• Smart Structures and Systems
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• 제2권3호
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• pp.209-224
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• 2006

The use of smart dampers to optimally control the response of structures is on the increase. To maximize the potential use of such damper systems, their accurate modeling and assessment of their performance is of vital interest. In this study, the performance of a controllable fluid dashpot damper, in terms of damper forces, damper dynamic range and damping force hysteretic loops, respectively, is studied mathematically. The study employs a damper Bingham-Maxwell (BingMax) model whose mathematical formulation is developed using a Fourier series technique. The technique treats this one-dimensional Navier-Stokes's momentum equation as a linear superposition of initial-boundary value problems (IBVPs): boundary conditions, viscous term, constant Direct Current (DC) induced fluid plug and fluid inertial term. To hold the formulation applicable, the DC current level to the damper is supplied as discrete constants. The formulation and subsequent simulation are validated with experimental results of a commercially available magneto rheological (MR) dashpot damper (Lord model No's RD-1005-3) subjected to a sinusoidal stroke motion using a 'SCHENK' material testing machine in the Materials Laboratory at the University of Technology, Sydney.

• 조명전기설비학회논문지
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• 제24권5호
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• pp.70-76
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• 2010

유도 전동기의 인버터 사용이 증가하면서, 인버터의 고주파 스위칭에 대한 유도전동기의 특성 해석 연구가 요구되고 있다. 그러나 기존의 연구들은 인버터와의 결합 모델의 개발 필요성을 느끼고 있으면서도 인버터 모델링의 어려움뿐만 아니라 결합 어려움 때문에 고정된 전원을 가정하고, 유도기 모델을 단순화 시켜서 모사를 하고 있는 경우가 대부분이다. 이에 인버터로 구동되는 유도 전동기의 고주파 해석 모델과 고주파 고려 유도 전동기 해석 모델 및 인버터 동작을 시뮬레이션할 수 있는 모델을 개발하여, 위와 같은 경우의 시뮬레이션을 가능하게 하고자 한다. 이로부터, 인버터에 의한 유도전동기 구동에서의 고주파에 의한 영향을 해석할 수 있다.

• 대한전기학회논문지
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• 제43권7호
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• pp.1206-1213
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• 1994

This paper presents the operation principle and design rule of the Rogowski coil which can measure the transient current and describes the calibration and application experimental results for performance evaluation. It is obtained that the response curves of the Robowski coil with the turns of 300 and the passive integrator to sinusoidal input give a good linearity up to the frequency of 500 [kHz] and the current measurement system gaving the Rogowski coil is the frequency bandwidth of 40 [Hz]~700 [kHz]. As an application experiment for the fabricated modeling power transmission line, the impulse current, which limitates the direct lightning return stroke to overhead ground wire, is measured by the Rogowski coil and its fast Fourier transformation is carried out. The equivalent circuit of the Rogowski coil considering the stray capacitances is proposed, and the theoretical analysis is in good agreement with the measurement results. Also, it is found that for high frequency domain the stray capacitance such as a distributed capacitance to the shield and the capacitance between windings of coil should be considered in designing the Rogowski coils since the resonance originates from the stray capacitance and the self-inductance of the Rogowski coil.

• Structural Engineering and Mechanics
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• 제52권3호
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• pp.633-646
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• 2014

A semi-analytical numerical approach for the effective structural dynamic response analysis of spar floating substructure for offshore wind turbine subject to wave-induced excitation is introduced in this paper. The wave-induced rigid body motions at the center of mass are analytically solved using the dynamic equations of rigid ship motion. After that, the flexible structural dynamic responses of spar floating substructure for offshore wind turbine are numerically analyzed by letting the analytically derived rigid body motions be the external dynamic loading. Restricted to one-dimensional sinusoidal wave excitation at sea state 3, pitch and heave motions are considered. Through the numerical experiments, the time responses of heave and pitch motions are solved and the wave-induced dynamic displacement and effective stress of flexible floating substructure are investigated. The hydrodynamic interaction between wave and structure is modeled by means of added mass and wave damping, and its modeling accuracy is verified from the comparison of natural frequencies obtained by experiment with a 1/100 scale model.

• Steel and Composite Structures
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• 제24권4호
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• pp.499-512
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• 2017

This paper deals with nonlinear dynamic stability of embedded piezoelectric nano-composite separators conveying pulsating fluid. For presenting a realistic model, the material properties of structure are assumed viscoelastic based on Kelvin-Voigt model. The separator is reinforced with single-walled carbon nanotubes (SWCNTs) which the equivalent material properties are obtained by mixture rule. The separator is surrounded by elastic medium modeled by nonlinear orthotropic visco Pasternak foundation. The separator is subjected to 3D electric and 2D magnetic fields. For mathematical modeling of structure, three theories of classical shell theory (CST), first order shear deformation theory (FSDT) and sinusoidal shear deformation theory (SSDT) are applied. The differential quadrature method (DQM) in conjunction with Bolotin method is employed for calculating the dynamic instability region (DIR). The detailed parametric study is conducted, focusing on the combined effects of the external voltage, magnetic field, visco-Pasternak foundation, structural damping and volume percent of SWCNTs on the dynamic instability of structure. The numerical results are validated with other published works as well as comparing results obtained by three theories. Numerical results indicate that the magnetic and electric fields as well as SWCNTs as reinforcer are very important in dynamic instability analysis of structure.

• 한국소음진동공학회논문집
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• 제22권10호
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• pp.1020-1026
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• 2012

This paper proposes a new type of high-frequency directional valve controlled by the piezostack actuator associated with displacement amplifier. As a first step, a dynamic model of directional valve which can operate at 200 Hz with a flow rate of 12 litter/min is derived by considering pressure drop and flow force. As a second step, an appropriate piezostack is selected by considering actuation force as well as field-dependent displacement. Subsequently, in order to control spool displacement and flow rate a proportional-derivative(PD) controller is designed based on the 3rd-order valve system. Control performances such as sinusoidal trajectory tracking of the spool displacement in time domain are evaluated. In addition, the field-dependent flow rate is also presented to verify the required performance of the valve system.

• Advances in aircraft and spacecraft science
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• 제5권3호
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• pp.335-348
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• 2018

The structural dynamics (SD) behavior of Elastic Flapping Wings (EFWs) is investigated analytically as a novel approach in EFWs analysis. In this regard an analytical SD solution of EFW undergoing a prescribed rigid body motion is initially derived, where the governing equations are expressed in modal space. The inertial forces are also analytically computed utilizing the actuator induced acceleration effects on the wing structure, while due to importance of analytical solution the linearity assumption is also considered. The formulated initial-value problem is solved analytically to study the EFW structural responses, where the effect of structure-actuator frequency ratio, structure-flapping frequency ratio as well as the structure damping ratio on the EFW pick amplitude is analyzed. A case study is also simulated in which the wing is modeled as an elastic beam with shell elements undergoing a prescribed sinusoidal motion. The corresponding EFW transient and steady response in on-off servo behavior is investigated. This study provides a conceptual understanding for the overall EFW SD behavior in the presence of inertial forces plus the servo dynamics effects. In addition to the substantial analytical results, the study paves a new mathematical way to better understanding the complex role of SD in dynamic EFWs behavior. Specifically, similar mathematical formulations can be carried out to investigate the effect of aerodynamics and/or gravity.

• Advances in aircraft and spacecraft science
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• 제6권5호
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• pp.409-426
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• 2019

The aim of the present work is to study the nonlinear behavior of the laminated composite plates under transverse sinusoidal loading using a new inverse trigonometric shear deformation theory, where geometric nonlinearity in the Von-Karman sense is taken into account. In the present theory, in-plane displacements use an inverse trigonometric shape function to account the effect of transverse shear deformation. The theory satisfies the traction free boundary conditions and violates the need of shear correction factor. The governing equations of equilibrium and boundary conditions associated with present theory are obtained by using the principle of minimum potential energy. These governing equations are solved by eight nodded serendipity element having five degree of freedom per node. A square laminated composite plate is considered for the geometrically linear and nonlinear formulation. The numerical results are obtained for central deflections, in-plane stresses and transverse shear stresses. Finite element Codes are developed using MATLAB. The present results are compared with previously published results. It is concluded that the geometrically linear and nonlinear response of laminated composite plates predicted by using the present inverse trigonometric shape function is in excellent agreement with previously published results.

• 대한기계학회논문집A
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• 제38권11호
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• pp.1231-1237
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• 2014

군용 차량의 경우 야지 주행에 대한 성능 시험이 필수적인데 실차 시험의 경우 비용과 시간에 의한 제약을 받게 되므로, 시뮬레이션을 통한 성능 분석이 효율적이다. 본 연구에서는 상용 다물체 해석프로그램인 MSC.ADAMS 를 이용하여 차량 모델을 개발한다. 타이어 수직 강성 시험을 수행하고 FTire 모델에 반영하여 타이어 모델을 생성한다. 댐퍼의 경우 비선형 특성 시험을 통해 얻은 결과를 반영하여 댐퍼를 모델링 하였으며, 겹판 스프링은 빔 요소 모델로 차량 모델을 구성한다. 단순 장애물 통과 시험 및 파형로 통과 시험을 수행하고 가속도 응답 및 휠 하중 응답 분석을 통해 차량 모델의 신뢰성을 검증하였다.

• 대한전자공학회논문지SP
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• 제48권5호
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• pp.129-136
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• 2011

본 논문에서는 입력신호에 따라 효율적인 부호화를 위해 다중모드를 가지는 초광대역 부호화기를 제안하였다. 최근에 개발된 G.718기반의 초광대역 확장 코덱은 초광대역에 존재하는 오디오 신호를 부호화하기 위하여 Generic모드와 Sinusoidal모드로 신호를 분류하여 부호화 하지만, 현악기, 관현악기와 같은 오디오 신호에 존재하는 멀티플 피치 및 하모닉 성분과 타악기와 같은 오디오 신호에 존재하는 Individual-Line 성분을 효율적으로 부호화하지 못하였다. 제안하는 방법은 오디오 신호에 존재하는 하모닉과 Individual-Line성분의 특징을 고려하여 모드를 세분화하였다. 성능평가를 위하여 객관적인 평가로 MDCT 도메인에서 SNR을 이용하였으며 MUSHRA 테스트를 통해 주관적인 평가를 하였다. 실험 결과 제안한 방법은 기존의 G.718 초광대역 부호화기보다 Individual-Line신호 경우 약 3dB, 하모닉 신호의 경우 약 0.8dB 높은 SNR을 보였으며 MUSHRA 테스트 역시 평균 5점 음질 향상을 확인하였다.