• Proceedings of the KIEE Conference
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• 1995.07b
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• pp.817-819
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• 1995

Applied by periodic Stimulating Currents in Bonhoeffer-Van der Pol(BVP) model, chaotic and periodic phenomena occured at specific conditions. The conditions of the chaotic motion in BVP comprised 0.7182< $A_{1}$ <0.792 and 1.09< $A_{1}$ <1.302 proved by the analysis of phase plane, bifurcation diagram, and lyapunov exponent. To control the chaotic motion, two methods were suggested by the first used the amplitude parameter $A_{1}$,$A_{1}={\varepsilon}((x-x_{s})-(y-y_{s}))$ and the second used the temperature parameter c, c=c$(1+ {\eta}cos{\Omega}t)$ which the values of $\eta$, ${\Omega}$ varied respectlvly, and $x_{s}$, $y_{s}$ are the periodic signal. As a result of simulating these methods, the chaotic phenomena was controlled with the periodic motion of periodisity. The feasibilities of the chaotic and the periodic phenomena were analysed by phase plane and lyapunov exponent.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.6
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• pp.457-464
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• 2021

To analyze the buffet phenomenon that causes serious vibration loads on a satellite launch vehicle, the pressure fluctuations on a hammerhead launch vehicle at transonic speeds are predicted by coupling CFD analysis and semi-empirical methods. From the RANS simulation, shock oscillation region, separation region, and separation reattachment region are identified, and the boundary layer thickness, the displacement thickness, and flow properties at boundary layer edge are calculated. The pressure fluctuations and power spectra on the hammerhead fairing are predicted by coupling RANS results and semi-empirical methods considering spatial distribution, and compared with the experimental data.

• Journal of Digital Convergence
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• v.13 no.9
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• pp.209-218
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• 2015

Computer simulation plays an important role for a theoretical foundation in convergence technology and the interpolation is to know the unknown values from known values on grid points. Therefore it is an important problem to select an interpolation method for digital simulation. The aim of this paper is to compare analysis of interpolation methods for digital simulation. we test six different interpolation methods namely: Quartic-Lagrangian, Cubic Spline, Fourier, Hermit, PWENO and SL-WENO. Through digital simulation of a linear advection equation, we analyse pros and cons for each method. In order to compare performance, we introduce accuracy computing and Error functions. The accuracy computing is used well-known $L^1-norm$ and the Error functions are dispersion function, dissipation function and total error function. High-order methods well apply to computer simulation, unfortunately, side-effects (Oscillation) happen.

• Journal of Korean Medicine Rehabilitation
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• v.20 no.4
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• pp.147-157
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• 2010

Objectives : The study is performed to investigate the influence of psychological stress on neck muscles tone and heart rate variability(HRV). Methods : This study was carried out with the data from stress response index score(SRI), surface electromyography(sEMG) and HRV. First subjects were divided into two group according to the SRI points. Subjects in group A had points of SRI in which lower than 30 points. Subjects in group B had points of SRI in which higher than 30 points. Then we investigated how to difference of the index of sEMG and HRV according to each groups. Results : In this study, the muscle contraction of both upper trapezius muscle in stress group were higher than non-stress group significantly. Complexity, root mean square of successive differences of R-R intervals(RMSSD), standard deviation difference between adjacent normal to normal intervals(SDSD), high frequency oscillation power(Ln(HF)), normalized HF(Norm HF) in stress group were lower than non-stress group significantly and normalized LF(Norm LF) was higher. Conclusions : This results show that the stress was associated with neck muscle condition and autonomic nervous system.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.16 no.4
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• pp.281-292
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• 2016

The proposed scheme is based on the modified perturb and observe (P&O) algorithm combined with the sliding mode technique. A modified P&O algorithm based sliding mode controller is developed to study the effects of partial shade, temperature, and insolation on the performance of maximum power point tracking (MPPT) used in photovoltaic (PV) systems. Under partially shaded conditions and temperature, the energy conversion efficiency of a PV array is very low, leading to significant power losses. Consequently, increasing efficiency by means of MPPT is particularly important. Conventional techniques are easy to implement but produce oscillations at MPP. The proposed method is applied to a model to simulate the performance of the PV system for solar energy usage, which is compared to the conventional methods under non-uniform insolation improving the PV system utilization efficiency and allowing optimization of the system performance. The modified perturb and observe sliding mode controller successfully overcomes the issues presented by non-uniform conditions and tracks the global MPP. Compared to MPPT techniques, the proposed technique is more efficient; it produces less oscillation at MPP in the steady state, and provides more precise tracking.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.530-535
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• 2001

Variations of temperature field in a Hele-Shaw convection cell (HSC) were measured using a holographic interferometry with varying Rayleigh number. Experimental results show a steady flow pattern at low Rayleigh numbers and a time-dependent periodic flow at high Rayleigh numbers. Especially, the period of oscillation at $Ra = 6.35{\times}10^6$ was 62 seconds. Two different measurement methods of holographic interferometry, double-exposure method and real-time method, were employed to measure the temperature field variations of HSC convective flow. In the double-exposure method, unwanted waves can be eliminated and reconstruction images are clear, but transient flow structure cannot be observed clearly. On the other hand, transient flow can be observed and reconstructed well using the real-time method. However, the fringe patterns reconstructed by the real-time method contain more noise, compared with the double-exposure method. The two holographic interferometer techniques employed complementary in this study were proved to be useful for analyzing the temperature field variations of unsteady thermal fluid flows.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.7
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• pp.345-351
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• 2005

An out-of-step condition results from the loss of the synchronism of the generators. A disturbance in a power system causes the generator angle to oscillate. When there is a severe disturbance such as a heavy current fault loss of major generation or loss of a large block of load, the oscillation can be severe and even increase largely and finally the out-of-step condition may un. During the power swing and out-of-step conditions, the apparent impedance at a relay location changes, and the power flow also changes as the angle difference is varied. This paper presents a method to analyze the trajectory of complex power during a power swing and out-of-step condition. The trajectory of the complex power is analyzed when a power swings and a fault occurs. Moreover, the complex power is analyzed when the ratios between the voltages at both sides and the line impedances are changed. These methods are verified through simulation using the ATP/EMTP MODELS.

• Annals of Clinical Neurophysiology
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• v.2 no.2
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• pp.114-118
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• 2000

Purpose : The pathophysiology of essential tremor(ET) remains unknown. PET studies of ET showed some conflicting data. One study reported significant glucose hypermetabolism of the medulla and thalami, but other studies reported abnormal bilateral overactivity of cerebellar and red nuclear connections. The previous experimental studies suggested that each PET finding reflects a part of neural circuit which is responsible for ET. So it can be imagined that olivocerebellar oscillation may be transmitted by the way of cerebellar projections to the thalamus in ET. It has been reported that the cerebellar dentate nucleus neurons are involved in the generation and/or guidance of movement based on visual cues. The purpose of this study is to clarify the role of dentato-thalamic tract in ET. Methods : Tremor amplitudes were recorded as each patient perform two kinds of task, one involving sensory-guided movement and the other involving memory-guided movement. Each patient was asked to move his/her index finger following a smoothly moving target. He/She also was asked to perform the same movements with his/her eyes closed ET. Results : The results showed that average amplitudes of tremor were significantly higer during visually guided task than during memory guided task in ET patients. Conclusions : Our results led us to conclude that dentato-thalamic tract might be related to the control of tremor in ET.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.4
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• pp.72-78
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• 2010

Textile machinery affects various industry, such as sport leisure industry, metal and chemistry material, electric electron, mechanical energy, packing and printing industry. In case of design of textile machine, the very important fact is absorbing the minute vibration induced by spinning thread and insert which is the part of spindle plays a role of reduction of impact caused by oscillation of thread bobbin. Therefore, Optimal design was executed by design of experiments and kriging optimal design methods to prevent fracture of spindle insert under the fatigue condition and deduced the best value of design parameter to improve the stability of the products. The highest sensitivity is showed at the design parameter A and D. As the spiral number of insert is increase, tension force applied its edge is distributed at whole model and the stress concentration is reduced.

• The KIPS Transactions:PartC
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• v.12C no.4 s.100
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• pp.519-524
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• 2005

Due to various types of errors added to dynamic weight measurement data, proper methods to reduce measurement errors are required to produce reliable weights. It is very difficult to reduce the measurement error due to excessive oscillation of the system. To cope with parasitic types of errors in real systems, information provided by the photo sensors are utilized and combined in such a way to reduce the measurement errors of load cells. In addition to four channels of load cells from a model trailer, photo sensors are used to obtain the information to compensate the error induced from vertical movement of the vehicle due to the variation of ground level. A model trailer system is run to verify the effectiveness of the proposed method to reduce noise of dynamic weight measurements.