• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.10
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• pp.1990-1998
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• 2017

The success of naval operation prioritizes the implementation of a robust communication network that delivers accurate and prompt communications to one another. The satellite, which is the main communication network of the military, is required to construct a preliminary communication network because of the enemy radio disturbance and weak point of fixed antenna. The military operational communication network has been in transition from voice-centered wireless communication network to text message-based communication network. In this paper we suggest an enhanced communication method built on Roll Call, the main communication method of ROK Navy operating tactical data link called Link-11. Simulation results display that the proposed method reduces the transmission time per unit frame by 4.3 times compared to the Roll Call and 6.3 times compared with the Round Robin & Broadcasting; it is also proved that the higher the direct reception rate, the shorter the transmission time required by 1.6 times maximum.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.2
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• pp.202-208
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• 2001

A Switched Reluctance Motor(SRM) has double salient poles structure and the phase windings are wound in stator. SRM hase more simple structure that of other motor, thus manufacture cost is low, mechanically strong, reliable to a poor environment such as high temperature, and maintenance cost is low because of brushless. SRM needs position detector to get rotator position information for phase excitation and tachometer or encoder for constant speed operation. But, this paper doesn\`s use an encoder of high cost for velocity measurement of rotator. Instead of it, the algorithm for position detection and velocity estimation from simple slotted disk has been proposed and developed. To implement variable speed digital control system with velocity estimation algorithm, the TMS320F240-20MIPS fixed point arithmetic processor of TI corporation is used. The experimental results of the developing system are enable to control speed with wide range, not only single pulse, hard chopping mode and soft chopping, ut also variable speed control, and advance angle control.

• The KSFM Journal of Fluid Machinery
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• v.17 no.2
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• pp.41-47
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• 2014

Experimental results are given for the vertical motion of water in the water chambers for wave energy converter aligned along the wave propagation direction in order to avoid the impulsive wave forces. This paper mainly focuses on the property of the amplitude of the vertical motion of the water surface in the chambers. The amplification has been investigated by dimensionless parameters of wave period to resonance period ratio of the U-shaped oscillation, $T/T_r$, chamber size to wave length ratio, l/L, water depth to wave length ratio, h/L, amplitude of up-down motion of water particles to draft of the front wall ratio, ${\zeta}/D$. It has been shown that l/L should be less than 0.1 and as $T/T_r$ approaches unity the up-down of the water in the chambers is amplified. Also, the structure of the walls which form th water chambers has been examined roughly. It is deduced that the chambers set on both sides of the hull of a single-point moored floating vessel is preferable to those set along a fixed structure such as breakwaters.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.4
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• pp.581-589
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• 2015

This paper describes a monocular vision-based formation flight technology using two fixed wing unmanned aerial vehicles. To measuring relative position and attitude of a leader aircraft, a monocular camera installed in the front of the follower aircraft captures an image of the leader, and position and attitude are measured from the image using the KLT feature point tracker and POSIT algorithm. To verify the feasibility of this vision processing algorithm, a field test was performed using two light sports aircraft, and our experimental results show that the proposed monocular vision-based measurement algorithm is feasible. Performance verification for the proposed formation flight technology was carried out using the X-Plane flight simulator. The formation flight simulation system consists of two PCs playing the role of leader and follower. When the leader flies by the command of user, the follower aircraft tracks the leader by designed guidance and a PI control law, and all the information about leader was measured using monocular vision. This simulation shows that guidance using relative attitude information tracks the leader aircraft better than not using attitude information. This simulation shows absolute average errors for the relative position as follows: X-axis: 2.88 m, Y-axis: 2.09 m, and Z-axis: 0.44 m.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.8
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• pp.750-757
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• 2011

Wireless Sensor Network is composed of a lot of sensor nodes that are densely deployed in a field. So generally this sensor nodes are spreaded using Helicopter or Fixed wing. Each node delivers own location and acquired information to user when it detects specific events. In this paper, we propose localization algorithm without range information in wireless sensor network using helicopter. Helicopter broadcasts periodically beacon signal for sensor nodes. Sensor nodes stored own memory this beacon signal until to find another beacon point(satisfied special condition). This paper develops a localization mechanism using the geometry conjecture(perpendicular bisector of a chord) to know own location. And the simulation results demonstrate that our localization scheme outperforms Centroid, APIT in terms of a higher location accuracy.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.88.2-88.2
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• 2011

Fast Imaging Solar Spectrograph (FISS) is an instrument developed by Seoul National University and Korea Astronomy and Space Science Institute and installed at the 1.6 meter New Solar Telescope of Big Bear Solar Observatory. Using this instrument, we observed solar filaments and analyzed the data focusing on determining the temperature and non-thermal velocity. We inferred the Doppler absorption widths of $H{\alpha}$ and Ca II 8542$\bar{A}$ lines from the line profiles using the cloud model. From these values, we separately determined temperature and non-thermal velocity. Our first result came from a solar filament observed on 2010 July 29th. Temperature inside a small selected region of this ranges from 4500K to 12000K and non-thermal velocity, from 3.5km/s to 7km/s. We also found temperature varied a lot with time. For example temperature at a fixed point varied from 8000K to 18000K for 40 minutes, displaying an oscillating pattern with a period of about 8 minutes and amplitude of about 2000K. We will also present new results from filaments observed in 2011 summer.

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.521-529
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• 2002

We have recently proposed the new concept of a phase-measuring volumetric interferometer that enables us to accurately measure the xyz-coordinates of the probe without metrology frames. The interferometer is composed of a movable target and a fixed photo-detector array. The target is made of point diffraction sources to emit two spherical wavefronts, whose interference is monitored by an array of photo-detectors. Phase shifting is applied to obtain the precise phase values of the photo-detectors. Then the measured phases are fitted to a geometric model of multilateration so as to determine the xyz-location of the target by minimizing least square errors. The proposed interferometer has been designed and built with a volumetric uncertainty of less than 1.0 $\mu\textrm{m}$ within a cubic working volume of side 120 mm. Here, in this paper, we also present error sources, an evaluated uncertainty, and test results from the prototype system. The self-calibration of two-dimensional precision metrology stages is applied to test the performance of the interferometer.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.2
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• pp.10-23
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• 2009

The fundamental matrix and key frame selection are one of the most important techniques to recover full 3D reconstruction of objects from turntable sequences. This paper proposes a new algorithm that estimates a robust fundamental matrix for camera calibration from uncalibrated images taken under turn-table motion. Single axis turntable motion can be described in terms of its fixed entities. This provides new algorithms for computing the fundamental matrix. From the projective properties of the conics and fundamental matrix the Euclidean 3D coordinates of a point are obtained from geometric locus of the image points trajectories. Experimental results on real and virtual image sequences demonstrate good object reconstructions.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.1
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• pp.98-129
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• 1995

The purpose of this study was to evaluate how mandibular implant-supported fixed complete prosthesis, implant and mandible responded mechanically, according to curvature of arch, number and location of fixture, and amounts of load. The shape of mandibular arch was tapered or square form and, 4 or 6 fixtures were implanted in each arch model. A vertical load of 10kg was applied at the center of prosthesis and a vertical load of 20kg was applied at the location of the 10mm or 20mm cantilever posterior to the most distal implant. Three-dimensional finite element analysis was performed for stress distribution and deflection using commercial software(ABAQUS program) for Sun-SPARC Workstation. The results were as follows : 1. The case square arch form was more stable to compare with that of tapered arch form in respect of stress distribution and displacement under vertical load on the center of prosthesis. 2. 6-implants cases were more stable than 4-implants cases for decreasing bending torque under vertical load on the center of prosthesis. 3. Under vertical load on cantilever extension, the case of 10mm long cantilever was more stable than that of 20mm long cantilever in respect of stress distribution and displacement. 4. Under vertical load on cantilever extension, 6-implants cases had a tendency to reduce displacement and to increase the reaction force of supporting point due to increasing of the bending stiffness of the prosthesis than 4-implant case. 5. When the ends of 10mm or 20mm long cantilever were loaded, the most distal implant was under compressive stress but the second most distal implant was under the highest tensile stress and the remaining implants were under varying tensile stress. 6. Because 6-implants cases had smaller displacement than 4-implants cases, 6-implants cases were more favorable in respect of prevention of screw loosening under repeated loadings.

• Archives of Craniofacial Surgery
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• v.15 no.2
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• pp.53-58
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• 2014

Background: Maxillomandibular fixation (MMF) is usually used to treat double mandibular fractures. However, advancements in reduction and fixation techniques may allow recovery of the premorbid dental arch and occlusion without the use of MMF. We investigated whether anatomical reduction and microplate fixation without MMF could provide secure immobilization and correct occlusion in double mandibular fractures. Methods: Thirty-four patients with double mandibular fractures were treated with open reduction and internal fixation without MMF. Both fracture sites were surgically treated. For bony fixations, we used microplates with or without wire. After reduction, each fracture site was fixed at two or three points to maintain anatomical alignment of the mandible. Interdental wiring was used to reduce the fracture at the superior border and to enhance stability for 6 weeks. Mouth opening was permitted immediately. Results: No major complications were observed, including infection, plate exposure, non-union, or significant malocclusion. Five patients experienced minor complications, among whom the only one patient experienced a persistant but mild malocclusion with no need for additional management. Conclusion: This study showed that double mandibular fractures correction with two-or three-point fixation without MMF simplified the surgical procedure, increased patient comfort, and reduced complications, due to good stability and excellent adaptation.