• Journal of Korean Society for Geospatial Information Science
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• v.5 no.1 s.9
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• pp.57-70
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• 1997

Conventional procedures to determine vertical deflections and astronomical coordinates require the stellar observations which be under restraints of clear night-time weather conditions, surrounding environment, long observation time and the use of instruments, etc. Therefore the more effective observation method subjugatting these problems has requested. The objective of this study is to propose method to compute vertical deflections, astronomical coordinates(latitude and longitude), and astronomical azimuth by mixing GPS observation results and orthometric heights. For this study, programmed the program which able to obtain the change in geoid undulation by using the GPS- determined geodetic height difference and the orthometric height difference, and GPS satellite surveying was performed at both ten points of astronomical points and four triangulation points around each astronomical station in South Korea. The Astronomical results determined from GPS observations compared to those determined from both conventional astronomical measurements and the recent earth gravitational Model(EGM96).

• Journal of the Korea Society for Simulation
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• v.29 no.2
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• pp.21-33
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• 2020

This study develops a simulator for determining the sonar sensor configuration of unmanned underwater vehicles (UUVs) based on a scenario, in order for UUVs to conduct an effective anti-submarine warfare (ASW). First, we analyze the missions and operational concepts of UUVs in the field of ASW, and then select a Hold-at-Risk scenario as the one with the highest priority. Next, for modeling the components of a simulator, the motion, acoustic characteristic, and environment condition of the platforms (UUV and target submarine) are specified. Especially, based on the beam pattern of each sonar configuration considered in this paper, the passive sonar equation is used to verify target detection, and we further estimate the azimuth and elevation of the target using amplitude and phase of the received signal, respectively. The simulation results show the performance tendency depending on the sonar sensor configurations of a UUV, and the simulator provides a high applicability under various scenarios.

• Journal of the Korea Convergence Society
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• v.8 no.7
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• pp.1-6
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• 2017

This paper presents the design of a frequency measurement device using ADC, EP2AGX FPGA and STM32 processor to accurately measure the frequency of a broadband high frequency signal. The ADC device used in this paper has a sampling frequency of 250 MSPS and a processing frequency bandwidth of 100 MHz. Due to its high sampling frequency, it is difficult to process in ordinary computers or processors, so we implemented the frequency measurement algorithm using the Altra EP2AGX FPGA. The measured frequency is sent to the direction detection controller in real time and fused with the phase signal to calculate the incident azimuth angle of the high frequency signal. The designed frequency measurement device is about 0.2 Mhz in frequency measurement error and 30% less than Anaren DFD-x, which is considered to contribute greatly to the design of radio monitoring and direction detection device.

• The Korean Journal of Ecology
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• v.18 no.1
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• pp.121-136
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• 1995

The forest vegetation on Mt. Ch’ongnyang was investigated for phytosociological analysis of the vegetation types and interspecific association. The forest was classified into seven vegetation units; A: Quercus Mongolica community, A-1: Group of Quercus variabilis, A-1-a: Subgroup of Pinus densiflora, A-1-b: Typical subgroup, A-2: Group of Aconitum trilobum, A-3: Group of Quercus dentata, B: Zelkova serrata communty. The group of Quercus variabilis was distributed on southeast- and southwest-facing slopes in 400~830 m above the sea level, and organic matter in the soil was 3.36~4.67％. The group of Aconitum trilobum was distributed on northeast- and northwest-facing slopes in 650~830 m above the sea level, and organic matter in the soil was 7.18％. The group of Quercus dentata was distributed on southwest-facing solpes in the vicinity of 810 m above the sea level, and organic matter in the soil was 9.7％. The Zelkova serrata community was distributed in the vicinity of ravines, and organic matter in the soil was 7.6％. The contents of Mg and Ca, and electric conductivity in the Zelkova serrata community were relatively high, 11.82 me/100mg, and 11.27 me/100mg, 102.2 μ mos/cm, respectively. In the results of polar ordination, environmental gradient of axis Ⅰ and axis Ⅱwere correlated with moisture, inclination and azimuth, respectively. Group of Quercus variabilis has occurred in xeric, group of Aconitum trilobum in submesic, and the Zelrova serrata community in mesic sites. In the meantime the interspecific association analysis based on chi-square yielded three species groupings with high positive affinity(p<0.01), i.e.group Ⅰ consisted of 18 species, including Acer pseudo-sieboldianum, Ansliaea acerifolia, Aconitum trilobum and group Ⅲ consisted of 19 species, in cluding Zelrova serrata, Oplismenus undulatifolius, Acer truncatum var. barbinerve, respectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.7
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• pp.1713-1720
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• 2014

RFID technology has evolved from basic operation like the acquisition of tag IDs into a more complicated operation such as the simultaneous acquisition of tag IDs and their positions and recently, is raising the possibility of obtaining additional informations, which include their velocities, directions and distances. In this paper, we present a RFID system that can fullfil aforementioned advanced functions. In the proposed system, a tag transmits a sequence of FMCW pulses modulated by ID signals and a reader separates the tag signals in azimuth direction using an array antenna, followed by the FMCW demodulation from which distances, velocities as well as the tag IDs are extracted. We propose a receiver structure of the reader and theoretically analyze its operability. Moreover, its performance is examined by simulation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.10
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• pp.1860-1866
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• 2016

Helicopter-related collision accidents with structures mostly occur at landing, especially in a limited visibility environment, which necessitates some secondary equipment like a radar that can generate stationary clutter image. In this paper, we propose an algorithm that makes an image of stationary ground clutter in two dimensional range and azimuth angle domain. We present a mathematical model for the received signals from each clutter patch in the iso range ring and analyze their clutter and Doppler characteristics, assuming that a helicopter-borne radar has a rotational antenna. We propose a filter structure, which suppresses side lobe signal components while extracting a main lobe signal component, and suggest a solution for a problem stemmed from the filtering process. Finally, by conducting a simulation we show the performance of the suggested imaging algorithm on a two dimensional virtual scenario of the topographic clutter.

• The Journal of the Acoustical Society of Korea
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• v.36 no.1
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• pp.49-56
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• 2017

This paper proposes a method to improve the left right discrimination performance by eliminating the imaginary target based on the frequency features of the beam pattern for bow array. The beamwidth of the imaginary target is wider than that of the real target. If an azimuth axis is considered as a time axis, the real and the imaginary targets can be assumed as high and low frequencies, respectively. To eliminate the imaginary target which has a low frequency component, we design a cut-off frequency of the High Pass Filter (HPF) using the back-lobe imaginary beamwidth. The real target is estimated by eliminating the imaginary target by applying HPF to the entire power of the beamformer output. Computer simulations show that the proposed method can increase the left right discrimination performance above 8 dB on average.

• Geomechanics and Engineering
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• v.7 no.4
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• pp.403-430
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• 2014

Shale gas formations exhibit strong mechanical and strength anisotropies. Thus, it is necessary to study the effect of anisotropy on the hydraulic fracture initiation pressure. The calculation model for the in-situ stress of the bedding formation is improved according to the effective stress theory. An analytical model of the stresses around wellbore in shale gas reservoirs, in consideration of stratum dip direction, dip angle, and in-situ stress azimuth, has been built. Besides, this work established a calculation model for the stress around the perforation holes. In combination with the tensile failure criterion, a prediction model for the hydraulic fracture initiation pressure in the shale gas reservoirs is put forward. The error between the prediction result and the measured value for the shale gas reservoir in the southern Sichuan Province is only 3.5%. Specifically, effects of factors including elasticity modulus, Poisson's ratio, in-situ stress ratio, tensile strength, perforation angle (the angle between perforation direction and the maximum principal stress) of anisotropic formations on hydraulic fracture initiation pressure have been investigated. The perforation angle has the largest effect on the fracture initiation pressure, followed by the in-situ stress ratio, ratio of tensile strength to pore pressure, and the anisotropy ratio of elasticity moduli as the last. The effect of the anisotropy ratio of the Poisson's ratio on the fracture initiation pressure can be ignored. This study provides a reference for the hydraulic fracturing design in shale gas wells.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.8
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• pp.799-804
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• 2011

The LFLP (Linear Fresnel Light Pipe) system uses a linear Fresnel lens to follow the sun and concentrates the parallel sunlight into a line. A LFLP daylighting system has been developed and updated to a DBLP (Double Blind Light Pipe) daylighting system to improve the overall system efficiency in the morning and afternoon. The new design consists of a double-blind style with a cone-shaped light transformer. The blinds are used to collect the sun's altitude and azimuth movements through the day. Behind the two sets of blinds is the light transformer, which is based on a parabolic-shaped light concentrator. The light transformer is designed to efficiently deliver light within a thirty-degree radial spread so that the light pipe can internally reflect the light. The results of scale-model tests are encouraging, and the efficiency is three times higher than that of the previous LFLP system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.6
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• pp.275-286
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• 2014

Light shelf is an efficient system that reduces the energy consumption by bringing the natural light down to the deep spaces inside of a building. However, the existing light shelves have limits in reducing energy usage, because the direction of the light flow is determined by the external environment such as the altitude of the sun and the azimuth. This current study presents a system that increases the efficiency of the light shelf by applying the Location-Awareness technology, in which the efficiency was verified through the performance evaluation. According to the examination of the technology for the Location-Awareness within residential space, 'Zigbee' type appears to be the most appropriate. The Location-Awareness technology operates the light shelf based on both the angle control axis and the light shelf angle control axis through the modularization of the reflector surface which is less affected by the external environment. The results of the performance evaluation showed that the movable light shelf that employs the Location-Awareness technology can reduce the energy consumption for lighting by 98.3% compared to the fixed light shelf and by 97.3% compared to the movable light shelf without Location-Awareness.