• 한국추진공학회지
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• 제21권1호
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• pp.72-83
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• 2017

본 연구에서는 유도탄 사출관 내부의 수치모사를 통해 이상 유동에 대한 열 유체역학적 분석을 수행하였다. 고정된 해석영역에서 계산이 진행되었고 증발이 완료된 물을 냉각제로 사용하였다. 고온의 공기와 냉각제간의 상호작용 및 유동장을 해석하기 위해, Realizable $k-{\varepsilon}$ 난류 모델과 VOF (Volume Of Fluid) 모델을 선정하고 냉각제 유량에 따른 수치 해석을 진행하였다. 해석결과, 사출관 상부 압력은 냉각제 유량에 따라 비선형적으로 증가하였다. 그리고 내부에서의 유동 진행 과정과 온도분포, 냉각제분포가 밀접한 연관이 있음을 확인하였다. 사출관 하부의 초기 온도는 냉각제량의 증가에 비례하여 감소하지만, 특정시간 이후 경향이 역전되면서 오히려 온도의 상승을 유발하였다. 또한, 혼합가스의 순환유동에 의해 초기의 온도변화가 요동하는 경향도 확인되었다.

• 마이크로전자및패키징학회지
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• 제20권2호
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• pp.65-74
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• 2013

Through-Silicon Via (TSV) 기술은 3차원 적층 패키징를 위한 핵심 기술로서 큰 관심을 받고 있다. 그러나 TSV 기술은 아직 다양한 공정상의 문제와 신뢰성 문제를 해결해야 하는 난제가 남아 있다. 특히 구리 비아(via)와 실리콘 기판의 큰 열팽창계수의 차이로 인한 열응력은 계면 박리, 크랙 발생, 구리 protrusion 등 다양한 신뢰성 문제를 발생시킨다. 본 연구에서는 구리 TSV 구조의 열응력을 수치해석을 이용하여 분석하였으며, 3차원 TSV 비아와 실리콘 기판의 응력 및 변형을 해석하였다. 비아의 크기, 비아와 비아 사이의 간격 및 비아의 밀도가 TSV 구조의 응력에 미치는 영향을 분석하였으며, 또한 어닐링(annealing) 온도 및 비아의 크기가 구리 protrusion에 미치는 영향을 관찰하였다. 구리 TSV 구조의 신뢰성을 향상시키기 위해서는 적절한 비아와 비아 사이의 간격을 유지한 상태에서, 비아의 크기 및 비아의 밀도는 작아야 한다. 또한 구리 protrusion을 감소시키기 위해서는 비아의 크기 및 어닐링 공정과 같은 공정의 온도를 낮추어야 한다. 본 연구의 결과는 TSV 구조의 열응력과 관련된 신뢰성 이슈를 이해하고, TSV 구조의 설계 가이드라인을 제공하는데 도움을 줄 수 있을 것으로 판단된다.

• 대한기계학회논문집B
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• 제32권2호
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• pp.141-148
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• 2008

A numerical simulation of brushless DC motor is performed to elucidate thermo-flow characteristics in winding and bearing with heat generation. Rotation of rotor and blades drives influx of ambient air into the rotor inlet. Recirculation zone exists in the tiny interfaces between windings. The flow separation causes poor cooling performance in bearing part and therefore the redesign of the bearing groove is required. The design parameters such as the inlet location, geometry and bearing groove threshold angle have been selected in the present simulation. As the inlet location moves inward in the radial direction, total incoming flow rate and heat transfer rate are increased. Total incoming flow rate is increased with increasing the inlet inner length. The effect of the bearing groove threshold angle on the thermal performance is less than that of other design parameters.

• 대한기계학회논문집
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• 제17권12호
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• pp.2970-2981
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• 1993

In hot closed-die forging the load increases rapidly near the final stage. Preforming operation is important to both the sound final forging and die-service life. In this study, the material flows during preforming and final forging are investigated. The physical modeling with Plasticine as a model material showed clear flow patterns. The forging process were numerically simulated by the finite element method with the isothermal and the non-isothermal models. The flow patten of the isothermal simulation showed good agreements with the experiments. Temperature changes and pressure distributions on the die surfaces during one cycle of the forging process were obtained from the non-isothermal simulation. High pressure and temperature were developed at certain areas of the die surfaces. It was concluded that those areas usually coincide with each other and should be distributed by the preforming operations to enhance the die life.

• 한국자동차공학회논문집
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• 제19권1호
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• pp.45-50
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• 2011

Hot-Press-Forming (HPF), an advanced sheet metal forming method using stamping at a high temperature of about $900^{\circ}C$ and quenching in an internally cooled die set, is one of the most successful forming process in producing crash-resistant parts such as pillars and bumpers with complex shape, ultrahigh strength, and minimum springback. To optimize conditions of a forming quality in HPF process and secure a safe product without any failures, such as fractures and wrinkling, the simulations based on the coupled thermo-mechanical analysis for a hot-press-formed lower control arm are applied with Taguchi's orthogonal array experiment. Three factor variables - the friction coefficient, blank shape, and hole location for burring - are selected to be optimized. The most effective condition of a forming quality for a hot-press-formed lower control arm is suggested. The simulation results are confirmed with experimental ones.

• 한국레이저가공학회지
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• 제4권1호
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• pp.21-28
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• 2001

Simulation on the electron beam welding of Al 2219 alloy was carried out by using commercial FEM code MARC, which encounters moving heat sources. Due to axisymmetry of geometry, a half of the cylinder was simulated. A coupled thermo-mechanical analysis was carried out and subroutine for heat flux was substituted in the program. The material properties such as specific heat, heat transfer coefficient and thermal expansion coefficient were given as a function of temperature and the latent heat associated with a given temperature range is considered. As a result, the proper beam power is 60㎸${\times}$60㎃ and welding speed is 1∼1.5 m/min. The residual stress in the heat-affected zone as well as the fusion zone does not increase. It is necessary to use jigs for preventing distortion of cylinder and improving weld quality.

• 대한의용생체공학회:의공학회지
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• 제31권6호
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• pp.472-480
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• 2010

Mechanically deformed cartilage undergoes a temperature dependent phase transformation resulting in reshaping of cartilage. Laser-assisted cartilage reshaping (LCR) is recently introduced to recreate the underlying cartilage framework in structures such as ear, larynx, trachea, and nose. However, this procedure has not been fully supported by confirmed efficacy because of the lack of scientific research and its safety issues. The purpose of this study is to evaluate current laser sources to determine optimal laser wavelength for LCR using mathematical simulations and investigate optical, thermo-mechanical, and backscattering properties of cartilage after laser irradiation. The results showed that 1444 nm wavelength was effective for reshaping of cartilage with minimal thermal damage in the surrounded tissues by monte carlo simulations. Analysis of bend angle changes, thermo-mechanical characteristics, and backscattered properties may be useful to better identify the biophysical transformation responsible for stress relaxation in cartilage and develop an optical feedback control methodologies.

• 마이크로전자및패키징학회지
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• 제20권2호
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• pp.33-38
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• 2013

In this study, both a finite element analysis and an experimental analysis are executed to investigate the mechanical characteristics of dielectric material effects on warpage. Also, viscoelastic material properties are measured by DMA and are considered in warpage simulation. A finite element analysis is done by using both thermal elastic analysis and a thermo-viscoelastic analysis to predict the nonlinear effects. For experimental study, specimens warpage of non-symmetric structure with body size of $22.5{\times}22.5$ mm, $37.5{\times}37.5$ mm and $42.5{\times}42.5$ mm are measured under the reflow temperature condition. From the analysis results, experimental warpage is not similar to FEA results using thermal elastic analysis but similar to FEA results using thermo-viscoelastic analysis. Also, its effect on substrate warpage is increased as core thickness is decreased and body size is getting larger. These FEA and the experimental results show that the nonlinear characteristics of dielectric material play an important role on substrate warpage. Therefore, it is strongly recommended that non-linear behavior characteristics of a dielectric material should be considered to control warpage of FCBGA substrate under conditions of geometry, structure and manufacturing process and so on.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.471-472
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• 2010

In this study, a new modeling framework for predicting temperature and structural behaviors of structures under fire condition is proposed. The proposed modeling framework including fire simulation, heat transfer and structural analysis is applied to simulate fire tests performed on the steel-concrete composite structures in Cardington, UK, for model validations. Good predictions are shown for spatial-temporal temperatures and deflections of fire-damaged steel-concrete structures.

• Journal of Mechanical Science and Technology
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• 제16권1호
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• pp.116-124
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• 2002

In order to investigate the soot formation and oxidation processes, we employed the two variable approach and its source terms representing soot nucleation, coagulation, surface growth and oxidation. For the simulation of the taxi-symmetric turbulent reacting flows, the pressure-velocity coupling is handled by the pressure based finite volume method. We also employed laminar flamelet model to calculate the thermo-chemical properties and the proper soot source terms from the information of detailed chemical kinetic model. The numerical and physical models used in this study successfully predict the essential features of the combustion processes and soot formation characteristics in the reacting flow field.