力学系与湍流国家重点实验室学术报告4.14
发布时间: 2010-04-13 11:36:00
SEMINAR SERIES
北京大学工学院 ![]()
力学与空天技术系
力学与空天技术系 湍流与复杂系统国家重点实验室
题目一：Hydrodynamnic Flows in Electrowetting
报告人 Prof. Kwan Hyoung Kang
Department of Mechanical Engineering,
Pohang University of Science and Technology
报告一容摘要：
In the first part, I will present the hydrodynamic flows generated inside a droplet in electrowetting when an ac voltage is applied. In order to find out the characteristics and origin of the flows, we investigated the flow pattern for a sessile droplet for various conditions. A shape oscillation of a droplet was observed in the low-frequency range by a high-speed camera. The shape oscillation is responsible for the low-frequency flow. The flow at high frequency is caused by some electrohydrodynamic effect.
In the second part, an experimental and theoretical work will be presented concerning the shape oscillation of sessile droplet. A set of shape mode equations is derived to describe unsteady motions of a sessile drop actuated by electrowetting. It is revealed that resonance occurs at certain frequencies and the oscillation pattern is significantly dependent on the applied AC frequencies. The domain perturbation method is used to derive the shape mode equations under the assumptions of weak viscous effect and small deformation of drop. The electrical force concentrated on the three-phase contact line is approximated as a delta function, which is decomposed and substituted into each shape mode equation as a forcing term. The theoretical results on the shape and the frequency responses are compared with experimental results, which shows a qualitative agreement.
Finally, I will present a novel method to actuate oscillation of a sessile bubble or oil drop in a fluid to produce steady streaming within the fluid. This method is based on time-periodic control of the wettability of the bubble or drop by electrowetting. Jet velocity is proportional to oscillation amplitude and is greatest at natural oscillation frequencies. Analytical and numerical analyses indicate that the jet is produced by steady streaming in the Stokes layer.
题目二：Micro-Manufacturing and Its Research Trends
报告人 Prof. PARK SUNG JIN
Pohang University of Science and Technology, Pohang, Korea
报告二容摘要：
The micro-manufacturing (-manufacturing) of high-precision 3D products with sizes ranging from 10 mm to 1 mm for non-silicon materials is a major engineering challenge. The global technical community is making heavy investments in the research needed to meet the trends in industrial and military products that demand miniaturization. The needs include design flexibility, reduced energy consumption, and high accuracy – especially in the medical, biotechnology, telecommunication, energy, and automotive fields. In parallel, multiscale modeling and simulation is a rapidly evolving area of research that will have a fundamental impact on computational science and applied mathematics and will influence the way we view the relation between mathematics and science. The effort to combine these two technologies is under research with the following topics:
•The micro power injection molding (-PIM) of nanopowders based feedstock is being developed and used as one of the candidates in -manufacturing of metal, ceramic, and carbide materials with the aim to overcome mechanical and electrical property limitations of polymers - a currently winning material in -manufacturing. In order to keep the -PIM approach the size of powder should be less than 1/20 of smallest micro-feature (e.g. < 100 nm particle for 2 mm m feature). Researches include the binder design and the rheological behaviour of binder-nanopowder mixture, micro injection molding, debinding, and sintering.
•Multiscale modeling and simulation (MMS) by integrating atomistic (MD), discrete element (DEM), and finite element (FEM) simulations is under development for analyzing -manufacturing processes with material informatics. This research is possible through wide interdisciplinary collaborations with the physics, mathematics, and computer science departments. The multiscale simulation is followed by multiscale sensitivity analysis and multi-objective optimization for final -manufactured product of nanopowders.
•Bio-inspired design (BID) capitalizes on the rich source of design solutions present in biological materials by investigating the structure-property relationships with modeling and simulation. Current research includes turtle shell for armor design and bighorn ram for crashworthiness design. Investigated porous multiscale structure is made by m-manufacturing process.
时 间：4月14日（周三）下午2:00
地 点：力学楼434会议室
报告人简介：
Kwan Hyoung Kang is an Assistant Professor of Department of Mechanical Engineering at Pohang University of Science and Technology (POSTECH). He works in the microfluidics field with a particular interest in electrical control of microscale fluids and particles including electrowetting, dielectrophoresis, electrokinetics, and electrohydrodynamics. He developed an electromechanical theory of electrowetting and found out the origin of electrowetting phenomenon. He found hydrodynamic flows in ac electrowetting including a synthetic jet produced by an oscillating sessile droplet. He discovered an electrohydrodynamic flow produced by nonuniform electric fields in dielectric liquids. His laboratory has been assigned as one of the National Research Laboratory (NRL) by the Korean government with the title of “Electro-Microfluidics Lab” since year 2007. The project is entitled “Development of an electromechanics-based multi-functional microfluidic platform for handling of microscale fluids and particles.” Ongoing project includes investigations on the switching speeds of electrowetting-based switches and electrophoresis-based electric papers. Prof. Kang received his PhD, MS, and BS in Mechanical Engineering from the POSTECH in 1996, 1993, and 1991, respectively. He is an editorial-board member of an AIP journal Biomicrofluidics.
Kwan Hyoung Kang is an Assistant Professor of Department of Mechanical Engineering at Pohang University of Science and Technology (POSTECH). He works in the microfluidics field with a particular interest in electrical control of microscale fluids and particles including electrowetting, dielectrophoresis, electrokinetics, and electrohydrodynamics. He developed an electromechanical theory of electrowetting and found out the origin of electrowetting phenomenon. He found hydrodynamic flows in ac electrowetting including a synthetic jet produced by an oscillating sessile droplet. He discovered an electrohydrodynamic flow produced by nonuniform electric fields in dielectric liquids. His laboratory has been assigned as one of the National Research Laboratory (NRL) by the Korean government with the title of “Electro-Microfluidics Lab” since year 2007. The project is entitled “Development of an electromechanics-based multi-functional microfluidic platform for handling of microscale fluids and particles.” Ongoing project includes investigations on the switching speeds of electrowetting-based switches and electrophoresis-based electric papers. Prof. Kang received his PhD, MS, and BS in Mechanical Engineering from the POSTECH in 1996, 1993, and 1991, respectively. He is an editorial-board member of an AIP journal Biomicrofluidics.
Seong Jin Park
Professional Preparation
B.S. (Mechanical Engineering), 1991, Pohang University of Science and Technology, Pohang, Korea
M.S. (Mechanical Engineering), 1993, Pohang University of Science and Technology, Pohang, Korea
Ph.D. (Mechanical Engineering), 1996, Pohang University of Science and Technology, Pohang, Korea
Appointments
2009–Present, Assistant Professor, Pohang University of Science and Technology, Pohang, Korea
2006–2009, Associate Research Professor, Center for Advanced Vehicular System, Mississippi State University, Mississippi State, MS
2001–2005: Research Associate, Center for Innovative Sintered Products, Penn State University, University Park, USA
2001–2009: Chief Technical Officer, CetaTech, Inc., Sacheon, Korea
1996–2000: Research Engineer, LG Product engineering Research Center, LG Electronics, Inc., Pyungtaek, Korea
Fields of Specialization and Interest:
Micro-Manufacturing: Polymer Assisted Powder Metallurgy and Polymer Processing
Mechanics of Biological Materials
Non-Newtonian Flow & Heat Transfer / Rheology / Sintering /High Strain Rate Deformation
Multiscale Simulation and Material Informatics
Historical Integration / FEM / BEM / Sensitivity / Optimization
Publications
6 Books and Book Chapters
4 Patents
4 Commercialized Software
64 Journal Papers
155 Conference Papers and Presentations
18 Magazine Articles and Workshop Presentations
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