• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.2
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• pp.243-253
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• 1999

The dual reciprocity boundary element method (DRBEM) is used to solve the Graetz problem of laminar flow inside circular duct. In this method the domain integral tenn of boundary integral equation resulting from source term of governing equation is transformed into equivalent boundary-only integrals by using the radial basis interpolation function, and therefore complicate domain discretization procedure Is completely removed. Velocity profile is obtained by solving the momentum equation first and then, using this velocities as Input data, energy equation Is solved to get the temperature profile by advancing from duct entrance through the axial direction marching scheme. DRBEM solution is tested for the uniform temperature and heat flux boundary condition cases. Local Nusselt number, mixed mean temperature and temperature profile inside duct at each dimensionless axial location are obtained and compared with exact solutions for the accuracy test Solutions arc in good agreement at the entry region as well as fully developed region of circular duct, and their accuracy are verified from error analysis.

• The Journal of the Acoustical Society of Korea
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• v.18 no.8
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• pp.48-53
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• 1999

This paper presents an analytic derivation of the erroneous effect when the sliding-DFT is implemented in a recursive way with the finite-bit approximation of the twiddle factors. The analysis result is obtained in a closed form equation of the noise-to-signal power ratio(NSR) employing the zero-mean white Gaussian signal as the target input of the DFT. The parameters of the wordlength used in representing the twiddle factors and the blocklength of the DFT appear in the NSR explicitly as its function variables. The derivation is based on the error dynamic equation which is derived from the recursive SDFT, and on the analytic exploration of the statistical characteristics of the approximation coefficients treating them as random variables of having spatial distributions. The analytically derived results are verified through the comparison with the data actually measured from the computer simulation experiment.

• Korean Journal of Materials Research
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• v.11 no.10
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• pp.841-845
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• 2001

The steam generator tubes of power plant damaged by sliding wear due to flow-induced motion of foreign object. Amount of wear have been predicted by Achard's wear equation until now. However, there are large error and low reliability, because this equation regards wear coefficient(k) as constant. The sliding wears tests have been performed at room temperature to examine parameters of wear (wear distance, contact stress). The steam generator tube material for wear test is used Inconel 600 and foreign object material is used 304 austenite stainless steel. The sliding wear tests show that the amount of wear is not linearly proportional to the wear distance(for 374 austenite stainless steel). According to experimental result, wear coefficient is not constant k but function k(s) of wear distance. The newly modified wear predictive equation V=k(s)F have small error and high reliability.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.4
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• pp.11-20
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• 1994

The error rate equation of DS-CDMA/DQPSK skgnal adopting ARQ scheme has been derived in indoor radio channel which is characterized by AWGN, multi-user interference (MUI) and Rician fading, Using the derived equation the error performance has been evaluated and shown in figures as a function of direct to diffuse signal power ratio(KS1rT), the number of active users (K), PN code sequence length (N), the number of parity bit of linear code (b), forward channel BER, and ES1bT/NS1OT. From the results it is known that in severe fading environments (KS1rT=6) the performance of DS-CDMA/DQPSK system is not reliable so it is needed to adopt techniques for improvement. When an ARQ scheme is adopted, as a method for improving error performance, the performance improves compared with that of non-ARQ scheme and the degree of improvement is proportional to the number of parity bits of linear code. As increasing the number of parity bits, system performance is improved vut system throughput efficiency must be considered. In severe fading channel Hybrid ARQ scheme is more effective than ARQ scheme. As a result, ARQ scheme is appropriate for the high-reliability data communication systems over the radio channel in which the real time processing is not required.

• Journal of the Korean Mathematical Society
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• v.61 no.4
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• pp.621-657
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• 2024

In this study, the numerical solution of a space-fractional Burgers' equation with initial and boundary conditions is considered. This equation is the simplest nonlinear model for diffusive waves in fluid dynamics. It occurs in a variety of physical phenomena, including viscous sound waves, waves in fluid-filled viscous elastic pipes, magneto-hydrodynamic waves in a medium with finite electrical conductivity, and one-dimensional turbulence. The proposed QBS/CNG technique consists of the Galerkin method with a function basis of quadratic B-splines for the spatial discretization of the space-fractional Burgers' equation. This is then followed by the Crank-Nicolson approach for time-stepping. A linearized scheme is fully constructed to reduce computational costs. Stability analysis, error estimates, and convergence rates are studied. Finally, some test problems are used to confirm the theoretical results and the proposed method's effectiveness, with the results displayed in tables, 2D, and 3D graphs.

• Tribology and Lubricants
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• v.36 no.2
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• pp.68-74
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• 2020

In this study, the effect of the shape error of a guideway on the movement of a stage that uses an air bearing is analyzed. The shape error of moving parts supported by the air bearing is known not to affect the vibrations of moving parts as much as the magnitude of the shape error. This is called the "averaging effect." In this study, the effect of shape error on a guideway, as well as the averaging effect of an air-bearing system, is analyzed theoretically using a dynamic-analysis program. The dynamic-analysis program applies a commercially available code in COMSOL and solves the Reynolds equation between the stage and the guideway, along with the equation of motion of the stage. The stage is modeled as a two-degree-of-freedom system. The shape error is applied to the film thickness function in the form of a sine wave. The stage movement is analyzed using the fast Fourier transform process. The eccentricity and tilting are found to be proportional to the amplitude of the shape error of the guideway. Stage vibrations are less than 10% of the amplitude of the shape error on the guideway. This means that the averaging effect of the air bearing is verified quantitatively. Moreover, if the air supply position matches the shape error in the guideway, there is a notable change in eccentricity and tilting.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.7189-7195
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• 2015

The method of moments (MoM) is implemented to simulate scattering from a PEC (perfectly electric conductor) cylinder in the TE(transversw electric) EFIE (Electric Field Integral Equation) approach. The procedure expresses the singularity integral and the hypersingularity integral in terms of an analytic function and employs a singularity isolation process coupled with numerical technique along the discretized segment to evaluate the self terms. It is known that, in the MoM technique, the choice of base functions and test functions is very important for the accuracy and convergence of the numerical analysis. Thus, in this paper, three conditions, obtained from the combination of basis functions and test functions, are adopted to get the induced currents on the PEC surface. These currents are compared to the analytical one in the relative rms current error to get the condition that shows fast convergence rate. The fast order of convergence of the current error, 2.528, is obtained under the combination of pulse basis function/delta test function.

• Journal of Internet Computing and Services
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• v.25 no.2
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• pp.93-99
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• 2024

In this paper, we derive the Partial Differential Bond Price Equation (PDBPE) by using Ito's Lemma to determine the pricing of bond on term-structure of interest rate (TSIR) model with jump. From PDBPE, the Maclaurin series (MS) and the moment-generating function (MGF) for the exponential function are used to obtain a numerical solution (NS) of the bond prices. And an algorithm for determining bond prices using Monte Carlo Simulation (MCS) techniques is proposed, and the pricing of bond is determined through the simulation process. Comparing the results of the implementation of the above two pricing methods, the relative error (RE) is obtained, which means the ratio of NS and MCS. From the results, we can confirm that the RE is less than around 2.2%, which means that the pricing of bond can be predicted very accurately using the proposed algorithms as well as numerical analysis. Moreover, it was confirmed that the bond price obtained using the MS has a relatively smaller error than the pricing of bond obtained by using the MGF.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.528-538
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• 1985

A R-S-S-R three dimensional mechanism is designed for crank-rocker type through the optimization technique. The nonlinear kinematic equation of the mechanism is formulated by adopting the concept of structural error and precision points. Taking this equation as an objective function, the required mechanism is optimally synthesized by the Fletcher-Davidon-Powell's method of optimization techniques. The structural errors due to the various positions of precision points are compared, and the results from the use of two penalty functions suggested respectively by Fiacco-McCormick and by Powell are also compared on their effectiveness. The mobility of the optimally designed mechanism is checked for the possibility of its motion, and when a mechanism is optimally designed, it is strongly suggested that the mobility must be checked on the designed mechanism.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2023.05a
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• pp.254-255
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• 2023

This paper discovers a robust managerial strategy for a stochastic inventory of perishable products, where the model experiences changing factors including inner parameters and an external disturbance with unknown form. An analytical solution for the optimization problem can be obtained by applying the Hamilton-Bellman-Jacobi equation, however the policy result cannot completely suppress the oscillation from the external disturbance. Therefore, an intelligent approach named Radial Basis Function Neural Networks is applied to estimate the unknown disturbance and provide a robust controller to manipulate the inventory level more effective. The final results show the outstanding performance of RBFNN controller, where both the estimation error and control error are guaranteed in the predefined limit.