• Structural Engineering and Mechanics
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• v.12 no.3
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• pp.313-328
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• 2001

A multi-span bridge has the peak value of resultant girder moment or membrane stress at the interior support. In this paper, the spline finite strip method (FSM) is modified to obtain the more appropriate solution at the interior support where the peak values of solution exist. The modification has been achieved by expressing the shape function with non-periodic B-splines which have multiple knots at the boundary. The modified B-splines have the useful feature for interpolating the curve with sudden change in curvature. Moreover, the modified spline FSM is very efficient in analyzing multi-span box girder bridges, since a bridge can be modeled by an assembly of strips extended along the entire bridge length. Numerical examples of the bridge analysis have been performed to verify the efficiency and accuracy of the new spline FSM.

• Journal of the Korean Data and Information Science Society
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• v.23 no.4
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• pp.843-850
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• 2012

The inferences of data obtained from periodic inspection and type I censoring for the three step stress accelerated life test are studied in this paper. The failure rate function that a log-quadratic relation of stress and the tampered failure rate model are considered under the exponential distribution. The optimal stress change times which minimize the asymptotic variance of maximum likelihood estimators of parameters is determined and the maximum likelihood estimators of the model parameters are estimated. A numerical example will be given to illustrate the proposed inferential procedures.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.1083-1085
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• 1996

Controlling chaos is a new concept, which transform chaotic signal to fixed points, or low periodic orbits. In this paper we propose state feedback method in order to control chaotic signal in canonical Chua's circuit Canonical Chua's circuit is a simple electronic circuit consists of two linear resistors, a linear inductor, two linear capacitors, and only one nonlinear element so called Chua's diode. This nonlinear element supplies power to the circuit and drives the chaotic oscillations. Proposed control method is successful to control chaotic signal in canonical Chua's circuit Result shows that chaotic trajectory change rapidly its orbit to stable fixed points, 1 periodic orbit, or 2 periodic orbit when control signal applies.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.3
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• pp.771-783
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• 1995

A simplified model for the so-called ACRT(accelerated crucible rotation technique) Bridgman crystal growth was considered in order to investigate the principal effects of the periodic variation of angular velocity. Numerical solutions were obtained for Ro=0.5, Ra=4.236*10$_{6}$ and E=2.176*10$^{-3}$ . The effects of spin-up process combined with natural convection was investigated as a preliminary study. The spin-up time scale for the present problem was a little larger than that observed for homogeneous spin-up problems. Numerical results reveal that over a time scale of (H$^{2}$/.nu..omega.$_{f}$)$^{1}$2/ the forced convection due to the formation of Ekman layer predominates. When the state of rigid body rotation is attained, natural convection due to buoyancy emerges as the main driving force and them the steady-state is approached asymptotically. Based on our preliminary results with simple spin-up, several fundamental features associated with variation of rotation speed are successfully identified. When a periodic variation of angular velocity was imposed, the system response was also periodic. Due to effect of mixing, the heat transfer was enlarged. From the analysis of time-averaged Nusselt number along the bottom surface the effect of a periodic variation of angular velocity on the interface location could be indirectly identified.d.

• Ocean and Polar Research
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• v.34 no.3
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• pp.287-296
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• 2012

In the theory of source-driven abyssal circulation, the forcing is usually assumed to be steady source (deep-water formation). In many cases, however, the deep-water formation occurs instantaneously and it is not clear whether the theory can be applied well in this case. An attempt is made to resolve this problem by using a simple reduced gravity model. The model basin has large depth change compared for its size, like the East Sea, such that isobaths nearly coincide with geostrophic contours. Deep-water is formed every year impulsively and flows into the model basin through the boundary. It is found that the circulation driven by the impulsive source is generally the same as that driven by a steady source except that the former has a seasonal fluctuation associated with unsteadiness of forcing. The magnitudes of both the annual average and seasonal fluctuations increase with the rate of deep-water formation. The problem can be approximated to that of linear diffusion of momentum with boundary flux, which well demonstrates the essential feature of abyssal circulation spun-up by periodic impulsive source. Although the model greatly idealizes the real situation, it suggests that abyssal circulation can be driven by a periodic impulsive source in the East Sea.

• Wind and Structures
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• v.36 no.3
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• pp.215-220
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• 2023

We study the progressive full-scale wind tunnel tests on a high solidity vertical axis wind turbine (VAWT) for various tip speeds and pitch angles to understand the VAWT shaft system's dynamics using 0-1 Test for chaos. We identify that while varying rotor speed (tip speed) of the turbine, the system's dynamics change from periodic to chaotic through quasiperiodic and strange non-chaotic (SNA) states. The present study is the first experimental evidence for the existence of these states in the VAWT shaft system to the best of our knowledge. Using the asymptotic growth value Kc in 0-1 test, when the turbine operates at the low tip speeds and high pitch angles for low incoming wind speeds, the system behaves periodic (Kc ≈ 0). However, when the incoming wind speed increases further the system's dynamics shift from periodic to chaotic vibrations through quasi-periodic and SNA. This phenomenon is due to the dynamic stalling of blades which induces chaotic vibration in the VAWT shaft system. Further, the singular continuous spectrum method validates the presence of SNA and differentiates the SNA from chaotic vibrations.

• Journal of Korean Academy of Nursing
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• v.26 no.2
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• pp.271-280
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• 1996

The purpose of this study was to determine the effect of periodic walking during hindlimb suspension on the mass, relative weight, fiber type distribution and cross-sectional area of Type I and II fibers in the developing Type II plantaris muscle. To examine the effectiveness of periodic walking on mass and fiber size, the hindlimbs of young female Wistar rats were suspended (HS group) and half of these rats walked on a treadmill for 45 min／day(15 min every 4 hours) at 5 meters／min at a 15 degree grade(HS-W group) After seven days of hindlimb suspension, the plantaris muscle wet weight was 28.40％ significantly smaller（P＜0.005） and relative plantaris muscle weight was 26.97％ smaller compared with those of control rats（P＜0.05）. The plantaris muscle wet weight and the relative plantaris muscle weight increased by 46.60％ and 49.23％ respectively with periodic walking, moreover. the plantaris muscle wet weight and the relative plantaris muscle weight of the HS-W rats recovered to the level of the control rats. No change was observed in fiber type percentage of the developing plantaris muscle following one week of hindlimb suspension or periodic walking during hindlimb suspension. Type I and II fiber cross-sectional areas of the developing plantaris muscle were 42.51％ and 43. 68％ lower in the HS group than in the control group（p＜0.0001）, Type I and II fiber cross-sectional areas of the developing plantaris were 30.82％ and 45.97％ greater in the HS-W group than in the HS group（p＜0.0001）, whereas Type I and II fiber cross-sectional area of HS-W group were less than those of the control group（P＜0.0001） The results suggest that periodic walking can attenuate developing plantaris muscle atrophy induced by hindlimb suspension.

• Journal of the Korean Institute of Gas
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• v.23 no.3
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• pp.27-32
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• 2019

In this study, the vorticity distribution and the temperature distribution change around a circular cylinder were compared and analyzed with time for constant inlet velocity and periodic inlet velocity. Also, the frequency characteristics of the flow were analyzed by analyzing the time variation of lift and drag and their PSD(power spectral density). In the case of constant inlet velocity, the well known Karman vorticity distribution was shown, and vortices were alternately generated at the upper and lower sides of the circular cylinder. In case of periodic inlet velocity, it was observed that vortex occurred simultaneously in the upper and lower sides of the circular cylinder. In both cases, it was confirmed that the time dependent temperature distribution changes almost the same behavior as the vorticity distribution. For the constant inlet velocity, the vortex flow frequency is 31.15 Hz, and for the periodic inlet velocity, the vortex flow frequency is equal to the preriodic inlet velocity at 15.57 Hz. The mean surface Nusselt number was 99.6 for the constant inlet velocity and 110.7 for the periodic inlet velocity, which showed 11.1% increase in surface heat transfer.

• Korean Journal of Remote Sensing
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• v.38 no.5_1
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• pp.587-596
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• 2022

Sea levels are rising as a result of climate change, and low-lying areas along the coast are at risk of flooding. Therefore, we tried to investigate the relationship between sea level change and climate indices using satellite altimeter data (Topex/Poseidon, Jason-1/2/3) and southern oscillation index (SOI) and the Pacific decadal oscillation (PDO) data. If time domain data were converted to frequency domain, the original data can be analyzed in terms of the periodic components. Fourier transform and Wavelet transform are representative periodic analysis methods. Fourier transform can provide only the periodic signals, whereas wavelet transform can obtain both the periodic signals and their corresponding time location. The cross-wavelet transformation and the wavelet coherence are ideal for analyzing the common periods, correlation and phase difference for two time domain datasets. Our cross-wavelet transform analysis shows that two climate indices (SOI, PDO) and sea level height was a significant in 1-year period. PDO and sea level height were anti-phase. Also, our wavelet coherence analysis reveals when sea level height and climate indices were correlated in short (less than one year) and long periods, which did not appear in the cross wavelet transform. The two wavelet analyses provide the frequency domains of two different time domain datasets but also characterize the periodic components and relative phase difference. Therefore, our research results demonstrates that the wavelet analyses are useful to analyze the periodic component of climatic data and monitor the various oceanic phenomena that are difficult to find in time series analysis.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1257-1260
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• 1996

This paper describes a fully digitalized driver for BLDC motors and the driver is realized by a single chip microprocessor. The speed change can be done by using the signal obtained from the position detecting sensor and adjusting the pulse width at the input channel of power module. In order to verify the effectiveness, an repetitive control method is adopted in the speed control tracking a periodic reference change in the BLDC motor system. The experimental results are shown for the reference tracking accurately according to the design parameter variation in the repetitive controller design.