• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.3
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• pp.139-146
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• 1996

An extended $k-\varepsilon$ tuebulence model modified by considering the streamline curvature effect and standard $k-\varepsilon$ turbulence model have been applied for three dimensional analysis of turbulece flow in a $90^{\circ}$ curved duct. By comparision of the results with the experimental data, the modified extended $k-\varepsilon$ model gave closer agreement with experimental data than the results from standard $k-\varepsilon$ model owing to an extra time scale of the production rate and parameter describing effects of streamline curvature included in the dissipation rate equation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.268-270
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• 2002

For analysis of semiconductor's electrons transmission characteristics, Impact ionization(I.I.) is very important. I.I. are generation process of electron-hole pairs. Therefore, the characteristics of device can change along with applied voltage or temperature. In this paper, we are scaled down the gate length to 50nm. Also, using TCAD simulator, we are analyzed I.I. and breakdown about three models-Van Overstraeten , Okuto and Ours models.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.542-545
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• 2010

재료의 마이크로 스케일 해석에서 결정의 geometrically necessary dislocation (GND) 효과에 의한 소성구배(plastic gradient)를 고려하는 것은 재료의 소성 거동을 분석하는데 영향을 미친다. 본 연구에서는 먼거리(long range)에서 전위(dislocation)의 영향을 고려하는 GND의 효과를 적용하여 소성 구배의 영향을 받는 다결정(polycrystal) 고체의 거동을 유한요소해석을 이용하여 살펴보았다. 재료의 거동을 분석하기 위해 탄성(elastic)과 소성(plastic) 변형에 먼 거리 변형률(long range strain)을 고려한 항(term)이 포함된 변형 구배(deformation gradient)의 multiplicative decomposition 모델을 사용하였다. 먼 거리 변형률에 의한 영향을 고려하기 위해 구배 경화 계수(gradient hardness coefficient)와 먼 거리 변형률 길이에 대한 재료변수(parameter)가 사용되었다. 각각의 계수들이 다결정 고체의 거동에 미치는 영향을 확인하기 위해 두 변수의 적용에 따른 다결정 고체의 거동을 분석하였다. 다결정 재료의 GND 효과에 의한 소성 구배 효과를 고려해서, 고려하지 않은 경우와 비교하여 발생하는 경화(hardening)의 차이를 분석함으로서 GND에 의한 다결정 고체 거동의 영향을 확인하였다.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.17 no.6
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• pp.25-37
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• 2022

The purpose of this study is to survey startup founders within 7 years of founding the importance and satisfaction of the components of the scale-up entrepreneurial ecosystem at the national level in Korea and analyze the direction of scale-up policy by component using IPA (importance-performance analysis). Since the perception of founders, who are the subjects of the entrepreneurial ecosystem, affects the quantity and quality of start-ups, research is needed to analyze and diagnose the perception of scale-up components. For the development of the national economy and entrepreneurial ecosystem, companies that emerge from startups to scale-up and unicorns must be produced, and for this, elements for the scale-up entrepreneurial ecosystem are needed. The results of this study are as follows. First, the importance ranking of the components of the scale-up entrepreneurial ecosystem recognized by founders was in the order of "Financial support by growth stage," "Support for customized scale-up for enterprises," "Improvement of regulations," "Funds dedicated to scale-up," "large-scale investment," and "nurturing technical talents." Second, the factors that should be intensively improved in the importance-satisfaction matrix in the future were 'Pan-Government Integration Promotion Plan', 'Scale-Up Specialized Organization Operation', 'Company Customized Scale-Up Support', 'Regulatory Improvement', and 'Building a Korean Scale-Up Model'. As a result, various and large financial capital for the scale-up entrepreneurial ecosystem, diversification of scale-up programs by business sector, linkage of start-ups and scale-up support, deregulation of new technologies and new industries, strengthening corporate-tailored scale-up growth capabilities, and providing overseas networking opportunities can be derived. In addition, it is expected to contribute to policy practice and academic work with research that derives the components of the domestic scale-up entrepreneurial ecosystem and diagnoses its perception.

• Composites Research
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• v.31 no.5
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• pp.251-259
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• 2018

In this paper, statistical volume element modeling method was developed for multi-scale progressive failure analysis of fiber reinforced composite materials. Big-size statistical volume elements (BSVEs) was considered to minimize the size effect in the micro-scale, by including as many fibers as possible. For that purpose, a mesh cutting method is suggested and adapted into the fiber model generator that creates finite element domain rapidly. The fiber defect model was also developed based on the experimental distribution of the fiber strength. The size effects from the local load sharing (LLS) are evaluated by increasing the fiber inclusion in the micro-scale model. Finally, continuum damage mechanics (CDM) model to the fiber direction was extracted from numerical analysis on BSVEs. And it was compared with strength prediction from typical representative volume element (RVE) model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1691-1701
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• 1995

Two aspects of Large-Eddy Simulation(LES) are investigated in order to improve its performance. The first one is on how to determine the model coefficient in conjunction with a dynamic subgrid-scale model, and the second one is on a wall-layer model(WLM) which allows one to skip near-wall regions to save a large number of grid points otherwise required. Especially, a WLM suitable for a separated flow is considered. Firstly, an averaging technique to calculate the model coefficient of dynamic subgrid-scale modeling(DSGSM) is introduced. The technique is based on the concept of local averaging, and useful to stabilize numerical solution in conjunction with LES of complex turbulent flows using DSGSM. It is relatively simple to implement, and takes very low overhead in CPU time. It is also able to detect the region of negative model coefficient where the "backscattering" of turbulence energy occurs. Secondly, a wall-layer model based on a local turbulence intensity is considered. It locally determines wall-shear stresses depending on the local flow situations including separation, and yields better predictions in separated regions than the conventional WLM. The two techniques are tested for a turbulent obstacle flow, and show the direction of further improvements.rovements.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.303-306
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• 2011

본 논문은 콘크리트의 양생 강도 발현을 모니터링하기 위하여 매립형 압전 센서를 이용하여 콘크리트 내부의 임피던스 및 유도초음파 신호를 측정함으로써, 콘크리트의 양생 강도를 실시간 추정할 수 있는 기법을 개발하였다. 임피던스 및 유도초음파 신호는 구조물의 물성을 나타내며 특히 양생 기간 중 임피던스 및 유도초음파의 변화는 해당 콘크리트 구조물의 강도변화를 나타낼 수 있다. 이를 이용하여 매립형 압전 센서로부터 저비용의 셀프 센싱 기반 임피던스 및 유도초음파를 계측하여 콘크리트의 임피던스 공진 주파수 및 유도초음파의 전달 강도를 측정하고 측정된 신호를 통하여 콘크리트 양생 강도를 추정할 수 있게 된다. 제안된 기법의 적용가능성을 검증하기 위하여 설계 압축강도 30MPa의 콘크리트 슬라브 내부에 매립형 압전 센서를 매립하고 양생기간 동안 임피던스 및 유도초음파 신호를 측정, 비교 분석 하였다. 측정된 신호 및 압축강도를 통하여 임피던스 및 유도초음파 기반 강도 추정 모델을 도출하고 보다 높은 정확도를 얻기 위해 다중스케일 강도 추정 모델을 개발하였다. 결과적으로 본 연구를 통해 매립형 압전 센서를 이용하여 콘크리트의 양생 강도를 실시간 모니터링할 수 있음이 검증되었다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• fall
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• pp.139-143
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• 2021

본 논문에서는 꾸준히 연구되어 오던 이미지 복원 문제에서 초해상화와 인페인팅이라는 복합적 이미지 복원을 동시에 처리하는 해결 방법을 제안한다. 초해상화는 국지적 픽셀 정보를 이용하여 고해상도의 영상을 복원하고, 인페인팅은 이미지 전체 정보를 활용하여 영상 내 비어 있는 영역을 생성해야 하므로, 이러한 두 가지 영상 복원 기법을 동시에 수행하는 것은 상당히 어려운 문제이다. 그렇기에 인페인팅과 초해상화는 이미지 복원에서 널리 활용되는 기술인 만큼 동시에 해결할 수 있는 기법에 대한 수요는 있음에도 지금까지 거의 연구되지 않았다. 본 논문은 초해상화 및 인페인팅 합동 처리에 있어 복합적인 정보를 모두 다뤄야하는 네트워크가 서로의 성능을 저하시키지 않도록 개략적 복원 네트워크 (Coarse network), 디테일 복원 네트워크 (Refinement network), 초해상화 네트워크 (SR network)로 분리하여 초해상화 및 인페인팅 합동 처리를 수행하며, 각 단계마다 결과 영상을 얻어 스케일 별 정답 영상과 손실함수를 계산하여 복합적인 성능을 올릴 수 있는 방법을 제시한다. 또한 순차적 단일 모델에 비하여 인페인팅과 초해상화를 합동 학습하는 제안 모델이 개선된 화질의 결과 영상을 획득할 수 있다는 것을 실험적으로 보인다.

• KIISE Transactions on Computing Practices
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• v.20 no.10
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• pp.534-542
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• 2014

Multiscale modeling is a new simulation approach which can manage different spatial and temporal scales of system. In this study, as part of multiscale modeling research, we propose the way of combining two different simulation methods, molecular dynamics(MD) and stochastic rotation dynamics(SRD). Our conceptual implementations are based on LAMMPS, one of the well-known molecular dynamics programs. Our prototype of multiscale modeling follows the form of the third party implementation of LAMMPS. It added MD to SRD in order to simulate the boundary area of the simulation box. Because it is important to guarantee the seamless simulation, we also designed the overlap zones and communication zones. The preliminary experimental results showed that our proposed scheme is properly worked out and the execution time is also reduced.

• Composites Research
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• v.34 no.1
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• pp.70-75
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• 2021

This paper presents a novel algorithm to reconstruct meso-scale representative volume elements (RVE), referring to experimentally observed features of Sheet Molding Compound (SMC) composites. Predicting anisotropic mechanical properties of SMC composites is challenging in the multiscale virtual test using finite element (FE) models. To this end, an SMC RVE modeler consisting of a series of image processing techniques, the novel reconstruction algorithm, and a FE mesh generator for the SMC composites are developed. First, micro-CT image processing is conducted to estimate probabilistic distributions of two critical features, such as fiber chip orientation and distribution that are highly related to mechanical performance. Second, a reconstruction algorithm for 3D fiber chip packing is developed in consideration of the overlapping effect between fiber chips. Third, the macro-scale behavior of the SMC is predicted by the multiscale analysis.