• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.857-862
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• 2007

In this paper, we studied about the antenna designed by heart-shape beam pattern for 4G mobile communication applications. The proposed whole size of structure was identical if it compare with the basis structure. But size of the patch was improved a little(upaward 1.3). The impedance bandwidth was improved about 258% which compares with the basis structure. And the structure could get very good characteristic applicatory to IMT-Advanced. Impedance bandwidth of antenna was about 22%(870MHz). The gain of above 8.7dBi was achieved extended IMT-Advanced all frequency band.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.2 s.107
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• pp.190-197
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• 2006

It is well known that the acoustic characteristics of the sea are significantly affected by bubbles which have their own inherent characteristics at the undersea. In this study, the shape and acoustic characteristics of air bubbles generated by an underwater nozzle are calculated numerically, and are measured with a high speed camera and a hydrophone at various air flow rates in the experimental apparatus. As a result of analysis, the shape calculated numerically well matched with measured values at low flow rates, but in case of relatively higher flow rates. the use of correction coefficient is needed for more accurate estimation of the bubble shape. And also the rising velocity of a single bubble is constant regardless of both the bubble size and the flow rate. and the acoustic signal generated when the bubble is produced by an underwater nozzle has the same characteristic of natural frequency of the bubble pulsation, and is agreed with Minnaert's equation if the correction coefficient is considered in accordance with the flow rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.3 s.258
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• pp.225-233
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• 2007

The growth of GaN on the patterned substances has proven favorable to achieve thick, crack-free GaN layers. In this paper, numerical modeling of transport and reaction of species is performed to estimate the growth rate of GaN from tile reaction of TMG(trimethly-gallium) and ammonia. GaN growth rate was estimated through the model analysis including the effect of species velocity, thermal convection and chemical reaction, and thermal condition for the uniform deposition was to be presented. The effect of shape and construction of microscopic pattern was also investigated using a simulator to perform surface analysis, and a review was done on the quantitative thickness and shape in making GaN layer on the pattern. Quantitative analysis was especially performed about the shape of reactor geometry, periodicity of pattern and flow conditions which decisively affect the quality of crystal growth. It was found that the conformal deposition could be obtained with the inclination of trench ${\Theta}>125^{\circ}$. The aspect ratio was sensitive to the void formation inside trench and the void located deep in trench with increased aspect ratio.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.12 s.105
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• pp.1347-1354
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• 2005

The free vibration characteristics of Al cantilever square plates with a brass inclusion were analyzed experimentally and numerically The experimentally obtained natural frequencies and mode shapes were compared with the FEM analysis results. The impulse exciting method was used for experiment and ANSYS software package was used for FEM analysis. The natural frequencies obtained iron experiment and numerical analysis matched within $0\%$. It was found that the natural frequencies of the Al cantilever square plates with a brass inclusion decrease as the size of inclusion increases. For the third mode shape, comparing the nodal line of the Al plate and the Al plate with a inclusion, the mode shape showed the reversed quadratic curve. The natural frequencies of inclusion plate were decreased as the location of inclusion moves from the clamped edge to the tree edge.

• Smart Structures and Systems
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• v.16 no.3
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• pp.555-577
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• 2015

In the work at hand, the development of a morphing flap, actuated through shape memory alloy load bearing elements, is described. Moving from aerodynamic specifications, prescribing the morphed shape enhancing the aerodynamic efficiency of the flap, a suitable actuation architecture was identified, able to affect the curvature. Each rib of the flap was split into three elastic elements, namely "cells", connected each others in serial way and providing the bending stiffness to the structure. The edges of each cell are linked to SMA elements, whose contraction induces rotation onto the cell itself with an increase of the local curvature of the flap airfoil. The cells are made of two metallic plates crossing each others to form a characteristic "X" configuration; a good flexibility and an acceptable stress concentration level was obtained non connecting the plates onto the crossing zone. After identifying the main design parameters of the structure (i.e. plates relative angle, thickness and depth, SMA length, cross section and connections to the cell) an optimization was performed, with the scope of enhancing the achievable rotation of the cell, its ability in absorbing the external aerodynamic loads and, at the same time, containing the stress level and the weight. The conceptual scheme of the architecture was then reinterpreted in view of a practical realization of the prototype. Implementation issues (SMA - cells connection and cells relative rotation to compensate the impressed inflection assuring the SMA pre-load) were considered. Through a detailed FE model the prototype morphing performance were investigated in presence of the most severe load conditions.

• Journal of Power System Engineering
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• v.16 no.5
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• pp.26-31
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• 2012

A numerical study has been carried out to investigate the heat and mass transfer of an oil pumping system with a variable shape of the housing using the CFD method. Especially, the electric motor and the pump combined together, accomplishes a research about the oil supplying system. In this study, the temperature and velocity distribution of the oil pumping system by varying the flow rate of supplying oil have been investigated. The temperature changes with each five conditions(flow rate of supply oil : 2, 4, 8, 12, and 16 liter/min) have also been studied. The numerical results show that the exhaust temperature decreases as the flow rate of the supplying oil increases. It also reveals that the temperatures change differently with the housing shape.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1079-1083
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• 2009

In this study, the pullout resistance characteristic of a wedge-shaped soil nail, made by attaching small steel sticks to the tip of a nail in a wedge shape, was investigated. It was developed to improve the overall pullout resistance capacity of the existing soil nail system, composed of nail and grout, by making the wedge provide additional pullout resistance. In order to evaluate the pullout resistance of the wedge shape-soil nail, field pullout tests were conducted, and the results were compared with those for the existing soil nail without the wedge. The field test results showed that the pullout resistance capacity of the wedge-shaped soil nail was 50% larger than that of the existing soil nail without the wedge.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.849-851
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• 2000

The value of $I_c$(critical current) in HTS (High Temperature Superconductor) tape has a great influence on $B{\bot}$ (vertical field). Therefore, in shape design of field coil for the HTSG(High Temperature Superconducting Generator), a method to reduce the $B{\bot}$ should be considered in order to maintain the stability and substantial improvement on the performance. On the basis of the magnetic field analysis, this paper deals with various field coil shape to obtain small $B{\bot}$ by using Biot-Savart's law and image method. Moreover the analysis is verified by comparison with experimental results. And also this paper presents the advanced model by using 3D FEM(3 Dimensional Finite Element Method), in which flux density at armature is calculated in 5kVA class HTSG.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.9
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• pp.916-921
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• 2009

The technology to inspect and measure an inner structure of micro parts has become an important tool in the semi-conductor industrial field with the development of automation and precision manufacturing. Especially, the inspection skill on the inside of highly integrated electronic device becomes a key role in detecting defects of a completely assembled product. X-ray inspection technology has been focused as a main method to inspect the inside structure. However, there has been insufficient research done on the customized inspection technology for the flip-chip assembly due to the interior connecting part of flip chip which connects the die and PCB electrically through balls positioned on the die. In this study, therefore, it is implemented to detect shape error of flip chip bonding without damaging chips using an x-ray inspection system. At this time, it is able to monitor the solder bump shape by introducing an edge-extracting algorithm (exponential approximation function) according to the attenuating characteristic and detect shape error compared with CAD data. Additionally, the bonding error of solder bumps is automatically detectable by acquiring numerical size information at the extracted solder bump edges.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.100-106
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• 2006

NiTi alloy known as its shape memory effect also has superelastic characteristic, which makes it possible to be elastic under large deformation. Since the tensile strength of the alloy is very high and density is low compared to carbon steel, it can be applied to lightweight structural design. In order to design structures with shape memory alloy, finite element analysis is used and a constitutive algorithm based on Aurrichio's model is added to LS-DYNA as a user subroutine. Explicit time integration and shell element formulation are used to simulate thin-walled structures. The algorithm uses Drucker-Prager type loading condition to calculate martensite volume fraction during the transformation. The implemented algorithm is verified in uni-axial loading condition and martensite phase transformation can be detected well with the algorithm. In this study, as a energy absorbing structure, thin-walled tube is modeled with finite elements and the deformation behavior is studied. Simulation results has shown that the martensite transformation was generated in loading condition. After plastic deformation reached, the load decreases linearly without reverse martensite transformation.