• 한국소음진동공학회논문집
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• 제11권4호
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• pp.5-12
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• 2001

This paper presents the simulation methodology of the interior noise of vehicle using the frequency response function based hybrid modeling of the system which consists of multi-subsystem models obtained by the test or analysis. The complex systems such as a trimmed body of high modal density and a powertrain were modeled by using experimental data, and a sub-frame of a vehicle of low modal density was modeled by finite element data. Modeling of the whole system was executed and validated in the two stages. The first stave is combining the trimmed body and the sub-frame, and the second stage is attaching the powertrain, which is a exciting source, to the combined model of the first stage. The input force to the system was modeled as an equivalent force in the virtual space, which was obtained from impedance method using the FRFs of the powertrain and the responses. The interior noise predicted by the proposed method was very close to the direct measurement, which showed feasibility of the proposed modeling procedure. Since the methodology is easily applied to both the transfer path analysis of structure-borne noise and the analysis of noise contribution of a sub-system, it is expected to be a strong tool for design change of a vehicle in the earlier stare.

• Smart Structures and Systems
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• 제19권1호
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• pp.67-90
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• 2017

The interdisciplinary research area of small scale energy harvesting has attracted tremendous interests in the past decades, with a goal of ultimately realizing self-powered electronic systems. Among the various available ambient energy sources which can be converted into electricity, wind energy is a most promising and ubiquitous source in both outdoor and indoor environments. Significant research outcomes have been produced on small scale wind energy harvesting in the literature, mostly based on piezoelectric conversion. Especially, modeling methods of wind energy harvesting techniques plays a greatly important role in accurate performance evaluations as well as efficient parameter optimizations. The purpose of this paper is to present a guideline on the modeling methods of small-scale wind energy harvesters. The mechanisms and characteristics of different types of aeroelastic instabilities are presented first, including the vortex-induced vibration, galloping, flutter, wake galloping and turbulence-induced vibration. Next, the modeling methods are reviewed in detail, which are classified into three categories: the mathematical modeling method, the equivalent circuit modeling method, and the computational fluid dynamics (CFD) method. This paper aims to provide useful guidance to researchers from various disciplines when they want to develop and model a multi-way coupled wind piezoelectric energy harvester.

• 한국음향학회지
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• 제20권3호
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• pp.98-103
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• 2001

인간의 청각기관은 소리의 방향과 거리인지에 있어서 여러 가지의 정보들을 복합적으로 이용한다. 이러한 양 귀에 들어오는 소리세기의 차이, 위상의 차이, 그리고 주파수 스펙트럼의 차이 등의 정보들을 종합적으로 포함하고 있는 것이 머리전달함수이다. 본 논문에서는 이 머리전달함수를 이용한 3차원 음상정위를 위해 사람의 청각기관에 알맞은 1/3-옥타브 대역통과필터를 이용한 알고리즘을 제안한다. 먼저 측정된 머리전달함수의 음색왜곡 및 음질저하를 최소화하기 위해 1/3-옥타브 대역통과필터를 이용해 간략화시켰으며, 간략화된 데이터베이스를 크기와 시간의 부분으로 나누어 모듈을 구성하였다. 이의 성능평가를 위해 객관평가와 주관평가를 실시하였으며, 실험결과 85.7％정도의 음상정위의 성능 개선을 가져왔다.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.286-294
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• 2009

Hydroelectric power plants are known for their ability to cover variations of the consumption in electrical power networks. In order to follow this changing demand, hydraulic machines are subject to off-design operation. In that case, the swirling flow leaving the runner of a Francis turbine may act under given conditions as an excitation source for the whole hydraulic system. In high load operating conditions, vortex rope behaves as an internal energy source which leads to the self excitation of the system. The aim of this paper is to identify the influence of the full load excitation source location with respect to the eigenmodes shapes on the system stability. For this, a new eigenanalysis tool, based on eigenvalues and eigenvectors computation of the nonlinear set of differential equations in SIMSEN, has been developed. First the modal analysis method and linearization of the set of the nonlinear differential equations are fully described. Then, nonlinear hydro-acoustic models of hydraulic components based on electrical equivalent schemes are presented and linearized. Finally, a hydro-acoustic SIMSEN model of a simple hydraulic power plant, is used to apply the modal analysis and to show the influence of the turbine location on system stability. Through this case study, it brings out that modeling of the pipe viscoelastic damping is decisive to find out stability limits and unstable eigenfrequencies.

• Journal of Electrical Engineering and Technology
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• 제10권1호
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• pp.30-40
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• 2015

For a shunt power quality controller (SPQC) the DC side voltage value which is closely related to the compensation performance is a significant parameter. Buy so far, very little discussion has been conducted on this in a quantitative manner by previous publications. In this paper, a method to design the DC side voltage of SPQC is presented according to the compensation performance in the single-phase system and the three-phase system respectively. First, for the reactive current and the harmonic current compensation, a required minimal value of the DC side voltage with a zero total harmonic distortion (THD) of the source current and a unit power factor is obtained for a typical load, through the equivalent circuit analysis and the Fourier Transform analytical expressions. Second, when the DC side voltage of SPQC is lower than the above-obtained minimal value, the quantitative relationship between the DC side voltage and the THD after compensation is also elaborated using the curve diagram. Hardware experimental results verify the design method.

• 조명전기설비학회논문지
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• 제18권1호
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• pp.73-77
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• 2004

전력 시스템의 오손에 의한 사고 방지를 위한 가장 효과적인 방법은 오손도를 정확하게 예측하는 것이다. 전력시스템은 옥외에 노출되어 있으므로 오손 및 열화가 불가피하며, 오손의 증가는 사고의 위험성을 악화시킨다. 한편, 오손의 주요소는 염분이며, 오손도는 등가 염분 부착 밀도(ESDD)로서 나타낼 수 있다. 기후 조건은 지속적으로 오손도를 증감시키고 있다. 기후와 오손도의 상관관계를 해석하여 오손도를 예측할 수 있으며, 다중 회귀 분석방법를 통하여 분석이 가능하다. 이와 관련된 선행연구에서는 높은 신뢰도를 확인할 수 있었다(0.874). 그러나 이러한 방법은 다른 시기에 적용한 경우 상관성이 상당히 하강하였다. 본 연구는 이와 같은 신뢰도를 더욱 향상 시키고(0.898), 정밀한 오손도 예측을 위한 통계처리를 수행하였다.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.800-811
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• 2018

This paper presents a regenerative braking control scheme for Switched Reluctance Machine (SRM) drive in Electric Vehicles (EVs). The main purpose is to maximize the recovered energy during battery charging by taking into account the nonlinear physical characteristics of the Switched Reluctance Machine. The proposed regenerative braking method employs the back-EMF in the generation process as a complicated position-dependent voltage source. The proposed maximum power recovery (MPR) operation of the regenerative braking is first based on the maximization of the extracted power from the machine and then the maximization of the power transferred to the battery. The maximum power extraction (MPE) from SRM is based on maximizing the energy conversion ratio by the calculation of the optimum PWM switching duty cycle, turn-on, and turn-off angles. By using the impedance matching theorem that allows the maximum power transfer (MPT) of the MPE, the proposed MPR is achieved. The parametric averaged value modeling of the machine phase currents in the chopping control mode is used for MPR realization. By following this model, a nonlinear equivalent input resistance is derived for the battery internal resistance matching. The effectiveness of the proposed regenerative braking method is demonstrated through simulation results and experimental implementation.

• 한국정보통신학회논문지
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• 제13권12호
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• pp.2655-2661
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• 2009

단채널 MOSFET의 열잡음 모델링을 위한 정밀한 잡음 파라메터를 유도하고 추출했다. MOSFET의 잡음 파라메터를 계산하기 위한 Fukui모델을 단채널에서의 기생성분의 영향을 고려하여 수정하였고, 기존의 모델식과 비교하였다. 또한 소자 고유의 잡음원을 얻기 위해서 서브마이크론 MOSFET의 잡음 파라메터(최소잡음지수 $F_{min}$, 등가잡음 저항 $R_n$, 최적 소스어드미턴스 $Y_{opt}=G_{opt}+B_{opt}$)를 추출하는 방법을 제시하였다. 이러한 추출방법을 통하여 프로브패드의 영향과 외부기생소자 영향을 제거한 MOSFET 고유의 잡음 파라메터가 RF잡음측정으로부터 직접 얻어지게 된다.

• Nuclear Engineering and Technology
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• 제47권7호
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• pp.939-944
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• 2015

The calibration methods of neutron-measuring devices such as the neutron survey meter have advantages and disadvantages. To compare the calibration factors obtained by the shadow cone method and semi-empirical method, 10 neutron survey meters of five different types were used in this study. This experiment was performed at the Korea Atomic Energy Research Institute (KAERI; Daejeon, South Korea), and the calibration neutron fields were constructed using a $^{252}Californium$ ($^{252}Cf$) neutron source, which was positioned in the center of the neutron irradiation room. The neutron spectra of the calibration neutron fields were measured by a europium-activated lithium iodide scintillator in combination with KAERI's Bonner sphere system. When the shadow cone method was used, 10 single moderator-based survey meters exhibited a smaller calibration factor by as much as 3.1-9.3% than that of the semi-empirical method. This finding indicates that neutron survey meters underestimated the scattered neutrons and attenuated neutrons (i.e., the total scatter corrections). This underestimation of the calibration factor was attributed to the fact that single moderator-based survey meters have an under-ambient dose equivalent response in the thermal or thermal-dominant neutron field. As a result, when the shadow cone method is used for a single moderator-based survey meter, an additional correction and the International Organization for Standardization standard 8529-2 for room-scattered neutrons should be considered.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.34-34
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• 2017

Various extracts of roots, stems, and leaves of Phalaenopsis Sogo Yukidian 'V3' were evaluated for total phenolics, total flavonoids, and antioxidant capacity. The conjugate form of stem samples contained the highest total phenolics ($5.092{\pm}0.739mg$ gallic acid equivalent per g dry weight） and the highest total flavonoids ($2.218{\pm}0.021mg$ rutin equivalent per g dry weight) was found in the hexane extract of leaves. The ethyl acetate extract of roots showed the maximum antioxidant activity as compared to other extracts. Of which, the $IC_{50}$ value of this sample were 0.070 mg/mL and 0.450 mg/mL in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay and reducing power, respectively, while the lipid peroxidation inhibition (LPI) value was as 94.2% by ${\beta}$-carotene bleaching method. Five phenolic compounds including caffeic acid, syringic acid, vanillin, ellagic acid, and cinnamic acid were quantified by high-performance liquid chromatography (HPLC). It is suggested that roots of the hybrid Phalaenopsis Sogo Yukidian 'V3' can be explodited as an effective source of antioxidants.