• 한국전기전자재료학회논문지
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• 제26권7호
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• pp.515-521
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• 2013

Magnetoelectric(ME) bulk composites with PZT-PNN-PZN/$Fe_2O_4$ were prepared by using a conventional ceramic methods and investigated on the ME voltage vs frequency of ac magnetic fields. We made the electric equivalent circuits by using the Maxwell-Wagner model and simulated the frequency dependence of ME voltage in low frequency region. ME devices were described by a series of two equivalent circuits of piezoelectric and magnetic, which have the relaxation time ${\tau}$ due to the interaction between ME device and load resistor. Equivalent circuit of piezoelectric material is independent of frequency. However ferrite magnetic materials have Debye absorption and dipolar dispersion, whose equivalent circuit is a function of frequency. Therefore we suggest the resistance in the equivalent circuit is proportion to $1+{\omega}^2{\tau}^2$ and the capacitance is in inverse proportion to $1+{\omega}^2{\tau}^2$ in the magnetic materials.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.236-240
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• 2013

Due to difficulty of considering dynamic load in side of a computer resource and computing time, it is common that external load is assumed as ideal static load. However, structural analysis under static load cannot guarantee the safety of structural design. Recently, the systematic method to construct equivalent static load from the given dynamic load has been proposed. Previous study has calculated equivalent static load through the optimization procedure under displacement constraints. And previously reported works to distribute equivalent static load were based on ad hoc methods. However, it is appropriate to take into account the stress constraint for the safety design. Moreover, the improper selection of loading position may results in unreliable structural design. The present study proposes the methodology to optimize an equivalent static which distributed on the primary DOFs, DOFs of the constraint elements, DOF of an external load as positions. In conclusion, the reliability of proposed method is demonstrated through a global optimization.

• KEPCO Journal on Electric Power and Energy
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• 제8권2호
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• pp.73-77
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• 2022

Recently, as the number of years of operation has increased for more than 30 years, interest in evaluating the remaining life of major power facilities such as transformers and ultra-high voltage cables is increasing. In particular, the risk of failure is increasing because the underground transmission XLPE cable has been built since 1980 and has been operating in excess of 30 years of design life or close proximity. Therefore, it is necessary to develop an algorithm to evaluate the residual life of the XLPE cable considering the load to determine the risk of failure. Since load data is large amount of data, it is necessary to make the variable load information equivalent to the time unit first in order to calculate the remaining life of the system quickly. In overseas literature, transformers are reported to be standardized for variable load equivalent conversion formulas, but they have not been reported for ultra-high voltage cables. Therefore, in this paper, whether the equivalent conversion formula of a transformer can be applied to XLPE cables was reviewed through accelerated degradation tests under equivalent and variable temperature conditions, and considerations were studied when evaluating the remaining operating life of XLPE cables based on the experimental results.

• 한국수자원학회논문집
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• 제44권4호
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• pp.327-338
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• 2011

본 연구에서는 등가타원을 이용하여 호우사상의 공간분포를 정량화 하는 문제를 살펴보았다. 주어진 호우사상의 등가 타원을 매 시간별 한계강우강도에 따라 추정하고, 이 등가타원의 개수와 규모의 변화를 살펴보았다. 또한 한계강우강도 별로 평균 등가타원을 결정하고, 이 평균 등가타원이 주어진 호우사상을 대표할 수 있는지 판단하기 위해 평균 등가타원의 장축과 단축, 그리고 회전각에 대한 신뢰구간을 산정하여 평가하였다. 연구결과, 한계강우강도가 커짐에 따라 등가타원의 개수와 크기는 감소하고 등가타원이 나타나는 시간도 늦어지는 것을 확인하였다. 또한 등가타원의 장축과 단축의 비는 2 : 1이 적절한 것으로 나타났으며, 한계강우강도별로 추정된 등가타원의 평균 회전각은 모든 등가타원의평균 회전각과 통계학적으로 유사함을 확인하였다.

• International Journal of Aeronautical and Space Sciences
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• 제13권4호
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• pp.458-467
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• 2012

In this study, the linear viscoelastic response of a rectangular laminated plate is investigated. The viscoelastic properties, expressed by two basic spring-dashpot models, that is Kelvin and Maxwell models, is assumed in the range to investigate the influence of viscoelastic coefficients to mechanical behavior. In the present study, viscoelastic responses are performed for two popular equivalent single-layered theories, such as the first-order shear deformation theory (FSDT) and third-order shear deformation theory (TSDT). Compliance and relaxation modulus of time-dependent viscoelastic behavior are approximately determined by Prony series. The constitutive equation for linear viscoelastic material as the Boltzmann superposition integral equation is simplified by the convolution theorem of Laplace transformation to avoid direct time integration as well as to improve both accuracy and computational efficiency. The viscoelastic responses of composite laminates in the real time domain are obtained by applying the inverse Laplace transformation. The numerical results of viscoelastic phenomena such as creep, cyclic creep and recovery creep are presented.

• 전기학회논문지
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• 제65권9호
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• pp.1518-1523
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• 2016

In this study, in order to understand the degradation characteristics of oil-paper insulation for power transformers and OF cables, tan delta was measured using cable model specimens with long-term accelerated thermal and electrical aging. In addition, to find out the degradation level due to the accelerated aging, tensile strengths of aged papers were measured. As a result, tan ${\delta}$ showed the characteristics of slight decrease at the first stage and then increase with the aging time, which could be analyzed due to the evaporation of remaining moisture and the change of aging rate with time. Also, the trend of tensile strengths with aging temperature and time was appeared to be exponentially decreased and by use of these data equivalent calculated lifetimes and accelerated aging factors were derived for each aging temperatures. After then, tan ${\delta}$ was analyzed with the equivalent operating years. For all different aging temperatures, the aged data were very well fit to the equivalent operating years and it is shown that tan ${\delta}$ was increased with the decrease of tensile strength.

• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.1960-1966
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• 2014

The rotor overhang is used to enhance the air-gap flux and improve the power density. Due to the asymmetry in the axial direction caused by the overhang, a time consuming 3D analysis is necessary when designing a motor with overhang. To solve this problem, this paper proposes an equivalent magnetic circuit model (EMCM) which takes account overhang effects without a 3D analysis by using effective air-gap length. The analysis time can be reduced significantly via the proposed EMCM. A reduction in the analysis time is essential for a preliminary design of a motor. In order to verify the proposed model, a 3-D finite-element method (FEM) analysis is adopted. 3-D FEM results confirm the validity of the proposed EMCM.

• 대한안전경영과학회:학술대회논문집
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• 대한안전경영과학회 2011년도 추계학술대회
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• pp.75-84
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• 2011

본 논문에서는 지하공간에 설치되는 지중구조물에 대한 내진해석에 관한 연구로 구조물의 거동특성과 내진설계방법의 종류에 따라 수치해석을 실시하였다. 이를 위해 현재 가장 많이 실무에 적용되고 있는 내진설계방법인 등가정적해석법과 응답변위법을 적용하고 정밀한 해석이 가능한 시간이력해석법에 의해 검증을 시행하였으며 구조물 내진해석은 3-D 모델링에 의해 구조물-지반 상호작용을 고려하고 국내의 콘크리트구조설계기준에 따라 수행하였다. 해석 결과 현재 실무에서 적용되고 있는 등가정적해석법과 응답변위법을 적용하는 경우 정밀한 동적해석법 보다 다소 크게 산정되어 실무적용에 문제가 없음을 확인 할 수 있었다.

• Journal of Electrochemical Science and Technology
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• 제13권4호
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• pp.479-485
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• 2022

The power of energy storage devices is characterized by capacitance and the internal resistance. The capacitance is measured on an assumption that the charges are stored at the electrode interface and the electric double layer behaves like an ideal capacitor. However, in most cases, the electric double layer is not ideal so a constant phase element (CPE) is used instead of a capacitor to describe the practical observations. Nevertheless, another problem with the use of the CPE is that CPE does not give capacitance directly. Fortunately, a few methods were suggested to evaluate the effective capacitance in the literature. However, those methods may not be suitable for supercapacitors which are modeled as an equivalent circuit of a CPE and resistor connected in series because the time constant of the equivalent circuit is not clearly studied. In this report, in order to study the time constant of the CPE and find its equivalent capacitor, AC and DC methods are utilized in a complementary manner. As a result, the time constants in the AC and DC domains are compared with digital simulation and a proper equation is presented to calculate the effective capacitance of a supercapacitor, which is extended to an electrochemical system where faradaic and ohmic processes are accompanied by imperfect charge accumulation process.

• 한국전자통신학회논문지
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• 제18권5호
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• pp.835-840
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• 2023

2D FEM은 3D FEM에 비하여 모델 및 조건을 간소화하여 해석할 수 있다. 하지만 코일의 조건에 대하여는 실제 코일의 인입과 반출을 순차적으로 구성하여 해석 조건에 입력하는 경우가 많다. 본 논문은 다수의 슬롯을 가지더라도 하나의 FEM Coil로 구성한 등가 권선법을 적용하여 코일 조건의 단순화 및 해석 시간의 단축을 나타내고 권선형 마그네틱 기어에 적용하여 결과의 일치성을 보인다.