• Journal of Electrical Engineering and Technology
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• 제12권6호
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• pp.2262-2267
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• 2017

A new force expression on dielectrics subjected to electric field is proposed in this paper. It is the electric version of the equivalent magnetizing current method in magnetic field. From the idea of electromagnetic duality, virtual equivalent electrifying magnetic current method is conjectured in the field of dielectric force problem. Numerical results show that the proposed method has good agreements with the conventional methods. The merits and demerits of the proposed method are also discussed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.216-221
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• 2001

The equivalent source method(ESM) is used for the calculation of the internal pressure field for an enclosure which can have arbitrary boundary conditions and may include internal objects which scatter the sound field. The advantage of using ESM is that it requires relatively low computing cost and is easy to model the internal diffracting objects. In the ESM modelling, some of the equivalent positions are chosen to be the same as the first order images of the source inside the enclosure, some are positioned on a spherical surface some distance outside the enclosure. The normal velocity on the surfaces of the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and the expected is minimized by adjusting the strength of the equivalent sources. This study is on the optimal equivalent source positions, the far field sources. Typically, the far field sources are evenly distributed on a surface of a virtual sphere which is centered at the enclosure with a sufficiently large radius. In this study, optimal far field source locations are searched using simulated annealing method and simulation results showed that optimally located sources gave better accuracy even with a smaller number of far field sources.

• 한국소음진동공학회논문집
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• 제13권10호
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• pp.743-750
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• 2003

The equivalent source method(ESM) is used for the calculation of the internal pressure field for an enclosure which can have arbitrary boundary conditions and nay include internal objects which scatter the sound field. The advantage of using ESM is that it requires relatively low computing cost and is easy to model the internal diffracting objects. Typical ESM modeling uses two groups of equivalent source positions. One group includes the first order images of the source inside the enclosure. The Positions of the other group are usually on a spherical surface some distance outside the enclosure. The normal velocity on the surfaces of the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and the expected is minimized by adjusting the strength of the equivalent sources. This study is on the optimal far field sources positions when using the equivalent source method. In general, the far field sources are evenly distributed on a surface of a virtual sphere which is centered at the enclosure with a sufficiently large radius. In this study. optimal far field source locations are searched using simulated annealing method for various radii of spheres where far field sources are located. Simulation results showed that optimally located sources with adequate distance away from the enclosure center gave better result than sources with even distribution even with a smaller number of far field sources.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.1101-1106
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• 2004

This study presents the reconstruction of sound field radiated from an automotive engine using equivalent sources. Basic concept of the method presented is to replace the engine noise source with elementary sources of multipoles, e.g., monopoles and dipoles. The so-called Helmholtz equation least-squares (HELS) method can reconstruct the sound radiation fields from spherical geometries in a series expansion of spherical Hankel functions and spherical harmonics. In this paper, multi-Point, multipole equivalent sources are employed to reconstruct the sound field radiated from an automotive engine with a fixed rotation speed. To ensure and improve the accuracy of reconstruction, the spatial filters of multipole coefficients and wave-vectors are adopted for suppressing the adverse effect of high-order multipoles. Optimal filter shapes are designed with regularization parameters minimizing the generalized cross validation (GCV) function between actual and reproduced model. After regeneration of field pressures using the proposed method as many as necessary, the vibro-acoustic field of an engine could be reconstructed by using the BEM-based near-field acoustic holography (NAH) technique in a cost-effective manner.

• 한국의학물리학회지:의학물리
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• 제9권4호
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• pp.195-200
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• 1998

연구 목적: 등가면법은 장방형의 X-선 조사면의 출력인자 계산에 널리 이용되고 있다. 본 연구에 서는 출력인자 계산시 등가면법의 적용에 영향을 줄 수 있는 선질, 조사면의 두 변의 길이의 비, 측정점의 깊이 등을 조사하였다. 또한 등가면법의 타당성이 유지되는 영역을 밝히는 어림계산법을 제시하였다. 대상 및 방법 : 본 연구에 사용된 X-선의 선원은 4-, 6-, l0-MV 이었다. 조사면의 폭을 5-40 cm 까지 변화시키고 각 조사면에서 두 변의 비를 1:1 에서 10:1 까지 변화시켰다. 조사면의 장방효과는 물팬톰을 이용하였으며, dmax, 5-cm, 10-cm 깊이에서 시행하였다. 장방형의 조사면과 각 조사면에 대한 등가정사각형면에서의 출력인자를 구하여 이들 두 방법에서의 차이를 나타냈다. 결과 및 토의: 장방형의 조사면과 이에 대응하는 등가면 간의 출력인자의 차이는 일반적으로 장방비가 커질수록 증가하였다. 장방형의 조사면에 대한 출력인자의 측정값은 일반적으로 각 조사면의 등가정사각형면을 이용하여 계산한 값보다 높게 나타나서 크게는 10%의 차이를 나타냈다. 똑같은 두 변의 비에 대하여 장방형의 조사면과 둥가정사각형면에 대한 출력인자의 차이는 조사면의 크기가 작을수록 크게 나타났다. 실험에 사용한 각각에서 선질의 종류와 각각의 선질에서 측정깊이에서 두 값은 큰 차이를 보이지 않았다. 결론 : 본 연구결과에 의하여 등가면법을 출력인자 계산에 사용할 경우 이를 판단할 어림계산법을 구할 수 있다. 한 변의 길이가 25-cm 이하인 조사면에 대하여 만일 장방비 < (0.48) (긴 변의 길이) - 0.5를 만족하는 경우에는 출력인자의 오차를 2% 안에서 등가면법을 이용할 수 있다. 이와는 다른 경우에는 출력인자를 직접 측정하여야 한다. 이러한 기준은 4-10MV X-선원에 대하여 10-cm 깊이의 측정점까지 타당하다.

• 대한기계학회논문집B
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• 제29권7호
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• pp.814-819
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• 2005

The phase change heat transfer has been applied to the processes of machines as well as of manufacturing. The cycle in a heat exchanger includes the phase change phenomena of coolant for air conditioning, the solidification in casting process makes use of the characteristics of phase change of metal, and the welding also proceeds with melting and solidification. To predict the phase change processes, the experimental and numerical approaches are available. In the case of numerical analysis, the Enthalpy method is most widely applied to the phase change problem, comparing to the other numerical methods, i.e. the Equivalent Specific Heat method and the Temperature Recovery method. It's because that the Enthalpy method is accurate and straightforward. The Enthalpy method does not include any correction step while the correction of final temperature field is inevitable in the Equivalent Specific Heat method and the Temperature Recovery method. When the temperature field is to be used in the calculation, however, there must be converting process from enthalpy to temperature in the calculation scheme of Enthalpy method. In this study, an improved method for the Equivalent Specific Heat method is introduced whose method dose not include the correction steps and takes temperature as an independent variable so that the converting between enthalpy and temperature does not need any more. The improved method is applied to the solidification process of pure metal to see the differences of conventional and improved methods.

• 한국음향학회지
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• 제23권1호
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• pp.40-46
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• 2004

등가음원법은 일반적으로 실내에 위치한 음원에 의한 실내 음장을 모델링하기 위하여 원거리에 위치한 다수의 등가음원과 상대적으로 근방에 위치한 소수의 이미지음원들을 사용한다. 원거리음원은 일반적으로 실내 음장의 중심으로부터 적당히 먼 거리에 균일하게 위치시킨다. 이러한 원거리음원의 위치는 적절한 선택 여부에 따라, 계산 결과의 정확도와 이를 만족시키기 위해 필요한 음원의 수에 큰 영향을 미치게 된다. 본 연구에서는 등거리 상의 가상의 구형 표면에 위치시키는 기존의 방법 대신 모델링하는 실내 공간의 경계면과 닮은 꼴 형상으로 배치하여 그 영향을 조사하였다. 즉 가상의 직육면체 표면에 격자 형태로 균일하게 원거리음원들을 배치시키되, 음장의 중심으로부터의 거 리를 변화시켜가며 각 경우에 대하여 최적화 기법을 이용하여 최적의 원거리음원 위치들을 찾아내어 비교, 분석하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.581-586
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• 2000

The equivalent source method is used to calculate the internal pressure field for an enclosure which can have arbitrary boundary conditions and may include internal objects which scatter the sound. Some of the equivalent positions are chosen to be the same as the first order images of the source inside the enclosure, some are positioned on a spherical surface some distance outside the enclosure. The normal velocity on the surfaces of the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and the expected is minimized by adjusting the strength of the equivalent sources. The convergence of this method is checked by evaluating the velocity error at a larger number of monitoring positions. Example results are presented for various numbers of sources and evaluation points. The results showed that in general the more equivalent sources increased the accuracy of the sound field predictions but the accuracy is not too much sensitive to the numbers of evaluation points.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2000년도 춘계학술대회 논문집(Proceeding of the KOSME 2000 Spring Annual Meeting)
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• pp.122-126
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• 2000

In particle or short-fiber reinforced composites cracking of the reinforcements is a significant damage mode because the broken reinformcements lose load carrying capacity . The average stress in the inhomogeneity represents its load carrying capacity and the difference between the average stresses of the intact and broken inhomogeneities indicates the loss of load carrying capacity due to cracking damage. The composite in damage process contains intact and broken reinforcements in a matrix, An incremental constitutive relation of particle or short-fiber reinforced composites including the progressive cracking damage of the reinforcements have been developed based on the Eshelby's equivalent inclusion method and Mori-Tanaka's mean field concept. influence of the cracking damage on the Eshelby's equivalent inclusion method and Mori-Tanaka's mean field concept. Influence of the cracking damage on the stress-strain response of the composites is demonstrated.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.1025-1034
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• 2015

This paper presented an improved analytical method for calculating the open-circuit magnetic field in the surface-mounted permanent magnet machines accounting for slots and eccentric magnet pole. Magnetic field produced by radial and parallel permanent magnet is equivalent to that produced by surface current according to equivalent surface-current method of permanent magnet. The model is divided into two types of subdomains. The field solution of each subdomain is obtained by applying the interface and boundary conditions. The magnet field produced by equivalent surface current is superposed according to superposition principle of vector potential. The investigation shows harmonic contents of radial flux density can be reduced a lot by changing eccentric distance of eccentric magnet poles compared with conventional surface-mounted permanent-magnet machines with concentric magnet poles. The FE(finite element) results confirm the validity of the analytical results with the proposed model.