• Journal of Magnetics
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• 제16권3호
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• pp.276-280
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• 2011

This paper presents a non-destructive evaluation study on a radiator with cooling fins as a complex shaped specimen. Radiator structures are used in various heat exchangers, such as automobiles, air conditioners and refrigerators. An eddy current testing method, namely multi-frequency excitation and spectrogram method (MFES), was employed to detect a defect on the radiator tube surrounded by cooling fins. Overall, experimental results suggested that the influence of cooling fin is not as noticeable as that of the defect signals.

• 국제학술발표논문집
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• The 9th International Conference on Construction Engineering and Project Management
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• pp.213-221
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• 2022

Defects are the risk factors in the construction process of buildings. They cause damage, delaying the construction duration. They especially cause adverse effects on the top-down construction method. This study analyzed the degree of construction delay induced by each work type, focusing on defects in the top-down method. Then, we derived construction delay induction coefficient from different work types in order by using the severity of construction delay per defect and the occurrence probability of defect; this assessment model measures the impact of defects on construction delay for each work type. Furthermore, by comparing each work type based on the defect frequency and the construction delay induction coefficient, we found work types that need to be administered attentively. We identified that plastering work was easy to overlook, requiring caution in defect management. This study provides an efficient defect management system suitable for the buildings that are built using the top-down construction method.

• 비파괴검사학회지
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• 제19권3호
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• pp.173-179
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• 1999

고주파를 이용하여 금속 표면의 원형 프레스 결함, 원형 관통 결함 및 선형 프레스 결함 등을 조사하였다. 본 실험에서는 3kHz 변조된 9.2GHz의 주파수를 사용했으며, 조사 방법으로는 반사법, 투과법, 주파수 고정법 등을 이용하였다. 고주파가 원형 프레스 결함과 원형 관통 결함에서 반사 신호의 크기가 큰 폭으로 변했다. 원형 프레스 결함에서는 반사신호에 의한 결함의 크기가 원래 크기의 2.5배로 확대되어 측정되었으며, 원형 관통 결함에서는 결함의 크기가 두 배로 확대되어 측정되었다. 또한, 선형 결함에서 고주파 반사신호의 크기는 결함폭의 증가와 함께 커졌으며, 결함 깊이가 2.4mm일 때 결함폭이 50mm에서, 결함 깊이가 1.2mm 및 0.45mm에서는 결함폭이 55mm일 때 각각 최대값을 나타냈다.

• 한국건설관리학회논문집
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• 제19권4호
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• pp.34-42
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• 2018

공동주택은 국민 대다수가 선호하는 대표적인 주거양식으로 자리매김한 반면, 완공된 공동주택의 기초 골조 설비 마감 및 조경 등의 수많은 구조체와 마감재에서 균열 침하 파손 누수 결로 및 탈락 등의 다양한 결함이 발생하여 하자없는 신축 공동주택을 원하는 입주자와 하자가 발생하는 것은 불가피하다고 주장하는 사업주체간에 분쟁이 지속적으로 발생하고 있다. 이러한 하자분쟁은 입주자와 건설업체 모두에게 경제적 손실을 발생시킨다. 이러한 관점에서 본 논문에서는 하자분쟁사례를 활용하여 공종별 각 보증기간의 하자보수 빈도 및 비용을 분석하고, 이를 종합하여 공종별 각 보증기간의 하자보수위험을 평가하여 하자보수보증금 산정에 대한 시사점을 도출하는 것을 목적으로 한다. 이를 위해 본 논문에서는 준공 이후 10년 이상된 공동주택 하자분쟁사례 32건, 5337개의 하자아이템을 활용하여 공종별 각 보증기간의 하자보수위험을 평가하였다. 하자빈도와 하자비용을 종합하여 공종별 하자보수보증기간의 하자비용을 분석한 결과, 철근콘크리트공사와 마감공사의 하자위험이 매우 높은 것으로 파악되었다. 이는 결국 하자보수보증금이 일률적으로 연차별로 배분되어 있는 것에 문제점이 있음을 나타낸다. 또한 하자보수보증금의 경과년수에 따른 반환비율과 경과년수에 따른 하자위험을 비교한 결과, 기존 반환비율에 대한 조정이 필요할 것으로 나타났다.

• 대한치과보철학회지
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• 제43권6호
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• pp.736-744
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• 2005

Statement of problem. Initial stability of implant is an important factor for predicting osseointegration. It requires a rapid, non-invasive, user-friendly technique to frequently assess the implant stability and the degree of osseointegration. Purpose. The aim of this study was to evaluate the correlation between the resonance frequency analysis (RFA) and the radiographic method for peri-implant bone change under in vitro conditions. Material and Method. Twenty implants of 3.75 mm in diameter(Neoplant, Neobiotech, Korea) were used. To simulate peri-implant bone change, 2 mm-deep $45^{\circ}$ range horizontal defect and 2 mm-deep $90^{\circ}$ range horizontal defect area were serially prepared perpendicular to the X-ray beam after conventional implant insertion. Customized film holding device was fabricated to standardize the projection geometry for serial radiographs of implants and direct digital image was obtained. ISQ values and gray values inside threads were measured before and after peri-implant bone defect preparation. Results. Within a limitation of this study, ISQ value of resonance frequency analysis was changed according to peri-implant bone change (p<0.05) and gray value of radiographic method was changed according to peri-implant bone change (p<0.05). There was no correlation between the ISQ value and the gray value for peri-implant bone change (p>0.05). But, in horizontal defect condition, relatively positive correlation were between ISQ and gray values(r=0.663). Conclusion. This results provided a possibility that peri-implant bone change may be evaluated by both RFA and radiographic method.

• 대한치과보철학회지
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• 제43권4호
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• pp.487-497
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• 2005

Purpose: Resonance frequency analysis (RFA) , a non-invasive technique for the clinical measurement of implant stability, was investigated. Peri-implant bony defect may contribute to implant failure. This in vitro study evaluated the resonance frequencies according to various bony defects and determined whether the directional bone defect can affect the value of frequency analysis. Material and Method: Fifteen 3.75 mm in diameter and 10 mm in length, machined self-tapping implant future were used. Twelve types of bone defects that have different horizontal and vertical dimensions were simulated. Embedded implants were attached to the dental surveyor. Then, the transducer was connected with the implant fixture and the ISQ value was measured at four different directions. Two-way analysis of variance and post hoc $Sch\`{e}ffe'$ test were performed at the 95% significance level. Results: The control group showed the highest ISQ value and 5 thread-$360^{\circ}$ group had the lowest one. As the vertical exposure of implants in each angle was increased, the ISQ value was decreased. Although the horizontal exposure in each thread was increased, the ISQ value was not significantly decreased. Conclusion : Although the simulated defect type was different from each other, the ISQ value was similar among groups.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 C
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• pp.1673-1675
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• 2001

In this paper, Partial Discharge(PD) patterns are compared by means of Low Frequency PD(LFPD, based on the IEC 270) and recently proposed High Frequency PD(HFPD). For this purpose, three different types of artificial defects are provided such as corona in air, void in epoxy insulator and needle defect in XLPE cable insulation. PD were generated from each defect and then detected respectively by two different methods such as LFPD and HFPD. As a result, remarkable resemblance in PD pattern for differ detecting method have been observed from each defect. Accordingly, it could be deduced that the pattern recognition by LFPD could be regarded as the reference for the investigations by HFPD.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.53-55
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• 2005

The signals of the eddy current testing(ECT) for the examination of the steam generator(SG) tubes in the nuclear power plant(NPP) determine the existence, size, and kind of defects using the variation of impedance signals when a testing coil, driven by alternating current, passes through the SG tube contains defects. The aim of this paper is building a database of the RPC probe signals on the basis of the sizes variation of defects and frequency variation of probe. In this paper 3-D numerical analysis of the ECT signals using the finite element method is performed. Through this study, it is shown variation of magnitude and phase of impedance according to variation of defect size and frequency. From the result of this paper, we can obtain the information which is useful in defect discrimination of SG tube in nuclear power plant.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.32-32
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• 2009

Electric Resistance Welding (ERW) process is the most efficient process to manufacture the linepipe. To develop the high performance ERW linepipe using the high strength and the high alloy steels, the modulation of input power waveform such as sinusoidal waveform is introduced because the conventional ERW technology is not sufficient enough to produce the high quality linepipe due to its strength and high alloy contents (high Ceq). In this article, the material used for the experiment was API X60 with 8.2mm thickness, and ERW simulator at POSCO was used to develop a waveform control system for the power modulation. The frequency of power modulation was varied from 50Hz to 150Hz with the fixed amplitude of ${\pm}2%$ power. The non-modulated power input and the modulated power input cases are conducted to demonstrate the variation of the narrow gap length and the arcing frequency due to power modulation. From results of the non-modulated power input case, the excessive power causes the longer narrow gap length and the low arcing frequency due to the large heat input and the strong electro magnetic force that increase the weld defect. On the contrary, the small narrow gap length and the high arcing frequency reduce the weld defect. After modulating the power input with 50Hz and 100Hz at the fixed power, the arcing frequency increases, but the narrow gap length does not change much. The high arcing frequency prevents the formation of weld defect because the sweeping frequently cleans the oxides on the narrow gap edges. As a result, the manufacturing window can be expanded by the power modulation that provides the stable ERW process for the quality improvement of the linepipe made from the high strength/high alloy steels.

• Journal of Chest Surgery
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• 제13권3호
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• pp.233-236
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• 1980

Left Ventricular-Right atrial canal, which permits a communication between the left ventricle and right atrium has been reported with increasing frequency. Kirby made the first successful surgical correction in 1957. Recently we experienced 3 cases of left ventricular-Right atrial canal, which were corrected surgically. In one patient the diagnosis of left ventricular-Right atrial canal had been suggested before operation. Preoperative diagnosis had been incorrect in 2 cases; one as an atrial septal defect and the other as combined atrial septal defect and ventricular septal defect. The entire patients were discharged with good results within 2 weeks after operation.