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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.
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.
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.
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.
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.
시뮬레이션 평가 기준 및 방법에 따른 창세트 열관류율 비교
강혜숙(Kang, Hye-Suk),유동철(Yoo, Dong-Chul),이건호(Lee, Keon-Ho),장대희(Jang, Dae-Hee),최창호(Choi, Chang-Ho) 한국건축친환경설비학회 2015 한국건축친환경설비학회 논문집 Vol.9 No.5
The purpose of this study was to verify the suitability of the simulation test for domestic and international window-set U-values by discussing the input conditions and calculation methods for the same simulation test and comparing the calculated results for various window-sets. To this end, a total of 18 cases were selected, where glass, cavities, frames, spacers, windows sizes, etc, for double glazing fixed-windows and triple glazing fixed-windows have been changed. Then, domestic and international U-values by criteria were compared by performing a simulation using WINDOW&THERM, a certified program. The analytic results of domestic and international standards revealed that domestic standards and NFRC used the calculation method through the Edge area and that CEN used linear thermal transmittance(ψ) as a calculation method. In the Indoor and outdoor temperature conditions, domestic standards and CEN were similar but NFRC was somewhat different. The results of comparing U–value errors based on the Korea test found NFRC -6.22% ~+9.50%, CEN -4.98% ~ -1.23%. The U-value of the case calculated based on CEN standards tended to be mostly higher than that in domestic conditions. This tendency may have been caused by the difference between convective heat transfer coefficient and frame effective thermal conductivity in air space. The results of the domestic standards-applied simulation of window-set thermal transmittance showed an error rate within 10%, compared to NFRC and CEN. The above study confirmed the suitability of the simulation test for domestic window-set U-values.
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.