• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.5
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• pp.89-100
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• 2001

The Ritz method Is applied In a three-dimensional (3-D) analysis to obtain accurate frequencies for thick. linearly tapered. annular plates. The method is formulated for annular plates haying any combination of free or fixed boundaries at both Inner and outer edges. Admissible functions for the three displacement components are chosen as trigonometric functions in the circumferential co-ordinate. and a1gebraic polynomials in the radial and thickness co-ordinates. Upper bound convergence of the non-dimensional frequencies to the exact values within at least four significant figures is demonstrated. Comparisons of results for annular plates with linearly varying thickness are made with ones obtained by others using 2-D classical thin place theory. Extensive and accurate ( four significant figures ) frequencies are presented 7or completely free. thick, linearly tapered annular plates haying ratios of average place thickness to difference between outer radius (a) and inner radius (b) radios (h$_{m}$/L) of 0.1 and 0.2 for b/L=0.2 and 0.5. All 3-D modes are included in the analyses : e.g., flexural, thickness-shear. In-plane stretching, and torsional. Because frequency data liven is exact 7o a\ulcorner least four digits. It is benchmark data against which the results from other methods (e.g.. 2-D 7hick plate theory, finite element methods. finite difference methods) and may be compared. Throughout this work, Poisson\`s ratio $\upsilon$ is fixed at 0.3 for numerical calculations.s.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.593-599
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• 2007

PC based DVR replaces existing analog CCTV system therefore expands the field and DVR is used for monitoring and security so it requires exact time(clock). But DVR system can't maintains exact clock causing several reasons. For providing exact time information we should use additional system. For economical and usable environment, using GPS system is most suitable suggested solution than use WAN(Wide Area Network). Therefore in this paper for analysis the result of PC based DVR's system clock using GPS system, 1) clock source receiving module that receives the clock form GPS satellite and 2) GPSW H/W units that provide clock source to PC Based DVR 3)Daemon software named PCSW which adjust PC's clock so system could reduced the clock difference with UTC clock and measured the result.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.12
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• pp.1935-1944
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• 1993

We calculate the optimum refractive index and thickness for a single layer antireflection coating as a function of active layer thickness of a laser diode using three different simplified numerical methods. The difference of the results using three methods comes from that of the effective refractive index of a laser used in three methods. We compare three simplified methods to an exact method to check the validity of the simplified methods. We conclude that the simplified method, choosing the effective index of a laser diode as a function of incidence angle of each plane wave composing of a guided mode agree well to an exact method for both TE and TM modes and the cases of strongly and weakly guiding.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.377-383
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• 2011

The paper is to perceive accurately speed of the train through redundant processor operation. When Slip/slide is occurred at the axle, the train is applied brake force using the Tachometer and the Doppler sensor which assistance equipment. One of the main features of railway signaling system is that rolling stock is made stop to avoid collision with the rolling stock ahead when the rolling stock exceeds its maximum operating speed in line. In addition, in the case of the rolling stock with automatic train operation, it carries out activities such as braking and propulsion using the difference between its actual speed and target speed at the point. To perform these functions, it is essential to calculate the exact speed of the rolling stock in signaling equipment on vehicles. Train speed detection unit are composed of the Tachometer and the Doppler sensor, and speed information is sent to the SDU unit. The processor of SDU unit calculates the speed of the train using compare logic the received speed information. Even if there are Slip/Slide, signaling system is available to apply exact braking, to improve stop on position and to guarantee the safety of trains.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.2
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• pp.338-348
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• 1988

This study presents an analysis of periodic heat diffusion in an annular fin with uniform thickness. When the temperature of the fin base is changed in the form of a sinusoidal function, the exact temperature solution can be obtained by Laplace transformation in terms of the dimensionless parameters in the infinite series. Local heat flux and average heat flux, local fin efficiency and average fin efficiency were obtained. Particularly, the table of eigenvalues that are the indispensable condition in solving the heat transfer problem of annular fin in a transient state with convection phenomena at the fin edge is provided. The tables of heat fluxes and average heat fluxes, fin efficiencies and average fin efficiencies are also provided from the computed results. Also, substituting the variations of dimensionless parameters into the these exact solutions, the characteristics of these response are investigated.

• Journal of computational fluids engineering
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• v.12 no.3
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• pp.47-54
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• 2007

A periodic CFD approach for the performance analysis of compact high temperature heat exchangers is introduced and applied to selected benchmark problems, which are a fully developed 2D laminar heat transfer, a conjugate heat transfer between parallel plates which have exact solutions, and a heat transfer in a real high temperature heat exchanger module. The results for the 2D laminar heat transfer and the 2D conjugate heat transfer showed a very good agreement with the exact solutions. For the high temperature heat exchanger module, the pressure drops were predicted well but some difference was observed in the temperature parameters when compared to the full channel CFD analysis due to assumptions introduced into the periodic approach. Considering its assumptions and simplicities, however, the results showed that the periodic approach provides physically reasonable results and it is sufficient to predict the performance of a heat exchanger within an engineering margin and with much less CPU time than the case of a full channel analysis.

• Steel and Composite Structures
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• v.26 no.4
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• pp.453-461
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• 2018

In this paper, nonlinear vibrations of the unsymmetrical laminated composite beam (LCB) on a nonlinear elastic foundation are studied. The governing equation of the problem is derived by using Galerkin method. Two different end conditions are considered: the simple-simple and the clamped-clamped one. The Hamiltonian Approach (HA) method is adopted and applied for solving of the equation of motion. The advantage of the suggested method is that it does not need any linearization of the problem and the obtained approximate solution has a high accuracy. The method is used for frequency calculation. The frequency of the nonlinear system is compared with the frequency of the linear system. The influence of the parameters of the foundation nonlinearity on the frequency of vibration is considered. The differential equation of vibration is solved also numerically. The analytical and numerical results are compared and is concluded that the difference is negligible. In the paper the new method for error estimation of the analytical solution in comparison to the exact one is developed. The method is based on comparison of the calculation energy and the exact energy of the system. For certain numerical data the accuracy of the approximate frequency of vibration is determined by applying of the suggested method of error estimation. Finally, it has been indicated that the proposed Hamiltonian Approach gives enough accurate result.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.225-229
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• 2003

The exact performance simulation of propulsion system is a key element in the prediction of the aircraft performance. The specification performance analysis using the installed loss of KT-1 showed a large difference with the engine performance measured during the flight tests. This indicates that a method to estimate the more exact performance is needed. The study on the performance simulation with performance map correction along the engine operating line shows the good consistent results through all the flight conditions and engine conditions. The correction factors of the map were resulted from the comparative analysis between the flight test and the simulation of installed engine performance.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.5
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• pp.418-426
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• 2003

To show a retina shape and thickness on the computer monitor, a laser has been used in Scanning Laser Ophthalmoscope(SLO) equipment using the traveling difference. This method requires exact synchronous control of laser traveling in optic system to show a clear 3-dimensional image of retina To obtain this image, this exact synchronism is very important for making the perfect plane scanning. In this study, a high speed and synchronous control of the galvanometer to make 3-dimensional retina image is presented. For the more, deadbeat load torque observer is added to the PI controller for compensation of the position error arisen in the high speed control. As a result, the proposed control system has a robust and precise response against the load torque variation appeared in high speed control. A stability and usefulness are verified by the computer simulation and the experiment.

• Journal of Korea Foundry Society
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• v.13 no.4
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• pp.323-332
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• 1993

An implicit finite difference formulation with three methods of latent heat treatment, such as equivalent specific heat method, temperature recovery method and enthalpy method, was applied to solidification analysis. The Neumann problem was solved to compare the numerical results with the exact solution. The implicit solutions with the equivalent specific heat method and the temperature recovery method were comparatively consistent with the Neumann exact solution for smaller time steps, but its error increased with increasing time step, especially in predicting the solidification beginning time. Although the computing time to solve energy equation using temperature recovery method was shorter than using enthalpy method, the method of releasing latent heat is not realistic and causes error. The implicit formulation of phase change problem requires enthalpy method to treat the release of latent heat reasonably. We have modified the enthalpy formulation in such a way that the enthalpy gradient term is not needed, and as a result of this modification, the computation stability and the computing time were improved.