| 1. |
- Boere, Stijn, et al.
(författare)
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Tyre/road interaction model for the prediction of road texture influence on rolling resistance
- 2014
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Ingår i: International Journal of Vehicle Design. - 0143-3369 .- 1741-5314. ; 65:2-3, s. 202-221
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Tidskriftsartikel (refereegranskat)abstract
- A novel modelling approach to predict the influence of road texture on the rolling resistance of car tyres is presented where the large static tyre deformations and the small texture induced tyre vibrations are treated separately. The energy dissipation due to the large continuous cyclic deformation of the tyre cross section for a treadless tyre subject to nominal load on a smooth road is determined in a non-linear steady-state rolling analysis on an FEM tyre model. The additional energy dissipation resulting from the con tact forces and tyre vibrations due to the combined effect of the tread profile and the road texture, are determined based on a modal representation of the deformed tyre. The predicted rolling resistance coefficients are compared to experimental data. Although an offset in the absolute rolling resistance levels can be observed, the model predicts the correct trend regarding the increase of rolling resistance with increasing texture depth.
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| 2. |
- Hoeijmakers, Maarten, et al.
(författare)
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Accuracy assessment of thermoacoustic instability models using binary classification
- 2013
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Ingår i: International Journal of Spray and Combustion Dynamics. - : SAGE Publications. - 1756-8277 .- 1756-8285. ; 5:3, s. 201-223
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Tidskriftsartikel (refereegranskat)abstract
- We apply binary classification theory to assess the (in)stability prediction accuracy of thermoacoustic models. It is shown that by applying such methods to compare a large set of stability predictions and experiments it is possible to gain valuable qualitative insight in different aspects of prediction quality. The approach is illustrated with a 2-port model and a large experimental data set. The presented framework provides an unified and practical tool to answer questions such as (i) What is the chance that a stable prediction will be correct? and (ii) How conservative is the model? It is shown that the most suitable quality indicator is strongly dependent on the actual purpose of the model. The method provides a solid starting point for model comparison and optimization.
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| 3. |
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| 4. |
- Hoeijmakers, Maarten, et al.
(författare)
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Intrinsic instability of flame-acoustic coupling
- 2014
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180 .- 1556-2921. ; 161:11, s. 2860-2867
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Tidskriftsartikel (refereegranskat)abstract
- This paper shows that a flame can be an intrinsically unstable acoustic element. The finding is clarified in the framework of an acoustic network model, where the flame is described by an acoustic scattering matrix. The instability of the flame acoustic coupling is shown to become dominating in the limit of no acoustic reflections. This is in contrast to classical standing-wave thermoacoustic modes, which originate from the positive feedback loop between system acoustics and the flame. These findings imply that the effectiveness of passive thermoacoustic damping devices is limited by the intrinsic stability properties of the flame.
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| 5. |
- Hosseini, N., et al.
(författare)
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Development of a numerical model for obtaining flame transfer function in a simplified slit burner with heat exchanger
- 2014
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Ingår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014. ; , s. 1581-1588
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Konferensbidrag (refereegranskat)abstract
- The goal of the present work is to develop a model to investigate the interactions between a burner and a heat exchanger, looking from a hydrodynamic and thermo-acoustic point of view. Thermo-acoustics of laminar premixed flames in open air have been studied by several researchers in the past decades. However, a burner in open air may behave differently compared to if situated in a combustion chamber enclosure. This could be related to the effect of temperature, the effect of flame shape (e.g. flames impinging on the heat exchanger walls in compact boilers), distribution of the flame on the burner deck, etc. The behavior of a linear array of a multiple Bunsen-type flames is studied on a 2D geometry in a CFD code to simulate the effects of heat exchanger addition on the thermo-acoustics of the flames. The location of the heat exchanger surface is varied for different conditions of power. A step profile velocity perturbation is used for obtaining the response of the flame represented within the flame transfer function approach. The calculated gain and phase of the flame transfer function are compared for different cases as the indicator of the thermo-acoustic behavior. Results show that the main parameter having considerable influence is the burner load and flame shape. The setup to experimentally investigate these effects will be constructed in near future.
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| 6. |
- Jerrelind, Jenny, et al.
(författare)
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Effects of non-linear wheel suspension bushing on vehicle response
- 2012
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Ingår i: Proceedings of the ASME Design Engineering Technical Conferences And Computers And Information In Engineering Conference, Vol 6. - : ASME Press. - 9780791845059 ; , s. 615-622
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Konferensbidrag (refereegranskat)abstract
- This work presents an analysis of the effects of non-linear characteristics of a top mount bushing in the wheel suspension of a vehicle when evaluating vehicle characteristics such as comfort and handling. The investigation is performed by comparing simulation results from a quarter car model when using a non-linear bushing model and an approximated linear bushing model. It is revealed when analysing the results that there are differences in the response when comparing measures such as sprung mass acceleration, rattle space ratio and tyre-ground contact force. The conclusion is that the more detailed bushing model mainly affects the acceleration levels especially at high frequencies where the linear model underestimates the acceleration. The rattle space ratio and tyre-ground contact force are also affected but not to the same extent.
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| 7. |
- Liu, Hao, 1986-
(författare)
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Wave Modelling Techniques for Medium and High Frequency Vibroacoustic Analysis Including Porous Materials
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Numerical methods based on wave modelling are explored for the vibroacoustic analysis of wave propagation, sound transmission and interior noise in vehicles and buildings at medium and high frequencies. The presence of sound absorbing porous materials in practical engineering structures is also considered. The wave modelling techniques provide computational efficiency and physical insight, and two such methods having these advantages are developed in this thesis namely: the semi-analytical finite element method and the wave expansion method.The semi-analytical finite element method is applicable to structures which have constant properties in one direction, and it uses a finite element discretization of the cross-section and analytical functions in the third direction. Equations of motion are derived from this method to study wave propagation characteristics, which help understand the vibroacoustic behavior of structures. These characteristics may also be used by high frequency techniques, such as statistical energy analysis. The wave propagation in sandwich panels with a poroelastic core, which is modeled with Biot's theory, is investigated thoroughly.The semi-analytical finite element method retains the flexibility of the finite element method on geometry and also dramatically increases the computational speed thanks to the orthogonality of the analytical functions when used to calculate forced response. The calculated response of partitions is integrated into diffuse field sound transmission loss calculations of, for example, built-up train floor partitions and multilayer panels lined with porous materials. The calculations are computationally efficient and show good agreement with measurements, thus it is interesting for industrial optimizations.The wave expansion method uses a priori defined plane wave solutions to the Helmholtz equation for approximation of the sound field in geometrically complex enclosures. It reduces the requirements regarding the number of degrees of freedom compared to the finite element method, which, furthermore, is polluted by dispersion errors. Therefore, the wave expansion method is particularly appealing for high frequency (or large wavenumber) calculations. Its application in interior sound field predictions is assessed within the automobile context.
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| 8. |
- Liu, Hao, et al.
(författare)
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Wave propagation in sandwich panels with a poroelastic core
- 2014
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 135:5, s. 2683-2693
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Tidskriftsartikel (refereegranskat)abstract
- Wave propagation in sandwich panels with a poroelastic core, which is modeled by Biot's theory, is investigated using the waveguide finite element method. A waveguide poroelastic element is developed based on a displacement-pressure weak form. The dispersion curves of the sandwich panel are first identified as propagating or evanescent waves by varying the damping in the panel, and wave characteristics are analyzed by examining their motions. The energy distributions are calculated to identify the dominant motions. Simplified analytical models are also devised to show the main physics of the corresponding waves. This wave propagation analysis provides insight into the vibro-acoustic behavior of sandwich panels lined with elastic porous materials.
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| 9. |
- Lopez Arteaga, Ines, et al.
(författare)
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Example of good practice of a learning environment with a classroom response system in a mechanical engineering bachelor course
- 2013
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Ingår i: European Journal of Engineering Education. - : Informa UK Limited. - 0304-3797 .- 1469-5898. ; :6, s. 652-660
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Tidskriftsartikel (refereegranskat)abstract
- Results of a successful pilot study are presented, in which quizzes are introduced in a second year bachelor course for mechanical engineering students. The pilot study course entailed the basic concepts of mechanical vibrations in complex, realistic structures. The quiz is held weekly using a SharePoint application. The purpose of the quizzes is to repeat important course material, give instantaneous feedback (i.e. formative assessment), stimulate peer instruction and, as a consequence, increase the students’ comprehension of the basic concepts taught in the course so that their deeper understanding of the subject matter improves. Students can earn half a point bonus, on a scale from 0 to 10, on top of their exam mark if they correctly answer 55% of all the quiz questions. The efficacy of the pilot study is determined by investigating the percentage of students that pass the course on their first attempt, i.e. the first time pass rate, and asking students for feedback through questionnaires. The first time pass rate of the students in the pilot study groups has, on average, increased significantly in comparison to groups in which the quizzes are not performed. Students indicated that the feedback from the quizzes helps them to identify gaps in their knowledge. Therefore, the pilot study is considered effective.
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| 10. |
- Lopez Arteaga, Ines
(författare)
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Green's functions for a loaded rolling tyre
- 2011
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 48:25-26, s. 3462-3470
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Tidskriftsartikel (refereegranskat)abstract
- A new formulation to determine the unit impulse response (Green's) functions of a loaded rotating tyre in the vehicle-fixed (Eulerian) reference frame for tyre/road noise predictions is presented. The proposed formulation makes use of the set of eigenfrequencies and eigenmodes for the statically loaded tyre obtained from a finite element (FE) model of the tyre. A closed-form expression for the Green's functions of a rotating tyre in the Eulerian reference system as a function of the eigenfrequencies and eigenmodes of the statically loaded tyre is found. Non-linear effects during loading are accounted for in the FE model, while the frequency shift due to the rotational velocity is included in the calculation of the Green's functions. In the literature on tyre/road noise these functions are generally used to determine the tyre response during tyre/road contact calculations. The presented formulation opens the possibility to solve the contact problem directly in the Eulerian reference frame and to include local tyre softening due to non-linear effects while keeping the computational advantage of describing the tyre dynamics as a set of impulse response functions. The advantage of obtaining the Green's functions in the Eulerian reference system is that only the Green's functions corresponding to the potential contact zone need to be determined, which significantly reduces the computational cost of solving the tyre/road contact and since the mesh is fixed in space, a finer mesh can be used for the potential contact zone, improving the accuracy of the contact force calculations. Although these effects might be less pronounced if a more accurate tyre model is used, it is found that using the Green's functions of the loaded tyre in a contact force calculation leads to smaller forces than in the unloaded case, lower frequencies are present in the response and they decrease faster as the rotational velocity increases.
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| 11. |
- Lopez Arteaga, Ines, et al.
(författare)
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Improved source reconstruction in Fourier-based Near-field Acoustic Holography applied to small apertures
- 2012
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Ingår i: Mechanical systems and signal processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 32, s. 359-373
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that Fourier-based Near-field Acoustic Holography fails to produce good source reconstructions when the aperture size of the microphone array is smaller than the source size. In this paper this problem is overcome by pre-conditioning the spatial hologram data using Linear Predictive Border Padding (LPBP) before it is Fourier-transformed to the wave-number domain. It is shown that LPBP allows for very small aperture sizes with a good reconstruction accuracy. An exhaustive analysis of LPBP is presented based on numerical experiments and measured data. The numerical experiments are performed on two different source types: modal patterns and point sources. These two types of sources represent the two limit situations that one can find in practice: modal patterns have a tonal spectrum in the spatial wave-number domain and are relatively easy to reconstruct accurately, while point sources have a broad-band wave-number spectrum which makes them very challenging to reconstruct. In order to illustrate the accuracy of the method in practice, results of measurements on a hard disk drive are presented as well. For a given distance to the source, the position and size of the hologram plane apertures is varied and the reconstructed source information is compared to the original source data. The reconstructed sources are compared both qualitatively and quantitatively. The results show that LPBP is an efficient and accurate extrapolation method, which leads to accurate reconstructions even for very small aperture sizes.
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| 12. |
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| 13. |
- Lopez Arteaga, Ines
(författare)
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Tyre/road noise and vibration : Understanding their interaction and contribution to vehicle noise and fuel consumption
- 2014
-
Ingår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014. ; , s. 51-63
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Konferensbidrag (refereegranskat)abstract
- Tyre/road noise and vibration are the main sources of road traffic noise, which is an increasingly big problem in densely populated areas. At the same time, rolling resistance, caused by the energy losses in the tyre, is a significant part of the total vehicle losses and, therefore, directly affects fuel consumption and C02 emissions. In order to reduce both noise emissions and energy consumption a good understanding of tyre/road interaction and of the influence of tyre and road properties is needed. In this paper the main tyre and road parameters that influence tyre/road noise and rolling resistance are discussed. Special emphasis is placed on tyre/road contact, since the contact forces between tyre and road are the key to a reliable prediction of tyre/road noise, rolling resistance and wear. Although tyre/road models are widely applied to the prediction of tyre/road noise and low-noise road design, the potential of these models for low-rolling resistance road design is not yet fully exploited.
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| 14. |
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| 15. |
- Lopez Arteaga, Ines, et al.
(författare)
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Viscoelastic contact model for the prediction of tire/road contact forces and rolling resistance
- 2011
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Ingår i: 18th International Congress on Sound and Vibration 2011, ICSV 2011. - 9781618392596
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A combined Hertz/Maxwell model is presented to approximately describe the interaction between a rigid indenter and a viscoelastic half-space, and therefore the force-indentation relationship including the deformation rate and energy losses. Thismodel is a numerically efficient alternative to the exact viscoelastic half-space formulation, to be implemented in a tyre/road interaction model for the prediction of tyre vibrations, rolling resistance and noise. Here the combined Hertz/Maxwell model is used to assess the influence of road texture on the contact stiffness and damping based on the analysis of 30 road surface types. The parameters of this model are obtained by fitting the load-penetration curves obtained from the exact viscoelastic half-space calculation. It is shown that both the stiffness and damping parameters decrease as the road texture depth increases, since, for a given penetration depth, the effective contact area decreases as the road texture depth increases. Assessing the relevance of these effects for the accurate prediction of tyre/road interaction is subject of ongoing work.
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| 16. |
- Lundberg, Oskar Erik, 1980-
(författare)
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Vibrations induced by surface roughness in nonlinear rolling contacts
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For efficient transportation in either trains, busses or passenger cars, rolling elements such as wheels, tyres, bearings and transmission elements are fundamental. The energy efficiency and the generation of noise and vibrations in rolling contacts depend on the surface roughness of contacting bodies. In order to optimize the surfaces of rolling elements, prediction of its impact on the dynamic response from rolling excitation is required. A computationally efficient method to include surface roughness in the modelling of rolling contacts is presented. More specifically, nonlinear effects on the contact force due to the threedimensional shape and roughness of the contacting surfaces are introduced in a moving point force formulation. As a consequence of the point force approximation follows the assumption that any dynamic wave motion within the contact area is negligible.The rolling contact force is nonlinear due to a varying relative displacement between contacting bodies and is therefore referred to as state-dependent. A study case for the state-dependent method consisting of a steel ball rolling on a steel beam showed good agreement between numerical predictions and measured beam vibrations. Furthermore, an application to the wheel-rail interaction show that roughness-induced contact nonlinearities have a significant impact on the dynamic response caused by rolling excitation.
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| 17. |
- Lundberg, Oskar, et al.
(författare)
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Estimation of nonlinearities in the wheel-rail rolling noise generation process
- 2014
-
Ingår i: Proceedings of ISMA 2014 - International Conference on Noise and Vibration Engineering and USD 2014 - International Conference on Uncertainty in Structural Dynamics. - 9789073802919 ; , s. 3485-3496
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The dynamics of wheel-rail interaction is predicted using a time-domain rolling contact model and a state-dependent method to model nonlinear contact forces in the wheel-rail interaction. Contact stiffness and contact filters are pre-calculated as functions of the vertical wheel-rail relative displacement (state-dependency) using three-dimensional surface data in quasi-static contact computations. By including the state-dependent functions in time-domain prediction of wheel-rail interaction, a computationally efficient method to include nonlinear effects is obtained. Results from predictions of contact forces as well as rail vibrations are presented for two conditions; first, both wheel and rail have surface roughness of broadband character and secondly, a rail corrugation is simulated by superimposing a sinusoidal component on the broadband rail roughness. For a train speed of 200 kph, the contact forces and the dynamic response of the rail exhibit nonlinear contact conditions for both the broadband roughness case as well as for the case where a rail corrugation is simulated.
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| 18. |
- Lundberg, Oskar, 1980-, et al.
(författare)
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Non-linear contact forces for beam/ball-interaction and its influence on the dynamic response of the beam
- 2013
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Ingår i: 42nd International Congress and Exposition on Noise Control Engineering 2013, INTER-NOISE 2013. - : OAL-Osterreichischer Arbeitsring fur Larmbekampfung. - 9781632662675 ; , s. 238-247
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Konferensbidrag (refereegranskat)abstract
- A well-defined rolling contact problem is studied with the intention to cover interesting aspects of tyre-road contact modeling and rolling contact in general. More specifically, the dynamic response in a steel beam caused by a steel ball rolling over it is studied by theoretical modeling of the beam- And ball dynamics as well as the contact forces. Validation of the dynamic response simulations is achieved by comparison with measurements. The contact model is shown to be greatly dependent on an accurate estimate of the real contact stiffness. A method to estimate the contact stiffness which leads to good accuracy in dynamic response simulations is presented. Although the contact stiffness is significantly lower for rubber- Asphalt interaction than for steel-steel contact, the results give useful insight for tyre-road contact modeling.
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| 19. |
- Lundberg, Oskar, 1980-, et al.
(författare)
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Non-linear contact stiffness and dynamic contact filter for rolling contacts
- 2014
-
Ingår i: FISITA 2014 World Automotive Congress - Proceedings. - : FISITA.
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Konferensbidrag (refereegranskat)abstract
- Rolling contacts present in passenger cars such as in bearings and transmission elements are sources of noise and vibration, principally for interior comfort concerns. Moreover, tyre/road noise is the main source of road traffic noise which in turn leads to sleep disturbance and annoyance. In order to simulate friction losses as well as generated noise and vibrations in any rolling contact, it is crucial to have a correct description of the dynamic excitation caused by the roughness of the surfaces in contact. In this paper, a state-dependent modelling approach previously proposed by the authors is applied to a well-defined steel-steel rolling contact. A parametric study investigating the influence of rolling speed on contact conditions is performed, indicating the limits for the use of linear point force expressions for the rolling contact investigated. The state-dependent method is based on pre-calculation of contact stiffness and contact filtering as functions of vertical relative displacement. This leads to a computationally efficient way to include the influence of surface roughness and shape of the contacting bodies in a point force expression. Only vertical contact forces are studied within the scope of this work. Tangential friction forces are likely to affect the resulting vibrations and should therefore be further studied.
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| 20. |
- Moers, E. M. T., et al.
(författare)
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Detection of plate vibration modes by means of Near-field Acoustic Holography in the presence of reflective surfaces
- 2012
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Ingår i: International Conference on Noise and Vibration Engineering 2012, ISMA 2012, including USD 2012. - : Katholieke Universiteit Leuven. - 9781622768257 ; , s. 3571-3584
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Konferensbidrag (refereegranskat)abstract
- A numerical and experimental study is presented on the influence of reflections on the reconstruction accuracy of the surface velocity of vibrating plates by means of Fourier-based Planar Near-field Acoustic Holography (PNAH) and a single-layer microphone array. At low frequencies (well below coincidence), it is shown that the effect of the presence of the reflective surface on the reconstruction depends on the source. When measuring close to the source, the classical PNAH transformation, based on the free-field radiation assumption, provides a good quantitative reconstruction of the surface vibration velocity. The effectiveness of a modified propagator is investigated which includes the effect of reflections on the inverse propagation from measured pressure at the hologram plane to surface vibration velocity at the source plane. This is done by simulations and measurements for sources that differ in velocity profile and size and that are radiating well below coincidence. Measurements are performed for a free plate in a large baffle in front of a granite block which is less than one acoustic wavelength apart.
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| 21. |
- Peerlings, Luck, et al.
(författare)
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Aero-acoustic characterization of the sudden area expansion
- 2014
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Ingår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014. - 9781634392389 ; , s. 2174-2181
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Konferensbidrag (refereegranskat)abstract
- In combustion devices, thermo-acoustic instabilities are often encountered and are formed by the complex interaction between acoustics, hydrodynamics and combustion. A common geometrical feature found in these devices is the sudden area expansion. Downstream of the area expansion a recirculation zone is formed together with an unstable shear layer when flow is present. This shear layer creates a pathway for interactions between the acoustic and the hydrodynamic field and this interaction could be a precursor for thermo-acoustic instabilities. The work presented here takes a step to gain more insight into these interactions by experimentally investigating the aero-acoustic properties of a sudden area expansion with mean flow. The aero-acoustic properties are characterized by a linear two port model and the scattering matrix representation is used to relate the state variables up-and downstream of the area expansion. The scattering coefficients of the area expansion have been determined for frequencies up to the first cut on frequency of the duct system and for a range of subsonic flow speeds. The measurements have been performed by applying a stepped sine excitation as sound excitation and by using the multi-microphone method.
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| 22. |
- Sun, Jia, et al.
(författare)
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A dynamic rotating blade model at an arbitrary stagger angle based on classical plate theory and the Hamilton's principle
- 2013
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 332:5, s. 1355-1371
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Tidskriftsartikel (refereegranskat)abstract
- A dynamic model based on classical plate theory is presented to investigate the vibration behavior of a rotating blade at an arbitrary stagger angle and rotation speed. The Hamilton's principle is applied to derive the equations of motion, which are discretised by a novel implementation of the fast and efficient collocation method for rotating structures and by the traditional Extended Galerkin method. The results obtained with these methods are compared and validated with results found in the literature and from commercial finite element software. The proposed collocation method leads to a significantly lower computation time than the Extended Galerkin method for the same accuracy. The results show a good agreement with those of the finite element method. Finally, the forced response analysis is determined for two cases; a point force and a distribution force, using a proportional damping model.
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| 23. |
- Sun, Jia, 1981-, et al.
(författare)
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Dynamic modeling of a multilayer rotating blade via quadratic layerwise theory
- 2013
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Ingår i: Composite structures. - : Elsevier. - 0263-8223 .- 1879-1085. ; 99, s. 276-287
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Tidskriftsartikel (refereegranskat)abstract
- A novel dynamic model for a multilayer rotating blade mounted at an arbitrary stagger angle using a quadratic layerwise theory is developed to study structural dynamics of the blade, particularly damping properties, using various coating layer configurations. A reduced two-dimensional (2D) model is used to describe the dynamic behavior of each layer in the weak form, while the quadratic layerwise theory is applied to interpolate the transverse shear stresses along the thickness direction. Results of numerical simulations with the reduced 2D model are compared to the full three-dimensional (3D) model showing an excellent agreement, comparable to the cubic layerwise theory, for both modal analysis and frequency response calculations. Moreover, damping analyses are performed on two types of multilayer blades: two-layer (free damping) and three-layer (constrained layer), in both non-rotating and rotating situations, and, parametric analyses with varying coating thickness and rotation speed are carried out. It is shown that damping decreases as the rotation speed increases due to inertial and Coriolis effects. Furthermore, frequency loci veering as a result of the rotation speed is observed. The proposed model gives an efficient and accurate way to study the dynamic behavior of rotating multilayer structures, such as compressor blades.
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| 24. |
- Sun, Jia, 1981-, et al.
(författare)
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General shell model for a rotating pretwisted blade
- 2013
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Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 332:22, s. 5804-5820
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Tidskriftsartikel (refereegranskat)abstract
- A novel dynamic model for a pretwisted rotating compressor blade mounted atan arbitrary stagger angle using general shell theory and including the rotationalvelocity is developed to study the eigenfrequencies and damping properties of thepretwisted rotating blade. The strain-displacement relation and constitutive modelbased on the general (thick) shell theory are applied to bring out the strain energyof the rotating blade. Using the Hamilton’s principle, the variational form of thetotal energy is derived in order to obtain the corresponding weak form for thenumerical simulation. The model is validated by comparing to literature resultsand Ansys results, showing good agreement. Parametric analyses are carried outto study the influence of the rotation velocity, the stagger angle and the radius ofthe disk on the eigenfrequencies of the pretwisted blade. Proportional dampingis included into the proposed model to investigate the influence of rotational velocityon the damping characteristics of the pretwisted rotating blade system. It isshown that, due to inertial and Coriolis eects, damping decreases as the rotation velocity increases for the lower part of the velocity range considered and eitherdecreases or increases depending on the mode order for higher velocities. Furthermore,frequency loci veering as a result of the rotation velocity is observed.The proposed model is an ecient and accurate tool for predicting the dynamicbehavior of compressor blades of arbitrary thickness, stagger angle and pretwist,potentially during the early designing stage of turbomachinery.
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| 25. |
- van Dalen, P. L., et al.
(författare)
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Experimental reconstruction of non-stationary sound and vibration sources by means of Transient Planar Near-field Acoustic Holography
- 2012
-
Ingår i: International Conference on Noise and Vibration Engineering 2012, ISMA 2012, including USD 2012. - : Katholieke Universiteit Leuven. - 9781622768257 ; , s. 3631-3643
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Konferensbidrag (refereegranskat)abstract
- A novel algorithm called Transient Planar Near-field Acoustic Holography is presented to analyse nonstationary sound and vibration sources. The method is able to obtain the time-dependent pressure, particle velocity and intensity field at the source plane without any pre-knowledge of the source by inverse propagation of measured pressure fields. This makes it possible to analyse phenomena like transients and run-ups for all kinds of vibrating and sound radiating objects. Transient responses of thin plates are analysed to experimentally validate the performance of the algorithm. The determined velocity at the center of the plate is validated using a laser vibro-meter directed at the center of the plate and the spatial fields are qualitatively compared with theoretical mode shapes. It is shown that the algorithm is able to analyse transient responses of plates with good quantitative as well as qualitative results.
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| 26. |
- Van Der Steen, R., et al.
(författare)
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Experimental and numerical study of friction and braking characteristics of rolling tires
- 2011
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Ingår i: Tire Science and Technology. - : The Tire Society. - 0090-8657 .- 1945-5852. ; 39:2, s. 62-78
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Tidskriftsartikel (refereegranskat)abstract
- Throughout the tire industry, virtual testing has been widely adopted in the design process. Both static deformation and dynamic response of the tire rolling on the road must be accurately predicted to evaluate the handling performance of a tire. Unfortunately, experimental characterization of rubber compound frictional properties is limited, and therefore, the Coulomb friction model is still often used in finite element (FE) simulations. To overcome this limitation, a different strategy is developed to capture observed effects of dry friction. The proposed friction model is decomposed into the product of a contact pressure dependent part and a slip velocity dependent part. The identification of the parameters of the slip velocity dependent part, using measured axle forces, is presented in this paper. The complete phenomenological friction model is coupled to a FE model of the tire under testing. A steady-state transport approach is used to efficiently compute the steady-state longitudinal slip characteristics, which show good quantitative agreement with experiments.
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| 27. |
- Van Der Steen, R., et al.
(författare)
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Experimental and numerical study of friction and stiffness characteristics of small rolling tires
- 2011
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Ingår i: Tire Science and Technology. - : The Tire Society. - 0090-8657 .- 1945-5852. ; 39:1, s. 5-19
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Tidskriftsartikel (refereegranskat)abstract
- Virtual testing is nowadays the standard in the design process of new tires. Besides modeling the static response of the tire itself, the dynamics of a rolling tire in contact with the road needs to be incorporated. Due to the uncontrollable environmental conditions and the complex structure of the tires, it is advantageous to use small-scale testing under more controlled conditions. Experimental characterization of frictional properties of rubber compounds is, however, limited due to the necessity of complex measurement systems. In this paper a commercially available laboratory abrasion and skid tester is used to identify both friction and stiffness characteristics of the same rubber compound. The obtained friction properties are implemented in a finite element model of the setup, and different validation steps are presented. Finally, a steady-state transport approach is used to efficiently compute a steady-state solution, which is compared with the experimental results. The numerical results show a good qualitative agreement with the experimental results.
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| 28. |
- Zea, Elias, 1989-, et al.
(författare)
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A single-layer formulation of Fourier-based planar NAH for enclosed spaces
- 2014
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Ingår i: Proceedings of EAA. - : European Acoustics Association (EAA).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- One of the limitations of Fourier-based planar near-field acoustic holography (P-NAH) is that the wave-field extrapolation only holds for outgoing waves, making the study of certain vibro-acoustic sources in reverberant environments a costly and difficult procedure. The present paper is concerned with a single-layer formulation of Fourier-based P-NAH that accounts for the presence of partially absorbing surfaces. The underlying theory is based on the WRW model, which is a rather popular technique in the seismic processing community. Unlike P-NAH, the WRWmodel proposes a solution to the forward acoustic problem, by performing the spatial convolutions via matrix multiplications. The aim of this paper is to investigate the use of the WRW model for inverse acoustics, particularly in the context of P-NAH. Numerical reconstructions with baffled point sources are carried out, investigating a geometrical case with one reflector under noise-free conditions. Several combinations of frequencies, reflection coefficients, measurement apertures and reflector positions are explored. Opportune observations are made regarding the influence of the propagation distances on the numerical implementation of the Green’s functions. The source reconstructions are performed via free-field P-NAH and via the present formulation, aiming towards a quantitative and qualitative understanding of the influence of the partially absorbing surfaces.
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| 29. |
- Zhu, Yi, 1984-
(författare)
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Adhesion in the wheel-rail contact under contaminated conditions
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Railway vehicles require a certain level of adhesion between wheel and rail to operate efficiently, reliably, and economically. Different levels of adhesion are needed depending on the vehicle running conditions. In the wheel tread–railhead contact, the dominant problem is low adhesion, as low adhesion on the railhead negatively affects railway operation: on one hand, the vehicle will lose traction resulting in delay when driving on low-adhesion tracks; on the other hand, low adhesion during deceleration will extend the braking distance, which is a safety issue. This thesis examines the influence of several contaminants, i.e., water, oil, and leaves, on the adhesion in the wheel tread–railhead contact. This study will improve our knowledge of the low-adhesion mechanism and of how various contaminants influence adhesion. The thesis consists of a summary overview of the topic and three appended papers (A–C). Papers A and B focus mainly on water and oil contamination examined using two methods, numerical simulation and lab testing. In paper A, real measured wheel and rail surfaces, low- and high-roughness surfaces, along with generated smooth surfaces are used as input to the numerical model for predicting the adhesion coefficient. Water-lubricated, oil-lubricated, and dry contacts are simulated in the model. In the research reported in paper B, scaled testing using a mini traction machine (MTM) was carried out to simulate the wheel–rail contact under lubricated conditions. Two types of disc surfaces of different roughnesses were run at different contact pressures and temperatures. A stylus machine and atomic force microscopy (AFM) were used to measure the surface topography. A study of leaf contamination on the railhead surface, based on field testing, is presented in paper C. Railhead surface samples were cut and the friction coefficient was measured on five occasions over the course of a year. Electron spectroscopy for chemical analysis (ESCA) and glow discharge optical emission spectrometry (GD-OES) were used to detect the chemical composition of the leaf-contamination layer on the railhead surface. The main conclusion of the thesis is that different contaminants reduce the adhesion coefficient in different ways. Oil reduces the adhesion coefficient by carrying the normal force due to its high viscosity. Water can reduce the adhesion coefficient to different degrees depending on the surface topography and water temperature. The mixture of an oxide layer and water contamination may have an essential impact. A leaf-formed blackish layer causes low adhesion by means of a chemical reaction between the leaves and bulk material. The thickness of the friction-reducing oxide layer predicts the friction coefficient and the extent of leaf contamination.
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