• 대한조선학회논문집
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• 제60권5호
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• pp.367-374
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• 2023

As the Fourth Industrial Revolution accelerating, countries worldwide are developing technologies to digitize and automate various industrial sectors. Building smart factories not only reduces costs through improved process productivity but also allows for preemptive identification and removal of risk factors through the practice of Health, Safety, and Environment (HSE) management, thereby reducing industrial accident risks. In this study, we visualized pressure, temperature, power, and wind speed data measured in real-time via a monitoring GUI, enabling field managers and workers to easily access related information. Through the work environment monitoring system developed in this study, it is possible to conduct economic analysis on per-unit basis, based on the digitization of production management elements and the tracking of required resources. By implementing HSE in shipyards, potential risk factors can be improved, and gas and electrical leaks can be identified, which are expected to reduce production costs.

• 한국지반공학회논문집
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• 제40권3호
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• pp.33-39
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• 2024

구조물의 상태를 파악하기 위한 균열조사는 정밀안전 진단에 필수적인 검사 항목이다. 그러나 육안으로 이루어지는 균열조사 방식은 현장 상황의 변화에 따라 주관적으로 수행될 수 있다. 이러한 육안검사의 한계를 극복하기 위해 본 연구에서는, ResNet, FPN, Mask R-CNN을 백본(Backbone), 넥(Neck), 헤드(head)로 구성한 합성곱 신경망을 바탕으로, 이미지 데이터에서의 콘크리트 균열 탐지를 자동화하고. 그 성능을 IoU 값을 바탕으로 분석하였다. 해석에 사용된 데이터는 총 1,203개의 이미지 데이터로 구성하였으며, 이 중 70%를 훈련(Training)에, 20%를 검증(Validation)에, 그리고 10%의 데이터를 시험(Testing)에 사용하였다. 시험 결과의 평균 IoU값은 95.83%로 산정되었고, 또한 이미지 내 균열이 전혀 탐지되지 않는 경우는 존재하지 않아, 본 연구에 가정한 모델이 콘크리트의 균열 탐지를 성공적으로 수행하는 것을 확인하였다.

• 자원ㆍ환경경제연구
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• 제33권2호
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• pp.135-157
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• 2024

본 연구에서는 국제 구리 가격 변동에 따른 국내 수요 변화를 분석하여 국내 구리(전기동)의 가격탄력성을 분석하였다. 이를 위해 구리의 순 수입량, 가격, 생산지수를 변수로 1989년 1월부터 2022년 12월까지 총 408개의 시계열 자료에 대해 벡터자기회귀(Vector autoregressive, VAR) 모형을 구성하고, 시간의 흐름에 따른 변수 간의 상관관계 변화를 파악하고자 시변 모형(Time Varying VAR)을 사용하여 변수 간의 동적 관계를 분석하였다. 분석 결과 국내 구리의 가격탄력성은 -0.1835로 음의 가격탄력성이 존재함을 확인하였고, 사분위수 범위는 -0.3130 ~ 0.0886으로 시간의 흐름에 따라 일관성 있는 추세는 없지만 주로 음의 탄력성을 띠면서 탄력성이 변화하는 것을 확인하였다. 본 연구의 결과는 비축을 포함한 광물자원 관련 정책 수립 시 파생되는 기대효과를 정량화하여 제시하는 데 활용할 수 있다.

• 농업과학연구
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• 제49권4호
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• pp.871-879
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• 2022

An increasing global population requires a greater food supply, and accordingly there is demand for enhanced production of rice, as a major crop plant that covers half of the world's population. Rice production in arid area is extremely difficult due to poor soil fertility, salinity, deficit of irrigation water, and weather conditions. The aim of the present study was to determine whether various fertilization recipes could provide a countermeasure to allow rice production while also providing soil amendment such as soil pH adjustment. The study was conducted at an experimental field of the United Arab-Emirates (UAE) from January to April, 2022. Rice seedlings (cv. Asemi, alkaline-resistant) were transplanted in plastic containers, and different types of water and nutrient managements were employed as follows: water management (flooding and aerobic for NPKs treatment group) and nutrient management (NPKs, slow release fertilizers [SRFs] and SRFs + NPK-1 treatment groups with flooding). Water and nutrient management did not show any effect on soil pH adjustment. Rice growth was significantly enhanced in the flooding compared to the aerobic condition, whereas the effect of nutrient management clearly differed among the treatment groups, with SRFs + NPK-1 showing the best results followed by SRFs and NPKs. Most of the fertilization groups markedly accumulated soluble sugars in the shoots and grains of rice plants, but concomitantly a decrease in the roots. Overall, the level of starch showed a tendency of relatively slight perturbation by fertilization. Taken together, the results indicate that soil physical structure should be preferentially amended to find the key for suitable rice production.

• Journal of Welding and Joining
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• 제33권5호
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• pp.35-40
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• 2015

Characterization of microstructures and mechanical properties of 83mm thickness EH36-TM welds produced by the combined flux cored arc (FCA) and electro gas (EG) welding processes has been studied with the two different groove conditions, single-V (SV) and double-V (DV) bevels. The welding consumables used for FCA and EG welding processes were ASME/AWS A5.29 (E81T1-K2) and A5.26 (EG72T), respectively. Experimental results showed that all the mechanical properties of welds such as tensile property, CVN toughness and Vickers hardness met IACS requirements. The tensile strength of EG welded plates were reduced by approximately 4% (DV: 3.8%, SV: 4.2%) compared to the base metal. The hardness value of SV-beveled weld metal was slightly lower than that of DV-beveled one. There were no significant differences as per welding groove conditions except for the weld metal. In addition, at the fusion line, the toughness of SV condition was 20J lower and the weld metal was 40J lower than DV condition, respectively. On the basis of microstructural analysis, grain boundary ferrite (GBF) structures for SV condition were 2 times higher volume fraction than for DV condition and their packet sizes were coarsened to almost double. It was thus suggested that the GBF volume fractions and packet sizes in the weld metal of EH36-TM steel plates are the most important factors affecting the mechanical properties of the combined FCA and EG welded joint. Nevertheless, all the results of welds with both DV and SV conditions were found to be excellent.

• Current Photovoltaic Research
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• 제4권3호
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• pp.108-113
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• 2016

III-V compound semiconductor based thin film solar cells promise relatively higher power conversion efficiencies and better device reliability. In general, the thin film III-V solar cells are fabricated by an epitaxial lift-off process, which requires an $Al_xGa_{1-x}As$ ($x{\geq}0.8$) sacrificial layer and an inverted solar cell structure. However, the device performance of the inversely grown solar cell could be degraded due to the different internal diffusion conditions. In this study, InGaP/GaAs double-junction solar cells are inversely grown by MOCVD on GaAs (100) substrates. The thickness of the GaAs base layer is reduced to minimize the thermal budget during the growth. A wide band gap p-AlGaAs/n-InGaP tunnel junction structure is employed to connect the two subcells with minimal electrical loss. The solar cell structures are transferred on to thin metal films formed by Au electroplating. An AlAs layer with a thickness of 20 nm is used as a sacrificial layer, which is removed by a HF:Acetone (1:1) solution during the epitaxial lift-off process. As a result, the flexible InGaP/GaAs solar cell was fabricated successfully with an efficiency of 27.79% under AM1.5G illumination. The efficiency was kept at almost the same value after bending tests of 1,000 cycles with a radius of curvature of 10 mm.

• 한국토양비료학회지
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• 제48권5호
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• pp.428-435
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• 2015

Pedotransfer functions (PTFs) were developed for each soil horizon to estimate hydraulic characteristics of mountainous forest soils in South Korea. Twenty one dominant soil series from 8 soil catenae such as granite-originated catena and volcanic ash-originated catena were selected for the study; gravel contents of selected soils were 10% or lower. Saturated conductivity (Ks) was measured for each horizon in situ. Particle size distribution and organic matter content of each horizon were also determined. Based on correlation analysis with total data set, sand separate showed positive relationship with Ks ($r=0.24^*$) while clay separate had negative relationship with Ks ($r=-0.29^{**}$). The correlation coefficients of sand, clay, and organic matter content with Ks increased to $0.41^{**}$, $-0.67^{***}$, and $0.58^{***}$, respectively, using data from granite- or gneiss-originated catena with exception of volcanic ash-originated catena and sedimentary rock-originated catena. Determination coefficients of PTFs were 0.31 for A horizon, 0.25 for B, and 0.35 for C with all data set while those were 0.74 for A, 0.48 for B, and 0.54 for C. Organic matter was a dominant factor affecting Ks in A horizon but clay content was selected as the only factor influencing Ks in C horizon. It implies that PTFs should be developed with understanding characteristics of parent materials and horizons. Developed PTFs for granite- or gneiss-originated catena were following: A horizon: Log ($K_s{\times}10^7$) = -0.031C + 0.398OM + 3.49 B horizon: Log ($K_s{\times}10^7$) = -0.028C + 0.141OM + 4.05 C horizon: Log ($K_s{\times}10^7$) = -0.072C + 4.66 where C is clay separate (%) and OM is organic matter content ($g\;kg^{-1}$). The unit of Ks is cm $sec^{-1}$.

• 동양고전연구
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• 제68호
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• pp.9-34
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• 2017

본고는 일옹 최희량의 무인의 삶과 시세계를 살펴보는데 목적을 두었다. 최희량은 무인으로서는 드물게 227수의 한시를 남겼으며 후대 문인들에게 시적 성취를 인정받고 있다. 따라서 최희량 한시를 살펴보는 일은 무인(武人)의 의식세계를 밝힌다는 점에서 의의가 있을 것으로 판단된다. II장에서는 최희량 한시를 이해하기 위한 기저단계로서 생애를 살펴보았다. 최희량은 젊은 시절 학문을 배웠으나 21세 때 무과(武科)로 전향하였다. 이는 문무(文武)를 가리지 않는 집안의 가풍과 최희량의 장대한 신체적 조건, 그로 인한 무인적 기질에서 비롯된 것이다. 최희량은 무과에 급제한 후 이순신의 막하에서 7차례나 전공을 세운다. 하지만 이순신이 노량에서 전사하자 벼슬을 버리고 고향인 나주에 은거하여 92세로 생을 마감할 때까지 재출사하지 않았다. 이는 최희량이 당대의 현실을 난세로 인식하고 명철보신(明哲保身)했기 때문이다. III장에서는 II장을 토대로 최희량의 시세계를 살펴보았다. 최희량의 시세계는 크게 무인의 기질을 드러내는 것과 강호에서 자락하는 삶 및 우국지정을 드러내는 것들로 나눌 수 있다. 무인의 기질을 드러내는 시들은 은거 이전 전쟁에 임하거나 은거 이후 병란과 관련하여 읊은 것으로 감각적인 시어와 직설적인 화법으로 시화(詩化)되고 있었다. 강호에서 자락적인 삶을 보여주는 시는 귀거래 한 후 나주에서의 평화로운 삶을 읊은 것이며, 우국지정을 드러내는 시는 병란(丙亂)을 당하자 전직 무인으로서 나라를 근심하는 마음을 나타낸 것이다. 최희량이 현실을 벗어나 은거하면서도 우국지정을 강하게 드러낸 것은 최희량의 은거가 자의에 의한 것이 아니라 타의에 의한 것이었기 때문에 현실을 완전히 외면할 수 없었던 것이다.

• 대한조선학회논문집
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• 제60권4호
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• pp.278-287
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• 2023

This study aims to analyze and evaluate the structural strength of a 53ft Liquefied Natural Gas (LNG) tank container according to International Organization for Standardization (ISO) 1496-3, amidst growing global demand for LNG transportation. The research was conducted in two main stages: structural analysis using Finite Element Analysis (FEA) under various load conditions, and structural strength tests following ISO 1496-3 test procedures. The structural analysis was performed considering different loading conditions to assess the structural safety of the tank container. Calculated stresses were compared with allowable stress under specified load conditions. The structural strength tests were conducted at Mokpo National University's Subsea Umbilical cable Riser Flowline R&D Center, which provided a suitable testing environment. The study found that calculated stresses met the allowable stress under specified load conditions, confirming the structural safety of the tank container. Additionally, the maximum deformation and permanent deformation satisfied the design criteria for all test cases, indicating the container's structural strength meets requirements. The research also contributed valuable data for future structural strength tests of similar products and facilitated the development of safe and efficient LNG transportation solutions by developing effective test procedures in accordance with ISO 1496-3 standards.

• 대한조선학회논문집
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• 제60권5호
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• pp.375-387
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• 2023

The subsea power cables are increasingly important for harvesting renewable energies as we develop offshore wind farms located at a long distance from shore. Particularly, the continuous flexural motion of inter-array dynamic power cable of floating offshore wind turbine causes tremendous fatigue damages on the cable. As the subsea power cable consists of the helical structures with various components unlike a mooring line and a steel pipe riser, the fatigue analysis of the cables should be performed using special procedures that consider stick/slip phenomenon. This phenomenon occurs between inner helically wound components when they are tensioned or compressed by environmental loads and the floater motions. In particular, Vortex-induced vibration (VIV) can be generated by currents and have significant impacts on the fatigue life of the cable. In this study, the procedure for VIV fatigue analysis of the dynamic power cable has been established. Additionally, the respective roles of programs employed and required inputs and outputs are explained in detail. Demonstrations of case studies are provided under severely sheared currents to investigate the influences on amplitude variations of dynamic power cables caused by the excitation of high mode numbers. Finally, sensitivity studies have been performed to compare dynamic cable design parameters, specifically, structural damping ratio, higher order harmonics, and lift coefficients tables. In the future, one of the fundamental assumptions to assess the VIV response will be examined in detail, namely a narrow-banded Gaussian process derived from the VIV amplitudes. Although this approach is consistent with current industry standards, the level of consistency and the potential errors between the Gaussian process and the fatigue damage generated from deterministic time-domain results are to be confirmed to verify VIV fatigue analysis procedure for slender marine structures.