• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.4
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• pp.350-358
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• 2009

This paper describes a result of the guidance and control for re-entry vehicle during TAEM phase. TAEM phase (Terminal Aerial Energy Management phase) has many conditions, such as density, velocity, and so on. Under these conditions, we have optimized trajectory and other states for guidance in TAEM phase. The optimized states consist of 7 variables, down-range, cross range, altitude, velocity, flight path angle, vehicle's azimuth and flight range. We obtained the optimized reference trajectory by DIDO tool, and used feedback linearization with neural network for control re-entry vehicle. By back propagation algorithm, vehicle dynamics is approximated to real one. New command can be decided using the approximated dynamics, delayed command input and plant output, NARMA-L2. The result by this control law shows a good performance of tracking onto the reference trajectory.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.1
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• pp.16-23
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• 2011

This paper suggests a motion compensation technique using GPS/IMU data in order to compensate for phase error caused by undesired motion of radar platform. An actual flight trajectory would be deviate from an ideal straight-constant trajectory with a constant velocity for SAR imaging, due to pitch, roll and yaw motion of aircraft caused by turbulence. This leads to blurred SAR images due to inter-pulse phase errors as well as along-track velocity errors. If the motion compensation is carried out to reduce those errors, SAR image quality can be significantly improved. Simulation results show that the motion compensation technique introduced in this paper is an effective tool to improve SAR image quality against severe motion of radar platform.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.8
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• pp.729-736
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• 2009

In order to understand flow characteristics and flight mechanism of hummingbird's flapping flight, two-dimensional numerical analysis is carried out on the flapping motion of hummingbird, Selasphorus rufus. Hummingbird's flapping wing motion is realistically modeled from wind tunnel experimental data to perform numerical analysis. Numerical simulation shows that, as freestream velocity changes, wing trajectory is also adjusted and it substantially affects lift and thrust generation mechanism. According to this tendency, flight domain is separated as "low speed" and "high speed" regime, and each flight domain is studied for physical understanding. As a result, the lift generation during downstroke can be explained by the well-known effects, such as leading edge vortex effect, delayed stall, wake capture and so on. In addition, the lift generation during upstroke, the unique character of hummingbird, is also examined by detailed flow analysis. The thrust generation mechanism is investigated by examining the hummingbird's wing bone structure, vortex generation pattern and the resulting pressure gradient.

• Journal of the Society of Naval Architects of Korea
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• v.61 no.4
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• pp.258-266
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• 2024

It is necessary to predict the ship's manoeuvrabilities in waves for its safe operations in adverse weather. At the early design stage, free-running model tests can be performed to estimate the ship's manoeuvring performance in irregular wave conditions. The wave elevations are randomly varied with times in irregular waves, large deviations of the manoeuvring performance indices are likely to occur depending on the start time of steering scenarios. In this study, a KSUPRAMAX model ship's manoeuvres in long-crested irregular waves are reproduced in the equivalent regular waves. The equivalent regular waves are searched from the energy flux relations between long-crested irregular and regular waves. But there are differences of forward speeds in the model tests, regular wave height and period are modified so that both the forward speed and the trajectory drift in regular waves are similar to those in irregular waves. In addition, low speed course-keeping tests are performed with various wave incident angles in irregular and regular waves. It is confirmed that check helms, drift angles, and speeds as well as trajectories in irregular waves are similar to those in equivalent regular waves.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2022.11a
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• pp.187-187
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• 2022

최근 선박의 자율운항기술이 활발하게 연구되어 오면서, 경로추종 제어 및 충돌회피 등의 자율운항 기술 연구가 많이 진행되고 있으며 그에 따른 시뮬레이션과 실해역 시험 등도 활발하게 수행되고 있다. 이러한 자율운항기술 중 본 연구에서는 AUV(Autonomous Underwater Vehicle) 진회수 시 모함에 활용되며 쌍동선형을 갖는 쌍동형 무인수상선을 대상으로 경로추종 제어에 대한 실해역 시험을 수행한 내용을 소개한다. 대상선인 쌍동형 무인수상선은 배수량이 약 10ton, 최대속도 10knots를 기준으로 설계된 선형이며 Sail drive 타입의 쌍축 추진기를 탑재하고 있으며 Fig. 1에 나타내었다. 실해역 시험은 경기도 화성시에 위치한 제부마리나 전면 해역에서 여러 속도에 대해 Fig. 2의 경로(빨간색)를 활용하여 수행되었다. 해당 경로는 변침각이 45도까지 이루어져 있다. 경로추종 제어 알고리즘은 목표경유점을 향하기 위해 선수각을 제어하는 부분과 목표속도로 추진하기 위해 속도를 제어하는 부분으로 나뉘어져 있다. 선수각 제어 시 경로와 무인선과의 위치 오차를 줄이는 방향으로 선수각이 향할 수 있도록 알고리즘이 설계되었다. 속도 제어의 경우 RPM 별로 실제 속도를 계측하여 데이터화 한 후, 실제 속도가 명령 속도와 다를 경우 RPM을 가감하여 명령 속도로 추진하기 위해 제어할 수 있도록 하였다. Fig. 2에서 파란색 선은 설계한 알고리즘을 활용하여 경로추종 제어를 한 결과의 궤적을 보여준다.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1379-1380
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• 2015

본 논문에서는 고도유지 제어기를 포함한 자율이동체의 수직 채널 안정화 루프를 제안한다. 제안된 방법은 일반적으로 널리 사용되고 있는 고전적인 수직채널 댐핑루프와 달리 고도정보와 함께 속도정보를 이용하여 궤적의 고도변화가 큰 이동체에 대하여 빠른 응답특성을 갖도록 한다. 루엔-버거(Luenberger) 관측기 구조를 이용함으로써 속도정보를 활용한 수직채널 안정화루프의 체계적 설계가 가능함을 보인다. 제안된 설계 방법에 대하여 모의실험을 통해 제안한 기법의 성능 및 유용성을 확인한다.

• Transactions of The Korea Fluid Power Systems Society
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• v.4 no.2
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• pp.21-27
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• 2007

This paper deals with the issue of trajectory tracking control of a clamping cylinder for injection moulding machine, which is directly driven by speed controlled hydraulic pump in combination with AC servomotor. As a fundamental step prior to tracking controller design, feedback control system is developed by implementing a position control loop parallel with a system pressure control loop. A sliding mode controller combining velocity feedforward scheme is developed for enhancing the tracking performance. Consequently a significant reduction in tracking error is achieved for both position and pressure control applications.

• Journal of the Korean Ceramic Society
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• v.40 no.10
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• pp.981-984
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• 2003

A novel linear ultrasonic motor for precision position control was designed and fabricated. It was composed of two piezoelectric actuators with longitudinal ultrasonic fluctuations and shaking beam. When two AC electric fields (Usinwt, Ucoswt) were applied to piezoelectric actuators respectively, the middle part of shaking beam had an elliptical trajectory. According to experimental results, the generative force was proportional to pre-load force but the speed of slider was in inverse proportion. And the bar of shaking beam had a same trajectory with simulation result.

• Proceedings of the Korea Information Processing Society Conference
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• 2004.11a
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• pp.59-62
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• 2004

이동객체 색인에 관한 기존 연구는 실외 환경의 빠른 속도로 이동하는 많은 이동객체들을 대상으로 과거 궤적과 현재 위치 및 미래 위치를 검색하는 색인 기법들이었다. 그러나 쇼핑몰이나 대형 박물관과 같은 건물의 실내나 놀이동산과 같은 한정된 영역의 이동객체들은 실외 환경에서처럼 빠른 이동속도를 가지고 있지 않다. 또한 이동객체들의 이동하는 영역이 한정되어 있을 뿐만 아니라 최대 수용인원 등이 정해져 있다. 본 논문에서는 이러한 특성을 갖는 실내 환경에 적합한 색인 기법으로 현재 그리고 미래 위치 질의 처리를 위한 공간색인과 시간 색인을 분리한 두 개의 색인 구조를 갖는 새로운 색인 기법과 가까운 미래 시간의 특정 영역에 있는 이동객체들의 수에 대한 질의응답을 위한 시공간 히스토그램을 구성하고, 적용하는 방법을 제안한다.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.36T no.1
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• pp.93-102
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• 1999

In this paper, we propose a data model and a retrieval method for content-based video query After partitioning a video into frame sets of same length which is called video-window, each video-window can be mapped to a point in a multidimensional space. A video can be represented a trajectory by connection of neighboring video-window in a multidimensional space. The similarity between two video-windows is defined as the euclidean distance of two points in multidimensional space, and the similarity between two video segments of arbitrary length is obtained by comparing corresponding trajectory. A new retrieval method with filtering and refinement step if developed, which return correct results and makes retrieval speed increase by 4.7 times approximately in comparison to a method without filtering and refinement step.