Direct simulations of orientational dispersion of platelet particles in a viscoelastic fluid subjected to a partial drag flow for effective coloring of polymers

황욱렬,김월용,이언석,박정해 한국유변학회 2011 Korea-Australia rheology journal Vol.23 No.3

In this study, we performed three dimensional viscoelastic flow simulations with freely suspended platelet particles for the application of effective coloring of polymers. The model problem with a partial drag surface mimics a recently proposed design to remove typical platelet particle orientation near the weld line. A standard combination for the particulate viscoelastic flow simulation techniques is employed: (i) the discrete viscous elastic stress splitting (DEVSS) scheme for the stable solution of the viscoelastic flow; (ii) the discontinuous Galerkin (DG) method to deal with the convection term in the viscoelastic stress evolution equation; (iii) a fictitious domain method (the rigid-shell description) for implicit treatment of the hydrodynamic interaction between particles and fluid. Through example problems with a single, two and many platelet particles, we report that the angular rotation of platelet particles is significantly reduced in a viscoelastic (Giesekus) fluid compared with that in a Newtonian fluid and that non-uniform angular rotation of particles can be generated by the spatial distribution of particles, which facilitates enhanced orientational dispersion by randomizing the platelet particle orientation.

Direct simulations on 2D mold-filling processes of particle-filled fluids

황욱렬,Worl-Yong Kim,Shin Hyun Kang,김시조 한국유변학회 2009 Korea-Australia rheology journal Vol.21 No.3

We present a direct simulation technique for two-dimensional mold-filling simulations of fluids filled with a large number of circular disk-like rigid particles. It is a direct simulation in that the hydrodynamic interaction between particles and fluid is fully considered. We employ a pseudo-concentration method for the evolution of the flow front and the DLM (distributed Lagrangian multipliers)-like fictitious domain method for the implicit treatment of the hydrodynamic interaction. Both methods allow the use of a fixed regular discretization during the entire computation. The discontinuous Galerkin method has been used to solve the concentration evolution equation and the rigid-ring description has been introduced for freely suspended particles. A buffer zone, the gate region of a finite area subject to the uniform velocity profile, has been introduced to put discrete particles into the computational domain avoiding any artificial discontinuity. From example problems of 450 particles, we investigated the particle motion and effects of particles on the flow for both Newtonian and shear-thinning fluid media. We report the prolonged particle movement toward the wall in case of a shear-thinning fluid, which has been interpreted with the shear rate distribution.

Finite element analysis of elastic solid/Stokes flow interaction problem

황욱렬,명진석,원호윤,안경환,이승종 한국유변학회 2007 Korea-Australia rheology journal Vol.19 No.4

We performed a numerical investigation to find out the optimal choice of the spatial discretization in thedistributed-Lagrangian-multiplier/fictitious-domain (DLM/FD) method for the solid/fluid interaction prob-lem. The elastic solid bar attached on the bottom in a pressure-driven channel flow of a Newtonian fluidbetween flexible bodies and fluid. A fixed regular rectangular discretization was applied for the descriptionof solid and fluid domain by using the fictitious domain concept. The hydrodynamic interaction betweensolid and fluid was treated implicitly by the distributed Lagrangian multiplier method. Considering a sim-plified problem of the Stokes flow and the linearized elasticity, two numerical factors were investigated toclarify their effects and to find the optimum condition: the distribution of Lagrangian multipliers and theand a pseudo-time step test. We found that the fluid stress in a fictitious solid domain can be neglected andthat the Lagrangian multipliers are better to be applied on the entire solid domain. These results will be usedto extend our study to systems of elastic particle in the Stokes flow, and of particles in the viscoelastic fluid.

Toward the computational rheometry of filled polymeric fluids

황욱렬,Martien A. Hulsen 한국유변학회 2006 Korea-Australia rheology journal Vol.18 No.4

We present a short review for authors' previous work on direct numerical simulations for inertialess hard particle suspensions formulated either with a Newtonian fluid or with viscoelastic polymeric fluids to understand the microstructural evolution and the bulk material behavior. We employ two well-defined bi-periodic domain concepts such that a single cell problem with a small number of particles may represent a large number of repeated structures: one is the sliding bi-periodic frame for simple shear flow and the other is the extensional bi-periodic frame for planar elongational flow. For implicit treatment of hydrodynamic interaction between particle and fluid, we use the finite-element/fictitious-domain method similar to the distributed Lagrangian multiplier (DLM) method together with the rigid ring description. The bi-periodic boundary conditions can be effectively incorportated as constraint equations and implemented by Lagrangian multipliers. The bulk stress can be evaluated by simple boundary integrals of stresslets on the particle boundary in such formulations. Some 2-D example results are presented to show effects of the solid fraction and the particle configuration on the shear and elongational viscosity along with the micro-structural evolution for both particles and fluid. Effects of the fluid elasticity has been also presented.

카오스 이론과 유체혼합 -3차원 혼합의 적용예를 중심으로-

황욱렬,권태헌 대한기계학회 2002 기계저널 Vol.42 No.4

Numerical simulations of elliptic particle suspensions in sliding bi-periodic frames

황욱렬,정희택,Shin Hyun Kang 한국유변학회 2005 Korea-Australia rheology journal Vol.17 No.4

We present numerical results for inertialess elliptic particle suspensions in a Newtonian fluid subject to simple shear flow, using the sliding bi-periodic frame concept of Hwang et al. (2004) such that a particulate system with a small number of particles could represent a suspension system containing a large number of particles. We report the motion and configurational change of elliptic particles in simple shear flow and discuss the inter-relationship with the bulk shear stress behaviors through several example problems of a single, two-interacting and ten particle problems in a sliding bi-periodic frame. The main objective is to check the feasibility of the direct simulation method for understanding the relationship between the microstructural evolution and the bulk material behaviors.

An efficient iterative scheme for the highly constrained augmented Stokes problem for the numerical simulation of flows in porous media

황욱렬,Oliver G. Harlen,Mark A. Walkley 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.1

In this work, we present a new efficient iterative solution technique for large sparse matrix systems that are necessary in the mixed finite-element formulation for flow simulations of porous media with complex 3D architectures in a representative volume element. Augmented Stokes flow problems with the periodic boundary condition and the immersed solid body as constraints have been investigated, which form a class of highly constrained saddle point problems mathematically. By solving the generalized eigenvalue problem based on block reduction of the discrete systems, we investigate structures of the solution space and its subspaces and propose the exact form of the block preconditioner. The exact Schur complement using the fundamental solution has been proposed to implement the block-preconditioning problem with constraints. Additionally, the algebraic multigrid method and the diagonally scaled conjugate gradient method are applied to the preconditioning sub-block system and a Krylov subspace method (MINRES) is employed as an outer solver. We report the performance of the present solver through example problems in 2D and 3D, in comparison with the approximate Schur complement method. We show that the number of iterations to reach the convergence is independent of the problem size, which implies that the performance of the present iterative solver is close to O(N).

미세입자분산 액적의 고체면에서 모세퍼짐 현상에 관한 직접수치해석 기법개발

황욱렬(Wook Ryol Hwang),정현준(Hyun Jun Jeong),김시조(See Jo Kim),김종엽(Chongyoup Kim) 한국전산유체공학회 2007 한국전산유체공학회지 Vol.12 No.4

We present a direct numerical simulation technique and some preliminary results of the capillary spreading of a droplet containing particles on the solid substrate. We used the level-set method with the continuous surface stress for description of droplet spreading with interfacial tension and employed the discontinuous Galerkin method for the stabilization of the interface advection equation. The distributed Lagrangian-multipliers method has been combined for the implicit treatment of rigid particles. We investigated the droplet spreading by the capillary force and discussed effects of the presence of particles on the spreading behavior. It has been observed that a particulate drop spreads less than the pure liquid drop. The amount of spread of a particulate drop has been found smaller than that of the liquid with effectively the same viscosity as the particulate drop.

제약용 동물세포배양기 개발사례

황욱렬(W.R. Hwang) 한국전산유체공학회 2016 한국전산유체공학회 학술대회논문집 Vol.2016 No.7

미세입자분산 고분자 현탁액의 3차원 직접수치해석

황욱렬(W.R. Hwang),M.A. Hulsen,H.E.H. Meijer 한국전산유체공학회 2009 한국전산유체공학회지 Vol.14 No.4

We present a new finite-element scheme for direct numerical simulation of particle suspensions in simple shear flow of a viscoelastic fluid in 3D. The sliding tri-periodic representative cell concept has been combined with DEVSS/DG finite element scheme by introducing constraint equations along the domain boundary. Rigid body motion of the freely suspended particle is described by the rigid-shell description and implemented by Lagrangian multipliers on particle boundaries. We present the bulk rheology of suspensions through the numerical examples of single-, twoand many-particle problems, which represent a large number of such systems in simple shear flow. We report the steady bulk viscosity and the first normal stress coefficient, which show shear-thickening behavior for both properties.