| 1. |
- Fazilati, Mina, et al.
(författare)
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Thixotropy of cellulose nanocrystal suspensions
- 2021
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Ingår i: Journal of rheology (New York, N.Y.). - : The Society of Rheology. - 0148-6055 .- 1520-8516. ; 65:5, s. 1035-1052
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Tidskriftsartikel (refereegranskat)abstract
- The thixotropy of cellulose nanocrystal (CNC) water suspensions is intrinsically dependent on the hierarchical structure of the suspension. The diverse hierarchies that comprise individual CNC nanoparticles and mesophase liquid crystalline domains, chiral nematic and nematic structures, contribute selectively to the rheological material response. Here, we combine rheology with polarized light imaging (PLI) to elucidate the thixotropic behavior of CNCs suspended in water. The simultaneous monitoring of PLI and rheological tests enables the observation of mesogens and their orientation dynamics. Creep, dynamic time sweep, ramped hysteresis loop, and thixotropic recovery tests combined with PLI aim to differentiate the contribution of the different hierarchical levels of CNC suspensions to their thixotropy. The range of concentrations investigated comprised biphasic (4 and 5 wt. %) and liquid crystalline phase suspensions (6, 7, and 8 wt. %). The CNC suspensions exhibited complex thixotropy behavior, such as viscosity bifurcations in creep tests and overshoot in ramped hysteresis loop tests. The restructuring and destructuring appeared to correspond to different levels of their hierarchical structure, depending mainly on the phase, in agreement with previous studies. Restructuring was attributed to re-organizations of an individual CNC, e.g., in the isotropic fraction of biphasic suspensions and at the mesogen interfaces in liquid crystalline phase suspensions. However, by increasing liquid crystalline fraction in the biphasic concentrations, restructuring could also involve mesogens, as indicated in the creep tests. For flow conditions above the yield stress, as evidenced by the ramped hysteresis and thixotropy recovery tests, destructuring was dominated by orientation in the flow direction, a process that is readily observable in the form of PLI "Maltese-cross" patterns. Finally, we show that a simple thixotropy model, while unable to capture the finer details of the suspension's thixotropic behavior, could be employed to predict general features thereof.
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| 2. |
- Ingelsten, Simon, 1990, et al.
(författare)
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A Backwards-Tracking Lagrangian-Eulerian Method for Viscoelastic Two-Fluid Flows
- 2021
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Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 11:1, s. 1-25
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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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| 3. |
- Ingelsten, Simon, 1990, et al.
(författare)
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A Lagrangian-Eulerian framework for simulation of transient viscoelastic fluid flow
- 2019
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Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257. ; 266, s. 20-32
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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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| 4. |
- Ingelsten, Simon, 1990
(författare)
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A Lagrangian-Eulerian simulation framework for viscoelastic fluid flows
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Viscoelastic fluids appear in various industrial applications, including adhesive application, additive manufacturing, seam sealing and parts assembly with adhesive. These processes are characterized by complex geometry, moving objects and transient multiphase flow, making them inherently difficult to simulate numerically. Furthermore, substantial amount of work is typically necessary to setup simulations and the simulation times are often unfeasible for practical use. In this thesis a new Lagrangian-Eulerian numerical method for viscoelastic flow is proposed. The viscoelastic constitutive equation is solved in the Lagrangian frame of reference, while the momentum and continuity equations are solved on an adaptive octree grid with the finite volume method. Interior objects are modeled with implicit immersed boundary conditions. The framework handles multiphase flows with complex geometry with minimal manual effort. Furthermore, compared to other Lagrangian methods, no re-meshing due to grid deformation is necessary and a relatively small amount of Lagrangian nodes are required for accurate and stable results. No other stabilization method than both sides diffusion is found necessary. The new method is validated by numerical benchmarks which are compared to analytic solutions as well as numerical and experimental data from the literature. The method is implemented both for CPU computation and in a hybrid CPU-GPU version. A substantial increase in simulation speed is found for the CPU-GPU implementation. Finally, an industrially suitable model for swirl adhesive application is proposed and evaluated. The results are found to be in good agreement with experimental adhesive geometries.
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| 5. |
- Ingelsten, Simon, 1990
(författare)
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A Lagrangian-Eulerian simulation method for viscoelastic flows applied to adhesive joining
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Viscoelastic flows are important for many industrial processes, such as adhesive joining, polymer extrusion and additive manufacturing. Numerical simulations enable virtual evaluation and product realization, which can support the design phase and reduce the amount of costly physical testing. However, such applications are challenging to simulate. Thus, efficient, robust and user-friendly simulation methods are needed. In this thesis, a Lagrangian--Eulerian simulation framework for viscoelastic flow is presented. The constitutive equation is solved at Lagrangian nodes, convected by the flow, while the momentum and continuity equations are discretized with the finite volume method. The volume of fluid method is used to model free-surface flow, with an injection model for extrusion along arbitrary nozzle paths. The solver combines an automatic and adaptive octree background grid with implicit immersed boundary conditions. In contrast to boundary-conformed mesh techniques, the framework handles arbitrary geometry and moving objects efficiently. Furthermore, novel coupling methods between the Lagrangian and Eulerian solutions as well as unique treatment of the Lagrangian stresses at the fluid-fluid interface are developed. Consequently, the resulting method can simulate the complex flows associated with the intended applications, without the need for advanced stabilization techniques. The framework is validated for a variety of flows, including relevant benchmarks as well as industrial adhesive joining applications. The latter includes robot-carried adhesive extrusion onto a car fender as well as a hemming application. The results agree with the available experimental data. As such, the research presented in this thesis can contribute to enable virtual process development for joining applications.
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| 6. |
- Ingelsten, Simon, 1990, et al.
(författare)
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A numerical framework for simulation of swirled adhesive application
- 2019
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Ingår i: Annual Transactions - The Nordic Rheology Society. - 1601-4057. ; 27, s. 103-108
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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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| 7. |
- Ingelsten, Simon, 1990, et al.
(författare)
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Computationally efficient viscoelastic flow simulation using a Lagrangian-Eulerian method and GPU-acceleration
- 2020
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Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257. ; 279
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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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| 8. |
- Ingelsten, Simon, 1990, et al.
(författare)
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Simulation of viscoelastic squeeze flows for adhesive joining applications
- 2022
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Ingår i: Journal of Non-Newtonian Fluid Mechanics. - : Elsevier BV. - 0377-0257. ; 300
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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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| 9. |
- Mark, Andreas, 1980, et al.
(författare)
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Lay Down Simulation of Viscoelastic Fluids Using the Hybrid Immersed-Boundary Method
- 2016
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Ingår i: ICMF-2016 – 9th International Conference on Multiphase Flow, May 22nd – 27th 2016, Firenze, Italy.
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Konferensbidrag (refereegranskat)abstract
- Lay down of viscoelastic fluids is common in several manufacturing processes. In the automotive industry, sealing material is sprayed onto the vehicle body to prevent water leakage into cavities and to reduce noise. To predict the deposition and lower the environmental impact by reducing material consumption, a detailed physical understanding of the process is important. In this work the resulting surface multi-phase flow is modeled and simulated in IBOFlow, the in-house multi-phase flow solver at the Fraunhofer-Chalmers Centre. In the solver the two phase flow is modelled by the volume of fluid method and the viscoelastic fluid by a general Carreu rheology model. In the solver the scanned or CAD geometry is handled by the hybrid immersed boundary method and the material interface is resolved by the adaptive anisotropic octree grid. The resulting hanging octree and triangular nodes along the geometry are automatically handled by the immersed boundary method. To boost the computational performance the simulation domain is in a novel way dynamically divided into an active and an inactive part. The governing equations are only assembled and solved for in theactive part, which is determined by the local position of the injection nozzle. The interface between the active and the inactive cells are handled by symmetry boundary conditions and the pressure is always set for a point inside the active domain. The sealing lay down simulation is successfully validated for a number of real sealing beads on a plate and on a Volvo V40 vehicle. Finally, the importance of resolving the nozzle in the simulation is investigated for a static case.
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