| 1. |
- Akiyama, Kazunori, et al.
(författare)
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First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
- 2019
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 875:1
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Tidskriftsartikel (refereegranskat)abstract
- The Event Horizon Telescope (EHT) has mapped the central compact radio source of the elliptical galaxy M87 at 1.3 mm with unprecedented angular resolution. Here we consider the physical implications of the asymmetric ring seen in the 2017 EHT data. To this end, we construct a large library of models based on general relativistic magnetohydrodynamic (GRMHD) simulations and synthetic images produced by general relativistic ray tracing. We compare the observed visibilities with this library and confirm that the asymmetric ring is consistent with earlier predictions of strong gravitational lensing of synchrotron emission from a hot plasma orbiting near the black hole event horizon. The ring radius and ring asymmetry depend on black hole mass and spin, respectively, and both are therefore expected to be stable when observed in future EHT campaigns. Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity. If the black hole spin and M87's large scale jet are aligned, then the black hole spin vector is pointed away from Earth. Models in our library of non-spinning black holes are inconsistent with the observations as they do not produce sufficiently powerful jets. At the same time, in those models that produce a sufficiently powerful jet, the latter is powered by extraction of black hole spin energy through mechanisms akin to the Blandford-Znajek process. We briefly consider alternatives to a black hole for the central compact object. Analysis of existing EHT polarization data and data taken simultaneously at other wavelengths will soon enable new tests of the GRMHD models, as will future EHT campaigns at 230 and 345 GHz.
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| 2. |
- Hörmann, Ulrich, et al.
(författare)
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Voc from a Morphology Point of View : the Influence of Molecular Orientation on the Open Circuit Voltage of Organic Planar Heterojunction Solar Cells
- 2014
-
Ingår i: Journal of physical chemistry C. - : American Chemical Society (ACS). - 1932-7455 .- 1932-7447. ; 118:46, s. 26462-26470
-
Tidskriftsartikel (refereegranskat)abstract
- The film morphology and device performance of planar heterojunctionsolar cells based on the molecular donor material α-sexithiophene (6T) are investigated.Planar heterojunctions of 6T with two different acceptor molecules, the C60 fullerene anddiindenoperylene (DIP), have been prepared. The growth temperature of the 6T bottomlayer has been varied between room temperature and 100 °C for each acceptor. By meansof X-ray diffraction and X-ray absorption, we show that the crystallinity and the molecularorientation of 6T is influenced by the preparation conditions and that the 6T filmtemplates the growth of the subsequent acceptor layer. These structural changes areaccompanied by changes in the characteristic parameters of the correspondingphotovoltaic cells. This is most prominently observed as a shift of the open circuitvoltage (Voc): In the case of 6T/C60 heterojunctions, Voc decreases from 0.4 to 0.3 V,approximately, if the growth temperature of 6T is increased from room temperature to 100°C. By contrast, Voc increases from about 1.2 V to almost 1.4 V in the case of 6T/DIP solarcells under the same conditions. We attribute these changes upon substrate heating toincreased recombination in the C60 case while an orientation dependent intermolecular coupling seems to change the origin of the photovoltaic gap in the DIP case.
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| 3. |
- Mark, Andreas, 1980, et al.
(författare)
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Microstructure Simulation of Early Paper Forming Using Immersed Boundary Methods
- 2011
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Ingår i: Paper360. - 1933-3684. ; 10:11, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- Paper forming is the first step in the paper machine where a fibersuspension leaves the headbox and flows through a forming fabric.Complex physical phenomena occur during paper forming due to theinteraction between fibers, fillers and fines as well as chemicalsadded to the suspension. Understanding this process is important forthe development of improved paper products because the configurationof the fibers during this step has a large influence on the finalpaper quality. Since the effective paper properties depend on themicro-structure of the fiber web, a continuum model is inadequate andthe properties of each fiber need to be accounted for in thesimulations.In the present work, a framework for microstructure simulation ofearly paper forming has been developed. The simulation frameworkincludes a Navier-Stokes solver and immersed boundary methods are usedto resolve the flow around the fibers. The fibers are modeled with afinite element discretization of the Euler-Bernoulli beam equation ina co-rotational formulation. The contact model is based on a penaltymethod and includes friction as well as elastic and inelasticcollisions.The fiber model and the contact model are validated against demandingtest cases from the literature with excellent results. Thefluid-structure interaction in the model is examined by simulating anelastic beam oscillating in a cross flow. Finally, a simulation ofearly paper forming is performed to demonstrate the potential of theproposed framework. The unique modeling approach can be used toincrease the fundamental understanding of paper forming and supportprocess optimization.
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| 4. |
- Mark, Andreas, 1980, et al.
(författare)
-
Microstructure Simulation of Early Paper Forming Using Immersed Boundary Methods
- 2011
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Ingår i: Progress in Paper Physics Seminar. - 9783851251630 ; , s. 283-290
-
Konferensbidrag (refereegranskat)abstract
- Paper forming is the first step in the paper machinewhere a fiber suspension leaves the headbox and flowsthrough a forming fabric. Understanding this processis important for the development of improved paperproducts because the configuration of the fibers duringthis step has a large influence on the final paperquality.The simulation framework includes IBOFlow, a stateof-the-art Navier-Stokes solver, and PaperGeo, the virtualpaper structure generator in GeoDict. ImmersedBoundary Methods are used to resolve the flow aroundthe fibers. The fibers are modeled with a finite elementdiscretization of the Euler-Bernoulli beam equationin a co-rotational formulation. The contact modelis based on a penalty method and includes friction aswell as elastic and inelastic collisions.The fiber model and the contact model are validatedagainst demanding test problems from the literaturewith excellent result. The fluid-structure interaction inthe model is examined by simulating an elastic beamoscillating in a cross flow. Finally, a simulation of initialpaper forming is performed, which demonstratesthe capabilities of the simulation framework.
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| 5. |
- Mark, Andreas, 1980, et al.
(författare)
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Modeling and Simulation of Paperboard Edge Wicking
- 2012
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 27:2, s. 397-402
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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 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 paper industry as well as to packaging manufacturers. The aim of this paper is to present a new analytical theory for prediction of the edge wicking properties of paperboard. The theory is based on Darcy’s law and the ideal gas law to describe the physical behavior of water flow in paperboard. The theory is compared to a recently published multi-scale framework and with pressurized edge wick experiments. The agreement is very good for paperboard samples of different sizes. The conclusion from the work is that both analytical theory and detailed simulations are useful to predict edge wicking properties of paperboard material.
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| 6. |
- Mark, Andreas, 1980, et al.
(författare)
-
Multi-scale simulation of paperboard edge wicking using a fiber-resolving virtual paper model
- 2012
-
Ingår i: Tappi Journal. - 0734-1415. ; 11:6, s. 9-16
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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 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 paper industry as well as to packaging manufacturers. In this paper a multi-scale framework is proposed that allows for detailed simulation of the edge wicking process.On the fiber micro-scale virtual paper models are generated based on input from tomographic and SEM images. A pore morphology method is used to calculate capillary pressure curves, and on the active pores one-phase flow simulations are performed for relative permeabilities. The results as functions of saturation and porosity are stored in a database. The database is used as input for two-phase flow simulations on the paper macro-scale. The resulting fluid penetration is validated against pressurized edge wick measurements on paper lab sheets with very good agreement. The proposed multi-scale approach can be used to increase the understanding of how edge wicking in paperboard packages depends on the micro-structure.
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| 7. |
- Mark, Andreas, 1980, et al.
(författare)
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Multi-scale simulation of paperboard edge wicking using a fiber-resolving virtual paper model
- 2011
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Ingår i: Progress in Paper Physics Seminar. - 9783851251630 ; , s. 41-47
-
Konferensbidrag (refereegranskat)abstract
- When liquid paperboard based package material ismade aseptic, unsealed edges of the board are exposedto a liquid front which in some circumstances may soakthe material to some extent. This is not desired since itmay lead to aesthetic as well as functional defects. Inorder to make a priori predictions of the edge wickingproperties of a given paper material, something whichis of great interest to paperboard industry as well aspackaging manufacturers, micro simulations are required.To calculate the penetration of fluid in the open edgeof a paper sheet a multi-scale framework is developed.On the fiber micro-scale, virtual paper models are generatedin PaperGeo [6]. In IBOFlow [7] a pore morphologymethod is used to calculate capillary pressurecurves, and the active pores one-phase flow simulationsare performed for relative permeabilities. Theresult is a database of capillary pressure curves andrelative permeabilities as functions of saturation andporosity. The database is used as an input for a twophaseflow simulation on a 2D virtual macro sheet tocalculate the penetration of fluid in the paper. Themulti-scale framework is validated against pressurizededge wick measurements with good agreement.
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| 8. |
- Ramesh Sagar, Vaishak, 1988, et al.
(författare)
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Investigating the sensitivity of particle size distribution on part geometry in additive manufacturing
- 2020
-
Ingår i: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE). ; 2B-2020
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Konferensbidrag (refereegranskat)abstract
- Selective laser melting process is a powder bed fusion additive manufacturing process that finds applications in aerospace and medical industries for its ability to produce complex geometry parts. As the raw material used is in powder form, particle size distribution (PSD) is a significant characteristic that influences the build quality in turn affecting the functionality and aesthetics aspects of the end product. This paper investigates the effect of PSD on deformation for 316L stainless steel powder, where three coupled in-house simulation tools based on Discrete Element Method (DEM), Computational Fluid Dynamics (CFD), and Structural Mechanics are employed. DEM is used for simulating the powder distribution based on the different particle size distribution of the powder. The CFD is used as a virtual test bed to determine thermal parameters such as density, heat capacity and thermal conductivity of the powder bed viewed as a continuum. The values found as a stochastic function of the powder distribution is used to test the sensitivity of the melted zone and distortion using Structural Mechanics. Results showed significant influence of particle size distribution on the packing density, surface height, surface roughness, the stress state and displacement of the melted zone. The results will serve as a catalyst in developing geometry assurance strategies to minimize the effect of particle size distribution on the geometric quality of the printed part.
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| 9. |
- Svenning, Erik, 1986, et al.
(författare)
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Multiphase Simulation of Fiber Suspension Flows Using Immersed Boundary Methods
- 2012
-
Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 27:2, s. 184-191
-
Tidskriftsartikel (refereegranskat)abstract
- Fiber suspension simulations are challenging since they involve transient fluid flow with immersed solid objects subject to large displacements and rotations. In the present work, a beam model in co-rotational formulation is coupled with a fluid solver using immersed boundary methods. The model is used to simulate a fiber in a shear flow and excellent agreement is found with Jeffery's equations. The shapes of fibers deforming in a shear flow are found to be in qualitative agreement with shapes observed in experiments.The flow of a fiber suspension is studied by simulating early paper forming with one-way and semi-two-way coupling. It is found that the flow through the fiber web needs to be resolved in order to predict the retention of fibers in the fiber web.
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| 10. |
- Andersson, Björn O, 1982, et al.
(författare)
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A Modified TAB Model for Simulation of Atomization in Rotary Bell Spray Painting
- 2013
-
Ingår i: Journal of Mechanical Engineering and Automation. - 2163-2413. ; 3:2, s. 54-61
-
Tidskriftsartikel (refereegranskat)abstract
- The Rotary bell spray applicator technique is commonly used in the automotive industry for paint application because of its high transfer efficiency and high-quality result. The bell spins rapidly around its axis with a tangential velocity at the edge in the order of 100 m/s. The paint falls off the edge and enters the air with a large relative velocity, driving the atomization into small droplets where the resulting size distribution depends on the process conditions. Especially the rotation speed of the bell is an important parameter governing the size distribution. The main research question in this work is to investigate if the Taylor Analogy Breakup (TAB) model can be used to predict the resulting droplet size distributions in spray painting. As the paint is a viscous fluid a modification of the TAB model taking non-linear effects of large viscosity into account is proposed. The parameters in the breakup model are tuned by optimization to match droplet size distributions obtained in CFD simulations with measured ones. Results are presented for three cases with rotation speeds from 30 to 50 thousand RPM where the full droplet size distributions are compared with measurements. Good results are obtained for all three cases where the simulated size distributions compare well to measurements over a wide range of droplet sizes. The TAB method is able to quantitatively predict the result of the breakup process and can be used in a preprocessing stage of a full spray painting simulation, thereby reducing the need for costly and cumbersome measurements.
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| 11. |
- Andersson, Björn O, 1982, et al.
(författare)
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Modeling Surface Tension in SPH by Interface Reconstruction using Radial Basis Functions
- 2010
-
Ingår i: Proceedings of the 5th International SPHERIC Workshop, 22-25 June 2010, Manchester, U.K., edited by B. D. Rogers. ; , s. 7-14
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A novel method for reconstructing the interface between two fluids is described and evaluated. The method uses a different basis for approximating the color function than what is common practice in SPH simulations. The key feature of the new method is the ability to omit small length scale structures in order to obtain a smoother representation. A smoother interface is more suitable to derive a surface tension force from, as the magnitude of the force is proportional to the curvature which is related to the second derivative along the interface.
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| 12. |
- Andersson, Björn O, 1982, et al.
(författare)
-
Modified TAB Model for Viscous Fluids applied to Breakup in Rotary Bell Spray Painting
- 2012
-
Ingår i: ICLASS 2012 - 12th International Conference on Liquid Atomization and Spray Systems.
-
Konferensbidrag (refereegranskat)abstract
- The Taylor Analogy Breakup (TAB) model is applied to droplet breakup in rotary bell spray painting commonly used in the automotive industry. The bell spins rapidly around its axis with a tangential velocity at the edge in the order of 100 m/s. The paint falls off the edge and enters the air with a large relative velocity, driving the atomization. The paint is a viscous fluid and a modification of the TAB model taking non-linear effects of large viscosity into account is described. The parameters in the breakup model are tuned to match droplet size distributions obtained in CFD simulations with measured ones. Results are presented for three cases with rotation speeds from 30 to 50 thousand RPM where the full droplet size distributions are compared with measurements. Good results are obtained for all three cases where the simulated size distributions compare well to measurements over a wide range of droplet sizes. The obtained results can be used in a preprocessing stage of a full spray painting simulation thereby reducing the need for costly and cumbersome measurements.
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| 13. |
- Andersson, Björn O, 1982, et al.
(författare)
-
MPI-Parallelization of a Structured Grid CFD Solver including an Integrated Octree Grid Generator
- 2013
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- An existing Computational Fluid Dynamics (CFD) solver is parallelized by means of MPI. The solver includes a dynamic and adaptive grid generator for Cartesian Quadtree and Octree grids, which therefore also have to be parallelized. The grid generator generates grids fulfilling a specific set of rules, that have to be enforced also in parallel. The assembly of the large sparse matrices resulting from the implicit discretization of Navier-Stokes equations is done in parallel, as is the solving process. The parallel performance of both of these processes depends heavily on a good load balancing in order to reach satisfactory speedup. Two versions of load balancing are demonstrated, one based on block swapping, and the other by utilizing the Metis or Parmetis software packages for load balancing of graphs. Results are presented for load balancing and for the parallel speedup of solving the linear algebra system of equations.
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| 14. |
- 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
-
Ingår i: Journal of Heat Transfer. - : ASME International. - 1528-8943 .- 0022-1481. ; 140:10, s. 102002 -
-
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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| 15. |
- Andrä, Heiko, et al.
(författare)
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Micromechanical network model for the evaluation of quality controls of paper
- 2011
-
Ingår i: Progress in Paper Physics Seminar. - 9783851251630 ; , s. 49-55
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we discuss the challenges in modelling and simulating infinitesimal and large deformations of cellulose fiber networks, mainly in the context of the prediction of quality controls for paper.Understanding the influence and sensitivity of macroscopic production parameters like grammage and thickness of paperboard and understanding the influence of the fiber suspension on the quality of paper is important for the development of better papers and for preserving raw materials and energy.The new simulation framework consists of the virtual stochastic paper structure generator PaperGeo, that was integrated in the GeoDict 1 software suite, and the finite element solver FeelMath (Finite Elements for Elastic Materials and Homogenization) for solving the equations of elasticity. The fibers and the contacts are modelled by using geometrically exact beams of Simo-type [1].The microstructural model and the fiber network model are validated against standard measurements of existing papers in the following way: At first we perform tensile and bending tests to measure the macroscopic stress-strain relations. In the next step we apply a representative macroscopic stress or strain onto the boundaries of realizations of the stochastic fiber network model and compute by homogenization the effective (stiffness) coefficients. Finally we compare the numerical results with the measurements.This procedure can also be used for an identification of elastic parameters on the microscale and to study the sensitivity of the effective (macroscopic) stiffness with regard to the parameters of the microstructure
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| 16. |
- Aquila, Andrew, et al.
(författare)
-
Time-resolved protein nanocrystallography using an X-ray free-electron laser
- 2012
-
Ingår i: Optics Express. - 1094-4087. ; 20:3, s. 2706-2716
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the use of an X-ray free electron laser synchronized with an optical pump laser to obtain X-ray diffraction snapshots from the photoactivated states of large membrane protein complexes in the form of nanocrystals flowing in a liquid jet. Light-induced changes of Photosystem I-Ferredoxin co-crystals were observed at time delays of 5 to 10 µs after excitation. The result correlates with the microsecond kinetics of electron transfer from Photosystem I to ferredoxin. The undocking process that follows the electron transfer leads to large rearrangements in the crystals that will terminally lead to the disintegration of the crystals. We describe the experimental setup and obtain the first time-resolved femtosecond serial X-ray crystallography results from an irreversible photo-chemical reaction at the Linac Coherent Light Source. This technique opens the door to time-resolved structural studies of reaction dynamics in biological systems.
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| 17. |
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| 18. |
- Edelvik, Fredrik, 1972, et al.
(författare)
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Math-Based Algorithms and Software for Virtual Product Realization Implemented in Automotive Paint Shops
- 2017
-
Ingår i: Math for the Digital Factory. - 2198-3283. ; 27, s. 231-251
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Tidskriftsartikel (refereegranskat)abstract
- We present a simulation framework that makes it possible to accurately simulate spray painting of e.g. a truck cab in only a few hours on a standard computer. This is an extreme improvement compared to earlier approaches that require weeks of simulation time. Unique algorithms for coupled simulations of air flows, electrostatic fields and charged paint particles make this possible. In addition, we demonstrate that the same framework can be used to efficiently simulate the laydown of sealing or adhesive material. In the virtual paint factory the production preparation process can be performed in the computer, which allows the engineers to replace physical prototypes with virtual ones to shorten the lead time in product development, and avoid future unforeseen technological and environmental problems that can be extremely costly if they are discovered at the end of the production line, or even worse by the costumer.
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| 19. |
- Gonzalez Caceres, Alex Arnoldo, 1982, et al.
(författare)
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Towards digital twinning for multi-domain simulation workflows in urban design: a case study in Gothenburg
- 2024
-
Ingår i: Journal of Building Performance Simulation. - 1940-1493 .- 1940-1507. ; In Press
-
Tidskriftsartikel (refereegranskat)abstract
- This work proposes an automated workflow using digital twinning for multi-domain environmental performance analysis of urban developments. Digital twins can potentially provide a common basis for multi-domain simulations and help overcome data availability and interoperability issues. The proposed workflow consists of five steps: (1) creating a procedural urban 3D model, (2) generating design alternatives parametrically, (3) exporting the context and each design alternative to each simulation tool, (4) running simulations for wind comfort, energy demand, and noise for each design alternative, and (5) combining and visualizing the simulation results using the digital twin. The workflow was applied to a neighbourhood in Sweden, the resultsreveal significant reduction in manual work when applying multiple simulation software for different domains. This is one step forward in streamlining the workflow for urban analysis, crucial for multi-domain optimization. In the future, further domains and simulation tools can be added to the workflow.
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| 20. |
- Göhl, Johan, 1989, et al.
(författare)
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An Immersed Boundary Based Dynamic Contact Angle Framework for Handling Complex Surfaces of Mixed Wettabilities
- 2018
-
Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322. ; 109, s. 164-177
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a comprehensive immersed boundary-based dynamic contact angle framework capable of handling arbitrary surfaces of mixed wettabilities in three dimensions. We study a number of dynamic contact angle models and implement them as a boundary condition for the Continuum Surface Force method. Special care is taken to capture the contact angle hysteresis by using separate models for the advancing and receding contact lines. The framework is able to account for surfaces of varying wettability by making the contact angle dependent on the local boundary condition. We validate our framework using cases where glycerol droplets impact solid surfaces at low Weber numbers. We show how a truly dynamic contact angle model is needed for advancing contact lines and how a separate dynamic model is needed for receding contact lines. To test our framework for industrially relevant problems on a more complex surface, we simulate droplet impact on a printed circuit board. We show how the local surface properties control the final droplet deposition and that the framework is capable of handling adjacent surfaces of considerably different wettabilities.
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| 21. |
- Göhl, Johan, 1989, et al.
(författare)
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Simulations of 3D bioprinting : Predicting bioprintability of nanofibrillar inks
- 2018
-
Ingår i: Biofabrication. - : IOP Publishing. - 1758-5082 .- 1758-5090. ; 10:3
-
Tidskriftsartikel (refereegranskat)abstract
- 3D bioprinting with cell containing bioinks show great promise in the biofabrication of patient specific tissue constructs. To fulfil the multiple requirements of a bioink, a wide range of materials and bioink composition are being developed and evaluated with regard to cell viability, mechanical performance and printability. It is essential that the printability and printing fidelity is not neglected since failure in printing the targeted architecture may be catastrophic for the survival of the cells and consequently the function of the printed tissue. However, experimental evaluation of bioinks printability is time-consuming and must be kept at a minimum, especially when 3D bioprinting with cells that are valuable and costly. This paper demonstrates how experimental evaluation could be complemented with computer based simulations to evaluate newly developed bioinks. Here, a computational fluid dynamics simulation tool was used to study the influence of different printing parameters and evaluate the predictability of the printing process. Based on data from oscillation frequency measurements of the evaluated bioinks, a full stress rheology model was used, where the viscoelastic behaviour of the material was captured. Simulation of the 3D bioprinting process is a powerful tool and will help in reducing the time and cost in the development and evaluation of bioinks. Moreover, it gives the opportunity to isolate parameters such as printing speed, nozzle height, flow rate and printing path to study their influence on the printing fidelity and the viscoelastic stresses within the bioink. The ability to study these features more extensively by simulating the printing process will result in a better understanding of what influences the viability of cells in 3D bioprinted tissue constructs.
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| 22. |
- Görtz, Morgan, 1994, et al.
(författare)
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A numerical multiscale method for fiber networks
- 2021
-
Ingår i: World Congress in Computational Mechanics and ECCOMAS Congress. - : CIMNE. - 2696-6999. ; 300
-
Konferensbidrag (refereegranskat)abstract
- Fiber network modeling can be used for studying mechanical properties of paper [1]. The individual fibers and the bonds in-between constitute a detailed representation of the material. However, detailed microscale fiber network models must be resolved with efficient numerical methods. In this work, a numerical multiscale method for discrete network models is proposed that is based on the localized orthogonal decomposition method [4]. The method is ideal for these network problems, because it reduces the maximum size of the problem, it is suitable for parallelization, and it can effectively solve fracture propagation. The problem analyzed in this work is the nodal displacement of a fiber network given an applied load. This problem is formulated as a linear system that is solved by using the aforementioned multiscale method. To solve the linear system, the multiscale method constructs a low-dimensional solution space with good approximation properties [5, 2]. The method is observed to work well for unstructured fiber networks, with optimal rates of convergence obtainable for highly localized configurations of the method.
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| 23. |
- Ingelsten, Simon, 1990, et al.
(författare)
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A Backwards-Tracking Lagrangian-Eulerian Method for Viscoelastic Two-Fluid Flows
- 2021
-
Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 11:1, s. 1-25
-
Tidskriftsartikel (refereegranskat)abstract
- A new Lagrangian–Eulerian method for the simulation of viscoelastic free surface flow is proposed. The approach is developed from a method in which the constitutive equation for viscoelastic stress is solved at Lagrangian nodes, which are convected by the flow, and interpolated to the Eulerian grid with radial basis functions. In the new method, a backwards-tracking methodology is employed, allowing for fixed locations for the Lagrangian nodes to be chosen a priori. The proposed method is also extended to the simulation of viscoelastic free surface flow with the volume of fluid method. No unstructured interpolation or node redistribution is required with the new approach. Furthermore, the total amount of Lagrangian nodes is significantly reduced when compared to the original Lagrangian–Eulerian method. Consequently, the method is more computationally efficient and robust. No additional stabilization technique, such as both-sides diffusion or reformulation of the constitutive equation, is necessary. A validation is performed with the analytic solution for transient and steady planar Poiseuille flow, with excellent results. Furthermore, the proposed method agrees well with numerical data from the literature for the viscoelastic die swell flow of an Oldroyd-B model. The capabilities to simulate viscoelastic free surface flow are also demonstrated through the simulation of a jet buckling case.
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| 24. |
- Ingelsten, Simon, 1990, et al.
(författare)
-
A Lagrangian-Eulerian framework for simulation of transient viscoelastic fluid flow
- 2019
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257. ; 266, s. 20-32
-
Tidskriftsartikel (refereegranskat)abstract
- A novel framework for simulation of transient viscoelastic fluid flow is proposed. The viscoelastic stresses are calculated at Lagrangian nodes which are distributed in the computational domain and convected by the fluid. The coupling between the constitutive equation and the fluid momentum equations is established through robust interpolation with radial basis functions. The framework is implemented in a finite volume based flow solver that combines an octree background grid with immersed boundary techniques. Since the distribution of the Lagrangian node set is performed entirely based on spatial information from the fluid solver, the ability to simulate flows in complex geometries is therefore as general as for the fluid solver itself. In the Lagrangian formulation the discretization of the convective terms in the constitutive equations is avoided. No re-formulation of the constitutive equation is required for stable solutions. Numerical experiments are performed of UCM and Oldroyd-B fluids in a channel flow and of a four mode PTT fluid in a confined cylinder flow. The computed flow quantities consistently converge and agree excellently with analytical and numerical data for fully developed and transient flow.
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| 25. |
- Ingelsten, Simon, 1990, et al.
(författare)
-
A numerical framework for simulation of swirled adhesive application
- 2019
-
Ingår i: Annual Transactions - The Nordic Rheology Society. - 1601-4057. ; 27, s. 103-108
-
Konferensbidrag (refereegranskat)abstract
- A numerical framework for simulation of swirled adhesive application along arbitrary robot motions and substrate geometries is pre- sented. The momentum and continuity equa- tions are solved on a Cartesian octree grid using a finite volume discretization. A viscoelastic constitutive model is used to describe the com- plex rheology of the adhesive and is solved us- ing a previously presented Lagrangian-Eulerian method. The flow from the nozzle to the target surface is modelled using experimental data, and a projected injection model is used to add adhesive material in the simulation close to the surface. The two-phase flow of adhesive and air is then simulated. Numerical results are com- pared with experimental data and good agree- ment is found.
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| 26. |
- Ingelsten, Simon, 1990, et al.
(författare)
-
Computationally efficient viscoelastic flow simulation using a Lagrangian-Eulerian method and GPU-acceleration
- 2020
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257. ; 279
-
Tidskriftsartikel (refereegranskat)abstract
- A recently proposed Lagrangian-Eulerian method for viscoelastic flow simulation is extended to high performance calculations on the Graphics Processing Unit (GPU). The two most computationally intensive parts of the algorithm are implemented for GPU calculation, namely the integration of the viscoelastic constitutive equation at the Lagrangian nodes and the interpolation of the resulting stresses to the cell centers of the Eulerian grid. In the original CPU method, the constitutive equations are integrated with a second order backward differentiation formula, while with the proposed GPU method the implicit Euler method is used. To allow fair comparison, the latter is also implemented for the CPU. The methods are validated for two flows, a planar Poiseuille flow of an upper-convected Maxwell fluid and flow past a confined cylinder of a four-mode Phan Thien Tanner fluid, with identical results. The calculation times for the methods are compared for a range of grid resolutions and numbers of CPU threads, revealing a significant reduction of the calculation time for the proposed GPU method. As an example, the total simulation time is roughly halved compared to the original CPU method. The integration of the constitutive equation itself is reduced by a factor 50 to 250 and the unstructured stress interpolation by a factor 15 to 60, depending on the number of CPU threads used.
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| 27. |
- Ingelsten, Simon, 1990, et al.
(författare)
-
Simulation of viscoelastic squeeze flows for adhesive joining applications
- 2022
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257. ; 300
-
Tidskriftsartikel (refereegranskat)abstract
- A backwards-tracking Lagrangian–Eulerian method is used to simulate planar viscoelastic squeeze flow. The momentum and continuity equations are discretized with the finite volume method and implicit immersed boundary conditions are used to describe objects in the domain. The viscoelastic squeeze flow, which involves moving solid geometry as well as free surface flow, is chosen for its relevance in industrial applications, such as adhesive parts assembly and hemming. The main objectives are to validate the numerical method for such flows and to outline the grid resolution dependence of important flow quantities. The main part of the study is performed with the Oldroyd-B model, for which the grid dependence is assessed over a wide range of Weissenberg numbers. An important conclusion is that the load exerted on the solids can be predicted with reasonable accuracy using a relatively coarse grid. Furthermore, the results are found to be in excellent agreement with theoretical predictions as well as in qualitative resemblance with numerical results from the literature. The effects of different viscoelastic properties are further investigated using the PTT model, revealing a strong influence of shear-thinning for moderate Weissenberg numbers. Finally, a reverse squeeze flow is simulated, highlighting important aspects in the context of adhesive joining applications.
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| 28. |
- Johansson, Linda C, 1983, et al.
(författare)
-
Lipidic phase membrane protein serial femtosecond crystallography.
- 2012
-
Ingår i: Nature methods. - : Springer Science and Business Media LLC. - 1548-7105 .- 1548-7091. ; 9:3, s. 263-265
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray free electron laser (X-FEL)-based serial femtosecond crystallography is an emerging method with potential to rapidly advance the challenging field of membrane protein structural biology. Here we recorded interpretable diffraction data from micrometer-sized lipidic sponge phase crystals of the Blastochloris viridis photosynthetic reaction center delivered into an X-FEL beam using a sponge phase micro-jet.
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| 29. |
- Johnson, Tomas, 1979, et al.
(författare)
-
A finite volume method for electrostatic three species negative corona discharge simulations with application to externally charged powder bells
- 2015
-
Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886. ; 74, s. 27-36
-
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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| 30. |
- Johnson, Tomas, 1979, et al.
(författare)
-
A multi-scale simulation method for powder coating with moving powder guns
- 2023
-
Ingår i: Journal of Electrostatics. - 0304-3886. ; 125
-
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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| 31. |
- Johnson, Tomas, 1979, et al.
(författare)
-
A Multi-Scale Simulation Method for the Prediction of Edge Wicking in Multi-Ply Paperboard
- 2015
-
Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 30:4, s. 640-650
-
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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| 32. |
- Johnson, Tomas, 1979, et al.
(författare)
-
Efficient Simulation of Convective Ovens in Automotive Paintshops
- 2023
-
Ingår i: Journal of Heat Transfer. - : ASME International. - 1528-8943 .- 0022-1481. ; 144:9
-
Tidskriftsartikel (refereegranskat)abstract
- Heat transfer modeling of large industrial ovens such as those used in automotive paintshops is difficult due to the large and multiple scales and long curing times. The flow inside a convective oven is turbulent, and the process includes large temperature gradients. An efficient simulation requires a simplified and localized model of the heat transfer coupling. We present a novel method with three ingredients: localization using local Nusselt numbers of the oven nozzles, projection of Nusselt number profiles onto the target, and efficient conduction modeling on a coarse background mesh. The approach, which was developed in a research project together with the Swedish automotive industry, makes it possible to accurately simulate a curing oven with close to real-time performance. The simulation results are demonstrated to be in close agreement with measurements from automotive production.
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| 33. |
- Johnson, Tomas, 1979, et al.
(författare)
-
Simulation of the spherical orientation probability distribution of paper fibers in an entire suspension using immersed boundary methods
- 2016
-
Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257. ; 229, s. 1-7
-
Tidskriftsartikel (refereegranskat)abstract
- A numerical model based on the Fokker–Planck equation for studying the orientation of paper fibers in a suspension is presented. The model is implemented in a finite volume framework. The rotational operators are discretized on a triangulated half sphere and the spatial operators are discretized on a Cartesian octree grid, where internal walls are handled with immersed boundary methods. Transient solutions of the two dimensional fiber orientation distribution are computed in the entire fluid domain. This is in contrast to earlier approaches that either only compute along streamlines or one dimensional projected orientations. The fibers are assumed to have negligible inertia and thus to follow the fluid perfectly and to be evenly distributed. A head-box geometry relevant for paper forming is used to exemplify the usefulness of the method. The influence of translational and rotational diffusion is included in the presented method.
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| 34. |
- Johnson, Tomas, et al.
(författare)
-
The Virtual PaintShop: Simulation of Oven Curing
- 2022
-
Ingår i: PROGRESS IN INDUSTRIAL MATHEMATICS AT ECMI. - Cham : Springer International Publishing. - 1612-3956 .- 2198-3283. - 9783031118203 ; 39, s. 221-226
-
Konferensbidrag (refereegranskat)abstract
- The modeling and simulation of oven curing in automotive paintshops is very challenging including multiple scales, turbulent air flows, thin boundary layers, large temperature gradients and long curing times. A direct brute force conjugate heat transfer simulation of an oven resolving all time and length scales would be enormously time and resource consuming. It is therefore clear that mathematical modeling must be performed, including separation of scales, and a simplification of the heat transfer coupling. We present a novel approach developed in a research project together with the Swedish automotive industry, which makes it possible to accurately simulate a curing oven with close to real time performance. The simulation results are demonstrated to be in close agreement with measurements from automotive production.
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| 35. |
- Johnson, Urban, 1961-, et al.
(författare)
-
A study on the benefits of participation in an electronic tracking physical activity program and motivational interviewing during a three-month period
- 2023
-
Ingår i: Movement & sport sciences. - Les Ulis : EDP Sciences. - 2118-5735. ; :119, s. 1-8
-
Tidskriftsartikel (refereegranskat)abstract
- Background: The purpose was to investigate if participation in a three-month electronic tracking outdoor physical activity and a motivational interviewing (MI) intervention led to positive behavioural, psychological, and physiological outcomes. Methods: Based on a two-group pre-post design, 12 middle-aged women and 6 men were randomly assign to an experimental and a control group. Physical activity data were collected by wrist-worn activity sensors, and pre-post data were collected on the GHQ-12, the BREQ-2, body mass, body fat mass and total body muscle. Measures of cardiovascular fitness were taken pre to post. The experimental group was supported through individual MI coaching sessions and resistance-training for use in an outdoor gym. Magnitude based inferences (MBI) were calculated based on the disposition of the confidence limits for the mean differences to the smallest worthwhile changes. Results: The experimental group had a beneficial increase in its physical activity behaviour (steps). The control group had a medium decrease in identified regulation, the experimental group maintained the same level at the post-measure. Conclusion: Few studies have investigated how the combination of MI and the use of activity-tracking devices effect physical and mental health. This study investigates the use of both MI and activity-tracking devices on psychological well-being, motivation, and physical health in an outdoor context. Future research recommendations are given. © 2022 ACAPS
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| 36. |
- Johnson, Urban, 1961-, et al.
(författare)
-
Connection in the Fresh Air : A Study on the Benefits of Participation in an Electronic Tracking Outdoor Gym Exercise Programme
- 2019
-
Ingår i: Montenegrin Journal of Sports Science and Medicine. - Podgorica : Montenegrin Sports Academy. - 1800-8755 .- 1800-8763. ; 8:1, s. 61-67
-
Tidskriftsartikel (refereegranskat)abstract
- This study aimed to explore whether a six-week intervention, based on participation in outdoor exercise, including activity-tracking devices and combined with individual consulting sessions, can both increase physical activity and yield positive changes in physiological and psychological health measures. A total of six participants, with a mean age of 41.2 (range 33-50 years), completed the ten-week study and the six-week intervention. The full study consisted of a four-week control/baseline and a six-week intervention period in which each participant acted as their own controls. Continuous measures of physical activity data were collected using a wrist-worn activity sensor during the ten-week study, along with pre- and post-measures of cardiovascular fitness, upper-body strength, BMI, general health, and motivation to exercise. The intervention consisted of a resistance-training programme for an outdoor gym and three motivational interviewing sessions. Effect sizes (percentage) for changes pre- to post-training were calculated. The results, because of the small sample size, are presented as individual cases, but the group, as a whole, showed average increases from baseline (pre-) to post-measures in strength (maximum row; 15.33%), time to exhaustion (3.58%), number of steps per day (4%), and autonomous motivation (12%) and average decreases in body weight (-1.08%), fat percentage (-7.58%), strength (chest; -2.5%), and stress symptoms (-2.17%). The six-week intervention programme showed promising results regarding physical activity changes. This study contributes to the limited evidence of the impact of resistance training programmes using outdoor gyms, electronic tracker, and motivational interviewing on physical activity outcomes. © 2019 by the authors.
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| 37. |
- Kamanzi, Albert, et al.
(författare)
-
Simultaneous, Single-Particle Measurements of Size and Loading Give Insights into the Structure of Drug-Delivery Nanoparticles
- 2021
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 15:12, s. 19244-19255
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles are a promising solution for delivery of a wide range of medicines and vaccines. Optimizing their design depends on being able to resolve, understand, and predict biophysical and therapeutic properties, as a function of design parameters. While existing tools have made great progress, gaps in understanding remain because of the inability to make detailed measurements of multiple correlated properties. Typically, an average measurement is made across a heterogeneous population, obscuring potentially important information. In this work, we develop and apply a method for characterizing nanoparticles with single-particle resolution. We use convex lens-induced confinement (CLiC) microscopy to isolate and quantify the diffusive trajectories and fluorescent intensities of individual nanoparticles trapped in microwells for long times. First, we benchmark detailed measurements of fluorescent polystyrene nanoparticles against prior data to validate our approach. Second, we apply our method to investigate the size and loading properties of lipid nanoparticle (LNP) vehicles containing silencing RNA (siRNA), as a function of lipid formulation, solution pH, and drug-loading. By taking a comprehensive look at the correlation between the intensity and size measurements, we gain insights into LNP structure and how the siRNA is distributed in the LNP. Beyond introducing an analytic for size and loading, this work allows for future studies of dynamics with single-particle resolution, such as LNP fusion and drug-release kinetics. The prime contribution of this work is to better understand the connections between microscopic and macroscopic properties of drug-delivery vehicles, enabling and accelerating their discovery and development.
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| 38. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
-
A continuum-based multiphase DNS method for studying the Brownian dynamics of soot particles in a rarefied gas
- 2019
-
Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 210
-
Tidskriftsartikel (refereegranskat)abstract
- In the mitigation of particulate matter (PM) using filters, the interplay between particle motion, geometry and flow conditions determines the overall performance. In such flows, molecular effects on the particle motion manifest as impeded momentum transfer and a meandering Brownian motion. Other particles and walls induce hydrodynamic interactions, which may further influence PM nucleation, growth and aggregation. Here, we formulate a multiphase direct numerical simulation framework to investigate these complex flows by including the molecular interactions in a consistent manner. The basis for this framework is a coupling between the Langevin description of particle motion with a mirroring immersed boundary method. We show that the method is able to capture the diffusion dynamics of a Brownian particle, including its transition from a particle-inertia dominated, correlated ballistic regime to a non-correlated diffusive one, and that the method also can be used to reproduce the meandering motion of realistic soot particles.
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| 39. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
-
A hydrodynamic basis for off-axis Brownian diffusion under intermediate confinements in micro-channels
- 2021
-
Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322. ; 143
-
Tidskriftsartikel (refereegranskat)abstract
- The mobility of a Brownian particle diffusing in a micro-channel is heterogeneous and spatially dependent on the surrounding hydrodynamic resistance fields. The positional asymmetry of such a diffusing particle leads to anisotropies in the observed diffusive behavior. In this paper, we probe such directionally varying diffusive behavior of a spherical nanoparticle diffusing at a location off-set from the centerline of a square micro-channel in a quiescent fluid. This investigation is carried out over varying degrees of intermediate hydrodynamic confinements. A coupled Langevin-immersed boundary method is used for these assessments. We observe that the co-axial diffusivity may be slightly enhanced during off-axis hindered diffusion when compared with a corresponding centerline diffusive behavior. We attribute this increased particle diffusivity to a reduced co-axial fluid resistance through a hydrodynamic basis derived using steady-state CFD solutions to the corresponding Stokes problem. For co-axial motion, the particle creates a recirculating flow pattern around itself when moving along the centerline, whereas it drags along the fluid in between itself and the wall when in close proximity to the latter. These contrasting flow behaviors are responsible for the unexpected enhancement of the co-axial diffusivity for some off-axis positions under intermediate hydrodynamic confinements.
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| 40. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
-
A novel multiphase DNS method for the resolution of Brownian motion in a weakly rarefied gas using a continuum framework
- 2019
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, we formulate an Immersed boundary based direct numerical simulation (DNS) technique for resolving the particle-fluid coupling between a nano-particle and a (weakly) rarefied gas. Such a method resolves the mobility of these solid particles by incorporating the hydrodynamics of the fluid more rigorously within the conventional Langevin description of the system. We analyse the consequences of resolving the subsequent Brownian motion of spherical soot-like hydrocarbon (HC) nano-particles in an unbounded domain using such a framework. The proposed method is able to capture the transition from a particle-inertia dominated (highly correlated) ballistic regime (t^2) to a non-correlated diffusive one (2Dt as given by the Stokes-Einstein relation) and further accurately estimate the resulting diffusivity of the nano-particle. This method can be used within any multiphase DNS framework to reproduce the meandering motion of soot-like Brownian particles under similar conditions.
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| 41. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
-
Assessment of hindered diffusion in arbitrary geometries using a multiphase DNS framework
- 2021
-
Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 230
-
Tidskriftsartikel (refereegranskat)abstract
- The hydrodynamics around a Brownian particle has a noticeable impact on its hindered diffusion in arbitrary geometries (such as channels/pores) due to reduced mobility close to walls. These effects are difficult to describe at sub-pore scales, wherein a complete analytical solution of the underlying hydrodynamics is challenging to obtain. Here, we propose a coupled Langevin-multiphase direct numerical simulation (DNS) framework, that fully resolves the hydrodynamics in such systems and consequently provides an on-the-fly capability to probe local instantaneous particle diffusivities. We validate and establish the capabilities of this framework in square micro-channels (under varying degrees of hydrodynamic confinement) and in an arbitrary pore. Our results show that directional variations in mean-squared displacements, velocity auto-correlation functions and diffusivities of the Brownian particle, due to inherent asymmetries in the geometry are adequately captured. Further, a local anisotropy in the hydrodynamic resistances along the co-axial direction of the channel is also noted.
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| 42. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
-
The Knudsen Paradox in Micro-Channel Poiseuille Flows with a Symmetric Particle
- 2021
-
Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 11:1, s. 1-13
-
Tidskriftsartikel (refereegranskat)abstract
- The Knudsen paradox—the non-monotonous variation of mass-flow rate with the Knudsen number—is a unique and well-established signature of micro-channel rarefied flows. A particle which is not of insignificant size in relation to the duct geometry can significantly alter the flow behavior when introduced in such a system. In this work, we investigate the effects of a stationary particle on a micro-channel Poiseuille flow, from continuum to free-molecular conditions, using the direct simulation Monte-Carlo (DSMC) method. We establish a hydrodynamic basis for such an investigation by evaluating the flow around the particle and study the blockage effect on the Knudsen paradox. Our results show that with the presence of a particle this paradoxical behavior is altered. The effect is more significant as the particle becomes large and results from a shift towards relatively more ballistic molecular motion at shorter geometrical distances. The need to account for combinations of local and non-local transport effects in modeling reactive gas–solid flows in confined geometries at the nano-scale and in nanofabrication of model pore systems is discussed in relation to these results.
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| 43. |
- Kettil, Gustav, 1990, et al.
(författare)
-
A Multiscale Method for Discrete Fiber Network Models
- 2018
-
Ingår i: 6th European Conference on Computational Mechanics (Solids, Structures and Coupled Problems). 7th European Conference on Computational Fluid Dynamics, 11-15 June 2018, Glasgow, UK.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The mechanics of paper depends on the properties of its fibers and bonds. Modeling paper as a network [1] will include effects of single fibers and bonds, capturing heterogeneous properties. In the ISOP (Innovative Simulation of Paper) project at Fraunhofer-Chalmers Centre, the forming process is simulated [2, 3]. To investigate the mechanical properties of the resulting simulated paper sheets a network approach is utilized. Numerical investigation of fiber networks is demanding due to the large number of fibers and bonds, fluctuation of their properties, and the non-regular network structure. Multiscale methods are useful tools to circumvent such problems. In this work a multi-scale approach for fiber networks is developed, based on a FEM-method for continua [4]. Consider a fiber network governed by a model resulting in an equation Kx = F, where K describes the network properties, x are node displacements, and F are applied forces. The idea of the multi-scale method is to consider a subset of all nodes, denoted coarse nodes, which in turn represents a coarse grid. At each coarse node a basis function is defined similarly as in the finite element method. By solving a system including the coarse nodes an approximation would be attained, however this approximation would leave out the fine scale effects of the heterogeneous network. Instead the coarse basis functions are modified by solving a local system at each coarse node, including surrounding fine nodes. These modified basis functions are thereafter used when solving the global system, resulting in an approximation of the network displacements now including effects from the fine scale.
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| 44. |
- Kettil, Gustav, 1990, et al.
(författare)
-
A Multiscale Methodology for Simulation of Mechanical Properties of Paper
- 2020
-
Ingår i: Proceedings of the 6th European Conference on Computational Mechanics: Solids, Structures and Coupled Problems, ECCM 2018 and 7th European Conference on Computational Fluid Dynamics, ECFD 2018. - 9788494731167 ; 2020, s. 2795-2806
-
Konferensbidrag (refereegranskat)abstract
- In this work a multiscale framework developed for simulation of mechanical properties of paper is presented. The framework consists of two major parts. In the first part the forming process of a paper machine is simulated using the fiber suspension model developed in [8]. Fluid dynamics together with an advanced contact calculation method enables detailed simulation of the lay down process. The resulting paper sheet is used as input to the second part of the framework. In the second part the fiber configuration attained from the unique forming simulations is transformed into a network representation, enabling simulation of mechanical properties. The paper mechanics is governed by a fiber network model. To study macroscale properties a novel numerical upscaling method for networks has been developed. In this paper the complete simulation methodology is outlined and discussed.
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| 45. |
- Kettil, Gustav, 1990, et al.
(författare)
-
Detailed Simulations of Early Paper Forming
- 2015
-
Ingår i: COST FP1005 Fibre Suspension Flow Modelling Final Conference Trondheim 2015 June 9-11.
-
Konferensbidrag (refereegranskat)abstract
- Computer simulations are important to increase the knowledge of the processes involved in paper making. Because of the complexity of the paper processes the development of simulation tools requires models and numerical methods which capture as much as possible of the real physical phenomena. In this paper a framework for simulation of fiber suspension flow is presented. The framework is founded on a fluid solver for the Navier-Stokes equations and a fiber model based on finite strain beam theory including shearing. Moreover, the coupling between fibers and fluid is resolved with the immersed boundary method and the interaction between the fibers is calculated using a model based on DLVO-theory.
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| 46. |
- Kettil, Gustav, 1990, et al.
(författare)
-
Novel Contact Forces for Immersed Boundary Paper Forming Simulations
- 2015
-
Ingår i: Online proceedings: http://tappi.sclivelearningcenter.com/; PF2 - The Past, Present and Future of CFD Papermaking; PaperCon 2015 Atlanta April 19-22.
-
Konferensbidrag (refereegranskat)abstract
- To be able to simulate the different processes involved in paper machines, models, numerical methods and algorithms have to be developed which capture as much as possible of the real physical phenomena. In this paper a model for calculation of the chemical and physical interaction between objects included in a fiber suspension is presented. The contact force model is based on DLVO theory [1, 2] and uses so-called contact points distributed along the fiber suspension objects. The contact model has been used in an existing framework to simulate the build-up of low density paper webs. In the framework fibers are modeled as elliptical cylinders whose movements are described by finite-strain beam theory which includes shearing. The fluid flow is computed using a Navier-Stokes solver and immersed boundary methods are utilized to resolve the flow around each fiber. For validation, the air permeability and thickness of the paper webs have been measured and compared with simulated data. The result demonstrates that the software can be used to simulate paper forming.
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| 47. |
- Kettil, Gustav, 1990, et al.
(författare)
-
Numerical investigation of upstream cylinder flow and characterization of forming fabrics
- 2019
-
Ingår i: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 34:3, s. 371-393
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, the fundamentals of upstream flow over cylinders and forming fabrics are investigated, and measures for characterization of fabrics are proposed. Two-dimensional flow over one cylinder, two cylinders, and one and two rows of cylinders, are analysed numerically. By studying different configurations and various Reynolds numbers, the upstream flow features are characterized. It is concluded that cylinders have a short range of upstream flow impact, shortest for rows of cylinders with small spacings. For R e - [ 10, 80 ]Re\in [10,80], the Reynolds number dependency is weak. It is shown that a downstream row positioned in tandem has negligible impact on the upstream flow, while a displaced second row influences the upstream flow if the spacing in the first row is larger than one diameter. The pressure drop required to drive the flow over the cylinders depends non-linearly on the porosity of the configuration. Flow measures of the upstream flow are proposed, which in addition to the volume flow per area are used to characterize fabric flow properties. The conclusions from the cylinder study also hold for industrial fabrics, and it can be explained how properties of the fabric influence the final paper. The wave-length of flow periodicity is studied in relation to drainage marking. This study demonstrates that simulations can greatly improve pure experimental-based fabric characterization. © 2019 Walter de Gruyter GmbH, Berlin/Boston.
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| 48. |
- Kettil, Gustav, et al.
(författare)
-
Numerical upscaling of discrete network models
- 2020
-
Ingår i: BIT (Copenhagen). - : Springer Science and Business Media LLC. - 0006-3835 .- 1572-9125. ; 60:1, s. 67-92
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper a numerical multiscale method for discrete networks is presented. The method gives an accurate coarse scale representation of the full network by solving sub-network problems. The method is used to solve problems with highly varying connectivity or random network structure, showing optimal order convergence rates with respect to the mesh size of the coarse representation. Moreover, a network model for paper-based materials is presented. The numerical multiscale method is applied to solve problems governed by the presented network model.
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| 49. |
- Konstantinidis, Konstantinos, 1991, et al.
(författare)
-
Coalescence-induced jumping of droplets from superhydrophobic surfaces - the effect of contact-angle hysteresis
- 2022
-
Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 34:11
-
Tidskriftsartikel (refereegranskat)abstract
- Droplets coalesce and jump from superhydrophobic surfaces, a result that stems from the dominance of capillary and inertial forces and the presence of high contact angles. This phenomenon has been a subject of intensive numerical research mostly for cases when the degree of hydrophobicity is described by a single contact-angle value (a static contact angle). The introduction of various degrees of contact-angle hysteresis complicates the numerical modeling of the jumping process due to the sensitivity to the effective value of the contact angle. We have developed and validated a comprehensive volume-of-fluid(VOF)-immersed boundary numerical framework that accounts for the effect of hysteresis by focusing on the representation of actual values of dynamic contact angles. By comparing the behavior of jumping droplets on superhydrophobic surfaces with several degrees of hysteresis (up to 15o), we quantified the influence of hysteresis on the jumping process and identified various stages of the merged droplet's detachment and re-attachment. The latter phenomena were observed in all our simulations with droplets of different initial radii. In all the cases with hysteresis, the merged droplet eventually jumps, but we point out the decrease in the jumping velocity as compared to cases with only a static contact angle imposed. Finally, by using the Kistler dynamic contact-angle model, we demonstrate the importance of accurately capturing the dynamic receding contact angle when droplets jump from superhydrophobic surfaces with various degrees of hysteresis.
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| 50. |
- Konstantinidis, Konstantinos, 1991, et al.
(författare)
-
Coalescence-induced jumping of microdroplets on superhydrophobic surfaces – A numerical study
- 2022
-
Ingår i: Canadian Journal of Chemical Engineering. - : Wiley. - 1939-019X .- 0008-4034. ; 100:12, Special Issue Article, s. 3517-3530
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Tidskriftsartikel (refereegranskat)abstract
- We develop a numerical framework for simulating the coalescence and jumping of microdroplets on superhydrophobic surfaces. The framework combines the VOF method with models for advancing and receding contact angles on a number of superhydrophobic surfaces. We demonstrate the temporal and spatial convergence of the framework and show agreement between our numerical results and other experimental studies. The capillary-inertial scaling is investigated together with the existence of a cut-off behaviour frequently observed in the lower size-range of that regime. We investigate findings in some of the previous studies that the cut-off behaviour can be attributed to viscosity effects and dissipation due to interaction with surface microstructures. We exemplify specific features related to the jumping process and the corresponding energy budget analysis when microdroplets coalesce and jump. We have tested droplets of a radius as small as 0.5 μm that are still jumping but recorded a decrease in the jumping velocity and the degree of energy conversion compared to the jumping of larger droplets. We argue and prove that strong capillary forces originating from the high curvature oscillations dissipate the energy of the system significantly faster in the case of microdroplets.
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