• Title/Summary/Keyword: 구조응답해석

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Modal Parameter Estimations of Wind-Excited Structures based on a Rational Polynomial Approximation Method (유리분수함수 근사법에 기반한 풍하중을 받는 구조물의 동특성 추정)

  • Kim, Sang-Bum;Lee, Wan-Soo;Yun, Chung-Bang
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.11a
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    • pp.287-292
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    • 2005
  • This paper presents a rational polynomial approximation method to estimate modal parameters of wind excited structures using incomplete noisy measurements of structural responses and partial measurements of wind velocities only. A stochastic model of the excitation wind force acting on the structure is estimated from partial measurements of wind velocities. Then the transfer functions of the structure are approximated as rational polynomial functions. From the poles and zeros of the estimated rational polynomial functions, the modal parameters, such as natural frequencies, damping ratios, and mode shapes are extracted. Since the frequency characteristics of wind forces acting on structures can be assumed as a smooth Gaussian process especially around the natural frequencies of the structures according to the central limit theorem (Brillinger, 1969; Yaglom, 1987), the estimated modal parameters are robust and reliable with respect to the assumed stochastic input models. To verify the proposed method, the modal parameters of a TV transmission tower excited by gust wind are estimated. Comparison study with the results of other researchers shows the efficacy of the suggested method.

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A Study on the Dynamic Response Analysis of Shell Structure with Impulsive Load by Reanalysis Technique (재해석 기법에 의한 충격 하중을 받는 쉘 구조물의 동적 응답 해석에 관한 연구)

  • 배동명
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.29 no.2
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    • pp.132-151
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    • 1993
  • The proposed method in this paper. termed the substructural reanalysis technique, utilizes the computational merits of the component mode synthesis technique and of reanalysis technique for the design sensitivities of the dynamic characteristics of substructurally combined structure. It is shown that the dynamic characteristics of the entire structure can be obtained by synthesizing the substructural eigensolution and the characteristics of the eigensolution for the design variables of the modifiable substructure. In this paper , the characteristics of the eigenvalue problems obtained by this proposed method are compared to exact eigensolution in terms of accuracy and computational efficiency. and the advantage of this proposed method as compared to the direct application of the whole structure and experimental results is demonstrated through examples of numerical calculation for the dynamic characteristics (natural frequencies and mode shapes) of a flexible vibration of thin cylinderical shell with branch shell under 2-end fixed positions, boundary condition. Thin cylinderical shell of overall length 1280mm, external diameter 360mm, thickness 3mm with branch shell is made of mild steel. The load condition for dynamic response in this paper is impulsive load of which magnitude is 10kgf, which have short duration of 0.1 sec. and time interval applied to calculate. $\Delta$T is 1.0$\times$10 super(-4) seconds.

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Analysis of Three-dimensional Earthquake Responses of a Floating Offshores Structure with an Axisymmetric Floating Structure (축대칭 부유구조물을 가지는 부유식 해양구조물의 3차원 지진응답 해석기법 개발)

  • Lee, Jin Ho;Kim, Jae Kwan
    • Journal of the Earthquake Engineering Society of Korea
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    • v.19 no.4
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    • pp.145-159
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    • 2015
  • A seismic response analysis method for three-dimensional floating offshore structures due to seaquakes is developed. The hydrodynamic pressure exerted on the structure is calculated taking into account the compressibility of the sea water, the fluid-structure interaction, the energy absorption by the seabed, and the energy radiation into infinity. To validate developed method, the hydrodynamic pressure induced by the vibration of a floating massless rigid circular disk is calculated and compared with an exact analytical solution. The developed method is applied to seismic analysis of a support structure for a floating offshore wind turbine subjected to the hydrodynamic pressures induced from a seaquake. Analysis results show that earthquake response of a floating offshore structure can be greatly influenced by the compressibility of fluid, the depth (natural frequencies) of the fluid domain, and the energy absorption capacity of the seabed.

Fluidic Thrust Vector Control Using Shock Wave Concept (충격파 개념에 기반한 유체 추력벡터제어에 관한 연구)

  • Wu, Kexin;Kim, Heuy Dong
    • Journal of the Korean Society of Propulsion Engineers
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    • v.23 no.4
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    • pp.10-20
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    • 2019
  • Recently, fluidic thrust vector control has become a core technique to control multifarious air vehicles, such as supersonic aircraft and modern rockets. Fluidic thrust vector control using the shock vector concept has many advantages for achieving great vectoring performance, such as fast vectoring response, simple structure, and low weight. In this paper, computational fluid dynamics methods are used to study a three-dimensional rectangular supersonic nozzle with a slot injector. To evaluate the reliability and stability of computational methodology, the numerical results were validated with experimental data. The pressure distributions along the upper and lower nozzle walls in the symmetry plane showed an excellent match with the test results. Several numerical simulations were performed based on the shear stress transport(SST) $k-{\omega}$ turbulence model. The effect of the momentum flux ratio was investigated thoroughly, and the performance variations have been clearly illustrated.

Quantitative Nondestructive Evaluation in Composite Beam Using Piezoelectric Transducers (압전 변환기를 이용한 복합재료 보의 비파괴 평가)

  • Lee, Sang-Hyoup;Choi, Young-Geun;Kim, Sang-Tae
    • Composites Research
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    • v.20 no.3
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    • pp.31-36
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    • 2007
  • A quantitative prediction method for initial crack length in a carbon/epoxy (CF/EP) composite beam using active piezoelectric transducers was established in this study. Wavelet Transform (WT)-based signal processing and identification technique in time-frequency domain was developed to facilitate the determination of damage presence and severity. Dynamic response of a CF/EP composites beam containing a continuously expanding crack, coupled with a pair of active piezoelectric disks, was examined under a narrow band excitation, and then applied with the proposed signal processing technique.

Dynamic Characteristics of a Cable-stayed Bridge Using Global Navigation Satellite System (GNSS를 이용한 사장교의 동특성 평가)

  • Park, Jong Chil;Gil, Heung Bae;Kang, Sang Gyu;Lim, Chae Woon
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.30 no.4A
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    • pp.375-382
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    • 2010
  • This paper presents the extraction of natural frequencies and mode shapes of a cable-stayed bridge using data acquired from GNSS. The response signals of 6 GNSS measuring points installed at the Seohae cable-stayed bridge are used for analysis of dynamic characteristics. Using normalization process and a third order Butterworth filter for the measured signals, the related pass band's signals have been isolated. Then, the acceleration data by double differentiation for these signals are obtained. Total five natural frequencies have been extracted by the fast Fourier transform and compared to the results of different studies. For the acceleration obtained from GNSS signals, the mode shapes of the bridge have been successfully extracted by TDD technique.

Reliability Analysis of Offshore Wind Turbines Considering Soil-Pile Interaction and Scouring Effect (지반과 말뚝의 상호작용 및 세굴현상을 고려한 해상풍력터빈의 신뢰성 해석)

  • Yi, Jin-Hak;Kim, Sun-Bin;Yoon, Gil-Lim
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.28 no.4
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    • pp.222-231
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    • 2016
  • Multi-member lattice-type structures including jackets and tripods are being considered as good alternatives to monopile foundations for relatively deep water of 25-50 m of water depth owing to their technical and economic feasibility. In this study, the reliability analysis of bottom-fixed offshore wind turbines with monopile and/or multi-member lattice-type foundations is carried out and the sensitivities of random variables such as material properties, external wind loadings and scouring depth are compared with respect to different types of foundations. Numerical analysis of the NREL 5 MW wind turbine supported by monopile, tripod and jacket substructures shows that the uncertainties of soil properties affect the reliability index more significantly for the monopile-supported OWTs while the reliability index is not so sensitive to the material properties in the cases of tripod- and jacket-supported OWTs. In conclusion, the reliability analysis can be preliminarily carried out without considering soil-pile-interaction in the cases of tripod- and jacket-supported OWTs while it is very important to use the well-measured soil properties for reliable design of monopile-supported OWTs.

Behavior of Truss Railway Bridge Using Periodic Static and Dynamic Load Tests (주행 열차의 정적 및 동적 재하시험 계측 데이터를 이용한 트러스 철도 교량의 주기적 거동 분석)

  • Jin-Mo Kim;Geonwoo Kim;Si-Hyeong Kim;Dohyeong Kim;Dookie Kim
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.27 no.6
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    • pp.120-129
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    • 2023
  • To evaluate the vertical loads on railway bridges, conventional load tests are typically conducted. However, these tests often entail significant costs and procedural challenges. Railway conditions involve nearly identical load profiles due to standardized rail systems, which may appear straightforward in terms of load conditions. Nevertheless, this study aims to validate load tests conducted under operational train conditions by comparing the results with those obtained from conventional load tests. Additionally, static and dynamic structural behaviors are extracted from the measurement data for evaluation. To ensure the reliability of load testing, this research demonstrates feasibility through comparisons of existing measurement data with sensor attachment locations, train speeds, responses between different rail lines, tendency analysis, selection of impact coefficients, and analysis of natural frequencies. This study applies to the Dongho Railway Bridge and verifies the applicability of the proposed method. Ten operational trains and 44 sensors were deployed on the bridge to measure deformations and deflections during load test intervals, which were then compared with theoretical values. The analysis results indicate good symmetry and overlap of loads, as well as a favorable comparison between static and dynamic load test results. The maximum measured impact coefficient (0.092) was found to be lower than the theoretical impact coefficient (0.327), and the impact influence from live loads was deemed acceptable. The measured natural frequencies approximated the theoretical values, with an average of 2.393Hz compared to the calculated value of 2.415Hz. Based on these results, this paper demonstrates that for evaluating vertical loads, it is possible to measure deformations and deflections of truss railway bridges through load tests under operational train conditions without traffic control, enabling the calculation of response factors for stress adjustments.

Investigation of Pohang Earthquake Liquefaction Using 1D Effective-Stress Site Response Analysis (1차원 유효응력개념의 지반응답해석을 통한 포항지진의 액상화 현상 규명)

  • Ahn, Jae-Kwang;Baek, Woo-Hyun;Choi, Jae-Soon;Kwak, Dong Youp
    • Journal of the Korean Geotechnical Society
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    • v.34 no.8
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    • pp.37-49
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    • 2018
  • Since the observation of ground motions in South Korea, liquefaction manifestation was the first to be observed in Pohang earthquake in 2017 with $M_L$ 5.4. Because liquefaction causes ground settlement and lateral spread damaging in-ground or super structures, various researchers have been analyzing the Pohang liquefaction case history to better understand and predict liquefaction consequence and to prevent future disasters. In prior research at the 2018 EESK conference, a map of Liquefaction Potential Index (LPI), indicating the severity of liquefaction, in Pohang was created and compared with damage observations. The LPI correlated well with the observations, but the severity categorized by LPI range was significantly higher than the actual observations in most regions. The prior LPI map was created evaluating ground motions using the simplified approach. In this research, we perform the effective site response analyses with porewater pressure generation model for the detailed evaluation of liquefaction on the liquefied sites in Pohang. We found that the simplified approach for LPI evaluation can overestimate the severity.

Propagation Characteristic Analysis of Square and Gaussian Pulse Signals on the Microstrip Line (구형 및 가우시안 펄스신호의 마이크로스트립 선로상 전파특성 해석)

  • Park, Sun-Kuen;kim, Nam;Rhee, Sung-Yup;Choi, Jung-Hyun
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.7 no.5
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    • pp.384-394
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    • 1996
  • The propagation properties of square and Gaussian pulse signals on the microstrip line are investigated by using proper conventional models to meet the frequency range of a pulse, accuracy, and geometrical requirements of the microstrip line. Numerical integration technique which has its accuracy and is easily simulated, is used to obtain the time domain response of pulse signals. The dispersion of pulse signals is analyzed regarding to the relative permittivity $\varepsilon_r$, substrate height h, strip width w of the microstrip line and pulse width $\tau$ of signal pulse. The simulation results show that small relative permittivity and small rationale of w/h are advantageous for the dispersion of the pulse signals, and that pulse signals with small bandwidth cause smaller dispersion. The results of this paper are compatible to the trade-off determination of relative permittivity, substrate height, strip width and pulse width of signal pulse when a design of MIC and MMIC is necessary.

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