• Advances in nano research
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• 제10권5호
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• pp.481-491
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• 2021

Graphene Nanosheets play an important role in nanosensors due to their proper surface to volume ratio. Therefore, the main purpose of this paper is to consider the nonlinear vibration behavior of graphene nanosheets (GSs) under the influence of electromagnetic fields and electrical current create forces. Considering more realistic assumptions, new equations have been proposed to study the nonlinear vibration behavior of the GSs carrying electrical current and placed in magnetic field. For this purpose, considering the influences of the magnetic tractions created by electrical and eddy currents, new relationships for electromagnetic interaction forces with these nanosheets have been proposed. Nonlinear coupled equations are discretized by Galerkin method, and then solved via Runge-Kutta method. The effect of different parameters such as size effect, electrical current magnitude and magnetic field intensity on the vibration characteristics of GSs is investigated. The results show that the magnetic field increases the linear natural frequency, and decreases the nonlinear natural frequency of the GSs. Excessive increase of the magnetic field causes instability in the GSs.

• 수산해양기술연구
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• 제55권3호
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• pp.252-263
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• 2019

In order to understand the tidal current and mean flow at the west channel of Yeoja Bay in the South Sea of Korea, numerical model experiments and vorticity analysis were carried out. The currents flow north at flood and south at ebb respectively and have the reversing form in the west channel. Topographical eddies are found in the surroundings of Dunbyong Island in the east of the channel. The flood currents flow from the waters near Naro Islands through the west channel and the coastal waters near Geumo Islands through the east channel. The ebb currents from the Yeoja Bay flow out along the west and the east channels separately. The south of Nang Island have weak flows because the island is located in the rear of main tidal stream. Currents are converged at ebb and diverged at flood in the northwest of Jeokgum Island. Tidal current ellipses show reversing form in the west channel but a kind of rotational form in the east channel. As the results of tide induced mean flows, cyclonic and anticyclonic topographical eddies at the northern tip but eddies with opposite spin at the southern tip are found in the west channel of Yeoja Bay. The topographical eddies around the islands and narrow channels are created from the vorticity formed at the land shore by the friction between tidal currents and the west channel.

• 조명전기설비학회논문지
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• 제27권10호
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• pp.30-40
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• 2013

In this study the method based on flux linkage in cell was introduced in calculation of eddy currents by cell method. According to this method eddy current distribution and the loss can be evaluated and since the shielding effectiveness by flux cancelation of eddy current can be analyzed, this method is applicable to design of conductive shield. And also the formula of shielding factor were so deduced as to be applicable to finite-width infinite-length shielding sheets and infinite-length underground cable shield. These formula are adaptable to magnetic materials as well as conductive materials. As the results of calculation in model shields are follows. In case of finite-width infinite-length shielding sheet, shielding effectiveness increases with increasing of conductivity. In case of infinite-length underground cable shield, the effectiveness become higher with increasing of permeability. Especially the effectiveness is very high in materials with both high conductivity and permeability in underground cable shield.

• 대한토목학회논문집
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• 제34권3호
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• pp.833-840
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• 2014

본 연구에서는 OpenFOAM에서 제공하는 소스 코드를 이용하여 폭-수심비가 2인 직사각형 개수로 흐름에 대해 수치모의를 수행하였다. 여과된 연속 방정식과 운동량 방정식을 해석하기 위하여 큰 와 수치모의를 이용하였고, 비등방성 잔여 응력항을 산정하기 위하여 Smagorinsky 모형(1963)을 사용하였다. LES 모형을 Tominaga et al. (1989)의 폭-수심비가 2인 실험수로에 적용하고 평균흐름 및 난류량을 비교하였다. 추가로 Nezu and Rodi (1985)의 실험 결과와 Shi et al. (1999)의 LES 모의 결과와 함께 비교를 수행하였다. 비교 결과 평균흐름 및 난류량 모두 기존 실험 및 모의 결과를 잘 재현하는 것으로 확인되었다. 특히 이차흐름 분포도에서 측벽과 자유수면의 접합부에서 발생하는 내부이차흐름이 발생하는 것을 확인하였다. 또한 수심방향 난류강도의 경우 측벽과 바닥벽에서 난류강도의 등치선도가 측벽과 바닥벽의 접합부 방향으로 편향되는 현상을 확인하였다.

• 한국해양학회지
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• 제29권2호
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• pp.119-131
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• 1994

모드분리기법의 gird-box형 3차원 수치모형을 이용하여 등밀도 등수심 유한영역에 서의 연직과점성 개수에 따른 취송유와 조류의 수평 유속 연직구조를 분석하였다. 연) 직과점성 계수가 수심에 일정할 경우 선영적으로 감소또는 증가하는 경우 이차함수 및 지수함수적으로 변하는 경우에 대한 해석해와의 비교를 통하여 모형 검증 및 연직유속 구조 분석이 실시되었다. 아울러 취송유에 경우 유속의 연직구조에 대한 해수표면 근 처에 "wall layer" 영향을 수치적으로 검토하였다. 모든 수직계산에서 연직층수는 열 세개로 가변 객자가 사용되었다. 수치모형은 유속의 연직구조를 만족스럽게 재연하게 으나 연직과점성 개수가 수심에 대하여 2차함수 및 지수적으로 감소하는 경우 해저면 부근에서 유속의 연직변화가 크게 나타나면서 해석해와 수치모형 결과간에 약간에 차 이가 나타났다. 수평 유속의 연직구조는 연직과점성 계수의 절대값 및 함수형태에 따 라 달라지며 해저면과 해수표면 부근의 유속은 wall layer 내의 연직과점성 계수에 민 감하게 반응하였다. 취송유에 경우에 해수표면에서의 연직 과점성 계수가 작을수록 강 한 shear가 표층에 형성되었으며 조류에 경우 연직 과점성 계수의 분포와 상관없이 해 저 한계층 상부의 유속은 거의 일정하게 나타나고 해조표내의 유속은 연직과점성 계수 가 줄어들수록 강한 shear 보였다.shear 보였다.

• 대한기계학회논문집B
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• 제20권7호
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• pp.2337-2346
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• 1996

One of the most useful method for increasing combustion loading of premixed flame is to strengthen the turbulent intensity of unburned mixture. It produces an important information to a design of efficient combustion equipment that analysing microstructure of strong turbulence premixed flame. The flame structure and characteristics are depend on the turbulence of unburned mixture. Therefore, to strengthen the turbulent intensity of unburned mixture make flame scale small and accomplish efficient combustion. We measured the velocity of local flame front movements, local eddy radius and local reaction zone thickness quantitatively with increasing turbulent intensity of unburned mixture. We researched the microstructure of flame using ion currents that react sensitively in the reaction zone. Consequently, the velocity of local flame front movements is depend on the velocity of unburned mixture and local eddy scale is to be small with increasing turbulent intensity. But there is no change in local reaction zone thickness with turbulence.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제17권3호
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• pp.139-170
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• 2013

We extend a p-hierarchical decomposition of the second degree finite element space of N$\acute{e}$d$\acute{e}$lec for tetrahedral meshes in three dimensions given in [1] to meshes with hexahedral elements, and derive p-hierarchical decompositions of the second degree finite element space of Raviart-Thomas in two dimensions for triangular and quadrilateral meshes. After having proved stability of these subspace decompositions and requiring certain saturation assumptions to hold, we construct a local a posteriori error estimator for fem and bem coupling of a time-harmonic electromagnetic eddy current problem in $\mathbb{R}^3$. We perform some numerical tests to underline reliability and efficiency of the estimator and test its usefulness in an adaptive refinement scheme.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.274-277
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• 2008

Pohang Wind Energy Research Center (PoWER-C) is developing a 3 MW Radial Flux Permanent Magnet (RFPM) Synchronous Generator for offshore Wind Energy Converter (WEC). The blade rotor rpm is 15.7 and the gear ratio is set to be 92.93. The nominal generator rpm at the rated load is about 1459. Baseline design with surface mounted PM magnets are completed. However, there is some concern about the excessive eddy current heating in the magnets. To alleviate this problem, another design with embedded magnet is going on. With embedded magnets, the generator length should be increased to compensate the increased flux leakage. But the field fluctuation in the magnets due to the slots are greatly reduced. This means less eddy currents and lower magnet operating temperature. In this report, engineering efforts for embedded rotor is presented.

• 한국정밀공학회지
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• 제21권4호
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• pp.72-78
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• 2004

In this paper, a development of an inductive position sensor is described. The sensor is similar to a radial magnetic bearing in that the sensor stator is shaped like a heteropolar magnetic bearing and is driven by a switching amplifier. A demodulation filter extracts the gap information from the switching current ripples. A prototype sensor exhibits the resolution of $0.43\mum$ and the dynamic bandwidth of about 800Hz. The dynamic performance can be improved by increasing the switching frequency. However, the eddy current effects become noticeable at high switching frequency, thus limiting the improvement of the bandwidth.

• Journal of Electrical Engineering and Technology
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• 제10권5호
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• pp.2001-2008
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• 2015

This paper proposes the concept of FlexPCB(flexible Printed Circuit Board) conductive structure for electrodynamic bearings. It has three main advantages: easy “printing” of considerably thin conductive wires, resulting in potential reduction in stray eddy currents; realization of specific conductive configurations with high precision to optimize the eddy current flowing; simplicity in being wound to cylinders or hollow cylinders of different diameters. To verify this new concept, the FlexPCB conductive structure was manufactured, an axial electrodynamic bearing test rig was built and the conductive structure's induced voltage was measured along the axial displacements from 0mm to 56mm at three rotating speeds. The finite element method was used to calcuatlate the flux density of electrodynamic bearing and induced voltage of the FlexPCB conductive structure. The experimental results are compared with the results from the FEM calculation. It is concluded that the measured and calculated induced voltages have consistency in the middle part of the bearing.