• Bulletin of the Korean Space Science Society
• /
• 2008.10a
• /
• pp.34.3-34.3
• /
• 2008

Relative navigation system is presented using measurements from a single-channel global positioning system (GPS) simulator. The objective of this study is to provide real-time relative navigation results as well as absolute navigation results for two formation flying satellites separated about 1km in low earth orbit. To improve the performance, more accurate dynamic model and modified relative measurement model are developed. This modified method prevents non-linearity of the measurement model from degrading precision by applying linearization about the states from absolute navigation algorithm not about a priori states. Furthermore, absolute states are obtained using ion-free GRAPHIC pseudo-ranges and precise relative states are provided using double differential carrier-phase data based on Extended Kalman Filter. The software-based simulation is performed and achieved meter-level precision for absolute navigation and millimeter-level precision for relative navigation. The absolute and relative accuracies at steady state are about 0.77m and 4mm respectively (3D, r.m.s.). In addition, Integer ambiguity algorithm (LAMBDA method) improves simulation performances.

• Ocean and Polar Research
• /
• v.37 no.3
• /
• pp.235-247
• /
• 2015

The main purpose of procuring the oceanographic research vessel with state-of-the-art technology is to provide a floating laboratory to conduct field work on the global oceans. The vessel should be properly utilized to locate and evaluate unexplored natural resources as well as to contribute international efforts to better understand and manage global environmental issues. Top priorities in the vessel design are high safety standards, noise and vibration control efficiency, and effective application of research equipment. For the accomplishment of all activities, the vessel length over all should be extended ~100 m with a gross tonnage of ~5,900 ton. In particular, the dynamic positioning system II will essentially operate at sea state 6. The high efficiency emissions reduction system will also be adopted in preparation for entry into force of 3rd exhaust emission control (Tier III). About 130 navigational and scientific instruments will be installed. The final design and model test of the new research vessel were reviewed and completed, respectively, in 2014. Currently, the ship is being built on schedule and expected to be delivered in December 2015. Within the near future, the new vessel will assume the role of carrying out multidisciplinary oceanographic researches of the highest standards in a technologically advanced and environment friendly manner.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.4
• /
• pp.1453-1459
• /
• 2012

The dual stage manipulator is composed of the voice coil motor (VCM) and piezoelectric ceramics transducer (PZT), which can produce the high precise displacement and express a well dynamic performance. However, inaccurate modeling of the dual stage will exacerbate the positioning accuracy. This paper presents an approach to model the dual stage system by using bond graph theory. And the state space equations can be derived through the bond graph straightforwardly, which can be used in computing simulations. Through designing the compensators for the dual stage system and simulating, the dual stage performs better dynamics characteristic than the single actuator system.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2007.06a
• /
• pp.724-727
• /
• 2007

선박 운항 자동화 시스템은 선내 노동력 감소, 작업 환경 개선, 운항 안전성 확보 및 운항 능률의 향상을 목표로 하며, 궁극적으로는 운항 경제성확보를 위한 승선 인원의 최소화에 그 목적이 있다. 최근에는 적응 제어방법 등을 응용하여 선박의 비선형성을 보상하여 선박의 회두각 유지제어(Course Keeping Control), 항로 추적제어(Track Keeping Control), 롤-타각제어(Roll-Rudder Stabilization), 선박 위치제어(Dynamic Ship Positioning), 선박자동 접이안(Automatic Mooring Control) 등에 관한 연구를 수행하고 있으며 실제의 선박으로 대상으로 응용연구가 진행 중이다. 선박은 Steering Machine에 의해 조정되는 Rudder angle과 선박의 회두각의 관계는 비선형적이며, 선박의 Load Condition은 선박의 Parameter에 영향을 주는 비선형적인 요소로서 작용한다. 또한 외란요소인 파도의 유속(流速)과 방향, 풍속과 풍량 등이 비선형적인 형태로 작용하므로 선박의 운항을 힘들게 하는 요인이 된다. 따라서 선박의 운항시스템에는 비선형성을 극복할 수 있는 강인한 제어 알고리즘을 요구한다. 본 논문에서는 퍼지 알고리즘을 이용하여 선박의 비선형적인 요인 및 외란을 극복할 수 있는 선박의 자율운항 시스템을 설계하고 시뮬레이션을 통해 그 결과를 살펴보았다.

• Journal of Ocean Engineering and Technology
• /
• v.32 no.1
• /
• pp.43-50
• /
• 2018

Recently, various efforts have been made to develop oil and gas in the Arctic Ocean. It is very important to consider the load caused by ice in designing floating structures in the area. The magnitude of the ice load and its impact on a structure should be considered. In this paper, we analyze ice parameters affecting the DP performance of FPSO with a DP-assisted mooring system. Several ice characteristics are selected, and the resulting ice load is calculated using GEM software. Numerous simulations are conducted while changing the values of the parameters, and DP capability plots are generated to visualize the effects of changing these parameters. It is shown that the ice drift speed and thickness are the major properties to be considered in DP system design. The limitations of the analysis and future work are discussed in the conclusion.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.7 no.4
• /
• pp.96-103
• /
• 1998

With the advance of processing technology , so as to spare fuel, piston heads used in automobile reciprocating engine have complex 3-dimension, with respect to shape such as ovality, profile, eccentricity, offset, recess. Therefore, coming out of the existing process work used master cam. the process work is performed using a CNC lathe. For a precision processing, the processing work is need to make study of high speed feed gear synchronized with the rotative speed of main spindle. And then the high speed feeding system must maintain high dynamic stiffness, high speed and high positioning accuracy . In this paper, in order to achieve high speed cutting tool feeding. The linear brushless DC motor is used for satisfying this process work. The ball bush and turicite is used as the guidance of the feed gear system. Also linear encoders, digital servo amplifiers and controller are used for controlling driving motor. This paper presents the design and simulation of the new tool feed system for noncircular machining.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.7
• /
• pp.1029-1037
• /
• 2004

High-speed/precision servomechanisms have been widely used in the manufacturing and semiconductor industries. In order to ensure the required high-speed and high-precision specifications in servomechanisms, an integrated design methodology is required, where the interactions between mechanical and electrical subsystems will have to be considered simultaneously. For the first step of the integrated design process, it is necessary to obtain not only strict mathematical models of separate subsystems but also formulation of an integrated design problem. A two-degree-of-freedom controller described in the discrete-time domain is considered as an electrical subsystem in this paper. An accurate identification process of the mechanical subsystem is conducted to verify the obtained mathematical model. Mechanical and electrical constraints render the integrated design problem accurate. Analysis of the system performance according to design and operating parameters is conducted for better understanding of the dynamic behavior and interactions of the servomechanism. Experiments are performed to verify the validity of the integrated design problem in the x-Y positioning system.

• Journal of the Korean Society for Precision Engineering
• /
• v.19 no.10
• /
• pp.120-129
• /
• 2002

An integrated structure and controller design approach for rotating cantilever beam is presented. An optimization method is developed for improving positioning performance considering the elastic deformations during high speed rotation and adopting the beam shape and the control gains as design variables. For this end, a dynamic model is setup by the finite element method according to the shape of the beam. The mass and stiffness of the beam are distributed in such a way that the closed-loop poles of the control system should be located leftmost in the complex s-plane. For optimization method, the simulated annealing method is employed which has higher probability to find the global minimum than the gradient-based down-hill methods. Sequential design and simultaneous design methods are proposed to obtain the optimal shape and controller. Simulations are performed with new designs by the two methods to verify the effectiveness of the approach and the results show that the settling time is improved for point-to-point position controls.

• Journal of Ocean Engineering and Technology
• /
• v.29 no.4
• /
• pp.300-308
• /
• 2015

With the increases in oil and gas prices, and energy consumption, drillship construction has increased during the last decade. A drillship using a dynamic positioning (DP) system to maintain its position and heading angle during drilling operations. In addition, a drillship is equipped with a moonpool structure to allow its drilling systems to be operated in the midship section. A drillship for the North Sea is specially designed to endure harsh environmental loads. For safe operation in the North Sea, the drillship should have good motion response and robust hull strength. A break water should be considered on the bow and side deck to prevent the green water on deck phenomenon from incoming waves. In addition, the moonpool should be designed to reduce the speed loss and resonance motion. In this study, the hydrodynamic characteristics of a drillship for the North Sea were examined in relation to the motion, wave loads, green water, and moonpool resonance in the initial design stage.

• Korean Journal of English Language and Linguistics
• /
• v.3 no.3
• /
• pp.453-497
• /
• 2003

The purpose of this study is to investigate social aspects of young EFL learners' interaction at the computer. Data were taken from the interactions of three pairs of fourth-grade primary school children who worked together on English learning software. Their interactions at the computer were videotaped and then all the talk produced by the students and the utterances emitted from the computer were transcribed. As for the analytical tools, the notion of ‘contextualization cues’ (Gumperz, 1982) and the concept of ‘positioning’ (Davies & Harre,1990) were employed. The analysis reveals that the roles of the students were not tied to a certain position, but rather dynamically changed during the course of interactive work according to the situation at hand. The dynamic changes in their positions were realized through various means; their capability in solving problems, their taking responsibility or assigning it to each other, or cooperation. There were also instances of peer teaching and motivated learning. In addition, the students showed autonomy in their learning activity. These findings suggest that both students in a dyad had their own place in performing task activities, contributing to solving problems and getting benefits from peer interaction. Furthermore, students' working together on English learning software may provide an environment which can promote cooperative attitude and responsibility for learning and enhance motivation and autonomy in their learning process.