• Title/Summary/Keyword: 고유진동 해석

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Eigenvalue Analysis and Detection of Low Frequency Oscillation using PMU Data in KEPCO System (위상동기신호를 이용한 한전계통의 저주파진동 검출과 고유치해석)

  • Shim, Kwan-Shik;Kim, Sang-Tae;Kim, Tae-Kyun;Ahn, Seon-Ju;Choi, Joon-Ho
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.66 no.2
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    • pp.261-284
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    • 2017
  • This paper describes the results of a low-frequency oscillation analysis using data measured in PMU installed in the KEPCO system, and the comparison with eigenvalues computed from the linear model. The dominant oscillation modes are estimated by applying various algorithms. The algorithms are: the extended Prony method; multiple time interval parameter estimation method; subspace system identification method; and spectral analysis. From the measurement data, modes of frequency 0.68[Hz] and 0.92[Hz] were estimated, and modes of frequency 0.63[Hz] and 0.80[Hz] were computed from the eigenvalue calculation. There was a difference between the mode estimated from measurement data and that from the linear model. This is possibly because of an error in the dynamic data of the KEPCO system used in eigenvalue calculation. Because wide area modes exist in the KEPCO system, these modes should be monitored continuously for the reliable operation of the system. In order to prevent total blackouts caused by wide area oscillation, moreover, contingency analysis should be performed in relation to this mode and appropriate measures should be established.

Finite Element Model Updating of Simple Beam Considering Boundary Conditions (경계조건을 고려한 단순보의 유한요소모델개선)

  • Kim, Se-Hoon;Park, Young-Soo;Kim, Nam-Gyu;Lee, Jong-Jae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.22 no.2
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    • pp.76-82
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    • 2018
  • In this present study, in order to update the finite element model considering the boundary conditions, a method has been proposed. The conventional finite element model updating method, updates the finite element model by using the dynamic characteristics (natural frequency, mode shape) which can be estimated from the ambient vibration test. Therefore, prediction of the static response of an actual structure is difficult. Furthermore, accurate estimation of the physical properties is relatively hard. A novel method has been proposed to overcome the limitations of conventional method. Initially, the proposed method estimates the rotational spring constant of a finite element model using the deflection of structure and the rotational displacement of support measurements. The final updated finite element model is constructed by estimating the material properties of the structure using the finite element model with updated rotational spring constant and the dynamic characteristics of the structure. The proposed finite element model updating method is validated through numerical simulation and compared with the conventional finite element model updating method.

Displacement Measurement of Cable Stayed Bridge using Digital Image Processing (디지털 영상처리를 이용한 사장교의 변위 측정)

  • Son, Byung Jik;Jeon, Seung Gon;Heo, Gwang Hee
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.17 no.5
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    • pp.237-242
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    • 2016
  • This paper introduces a method of measuring the displacement of a cable-stayed bridge using digital image processing (DIP). The validity of the DIP technique was confirmed by comparing the results with those obtained using a displacement meter and ANSYS analysis. The normalized cross-correlation (NCC) coefficient was used. 100 kgf and 200 kgf loading experiments were carried out, which showed that when the displacement is large, the reliability of the DIP technique is increased. That is, when the load was increased from 100 kgf to 200kgf, it decreased from 31% to 14% compared to the ANSYS results and from 14% to 4% compared to the displacement meter results. Therefore, the image processing method is able to measure the displacement sufficiently accurately.

Establishment of Testing Method for Abutment Scour Stability by Real-scale Model Test (실대형 교각 실험을 통한 교각 세굴안정성 평가 실험 기법 정립)

  • Lee, Myungjae;Yoo, Mintaek;Kim, Kihyun;Lee, Il-Wha
    • Journal of the Korean Geotechnical Society
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    • v.35 no.7
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    • pp.5-14
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    • 2019
  • In this study, a prototype abutment was constructed to establish a safety assessment technique of pier and a series of non-destructive tests using impact load. The surcharge load was loaded from 0 tonf to 2.5 tonf on the prototype abutment, and maximum surcharge load was up to 25 tonf. To analyze the behavior of the piers according to the direction of impact, a total of three types of analysis were performed: the direction of the pier, the direction perpendicular to the pier, and the outer direction of the pier. The height of the impact was also tested at each top and bottom. The measuring instrument used an accelerometer to measure the acceleration response when impacted. Based on the series of experimental results, specific values were calculated according to the direction of an impact and the surcharge load using the Fast Fourier Transform (FFT). In addition, the phase difference was used to analyze the pier from the primary 1st mode to the 4th mode.

Effects of Interactions between the Concrete Deck and Steel Girders on the Dynamic Behavior of Simply Supported Skew Bridges (주형과 상판과의 상호작용이 단순 사교의 동적거동에 미치는 영향)

  • Moon, Seong-Kwon
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.20 no.5
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    • pp.593-604
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    • 2007
  • Although composite construction has more mechanical advantages compared to noncomposite construction, the design of noncomposite construction for skew bridges with large skew angels has been often checked because composite construction may cause large stresses in the bridge deck. In this study, the analytical model considered dynamic behaviors for noncomposite skew bridges was proposed. Using the proposed analytical model, the validity of the application of noncomposite construction to skew bridges was checked. Also, the effects of interactions between the concrete deck and steel girders such as composite construction, partial composite construction, and noncomposite construction on the dynamic characteristics and dynamic behaviors of simply supported skew bridges were investigated. A series of parametric studies for the total 27 skew bridges was conducted with respect to parameters such as girder spacing, skew angle, and deck aspect ratio. Although the slip at the interfaces between the concrete deck and steel girders results in the reduction of seismic total base shear in the transverse direction due to period elongation, it causes an undesirable behavior of skew bridges by the modification in mode shapes and distributions of stiffness. Shear connectors placed by minimum requirements for partial composite action have an effect on reducing the girder stresses and deck stresses; except case of some skew bridges, the magnitude of the girder stresses and deck stresses obtained from partial composite skew bridges is similar to or slightly more than those acquired from composite skew bridges.

A Numerical Study on the Strain Based Monitoring Method for Lateral Structural Response of Buildings using FBG Sensors (FBG를 이용한 변형률 기반 건물의 횡방향 구조반응 모니터링 기법에 관한 해석적 연구)

  • Choi, Se Woon;Park, Keunhyoung;Kim, Yousok;Park, Hyo Seon
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.26 no.4
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    • pp.263-269
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    • 2013
  • In this study, the strain based monitoring method to evaluate the lateral structural response of buildings is presented and an applicability of the proposed method is confirmed through the numerical study. It is assumed that the fiber Bragg grating(FBG) strain sensor is employed to measure the strain response of members due to the excellent properties such as multiplexing, and higher sampling frequency. These properties of FBG sensors is proper for buildings the a lot of sensors are required to monitor the reponses of those. FBG sensors measure the strain response of vertical members and are employed to calculate the curvatures of members using the measured strain responses. Then the lateral displacement, and lateral acceleration is evaluated based on the curvatures of vertical members. Additionally, these dynamic responses of buildings are used to evaluate the dynamic properties of buildings such as the natural frequencies and mode shapes using the frequency domain decomposition(FDD) method. Through the application of nine-story steel moment frame example structure, it is confirmed that the proposed method is appropriate to evaluate the lateral structural responses and dynamic properties of buildings.

Analysis Model for Design Based on Stiffness Requirement of Direct Drive Electromechanical Actuator (직구동 전기기계식 구동기의 강성요구규격에 기반한 설계용 해석모델)

  • Oh, Sang Gwan;Lee, Hee Joong;Park, Hyun Jong;Oh, Dongho
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.47 no.10
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    • pp.738-746
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    • 2019
  • Instead of hydraulic actuation systems, an electromechanical actuation system is more efficient in terms of weight, cost, and test evaluation in the thrust vector control of the 7-ton gimbal engine used in the Korea Space Launch Vehicle-II(KSLV-II) $3^{rd}$ stage. The electromechanical actuator is a kind of servo actuator with position feedback and uses a BLDC motor that can operate at high vacuum. In the case of the gimballed rocket engine, a synthetic resonance phenomenon may occur due to a combination of a vibration mode of the actuator itself, a bending mode of the launcher structure, and an inertial load of the gimbals engine. When the synthetic resonance occurs, the control of the rocket attitude becomes unstable. Therefore, the requirements for the stiffness have been applied in consideration of the gimbal engine characteristics, the support structure, and the actuating system. For the 7-ton gimbal engine of the KSLV-II $3^{rd}$ stage, the stiffness requirement of the actuation system is $3.94{\times}10^7N/m$, and the direct drive type electromechanical actuator is designed to satisfy this requirement. In this paper, an equivalent stiffness analysis model of a direct drive electromechanical actuator designed based on the stiffness requirements is proposed and verified by experimental results.

Dynamic Performance Estimation of the Incrementally PSC Girder Railway Bridge by Modal Tests and Moving Load Analysis (다단계 긴장 PSC 거더 철도교량의 동특성 실험 및 주행열차하중 해석에 의한 동적성능 평가)

  • Kim, Sung Il;Kim, Nam Sik;Lee, Hee Up
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.4A
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    • pp.707-717
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    • 2006
  • As an alternative to conventional prestressed concrete (PSC) girders, various types of PSC girders are either under development or have already been applied in bridge structures. Incrementally prestressed concrete girder is one of these newly developed girders. According to the design concept, these new types of PSC girders have the advantages of requiring less self-weight while having the capability of longer spans. However, the dynamic interaction between bridge superstructures and passing trains is one of the critical issues concerning these railway bridges designed with more flexibility. Therefore, it is very important to evaluate modal parameters of newly designed bridges before doing dynamic analyses. In the present paper, a 25 meters long full scale PSC girder was fabricated as a test specimen and modal testing was carried out to evaluate modal parameters including natural frequencies and modal damping ratios at every prestressing stage. During the modal testing, a digitally controlled vibration exciter as well as an impact hammer is applied, in order to obtain precise frequency response functions and the modal parameters are evaluated varying with construction stages. Prestressed force effects on changes of modal parameters are analyzed at every incremental prestressing stage. With the application of reliable properties from modal experiments, estimation of dynamic performances of PSC girder railway bridges can be obtained from various parametric studies on dynamic behavior under the passage of moving train. Dynamic displacements, impact factor, acceleration of the slab, end rotation of the girder, and other important dynamic performance parameters are checked with various speeds of the train.

Fuzzy Control of Smart TMD using Multi-Objective Genetic Algorithm (다목적 유전자알고리즘을 이용한 스마트 TMD의 퍼지제어)

  • Kang, Joo-Won;Kim, Hyun-Su
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.24 no.1
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    • pp.69-78
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    • 2011
  • In this study, an optimization method using multi-objective genetic algorithm(MOGA) has been proposed to develop a fuzzy control algorithm that can effectively control a smart tuned mass damper(TMD). A 76-story benchmark building subjected to wind load was selected as an example structure. The smart TMD consists of 100kN MR damper and the natural period of the smart TMD was tuned to the first mode natural period of the example structure. Damping force of MR damper is controlled to reduce the wind-induced responses of the example structure by a fuzzy logic controller. Two input variables of the fuzzy logic controller are the acceleration of 75th floor and the displacement of the smart TMD and the output variable is the command voltage sent to MR damper. Multi-objective genetic algorithm(NSGA-II) was used for optimization of the fuzzy logic controller and the acceleration of 75th story and the displacement of the smart TMD were used as objective function. After optimization, a series of fuzzy logic controllers which could appropriately reduce both wind responses of the building and smart TMD were obtained. Based on numerical results, it has been shown that the control performance of the smart TMD is much better than that of the passive TMD and it is even better than that of the sample active TMD in some cases.

Analysis of Response Characteristics According to Permanent Displacement in Seismic Slope (지진시 비탈면의 영구변위 발생에 따른 응답특성 분석)

  • Ahn, Jae-Kwang;Park, Sangki;Kim, Wooseok;Son, Su-Won
    • Journal of the Korean Geotechnical Society
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    • v.35 no.12
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    • pp.135-145
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    • 2019
  • The slope collapse can be classified into internal and external factors. Internal factors are engineering factors inherent in the formation of slopes such as soil depth, slope angle, shear strength of soil, and external factors are external loading such as earthquakes. The external factor for earthquake can be expressed by various values such as peak ground acceleration (PGA), peak ground velocity (PGV), Arias coefficient (I), natural period (Tp), and spectral acceleration (SaT=1.0). Specially, PGA is the most typical value that defines the magnitude of the ground motion of an earthquake. However, it is not enough to consider the displacement in the slope which depends on the duration of the earthquake even if the vibration has the same peak ground acceleration. In this study, numerical analysis of two-dimensional plane strain conditions was performed on engineered block, and slope responses due to seismic motion of scaling PGA to 0.2 g various event scenarios was analyzed. As a result, the response of slope is different depending on the presence or absence of sliding block; it is shown that slope response depend on the seismic wave triggering sliding block than the input motion factors.