• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3119-3124
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• 2010

The purpose of this paper is to analyze dynamic behaviors of the oil film thickness and engine bearings in both aligned and misaligned operation conditions of a crankshaft using computer simulation techniques. A crankshaft as an elastic body is modeled for a misaligned crankshaft which is very important design parameter of the film thickness and engine bearings. In this analysis, a dynamic characteristic of a minimum oil film is analyzed based on the elastohydrodynamic lubrication theory. The boundary conditions for analyzing the film behaviors include non-linear constraint forces and bending moments in engine bearings. The more expedient model of an engine bearing is extended to consider the effect of crankshaft misalignment. The computed results indicate that the minimum oil film thickness that causes a major influence on the performance of engine bearings has showed a decrease of 16% to 24% for the misaligned crankshaft compared with an aligned crankshaft. The computed results show that the misalignment of a crankshaft inevitably brings the reduction of minimum oil film thickness and this may increase the failure of a bearing. These results as design parameters are very useful for a bearing designer as a firm reference data of an automotive engine.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.12
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• pp.2963-2967
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• 2015

The pump-probe scheme is used to analyze the cross-phase modulation penalty of a single-mode fiber in a WDM system. The pump signal is assumed to be a periodically modulated input like a raised sinusoidal. The periodic signal models an alternating bit sequence, and leads to an analytical expression of CPM penalty which is measured by EOP. The derived expression shows good agreement with numerical results in conventional single-mode fiber systems over a wide range of channel spacing, ${\Delta}f$. In dispersion-shifted fiber systems when ${\Delta}f$ < 100GHz, the derived expression shows increased discrepancy with the numerical results due to the increased FWM. This is not a surprising because the pump-probe scheme is used to analyze system performance degradation due to CPM.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.328-336
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• 1999

To characterize the hydro-mechanical behavior of a rock joint, a rotary shear testing apparatus was devised in this study. Shear stress was driven by twisting the end of a sample in the rotary shear testing apparatus. The test results show that the rotary shear test underestimates the peak shear strength of a rock joint. The torque is known as a function of the radial distance from the axis of rotation, resulting in the radial variation of the shear stress. Fluid flow through rock joints is mainly dependent on the Joint roughness, contact area, initial aperture. To examine the dependency, the relationship between the hydraulic and the mechanical apertures for shear-flow was established by measuring the initial aperture. It shows that the mechanical aperture and the hydraulic aperture increase linearly with the dilatancy. The difference between the hydraulic and mechanical apertures describes the deviation from the behavior predicted by the parallel plate model.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.489-494
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• 2013

This study aims to understand the mode characteristics of a droplet under a periodic forced vibration. To predict the resonance frequency of a droplet, theoretical and experimental approaches were employed. A high-speed camera was used to capture the various deformation characteristics of a droplet-mode shape, detachment, separated secondary droplet, and skewed deformation. The comparison between the theoretical and the experimental approaches shows a ~10% discrepancy in the prediction of the resonance frequency, which appears to be caused by the effect of contact line friction, nonlinear wall adhesion, and experimental uncertainty. Owing to contact-line pinning and smaller amplitude, the droplet shape becomes symmetric and the size of each lobe at the resonance frequency exceeds that at the neighbor, which is out of resonance.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2015.07a
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• pp.78-80
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• 2015

광적응(Luminance Adaptation; LA) 효과는 영상의 배경 밝기에 따른 왜곡에 대한 시각 인지 민감도가 달라지는 특성을 의미한다. 기존 영상 화질 측정(Image Quality Assessment; IQA) 방법들은 베버의 법칙(Weber' s law) 모델을 이용하여 LA 효과를 IQA 방법에 반영해왔다. 그러나, 이러한 IQA 방법들에 있어서 베버의 법칙 기반 LA 효과 모델은 다음 두 가지 이유로 부정확하게 동작한다: (i) 전통적인 베버의 법칙 모델은 실제 광도(luminance)에 대한 인지 민감도 응답값을 정확히 반영할 수 없다는 것이 밝혀졌다, (ii) 대부분 IQA 방법들은 픽셀 강도 영역에서 계산되지만, 베버의 법칙과 같은 LA 효과 모델들은 광도 영역에서 개발되었다. 따라서 광도와 픽셀 강도간 비선형 관계로 인해 IQA 방법에 반영된 베버의 법칙 기반 LA 효과 모델들은 부정확하게 동작한다. 이 문제를 해결하기 위해, 본 논문에서 처음으로 픽셀 강도 영역에서의 LA 모델을 이론적으로 유도한다. 본 논문에서 제안하는 픽셀 강도 영역에서의 LA 효과 모델은 감마 교정 함수(Gamma correction function)와 광도 영역에서의 LA 효과 모델인 제곱-법칙(power-law) 모델을 기반으로 하는 테일러 급수 확장 근사화를 통해 유도된다. 제안하는 픽셀 강도 영역 LA 효과 모델의 효과를 검증하기 위해, 제안하는 LA 효과 모델을 PSNR 에 도입하여 광범위한 실험을 수행한다. 실험 결과, 제안하는 LA 효과 모델 기반 PSNR 은 PSNR 및 베버의 법칙 기반 PSNR 대비 괄목할 만한 주관적 화질 예측 성능 향상을 보였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.2
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• pp.408-414
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• 2005

The VCDRO(Voltage Controlled Dielectric Resonate. Oscillator) with low phase noise is designed using nonlinear analysis, and its phase noise characteristics are compared with that of Lesson's equation. The microstripline coupled with dielectric resonator is realized as a high impedance inverter to improve the phase noise performance, and the quality factor of resonator circuit can be transferred to active device with the enhanced the loaded quality factor. The worst case and part stress analyses are achieved to obtain the high reliability of VCDRO and the reliability analysis is accomplished to estimate the probability of operation at the end of life. The developed VCDRO has the oscillating tuning factor of 0.56MHZ1V for the control voltage range of 0-l2V. This VCDRO requires the DC power of 136mW. The phase noise characteristics exhibit good performances of -94.18dBc/Hz (a)10KHz and -116.3dBc/Hz (a)100KHz. And, the output power over 7.33dBm is measured.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.11
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• pp.2488-2497
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• 1997

In this paper, a computer simulation of the Lornz discrete chaotic system is described. The chotic behavior closely matches the results predicted by numerical simulations. Using the concept of discrete synchronized chaotic systems, the possibility of a secure communication is proved by simulating the Lorenz system in both the transmitter and receiver. In the proposed approach, at first, a chaotic modulating signal is multiplied with the message, and these are transmitted with adding a chaotic modulating signals, and then at the receiver, the chaotic modulating signal is regenerated and divided from the receiver signal. Varying a smapling time interval to calibrate the robustness of the Lorenz discrete synchronized chaotic system as a nonlinear state estimator, we measured the performance of the Lorenz discrete syncrhonized chaotic system by comparing the synchronization error and the error between transmitted signal and received signal.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.4
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• pp.274-282
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• 2014

Time series of the dynamic response of a slender marine structure was predicted using quadratic Volterra series. The wave-structure interaction system was identified using the NARX(Nonlinear Autoregressive with Exogenous Input) technique, and the network parameters were determined through the supervised training with the prepared datasets. The dataset used for the network training was obtained by carrying out the nonlinear finite element analysis on the freely standing riser under random ocean waves of white noise. The nonlinearities involved in the analysis were both large deformation of the structure under consideration and the quadratic term of relative velocity between the water particle and structure in Morison formula. The linear and quadratic frequency response functions of the given system were extracted using the multi-tone harmonic probing method and the time series of response of the structure was predicted using the quadratic Volterra series. In order to check the applicability of the method, the response of structure under the realistic ocean wave environment with given significant wave height and modal period was predicted and compared with the nonlinear time domain simulation results. It turned out that the predicted time series of the response of structure with quadratic Volterra series successfully captures the slowly varying response with reasonably good accuracy. It is expected that the method can be used in predicting the response of the slender offshore structure exposed to the Morison type load without relying on the computationally expensive time domain analysis, especially for the screening purpose.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.10
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• pp.809-815
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• 2014

The co-bonded dissimilar composite under a wide range of temperature change shows thermal distortion due to the differences in thermal expansion characteristics of the composite materials. Analysis of the thermal expansion characteristics of each composite is required for the design of co-bonded dissimilar composite structure with considering the shape distortion during the manufacturing process. In this work, digital image correlation (DIC) technique is introduced for measuring the thermal distortion characteristics of co-bonded dissimilar composite specimen, carbon/epoxy and silica/phenolic. The thermal distortion of co-bonded dissimilar composite specimen is numerically estimated and compared with the experiments. The estimated results is successfully validated using the measured results.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.29-29
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• 2011

국내에서 기존건축물의 내진성능평가 기법이 연구되기 시작한지 20여 년간 다양한 평가방법이 제안되었다. 그러나, 제안된 평가방법은 미국이나 일본의 평가 방법을 도입 및 수정하는 내용이 주가 되어 국내실정에 맞지 않는 부분도 많이 발견되었다. 따라서 국내에서 제안된 기존 건축물의 내진성능 평가기법, 지진피해예측에 근거한 보강건축물의 합리적인 선정방법 및 이들 건축물에 적합한 내진보강방법 등의 연구는 아직까지 초보적인 단계라고 할 수 있다. 이에 본 연구의 목적은 이러한 평가 기법을 적용한 국내 저층구조물의 내진성능을 평가하는 것이다. 저층구조물의 내진성능을 평가하기 위하여 1988년 내진설계가 도입되기 이전에 건립된 4층 규모의 학교구조물을 해석대상 구조물로 선정하였다. 대상 해석구조물의 내진성능평가는 일본의 내진성능 평가법을 참고하여 평가절차가 다소 복잡한 부분을 국내 실정에 맞게 개선시킨 내진화 우선도 평가방법과 정밀한 내진성능을 평하는 방법으로 세계적으로 널리 사용되고 있는 ATC-40 성능평가방법에서 등가단자유 모델로 변환 과정에서 등가유효감쇠 및 등가유효주기 산정 관계식의 문제점을 개선한 FEMA-440의 선형화 성능평가방법(Linearization Method)을 사용하여 구조물의 성능을 평가하였다. 내진 성능 평가를 위해 현재 전 세계적으로 널리 사용되고 있는 구조물 비선형 전용 해석 프로그램인 Perform-3D를 이용하여 해석을 수행하였다. 본 연구를 통해 기존 저층구조물로 선정한 학교구조물에 대한 내진성능을 평가한 결과, 내진화 우선도 평가법 및 FEMA-440의 내진성능 평가는 유사한 경향의 결과를 나타내었고, 두 평가결과를 요약하면 Y방향은 보와 기둥에 끼인 조적벽체의 영향으로 별도의 내진성능이 향상 보강이 필요없으나, X방향은 창문하부 허리 조적벽 등의 영향으로 다소 취성적인 내진성능을 보유하고 있어 충분한 내진성능 확보를 위한 추가적인 보강이 필요한 것으로 판단된다.