• 한국정밀공학회지
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• 제34권4호
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• pp.259-264
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• 2017

Spectrally resolved interferometry (SRI) is an attractive technique to measure absolute distances without any moving components. In the spectral interferogram obtained by a spectrometer, the optical path difference (OPD) can simply be extracted from the linear slope of the spectral phase. However, SRI has a fundamental measuring range limitation due to maximum and minimum measurable distances. In addition, SRI cannot distinguish the OPD direction because the spectral interferogram is in the form of a natural sinusoidal function. In this investigation, we describe a direction determining SRI and propose the optimal conditions for determining OPD direction. Spectral phase nonlinearity, caused by a dispersive material, effects OPD direction but deteriorates spectral interferogram visibility. In the experiment, various phase nonlinearities were measured by adjusting the dispersive material (BK7) thickness. We observed the interferogram visibility and the possibility of direction determination. Based on the experimental results, the optimal dispersion conditions are provided to distinguish OPD directions of SRI.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2004년도 학술발표회
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• pp.479-483
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• 2004

A new calculation method of expected overtopping probability of rubble mound breakwater considering real tide occurrence has been proposed. A calculation method of expected overtopping probability of rubble mound breakwater was proposed by Kweon and Suh (2003). In their calculation, the fluctuation of tidal elevation was expressed by the sinusoidal change that yields the uniform distribution of occurrence frequency. However, the realistic distribution of tidal elevation should influence on the overtopping chance. In this study, the occurrence frequency of tidal elevation obtained from the real sea is included. The tidal elevation used in this study is collected from the east coastal part of Korean peninsular. Analyzing the annual data of the tidal fluctuation measured hourly during 355 days, the distribution of occurrence frequency is formulated utilizing by the normal distribution with one peak. Among the calculation procedures of annual maximum wave height, wave height-period joint distribution, wave run-up height and occurrence frequency of tide, only the annual maximum wave height is again chosen randomly from normal distribution to consider the uncertainty. The others are treated by utilizing the distribution function or relationship itself, It is found that the inclusion of the variability of tidal elevation has great influence on the computation of the expected overtopping probability of rubble mound breakwater. The bigger standard deviation of occurrence frequency is, the lower the overtopping probability of rubble mound breakwater is.

• 조명전기설비학회논문지
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• 제14권5호
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• pp.43-49
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• 2000

MH 랭프의 전자식 안정기에서 발생하는 음향공명의 감소를 위한 새로운 제어 방법올 제시한다. 주파수 가변 공전 인버터를 해석하고 전달함수를 구한다. 안정기의 전류제어기로 적분길를 채용한다. 램프전력 교란 및 주파수 확산을 이용하며 음향공명올 감소시키 위해 전류제어기 입력에 200[Hz] 정현파를 부가하여 램프 전류를 진폭 변조시킨다.MH 250[W] 램프를 대상으로 변조도에 따른 램프의 아크 안정성을 조사하고 제안된 진폭변조에 의한 음향공명 감소법 및 전류 제어기 설계법의 타당성을 확인하였다.

• Advances in materials Research
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• 제8권3호
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• pp.155-177
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• 2019

In this paper, a new displacement based high-order shear deformation theory is introduced for the static response of functionally graded sandwich plate with new definition of porosity distribution taking into account composition and the scheme of the sandwich plate. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, has strong similarity with classical plate theory in many aspects, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. Material properties of FGM layers are assumed to vary continuously across the plate thickness according to either power-law or sigmoid function in terms of the volume fractions of the constituents. The face layers are considered to be FG across each face thickness while the core is made of a ceramic homogeneous layer. Governing equations are derived from the principle of virtual displacements. The closed-form solution of a simply supported rectangular plate subjected to sinusoidal loading has been obtained by using the Navier method. Numerical results are presented to show the effect of the material distribution, the sandwich plate geometry and the porosity on the deflections and stresses of FG sandwich plates. The validity of the present theory is investigated by comparing some of the present results with other published results.

• 전기전자학회논문지
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• 제5권1호
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• pp.91-99
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• 2001

공기 갭을 갖는 이방성 매질의 기판과 덮개층 구조에서 사각 마이크로스트립 안테나 공진 주파수의 파수 영역에 대해 해석하였다. 일축성 매질의 특성을 나타내는 텐서의 구성 관계식으로부터 파수영역에서의 다이애딕 그린 함수를 유도하였으며 이 결과를 푸리에 변환을 사용하여 공간에서의 전계 적분 방정식으로 수식화하였다. 캘러킨 모멘트법을 사용하여 적분 방정식을 이산화하였으며 기저함수로는 정현적 함수를 선택하였다. 수치해석 결과의 타당성을 검증하기 위해 기존의 결과와 비교, 일치된 결과를 얻었으며 공기 갭의 두께, 패치 길이 그리고 덮개층의 비유전율과 이방성 덮개층의 이방성 비의 변화에 따른 공진 주파수의 변화가 제시되고 분석되었다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권7호
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• pp.452-461
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• 2004

A novel multilevel PWM inverter is presented for the use of stand-alone photovoltaic power generation system. In appearance, it consists of three full-bridge modules and three cascaded transformers; therefore, the configuration of the proposed multilevel PW inverter is equal to that of a prior 11-level PWM inverter. Only the turn-ratio of a transformer and its corresponding switching function are different from each other. Owing to these differences, the proposed 19-level PWM inverter has two promising advantages. First, output voltage levels increase almost twofold. Consequently, it can generate more sinusoidal output voltage waveform. Second, due to a revised switching pattern, it lightens power imposed on the transformer, which is used for compensating output voltages with chopped pulses between steps. The validity of the proposed inverter system is verified by computer-aided simulations and experimental results based on a 1 ［kW］ prototype. The performance of the proposed 19-level PWM inverter is compared with the Prior 11-level PWM inverter and other counterparts.

• Structural Engineering and Mechanics
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• 제75권6호
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• pp.713-722
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• 2020

This article aims to illustrate the damped dynamic responses of layered functionally graded (FG) thick 2D beam under dynamic pulse sinusoidal load by using finite element method, for the first time. To investigate the response of thick beam accurately, two-dimensional plane stress problem is assumed to describe the constitutive behavior of thick beam structure. The material is distributed gradually through the thickness of each layer by generalized power law function. The Kelvin-Voigt viscoelastic constitutive model is exploited to include the material internal damping effect. The governing equations are obtained by using Lagrange's equations and solved by using finite element method with twelve -node 2D plane element. The dynamic equation of motion is solved numerically by Newmark implicit time integration procedure. Numerical studies are presented to illustrate stacking sequence and material gradation index on the displacement-time response of cantilever beam structure. It is found that, the number of waves increases by increasing the graduation distribution parameter. The presented mathematical model is useful in analysis and design of nuclear, marine, vehicle and aerospace structures those manufactured from functionally graded materials (FGM).

• 한국광학회지
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• 제4권1호
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• pp.90-100
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• 1993

단면의 모양이 반달꼴인 이산화규소 광도파로의 모우드특성을 분석할 수 있는 수치계산 프로그램을 구성하고, 이것을 써서 광도파로의 도파특성을 살펴보았다. 수치계산의 기본 원리는 파동함수를 비교적 모양이 간단한 조화함수로 전개함으로써 파동방정식을 행렬방정식으로 바꾸고, 이 행렬을 대각화하여 고유값과 고유벡터를 구하는 것이다. 이 논문에서는 이 원리를 실제 프로그램에 실현시키는 과정과 그때 생기는 문제점들의 해결방법을 설명하였다. 이 프로그램을 써서 단면의 모양이 반달꼴인 이산화규소 광도파로와 그외에 다른 몇몇 전형적인 단면을 갖는 광도파로의 도파모우드의 특성을 분석하였다.

• 조명전기설비학회논문지
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• 제12권1호
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• pp.51-57
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• 1998

본 논문은 구동신호 위상제어 기능을 갖는 SIT고주파공진 인버터를 제안하였다. SIT를 이용한 위상제어형인버터는 낮은 스위칭 손실로서 높은 스위칭 주파수의 전력변환을 실현시킬 수 있다. 특히 2단위 인버터의 출력전압을 직렬로 연결하여 높은 출력을 얻을 수 있다. 과전류에 대해서 보호회로를 이용한 시스템의 안정성과 그리고 PLL에 의해 부하변화에 따른 자동추종제어를 실현하였다. 특히 제안된 인버터는 고주파에서도 거의 정현파에 가까우며, 스위칭 주파수 범위는 180∼220〔kHz〕이고, 2〔kW〕의 유도가열에 응용하였다. 본 인버터의 동작 특성에 대해서 이론과 실험결과를 비교 검토하였다.

• Journal of Power Electronics
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• 제15권1호
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• pp.131-145
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• 2015

The voltage-source inverters (VSI) supplying a motor drive are prone to open transistor faults. To address this issue in fault-tolerant drives applicable to electric vehicles, a new open transistor fault diagnosis (FD) method is presented in this paper. According to the proposed method, in order to define the FD index, the phase angle of the converter output current is estimated by a simple trigonometric function. The proposed FD method is adaptable, simple, capable of detecting multiple open switch faults and robust to load operational variations. Keeping the FD in mind as a mandatory part of the fault tolerant control algorithm, the FD block is applied to a five-phase converter supplying a multiphase fault-tolerant PM motor drive with non-sinusoidal unbalanced current waveforms. To investigate the performance of the FD technique, the fault-tolerant sliding mode control (SMC) of a five-phase brushless direct current (BLDC) motor is developed in this paper with the embedded FD block. Once the theory is explained, experimental waveforms are obtained from a five-phase BLDC motor to show the effectiveness of the proposed FD method. The FD algorithm is implemented on a field programmable gate array (FPGA).