• Journal of Advanced Navigation Technology
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• v.10 no.3
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• pp.256-262
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• 2006

This paper proposes a new predistortion linearizer to compensate for AM/AM and AM/PM in the nonlinear characteristics of amplifier. This consists of common-emitter amplifier and schottky diode that is connected between emitter and ground. When effective resistance of the schottky diode with bias condition varies, common-emitter amplifier with series feedback has a increase of amplitude and expansion of phase. This makes a amplifier nonlinear characteristics are to be improved. The proposed linearizer and amplifier has been manufactured and tested to operate in cellular base station frequency (869~894MHz). The test results show that third order intermodulation distortion (IMD3) cab be removed by more than 10.4dB in case of CW 2-tone signals ${\Delta}f$=1MHz, and the adjacent channel power ratio (ACPR) also can be improved by more than 9.6dB for CDMA IS-95 1FA signals.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.1
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• pp.116-124
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• 2002

The bubble model by Keller and Prosperetti is adapted to solve the nonlinear oscillation of a gas bubble. This formulation leads to accurate results since it introduces the energy equation instead of the polytropic assumption for the bubble interior. The numerical method used in this study is stable enough to handle large amplitude of bubble oscillation. The numerical results show some interesting nonlinear phenomena fur the bubble oscillator. The excitation changes the natural frequency of the bubble and makes some harmonic resonances at $f/f_0=1/2, 1/3$ and so on. The natural frequency of a bubble oscillator decreases compared with the linear case result, which means that the nonlinear bubble oscillation system is a "softening"system. In addition, the frequency response curve jumps up or down at a certain frequency. It is also found that there exist multi-valued regions in the frequency response curve depending on the initial conditions of bubble. The dependency of the bubble motion on the initial condition can generate extremely large pressure and temperature which might be the cause of the acoustic cavitation and the sonoluminescence.inescence.

• Journal of Korean Association for Spatial Structures
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• v.10 no.1
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• pp.119-126
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• 2010

The some papers which deal with the dynamic instability for shell-like structures under the dynamic excitation have been published, but there are few papers which treat the essential phenomenon of the dynamic buckling using the phase plane for investigating occurrence of chaos. In nonlinear dynamic, examining the characteristics of attractor on the phase plane and investigating the dynamic buckling process are very important thing for understanding why unstable phenomena are sensitively originated by various initial conditions. In this study, the direct and indirect snapping of shallow EP shell considering geometrical nonlinearity are investigated by Galerkin method numerically. This finding out the characteristic of the dynamic instability through the phases curves and running response spectrum.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.3
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• pp.47-55
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• 1990

This paper presents the quasi-static mooring analysis model for a vessel moored at the quay. The results of this analysis will aid the designer in determining the mooring configuration for the surface vessels subjected to wind, current and wave forces. And it will also help him in selecting the equipment for the fixed mooring system. The cumulative elastic behavior of the mooring lines invokes a complicated nonlinear problem since the mooring lines are relatively short and hang in air as noncoplanar configurations. This nonlinear mooring problem is solved in this paper by the load increment technique in which the external load is increased step by step taking all sources of nonlinearity into account.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3B
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• pp.307-313
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• 2008

Tidal amplification by construction of sea-dike and sea-walls had been detected not only near Mokpo North Harbor but also at Chungkye Bay which is connected with Mokpo North Harbor by a narrow channel. This brings about increase of tidal flat area and in particular increase of runup height and inundation area during storms. In this study, a simulation process is composed of wind wave generation model for large area and wave inundation model for small coastal zone. The nonlinear version of mild-slope equation is modified for simulating wind-driven surge and wave inundation at a small area. The models are applied to Chungkye Bay, and possible inundation features at Mokpo North Harbor are investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.6
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• pp.1037-1048
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• 2016

In this study, nonlinear wave interaction in the presence of a uniform current is studied using numerical model, named CADMAS-SURF which is based on the Navier-Stokes equations coupled with Volume of Fluid for tracking free surface deformation. The original CADMAS-SURF developed for interaction of wave with structure is modified/extended to simulate nonlinear fluid dynamic motions within wave-current coexisting field. The capability of Numerical Wave-Current Tank (NWCT) in this study is validated by comparing with available existing laboratory experiments for both wave-following and wave-opposing current. The numerical results for interaction between wave and current are shown to be in good agreement with experimental data. Then, this study focused on the dynamic motions of the water velocity, surface elevation and vorticity within combined wave-current field in demonstrating complex nonlinear physical phenomena due to interaction between wave and current. In addition, NWCT is applied to simulate a more complex wave-current-structure field for wave propagating over a submerged breakwater associated with current. Detailed discussion including characteristics of velocity and vorticity fields and the relation between free surface and vorticity are given.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.3
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• pp.105-111
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• 2009

In this paper, we propose a locally adaptive image restoration method based on nonlinear extrapolation in frequency domain. In general, the conventional method causes ringing artifacts on the object boundary. To solve this problem, we introduce an improved restoration method which considers textures of an image block. In the proposed method, a blurred image is divided into several blocks, and each block is classified into three groups; simple, one edge, and complex blocks according to the contained texture. Depending on the classification result, adaptive nonlinear extrapolation is applied to each block in a blurred image. Experimental results show that the proposed algorithm can achieve higher quality image in both subjective and objective views as compared with the conventional method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.10
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• pp.895-902
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• 2012

In this paper, we propose a novel equalizer to compensate for the group delay including AM/PM nonlinear distortion characteristics by the nonlinear power amplifier (PA). The group delay characteristic is a nonlinear non-constant time delay that appears differently depending on each frequency component. The phase distortion by AM/PM characteristics arising from the power amplifier is a major factor to increase group delay. By the group delay distortion, the signal in the constellation expands and is rotated. Considering the problem mentioned above, the nonlinear time delay that appears differently depending on each frequency component is classified as a static group delay and AM/PM characteristic of PA, the different phase transitions depending on the size of input signal as a dynamic group delay. Static group delay estimates and compensate for phase distortions in the frequency domain with type-based method and dynamic group delay compensates for phase rotation in the time domain. We confirmed that the group delay compensation techniques were enough to compensate the group delay characteristics including AM/PM characteristics of the power amplifier.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.966-972
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• 2010

Damping characteristics of a Helmholtz resonator to passively control the combustion instability were investigated by linear acoustic analysis and atmospheric acoustic tests. Its orifice length and diameter were selected as the design parameters and supplied SPL(sound pressure level) effect on damping characteristics were investigated. Damping capacity is improved by decreasing the orifice length as well as by increasing the orifice diameter. Also, the results showed that the damping capacity of the resonator decreased nonlinearly about above 110 dB and instabilities in the nonlinear region were more effectively suppressed by increasing the orifice diameter.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1448-1452
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• 2010

최근 기상변동성 증가 및 기후변화 영향으로 수문순환과정이 과거와는 다른 양상으로 전개되고 있으며 전반적으로 극치사상의 빈도 및 강도의 증가현상이 지배적이다. 이러한 영향을 정량적으로 검토하기 위해서 경향성분석 방법 등이 도입되어 극치수문사상의 변동경향을 평가하는데 이용되고 있다. 대표적인 방법으로 선형회귀분석, Mann-Kendall 경향성 분석 등이 있으나 기본적인 가정(assumption)의 제약으로 극치수문자료 계열의 특성을 효과적으로 분석하는데 무리가 있다. 대표적이고 일반적으로 적용되는 선형회귀분석의 경우 자료가 정규분포(normal distribution)의 특성을 가질 때 유효한 방법으로서 극치수문자료와 같이 Heavy Tail를 가지는 분포특성을 표현하는 데는 무리가 따른다. 이밖에도 기존 선형회귀분석을 극치수문자료에 적용할 경우 추정된 결과를 수자원설계의 관심사항인 빈도해석 등에 직접적으로 연계시켜 해석할 수 없는 단점이 있다. 이는 자료계열의 분포특성을 정규분포로 가정하기 때문에 발생하는 문제로서 극치수문자료계열의 분포 특성을 반영할 수 있는 방법론의 개발이 필요하다. 본 연구에서는 이러한 점을 개선하기 위해서 극치분포(extreme distribution)를 선형회귀분석에 적용하는 비정상성빈도해석(nonstationary frequency analysis) 방법론의 개념을 제시하고자 한다. 비정상성빈도해석을 위해서 Bayesian 기법이 도입되며 Bayesian 기법의 특성상 관련변수들이 사후분포(posterior distribution)로 귀결되기 때문에 경향성에 대한 정량적이고 확률적인 분석이 가능한 장점이 있다. 본 연구를 통해 개발된 방법론은 국내외 주요 강수지점에 대해서 적용되며 경향성, 분포특성, 빈도별 강수량에 대한 체계적인 분석이 이루어진다.