• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.439-445
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• 2006

Analysis problems of tunnels whose geometrical dimensions are very small compared with surrounding media can be treated as infinite region problems. In such cases, even if finite element models can be applied, excessive number of elements is required to obtain satisfactory accuracy. However, inaccurate results may be produced due to assumed artificial boundary conditions. To solve these problems, a hybrid model, which models the region of interest with finite elements and the surrounding infinite media with infinite elements, is introduced for the analysis of infinite region. Three-dimensional isoparametric infinite elements with various decay characteristics are formulated in this paper and the corresponding parameters are presented by means of parametric studies. Three-dimensional tunnel analysis performed on a representative example verifies the applicability of hybrid model using infinite elements.

• Journal of the Korean Society for Marine Environment & Energy
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• v.16 no.4
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• pp.263-267
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• 2013

In this research, a novel optical measuring methodology for the measurement of oil thickness in seawater is suggested by evaluating the light absorption which is occurred in the process of penetrating through oil layer on seawater. Laser having monochromatic wave is used as a light source and photodiode which can convert the intensity of the light into an electrical signal is applied to measure the intensity of the penetrating light through the oil-water mixtures. In the experiment, bunker C and lubricating oil are used, and three different lasers having different wavelengths are applied and compared for the selection of an optimal light source. As a result, it is observed that in the case of blue laser, the intensity of the light on the optical sensor decreases with an increase in the oil thickness. Through this relation, both the presence of oil and the thickness of oil can be determined.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.6
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• pp.758-765
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• 2016

In this study, wave damping due to a permeable bed of finite depth was modelled using a complementary mild-slope equation for stream function. The energy dissipating term in the mild-slope equation was presented in terms of stream function. In order to prevent re-reflection of reflected waves along the outer boundary, a delta-function-shaped source function was derived to generate a wave in a computational domain. Numerical experiments were conducted to measure the reflection coefficient of waves over a planar slope for various incident wave periods. The numerical result of the proposed model was compared with that of an integral equation method, showing good agreement in general. However, the proposed model showed relatively higher transmission rate for the larger permeability and the longer wavelength.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.2
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• pp.175-180
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• 2002

In this paper, the system performace with the convolution rode using a Viterbi decoding and the one tap LMS(Least Meam Square) equalizer applied to the OFDM(Orthogonal Frequency Division Multiplexing) system, is analyzed through computer simulation. DMRS(Digital Microwave Radio System)is modeled as Rummler fading channel. In Simulation result, we known that the coding system improved about 3.6dB~10.5dB when BER is 10 $^3$and b is 0.1~0.2 in case of 16QAM(Qurdrature Amplitude Modulation). Also, we known that was improved about 19.7dB when the b is 0.1 and was demanded about 10.5dB when the b is 0.2 in case of 64QAM. we known that the soft decision improved about 2~0.9dB when the b is 0.1~0.2 in case of 16QAM and about 3.3~7.8dB in case of 64QAM. In the equalizer system, efficiency improved from the case of that Eb/No is more than 13dB.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.4
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• pp.232-238
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• 2012

In this study, the noise mapping simulation is executed to design an effective barrier reducing noise levels of a school site. The geographical features of the ambient site and the school buildings are modelled in detail in order to consider sound propagation, deflection, and absorption phenomena etc. The main sound source, sound power level of expressway, is estimated on the basis of measured noise levels at several points of the site. The noise mapping simulation is performed by using ENPro, environmental noise prediction program based on ISO 9613 to analysis the effectiveness of noise barrier. Consequently, the noise barrier is designed to meet an environmental noise standard and satisfy low cost and safety conditions.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.688-696
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• 2023

In the present study, free roll decay and resistance performances of fishing vessels were evaluated with the combinations and variations of in the parameters of appendages which are attached to improve motion performance of fishing vessels. Computational Ffluid Ddynamics was used to perform free roll decay and resistance analysis. The roll period and decay coefficient were derived by the variations in the combination and dimensions of the primary appendages of the bilge keel and the under keel. It was observed thatThe variations of in the length of the under keel did not significantly impact to the roll damping coefficient. Conversely, for the bilge keel, an increase in the length and angle resulted in an increase in the roll damping coefficient. Comparison of resistance performance was additionally assessed among the selected hulls with the appendages and bare hull. The resistance of the hull with the appendages was higher than that of the bare hull due owing to the changes of in the pressure on the surface of the hull and trim angle. Throughout the present study, the impact of appendage parameter and arrangement on the free roll decay and resistance performance of fishing vessels were was assessed,. which This will be beneficial for the application of appendages to fishing vessels.

• Proceedings of KOSOMES biannual meeting
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• 2017.04a
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• pp.250-250
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• 2017

• Journal of Korean Society of Water and Wastewater
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• v.26 no.6
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• pp.861-869
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• 2012

The chlorine's residual concentration prevents the regrowth of microorganism in water transport along the pipeline system. Precise prediction of chlorine concentration is important in determining disinfectant injection for the water distribution system. In this study, a pilot scale water distribution system was designed and fabricated to measure the temporal variation of chlorine concentration for three flow conditions (V = 0.88, 1.33, 1.95 m/s). Various kinetic models were applied to identify the relationship between hydraulic condition and chlorine decay. Genetic Algorithm (GA) was integrated into five kinetic models and time series of chlorine were used to calibrate parameters. Model fitness was compared by Root Mean Square Error (RMSE) between measurement and prediction. Limited first order model and Parallel first order showed good fitness for prediction of chlorine concentration.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2006.11a
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• pp.99-101
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• 2006

군산의 C-Band 레이더로 호남지방의 에코관측에는 무리가 있으며, 그이유는 C-Band의 특성상 관측범위가 짧은 것도 있겠지만, 강수에코에 의한 감쇠가 심하기 때문인 것으로 판단된다. 호남지방에서 진도의 S-Band 레이더는 AWS값과 상당부분 일치함을 보였으며, 그 탐지거리 역시 C-Band인 군산레이더보다 길고 감쇠 역시 적었다. 그러나 무안 부근의 경우에서는 진도의 S-band 레이더가 감지하지 못하는 에코영상을 무안레이더가 감지하는 경우도 있었다. 무안의 X-Band 레이더는 진도의 S-Band레이더의 값과 대부분 유사한 결과 값을 보였으나, 근거리에 에코관측 시 진도레이더가 관측하지 못했거나 감지했더라도 그 강도에 있어서 조금 더 정확한 값을 보였다. 각 레이더의 관측특성을 고려하여 악기상과 돌발적인 기상현상을 관측한다면 단시간예보에의 활용과 보다 정확하게 예측하고 예보하는데 크게 기여하리라 판단된다.

• The Journal of the Acoustical Society of Korea
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• v.17 no.3
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• pp.78-89
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• 1998

도심에서 발생하는 건설소음은 건설현장 주변의 주민들에게 불쾌감을 유발하고 있 으며 점차 주거환경을 위협하는 환경 오염원으로 등장하고 있다. 이러한 건설소음은 일반적 으로 건설기계소음과 건설공사소음으로 분류될 수 있는데, 전자의 경우 최근에 정부차원에 서 그 심각성을 인정하여 정책적으로 기초적인 연구가 수행되고 있지만 후자의 경우에는 기 초적인 자료 및 연구가 거의 전무한 상태이다. 따라서 국내에서는 이러한 건설소음을 저감 시키기 위한 실질적인 방법들이 강력히 요구되고 있으나, 기존의 연구부족과 자료의 결핍 등으로 인해 많은 어려움을 겪고 있는 실정이다. 이러한 관점에서 본 연구에서는 건설현장 에서 발생하는 건설공사소음의 전달 및 감쇠특성을 파악하고자 하였으며 향후 건설소음의 기준 설정시 기초적인 자료를 제시하고자 한다.