• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.140-146
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• 2008

The damage evaluation method for framed structures using continuous wavelet transform (CWT) is proposed. CWT is applied to the response acceleration of a structure subjected to earthquake load to decompose the response acceleration corresponding to each scale, then the normalized energy value for each scale is calculated. The difference between the normalized energy curvature (NEC) in each node before and after damage indicates a damaged element, which makes it possible to assess the soundness of structural elements. As damage becomes more severe the difference in normalized energy curvature becomes larger. The NEC calculated from the signal corresponding to high scale in CWT analysis is found to be a good index that shows the location and severity of damage.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.311-314
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• 2011

최근 콘크리트 구조물의 안전성강화를 위해 탄소섬유 강화 플라스틱(CFRP) 보강 공법이 널리 사용되고 있지만 잘 알려진 바와 같이 CFRP 보강재와 콘크리트 표면사이의 부착면 탈락은 보강재 자체의 손상보다 발생할 확률이 높고 이러한 부착면 탈락은 보강의 효과를 무의미하게 만들기 때문에 구조물 전체의 파괴로 직결될 수 있다. 이에 본 연구에서는 CFRP 부착면 탈락손상을 실시간으로 검색하기 위해 압전센서를 사용하는 구조물 건전성 평가 기술을 적용하였다. 이의 검증을 위해 CFRP로 보강된 콘크리트 보를 제작하였고 3단계로 증가하는 부착면 탈락 손상을 발생시켰다. 손상 증가 단계마다 CFRP 표면에 배열된 압전센서로부터 임피던스와 유도초음파 신호를 계측하였고 손상에 따른 신호변화를 정량화하기 위해 손상지수인 RMSD를 계산하였다. 더 구체적인 부착면 탈락 손상위치 탐색을 위해서 두 가지 계측 기법으로부터 구해진 RMSD 값를 중첩시키는 Superposed RMSD 가 제안되었다. 구해진 Superposed RMSD 값을 사용하여 커브 피팅이 수행되었고 도출된 커브의 최고값에 해당하는 위치값을 찾아 실제 손상위치와 비교함으로써 제안된 기법의 가능성을 검증해 보았다.

• Radiation Oncology Journal
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• v.18 no.4
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• pp.277-282
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• 2000

Purpose : Though It has been known that the to tolerance of the liver to external beam irradiation depends on the irradiated volume and dose, few data exist which Quantify this dependence. However, recently, with the development of three dimensional (3-D) treatment planning, have the tools to Quantify the relationships between dose, volume, and normal tissue complications become available. The objective of this study is to investigate the relationships between normal tissue complication probabili쇼 (WCP) and the risk of radiation hepatitis for patients who received variant dose partial liver irradiation. Materials and Methods : From March 1992 to December 1994, 10 patients with hepatoma and 10 patients with bile duct cancer were included in this study. Eighteen patients had normal hepatic function, but 2 patients (prothrombin time 73$\%$, 68$\%$) had mild liver cirrhosis before irradiation. Radiation therapy was delivered with 10MV linear accelerator, 180$\~$200 cGy fraction per day. The total dose ranged from 3,960 cGy to 6,000 cGy (median dose 5,040 cGy). The normal tissue complication probability was calculated by using Lyman's model. Radiation hepatitis was defined as the development of anicteric elevation of alkaline phosphatase of at least two fold and non-malignant ascites in the absence of documented progressive. Results: The calculated NTCP ranged from 0.001 to 0.840 (median 0.05). Three of the 20 patients developed radiation hepatitis. The NTCP of the patients with radiation hepatitis were 0.390, 0.528, 0.844(median : 0.58$\pm$0.23), but that of the patients without radiation hepatitis ranged fro 0.001 to 0.308 (median .0.09$\pm$0.09). When the NTCP was calculated by using the volume factor of 0.32, a radiation hepatitis was observed only in patients with the NTCP value more than 0.39. By contrast, clinical results of evolving radiation hepatitis were not well correlated with NTCP value calculated when the volume factor of 0.69 was applied. On the basis of these observations, the volume factor of 0.32 was more correlated to predict a radiation hepatitis. Conclusion : The risk of radiation hepatitis was increased above the cut-off value. Therefore the NTCP seems to be used for predicting the radiation hepatitis.

• Journal of Korean Society of Steel Construction
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• v.25 no.4
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• pp.441-449
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• 2013

Damaged structures change the value of natural properties. The purpose of this study is to detect damage using the difference of natural properties between the healthy state and the damaged state. Anti-optimization method is used to find the conditions that maximize the difference in characteristics between the two contrasting models. In this paper, a algorithm for finding the loading conditions which can maximize the difference of strain energy between the healthy state and the damaged state of truss structures is developed. Numerical examples show that the proposed method is accurate and efficient for truss structures.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.287-292
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• 2012

In this study, Multi-Channel Magnetic Flux Leakage(MFL) sensor - based inspection system was applied to monitor the condition of cables. This inspection system measures magnetic flux to detect the local faults(LF) of steel cable. To verify the feasibility of the proposed damage detection technique, an 8-channel MFL sensor head prototype was designed and fabricated. A steel cable bunch specimen with several types of damage was fabricated and scanned by the MFL sensor head to measure the magnetic flux density of the specimen. To interpret the condition of the steel cable, magnetic flux signals were used to determine the locations of the flaws and the level of damage. Measured signals from the damaged specimen were compared with thresholds set for objective decision making. In addition, the magnetic flux density values measured from every channel were summed to focus on the detection of axial location. And, sum of flux density were displayed with threshold. Finally, the results were compared with information on actual inflicted damages to confirm the accuracy and effectiveness of the proposed cable monitoring method.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.805-812
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• 2002

The number of old concrete structure which needs to be strengthened has been increased. The repair and strengthening methods have to be determined based on the current status of the structure. Consequently the estimation method for the damage status of the structure has been desperately needed, but no studies have been tried to use the crack and deflection characteristics to estimate the damage status. In this study, the crack characteristics depending on load level were measured and analysed. The crack characteristics observed from 11 samples were compared with damage status, and load level, The crack characteristics examined in this study include crack number, crack length, crack range, crack interval, maximum crack length, crack area, and average crack length. The deflections were normalized based on yield deflection, and the relationship between the relative deflection and the standardized crack characteristics were compared. Among the crack characteristics, crack interval, crack area, crack range, and maximum crack length, have been showed a close relationship to the relative deflection. Therefore, if such crack characteristics are evaluated, the maximum load applied to the structure is believed to be estimated. if additional parameters such as size of specimen, strength of concrete and steel, and steel ratio are studied, the damage status of structure can be estimated more accurately.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.11
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• pp.1315-1321
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• 2013

This study presents a prognostic technique for the damage state of a ball bearing. A stochastic bearing fatigue defect-propagation model is applied to estimate the damage progression rate. The damage state and the time to failure are computed by using RMS data from noisy acceleration signals. The parameters of the stochastic defect-propagation model are identified by conducting a series of run-to-failure tests for ball bearings. A regularized particle filter is applied to predict the damage progression rate and update the degradation state based on the acceleration RMS data. The future damage state is predicted based on the most recently measured data and the previously predicted damage state. The developed method was validated by comparing the prognostic results and the test data.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.1
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• pp.127-136
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• 2002

This papers presents a practical damage detection algorithm based on damage index method that accurately assesses both the location and severity of the localized detriment in a bridge structure using only limited mode shapes. In the algorithm, the ratio of the modal vector sensitivity of an undamaged structure to that of a damaged structure is used as an indicator of damage. However, a difficulty arises when the damaged element is located at a node of mode where the amplitude of medal vector is close to zero, leading the singularity of the ratio (i.e., division-by-zero). This singularity problem is overcome by introducing a parameter denoted a sensitivity filter, a function of mode shape of the structure, in modal vector sensitivity. Using this concept, an improvement can be considerably achieved in the estimation of both degree of severity and location of damage. To verify the proposed algorithm, its numerical implementations are conducted for a simply supported beam and a 2-span continuous beam.

• Proceedings of the Korean Vacuum Society Conference
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• 1998.02a
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• pp.179-179
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• 1998

실리콘 집적회로 제조시 sub-micron 의 contact 형성 공정은 질연막 형성 후 이의 식각 및 세정, c contact 실리사이드, 획산방지막, 배선 금속층의 형성 과정올 거치게 된다. 본 연구팀에서는 C.F야f2 헬리 콘 플라즈마훌 이용한 고선택비 contact 산화막 식각공정시 형성된 잔류막충과 오염 손상올 관찰하고 산소 플라즈마 처리와 후속 열처리에 따른 이들의 제거 정도를 관찰하여 이에 대한 결과를 발표하였다. 본 연구메서는 식각 및 후처리에 따라 잔류하는 잔류막과 손상층이 후속 공정인 contact 실리사이드 형 섬에 미치는 영향올 관찰하였다. C C.F바f2 웰리콘 풀라즈마률 이용한 식각시 공정 변수로는 수소가스 첨가, bias voltage 와 과식각 시간 의 효과를 관찰하였으며 다른 조건은 일정하게 하였다 .. Contact 실리사이드로는 Ti, Co-싫리사이드를 선 택하였으며 Piranha cleaning, 산소 플라즈마 처리, 산소 풀라즈마+600 'C annealing으로 각각 후처리된 시 편을 후처리하지 않은 시펀돌과 함께 실리사이드 형성용‘시펀으로 이용하였다 각각 일정 조건에서 동 일 두께의 실리사이드훌 형성시킨 후 4-point probe룰 이용하여 면저황올 측정하였다 후처리하지 않은 시편의 경무 실리사이드 형성은 아주 시펀의 일부분에서만 형성되었으며 후속 세정 및 얼처리훌 황에 따라 실리사이드의 면저항은 감소하여 식각 과정을 거치지 않은 깨끗한 실리콘 웨이퍼위에 실리사이드 를 형성시킨 값(control 값)에 접근하였다. 실리사이드의 면저항값은 식각시 노훌된 실리콘 표면 위에 형 성된 손상충보다는 잔류막에 큰 영향을 받았으며 수소 가스가 첨가된 식각 가스로 식각한 시편으로 형 성한 실리사이드의 면저항값이 손상이 상대적으로 적은 것으로 관찰된 수소훌 첨가하지 않은 식각 가 스로 식각한 시펀 위에 형성된 실리사이드의 면저황에 비해 낮은 값을 나타내었다. 실리사이드의 전기적 륙성에 미치는 손상층의 영향올 좀더 면밀히 관찰하고자 bare 실리콘 wafer 에 잔류막이 거의 없이 손상층을 유발시키는 식각 조건들 (100% HBr, 100%H2, 100%Ar, Cl싸fz)에 대하여 실 리콘 식각을 수행한 후 Co-실리사이드률 형성하여 이의 면저황을 측정한 걸과 100% Ar 가스로 식각된 시편을 이용하여 형성한 실리사이드의 면저항은 control 에 기까운 면저항값올 지니고 따라서 손상층이 실리사이드 형섬메 미치는 영향은 크지 않음을 알 수 있었다. 이상의 연구 결과훌 통해 손상층이 실리사이드의 형성이나 전기적 톡섬에 미치는 영황은 잔류막층 에 의한 영향보다 적다는 것을 알 수 았으며 잔류막층의 두께보다는 성분이나 걸합상태, 특히 식각 및 후처리 후 잔류하는 탄소 싱분과 C-Si 결함에 큰 영향올 받는 것올 알 수 있었다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06c
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• pp.185-188
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• 1998

실제의 음성 인식 및 음성 통신 등의 음성 처리 시스템에서는 음성 신호를 손상시키는 배경 잡음 신호의 존재로 그 성능이 많이 저하된다. 특히 차량 내와 같은 잡음이 극심한 상황에서는 전처리 부분에서 이러한 잡음을 제거시켜 주어야한다. 본 연구는 자동차 내의 배경 잡음에 의해 손상된 음성에서 배경 잡음을 주파수 차감에 의하여 제거시킨다. 특히 음성 정보의 손실이 적은 잡음 추정 방법으로 가중치를 이용하여 잡음을 추정하는 가중치 주파수 차감법을 이용하였다. 이러한 가중치 주파수 차감법 사용의 전제 조건은 잡음의 변화가 완만한 경우에 적당하다. 그러나 실제적인 상황에서 배경잡음신호의 변화가 큰 경우가 존재한다. 이러한 이유에서 본 연구는 잡은 추정시 잡음 추정값을 이용하여 추정 잡음 경계값을 적응적으로 변화하는 차감법을 제안한다. 이러한 방법은 추정된 잡음 신호의 변화율을 이용하여 경계값을 상황에 따라 적응적으로 변화시키는 방법이다. 모의 실험에 의하여 고정적인 경계값을 갖는 가중치 주파수 차감법에 비해 제안한 적응적 경계값을 갖는 가중치 주파수 차감법의 출력 SNR이 증가함을 확인하였고, 음성 인식 시스템에 정용한 인식 실험에서도 성능이 향상됨을 확인하였다.