• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.04a
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• pp.43-51
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• 1997

Steady and unsteady numerical simulations are conducted for the experiments performed to investigate the ram accelerator flow field by using the expansion tube facility in Stanford University. Navier-Stokes equations for chemically reacting flows are analyzed by fully implicit and time accurate numerical methods with Jachimowski's detailed chemistry model for hydrogen-air combustion involving 9 species and 19 reaction steps. Although the steady state assumption shows a good agreement with the experimental schlieren and OH PLIF images for the case of $2H_2$+$O_2$+$17N_2$, it fails in reproducing the combustion region behind the shock intersection point shown in the case of $2H_2$+$O_2$+$12N_2$, mixture. Therefore, an unsteady numerical simulation is conducted for this case and the result shows all the detailed flow stabilization process. The experimental result is revealed to be an instantaneous result during the flow stabilization process. The combustion behind the shock intersection point is the result of a normal detonation formed by the intersection of strong oblique shocks that exist at early stage of the stabilization process. At final stage, the combustion region behind the shock intersection point disappears and the steady state result is retained. The time required for stabilization of the reacting flow in the model ram accelerator is found to be very long in comparison with the experimental test time.

• Korea-Australia Rheology Journal
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• v.19 no.4
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• pp.211-219
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• 2007

Here we demonstrate complex transient behavior of viscoelastic liquid described numerically with the Leonov model in straight and contraction channel flow domains. Finite element and implicit Euler time integration methods are employed for spatial discretization and time marching. In order to stabilize the computational procedure, the tensor-logarithmic formulation of the constitutive equation with SUPG and DEVSS algorithms is implemented. For completeness of numerical formulation, the so called traction boundaries are assigned for flow inlet and outlet boundaries. At the inlet, finite traction force in the flow direction with stress free condition is allocated whereas the traction free boundary is assigned at the outlet. The numerical result has illustrated severe forward-backward fluctuations of overall flow rate in inertial straight channel flow ultimately followed by steady state of forward flow. When the flow reversal occurs, the flow patterns exhibit quite complicated time variation of streamlines. In the inertialess flow, it takes much more time to reach the steady state in the contraction flow than in the straight pipe flow. Even in the inertialess case during startup contraction flow, quite distinctly altering flow patterns with the lapse of time have been observed such as appearing and vanishing of lip vortices, coexistence of multiple vortices at the contraction comer and their merging into one.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.848-854
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• 2006

In this study, a computational analysis system has been developed in order to investigate flow-induced vibration(FIV) phenomenon for general stator-rotor cascade configurations. Relative movement of the rotor with respect to stator is reflected by modeling independent two computational domains. Fluid domains are modeled using the unstructured grid system with dynamic moving and local deforming methods. Unsteady, Reynolds-averaged Navier-Stokes equations with one equation Spalart-Allmaras and two-equation SST $k-\omega$ turbulence models are solved for unsteady flow problems. A fully implicit time marching scheme based on the Newmark direct integration method is used flow computing the coupled governing equations of the fluid-structure interaction problem. Detailed FIV responses for different flow conditions are presented with respect to time and vibration characteristics are also physically investigated in the time domain.

• Journal of Korea Multimedia Society
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• v.4 no.3
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• pp.270-279
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• 2001

Since most program execution time is spent in the loop structure, extracting parallelism from sequential loop programs hale been focused. But, most programs hare implicit parallelism of interprocedure. This paper presents a generalized Parallelism extraction in loop\ulcorner with procedure calls. Most parallelization of loops with Procedure calls just focus on the uniform code which data dependency distance is constant. We presents algorithms which can be applied with uniform code, nonuniform code, and complex code. The proposed algorithm, loop extraction, loop embedding and procedure cloning transformation methods evaluate using CRAY-T3E. The result of performance evaluation is that proposed algorithm is an effect.

• Journal of Ocean Engineering and Technology
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• v.25 no.6
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• pp.116-122
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• 2011

A realtime simulator using an explicit integration method is introduced to improve the solving performance for the dynamic analysis of a wheeled vehicle. Because a full vehicle system has many parts, the development of a numerical technique for multiple d.o.f. and ground contacts has been required to achieve a realtime dynamics analysis. This study proposes an efficient realtime solving technique that considers the wheeled vehicle dynamics behavior with full degrees of freedom and wheel contact with soft ground such as sand or undersea ground. A combat vehicle was developed to verify this method, and its dynamics results are compared with commercial programs using implicit integration methods. The combat vehicle consists of a chassis, double wishbone type front and rear suspension, and drive train. Some cases of vehicle dynamics analysis are carried out to verify the realtime ratio.

• Journal of the Korea Computer Industry Society
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• v.2 no.8
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• pp.1025-1034
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• 2001

We suggest how to use DSS(Decision Support System) as one alternative way of taking advantage of IT in order to develop and maintain Knowledge-Intensive Organization. As organizations support decision making by structuring decision making process, each organization should share implicit knowledge with each member and convert it into explicit one through structuring and synthesizing. Also we show that knowledge management system, which has not been efficiently applied to organization until now, could be used by DSS. Though there are not many cases of successful use of KMS benifits to provide such functions as share, synthesize and solve with organization, it is expected to use DSS frequently by adopting these If methods for achieving and maintaining Knowledge-Intensive Organization.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.117-120
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• 2005

The present study describes unsteady flow phenomena generated in a supersonic flow passing over a rectangular cavity and suggests a way of control of pressure oscillation, doing harm to overall performance and stable operation of aerodynamic and industrial applications. The three-dimensional, unsteady, compressible Navier-stokes equations are numerically solved based on a fully implicit finite volume scheme and large eddy simulation. The cavity flow are simulated with and without control methods, including a triangular bump and blowing jet installed near the leading edge of the cavity. The results show that the pressure oscillation is attenuated by both control techniques, especially near the trailing edge of cavity.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.157-163
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• 2003

A systematic numerical experiment has been conducted to study droplet gasification in high pressure environments with pressure oscillations. The general frame of previous rigorous model[1] is retained but tailored for flash equilibrium calculation of vapor-liquid interfacial thermodynamics. Time-dependent conservation equations of mass, momentum, energy, and species concentrations are formulated in axisymmetric coordinate system for both the droplet interior and ambient gases. In addition, a unified property evaluation scheme based on the fundamental equation of state and empirical methods are used to find fluid thermophysical properties over the entire thermodynamic domain of interest. The governing equations with appropriate physical boundary conditions are numerically time integrated using an implicit finite-difference method with a dual time-stepping technique. A series of calculation have been carried out to investigate the gasification of an isolated n-pentane droplet in a nitrogen gas environment over a wide range of ambient pressures and frequencies. Results show that the mean pressures and frequencies of the ambient gas have strong influences on the characteristics of the droplet gasification. The amplitude of the response increases with increasing pressure, and the magnitude of the vaporization response increases with the frequency.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.178-184
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• 2007

A new adaptive alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is proposed to obtain isotropic wave propagation for all directional angles. We add the square terms of time-step multiplied by the spatial derivatives of x and y as a perturbed term to the conventional ADI-FDTD and can find the optimization coefficient of square terms of time-step to generate the minimum anisotropy. The new ADI-FDTD is also stable, even when its time-step is greater than the Courant-Friedrich-Levy (CFL) limit. The characteristic equation of the dispersion relation governing the new method is derived and compared with the theoretical and numerical results for the conventional ADI-FDTD and perturbed ADI-FDTD methods.

• Korean Journal of Social Welfare
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• v.46
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• pp.7-36
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• 2001

The current benefit expenditure of National Pension Scheme is comparatively small, as it stands in the early stage in reference to the historical development. On the other hand, the current contribution rate of National Pension is set up beyond which is sufficient to cover the current benefit expenditure. Therefore, National Pension makes big surplus every year such that the size of accumulated fund increases very fast. Nevertheless, the apprehension of financial instability of National Pension prevails these days. If so, is it really well-grounded? In terms of the method of financing. public pension schemes of most of all nations in the world are based on pay-as you go or partial funding. Under these financing methods, financial soundness fundamentally depends on the power that the government is able to impose the burden which is equivalent to benefit expenditure and the attitude of the public which represents whether they will admit it or not. Under this perspective, the judgement of financial soundness of public pension can not be made arithmetically and technically only on the basis of the balance between receipts and expenditure but should be accomplished considering the very complex and diverse aspects. In these context, this paper defines what the financial soundness of public pension means specifically and presents the objective indices which help judge it, that is, implicit debt, cost rate, summarized cost rate, pension expenditure as percentage of GDP, and fund rate. Then, applying the indices, this paper analyzes the long-term financial situation of National Pension empirically and evaluates its financial soundness in exploratory perspective.