• International Journal of Fluid Machinery and Systems
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• 제6권2호
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• pp.87-93
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• 2013

In order to study the effect of the fluid-structure interaction (FSI) on the simulation results, the external characteristics and internal flow features of a diffuser pump were analyzed with a two-way flow solid coupling method. And the static and dynamic structure analysis of the blade was also caculated with the FEA method. The steady flow field is based on Reynolds Averaged N-S equations with standard $k-{\varepsilon}$ turbulent model, the unsteady flow field is based on the large eddy simulation, and the structure response is based on elastic transient structural dynamic equation. The results showed that the effect of FSI on the head prediction based on CFD really exists. At the same radius, the van mises stress on the nodes closed shroud and hub was larger than other nodes. A large deformation region existed near inlet side at the middle of blades. The strength of impeller satisfied the strength requirement with static stress analysis based on the fourth strength theory. The dynamic stress varied periodically with the impeller rotating. It was also found that the fundamental frequency of the dynamic stress is the rotating frequency and its harmonic frequency. The frequency of maximum stress amplitude at node 1626 was 7 times of the rotating frequency. The frequency of maximum stress amplitude at node 2328 was 14 times of the rotating frequency. No matter strength failure or fatigue failure, the root of blades near shroud is the key region to analyse.

• 한국음향학회지
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• 제39권3호
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• pp.216-225
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• 2020

본 논문은 음선 경로법에 기반한 광대역 수중음향 전달 채널을 모델링하는 방법을 다루었다. 수중음향 전달 채널은 종종 주파수 영역에서 시간 조화 함수로 취급되어, 광대역 시계열 신호 모의 시 활용이 어렵다. 따라서 수중 음파 전달 환경을 반영한 광대역 시간영역 모델링 기법이 요구되며, 본 논문에서는 이를 위해 시간영역에서 다중 경로의 도달 시간지연이 계산 가능한 고유 음선 분석 기법을 활용하였다. 또한 연속 시간의 파동방정식으로부터 산출된 고유 음선의 분석 결과를 컴퓨터 모의가 가능한 이산시간 시스템에 적용하기 위해, 음선의 위상, 주파수별 손실 및 도달 시간지연을 유한 임펄스 응답으로 근사하여, 광대역 수중음향 전달 채널을 모의하는 방법을 제안하였다.

• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1714-1728
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• 2016

This paper presents improved harmonics extraction based on Adaptive Linear Neuron (ADALINE) algorithm for single phase photovoltaic (PV) shunt active power filter (SAPF). The proposed algorithm, named later as Improved ADALINE, contributes to better performance by removing cosine factor and sum of element that are considered as unnecessary features inside the existing algorithm, known as Modified Widrow-Hoff (W-H) ADALINE. A new updating technique, named as Fundamental Active Current, is introduced to replace the role of the weight factor inside the previous updating technique. For evaluation and comparison purposes, both proposed and existing algorithms have been developed. The PV SAPF with both algorithms was simulated in MATLAB-Simulink respectively, with and without operation or connection of PV. For hardware implementation, laboratory prototype has been developed and the proposed algorithm was programmed in TMS320F28335 DSP board. Steady state operation and three critical dynamic operations, which involve change of nonlinear loads, off-on operation between PV and SAPF, and change of irradiances, were carried out for performance evaluation. From the results and analysis, the Improved ADALINE algorithm shows the best performances with low total harmonic distortion, fast response time and high source power reduction. It performs well in both steady state and dynamic operations as compared to the Modified W-H ADALINE algorithm.

• 한국전자파학회논문지
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• 제17권2호
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• pp.117-123
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• 2006

본 논문에서는 고조파 제거 특성을 갖는 DGS 형태의 CPW 저역 통과 여파기를 설계하였다. 서로 다른 불요응답 특성을 갖는 2개의 저역 통과 여파기를 설계하고 결합하여 불요 응답을 -15 dB 이하로 줄일 수 있었다. 추가적으로 아령 모양의 DGS를 설계하여 여파기와 결합함으로써 -25 dB 이하의 우수한 불요 응답제거 특성을 얻을 수 있었다. 제작된 여파기는 $17.2mm\times6.8mm$의 작은 크기로, 6 GHz의 차단 주파수를 가지며, 2개의 감쇄극을 갖는 7차의 급격한 감쇄 특성을 나타내었다. 측정된 주파수 특성 결과는 시뮬레이션 결과와 잘 일치하였다.

• 정보통신설비학회논문지
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• 제2권1호
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• pp.52-62
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• 2003

본 논문에서는 그라운드 판에 주기적으로 에칭된 원으로 구성된 Photonic Bandgap(PBG) 여파기가 광대역 하모닉 성분을 제거할 수 있음을 보인다. FDTD법과 제작, 실험을 통해 얻은 결과를 이용하여 PBG 구조의 특성을 분석해 보았고, FDTD법은 다양한 3차원 구조를 시뮬레이션을 할 수 있고 광대역의 주파수 응답을 볼 수 있다. 분석 결과는 에칭된 원들을 2차원으로 배열한 경우와 일렬로 배열한 경우 모두 똑같은 결과가 나오는 것을 나타냈다. 그리고 에칭된 원과 원 사이의 공진기의 특성을 필드패턴을 통해서 알아 보았고, 에칭된 원들의 수 n, 에칭된 원의 반지름 r과 주기 a의 변화에 따른 주파수의 특성을 보았다.

• Journal of Power Electronics
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• 제16권4호
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• pp.1513-1525
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• 2016

Rapid and accurate phase synchronization is critical for the reliable control of grid-tied inverters. However, the commonly used software phase-locked loop methods do not always satisfy the need for high-speed and accurate phase synchronization under severe grid imbalance conditions. To address this problem, this study develops a novel open-loop phase locking scheme based on a synchronous reference frame. The proposed scheme is characterized by remarkable response speed, high accuracy, and easy implementation. It comprises three functional cascaded blocks: fast orthogonal signal generation block, fast fundamental-frequency positive sequence component construction block, and fast phase calculation block. The developed virtual orthogonal signal generation method in the first block, which is characterized by noise immunity and high accuracy, can effectively avoid approximation errors and noise amplification in a wide range of sampling frequencies. In the second block, which is the foundation for achieving fast phase synchronization within 3 ms, the fundamental-frequency positive sequence components of unsymmetrical grid voltages can be achieved with the developed orthogonal signal construction strategy and the symmetrical component method. The real-time grid phase can be consequently obtained in the third block, which is free from self-tuning closed-loop control and thus improves the dynamic performance of the proposed scheme. The proposed scheme is adaptive to severe unsymmetrical grid voltages with sudden changes in magnitude, phase, and/or frequency. Moreover, this scheme is able to eliminate phase errors induced by harmonics and random noise. The validity and utility of the proposed scheme are verified by the experimental results.

• Geomechanics and Engineering
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• 제12권1호
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• pp.161-183
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• 2017

This paper investigates the damage identification of the concrete pile element through axial wave propagation technique using computational and experimental studies. Now-a-days, concrete pile foundations are often common in all engineering structures and their safety is significant for preventing the failure. Damage detection and estimation in a sub-structure is challenging as the visual picture of the sub-structure and its condition is not well known and the state of the structure or foundation can be inferred only through its static and dynamic response. The concept of wave propagation involves dynamic impedance and whenever a wave encounters a changing impedance (due to loss of stiffness), a reflecting wave is generated with the total strain energy forked as reflected as well as refracted portions. Among many frequency domain methods, the Spectral Finite Element method (SFEM) has been found suitable for analysis of wave propagation in real engineering structures as the formulation is based on dynamic equilibrium under harmonic steady state excitation. The feasibility of the axial wave propagation technique is studied through numerical simulations using Elementary rod theory and higher order Love rod theory under SFEM and ABAQUS dynamic explicit analysis with experimental validation exercise. Towards simulating the damage scenario in a pile element, dis-continuity (impedance mismatch) is induced by varying its cross-sectional area along its length. Both experimental and computational investigations are performed under pulse-echo and pitch-catch configuration methods. Analytical and experimental results are in good agreement.

• Smart Structures and Systems
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• 제19권6호
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• pp.665-678
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• 2017

In this paper the tuned mass-damper-inerter (TMDI) is considered for passive vibration control and energy harvesting in harmonically excited structures. The TMDI couples the classical tuned mass-damper (TMD) with a grounded inerter: a two-terminal linear device resisting the relative acceleration of its terminals by a constant of proportionality termed inertance. In this manner, the TMD is endowed with additional inertia, beyond the one offered by the attached mass, without any substantial increase to the overall weight. Closed-form analytical expressions for optimal TMDI parameters, stiffness and damping, given attached mass and inertance are derived by application of Den Hartog's tuning approach to suppress the response amplitude of force and base-acceleration excited single-degree-of-freedom structures. It is analytically shown that the TMDI is more effective from a same mass/weight TMD to suppress vibrations close to the natural frequency of the uncontrolled structure, while it is more robust to detuning effects. Moreover, it is shown that the mass amplification effect of the inerter achieves significant weight reduction for a target/predefined level of vibration suppression in a performance-based oriented design approach compared to the classical TMD. Lastly, the potential of using the TMDI for energy harvesting is explored by substituting the dissipative damper with an electromagnetic motor and assuming that the inertance can vary through the use of a flywheel-based inerter device. It is analytically shown that by reducing the inertance, treated as a mass/inertia-related design parameter not considered in conventional TMD-based energy harvesters, the available power for electric generation increases for fixed attached mass/weight, electromechanical damping, and stiffness properties.

• 한국정보통신학회논문지
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• 제13권5호
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• pp.922-930
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• 2009

유도 전동기를 전압 제어하기 위한 최적 PWM 스위칭 방법을 제시하려한다. 전압 인버터의 공간 벡터 변조 방식은 DC-버스 이용을 향상시키고 정류 손실을 감소시키기 때문에 디지털 구현의 경우 특히 선호하는 PWM 방법이다. 유도 전동기 전압 제어를 위한 최적 PWM 스위칭 방법은 제시한 최적 PWM 알고리즘을 사용하여 두 개의 활성 전압 벡터(active voltage vector)와 하나의 영 전압 벡터(zero voltage vector)로 구성하였다. 선택된 스위칭 순차 열은 변조 지수(modulation index)와 운송파(carrier wave) 주기의 함수로 정의 된다. 순차 열은 인버터 스위칭 손실과 전류 리플 값을 기준으로 사용하여 선택된다. 실험 결과 중 저 전력용으로 사용할 경우 스위칭 주파수를 증가시킴에 따라 고조파 왜곡이 감소하고 동특성이 좋아짐을 확인할 수 있었다.

• Steel and Composite Structures
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• 제26권6호
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• pp.673-691
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• 2018

The main goal of this research is to examine the in-plane and out-of-plane forced vibration of a curved nanocomposite microbeam. The in-plane and out-of-plane displacements of the structure are considered based on the first order shear deformation theory (FSDT). The curved microbeam is reinforced by functionally graded carbon nanotubes (FG-CNTs) and thus the extended rule of mixture is employed to estimate the effective material properties of the structure. Also, the small scale effect is captured using the strain gradient theory. The structure is rested on a nonlinear orthotropic viscoelastic foundation and is subjected to concentrated transverse harmonic external force, thermal and magnetic loads. The derivation of the governing equations is performed using energy method and Hamilton's principle. Differential quadrature (DQ) method along with integral quadrature (IQ) and Newmark methods are employed to solve the problem. The effect of various parameters such as volume fraction and distribution type of CNTs, boundary conditions, elastic foundation, temperature changes, material length scale parameters, magnetic field, central angle and width to thickness ratio are studied on the frequency and force responses of the structure. The results indicate that the highest frequency and lowest vibration amplitude belongs to FGX distribution type while the inverse condition is observed for FGO distribution type. In addition, the hardening-type response of the structure with FGX distribution type is more intense with respect to the other distribution types.