• Journal of the Korean Society of Propulsion Engineers
• /
• v.12 no.6
• /
• pp.12-20
• /
• 2008

The efficient plan and numerical methods for development of the interior ballistics code have been investigated. The schemes of the numerical code for the moving boundary with the projectile movement have been compared and verified through the free piston motion problem. The combustion of solid propellants and the pressure gradient in the chamber by the porosity effect have been predicted based on the numerical calculation of the initial combustion of the interior ballistics. Computerization techniques of the fundamental schemes and plans for development of the numerical analysis code for the interior ballistics have been obtained.

• Journal of ILASS-Korea
• /
• v.5 no.1
• /
• 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.

• Journal of Environmental Impact Assessment
• /
• v.15 no.1
• /
• 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.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.4 s.235
• /
• 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.

• Journal of Ocean Engineering and Technology
• /
• v.21 no.6
• /
• 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
• /
• v.16 no.4
• /
• 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
• /
• v.90 no.4
• /
• 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.

• Journal of the Korea Society of Computer and Information
• /
• v.17 no.4
• /
• pp.41-49
• /
• 2012

This paper proposes a detection method of wipes including horizontal wipes with linear moving borders, such as horizontal or vertical wipes, Barn Doors, and Iris Rounds with circular moving borders. The suggested method first obtains a difference image between two adjacent frames, and extracts lines and circles by applying Hough transformation to the extracted difference image. Then, we detect wipe transitions by employing an evaluation function that analyzes the number of moving trajectories of lines or circles, their moving direction and magnitude. To evaluate the performance of the suggested algorithm, experimental results show that the proposed method can effectively detect wipe transitions with linear and circular moving borders rather than some existing methods.

• Journal of KIISE:Computing Practices and Letters
• /
• v.8 no.4
• /
• pp.430-441
• /
• 2002

Video object segmentation is an important component for object-based video coding scheme such as MPEG-4. In this paper, a robust algorithm for segmentation of moving objects in video sequences and VOP(Video Object Planes) extraction is presented. The points of this paper are detection, of an accurate object boundary by associating moving object edge with spatial object edge and generation of VOP. The algorithm begins with the difference between two successive frames. And after extracting difference image, the accurate moving object edge is produced by using the Canny algorithm and morphological operation. To enhance extracting performance, we app]y the morphological operation to extract more accurate VOP. To be specific, we apply morphological erosion operation to detect only accurate object edges. And moving object edges between two images are generated by adjusting the size of the edges. This paper presents a robust algorithm implementation for fast moving object detection by extracting accurate object boundaries in video sequences.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1995.05a
• /
• 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.