| 1. |
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| 2. |
- Andersson, Tommy, et al.
(författare)
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Multiobjective Optimization of a Heat-Sink Design Using the Sandwiching Algorithm and an Immersed Boundary Conjugate Heat Transfer Solver
- 2018
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Ingår i: Journal of Heat Transfer. - : ASME International. - 1528-8943 .- 0022-1481. ; 140:10, s. 102002 -
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Tidskriftsartikel (refereegranskat)abstract
- The thermal management is an ever increasing challenge in advanced electronic devices. In this paper, simulation-based optimization is applied to improve the design of a plate-fin heat-sink in terms of operational cost and thermal performance. The proposed framework combines a conjugate heat transfer solver, a CAD engine and an adapted Sandwiching algorithm. A key feature is the use of novel immersed boundary (IB) techniques that allows for automated meshing which is perfectly suited for parametric design optimization.
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| 3. |
- Engström, Gunnar, et al.
(författare)
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Pulmonary function and atherosclerosis in the general population : causal associations and clinical implications
- 2024
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Ingår i: European Journal of Epidemiology. - : Springer Nature. - 0393-2990 .- 1573-7284. ; 39:1, s. 35-49
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Tidskriftsartikel (refereegranskat)abstract
- Reduced lung function is associated with cardiovascular mortality, but the relationships with atherosclerosis are unclear. The population-based Swedish CArdioPulmonary BioImage study measured lung function, emphysema, coronary CT angiography, coronary calcium, carotid plaques and ankle-brachial index in 29,593 men and women aged 50–64 years. The results were confirmed using 2-sample Mendelian randomization. Lower lung function and emphysema were associated with more atherosclerosis, but these relationships were attenuated after adjustment for cardiovascular risk factors. Lung function was not associated with coronary atherosclerosis in 14,524 never-smokers. No potentially causal effect of lung function on atherosclerosis, or vice versa, was found in the 2-sample Mendelian randomization analysis. Here we show that reduced lung function and atherosclerosis are correlated in the population, but probably not causally related. Assessing lung function in addition to conventional cardiovascular risk factors to gauge risk of subclinical atherosclerosis is probably not meaningful, but low lung function found by chance should alert for atherosclerosis.
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| 4. |
- Gaidashev, Denis, 1973-, et al.
(författare)
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A numerical study of infinitely renormalizable area-preserving maps
- 2012
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Ingår i: Dynamical systems. - : Informa UK Limited. - 1468-9367 .- 1468-9375. ; 27:3, s. 283-301
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Tidskriftsartikel (refereegranskat)abstract
- It has been shown in Gaidashev and Johnson [D. Gaidashev and T. Johnson, Dynamics of the universal area-preserving map associated with period doubling: stable sets, J. Mod. Dyn. 3(4) (2009), pp. 555–587.] and Gaidashev et al. [D. Gaidashev, T. Johnson, and M. Martens, Rigidity for infinitely renormalizable area-preserving maps, in preparation.] that infinitely renormalizable area-preserving maps admit invariant Cantor sets with a maximal Lyapunov exponent equal to zero. Furthermore, the dynamics on these Cantor sets for any two infinitely renormalizable maps is conjugated by a transformation that extends to a differentiable function whose derivative is Hölder continuous of exponent α > 0. In this article we investigate numerically the specific value of α. We also present numerical evidence that the normalized derivative cocycle with the base dynamics in the Cantor set is ergodic. Finally, we compute renormalization eigenvalues to a high accuracy to support a conjecture that the renormalization spectrum is real.
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| 5. |
- Gaidashev, Denis, 1973-, et al.
(författare)
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Dynamics of the Universal Area-Preserving Map Associated with Period Doubling : Stable Sets
- 2009
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Ingår i: Journal of Modern Dynamics. - : American Institute of Mathematical Sciences (AIMS). - 1930-5311 .- 1930-532X. ; 3:4, s. 555-587
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Tidskriftsartikel (refereegranskat)abstract
- It is known that the famous Feigenbaum-Coullet-Tresser period doubling universality has a counterpart for area-preserving maps of ${\fR}^2$. A renormalization approach has been used in \cite{EKW1} and \cite{EKW2} in a computer-assisted proof of existence of a ``universal'' area-preserving map $F_*$ --- a map with orbits of all binary periods $2^k, k \in \fN$. In this paper, we consider {\it infinitely renormalizable} maps --- maps on the renormalization stable manifold in some neighborhood of $F_*$ --- and study their dynamics. For all such infinitely renormalizable maps in a neighborhood of the fixed point $F_*$ we prove the existence of a ``stable'' invariant Cantor set $\cC^\infty_F$ such that the Lyapunov exponents of $F \arrowvert_{\cC^\infty_F}$ are zero, and whose Hausdorff dimension satisfies$${\rm dim}_H(\cC_F^{\infty}) < 0.5324.$$ We also show that there exists a submanifold, $\bW_\omega$, of finite codimension in the renormalization local stable manifold, such that for all $F\in\bW_\omega$ the set $\cC^\infty_F$ is ``weakly rigid'': the dynamics of any two maps in this submanifold, restricted to the stable set $\cC^\infty_F$, is conjugated by a bi-Lipschitz transformation that preserves the Hausdorff dimension.
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| 6. |
- Gaidashev, Denis, 1973-, et al.
(författare)
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Dynamics of the Universal Area-Preserving Map Associated with Period Doubling : Hyperbolic Sets
- 2009
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Ingår i: Nonlinearity. - : IOP Publishing. - 0951-7715 .- 1361-6544. ; 22:10, s. 2487-2520
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Tidskriftsartikel (refereegranskat)abstract
- It is known that the famous Feigenbaum-Coullet-Tresser period doubling universality has a counterpart for area-preserving maps of R-2. A renormalization approach has been used in Eckmann et al (1982 Phys. Rev. A 26 720-2) and Eckmann et al (1984 Mem. Am. Math. Soc. 47 1-121) in a computer-assisted proof of existence of a 'universal' area-preserving map F-*-a map with orbits of all binary periods 2(k), k is an element of N. In this paper, we consider maps in some neighbourhood of F-* and study their dynamics. We first demonstrate that the map F* admits a 'bi-infinite heteroclinic tangle': a sequence of periodic points {z(k)}, k is an element of Z, vertical bar z(k vertical bar) ->(k ->infinity) 0, vertical bar z(k vertical bar) k ->(k ->infinity) infinity, (1) whose stable and unstable manifolds intersect transversally; and, for any N is an element of N, a compact invariant set on which F-* is homeomorphic to a topological Markov chain on the space of all two-sided sequences composed of N symbols. A corollary of these results is the existence of unbounded and oscillating orbits. We also show that the third iterate for all maps close to F* admits a horseshoe. We use distortion tools to provide rigorous bounds on the Hausdorff dimension of the associated locally maximal invariant hyperbolic set: 0.7673 >= dim(H) (C-F) >= epsilon approximate to 0.00013 e(-7499).
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| 7. |
- Guckenheimer, John, et al.
(författare)
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Rigorous enclosures of a slow manifold
- 2012
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Ingår i: SIAM Journal on Applied Dynamical Systems. - : Society for Industrial & Applied Mathematics (SIAM). - 1536-0040. ; 11:3, s. 831-863
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Tidskriftsartikel (refereegranskat)abstract
- Slow-fast dynamical systems have two time scales and an explicit parameter representing the ratio of these time scales. Locally invariant slow manifolds along which motion occurs on the slow time scale are a prominent feature of slow-fast systems. This paper introduces a rigorous numerical method to compute enclosures of the slow manifold of a slow-fast system with one fast and two slow variables. A triangulated first order approximation to the two dimensional invariant manifold is computed “algebraically.” Two translations of the computed manifold in the fast direction that are transverse to the vector field are computed as the boundaries of an initial enclosure. The enclosures are refined to bring them closer to each other by moving vertices of the enclosure boundaries one at a time. As an application we use the method to prove the existence of tangencies of invariant manifolds in the problem of singular Hopf bifurcation and to give bounds on the location of one such tangency.
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| 8. |
- Johnson, Tomas, 1979, et al.
(författare)
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A finite volume method for electrostatic three species negative corona discharge simulations with application to externally charged powder bells
- 2015
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Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886. ; 74, s. 27-36
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Tidskriftsartikel (refereegranskat)abstract
- A three species model for steady-state negative corona discharge is studied. Ionization, attachment, and recombination reactions are modeled. A novel unstructured finite volume algorithm to solve the equations is presented, using the secondary emission of electrons from the cathode to set boundary values for the electrons.To show the usefulness of the method for industrial applications it is used to characterize the electrostatic properties of an externally charged rotary powder bell used in the automotive industry. Experimental current density profiles are reconstructed with good accuracy, which validates the model and the method with real experimental data.
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| 9. |
- Johnson, Tomas, 1979, et al.
(författare)
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A multi-scale simulation method for powder coating with moving powder guns
- 2023
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Ingår i: Journal of Electrostatics. - 0304-3886. ; 125
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Tidskriftsartikel (refereegranskat)abstract
- A mathematical model and numerical method, supported by experiments, to simulate industrial scale powder coating for moving coating guns is developed. The numerical method is based on a model reduction procedure that starts with a three species electrostatic model for the negative corona discharge at the nozzle exit of the gun. It is reduced to a one species electrostatic model away from the gun, which is coupled to a RANS fluid model and Lagrangian particle tracking and charging in a detailed stationary simulation. The final part consists of coating simulation with a moving gun, enabled by immersed boundary methods that do not require a body fitted mesh. In the coating simulation the detailed simulation results are reinjected, preserving the size and charge distribution of the powder particles. The method is validated with coating thickness measurements for horizontal and vertical lines on flat and two sets of bent panels: towards and away from the applicator. The bent panels are used to validate the performance on highly convex and concave objects.
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| 10. |
- Johnson, Tomas, 1979, et al.
(författare)
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A Multi-Scale Simulation Method for the Prediction of Edge Wicking in Multi-Ply Paperboard
- 2015
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 30:4, s. 640-650
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Tidskriftsartikel (refereegranskat)abstract
- When liquid packaging board is made aseptic in the filling machine the unsealed edges of the board are exposed to a mixture of water and hydrogen peroxide. A high level of liquid penetration may lead to aesthetic as well as functional defects. To be able to make a priori predictions of the edge wicking properties of a certain paperboard material is therefore of great interest to the paper industry as well as to packaging manufacturers. In this paper an extended multi-scale model of edge wicking in multi-ply paperboard is presented. The geometric and physical properties of the paperboard are modeled on the micro-scale, and include fillers and fines. The absolute air permeabilities and pore size distributions are validated with experimental and tomographic values. On the macro-scale random porosity and sizing distributions, time and sizing dependent contact angles, and inter-ply dependence are modeled. Arbitrary shapes of the paperboard are handled through an unstructured 3D surface mesh. Stationary and transient edge wicking simulations are validated against experiments with excellent agreement. The simulations show that the diffusive menisci between the liquid and air phases together with the two-ply model is necessary to achieve good agreement with the transient edge wicking experiments.
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