• Journal of Korea Entertainment Industry Association
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• v.13 no.6
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• pp.25-32
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• 2019

According to a recent KOFICE survey, K-Pop's popularity factor is divided into visual and auditory elements, and the importance of hearing elements is found. Among the various types of singers, idol groups led K-Pop and Black Pink, which topped the list of favorite K-Pop singers in 2018, was selected as the study target. In addition, Twice's music, which is similar to Black Pink's period of activity, has been set as a comparative research scope. The common features in the music of the two groups are the chorus and rhythm structure implemented around melody and Harmony rhythm, and the frequency of use of Major and Minor is greatly different. Through this method and modal interchange, K-Pop from 2016 to 2018 is analyzed. Research shows that first, more than one mode is used as a main melody. When more than one mode is used, different lines in the same line will vary depending on the functional form of the song. Second, the rhythm of the melody expressed with vocals and instruments is repeated based on a two-bar pattern. Finally, when using less chord and slowly expressing the igneous rhythms, there is a way to omit or modify the third notes that determine chord characteristics. Through this study, we can see that the usage patterns of the mode and modal interchange are divided according to the major and minor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.9
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• pp.933-941
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• 2014

This paper provides a comparison between the Krylov subspace method (KSM) and modal truncation method (MTM), which are typical projection-based model order reduction methods. The frequency responses are compared to determine the numerical accuracies and efficiencies. In order to compare the numerical accuracies of the KSM and MTM, the frequency responses and relative errors according to the order of the reduced model and frequency of interest are studied. Subsequently, a numerical examination shows whether a reduced order can be determined automatically with the help of an error convergence indicator. As for the numerical efficiency, the computation time needed to generate the projection matrix and the solution time to perform a frequency response analysis are compared according to the reduced order. A finite element model for a car suspension is considered as an application example of the numerical comparison.

• Smart Structures and Systems
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• v.22 no.1
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• pp.41-55
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• 2018

Damping ratio and frequency have influence on dynamic serviceability or instability such as vortex-induced vibration and displacement amplification due to earthquake and critical flutter velocity, and it is thus important to make determination of damping ratio and frequency accurate. As bridges are getting longer, small scale model test considering similitude law must be conducted to evaluate damping ratio and frequency. Analysis conditions modified by similitude law are applied to experimental test considering different scale ratios. Generally, Nyquist frequency condition based on natural frequency modified by similitude law has been used to determine sampling rate for different scale ratios, and total time length has been determined by users arbitrarily or by considering similitude law with respect to time for different scale ratios. However, Nyquist frequency condition is not suitable for multimode system with noisy signals. In addition, there is no specified criteria for determination of total time length. Those analysis conditions severely affect accuracy of damping ratio. The focus of this study is made on the determination of minimum analysis conditions for different scale ratios. Influence of signal to noise ratio is studied according to the level of noise level. Free initial value problem is proposed to resolve the condition that is difficult to know original initial value for free vibration. Ambient and free vibration tests were used to analyze the dynamic properties of a system using data collected from tests with a two degree-of-freedom section model and performed on full bridge 3D models of cable stayed bridges. The free decay is estimated with the stochastic subspace identification method that uses displacement data to measure damping ratios under noisy conditions, and the iterative least squares method that adopts low pass filtering and fourth order central differencing. Reasonable results were yielded in numerical and experimental tests.

• Structural Engineering and Mechanics
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• v.72 no.6
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• pp.747-762
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• 2019

Based on the ball-screw mechanism, a tuned viscous mass damper (TVMD) has been proposed, which has functions of amplifying physical mass of the system and frequency tuning. Considering the sensitivity of a single TVMD's effectiveness to frequency mistuning like that of the conventional tuned mass damper (TMD) and according to the concept of the conventional multiple tuned mass damper (MTMD), in the present paper, multiple tuned mass viscous dampers (MTVMD) consisting of many tuned mass dampers (TVMD) with a uniform distribution of natural frequencies are considered for attenuating undesirable vibration of a structure. The MTVMD is manufactured by keeping the stiffness and damping constant and varying the mass associated with the lead of the ball-screw type inerter element in the damper. The structure is represented by its mode-generalized system in a specific vibration mode controlled using the mode reduced-order method. Modal properties and fundamental characteristics of the MTVMD-structure system are investigated analytically with the parameters, i.e., the frequency band, the average damping ratio, the tuning frequency ratio, the total number of TVMD and the total mass ratio. It is found that there exists an optimum set of the parameters that makes the frequency response curve of the structure flattened with smaller amplitudes in a wider input frequency range. The effectiveness and robustness of the MTVMD are also discussed in comparison with those of the usual single TVMD (STVMD) and the results shows that the MTVMD is more effective and robust with the same level of total mass.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.4
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• pp.299-307
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• 2011

The offshore plants such as FPSO are subjected to combination loading of environmental conditions (swell, wave, wind and current). Therefore the fatigue damage is occurred in the operation time because the units encounter the environmental phenomena and the structural configurations are complicated. This paper is a research for frequency domain fatigue analysis of wide-band random loading focused on accuracy of fatigue damage estimation regarding the proposed methods. We selected ideal bi-modal spectrum. And comparison between time-domain fatigue analysis and frequency-domain fatigue analyses are conducted through the fatigue damage ratio. Fatigue damage ratios according to Vanmarcke's bandwidth parameter are founded for wide-band. Considering safety, we recommend that Jiao-Moan and Tovo-Benasciutti methods are optimal way at the fatigue design for wide-band response. But, it is important that these methods based on frequency-domain unstably change the accuracy according to the material parameter of S-N curve. This study will be background and guidance for the new frequency-domain fatigue analysis development in the future.

• Journal of the Semiconductor & Display Technology
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• v.16 no.2
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• pp.32-38
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• 2017

This paper is about the analysis on the vibration characteristic of tooling units on the precision bed in high-speed automatic lathe for precision machining. An automatic lathe operating at about 25,000 RPM is a critical factor in the self-weight stress and deformation of the bed. Especially, the resonance frequency should be grasped in advance to prevent abnormal vibration that may occur during processing. If the wrong bed is used, the resonant frequency can have a fatal influence on the precision machining and increase the defective rate of precision machined parts such as semiconductor parts. In this paper, vibration characteristics were evaluated through static load and resonance frequency analysis of automatic lathe bed. As a result, the maximum stress was 0.14MPa, the maximum deformation amount was $17.9{\mu}m$, and the natural frequency was 364.72Hz. The resonance frequency was calculated as 718Hz, and the stability was confirmed by being in the range of 400Hz or more, which is the processing condition.

• Journal of the Semiconductor & Display Technology
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• v.17 no.1
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• pp.66-70
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• 2018

This paper is about the analysis on the vibration characteristic of tooling units on the precision bed in turning and hobbing automatic lathe for precision machining. An automatic lathe operating at about 12,000 RPM is a critical factor in the self-weight stress and deformation of the bed. Especially, the resonance frequency should be grasped in advance to prevent abnormal vibration that may occur during processing. If the wrong bed is used, the resonant frequency can have a fatal influence on the precision machining and increase the defective rate of precision machined parts such as semiconductor parts. In this paper, vibration characteristics were evaluated through static load and resonance frequency analysis of automatic lathe bed. As a result, the maximum stress was 14.52 MPa, the maximum deformation amount was $12.15{\mu}m$, and the natural frequency was 189.43 Hz. The resonance frequency was calculated as 500 Hz, and the stability was confirmed by being in the range of 200 Hz or more, which is the processing condition.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.4
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• pp.245-253
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• 2020

In this study, natural frequencies are compared using several pile-soil interaction (PSI) models to evaluate the effects of each model on resonance safety checks for a monopile type of wind turbine structure. Base spring, distributed spring, and three-dimensional brick-shell models represented the PSIs in the finite element model. To analyze the effects of the PSI models on a natural frequency, after a stiffness matrix calculation and Winkler-based beam model for base spring and distributed spring models were presented, respectively; natural frequencies from these models were investigated for monopiles with different geometries and soil properties. These results were compared with those from the brick-shell model. The results show that differences in the first natural frequency of the monopiles from each model are small when the small diameter of monopile penetrates hard soil and rock, while the distributed spring model can over-estimate the natural frequency for large monopiles installed in weak soil. Thus, an appropriate PSI model for natural frequency analyses should be adopted by considering soil conditions and structure scale.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.85-100
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• 2006

This paper proposes an optimal design method of linear viscous dampers for the seismic performance of two adjacent structures with different heights. Accordingly, connection method using diagonal bracing between two floors and connection method between two structures are considered, and the effectiveness of the latter method is confirmed through the comparison of the frequency response functions with respect to damping capacity. Moreover, optimal damping to minimize the response of the adjacent structures in the frequency domain is found. The sensitivity of natural frequency and modal damping according to the damper capacity at each floor is obtained for the optimally designed system. From the sensitivity analysis, the modal damping is evaluated to be very sensitive to the damper installed at higher floor. Therefore, sensitivity-based damping distribution method is proposed. Diagonal bracing connection method, uniform distribution method and sensitivity-based distribution method are compared to each other in terms of seismic performance. The comparative results demonstrate that the proposed method is an effective seismic design method for the adjacent structures.

• The Journal of the Acoustical Society of Korea
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• v.25 no.2
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• pp.49-55
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• 2006

Measurement of impact sound insulation of floor, by current Korean Standard KS F 2810-2. is to be made with peak levels over 4 point in a receiving room. But it is often the case that there is inconsistency in results at various receiving points in the receiving room. Such variations obviously have effects on the repeatability and reproducibility of measured data. The result shows that there are even 10 dB deviations in 63Hz octave band frequency range and relatively less variations are occurred in other low frequency ranges. Such variations seems to be coming from modal overlaps of the receiving room. According to current rating method of floor impact sound. KS F 2863-2, that may affect on the single number latins scheme. From the result of tests in this study, there are 2dB to 6dB differences in the sin91e number with the combination of measurement points. This means that the reduction of measurement variations from the microphone positions is needed for a better credibility of measurement results.