• Earthquakes and Structures
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• v.13 no.5
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• pp.429-442
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• 2017

Dry bridges have been widely applied in the Qinghai-Tibet Railway (QTR) to minimize the thermal disturbance of engineering to the permafrost. However, because the Qinghai-Tibet Plateau is an area with a high potential occurrence of earthquakes, seismic action can easily destroy the dry bridges. Therefore, a three-dimensional numerical model, with consideration of the soil-pile interactions, is established to investigate the thermal characteristics and their impact on the seismic response of the dry bridge in permafrost region along the QTR. The numerical results indicate that there exist significant differences in the lateral displacement, shear force, and bending moment of the piles in different thermal conditions under seismic action. When the active layer become from unfrozen to frozen state, the maximum displacement of the bridge pile reduces, and the locations of the zero and peak values of the shear force and bending moment also change. It is found that although the higher stiffness of frozen soil confines the lateral displacement of the pile, compared with unfrozen soil, it has an adverse effect on the earthquake energy dissipation capacity.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2753-2756
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• 2007

In the present study, we reduce the drag and lift fluctuations of the sphere by providing a linear proportional control. For this purpose, we measure the radial velocity along the centerline in the wake and provide blowing and suction at a part of sphere surface based on the measured velocity. Zero-net mass flow rate is satisfied during the control. This control is applied to the flow over a sphere at Re=300 and 425. We vary the sensing location at $0.8d{\leq}X_s{\leq}1.3d$ and find that the most effective sensing region coincides with the location at which minimum correlation between the lift and sensing-velocity directions occurs. As a result, the lift and drag fluctuations are significantly reduced.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.64.1-64.1
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• 2015

In the present study, we examine the dependence of solar proton peak flux at SOHO and STEREO on 3-D CME parameters (radial speed, angular width, and longitudinal angular separation between its source region and the magnetic footpoints of spacecraft). For this we consider 38 proton enhancements of 16 SEP events observed by SOHO, STEREO-A, and/or B from 2010 August to 2013 June. As a result, we find that the enhancements are strongly dependent on these three parameters. The correlation coefficient between proton peak flux and CME speed is about 0.42 for the cases the footpoints are located inside the lateral boundaries of angular widths, while there is no correlation for the events outside the boundaries. The correlation coefficient between peak flux and angular separation is -0.51. We find that most of strong proton events occur when their angular separations are closer to zero, supporting that most of the proton fluxes are generated near the CME noses rather than their flanks.

• Proceedings of the IEEK Conference
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• 2003.07c
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• pp.2749-2752
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• 2003

Magnetocardiography is a very weak biomagnetic field generated from the heart. Since the magnitude of the biomagnetic field is in the order of a few pico Tesla, it is measured with a superconducting quantum interference device (SQUID). SQUID is a transducer converting magnetic flux to voltage, however, its range of linear conversion is very restricted. In order to overcome the narrow dynamic range. a flux locked loop is used to feedback the output field with opposite polarity to the input field so that the total Held becomes zero. This prevents the operating point of the SQUID from moving too far away from the null point thereby escape from the linear region. In this paper, an emulator for the SQUID sensor and feedback coil is proposed. Magnetic courting between the original field and the generated field by the feedback coil is emulated by electronic circuits. By using the emulator, FLL circuits are analyzed and optimized without SQUID sensors. The emulator may be used as a test signal for multi-channel gain calibration and system maintenance.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.521-522
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• 2016

This paper presents a novel scheme to estimate the rotor position of a single-phase hybrid switched reluctance motor (HSRM). The proposed method uses the differential of back-EMF within a position region to estimate rotor position. By detecting the crossing-zero signal of back-EMF differential value, the minimum position of back-EMF corresponding to an absolute rotor position can be captured and used for position estimation four times in every mechanical rotation. In this way, a sensorless operation with adjustable turn on/off angle can be achieved without substantial computation. For the starting, two current comparators are adopted. The experimental verification using a prototype drive system is provided to demonstrate the viability of the proposed sensorless scheme.

• Proceedings of the KIEE Conference
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• 1997.07f
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• pp.2043-2046
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• 1997

GTO 소자의 최소 턴온 시간(minimum turn-on time, Tmin)때문에 발생된 지령전압 오차를 보상하는 기법을 제안한다. 공간백터전압$(V_1)$의 턴온시간이 Tmin보다 작을 경우에는 전압오차를 PI 제어기로 보상한다. 또한, 지령전압벡터의 크기가 특정한 값(Vmin)보다 작은 경우, 영벡터(zero vector)가 PWM 추기에서 중간에 매치가 되도록 스위칭 순서를 바꿔준다. 시뮬레이션을 통해 이러한 지령전압 오차의 보상으로 펄스 누락(pulse dropping) 영역에서 출력전압의 대칭성이 향상되고 고조파 함유량이 감소한다는 사실을 보인다.

• Journal of Korean Society for Atmospheric Environment
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• v.19 no.6
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• pp.733-743
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• 2003

The flow field in multiple fluid sphere systems was studied analytically. The expanded zero vorticity cell model based on Kuwabara's theory (1959) was applied and the effects of gas slippage at the collecting surface were considered. Also, the solid sphere system was extended to fluid sphere including the effects of the induced internal circulation inside the liquid droplet spheres or gas bubble systems. As a result, the obtained analytic solution was converged to the existing solutions for flow field around solid and bubble sphere systems with proper boundary conditions. Based on the resolved flow field, the terminal velocity around the collecting fluid spheres was obtained. Subsequently, this study evaluated the most general solution for flow field around the multiple fluid sphere systems. The obtained flow field in multiple fluid sphere could be used as a fundamental consideration of wet scrubber design and devices for removing particles by fluid-fluid interactions.

• Proceedings of the KIPE Conference
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• 2017.11a
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• pp.95-96
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• 2017

A three-level inverter is widely used thanks to its excellent performances, but the voltage may fluctuate at the neutral point of the split DC-Link. Neutral point voltage fluctuations cause inverter performance degradation and switching element damage, so the neutral point voltage control is essential. However, the neutral point control can be also limited by modulation index and power factor. This paper analyzes the limitation of the neutral point voltage control due to the limitation of zero-sequence voltage, and suggests a method to determine the region where the PWM has to be changed for a better neutral point control.

• Geomechanics and Engineering
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• v.3 no.4
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• pp.323-337
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• 2011

Israel's coastal region consists, mainly, of Pleistocene and Holocene sands with varying degrees of calcareous cementation, known locally as "kurkar". Previous studies of these materials emphasized the difficulty in their geotechnical characterization, due to their extreme variability. Consequently, it is difficult to estimate construction stability, displacements and deformations on, or within these soils. It is suggested that SPT and Menard pressuremeter tests may be used to characterize the properties of these materials. Values of elastic modulus obtained from pressuremeter tests may be used for displacement analyses at different strain levels, while accounting for the geometric dimensions (length/diameter ratio) of the test probe. A relationship was obtained between pressuremeter modulus and SPT blow count, consistent with published data for footing settlements on granular soils. Cohesion values, for a known friction angle, are estimated, by comparing field pressuremeter curves to curves from numerical (finite element or finite difference) analyses. The material analyzed in the paper is shown to be strain-softening, with the initial cohesion degrading to zero on development of plastic shear strains.

• Journal of Powder Materials
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• v.4 no.4
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• pp.291-297
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• 1997

Titanium cabide, TiC-x mole% Al composites, and functionally-graded materials (FGMs) of TiC-x mole% Al were synthesized by an electrothermal combustion (ETC) method. TiC-70 mole% Al composite was not ignited by indirect tungsten coil heating, but can be synthesized by an electrothermal combustion. The velocity of the combustion wave decreased with increasing addition of Al and increased with an increase in the applied electric field. Functionally-graded TiC-Al materials were made from reactant layers with compositions of Ti+C+x moles Al with x ranging from zero to 70 by an electrothermal combustion. In the FGM products a nearly linear change in composition in the graded region was observed in samples with 0$\leq$ x $\leq$ 70 with x being the mole% Al.