| 51. |
- Liu, Yang, et al.
(author)
-
A Study Towards Reliability- and Delay-Critical Wireless Communication for RoboCup Robotic Soccer Application
- 2007
-
In: 2007 International Conference on Wireless Communications, Networking and Mobile Computing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1424413117 - 9781424413119 - 1424413125 - 1424413125 - 1424413117 ; , s. 633-636
-
Conference paper (peer-reviewed)abstract
- RoboCup is an international competition for a team of multiple fast-moving robots under a dynamic environment to autonomously play soccer game against another team. Due to the nature of the competition, the requirements and constraints for the wireless communication are extremely tight. The challenge is that wireless communication is involved in the control loop and therefore the reliability and propagation delay are vital factors which directly affect the team performance. Beside, various interferences with known and unknown frequency / transmission power usually exist at the competition site, which are hazardous environment to achieve reliable and low latency performance for wireless communication. This paper investigates the performance strengths and weaknesses of wireless communication means e.g. RF, IEEE 802.11a/b, IEEE 802.15.4, DECT, Linx, etc, which are commonly used nowadays in different RoboCup teams and propose improvements towards reliable and delay-critical wireless communication.
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| 52. |
- Roditcheva, Olga
(author)
-
Numerical Modelling of Soot Formation in Turbulent Non-Premixed Flames
- 2000
-
Doctoral thesis (other academic/artistic)abstract
- This thesis describes an extended flamelet approach for modelling of soot formation in turbulent hydrocarbons diffusion flames. Detailed chemical kinetic mechanisms are used to compute species concentrations, temperature, density and soot formation rates as functions of flamelet coordinates in the space of mixture fraction and scalar dissipation rate. An ensemble average based on a presumed probability density function of the mixture fraction and scalar dissipation rate provides the mean density, species concentrations, mixture enthalpy, temperature and soot formation rates. A semi-empirical two-equation model of finite rate soot formation is applied to methane/air turbulent diffusion flames at different pressures and to propane/air turbulent flames with different air temperatures. Soot number density and soot volume fraction are modelled by transport equations with empirical expressions for source terms, which represent soot formation and oxidation rates. It is shown that the model gives reasonable results for the flames at atmospheric pressure. It, however, over-predicts the soot yield, if the model parameters calibrated for the atmospheric pressure flames are used. It is shown that a decrease of the surface growth rate constant in proportion to 1/p leads to good agreement with the experiment. Models of soot oxidation due to different chemical species, such as O2, H2O, CO2, OH, O and H, are evaluated at the pressure range from 1 to 3 atm. It is found that oxidation of soot by hydroxyl radicals, OH, is the dominating factor in soot burnout. The ability of an extended flamelet approach, with semi-empirical modelling of soot formation, to reproduce the effect of residence time in the process of soot formation is examined. A decrease in residence time is achieved by controlling fuel injection diameter while fuel mass flow rate is kept the same. It is shown that the semi-empirical soot model is able to predict a decrease in soot volume fraction when there is a decrease in the residence time. The effect of air preheat on soot formation is investigated numerically for propane/air diffusion flames at two incoming air temperatures Ta=323 K and Ta=773 K. The air preheat leads to an increase in the flame temperature and in the concentration of soot precursor species, which leads to an increase in soot concentration in the flame. However, the increase in temperature in the post flame zone leads to an increase in the soot oxidation rate and the amount of soot in the exhaust gases is drastically reduced. To account for the temperature effect on the soot formation modifications to an existing semi-empirical model are proposed, which take into account bell-shape soot dependence on temperature. A presumed probability density function and flamelet library approach is developed further in order to incorporate the influence of turbulence on soot formation. The numerical calculations are compared with experimental measurements and previous numerical simulations with a simple model for calculating mean source terms.
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| 53. |
- Wu, Zhilei
(author)
-
Numerical Study of Dispersed Two-phase Flows
- 2000
-
Doctoral thesis (other academic/artistic)abstract
- This thesis considers the numerical study of dispersed two-phase flows.Numerical simulations have been done to investigate the particle trasportation/dispersion effect in turbulent two-phase flows. Both turbulent bubble/water flows and turbulent particle/air flows are studied. Eulerian/Eulerian approach and Eulerian/Lagrangian approachs were both used in the studies. In the Eulerian-Eulerian approach, k-epsilon model is used to model the continuous phase turbulence. The effect of interfacial forces due to mean properties and also fluctuating motions are studied in the bubbly flow simulations. In Eulerian/Lagrangian approach, Large Eddy Simulation is used to model the continuous phase turbulence, and discrete particles are tracked within the flow field predicted by LES. LES of a baffled stirred reactor in the presence of bubbles is performed. The effect of bubbles on the properties of the continuous phase are investigated. A Eulerian/Eulerian model is studied by using data obtained from LES-LPT (Large Eddy Simulation-Lagrangian Particle Tracking) of the flow in a stirred reactor. The turbulent kinetic energy of the dispersed phase and fluid-particle turbulent covariance were obtained both from direct statistics of LES simulation and closure model calculations. Results show the applicability of certain Eulerian/Eulerian models to gas-liquid reactors. Foundamental experimental studies on simulataneous two-phase DPIV are carried out. Two cameras are used to catch the information of both phases simultaneously. One camera pick up the infomationn of one phase and the other pick up the information of both phases. By post-processing, the simultaneous flow field for each phase can be obtained. LES-LPT (Large Eddy Simulation-Lagrangian Particle Tracking) is also carried out to study the same flow case. Good agreement of the results between experiment and LES-LPT shows the ability of both methods in the study of two-phase flow systems.
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| 54. |
- Dyverfeldt, Petter, 1980-, et al.
(author)
-
Quantification of intravoxel velocity standard deviation and turbulence intensity by generalizing phase-contrast MRI
- 2006
-
In: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 56:4, s. 850-858
-
Journal article (peer-reviewed)abstract
- Turbulent flow, characterized by velocity fluctuations, is a contributing factor to the pathogenesis of several cardiovascular diseases. A clinical noninvasive tool for assessing turbulence is lacking, however. It is well known that the occurrence of multiple spin velocities within a voxel during the influence of a magnetic gradient moment causes signal loss in phase-contrast magnetic resonance imaging (PC-MRI). In this paper a mathematical derivation of an expression for computing the standard deviation (SD) of the blood flow velocity distribution within a voxel is presented. The SD is obtained from the magnitude of PC-MRI signals acquired with different first gradient moments. By exploiting the relation between the SD and turbulence intensity (TI), this method allows for quantitative studies of turbulence. For validation, the TI in an in vitro flow phantom was quantified, and the results compared favorably with previously published laser Doppler anemometry (LDA) results. This method has the potential to become an important tool for the noninvasive assessment of turbulence in the arterial tree.
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| 55. |
- Ekelin, Annelie, et al.
(author)
-
Exploring Digital Storytelling as a method for participatory design
- 2008
-
In: PDC '08 Proceedings of the Tenth Anniversary Conference on Participatory Design 2008. - : ACM Press. - 9780981856100 ; , s. 297-298
-
Conference paper (peer-reviewed)abstract
- The core of Participatory Design builds on collaborative processes of users, designers and other stakeholders. [2] In order to realize this ambition a range of methods and techniques have been developed and used. Initially it was the ethnographic methods that were regarded as the most valuable ones, especially when investigating the userś everyday practices. [3] During the last years the methods repertoire has been expanded to also include methods inspired by narrative and visualization methods (games, story boards, digital scenarios etc.) [1, 7]
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| 56. |
- Chronéer, Diana, et al.
(author)
-
Systems Thinking Benefits in Supply Change Management : An illustration of the viable systems model in a supply chain
- 2009
-
In: International Journal of Intelligent Systems Technologies and Applications. - : Inderscience Publishers. - 1740-8865 .- 1740-8873. ; 6:3/4, s. 227-248
-
Journal article (peer-reviewed)abstract
- Existing product development models are solely an organisational matter. They do not take into consideration the whole Supply chain (SC) and its different actors. In this article, we investigate how Supply Chain Management and Viable System Model (VSM) can support and create an effective use of information in product development and hence identify critical linkages in the SC. The aim is to introduce VSM as a framework that enables an analysis of companies’ SCs and visualise vital inter-organisational relationships that should be integrated in product development.
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| 57. |
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| 58. |
- Almgren, Karin, et al.
(author)
-
Role of fibre-fibre and fibre-matrix adhesion in stress transfer in composites made from resin-impregnated paper sheets.
- 2009
-
In: International Journal of Adhesion and Adhesives. - : Elsevier BV. - 0143-7496 .- 1879-0127. ; 29:5, s. 551-557
-
Journal article (peer-reviewed)abstract
- Paper-reinforced plastics are gaining increased interest as packaging materials, where mechanical properties are of great importance. Strength and stress transfer in paper sheets are controlled by fibre-fibre bonds. In paper-reinforced plastics, where the sheet is impregnated with a polymer resin, other stress-transfer mechanisms may be more important. The influence of fibre-fibre bonds on the strength of paper-reinforced plastics was therefore investigated. Paper sheets with different degrees of fibre-fibre bonding were manufactured and used as reinforcement in a polymeric matrix. Image analysis tools were used to verify that the difference in the degree of fibre-fibre bonding had been preserved in the composite materials. Strength and stiffness of the composites were experimentally determined and showed no correlation to the degree of fibre-fibre bonding, in contrast to the behaviour of unimpregnated paper sheets. The degree of fibre-fibre bonding is therefore believed to have little importance in this type of material, where stress is mainly transferred through the fibre-matrix interface.
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| 59. |
- Hilletofth, Per
(author)
-
Differentiated Supply Chain Strategy - Response to a fragmented and complex market
- 2008
-
Licentiate thesis (other academic/artistic)abstract
- Supply Chain Management (SCM) aims to synchronize the requirements of customers with the flow of materials from suppliers, in order to satisfy the needs of the customers as costefficiently as possible. This has become a difficult task due to several developments in the market, such as increased competition, increased demand variability, increased product variety, increased amounts of customer-specific products, and shortening product life cycles. These developments, due in part to globalization, provide additional management challenges and new practices in which supply chains are designed and managed, and can eventually make the difference between companies staying competitive or not. The overall purpose of this thesis is to investigate how complexity and globalization affect supply chain design and operations. The main emphasis has been on producing descriptive results of the studied phenomenon. This research involves five case studies covering international transportation structures used in SCM, the selection of supply chain strategies in different business environments, and the role of information systems and technology in achieving the objective of SCM. In this thesis it has been concluded that in order to cope with increasingly complex and fragmented markets companies need more differentiated transportation structures, modes, and supply chains. Furthermore, to effectively manage this, information systems and advanced decision support tools are required. In addition, this thesis has shown that current taxonomies for supply chain strategy selection are too simplistic due to three major problems: they mediate that it is a question of choosing one supply chain strategy for the entire company,they regard markets as rather homogeneous, and they link each supply chain strategy to a specific business context. Instead, it has been concluded that in order to better satisfy differing customer needs in various markets it is increasingly necessary to develop a differentiated supply chain strategy by utilizing different manufacturing and delivery strategies concurrently. Thus, a need exists for new taxonomies for supply chain strategy selection which recognize that the markets are becoming more fragmented and complex, that customer preferences differ across customer/market segments, and that there is a need to differentiate the supply chain strategy. This thesis also highlights several requirements of a differentiated supply chain strategy. Firstly, extended supply chain collaboration is required, since a differentiated supply chain strategy will involve more supply chain partners than a traditional supply chain strategy. Secondly, there is a need for more transportation mode alternatives, particularly intermodal, both in supply and distribution operations, due to the fact that differentiation requires diversity. In this thesis, intermodal landbridge freight services are highlighted as one interesting avenue, which could potentially facilitate a more differentiated supply chain strategy. Thirdly, more integrated information systems are needed along with decision support tools. This study illustrates that agent based modeling appears to be an interesting method for developing realistic decision support tools in the context of complex supply chains. An interesting aspect for further research is to investigate how different manufacturing and delivery strategies can be used concurrently in international supply chains. Moreover, there are several requirements and opportunities of a differentiated supply chain strategy, and these have to be investigated further
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| 60. |
- Wang, Tiesheng, 1975, et al.
(author)
-
Tracking moving objects in video using enhanced mean shift and region-based motion field
- 2007
-
In: proc. of European Signal Processing Conference ( EUSIPCO '07), Sept. 2007, Poland.
-
Conference paper (peer-reviewed)abstract
- In this paper, we propose a scheme for moving object tracking from videos by combining mean shift and motion field statistics. For mean shift, we employ an enhanced spatial-range mean shift that enables a reduced number of oversegmentation. For motion statistics, we combine the optical flow and high-order moment to generate motion regions that are associated with moving objects (or object parts). Experiments have been conducted on several indoor and outdoor (color/gray-scale) image sequences ranging from simple to median complexity. To evaluate the performance, three objective criteria are applied in addition to the visual inspection. The results show that the proposed method is promising for moving object tracking in video, with an averaging detection rate of 95%. Further, the proposed scheme is compared with that using the conventional mean shift for the tracking, indicating a significantly reduction in false alarm (≈ 30%).
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