• Journal of the Korean Society for Railway
• /
• v.13 no.1
• /
• pp.9-15
• /
• 2010

When designing the size of a heavy maintenance shop for rolling stock, it is required to arrange buildings and facilities in the minimum site so as to improve the maintenance efficiency. However, the fluctuation rate (hereinafter "allowance rate") on which factors such as service and maintenance fluctuation should be applied when estimating the size of the maintenance shop has been used without verification. The objective of the study is to calculate a reasonable allowance rate and to review its appropriateness through the analysis of the facilities layout and process simulation to absorb the above elements into the staying time in the heavy maintenance shop. Since the working time, in this study, is assumed to be average working time, 10~20% was given to the standard deviation of working time in consideration of difference between workers, and possible allowance rate was drawn by analysis of the simulation results. In the future, it is required to optimize the size of the shop by applying appropriate allowance rate through scientific review of such factors as O&M plan, R/S reserve rate, capability of the shop, outsourcing rate, standard work amount, and so on.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.14 no.1
• /
• pp.19-33
• /
• 2002

A numerical method to efficiently secure necessary design informations of the hydraulic characteristics of rubble mound breakwater was attempted here. The method combines the exterior wave field with the interior wave field which is formulated incorporating porous media flow inside the breakwaters. An approximate method based on the long wave assumption was used for the exterior wave field while a boundary element method was used for the interior wave field. A hydraulic experiment was also performed to verify the validity of the numerical analysis. The numerical results were compared with experimental data and results from existing formulae. They generally agreed in both reflection and transmission coefficients. The calculated pore pressures also showed a similar pattern with experimental data, even if they gave some significant differences in their values fur some cases. The main cause of such differences can be attributed to the strongly nonlinear wave field occurring on the frontal slope of the breakwater. The direct input of dynamic pressures(measured from hydraulic experiment) into the numerical method was suggested as a promising method to enhance the predictability of pore pressures.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.8 no.4
• /
• pp.55-66
• /
• 2004

In this paper a method for finding solutions of acoustic, vortex and entropy wave equations in a cylindrical tube with variable section area was suggested under the consideration of that the high frequency instability in a rocket engine combustion chamber is an acoustic phenomena, which Is coupled with combustion reaction. and that a combustion chamber and exhaust nozzle are usually shaped cylindrically As a consequence of that some method. which enable the mathematical analysis of the influence of entropy and vortex waves to acoustic wave. was suggested. According to the method reflection coefficients of acoustic wave on a supercritical nozzle was numerically calculated, through which it was presented that entropy or vortex waves can strengthen or weaken the reflection rate of acoustic wave.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.2 no.2
• /
• pp.99-109
• /
• 1999

This paper is concerned with instability of flow fields which are dominated by the entropy mode with the presence of usual acoustic and vortical modes. These combined modes lead to nonlinear unstable waves which may occur in automobile, aircraft, or rocket engines. In this study instability in a side-burning rocket is investigated. It is shown that the energy growth rate parameters increase with an increase of the energy growth factor. The energy growth rate parameters for turbulent flows are larger than those for laminar flows. It is further shown that unstable wave motions for the high-temperature side-burning rocket are dictated mostly by the entropy mode, somewhat by the vortical mode, and least by the acoustic mode.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.20 no.2
• /
• pp.191-206
• /
• 2007

The general theoretical solutions for the wavespeed and damping derived in Part 1 of this work, are incorporated into the computer code. In this paper the code is used in a parametric study of the influence of excitation frequency and variations in material properties on propagation velocity and damping. Compressional wave velocity for waves of the first kind is shown to vary as a function of the frequency-permeability product, with a zone where wavespeed transitions from a lower bound value to a higher bound value with increasing values of the product. Damping is seen to be a maximum where the rate of change in wavespeed is greatest. Waves of the second kind also show a transition in wavespeed from near zero at low values of the frequency-permeability product to an upper bound value at higher values of the product.

• Journal of the Korean Society of Industry Convergence
• /
• v.7 no.1
• /
• pp.5-11
• /
• 2004

벽면에 충돌하는 액체 분무의 충돌 거동과 액적 비산에 관하여 실험을 통하여 조사하였다. 액체 분무는 홀노즐에 의해 직경 40mm의 충돌판에 분사하게 된다. 액체 분무는 반경방향으로 퍼져나가 5개의 영역으로 분류되어 나타내게 된다. 난류 혹은 층류 분무의 경우, 충돌판에 충돌한 후 두꺼운 액막을 형성하게 되며, 이러한 상태에서 충돌하는 분무의 비산량은 매우 적으며 충돌 거리에 영향을 받지 않는다. 한편, 파동이 있는 분무의 충돌은 수력도약(Hydraulic jump)과 함께 반경방향으로 엷은 액막을 형성하게 되며 비산율도 증가하게 된다. 액체분무의 초속도가 증가하면 비산율도 증가하게 된다. 분열이 일어난 후에 충돌하는 파동 분무의 비산율은 분열이 일어나기 전에 비해 약 2~3배 정도 크게 나타난다. 비산율은 웨버수(Weber number)를 이용하여 요약할 수가 있다.

• Korean Journal of Optics and Photonics
• /
• v.14 no.4
• /
• pp.429-433
• /
• 2003

We try to analyse the localization phenomenon of a lightwave in random media by means of considering the solution of the propagation equation on a transmission line in which the propagation constants are randomly distributed. Lightwave localization is generated at the turning point where the solution is changed suddenly from an increase to a decrease. First, in order to investigate the changing process of the solution, we have derived the approximated one-dimensional Schrodinger equation from the two-dimensional wave equation by using the Brags condition. Considering the many types of solutions of the wave equation, we have investigated the conditions that allow the solutions to exist. Also, we have investigated the relationships between the localization of the solution and the variation of the propagation constant. In case of the exponential solution, we know that the permittivity $\varepsilon$=(0,0$\varepsilon$$_{0}$) is a very important parameter to influence the phase of the lightwave and to generate the localization.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2008.05a
• /
• pp.2175-2178
• /
• 2008

본 연구에서는 전면에 투과성 구조물이 위치한 직립케이슨 및 유공케이슨에 대해 수치모의를 실시하여 케이슨의 형태 및 투과성 구조물의 존재유무에 따른 반사율의 감소효과에 대하여 알아보았다. 수치모의에 사용된 모델은 비압축성 점성유체에 대한 복잡한 자유수면 변위의 표현이 가능한 VOF법을 적용하여 Navier-Stokes 방정식을 보다 정확하게 해석하는 CADMAS-SURF(수치파동수로)를 사용하였다. 상기 구조물에 규칙파를 입사하여 반사율을 산정한 결과 주기에 따라 차이가 있지만, 직립케이슨만이 존재하는 경우에 비해 직립케이슨 전면에 투과성 구조물이 위치한 경우 대략 5%정도의 반사율 감소효과를 얻을 수 있었고 유공케이슨만이 존재하는 경우에 비해 유공케이슨과 투과성 구조물이 조합 된 경우에는 20%이상의 감소효과를 얻을 수 있었다. 따라서, 방파제 전면에 위치한 구조물에 대한 반사파의 피해 감소 및 항만 내부 정온도를 고려한 안벽의 시공이 요구되어 질 경우에 투과성 구조물은 직립케이슨과의 조합보다는 반사율을 상대적으로 크게 감소시킬 수 있는 유공케이슨과의 조합이 적절함을 알 수 있었다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.35 no.5
• /
• pp.1061-1071
• /
• 2015

In the present study, the Navier-Stokes (N-S) equations delineating water flows inside porous media were derived applying Reynolds transport theorem in order to provide a basis for analyzing water wave problems inside the porous media. Then, the derived N-S equations were compared with the same species of equations in existing researches. Based on the N-S equations, a set of Boussinesq equations was then derived in such a form that the dispersiveness and nonlinearity of water waves inside the porous media can be properly reproduced. Finally, numerical analyses were carried out to demonstrate the validity of the equations. The reflection and transmission coefficients of porous breakwaters were calculated and compared with the results of existing hydraulic experiments. The numerical results showed a rather sensitive dependency on the virtual mass coefficient of grains constituting the porous media. The selection of the coefficient with zero turned out to give nice agreements with numerical and experimental results.

• Journal of Ocean Engineering and Technology
• /
• v.7 no.2
• /
• pp.44-56
• /
• 1993

The purpose of this paper is to analyze the impact response behaviors of glass/epoxy laminated composite plates subjected to the transversely impact of a steel ball. For this purpose, dynamic finite element analysis based on the higher-order shear defomation plate theory is used to compute the contact forces, rebound velocity of a steel ball, and dynamic strain response histories. And low-velocity and high-velocity impact experiments were conducted to compare the results and compute the wave propagation velocities. The results obtained from impact experiments are in good agreement with those of dynamic finite element analysis. Also the wave propagation velocities obtained from high-velocity impact experiments and wave propagation theory agree well, and wave velocities were higher in the smaller radius of steel ball.