• Title/Summary/Keyword: FE modal analysis

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Prestress-Loss Monitoring Technique for Prestressd Concrete Girders using Vibration-based System Identification (진동기반 구조식별을 통한 프리스트레스트 콘크리트 거더의 긴장력 손실 검색 기법)

  • Ho, Duc-Duy;Hong, Dong-Soo;Kim, Jeong-Tae
    • Journal of Ocean Engineering and Technology
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    • v.24 no.1
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    • pp.123-132
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    • 2010
  • This paper presents a prestress-loss monitoring technique for prestressed concrete (PSC) girder structures that uses a vibration-based system identification method. First, the theoretical backgrounds of the prestress-loss monitoring technique and the system identification technique are presented. Second, vibration tests are performed on a lab-scaled PSC girder for which the modal parameter was measured for several prestress-force cases. A numerical modal analysis is performed by using an initial finite element (FE) model from the geometric, material, and boundary conditions of the lab-scaled PSC girder. Third, a vibration-based system identification is performed to update the FE model by identifying structural parameters since the natural frequency of the FE model became identical to the experimental results. Finally, the feasibility of the prestress-loss monitoring technique is evaluated for the PSC girder model by using the experimentally measured natural frequency and numerically identified natural frequency for several prestress-force cases.

Analysis of Vibration and Electromagnetic Forces on a Generator End-winding for 500 MW Fossil Power Plant (500MW 급 대형 발전기 권선단부의 전자기력과 동특성 해석)

  • 김철홍;주영호
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.11b
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    • pp.826-831
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    • 2001
  • Electromagnetic forces generate vibrations in the end-winding of large generators. A finite element analysis using a commercial S/W is performed to calculate electromagnetic force of end-winding in two pole generator for 500 MW fossil power plant. Also, this paper presents analytical and experimental modal analysis results of generator end- winding. Using validated FE model, 3D electromagnetic model which computes the forces on the end-winding is coupled with a 3D mechanical model which calculates the dynamic displacement and stress under electromagnetic forces. These results will be used to evaluate reliability of end-winding and applied to update model.

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FE model updating based on hybrid genetic algorithm and its verification on numerical bridge model

  • Jung, Dae-Sung;Kim, Chul-Young
    • Structural Engineering and Mechanics
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    • v.32 no.5
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    • pp.667-683
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    • 2009
  • FE model-based dynamic analysis has been widely used to predict the dynamic characteristics of civil structures. In a physical point of view, an FE model is unavoidably different from the actual structure as being formulated based on extremely idealized engineering drawings and design data. The conventional model updating methods such as direct method and sensitivity-based parameter estimation are not flexible for model updating of complex and large structures. Thus, it is needed to develop a model updating method applicable to complex structures without restriction. The main objective of this paper is to present the model updating method based on the hybrid genetic algorithm (HGA) by combining the genetic algorithm as global optimization method and modified Nelder-Mead's Simplex method as local optimization method. This FE model updating method using HGA does not need the derivation of derivative function related to parameters and without application of complicated inverse analysis methods. In order to allow its application on diversified and complex structures, a commercial FEA tool is adopted to exploit previously developed element library and analysis algorithms. Moreover, an output-level objective function making use of measurement and analytical results is also presented to update simultaneously the stiffness and mass of the analysis model. The numerical examples demonstrated that the proposed method based on HGA is effective for the updating of the FE model of bridge structures.

Development of Connection Model based on FE Analysis to Ensure Stability of Steel Storage Racks (적재설비 안정성 확보를 위한 FE 해석 기반의 연결부 모델 개발)

  • Heo, Gwanghee;Kim, Chunggil;Yu, Darly;Jeon, Jongsu;Lee, Chinok
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.38 no.2
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    • pp.349-356
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    • 2018
  • This paper attempts to develop a connection model based on FE analysis that can be applied to the evaluation of earthquake fragility of Steel Storage Racks lacking research in Korea. In order to accomplish this goal, shaking table tests, modal tests, and various member tests (8 case, push-over test) for structural members have been conducted to understand the behavior of steel storage racks. Based on the experimental results, detailed modeling of the joints was conducted using the NX-Nastran program in order to develop a connection model for Steel storage racks to be applied to the seismic vulnerability assessment. Especially, surface to surface contact element and spring element are applied to simulate the connection between the column member and the beam member connected by the simple latch method. Spring element model developed and applied ARX (Auto Regressive eXogenous) based mathematical model. The simulation results based on the FE model showed excellent reliability with a mutual error rate of less than 8% when compared with the member test results. As a result, it was confirmed that the FE model based connection model developed in the study can be applied to the analytical model for the seismic vulnerability assessment of Steel storage racks.

A study on the Base Plate to reduce vibration for Refrigerator (Base Plate 연구를 통한 냉장고 진동 저감 방안 고찰)

  • Kim, Jung-Seon;Thuy, Tran Ho Vinh;Kook, Jung-Hwan;Wang, Se-Myung;Lee, Dong-Hyun
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.05a
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    • pp.340-343
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    • 2007
  • In this paper, we present our method to reduce vibration of the base plate of a refrigerator by avoiding resonance between base plate and compressor operation. To verify the modes of the base plate, FE models of the base plate with free-free condition and applied boundary condition were built and validated by results from experimental modal analysis. Operating Deflection Shape analysis was applied to find the sensitive area on the base plate during compressor operation. In optimization process, Finite Difference Method - based sensitivity analysis is used to detect the most sensitive area. Finally, based on this numerical result, we will make beads on the base plate to reduce vibration of refrigerator.

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Automated Simulation System for Micromachines (마이크로머쉰의 자동 시뮬레이션시스템)

  • 이준성
    • Journal of the Korea Society for Simulation
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    • v.5 no.1
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    • pp.28-42
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    • 1996
  • This paper describes a new automated simulation system for micromachines whose size range $10^{-6}$ to $10^{-3}$ m. An automic finite element (FE) mesh generation technique, which is bases on the fuzzy knowledge processing and computation al geometry technique, is incorporated into the system, together with one of commerical FE analysis codes, MARC ,and one of commerical solid modelers, Designbase. The system allows a geometry model of concern to be automatically converted to different FE models, depending on physical phenomena of micromachines to be analyzed , i,e. electrostatic analysis, stress analysis, modal analysis and so on. The FEmodels are then automatically analyzed using the FE analysis code, Among a whole process of analysis, the definition of a geometry model, the designation of local node patterns and the assignment of material properties and boundary conditions onto the geometry model are only the interactive process to be done by a user. The interactive operations can be processed in a few minutes. The other processes which are time consuming and labour-intensive in conventional CAE systems are fully automatically performed in a popular engineering workstation environment. This automated simulation system is successfully applied to evaluate an electrostatic micro wobble actuator.

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Free vibration of actual aircraft and spacecraft hexagonal honeycomb sandwich panels: A practical detailed FE approach

  • Benjeddou, Ayech;Guerich, Mohamed
    • Advances in aircraft and spacecraft science
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    • v.6 no.2
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    • pp.169-187
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    • 2019
  • This work presents a practical detailed finite element (FE) approach for the three-dimensional (3D) free-vibration analysis of actual aircraft and spacecraft-type lightweight and thin honeycomb sandwich panels. It consists of calling successively in $MATLAB^{(R)}$, via a developed user-friendly GUI, a detailed 3D meshing tool, a macrocommands language translator and a commercial FE solver($ABAQUS^{(R)}$ or $ANSYS^{(R)}$). In contrary to the common practice of meshing finely the faces and core cells, the proposed meshing tool represents each wall of the actual hexagonal core cells as a single two-dimensional (2D) 4 nodes quadrangularshell element or two 3 nodes triangular ones, while the faces meshes are obtained simply using the nodes at the core-faces interfaces. Moreover, as the same 2D FE interpolation type is used for meshing the core and faces, this leads to an automatic handling of their required FE compatibility relations. This proposed approach is applied to a sample made of very thin glass fiber reinforced polymer woven composite faces and a thin aluminum alloy hexagonal honeycomb core. The unknown or incomplete geometric and materials properties are first collected through direct measurements, reverse engineering techniques and experimental-FE modal analysis-based inverse identification. Then, the free-vibrations of the actual honeycomb sandwich panel are analyzed experimentally under different boundary conditions and numerically using different mesh basic cell shapes. It is found that this approach is accurate for the first few modes used for pre-design purpose.

Study on Analysis of Vibration Characteristics and Modal Test for a Quad-Rotor Drone (쿼드로터형 드론의 진동특성 분석 및 실험에 관한 연구)

  • Kim, Minsong;Kim, Jaenam;Byun, Youngseop;Kim, Jeong;Kang, Beomsoo
    • Journal of the Korean Society for Precision Engineering
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    • v.33 no.9
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    • pp.707-714
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    • 2016
  • This paper describes analysis results of vibration characteristics and modal test for a small-scale quad-rotor drone. The rotor arm has a slender body with a propeller and motor at its tip. Rotor system generates excitation for an unbalanced mass. Therefore, the drone platform is involved in the possibility of resonance. For advance identification of the possibility of resonance, confirmation of eigen-mode being closest to the propeller operation range is necessary. Material properties of CFRP tubes used for the rotor arm were acquired by finding the natural frequency based on Rayleigh method. A simplified quad-rotor FE model consisting of rotor arm assembly with tip mass was built to perform numerical analysis, and a free-free boundary condition was applied to provide flight status. Modal tests for the actual platform with impact hammer instrument were performed to verify analysis results. Separation margin from hazardous eigen-mode was checked on the propeller operation range.

Ambient Vibration Testing and System Identification for Tall Buildings (고층건물의 자연 진동실험 및 시스템판별)

  • Cho, Soon-Ho
    • Journal of the Earthquake Engineering Society of Korea
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    • v.16 no.3
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    • pp.23-33
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    • 2012
  • Dynamic response measurements from natural excitation were carried out for three 18-story office buildings to determine their inherent properties. The beam-column frame system was adopted as a typical structural form, but a core wall was added to resist the lateral force more effectively, resulting in a mixed configuration. To extract modal parameters such as natural frequencies, mode shapes and damping ratios from a series of vibration records at each floor, the most advanced operational system identification methods based on frequency- and time-domain like FDD, pLSCF and SSI were applied. Extracted frequencies and mode shapes from the different identification methods showed a greater consistency for three buildings, however the three lower frequencies extracted were 1.2 to 1.7 times as stiff as those obtained using the initial FE models. Comparing the extracted fundamental periods with those estimated from the code equations and FE analysis, the FE analysis results showed the most flexible behavior, and the most simple equation that considers the building height as the only parameter correlated fairly well with test results. It is recognized that such a discrepancy arises from the fact that the present tests exclude the stiffness decreasing factors like concrete cracking, while the FE models ignore the stiffness increasing factors, such as the contribution of non-structural elements and the actual material properties used.

A Study on the Numerical Methodologies of Hydroelasticity Analysis for Ship Springing Problem (스프링잉 응답을 위한 유탄성 해석의 수치기법에 대한 연구)

  • Kim, Yoo-Il;Kim, Kyong-Hwan;Kim, Yong-Hwan
    • Journal of the Society of Naval Architects of Korea
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    • v.46 no.3
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    • pp.232-248
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    • 2009
  • Numerical methodology to solve ship springing problem, which is basically fluid-structure interaction problem, was explored in this study. Solution of this hydroelasticity problem was sought by coupling higher order B-spline Rankine panel method and finite element method in time domain, each of which is introduced for fluid and structure domain respectively. Even though varieties of different combinations in terms of numerical scheme are possible and have been tried by many researchers to solve the problem, no systematic study regarding the characteristics of each scheme has been done so far. Here, extensive case studies have been done on the numerical schemes especially focusing on the iteration method, FE analysis of beam-like structure, handling of forward speed problem and so on. Two different iteration scheme, Newton style one and fixed point iteration, were tried in this study and results were compared between the two. For the solution of the FE-based equation of motion, direct integration and modal superposition method were compared with each other from the viewpoint of its efficiency and accuracy. Finally, calculation of second derivative of basis potential, which is difficult to obtain with accuracy within grid-based method like BEM was discussed.