• 대한토목학회논문집
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• 제43권5호
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• pp.675-687
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• 2023

한반도 비무장지대에 인접한 접경지역은 DMZ(DemilitarizedZone) 그린평화 지대화를 위한 그린데탕트(GreenDétent) 실천무대로 주목 받고있다. 본논문은 접경지역에 계획된 생태·환경 분야 산업·인프라 사업의 복합적 성격을 판단 할 수있는 항목으로 구성된 프로슈밍지표(Prosuming-index)를 제안하고, 이 를 통해 그린데탕트 실천 대상지로서의 잠재력과 방향성을 시각화 하였다. 그 결과, 접경 지역중 인천·강화 지역은 '물류·인적 네트워크 중심 권역이자 특화 농수산물 생산지' 로서, 경기 북부지역은 '스마트기술 활용 산업을 기반으로하는 교류 네트워크 중심권역' 으로서, 강원 서부지역과 경기 연천 지역은 '탄소 감축 기술을 골자로 하는 생산-소비 복합권역' 으로서, 강원 동부지역은 '재생에너지 산업을 통한 유휴·노후 인프라의 그린 인프라 전환권역' 으로서, 크게 4가지 권역으로 그린데탕트 실천 잠재력을 유형화 할 수 있었다.

• 문화기술의 융합
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• 제9권1호
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• pp.605-611
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• 2023

본 연구에서는 자연환경에 영향을 주는 에너지를 절감하기 위해 피복아크용접에서 가동철심형 용접기와 전력사용량이 적은 디지털 용접기(인버터 방식)를 비교하여 전력 사용은 적으며 용접성은 동일한 조건을 갖춰야 하는 부분을 확인하고자 한다. 가동철심형 용접기는 정현파를 출력하는 교류를 사용하며 디지털 용접기 또한 정현파 교류를 발생시켜 동일 조건을 갖추고 전력사용량은 적으며 같은 용접성을 갖추어야 한다. 다만 용접성은 다양하게 검증할 수 있으나 국가기술자격 용접 분야의 자격시험으로 한정하여 분석하고자 한다.

• Smart Structures and Systems
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• 제31권2호
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• pp.101-111
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• 2023

Structural health monitoring (SHM) covers a range of damage detection strategies for buildings. In real-time, SHM provides a basis for rapid decision making to optimise the speed and economic efficiency of post-event response. Previous work introduced an SHM method based on identifying structural nonlinear hysteretic parameters and their evolution from structural force-deformation hysteresis loops in real-time. This research extends and generalises this method to investigate the impact of a wide range of flag-shaped or pinching shape nonlinear hysteretic response and its impact on the SHM accuracy. A particular focus is plastic stiffness (K_p), where accurate identification of this parameter enables accurate identification of net and total plastic deformation and plastic energy dissipated, all of which are directly related to damage and infrequently assessed in SHM. A sensitivity study using a realistic seismic case study with known ground truth values investigates the impact of hysteresis loop shape, as well as added noise, on SHM accuracy using a suite of 20 ground motions from the PEER database. Monte Carlo analysis over 22,000 simulations with different hysteresis loops and added noise resulted in absolute percentage identification error (median, (IQR)) in K_p of 1.88% (0.79, 4.94)%. Errors were larger where five events (Earthquakes #1, 6, 9, 14) have very large errors over 100% for resulted K_p as an almost entirely linear response yielded only negligible plastic response, increasing identification error. The sensitivity analysis shows accuracy is reduces to within 3% when plastic drift is induced. This method shows clear potential to provide accurate, real-time metrics of non-linear stiffness and deformation to assist rapid damage assessment and decision making, utilising algorithms significantly simpler than previous non-linear structural model-based parameter identification SHM methods.

• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2020년도 제62차 하계학술대회논문집 28권2호
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• pp.135-138
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• 2020

무선 센서 네트워크에서 모바일 싱크의 도입은 기존의 고정된 위치의 싱크를 사용하는 WSN에서 발생하는, 싱크 주변 노드들과 외곽 노드들 간의 에너지 불균형 문제(에너지 핫스팟 문제)를 어느 정도 해결할 수 있게 하였다. 그러나 모바일 싱크의 에너지 제약으로 인해 싱크가 모든 노드를 방문하여 데이터를 수집할 수 없기 때문에, 앵커(또는 헤드)라고 불리는 특정 노드에서 데이터를 모으고, 모바일 싱크는 이러한 앵커 노드들만을 방문하는 방법이 널리 사용되고 있다. 최근 연구에서는 모바일 싱크가 보다 효율적으로 에너지 불균형 문제를 해결하기 위하여 모바일 싱크 이동 경로 및 앵커 노드 선정 최적화 방법이 활발히 연구되고 있다. 본 연구에서는 태양 에너지 기반 센서 네트워크를 위한 영역 기반 앵커 선정 기법 및 모바일 싱크 이동 경로 선택 기법을 제안한다. 제안 기법은 각 노드가 수집하는 태양 에너지의 활용을 최대화하고, 에너지 핫스팟 문제를 완화하기 위해 두 개의 라인(영역)을 설정하고 이 라인을 따라 앵커 노드가 선정된다. 모바일 싱크는 데이터 수집을 위해 이 두 라인을 왕복 이동 경로로 택하여 라인 내의 앵커 노드를 방문한다. 실험을 통해 제안 기법이 기존 기법보다 에너지 불균형 문제가 완화되어 노드의 정전 시간이 줄어들고, 이에 따라 모바일 싱크에서 수집되는 데이터의 양이 증가하는 것을 확인하였다.

• Smart Structures and Systems
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• 제31권1호
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• pp.13-27
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• 2023

Fatigue crack is a fatal problem for steel structures. Early detection and maintenance can help extend the service life and prevent hazards. This paper presents the ultrasonic guided waves-based (UGWs-based) fatigue crack detection of a steel I-beam. The semi-analytical finite element model has been built to obtain the wave propagation characteristics. Damage indices in both time and frequency domains were analyzed by considering the characteristic variations of UGWs including the amplitude, phase angle, and wave packet energy. The pulse-echo and pitch-catch methods were combined in the detection scheme. Lab-scale experiments were conducted on welded steel I-beams to verify the proposed method. Results show that the damage indices based on the characteristic variations in the time domain can identify and localize the fatigue crack before it enters the rapid growth stage. The damage severity can be reasonably evaluated by analyzing the time-domain damage indices. Two nonlinear damage indices in the frequency domain give earlier warnings of the fatigue crack than the time-domain damage indices do. The identification results based on the above two nonlinear indices are found to be less consistent under various excitation frequencies. More robust nonlinear techniques needed to be searched and tested for early crack detection in steel I-beams in further study.

• 한국산업융합학회 논문집
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• 제26권5호
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• pp.953-965
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• 2023

The stratospheric drones are developed to perform missions such as weather observation, communication relay, surveillance, and reconnaissance at 18km to 20km, where climate change is minimal and there is no worry about a collision with aircraft. It uses solar panels for daytime flights and energy stored in batteries for night flights, providing many advantages over existing satellites. The electrical and power systems essential for stratospheric drone flight must ensure reliability, efficiency, and lightness by selecting the optimal circuit topology. Therefore, it is necessary to analyze the circuit topology of various types of multi-level inverters with high redundancy that can ensure the reliability and efficiency of the motor driving power required for stable long-term flight of stratospheric drones. By quantifying the switch element voltage drop and the number and weight of inverter components for each topology, we evaluate efficiency and lightness and propose the most suitable circuit topology for stratospheric drones.

• 농업과학연구
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• 제50권3호
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• pp.417-425
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• 2023

Because an irradiation of 405 nm violet light could have a strong energy, it was used to be sterilized against various microbes in the indoor air condition or fresh food. Escherichia coli is a representative bio-pollutant in the indoor air-borne bacteria, and a hygienic microbe in the horticultural food. This study evaluated the inactivation influences on E. coli DS5α after exposure to 405 nm violet-light (VL) by investigating irradiating time, and the vertical and horizonal distance from light source. The illumination of 405 nm VL was inversely proportional to the distance from the VL source. E. coli DS5α on nutrient agar (NA) was inactivated approximately 50% more than the control when irradiated at 65 cm from 405 nm VL for 3 hours. When compared to the control, E. coli DS5α was inactivated approximately 50% within 70 cm from 405 nm VL for 3 hours. As it was irradiated for 3 hours 70 cm away from 405 nm VL, the horizonal distance from the point was negatively correlated to the inactivation of E. coli DS5α. These results indicated that the inactivation of E. coli DS5α grown on NA medium needs to be irradiated with 405 nm within 70 cm from the light source for 3 hours.

• Smart Structures and Systems
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• 제32권4호
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• pp.253-266
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• 2023

The time-reversal method is employed to improve the ability of pipeline defect detection, and a new approach of identifying the pipeline defect depth is proposed in this research. When the L(0,2) mode ultrasonic guided wave excited through a lead zirconate titinate (PZT) transduce array propagates along the pipeline with a defect, it will interact with the defect and be partially converted to flexural F(n, m) modes and longitudinal L(0,1) mode. Using a receiving PZT array attached axisymmetrically around the pipeline, the L(0,2) reflection signal as well as the mode conversion signals at the defect are obtained. An appropriate rectangle window is used to intercept the L(0,2) reflection signal and the mode conversion signals from the obtained direct detection signals. The intercepted signals are time reversed and re-excited in the pipeline again, result in the guided wave energy focusing on the pipeline defect, the L(0,2) reflection and the L(0,1) mode conversion signals being enhanced to a higher level, especially for the small defect in the early crack stage. Besides the L(0,2) reflection signal, the L(0,1) mode conversion signal also contains useful pipeline defect information. It is possible to identify the pipeline defect depth by monitoring the variation trend of L(0,2) and L(0,1) reflection coefficients. The finite element method (FEM) simulation and experiment results are given in the paper, the enhancement of pipeline defect reflection signals by time-reversal method is obvious, and the way to identify pipeline defect depth is demonstrated to be effective.

• 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.

• 한국구조물진단유지관리공학회 논문집
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• 제27권5호
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• pp.105-112
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• 2023

강섬유보강콘크리트는 일반 콘크리트에 비해 높은 강도 및 우수한 에너지 소산 능력을 보이며, 폭발하중 작용 시 균열 전파 및 파편 발생을 감소시킬 수 있다. 본 연구에서는 유한요소해석 프로그램인 LS-DYNA에 SFRC 재료물성을 구현하고자 콘크리트 비선형 재료모델인 K&C 모델의 파괴 곡면(Failure surface) 및 손상 함수(Damage function)를 정의하는 파라미터를 제안하였다. 제안 파라미터 검증을 위하여 단일요소해석을 수행하였으며, 제안 파라미터가 적용된 재료모델은 SFRC 재료시험 거동을 상당히 유사하게 모사하는 것으로 나타났다. 또한, 강섬유 혼입률에 따른 SFRC 기둥의 성능을 평가하기 위하여 내폭해석을 수행하였으며, KOSHA 규정을 참조하여 섬유 혼입률에 따른 SFRC 기둥의 내폭성능을 정량적으로 분석하였다.