• Journal of KSNVE
• /
• v.6 no.5
• /
• pp.595-605
• /
• 1996

If the control force designed on the basis of the mathematical model with parameter errors is applied to control the actual system, the closed-loop performance of the actual system will be degraded depending on the degree of the errors, In this study, the effect of parameter errors on the robustness of several natural controls has been analyzed and compared. Every asymptoic stability condition for the natural controls has been derived using Lyapunov approach, and the characteristics of the stability conditions has also been compared. The extent of deviation of the closed-loop performance from the designed one for the natural controls is derived using operator techniques, and evaluated by numerical method. It has been found that the optimal control, acceleration feedback control, and acceleration-position feedback control among the considered natural controls would be robust one with respect to the parameter errors.

• 한국전산유체공학회:학술대회논문집
• /
• 2004.10a
• /
• pp.7-14
• /
• 2004

It is well known that preconditioning methods are efficient for convergence acceleration at compressible low Mach number flows. In this study, the original Euler equations and three preconditioners nondimensionalized differently are implemented in two dimensional inviscid bump flows using the 3rd order MUSCL and DADI schemes as flux discretization and time integration respectively. The multigrid and local time stepping methods are also used to accelerate the convergence. The test case indicates that a properly modified local preconditioning technique involving concepts of a global preconditioning one produces Mach number independent convergence. Besides, an asymptotic analysis for properties of preconditioning methods is added.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.6
• /
• pp.792-801
• /
• 2000

The problem of phase change from liquid to solid in the inviscid plane-stagnation flow is theoretically investigated. The solution at the initial stage of freezing is obtained by expanding it in powers of time, and the final equilibrium state is determined from the steady-state governing equations. The transient solution is dependent on the three dimensionless parameters, but the equilibrium state is determined by one parameter of (temperature ratio/conductivity ratio). The effect of the fluid flow on the growth rate of the solid in the pure conduction problem can be clearly seen from the solution of the initial stage and the final equilibrium state. The characteristics of the transient heat transfer at the surface of the solid and the liquid side of the solid-liquid interface for all the dimensionless parameters are elucidated.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.2
• /
• pp.232-240
• /
• 1986

Extinction characteristics of the two interacting premixed flames are analyzed for the effects of flame stretch and preferential diffusion using large activation energy asymptotic analysis by adopting counterflow system as a model problem. Results show that the flammable limit of the thermally interacting premixed flames is extended compared to the single flame, and the extinction mechanism is classified into weak and strong interactions. As the lewis number of the deficient species increases, the region of strong interaction diminishes which can explain the different characteristics of the extinction boundaries of the lean (rich) methane/air and butane/air flames. The influence of the flame stretch to the interaction boundaries is also studied.

• Nuclear Engineering and Technology
• /
• v.4 no.2
• /
• pp.102-108
• /
• 1972

Time-dependent neutron transport equation with delayed neutrons is analytic-ally solved in the case of isotropic scattering with constant cross sections. The equations in the two divided time regions are obtained from the original equation by the asymptotic method. It is shown that the approximate solutions in each time region are uniformly valid in time to the order of the inverse magnitude of the velocity.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.20 no.2
• /
• pp.72-79
• /
• 2021

The present paper aims to set forth a two-dimensional theory for the dynamics of plates that is valid over a large range of excitation. To construct a dynamic plate theory within the long-wavelength approximation, two dimensional-reduction procedures must be used for analyzing the low- and high-frequency behaviors under the dynamic variational-asymptotic method. Moreover, a separate and logically independent step for the short-wavelength regime is introduced into the present approach to avoid violation of the positive definiteness of the derived energy functional and to facilitate qualitative description of the three-dimensional dispersion curve in the short-wavelength regime. Two examples are presented to demonstrate the capabilities and accuracy of all of the formulas derived herein by using various dispersion curves through comparison with the three-dimensional finite element method.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.10
• /
• pp.1393-1400
• /
• 2003

Ignition of hydrogen and oxygen in the "third limit" is theoretically investigated in the stagnation point flow with activation energy asymptotics. With the steady-state approximations of H, OH, O and HO$_2$, a two-step reduced kinetic mechanism is derived for the regime lower than the crossover temperature T$_{c}$ at which the rates of production and consumption of all radicals are equal. Appropriate scaling of Damkohler number successfully provides the explicit relationship between pressure, temperature and strain rate at ignition. It is shown that, compared with those for the counterflow, ignition temperatures for the stagnation point flow are considerably increased with increasing the system pressure. This is because ignition in the "third limit" is characterized by the production of reduction of $H_2O$$_2$, which is reduced by wall effect. Strain rate substantially affects ignition temperature because key reaction rates of $H_2O$$_2$ are comparably with its transport rate, while the mixture temperature and the hydrogen composition do not significantly affect ignition temperature.e.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.1 no.1
• /
• pp.64-72
• /
• 1997

An analytical study has been performed to investigate the unsteady ignition characteristics of pulse combustion. In many combustion applications, strain rate of the flow can significantly affect the combustion features; ignition, extinction, and reignition. In the pulse combustion, two jets (hot combustion gases and fresh mixtures) coming from the opposite side of the combustor will collide in the combustor forming a stagnation region where the chemical reaction is suppressed by the strain rate until this becomes below the critical value. In this research, the method of large activation energy asymptotic is adopted with one step irreversible kinetics to examine the ignition response to the periodic variation of the strain rate of flow. The results show the variation of the maximum value of strain rate can determine whether the ignition or extinction occur.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.47 no.11
• /
• pp.30-35
• /
• 2010

Network coding is a new research area that may have interesting applications in practical networking systems. With network coding, intermediate nodes may send out packets that are linear combinations of previously received information. The exploration of numerical, theoretical and operational networking issues from new perspectives that consider coding at network nodes. We have presented a network coding approach which asymptotically achieves optimal capacity in multi-source multicast networks. Our analysis uses connections that we make between network coding. In this paper we analysed with and without network coding performance. Also we discussed the simulation results on network coding with linear optimization problem and it shows how network coding can be used.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.2
• /
• pp.277-284
• /
• 1993

Interfacial surface crack perpendicular to the surface, which is imbedded into bonded quarter planes under single anti-plane shear load is analyzed. The problem is formulated using Mellin transform, form which single Wiener-Hopf equation is derived. By solving the equation stress intensity factor is obtained in closed form. This solution can be used as a Green's function to generate the solutions of other problems with the same geometry but of different loading conditions.