• Journal of Institute of Control, Robotics and Systems
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• v.6 no.1
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• pp.51-56
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• 2000

This paper presents the characteristics of the dynamic response and calibration technique on a linear variable differential transformer(LVDT). The linear error of the LVDT was proven $\pm$1% in the static calibration and $\pm$0.5% in the dynamic calibration. In this paper, the linearity error generated in the static and dynamic state of the core movement can be eliminated using the correction algorithem of the static and dynamic state derived from the least square linear approximation for the nonlinearity of the curves of direct data fitting and Lagrange polynomials. With the static and dynamic calibration method, the calibration accuracy of the LVDT can be reduced to within $\pm{0.5%.}$.

• Advances in materials Research
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• v.9 no.1
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• pp.33-48
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• 2020

With the use of differential quadrature method (DQM), forced vibrations and resonance frequency analysis of functionally graded (FG) nano-size beams rested on elastic substrate have been studied utilizing a shear deformation refined beam theory which contains shear deformations influence needless of any correction coefficient. The nano-size beam is exposed to uniformly-type dynamical loads having partial length. The two parameters elastic substrate is consist of linear springs as well as shear coefficient. Gradation of each material property for nano-size beam has been defined in the context of Mori-Tanaka scheme. Governing equations for embedded refined FG nano-size beams exposed to dynamical load have been achieved by utilizing Eringen's nonlocal differential law and Hamilton's rule. Derived equations have solved via DQM based on simply supported-simply supported edge condition. It will be shown that forced vibrations properties and resonance frequency of embedded FG nano-size beam are prominently affected by material gradation, nonlocal field, substrate coefficients and load factors.

• Proceedings of the Korea Information Processing Society Conference
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• 2024.05a
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• pp.243-244
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• 2024

IoT 장치의 개수가 급증함에 따라 네트워크 환경에서 송수신되는 데이터 양이 증가하였고, 이에 따라 데이터 전송과정의 보안 강화가 중요해지고 있다. 기존에는 데이터에 인공 노이즈를 추가하는 차등 프라이버시 기법(Differential Privacy, DP)을 적용하여 데이터를 보호하고 있다. 하지만 DP가 적용된 데이터를 수신하는 정상 사용자의 머신러닝 학습 정확도가 감소되는 문제가 있다. 본 논문에서는 고신뢰 데이터 전송을 위한 데이터 인코딩 기반의 DP 기법인 EN-DP (Encoding-based DP) 모델을 제안한다. 실험 결과에 따르면, EN-DP 를 통한 정상 사용자와 공격자 간의 학습 능력 정확도 간극을 종래 모델 대비 최대 17.16% 개선할 수 있음을 입증하였다.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.13 no.1
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• pp.39-49
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• 2013

This paper presents a method of improving the performance of a day-ahead 24-h load curve and peak load forecasting. The next-day load curve is forecasted using radial basis function (RBF) neural network models built using the best design parameters. To improve the forecasting accuracy, the load curve forecasted using the RBF network models is corrected by the weighted sum of both the error of the current prediction and the change in the errors between the current and the previous prediction. The optimal weights (called "gains" in the error correction) are identified by differential evolution. The peak load forecasted by the RBF network models is also corrected by combining the load curve outputs of the RBF models by linear addition with 24 coefficients. The optimal coefficients for reducing both the forecasting mean absolute percent error (MAPE) and the sum of errors are also identified using differential evolution. The proposed models are trained and tested using four years of hourly load data obtained from the Korea Power Exchange. Simulation results reveal satisfactory forecasts: 1.230% MAPE for daily peak load and 1.128% MAPE for daily load curve.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2017.11a
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• pp.199-200
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• 2017

In order to meet the international performance requirements for eLoran testbed operation, it is necessary to measure ASF (Additional Secondary Factor) of vessel's route as well as differential correction and the provision using differential Loran (dLoran) station operation. According to HEA (Harbor Entrance and Approach) performance of the IMO, the position accuracy should be within 10meters. Therefore this paper presents the possibility to meet the position accuracy of the IMO HEA through simulation results.

• Steel and Composite Structures
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• v.34 no.1
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• pp.75-89
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• 2020

The current paper illustrates the effect of in-plane varying compressive force on critical buckling loads and buckling modes of sandwich composite laminated beam rested on elastic foundation. To generalize a proposed model, unified higher order shear deformation beam theories are exploited through analysis; those satisfy the parabolic variation of shear across the thickness. Therefore, there is no need for shear correction factor. Winkler and Pasternak elastic foundations are presented to consider the effect of any elastic medium surrounding beam structure. The Hamilton's principle is proposed to derive the equilibrium equations of unified sandwich composite laminated beams. Differential quadrature numerical method (DQNM) is used to discretize the differential equilibrium equations in spatial direction. After that, eigenvalue problem is solved to obtain the buckling loads and associated mode shapes. The proposed model is validated with previous published works and good matching is observed. The numerical results are carried out to show effects of axial load functions, lamination thicknesses, orthotropy and elastic foundation constants on the buckling loads and mode shapes of sandwich composite beam. This model is important in designing of aircrafts and ships when non-uniform compressive load and shear loading is dominated.

• Structural Engineering and Mechanics
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• v.54 no.6
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• pp.1061-1073
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• 2015

This paper presents a nonlocal sinusoidal shear deformation beam theory (SDBT) for the nonlinear vibration of single walled carbon nanotubes (CNTs). The present model is capable of capturing both small scale effect and transverse shear deformation effects of CNTs, and does not require shear correction factors. The surrounding elastic medium is simulated based on Pasternak foundation. Based on the nonlocal differential constitutive relations of Eringen, the equations of motion of the CNTs are derived using Hamilton's principle. Differential quadrature method (DQM) for the natural frequency is presented for different boundary conditions, and the obtained results are compared with those predicted by the nonlocal Timoshenko beam theory (TBT). The effects of nonlocal parameter, boundary condition, aspect ratio on the frequency of CNTs are considered. The comparison firmly establishes that the present beam theory can accurately predict the vibration responses of CNTs.

• Journal of Energy Engineering
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• v.26 no.1
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• pp.9-22
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• 2017

A combined thermal and flow analysis was carried out to study the behavior and performance of a small, commercial LTD (Low-Temperature-Differential) heat engine. Laminar-flow solutions for annulus and channel flows were employed to estimate the viscous drags on the piston and the displacer and the pressure difference across the displacer. Temperature correction factors were introduced to account for the departure from the ideal heat transfer processes. The analysis results indicate that the work required to overcome the viscous drags on engine moving parts and to move the displacer is much smaller than the moving-boundary work produced by the power piston for temperature differentials in the neighborhood of $20^{\circ}C$ and engine speeds below 10 RPS. A comparison with experimental data reveals large degradations from the ideal heat transfer processes. Thus, heat-transfer devices inside the displacer cylinder are recommended.

• Steel and Composite Structures
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• v.34 no.2
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• pp.241-260
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• 2020

This article presented a comprehensive model to study static buckling stability and associated mode-shapes of higher shear deformation theories of sandwich laminated composite beam under the compression of varying axial load function. Four higher order shear deformation beam theories are considered in formulation and analysis. So, the model can consider the influence of both thick and thin beams without needing to shear correction factor. The compression force can be described through axial direction by uniform constant, linear and parabolic distribution functions. The Hamilton's principle is exploited to derive equilibrium governing equations of unified sandwich laminated beams. The governing equilibrium differential equations are transformed to algebraic system of equations by using numerical differential quadrature method (DQM). The system of equations is solved as an eigenvalue problem to get critical buckling loads and their corresponding mode-shapes. The stability of DQM in determining of buckling loads of sandwich structure is performed. The validation studies are achieved and the obtained results are matched with those. Parametric studies are presented to figure out effects of in-plane load type, sandwich thickness, fiber orientation and boundary conditions on buckling loads and mode-shapes. The present model is important in designing process of aircraft, naval structural components, and naval structural when non-uniform in-plane compressive loading is dominated.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2768-2774
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• 2011

In this paper, we investigate the methods to improve the position accuracy using DGNSS(Differential Global Navigation Satellite System). Then we configure the real-time DGNSS environment with use of GPS and MSAS as SBAS(Satellite Based Augmentation System) currently being in service by Japan. And we verify the improvement of position accuracy and the continuity of GPS correction data through the realtime DGNSS test in Joongang line, Kyungbu line, Honam line.