• Interaction and multiscale mechanics
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• 제2권1호
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• pp.1-14
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• 2009

This paper proposes an interaction field concept based on the field theory of plasticity. Relative deformation between two arbitrary scales, e.g., macro and micro fields, is defined which can be implemented in the crystal plasticity-based constitutive framework. Differential geometrical quantities responsible for describing dislocations and defects in the interaction field are obtained, based on which dislocation density and incompatibility tensors are further derived. It is shown that the explicit interaction exists in the curvature or incompatibility tensor field, whereas no interaction in the torsion or dislocation density tensor field. General expressions of the interaction fields over multiple scales with more than three scale levels are derived and implemented into the present constitutive equation.

• Journal of the Optical Society of Korea
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• 제19권6호
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• pp.575-585
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• 2015

Magnetic field in magnetic bearings is the physical medium to realize magnetic levitation, the distribution of the magnetic field determines the operating performance of magnetic bearings. In this paper, a thin-slice Fiber Bragg Grating-Giant Magnetostrictive Material magnetic sensor used for the air gap of magnetic bearings was proposed and tested in the condition of dynamic magnetic field. The static property of the sensor was calibrated and a polynomial curve was fitted to describe the performance of the sensor. Measurement of dynamic magnetic field with different frequencies in magnetic bearings was implemented. Comparing with the finite element simulations, the results showed the DC component of the magnetic field was detected by the sensor and error was less than 5.87%.

• Journal of Magnetics
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• 제20권1호
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• pp.8-10
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• 2015

The magnetic anisotropy field plays an important role in spin-orbit-torque-induced magnetization dynamics with electric current injection. Here, we propose a magnetometric technique to measure the magnetic anisotropy field in nanostructured ferromagnetic thin films. This technique utilizes a magneto-optical Kerr effect microscope equipped with two-axis electromagnets. By measuring the out-of-plane hysteresis loops and then analyzing their saturated magnetization with respect to the in-plane magnetic field, the magnetic anisotropy field is uniquely quantified within the context of the Stoner-Wohlfarth theory. The present technique can be applied to small nanostructures, enabling in-situ determination of the magnetic anisotropy field of nanodevices.

• 한국태양에너지학회 논문집
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• 제32권5호
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• pp.41-51
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• 2012

Heliostat field is the most important subsystem in the tower type solar thermal power plant since its optical performance affects the total system efficiency most significantly while the construction cost of it is the major part of total construction cost in such a power plant. Thus a well designed heliostat field to maximize the optical efficiency as well as to minimize the land usage is very important. This work presents methodology, procedures and result of heliostat filed design for 200kW solar thermal power plant built recently in Daegu, Korea. A $2{\times}2(m)$ rectangular shaped receiver located at 43(m) high and tilted $28^{\circ}$ toward heliostat field, 450 of heliostats of which the reflective surface is formed by 4 of $1{\times}1(m)$ flat plate mirror facet, and the land area having about $140{\times}120(m)$ size are used to form the heliostat field. A procedure to deploy 450 heliostats in radial staggered nonblocking formation is developed. Also the procedures to compute the cosine effect, intercept ratio, blocking and shading ratio in the field are developed. Finally the heliostat filed is designed by finding the optimal radial distance and azimuthal spacing in radial staggered nonblocking formation such that the designed heliostat field optical efficiency could be maximized. The designed heliostat field has 77% of annual average optical efficiency, which is obtained by annually averaging the optical efficiencies computed between the time of where sun elevation angle becomes $10^{\circ}$ after sunrise and the time of where sun elevation angle becomes $10^{\circ}$ before sunset in each day.

• Asian-Australasian Journal of Animal Sciences
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• 제14권10호
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• pp.1367-1373
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• 2001

This study used fowl sperm from three White Leghom rooster reared at our laboratory. Semen samples were exposed to the magnetic field strengths of from 650 to 5700 Gauss for one. two, or three days to investigate the influence of magnetic field on the orientation of fowl spermatozoa. Fowl spermatozoa were found to orient with their long axis of heads perpendicular to the magnetic field direction. The fowl spermatozoa were initially influenced when magnetic field intensities were from 650 to 5700 Gauss and the highest values (70.67, 72.49 and 71.79%) were found in the 5700 Gauss treatment at one, two, and three days exposure, respectively. Although percentages of the perpendicular oriented fowl spermatozoa increased along with the enhancement of the magnetic field intensity, the degree of orientation was only significantly higher in the treatments having the magnetic field strength from 1500 to 5700 Gauss than that in the control treatment at all exposure time. In addition, the experimental results also showed that the percentages of all orientational types of fowl spermatozoa (perpendicular category including upward perpendicular and downward perpendicular and parallel type consisting of leftward parallel and rightward parallel) in all treatments tended to be stable during exposure time. From the results of this study. it is suggested that (1) the diamagnetic anisotropy of the inside structural components of fowl spermatozoa induce them to orient perpendicular to the magnetic field direction, (2) the degree of orientation increased according to the enhancement of magnetic field strengths, (3) fowl spermatozoa had not an high sensitivity to the magnetic field, and the level of perpendicular orientation of fowl spermatozoa in this study is nearly similar to that of cattle sperm in the study of Suga et al. (2000).

• 대한전기학회논문지
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• 제35권12호
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• pp.579-585
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• 1986

A Reversed Field Pinch(RFP) Plasma automatically forms the reversed field configuration in a stable state by the self-reversal phenomenon. But this process of formation of the reversed field configuration has a problem that instabilities occur. In order to form a RFP configuration in a stable state by removing instabilities, this experimental study attempts to restrain Toroidal magnetic fields and supplement Toroidal flux by employing high frequency rotating fields. As a result, the reversed magnetic field configuration is stably formed in a short period because high frequency rotating fields can deflect poloidal currents and produce magnetic fields in the Toroidal direction.

• Wind and Structures
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• 제17권2호
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• pp.123-133
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• 2013

Pressure field and velocity profiles in a thunderstorm downburst are significantly different from that of an atmospheric boundary layer wind. A model of the pressure field in a downburst is presented in accordance with the experimental and numerical results. Large eddy simulation method is employed to investigate transient pressure field on impingement ground of a downburst. In addition, velocity profiles of the downburst are studied, and good agreement is achieved between the present results and the data obtained from empirical models.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.540-541
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• 2005

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1657-1661
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• 2005

The velocity dipole field method is presented for real-time collision avoidance of mobile robots. The direction of motion of the obstacle is used as the axis of the dipole field, and the speed of the obstacle is used to proportionally strengthen the dipole field. The elliptical field lines of the dipole field are useful to skillfully guide the robot around obstacles, quite similar to the way humans avoid moving obstacles. Field modulation coefficient is also introduced to weaken the field effect as the obstacle recedes. The real-time algorithm of the velocity dipole field has been devised and experimentally tested on the robot soccer test-bed. The results show the capability of the new real-time collision avoidance strategy and how it can overcome the weaknesses in the conventional potential field method. The new method makes an explicit and proactive action of collision avoidance, unlike the conventional method, which forces the robot merely away from the obstacle aimlessly. The proposed method delivers greater capability with no considerable computational overhead

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.684-689
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• 2003

One field identified by an inverse method is one of multiple candidate solutions those are independently obtained through a specific estimation technique. While averaging of optimized fields can provide a better description of the spatial feature of an unknown field, it deteriorates the flow and transport characteristics of the optimized fields. As a result, the averaged field is not suited for modeling aquifer performances. Based on genetic algorithm, an optimal field synthesis technique is developed, which combines diversely optimized fields into a refined group of fields. Each field in the population is paired, and a sub-region of each field is exchanged by crossover operation to create a group of synthesized fields of enhanced modeling capability. The population of the fields is evolved till the synthesized fields become sufficiently similar. Applications of the optimal field synthesis to synthetic cases indicate that the objective functions of the fields assessing the modeling capabilities are further reduced after the optimal field synthesis. The identified fields from various inverse techniques may yield a range of modeling results under varied flow situations. The uncertainty is narrowed down through the optimal field synthesis and the associated modeling results converge on that of the reference field. The developed inverse modeling facilitates the construction of a reliable simulation model and hence trustworthy predictions of the future performances.