• 대한기계학회논문집A
• /
• 제27권9호
• /
• pp.1562-1570
• /
• 2003

The prediction of the inelastic behavior of the structure is an essential part of reliability assessment procedure, because most of the failures are induced by the inelastic deformation, such as creep and plastic deformation. During decades, there has been much progress in understanding of the inelastic behavior of the materials and a lot of inelastic constitutive equations have been developed. The complexity of these constitutive equations generally requires a stable and accurate numerical method. The radial return mapping is one of the most robust integration scheme currently used. Nonlinear kinematic hardening model of Armstrong-Fredrick type has recovery term and the direction of kinematic hardening increment is not parallel to that of plastic strain increment. In this case, The conventional radial return mapping method cannot be applied directly. In this investigation, we expanded the radial return mapping method to consider the nonlinear kinematic hardening model and implemented this integration scheme into ABAQUS by means of UMAT subroutine. The solution of the non-linear system of algebraic equations arising from time discretization with the generalized midpoint rule is determined using Newton method and bisection method. Using dynamic yield condition derived from linearization of flow rule, the integration scheme for elastoplastic and viscoplastic constitutive model was unified. Several numerical examples are considered to demonstrate the efficiency and applicability of the present method.

• 한국강구조학회 논문집
• /
• 제23권5호
• /
• pp.535-546
• /
• 2011

본 연구에서는 다양한 명시적 호장법을 사용하여 공간프레임의 반강접 탄소성 후좌굴 해석을 수행하였다. 이를 위해 이전 연구를 발전시켜 다양한 명시적 알고리즘의 호장법과 명시적, 묵시적 해석법에 동시에 적용 가능한 반강접 탄소성 공간프레임요소를 제안하였다. 다양한 명시적 호장법은 예측단계와 수렴단계에 명시적 해석법인 동적이완법을 적용한 것을 의미한다. 따라서 명시적 호장법에는 명시적(예측단계)-명시적(예측단계) 호장법, 명시적(예측단계)-묵시적(수렴단계) 호장법, 묵시적(예측단계)-명시적(수렴단계) 호장법으로 구분된다. 또한 명시적 호장법에 적용 가능하도록 수정된 반강접 탄소성 공간프레임요소는 오일러리안 유한변형이론에 의해 강체회전변형을 고려하였기 때문에 대변위가 발생하는 기하학적 비선형 문제에 적용될 수 있고, 완전 탄소성 소성힌지 알고리즘에 의한 재료적 비선형성을 고려하였으며, 부재내부에 정적 응축된 회전 및 축방향 성분의 선형 스프링에 의해 접합부 반강접 특성을 반영하였다. 제안된 해석법을 이용하여 검증예제를 수행함으로써 본 연구에서 제안된 다양한 명시적 호장법 및 공간프레임요소의 정확성을 검증한다.

• Nuclear Engineering and Technology
• /
• 제52권6호
• /
• pp.1172-1179
• /
• 2020

As a Lagrangian particle method, Moving Particle Semi-implicit (MPS) method has great capability to capture interface/surface. In recent years, the multiphase flow simulation using MPS method has become one of the important directions of its developments. In this study, some key methods for multiphase flow have been introduced. The interface tension model in multiphase flow is modified to maintain the smooth of the interface and suitable for the three-phase flow. The mass transfer at immiscible liquid interface entrained by single bubble which could occur in Molten Core-Concrete Interaction (MCCI) has been investigated using this particle method. With the increase of bubble size, the height of entrainment column also increases, but the time of film rupture is slightly different. With the increase of density ratio between the two liquids, the height of entrained column decreases significantly due to the decreasing buoyancy of the denser liquid in the lighter liquid. In addition, the larger the interface tension coefficient is, the more rapidly the entrained denser liquid falls. This study validates that the MPS method has shown great performance for multiphase flow simulation. Besides, the influence of physical parameters on the mass transfer at immiscible interface has also been investigated in this study.

• 한국분무공학회지
• /
• 제8권1호
• /
• pp.1-8
• /
• 2003

The flow analysis of the axial fan of rotary burner was performed by SIMPLE(Semi Implicit Method for Pressure Linked Equations) algorithm and finite volume mothod performed in the case of 3-D, incompressible, turbulent flow. In this study, the coordinate transformation was adapted for the complex geometry of axial fan, and the standard $k-{\varepsilon}$ model and wall function method were used for analysis of turbulent flow. Multi-block grid system was used for flow field and divided into four domains such as the inlet, outlet, flow field of rotating vane, and tip clearance. Fan rotation was simulated by rotational motion using MRF(Multiple Rotating Reference Frame) in steady, incompressible state flow.

• 대한기계학회논문집A
• /
• 제25권4호
• /
• pp.574-581
• /
• 2001

Transient linear elastodynamic problems are numerically analyzed in a time-domain by the Finite Element Method, for which the variational formulation based upon the equations of motion in convolution integral is newly derived. This formulation is implicit and does not include the time derivative terms so that the computation procedure is simple and less assumptions are required comparing to the conventional time-domain dynamic numerical algorithms, being able to get the improved numerical accuracy and stability. That formulation is expanded using the semi-discrete approximation to obtain the finite element equations. In the temporal approximation, the time axis is divided equally and constant and linear time variations are assumed in those intervals. It is found that unconditionally stable numerical results are obtained in case of the constant time variation. Some numerical examples are given to show the versatility of the presented formulation.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2011년 춘계학술대회논문집
• /
• pp.278-285
• /
• 2011

In the present study, the numerical prediction of the oil amount leaked from the hole of a damaged tank is investigated using the improved MPS (Moving Particle Semi-implicit) method, which was originally proposed by Koshizuka and Oka (1996) for incompressible flow. The governing equations, which consist of the continuity and Navier-Stokes equations, are solved by Lagrangian moving particles, and all terms expressed by differential operators should be replaced by the particle interaction models based on a Kernel function. The simulation results are validated though the comparison with the analytic solution based on Torricelli's equilibrium relation. Furthermore, a series of numerical simulations under the various conditions are performed in order to estimate more accurately the initial amount of leaked oil.

• Nuclear Engineering and Technology
• /
• 제42권3호
• /
• pp.279-296
• /
• 2010

For the analysis of transient two-phase flows in nuclear reactor components, a three-dimensional thermal hydraulics code, named CUPID, has been developed. The CUPID code adopts a two-fluid, three-field model for two-phase flows, and the governing equations were solved over unstructured grids, which are very useful for the analysis of flows in complicated geometries. To obtain numerical solutions, the semi-implicit numerical method for the REALP5 code was modified for an application to unstructured grids, and it has been further improved for enhanced accuracy and fast running. For the verification of the CUPID code, a set of conceptual problems and experiments were simulated. This paper presents the flow model, the numerical solution method, and the results of the preliminary assessment.

• 한국표면공학회:학술대회논문집
• /
• 한국표면공학회 2007년도 춘계학술발표회 초록집
• /
• pp.76-77
• /
• 2007

화학 기상 증착법 (Chemical Vapor Deposition)은 기체 원료의 화학반응을 이용하여 박막, 미립자, nano-tube등 고체 재료를 합성하는 증착 방법이며, 현재 공업적으로 확산되어 반도체 공정과 같은 박막제조에 이용되고 있다. 박막제조에 있어서 중요한 관심사인 기판의 증착률은 기판의 회전 속도에 의하여 영향 받을 수 있다. 따라서 본 연구에서는 최적의 회전 속도를 찾아내기 위해 박막특성에 직접적으로 연관이 있는 CVD 반응기 내의 유동특성을 유한체적법 (Finite volume method)과 SIMPLE (Semi-Implicit Method for Pressure-Linked Equation) 알고리즘을 사용하여 수치모사 하였고 기판에서 화학 반응을 계산하기 위해 Arrhenius 모델을 사용하였다.

• 한국항만학회지
• /
• 제12권2호
• /
• pp.303-312
• /
• 1998

It is necessary to quantitatively asses the influence of tidal currents to analysis the coastal current patterns before or after constructing offshore structures like as breakwaters. This assesment can be made through the use of simulation models designed to reproduce the water movements of the area. And it is very important to predict a phenomenon of pollutant dispersion in the area. In this study, in order to predict the changes of sea water quality for the port development plan, Ilgwang harbour, located at the east coast of Pusan, the numerical computations were carried out. The flow patterns were investigated before and after the development of the harbour bay and coastal area connected on it. The computational models are an extension of earlier work on the flow which used the ADI Method (Alternating Direction Implicit Method) in appling to Osaka Bay by KANEKO et al. The transport of pollutant constituents depends upon the currental characteristics of the water-transporting medium. In the currental flow model, water velocities and water levels are computed throughout the regions of it. These value are then used in the mass-balance equation to obtain the pollutant-constituent transport. As a result of this research, the present water quality of Ilgwang harbour and the coastal areas connected on it was proved out some good condition. The changes of sea water quality due to the port development plan of the Ilgwang habour bay and the coastal area were not large compared with the present condition, but it will be likely able to get worse by increasing the semi-enclosed areas in the harbour bay. In order to improve the water quality of the area after development, the method to activate tidal exchange in the area can be needed, as a mitigation technique.

• 한국해양공학회지
• /
• 제21권4호
• /
• pp.8-14
• /
• 2007

A particle method recognized as one of gridless methods has been developed to investigate incompressible viscous flaw. The method is more feasible and effective than conventional grid methods for solving the flaw field with complicated boundary shapes or multiple bodies. The method is consists of particle interaction models representing pressure gradient, diffusion, incompressibility and the boundary conditions. In the present study, the models in case of various simulation condition were checked with the analytic solution, and applied to the two-dimensional Poiseuille flow in order to validate the developed method.