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| 2. |
- Hoffman, Johan, et al.
(författare)
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Unicorn : Parallel adaptive finite element simulation of turbulent flow and fluid-structure interaction for deforming domains and complex geometry
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present a framework for adaptive finite element computation of turbulent flow and fluid-structure interaction, with focus on general algorithms that allow for complex geometry and deforming domains. We give basic models and finite element discretization methods, adaptive algorithms and strategies for e cient parallel implementation. To illustrate the capabilities of the computational framework, we show a number of application examples from aerodynamics, aero-acoustics, biomedicine and geophysics. The computational tools are free to download open source as Unicorn, and as a high performance branch of the finite element problem solving environment DOLFIN, both part of the FEniCS project
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| 3. |
- Hoffman, Johan, et al.
(författare)
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Adaptive modeling of turbulent flow with residual based turbulent kinetic energy dissipation
- 2011
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Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier BV. - 0045-7825 .- 1879-2138. ; 200:37-40, s. 2758-2767
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we first review our recent work on a new framework for adaptive turbulence simulation: we model turbulence by weak solutions to the Navier-Stokes equations that are wellposed with respect to mean value output in the form of functionals, and we use an adaptive finite element method to compute approximations with a posteriori error control based on the error in the functional output. We then derive a local energy estimate for a particular finite element method, which we connect to related work on dissipative weak Euler solutions with kinetic energy dissipation due to lack of local smoothness of the weak solutions. The ideas are illustrated by numerical results, where we observe a law of finite dissipation with respect to a decreasing mesh size.
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| 4. |
- Hoffman, Johan, et al.
(författare)
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Unified Continuum modeling of fluid-structure interaction
- 2011
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Ingår i: Mathematical Models and Methods in Applied Sciences. - : World Scientific. - 0218-2025. ; 21:3, s. 491-513
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we describe an incompressible Unified Continuum(UC) model in Euler (laboratory) coordinates with a moving mesh for tracking the fluid-structure interface as part of the discretization, allowing simple and general formulation and efficient computation. The model consists of conservation equations for mass and momentum, a phase convection equation and a Cauchy stress and phase variable theta as data for defining material properties and constitutive laws. We target realistic 3D turbulent fluid-structure interaction (FSI) applications, where we show simulation results of a flexible flag mounted in the turbulent wake behind a cube as a qualitative test of the method, and quantitative results for 2D benchmarks, leaving adaptive error control for future work. We compute piecewise linear continuous discrete solutions in space and time by a general Galerkin (G2) finite element method (FEM). We introduce and compensate for mesh motion by defining a local arbitrary Euler-Lagrange (ALE) map on each space-time slab as part of the discretization, allowing a sharp phase interface given by theta on cell facets. The Unicorn implementation is published as part of the FEniCS Free Software system for automation of computational mathematical modeling. Simulation results are given for a 2D stationary convergence test, indicating quadratic convergence of the displacement, a simple 2D Poiseuille test for verifying correct treatment of the fluid-structure interface, showing quadratic convergence to the exact drag value, an established 2D dynamic flag benchmark test, showing a good match to published reference solutions and a 3D turbulent flag test as indicated above.
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| 5. |
- Jansson, Johan, 1978-, et al.
(författare)
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Gestural 3D Interaction with a Beating Heart : Simulation Visualization and Interaction
- 2011
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Ingår i: Proceedings of SIGRAD 2011. - : Linköping University Electronic Press. - 9789173930086
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Konferensbidrag (refereegranskat)abstract
- The KTH School of Computer Science and Communication (CSC) established a strategic platform in Simulation-Visualization-Interaction (SimVisInt) in 2009, focused on the high potential in bringing together CSC core com-petences in simulation technology, visualization and interaction. The main part of the platform takes the form aset of new trans-disciplinary projects across established CSC research groups, within the theme of ComputationalHuman Modeling and Visualization: (i) interactive virtual biomedicine (HEART), (ii) simulation of human mo-tion (MOTION), and (iii) virtual prototyping of human hand prostheses (HAND). In this paper, we present recentresults from the HEART project that focused on gestural and haptic interaction with a heart simulation.
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| 6. |
- Abreu, Rodrigo, et al.
(författare)
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Adaptive computation of aeroacoustic sources for a rudimentary landing gear using lighthill's analogy
- 2011
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Ingår i: 17th AIAA/CEAS AeroacousticsConference 2011.
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Konferensbidrag (refereegranskat)abstract
- We present our simulation results for the benchmark problem of the ow past a Rudimentary Landing Gear (RLG) using a General Galerkin (G2) nite element method, also referred to as Adaptive DNS/LES. In G2 no explicit subgrid model is used, instead the compuational mesh is adaptively re ned with respect to an a posteriori error es-timate of a quantity of interest in the computation, in this case the drag force on the RLG. Turbulent boundary layers are modeled using a simple wall layer model with the shear stress at walls proportional to the skin friction, which here is assumed to be small and, therefore, can be approximated by zero skin friction. We compare our results with experimental data and other state of the art computations, where we nd good agreement in sound pressure levels, surface velocities and ow separation. We also compare with detailed surface pressure experimental data where we nd largely good agreement, apart from some local dierences for which we discuss possible explanations.
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| 7. |
- Ahlström, Christine, et al.
(författare)
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Feedback modeling of non-esterified fatty acids in rats after nicotinic acid infusions
- 2011
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Ingår i: JOURNAL OF PHARMACOKINETICS AND PHARMACODYNAMICS. - 1567-567X. ; 38:1, s. 1-24
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Tidskriftsartikel (refereegranskat)abstract
- A feedback model was developed to describe the tolerance and oscillatory rebound seen in non-esterified fatty acid (NEFA) plasma concentrations following intravenous infusions of nicotinic acid (NiAc) to male Sprague-Dawley rats. NiAc was administered as an intravenous infusion over 30 min (0, 1, 5 or 20 μmol kg(-1) of body weight) or over 300 min (0, 5, 10 or 51 μmol kg(-1) of body weight), to healthy rats (n = 63), and serial arterial blood samples were taken for measurement of NiAc and NEFA plasma concentrations. Data were analyzed using nonlinear mixed effects modeling (NONMEM). The disposition of NiAc was described by a two-compartment model with endogenous turnover rate and two parallel capacity-limited elimination processes. The plasma concentration of NiAc was driving NEFA (R) turnover via an inhibitory drug-mechanism function acting on the formation of NEFA. The NEFA turnover was described by a feedback model with a moderator distributed over a series of transit compartments, where the first compartment (M (1)) inhibited the formation of R and the last compartment (M ( N )) stimulated the loss of R. All processes regulating plasma NEFA concentrations were assumed to be captured by the moderator function. The potency, IC (50), of NiAc was 45 nmol L(-1), the fractional turnover rate k ( out ) was 0.41 L mmol(-1) min(-1) and the turnover rate of moderator k ( tol ) was 0.027 min(-1). A lower physiological limit of NEFA was modeled as a NiAc-independent release (k ( cap )) of NEFA into plasma and was estimated to 0.032 mmol L(-1) min(-1). This model can be used to provide information about factors that determine the time-course of NEFA response following different modes, rates and routes of administration of NiAc. The proposed model may also serve as a preclinical tool for analyzing and simulating drug-induced changes in plasma NEFA concentrations after treatment with NiAc or NiAc analogues.
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| 8. |
- Bjarnestam, Jesper, 1974-
(författare)
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En hållbar trafiklösning för nya Slussen? : Uppfattningar om hållbarhet och hållbar stadsutveckling i Slussenprojektet
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis examines perceptions of sustainability and sustainable urban development among actors involved in the project of rebuilding Slussen in central Stockholm. Views on the suggested new traffic solution and what would make a sustainable solution, the concepts of sustainability and sustainable urban development and how these concepts are interpreted and applied as policy, are especially investigated. A semi-structured qualitative interview study has been carried out and the respondents include city officials, politicians, representatives of interest groups, consultants and researchers. Stockholm, European Green Capital in 2010, sets high goals for sustainability. As concept, sustainability is also frequently used in much of the city´s planning material such as the budget, environmental programme and urban development documents. However, it has not been included in the goals of the Slussen project. Even though, interviewees representing the city view the project as a sustainability project whereas other respondents clearly question this view. The study suggests that a determining factor for this division is how the sustainability concept is defined (or not), also how car traffic is viewed in urban sustainable development. The thesis shows that instead of planning for sustainable transportation, traditional business-as-usual traffic planning has dominated the Slussen project. The main reasons are that the new traffic solution, although including new walking and cycling bridges as well as a new bus terminal, includes planning for increased car traffic, an eight lane bridge to provide for it and a high degree of separation instead of integration of transport modes. Many of the interviewees also perceive of the suggested new main bridge as a motorway and the walking bridge as being both socially and culturally unsustainable in its long and narrow design. The new traffic solution in itself is viewed as unsustainable since it would bring about the abandonment of a more than 300 year old tradition of double and equal bridges at Slussen. Finally, the study suggests that the planned new traffic solution would have both looked different and been perceived of as more sustainable if sustainability had been included in the project goals. However, this would only have been the case if the concept was properly defined and implemented.
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| 9. |
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| 10. |
- Ekblom, Kim, 1970-, et al.
(författare)
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Iron stores and HFE genotypes are not related to increased risk of first-time myocardial infarction : a prospective nested case-referent study
- 2011
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Ingår i: International Journal of Cardiology. - : Elsevier BV. - 0167-5273 .- 1874-1754. ; 150:2, s. 169-172
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Our objectives were to study the relationship between iron stores, HFE genotypes and the risk for first-ever myocardial infarction. Methods: First-ever myocardial infarction cases (n=618) and double matched referents from the Northern Sweden Health and Disease Cohort Study were studied in a prospective nested case-referent setting. Plasma iron, total iron binding capacity, transferrin iron saturation and ferritin were analyzed, as well as several confounders. HFE C282Y and H63D genotypes were determined. Results: There was an inverse risk association for myocardial infarction in the highest quartiles of iron (OR 0.68; 95% CI 0.48-0.96) and transferrin iron saturation (OR 0.62; 95% CI 0.42-0.89) in men. This association, however, was lost after adjusting for C-reactive protein. Women homozygous for H63D had a higher risk for myocardial infarction. Conclusions: No risk association between high iron stores and first-ever myocardial infarction was found. The higher risk in female H63D homozygotes is probably not related to iron metabolism.
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