• 한국전산유체공학회지
• /
• 제12권4호
• /
• pp.44-53
• /
• 2007

A three-dimensional (3D) unstructured hydrodynamic solver for transient two-phase flows has been developed for a 3D component of a nuclear system code and a component-scale analysis tool. A two-fluid three-field model is used for the two-phase flows. The three fields represent a continuous liquid, an entrained liquid, and a vapour field. An unstructured grid is adopted for realistic simulations of the flows in a complicated geometry. The semi-implicit ICE (Implicit Continuous-fluid Eulerian) numerical scheme has been applied to the unstructured non-staggered grid. This paper presents the numerical method and the preliminary results of the calculations. The results show that the modified numerical scheme is robust and predicts the phase change and the flow transitions due to boiling and flashing very well.

• 한국산학기술학회논문지
• /
• 제20권1호
• /
• pp.470-476
• /
• 2019

일반적으로 열차 제동을 위한 제동력은 압축공기를 활용하여 제공된다. 열차에 상황별로 적절 제동력을 가하기 위해 사용하는 압력밸브 시스템은 복잡한 유동 회로를 가진다. 이를 일반적인 기계가공으로 제작 시, 유로형상 설계에 제약이 있는 반면, 3D 프린팅 기법으로 제작시 유동 효율을 증대할 수 있는 유로형상 제작이 가능하다. 따라서 이번 연구에서는 기존의 제작 방식으로 유로를 제작하는 경우와, 3D프린팅의 장점을 살려, 자유로운 형상의 유로를 제작하는 경우를 비교하여, 압력 밸브 시스템 내의 압축공기 유동의 현상을 해석적으로 분석하였다. 해석을 위한 조건으로는, 유로 방향이 바뀔 때 유로의 곡률 크기, 유로의 직경, 입구 및 저장소 압력의 크기, 그리고 압축공기의 초기 온도로 구분하였다. 압력손실의 최소화 및 유동 특성의 균일성이 제동 효율 개선에 영향을 주는 요인이므로, 수치해석을 통한 연구를 통해 일반적인 기계가공을 통한 직각 유로 형상보다는 3D 프린팅을 통한 곡률 유로의 경우가 제동효율 개선에 유리함을 확인하였다.

• 한국도로학회논문집
• /
• 제19권4호
• /
• pp.19-25
• /
• 2017

PURPOSES : In this paper, the flow of construction material was simulated using computational fluid dynamics in a 2D axisymmetric condition to evaluate the effect of initial or varying material properties on the final shape of a specimen. METHODS : The CFD model was verified by using a well-known analytical solution for a given test condition followed by performing a sensitivity analysis to evaluate the effect of material properties on the final shape of material. Varying dynamic viscosity and yield stress were also considered. RESULTS : The CFD model in a 2D axisymmetric condition agreed with the analytical solution for most yield stress conditions. Minor disagreements observed at high yield stress conditions indicate improper application of the pure shear assumption for the given material behavior. It was also observed that the variation of yield stress and dynamic viscosity during curing had a meaningful effect on the final shape of the specimen. CONCLUSIONS : It is concluded that CFD modeling in a 2D axisymmetric condition is good enough to evaluate fluidal characteristics of material. The model is able to consider varying yield stress and viscosity during curing. The 3D CFD-DEM coupled model may be required to consider the interaction of aggregates in fluid.

• 한국유체기계학회 논문집
• /
• 제11권5호
• /
• pp.7-14
• /
• 2008

Open channel type regenerative pump has been used in various industrial fields. It generates high pressure with low flow rate. However, it has low efficiency because of its complex flow pattern, We studied performance experiments and 3D numerical flow analysis of a regenerative pump. Through the numerical analysis, we could get the internal flow pattern and profile of a regenerative pump. Also, we examined leakage flow effects due to the gap between casing and impeller and stripper clearance. For the numerical analysis verification, we performed experiments and they had similar tendency at the design point.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집C
• /
• pp.592-597
• /
• 2001

An automobile lower arm has been fabricated in a prototype form by hydroforming with the aids of numerical analysis and experiments. For the numerical process design, a program called HydroFORM-3D developed here on the basis of a rigid-plastic model, has been applied to the lower arm hydroforming. The friction calculation between die and workpiece has been dealt carefully by introducing a new scheme in three-dimensional surface integration. To accomplish successful hydroforming process design, thorough investigation on proper combination of process parameters such as internal hydraulic pressure, axial feeding, and tool geometry has been performed. Results obtained from numerical simulation for a lower arm in hydroforming process are compared with a series of experiments. The comparison shows that the numerical analysis successfully provides the manufacturing information on the lower arm hydroforming, and it predicts the geometrical deformation and the thinning.

• Computers and Concrete
• /
• 제4권3호
• /
• pp.221-241
• /
• 2007

Based on the experiment results, the damage and fracture behavior of concrete at the ages of 1d, 2d, 7d and 28d, in three-point bending and uniaxial tensile tests, were simulated with a finite element program, ABAQUS. The critical stress intensity factor $K_{IC}^s$ and the critical crack tip opening displacement ($CTOD_C$) of concrete were calculated with effective-elastic crack approach for the three-point bending test of grade C30 concrete. Based on the crack band model, a bilinear strain-softening curve was derived to simulate the LOAD-CMOD curves and LOAD-Displacement curves. In numerical analysis of the uniaxial tension test of concrete of grade C40, the damage and fracture mechanics were combined. The smeared cracking model coupling with damaged variable was adopted to evaluate the onset and development of microcracking of uniaxial tensile specimen. The uniaxial tension test was simulated by invoking the damage plastic model which took both damage and plasticity as inner variables with user subroutines. All the numerical simulated results show good agreement with the experimental results.

• 한국정보통신학회:학술대회논문집
• /
• 한국정보통신학회 2012년도 추계학술대회
• /
• pp.1019-1022
• /
• 2012

집적 영상 (Integral Imaging) 기술은 3차원 이미징 (Imaging)과 디스플레이를 위한 기술이다. 많은 파라미터들이 3차원 집적 영상 시스템의 성능에 영향을 준다. 3차원 시스템 성능의 척도 (Performance Metric)를 정의하고 이러한 파라미터들을 최적화함으로써 향상된 시스템 성능을 얻을 수 있다. 본 논문에서는 주어진 시스템 조건하에서 성능 척도를 사용하여 3차원 집적 영상 시스템의 성능을 최적화하는 방법에 대해 설명한다. 이 분석에서, 성능 척도를 최적화하기 위해 렌즈의 개구수 (Numerical Aperture), 영상 센서간의 거리, 영상 센서의 수, 픽셀 크기, 그리고 픽셀 수와 같은 시스템 파라미터들을 최적화하여 선택한다. 이미징 처리과정을 설명하기 위해 파동 광학 (Wave Optics)을 사용하였다.

• 한국도로학회논문집
• /
• 제10권4호
• /
• pp.213-224
• /
• 2008

트럭 축하중에 의한 도로포장체의 응력과 변형은 대부분 다층 탄성 이론에 의해 예측된다. 대부분의 다층 탄성 이론에 의한 이론적 계산값이 연성 포장 재료의 점탄성적 거동특성, 동적 트럭 축하중, 비균등 타이어 접지압 및 형상등을 해석에 고려하지 못하므로, 계측값에 비해 매우 작은 값을 예측하므로서 도로 포장 두께설계가 과소 설계될 우려가 크다. 이와 같은 도로 포장체 구조해석시 이용되는 중요한 변동요소를 포장 재료의 물성 모델 측면, 비균등 접지압 및 형상 측면, 동적 유한요소해석 측면에서 분석하여 이용 가능한 모델을 본 논문에서 제안하였다. 경계조건 및 민감도 분석을 수행을 통한 효과적인 3차원 연성포장의 유한요소해석모델을 결정하는 방법론을 제안하였으며, 최적 유한요소모델 분석결과와 현장에서 취득한 결과와의 상호비교를 통하여 모델의 유의성을 검증하였으며, 동적 접지하중조건, 점탄성물성 모델 등을 3차원 유한요소 모델에 접목하고, 최적 경계조건을 결정하였다.

• 대한기계학회논문집B
• /
• 제29권9호
• /
• pp.1057-1064
• /
• 2005

A conservative finite-volume numerical method using unstructured meshes, which is developed by the authors, is evaluated for its application to several 2-D benchmark problems using a variety of quadrilateral, triangular and hybrid meshes. The present pressure-based numerical method for unstructured mesh clearly demonstrates the same accuracy and robustness as that fur typical structured mesh.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.589-592
• /
• 2002

A commercial CFD code is applied to analyze the 3-D viscous flow field within vertical multi-stage centrifugal pump including impeller of centrifugal pump with 6 blades and guide vain with 11 blades. The numerical analysis of vertical multi-stage centrifugal pump is performed by changing flow rate from $8\;to\;26\;m^{3}/h$ at the constant 3500rpm. The characteristics such as total pressure coefficient, total head, water horse power, power efficiency are represented according to flow rate changing. In the future, we will need to perform flow calculation of vertical multi-stage centrifugal pump by considering meridional shape of impeller.