• Journal of Electrical Engineering and Technology
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• 제9권2호
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• pp.670-676
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• 2014

The objective of this research is to utilize the ultrasonic method to analyze the property of partial discharge (PD) which is generated by the winding of the insulation stator in the generator. Therefore, a PD measurement system is built based on ultrasonic and virtual instruments. Three types of PD models (internal PD model, surface PD model and slot PD model) have been constructed. With the analysis of these experimental results, this research has identified the ultrasonic signals of the discharges which were produced by three types of PD models. This analysis shows the different features among these PD types. Both the time domain and frequency domain of the ultrasonic signals are obviously different. In addition, an experiment based on a large rotating machine has been done to analyze ultrasonic noises. The result indicates that the ultrasonic noises can be wiped off by the filters and algorithms. The application of this system is convenient for the detection of early signs of insulation failure, which is an effective method for diagnosis of insulation faults.

• 대한한방부인과학회지
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• 제24권4호
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• pp.186-193
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• 2011

Purpose: This study was performed to find correlations between Edema Index and Heart Rate Variability(HRV) conducted in early postpartum period. Methods: 17 postpartum women were participated in this study which was conducted with Inbody 720(Biospace Co. Ltd.) and SA-6000(Medicore Co. Ltd.). Edema Index(Extra Cellular Water/Total Body Water) was calculated after body composition analysis and HRV result(TP, VLF, LF, HF, HF norm, LF norm, LF/HF ratio) was analysed within a week after delivery. Results: There was no significant correlations between Edema Index and HRV results in time domain analysis. also Edema Index and TP, LF, HF, LF/HF ratio have no significant correlations in frequency domain analysis. but only VLF data has significance compared with Edema Index. Conclusions: It can be suggested that VLF results analysed by HRV can be useful reference estimating postpartum edema especially occurs in early postpartum period.

• 대한기계학회논문집A
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• 제27권9호
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• pp.1579-1588
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• 2003

In this paper, the finite element equations for the transient linear viscoelastic stress analysis are presented in time domain, whose variational formulation is derived by using the Galerkin's method based on the equations of motion in time integral. Since the inertia terms are not included in the variational formulation, the time integration schemes such as the Newmark's method widely used in the classical dynamic analysis based on the equations of motion in time differential are not required in the development of that formulation, resulting in a computationally simple and stable numerical algorithm. The viscoelastic material is assumed to behave as a standard linear solid in shear and an elastic solid in dilatation. To show the validity of the presented method, two numerical examples are solved nuder plane strain and plane stress conditions and good results are obtained.

• 한국전자파학회논문지
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• 제29권3호
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• pp.225-232
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• 2018

본 논문은 H(2,4) 기법을 기반으로 한 저분산 유한차분 시간영역법(Finite-Difference Time-Domain: FDTD)을 이용하여 상수 도전율과 비유전율을 갖는 유전체의 광대역 전자기 특성을 정확하게 해석하는 방법을 제안했다. 수치분산오차를 최소화하기 위해서 제안한 FDTD 기법에서 이용하는 세 개의 변수의 최적값을 계산하였다. 잘 알려진 정확한 FDTD 기법들과 제안한 FDTD 방법으로 2차원 원형 유전체 실린더의 광대역 산란 문제를 계산하였고, 그 결과를 이론값과 비교하여 제안한 방법의 우수성을 검증하였다.

• 한국전자파학회논문지
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• 제7권2호
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• pp.105-116
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• 1996

급전선과 직교된 전자기결합 마이크로스트립 다이폴안테나는 주로 주파수 영역의 적분방정식 및 모멘트법에 의해, 다이폴의 전류분포를 구하므로써 설계 및 해석이 이루어졌으나, 본 연구에서는 FDTD 방법을 이용하여 각 다이폴의 전류분포를 직접 계산하여, 전자기결합 다이폴 배열안테나의 설계 및 해석 가능성을 제시하였다. 이 경우, 맥스웰방정식 적분형을 유한차분형태로 표현한 수식을 적용하였으며, 계산된 각 다이폴의 전류분포에 의해 복사전계를 구하므로써, 표면전류 및 자류밀도를 계산하여 복사패턴을 구하는 방법에 비해 계산과정과 시간이 크게 단축됨을 보였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.920-927
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• 2008

This study deals with modeling of Head-Related Transfer Functions (HRTFs) using Principal Components Analysis (PCA) in the time and frequency domains. Four PCA models based on Head-Related Impulse Responses (HRIRs), complex-valued HRTFs, augmented HRTFs, and log-magnitudes of HRTFs are investigated. The objective of this study is to compare modeling performances of the PCA models in the least-squares sense and to show the theoretical relationship between the PCA models. In terms of the number of principal components needed for modeling, the PCA model based on HRIR or augmented HRTFs showed more efficient modeling performance than the PCA model based on complex-valued HRTFs. The PCA model based on HRIRs in the time domain and that based on augmented HRTFs in the frequency domain are shown to be theoretically equivalent. Modeling performance of the PCA model based on log-magnitudes of HRTFs cannot be compared with that of other PCA models because the PCA model deals with log-scaled magnitude components only, whereas the other PCA models consider both magnitude and phase components in linear scale.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
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• pp.315-318
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• 2006

This paper concerns about coupled dynamic analysis of the deep-seabed mining system in launching operation. The dynamic behavior of mining system consisting of lifting pipe, buffer station, flexible conduit and self-propelled miner is simulated in time domain. The launching operation is divided into four critical phases: (1) deployment of miner and flexible conduit, (2) deployment of lifting pipe, flexible conduit and miner, (3) touch-down of miner, (4) final launching. The dynamic responses of sub-systems - miner, flexible conduit, buffer and lifting pipe - are analyzed in each launching phase. According to the changing periods of forced excitation at the top, the dynamic responses of sub-systems are diverse in their characteristics. It has been shown that the total integrated responses of sub-systems are strongly affected by the design parameters. Especially, the principal dimensions of flexible conduit seem to be significant in determining of the global response. Based on the simulation results, safe operation conditions are investigated.

• 한국전자파학회논문지
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• 제11권5호
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• pp.839-848
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• 2000

본 논문은 전자파 장해 및 복사내성 측정에 사용되는 전자파 무반사실의 대용 방법으로 활용될 수 있는 전자파 잔향실의 전자기장 특성에 관하여 연구하였다. 체적이 동일한 직사각형 및 삼각형 구조의 잔향실 내부 필드균일성을 확보하기 위하여 Shroeder diffuser 방식을 적용하였으며, FDTD(Finite-Difference Time-Domain) 방법을 사용하여 잔향실 내부의 필드 특성을 조사하였다. 앞에서 언급한 두 가지 형태의 잔향실 내부에서 필드 특성을 조사하기 위해 시험공간 내의 75% 샘플을 가지고 분석하였다. 직사각형 잔향실의 경우 최대 $\pm$3dB, 삼각형 잔향실의 경우 최대 $\pm$4.4dB 내의 tolerance를 나타내었으며, 또한 직사각형 잔향실의 경우 편파에 대해서도 독립적이라는 결과를 얻을 수 있었다.

• 한국전자파학회지:전자파기술
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• 제6권1호
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• pp.48-65
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• 1995

전전자 교환기 가입자 회로에서의 불요 전자파 잡음의 복사를 해석하였다. 디지탈 스스템과 빠른 스위칭소자의 사용에 따라 증가하고 있는 불요전자파 잡음은 넓은 주파수 스펙트럼을 점유하여 여러가지의 EMI 현상을 발생시킬 수 있는 가능성을 가지고 있다. 그렇기 때문에 시간영역 유한차분법(Finite Difference Time Domain:FDTD)을 이용하여 좀더 정확한 불요 전자파 복사 현상을 해석하였으며, 규정된 시험 방법(on-promises test)을 통하여 비교 검토 하였ㄷ 이 연구의 결과는 대형 디지탈시스템에서의 EMI 모델링과 EMI 현상의 예측에 응용가능하여, 또한 국제적 EMI/EMC 규정에 합당한 디지탈 스스템의 EMI 대책설계에 활용가능할 것으로 생각된다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 추계 학술발표회논문집
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• pp.481-488
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• 2003

A fluid-structure-isolator interaction program was developed in this study. The behavior of liquid regions are simulated by the boundary element method, and then the technique of analyzing the free surface motion in time domain is developed by using the nonlinear free surface boundary condition(NFBC) and the condition of interface between the structure and the fluid. Structure regions are modeled by the finite element method. In order to construct the governing equation of the fluid structure interaction(FSI)problem in time domain, the finite elements for a structure and boundary elements for liquid are coupled using the equilibrium condition, the compatibility condition and NFBC. The isolator is simulated by equation proposedin 3D Basis Me. In order to verify the validity and the applicability of the developed fluid- structure -Isolator interaction program, The horizontal forced vibration analysis was performed. The applicability of the developed method is verified through the artificial seismic analysis of real size liquid storage tank.