| 41. |
- Jansson, Johan, et al.
(författare)
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Adaptive simulation of unsteady flow past the submerged part of a floating wind turbine platform
- 2015
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Ingår i: MARINE 2015 - Computational Methods in Marine Engineering VI. - : International Center for Numerical Methods in Engineering (CIMNE). - 9788494392863 ; , s. 35-46
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Konferensbidrag (refereegranskat)abstract
- Offshore floating platforms for wind turbines represent challenging concepts for designers trying to combine an optimal compromise between cost effectiveness and performance. Modelling of the hydrodynamic behaviour of the structure is still the subject of wide debate in the technical communities. The assessment of the hydrodynamics of the support structure is not an easy task as the floaters consist of an assembly of columns, braces and pontoons, commonly also with heave plates: Each of these components corresponds to a different hydrodynamic model and it further interacts with the other elements. This results in very complex non-linear modeling, which makes it necessary to resort to computational fluid dynamics (CFD) methods for the evaluation of the combined hydrodynamics. In the framework of the collaboration between the Basque Centre for Applied Mathematics (BCAM) and Tecnalia R&I, the interaction of the sea flow with a semisubmersible floating offshore wind platform have been calculated by using the open source solver Unicorn in the FEniCS-HPC framework when subject to a steady inflow. The prototype of the platform consists in a semi-submersible 4-columns column stabilized platform - NAUTILUS Floating Solutions concept-; columns are connected by a rigid ring pontoon provided with heave damping plates at the bottom. The novelty of the approach in FEniCS-HPC hinges upon an implicit formulation for the turbulence, a cheap free slip model of the boundary layer and goal-oriented mesh adaptivity [8, 6, 9, 20, 1]. We find that the results are consistent with experimental results for cylinders at high Reynolds number.
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| 42. |
- Jansson, Johan, et al.
(författare)
-
Adaptive stabilized finite element framework for simulation of vocal fold turbulent fluid-structure interaction
- 2013
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Ingår i: Proceedings of Meetings on Acoustics. - : Acoustical Society of America (ASA). ; , s. 1-9
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Konferensbidrag (refereegranskat)abstract
- As a step toward building a more complete model of voice production mechanics, we assess the feasibility of a fluid-structure simulation of the vocal fold mechanics in the Unicorn incompressible Unified Continuum framework. The Unicorn framework consists of conservation equations for mass and momentum, a phase function selecting solid or fluid constitutive laws, a convection equation for the phase function and moving mesh methods for tracking the interface, and discretization through an adaptive stabilized finite element method. The framework has been validated for turbulent flow for both low and high Reynolds numbers and has the following features: implicit turbulence modeling (turbulent dissipation only occurs through numerical stabilization), goal-oriented mesh adaptivity, strong, implicit fluid-structure coupling and good scaling on massively parallel computers. We have applied the framework for turbulent fluid-structure interaction simulation of vocal folds, and present initial results. Acoustic quantities have been extracted from the framework in the setting of an investigation of a configuration approximating an exhaust system with turbulent flow around a flexible triangular steel plate in a circular duct. We present some results of the investigation as well as results of the framework applied to other problems.
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| 43. |
- Jansson, Johan, et al.
(författare)
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Adaptive unified continuum FEM modeling of a 3D FSI benchmark problem
- 2017
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley-Blackwell. - 2040-7939 .- 2040-7947. ; 33:9
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we address a 3D fluid-structure interaction benchmark problem that represents important characteristics of biomedical modeling. We present a goal-oriented adaptive finite element methodology for incompressible fluid-structure interaction based on a streamline diffusion–type stabilization of the balance equations for mass and momentum for the entire continuum in the domain, which is implemented in the Unicorn/FEniCS software framework. A phase marker function and its corresponding transport equation are introduced to select the constitutive law, where the mesh tracks the discontinuous fluid-structure interface. This results in a unified simulation method for fluids and structures. We present detailed results for the benchmark problem compared with experiments, together with a mesh convergence study.
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| 44. |
- Jansson, Johan, 1978-, et al.
(författare)
-
Automated adaptive error control in finite element methods using the error representation as error indicator
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we present a new adaptive finite element method directly using the a posteriori error representation as a local error indicator, and representing the primal and dual solutions in the same finite element space (here piecewise continuous linear functions on the same mesh). Since this approach gives a global a posteriori error estimate that is zero (due to Galerkin orthogonality), the error representation has traditionally been thought to contain no information about the error. However, we show the opposite, that locally, the orthogonal error representation behaves very similar to the non-orthogonal error representation using a higher order approximation of the dual, which is a standard approach to overcome the problem of a zero error estimate. We present evidence of this both in the form of an a priori estimate for the local error indicator for an elliptic model problem and a detailed computational investigation showing that the two methods exhibit very similar behavior and performance, and thus confirming the theoretical prediction. We also present computational results using a stabilized version of the method for non-elliptic partial differential equations where the error representation is no longer orthogonal, and where both the local error indicator and global error estimate behave similar to the error representation using a higher order approximation of the dual. The benefits of this adaptive method are generality and simplicity in formulation, sharpness, and efficiency since high order approximation of the dual and computation of additional constructs such as jump terms over interior facets or local problems are avoided.
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| 45. |
- Jansson, Johan, 1978-, et al.
(författare)
-
Automated error control in finite element methods withapplications in fluid flow
- 2014
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we present a new adaptive finite element method for thesolution of linear and non-linear partial differential equationsdirectly using the a posteriori error representation as a local errorindicator, with the primal and dual solutions approximated in the samefinite element space, here piecewise continuous linear functions onthe same mesh. Since this approach gives a global a posteriori errorrepresentation that is zero due to Galerkin orthogonality, the errorrepresentation has traditionally been thought to contain noinformation about the error. However, for elliptic andconvection-diffusion model problems we show the opposite, that locallythe orthogonal error representation behaves very similar to thenon-orthogonal error representation using a higher order approximationof the dual. We have previously proved an a priori estimate of thelocal error indicator for elliptic problems, and in this paper weextend the proof to convection-reaction problems. We also present aversion of the method for non-elliptic and non-linear problems using astabilized finite element method where the a posteriori errorrepresentation is no longer orthogonal. We apply this method to thestationary incompressible Navier-Stokes equation and perform detailednumerical experiments which show that the a posteriori error estimateis within a factor 2 of the error based on a reference value on a finemesh, except in a few data points on very coarse meshes for anon-smooth test case where it is within a factor 3.
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| 46. |
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| 47. |
- Jansson, Johan, 1978-, et al.
(författare)
-
Direct finite element simulation of turbulent flow for marine based renewable energy
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this article we present a computational framework for simulation ofturbulent flow in marine based renewable energy applications. Inparticular, we focus on floating structures and rotatingturbines. This work is an extension to multiphase turbulent flow, ofour existing framework of residual based turbulence modeling forsingle phase turbulent incompressible flow. We illustrate theframework in four examples: a regular wave test where we compareagainst an exact solution, the standard MARIN wave impact benchmarkwith experimental validation data, a vertical axis turbine withcomplex geometry from an existing turbine, and finally a prototypesimulation of decay test in a coupled moving boundary rigid-body andtwo-phase fluid simulation.
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| 48. |
- Jansson, Johan, et al.
(författare)
-
Framework for adaptive fluid-structure interaction with industrial applications
- 2013
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Ingår i: International Journal of Materials Engineering Innovation. - 1757-2754. ; 4:2, s. 166-186
-
Tidskriftsartikel (refereegranskat)abstract
- We present developments in the Unicorn-HPC framework for unified continuum mechanics, enabling adaptive finite element computation of fluid-structure interaction, and an overview of the larger FEniCS-HPC framework for automated solution of partial diffential equations of which Unicorn-HPC is a part. We formulate the basic model and finite element discretisation method and adaptive algorithms. We test the framework on a 2D model problem consisting of a flexible beam in channel flow, and to illustrate the capabilities of the computational framework, we show two application examples from industry and medicine. We simulate a flexible mixer plate in turbulent flow in an exhaust system where the target output is aeroacoustic quantities. The second example is a self-oscillating vocal fold configuration, where the ultimate goal is to predict how the voice is affected by physiological changes from aerodynamics. Here we give the displacement signal of a point on the folds.
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| 49. |
- 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
-
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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| 50. |
- Jansson, Jan-Håkan, et al.
(författare)
-
Snus (Swedish smokeless tobacco) use and risk of stroke: pooled analyses of incidence and survival
- 2014
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Ingår i: Journal of Internal Medicine. - : Wiley. - 1365-2796 .- 0954-6820. ; 276:1, s. 87-95
-
Tidskriftsartikel (refereegranskat)abstract
- Background. Snus is a moist smokeless tobacco product with high nicotine content. Its use has a short-term effect on the cardiovascular system, but the relationship between snus use and stroke is unclear. Objective. The aim of this study was to assess the associations between use of snus and incidence of and survival after stroke, both overall and according to subtypes. Methods. Pooled analyses of eight Swedish prospective cohort studies were conducted, including 130 485 men who never smoked. We estimated hazard ratios (HRs) with 95% confidence intervals (CIs) of incidence and death after diagnosis using Cox proportional hazard regression models and case fatality and survival using logistic regression and Kaplan-Meier methods, respectively. Results. No associations were observed between the use of snus and the risk of overall stroke (HR 1.04, 95% CI 0.92-1.17) or of any of the stroke subtypes. The odds ratio (OR) of 28-day case fatality was 1.42 (95% CI 0.99-2.04) amongst users of snus who had experienced a stroke, and the HR of death during the follow-up period was 1.32 (95% CI 1.08-1.61). Conclusion. Use of snus was not associated with the risk of stroke. Hence, nicotine is unlikely to contribute importantly to the pathophysiology of stroke. However, case fatality was increased in snus users, compared with nonusers, but further studies are needed to determine any possible causal mechanisms.
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