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최창호,노준구,김진한,Choi, Chang-Ho,Noh, Jun-Gu,Kim, Jin-Han 한국유체기계학회 2004 한국유체기계학회 논문집 Vol.20 No.2
This paper is concerned with the numerical analyses of an S-shaped duct for the inter-channel between compressor spools. For the compactness and lightweight of an engine, the length of the S-shaped duct is desired to be minimized. Shortening the S-shaped duct, however, flow separation is likely to occur. Numerical investigation using a three-dimensional Navier-Stokes flow solver was performed to determine the availability of the minimization of an S-shaped duct. Computations were performed introducing the experimental data as the inlet flow condition of the OGV in determining the minimum length of the S-shaped duct. Also, the leaning effect of the OGV which assists the flow to turn radially inward was studied adopting mixing-plane method to consider the rotor/OGV interaction.
레이다용 낮은 위상잡음을 갖는 초고속 주파수 합성기에 관한 연구
최창호,이승주,Choi, Chang-Ho,Lee, Seung-Joo 한국정보기술전략혁신학회 2009 情報學硏究 Vol.12 No.4
In this paper, frequency synthesizer for radar system is designed and developed. Optimizing the phase noise and lock time, each module is designed as two-type PLL circuit, and then the performance of PLL frequency synthesizer is compared. The experiment result shows the lock time of 70 usec, the phase noise of less then 100 dBc, the bandwidth above 500MHz.
저레이놀즈수 난류모델을 사용한 정익-동익 상호작용 해석
최창호,유정열,Choi, Chang Ho,Yoo, Jung Yul 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.10
A computational study on unsteady compressible flows has been performed by adopting a low Reynolds number $k-{\omega}$ turbulence model in conjunction with dual time stepping scheme. An explicit four-stage Runge-Kutta scheme for the Navier-Stokes equations and an approximate factorization scheme for the $k-{\omega}$ turbulence model equations are used. Computational results obtained for blade surface pressure distributions in the process of rotor-stator interaction in a turbine stage are in good agreement with extant experimental data. The effects of the wake from the stator on the boundary-layer transition over the rotor blade surface are discussed by showing that high intensity turbulence of the stator wake induces an early transition.
Implementation of Semi-infinite Boundary Condition for Dynamic Finite Element Analysis
최창호,정하익,Choi, Chang-Ho,Chung, Ha-Ik Korean Geotechnical Society 2006 한국지반공학회논문집 Vol.22 No.9
Dynamic numerical analysis of geotechnical problems requires a way to simulate the decrease of energy as the domain of interest gets larger. This phenomenon is usually referred to as radiation damping or geometric attenuation and it is distinguished from material damping in which elastic energy is actually dissipated by viscous, hysteretic, or other mechanism. The fact that the domain of analysis in numerical modeling must be chosen, however, causes a need for special attention at the boundary. This observation leads directly to the idea of determining the dynamic response of the interior region from a finite model consisting of the interior region subjected to a boundary condition which ensures that all energy arriving at the boundary is absorbed. This paper presents a simple methodology to simulate transmitting boundaries condition using viscoelastic infinite elements within the recently developed "OpenSees" finite element code. The methodology used here provides that the level of absorption for traveling waves is efficient enough for practical purposes, but unsatisfactory for the case of sharp incident angles. The effectiveness of the infinite elements for the absorption of incident waves at boundaries is evaluated via example analysis.
Implicit Numerical Integration of Two-surface Plasticity Model for Coarse-grained Soils
최창호,Choi, Chang-Ho Korean Geotechnical Society 2006 한국지반공학회논문집 Vol.22 No.9
The successful performance of any numerical geotechnical simulation depends on the accuracy and efficiency of the numerical implementation of constitutive model used to simulate the stress-strain (constitutive) response of the soil. The corner stone of the numerical implementation of constitutive models is the numerical integration of the incremental form of soil-plasticity constitutive equations over a discrete sequence of time steps. In this paper a well known two-surface soil plasticity model is implemented using a generalized implicit return mapping algorithm to arbitrary convex yield surfaces referred to as the Closest-Point-Projection method (CPPM). The two-surface model describes the nonlinear behavior of coarse-grained materials by incorporating a bounding surface concept together with isotropic and kinematic hardening as well as fabric formulation to account for the effect of fabric formation on the unloading response. In the course of investigating the performance of the CPPM integration method, it is proven that the algorithm is an accurate, robust, and efficient integration technique useful in finite element contexts. It is also shown that the algorithm produces a consistent tangent operator $\frac{d\sigma}{d\varepsilon}$ during the iterative process with quadratic convergence rate of the global iteration process.
자산구성 및 자본구조가 경영성과에 미치는 영향에 관한 연구 -중소기업의 재무컨설팅 활용 중심-
최창호 ( Chang Ho Choi ),유연우 ( Yen Yoo You ) 한국생산성학회 2011 生産性論集 Vol.25 No.3
The purpose of this study is to verify the effects of assets component and capital structure on management performance for financial consulting through 562 small and medium sized enterprises.(manufacturing industries 272, non manufacturing industries 290) The results of empirical analysis are as follows. First of all, the relevances of assets component and management performance are as follows. The first, the non current assets ratio have a positive effect on gross profit on sale with level of significance 1% in total and non manufacturing industries. The second, the non current assets ratio have no effect on net profit on sale in total, manufacturing and non manufacturing industries. The last, the non current assets ratio have no effect on gross profit on assets in total, manufacturing and non manufacturing industries. The next, the relevances of capital structure and management performance are as follows. The first, the debt ratio have no effect on gross profit on sale in total, manufacturing and non manufacturing industries. The second, the debt ratio have a negative effect on net profit on sale with level of significance 5% in total industries. The last, the debt ratio have a negative effect on net profit on sale with level of significance 1% in non manufacturing industriestotal industries.
최창호(Changho Choi) 한국지반신소재학회 2013 한국지반신소재학회 논문집 Vol.12 No.1
조립재료는 댐, 철도, 교량 구조물 건설시 제체, 성토재, 뒤채움재, 배수재 등으로 널리 사용되고 있으며, 이러한 구조물의 거동해석을 위한 수치해석을 위해 구성모델에 대한 연구가 다양하게 진행되어 왔다. 본 논문에서는 조립재료의 거동을 예측하기 위해 개발된 구성모델에 대한 변수 연구를 수행하였다. 구성모델은 한계상태이론에 근간한 bounding surface 모델로서 한 세트의 모델 정수를 활용하여 배수 조건, 구속압, 간극비에 상관없이 조립재료의 거동을 구현할 수 있는 장점을 지니고 있다. 구성모델은 탄성 파라미터, 한계상태 파라미터, 모델 고유파라미터를 활용하여 재료의 거동을 분석하며, 본 연구에서는 모델 고유 파라미터에 대한 변수 연구를 수행하였다. 변수 연구를 통해 구성모델이 조립재료의 가장 큰 특징인 비관계유통법칙(non-associative flow rule)에 따른 체적팽창 및 응력경로 변화에 따른 이동경화 현상을 적절히 모사할 수 있음을 파악하였다. Coarse-grained soils are typical engineering materials commonly used in many civil engineering applications such as structural fills, subgrade and drainage fills for dam, railway and bridge. Various researches have been performed with related to constitutive laws for numerical analysis of such structures. This paper presents a parametric study for a constitutive model for coarse grained materials. The model is a kind of the bounding surface models based on critical state theory. A distinct feature of the model is to capture the response of coarse-grained materials with different void ratios and confining pressures using a single set of model parameters. The model behavior is defined with a set of elastic parameters, critical state parameters, and model-specific parameters. The parametric study was performed for the model-specific parameters. The result of parametric study shows that the model is capable to capture stress-dilatancy behavior and kinematic-hardening under non-associative plastic flow.