• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.3
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• pp.204-212
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• 2002

The ride comfort is one of the important dynamic performances of railway vehicle and is affected by the various factors, such as vibration, sound, temperature, humidity, etc. In general, vibration is known to be a major effect of rode comfort. There are many studies on the evaluation methods of ride comfort in the railway vehicle vibration. Each of the evaluation methods suggested by Spelling and in the standards recommends a different evaluation method and guidance. So users must review whether they can apply it to their railway system or not. In this study, we have suggested the relationship between several evaluation methods using the statistical vibration model based on the experimental data.

• Wind and Structures
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• v.31 no.3
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• pp.209-216
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• 2020

Aiming at the wind-resistant design of a sea-crossing arch bridge, the static aerodynamic coefficients of its girder (composed of stretches of π-shaped cross-section and box cross-section) were studied by using computational fluid dynamics (CFD) numerical simulation and wind tunnel test. Based on the comparison between numerical simulation, wind tunnel test and specification recommendation, a combined calculation method for the horizontal force coefficient of intermediate and small span bridges is proposed. The results show that the two-dimensional CFD numerical simulations of the individual cross sections are sufficient to meet the accuracy requirements of engineering practice.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.3
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• pp.753-762
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• 1996

In this paper, aperture coupled stacked microstrip array antennas are proposed and their operating characteristics are analyzed based on analytical. In order to evaluate mutual coupling between slot-coupled microstrip patches in finite array, analysis uses the reciprocity theorem and the spectral domain Green's functions for dielectric slab in a moment method solution for the unknown patches and solts current distrbution. By introducing an N-port equivalent network, the impedance matrix of an affay of N-element slot-coupled patches is evaluated directly from its network current matix of order N$^{2}$, and it can be programmed to be run on a PC. Numerical results show mutual coupling, radiation pattern, active reflection coefficient versus scan angle, radiation efficiency and active element gain pattern.

• Wind and Structures
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• v.1 no.3
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• pp.271-284
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• 1998

This paper uses the numerical simulation to investigate the interference effect of 3-D turbulent flow around two high rise buildings in proximity at the different relative heights, gaps, and wind velocities. The computer program used to carry out the simulation is based on the control volume method and the SIMPLEST algorithm. The ${\kappa}-{\varepsilon}$ model was used to simulate turbulence effects. Since the contracted flow between two adjacent buildings enhances the strength of vortex shedding from the object building, the pressure coefficient on each side wall of the object building is generally increased by the presence of apposed building. The effect is increased as the relative height or the gap between the two buildings decreases. The velocity on the vertical center line between two buildings is about 1.4 to 1.5 times the upstream wind velocity.

• Nuclear Engineering and Technology
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• v.3 no.2
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• pp.59-64
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• 1971

This paper presents an approach to control that if a result of modern control theory, and is based on tile control philosophy of feeding back all tile state variable through constant gain frequency independent elements. The values of these elements or feedback coefficients are determined by equating like coefficients of the desired system transfer function to the transfer function of the system containing the unspecified coefficient s. This application of modern control law is a simple design method depending on feedingback all the system variables for reactor control and it is particuraly amenable to the control of Pressurized Water Reactor.

• Bulletin of the Society of Naval Architects of Korea
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• v.20 no.2
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• pp.27-36
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• 1983

This paper presents numerical results of the added mass and damping coefficients of vertical axisymmetric bodies on or under the free surface. Also computed are the excitation forces on these bodies due to an incident regular wave system. The numerical scheme employs a localized finite-element method, which is based on the theory of the calculus of variations. The excitation forces and moments on a submerged half-spheroid lying on the bottom are computed and compared with the results obtained by others. he agreement is good. Several specific types of floating vertical axisymmetric platforms are considered for ten different wave lengths, in connection with the design of an ocean-thermal-energy converter platform. The added mass and damping coefficient, as well as the excitations, are presented. It is shown that simple strip theory gives a good approximation of the sway(and pitch) added mass for a disc platform having a long circular cylinder.

• Nuclear Engineering and Technology
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• v.44 no.6
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• pp.683-688
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• 2012

The structural integrity of mechanical components during several transients should be assured in the design stage. This requires a fatigue analysis including thermal and stress analyses. As an example, this study performs a fatigue analysis of the reactor pressure vessel of SMART during arbitrary transients. Using heat transfer coefficients determined based on the operating environments, a transient thermal analysis is performed and the results are applied to a finite element model along with the pressure to calculate the stresses. The total stress intensity range and cumulative fatigue usage factor are investigated to determine the adequacy of the design.

• Transactions of Materials Processing
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• v.13 no.8
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• pp.696-703
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• 2004

The purpose of this study is to examine the bulk/sheet forming characteristics of bulk amorphous alloys in the super cooled liquid state. Recently it is reported that amorphous alloys exhibit stress overshoot/undershoot and non-Newtonian behaviors even in the super cooled liquid state. The stress-strain curves with the temperature-dependences as well as strain-rate dependence of Newtonian/non-Newtonian viscosities of amorphous alloys are obtained based on the previous experimental works. Then, those curves are directly used in the thermo-mechanical finite element analyses. Upsetting and deep drawing of amorphous alloys are simulated to examine the effects of process parameters such as friction coefficient, forming speed and temperature. It could be concluded that the superior formability of an amorphous alloy can be obtained by taking the proper forming conditions.

• Journal of the Korean Institute of Telematics and Electronics
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• v.19 no.4
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• pp.1-5
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• 1982

A new algorithm, based upon a lattice formulation, is presented for linear prediction. The output of the algorithm is the reflection coefficients that guarantee the stability of the all-pole model. The equations are derived that compute the covariance of the residuals recursively at each prediction stage, and in processing of computing that eqations, the reflection coefficients are estimated without computing the predictor coefficients. Comparing with covariance-lattice method, it can be said that the new algorithm reduce the number of computations to about half and is more efficient for fitting of the high-order model.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1471-1473
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• 2000

In this study capacitance and dielectric loss factor were measured with low-voltage signal and the simulation of equivalent circuits for the data were conducted. As the result it was showed that the equivalent circuit model considered the gram-boundary structure with semiconducting layer, dielectric layer and depletion layer was well approximated with the observed data. Various parameters were determined by a optimum curve-fitting method and could be used to analyze the varistor-voltages and the nonlinear coefficient of varistors. It also seems that the proposed equivalent circuit model will be adopted for other BL type varistors.