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Sökning: LAR1:lu > Chalmers tekniska högskola > Konferensbidrag

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  • Abou-Taouk, Abdallah, et al. (författare)
  • A Four-Step Global Reaction Mechanism for CFD Simulations of Flexi-Fuel Burner for Gas Turbines
  • 2012
  • Ingår i: Turbulence, Heat and Mass Transfer 7. - 9781567003017 - 978-1-56700-301-7 ; 7, s. 785-788
  • Konferensbidrag (refereegranskat)abstract
    • A reduced four-step scheme for Computational Fluid Dynamics (CFD) analysis is presented here in the context of industrial type laboratory combustor. The present scheme has been optimized for a syngas mixture consisting of 10% CH4, 22.5% CO and 67.5% H2 by volume, and for a methane-air mixture. The optimization of the global scheme is done by comparing with the detailed San Diego mechanism using perfectly stirred reactor (PSR) and laminar flame speed calculations. The four-step global scheme has been applied to the CFD analysis of a swirl-stabilized flexi-fuel burner. Both reacting and non-reacting cases has been computed, using a hybrid Unsteady RANS/Large Eddy Simulation (URANS/LES) technique. Comparisons between CFD results and experimental data in the form of Particle Image Velocimetry (PIV) data, Planar Laser Induced Fluorescence (pLIF) and Proper Orthogonal Decomposition (POD) analysis from an atmospheric burner test rig at Lund University are presented. The CFD results scheme show good agreement with the experimental data.
  • Akenine-Möller, Tomas, 1970-, et al. (författare)
  • Approximate Soft Shadows on Arbitrary Surfaces using Penumbra Wedges
  • 2002
  • Ingår i: EGRW '02 Proceedings of the 13th Eurographics workshop on Rendering. - 1-58113-534-3 ; s. 297-306
  • Konferensbidrag (refereegranskat)abstract
    • Shadow generation has been subject to serious investigation in computer graphics, and many clever algorithms have been suggested. However, previous algorithms cannot render high quality soft shadows onto arbitrary, animated objects in real time. Pursuing this goal, we present a new soft shadow algorithm that extends the standard shadow volume algorithm by replacing each shadow quadrilateral with a new primitive, called the penumbra wedge. For each silhouette edge as seen from the light source, a penumbra wedge is created that approximately models the penumbra volume that this edge gives rise to. Together the penumbra wedges can render images that often are remarkably close to more precisely rendered soft shadows. Furthermore, our new primitive is designed so that it can be rasterized efficiently. Many real-time algorithms can only use planes as shadow receivers, while ours can handle arbitrary shadow receivers. The proposed algorithm can be of great value to, e.g., 3D computer games, especially since it is highly likely that this algorithm can be implemented on programmable graphics hardware coming out within the next year, and because games often prefer perceptually convincing shadows.
  • Askerdal, Örjan, 1973-, et al. (författare)
  • A Control Theory Approach for Analyzing the Effects of Data Errors in Safety-Critical Control Systems
  • 2002
  • Ingår i: Pacific Rim International Symposium on Dependable Computing, 2002. Proceedings. 2002. - IEEE. - 0-7695-1852-4 ; s. 105-114
  • Konferensbidrag (refereegranskat)abstract
    • Computers are increasingly used for implementing controlalgorithms in safety-critical embedded applications, such asengine control, braking control and flight surfacecontrol. Addressing the consequent coupling of control performancewith computer related errors, this paper develops a composite computerdependability/control theory methodology for analyzing the effectsdata errors have on control system dependability. The effect is measured as theresulting control error (defined as the difference between the desired value ofa physical property andits actual value). We use maximum bounds on this measure as the criterion forcontrol system failure (i.e., if the control error exceeds a certain threshold,the system has failed).In this paper we a) present suitable models of computer faults for analysis of control level effects andrelated analysis methods, and b) apply traditional control theoryanalysis methods for understanding the effects of data errors onsystem dependability. An automobile slip-control brake-system is used as an example showing the viability of our approach.
  • Assarsson, Ulf, 1972-, et al. (författare)
  • A Geometry-based Soft Shadow Volume Algorithm using Graphics Hardware
  • 2003
  • Ingår i: ACM Transactions on Graphics. Annual Symposium of the ACM SIGGRAPH, San Diego, 27-31 July 2003. - 0730-0301. ; 22:3, s. 511-520
  • Konferensbidrag (refereegranskat)abstract
    • Most previous soft shadow algorithms have either suffered from aliasing, been too slow, or could only use a limited set of shadow casters and/or receivers. Therefore, we present a strengthened soft shadow volume algorithm that deals with these problems. Our critical improvements include robust penumbra wedge construction, geometry-based visibility computation, and also simplified computation through a four-dimensional texture lookup. This enables us to implement the algorithm using programmable graphics hardware, and it results in images that most often are indistinguishable from images created as the average of 1024 hard shadow images. Furthermore, our algorithm can use both arbitrary shadow casters and receivers. Also, one version of our algorithm completely avoids sampling artifacts which is rare for soft shadow algorithms. As a bonus, the four-dimensional texture lookup allows for small textured light sources, and, even video textures can be used as light sources. Our algorithm has been implemented in pure software, and also using the GeForce FX emulator with pixel shaders. Our software implementation renders soft shadows at 0.5-5 frames per second for the images in this paper. With actual hardware, we expect that our algorithm will render soft shadows in real time. An important performance measure is bandwidth usage. For the same image quality, an algorithm using the accumulated hard shadow images uses almost two orders of magnitude more bandwidth than our algorithm.
  • Blomé, Mikael, et al. (författare)
  • Identifying Time Consuming Human Modelling Tool Activities
  • 2006
  • Ingår i: Proceedings of the 2006 SAE Digital Human Modeling for Design and Engineering Conference and Exhibition.
  • Konferensbidrag (refereegranskat)abstract
    • The aim of this study was to identify and measure time-consuming human modelling tool activities. Five human modelling tool users at Volvo were observed for five days each. The results showed a wide distribution of both indirect and direct working tasks, as well as non-value added tasks such as waiting time. Most of the activities identified appear to be necessary to perform human modelling simulations of high quality. However, the time distribution could be questioned to some extent. There are many activities associated with communication, including a variety of contacts and meetings, where there appears to be potential to increase efficiency
  • Blomé, Mikael, 0, et al. (författare)
  • Structured time observation of human modelling tool users' activites.
  • 2006
  • Ingår i: In: Proceedings of 16th Triennial World Congress on Ergonomics, International Ergonomics Association, 2006, July 10-14, Maastricht, The Netherlands..
  • Konferensbidrag (refereegranskat)abstract
    • Most statements regarding human modeling tools efficiency are based on perceived time. No structured time observation of task activities performed by a simulation engineers working with the tools are previous performed. The aim of the study is to identify digital human modelling tool users’ activates and measure the time distribution of the activities. Furthermore, measured time distribution is compare with users perceived time distribution. Five simulation engineers at Volvo were observed for five days each. The simulation engineers’ activities can be categorised in twelve groups. The direct value added work and the indirect value added work important for a new introduced tool were of similar size as direct value added work for a vehicle disassembly worker. Waiting time, there simulation is out of control e.g. waiting for information from colleague and computer processor, was perceived much longer compared to measured time. The human modelling tool seems to have matured and most of the activities identified seems to be necessary to perform human modelling simulations of high quality; however the time distribution could to some extend be questioned. There are a lot of activities associated with communication, i.e. different kinds of contacts and meetings. Therefore it appears to be a potential to increase efficiency with respect to communication.
  • Coldrey, M., et al. (författare)
  • Higher order MIMO outdoor-to-indoor measurements using repeaters
  • 2010
  • Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 978-142442519-8 - 978-1-4244-2518-1
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • In this paper we present results from a outdoorto-indoor MIMO measurement campaign where we study the effect of repeaters on singular values, spatial richness, capacity,and delay spread distributions. We present results from different repeater scenarios such as, e.g. different outdoor/indoor repeater deployments with ngle/dual polarized antennas. The measurements show that repeaters significantly enhance the received SNR while they increase the delay spread and decrease the spatial richness of the MIMO channel. However, the main conclusion is that a significant increase in channel capacity is attained when deploying repeaters mostly thanks to their ability to provide spatial multiplexing over the high-quality eigenmodes they may provide. The number of such eigenmodes is limited by the number of repeaters, deployment, and their antennas.
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