• Geophysics and Geophysical Exploration
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• v.18 no.3
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• pp.133-142
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• 2015

Displacement of the Earth's surface due to atmospheric loading has been recognized since a century years ago, and its accurate estimation is required in present day geodesy and surveying, particularly in space geodesy. Atmospheric load deformation in continental region can readily be calculated with the given atmospheric pressure field and the load Green's function, and, in near coastal area, approximate model is used for the calculation. The changes in the Earth's atmospheric circulation and the seasonal variation of atmospheric pressure on two hemispheres of the Earth are the each main causes of variation of the Earth's spin angular velocity and polar motion respectively. Wind and atmospheric pressure do the major role in other periodic and non-periodic perturbations of the positions in the Earth's reference frame and variations in the Earth's spin rotational state. In this reviewing study, the developments of related theories and models are summarized along with brief description of phenomena, and the geodetic perturbing effects of a hypothetical typhoon passing Korea are shown as an example. Finally related existing problems and further necessary studies are discussed in general.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.5
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• pp.243-250
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• 2002

In the synthesis of the current source distribution function of an array antenna with the arbitrary radiation pattern, the Woodward-Lawson sampling method has been mainly used for the synthesis of an even function lobe pattern. In this paper, the method is extended to the synthesis of the odd function pattern and then the optimum synthesis method for the nonlinear source distribution function is proposed. The proposed method is applied to the design of nonuniform transmission lines with arbitrary reflection responses. The both dispersive impedance profiles of single and coupled nonuniform lines with arbitrary reflection responses are directly synthesized by the sampled values of a reflected spectral pattern which is optimally shaped by a perturbation of its complex null positions, hence removing the conventional step-by-step segmentation process and global optimization routines. The control problem in the case that all of port impedances are identical is also solved. The generality of the proposed method is verified by a filter design with the controlled arbitrary passband

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.1
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• pp.43-58
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• 2002

A methodology to nondestructively locate and estimate size of damage in beam-type structures using a few natural frequencies or a few mode shapes is presented. A damage-localization algorithm to locate damage from changes in natural frequencies and a damage-sizing algorithm to estimate crack-size from natural frequency perturbation are outlined. A damage index algorithm to localize and estimate severity of damage from monitoring changes in mode shapes is outlined. The frequency-based method and the mode-shape-based method are evaluated for several damage scenarios by locating and sizing damage in PS concrete beams lot which a few natural frequencies and mode shapes are generated from finite element models. The result of the analyses indicates that the two methods correctly localize and closely estimate the size of the crack simulated in the test beam.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.89-94
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• 2010

Fuselage propellant feeding system should supply propellants to engine with required flow rate, temperature and pressure. Propellant vibration in engine and feeding line changes feeding characteristics, and frequently inhibits to satisfy the required feeding requirements. Sloshing and POGO vibration are known to be the major vibration phenomena. Concerning sloshing and POGO, vehicle control and structural dynamics aspects are extensively studied, whereas, its effect on propellant feeding performance is not clearly understood. This paper focuses on the deviation of required feeding performance due to propellant vibration. Overall characteristics of propellant vibration and its effect on propellant supply to engine are reviewed and control mechanism for suppressing vibration is introduced.

• Journal of Korea Water Resources Association
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• v.31 no.3
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• pp.223-234
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• 1998

Recently, the interests of the construction of the permeable submerged breakwaters have been increased to preserve and to improve the coastal environment, and to control the incident waves and littoral transport. It is very important to predict the wave transformation precisely over the permeable submerged breakwaters. This study discusses nonlinear wave transformation and characteristics by using BEM based on the frequency domain method of the 3rd-order Stokes waves. The Dupuit-Forchheimer formula is applied to the analysis of the fluid resistance of rubble stones, and the equation about equivalent linear frictional coefficient is newly modified based on the Lorentz's condition for the equivalent work. The numerical results are compared with the experimental ones for verification. These two results give a close agreement each other. It is confirmed that the present method of the 3rd-order Stokes waves estimates more precisely than that of the 2nd-order Stokes waves.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.14 no.4
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• pp.183-194
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• 2004

The proliferation of the Internet and the rapid progress of wire/wireless communication technology makes security of digital images more and more important since the exchanges of digital images occur more and more frequently. And as the tight relationship between chaos theory and cryptography, many researches for development of new encryption systems based on chaotic maps have been widely progressed recently. In this paper, we propose a digital image encryption system based on both one-dimensional PLCM(Piecewise Linear Chaotic Map) and two-dimensional baker map. This proposed system is a product cipher that contains a perturbance-based chaotic stream cipher based on ID PLCM and a chaotic block cipher based on 2D baker map and is very high secure and easily implementable cipher having both a good confusion property and a good diffusion property. And with test results, we showed this system is very secure against statistical attacks.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.348-348
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• 2023

최근 전세계 곳곳에서는 다양한 유형의 물 관련 복합재해가 발생하고 있다. 일례로 미국 캘리포니아 지역은 2014년부터 2017년까지 극심한 가뭄에 시달리다가 대기강(atmospheric river)의 영향으로 인하여 대규모의 홍수가 잇달아 발생하였다. 유럽에서는 2021년 전례 없는 홍수 직후 500년 빈도의 가뭄이 발생하면서 심각한 인명 및 재산피해가 발생하였다. 짧은 시간 동안 양극단의수재해가 연속적으로 발생하거나, 가뭄과 폭염, 홍수와 산사태의 결합, 또는 동시에 여러 지역에서 홍수나 가뭄이 발생하는 현상 등도 복합재해에 해당한다. 즉, 복합재해는 서로 다른 특성의 독립적인 수재해가 결합되어 나타나는 재해의 한 형태로써, 발생 빈도는 적으나 유발되는 피해는 매우 크다. 더욱이 복합재해는 미래에 더욱 빈번하게, 극심하게 발생할 것으로 예상되고 있다. Single Model Initial-condition Large Ensemble (SMILE)은 복합재해의 분석에 적합한 자료로 최근 활용사례가 증가하고 있다. 기존의 기후변화 관련 연구는 여러 기후모델에서 생산한 단일 모의자료를 앙상블의 형태로 이용하여 기후요소 및 기후재해의 미래 전망이나 거동을 분석하는 과정에 기반해왔다. 이 기후모델 앙상블은 모델 간 불확실성은 고려할 수 있으나 기온 상승 시나리오의 불확실성 및 기후 시스템 내부의 변동성은 고려하지 못하는 한계가 있다. 이에 미국의 National Center for Atmospheric Research에서는 자연 자체의 변동에 의한 불확실성을 모의할 수 있는 SMILE을 개발하였다. SMILE은 단일 기후모델에서 N개의 다중 모의자료 앙상블을 출력한다. 기존의 기후모델과 유사한 과정으로 모의를 수행하되, 미세한 섭동을 부여함으로써 자연적으로 발생하는 기후시스템 내부의 변동성을 고려한다. 이러한 실험 설정은 카오스 이론에 근거한다. 여러 기후모델에 대해 SMILE 기반 모의를 수행하면 앙상블의 앙상블 개념(large ensemble)이므로 방대한 양의 기후모의 자료가 확보되어 다양한 목적의 연구에 활용할 수 있다. SMILE은 기존의 다중 기후모델 앙상블이 고려할 수 없었던 종류의 불확실성을 추가적으로 고려함으로써 인간의 활동과 자연적 변동성이 복합재해에 미치는 상대적 영향을 정량적으로 평가할 수 있게 한다. 복합재해 연구에 필수적인 표본 수 부족의 한계를 극복할 수 있기 때문에 최근 기후변화 및 수자원 관련 연구에서 적극적으로 활용되고 있다. 또한, 미래 기후를 모의하기 때문에 복합재해 발생의 특성 및 거동을 전망할 수 있고, 충분한 수의 표본은 통계분석 결과에 신뢰성을 부여할 수 있다. 이러한 SMILE의 장점은 향후 더욱 다양한 연구의 기회를 제공할 것이다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.21-33
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• 2006

The reliability analysis can be conducted more effectively by formulating the stochastic finite element method suitable for the reliability theory about the cable stayed bridge. After conducting the initial equilibrium analysis of the cable stayed bridge, the program which can conduct the linear and nonlinear stochastic finite element analysis using the perturbation method and the reliability analysis considered to the correlation of the random variable is developed. Using the results of this program about the cable stayed bridge, the characteristic of the node displacement, element force and cable tension according to the correlation of the random variable is investigated quantitatively. Also the reliability index and the failure probability are examined by the compounding the correlation of the random variable.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.539-549
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• 2006

The performance of a pontoon-type floating breakwater (FB) is investigated numerically with the use of a second-order time domain model. The model has been developed based on potential theory, perturbation theory and boundary element method. This study is focused on the effects of weakly nonlinear wave on the hydrodynamic characteristics of the FB. Hydrodynamic forces, motion responses, surface elevation, and wave transmission coefficient around the floating breakwater are evaluated for various wave and geometric parameters. It is shown that the second-order wave component is of significant importance in calculating magnitudes of the hydrodynamic forces, mooring forces and the maximum response of a structure. The weak non-linearity of incident waves, however, can have little influence on the efficiency of the FB. From numerical simulations, the ratio of draft and depth, the relationship of wave number and width are presented for providing an effective means of reducing wave energy.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6A
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• pp.1001-1011
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• 2006

It is a general agreement that exact statistical solutions can be found by a Monte Carlo technique. Due to difficulties, however, in the numerical generation of random fields, which satisfy not only the probabilistic distribution but the spectral characteristics as well, it is recognized as relatively difficult to find an exact response variability of a structural response. In this study, recognizing that the random field assumes a constant over the domain under consideration when the correlation distance tends to infinity, a semi-theoretical solution of response variability is proposed for general structures. In this procedure, the probability density function is directly used. It is particularly noteworthy that the proposed methodology provides response variability for virtually any type of probability density function, and has capability of considering correlations between multiple random variables.