• Journal of computational fluids engineering
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• v.17 no.4
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• pp.49-55
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• 2012

Research has importance in proposing the design of a tunnel with a vertical vent to secure passengers in a comfortable environment and safe against pressure. Using several analysis methods, the magnitude of the pressure induced by the vertical vent in the tunnel can be analyzed. In addition to the 3-dimensional method, the 2-dimensional method and the 2-dimensional axis-symmetric method are also used to analyze the strong and weak points of each so that the optimum analysis method can be obtained. As a result, it appears that the 2-dimensional axis-symmetric method is the most suitable in analyzing tunnel pressure consider to accuracy and time effective aspect. Also, the 3-dimensional method is disadvantageous in that it takes longer in calculating results, but is more effective in predicting phenomena around the vertical vent in the tunnel.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.47 no.6
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• pp.43-50
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• 2010

In this paper, the TWTA (Traveling Wave Tube Amplifier) maintenance system for the low altitude surveillance Radar was developed using the embedded Linux system, and its superiority was demonstrated through the performance test. Nowadays, the necessity of maintenance system and reliability testing on military equipments has been increasing steadily. In addition, nonlinear characteristics of the maintenance system for the low altitude surveillance Radar are more likely to have serious problems as well as to slow down durability. Therefore, after analyzing characteristics of RF input-output signal and TWTA, we designed interface circuits between the TWTA equipment and the embedded Linux system. The Linux kernel on the system was optimized to improve the efficiency and reliability. And our new TWTA maintenance system was evaluated in the real field. As a result, the proposed system was contented with desired specifications, and demonstrated military's fighting capabilities. Therefore, our novel system will advance military maintenance technology and will help to develop similar equipments.

• Journal of Electrical Engineering and Technology
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• v.1 no.1
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• pp.101-105
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• 2006

In this paper, a disk-type ultrasonic motor using a combination of radial and bending vibration modes is newly designed and fabricated. The characteristics of the test motor are also measured. By means of traveling elastic wave induced at the surface of circumference of the elastic disk, a steel bar in contact with the surface of circumference of the elastic disk bonded onto the piezoelectric ceramic disks is driven in both directions by changing the sine and cosine voltage inputs. The stator of the motor is composed of two sheets of piezoelectric ceramic disks to bond onto both surfaces of an elastic disk, respectively. As a result, the diameter of the elastic body is increased and the resonant frequency is decreased. The resonant frequency of the stator is about 92 kHz, which is composed with piezoelectric ceramic disks of 28 mm in diameter and 2 mm in thickness, and an elastic body of 32 mm in diameter and 2 mm in thickness. A driving voltage of 20 VPP Produces 200 rpm with a torque of 1Nm and an efficiency of about 10%.

• Investigative Magnetic Resonance Imaging
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• v.24 no.3
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• pp.95-122
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• 2020

In this article, we evaluated the performance of radiofrequency (RF) coils in terms of the signal-to-noise ratio (S/N) and homogeneity of magnetic resonance images when used for ultrahigh-frequency (UHF) 7T magnetic resonance imaging (MRI). High-quality MRI can be obtained when these two basic requirements are met. However, because of the dielectric effect, 7T magnetic resonance imaging still produces essentially a non-uniform magnetic flux (|B₁|) density distribution. In general, heterogeneous and homogeneous RF coils may be designed using electromagnetic (EM) modeling. Heterogeneous coils, which are surface coils, are used in consideration of scalability in the |B₁| region with a high S/N as multichannel loop coils rather than selecting a single loop. Loop coils are considered state of the art for their simplicity yet effective |B₁|-field distribution and intensity. In addition, combining multiple loop coils allows phase arrays (PA). PA coils have gained great interest for use in receiving signals because of parallel imaging (PI) techniques, such as sensitivity encoding (SENSE) and generalized autocalibrating partial parallel acquisition (GRAPPA), which drastically reduce the acquisition time. With the introduction of a parallel transmit coil (pTx) system, a form of transceiver loop arrays has also been proposed. In this article, we discussed the applications and proposed designs of loop coils. RF homogeneous coils for volume imaging include Alderman-Grant resonators, birdcage coils, saddle coils, traveling wave coils, transmission line arrays, composite right-/left-handed arrays, and fusion coils. In this article, we also discussed the basic operation, design, and applications of these coils.

• Journal of Korea Society of Digital Industry and Information Management
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• v.12 no.2
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• pp.15-24
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• 2016

GPS(Global Positioning System) location tracking is a method for taking the precise coordinates after the coordinates are obtained by a GPS receiver, and displaying them on the map. In this paper with WAVE(Wireless Access for Vehicular Environment) simulation, we show that various services such as vehicle tracking service, real-time road conditions service and logistics can go tracking service, control and operation services according to the vehicle position and the traveling direction by using the GPS position data. A vehicle tracking system using GPS is automatically able to manage multiple RCP when exchanging data between RMA and the RCP, and it provides rapid requests and responses. To verify that multiple sessions between RMA and RM, as well as multiple sessions between RMA and RCP are able to be implemented, we take RMA as a RCP application on an OBU, until the RMA is receiving data response from corresponding RM. As a result of this experiment, we show that the response speeds of single session between RMA and RM using 1, 2, 3, and 4 kbyte unit data are similar, 62.32ms, 62.65ms, 63.02ms, and 63.48ms, respectively. Likewise, those of 128 muliple sessions using 1, 2, 3, and 4 kbyte unit data are not much more time difference, 298.08ms, 302.21ms, 322.85ms, and 329.62ms, respectively.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1996.06c
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• pp.591-597
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• 1996

To straighten the path that farm machinery follows in paddy fields, it is necessary to measure and evaluate the tracks that these machines leave behind. However, there are no known methods for making such measurements and evaluations since it is difficult to accurately trace the paths that the machine make in paddy fields. Therefore, a measuring system has been developed which can accurately recored the path of a farm machinery in a field by measuring the horizontal straight-line distance from the side of the field to the machine. This system consists of a track subsystem on the machine and a range finder system. A measuring appraratus is installed on a flatcar which runs on rails over 50 m long at the side of the filed. The track subsystem uses a CCD camera to track the movement of the machine in the field which is following a lengthwise path. The range finder subsystem measures the distance that the measuring apparatus has traveled on the rails and the distance from the app ratus to the machine in the field. This system makes it possible to record the path that the machine travels. Even though differences in traveling distance arise between the measuring apparatus and the farm machine, these differences are detected by image processing , which allows the machine in the field to be located accurately. The short(0.05 second) time required for image processing is enough to follow an object . In the present study, this system was able to measure the path that a moving tractor makes. Even though a lag of up to 0.4 meters occurred, this system did not miss its target during operation of the track subsystem. Thus the path measuring system developed here is able to record vehicle paths automatically by following the movement of vehicles in the field and measuring the distance to them. It is expected to come into use in such applications as unmanned moving vehicle tests.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.233-233
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• 2011

ECR 이온원을 가볍고 작게 하면서 운전을 단순화함으로써 유지보수를 최소화하는 것은 특히 의료용 중입자 가속기에서 매우 중요한 조건 중 하나가 된다. 탄소 다가 이온을 만들어내기 위한 의료용 중입자가속기의 이온원으로 영구자석형 ECR 이온원을 개념 설계하였다. 영구자석은 이온원 입출구에서 강력한 축방향 자장을 만들기 위한 솔레노이드 자석 두 개와 반경방향 자장을 만들어 주기 6극 자석으로 구성된다. 또한 축방향 자장 흐름을 효과적으로 만들어주기 위한 두 개의 링 형 자석을 추가하여 자장의 강도를 높였다. 그러나 영구자석으로만 만들어진 자장 구조는 제작과 동시에 고정이 되어 수정이 불가능하기 때문에 제작 후 매우 제한적인 운전영역을 가질 뿐 만 아니라 최악의 경우에는 운전조건을 찾지 못하는 경우도 발생할 수 있다. 따라서 본 설계에서는 그림과 같이 두 개의 작은 보조 솔레노이드 전자석을 추가하여, 최소한의 운전조건으로 ECR 이온원의 공명영역을 결정하는 최소 자장의 구조뿐만 아니라 축방향 자장의 세기도 각각 능동적으로 제어할 수 있도록 하였다. 또한 마이크로파원으로는 TWT (Traveling Wave Tube)를 사용하여 10 GHz에서 14 GHz 까지 다양한 주파수에서 운전이 가능할 수 있도록 설계하였다. 이러한 설계를 통하여 다양한 운전조건을 가질 수 있는 안정된 ECR 이온원을 부피가 작으면서도 유지보수를 최소화하는 구조로 만들 수 있으며, 본 이온원은 탄소 다가 이온을 만들어내기 위한 목적뿐 만 아니라 다양한 중이온을 작은 규모로 만들어내기 위한 장치에서도 사용될 수 있다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.1
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• pp.35-41
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• 1997

A series-fed microstrip array antenna of beamwidth $10^{\circ}$, squint angle $80^{\circ}$ and SLL -15 dB below is designed. Series-fed arrays are formed by interconnecting all the elements by high-impedance transmission lines and feeding the power at the first element and it is a traveling-wave antenna which is terminated with a matched load. Radiation patterns and impedance matching of the antenna are analyzed by Ensemble 4.0, which is a popular software package for designing printed antennas and arrays. The squint angle of beam can be controlled by the spacing between the elements. The major advantages of series-fed array antennas are that feed arangement is compact and the losses associated with the feeding network are less than those of a corporate feed type. The antennas are fabricated on the RT/Duroid Laminates of 62 mil thickness. The experimental results are very close to the specifications to be designed.

• Nuclear Engineering and Technology
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• v.40 no.3
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• pp.213-224
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• 2008

The pumping of coolant in a liquid metal fast reactor may be performed with an annular linear induction electro-magnetic (EM) pump. Linear induction pumps use a traveling magnetic field wave created by poly-phase currents, and the induced currents and their associated magnetic field generate a Lorentz force, whose effect can be the pumping of the liquid metal. The flow behaviors in the pump are very complex, including a time-varying Lorentz force and pressure pulsation, because an induction EM pump has time-varying magnetic fields and the induced convective currents that originate from the flow of the liquid metal. These phenomena lead to an instability problem in the pump arising from the changes of the generated Lorentz forces along the pump's geometry. Therefore, a magneto-hydro-dynamics (MHD) analysis is required for the design and operation of a linear induction EM pump. We have developed a time-harmonic 2-dimensional axisymmetry MHD analysis method based on the Maxwell equations. This paper describes the analysis and numerical method for obtaining solutions for some MHD parameters in an induction EM pump. Experimental test results obtained from an induction EM pump of CLIP-150 at the STC "Sintez," D.V. Efremov Institute of Electro-physical Apparatus in St. Petersburg were used to validate the method. In addition, we investigated some characteristics of a linear induction EM pump, such as the effect of the convective current and the double supply frequency (DSF) pressure pulsation. This simple model overestimated the convective eddy current generated from the sodium flow in the pump channel; however, it had a similar tendency for the measured data of the pump performance through a comparison with the experimental data. Considering its simplicity, it could be a base model for designing an EM pump and for evaluating the MHD flow in an EM pump.

• Physical Therapy Rehabilitation Science
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• v.3 no.1
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• pp.27-32
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• 2014

Objective: The aim of this study was to compare the radial bone strength, sitting balance ability and global self-esteem of wheelchair martial arts practitioners and healthy control participants. Design: Cross-sectional study. Methods: Nine wheelchair martial art practitioners with physical disabilities and 28 able-bodied healthy individuals participated in the study. The bone strength of the distal radius was assessed using the Sunlight Mini-Omni Ultrasound Bone Sonometer; sitting balance was quantified using the modified functional reach test (with reference to a scale marked on the wall); and the self-administered Rosenberg self-esteem (RSE) scale was used to measure the global self-esteem of the participants. The velocity of the ultrasound wave (speed of sound, m/s) traveling through the outer surface of the radial bone was measured and was then converted into a T-score and a Z-score. These ultrasound T-score and Z-score that represent bone strength; the maximum forward reaching distance in sitting (cm) that represents sitting balance; and the RSE total self-esteem score that indicates global self-esteem were used for analysis. Results: The results revealed that there were no statistically significant between-group differences for radial bone-strength, maximum forward reaching distance, or self-esteem outcomes. Conclusions: The wheelchair martial arts practitioners had similar radial bone strength, sitting balance performance and self-esteem to able-bodied healthy persons. Our results imply that wheelchair martial arts might improve bone strength, postural control and self-esteem in adult wheelchair users. This new sport-wheelchair martial arts-might be an exercise option for people with physical disabilities.