• Smart Structures and Systems
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• v.25 no.1
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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.

• The Journal of the Acoustical Society of Korea
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• v.23 no.3
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• pp.206-213
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• 2004

This paper presents a steering angle error compensation (SAEC) algorithm that is appropriate for rapidly moving sources. The Proposed algorithm utilizes a modal covariance matrix from multiple frequency components instead of the multiple snapshots in a narrowband SAEC, and estimates the steering error by maximizing the wideband WVDR output power using a first-order Taylor series approximation of the modal steering vector in terms of the steering error. As such, the steering error can be compensated with short observation times. Several simulations using artificial and sea trial data are used to demonstrate the Performance of the proposed algorithm.

• The Journal of Art Theory & Practice
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• no.3
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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.