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- Andric, Jelena, 1979, et al.
(författare)
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A particle-level rigid fiber model for high-Reynolds number flow, implemented in a general-purpose CFD code
- 2013
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Ingår i: 8th International Conference on Multiphase Flow ICMF 2013, Korea.
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Konferensbidrag (refereegranskat)abstract
- A particle-level rigid fiber model has been integrated into a general-purpose, open source computational fluid dynamics code to carry out detailed studies of fiber–flow interactions in realistic flow fields. The fibers are modeled as chains of cylindrical segments, and their translational and rotational degrees of freedom are considered. The equations of motion contain the contributions from hydrodynamic forces and torques, and the segment inertia is taken into account. The model is validated for the rotational motion of isolated fibers in simple shear flow, and the computed period of rotation is in good agreement with the one computed using Jeffery’s equation for a prolate spheroid with an equivalent aspect ratio. The model is applied by suspending a number of fibers in the swirling flow of a conical diffuser, resembling one stage in the dry-forming of pulp mats. The Reynolds-averaged Navier–Stokes equations with an eddy-viscosity turbulence model are employed to describe the fluid motion, and a one-way coupling between the fibers and the fluid phase is included. The dependence of the fiber motion on initial position and density is analyzed.
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| 4. |
- Andric, Jelena, 1979, et al.
(författare)
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A study of a flexible fiber model and its behavior in DNS of turbulent channel flow
- 2013
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Ingår i: Acta Mechanica. - : Springer Science and Business Media LLC. - 0001-5970 .- 1619-6937. ; 224:10, s. 2359-2374
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of individual flexible fibers in a turbulent flow field have been analyzed, varying their initial position, density and length. A particlelevel fiber model has been integrated into a general-purpose, open source Computational Fluid Dynamics (CFD) code. The fibers are modeled as chains of cylindrical segments connected by ball and socket joints. The equations of motion of the fibers contain the inertia of the segments, the contributions from hydrodynamic forces and torques, and the connectivity forces at the joints. Direct Numerical Simulation (DNS) of the incompressible Navier–Stokes equations is used to describe the fluid flow in a plane channel and a one-way coupling is considered between the fibers and the fluid phase. We investigate the translational motion of fibers by considering the mean square displacement of their trajectories. We find that the fiber motion is primarily governed by velocity correlations of the flow fluctuations. In addition, we show that there is a clear tendency of the thread-like fibers to evolve into complex geometrical configurations in a turbulent flow field, in fashion similar to random conformations of polymer strands subjected to thermal fluctuations in a suspension. Finally, we show that fiber inertia has a significant impact on reorientation time-scales of fibers suspended in a turbulent flow field.
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- Andrić, J., et al.
(författare)
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Description and validation of a flexible fiber model, implemented in a general purpose CFD code
- 2013
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Ingår i: Proc. 8th Int. Conf. Multiphase Flow.
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Konferensbidrag (refereegranskat)abstract
- A flexible fiber model has been implemented in a general purpose open-source Computational Fluid Dynamics code. The fibers are modeled as chains of cylindrical segments, and all the degrees of freedom necessary to realistically reproduce the dynamics of real fibers, are taken into account. Each segment is tracked individually and their equations of motion account for the hydrodynamic forces and torques from the interaction with the fluid, the elastic bending and twisting torques, and the connectivity forces and moments that ensure the fiber integrity. The segment inertia is taken into account and a one-way coupling with the fluid phase is considered. The model is applied to simulate the rotational motion of an isolated fiber in a low segment Reynolds number shear flow. In the case of a stiff fiber, the computed period of rotation is in good agreement with the one computed using Jeffery’s equation for an equivalent spheroid aspect ratio. A qualitative comparison is made with experimental data for flexible fibers. Further, a generic test case is described and used to validate the energy conservation and the response time of the fiber model concept. These results show that the implemented model can reproduce the known dynamical behavior of rigid and flexible fibers successfully.
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- Bryant, Lia, et al.
(författare)
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Location and Unlocation : Examining Gender and Telephony through AutoEthnographic Textual and Visual Methods
- 2013
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Ingår i: International Journal of Qualitative Methods. - : SAGE Publications. - 1609-4069. ; 12, s. 403-419
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Tidskriftsartikel (refereegranskat)abstract
- Studies on gender and telephony tend to be quantitative and depict the purposes for which women and men use mobile telephones and landlines. Qualitative studies on the topic predominantly rely on face-to-face interviews to examine how telephone use genders space. We suggest these traditional methods of data collection leave unexamined the emotional and social relationships that emerge and are enabled by telephone use which at times reconfigure and gender social spaces. In this article we present a collaborative autoethnographic inquiry based on our own telephone lives. We introduce a reflexive visual and textual methodological design, specifically diary notes, memory work, and photography, developed from our lives as researcher and researched. We examine an important theme in our findings, the physical placement of the telephone and the phone holder’s awareness of the physicality of the telephone, which illustrates the importance of our methodological choices. We show how the placement of the phone by the users both genders space and creates emotional spaces.
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- Dalal, Koustuv, 1969-, et al.
(författare)
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Interactions between microfinance programmes and non-economic empowerment of women associated with intimate partner violence in Bangladesh : a cross-sectional study
- 2013
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Ingår i: BMJ Open. - : BMJ Publishing Group Ltd. - 2044-6055. ; 3:12
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Tidskriftsartikel (refereegranskat)abstract
- Objective: This study aims to examine the associations between microfinance programme membership and intimate partner violence (IPV) in different socioeconomic strata of a nationally representative sample of women in Bangladesh. Methods: The cross-sectional study was based on a nationally representative interview survey of 11 178 ever-married women of reproductive age (15-49 years). A total of 4465 women who answered the IPV-related questions were analysed separately using chi(2) tests and Cramer's V as a measure of effect size to identify the differences in proportions of exposure to IPV with regard to microfinance programme membership, and demographic variables and interactions between microfinance programme membership and factors related to non-economic empowerment were considered. Results: Only 39% of women were members of microfinance programmes. The prevalence of a history of IPV was 48% for moderate physical violence, 16% for severe physical violence and 16% for sexual violence. For women with secondary or higher education, and women at the two wealthiest levels of the wealth index, microfinance programme membership increased the exposure to IPV two and three times, respectively. The least educated and poorest groups showed no change in exposure to IPV associated with microfinance programmes. The educated women who were more equal with their spouses in their family relationships by participating in decision-making increased their exposure to IPV by membership in microfinance programmes. Conclusions: Microfinance plans are associated with an increased exposure to IPV among educated and empowered women in Bangladesh. Microfinance firms should consider providing information about the associations between microfinance and IPV to the women belonging to the risk groups.
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- Fall, Andreas B., et al.
(författare)
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A physical cross-linking process of cellulose nanofibril gels with shear-controlled fibril orientation
- 2013
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 9:6, s. 1852-1863
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanofibrils constitute the smallest fibrous components of wood, with a width of approximately 4 nm and a length in the micrometer range. They consist of aligned linear cellulose chains with crystallinity exceeding 60%, rendering stiff, high-aspect-ratio rods. These properties are advantageous in the reinforcement components of composites. Cross-linked networks of fibrils can be used as templates into which a polymer enters. In the semi-concentrated regime (i.e. slightly above the overlap concentration), carboxy methylated fibrils dispersed in water have been physically cross-linked to form a volume-spanning network (a gel) by reducing the pH or adding salt, which diminishes the electrostatic repulsion between fibrils. By applying shear during or after this gelation process, we can orient the fibrils in a preferred direction within the gel, for the purpose of fully utilizing the high stiffness and strength of the fibrils as reinforcement components. Using these gels as templates enables precise control of the spatial distribution and orientation of the dispersed phase of the composites, optimizing the potentially very large reinforcement capacity of the nanofibrils.
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- Giritli Nygren, Katarina, et al.
(författare)
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Public e-services from inside : A case study on technology's influence on work conditions in a government agency
- 2013
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Ingår i: International Journal of Public Sector Management. - 0951-3558 .- 1758-6666. ; 26:6, s. 455-468
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The purpose of this paper is to discuss the consequences of citizens' increased use of public e-services for agency employees' work situation. Design/methodology/approach: In order to accomplish the purpose of the paper the authors focus on the way in which the increased use of public e-services also implies internal process and routine changes in public administration. The authors analyze work conditions for case officers at a government agency in Sweden by applying occupational ideal types to identify the specific work conditions in the studied case. The case study is based on qualitative data collected with a back office perspective. Findings: The findings indicate a new hybrid organization where the increased use of e-services challenges earlier demands for competence. The transformation of e-government has implications for job codification, rule observation, job specification, and interaction with the general public. Originality/value: The paper extends the knowledge on how the increased use of public e-services affects back-office work conditions, with an increased high level of complexity in work content, but with low level of work autonomy. It argues that studying back-office work conditions is an important management issue in public administration research as well as practice. © Emerald Group Publishing Limited.
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