• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2006.05a
• /
• pp.298-301
• /
• 2006

This paper describes the electron energy distribution function characteristics in $SF_6-Ar$ gas calculated for range of E/N values from $50\sim700[Td]$ by the Monte Carlo simulation(MCS) and Boltzmann equation(BE) method using a set of electron collision cross sections determined by the authors and the values of electron swarm parameters are obtained by time of flight(TOF) method. In this dissertation the results of the combined experimental and theoretical studies designed to understand and predict the spatial growth and transport coefficients for electrons in $SF_6$ and $SF_6-Ar$ mixtures have described. The ionization and attachment coefficients in pure $SF_6$ and $SF_6-Ar$ mixtures have been calculated over the range of 10$SF_6$ molecule and for Ar atom proposed by other authors. The results obtained in this work will provide valuable information on the fundamental behaviors of electrons in weakly ionized gases and the role of electron attachment in the choice of better gases and unitary gas dielectrics or electro negative components in dielectric gas mixtures.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.32 no.6
• /
• pp.471-478
• /
• 2008

Detached Eddy Simulation (DES) is performed for developing turbulent flow of the $270^{\circ}$ curved duct at a Reynolds number of 56,690. The curvature ratio on the basis of a centric radius $R_c$ and a duct height H is 3.357. Turbulence models adopted are k-$\omega$ model for Reynolds Average Navier-Stokes (RANS) equation Simulation and Shear Stress Transport (SST) model for DES. DES is used as the hybrid computation technique combined with RANS-SST and Large Eddy Simulation (LES). Predicted results are compared with measured results including the distributions of Reynolds stresses and the flow characteristics on the symmetric plane of curved duct are presented. Judging from the comparison between the predicted and the measured results, the DES approach is applicable to calculate the developing turbulent flow in a $270^{\circ}$ curved duct.

• Korean Journal of Remote Sensing
• /
• v.22 no.5
• /
• pp.403-406
• /
• 2006

An algorithm for detection of yellow sand aerosols has been developed with infrared bands. This algorithm is a hybrid algorithm that has used two methods combined. The first method used the differential absorption in brightness temperature difference between $11{\mu}m\;and\;12{\mu}m\;(BTD1)$. The radiation at $11{\mu}m$ is absorbed more than at $12{\mu}m$ when yellow sand is loaded in the atmosphere, whereas it will be the other way around when cloud is present. The second method uses the brightness temperature difference between $3.7{\mu}m\;and\;11{\mu}m(BTD2)$. This technique is sensitive to dust loading, which the BTD2 is enhanced by reflection of $3.7{\mu}m$ solar radiation. First the Principle Component Analysis (PCA), a form of eigenvector statistical analysis from the two methods, is performed and the aerosol pixel with the lowest 10% of the eigenvalue is eliminated. Then the aerosol index (AI) from the combination of BTD 1 and 2 is derived. We applied this method to Multi-functional Transport Satellite-l Replacement (MTSAT-1R) data and obtained that the derived AI showed remarkably good agreements with Ozone Mapping Instrument (OMI) AI and Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth.

• Smart Structures and Systems
• /
• v.24 no.6
• /
• pp.783-791
• /
• 2019

Prefabricated reinforced-concrete shear walls are used extensively in building structures because they are convenient to construct and environmentally sustainable. To make large walls easier to transport, they are divided into smaller segments and then assembled at the construction site using a variety of connection methods. The present paper proposes a precast shear wall assembled using steel shear keys, wherein the shear keys are fixed on the embedded steel plates of adjacent wall segments by combined plug and fillet welding. The anchoring strength of shear keys is known to affect the mechanical properties of the wall segments. Loading tests were therefore performed to observe the behavior of precast shear wall specimens with different anchoring components for shear keys. The specimen with insufficient strength of anchoring components was found to have reduced stiffness and lateral resistance. Conversely, an extremely high anchoring strength led to a short-column effect at the base of the wall segments and low deformation ability. Finally, for practical engineering purposes, a design approach involving the safety coefficient of anchoring components for steel shear keys is suggested.

• Structural Engineering and Mechanics
• /
• v.71 no.2
• /
• pp.175-183
• /
• 2019

This paper deals with damage detection in a girder bridge using transmissibility functions as input data to Artificial Neural Networks (ANNs). The original contribution in this work is that these two novel methods are combined to detect damage in a bridge. The damage was simulated in a real bridge in Vietnam, i.e. Ca-Non Bridge. Finite Element Method (FEM) of this bridge was used to show the reliability of the proposed technique. The vibration responses at some points of the bridge under a moving truck are simulated and used to calculate the transmissibility functions. These functions are then used as input data to train the ANNs, in which the target is the location and the severity of the damage in the bridge. After training successfully, the network can be used to assess the damage. Although simulated responses data are used in this paper, the practical application of the technique to real bridge data is potentially high.

• Acta Via Serica
• /
• v.3 no.2
• /
• pp.23-48
• /
• 2018

The Silk Road usually implies a network of trade and communications that stretched from east to west and connected China and the countries of the Far East via Central Asia and the Middle East to the eastern Mediterranean, or through the northern coast of the Caspian Sea and the Volga basin to the Black Sea coast. However, at certain historical stages, a network of maritime and overland routes stretching from north to south, commonly called the Volga-Caspian trade route, also played a significant role in international trade and cultural contacts. The geopolitical realities of the early Middle Ages relating to the relationship of Byzantium, the Sassanid Empire, and the West Turkic Khaganate, the advance of the Arab Caliphate to the north, the spread of Islam in the Volga region, the glories and fall of the Khazar State, and the Scandinavian campaigns in the Caucasus, closely intertwined with the history of transport and communications connecting the north and south through the Volga-Caspian route. In a later era, the interests of the Mongolian Uluses, and then the political and economic aspirations of the Ottoman Empire, the Safavid State, and Russia, collided or combined on these routes. The article discusses trade contacts existing between the north and the south in the 15th and first half of the 17th century along the routes on the western coast of the Caspian Sea.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.28 no.4
• /
• pp.416-424
• /
• 2018

Objective: The objective of this study was to estimate the numbers of employees occupationally exposed to noise according to their industry and size. Methods: A Delphi panel consisting of 15 occupational health experts estimated the exposure prevalence of noise in workplace. Data on Industrial Accident Compensation Insurance provided from Occupational Safety and Health Research Institute were combined to produce the exposure population. Results: In Korea, 16.0% of employees, 2,539,890 out of 15,838,926, was estimated to exposed to noise occupationally. The rate was 32.7% and 10.3% in manufacturing sector and non-manufacturing sector, respectively. The highest rate, 52.5%, was found in manufacturing industries of wood and of products of wood and cork(except furniture) and of other transport equipment. Sorted by their size of business, the rate was higher as the number of employee was larger in manufacturing sector. Conclusions: Compared to the same rate estimated in the US, 17.2%, the result of this study seems to be in a resonable range.

• Journal of Multimedia Information System
• /
• v.6 no.1
• /
• pp.23-30
• /
• 2019

A communications profile is a system that acquires information from communication links to an ambulance or other vehicle moving on a road and compiles a database based on this information. The equipment (six sets of HDTVs, fish-eye camera, satellite antenna with tracking system, and receiving power from the satellite beacon of the N-star) mounted on the roof of the vehicle, image data were obtained at Yokohama Japan. From these data, the polygon of the building was actually produced and has arranged on the map of the Geographical Survey Institute of a 50 m-mesh. The optical study (relationship between visibility rate and elevation angle) were performed on actual data taken by fish-eye lens, and simulated data by 3D-Map with polygons. There was no big difference. This 3D map system then predicts the communication links that will be available at a given location. For line-of-sight communication, optical analysis allows approximation if the frequency is sufficiently high. For non-line-of-sight communication, previously obtained electric power data can be used as reference information for approximation in certain cases when combined with predicted values calculated based on a 3D map. 3D maps are more effective than 2D maps for landing emergency medical helicopters on public roadways in the event of a disaster. Using advanced imaging technologies, we have produced a semi-automatic creation of a high-precision 3D map at Yokohama Yamashita Park and vicinity and assessed its effectiveness on telecommunications and ambulatory merits.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.44 no.4
• /
• pp.145-153
• /
• 2021

Automated Guided Vehicle (AGV) is commonly used in manufacturing plant, warehouse, distribution center, and terminal. AGV is self-driven vehicle used to transport material between workstations in the shop floor without the help of an operator, and AGV includes a material transfer system located on the top and driving system at the bottom to move the vehicle as desired. For navigation, AGV mostly uses lane paths, signal paths or signal beacons. Various predominant sensors are also used in the AGV. However, in the conventional AGV, there is a problem of not turning or damaging nearby objects or AGV in a narrow space. In this paper, a new driving system is proposed to move the vehicle in a narrow space. In the proposed driving system, two sets of the combined steering-drive unit are adopted to solve the above problem. A prototype of AGV with the new driving system is developed for the comparative analysis with the conventional AGV. In addition, the experimental result shows the improved performance of the new driving system in the maximum speed, braking distance and positioning precision tests.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.13 no.1
• /
• pp.858-876
• /
• 2021

Although widely used, the design of the bulbous bow for ships has been difficult due to the complex interference between the wave system generated by the bulb and the wave system of the ship hull. Until now, a bulbous bow has been often designed using Kracht charts, which were established based on model test data, but these charts apply only to ships with a block coefficient C_B = 0.56-0.82, Froude number Fn = 0.20-0.40, and the obtained bulb sizes are only close to optimal. This paper presents a new method for the optimal design of bulbous bow, starting from the design of an initial bulb using Kracht charts for ships with any block coefficient or Froude number, then resizing this initial bulb to define the optimal bulb sizes based on a multi-objective function of the required power reduction, and a combined solution of Computation Fluid Dynamics (CFD) analysis and surrogate models. This study was applied to a fishing vessel FAO 75, which has been model tested and used to design steel fishing vessels in Vietnam recently. The obtained quantitative results showed the same trend as the theory and practice, with a reduction of the ship's required power by about 14%.