• Journal of the Institute of Electronics Engineers of Korea SC
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• v.49 no.3
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• pp.26-30
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• 2012

This paper presents the observer design method for discrete-time nonlinear systems with delayed output. It is shown that by considering a nonlinear term of error dynamics as an additional state variable, the discrete-time nonlinear error dynamics with time delay can be transformed into the discrete-time linear one with time delay. Sufficient conditions for existence of state observer are characterized by linear matrix inequalities. Finally, an illustrative example is given in order to show the effectiveness of our design method.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.660-665
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• 2004

본 연구에서는 비선형적인 메커니즘을 갖는 수문현상의 불확실성을 해석하고자 하는 목적으로 새로운 개념의 지배방정식이 유도된다. 제안된 모형의 불확실성은 토양 특성치의 공간적 변동성에 기인하고 있는 것으로 가정하여, 유도된 방정식은 Fokker-Planckl 방정식의 형태를 가지고 있다. 실제 유역단위에서 토양 내 수분 흐름의 연직방향 흐름을 모의하기 위해 미소단위에서 유도된 Richards 방정식은 토양의 공간적 변동성으로 말미암아 불확실한 매개변수를 갖는 비선형 추계학적 편미분방정식의 형태를 갖게 된다. 이는 먼지 수직 방향적분을 통하여 단순화된 비선형 추계학적 상미분방정식으로 전환되고, 이렇게 전환된 비선형 추계학적 상미분방정식은 다시 추계학적 Liouville 방정식을 이용하여 선형 추계학적 편미분방정식으로 전환되어진다. 최종적으로 cumulant 급수방법을 이용하여 상기 방정식을 선형 결정론적 편미분방정식으로 전환시킴으로써, 강우 시 토양 내 수분 침투현상을 모형화할 경우 유역단위에서 토양의 공간적 변동성을 설명할 수 있는 지배방정식을 유도할 수 있다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.11
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• pp.5164-5171
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• 2011

In fuzzy modeling for nonlinear process, typically using the given data, the fuzzy rules are formed by the input variables and the space division by selecting the input variable and dividing the input space for each input variables. The premise part of the fuzzy rule is identified by selection of the input variables, the number of space division and membership functions and the consequent part of the fuzzy rule is identified by polynomial functions in the form of simplified and linear inference. In general, formation of fuzzy rules for nonlinear processes using the given data have the problem that the number of fuzzy rules exponentially increases. To solve this problem complex nonlinear process can be modeled by separately forming the fuzzy rules by means of fuzzy division of each input space. Therefore, this paper utilizes individual input space to generate fuzzy rules. The premise parameters of the fuzzy rules are identified by Min-Max method using the minimum and maximum values of input data set and membership functions are used as a series of triangular, gaussian-like, trapezoid-type membership functions. And lastly, using the data which is widely used in nonlinear process we evaluate the performance and the system characteristics.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.5
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• pp.285-290
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• 2013

Both full linear and shallow water edge waves are compared to get a better understanding of edge wave behavior. By using method of separation of variables, we are able to get solution of full linear edge wave presented by Ursell (1952) without derivation. The shallow water edge waves show dispersive features despite being derived from shallow water equations. When bottom slope is mild enough, shallow water edge wave tends to linear edge wave and has some advantages of manipulation. Solution of edge wave generated by a moving landslide of Gaussian shape is constructed by an expansion of shallow water normal modes. Numerical results are presented and discussed on their main features.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.2
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• pp.21-28
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• 1987

The paper describes the analysis of large displacement problems including instability phenomena. The element used in this is a degenerated isoparametric shell element with eight nodes. Total Lagrangian formulation has been adopted in this study using Newton-Raphson iteration method with incremental load. The linear stability analyses performed usually for the initial position can be repeated at several advanced fundamental states on the non-linear buckling path. Thus a current estimate of the failure load is given. The numerical examples of a cylindrical panel under uniform load, simply supported plate under axial load, and clamped plate under uniform load are carried out. The examples applying degenerated isoparametric elements to bifurcation buckling and nonlinear collapse problems are also performed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.3
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• pp.361-369
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• 2001

This paper deals with numerical efficiency of nonlinear solution technique for space trusses. It will propose the combined Arc-length method to trace structural behavior after reaching buckling load as opposed to the current Arch-length method. The combined Arc-length method uses the current stiffness parameter as a control variable. It uses Secant-Newton method in stable path and applies Arc-length method in unstable path. To evaluate efficiency of solution technique, the accuracy of solution, convergence, and computing time concerning illustrative numerical examples are compared with the current Arc-length method. It show that the combined Arc-length method, as proposed in this paper, is superior to the current Arc-length method in numerical nonlinear analysis.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.299-299
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• 2021

본 연구에서는 강우-유출 모형의 매개변수를 최적화하기 위해 머신러닝 기법을 활용하였다. 강우-유출 모형의 종류가 검토되었으며 이를 통해 선정된 강우-유출 모형의 매개변수 특성과 유출량 선정과의 관계성이 검토되었다. 이를 위해 다년간의 유출 측정 자료가 있는 연구지역이 선정되었다. 또한 매개변수 최적화를 위한 머신러닝 기법이 검토되었으며, 매개변수 최적화와 유출량 산정 정확성을 비교, 분석함으로써 관계성을 검토하였다. 본 연구의 결과를 요악하면 다음과 같다. (1) 여름 장마의 지속성은 매개변수 최적화 정확성에 영향을 주며 이 둘은 비선형적인 관계를 나타낸다. (2) 매개변수 최적화가 강우 심도에 따라 다른 결과를 나타내며 최적의 강우 심도는 연구 지역마다 차이가 있기 때문에 유역 특성을 반영한 머신러닝 기법 활용이 가능하다. 이를 통해 강우-유출 모형의 매개변수 최적화를 위한 머신러닝 기법의 활용 가능성을 확대하고, 모형의 정확도 개선을 기대 할 수 있다.

• 한국방재학회:학술대회논문집
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• 2009.02b
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• pp.105.1-105.1
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• 2009

• The Korean Journal of Rheology
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• v.10 no.1
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• pp.38-43
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• 1998

매니폴로 부분이 선형 경사진 옷걸이형 다이의 최적 설계를 수행하였다. 다이흐름을 3차원 이용하여 해석함으로써 정확한 최적 설계결과를 얻을수 있었으며 형상 최적화 과정을 고찰함으로써 최적 설계도구의 효율성을 조사하였다. 공정의여러 매개변수들이 매니폴드의 형상에 미치는 영향을 조사하기 위하여 멱법칙 유체의 멱법칙 지수, 다이 슬롯의 두께 및 매니폴드 각도를 변화시켜며 최적 설계를 수행하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.3
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• pp.237-244
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• 2016

This paper presents a nonlinear Moving Least Squares(MLS) difference method for material nonlinearity problem. The MLS difference method, which employs strong formulation involving the fast derivative approximation, discretizes governing partial differential equation based on a node model. However, the conventional MLS difference method cannot explicitly handle constitutive equation since it solves solid mechanics problems by using the Navier's equation that unifies unknowns into one variable, displacement. In this study, a double derivative approximation is devised to treat the constitutive equation of inelastic material in the framework of strong formulation; in fact, it manipulates the first order derivative approximation two times. The equilibrium equation described by the divergence of stress tensor is directly discretized and is linearized by the Newton method; as a result, an iterative procedure is developed to find convergent solution. Stresses and internal variables are calculated and updated by the return mapping algorithm. Effectiveness and stability of the iterative procedure is improved by using algorithmic tangent modulus. The consistency of the double derivative approximation was shown by the reproducing property test. Also, accuracy and stability of the procedure were verified by analyzing inelastic beam under incremental tensile loading.