• Smart Structures and Systems
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• 제25권1호
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• pp.65-80
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• 2020

In order to protect a structure over its full life cycle, a novel tuned mass damper (TMD), the so-called semi-active eddy current pendulum tuned mass damper (SAEC-PTMD), which can retune its frequency and damping ratio in real-time, is proposed in this study. The structural instantaneous frequency is identified through a Hilbert-Huang transformation (HHT), and the SAEC-PTMD pendulum is adjusted through an HHT-based control algorithm. The eddy current damping parameters are discussed, and the relationship between effective damping coefficients and air gaps is fitted through a polynomial function. The semi-active eddy current damping can be adjusted in real-time by adjusting the air gap based on the linear-quadratic-Gaussian (LQG)-based control algorithm. To verify the vibration control effect of the SAEC-PTMD, an idealized linear primary structure equipped with an SAEC-PTMD excited by harmonic excitations and near-fault pulse-like earthquake excitations is proposed as one of the two case studies. Under strong earthquakes, structures may go into the nonlinear state, while the Bouc-Wen model has a wild application in simulating the hysteretic characteristic. Therefore, in the other case study, a nonlinear primary structure based on the Bouc-Wen model is proposed. An optimal passive TMD is used for comparison and the detuning effect, which results from the cumulative damage to primary structures, is considered. The maximum and root-mean-square (RMS) values of structural acceleration and displacement time history response, structural acceleration, and displacement response spectra are used as evaluation indices. Power analyses for one earthquake excitation are presented as an example to further study the energy dissipation effect of an SAECPTMD. The results indicate that an SAEC-PTMD performs better than an optimized passive TMD, both before and after damage occurs to the primary structure.

• 한국음향학회지
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• 제23권3호
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• pp.206-213
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• 2004

본 논문에서는 수중에서 빠른 속도로 기동하는 표적 환경에 적합한 조향각 오차 보정기법을 제안한다. 기존의 협대역 조향각 오차 보정기법에서는 다수의 시간 데이터 단편을 이용한 반면, 제안한 기법은 하나의 시간 데이터 단편에서 다수의 주파수 성분들로부터 모드 공분산행렬을 구성하고, 이를 이용하여 얻어진 광대역 MVDR (Minimum Variance Distortionless Response) 빔출력을 최대화시키는 조향각 오차를 추정함으로써 짧은 관측시간 내에 정확한 표적의 방위각을 추정할 수 있다. 모의신호와 실제 해상 실험 데이터를 이용하여 제안한 기법의 성능을 기존의 기법과 비교, 분석하였다.

• 미술이론과 현장
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• 제3호
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• pp.155-172
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• 2005

Kim Whan-ki is an unusual instance in Korean modern artists, who payed attention to emotional and expressive effects of colors. The color of Whan-ki's paintings have been recognized as linked with 'blue' in spite that he used colors within the category of 'Colors of Five Directions(五方色)', which are traditional oriental colors composed of red, lue, yellow, white, green and black. Kim Whan-ki unearthed upon similarity of Five Directions Colors to the three(five) primary colors which modern abstract painter like Mondrian layed down. Whan-ki switched the five directions colors to modern ones. Kim Whan-ki's dot painting in which pure and watery color is sucked in ground is modernistic adaptation from ink painting. He packs a dot with sky and earth, moon and stars, forest and tree, birds and flowers, friends at his hometown, wind, sound and so on. Putting tens of thousands of these shapes and colors into a dot is modernistic version from ink painting. In that point there is a possibility to say that 'dark blue' of the dot painting is 'Hyun-saec(玄色)'. Eventually we can make sure that Kim Whan-ki's view of Art originated in oriental philosophy and beauty.