the elastic connection is considered in an analytical, compact and efficient way. The modelling technique results in realistic amplitudes of the pinned-pinned' vibration mode and, additionally, it leads to a smooth evolution of the contact force temporal response and to reduced amplitudes of the rail vertical oscillation, as compared to the results from concentrated support models. Simulations are performed for both parametric and sinusoidal roughness excitation. The model of support proposed here is compared with a previous finite length model developed by other authors, coming to the conclusion that the proposed model gives accurate results at a reduced computational cost.
Revista:
APPLIED ACOUSTICS
ISSN 0003-682X
Vol. 133
Año 2018
Págs.144 - 156
Air radiation caused by vibrating structural systems is a fundamental problem in acoustic engineering with a wide application range. Exact analytical solutions are possible for some simple structures but for complex ones analytical expressions are not easily established. In this paper a methodology for computing the acoustic radiation caused by any type of flat structural system is presented. A general equation is established in modal terms, including the interaction between the structure and the surrounding fluid through pressure fluctuations. These are defined using a potential function, whose description is based on Hankel or Green baffled functions depending on the radiating surface dimension. Solving the obtained equation modal displacements caused by a specific excitation are known. Through these displacements the radiated power by the structure as well as the energy stored are quantified. Relating both the coupling loss factors between the structural system and the surrounding fluid are determined. In order to achieve the statistical diffuse field assumption coupling loss factor values are averaged both in frequency and in space. Some examples are analysed and it is shown that accurate results can be obtained applying the developed methodology in simple structures. In complex configurations it is validated using the computed coupling loss factors to estimate the transmission loss values and compare them with the experimental ones.
Revista:
SHOCK AND VIBRATION
ISSN 1070-9622
Vol. 2016
Año 2016
Págs.7846369
This paper presents a theoretical study of the parameters that influence sandwich-type constrained layer damper design. Although there are different ways to reduce the noise generated by a railway wheel, most devices are based on the mechanism of increasing wheel damping. Sandwich-type constrained layer dampers can be designed so their resonance frequencies coincide with the wheel's resonant vibration frequencies, and thus the damping effect can be concentrated within the frequency ranges of interest. However, the influence of design parameters has not yet been studied. Based on a number of numerical simulations, this paper provides recommendations for the design stages of sandwich-type constrained layer dampers.
Revista:
NOISE CONTROL ENGINEERING JOURNAL
ISSN 0736-2501
Vol. 63
N° 5
Año 2015
Págs.448 - 459
The acoustic reductions achieved with the current damping solutions for railway wheels that appear in the state of the art were obtained with different railway wheel designs, under different measurement scenarios (laboratory and on track), under different testing conditions, making it impossible to compare these damping solutions in a straightforward manner. The aim of this paper is to analyse, measure and estimate the behaviour of damping solutions installed on the same railway wheel and under the same testing conditions. Experimental measurements were carried out in the laboratory on wheels that are currently in use in metro lines. Damping solutions that were evaluated are ring damper, friction damper and sandwich-type constrained layer damper. Results show that ring and friction dampers are dependent on the applied preload and that they can only dissipate energy at high frequencies. Sandwich-type constrained layer dampers are the only damping solution that can add damping at low frequencies, but it is essential that they be properly designed in order to significantly increase the final wheel damping.
Revista:
SHOCK AND VIBRATION
ISSN 1070-9622
Año 2014
Págs.473720
This paper presents the modelling and design of a constrained layer damper to eliminate squeal noise in a particular tram. Even though resilient wheels are installed in every bogie, squeal noise is generated at the frequency of 780-800 Hz due to the small radius curves that the tram has to draw. Tuned constrained layer dampers provide a solution to this particular problem. Butyl rubber is chosen as the viscoelastic material for the damper, and conventional steel is used for the metallic sheets. The modelling approach and the final design of the damper are presented, together with evaluation of its performance in a real application. Experimental measurements on track have demonstrated that the constrained layer damper is properly tuned to the squealing frequency and that there is a significant reduction in noise when the proposed damper is attached to the wheels.
Revista:
JOURNAL OF SOUND AND VIBRATION
ISSN 0022-460X
Vol. 333
N° 20
Año 2014
Págs.4897 - 4911
This paper presents a procedure for predicting the damping added to a railway wheel when sandwich-type dampers are installed. Although there are different ways to reduce the noise generated by a railway wheel, most devices are based on the mechanism of increasing wheel damping. This is why modal damping ratios are a clear indicator of the efficiency of the damping device and essential when a vibro-acoustic study of a railway wheel is carried out. Based on a number of output variables extracted from the wheel and damper models, the strategy explained herein provides the final damping ratios of the damped wheel. Several different configurations are designed and experimentally tested. Theoretical and experimental results agree adequately, and it is demonstrated that this procedure is a good tool for qualitative comparison between different solutions in the design stages.
Revista:
JOURNAL OF SOUND AND VIBRATION
ISSN 0022-460X
Vol. 332
N° 12
Año 2013
Págs.3032 - 3048
Rubber elements are widely used in the railway industry in order to achieve vibration transmission requirements. Although they are critical components in railway vehicles, their modelling in the dynamic models of railway vehicles is usually relatively simple: it is usual to characterise them using a simple linear model formed by a spring and a viscous dashpot in parallel. In this paper the behaviour of typical rubber elements is analysed and a model that allows more accurately the prediction of its behaviour is proposed. The methodology to implement this model in railway simulation programs is also discussed.
Revista:
APPLIED ACOUSTICS
ISSN 0003-682X
Vol. 74
N° 4
Año 2013
Págs.575 - 584
The indirect energy flow measurement method is extended to cover highly nonlinear, frequency, amplitude and magnetic field dependent magneto-sensitive natural rubber isolators applied in a real vibration isolation system. Energy flow is an effective measure of vibration isolation while being a single quantity that considers both force and velocity. The use of the indirect technique is of interest while requiring only accelerometers since it is usually difficult to directly measure the force in a real application. The vibration isolation system is composed of four magneto-sensitive rubber isolators that are inserted under a vibrating source consisting of a solid aluminium mass excited by an electro-dynamic shaker. Magneto-sensitive rubber isolators are more useful than conventional rubber isolators since the dynamic stiffness varies with the application of an external magnetic field, thus resulting in more effective vibration isolation. Various approximations regarding the indirect technique are investigated, concluding that average stiffness of magneto-sensitive isolators can be used and auto-spectrum of the foundation velocity ignored. In addition, various error analyses are performed. Finally, the indirect measurement of the energy flow is validated by direct measurements, showing very good agreement. (C) 2012 Elsevier Ltd. All rights reserved.
Revista:
INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE
ISSN 0020-7225
Vol. 65
Año 2013
Págs.22 - 39
A highly nonlinear model of the energy flow in a magneto-sensitive (MS) vibration isolation system is developed where it is possible to investigate the influences of MS rubber material parameters; magnetic field strength; MS isolator dimension and position; excitation force magnitude, position and frequency; engine mass, inertia and dimension and, finally, foundation inertance. The MS vibration isolation system consists of an engine modelled by a solid mass, excited by a vertical force and mounted upon four MS isolators being connected to a relatively stiff foundation characterised by its driving-point and transfer inertances at and between the connection points. The energy flow into the foundation is the most appropriate indicator of the effectiveness of a real vibration isolation system while considering both foundation velocity and force. The MS isolator model applied is a nonlinear MS rubber model including frequency, dynamic amplitude and magnetic field dependence. The energy flow model results are compared to those of measurements, showing good agreement. Finally, parameter studies are carried out. The developed energy flow model provides a basis for designing MS vibration isolation systems to meet specific requirements. (C) 2013 Elsevier Ltd. All rights reserved.
Revista:
ACTA ACUSTICA UNITED WITH ACUSTICA
ISSN 1610-1928
Vol. 99
N° 1
Año 2013
Págs.130 - 138
The purpose of this paper is to demonstrate that a recently published methodology for predicting flow generated noise by compact surfaces under free-field conditions [1] can be extended to a different and more complex configuration of industrial interest. In the previous paper, the methodology was applied to low Mach number flow past a circular cylinder in free-field, where the Green's function and its derivative were obtained analytically. In this paper, the method will be applied to the case of low Mach number flow past a complex confined scattering geometry where both compact and non-compact surfaces are involved. Here the generation of noise is dominated by the interaction of the flow with a surface whose maximum dimension is shorter than the wavelength of interest. The analysis is based on the surface-source term of the Ffowcs Williams-Hawkings equation. The acoustic source data of the flow are generated by use of a Computational Fluid Dynamics (CFD) simulation. Due to the complexity of the scattering surfaces, the derivative of the Green's function must be obtained numerically through a Computational Acoustics (CA) simulation. The results have been validated through comparison with sound power measurements.
Revista:
JOURNAL OF SOUND AND VIBRATION
ISSN 0022-460X
Vol. 331
N° 9
Año 2012
Págs.1994 - 2006
The effectiveness of highly nonlinear, frequency, amplitude and magnetic field dependent magneto-sensitive natural rubber components applied in a vibration isolation system is experimentally investigated by measuring the energy flow into the foundation. The energy flow, including both force and velocity of the foundation, is a suitable measure of the effectiveness of a real vibration isolation system where the foundation is not perfectly rigid. The vibration isolation system in this study consists of a solid aluminium mass supported on four magneto-sensitive rubber components and is excited by an electro-dynamic shaker while applying various excitation signals, amplitudes and positions in the frequency range of 20-200 Hz and using magneto-sensitive components at zero-field and at magnetic saturation. The energy flow through the magneto-sensitive rubber isolators is directly measured by inserting a force transducer below each isolator and an accelerometer on the foundation close to each isolator. This investigation provides novel practical insights into the potential of using magneto-sensitive material isolators in noise and vibration control, including their advantages compared to traditional vibration isolators. Finally, nonlinear features of magneto-sensitive components are experimentally verified. (C) 2012 Elsevier Ltd. All rights reserved.
Revista:
PLASTICS RUBBER AND COMPOSITES
ISSN 1465-8011
Vol. 41
N° 7
Año 2012
Págs.310 - 317
The dynamic shear modulus of magnetosensitive (MS) natural rubber composites is experimentally studied, where influences of carbon black, plasticiser and iron particle concentrations are investigated at various dynamic shear strain amplitudes and external magnetic fields within the lower structure borne frequency range. The iron particles embedded in natural rubber are irregularly shaped and randomly distributed; the plasticisers simplify the iron particle blending process, while carbon black reduces the production costs and improves the mechanical properties. The results show that the relative MS effect on the shear modulus magnitude increases with increased plasticiser and iron particle concentration and decreases with increased carbon black concentration. Furthermore, their relative contributions are quantified. Consequently, the study provides a basis for optimising the composition of MS natural rubber to meet a variety of requirements, including those of vibration isolation, a promising application area for MS materials.
Revista:
NOISE CONTROL ENGINEERING JOURNAL
ISSN 0736-2501
Vol. 60
N° 4
Año 2012
Págs.458 - 472
This paper presents a vibro-acoustic characterization of a railway wheel in the frequency domain with and without damping solutions. From a simple vibrational measure where modal damping ratios are calculated, the sound pressure at a certain distance from the railway wheel is predicted, avoiding time-consuming and expensive acoustic measurements. The approach is based on FEM (finite element method) and makes use of the submodeling technique which consists of decoupling the calculation first into a structural response, and then into the acoustic emission. This decoupling allows damping in the structure to be introduced in terms of modal damping ratios instead of Rayleigh damping, a commonly used approach that is, nonetheless, not very accurate. Due to the use of infinite elements in the boundaries, the size of the acoustic mesh is reduced to an ellipsoid surrounding the structure, thus decreasing calculation time. The results are compared with experimental measurements with satisfactory agreement. Thus, the approach described becomes a powerful tool to compare different damping treatments and to make a decision on which solution could be adopted in a particular application.
Revista:
ACTA ACUSTICA UNITED WITH ACUSTICA
ISSN 1610-1928
Vol. 97
N° 1
Año 2011
Págs.14 - 23
Sound generation has been widely studied using numerical hybrid methods. The aim of this paper is to introduce a flexible procedure where the acoustic source data may be synthesized and stored from commercially available Computational Fluid Dynamics (CFD) codes and later used to predict radiated noise. Different applications will require either analytical or numerical methods for the radiation calculations. Attention is restricted to low Mach number flows where the noise generation is dominated by the interaction of the flow with a surface with at least one characteristic dimension short compared to the wavelength of interest. This makes it possible to focus on the surface source term of the Ffowcs Williams-Hawkings equation. In this paper, in order to illustrate the basic method for storing and utilizing data from the CFD analysis, the flow past a circular cylinder at a Reynolds number of Re = 1.4 . 10(5) will be studied, where the cylinder is compact and therefore the analytical free-space Green's function may be used.
