• Title/Summary/Keyword: Maxwell stress tensor

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On the Physical Meaning of Maxwell Stress Tensor (맥스웰 응력텐서의 물리적 의미의 고찰)

  • Choi, Hong-Soon;Park, Il-Han;Moon, Won-Kyu
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.58 no.4
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    • pp.725-734
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    • 2009
  • Maxwell stress tensor is one of the methods which are generally used for electromagnetic force calculation. In this paper, it is presented that Maxwell stress tensor T and n${\cdot}$T have no physical meaning and therefore should not be used as sources of mechanical force for deformations or dynamics. The divergence of Maxwell stress tensor ${\nabla}{\cdot}T$ is the one which can acquire a physical identity and is electromagnetic body force density by an action at a distance like a gravity. This result can be derived from the principle of power balance, and also verified by some thought experiments. The virtual air-gap approach is proposed as a valid solution for the calculation of the body force.

Parameter design optimization of solenoid type magnetic actuator using response surface methodology (반응표면법을 이용한 솔레노이드형 자기액추에이터의 치수 최적화 설계)

  • Soh, Hyun-Jun;Yoo, Jeong-Hoon
    • Proceedings of the KSME Conference
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    • pp.579-584
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    • 2003
  • Solenoid type magnetic actuator is the device, which could translate the electromagnetic energy to mechanical force. The force generated by magnetic flux, could be calculated by Maxwell stress tensor method. Maxwell stress tensor method is influenced by the magnetic flux path. Thus, magnetic force could be improved by modification of the iron case, which is the route of the magnetic flux. Modified design is obtained by parameter optimization using by Response surface methodology.

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멀티그리드 고정용 전자석 해석 및 설계

  • Kim, Hoe-Seop
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.6 no.2
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    • pp.99-108
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    • 2002
  • 그리드 고정용 전자석은 절단금형에서 여러 조각으로 나누어진 매우 얇고 가벼운 그리드를 전자석에 흡착시켜 그리드를 부착한 장소까지 이송하는 역할을 하는 전자석이다. 설계목표는 (1)그리드 고정용 전자석이 착자, 탈자 및 이동시 전자석에 흡착된 그리드 조각의 정렬상태가 동요되지 않는 전자석의 설계, (2)금형(그리드 흡착면)에 잔류자기가 최소화되는 설계, (3)전자석이 탈자되었을 때, 잔류자기가 최소화되는 설계에 초점을 두었다. 자장분포는 유한요소법으로 계산하였고, 전자력 계산은 Maxwell stress tensor법을 사용하였다.

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The Study on Reducing Cogging Torque of Propulsion Motor for Electric Ship (함정용 추진전동기 코깅 토크 저감에 관한 연구)

  • Bin, Jae-Goo
    • Journal of the Korea Institute of Military Science and Technology
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    • v.8 no.3
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    • pp.18-23
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    • 2005
  • Ships have been propelled and maneuvered by electrical drives since trle late seventies. Recently, rare earth PMs allow the design of brushless motors with very high efficiency over a wide speed range. This is the most important factor in ship propulsion technology. Several types PM motors have been developing for ship propulsion system. However these have disadvantage such as cogging torque. It causes an undesired effect that contributes to output ripple, vibration, and noise of machine. Therefore several techniques may be adopted in designing PM motor in order to reduce the cogging torque. This paper describes cogging torque receding methods such as adjusting arigap length, magnet arc, and magnet thickness. That are analysed by using the finite element method(FEM) and the maxwell stress tensor method.

Comparison of Korteweg-Helmholtz Electromagnetic Force Density and Magnetic Charge Force Density in Magnetic Systems (자기시스템의 Korteweg-Helmholtz 전자력 밀도와 자하 전자력 밀도의 비교)

  • Lee, Se-Hui;Choe, Myeong-Jun;Park, Il-Han
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.49 no.4
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    • pp.226-232
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    • 2000
  • In magnetic systems, distribution of electromagnetic force density causes mechanical deformation, which results in noise and vibration. In this paper, Korteweg-Helmholtzs energy method and equivalent magnetic charge method are employed for comparison of their resulting distributions of force density. The force density from the Korteweg-Helmholtzs method is expresses with two Maxwell stresses on the inside and the outside fo magnetic material respectively. The other is calculated using the magnetic Coulombs law. In the numerical model of an electromagnet, their numerical results are compared. The distributions by the two methods are almost the same. And their total forces are also shown to be the same to the one calculated from the conventional Maxwell stress tensor. But the magnetic charge method is easier and more efficient in numerical calculation.

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Analytical Analysis of Cogging Torque in Motors of Permanent MagneticType (영구자석을 사용한 모터의 코깅토크에 관한 이론적 해석)

  • Go, Hong-Seok;Kim, Gwang-Jun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.7
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    • pp.1795-1800
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    • 2000
  • One of the principal sources of vibration and noise in permanent magnetic machines is cogging torque, which is induced by interaction between the rotor poles and the stator teeth. For its analysis, using finite element analysis is very time consuming and the calculation of performance factors is extremely sensitive to the discretization. Especially, Maxwell stress tensor method is sensitive to the location of integral path. In this paper, a cogging permeance fuction is defined and replaced by the straight line. And it is assumed that the flux density acting on the stator's tooth side is the euqal to the flux density of the slot area. Using this definition and assumption, analytical calculation of cogging torque is presented and validated. And several reduction method is introduced.

Analysis of Contact Force in Eddy-current System Using the Virtual Air-Gap Concept

  • Park, Byung Su;Kim, Hwi Dae;Choi, Hong Soon;Park, Il Han
    • Journal of Electrical Engineering and Technology
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    • v.10 no.3
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    • pp.1349-1355
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    • 2015
  • It is difficult to calculate the magnetic force of an object of magnetic material in contact with other objects using the existing methods, such as Maxwell stress tensor method, magnetic charge method, or magnetizing current method. These methods are applicable for force computation only when the object is surrounded by air. The virtual air-gap concept has been proposed for calculating the contact force. However, its application is limited to magneto-static system. In this paper, we present the virtual air-gap concept for contact surface force in the eddy-current system. Its validity and usefulness are shown by comparison between numerical and experimental examples.

The Design of High-power BLDC Motor with Maximum Torque at Low Speed for Ship Propulsion (선박 추진 장치를 위한 저속영역에서 최대토크를 가지는 고출력 BLDC 모터의 설계)

  • Cho, Seung-Hyun;Bin, Jae-Gu;Cho, Soo-Eok;Choi, Chul;Kim, Chul-Woo
    • The Transactions of the Korean Institute of Power Electronics
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    • v.9 no.2
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    • pp.112-118
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    • 2004
  • Recently, development of rare earth permanent magnet with the high remanence, high coercivity allows the design of brushless motors with very high efficiency over a wide speed range. Cogging torque is produced in a permanent magnet by magnetic attraction between the rotor mounted permanent magnet and the stator teeth. It is an undesired effect that contributes to output ripple, vibration, and noise of machine. This cogging torque can be reduced by variation of magnet arc length, airgap length, magnet thickness, shifting the magnetic pole and varying the radial shoe depth and etc. In this paper, some airgap length and magnet arc that reduce cogging torque are found by finite element method(FEM) and Maxwell stress tensor method. The SPM(Surface Permanent Magnet) type of high-power Brushless DC (BLDC) motor is optimized as a sample model.

Analysis of Coaxial Magnetic Gear with Low Gear Ratios for Application in Counter Rotating Systems

  • Shin, H.M.;Chang, J.H.
    • Journal of Magnetics
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    • v.20 no.2
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    • pp.186-192
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    • 2015
  • This paper describes the electromagnetic and mechanical characteristics of coaxial magnetic gear (CMG) with a low gear ratio. The analysis models are restricted to a CMG with a gear ratio of less than 2. The electromagnetic characteristics including transmitted torque and iron losses are presented according to the variation of the gear ratio. The pole pairs of high speed rotor are chosen as 6, 8 and 10 by considering the torque capability. As the gear ratio approaches 1, both iron losses on the ferromagnetic materials and eddy current losses on the rotor permanent magnets are increased. The radial and tangential forces on the modulating pieces are calculated using the Maxwell stress tensor. When the maximum force is exerted on the modulating pieces, the mechanical characteristics including stress and deformation are derived by structural analysis. In CMG models with a low gear ratio, the maximum radial force acting on modulating pieces is larger than that in CMG models with a high gear ratio, and the normal stress and normal deformation are increased in a CMG with a low gear ratio. Therefore, modulating pieces should be designed to withstand larger radial forces in CMG with a low gear ratio compared to CMG with a high gear ratio.

Direct-current Dielectrophoretic Motions of a Single Particle due to Interactions with a Nearby Nonconducting Wall (비전도성 벽과의 상호작용에 따른 단일 입자의 직류 유전영동 운동)

  • Kang, Sangmo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.39 no.5
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    • pp.425-433
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    • 2015
  • In this paper, we have numerically investigated two-dimensional dielectrophoretic (DEP) motions of a single particle suspended freely in a viscous fluid, interacting with a nearby nonconducting planar wall, under an externally applied uniform direct-current electric field. Particularly, we solve the Maxwell equation with a large sharp jump in the electric conductivity at the particle-fluid interface and then integrate the Maxwell stress tensor to compute the DEP force on the particle. Results show that, under an electric field parallel to the wall, one particle is always repelled to move far away from the wall and the motion depends strongly on the particle-wall spacing and the particle conductivity. The motion strength vanishes when the particle is as conductive as the fluid and increases as the conductivity deviates further from that of the fluid.