• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.151-158
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• 2009

To implement the insects' flapping flight for developing flapping MAVs(micro air vehicles), the unsteady flow characteristics of the insects' forward flight is investigated. In this paper, two-dimensional FSI(Fluid-Structure Interaction) simulations are conducted to examine realistic flow features of insects' flapping flight and to examine the flexibility effects of the insect's wing. The unsteady incompressible Navier-Stokes equations with an artificial compressibility method are implemented as the fluid module while the dynamic finite element equations using a direct integration method are employed as the solid module. In order to exchange physical information to each module, the common refinement method is employed as the data transfer method. Also, a simple and efficient dynamic grid deformation technique based on Delaunay graph mapping is used to deform computational grids. Compared to the earlier researches of two-dimensional rigid wing simulations, key physical phenomena and flow patterns such as vortex pairing and vortex staying can still be observed. For example, lift is mainly generated during downstroke motion by high effective angle of attack caused by translation and lagging motion. A large amount of thrust is generated abruptly at the end of upstroke motion. However, the quantitative aspect of flow field is somewhat different. A flexible wing generates more thrust but less lift than a rigid wing. This is because the net force acting on wing surface is split into two directions due to structural flexibility. As a consequence, thrust and propulsive efficiency was enhanced considerably compared to a rigid wing. From these numerical simulations, it is seen that the wing flexibility yields a significant impact on aerodynamic characteristics.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.11
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• pp.1127-1133
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• 2012

A finned-tube-type evaporator module has been proposed for a 2 t/h-class water-tube-type industrial boiler with multiple burners. The geometry of the fins was changed at each module to equalize the evaporation. The modules were designed by considering the energy balance at each row rather than by following a conventional bulk design procedure. The designed module was built into a 2 t/h-class water-tube-type boiler, and its performance was tested. A numerical simulation was also conducted to evaluate the two- or three-dimensional effects of factors such as the inlet conditions. The numerical simulation also included the conjugate heat transfer problem to predict the fin tip temperature. The heat transfer coefficient with fins is lower than that obtained from the empirical correlation of a bare tube. The fin tip temperature from CFD is higher than that from the analytical solution.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.7
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• pp.625-631
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• 2015

In this study, a numerical analysis on the discharging performance of a thermal storage tank completely filled with packing modules is investigated. The enthalpy-porosity method is adopted to analyze phase change phenomenon. Using this method, the melting process of a packing module in the thermal storage tank was studied as the HTF (heat transfer fluid) flows down from the top of the tank at the discharging mode. There are some design factors such as the module arrangement and the number of modules, but this study focuses on the effects of varying the flow rate of the HTF on the outlet temperature of the HTF, molten fraction, and thermal storage density. As the flow rate increases, the outlet temperature of the HTF gets higher and the total melting time of the PCM decreases. Additionally, the thermal storage density is increased so that it reaches about 93% for the desired value.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.1011-1019
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• 2015

Insulated-gate bipolar transistors (IGBTs) are the predominantly used power semiconductors for high-current applications, and are used in trains, airplanes, electrical, and hybrid vehicles. IGBT power modules generate a considerable amount of heat from the dissipation of electric power. This heat generation causes several reliability problems and deteriorates the performances of the IGBT devices. Therefore, thermal management is critical for IGBT modules. In particular, realizing a proper thermal design for which the device temperature does not exceed a specified limit has been a key factor in developing IGBT modules. In this study, we investigate the thermal behavior of the 1200 A, 3.3 kV IGBT module package using finite-element numerical simulation. In order to minimize the temperature of IGBT devices, we analyze the effects of various packaging materials and different thickness values on the thermal characteristics of IGBT modules, and we also perform a design-of-experiment (DOE) optimization

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.20 no.2
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• pp.1-10
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• 2024

The introduction of the sector coupling concept has expanded the scope of ESS utilization, resulting in the importance of thermal management of ESS. To ensure the safe use of the lithium-ion batteries that are used in ESS, it is important to use the batteries at the optimal temperature. To examine the utilization of liquid cooling in ESS, numerical study was conducted on the thermal characteristics of 21700 battery modules (16S2P array) during liquid cooling using Novec-649 as insulating fluid. The NTGK model, an MSMD model in ANSYS fluent, was used to investigate thermal characteristics on the battery modules with liquid immersion cooling. The results show that the final temperature of the battery module discharged at 5 C-rate is 68.9℃ using natural convection and 48.3℃ using liquid cooling. However, the temperature difference among cells in the battery module was up to 0.5℃ when using natural convection cooling and 5.8℃ when using liquid cooling, respectively, indicating that the temperature difference among cells was significantly increased when liquid cooling was used. As the mass flow rate increased from 0.01 kg/s to 0.05 kg/s, the average temperature of the battery module decreased from 48.3℃ to 38.4℃, confirming that increasing the mass flow rate of the insulating fluid improves the performance of liquid immersion cooling. Although partial liquid immersion cooling has a high cooling performance compared to natural convection cooling, the temperature difference between modules was up to 8.9℃, indicating that the thermal stress of the battery cells increased.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.907-910
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• 2010

This study has developed a numerical analysis technique newly which can evaluate the damage propagation characteristics of civil infrastructures. To do this, numerical techniques are incorporated for the concrete members up to the compressive damage due to the bending compressive forces after the tensile crack based on the deformation mechanism. Especially, for the compressive damage stage after the tensile crack, the crack propagation process will be analyzed numerically using the concept of an equivalent plastic hinged length. Using this concept, we investigate the reasonability of the developed module by comparing commercial program for the tunnel structure. It can be established from this study that section forces, such as axial forces and the moment cracks takes place, can be related to the width of the crack making it possible to analyze the crack extension.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2005.11b
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• pp.253-257
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• 2005

This research aims to demonstrate the regional and site scale groundwater flow simulation for the high level radioactive disposal research site in Yu-seong. We used the Modflow by a finite difference method for groundwater flow simulation, and Modpath module in Modflow package for particle tracking simulation. The range of numerical domain for regional groundwater flow model is $16.32km{\times}20.16km$. And, the depth of numerical domain was expanded to 6,000m. The area of numerical domain for the site scale groundwater flow simulation is $1.6km{\times}1.6km$. Since 2005, the underground research tunnel(URT) is being constructed at KAERI(Korea Atomic Energy Research Institute) site. In the site scale groundwater flow model, the groundwater flow around the KAERI site is simulated. And the change of groundwater level with tunnel excavation is also predicted.

• Transactions of Materials Processing
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• v.23 no.1
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• pp.41-48
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• 2014

The light guide plate has become the major component for the backlight module in general information technology products (e.g. mobile phones, monitors, etc.). High speed injection molding has been adopted for thin walled LGP giving advantages such as weight, shape, size, and reduction in production costs. In the current study, the rheological characteristics of high liquidity plastic resin PC(HL8000) were measured using a capillary rheometer to improve the reliability of the numerical analysis for high speed injection molding. With the measured viscosity and PVT of PC(HL8000), numerical analysis of injection molding was conducted using the simulation software(Moldflow). Filling time and deflection were predicted and compared with those of traditional PC resins(H3000, H4000). The results show that PC(HL8000) has significantly different rheological characteristics during high speed injection molding. Hence proper properties of the resin should be used to improve the accuracy of numerical predictions.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1732-1737
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• 2004

This paper proposes Internet-based checking technique for machine-tools with variant CNC (Computerized Numerical Controller). According to the architecture of CNC, CNC is classified into two types such as CAC (Closed Architecture Controller) which is conventional CNC, and OAC (Open Architecture Controller) which is a recently introduced PC-based controller. CAC has a closed architecture and it is dependent on CNC vender specification. Because of this, it has been very difficult for users to implement an application programs in CNC domain. Therefore, an additionally special module is required for Internet-based application such as remote checking. In this case, web I/O embedded module can be efficiently applied for Internet-based checking. The module is directly attached to TCP/IP network for communication. In order to obtain the monitoring data of CNC machines, the I/O signals of the module are assigned to PLC (Programmable Logic Controller) input and output (I/O) signals within CNC domain. On the other hand, OAC has a PC-based open architecture and an additional module is not necessary for the connection with external site. Because of this, a simple DAU is just used for signal sensing and data acquisition without additional communication modules. For Internet-based remote checking of machine-tools with OAC, a user-defined daemon and application programs are implemented as the form of internal function within the PC-based controller. Internet communication is performed between the daemon program in CNC domain and web script programs in external server. Checking points defined in this research are classified into two categories such as structured point and operational point. The formal includes the vibration of bearing, temperature of spindle unit and another periodical management. And the latter includes oil checking, clamp locking/unlocking and machining on/off status.

• Journal of Korea Water Resources Association
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• v.45 no.1
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• pp.53-64
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• 2012

In this study (II), the module developed in the previous study (I) has been tested on application and numerical stability. The runoff module was compared the result of analysis with two different models (FFC2Q and $Vflo^{TM}$) considering characteristic of infiltration. To examine the application and stability of developed module, runoff aspect was simulated under the variety case of rainfall intensity, effective soil depth, elapsed time. The development module was presented typical type of infiltration process looking physically, the different of saturation point on soil type, and characteristic of soil type. Also, the module was reflected in the runoff feature about rainfall intensity and time distribution. Finally, this paper drew a conclusion that result of rainfall-runoff analysis as compared with difference models (FFC2Q and $Vflo^{TM}$) has a high accuracy.