Papers by Author: Young H. Kim

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Authors: Young H. Kim, Sung Jin Song, Jin Soo Hur, Eui Lae Kim, Chang Jae Yim, Young Hwan Choi, Suk Chull Kang, Myung Ho Song
Abstract: Eddy current testing (ECT) is widely used in in-service inspection as well as pre-service inspection of the steam generator (SG) tubes in nuclear power plant of pressurized water reactor type. The interpretation of ECT signals, however, is truly a difficult task so that the reliability enhancement of signal interpretation is strongly desired. An enhanced interpretation tools for ECT signals have been developed by the novel combination of neural networks and finite element modeling for quantitative flaw characterization SG tubes. A database was constructed using synthetic ECT signals generated by the finite element models and principal component analysis (PCA) was adopted in order to optimize the feature set of ECT signals. The improvement in the performances by the features with PCA and the excellent performance for the experimental ECT signals demonstrate the high potential of the developed inversion tools for reliable interpretation of eddy current signals. To explore the possibility of applying the developed approach in practical inspection, we developed an automated system (laboratory prototype) that can acquire experimental ECT signals from SG tubes and carry out the quantitative flaw characterization in a real time fashion by applying the approach developed in the present work.
Authors: Young H. Kim, Sung Jin Song, Joon Soo Park, Jae Hee Kim, Heung Seop Eom
Abstract: Ultrasonic guided waves have been widely employed for the long range inspection of structures such as plates and pipes. In ultrasonic guided waves, however, there are numerous modes with different wave velocities, so that the generation and detection of the appropriate wave mode of the guided wave is one of key techniques in the application of guided waves. In the present work, mode tuning using an array transducer was investigated with hardware implements. For this purpose, 8-channel ultrasonic pulser and their controller which enables sequential activation of each channels with given time delay were developed. Transmitter tuning, group velocity measurements, reciver tuning, mode identification and long range transmission testing were carried out. As a result, the selective tuning of wave mode can be achieved by changing the time interval between adjacent elements of an array transducer.
Authors: Sung Jin Song, Hee Jun Jung, Joon Soo Park, Young H. Kim, Hak Joon Kim, Young Hwan Choi
Authors: Young H. Kim, Sung Jin Song, Jong Seok Heo, Hyang Beom Lee, Myung Ho Song
Authors: Sung Jin Song, Young H. Kim, Joon Soo Park, Hyung Ju Yu, Yong Moo Cheong, Hyun Kyu Jung, Dong Hun Lee
Abstract: In this paper, the dispersion curves of a bent cylindrical pipe are obtained by using the 3-dimensional finite element modeling and 2-dimenstional Fourier transform. The transient responses of the bent pipe are calculated by using a general-purpose finite element program, and the displacements are extracted at a series of sequential points as a function of spatial position and time, u(x,t). Then 2-dimentional FFT of u (x,t) offers U (k,ω), the relation between wave number and angular frequency so that the phase velocity and group velocity can be calculated. In addition, verification of the result is made by the mode identification using wavelet transform. The modes invoked by both methods agree very well.
Authors: Young H. Kim, Sung Jin Song, Eui Lae Kim, Chang Jae Yim, Ki Bok Kim, Young Hwan Choi
Authors: Sung Jin Song, Joon Soo Park, Young H. Kim, Hak Joon Kim, Hyun Jo Jeong
Authors: Young H. Kim, Sung Jin Song, Joon Soo Park, Shin Kim
Authors: Sung Jin Song, Hyeon Cho, Joon Soo Park, Young H. Kim, Soo Yong Lim, Nam Gyun Yun, Young Joo Park
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