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강태곤(T.G. Kang) 한국전산유체공학회 2009 한국전산유체공학회 학술대회논문집 Vol.2009 No.11
When exposed to uniform magnetic fields externally applied, paramagnetic particles acquire dipole moments and the induced moments interacting with each other lead to the formation of chainlike structures or clusters of particles aligned with the .field direction. A direct simulation method, based on the Maxwell stress tensor and a fictitious domain method, is applied to solve flows with magnetic chains in simple shear flow. We assumed that the particles constituting the chains are paramagnetic, and inertia of both flow and magnetic particles is negligible. The numerical scheme enables us to take into account both hydrodynamic and magnetic interactions between particles in a fully coupled manner, enabling us to numerically visualize breakup and reformation of the chains by the combined effect of the external field and the shear flow. Simple shear flow with suspended magnetic chains is solved in a periodic domain for a given magnetic field. Dynamics of interacting magnetic chains is found to be significantly affected by a dimensionless parameter called the Mason number, the ratio of the viscous force to the magnetic force in the shear flow. The effect of particle area Faction on the chain dynamics is investigated as well.
전산유체역학을 활용한 가전 제품용 원심팬 블레이드의 단계별 형상 최적화
김종수(J.S. Kim),강태곤(T.G. Kang) 한국전산유체공학회 2016 한국전산유체공학회지 Vol.21 No.3
We conducted a multi-stage optimization to secure the desired performance of a centrifugal fan for home appliance in an early stage of product development. In optimization, the static pressure at the outlet of the fan is chosen as an objective function that is to be maximized, providing the required flow rate at the operating point of the fan. The optimization procedure begins with parameters for an initial baseline fan design. The baseline design is optimized by using a commercial optimization package. Accordingly, the corresponding blade models with a set of geometrical parameters are generated. Flow through a fan is simulated by solving the Reynolds-averaged Navier-Stokes equations. A multi-stage optimization scheme is employed to determine the family of optimum values for the parameters, leading to the pressure increase at the outlet of the fan. To validate the numerically obtained optimal design parameters, we fabricated the three types of fans using rapid prototyping and assessed the performance using a fan tester. Experimental results show that the design parameters at each stage satisfy the goal of optimization. The multi-stage optimization process turned out to be a useful tool in the development of a centrifugal fan.
균일한 외부자기장 하에서의 원형 야누스 자기입자의 거동
성유진(Y.J. Seong),강태곤(T.G. Kang) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5
We numerically investigated the dynamics of circular Janus magnetic particles suspended in a viscous liquid, exposed to a uniform magnetic field applied externally. Each Janus particle has both magnetic part and non-magnetic one in a single particle. A direct simulation method, based on the Maxwell stress tensor and a fictitious domain method, is employed to solve the problem. Since we are concerned with a microfluidic application, we neglect inertia of particles and fluid. The previous numerical scheme for isotropic magnetic particles is improved further, enabling us to take into account the anisotropy of magnetic property. First, we validate the numerical scheme. Next, the dynamics of a single particle in the uniform field is investigated to see the effect of the material orientation on the rotational motion. The orientation of a single particle is aligned with the field direction due to the magnetic torque created by magnetic anisotropy. Then, we extended our interest to a two-particle problem. Depending on the initial angle between the field and the line-of-centers between the two particles, two distinct behaviors in particle path are observed. The detailed particle motions and the final conformations are also influenced by the intial orientations of the particles. As reported in several experimental studies on Janus particles, there exist two types of particle alignment: the straight configuration and the staggered one. We also discussed the difference in particle dynamics between Janus and isotropic particles.
회전 자기장이 가해지는 점성유체 내에 분산된 야누스 자기입자의 동적 거동
김희은(H. E. Kim),강태곤(T.G. Kang),김경범(K. B. Kim),마태영(T. Y. Ma) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
We numerically investigate the dynamics of circular Janus magnetic particles suspended in a non-magnetic viscous fluid in the presence of an externally applied rotating magnetic field. A direct simulation that is based on the Finite Element Method (FEM) and a fictitious domain is employed to solve the particulate flow in the Stokes flow regime. The particles are assumed to be non-Brownian and inertialess. The dynamics of a single particle in the rotating field are found to be significantly influenced by the Mason number (the ratio between the magnetic torque and the viscous torque) and the magnetic susceptibility. The particle dynamics in multi-particle problems are affected by the initial orientation of each particle as well as the Mason number. Using several initial configurations of the particles, we discuss the motions of the Janus particles affected by above-mentioned parameters.
굴삭기 상부작업체에서 틈새의 영향을 고려한 버켓의 거동의 편차에 대한 연구
신대영(D. Y. Shin),강태곤(T. G. Kang),황성호(S. H. Hwang) 유공압건설기계학회 2018 유공압건설기계학회 학술대회논문집 Vol.2018 No.11
The excavator consists of boom, arm and bucket, and the boom, arm and bucket are driven by hydraulic cylinder. The clearance of the upper part of the excavator reflects the clearance of the joint part of the hydraulic cylinder and compares the angles of the joint parts and studies the deviation of the bucket behavior due to the clearance of the joint. As the clearance of the joint increases, the angle of rotation of the joint increases, this ultimately affects the deviation of the bucket behavior.
점성유체에 분산된 타원형 야누스 입자의 자성 상호작용에 관한 직접수치해석
김희은(H.E. Kim),강태곤(T.G. Kang) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
The magnetic interaction between elliptic Janus particles are investigated using a direct simulation method. The particles are equally compartmentalized into magnetic and nonmagnetic areas and have the magnetic anisotropy coming from the non-uniform magnetic properties. Since microscale flows with tiny Janus particles belong to the creeping flow regime, the inertia of the fluid can be neglected. In addition, the inertia of the particles are also neglected, because the typical particle size is of the order of microns or less. A finite-element-based fictitious domain method is used to solve the particulate flow. In the magnetic problem, the magnetic field in a whole domain including the particles and the fluid is obtained by solving the governing equation for the magnetic potential. Then, the magnetic forces due to non-uniform magnetic fields around the particles are calculated via a Maxwell stress tensor formulation. The dynamics and the final conformation of the particles are significantly affected by the aspect ratio, the orientation, and the initial spatial positions of the particles. The self-assembly structure of the particles is not a fixed one, but it varies with the abovementioned factors.