• 전기학회논문지
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• 제60권5호
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• pp.942-948
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• 2011

This paper deals with characteristic analysis of axial flux permanent magnet (AFPM) machines with axially magnetized PM rotor using quasi-3-D analysis modeling. On the basis of magnetic vector potential and a two-dimensional (2-D) polar-coordinate system, the magnetic field solutions due to various PM rotors are obtained. In particular, 3-D problem, that is, the reduction of magnetic fields near outer and inner radius of the PM is solved by introducing a special function for radial position. And then, the analytical solutions for back-emf and torque are also derived from magnetic field solutions. The predictions are shown in good agreement with those obtained from 3-D finite element analyses (FEA). Finally, it can be judged that analytical solutions for electromagnetic quantities presented in this paper are very useful for the AFPM machines in terms of following items : initial design, sensitivity analysis with design parameters, and estimation of control parameters.

• 상하수도학회지
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• 제26권3호
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• pp.479-486
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• 2012

Runoff characteristics of pollutant loads of the lower Han River was studied before full implementation of Total Pollution Load Management System(TPLMS). Magnitude of macroscopic(annual) fluctuation was in the order of Namhan River > Han River > Bukhan River, gross weight TP > gross weight TN > gross weight BOD, gross weight deviation > concentration deviation. Flux variation was higher than that of concentration. Microscopic(weekly) fluctuation showed similar pattern to macroscopic scale. TP showed the highest deviation resulting in the lowest reliability. 60% of annual flux passed during summer 3months resulting in 43-46% pass of gross weight at the lower Han River. Strong correlation was found between flux and gross weight especially in gross weight TN. Gross weight pollution increased as high as 400% while passing Seoul area due to the concentration. The deviation from moving average increased during summer season in the gross weight TP and BOD. Seasonal tendency was confirmed especially in gross weight TN and TP using autocorrelation function.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.156-157
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• 2003

A simple method is proposed to split the flux vector of the Euler equations by introducing two artificial wave speeds. The direction of wave propagation can be adjusted by these two wave speeds. This idea greatly simplifies the upwinding, and leads to a new family of upwind schemes. Numerical flux function for multi-dimensional Euler equations is formulated for any grid system, structured or unstructured. A remarkable simplicity of the scheme is that it successfully achieves one-sided approximation for all waves without recourse to any matrix operation. Moreover, its accuracy is comparable with the exact Riemann solver. For 1-D Euler equations, the scheme actually surpasses the exact solver in avoiding expansion shocks without any additional entropy fix. The scheme can exactly resolve stationary contact discontinuities, and it is also freed of the carbuncle problem in multi­dimensional computations.

• 대한기계학회논문집B
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• 제25권6호
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• pp.845-852
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• 2001

The characteristics of evaporation cooling of single droplet on a heated surface were studied experimentally. The two kinds of heater modules were tested to measure cooling characteristics of metal surface (high conductivity) and Teflon surface (low-energy surface, low conductivity). The results showed that time averaged heat flux during droplet evaporation increased exponentially with initial surface temperatures of brass, copper and steel. The heat flux and evaporation time did not varied with metal conductivities. However, the temperature drop after the deposition of droplet was larger on Teflon than on the metals. Thus, the correlation of interface temperature between liquid droplet and metal surface was proposed as a function of the initial surface temperature of heating materials, which could be applied to both metal and non-metal ones.

• 대한기계학회논문집
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• 제6권3호
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• pp.247-255
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• 1982

The heat diffusion equation for an annular fin is analyzed by Laplace transformation. The fin has a uniform thickness, with its end insulated, and three different temperature profiles at the base such as step change, harmonic and exponential functions. The exact solutions for the temperature and heat flux of the fins are obtained with the infinite series. The series solutions converge rapidly for large values of dimensionless time, but slowly for small values. Therefore some approximate solutions are presented here to fine the temperature distribution and heat flux for small values of dimensionless time. Furthermore a simple approximate heat flux, .OMEGA.=1.13c.tau.$^{1}$2/ is found in the range of .tau. .leg. o.1/c for the exponential function at the base.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 전력전자학술대회 논문집
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• pp.388-394
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• 1998

In this paper, we propose a speed sensorless control of the saturated induction motor using the zero sequence third harmonic voltages and a compensation method of the stator resistance variations. The air-gap flux of the saturated induction motor contains the space harmonic components rorating synchronous frequency. As a function of the air-gap flux saturation, the dominant third harmonic voltage is used to compensate the non-linear variations of the mutual inductance depending on the saturation level of the motor. and also the stator resistance variations can be measured with the phase angle between the voltage vector and the zero sequencial voltages. The validity of the proposed compensation scheme in the speed sensorless control using rotor flux observer is verified by simulations.

• Bulletin of the Korean Chemical Society
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• 제28권8호
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• pp.1371-1374
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• 2007

The velocity auto-correlation (VAC) function of liquid argon in the Green-Kubo formula decays quickly within 5 ps to give a well-defined diffusion coefficient because the velocity is the property of each individual particle, whereas the stress (SAC) and heat-flux auto-correlation (HFAC) functions for shear viscosity and thermal conductivity have non-decaying, long-time tails because the stress and heat-flux appear as system properties. This problem can be overcome through N (number of particles)-fold improvement in the statistical accuracy, by considering the stress and the heat-flux of the system as properties of each particle and by deriving new Green-Kubo formulas for shear viscosity and thermal conductivity. The results obtained for the transport coefficients of liquid argon obtained are discussed.

• 천문학회보
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• 제37권2호
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• pp.134.1-134.1
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• 2012

The radiation belt structure can be approximately reproduced by a form of diffusion equation, which takes into account the radial diffusion process as well as those in pitch angle and energy. The solution of the equation depends on several factors including initial and boundary conditions, diffusion coefficients, and plasmapause location. In this paper, we have attempted to determine a set of approximate functions for the energetic electron fluxes near the outer edge of the outer belt in terms of solar wind variable. We used the electron flux data from SST onboard the THEMIS spacecraft and determined its correlation with solar wind conditions in a systematic way. The functions were determined separately for different energy channels from ~30 keV up to 719 keV. Our determination of these functions allows us to predict the radial boundary condition for the electron flux, which can be implemented in a forecast model.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권10호
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• pp.498-504
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• 2006

Thrust force of linear motor is one of the important factor to specify motor performance. In this study, we optimized maximizing the thrust force of TFLM(Transverse Flux Linear Motor) using Response Surface Methodology by the table of orthogonal way. The Response Surface Methodology was well adapted to make the analytical model of the maximum thrust force and enable the objective function to be easily created and a great deal of the time In computation to be saved. Therefore, it is expected that the proposed optimization procedure using the Response Surface Methodology can be easily utilized to solve the optimization problem of electric machine.

• 한국초전도ㆍ저온공학회논문지
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• 제10권3호
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• pp.14-18
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• 2008

This paper deals with the conceptual design and characteristic analysis of core type superconducting motor using iron cores in the field. As the objective function of conceptual design, the flux quantity per pole is selected. In order to reduce the quantity of superconductors, the variations of flux quantity per pole by changing the design variables and area are investigated. Finally, the quantity of superconductors between air-cored and core type superconducting motor is compared under the same motor capacity. In addition, the dimensions and volumes of motors are compared.