• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.3
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• pp.319-332
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• 2015

The pressure wave formed by the piston effects of the train proceeds within the tunnel when a train enters the tunnel with a high speed. Depending on the condition of tunnel exit, the compression waves reflect at a open end, change to the expansion waves, transfer to tunnel entrance back. Due to interference in the pressure waves and running train, passengers experience severe pressure fluctuations. And these pressure waves result in energy loss, noise, vibration, as well as in the passengers' ears. In this study, we performed comparison between numerical analysis and field experiments about the characteristics of the pressure waves transport in tunnel that appears when the train enter a tunnel and the variation of pressure penetrating into the train staterooms according to blockage ratio of train. In addition, a comparative study was carried out with the ThermoTun program to examine the applicability of the compressible 1-D model(based on the Method of Characteristics). Furthermore examination for the adequacy of the governing equations analysis based on compressible 1-D numerical model by Baron was examined.

• The Transactions of the Korea Information Processing Society
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• v.7 no.10
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• pp.3210-3218
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• 2000

In a IS-95 cellular systm, blocking will occur when the reverse link user interference power reaches a predepermmed level which is set to maintam acceptable signal quality. In this paper, it is assumed that a mobile rdio channel is a shadowing channel and Erlang capacity is calculated for the reverse limk of an imperfect power controlled IS-95 cellular system. the blocking probability is derived using lognornal pproximation and the results according to guassian and lognormal approximation method are compared and analyzed respcctively. Assuming that blocking probability is 1% at the data rate of $R_b$=9.6kbps and $R_b$=14.4kbps, it is shown that Erlang capacity using Iognormal approximation is 13.68 Erlang and 7.08 Erlang and then the approximation erroris occurred about 24.4% and 40.4% inthe garssian approximation, respectively. It is also observed that if the power control becomes periect, the Erlang capacity is increased more 6.99 and 4.21 Erlang than that of the imperfect power control that the power contrl error is 2.5dB, and if voice activity is considered as 10%, the Erlang capacity is increased more 8.21 and 1.25 Erlang than that using non voice activity, respectively.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.32 no.1
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• pp.63-73
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• 2014

Recently, researches on DBRN(DataBase Referenced Navigation) system are being carried out to replace GNSS(Global Navigation Satellite System), as weaknesses of GNSS were found that are caused by the intentional interference and the jamming of the satellite signal. This paper describes the gravity gradient modeling and the construction of EKF(Extended Kalman Filter) based GGRN(Gravity Gradient Referenced Navigation). To analyze the performance of GGRN, fourteen flight trajectories were made for simulations over whole South Korea. During the simulations, we considered the errors in both DB(DataBase) and sensor as well as the flight altitudes. Accurate performances were found, when errors in the DB and the sensor are small and they located at lower altitude. For comparative evaluation, the traditional TRN(Terrain Referenced Navigation) was also developed and performances were analyzed relative to those from the GGRN. In fact, most of GGRN performed better in low altitude, but both of precise gravity gradient DB and gradiometer were required to obtain similar level of precisions at the high altitude. In the future, additional tests and evaluations on the GGRN need to be performed to investigate on more factors such as DB resolution, flight speed, and the update rate.

• Journal of the Korean Institute of Gas
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• v.25 no.1
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• pp.20-29
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• 2021

During multi-stage fracturing in a low permeable shale formation, stress interference occurs between the stages which is called the "stress shadow effect(SSE)". The effect may alter the fracture propagation direction and induce ununiform geometry. In this study, the stress shadow effect on the hydraulic fracture geometry and the well productivity were investigated by the commercial full-3D fracture model, GOHFER. In a homogeneous reservoir model, a multi-stage fracturing process was performed with or without the SSE. In addition, the fracturing was performed on two shale reservoirs with different geomechanical properties(Young's modulus and Poisson's ratio) to analyze the stress shadow effect. In the simulation results, the stress change caused by the fracture created in the previous stage switched the maximum/minimum horizontal stress and the lower productivity L-direction fracture was more dominating over the T-direction fracture. Since the Marcellus shale is more brittle than more dominating over the T-direction fracture. Since the Marcellus shale is more brittle than the relatively ductile Eagle Ford shale, the fracture width in the former was developed thicker, resulting in the larger fracture volume. And the Marcellus shale's Young's modulus is low, the stress effect is less significant than the Eagle Ford shale in the stage 2. The stress shadow effect strongly depends on not only the spacing between fractures but also the geomechanical properties. Therefore, the stress shadow effect needs to be taken into account for more accurate analysis of the fracture geometry and for more reliable prediction of the well productivity.

• Journal of Astronomy and Space Sciences
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• v.22 no.3
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• pp.283-292
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• 2005

Ionosphere is deeply coupled to the space environment and introduces the perturbations to radio signal because of its electromagnetic characteristics. Therefore, the status of ionosphere can be estimated by analyzing the GPS signal errors which are penetrating the ionosphere and it can be the key to understand the global circulation and change in the upper atmosphere, and the characteristics of space weather. We used 9 GPS Continuously Operating Reference Stations (CORS), which have been operated by Korea Astronomy and Space Science Institute (KASI) , to determine the high precision of Total Electron Content (TEC) and the pseudorange data which is phase-leveled by a linear combination with carrier phase to reduce the inherent noise. We developed the method to model a regional ionosphere with grid form and its results over South Korea with $0.25^{\circ}\;by\;0.25^{\circ}$ spatial resolution. To improve the precision of ionosphere's TEC value, we applied IDW (Inverse Distance Weight) and Kalman Filtering method. The regional ionospheric model developed by this research was compared with GIMs (Global Ionosphere Maps) preduced by Ionosphere Working Group for 8 days and the results show $3\~4$ TECU difference in RMS values.

• Tunnel and Underground Space
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• v.22 no.1
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• pp.69-76
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• 2012

Theoretical backgrounds on the experimental methods of explosive welding, explosive forming and shock consolidation of powders are introduced. Explosive welding experiments of titanium (Ti) and stainless steel (SUS 304) plate were carried out. It was revealed that a series of waves of metal jet are generated in the contact surface between both materials; and that the optimal collision velocity and collision angle is about 2,100~2,800 m/s and $15{\sim}20^{\circ}$, respectively. Also, explosive forming experiments of Al plate were performed and compared to a conventional press forming method. The results confirmed that the shock-loaded Al plate has a larger curvature deformation than those made using conventional press forming. For shock consolidation of powders, the propagation behaviors of a detonation wave and underwater shock wave generated by explosion of an explosive are investigated by means of numerical calculation. The results revealed that the generation and convergence of reflected waves occur at the wall and center position of water column, and also the peak pressure of the converged reflected waves was 20 GPa which exceeds the detonation pressure. As results from the consolidation experiments of metal/ceramic powders ($Fe_{11.2}La_2O_3Co_{0.7}Si_{1.1}$), shock-consolidated $Fe_{11.2}La_2O_3Co_{0.7}Si_{1.1}$ bulk without cracks was successfully obtained by adapting the suggested water container and strong bonding between powder particles was confirmed through microscopic observations.

• Journal of Korea Society of Industrial Information Systems
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• v.19 no.1
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• pp.13-18
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• 2014

Sensor nodes are used for monitoring and collecting the environmental data via wireless sensor network. The wireless sensor network with various sensor nodes draws attention as a key technology in ubiquitous computing. Sensor nodes has very small memory capacity and limited power resource. Thus, it is essential to have energy efficient strategy for the sensor nodes. Since the sensor nodes are operating on the same frequency bands with ISM frequency bands, the interference by the devices operating on the ISM band degrades the quality of communication integrity. In this paper, the convolutional code is proposed instead of ARQ for the error control for the sensor network. The proposed convolutional code was implemented and the BER performance is measured. For the fixed transmitting powers of -19.2 dBm and -25dBm, the BER with various communication distances are measured. The packet loss rate and the retransmission rate are calculated from the measured BER. It is shown that the porposed method obtained about 9~12% and 12-19% reduction in retransmission rate for -19.2 dBm and -25 dBm respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.7
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• pp.39-47
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• 2012

The combination of the broadband property and the wide area coverage of satellite communications enables high speed transmission. Every user in the region under the satellite beam coverage can tranceiver and one can simultaneously communicate with multiple users. For these reasons, it is one of commendable telecommunication networks for information transfer. Since the satellite communications use open channels, it is likely to cause jamming with unwanted interference signals. In the thesis, APSK (Amplitude Phase Shift Keying) is employed, which is recommended for DVB-S2 due to high-speed transmission and excellent bandwidth efficiency. For obtaining reliable communication under the jamming environments, the communication satellite transponder rests on the polyphase filter bank structure, which enables switching among the subchannels and gain control on each subchannel, resulting in effectively eliminating jamming. Furthermore, the nulling scheme, one of the various anti-jamming approaches, is investigated, in which unwanted jamming signals are eliminated in the frequency domain after passing through the analysis part of the polyphase filter bank. The performance of the nulling scheme is evaluated for tone jamming and partial band jamming in terms of BER and EVM. The simulation results indicate that the nulling scheme improve the BER and EVM performance over the case without any anti-jamming approach.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.40 no.2
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• pp.44-58
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• 2022

Bunhwangsa Temple, Baekryulsa Temple and Sambulsa Temple are not famous cultural heritage area, but they are visited by many tourists and are located in Gyeongju National Park and Gyeongju Historic Areas, so environmental and cultural preservations are required. The purpose of this study is to manage the unique environment and landscape of cultural assets by analysing the invasive alien plant of traditional temple of Gyeongju. The whole flora were summarized as 188 taxa including 73 families, 136 genera, 154 species, 3 subspecies, 11 varieties, 4 forms, 5 hybrids and 12 cultivars., and the landscape plants were 163 taxa and 38 taxa of the invasive alien plants. The 13 taxa of invasive alien plants were planted in three temples. The ecosystem disturbance species were 3 taxa including Rumex acetosella, Lactuca seriola and Symphyotrichum pilosum. Invasive alien plants have artificial causes such as landscape planting, but there are also those that are introduced naturally from outside. The parking lot of the temple is expected to be a major propagation path for invasive alien plants due to the large amount of interference and disturbance. Based on the results of this study, the management plans are suggested as follows. First, it is necessary to use native species suitable for the natural environment and traditional landscape of Korea for landscape planting of traditional temples, and development of planting guidelines centered on cultural properties is required. Second, it is necessary to refrain from planting invasive alien plants because traditional temples are located in an important environment and historically. Third, for the preservation of the temple environment, it is necessary to promptly remove the ecosystem disturbance species. Fourth, in order to express the landscape characteristics of traditional temples, a unique planting plan should be established in consideration of the location environment and historicity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.8
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• pp.2052-2063
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• 1998

Various full-scale radio location systems have been developed since ground-based radio navigation systems appeared during World War II, and more recently global positioning systems (GPS) have been widely used as a representative location system. In addition, radio location systems based on cellular systems are intensively being studied as cellular services become more and more popular. However, these studies have been focused mainly on macrocellular systems of which based stations are mutually synchronized. There has been no study about systems of which based stations are asynchronous. In this paper, we proposed two radio location algorithms in microcellular CDMA systems of which base stations are asychronous. The one is to estimate the position of a personal station at the center of rectangular shaped area which approximates the realistic common area. The other, as a method based on road map, is to first find candidate positions, the centers of roads pseudo-range-distant from the base station which the personal station belongs to and then is to estimate the position by monitoring the pilot signal strengths of neighboring base stations. We compare these two algorithms with three wide-spread algorithms through computer simulations and investigate interference effect on measuring pseudo ranges. The proposed algorithms require no recursive calculations and yield smaller position error than the existing algorithms because of less affection of non-line-of-signt propagation in microcellular environments.