• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.5
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• pp.391-399
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• 2020

KASI (Korea Astronomy and Space Science Institute) has been developing the multipurpose laser tracking system with three functions of satellite laser tracking, adaptive optics and space debris laser tracking for scientific research and national space missions. The space debris laser tracking system provides the distance to space debris without a laser retro-reflector array by using a high power pulse laser, which employs a spinning disk to change the optical path between the transmit and receive beams. The spinning disk causes the collision band which is unable to reflect the returned signal to a detector and then has an effect on the tracking coverage of space debris. This study proposed the mathematical model for tracking coverage by taking into account the various specifications of spinning disk such as disk size, spinning velocity and collision rate between the disk and hole. In addition, the spinning disk specifications were analyzed in terms of tracking coverage and collision band based on the mathematical model to investigate tracking requirements of the Geochang laser tracking system.

• Journal of the Korean Arthroscopy Society
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• v.13 no.1
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• pp.39-45
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• 2009

Purpose: To investigate the outcome of arthroscopic treatment for the complications of knee arthroplasty and to evaluate the effectiveness of arthroscopy. Materials and Methods: We analyzed 25 patients who underwent arthroscopy to treat complications of knee arthroplasty between May 1992 and June 2008. Nineteen cases out of 25 had total knee arthroplasty (TKA) and the remaining 6 cases had unicompartmental knee arthroplasty (UKA). Before arthroscopy, physical examinations and radiographic evaluations were carried out to find out the causes of complications. Joint fluid aspiration and hematologic evaluation were added when infection was suspected. Results: Among the diagnosis at the time of arthroscopy, there were 11 cases of infection, 6 cases of stiffness due to adhesion and fibrosis, and 2 cases of soft tissue impingement in the cases of TKA. Among the cases of UKA, one for each case of meniscal tear, subluxation of mobile insert, hemarthrosis, cement loose body, soft tissue impingement, and stiff knee was found. Nine out of 11 patients who had infection were treated successfully with arthroscopy but the remaining 2 cases underwent revision arthroplasty. Seven patients with arthrofibrosis had improved range of motion from $65^{\circ}$ preoperatively to $105^{\circ}$ postoperatively. The others also showed successful results after arthroscopy. Conclusion: Arthroscopy to treat complications after knee arthroplasty was a safe and effective method when appropriate selection of patients was made.

• Clinics in Shoulder and Elbow
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• v.1 no.1
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• pp.109-117
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• 1998

We evaluated the results of the surgery for impingement syndromes and partial thickness tears of the rotator cuff with an average follow-up period of 15 months. One group(group I) of 43 patients, 46 cases underwent arthroscopic subacromial decompression. The other comparable group(group Ⅱ) of 10 patients, II cases underwent open acromioplasty. The average age at operation was 48 years, old. Arthroscopic subacromial decompression achieved slightly better pain relief, the range of the acti ve forward flexion, function, strength and the overall score with improvement from the preoperative condition than open acromioplasty. The patient's satisfaction was better in group I as well. Using the UCLA Shoulder Rating Scale, 89% of group I and 82% of group n had good or excellent results. Preservation of the origin of the deltoid during an arthroscopic acromioplasty reduced the postoperative morbidity and made it possible to start rehabilitation sooner and to achieve the better and more predictable results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.18-31
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• 2018

Rotorcrafts have more severe crashworthiness conditions than fixed wing aircraft owing to VTOL and hovering. Recently, with the increasing demand for highly efficient transportation system, application of composite materials to aircraft structures is increasing. However, due to the characteristics of composite materials that are susceptible to impact and crash, demand to prove the crashworthiness of composite structures is also increasing. The purpose of present study is to derive the structural concept of composite subfloor for rotorcrafts and verify it. In order to design a crashworthy composite subfloor, the conceptual design of the testbed helicopter for the demonstration and the derivation of energy absorbing requirement were carried out, and the composite energy absorber was designed and verified. Finally, the testbed for the demonstration of a crashworthy composite structure was fabricated, and performed free drop test. It was confirmed that the test results meet the criteria for ensuring occupant survivability.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.5
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• pp.471-479
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• 2009

In this paper, we proposed an improved ray tracing method with an amelioration of visible tree structure, a visible face determination method, and non-uniform random test point method. In a proposed visible tree structure, it reduces tree nodes by means of merging similar nodes. In a visible face determination method, it shows that a ray hit test with a packet ray method can reduce a test time. A ray tracing method involving with a packet ray hit test method can improve a tree construction time up to 3.3 times than a ray tracing method with a single ray hit test method. Furthermore, by seeding a non-uniform and random test point on a face, tree construction time is improved up to 1.11 times. Received powers from the proposed ray tracing results and measured results have good agreement with 1.9 dB RMS error.

• Clinics in Shoulder and Elbow
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• v.11 no.1
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• pp.19-23
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• 2008

Purpose: To evaluate the bursoscopic findings of refractory primary adhesive capsulitis of the shoulder and to determine the clinical correlation. Materials and Methods: Arthroscopic capsular release was performed in 21 refractory adhesive capsulitis patients who had not responded to conservative treatment. The VAS for pain, range of motion, UCLA score was checked before and after surgery, and at the last follow up. Results: Bursitis, mild friction and impingement on coracoacromial ligament, as well as adhesion were observed. The function and pain improved earlier than after simple acromiohumeral joint capsular release. Conclusion: Subacromial bursoscopy helps rule out a hidden secondary frozen shoulder or secondary changes with primary adhesion. In addition, it has the advantage of being both a treatment and procedure for making a prognosis.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.177-180
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• 2010

Two-stage light gas gun, sorted with Ballistic Range System, is used to research spray characteristics of supersonic liquid jets. When high pressure tube was pressurized to the 135 bar, diaphragm films which composed with OHP film are ruptured. Expansion gases accelerate a projectile approximately 250 m/s at the exit of pump tube. And accelerated projectile collides with liquid storage part and liquid jets were injected into supersonic conditions. Supersonic liquid jets show the multiple jets and generate shockwave at the forward region of jets. Supersonic liquid jets of speed and shockwave angle have different value at each case. Supersonic liquid jets with minimum velocities are injected with M=1.53 at the geometry condition of L/d=23.8.

• Journal of the Institute of Convergence Signal Processing
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• v.22 no.2
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• pp.79-84
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• 2021

The most important device of the AGV is the guide sensor, and the typical function of this sensor is high accuracy and extraction of the road. If the accuracy of the guide sensor is low or the sensor device is extracted the wrong track, this causes the problems such as the AGV collision, track-out, the load falling due to AGV swing. In order to improve these problems, this study is proposed a signal processing method of the guide sensor based on multi-maskings and the center of gravity method, and evaluated its performance. As a result, the proposed method showed that the mean error of absolute value is 2.32[mm] and it showed performance improvement of 27[%] than the center of gravity method of existence. Therefore, when the proposed signal processing method is applied, It is thought that the posture control and driving stability of the AGV will be improved.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.10a
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• pp.18-20
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• 2021

In order to prevent collision accidents of ships, which has been increasing recently, research on artificial intelligence-based autonomously operated ships (Maritime Autonomous Surface Ship, MASS) is underway. However, most of the studies related to autonomous ships mainly target medium-to-large ships due to the size and cost of the autonomous navigation system, and the sensors used here have a problem in that it is difficult to mount them on small ships. Therefore, this paper provides a path tracking system equipped with GPS and IMU sensors for autonomous operation of small ships. GPS and IMU sensors are utilized to determine the exact position of the vessel, which allows the proposed system to manually control the small vessel model to create a path and then when the small vessel travels the same path. Use the Pure Pursuit algorithm to follow the path. As a result, In this research, it is expected that a lightweight and low-cost sensor can be used to develop an autonomous operation system for small ships at low cost.

• 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.