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Sökning: LAR1:lu > Chalmers tekniska högskola > Konferensbidrag

  • Resultat 1-10 av 70
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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
  • 2011
  • Ingår i: Turbulence, Heat and Mass Transfer 7. - ICHMT. - 9781567003017 - 978-1-56700-301-7 ; 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, et al. (författare)
  • Approximate soft shadows on arbitrary surfaces using Penumbra wedges
  • 2002
  • Ingår i: ACM International Conference Proceeding Series. - 1-58113-534-3 ; 28, 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.
  • Ask, Erik, et al. (författare)
  • Tractable and Reliable Registration of 2D Point Sets
  • 2014
  • Ingår i: Lecture Notes in Computer Science (Computer Vision - ECCV 2014, 13th European Conference, Zurich, Switzerland, September 6-12, 2014, Proceedings, Part I). - Springer. - 0302-9743 .- 1611-3349. - 978-3-319-10590-1 (Online) - 978-3-319-10589-5 (Print) - 978-3-319-10589-5 ; 8689, s. 393-406
  • Konferensbidrag (refereegranskat)abstract
    • This paper introduces two new methods of registering 2D point sets over rigid transformations when the registration error is based on a robust loss function. In contrast to previous work, our methods are guaranteed to compute the optimal transformation, and at the same time, the worst-case running times are bounded by a low-degree polynomial in the number of correspondences. In practical terms, this means that there is no need to resort to ad-hoc procedures such as random sampling or local descent methods that cannot guarantee the quality of their solutions. <br /> <br /> We have tested the methods in several different settings, in particular, a thorough evaluation on two benchmarks of microscopic images used for histologic analysis of prostate cancer has been performed. Compared to the state-of-the-art, our results show that the methods are both tractable and reliable despite the presence of a significant amount of outliers.
  • Askerdal, Örjan, 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, 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.
  • Berntsson Svensson, Richard, et al. (författare)
  • A Case Study Evaluation of the Guideline-Supported QUPER Model for Elicitation of Quality Requirements
  • 2015
  • Ingår i: Requirements Engineering: Foundation for Software Quality/Lecture Notes in Computer Science. - Springer. - 1611-3349 .- 0302-9743. - 978-3-319-16100-6 - 978-3-319-16101-3 ; 9013, s. 230-246
  • Konferensbidrag (refereegranskat)abstract
    • [Context &amp; motivation] For market-driven software product developing organizations operating on a competitive open market, it is important to plan the product’s releases so that they can reach the market as early as possible with a competitive level of quality compared to its competitors&#39; products. Hence, quality requirements can be seen as a key competitive advantage. The QUPER model was developed with the aim to support high-level decision-making in release planning of quality requirements. [Question/problem] As a follow up on previous studies on QUPER, this study investigates: What are practitioner&#39;s views on the utilities of QUPER extended with guidelines including domain-specific examples? [Principal ideas/results] In the presented case study, a set of detailed guidelines of how to apply QUPER in practice, including how to handle cost dependencies between quality requirements, was evaluated at a case company in the mobile handset domain with 24 professionals using real quality requirements. [Contribution] The results point to the importance of having concrete guidelines combined with instructive examples from real practice, while it is not always obvious for a practitioner to transfer cost-dependency examples into the domains that are different from the example domain. The transferability of guidelines and examples to support methodology adoption is an interesting issue for further research.
  • Berntsson Svensson, Richard, et al. (författare)
  • Prioritization of quality requirements: State of practice in eleven companies
  • 2011
  • Ingår i: 2011 IEEE 19th International Requirements Engineering Conference, RE 2011; Trento; 29 August 2011 through 2 September 2011. - 978-145770923-4 ; s. 69-78
  • Konferensbidrag (refereegranskat)abstract
    • Requirements prioritization is recognized as an important but challenging activity in software product development. For a product to be successful, it is crucial to find the right balance among competing quality requirements. Although literature offers many methods for requirements prioritization, the research on prioritization of quality requirements is limited. This study identifies how quality requirements are prioritized in practice at 11 successful companies developing software intensive systems. We found that ad-hoc prioritization and priority grouping of requirements are the dominant methods for prioritizing quality requirements. The results also show that it is common to use customer input as criteria for prioritization but absence of any criteria was also common. The results suggests that quality requirements by default have a lower priority than functional requirements, and that they only get attention in the prioritizing process if decision-makers are dedicated to invest specific time and resources on QR prioritization. The results of this study may help future research on quality requirements to focus investigations on industry-relevant issues.
  • 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
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