• Title/Summary/Keyword: high waves

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A Study on Spatial Smoothing Technique for Angle of Arrival Estimation of Coherent Incoming Waves (코히어런트 입사파의 도래방향 추정을 위한 공간평균법의 개선에 관한 연구)

  • Jeong Jung-Sik
    • Journal of Navigation and Port Research
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    • v.29 no.5 s.101
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    • pp.403-408
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    • 2005
  • The techniques of estimating angle of arrival(AOA) have played a key role for enhancement of wireless communications using array antennas. Among those techniques, the superresolution algorithms, such as MUSIC and ESPRIT, calculate the covariance matrix of the array output vectors which are observed at the array antennas, and then by using eigen-decomposition of the covariance matrix, they estimate AOAs of the received signals with high accuracy. However, superresolution algorithms based eigenvalue decomposition fails to estimate AOAs under multipath environments. Under multipath environments, it is difficult to estimate AOAs of the received signals due to coherency and high-correlation. To resolve coherent signals, the covariance matrix is calculated by using the conventional spatial smoothing technique, and then the techniques based on eigen-descomposition is applied. The result of the conventional spatial smoothing technique, however, is obtained at the cost of losing effective spatial aperture. Moreover, the conventional technique ignores any information in the cross-correlations of the array outputs the subarrays. As the result, the performance for AOA estimation is degraded. In this paper, we propose a new spatial smoothing technique, which consider the cross-correlation for subarrays. By computer simulation, the AOA estimation performance of the proposed method is compared with the conventional method and evaluated.

Generation of Chemically Active Species in Hybrid Gas-Liquid Discharges (기체-액체 혼합 방전에 의한 화학적 활성종 생성 특성)

  • Chung, Jae-Woo;Locke, Bruce R.
    • Journal of Korean Society of Environmental Engineers
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    • v.29 no.5
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    • pp.556-563
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    • 2007
  • We carried out a laboratory scale experiment about the characteristics of chemically active species produced in hybrid gas-liquid discharges. The electrode configuration which had high voltage electrode in the gas phase and ground electrode in the liquid was utilized while high voltage electrode has been typically positioned in the liquid in other studies. Our electrode was configured in such a way as to increase the energy efficiency of chemical reactions by creating a higher electrical field strength and a narrower pulse width than the typical electrode configuration. The highest ozone concentration was obtained at 45 kV which was the medium value in operating voltages. The decrease of solution conductivity increased the resistance of liquid phase and the electric field strength through the gas phase, so ozone gene-ration rate was enhanced. The increase of voltage promoted the production rate of hydrogen peroxide by increasing the electric field strength. In a lower voltage, the increase of solution conductivity increased the degradation rate of $H_2O_2$, so the $H_2O_2$ generation rate decreased. On the other hand, the effects of UV radiation, shock waves etc. increased the $H_2O_2$ generation rate as the solution conductivity increased. A higher rate of $H_2O_2$ generation can be achieved by mixing argon to oxygen which generates a stronger and more stable discharges.

Half and Full-Bridge Cell based Stand-Alone Photovoltaic Multi-Level Inverter (하프ㆍ풀-브리지 셀을 이용한 독립형 태양광 멀티레벨 인버터)

  • Kang Feel-Soon;Oh Seok-Kyu;Park Sung-Jun;Kim Jang-Mok;Kim Cheul-U
    • The Transactions of the Korean Institute of Power Electronics
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    • v.9 no.5
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    • pp.438-447
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    • 2004
  • A new multilevel PWM inverter using a half-bridge and full-bridge cells is proposed for the use of stand-alone photovoltaic inverters. The configuration of the proposed multilevel PWM inverter is based on a prior 11-level shaped PWM inverter. Among three full-bridge cells employed in the prior inverter, one cell is substituted by a half-bridge cell. Owing to this simple alteration, the proposed inverter has three promising merits. First it increases the number of output voltage levels resulted in high quality output voltages. Second, it reduces two power switching devices by means of employing a half-bridge cell. Third, it reduces power imposed on a transformer connected with the half-bridge unit. That is to say, most power is transferred to loads via cascaded transformers connected with low switching inverters, which are used to synthesize the fundamental output voltage levels whereas the output of a transformer linked to a high switching inverter is used to improve the final output voltage waves; thus, it is desirable in the point of the improvement of the system efficiency. By comparing to the prior 11-level PWM inverter, it assesses the performance of the proposed inverter as a stand-alone photovoltaic inverter. The validity of the proposed inverter is verified by computer-aided simulations and experimental results.

A Full Scale Hydrodynamic Simulation of High Explosion Performance for Pyrotechnic Device (파이로테크닉 장치의 고폭 폭발성능 정밀 하이드로다이나믹 해석)

  • Kim, Bohoon;Yoh, Jai-ick
    • Journal of the Korea Society for Simulation
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    • v.28 no.2
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    • pp.1-14
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    • 2019
  • A full scale hydrodynamic simulation that requires an accurate reproduction of shock-induced detonation was conducted for design of an energetic component system. A detailed hydrodynamic analysis SW was developed to validate the reactive flow model for predicting the shock propagation in a train configuration and to quantify the shock sensitivity of the energetic materials. The pyrotechnic device is composed of four main components, namely a donor unit (HNS+HMX), a bulkhead (STS), an acceptor explosive (RDX), and a propellant (BPN) for gas generation. The pressurized gases generated from the burning propellant were purged into a 10 cc release chamber for study of the inherent oscillatory flow induced by the interferences between shock and rarefaction waves. The pressure fluctuations measured from experiment and calculation were investigated to further validate the peculiar peak at specific characteristic frequency (${\omega}_c=8.3kHz$). In this paper, a step-by-step numerical description of detonation of high explosive components, deflagration of propellant component, and deformation of metal component is given in order to facilitate the proper implementation of the outlined formulation into a shock physics code for a full scale hydrodynamic simulation of the energetic component system.

The Longitudinal Patterns of Marital Satisfaction since Unemployment - Difference in Self-esteem by Patterns - (실업 이후 부부관계만족도의 종단적 변화유형에 관한 연구: 유형에 따른 자아존중감의 차이를 중심으로)

  • Nam, Seok In;Kim, Junpyo;Lee, Su Jin;Yun, Heejung
    • Korean Journal of Family Social Work
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    • no.58
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    • pp.97-122
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    • 2017
  • The purpose of this study was to identify the longitudinal patterns of marital satisfaction, characteristics of each pattern, influencing factors and the difference on self-esteem, among married couples who experienced unemployment. To achieve this, the 443 married couples, who were initially employed in the first year but unemployed in next 5 years were extracted from the $2^{nd}$ to $11^{st}$ waves of Korean Welfare Panel Study(KoWePS) data. The results showed that there are five patterns on marital satisfactions of couple who experienced unemployment: maintaining low-level, mid-level, continuous declining, rebound after sharp declining, and maintaining high-level. In addition to this, the groups that maintain the marital satisfaction showed higher self-esteem than the groups that showed positive or negative change in marital relationship. Based on these results, this study suggested political and practical intervention to maintain the satisfaction of marital relationship and their self-esteem in a high level.

An Assessment of Applicability of Heat Waves Using Extreme Forecast Index in KMA Climate Prediction System (GloSea5) (기상청 현업 기후예측시스템(GloSea5)에서의 극한예측지수를 이용한 여름철 폭염 예측 성능 평가)

  • Heo, Sol-Ip;Hyun, Yu-Kyung;Ryu, Young;Kang, Hyun-Suk;Lim, Yoon-Jin;Kim, Yoonjae
    • Atmosphere
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    • v.29 no.3
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    • pp.257-267
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    • 2019
  • This study is to assess the applicability of the Extreme Forecast Index (EFI) algorithm of the ECMWF seasonal forecast system to the Global Seasonal Forecasting System version 5 (GloSea5), operational seasonal forecast system of the Korea Meteorological Administration (KMA). The EFI is based on the difference between Cumulative Distribution Function (CDF) curves of the model's climate data and the current ensemble forecast distribution, which is essential to diagnose the predictability in the extreme cases. To investigate its applicability, the experiment was conducted during the heat-wave cases (the year of 1994 and 2003) and compared GloSea5 hindcast data based EFI with anomaly data of ERA-Interim. The data also used to determine quantitative estimates of Probability Of Detection (POD), False Alarm Ratio (FAR), and spatial pattern correlation. The results showed that the area of ERA-Interim indicating above 4-degree temperature corresponded to the area of EFI 0.8 and above. POD showed high ratio (0.7 and 0.9, respectively), when ERA-Interim anomaly data were the highest (on Jul. 11, 1994 (> $5^{\circ}C$) and Aug. 8, 2003 (> $7^{\circ}C$), respectively). The spatial pattern showed a high correlation in the range of 0.5~0.9. However, the correlation decreased as the lead time increased. Furthermore, the case of Korea heat wave in 2018 was conducted using GloSea5 forecast data to validate EFI showed successful prediction for two to three weeks lead time. As a result, the EFI forecasts can be used to predict the probability that an extreme weather event of interest might occur. Overall, we expected these results to be available for extreme weather forecasting.

Spatial assessment of heat wave and river water quality (폭염과 하천 수질의 공간적 평가)

  • Lee, Jiwan;Kim, Sehoon;Han, Daeyoung;Shin, Hyungjin;Lim, Hyeokjin;Kim, Seongjoon
    • Journal of Korea Water Resources Association
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    • v.54 no.9
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    • pp.693-704
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    • 2021
  • The purpose of this study is to evaluate the relationship between heat wave and river water quality. The daily maximum air temperature (Tmax) of 91 meteorological stations of the Korea Meteorological Administration and 13 river water quality factors (DO, BOD, COD, TOC, TN, DTN, NH4-N, NO2-N, NO3-N, TP, DTP, PO4-P, Chl-a) of Ministry of Environment were analyzed. The correlation analysis was performed on Tmax and water quality factors, and the determination coefficients (R2) of DO, Chl-a, and TN with Tmax showed high values of 0.782, 0.609, and 0.691 respectively. To analyze the spatial impact between heat waves and water quality factors, the heat wave intensity (HWI) and heat wave duration (HWD) were calculated using the Tmax. The hotspot and spatial statistical analyses were applied for spatial impact evaluation. As a result of hotspot analysis, the heat wave index (HWD, HWI) showed high spatial pattern in the downstream of Nakdong River basin, and Chl-a and TN showed the same pattern. In case of spatial statistical analysis for water quality due to heat wave, the most obvious spatial variability was DO.

Target Length Estimation of Target by Scattering Center Number Estimation Methods (산란점 수 추정방법에 따른 표적의 길이 추정)

  • Lee, Jae-In;Yoo, Jong-Won;Kim, Nammoon;Jung, Kwangyong;Seo, Dong-Wook
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.38 no.6
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    • pp.543-551
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    • 2020
  • In this paper, we introduce a method to improve the accuracy of the length estimation of targets using a radar. The HRRP (High Resolution Range Profile) obtained from a received radar signal represents the one-dimensional scattering characteristics of a target, and peaks of the HRRP means the scattering centers that strongly scatter electromagnetic waves. By using the extracted scattering centers, the downrange length of the target, which is the length in the RLOS (Radar Line of Sight), can be estimated, and the real length of the target should be estimated considering the angle between the target and the RLOS. In order to improve the accuracy of the length estimation, parametric estimation methods, which extract scattering centers more exactly than the method using the HRRP, can be used. The parametric estimation method is applied after the number of scattering centers is determined, and is thus greatly affected by the accuracy of the number of scattering centers. In this paper, in order to improve the accuracy of target length estimation, the number of scattering centers is estimated by using AIC (Akaike Information Criteria), MDL (Minimum Descriptive Length), and GLE (Gerschgorin Likelihood Estimators), which are the source number estimation methods based on information theoretic criteria. Using the ESPRIT algorithm as a parameter estimation method, a length estimation simulation was performed for simple target CAD models, and the GLE method represented excellent performance in estimating the number of scattering centers and estimating the target length.

Development and Validation of the GPU-based 3D Dynamic Analysis Code for Simulating Rock Fracturing Subjected to Impact Loading (충격 하중 시 암석의 파괴거동해석을 위한 GPGPU 기반 3차원 동적해석기법의 개발과 검증 연구)

  • Min, Gyeong-Jo;Fukuda, Daisuke;Oh, Se-Wook;Cho, Sang-Ho
    • Explosives and Blasting
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    • v.39 no.2
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    • pp.1-14
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    • 2021
  • Recently, with the development of high-performance processing devices such as GPGPU, a three-dimensional dynamic analysis technique that can replace expensive rock material impact tests has been actively developed in the defense and aerospace fields. Experimentally observing or measuring fracture processes occurring in rocks subjected to high impact loads, such as blasting and earth penetration of small-diameter missiles, are difficult due to the inhomogeneity and opacity of rock materials. In this study, a three-dimensional dynamic fracture process analysis technique (3D-DFPA) was developed to simulate the fracture behavior of rocks due to impact. In order to improve the operation speed, an algorithm capable of GPGPU operation was developed for explicit analysis and contact element search. To verify the proposed dynamic fracture process analysis technique, the dynamic fracture toughness tests of the Straight Notched Disk Bending (SNDB) limestone samples were simulated and the propagation of the reflection and transmission of the stress waves at the rock-impact bar interfaces and the fracture process of the rock samples were compared. The dynamic load tests for the SNDB sample applied a Pulse Shape controlled Split Hopkinson presure bar (PS-SHPB) that can control the waveform of the incident stress wave, the stress state, and the fracture process of the rock models were analyzed with experimental results.

Development of Fender Segmentation System for Port Structures using Vision Sensor and Deep Learning (비전센서 및 딥러닝을 이용한 항만구조물 방충설비 세분화 시스템 개발)

  • Min, Jiyoung;Yu, Byeongjun;Kim, Jonghyeok;Jeon, Haemin
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.26 no.2
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    • pp.28-36
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    • 2022
  • As port structures are exposed to various extreme external loads such as wind (typhoons), sea waves, or collision with ships; it is important to evaluate the structural safety periodically. To monitor the port structure, especially the rubber fender, a fender segmentation system using a vision sensor and deep learning method has been proposed in this study. For fender segmentation, a new deep learning network that improves the encoder-decoder framework with the receptive field block convolution module inspired by the eccentric function of the human visual system into the DenseNet format has been proposed. In order to train the network, various fender images such as BP, V, cell, cylindrical, and tire-types have been collected, and the images are augmented by applying four augmentation methods such as elastic distortion, horizontal flip, color jitter, and affine transforms. The proposed algorithm has been trained and verified with the collected various types of fender images, and the performance results showed that the system precisely segmented in real time with high IoU rate (84%) and F1 score (90%) in comparison with the conventional segmentation model, VGG16 with U-net. The trained network has been applied to the real images taken at one port in Republic of Korea, and found that the fenders are segmented with high accuracy even with a small dataset.