• Journal of the Korean Society for Railway
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• v.10 no.3 s.40
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• pp.296-305
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• 2007

A numerical method for the analysis of train/slab-track interaction on the settled roadbed is developed based on the already developed analysis method of train/ballast-track interaction. The concrete slabs composed of the upper track concrete layer and the lower hydraulic bonded layer are modelled by a equivalent beam. The supporting stiffness of roadbed is evaluated with the modified boussinesq method suggested by Eisenmann. The track irregularity and the gap between slab and roadbed induced by settlement of roadbed are calculated by the effective method newly presented in this study. The validation of the developed method is investigated by a numerical example. The effects of train speed on train and slab track on the settled roadbed with sinusoidal shape of wave length 20m and amplitude 20mm are reviewed.

• Journal of the Korean Society for Railway
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• v.10 no.3 s.40
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• pp.355-364
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• 2007

Recently a concrete slab tracks are being constructed on roadbed in the Gyoeng-bu 2nd phase high speed railways. In respdnding to this trend, new design standards and track materials maintenance systems, based on the slab track material safety and usage perspective, are needed. This research provides a roadbed design criteria and the maintenance system. The proposed roadbed design criteria and the maintenance system are based on the developed analysis meathod of train/slab-track interaction. where the roadbed settlement and train speed are utilized as mediating variables. In the analysis, the dynamic response of train/slab-track interaction apply to various speeds and settlements. the roadbed settlement is shown in a sinusoidal shape of wave, the scope of the settlement occurrence presented in its wavelengths, include 6meters, 10meters, 15merwes, 20meters, 30meters. The train speeds involved are 50, 100, 150, 200, 250, 300, 350, 400kilometers per hour.

• Journal of the Semiconductor & Display Technology
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• v.17 no.3
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• pp.21-26
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• 2018

In this paper, the switching characteristics of the active clamp type flyback converter, which is deemed suitable for the miniaturization of the external power supply for home appliance, were analyzed and the process of reducing the switching loss was explained. The active clamp type flyback converter operating in the DCM has confirmed that the surge voltage of the main switch does not occur and the turn-off / on loss of the switch do not occur in principle. Also, in the case of the switch for synchronous rectifier, it was showed that the switch current showed half-wave rectified sinusoidal characteristic, and the switching loss was reduced. The switching characteristics of the experimental results gathered from 120 W class prototype were compared with the theoretical waveform in the steady-state and it was confirmed that the power conversion efficiency of the active clamp type flyback converter was maintained high due to the reduction of the switching loss.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.1
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• pp.56-67
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• 2012

In this thesis, to compensate the sweep nonlinearity occurring in the high resolution radar system using FMICW or FMCW, the method of the estimation of the nonlinearity is proposed. The nonlinear phase component caused by the nonlinear characteristic of the radar system is modelled as a linear combination of the sinusoidal functions consisting of various magnitudes and phases(systematic nonlinear phase error) and a random component(stochastic nonlinear phase error). From two IF signals that are measured respectively independently for two reference point targets lying in different distances which are known, a sparse linear equation is made and solved by least squares method to estimate the nonlinear phase component. The estimated component can be used for predistortion method to compensate the sweep nonlinearity.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2006.10a
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• pp.134-143
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• 2006

Out of all types of motions the critical motions leading to capsize is roll. The dynamic amplification in case of roll motion may be large for ships as roll natural frequency generally falls within the frequency range of wave energy spectrum typical used for estimation of motion spectrum. Roll motion is highly non-linear in nature. Den are various representations of non-linear damping and restoring available in literature. In this paper an uncoupled non-linear roll equations with three representation of damping and cubic restoring term is solved using a perturbation technique. Damping moment representations are linear plus quadratic velocity damping, angle dependant damping and linear plus cubic velocity dependant damping. Numerical value of linear damping coefficient is almost same for all types but non-linear damping is different. Linear and non-linear damping coefficients are obtained form free roll decay tests. External rolling moment is assumed as deterministic with sinusoidal form. Maximum roll amplitude of non-linear roll equation with various representations of damping is calculated using analytical procedure and compared with experimental results, which are obtained form forced tests in regular waves by varying frequency with three wave heights. Experiments indicate influence of non-linearity at resonance frequency. Both experiment and analytical results indicates increase in maximum roll amplitude with wave slope at resonance. Analytical results are compared with experiment results which indicate maximum roll amplitude analytically obtained with angle dependent and cubic velocity damping are equal and difference from experiments with these damping are less compared to non-linear equation with quadratic velocity damping.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.318-327
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• 2002

In this paper, heat transfer and pressure oscillation characteristics on oscillating capillary tube heat pipe(OCHP) according to input heat flux, mixture ratio of working fluid and inclination angle were investigated and were compared single working fluid(R-142b) with binary mixture working fluid(R-142b-Ethano1). OCHP was made to serpentine structure of loop type with 10 turns by drilling the channels of length 220mm, width 1.5mm, and depth 1.5mm on the surface of brass plate. In this study, R-l42b and R-l42b-Ethanol were used as working fluids, the charging ratio of working fluids was 40(vol.%), the input heat flux to evaporating section was changed from 0.3W/㎠ to 1.8W/㎠, and mixture ratio of working fluid was R(100%), R(95%)-E(5%), R(90%)-E(10%), and R(85%)-E(15%). From the experimental results, it was found that the effective thermal conductivity of single working fluid was better than that of binary mixture working fluid. But, in case of binary mixture working fluid, critical heat flux was higher than that of single working fluid. And, the higher the mixture ratios of working fluid, the lower heat transfer performance. In case of pressure oscillation, as the inclination angle was lower, pressure wave was more irregular. These phenomena were more serious when the working fluid was binary mixture. Besides, when mixture ratio was higher, saturated pressure was increased, more irregular wave was observed and the mean amplitude was increased. For the same input heat flux, inclination angle and charging ratio, when pressure oscillation has sinusoidal wave, mean amplitude was small, and saturated pressure was low value, the heat transfer was excellent.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.7
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• pp.109-116
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• 2007

The emf of a permanent magnet multi-phase BLAC(Brushless AC) motor is generally a non-sinusoidal or a non-ideal trapezoid wave. So, conventional modeling using a sinusoidal or an ideal trapezoid emf can result in errors to simulate and analyze the properties of a multi-phase BLAC motor. To reduce the modeling error, this paper proposes a phase variable model, which is obtained from a hybrid modeling technique consisting of Finite Element Analysis(FEA) based circuits and equations. Since the phase model parameters including the emf waveform were obtained using FEA, the proposed hybrid modeling technique can be used to implement a simulation model for multi-phase BLAC motors with any emf voltage waveforms. Adequacy of the proposed model was established from the simulation and experimental results for a seven-phase BLAC motor.

• Korean Journal of Remote Sensing
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• v.29 no.4
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• pp.351-360
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• 2013

Harmonic analysis enables to characterize patterns of variation in MODIS NDVI time series data and track changes in ground vegetation cover. In harmonic analysis, a periodic phenomenon of time series data is decomposed into the sum of a series of sinusoidal waves and an additive term. Each wave is defined by an amplitude and a phase angle and accounts for the portion of variance of complex curve. In this study, harmonic analysis was explored to tract ground vegetation variation through time for land-cover vegetation change detection. The process also enables to reconstruct observed time series data including various noise components. Harmonic model was tested with simulation data to validate its performance. Then, the suggested change detection method was applied to MODIS NDVI time series data over the study period (2006-2012) for a selected test area located in the northern plateau of Korean peninsula. The results show that the proposed approach is potentially an effective way to understand the pattern of NDVI variation and detect the change for long-term monitoring of land cover.

• Journal of Korea Water Resources Association
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• v.32 no.4
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• pp.417-426
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• 1999

A series of numerical experiments is performed to compare the characteristics of outflow hydrograph using linear and nonlinear Muskingum-Cunge methods for two cases: (a) sinusoidal inflow hydrographs and (b) rainfall inputs. The nonlinear method shows the steepening of the rising limb, coupled with a corresponding flattening of the receding limb. The linear method conserves mass exactly. In contrast, the nonlinear method is subject to a gain and a loss of mass. The loss of mass and the subsidence of peak outflow increases with a mild slope, a small baseflow $q_b$ and a large peak inflow to baseflow ratio $q_p/q_b$. A shock wave and associated numerical instability results in the increase of mass for a steep slope and a large $q_p/q_b$ ratio. While the linear method depends on the reference flow per unit-width, the nonlinear method depends on a baseflow and the $q_p/q_b$ ratio. It is found that, unlike for the sinusoidal inflow, the outflow for the rainfall inputs conserves mass fairly exactly in the nonlinear method.

• Smart Structures and Systems
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• v.12 no.3_4
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• pp.363-379
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• 2013

Dynamic displacement of structures is an important index for in-service structural condition and behavior assessment, but accurate measurement of structural displacement for large-scale civil structures such as long-span bridges still remains as a challenging task. In this paper, a vision-based dynamic displacement measurement system with the use of digital image processing technology is developed, which is featured by its distinctive characteristics in non-contact, long-distance, and high-precision structural displacement measurement. The hardware of this system is mainly composed of a high-resolution industrial CCD (charge-coupled-device) digital camera and an extended-range zoom lens. Through continuously tracing and identifying a target on the structure, the structural displacement is derived through cross-correlation analysis between the predefined pattern and the captured digital images with the aid of a pattern matching algorithm. To validate the developed system, MTS tests of sinusoidal motions under different vibration frequencies and amplitudes and shaking table tests with different excitations (the El-Centro earthquake wave and a sinusoidal motion) are carried out. Additionally, in-situ verification experiments are performed to measure the mid-span vertical displacement of the suspension Tsing Ma Bridge in the operational condition and the cable-stayed Stonecutters Bridge during loading tests. The obtained results show that the developed system exhibits an excellent capability in real-time measurement of structural displacement and can serve as a good complement to the traditional sensors.