• Journal of the Society of Naval Architects of Korea
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• v.51 no.1
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• pp.88-98
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• 2014

A supercavitation is modern technology that can be used to reduce the frictional resistance of the underwater vehicle. In the process of reaching the supercavity condition which cavity envelops whole vehicle body, a vehicle passes through transition phase from fully-wetted to supercaviting operation. During this phase of flight, unsteady hydrodynamic forces and moments are created by partial cavity. In this paper, analytical and numerical investigations into the dynamics of supercavitating vehicle in transition phase are presented. The ventilated cavity model is used to lead rapid supercavity condition, when the cavitation number is relatively high. Immersion depth of fins and body, which is decided by the cavity profile, is calculated to determine hydrodynamical effects on the body. Additionally, the frictional drag reduction associated by the downstream flow is considered. Numerical simulation for depth tracking control is performed to verify modeling quality using PID controller. Depth command is transformed to attitude control using double loop control structure.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.358-363
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• 2017

The high intercept probability depends on optimization of the system, which consists of target detection, tracking system, missile system and so on. To reduce the complexity of global optimization of the system performance, simplification of the relative dependances of each sub-system is done and design parameters for DACS configuration are identified. The conceptual design process is addressed based on the requirement of the design parameters and new methodology is suggested for higher performance.

• Journal of Power System Engineering
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• v.10 no.4
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• pp.139-146
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• 2006

In this paper vector code correlation(VCC) method and an algorithm to promote the image processing performance in building an effective measurement system using cameras are described for automatically berthing and controlling the ship equipped with side thrusters. In order to realize automatic ship berthing, it is indispensable that the berthing assistant system on the ship should continuously trace a target in the berth to measure the distance to the target and the ship attitude, such that we can make the ship move to the specified location. The considered system is made up of 4 apparatuses compounded from a CCD camera, a camera direction controller, a popular PC with a built in image processing board and a signal conversion unit connected to parallel port of the PC. The object of this paper is to reduce the image processing time so that the berthing system is able to ensure the safety schedule against risks during approaching to the berth. It could be achieved by composing the vector code image to utilize the gradient of an approximated plane found with the brightness of pixels forming a certain region in an image and verifying the effectiveness on a commonly used PC. From experimental results, it is clear that the proposed method can be applied to the measurement system for automatic ship berthing and has the image processing time of fourfold as compared with the typical template matching method.

• The Mathematical Education
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• v.44 no.4 s.111
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• pp.497-508
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• 2005

The investigation of the curriculum in other countries provides meaningful implications to reflect our own curriculum. Since Korea is now under the curriculum revision, international comparative research was conducted with the curricula of Singapore and India to elicit some implications. These two countries were especially chosen because their curricula have not been actively investigated yet. Singapore mathematics curriculum starts the tracking based on students' mathematical ability from the 4th grade, and provides different curricula for the three tracks. This differentiated curriculum provides rich implications to next Korean curriculum which aims to classify the contents based on students' mathematical achievements. Indians, who have contributed significantly in the history of mathematics, have unique mathematics curriculum, remote from so called 'canonical curriculum'. After the U.S. announced the Curriculum and Evaluation Standard for School Mathematics in 1989 and the Principles and Standards for School Mathematics in 2000, many countries benchmarked these NCTM documents, and Korea was no exception. Since each country has their own school system, educational environment, and national mentality, it is not desirable to just adopt the curriculum of other countries. In this regard, Indians who have preserved their own mathematics curriculum can be a model. In sum, when we revise the curriculum, it is required to keep the balance between the open-mindedness to accept the strengths of other curricula, and the conservative attitude to preserve our own characteristics of the curriculum.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.2
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• pp.63-71
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• 2003

This paper presents a robust slewing control of a flexible space structure based on sliding surface design. A sliding surface is designed for a single-axis rest-to-rest slewing in view of target angle, target angular velocity, and root monent of the flexible appendage. In comparison with the Lypunov control law, both controllers guarantee the stability and command tracking capabilities for nominal system. It is also shown that the designed control law provides further robustness to internal/external uncertainties. Extending the results of a single-axis maneuver, a sliding mode control law was sought for an arbitrary three-axis maneuver. Quaternion was used to determine the attitude of a space structure and sliding surfaces were designed for each axis, thereby a robust control law was derived considering the coupling effects between each rotational axis during the maneuver. Several numerical examples were demonstrated to show the effectiveness of the designed control law.

• Journal of the Korean earth science society
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• v.24 no.5
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• pp.467-476
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• 2003

For the seafloor acoustic image mapping of side scan sonar, the beginning step of the procedure is to fix the absolute sonar (tow-fish) position since the sonar is not hull mounted but towed astern. The technical algorithm used to calculate the actual sonar position without any other additional sub-system, i.e., the underwater acoustic position tracking system or the sonar attitude measuring device, was proposed. In the seafloor image mosaic mapping results using the sonar track (not ship track) developed in this study, any ambiguity or inconsistency of seafloor features was not found. The incidental effect from the sonar position determination procedure orients the towing direction of sonar to be smooth, consequently the swath pattern on the across-track direction becomes stable and the blanking phenomenon of the insonification area is reduced conspicuously. This technical method is considered to be an useful tool when applied toother underwater towing vehicle surveys.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.7
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• pp.610-617
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• 2017

In the recent weapon system trend, it is required to develop small and low cost guidance missile to track and strike the enemy target effectively. Controling the such small drone typed weapon demands a integrated electronic device that equipped with not only a wireless network interface, a high resolution camera, various sensors for target tracking, and position and attitude control but also a high performance processor that integrates and processes those sensor outputs in real-time. In this paper, we propose the android smartphone as a solution for that and implement the guidance and control application of the missile. Furthermore, the performance of the implemented guidance and control application is analyzed through the simulation.

• Journal of Korean Society for Geospatial Information Science
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• v.13 no.1 s.31
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• pp.63-69
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• 2005

Interferometric Synthetic Aperture Radar(InSAR) is a rapidly evolving technique. Spectacular results obtained in various fields such as the monitoring of earthquakes, volcanoes, land subsidence and glacier dynamics, as well as in the construction of Digital Elevation Models(DEMs) of the Earth's surface and the classification of different land types have demonstrated its strength. As InSAR is a remote sensing technique, it has various sources of errors due to the satellite positions and attitude, atmosphere, and others. Therefore, it is important to validate its accuracy, especially for the DEM derived from Satellite SAR images. In this study, Real Time Kinematic(RTK) GPS and Kinematic GPS positioning were chosen as tools for the validation of InSAR derived DEM. The results showed that Kinematic GPS positioning had greater coverage of test area in terms of the number of measurements than RTK GPS. But tracking the satellites near and/or under trees md transmitting data between reference and rover receivers are still pending tasks in GPS techniques.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.5
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• pp.431-437
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• 2006

In this paper vector code correlation(VCC) method and an algorithm to promote the image-processing performance in building an effective measurement system using cameras are described far automatically berthing and controlling the ship equipped with side-thrusters. In order to realize automatic ship berthing, it is indispensable that the berthing assistant system on the ship should continuously trace a target in the berth to measure the distance to the target and the ship attitude, such that we can make the ship move to the specified location. The considered system is made up of 4 apparatuses compounded from a CCD camera, a camera direction controller, a popular PC with a built-in image processing board and a signal conversion unit connected to parallel port of the PC. The object of this paper is to reduce the image-processing time so that the berthing system is able to ensure the safety schedule against risks during approaching to the berth. It could be achieved by composing the vector code image to utilize the gradient of an approximated plane found with the brightness of pixels forming a certain region in an image and verifying the effectiveness on a commonly used PC. From experimental results, it is clear that the proposed method can be applied to the measurement system for automatic ship berthing and has the image-processing time of fourfold as compared with the typical template matching method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.627-636
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• 2021

This paper deals with a study for the guidance control of reusable launch vehicle. For this purpose, modeling of the equation of motion of a reusable launch vehicle with 6 degrees of freedom was performed. With this model, an optimal re-entry path was created and a path-following guidance control simulation was performed to follow the optimal re-entry path. For the design of the path-following guidance controller, the attitude controller applying a time-delay technique that is resistant to modeling uncertainty, disturbance and failure. And the nonlinear path-following guidance law were used. Guidance control simulation using a classical PD controller was performed and compared with the guidance control simulation of a reusable launch vehicle applying a time delay technique.