Approximate velocity scale for primary and secondary dual-inlet side-dump flows

Effects of the bulk inlet velocity on the characteristics of dual-inlet side-dump flows are numerically investigated. Non-reacting subsonic turbulent flow is solved by a preconditioned Reynolds-averaged Navier-Stokes equation system with low-Reynolds number k − ɛ turbulence model. The numerical method is properly validated with measured velocity distributions in the head dome and the combustor. With substantial increase in the bulk inlet velocity, general profiles of essential primary and secondary flows normalized by the bulk inlet velocity are quantitatively invariant to the changes in the bulk inlet velocity. This paper was recommended for publication in revised form by Associate Editor Do Hyung Lee Seung-chai Jung received his B.S. degree in Mechanical Engineering from Yonsei University, Korea, in 2001. He then received his M.S. degree in Mechanical Engineering from Yonsei University, Korea, in 2005. Mr. Jung is currently a Ph. D. candidate at Yonsei University, where he is majoring in Mechanical Engineering. Mr. Jung’s research interests include propulsion system and particle-surface collision dynamics. Byung-Hoon Park received his B.S. degree in Mechanical Design and Production Engineering from Yonsei University in 2003. He is currently a Ph.D. candidate in Yonsei University in Seoul, Korea. His research interests include performance design of propulsion systems and nu-merical analysis of instability in multiphase turbulent reacting flow-fields. Hyun Ko received his B.S. degree in Aerospace Engineering from Chonbuk National University, Korea, in 1996. He then received his M.S. degree in Mechanical Design from Chonbuk National University, Korea, in 1998. In 2005, he obtained his Ph.D. degree from Yonsei University, where he majored in mechanical engineering. Dr. Ko is currently a Principal Research Engineer of the MicroFriend Co., Ltd. in Seoul, Korea. His research interests include propulsion related systems and computational fluid dynamics. Woong-sup Yoon received his B.S. degree in Mechanical Engineering from Yonsei University, Korea, in 1985. He then received his M.S. degree from University of Missouri-Rolla in 1989. In 1992, he obtained his Ph.D. degree from the University of Alabama in Huntsville, where he majored in mechanical and aerospace engineering. Dr. Yoon is currently a professor at the School of Mechanical Engineering at Yonsei University in Seoul, Korea. His research interests include propulsion system and particle-related environmental/ thermal engineering.     

Spray formation by like-doublet impinging jets in low speed cross-flows

Breakup and spray formation by impinging liquid jets introduced into a low-speed cross-flow are experimentally investigated. Effects of the cross-flows on the macroscopic and microscopic spray parameters are optically measured in terms of jet Weber number and liquid-to-gas momentum ratio. The liquid stream undergoes Rayleigh jet breakup at lower jet Weber numbers and bag/plume breakup at higher momentum ratio through Kelvin-Helmholtz instability. In particular, the first and the second wind breakup occur at an intermediate jet Weber number. At higher jet Weber numbers, the hydrodynamic impact waves commands and the effect of the convective gas flows is insignificant. The breakup length rises in proportion to the jet Weber number, but starts to decrease when the jet Weber number further rises over 1000. The cross-flow promotes the jet breakup and renders a finer spray in an entire range of injection velocities. This paper was recommended for publication in revised form by Associate Editor Gihun Son Woong-Sup Yoon is a Professor in the School of Mechanical Engineering at Yonsei University. His current research interests are in wave instabilities, unusual spray formation, emission control, and propulsion system modeling. He received a BS degree from the Department of Mechanical Engineering, Yonsei University, in 1985; an MS degree from the Department of Mechanical Engineering, University of Missouri-Rolla, in 1989; and a Ph.D degree from the Department of Mechanical and Aerospace Engineering, the Unversity of Alabama in Huntsville, in 1992. Sang-seung Lee received his B.S. degree in Weapons Engineering from Korea Military Academy, Korea, in 2002. He then received his M.S. degrees from Yonsei University, in 2006. Mr. Lee is currently a Lecturer at the School of Weapons Engineering at Korea Military Academy in Seoul, Korea. He serves as an Editor of the Journal of Mechanical Science and Technology. Mr. Lee’s research interests include Ramjet, Atomization of injector. Won-ho Kim received his B.S. degree in Mechanical Engineering from Yonsei University, Korea, in 2003. Mr. Kim has then gone on to do graduate work at the Ph.D in the School of Mechanical Engineering at Yonsei University in Seoul, Korea. Mr. Kim’s research interests include Atomization of 2phase flow and Dust collection efficiency.     

Optimal design of a variable stiffness joint in a robot manipulator using the response surface method

The response surface method combined with the design of experiment-based design optimization of a variable stiffness joint (VSJ) is presented in this article. A VSJ used in a manipulator of a robot arm to support 1 kg payload at the end is designed by considering the minimization of the total weight as the objective function. Owing to the requirement of large rotational stiffness of the VSJ, over 10 N · m, ring-type permanent magnets are adopted. First, a model composed of two permanent magnets was initially manufactured and tested for comparison with the analysis results. Then, a three-ring-type permanent magnet-based model is suggested and optimized to increase the torque of VSJ. The finite element method is used as a magnetic field analysis method to substitute for the expensive experimental process. Optimization results decrease the weight from 0.899 kg to 0.538 kg, still satisfying the requirement for the rotational stiffness. This paper was recommended for publication in revised form by Associate Editor Tae Hee Lee Jeonghoon Yoo received his B.S. and M.S. degrees in Mechanical Design and Production Engineering from Seoul National University, in 1989 and 1991, respectively. He then received his Ph.D. degrees from the University of Michigan, Ann Arbor, in 1999. Dr. Yoo is currently a Professor at the School of Mechanical Engineering at Yonsei University in Seoul, Korea. Dr. Yoo’s research interests include analysis and design of electromagnetic field systems. Myung Wook Hyun received his B.S. and M.S. degrees in Mechanical Engineering from Yonsei University, Korea, in 1995 and 1997, respectively. While studying for his M.S. degree, Mr. Hyun also studied variable stiffness unit design. He is now working at Samsung Electronics, Co. Ltd.. Jun Ho Choi received his B.S. and M.S. degrees in Mechanical Design from Hanyang University, Korea and his Ph.D. degree from the University of Michigan, Ann Arbor. He is currently a senior research scientist in the Korea Institute of Science and Technology. His research interests include nonlinear control, manipulator control, and safe-joint design. Sungchul Kang received his B.S., M.S., and Ph.D. degrees in Mechanical Design and Production Engineering from Seoul National University, Korea, in 1989, 1991, and 1998 respectively. Dr. Kang is currently a Principal Research Scientist in the Center for Cognitive Robotics Research, Korea Institute of Science and Technology, in Seoul, Korea. Dr. Kang’s research interests include mobility and manipulation of field and service robots and haptics. Seung-Jong Kim received his B.S. degree in Mechanical Engineering from Seoul University, Korea, in 1989, and his M.S. and Ph.D. degrees from KAIST in 1991 and 1998, respectively. Dr. Kim is currently a Principal Research Scientist at the Korea Institute of Science and Technology in Seoul, Korea. Dr. Kim’s research interests include the design, control, and dynamic analysis of mechatronic systems.     

Theoretical analysis and experiments of axial flux pm motors with minimized cogging torque

This paper deals with analysis and experiments of an axial flux PM (AFPM) brushless dc motor with minimized cogging torque. Recently, many optimal designs for the AFPM motor have been done by finite element (FE) analysis, but such analysis is time-consuming. In this study, the equation of magnetic flux lines existing between PMs and core is assumed mathematically and the minimum cogging torque is calculated theoretically and geometrically without FE analysis. The form of equation is assumed to be a 2^nd order polynomial. The skew angle that makes the cogging torque minimized is calculated theoretically, and the value of minimum cogging torque is compared with the results obtained by FE analysis and experiments. The maximum cogging torque of a proposed AFPM motor has the smallest value approximately at a skew angle of 4° in both the theoretical and FE analysis. Compared with the non-skewed motor, the cogging torque of the skewed motor can be decreased to over 90%, which has a value of 5% of the rated torque. Two types of stator cores, with the skew angle of 0° and 4°, are analyzed, manufactured, and tested experimentally. This paper was recommended for publication in revised form by Associate Editor Hong Hee Yoo Dong Ho Kim received B.S. and M.S. degrees in Mechanical Engineering from Pusan National University in 1982 and 1984, respectively. He then received his Ph.D. degree from Yonsei University in 2007. Dr. Kim is currently a Professor at the Department of Automation and Robots at Kyonggi Institute of Technology in Gyeonggi, Korea. His research interests are in the area of production automation. Jong Hyun Choi received B.S., M.S., and Ph.D. degrees in Mechanical Engineering from Yonsei University, Seoul, Korea, in 1996, 1998, and 2006, respectively. Dr. Choi is currently a post-doctor at the School of Mechanical Engineering at Yonsei University. His research interests are in the area of electromagnetic actuators and magnetic levitation system. Chang Woo Son received a B.S. from Kyungwon University, Seoul, Korea, in 2006, and his M.S. degree from Yonsei University in 2008, all in mechanical engi-neering. He is currently a research engineer at DA Laboratory of LG Electronics in Seoul, Korea. His research interests are in the area of electromagnetic actuators. Yoon Su Baek received B.S. and M.S. degrees from Yonsei University, Seoul, Korea, in 1979 and 1981, respectively, and M.S. and Ph.D. degrees from Oregon State University in 1986 and 1990, respectively, all in mechanical engineering. He worked for Samsung Heavy Industry Ltd. as head research engineer at Mechatronics Research Center from 1990 to 1993. Dr. Baek is currently a Professor at the School of Mechanical Engineering at Yonsei University. His research interests are motion devices and robotics, especially relating to multi-D.O.F. actuators. He is also interested in magnetic brake and levitation system.     

Effects of injection type on slot film cooling for a ramjet combustor

A slot film cooling technique has been used to protect a combustor liner from hot combustion gas. This method has been developed for gas turbine combustors. A ramjet combustor exposed to high temperature can be protected properly with a multi-slot film cooling method. An experimental study has been conducted to investigate the change of the first slot angle under recirculation flow and the influence of wiggle strip within a slot, which affects the film cooling effectiveness. The first slot angle has been changed to understand the effect of the injection angle on the film cooling effectiveness in a recirculation zone. The distribution of dimensionless temperature was obtained by a thermocouple rake to investigate the wiggle strip effect, and the adiabatic film cooling effectiveness on downstream wall was measured by a thermochromic liquid crystal (TLC) method. At the first slot position, the film cooling effectiveness decreases significantly because of the effects of recirculation flow. The lip angle of the first slot affects slightly on the film cooling effectiveness. The wiggle strip reinforces the structure of slot and keeps the uniform open area of slot. However, it induces three dimensional flows and enhances the flow mixing between the main flow and the injected slot flow. Therefore, the wiggle strip decreases slightly the overall film cooling effectiveness. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Kwanghoon Park received his M.S degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 2007. He is currently working for an education of an officer as a drillmaster in Army Consolidated Logistics School. Kang Mo Yang joined the Republic of Korea Army in 2004. He is currently working towards the M.S. degree at the Department of Mechanical Engineering, Yonsei University. Keon Woo Lee received his M.S. degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 2008. In 2008, he joined the Doosan heavy industries & Construction Co, LTD, where he is a member of the IGCC Business Team. Hyung Hee Cho received his PhD degree in Mechanical Engineering from University of Minnesota, Minneapolis, MN in 1992. In 1995, he joined the Department of Mechanical Engineering, Yonsei University, Seoul, Korea, where he is currently a full professor in the School of Mechanical Engineering. His research interests include heat transfer in turbomachineries, rocket/ramjet cooling as well as nanoscale heat transfer in thin films, and microfabricated thermal sensors. Hee Cheol Ham received his PhD degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 2001. In 1984, he joined the Agency for Defense Development, Daejeon, Korea, where he is currently a Principal Researcher. Ki Young Hwang received his Ph.D. degree in Mechanical Engineering from Yonsei University, Seoul, Korea in 1994. In 1979, he joined the Agency for Defense Development, Daejon, Korea, where he is currently a principal researcher in the Airbreathing Propulsion Directorate.     

Optimal operating points of PEM fuel cell model with RSM

The output power efficiency of the fuel cell system mainly depends on the required current, stack temperature, air excess ratio, hydrogen excess ratio, and inlet air humidity. Therefore, the operating conditions should be optimized to get maximum output power efficiency. In this paper, a dynamic model for the fuel cell stack was developed, which is comprised of a mass flow model, a gas diffusion layer model, a membrane hydration, and a stack voltage model. Experiments have been performed to calibrate the dynamic Polymer Electrolyte Membrane Fuel Cell (PEMFC) stack model. To achieve the maximum output power and the minimum use of hydrogen in a certain power condition, optimization was carried out using Response Surface Methodology (RSM) based on the proposed PEMFC stack model. Using the developed method, optimal operating conditions can be effectively selected in order to obtain minimum hydrogen consumption. This paper was recommended for publication in revised form by Associate Editor Tong Seop Kim Dong-Ji Xuan received his B.S. degree in Mechanical Engineering from Harbin Engineering University, China in 2000. He then received his M.S. degree in Mechanical Engineering from Chonnam National University, South Korea in 2006. Currently, he is a Ph.D. candidate of the Department of Mechanical Engineering, Chonnam National University, South Korea. His research interests include control and optimization of PEM fuel cell system, dynamics and control, and mechatronics. Zhen-Zhe Li received his B.S. degree in Mechanical Engineering from Yanbian University, China in 2002. He then received his M.S. degree in Aerospace Engineering from Konkuk University, South Korea in 2005 and his Ph.D. degree in Mechanical Engineering from Chonnam National University, South Korea in 2009. Dr. Li is currently a Researcher of the Department of Mechanical Engineering in Chonnam National University, South Korea. Dr. Li’s research interests include applied heat transfer, fluid mechanics, and optimal design of thermal and fluid systems. Jin-Wan Kim received his B.S. degree in Aerospace Engineering from Chosun University, South Korea in 1990. He then received his M.S. degree in Aerospace and Mechanical Engineering from Korea Aerospace University, South Korea in 2003 and his Ph.D degree in Mechanical Engineering from Chonnam National University, South Korea in 2008. He is currently a Post Doctor of the Department of Mechanical Engineering in Chonnam National University, South Korea. His research interests include control of hydraulic systems, dynamics and control, and mechatronics. Young-Bae Kim received his B.S. degree in Mechanical Design from Seoul National University, South Korea in 1980. He then received his M.S. degree in Mechanical Engineering from the Korean Advanced Institute of Science and Technology (KAIST), South Korea in 1982 and his Ph.D. degree in Mechanical Engineering from Texas A&M University, USA in 1990. Dr. Kim is currently a Professor of the School of Mechanical and Systems Engineering in Chonnam National University, South Korea. Dr. Kim’s research interests include mechatronics, dynamics and control, and fuel cell hybrid electric vehicle (FCHEV) systems.     

Kinematics, kinetics and muscle activities of the lower extremity during the first four steps from gait initiation to the steady-state walking

In this study, biomechanical characteristics during the whole process of gait initiation for twenty normal healthy volunteers were determined by the motion analysis with six near-infrared cameras, four forceplates, and an EMG system. Gait initiation, a transitional movement phenomenon from quiet stance to steady-state walking, involves a series of muscular activities, GRFs, movements of COP and COM, and joint motions. Results showed that the location of the net COP to be most lateral during double limb stance at the beginning of gait initiation. During gait initiation, changes in anteroposterior components of GRFs were first found and then changes in vertical components followed. Hip and knee motions were found before the ankle joint motion. Walking speed, step length, and stride length gradually increased until the second step. The interaction between the COM and COP is tightly regulated to control the trajectory of the COM and thereby control total body balance. This paper was recommended for publication in revised form by Associate Editor Hong Hee Yoo Sun-Woo Park received a B.S. degree in Biomedical Engineering from Yonsei University in 2006. He is currently a M.S. candidate in the Department of Biomedical Engineering, Yonsei University, Korea. His research interests in the area of Human Movement and detection of gait phase using motion sensors. Hue-Seok Choi received a B.S. degree in Computer Engineering from Daejeon University in 2004. He is currently a P.D. candidate at the Department of Biomedical Engineering at Yonsei University, Korea. His research interests are in the area of Human Movement and Rehabilitation Engineering. Ki-Hong Ryu received a B.S. and M.S. degrees in Biomedical Engineering from Yonsei University in 1998 and 2001, respectively. He is currently a P.D. candidate in the Department of Biomedical Engineering, Yonsei University, Korea. His research interests are in the area of Human Movement and Gait Training System using Functional Electrical Stimulation. Sa-Yup Kim received a B.S. degree in Electrical Engineering from Yeungnam University in 2002 and M.S. degrees in Biomedical Engineering from Yonsei University in 2006. He is currently working from Korea Institute of Industrial Technology in Cheonan, Korea. Young-Ho Kim received a B.S. degree in Mechanical Engineering from Hanyang University in 1982. He then went on to receive his M.S. and Ph.D. degrees from University of Iowa in 1989 and 1991, respectively. He is currently a Professor in the Department of Biomedical Engineering, Yonsei University, Korea. His research interests are in the area of Human Movement, Rehabilitation Engineering, and Biomechanics.     

Analysis of unavoidable geometric errors in the side wall of end-milled parts for corner surface

The location and the size of a geometrically defected region in the side wall of a corner, which is generated during the flat end-milling process, are investigated through experiments and geometrical analysis. A corner with inner and outer surfaces is assumed to be made up of one arc-surface patch and two flat-surface patches. Based on the previous findings that the change of material removal per tooth affects the geometry of the end-milled side wall, it is expected that the geometrically defected regions are located around the corner when the tool is approaching and leaving the arc surface. In this respect, analytic models are proposed to predict the location and the size of a geometrically defected region, which are then validated via comparison with the experimental results. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Kun Sang Lee received his B. S. degree in Mechanical Engineering from Seoul National University, Korea, in 1982. He then received his Dipl.-Ing. and Dr.-Ing. degrees from Technical University of Berlin, Germany, in 1991 and 1993, respectively. Dr. Lee is currently a Professor at the School of Mechanical and Automotive Engineering at Kookmin University in Seoul, Korea. He serves as a Staff of the Korea Engineering Education Research Center. His research interests include precision machining, high energy beam material processing, and creative design methodology. Kang Kim received his B. S. and M. S. degrees in Mechanical Design and Production Engineering from Seoul National University, Korea, in 1982 and 1984, respectively. He then received his Ph.D. degree from Purdue University, USA, in 1992. Dr. Kim is currently a Professor at the School of Mechanical and Automotive Engineering at Kookmin University in Seoul, Korea. His research interests include material removal processes, and concurrent engineering.     

A numerical study on oil retention and migration characteristics in the heat pump system

In HVAC system, the oil circulation is inevitable because the compressor requires the oil for lubrication and sealing. A small portion of the oil circulates with the refrigerant flow through the system components while most of the oil stays or goes back to the compressor. Because oil retention in refrigeration systems can affect system performance and compressor reliability, proper oil management is necessary in order to improve the compressor reliability and increase the overall efficiency of the system. This paper describes a numerical analysis of oil distribution in each component of the commercial air conditioning system including the suction line, discharge line and heat exchanger. In this study, system modeling was conducted for a compressor, discharge line, condenser, expansion valve, evaporator and suction line. Oil separation characteristics of the compressor were taken from the information provided by manufacturer. The working fluid in the system was a mixture of a R-410A refrigerant and PVE oil. When the oil mass fraction (OMF) was assumed, oil mass distribution in each component was obtained under various conditions. The total oil hold-up was also investigated, and the suction line contained the largest oil hold-up per unit length of all components. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Min Soo Kim received his B.S., M.S., and Ph.D. degree at Seoul National University, Korea in 1985, 1987, and 1991, respectively. After Ph.D. degree, Prof. Kim worked at National Institute of Standards and Technology (NIST) in U.S.A. for about three years. He is currently a professor at the School of Mechanical and Aerospace Engineering of Seoul National University, Korea. Jong Won Choi received B.S. degree in Mechanical Engineering from Korea University in Seoul, Korea, in 2004, and then received M.S. degrees from Seoul National University in 2006. He is currently a student in Ph.D. course at the School of Mechanical and Aerospace Engineering of Seoul National University in Seoul, Korea. His research interests include refrigeration system, micro-fluidic devices, and PEM fuel cell as an alternative energy for next generation. Mo Se Kim received B.S. degree in Mechanical and Aerospace Engineering from Seoul National University in Seoul, Korea, in 2007. He is currently a student in M.S. course at the School of Mechanical and Aerospace Engineering of Seoul National University in Seoul, Korea. He had studied on the oil migration in the heat pump system, and now he studies on the refrigeration system using an ejector. Baik-Young Chung received his B.S., M.S., and Ph.D. degrees in Mechanical Engineering from Inha University, Korea in 1984, 1986, and 2001, respectively. He is currently a research fellow of HAC Research Center at LG Electronics. He is responsible for the commercial air conditioner group. Sai-Kee Oh received B.S. degree in Mechanical Engineering from Seoul National University, Korea in 1989, and then received M.S. and Ph.D. degrees from KAIST, Korea in 1991 and 1997, respectively. He is currently a principal research engineer of HAC Research Center at LG Electronics. He is responsible for the residential air conditioner group. Jeong-Seob Shin received B.S. degree in Machine Design and Production Engineering from Hanyang University, Korea in 1988, M.S. degree in Mechanical Engineering from KAIST, Korea in 1991, and Ph.D. degree in Mechanical Engineering from POSTECH, Korea in 2004. He has joined HAC Research Center at LG Electronics since 2006 as a principal research engineer.     

Numerical simulation on soot deposition process in laminar ethylene diffusion flames under a microgravity condition

A numerical study on soot deposition in ethylene diffusion flames has been conducted to elucidate the effect of thermophoresis on soot particles under a microgravity environment. Time-dependent reactive-flow Navier-Stokes equations coupled with the modeling of soot formation have been solved. The model was validated by comparing the simulation results with the previous experimental data for a laminar diffusion flame of ethylene (C₂H₄) with enriched oxygen (35% O₂ + 65% N₂) along a solid wall. In particular, the effect of surrounding air velocity as a major calculation parameter has been investigated. Especially, the soot deposition length defined as the transverse travel distance to the wall in the streamwise direction is introduced as a parameter to evaluate the soot deposition tendency on the wall. The calculation result exhibits that there existed an optimal air velocity for the early deposition of soot on the surface, which was in good agreement with the previous experimental results. The reason has been attributed to the balance between the effects of the thermophoretic force and convective motion. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Jae Hyuk Choi received his B.S. and M.S. degrees in Marine System Engineering from Korea Maritime University in 1996 and 2000, respectively. He then went on to receive a Ph.D. degrees from Hokkaido university in 2005. Dr. Choi is currently a BK21 Assistant Professor at the School of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. Dr. Choi’s research interests are in the area of reduction of pollutant emission (Soot and NOx), high temperature combustion, laser diagnostics, alternative fuel and hydrogen production with high temperature electrolysis steam (HTES). Junhong Kim received his B.S., M.S., and Ph. D degrees in Mechanical Engineering from Seoul National University in 1998, 2000, and 2004, respectively. His research interests include lifted flames, edge flames, and numerical simulation. Sang Kyu Choi received his B.S. degree in Mechanical Engineering from Seoul National University in 2004. He is a Ph. D student in the School of Mechanical Engineering, Seoul National University. His research interests include edge flames, oxy-fuel combustion, and numerical simulation. Byoung ho Jeon received his B.S degrees in Mechanical Engineering from kangwon University in 1998, and M.S., Ph. D. degrees in Mechanical Engineering from Hokkaido University in 2002, 2008, respectively. Dr Jeon is working at Korea Aerospace Research Institute from 2007. June. as Gasturbine engine developer. Jeon’s research interests are in the area of reduction of pollutant emission (Soot and Nox), High temperature combustion, combustion system (Furnace, Combine Generation system, IGCC, CTL), and Fire safety in building. Osamu Fujita received his B.S., M.S., and Ph. D. degrees in Mechanical Engineering from Hokkaido University in 1982, 1984, and 1987, respectively. Prof. Fujita is currently a Professor at the division of Mechanical and space Engineering at Hokkaido University in sapporo, Japan. Prof. Fujita’s research interests are in the area of reduction of pollutant emission (Soot and Nox), solid combustion, catalytic combustion, high temperature combustion, alternative fuel and fire safety in space. Suk Ho Chung received his B.S. degree in Mechanical Engineering in 1976 from Seoul National University, and his M.S. and Ph. D. degree in Mechanical Engineering in 1980 and 1983, respectively from Northwestern University. He is a professor since 1984 in the School of Mechanical and Aerospace Engineering, Seoul National University. His research interests cover combustion fundamentals, pollutant formation, and laser diagnostics.     

Design and analysis of a twisting-type thermal actuator for micromirrors

This paper reports the design of a novel twisting-type micromirror actuation system. The actuating mechanism for driving the micromirror combines two paralleled bimorph actuators bending in opposite directions for rotational control of the micromirror. Each actuator is structured by gold and silicon dioxide or nickel and silicon nitride thin films with embedded polysilicon line heaters. With a size of only 15μm in width, 1.3μm in thickness, and 100μm in length, two bimorph actuators can result in a vertical displacement of 25μm at 10 volts dc with the span of 120μm, and thus the micromirror can rotate by angles over 20°, which is a significant improvement, compared to conventional tilting-type micromirrors. This paper was recommended for publication in revised form by Associate Editor Dongsik Kim Dong Hyun Kim received his B.S. and M.S. degrees in Mechanical Engineering from Hongik University, Korea, in 2005 and 2007, respectively. Mr. Kim is currently graduate student in the department of Mechanical Engineering at Hongik University in Seoul, Korea. His research interests include micro and nanoscale heat transfer and silicon crystallization technologies for displays. Kyung Su Oh received his B.S. and M.S. degrees in Mechanical Engineering from Hongik University, Korea, in 2005 and 2007, respectively. Mr. Oh is currently a research scientist at LG Chem. Ltd. His research interests include nanoscale heat transfer, nanotubes and fuel cells and molecular simulation technology. Seungho Park received his B.S. and M.S. degrees in Mechanical Engineering from Seoul National University, Korea, in 1981 and 1983, respectively. He then received his Ph.D. degree from U.C. Berkeley, U.S.A. in 1989. Dr. Park is currently a Professor at the department of Mechanical and System Design Engineering at Hongik University in Seoul, Korea. He served as a director of general affairs of KSME. Dr. Park’s research interests include micro and nanoscale heat transfer, molecular dynamics simulation and silicon crystallization technologies for displays.     

Friction-induced ignition modeling of energetic materials

The heat released during the external frictional motion is a factor responsible for initiating energetic materials under all types of mechanical stimuli including impact, drop, or penetration. We model the friction-induced ignition of cyclotrimethylenetrinitramine (RDX), cyclotetramethylene-tetranitramine (HMX), and ammonium-perchlorate/ hydroxylterminated-polybutadiene (AP/HTPB) propellant using the BAM friction apparatus and one-dimensional time to explosion (ODTX) apparatus whose results are used to validate the friction ignition mechanism and the deflagration kinetics of energetic materials, respectively. A procedure to obtain the time-to-ignition for each energetic sample due to friction is outlined. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Min-cheol Gwak received his B.S. degree in Mechanical Engineering from Korea Aerospace University, Korea, in 2007. Now he is a graduate student of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. His research interests are ignition of high energy material and combustion phenomena. Tae-yong Jung received his B.S. degree in Mechanical and Aerospace Engineering from Seoul National University, Korea, in 2007. Now he is a graduate student of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. His research interests are solid propellant combustion and phase transformation. Professor J. Yoh received his BSME from UC Berkeley in 1992 and MSME from UCLA in 1995. His doctoral degree is in Theoretical & Applied Mechanics from the University of Illinois at Urbana-Champaign, 2001. His research interest is in high energy system design using high power lasers and condensed energetic materials.     

Micromechanically consistent calculation of rotational stiffness of radial tire

The rotational stiffness of a radial tire is one of the most important structural properties of the sidewall, and it has been evaluated conventionally by using a simplified model. However, in this paper, it is found that the conventional shear modulus used for the calculation of the stiffness is not micromechanically consistent. We examine the conventional shear modulus of the sidewall from the viewpoint of micromechanics, and present a new micromechanically consistent shear modulus for evaluating the rotational stiffness attributed to the shear deformation of sidewall. The developed method is discussed and rationalized through an approximate quantitative analysis. The calculation based on the micromechanically consistent shear modulus is validated by comparing it with experimental stiffness and the conventionally-calculated stiffness. This paper was recommended for publication in revised form by Associate Editor Jeong Sam Han Yong-Woo Kim received his Bachelor degree in Mechanical Engineering from Yonsei University, Seoul, Korea, in 1982, and his Ph.D. degree from Yonsei Graduate School in 1991. Dr. Kim is currently Professor at Department of Mechanical Engineering at Sunchon National University in Sunchon, Korea. Dr. Kim’s research interests include structural analysis, machine design, and tire mechanics.     

Evolution of micro solder joints under electromigration and elastic field

This paper proposes a three-dimensional model for the evolution of micro and sub-micro scale flip chip solder joints. The coupled mechanisms of electromigration and the corresponding stress gradient are incorporated into a diffuse interface model. A semi-implicit Fourier spectral method and the preconditioned biconjugate-gradient method are proposed for the computation to achieve high efficiency and numerical stability. Our simulations demonstrate dynamic evolution of solder joints and breakages at the interface on the cathode side. It is also shown that the dynamically incorporated stress gradient considerably affects the evolution of solder joints counteracting the electromigration process. This paper was recommended for publication in revised form by Associate Editor Jeonghoon Yoo Dongchoul Kim received a B.S. degree in Mechanical Engineering from Yonsei University in 2000. He then went on to receive his M.S. and Ph.D. degrees from The University of Michigan in 2003 and 2005, respectively. Dr. Kim is currently an Assistant Professor at the School of Mechanical Engineering at Sogang University in Seoul, Korea. His research interests are in the area of computational analysis of micro/nanostructures.     

Evaporation of inkjet printed pico-liter droplet on heated substrates with different thermal conductivity

In this work, the evaporation phenomena of 20–45 picoliter water droplet (i.e. 50–65 μm diameter) on heated substrates with different thermal conductivity are studied experimentally. The effect of thermal conductivity of substrates and inter-distance between jetted droplets on the evaporation is investigated. In addition, the model to predict evaporation rate of the picoliter droplet on different substrates at a heated condition is developed using approximations for picoliter droplet. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Taewoong Lim received his B.S and M.S. degree in mechanical engineering from Korea University, Seoul, Korea in 2007 and 2009, respectively. His thesis topic was the evaporation of inkjet printed pico-liter droplet and He has been working at Hyundai Motor Company. Jaeik Jeong received his B.S. degree in mechanical engineering from Korea University in 2008. He is currently a M.S. candidate in mechanical engineering at Korea University. Jaewon Chung received his B.S. and M.S. degrees in mechanical engineering from Yonsei University, Seoul, Korea in 1995 and 1997, respectively and Ph.D. degree from University of California, Berkley in 2002. He was postdoctoral associate in Engineering System Research Center at University of California, Berkley in 2002–2004 and had worked in the Center of Micro and Nano Technology at Lawrence Livermore National Laboratory as a visiting collaborator. He is a currently an associate professor at the Department of Mechanical Engineering at Korea University in Seoul, Korea. His research interests include direct writing methods including drop on demand inkjet printing, electrohydrodynamic printing and laser material processing for printing electronics. Jin Taek Chung received his B.S. and M.S. degrees in mechanical engineering from Korea University, Seoul, Korea in 1983 and 1985, respectively and Ph. D. degree from University of Minnesota, U.S.A. in 1992. He is a currently a professor at the Department of Mechanical Engineering at Korea University in Seoul, Korea. His research interests are heat transfer and 3-D flow in gas turbines and thermal management of electronic devices.     

Experimental study on heat transfer characteristics of internal heat exchangers for CO2 system under cooling condition

This paper presents the heat transfer characteristics of the internal heat exchanger (IHX) for CO₂ heat pump system. The influence on the IHX length, the mass flow rate, the shape of IHX, the operating condition, and the oil concentration was investigated under a cooling condition. Four kinds of IHX with a coaxial type and a micro-channel type, a mass flow meter, a pump, and a measurement system. With increasing of the IHX length, the capacity, the effectiveness, and the pressure drop increased. For the mass flow rate, the capacity of micro-channel IHX are higher about 2 times than those of coaxial IHX. The pressure drop was larger at cold-side than at hot-side. In the transcritical CO₂ cycle, system performance is very sensitive to the IHX design. Design parameters are closely related with the capacity and the pressure drop of CO₂ heat pump system. Along the operating condition, the performance of CO₂ IHXs is different remarkably. For oil concentration 1, 3, 5%, the capacity decreases and the pressure drop increased, as compared with oil concentration 0%. This paper was recommended for publication in revised form by Associate Editor Yong Tae Kang Prof. Young-Chul Kwon received his B.S. degree in Precision Mechanical Engineering from Pusan National University, Korea, in 1989. He then received his M.S. and Ph.D. degrees from POSTECH, in 1991 and 1996, respectively. Dr. Kwon is currently a Professor at the Division of Mechanical Engineering at Sunmoon University in Chungnam, Korea. He serves as a chief of the Institute of Automation and Energy Technology. Dr. Kwon’s research interests include heat exchanger, CO₂ cycle, heat pump, and energy recovery ventilator for HVAC&R. Mr. Dae-Hoon Kim is currently Doctoral student at the Mechanical Engineering from Hanyang University in Seoul, Korea. His research topics include experimental and numerical of CO₂ heatpump system. He has conducted a study on the Analysis of Refrigerating & Air-Conditioning Equipment Industry and Its Forecasting Supervising and Testing for Performance of Refrigerator, Freezer and Air-Conditioner. Prof. Jae-Heon Lee received his B.S. degree in Mechanical Engineering from Seoul National University, Korea, in 1971. He then received his M.S. and Ph. D. degree from Seoul National University in 1977 and 1980, respectively. Dr. Lee is currently a Professor at the school of Mechanical Engineering at Hanyang University in Seoul, Korea. Dr. Lee is currently a president at the Korea Institute research interests include simulation of thermal fluid and Plant engineering and construction. Dr. Jun-Young Choi received his B.S. degree in Mechanical Engineering from Yonsei University, Republic of Korea, in 1989. He then received his M.S. and Ph. D. degrees from Yonsei University in 1991 and 1999, respectively. Dr. Choi is currently a chief researcher with the 18 years experience on the energy performance testing of HVAC/R product. He is now assigned to the Energy Technology Center at Basic Industry Division at Korea Testing Laboratory. He has been involved in the development of Design and Manufacturing Technology for Air-Conditioner E.E.R. and Performance Testing Equipment for Cooling and Heating System with Non-CFCs, and natural refrigerants. He has conducted a study on the Analysis of Refrigerating & Air-Conditioning Equipment Industry and Its Forecasting Supervising and Testing for Performance of Refrigerator, Freezer and Air-Conditioner. Dr. Sang Jae Lee received his Ph.D. degree in Mechanical Engineering from Hanyang University, KOREA, in 2008. Dr. Lee is currently a Researcher at the Korea Institute of Industrial Technology in Cheonan, Korea. Dr. Lee’s research interests CO₂ heatpump system, liquid desiccant air conditioning system and Micro heat exchanger.     

Three-dimensional model for electromigration induced evolution of flip chip solder joints

Recent experiments have shown failure in flip chip micro solder joints induced by electromigration. This paper proposes a computational model to simulate the evolution of micro and sub-micro scale solder joints due to electromigration induced diffusion. Complicated morphological changes of the solder bump and multiple mechanisms cause a computational challenge. This is addressed by employing a diffuse interface model with multiple concentrations. To efficiently resolve complications, a semi-implicit Fourier spectral scheme and a biconjugate-gradient method are adopted. Results have demonstrated rich dynamics and solder breakage at the interface on the cathode side. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Dongchoul Kim received a B.S. degree in Mechanical Engineering from Yonsei University in 2000. He then went on to receive his M.S. and Ph.D. degrees from The University of Michigan in 2003 and 2005, respectively. Dr. Kim is currently an Assistant Professor at the School of Mechanical Engineering at Sogang University in Seoul, Korea. Dr. Kim’s research interests are in the area of computational analysis of micro/nanostructures.     

Novel scan path generation method based on area division for SFFS

A solid freeform fabrication (SFF) system using selective laser sintering (SLS) is currently recognized as a leading process of fabrication using variable materials, and SLS extends the application to machinery and automobiles. Due to the time delay in the sintering process, shrinkage and warping often occur. Curling also occurs due to laser and scan delays. These problems affect not only the accuracy of the fabricated product but also the total system efficiency. These deficiencies can be overcome by reducing the total processing time of the SFF system. To accomplish this, the laser scanning time, from mark (laser on) to jump (laser off), must be reduced as it contributes the major part of the total processing time. This can be done by employing area division scan path generation, which promotes digital efficiency. A simulation and an experiment was carried out in this study to evaluate the developed scan path method. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Kyung-Hyun Choi received his B.S. and M.S. degrees in Mechanical Engineering from Pusan National University, Korea, in 1983 and 1990,. He then received his M.S. and Ph.D. degrees from University of Ottawa in 1995. Dr. Choi is currently a professor at the School of Mechanical Engineering at Cheju National University, Korea. His research interests include micro-machining, printed Electronics. Hyung-Chan Kim received his B. S. and M. S. degrees in Electronics Engineering from Cheju National University, Korea, in 2006 and 2008, respectively. Mr. Kim is currently a Ph.D. candidate at the School of Electronics Engineering at Cheju National University, Korea. His research interests include RP System, micro-machining, printed Electronics. Yang-Hoi Doh received his B.S. and M.S. degrees in Electronics Engineering from KyungBuk National University, Korea, in 1982 and 1984, respectively. He then received his Ph.D. degree from University of Kyung Buk National University, Korea, in 1988. Dr. Doh is currently a Professor at the School of Electronics Engineering at Cheju National University, Korea. His research interests include micro-machining, Digital signal processing. Dong-Soo Kim received his M.S. and Ph.D. degrees in Mechanical Engineering from Yung Nam University, Korea, in 1991 and 2001, respectively. Dr. Kim is currently the general manager at Nano Mechanical System Research Division at Korea Institute of Machinery & Materials. His research interests include printed Electronics, R2R printing, RP system.     

Reliability design of preventive maintenance scheduling for cumulative fatigue damage

As the cumulative running times of a locomotive truck increases, degradation such as fatigue, wear, and deterioration occur. Particularly the container train and uncovered freight train, their maintenance cost during their lifetime is three times more than the manufacturing cost. Generally, for the freight train, corrective maintenance to repair a bad part after a breakdown is not adapted; however, preventive maintenance that fixes a bad part before a breakdown is. Therefore, it is important and necessary to establish a system of optimal preventive maintenance and exact maintenance period. This study attempts to propose a preventive maintenance procedure that predicts a repair period using reliability function and instantaneous failure rate based on fatigue test and load history data. Additionally, this method is applied to the end beam of an uncovered freight train, which is the brake part, and its usefulness is examined and analyzed. This paper was recommended for publication in revised form by Associate Editor Chongdu Cho Seok-Heum Baek received a B.S. and M.S. degree in Mechanical Engineering from the Dong-A University in 2001 and 2003, respectively. He is currently a Ph.D. student at the School of Mechanical Engineering at Dong-A University in Busan, Korea. Student Baek works on ceramic composite design and robust and reliability-based design, and his research interests are in the areas of trade-off analysis in multicriteria optimization, design under uncertainty with incomplete information, and probabilistic design optimization. Seok-Swoo Cho received a B.S. degree in Mechanical Engineering from Dong-A University in 1991. He then went on to receive his M.S. from Dong-A University in 1993 and Ph.D. degree from Dong-A University in 1997. Dr. Cho is currently a Professor at the Vehicle Engineering at Kangwon National University in Kangwon-do, Korea. Dr. Cho works on crack growth modeling and composite design and optimization, and his research interests are in the areas of structural optimization and inverse and identification problems, and X-ray diffraction, brittle collapse and crack propagation, fatigue fracture phenomena. Hyun-Su Kim received a B.S. degree in Mechanical Engineering from Seoul National University in 1978. He then went on to receive his M.S. from KAIST in 1980 and Ph.D. degree from University of Iowa in 1989. Dr. Kim is currently a Professor at the Mechanical Engineering at Dong-A University in Busan, Korea. His research interests are in the area of high temperature creep fatigue, bio-engineering, design using the finite element method, optimization, and MEMS. Won-Sik Joo received a B.S. degree in Mechanical Engineering from Dong-A University in 1968. He then went on to receive his M.S. from Dong-A University in 1978 and Ph.D. degree from Kookmin University in 1988. Dr. Joo is currently a Professor at the Mechanical Engineering at Dong-A University in Busan, Korea. His research interests are in the area of creep and fatigue in high temperature alloy, fatigue design, and strength evaluation.     

Micro machining of an STS 304 bar by magnetic abrasive finishing

A magnetic abrasive finishing process is a method of non-traditional precision machining in which the finishing process is completed using magnetic force and magnetic abrasives. In this research, a STS 304 cylindrical workpiece was finished using a magnetic abrasive finishing process at 30,000 rpm, and the roughness, roundness, and changes in the micro-diameter were investigated. The study showed that it is possible to control the micro-diameter and weight of the STS 304 cylindrical workpiece by using a near linear approach. Surface roughness as fine as 0.06 μm (Ry) and roundness as fine as 0.12 μm (LZS) were achievable by using a diamond paste with 1 μm particles. Vibrational motion applied to the workpiece improved the surface roughness. The improvement of the surface roughness was achieved because the vibrational motion effectively removes unevenness in the rotational direction and the direction orthogonal to it. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.recommended for publication in revised form by Associate Editor Dae-Eun Kim Ik-Tae Im received the B.S., M.S. and Ph.D. degrees in Mechanical Engineering from Hanyang University, Seoul, Korea, in 1993, 1995 and 1999, respectively. He has been a visiting scientist at the Department of Materials Engineering, the University of Tokyo, Japan, where he studied on the film growth during the MOCVD process. His research interests include the numerical modeling on the transport phenomena in various materials processing. He is a professor at the Division of Mechanical Design Engineering at Chonbuk National University in Jeonju, Korea. Sang Don Mun received the B.S. degree and M.S. in Precision Mechanical Engineering from Chonbuk National University, Korea, in 1991 and 1993, respectively. He then received the Ph.D. in Precision Mechanical Engineering at the same university in 1997. Dr. Mun is currently a Professor at the Division of Mechanical Design Engineering at Chonbuk National University in Jeonju, Korea. His research interests include magnetic abrasive finishing, tool wear, and micro machining. Seong Mo Oh received his B.S. degree in Mechanical Engineering from Wonkwang University, Korea, in 1992. He then received his M.S. and Ph.D. degrees from Wonkwang in 1994 and 2000 respectively. Dr. Oh is currently a Lecturer at the Division of Mechanical and Automotive Engineering at Wonkwang University in Jeonbuk, Korea. Dr. Oh’s research interests include tribology, functional surfaces, and micromachining.