• Tunnel and Underground Space
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• v.19 no.2
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• pp.158-166
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• 2009

As a basic study for investigating the development of the stress-induced crack in Hoek-Brown rock, a homogenization technique of elastic cracks is proposed. The onset of crack is monitored by Hoek-Brown empirical criterion, while the orientation of the crack is determined by the critical plane approach. The concept of volume averaging in stress and strain component was invoked to homogenize the representative rock volume which consists of intact rock and cracks. The formulation results in the constitutive relations for the homogenized equivalent anisotropic material. The homogenization model was implemented in the standard FEM code COSMOSM. The numerical uniaxial tests were performed under plane strain condition to check the validity of the propose numerical model. The effect of friction between the loading plate and the rock sample on the mode of deformation and fracturing was examined by assuming two different contact conditions. The numerical simulation revealed that the homogenized model is able to capture the salient features of deformation and fracturing which are observed commonly in the uniaxial compression test.

• Fire Science and Engineering
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• v.15 no.2
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• pp.59-79
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• 2001

The paper proposes alternatives for fire safety in architectural planning through heat-smoke distribution related to openings so that we decrease casualty and property loss by fire and lay a great emphasis on building high-rise apartments with consideration of fire safety in Korea. An analysis program(HFA-Heat Fluid Analysis) is built to perform simultaneously numerical analysis and experimental analysis on rooms, units and buildings. In consequence, on the first, fire prevention methods are required to be set up related to openings for design rooms since the flow of heat and smoke is influenced by the type of openings in high-rise apartments. Second, the numerical analysis showed that different planning types cause to show differences in the spreading time of heat and smoke to design the units of high-rise apartments. On the third, each unit building showed different fire behavior depending on openings by numerical analysis and small scaled experiment on heat and smoke flow.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.2
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• pp.154-165
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• 2006

In the present study, a numerical model using Boussinesq equation is set up to predict the interacted equilibrium between waves and their induced currents in the occurrence of breaking waves over an underwater shoal, and the numerical results are compared with results of existing hydraulic experiments. A sensitivity analysis has been done to find out appropriate values of breaking wave parameters with the result (regular wave case) of Vincent and Briggs (1989)’ experiment. Then the numerical model is applied to the irregular wave cases of the experiment and the hydraulic model test of Ieodo which is a natural undersea shoal. The results show that a strong current forms in the wave direction at the downstream side of the shoals, causing the attenuation of wave heights there. The calculated wave heights generally show a similar pattern with the measured data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.3
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• pp.204-212
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• 2015

The infrared lock-on range of target aircraft plays a critical role in determining the aircraft survivability. In this investigation, the effects of various UAV engine nozzle configurations on the aircraft lock-on range were theoretically analyzed. A virtual subsonic aircraft was proposed first, based on the mission requirement and the engine performance analysis, and convergent-type nozzles were then designed. After determining thermal flow field and nozzle surface temperature distribution with the CFD code, an additional analysis was conducted to predict the IR signature. Also, atmospheric transmissivity for various latitude and seasons was calculated, using the LOWTRAN code. Finally, the lock-on and lethal envelopes were calculated for different nozzle configurations, assuming the sensor threshold of the given IR guided missile. It was shown that the maximum 55.3% reduction in lock-on range is possible for deformed nozzles with the high aspect ratio.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1677-1688
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• 1998

In this paper, we analyze the performance of a DS-CDMA system employing adaptive adaptive array antenna technology at base-station. For the analysis the receiving architecture of a multiple team adaptive base-station array antenna is proposed as a major system omponent, and signal to interference and noise ratio(SINR) on the proposed architecture is developed. We show that the perfomance enhancement of the CDMA system is represented as great reduction of interfreence by employing an array antenna capable of resolving the angular distribution of the mobile users as seen at the ase-station. The energy associated with each mobile or a group of mobiles is thus confined within the addressed volume, greatly reducing the amount of co-channel interference experienced from and by neighboring co-channel cells. In order to ascertain the benefits of such an antenna, a theoretical approach, which eis based on the conventional and proposed antenna systems in a typical mobile radio environment, is adopted. Finally computer simulation results show the insight into how the adaptive array antenna operates when used in conjunction with DS-CDMA and illustrate the potential benefits in the SINR point of view.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.4
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• pp.313-322
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• 2003

In this paper, the reverse link performance of imperfect power controlled cdma2000 cellular system that using array at a base station is analyzed, when MCGM beamforming algorithm and power control error is considered in shadowing. The blocking probability of the cdma2000 cellular system based on array parameters, E$\_$b//N$\_$0/ and interference statistics is calculated, and then the system capacity is calculated at a specific blocking probability. When the blocking probability is set 1 %, PCE(power control error) is 2 dB, M=2, 4, 8, 10, the capacity of cdma2000 is increased 2.3 ∼ 2.5 times higher than IS-95.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.3 s.106
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• pp.287-294
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• 2006

In the paper, characterization and analysis of UWB(Ultra Wide Band) antennas in time domain are described. The impulse propagation channel including UWB antennas is proposed for the analysis in time domain. Using the proposed propagation channel, the technique of obtaining impulse response of UWB antenna is proposed. Also, ringing, peak value of the impulse response, and the width of the impulse response are introduced as parameters for characterizing a UWB antenna in time domain. A modified UWB conical monopole antenna, a UWB TEM horn antenna, and a UWB stepped fat monopole antenna were fabricated. From the measurement of reflection coefficients, three antennas had bandwidth more than 3 GHz. The impulse responses of the antennas were measured in an anechoic chamber. The results showed that the TEM horn with highest gain has the highest peak amplitude and the stepped fat monopole antenna with narrowest bandwidth for reflection coeffcient had the widest width of the impulse response. Also, ringing in the stepped fat monopole antennas and the UWB conical monopole antenna were observed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7B
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• pp.583-591
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• 2008

This paper proposes a resource allocation algorithm for minimizing the overall distortion of multiple users in orthogonal frequency division multiplex (OFDM). The proposed algorithm exploits the diversity of multiuser and the rate-distortion function using packet distortion model in a system with limited resources. We first induce a rate-distortion function considering error concealment and error propagation properties of H.264 video structures. Then we perform adaptive resource allocation utilizing multiuser diversity for minimizing the overall video quality degradation. We also consider the proportional rate which is pre-determined for each user. Simulation results show that compared to the previous time division multiple access method and the resource allocation method maximizing data rate, the proposed rate allocation algorithm substantially improves the received video quality.

• Journal of the Korean Applied Science and Technology
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• v.33 no.1
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• pp.136-142
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• 2016

The influences of fluorescence, scattering, and flocculation in random media were interpreted for the scattered fluorescence intensity and wavelength, it has been studied the molecular properties by the spectroscopy of laser induced fluorescence(LIF). The effects of optical properties in scattering media have been found by the optical parameters(${\mu}_s$, ${\mu}_a$, ${\mu}_t$). Flocculation is an important step in many solid-liquid separation processes and is widely used in Photodynamic therapy. The interactions of several colloid particles can come into play which have major effect on the flocculation and LIF process. We measured scattering and fluorescence spectra of the sample in vitro as function of distance from lase source to detector. The value of scattering coefficient ${\mu}_s$ is and ${\beta}$-carotene were measured as larger values(I, ${\delta}$) by means of closer distance from source to detector.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.2
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• pp.119-126
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• 2008

In this paper, the loop coupling model for the analysis of end launcher rectangular waveguide adapter are proposed. The formula of input impedance from this model are presented. The influence of propagation mode and higher modes in rectangular waveguide are analyzed and design parameters of the end launcher adapter are investigated. The computational results between the proposed theoretical analysis and the previous papers are compared and are verified by HFSS. The end launcher rectangular waveguide adapter consists of the coupling geometry which is connected the inner conductor of $50{\Omega}$ coaxial line through into the 17.6mm feeding loop in a WR90 commercial waveguide, and the VSWR is maximum 2.0 over operating frequency from 7.5GHz to 10.6GHz.