| 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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