• 한국초전도ㆍ저온공학회논문지
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• 제16권1호
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• pp.1-5
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• 2014

We calculated the resonance tunneling energy band in the BCS gap for Type-II superconductor in which periodic potential is generated by external magnetic flux. In this model, penetrating magnetic flux was assumed to be in a fixed lattice state which is not moving by an external force. We observed the existence of two subbands when we used the same parameters as for the $Nd_{1.85}Ce_{0.15}CuO_X$ thin film experiment. The voltages at which the regions of negative differential resistivity (NDR) started after the resonant tunneling ended were in a good agreement with the experimental data in the field region of 1 T - 2.2 T, but not in the high field regions. Discrepancy occurred in the high field region is considered to be caused by that the potential barrier could not be maintained because the current induced by resonant tunneling exceeds the superconducting critical current. In order to have better agreement in the low field region, more concrete designing of the potential rather than a simple square well used in the calculation might be needed. Based on this result, we can predict an occurrence of the electromagnetic radiation of as much difference of energy caused by the 2nd order resonant tunneling in which electrons transit from the 2nd band to the 1st band in the potential wells.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권1호
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• pp.1-8
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• 2000

Switched reluctance motor(SRM) has simple magnetic structure, and requires simple power electronic driving circuit. It is very useful for wide range adjustable speed drive system. But, SRM drive generates large vibration and acoustic noise because it is commutated individually by step pulse m.m.f of each phase pole. In the vibration and acoustic noise characteristics. The considerable vibration and noise is induced by radial deforming of stator, so the frequency of dominant vibration and noise is coincident with the frequency of natural mode frequency of mechanical structure. This radial vibration force is generated in the phase commutation region. This paper suggests the new electromagnetic structure of SRM with auxiliary commutation winding which is excited by direct current. This phase and commutation winding are coupled magnetically between one phase winding and the other. Therefore, the switch-off phase current is absorbed by the another phase winding. By this interaction of phase and commutation winding in commutation mechanism, vibration and noise is reduced. And this reduction effect is examined by the test of prototype machine. As a result, SRM with DC exciting commutation winding is very useful to reduce vibration and acoustic noise.

• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1732-1739
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• 2018

With the explosion of digital devices, interaction technologies between human and devices are required more than ever. Especially, hand gesture recognition is advantageous in that it can be easily used. It is divided into the two groups: the contact sensor and the non-contact sensor. Compared with non-contact gesture recognition, the advantage of contact gesture recognition is that it is able to classify gestures that disappear from the sensor's sight. Also, since there is direct contacted with the user, relatively accurate information can be acquired. Electromyography (EMG) and force-sensitive resistors (FSRs) are the typical methods used for contact gesture recognition based on muscle activities. The sensors, however, are generally too sensitive to environmental disturbances such as electrical noises, electromagnetic signals and so on. In this paper, we propose a novel contact gesture recognition method based on Flexible Epidermal Tactile Sensor Array (FETSA) that is used to measure electrical signals according to movements of the wrist. To recognize gestures using FETSA, we extracted feature sets, and the gestures were subsequently classified using the support vector machine. The performance of the proposed gesture recognition method is very promising in comparison with two previous non-contact and contact gesture recognition studies.

• 조명전기설비학회논문지
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• 제26권10호
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• pp.52-59
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• 2012

In this paper, The cast resin transformer's vibration is measured using noncontact raser vibrometer(LV110D). The vibration characteristics of transformer windings and core are analyzed for relation between vibration magnitude and cause. Using the analysis results, the technique is presented to diagnose cast resin transformer. which is able to diagnose transformer' deformation in winding and core geometry. The magnetostriction and electromagnetic force act on the core and windings, causing them to vibrate. The vibration from windings and core penetrates into transformer cast resin and reaches the outside walls. The fundamental frequency of the core and windings vibration signal is twice that of the power frequency(120Hz). The results show that the magnitude of core vibration is linear to driving voltage amplitude and magnitude of windings vibration is increased to loading current under the some level and then stabilized.

• 대한전기학회논문지:전력기술부문A
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• 제48권1호
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• pp.1-7
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• 1999

In power transformers, vibration signals can occur at winding and core due to the change of current, voltage, and temperature and the deformation of winding and core. The deformation of winding and core occurs electromagnetic force induced by fault current in power systems. There firem the changes of vibration signals can be very different in normal or fault states of power transformers. We edtect and analyze the changes of vibration signals and use them as a tool for fault diagnosis of power transformers. This paper presents fault discriminating polliblility using the changes of fundamental waves and higher harmonics in power transformers. We showed the fault discriminating functions that are made at each case ; normal state and fault state. These functions are tested by the detected vibration signals, and we showed that the proposed method can discriminate the state of power transformers.

• 전력전자학회논문지
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• 제2권1호
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• pp.26-32
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• 1997

본 논문에서는 자동차나 항공기에서 많이 사용되고 있는 고속 솔레노이드 밸브의 플런저형 솔레노이드에 대한 설계기술을 확보하기 위하여, 수치해석을 통해 플런저의 이동시간에 대해 설계 파라메타들이 미치는 영향 및 솔레노이드의 동작특성을 검토하였다. 솔레노이드의 형상이 원통형이므로 축대칭원통좌표계를 이용하였고, 특히 전자기적 부분의 이론 해석시 와전류에 의한 영향을 고려하였으며, 가정자로법에 의해 퍼미언스를 계산하여 해석에 활용하였다. 구해진 파라메타의 해석 결과를 참고로 하여, 파라메타 값을 약간씩 변화시켜서 시간에 따른 플런저의 변위, 전류, 흡인력과의 관계등 동특성을 재해석하는 과정을 반복하여 최적치를 도출하였다. 도출된 최적치를 사용한 모의실험결과 플런저 이동시간은 1.8[ms] 정도의 고속이 됨을 알 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.242-247
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• 2004

In this study was proposed a transient response analysis technique of a rotor system, applying the generalized FE modeling method of a rotor-bearing system considering a base-transferred shock force and together the state-space Newmark method of direct time integration scheme based on the average velocity concept. Experiments were performed to a test rig of a mock-up rotor-bearing system with series of half-sine shock waves imposed by an electromagnetic shaker, and quantitative error analyses between analytical and experimental results were carried out. The transient reponses of the rotor were sensitive to duration times and shape-qualities of the shock waves, and overally the analytical results agreed quite well with the experimental ones. Particularly, in cases that the frequencies, $1/(2{\times}duration\;time)$, of the shock waves were close to the critical speed of the rotor-bearing system, resonances occurred and the transient responses of the rotor were amplified.

• Nuclear Engineering and Technology
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• 제51권3호
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• pp.654-664
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• 2019

The geometrical and electromagnetic variables of a rectangular-type magnetohydrodynamic (MHD) circulation system are optimized to solve MHD equations for the active decay heat removal system of a prototype Gen-IV sodium fast reactor. Decay heat must be actively removed from the reactor coolant to prevent the reactor system from exceeding its temperature limit. A rectangular-type MHD circulation system is adopted to remove this heat via an active system that produces developed pressure through the Lorentz force of the circulating sodium. Thus, the rectangular-type MHD circulation system for a circulating loop is modeled with the following specifications: a developed pressure of 2 kPa and flow rate of $0.02m^3/s$ at a temperature of 499 K. The MHD equations, which consist of momentum and Maxwell's equations, are solved to find the minimum input current satisfying the nominal developed pressure and flow rate according to the change of variables including the magnetic flux density and geometrical variables. The optimization shows that the rectangular-type MHD circulation system requires a current of 3976 A and a magnetic flux density of 0.037 T under the conditions of the active decay heat removal system.

• 한국기계가공학회지
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• 제20권1호
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• pp.103-109
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• 2021

Fine chips generated by machining have an impact on machine failure and quality of machined products, it is necessary to remove the chips, so the microchip collection and removal device by rotating conveyor belt with neodymium permanent magnets was developed. In this research, to solve the problem for reducing the existing microchips in the tank, a micro-chip removal device by rotating conveyor belt with neodymium permanent magnets developed. In the development of micro-chip removal device, 3D CATIA modeling was used, and the flow analysis and the electromagnetic force analysis were performed with COMSOL Multiphysics program. To evaluate the performance of the prototypes produced, design of experiments (DOE) is used to obtain the effect of neodymium conveyor movement speed on chip removal for the ANOVA analysis of recovered powders. An experiment was conducted to investigate the effect of the conveyor feed rate on the chip removal performance in detail. As a result of the experiment, it was confirmed that the slower the feeding speed of the fine chip removing device, the more efficient the chip removal.

• 한국방재학회 논문집
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• 제9권5호
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• pp.79-86
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• 2009

최근 도심 구조물의 규모가 급격히 대형화됨에 따라 인접구조물이 존재하는 상태에서 대규모의 기초구조물의 설치를 위한 넓고 깊은 범위의 굴착이 빈번히 시행되고 있어 안전관리의 중요성이 크게 부각되고 있다. 시공 및 사용 중에 토류구조물의 안전성을 확보하기 위해서는 쏘일앵커, 쏘일네일 및 락앵커 등의 지반보강재에 작용하는 프리스트레스 하중(prestress force) 및 변형을 지속적이고 효과적으로 관측할 수 있는 방법이 필요하다. 그러나 현재 현장에서 주로 사용되는 전기저항식 로드셀과 스트레인게이지, 바이브레이팅 타입의 변형율계를 이용한 변형 및 장력의 측정은 센서 자체의 자기열화 특성 때문에 장기적인 모니터링에는 효과적이지 않을뿐더러 시험체 내부에서 다수의 측정점을 측정하기 위해서는 많은 스트레인게이지를 설치하기 위해 리드선의 공간이 크게 필요한 단점이 있다. FBG(Fiber Bragg Grating)센서는 스트레인게이지와 비교해서 매우 작은 직경을 가지며 전자기파에 의한 노이즈가 없고 내구성이 커서 장기적인 모니터링이 필요한 구조물에 매우 유용하게 사용될 수 있다. 본 연구에서는 7연 강연선의 센터 킹케이블에 FBG 센서를 내장한 스마트 텐던을 이용하여 토류구조물의 보강에 활용되고 있는 앵커와 주변 그라우트면의 하중전이 특성에 대한 일련의 실내실험 결과를 기술하였다. 연구결과 스마트 텐던은 기존의 스트레인 게이지 변형율계로는 마땅히 측정할 수 없던 7연 강연선과 그라우트면의 변형률을 매우 효과적으로 측정할 수 있을 뿐 아니라 하나의 선으로 여러 위치의 변형을 효과적으로 측정할 수 있어 지반보강재의 장력모니터링 뿐만 아니라 그라우트로 부착된 부분의 하중전이 특성을 효과적으로 파악할 수 있는 것으로 나타났다.