• 한국멀티미디어학회논문지
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• 제13권1호
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• pp.122-132
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• 2010

해양 환경 분석은 해양탐사에 필수적인 정보들을 제공한다. 그러나 해양 환경은 해류에 의한 노드의 이동과 염수에 의한 부식, 전파감쇠와 다중경로 발생, 그리고 센서 노드 설치의 어려움 등 다양한 환경변수가 존재한다. 따라서 해양 데이터 통신은 지상통신 환경과는 달리 이러한 환경적 제약 요소로 인해 해양 환경의 데이터들을 수집하는 과정이 복잡하고 힘들다. 이를 해결하기 위해 해양 환경과 유사한 경포호에서 실제 실험을 통해 수질 환경 모니터링을 위한 해양 데이터 통신망을 구축한다. 따라서 본 논문은 경포호 환경 모니터링 시스템의 구축을 통해 환경적 장애요소를 극복하고 해양 환경 모니터링을 위한 센서 노드들의 배치, 그리고 통신 환경의 효과적인 구조를 정의하는데 목적이 있다.

• 한국군사과학기술학회지
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• 제20권4호
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• pp.528-535
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• 2017

Fuel cells have been spotlighted in the world for being highly efficient and environmentally friendly. A hydrogen which is the fuel of fuel cell can be obtained from a number of sources. Hydrogen source for operating the polymer electrolyte membrane fuel cell(PEMFC) in the current underwater environment, such as a submarine and unmanned underwater vehicles are currently from the metal hydride cylinder. However, metal hydride has many limitations for using hydrogen carrier, such as large volume, long charging time, limited storage capacity. To solve these problems, we suggest diesel reformer for hydrogen supply source. Diesel fuel has many advantages, such as high hydrogen storage density, easy to transport and also well-infra structure. However, conventional diesel reforming system for PEMFC requires a large volume and complex CO removal system for lowering the CO level to less than 10 ppm. In addition, because the preferential oxidation(PROX) reaction is the strong exothermic reaction, cooling load is required. By changing this PROX reactor to hydrogen separation membrane, the problem from PROX reactor can be solved. This is because hydrogen separation membranes are small and permeable to pure hydrogen. In this study, we conducted the pressurized diesel reforming and water-gas shift reaction experiment for the hydrogen separation membrane application. Then, the hydrogen permeation experiments were performed using a Pd alloy membrane for the reformate gas.

• 한국정보통신학회논문지
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• 제18권3호
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• pp.586-594
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• 2014

수중 통신 상에서 가장 중요한 요소는 한정된 전원을 보다 효율적으로 소모하여 운영 가능 시간을 최대화하는데 있다. 보다 효율적인 전압 소모를 위해 적용 가능한 기법으로는 동적 전압 스케일 기법이 있다. 해당 기법은 평상시에는 낮은 주파수로 동작하여 대기 전력을 최소화하며 복잡한 연산을 수행하는 경우에는 빠른 주파수로 계산함으로써 전체 소모되는 전력량을 줄인다. 복잡한 암호화 연산의 경우 빠른 주파수로 연산을 하는 것이 보다 효율적이다. 본 논문에서는 다양한 센서 상에서의 암호화 기법에 동적 전압 스케일 기법을 적용한 결과를 보여 줌으로써 수중 통신 상에서 적합한 저전력 암호화 방안에 대해 살펴본다.

• 박물관보존과학
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• 제18권
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• pp.93-114
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• 2017

현재 베트남에는 ①탕롱 유적, ②호 왕조의 성채, ③미선 유적, ④호이안 고도시, ⑤후에 유적 등 5곳의 세계문화유산, ⑥하롱 베이, ⑦퐁나케방 국립공원 등 2곳의 세계자연유산, 세계복합유산인 ⑧짱안 경관유적 1곳 등 총 8곳의 유네스코 세계유산이 등재되어 있다. 지역적으로 보면 북부지역에 4곳, 중부지역에 4곳으로 분포하며, 남부지역에는 하나도 없다. 베트남의 자연유산은 모두 전형적인 석회암 카르스트 지형 경관이며, 2000년대 이후 등재된 문화유산 지역들은 대부분 북부지역의 옛 왕조들의 수도였던 도성 유적이다. 지금까지 베트남의 세계문화유산 등재 정책은 북부지역의 역사적 정통성을 강조한 유적을 중심으로 진행되어 왔으나, 향후 베트남 정부의 문화 정책이 좀더 남북 지역간 격차를 줄이고 통합적으로 진행될 수 있기를 기대한다.

• 한국음향학회지
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• 제34권6호
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• pp.493-498
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• 2015

물로 채워진 음향 펄스 튜브 내에는 가진 조건들에 따라 복잡한 형태의 음향 신호들이 형성될 수 있다. 이는 펄스 튜브를 이용해 저주파수 대역에서 평면파 반사계수를 측정하는 것을 어렵게 한다. 본 연구에서는 COMSOL Multiphysics를 이용하여 튜브 벽이 가진되는 경우 펄스 튜브 내에 평면파 뿐 아니라 비평면파 모우드의 복잡한 음장이 발생됨을 보였다. 모우드 분리 방법인 이차원 푸리에 필터링으로 입사 또는 반사하는 평면파 모우드만을 각각 분리할 수 있었다. 이에 시간 게이팅을 적용하므로 음향 시편의 평면파 반사계수를 보다 정확하게 결정할 수 있게 하였다.

• Advances in Computational Design
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• 제5권3호
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• pp.233-260
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• 2020

The main purpose to introduce model based controller in proposed control technique is to provide better and fast learning of the floating dynamics by means of fuzzy logic controller and also cancelling effect of nonlinear terms of the system. An iterative adaptive dynamic programming algorithm is proposed to deal with the optimal trajectory-tracking control problems for autonomous underwater vehicle (AUV). The optimal tracking control problem is converted into an optimal regulation problem by system transformation. Then the optimal regulation problem is solved by the policy iteration adaptive dynamic programming algorithm. Finally, simulation example is given to show the performance of the iterative adaptive dynamic programming algorithm.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권4호
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• pp.499-507
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• 2018

Autonomous Underwater Vehicle (AUV), which are becoming more and more important in ocean exploitation tasks, needs energy conservation urgently when sailing the complex mission path in long time cruise. As hull lines optimization design becomes the key factor, which closely related with resistance, in AUV preliminary design stage, uncertainty parameters need to be considered seriously. In this research, Myring axial symmetry revolution body with parameterized expression is assumed as AUV hull lines, and its travelling resistance is obtained via modified DATCOM formula. The problems of AUV hull lines design for the minimum travelling resistance with uncertain parameters are studied. Based on reliability-based optimization design technology, Design For Six Sigma (DFSS) for high quality level is conducted, and is proved more reliability for the actual environment disturbance.

• 콘크리트학회논문집
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• 제12권5호
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• pp.13-23
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• 2000

In this study, an flexural test on half-scale spliced PSC-I girder was conducted to verify the efficiency of the long span spliced girder as suggested by the Korean Highway Design Specification. The experimental results showed that the specimens developed a complex failure mode due to flexural-compression and torsional stress. The cracking moment of each girder was higher the experiment than was calulated by the ACI and the ultimate strength were the almost same. To estimate the safety and the structural efficiency of the spliced girder, the proposed Yielding Resistance Index(YRI) and ductility index by American Concrete Institutes were used based on the energy concept. The proposed YRI defined the ratio of crack resisting energy and the total energy calculated from load-displacement relationship. Based on the analysis of YRI and ductility index, the flexural behavior of the spliced girder was found to be efficient. Through the experimental results, the structural behavior of proposed spliced PSC I-type girder for long span bridge was found to be more efficient than the exsisting PSC I-type girders.

• Journal of Ship and Ocean Technology
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• 제8권1호
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• pp.31-41
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• 2004

A ducted marine propulsor has been widely used for the thruster of underwater vehicles for protecting collision damage, increasing propulsive efficiency, and reducing cavitation. Since a single-stage ducted propulsor contains a set of rotor and stator inside an annular duct, the numerical analysis becomes extremely complex and computationally expensive. However, the accurate prediction of viscous flow past a ducted marine propulsor is essential for determining hydrodynamic forces and the propulsive performances. To analyze a ducted propulsor having rotor-stator Interaction, the present work has solved 3D incompressible RANS equations on the sliding multiblocked grid. The flow of a single stage turbine flow was simulated for code validation and time averaged pressure coefficients were compared with experiments. Good agreement was obtained. The hydrodynamic performance coefficients were also computed.

• 한국정밀공학회지
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• 제17권1호
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• pp.138-144
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• 2000

Robot manipulators, which are nonlinear structures and have uncertain system parameters, have complex in dynamics when are operated in unknown environment. To compensate for estimate errors of the uncertain system parameters and to accomplish the desired trajectory tracking, nonlinear robust controllers are appropriate. However, when estimation errors or tracking errors are large, they require large input torques, which may not be satisfied due to torque limits of actuators. As a result, their stability can not be guaranteed. In this paper, a new robust control scheme is presented to solve stability problem and to achieve fast trajectory tracking in the presence of torque limits. By using fuzzy logic, new desired trajectories which can be reduced are generated based on the initial desired trajectory, and torques of the robust controller are regulated to not exceed torque limits. Numerical examples are shown to validate the proposed controller using an uncertain two degree-of-freedom underwater robot manipulator.