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서동만,김환우,Suh, Dong-Man,Kim, Whan-Woo 한국음향학회 1997 韓國音響學會誌 Vol.16 No.1
스터드 볼트에 존재하는 작은 결함은 초기에 발견되지 않으면 작은 결함이라도 결함 크기가 급진전되어 전체적인 파손에 이른다. 그러나 이러한 나삿니의 응력부식결함이나 부식 찌꺼기와 같은 것은 가동중검사에서 일반적인 초음파 검사로써는 검출이 어렵다. 본 연구에서는 디지탈신호처리에 의한 결함 검출 방법을 보인다. 초음파가 나삿니에 평행하게 입사된다면 연속적인 나삿니로부터 발생되는 신호는 거의 일정한 시간 간격을 가지고 있다. 이러한 연속적인 나삿니신호는 예측 간격에 의해 처음 신호를 기초로 다음 신호를 추측할 수 있는 데 여기서 최적 연산자를 사용해 예측되는 연속적인 나삿니신호를 제거하여 결함 신호를 검출할 수 있다. If small cracks in stud bolts are not detected early enough, they grow rapidly and cause total fracture. It is difficult to detect, prior to failure, flaws such as stress-corrosion cracking in thread roots and corrosion wastages using conventional ultrasonic testing methods during inservice inspection. This study show a method of detecting a small crack by digital signal processing. When ultrasonic beams travels into threads in parallel way, the echoes from each successive threads has almost the same intervals between any two signals. We can estimate the next thread signal based on previous thread signal by the predictive distance. The optimized operator is used to remove the predicted successive thread signals so that a small crack signal can be detected.
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초음파의 시그날콘디쇼닝에 의한 STUD[BOLT] 나사산의 미세결함 검출
서동만,문홍진,최규훈,김종교,Suh, Dong-Man,Moon, Hong-Chin,Choi, Kyu-Hoon,Kim, Chong-Kyo 한국음향학회 1990 韓國音響學會誌 Vol.9 No.3
나사산에 존재하는 Stress-Corrosion Cracking이나 Corrosion Wastage(Loss of Bolt Diameter)는 검출하기가 어렵다. 결함의 크기가 1-2mm 정도에 이르면 성장이 급진전되어 파손에 이르는 경우가 많은데 본 논문에서는 Signal-Conditioning 기법에 통한 나사산신호의 시간차를 이용해서 매우 작은 결함도 쉽게 찾을 수 있는 방법에 관해 연구되었다. It is difficult to detect such flaws as stress-corrosion cracking or corrossion wastage(loss of bolt diameter) in the threads. In many cases the critical size of a flaw is very small(1-2mm order). This paper describes how it is possible to discriminate small flaw indications in threads using the time difference of thread signals [TDTS] by a signal-conditioning technique.
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북한연구에 대한 반성과 과제 : 1990년대 연구성과와 문제점
서동만 경남대학교 북한대학원 1998 현대북한연구 Vol.1 No.1
<Abstract>The IMF crisis and the bursting of the economic bubble has implications for every aspect of Korean society. We are now reflecting on our mistakes and self-examination in the field of North Korean studies is more important than in any other field. North Korean studies have not only been influenced by the post-Cold War situation, ut by the on-going confrontation between North and South Korea. Even though the ideological situation has been alleviated with the end of the Cold War, limitations in the classification and use of primary materials continue. The barriers to the use of primary materials must be eliminated as soon as possible-an anthology of primary materials on all aspects of politics, economy, military, society, culture, arts and science urgently needs to be produced.There are many journals published by government and corporate institutions, but there are few politically neutral academic journals. By supplying objective and exact information on North Korea, such journals could contribute to the advancement of North Korean studies. Scholars on North Korean studies should take a responsibility for improving the quality of these journals.Official documents are the most important materials in studying North Korea and scholars should be accustomed to using them, so teaching in the use and interpretation these documents must be given greater weight in undergraduate and graduate course. This requires the construction of "a North Korean studies culture." Theoretical works on North Korea should be actively prompted and levels of theorizing must be differentiated as follows : the level of the system or social formation, the regime, and power structure.Another problem in North Korean studies is the shortage of historical and the comparative studies. Owing to this deficiency, the images of both the early and recent periods of North Korea have been mixed indiscriminately. Moreover, in order to address the problems of universality and specificity, it is essential to make comparisons with other socialist countries. As a result of the Cold War, general studies on socialist countries were not accumulated in South Korea so comparative studies on North Korea were rare before the time of Perestroika.As studies on the politics and economy of North Korea are too often compared with other themes in humanitarian fields, studies on society, culture and the arts must be developed further. There are many broad or general studies but few on specific issues. Even in the field of politics, themes are not balanced.In accordance with the progress in relations between North and South Korea, North Korean studies in South Korea are starting to accomodate North Korea's self-understanding. From now on North Korean studies in South Korea will have an influence on North Korea's understanding of itself.
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성제중,서동만,신용훈,엄태건,서동섭 한국비파괴검사학회 2003 학술대회 논문집 Vol.- No.1
Ferromagnetic material like the steel tubes can easily distort eddy current testing signal due to increased magnetic permeability for defects. Because magnetic field of the test probe is affected in an inconsistent way when the material under the testing has permeability. This permeability effect can be reduced by magnetic saturation. In this paper eddy current testing system was developed to detect flaws on the steel tubes. Magnetic saturation probe with helmholtz coil was designed for saturation and inspection of the steel tubes. When using the designed test probe, the relationship between flaw signals and noises was obviously discriminated. Additionally, a high pass filter was included in the eddy current board to minimize noises due to DC magnetic field.
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