• 제어로봇시스템학회논문지
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• 제22권6호
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• pp.477-482
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• 2016

This paper presents a simple approximation-based design approach for consensus tracking of heterogeneous second-order nonlinear systems under a directed network. All nonlinearities of followers are assumed to be unknown and non-identical. In the controller design procedure, graph-independent error surfaces are used and an unimplementable intermediate controller for each follower is designed at the first design step. Then, by adding and subtracting a graph-based term at the second step, the actual controller for each follower is designed by using one neural network employed to estimate a lumped and distributed nonlinearity. Therefore, the proposed local controller for each follower has a simpler structure than existing approximation-based consensus tracking controllers for multi-agent systems with unmatched nonlinearities.

• Spatial Information Research
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• 제1권1호
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• pp.17-28
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• 1993

본 논문에서는 지리정보데이타베이스 구축과정에서 자원이 많이 소요되는 벡터화 작업을 최소화하면서도 센서스지도제작 업무를 효과적으로 지원할 수 있는 데이타베이스 구조에 대해 연구하였다. 센서스지도의 기본이 되는 전국지형도를 스캐닝하여 래스터자료형태로 저장하고 센서스작업을 위해 필요한 조사고경계 등의 일부자료 항목에 대해서만 벡터형태로 변환하여 이를 문자형태의 각종 관리정보와 결합시킴으로써 지도의 제작 및 검색시 필요한 요소들을 추출.결합할 수 있는 구조로 데이타베이스를 설계하였다. 센서스용 기본지도들은 데이타베이스내부에서 논리적으로 한장의 커다란 연속지도(Continuous Map)로 구성할 수 있도록 타일(Tile) 형식의 저장 구조를 갖게 하였고, 이미지자료와 벡타자료 그리고 이와 관련된 문자 속성정보들의 연결 미 통합을 위해 다중계?(Multi-Layer)구조를 갖게 하였다. 또한 축척이 상이한 지도의 종류에 따라 서로 다른 계층구조를 가지면서 물리적으로 분리된 데이타베이스 구조를 갖도록 하였으며 이들간의 연결을 위해서는 소축적 데이타베이스가 대축척 데이타베이스의 색인(Inedex)데이타베이스 역할을 하도록 설계하였기 때문에 사용자 관점에서는 전체가 하나로 통합될 수 있게 하였다. 상기 방법에 의하여 센서스매핑시스템을 구축할 경우, 예산, 인력 및 비용 측면에서 괄목할 만한 기대효과를 예측할 수 있었으며, 활용면에서도 고품질의 실용적인 지도제작이 가능한 것으로 나타나, 향후 본 시스템이 실제 구축되면 각종 통계조사는 물론, 통계자료를 이용하는 각 기관 및 개인에게 다양한 정보를 제공할 수 있게 될 것이다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1163-1164
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• 2006

TZM alloy having elongated coarse-grain structure was developed by three-step internal nitriding treatment at 1423 to 1873 K in $N_2$ and subsequent recrystallization treatment at 2173 K in vacuum. Some specimens were subjected to re-nitriding treatment at 1873 K for 16 h. After the recrystallization treatment, aspect ratio (L/W) of grains for rolling direction was about 50 at the maximum. Yield stress obtained at 1773 K after re-nitriding treatment was about 6 times as large as that of recrystallized specimen. Re-nitriding was very effective in the improvement in strength of TZM alloy having elongated coarse-grain structure.

• KIEE International Transactions on Electrophysics and Applications
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• 제5C권1호
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• pp.39-43
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• 2005

We proposed a structure for a 1.55 ㎛ strained separate confinement heterostructure (SCH) multi- quantum well (MQW) superluminescent diode (SLD), having a tapered active region. SLD was fabricated through a two-step procedure: the first step being metal organic chemical vapor deposition (MOCVD) and the second-step being liquid phase epitaxy (LPE). We used a 15 laterally tilted stripe and window region to suppress the lasing action of the SLD. The performance of the SLD showed output power of 11 mW with no lasing under 200 mA pulse driving. The full-width at half-maximum was 42 nm at 200 mA, 25℃.

• Corrosion Science and Technology
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• 제23권1호
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• pp.11-19
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• 2024

A Fe-Ni Bainitic steel as a weathering steel application was developed by combining its excellent mechanical properties and corrosion resistance in maritime environments. Nickel concentration (0.4-3 wt%) and inverted austempering multi-step (IAM) process were primary determinants of the microstructure of the Fe-Ni Bainitic steel. The initial austempering steel was performed at 300 ℃ for 600 seconds to obtain a partly bainitic transformation. The steel was heated again for 1800 s at 450 ℃. The microstructure was comprised of ferrite, a blocky martensite/austenite island, and a homogeneous lath-shape bainite structure with widths ranging from 4.67 to 6.89 ㎛. The maximum strength, 1480 MPa, was obtained with 3 wt% nickel. In this study, corrosion behavior was investigated utilizing potentiodynamic and electrochemical impedance spectroscopy (EIS) tests. A higher nickel content in Fe-Ni Bainitic steel refined the grain size, improved the bainite fraction, lowered the corrosion rate to 0.0257 mmpy, and increased the charge transfer of film resistance to 1369 Ω.

• 한국공간구조학회논문집
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• 제12권4호
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• pp.109-118
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• 2012

The large-space single-layer lattice dome is relatively simpler in terms of the arrangement of the various framework members and of the design of the junction than the multi-layered lattice dome, can reduce the numbers and quantity of the framework members, and has the merit of exposing the beauty of the framework as it stands. The single-layer lattice dome, however, requires a stability investigation of the whole structure itself, along with an analysis of the stress of the framework members, because an unstable phenomenon called "buckling" occurs when its weight reaches critical levels. Many researchers have systematically conducted researches on the stability evaluation of the single-layer lattice dome. No construction case of a single-layer lattice dome with a 300-m-long span, however, has yet been reported anywhere in the world. The large-space dome structure is difficult to erect due to the gigantic span and higher ceiling compared with other common buildings, and its construction cost is generally huge. The method of erecting a structure causes major differences in the construction cost and period. Therefore, many researchers have been conducting various researches on the method of erecting such structure. The step-up method developed by these authors can reduce the construction cost and period to a great extent compared with the other general methods, but the application of this method inevitably requires the development of system supports in the center section as well as pre-existing supports in the boundary sections. In this research, the safety during the construction of a single-layer lattice dome with 300-m-long span using pre-existing materials was examined in the aspect of structural strength, and the basic data required for manufacturing the supports in the application of the step-up method developed by these authors during the erection of the roof structure were obtained.

• International Journal of Precision Engineering and Manufacturing
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• 제3권4호
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• pp.54-63
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• 2002

In recent years, mechanical systems such as high speed vehicles and railway trains moving on elastic beam structures have become a very important issue to consider. In this paper, a general approach, which can predict the dynamic behavior of a constrained mechanical system moving on a flexible beam structure, is proposed. Various supporting conditions for the foundation support are considered for the elastic beam structure. The elastic structure is assumed to be a non-uniform and linear Bernoulli-Euler beam with a proportional damping effect. Combined differential-algebraic equation of motion is derived using the multi-body dynamics theory and the finite element method. The proposed equations of motion can be solved numerically using the generalized coordinate partitioning method and predictor-corrector algorithm, which is an implicit multi-step integration method.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권6호
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• pp.602-614
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• 2016

It is necessary to develop an efficient optimization technique to perform optimum designs which have given design spaces, discrete design values and several design goals. As optimization techniques, direct search method and stochastic search method are widely used in designing of ship structures. The merit of the direct search method is to search the optimum points rapidly by considering the search direction, step size and convergence limit. And the merit of the stochastic search method is to obtain the global optimum points well by spreading points randomly entire the design spaces. In this paper, Pareto Strategy (PS) multi-objective function method is developed by considering the search direction based on Pareto optimal points, the step size, the convergence limit and the random number generation. The success points between just before and current Pareto optimal points are considered. PS method can also apply to the single objective function problems, and can consider the discrete design variables such as plate thickness, longitudinal space, web height and web space. The optimum design results are compared with existing Random Search (RS) multi-objective function method and Evolutionary Strategy (ES) multi-objective function method by performing the optimum designs of double bottom structure and double hull tanker which have discrete design values. Its superiority and effectiveness are shown by comparing the optimum results with those of RS method and ES method.

• Journal of Power Electronics
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• 제15권4호
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• pp.886-898
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• 2015

The design feasibility of a micro unidirectional DC transmission system based on an input-parallel output-parallel (IPOP) converter is analyzed in this paper. The system consists of two subsystems: an input-parallel output-series (IPOS) subsystem to step up the DC link voltage, and an input-series output-parallel (ISOP) subsystem to step down the output voltage. The two systems are connected through a transmission line. The challenge of the delay caused by the communication in the control system is addressed by introducing a ring communication structure, and its influence on the control system is analyzed to ensure the feasibility and required performance of the converter system under practical circumstances. Simulation and experiment results are presented to verify the effectiveness of the proposed design.

• E2M - 전기 전자와 첨단 소재
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• 제10권7호
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• pp.645-650
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• 1997

We manufactured CoNbZr/Cu/CoNbZr multi-layer films by rf magnetron sputtering methods and formed the patterns on the deposited multi-layer films. In this study, we fabricated a new etchant for forming the patterns by the wet etching with etchant and we searched for the best etching conditions and the etchant composition. Cu was etched selectively independent on the concentration of iron chloride solution, but amorphous CoNbZr thin film did not. The etchant was achieved by iron chloride solution(17.5 mol%) mixed with HF (20 mol%) during 150 sec, which etched CoNbZr/Cu/CoNbZr multi-layer films at the same time. Also, the etchant etched CoNbZr/Cu/CoNbZr multi-layer films by the three-step. It was shown that the cross-section had the isotropic structure and excellent etching characteristics with the above etchant.