• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.1 s.244
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• pp.8-15
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• 2006

A Sparse Point Representation(SPR) based on interpolation wavelets is presented. The SPR is implemented for the purpose of CFD data compression. Unlike conventional wavelet transformation, the SPR relieves computing workload in the similar fashion of lifting scheme that includes splitting and prediction procedures in sequence. However, SPR skips update procedure that is major part of lifting scheme. Data compression can be achieved by proper thresholding method. The advantage of the SPR method is that, by keeping even point physical values, low frequency filtering procedure is omitted and its related unphysical thresholing mechanism can be avoided in reconstruction process. Extra singular feature detection algorithm is implemented for preserving singular features such as shock and vortices. Several numerical tests show the adequacy of SPR for the CFD data. It is also shown that it can be easily extended to nonlinear adaptive wavelets for enhanced feature capturing.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.6
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• pp.1028-1033
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• 2003

The purpose of this paper is to investigate the noise and vibration characteristics of externally pressurized air journal bearings with a circular slot restrictor. To do this, the nonlinear transient analysis including rotor imbalance was performed for a rotor-bearing system. The effects of radial clearance and the length of the bearing and mass eccentricity of the rotor on the noise and vibration characteristics of the bearing are also examined. The results show that the noise and vibration of the rotor-bearing system first increase up to critical speed of the system, and then decrease up to instability threshold speed of the system as the rotational speed of the rotor increases, and the noise of the bearing is markedly influenced by the mass eccentricity of the rotor and the radial clearance and the length of the bearing.

• Advances in aircraft and spacecraft science
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• v.4 no.4
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• pp.437-448
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• 2017

The problem of flow through the vent is formulated as an unsteady, nonlinear, ordinary differential equation and solved using Runge-Kutta method to obtain pressure inside payload faring. An inverse problem for prediction of the discharge coefficient is presented employing measured internal pressure of the payload fairing during the ascent phase of a satellite launch vehicle. A controlled random search method is used to estimate the discharge coefficient from the measured transient pressure history during the ascent period of the launch vehicle. The algorithm predicts the discharge coefficient stepwise with function of Mach number. The estimated values of the discharge coefficients are in good agreement with differential pressure measured during the flight of typical satellite launch vehicle.

• The Journal of the Acoustical Society of Korea
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• v.5 no.1
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• pp.11-16
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• 1986

지금까지 알려진 여러 가지 음성부호화 방식들 중 4.8에서 9.6kbits/s 사이의 전송속도에서 제일 좋은 성능을 갖는 것은 Residual-Excited linear prediction 방식이다. RELP 부호화 방식은 전송속도가 낮을 때 합성음이 거칠거나 금속성의 잡음을 갖는 단점이 있다. 본 논문에서는 이러한 단점을 보완하여 음질을 개선하는 세가지의 방법들을 제안하며, 그들은 다음과 같다. 첫째는 여러개의 baseband를 이용한 spectral folding 방법이고, 둘째는 spectral folding 방법과 pulsed excitation 방법을 조합한 방법이며, 마 지막 방법은 여러개의 baseband를 사용한 spectral folding 방법과 pulsed excitation 방법을 조합한 방법 이다. 이 방법들을 사용하여 RELP vocoder의 음질을 많이 개선할 수 있으며, 9.6kbits/s 근처의 전송속 도에서 사용하기 위한 첫 번째 방법과 세 번째 방법은 spectral fording 이나 nonlinear distortion 방법 에서 문제가 되는 roughness 나 tonal noise를 거의 인지 할 수 없으며, 세 번째 방법이 첫 번째 방법보 다 우수하다. 두 번째 방법은 4.8 kbits/s 근처의 전송속도에 적합하며, 기존의 RELP 방식들에 비해 많 은 음질향상을 가져왔다. 제안한 세가지 방법들을 같은 조건에서 비교할 때 세 번째 방법이 가장 우수 하며, 이 경우 합성음은 원음과 거의 흡사하다.

• Journal of the Korea Society for Simulation
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• v.14 no.4
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• pp.55-68
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• 2005

The advancement in semiconductor technology is leading toward smaller critical dimension designs and larger wafer manufactures. Due to such phenomena, semiconductor industry is in need of an accurate control of the process. Photolithography is one of the key processes where the pattern of each layer is formed. In this process, precise superposition of the current layer to the previous layer is critical. Therefore overlay parameters of the semiconductor photolithography process is targeted for this research. The complex relationship among the input parameters and the output metrologies is difficult to understand and harder yet to model. Because of the superiority in modeling multi-nonlinear relationships, neural networks is used for the simulator modeling. For training the neural networks, conjugate gradient method is employed. An experiment is performed to evaluate the performance among the proposed neural network simulator, stepwise regression model, and the currently practiced prediction model from the test site.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.123-128
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• 1996

Water in concrete has an effect on properties of concrete very much, such as shrinkage, creep, fire resistance, durability, freezing and thawing resistance. Therefore predicting the moisture distribution in concrete is very important. And since the diffusion process of water in concrete is strongly dependent on the temperature and pore humidity, the process is highly nonlinear phenomena. In this study, a finite element program which was capable of simulating the moisture distribution in concrete was developed, and differential drying shrinkage due to the water diffusion process was measured at the different positions of concrete. This F.E.M. program is shown that the analytical results of this study are in good agreement with experimental data. Shrinkage strain caused by moisture distribution was increased with the decrease of pore relative humidity.

• Journal of Ocean Engineering and Technology
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• v.16 no.1
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• pp.41-45
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• 2002

This paper is concerned with the erection and ultimate load test of dome shaped space structures by post-tensioning. It is a fast and economical method for constructing such a dome by post-tensioning of the cable in bottom chords. This structure consists of uniform pyramids in a flat layouts on the ground, and then the structure is shaped and erected into its final curved space structure. Ultimate load test was performed for dome shaped space structures. The feasibility of the proposed erection method and the reliability of the established geometric model were confirmed with numerical analysis and experimental investigation on a small scale steel model. As a results we can find the most reasonable modeling technique for the prediction of shape formation in practices and we can know the characteristic of the behaviour in ultimate load test for practical design purposes.

• Journal of Advanced Research in Ocean Engineering
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• v.4 no.3
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• pp.135-145
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• 2018

This paper deals with the added resistance of a ship in waves using computational fluid dynamics (CFD). The ship added resistance is one of the key considerations in the design of energy-efficient ship. In this study, the added resistance of a LNG carrier in head waves is computed using a CFD code to consider the nonlinearity and the viscous effects. The unsteady Reynolds Averaged Navier-Stokes equation (RANS) is numerically solved and the volume of fluid (VOF) approach is used to simulate the free surface flows. The length of incident wave varies from half the ship length to twice the ship length. To investigate the nonlinearity effect, both the linear wave condition and the nonlinear wave condition are considered. The heave and pitch motions are calculated along with the added resistance, and the wave contours are obtained. Grid convergence test is conducted thoroughly to achieve the converged motion and resistance values. The calculated results are compared and validated with experimental data.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.79-82
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• 2003

With the wide application of fiber-reinforced composite material in aero-structures and mechanical parts, the design of composite joint have become a very important research area because they are often the weakest areas in composite structures. In this paper, the failure area index method to predict the failure load of the mechanically fastened composite joint was used and the prediction accuracies of the linear finite element analysis were compared with those of nonlinear finite element analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.8
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• pp.773-778
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• 2009

Chevron rubber springs are used in primary suspensions for rail vehicle. Chevron rubber spring have function which reduce vibration and noise, support load carried in operation of rail vehicle. Prediction and evaluation of characteristics are very important in design procedure to assure the safety and reliability of the rubber spring. The computer simulation using the nonlinear finite element analysis program executed to predict and evaluate the load capacity and stiffness for the chevron spring. The non-linear properties of rubber which are described as strain energy functions are important parameters. These are determined by material tests which are uniaxial tension, equi-biaxial tension and shear test. The appropriate shape and material properties are proposed to adjust the required characteristics of rubber springs in the three modes of flexibility.