• Steel and Composite Structures
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• 제33권3호
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• pp.445-461
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• 2019

The ultrasonic guided wave-based technique has become one of the most promising methods in non-destructive evaluation and structural health monitoring, because of its advantages of large area inspection, evaluating inaccessible areas on the structure and high sensitivity to small damage. To further advance the development of damage detection technologies using ultrasonic guided waves for the inspection of welded components in structures, the transmission characteristics of the ultrasonic guided waves propagating through welded joints with various types of defects or damage in steel plates are studied and presented in this paper. A three-dimensional (3D) finite element (FE) model considering the different material properties of the mild steel, high strength steel and austenitic stainless steel plates and their corresponding welded joints as well as the interaction condition of the steel plate and welded joint, is developed. The FE model is validated against analytical solutions and experimental results reported in the literature and is demonstrated to be capable of providing a reliable prediction on the features of ultrasonic guided wave propagating through steel plates with welded joints and interacting with defects. Mode conversion and scattering analysis of guided waves transmitted through the different types of weld defects in steel plates are performed by using the validated FE model. Parametric studies are undertaken to elucidate the effects of several basic parameters for various types of weld defects on the transmission performance of guided waves. The findings of this research can provide a better understanding of the transmission behaviour of ultrasonic guided waves propagating through welded joints with defects. The method could be used for improving the performance of guided wave damage detection methods.

• 농업과학연구
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• 제45권4호
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• pp.823-837
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• 2018

The objective of this study was to evaluate the firmness and the sweetness index (SI) of tomatoes with a hyperspectral imaging (HSI) technique within the wavelength range of 1000 - 1550 nm. The hyperspectral images of 95 tomatoes were acquired with a push-broom hyperspectral reflectance imaging system, from which the mean spectra of each tomato were extracted from the regions of interest. The reference firmness and sweetness index of the same sample was measured and calibrated with their corresponding spectral data by partial least squares (PLS) regression with different preprocessing methods. The calibration model developed by PLS regression based on the Savitzky-Golay second-derivative preprocessed spectra resulted in a better performance for both the firmness and the SI of the tomatoes compared to models developed by other preprocessing methods. The correlation coefficients ($R_{pred}$) were 0.82, and 0.74 with a standard error of prediction of 0.86 N, and 0.63, respectively. Then, the feature wavelengths were identified using a model-based variable selection method, i.e., variable importance in projection, from the PLS regression analyses. Finally, chemical images were derived by applying the respective regression coefficients on the spectral image in a pixel-wise manner. The resulting chemical images provided detailed information on the firmness and the SI of the tomatoes. The results show that the proposed HSI technique has potential for rapid and non-destructive evaluation of firmness and the sweetness index of tomatoes.

• Structural Monitoring and Maintenance
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• 제5권4호
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• pp.463-488
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• 2018

In the last decades, research efforts have been spent to investigate the effect of prestressing on the dynamic behaviour of prestressed concrete (PSC) beams. Whereas no agreement has been reached among the achievements obtained by different Researchers and among the theoretical and the experimental results for simply supported beams, very few researches have addressed this problem in continuous PSC beams. This topic is, indeed, worthy of consideration bearing in mind that many relevant bridges and viaducts in the road and railway networks have been designed and constructed with this structural scheme. In this paper the attention is, thus, focused on the dynamic features of continuous PSC bridges taking into account the effect of prestressing. This latter, in fact, contributes to the modification of the distribution of the bending stress along the beam, also by means of the secondary moments, and influences the flexural stiffness of the beam itself. The dynamic properties of a continuous, two spans bridge connected by a nonlinear spring have been extracted by solving an eigenvalue problem in different linearized configurations corresponding to different values of the prestress force. The stiffness of the nonlinear spring has been calculated considering the mechanical behaviour of the PSC beam in the uncracked and in the cracked stage. The application of the proposed methodology to several case studies indicates that the shift from the uncracked to the cracked stage due to an excessive prestress loss is clearly detectable looking at the variation of the dynamic properties of the beam. In service conditions, this shift happens for low values of the prestress losses (up to 20%) for structure with a high value of the ratio between the permanent load and the total load, as happens for instance in long span, continuous box bridges. In such conditions, the detection of the dynamic properties can provide meaningful information regarding the structural state of the PSC beam.

• 농업과학연구
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• 제46권2호
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• pp.257-271
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• 2019

The use of food grade hexane (FGH) for edible oil extraction is responsible for the presence of benzene in the crude oil. Benzene is a Group 1 carcinogen and could pose a serious threat to the health of consumer. However, its detection still depends on classical methods using chromatography which requires a rapid non-destructive detection method. Hence, the aim of this study was to investigate the feasibility of using Fourier transform infrared (FTIR) spectroscopy combined with multivariate analysis to detect and quantify the benzene residue in edible oil (sesame and cottonseed oil). Oil samples were adulterated with varying quantities of benzene, and their FTIR spectra were acquired with an attenuated total reflectance (ATR) method. Optimal variables for a partial least-squares regression (PLSR) model were selected using the variable importance in projection (VIP) and the selectivity ratio (SR) methods. The developed PLS models with whole variables and the VIP- and SR-selected variables were validated against an independent data set which resulted in $R^2$ values of 0.95, 0.96, and 0.95 and standard error of prediction (SEP) values of 38.5, 33.7, and 41.7 mg/L, respectively. The proposed technique of FTIR combined with multivariate analysis and variable selection methods can detect benzene residuals in edible oils with the advantages of being fast and simple and thus, can replace the conventional methods used for the same purpose.

• 한국압력기기공학회 논문집
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• 제16권2호
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• pp.1-9
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• 2020

Large-scale industrial facility structures continue to deteriorate due to the effects of operating and environmental conditions. The problems of these industrial facilities are potentially causing economic losses, environmental pollution, casualties, and national losses. Accordingly, in order to prevent disaster accidents of large structures in advance, the necessity of diagnosing structures using non-destructive inspection techniques is being highlighted. The defect occurrence, location and defect type of the structure are important parameters for predicting the remaining life of the structure, so continuous defect observation is very important. Recently, many researchers have been actively researching real-time monitoring technology to solve these problems. Structure Health Monitoring Inspection is a technology that can identify and respond to the occurrence of defects in real time, but there is a limit to check the degree of defects and the direction of growth of defects. In order to compensate for the shortcomings of these technologies, the importance of defect imaging techniques is emerging, and in order to find defects in large structures, a method of inspecting a wide range using guided ultrasonic is effective. The work presented here introduces a calculation for the shape factor for evaluation of the damaged area, as well as a variable β parameter technique to correct a damaged shape. Also, we perform research in modeling simulation and an experiment for comparison with a suggested inspection method and verify its validity. The curved structure image obtained by the advanced RAPID algorithm showed a good match between the defect area and the shape.

• Composites Research
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• 제34권3호
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• pp.143-147
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• 2021

유리섬유 복합재료(GFRP) 내부 미세 박리에서 나타나는 테라헤르츠(THz) 중첩 신호의 FWHM 분석을 통한 미세 박리 검출 기술을 연구하였다. 테라헤르츠 시간영역 분광(THz-TDS) 시스템의 반사모드를 통해 유리섬유 복합재료 내부의 미세 박리 크기 별 THz 신호를 측정하였고, 미세 박리 위치에서 반사되어 검출되는 THz 중첩 신호의 Full Width Half Maximum (FWHM) 값을 추출하였다. 이후, 유리섬유 복합재료의 복소굴절률을 측정하여 미세 박리 크기에 따른 미세 박리 위치에서의 THz 중첩 신호 및 FWHM 값을 계산하여 비교하였다. 이론적으로 계산된 THz 중첩 신호로부터 미세 박리 크기와 중첩 신호에서의 FWHM 값의 상관관계를 도출하였으며, 미세 박리 위치에서의 THz 신호로부터 추출된 FWHM의 분석을 통해 미세 박리 크기를 예측할 수 있었다.

• Composites Research
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• 제35권6호
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• pp.469-476
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• 2022

본 논문에서는 주기패턴 레이더 흡수 구조(RAS)에 다양한 손상을 모사하기 위한 저속충격시험을 수행하고 파손모드에 따른 전자기파 흡수 성능 특성 변화를 평가하였다. 주기패턴 레이더 흡수 구조는 주기패턴시트(PPS) 및 유리섬유강화플라스틱(GFRP)으로 구성되며 설계 및 제작된 구조는 X-band(8.2-12.4 GHz)에서 효과적으로 전자기파를 흡수하였다. 제작된 레이더 흡수 구조에 다양한 손상을 유도하기 위해 충격에너지에 따른 저속충격시험을 수행하였으며, 육안검사, 비파괴 검사 및 이미지 프로세싱을 이용하여 발생한 손상모드 확인 및 손상영역을 정량화하였다. 충격 전, 후 레이더 흡수 구조의 전자기파 흡수 성능은 자유공간 측정 시스템을 이용하여 평가하였다. 시험결과, 15 J의 낮은 충격에너지로 인해 발생한 크기가 작은 층간분리는 레이더 흡수 구조의 전자기파 흡수성능 변화에 큰 영향을 미치지 않았다. 그러나 충격에너지를 40 J 또는 60 J로 증가시켜 상대적으로 넓은 영역의 섬유파손 또는 관통파손이 발생한 구조에서는 전자기파 흡수 성능이 크게 저하되는 것을 확인하였다.

• Composites Research
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• 제35권1호
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• pp.8-12
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• 2022

테라헤르츠(THz)파의 디컨벌루션을 통한 유리섬유 복합재 내부 결함 신호 분석 기법을 연구하였다. 결함이 존재하는 유리섬유 복합재료 시편을 제작하였고, Terahertz Time-Domain Spectroscopy (THz-TDS) 시스템의 반사모드를 통해 THz 신호를 측정하였다. 디컨벌루션을 위해 THz 입사 신호와 검출 신호의 Normalized Cross Correlation (NCC) 계산을 통해 THz 신호의 피크 위치를 증폭하였다. 증폭된 피크의 위치 및 세기를 임펄스로 추출하였고 THz 원신호에서 추출된 임펄스 위치의 신호를 제거하였다. 해당 과정을 반복함으로써 시편의 경계면을 나타내는 THz 검출 신호의 주요 임펄스를 도출하였다. 주요 임펄스와 기준 신호의 컨벌루션을 통해 노이즈가 제거된 THz 원신호의 복원이 가능한 것을 확인함으로써 디컨벌루션 과정을 검증하였다. 결과적으로 주요 임펄스들의 검출 시간을 통해 15 ㎛ 이내의 정확도로 유리섬유 복합재 내부 결함의 두께 판별이 가능하였다.

• 한국방사선학회논문지
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• 제17권4호
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• pp.625-631
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• 2023

24시간/7일 동안 높은 관전압 하에서 높은 프레임 속도로 검사 대상체의 불량을 검사하는 산업용 동영상 엑스레이 디텍터의 중요한 요구사양은 높은 방사선 내구성을 확보하는 것이다. 본 연구는 비정질 실리콘 (a-Si), 다결정 실리콘 (Poly-Si), In-Ga-Zn-O 산화물 (IGZO) 등의 반도체 층을 갖는 다양한 박막트랜지스터를 제작하여 각각의 방사선 내구성을 확인하였다. a-Si TFT 대비 수십 배 높은 전계효과 이동도로 고속 동영상 구현이 가능한 IGZO TFT의 경우, IGZO 반도체 층과 층간절연막 사이에 수소화 처리를 진행할 경우 산업용 요구사양인 10,000 Gy 누선선량까지 엑스레이 영상센서로 적용 가능한 수준 이상으로 전기적 특성의 변화가 없음을 확인하였다. 따라서 수소화한 IGZO TFT는 방사선 내구성을 확보함과 동시에 높은 전계효과 이동도로 동영상 디텍터의 영상센서에 적용 가능한 유일한 소자임을 확인하였다.

• 한국환경농학회지
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• 제42권2호
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• pp.121-130
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• 2023

The RGB (red, green, and blue) imagery analysis is an important remote sensing tool, which estimates the effect of environmental stress on turfgrass growth and physiology. Therefore, this study investigated the effect of continuous wear stress treatment on Zoysia japonica through RGB imagery analysis. The results of the growth measurement showed that the plant height substantially decreased, after nine hours of treatment with no considerable difference thereafter. Dry weight measurement showed a substantial difference in the morphological growth characteristics of the aerial part of the turfgrass, but none in the stolon and root zone. This could be attributed to the short period of compaction treatment. The ROS (reactive oxygen species) analysis showed that ROS rapidly increased due to wear stress treatment. The MDA content increased during the traffic process, whereas the green pixels increased and decreased repeatedly; however, overall, the trend declined but the overall trend decreased. Thus, this study confirmed that MDA was effective in reflecting the wear stress of turfgrass; however, it could through RGB image analysis.