• Journal of the Society of Naval Architects of Korea
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• v.32 no.2
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• pp.103-107
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• 1995

Longitudinal hull girder vibration has not been occurred severely since 1960's. However, recent low speed diesel driven ships equipped with overcritical shafting system, can be excited heavily in longitudinal direction by shaft axial farce coupled with torsional vibration. In this study the characteristics of longitudinal hull girder vibration of a 73,000 deadweight bulk carrier were investigated through onboard measurement, exciter test, and 3-D FEM analysis. Results showed that the longitudinal hullgirder vibration may occur in the ship which is not set up the barred speed range in engine operation. Moreover, this vibration occurs. only during the low speed voyage in harbour depending upon the ship loading condition.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.2230-2232
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• 2000

This paper reports an electrostatically driven and electromagnetically sensed planar vibratory gyroscope based on a surface-bulk combined micromachining. The fabricated structure has comb electrodes which are 400${\mu}m$ thick, 18${\mu}m$ wide, 600${\mu}m$ long and separated by 7${\mu}m$ so that the height-gap ratio is about 57. It also has electroplated gold springs which are 15${\mu}m$ wide, 14${\mu}m$ thick and 500${\mu}m$ long on both sides of the seismic mass. The open-loop characteristics of fabricated gyroscope at atmospheric pressure are measured on a rate table. The fabricated gyroscope has a sensitivity of 30mV/deg/sec, and a resolution of 0.1deg/sec at atmospheric pressure. It is expected that non linearity of full scale output is less than 0.8% with. the dynamic range of $\pm$500deg/sec.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.459-462
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• 2002

Many active and passive flow control methods have been studied since decades, but there are only few works about flow control methods using ion wind. This paper presents an experimental study on the wake control behind a circular cylinder using ion wind, a bulk motion of neutral molecules driven by locally ionized air of corona discharge. Experiments are done f3r different electrohydrodynamic numbers - the ratio of an electrical body farce to a fluid Inertial force - from 0 to 2 and for the Reynolds number ranging from $4{\times}10^3\;to\;8{\times}10^3$. Pressure distributions over a cylinder surface are measured and flow visualizations are carried out by smoke wire method. Flow visualizations confirm that ion wind affects significantly the wake structure behind a circular cylinder and pressure drag could be dramatically reduced by the superimposing ion wind.

• JSTS:Journal of Semiconductor Technology and Science
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• v.9 no.3
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• pp.148-152
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• 2009

Recent CMOS technology scaling has seriously eroded the bit-line noise immunity of register files due to the consequent increase in active bit-line leakage currents. To restore its noise immunity while maintaining performance, we propose and evaluate a $256{\times}40$-bit register file incorporating dual-$V_t$ bit-lines with a boosted gate overdrive voltage in 65 nm bulk CMOS technology. Simulation results show that the proposed bootsrapping scheme lowers leakage current by a factor of 450 without its performance penalty.

• Journal of the Korean Society of Visualization
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• v.2 no.2
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• pp.38-44
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• 2004

Theoretical and numerical studies are given to the sink flows within a rotating circular tank driven by the fluid withdrawal from a bottom circular hole. It was found that, when the upper free surface was set with no-slip boundary conditions, the Ekman boundary-layer develops not only above the bottom surface but under the top surface. The sink fluid is coming from the two Ekman layers, and the mass transfer from the bulk, inviscid region is dependent on the rotational speed. It is also remarkable to see that all the fluid gathered along the axis flows in a form of rapidly rotating fluid column haying almost the same diameter as the bottom hole.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.10a
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• pp.458-461
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• 2015

In this paper 2 types of voltage references and a current reference suitable for low-voltage, low-power circuits are proposed and designed with $0.35{\mu}m\;CMOS$ process. MOS transistors operating in weak inversion and bulk-driven technique are utilized to achieve low-voltage and low-power features. The first voltage reference consumes 1.43uA from a supply voltage of 1.2V while it has a reference voltage of 585mV and a TC(Temperature Coefficient) of $6ppm/^{\circ}C$. The second voltage reference consumes 48pW from a supply voltage of 0.3V while having a reference voltage of 172mV and a TC of $26ppm/^{\circ}C$. The current reference consumes 246nA from a supply voltage of 0.75V with a reference current of 32.6nA and a TC of $262ppm/^{\circ}C$. The performances of the designed references have been verified through simulations.

• Journal of Electrical Engineering and Technology
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• v.8 no.6
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• pp.1320-1327
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• 2013

In this paper, two different electromagnetic energy harvesters using bulk micromachined silicon spiral springs and Polydimethylsiloxane (PDMS) packaging technique have been fabricated, characterized, and compared to generate electrical energy from ultra-low ambient vibrations under 0.3g. The proposed energy harvesters were comprised of a highly miniaturized Neodymium Iron Boron (NdFeB) magnet, silicon spiral spring, multi-turned copper coil, and PDMS housing in order to improve the electrical output powers and reduce their sizes/volumes. When an external vibration moves directly the magnet mounted as a seismic mass at the center of the spiral spring, the mechanical energy of the moving mass is transformed to electrical energy through the 183 turns of solenoid copper coils. The silicon spiral springs were applied to generate high electrical output power by maximizing the deflection of the movable mass at the low level vibrations. The fabricated energy harvesters using these two different spiral springs exhibited the resonant frequencies of 36Hz and 63Hz and the optimal load resistances of $99{\Omega}$ and $55{\Omega}$, respectively. In particular, the energy harvester using the spiral spring with two links exhibited much better linearity characteristics than the one with four links. It generated $29.02{\mu}W$ of output power and 107.3mV of load voltage at the vibration acceleration of 0.3g. It also exhibited power density and normalized power density of $48.37{\mu}W{\cdot}cm-3$ and $537.41{\mu}W{\cdot}cm-3{\cdot}g-2$, respectively. The total volume of the fabricated energy harvesters was $1cm{\times}1cm{\times}0.6cm$ (height).

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.263-263
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• 2013

This work examines the dynamic properties of ice surfaces in vacuum for the temperature range of 140~180 K, which extends over the onset temperatures for ice sublimation and the phase transition from amorphous to crystallization ice. In particular, the study focuses on the transport processes of excess protons and chloride ions in ice and their segregative behavior to the ice surface. These phenomena were studied by conducting experiments with a relatively thick (~100 BL) ice film constructed with a bottom $H_2O$ layer and an upper $D_2O$ layer, with excess hydronium and chloride ions trapped at the $H_2O$/$D_2O$ interface as they were generated by the ionization of hydrogen chloride. The migration of protons, chloride ions, and water molecules to the ice film surface and their H/D exchange reactions were measured as a function of temperature using the methods of low energy sputtering (LES) and Cs+ reactive ion scattering (RIS). Temperature programmed desorption (TPD) experiments monitored the desorption of water and hydrogen chloride from the surface. Our observations indicated that both hydronium and chloride ions migrated from the interfacial layer to segregate to the surface at high temperature. Hydrogen chloride gas desorbs via recombination reaction of hydronium and chloride ions floating on the surface. Surface segregation of these species is driven by thermodynamic potential gradient present near the ice surface, whereas in the bulk, their transport is facilitated by thermal diffusion process. The finding suggests that chlorine activation reactions of hydrogen chloride for polar stratospheric ice particles occur at the surface of ice within a depth of at most a few molecular layers, rather than in the bulk phase.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.121.1-121.1
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• 2012

It has been suggested that oscillatory earthward bursty bulk flows (BBFs) in the magnetotail are driving Pi2 oscillations on the ground. However, only a few studies examined the BBF-driven Pi2 model. The goal of this study is to establish the relation between BBFs and Pi2s. In order to examine BBF-drive model, we will conduct the timing analysis between BBFs and Pi2s for the intervals during which both Pi2 and BBF are present. In our study BBFs are identified with earthward flow speeds up to 200 km/s from THEMIS probes with a geocentric distance between 7 and 12 RE in the nightside magnetosphere for the interval from January 2008 to March 2008. Pi2 pulsations are identified at three low/mid-latitude ground stations having different local times; Bohyun (L = 1.35, LT ~ UT +9 hr), Hermanus (L = 1.83, LT ~ UT +2 hr) and Carson city (L = 2.00, LT ~ UT -2 hr). It is found that ~28% of BBFs have onset timing nearly identical to Pi2 onset. To investigate whether there is high similarity in the waveform between BBF and Pi2 oscillations, the coherence analysis is applied to the time series of BBF and Pi2 events. We found that there is no high coherence between BBF and Pi2 oscillations. Thus our observations suggest that low-latitude Pi2 oscillations are not directly driven by earthward flow bursts.

• Computers and Concrete
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• v.31 no.5
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• pp.395-403
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• 2023

The paper investigates the effect of two parameters - sand content (SC) and grain migration during shearing - on the mechanical properties of gravel-sand mixtures. Consolidated undrained (CU) triaxial tests were carried out on eight series of mixtures containing gravel (1<d<16 mm) and sand (0.1<d<1 mm). The prepared mixtures have sand contents of 0, 10, 15, 20, 40, 54, 94 and 100%, and a relative density of 60%. The transition sand content (TSC) is experimentally defined and marks the transition from gravel-driven to sand-driven behavior. For SC<TSC, the dry density of the mixture increases with SC. This induces an increase in undrained peak strength and dilative trend. The slope and position of the critical state line (CSL) are also deeply dependent on SC. At SC=TSC, the mixtures exhibit the largest dry density and yield the highest undrained peak strength and the largest dilative trend. During shearing, large internal migration of grains was observed at the TSC, causing heterogeneity in the sample. Analysis of the CSL deduced from the final points of the triaxial tests shows that, at the TSC, failure appears to correspond to the behavior of the coarsest fraction of the soil. This fraction is located in the upper part of the sample, where the sand particles had been eliminated by suffusion. On the other hand, in the more stable materials, the CSL is consistent with the bulk grain size distribution of the soil.