• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.40.3-41
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• 2015

We performed simultaneous observations of H2O and SiO masers toward VX Sgr using the Korean VLBI Network (KVN) and Source Frequency Phase Referencing (SFPR) method. The observations were carried out at 5 epochs from 2014 February to 2015 June. The relative locations of the SiO with respect to the H2O maser emission were determined at two epochs by SFPR for the first time. The H2O masers show well developed asymmetric outflow features which are spread up to ~300 mas in diameter. On the other hand, the SiO masers show a ring-like structure close to the central star with ~ 30 mas diameter. The SFPR observational results at two epochs (${\varphi}=0.83$ and 0.99) provide similar relative locations of H2O and SiO maser features. These superposed maps of H2O and SiO masers lead us to investigate the development of outflow motions from relatively spherical SiO maser regions close to central star to aspherical H2O maser regions according to optical phase of stellar pulsation together with the prediction of the position of central star.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.16 no.4
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• pp.385-397
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• 2006

A high prevalence of farmer's work-related musculoskeletal disorders(MSDs) have been reported in precedent studies. To offer the basic data for reducing the melon farmer's MSDs, a questionnaire survey about MSDs symptoms and work loaded body part and video analysis by 3 checklist(REBA, RULA, OWAS) for musculoskeletal risk assessment were carried. 94 melon farmers for this questionnaire and 1 typical farm for risk assessment were participated. A total of 80.9% of the farmers reported musculoskeletal symptoms and 60.6% reported musculoskeletal symptoms over NIOSH standard. The mainly symptom body part is low back, knee and shoulders. Main risk factors in melon farm are awkward postures, heavey/frequent lifting and repetitive hand/arm motions. The high risk tasks induced by video analysis were harvesting, removing the sprouts and covering with rags. These result can be used practically for planning intervention strategy and programs to prevent farmer's MSDs.

• Journal of Powder Materials
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• v.10 no.6
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• pp.415-421
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• 2003

The study for producing the flake powders by milling of aluminum foil and gas atomized powders was carried out. The effects of lifter bars on the ball motions and milling of aluminum foils were also investigated. The aluminum foils were laminated each other, elongated, fragmented into small foils and finally formed into the flake powders during the dry ball-milling. The spherical atomized-powders were milled to coarse flake powders with high aspect ratio and then changed to fine flake powders with lower aspect ratio. Even though long times were required for making flake powders by milling of foils, the water covering areas of them were higher than those of powders milled using gas-atomized powders, suggesting aluminum foils were more plastically deformed by micro-forging. On the other hand, as the number of lifter bars increased, the necessary rotation speeds of milling jar for cascading mode and cataracting mode decreased drastically. It was possible to achieve same quality of milled flake powder by using the lifter bars under the lower milling speeds. The painting test showed that the appearance of painted surface was good and optimum content range of aluminum paste in car paint to maximize the degree of gloss was 3-5%.

• KIISE Transactions on Computing Practices
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• v.23 no.3
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• pp.148-155
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• 2017

In this paper, we develop a new system to estimate the step count for a smartphone user. The system analyzes data obtained from the accelerometer, magnetic sensor, and gyroscope of an android smartphone to extract pattern information of human steps. We conduct an experiment and evaluation to confirm that the proposed system successfully estimates the number of steps with 96% accuracy when hand-held and 95.5% accuracy when in-pocket. In addition, we found that detection errors were caused by human motions such as touching the screen, shaking the device up and down, sitting up and sitting down, and waving the phone around.

• Journal of the Korean Society of Safety
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• v.25 no.4
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• pp.42-47
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• 2010

Recently, many techniques have been developed for the inspection of pipelines using guided waves. However, few researches have been made on the application of those techniques for buried underground pipes. Guided wave motions in the buried pipes are somewhat different from those of on-ground pipes which have traction-free (air) boundary condition on outer pipe walls and thus are strongly affected by the mechanical property of the surrounding soils. Therefore, it should be investigated the effect of soil properties on the guided wave behavior in buried pipe. On the other hand, the mechanical property of soil is largely depending on its moisture conditions nevertheless of other influential factors such as void ratio. In this study, the effect of moisture conditions in soils on mode attenuation of guided waves in the buried pipe is investigated. To this end, numerical study is performed to characterize mode attenuation behavior in buried pipes and the effective mode which is suitable for long range inspection is identified.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.39.1-39.1
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• 2012

Nuclear rings in barred galaxies are sites of active star formation (SF). We investigate SF and its feedback effects occurring in barred galaxies, for the first time, using high-resolution grid-based hydrodynamic simulations. The gaseous medium is assumed to be infinitesimally thin, isothermal, and unmagnetized. The SF recipes include a density threshold corresponding to the Jeans condition, a SF efficiency of 1%, and momentum feedback via Type II supernova events together with stellar-wind mass loss. To investigate various environments, we vary the gas sound speed as well as the efficiency of momentum injection in the in-plane direction. We find that when the sound speed is small, the surface density of a ring becomes largely independent of the azimuthal angle, resulting in star-forming regions distributed over the whole length of the ring. When the sound speed is large, on the other hand, the ring achieves the largest density at the contact points between the dust lanes and the ring where SF occurs preferentially, leading to a clear age gradient of star clusters in the azimuthal direction. Since rings shrink with time, a radial age gradient of star clusters naturally develop regardless of sound speed, consistent with observations. SF persists over 200 Myr, with an average rate of ${\sim}1.3M_{\odot}/yr$ similar to observed values. Rings gradually become hostile to SF as they lose gas into stars and turbulent motions dominate.

• Journal of computational fluids engineering
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• v.12 no.2
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• pp.1-7
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• 2007

To develop an aerodynamic performance, two groups of studies have been achieved widely. One is about the geometric design of vehicles and the other is about aerodynamic devices. Geometric design is a credible and stable method. However, it is not flexible and each part is related interactively. Therefore, if one part of geometry is modified, the other part will be required to redesign. On the other hand, the flow control by aerodynamic devices is flexible and modulized method. Even though it needs some energy, a relatively small amount of input makes more advanced aerodynamic performance. Synthetic jet is one of the method in the second group. The device repeats suctions and blowing motions in constant frequency. According to the performance, the adjacent flow to flight surface are served momentum. This mechanism can reduce the aerodynamic loss of boundary layer and separated flow. A synthetic jet actuator has several parameters, which influences the flow control. This study focuses on the parameter effects of synthetic jet - orifice geometry, frequency, jet speed and etc.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.2
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• pp.174-180
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• 2004

Failure of tube bundles due to excessive flow-induced vibrations continues to affect the performance of nuclear power plant Early experimental studies concentrated on rigid structures and later investigators dealt with elastic structures because of their importance in many engineering fields. On the other hand, much less numerical work has been carried out, because of the numerical complexity associated with the problem. Conventional approaches usually decoupled the flow solution from the structural problem. The present numerical study proposes the methodology in analyzing the fluidelastic instability occurring in tube bundles by coupling the Computational fluid Dynamics (C%) with the tube equation of motions. The motion of the structures is modeled by a spring-damper-mass system that allows transnational motion in two directions (a two-degree-of-freedom system). The fluid motion and the cylinder response are solved in an iterative way, so that the interaction between the fluid and the structure can be accounted for property. The aim of the present work is to predict the fluidelstic instability of tube bundles and the associated phenomena, such as the response of the cylinder, the unsteady lift and drag on the cylinder, the vortex shedding frequency.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.423-425
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• 2001

The Proper Orthogonal Decomposition (POD) technique was applied to investigate the effects of Reynolds number and the characteristics of the organized motions or coherent structures as a function of downstream position from x/D=2 to 6 in a turbulent axisymmetric shear layer at Reynolds numbers of 78,400, 117,600, and 156,800. Data were collected simultaneously using the 138 hot-wire probe used by Citriniti and George (2000). The POD was then applied to a double Fourier transform in time and azimuthal direction of the double velocity correlation tensor. The lowest azimuthal mode for all POD modes, which dominated the dynamics at x=D = 3 in the previous experiments, dies off rapidly downstream. This is consistent with a trend toward homogeneity in the downstream evolution, and suggests that some residual value may control the growth rate of the far jet. On the other hand, for the higher azimuthal modes, the peak shifts to lower mode numbers and actually increases with downstream distance. These mixing layer data, normalized by similarity variables for the mixing layer, collapse at all downstream positions and are nearly independent of Reynolds numbers.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.1982-1992
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• 1999

This paper presents a novel concept of cargo handling system adapted for a sea port subjected to severe time-varying tide. The proposed system can perform loading or unloading by using a sort of hydraulic elevator associated with real-time position control. In order to achieve a proof-of-concept, a small-sized laboratory model of the cargo handling system is designed and built. The model consists of three principal components container palette transfer (CPT) car, platform with lifting columns, and cargo ship. The platform activated by electro-rheological (ER) valve-cylinders is actively controlled to track the position of the cargo ship subjected to be varied due to the time-varying tide and wave motion. Following the derivation of the dynamic model for the platform and cargo ship motions, an appropriate control scheme is formulated and implemented. The location of the CPT car is sensed by a set of photoelectric switches and controlled via sequence controller. On the other hand, a sliding mode controller (SMC) is adopted as the position controller for the platform. Both simulated and measured control results are presented to demonstrate the effectiveness of the proposed cargo system.