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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.
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.
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.
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.
에너지절약형 친환경주택의 성능 평가를 위한 IFC-BIM기반 요구정보 자동추출 방안 연구
김창민(Kim, Chang-Min),김연아(Kim, Yeon-Ah),홍종필(Hong, Jong-Pil),최창호(Choi, Chang-Ho),이현우(Lee, Hyun-Woo) 한국건축친환경설비학회 2017 한국건축친환경설비학회 논문집 Vol.11 No.2
The demand for green homes has been increasing consistently. However, the evaluation of green homes has been performed manually, which is time-consuming and low in reliability. The objective of this study was to propose a method in order to extract and input the information necessary for the construction criteria evaluation of green homes from BIM automatically. In order to develop a method, first, this study defined the information required for the evaluation of green homes. Second, this study proposed the methods to extract the information about the performance details by type, air leakage and solar irradiance from BIM. Finally, this study reviewed the feasibility of the IFC based BIM for the evaluation on the green homes and, based on review result, investigated the application plans for the proposed method. Since it is possible to automatically input the information required for the green home performance evaluation program through the proposed method, it is expected not only to increase the productivity of evaluation but also to improve the responsive power of evaluation task by reducing the repetitive tasks that occur during design changes.
김대진(Dae-Jin Kim),홍순삼(Soon-Sam Hong),최창호(Chang-Ho Choi),김진한(Jinhan Kim) 한국항공우주연구원 2010 항공우주기술 Vol.9 No.2
축추력의 효과적인 제어는 터보펌프의 작동 안정성을 확보하는 데 중요한 기술 중 하나이다. 현재 개발 중인 75톤급 로켓엔진용 연료펌프에 대한 축추력 측정을 상온의 물을 매질로 하여 실시하였다. 시험 결과, 연료펌프의 축추력은 펌프 베어링의 축방향 하중 조건을 만족하는 것으로 예상되었다. 또한 연료펌프의 축추력은 대체로 유량이 작을수록 커졌다. 그리고 플로팅 링 실과 임펠러 사이의 간극이 바뀌었을 때, 연료펌프의 축방향 하중과 후방 누설 유량이 변화하는 것을 확인하였다. An effective control of the axial thrust of a turbopump is one of the critical issues for obtaining its operational stability. Axial thrusts of the fuel pump for the 75-ton class rocket engine under development were measured with water as a test propellant at a room temperature. According to the test results, the axial thrust of the fuel pump seemed to satisfy the axial force condition of its bearing. Also, the thrust was increased as a whole when the flowrate of the pump was decreased. Furthermore it was found that the thrust and the leakage flowate were modified when the gaps between the floating ring seals and the impeller were changed.
상수도관로의 주변 지반침하 위험도 평가를 위한 안전감시 센서
곽필재 ( Pill Jae Kwak ),박상혁 ( Sang Hyuk Park ),최창호 ( Chang Ho Choi ),이현동 ( Hyun Dong Lee ) 한국센서학회 2015 센서학회지 Vol.24 No.5
IoT(Internet of Things) based underground risk assessment system surrounding water pipeline enables an advanced monitoring and prediction for unexpected underground hazards such as abrupt road-side subsidence and urban sinkholes due to a leak in water pipeline. For the development of successful assessment technology, the PSU(Water Pipeline Safety Unit) which detects the leakage and movement of water pipes. Then, the IoT-based underground risk assessment system surrounding water pipeline will be proposed. The system consists of early detection tools for underground events and correspondence services, by analyzing leakage and movement data collected from PSU. These methods must be continuous and reliable, and cover certain block area ranging a few kilometers, for properly applying to regional water supply changes.