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Allmaier H.,Virtual Vehicle Research Center | Offner G.,AVL List GmbH
SAE Technical Papers | Year: 2016

Elastohydrodynamic (EHD)-simulation is a widely applied simulation technique that is used in a very diverse field of applications ranging from the study of vibroacoustics to the calculation of friction power losses in lubricated contacts. In particular, but not limited to, the automotive industry, technical advances and new requirements put current EHD simulation methodology under test. Ongoing trends like downsizing, downspeeding, start-stop and the continuing demand for increasing fuel efficiency impose new demands and challenges also on the simulation methodology. Increasing computational capabilities enable new simulation opportunities on the other hand. In the following, an overview is given on the current state of the art and today's challenges for the elastohydrodynamic simulation of journal bearings and their wide range of applications from highly loaded main bearings supporting the crank shaft in the ICE to high speed turbocharger bearings. The topics addressed in this work span a wide range from mixed lubrication, low viscosity lubricants, polymer coatings, microstructured surfaces to the simulation of the thermal behavior and the simulation of hydraulically coupled journal bearings as they are commonly present in internal combustion engines. Copyright © 2016 SAE International.


Benedikt M.,Virtual Vehicle Research Center | Benedikt M.,University of Graz | Watzenig D.,Virtual Vehicle Research Center | Hofer A.,University of Graz
Mathematical and Computer Modelling of Dynamical Systems | Year: 2013

Concerning non-iterative co-simulation, stepwise extrapolation of coupling signals is required to solve an overall system of interconnected subsystems. Each extrapolation is some kind of estimation and is directly associated with an estimation error. The introduced disturbance depends significantly on the macro-step size, i.e. the coupling step size, and influences the entire system behaviour. In addition, for synchronization purposes, sampling of the coupling signals can cause aliasing. Instead of analysing the coupling effects in the time domain, as it is commonly practised, we concentrate on a model-based approach to gain more insight into the coupling process. In this work, we consider commonly used polynomial extrapolation techniques and analyse them in the frequency domain. Based on this system-oriented point of view of the coupling process, a relation between the coupling signals and the macro-step size is available. In accordance to the dynamics of the interconnected subsystems, the model-based relation is used to select the most critical parameter, i.e. the macro-step size. Besides a 'rule of thumb' for meaningful step-size selection, a co-simulation benchmark example describing a two degree of freedom (2-DOF) mechanical system is used to demonstrate the advantages of modelling and the efficiency of the proposed method. © 2013 Copyright Taylor and Francis Group, LLC.


Steiner A.,Virtual Vehicle Research Center | Rieberer R.,University of Graz
International Journal of Refrigeration | Year: 2015

Resistance heating with PTC elements to cover the heat demand of electric vehicles reduces significantly the cruising range at low outside temperatures. Reversible heat pump systems are one of the most promising solutions for this problem. However, in heat pump mode the frost formation on the exterior heat exchanger reduces the performance and efficiency of the system. Therefore, an efficient defrost method is crucial to benefit from the heat pump also under frosting conditions. In the present paper, a transient Modelica simulation model of a reversible CO2-heat pump system with hot gas defrost was set up in order to assess the impact of different defrost start times. The model is able to handle frost growth on the exterior heat exchanger as well as defrosting. The simulation results showed an optimal point of time to conduct defrost at chosen operating conditions in order to maximize the average COP including the frosting and defrost period. © 2015 Elsevier Ltd and IIR. © 2015 Elsevier Ltd and IIR. All rights reserved.


Steiner A.,Virtual Vehicle Research Center | Rieberer R.,University of Graz
Applied Thermal Engineering | Year: 2013

The use of resistance heaters with PTC elements to cover the heat demand of electric vehicles reduces significantly the cruising range. Reversible cooling and heating systems are one of the most promising solutions for this problem. However, in heat pump mode the frost formation on the exterior heat exchanger reduces the performance and efficiency of the system. Therefore, an efficient defrosting method is crucial to benefit from the heat pump also under frosting conditions. In the present paper, measurement results of a reverse cycle defrosting process on a reversible cooling and heating system using CO 2 as working fluid for an electric city car at chosen operating condition are discussed. Further, a transient Modelica simulation model was set up in order to assess the impact of different parameters during defrosting and to optimize the process. The simulation results showed the effect of different throttle valve openings on the defrosting process and a best performing valve-opening, where the defrost efficiency was higher and the defrost time was shorter compared to the other cases. © 2013 Elsevier Ltd. All rights reserved.


Richter A.,University of Federal Defense Munich | Stocker A.,Virtual Vehicle Research Center | Muller S.,University of Federal Defense Munich | Avram G.,University of Limerick
VINE | Year: 2013

Purpose: The purpose of this paper is to provide both practice-oriented researchers and practitioners with detailed insights into the social software goals and implementation strategies for corporate environments. Also, to illustrate the novelty and specificity of corporate social software (CSS) compared to other groupware or knowledge management systems. Design/methodology/approach: The paper is grounded in the ongoing discussion on differences and commonalities of knowledge management and Enterprise 2.0 applications and motivated by the lack of scientific studies on this topic. The authors have therefore made a comprehensive study of social software adoption in corporate environments, performing a cross-case analysis of 23 enterprises. The study was meant to enable researchers and practitioners to acquire a better understanding and appropriate related explanations of the relatively new phenomenon of CSS appropriation and use. Findings: From the cross-case analysis, six main goals of CSS adoption were derived and compared with the goals of knowledge management projects and initiatives. While some of the goals set for the introduction of CSS seem to coincide with those resulting from knowledge management studies (e.g. establishing networks of experts), others appear to be novel and specific for CSS (e.g. improving employee-to-employee communication). Originality/value: By investigating 23 different cases (most of these case studies being documented by the authors), this paper presents one of the most comprehensive cross-case analyses systematically exploring pursued goals and implementation approaches adopted for CSS. The contribution of the study is relevant for both research and practice and it is aimed to contribute to the ongoing scientific debate on social software in knowledge management and information systems research. © Emerald Group Publishing Limited.


Suhr B.,Virtual Vehicle Research Center | Six K.,Virtual Vehicle Research Center
Proceedings of the 4th International Conference on Particle-Based Methods - Fundamentals and Applications, PARTICLES 2015 | Year: 2015

In the discrete element simulation of granular materials, the modelling of contacts is crucial for the macroscopic material behaviour. From the tribological point of view, friction at contacts needs to be modelled carefully, as it depends on several factors, e.g. contact normal load or temperature to name only two. In discrete element method (DEM) simulations the usage of Coulomb's law of friction is state of the art. It reduces all tribological effects to only one constant coefficient of friction. Motivated by research on wheel-rail contacts, a pressure dependency of the interparticle coefficient of friction is introduced in a new DEM model. Direct shear tests are conducted on steel spheres of a certain size distribution. The strong influence of interparticle friction on the bulk friction is shown via a variation of the constant interparticle friction coefficient. Simulations with constant and pressure dependent interparticle friction are compared. For the pressure dependent interparticle friction a pressure dependency of the bulk friction is seen which matches qualitatively the behaviour known from testing reported in literature.


Suhr B.,Virtual Vehicle Research Center | Six K.,Virtual Vehicle Research Center
Powder Technology | Year: 2016

Contact friction is a key influence factor for the shearing behaviour of granular media. In the discrete element method (DEM) contact friction is usually modelled with Coulomb's law assuming a constant interparticle friction coefficient. From tribology it is known that friction is influenced by several factors, e.g., temperature, normal stress, surface condition, etc. None of these influences can be modelled with the constant interparticle friction coefficient from Coulomb's law. For a given granular material (particle shape distribution), the usage of constant interparticle friction in DEM models generally results in constant bulk friction coefficients in the simulation of direct shear tests. While this is frequently seen in experiments with equi-sized spherical particles, papers exist in literature which report a stress dependency of bulk friction for non-spherical particles of certain materials. In this work, a stress dependency of bulk friction is obtained by introducing a model for stress dependent interparticle friction in DEM simulations. For validation experimental results of direct shear tests conducted on single or paired glass beads are used. While the bulk friction of paired spheres clearly decreases with increasing normal stress, it is nearly constant for single spheres. DEM simulations with the stress dependent interparticle friction are in good accordance with the experimental results of both single and paired spheres. A comparison with simulations, using constant interparticle friction, clearly shows the advantage of the proposed model. © 2016 .


de Rijk S.,Virtual Vehicle Research Center | Nijman E.,Virtual Vehicle Research Center
Journal of Sound and Vibration | Year: 2016

A novel method for representing the transverse vibrations of sandwich beams as equivalent Timoshenko beams is developed. Special attention is given to damping modelling together with the evanescent parts of the solutions to assert applicability of the approach to any boundary conditions. Shear stiffness is evaluated based on current knowledge. The latter is then used to update the reference theory for vibrations in sandwich beams. Analytical case studies are presented to show the performance and limitations of the method and compared with experimental data. © 2016 Elsevier Ltd.


Stocker A.,Virtual Vehicle Research Center | Kaiser C.,Virtual Vehicle Research Center
Elektrotechnik und Informationstechnik | Year: 2016

A modern vehicle is a “computer on four wheels” equipped with many different types of sensors. The so enabled continuous collection of vehicle lifecycle data facilitates the generation of innovative products, services and business models. In analogy to the Quantified-Self-movement, the USA has already evolved a plethora of Quantified Car startup companies backed by enormous amounts of risk capital, reaching more than 20 million USD in some cases. These developments clearly demonstrate how high investors perceive the market value of a working digital ecosystem for Quantified Car. This paper provides an introduction into the Quantified-Car-phenomenon and analyses the business models of three different Quantified-Car-startups: Automatic, Mojio, and Dash. One major finding is that their use cases, services and underlying technologies show many similarities. The paper closes with a discussion on the increasing competition between the players from the ICT and the automotive domain on the supremacy in the development of a digital ecosystem for Quantified Car. © 2016 The Author(s)


Veronesi G.,Virtual Vehicle Research Center | Nijman E.J.M.,Virtual Vehicle Research Center
Journal of the Acoustical Society of America | Year: 2016

When experimentally investigating the sound radiating from vibrating structures the surface is discretised into elemental areas also referred to as patches in which the surface vibrations are considered uniform. In many cases the structural Nyquist criterion imposes very small patch sizes which turn the experimental analysis into an overwhelmingly elaborate and error-prone task. The possibility to use a coarse sampling scheme for the surface velocity can greatly enhance the practical feasibility of such experimental investigations. Here the special case of a simply supported baffled plate excited by a broadband point force is considered. It is shown that accurate approximations of the radiated power may be obtained well beyond the frequency limit imposed by the structural Nyquist sampling criterion, provided the complex-valued vibration field is averaged over each patch. This is due to the fact that the structural wave components with wavenumbers greater than the acoustic wavenumber tend to be averaged out, owing to the mutual canceling of areas which vibrate out-of-phase within each patch, leaving only those components that contribute significantly to the radiated sound. It turns out, however, that this canceling process is not complete and that an error is introduced by the spatial aliasing. An analytical expression is derived allowing one to quantify this error and to optimise the patch size given a desired accuracy level and frequency range for the assessment of the radiated power. The proposed sampling criterion not only allows one to significantly reduce the measurement efforts when the radiation of vibro-acoustic systems are experimentally investigated but can also be applied to reduce the size of numerical models for weakly coupled structural-acoustic systems. © 2016 Acoustical Society of America.

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