• 한국추진공학회지
• /
• 제12권6호
• /
• pp.12-20
• /
• 2008

강내탄도 전산해석 코드 개발을 위한 효율적인 방안과 수치 기법에 관해 연구하였다. 탄자이동에 의한 이동경계면에 대한 수치 해석 기법은 자유 피스톤 운동 문제를 통해서 비교 검증하였다. 강내탄도의 초기 연소를 수치적으로 계산하여 고체추진제의 연소와 기공률 효과에 의한 압력구배를 예측할 수 있었다. 본 연구를 통해서 강내탄도 전산 해석 코드 개발에 관한 방안과 기초 기법에 대한 전산화 기술을 확보하였다.

• 한국분무공학회지
• /
• 제5권1호
• /
• pp.13-22
• /
• 2000

The present study has numerically analyzed the vaporization characteristics of fuel droplets in the high temperature convective flow field. The axisymmetric governing equations for mass, momentum, energy, and species are solved by an iterative and implicite unstructured finite-volume method. The moving boundary due to vaporization is handled by the deformable unstructured grid technique. The pressure-velocity coupling in the density-variable flows is treated by the SIMPLEC algorithm. In terms of the matrix solver, Bi-CGSTAB is employed for the numerically efficient and stable convergence. The n-decane is used as a liquid fuel and the initial droplet temperature is 300K. Computations are performed for the nonevaporating and evaporating droplets with the relative interphase velocity(25m/s). The unsteady vaporization process has been simulated up to the nondimensional time, 25. Numerical results indicate that the mathematical model developed in this study succesfully simulates the main features of the droplet vaporization process in the convective environment.

• 환경영향평가
• /
• 제15권1호
• /
• pp.67-78
• /
• 2006

Global warming brings about changes of diverse environmental, especially changes of plant distribution. The purpose of this paper is to examine the relationship between temperature rise and changes of northern limit of vegetation growth in Korea. Bamboos (Phyllostachys) and boundary between the northern type and southern type of garlic (Allium sativum L.) were selected. The data of the distributions of bamboos and garlic are collected by field survey and interviews. Temperature is analyzed from 1904 to 2000. The northern limit of Phyllostachys moves 60-100 km northward, for about 100 years, the period of 1907-2003 and mean temperature of Korea increases about $2^{\circ}C$ during the same period. It means that the northern limit moves 30-50 km northward, for each $1^{\circ}C$ rising of January mean temperature. The boundary between the northern type and southern types of garlic moves northward 40-140 km from 1980s to 2000. The moving width is broad in the west coastal region while the width is narrow in the inland and mountain regions. The mean moving width is about 100 km.

• 대한기계학회논문집B
• /
• 제29권4호
• /
• pp.425-434
• /
• 2005

In order to analyze pulsating flows in elastic blood vessels, a method based on the ALE concept and finite volume method was reformed and modulated to include wall motion of elastic vessels and impedance phase angle(phase difference between wall motion and blood flow). Our study indicated wall shear rates(WSR) were significantly influenced by the wall motion and the impedance phase angle. For larger wall motion more than $5{\%},$ the computed WSR started to deviate from the results of the perturbation theory that assumed smaller wall motion. The study showed that oscillatory shear index increased as the impedance phase angle became more negative like $-70{\circ}\;or\;-80{\circ}$ due to reduced mean WSR and increased amplitude of WSR. This result indicated that hypertensive patients are more vulnerable to atherosclerosis than normal persons because of the role of more negative impedance phase angles usually observed in these patients.

• 한국해양공학회지
• /
• 제21권6호
• /
• pp.53-58
• /
• 2007

A particle method, recognized as one of gridless methods, has been developed to investigate non-linear free-surface motions interacting with structures. This method is more feasible and effective than conventional grid methods for solving flow fieldswith complicated boundary shapes. The method consists of particle interaction models representing pressure gradient, diffusion, incompressibility, and the free-surface boundary conditions without grids. In the present study, broken dam problems with various viscosity values are simulated to validate the developed method.

• Advances in nano research
• /
• 제16권4호
• /
• pp.395-412
• /
• 2024

This article develops a nonclassical size dependent nanoplate model to study the dynamic response of functionally graded carbon nanotube (FGCNT) nanoplates under a moving load. Both nonlocal and microstructure effects are incorporated through the nonlocal strain gradient elasticity theory. To investigate the effect of reinforcement orientation of CNT, four different configurations are studied and analysed. The FGM gradation thorough the thickness direction is simulated using the power law. In the context of the first order shear deformation theory, the dynamic equations of motion and the associated boundary conditions are derived by Hamilton's principle. An analytical solution of the dynamic equations of motion is derived based on the Navier methodology. The proposed model is verified and compared with the available results in the literature and good agreement is found. The numerical results show that the dynamic performance of FGCNT nanoplates could be governed by the reinforcement pattern and volume fraction in addition to the non-classical parameters and the moving load dimensionless parameter. Obtained results are reassuring in design and analysis of nanoplates reinforced with CNTs.

• Structural Engineering and Mechanics
• /
• 제90권4호
• /
• pp.357-370
• /
• 2024

Due to the fact that the mechanism of the effects of temperature and initial geometric imperfection on low-velocity impact problem of axially moving plates is not yet clear, the present paper is to fill the gap. In the present paper, the nonlinear dynamic behavior of axially moving imperfect graphene platelet reinforced metal foams (GPLRMF) plates subjected to lowvelocity impact in thermal environment is analyzed. The equivalent physical parameters of GPLRMF plates are estimated based on the Halpin-Tsai equation and the mixing rule. Combining Kirchhoff plate theory and the modified nonlinear Hertz contact theory, the nonlinear governing equations of GPLRMF plates are derived. Under the condition of simply supported boundary, the nonlinear control equation is discretized with the help of Gallekin method. The correctness of the proposed model is verified by comparison with the existing results. Finally, the time history curves of contact force and transverse center displacement are obtained by using the fourth order Runge-Kutta method. Through detailed parameter research, the effects of graphene platelet (GPL) distribution mode, foam distribution mode, GPL weight fraction, foam coefficient, axial moving speed, prestressing force, temperature changes, damping coefficient, initial geometric defect, radius and initial velocity of the impactor on the nonlinear impact problem are explored. The results indicate that temperature changes and initial geometric imperfections have significant impacts.

• 한국컴퓨터정보학회논문지
• /
• 제17권4호
• /
• pp.41-49
• /
• 2012

본 논문에서는 여러 가지 와이프 장면전환 중에서 이동 경계선의 형태가 선형 라인의 모양을 가지는 수평 와이프, 수직 와이프, 반도어(Barn Doors), 그리고 이동 경계선이 원의 모양을 가지는 아이리스 라운드(Iris Round) 와이프를 강건하게 검출하는 방법을 제안한다. 제안된 방법에서는 디지털 비디오 데이터를 입력 받아 차영상을 추출한 후 차영상에 허프변환을 적용하여 영상에 존재하는 라인과 원형의 이동 경계선을 강건하게 추출한다. 그런 다음, 평가함수를 통해 이들의 진행 방향과 형태를 효과적으로 분석하여 와이프의 발생 유무와 그 종류를 결정한다. 실험에서는 본 논문에서 제안된 와이프 검출 방법이 기존의 다른 방법에 비해 보다 정확하게 와이프를 검출한다는 것을 성능 비교를 통해 보여준다.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
• /
• 제8권4호
• /
• pp.430-441
• /
• 2002

비디오 객체 분할은 MPEG-4와 같은 객체기반 비디오 코딩을 위한 중요한 구성 요소이다. 본논문은 비디오 시퀸스에서 움직임 객체 분할을 위한 새로운 알고리즘과 VOP(Video Object Plane)추출 방법을 소개한다. 본 논문의 핵심은 시간적으로 변하는 움직임 객체 에지와 공간적 객체 에지 검출 결과를 효율적으로 조합하여 정확한 객체 경계를 추출하는 것이다. 이후 추출된 에지를 통하여 VOP를 생성한다. 본 알고리즘은 첫 번째 프레임을 기준영상으로 설정한 후 두 개의 연속된 프레임 사이의 움직임 픽셀 차이 값으로부터 시작된다. 차이영상을 추출한 후 차이영상에 Canny 에지 연산과 수리형태 녹임 연산(erosion)을 적용하고, 다음 프레임의 영상에 Canny 에지 연산과 수리형태 녹임 연산을 적용하여 두 프레임 사이의 에지 비교를 통하여 정확한 움직임 객체 경계를 추출한다. 이 과정에서 수리형태학 녹임 연산은 잘못된 객체 에지의 검출을 방지하는 작용을 한다. 두 영상 사이의 정확한 움직임 객체 에지(moving object edge)는 에지 크기를 조절하여 생성한다. 본 알고리즘은 픽셀 범위까지 고려한 정화한 객체의 경계를 얻음으로서 매우 쉬운 구현과 빠른 객체 추출을 보였다.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1995년도 추계학술발표회논문집(2)
• /
• pp.707-712
• /
• 1995

Grain boundary diffusion plays significant role in the fission gas release, which is one of the crucial processes dominating nuclear fuel performance. Gaseous fission products such as Xe and Kr generated inside fuel pellet have to diffuse in the lattice and in the grain boundary before they reach open space in the fuel rod. In the mean time, the grains in the fuel pellet grow and shrink according to grain growth kinetics, especially at elevated temperature at which nuclear reactors are operating. Thus the boundary movement ascribed to the grain growth greatly influences the fission gas release rate by lengthening or shortening the lattice diffusion distance, which is the rate limiting step. Sweeping fission gases by the moving boundary contributes to the increment of the fission gas release as well. Lattice and grain boundary diffusion processes in the fission gas release can be studied by 'tracer diffusion' technique, by which grain boundary diffusion can be estimated and used directly for low burn-up fission gas release analysis. However, even for tracer diffusion analysis, taking both the intragranular grain growth and the diffusion processes simultaneously into consideration is not easy. Only a few models accounting for the both processes are available and mostly handle them numerically. Numerical solutions are limited in the practical use. Here in this paper, an approximate analytical solution of the lattice and stationary grain boundary diffusion in a polycrystalline solid is developed for the tracer diffusion techniques. This short closed-form solution is compared to available exact and numerical solutions and turns out to be acceptably accurate. It can be applied to the theoretical modeling and the experimental analysis, especially PIE (post irradiation examination), of low burn up fission. gas release.