• Title/Summary/Keyword: modal analysis

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A Study on the Vibrational Characteristics of a Foot Mount Type Gearbox for Epicyclic Gear Train (바닥고정형 유성기어박스의 진동특성에 관한 연구)

  • Lee, Dong-Hwan;Yun, In-Seong;Cheon, Gil-Jeong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.10 s.181
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    • pp.2619-2627
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    • 2000
  • In this paper, the vibrational characteristics of a foot mount type gearbox for epicyclic gear train have been studied. The modal parameters and mode shapes of a gearbox have been computed using AN SYS code. Modal testing was carried out to verify the FEM analysis model. It has been shown that the analysis results are in good agreements with the experimental results. Harmonic analysis has been executed to verify the effect of thickness variance of gearbox housing on the modal response. Analyzing the calculated results, some guides for optimal vibration response has been deduced.

Seismic Fragility Analysis of the Structure Considering Composite Modal Damping (복합모드감쇠를 고려한 구조물의 지진취약도분석)

  • 조성국;조양희;박형기;황규호
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 2001.09a
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    • pp.200-207
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    • 2001
  • This paper introduces a methodology of seismic fragility analysis and discusses the basic input variables, focusing on the conservatism and variability of reference response spectrum. The procedures to consider the composite modal damping in the seismic fragility analysis is presented and its effects on the seismic capacity of structure is evaluated through an example analysis of the nuclear power plant structure which has typical composite modal damping characteristics. Two seismic fragility analyses were performed to obtain the seismic capacities which evaluated by considering the composite modal damping and the single damping characteristics. The results showed that the seismic fragility analysis without considering the different values of composite modal damping may considerably overestimate the seismic capacity of coupled structures.

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A Study on the Vibrational Characteristics of a Gearbox for Epicyclic Gear Train (유성기어박스의 진동특성에 관한 연구)

  • Lee, Dong-Hwan;Youn, In-Seong;Cheon, Gill-Jeong
    • Proceedings of the KSME Conference
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    • 2000.04a
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    • pp.837-842
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    • 2000
  • In this Paper, the vibrational characteristics of a gearbox for epicyclic Rear train have been studied The modal parameters and mode shapes of a gearbox have been computed using ANSYS code. Modal testing was carried out to verity the FEM analysis model. It has been shown that the analysis results are m good agreements with the experimental results. Harmonic analysis has been executed to verify the effect of thickness variance of gearbox housing on the modal response. Analyzing the calculated results, some guides fer optimal vibration response has been deduced.

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Modal analysis of asymmetric/anisotropic rotor system using modulated coordinates (변조좌표계를 이용한 비대칭/비등방 회전체의 모드 해석)

  • 서정환;홍성욱;이종원
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2003.11a
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    • pp.304-309
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    • 2003
  • A new modal analysis method for rotor systems with periodically time-varying parameters is proposed. The essence of method is to introduce modulated coordinates to derive the equivalent time-invariant equation. This paper presents a modal analysis method using modulated coordinates fur general rotors, of which rotating and stationary parts both possess asymmetric properties. The equation of motion with time-varying parameters is transformed to an infinite order matrix equation with the time-invariant parameters. A theory of modal analysis for the system is presented with the infinite order equation and a couple of reduced order equations. A numerical example with simple asymmetric rotor is provided to demonstrate the effectiveness of the proposed method

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Variability analysis on modal parameters of Runyang Bridge during Typhoon Masta

  • Mao, Jian-Xiao;Wang, Hao;Xun, Zhi-Xiang;Zou, Zhong-Qin
    • Smart Structures and Systems
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    • v.19 no.6
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    • pp.653-663
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    • 2017
  • The modal parameters of the deck of Runyang Suspension Bridge (RSB) as well as their relationships with wind and temperature are studied based on the data recorded by its Structural Health Monitoring System (SHMS). Firstly, frequency analysis on the vertical responses at the two sides of the deck is carried out to distinguish the vertical and torsional vibration modes. Then, the vertical, torsional and lateral modal parameters of the deck of RSB are identified using Hilbert-Huang Transform (HHT) and validated by the identified results before RSB was opened to traffic. On the basis of this, the modal frequencies and damping ratios of RSB during the whole process of Typhoon Masta are obtained. And the correlation analysis on the modal parameters and wind environmental factors is then conducted. Results show that the HHT can achieve an accurate modal identification of RSB and the damping ratios show an obvious decay trend as the frequencies increase. Besides, compared to frequencies, the damping ratios are more sensitive to the environmental factors, in particular, the wind speed. Further study on configuring the variation law of modal parameters related with environmental factors should be continued.

Theoretical research on the identification method of bridge dynamic parameters using free decay response

  • Tan, Guo-Jin;Cheng, Yong-Chun;Liu, Han-Bing;Wang, Long-Lin
    • Structural Engineering and Mechanics
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    • v.38 no.3
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    • pp.349-359
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    • 2011
  • Input excitation and output response of structure are needed in conventional modal analysis methods. However, input excitation is often difficult to be obtained in the dynamic load test of bridge structures. Therefore, what attracts engineers' attention is how to get dynamic parameters from the output response. In this paper, a structural experimental modal analysis method is introduced, which can be used to conveniently obtain dynamic parameters of the structure from the free decay response. With known damping coefficients, this analysis method can be used to identify the natural frequencies and the mode shapes of MDOF structures. Based on the modal analysis theory, the mathematical relationship of damping ratio and frequency is obtained. By using this mathematical relationship to improve the previous method, an improved experimental modal analysis method is proposed in this paper. This improved method can overcome the deficiencies of the previous method, which can not identify damping ratios and requires damping coefficients in advance. Additionally, this improved method can also identify the natural frequencies, mode shapes and damping ratios of the bridge only from the free decay response, and ensure the stability of identification process by using modern mathematical means. Finally, the feasibility and effectiveness of this method are demonstrated by a numerical example of a simply supported reinforced concrete beam.

Vibration modelling and structural modification of combine harvester thresher using operational modal analysis and finite element method

  • Zare, Hamed Ghafarzadeh;Maleki, Ali;Rahaghi, Mohsen Irani;Lashgari, Majid
    • Structural Monitoring and Maintenance
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    • v.6 no.1
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    • pp.33-46
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    • 2019
  • In present study, Operational Modal Analysis (OMA) was employed to carry out the dynamic and vibration analysis of the threshing unit of the combine harvester thresher as a mechanical component. The main study is to find the causes of vibration and to decrease it to enhance the lifetime and efficiency of the threshing unit. By utilizing OMA, structural modal parameters such as mode shapes, natural frequencies, and damping ratio was calculated. The combine harvester was excited by engine to vibrate different parts and accelerometer sensor collected acceleration signals at different speeds, and OMA was utilized by nonparametric and frequency analysis methods to obtain modal parameters while vibrating in real working conditions. Afterwards, finite element model was designed from the thresher and updated using the data obtained from the modal analysis. Using the conducted analyses, it was specified that proximity of the thresher pass frequency to one of the natural frequencies (16.64 Hz) was the most important effect of vibration in the thresher. Modification process of the structure was carried out by increasing mass required for changing the natural frequency location of the first mode to 12.4 Hz in order to reduce resonance and vibration of the thresher.

Modal Nodal Transport Analysis

  • Johnson, R.Douglas
    • Nuclear Engineering and Technology
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    • v.3 no.3
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    • pp.121-128
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    • 1971
  • A unified modal-nodal expansion of tile angular distribution of neutron flux in one spatial dimension is considered, following the proposal of Harms. Several standard nodal and/or modal methods of analysis are shown to be specializations of this technique. The modal-nodal moment from of the mono-energetic transport equation with isotropic sources and scattering is derived and the infinite medium eigenvalue problem solved. The technique is shown to yield results which approximate the exact value of the inverse diffusion length in non-multiplying media more accurately than standard methods of equal or somewhat greater computational complexity.

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Study on the Analysis of Structural Dynamic Characteristics and Modal Test of Unmanned Helicopter Rotor Blades (무인헬리콥터 로터 블레이드의 구조적 진동특성 분석 및 시험에 관한 연구)

  • 정경렬;이종범;한성호;최길봉
    • Journal of KSNVE
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    • v.5 no.2
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    • pp.215-224
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    • 1995
  • In this paper, the three-dimensional finite element model is established to investigate the structural dynamic characteristics of rotor blade using a finite element analysis. Six natural frequencies and mode shapes are calculated by computer simulation. The first three flapping modal frequencies, the first two lead-lag modal frequencies, and the first feathering modal frequency are validated through comparison with the modal test results of the fixed rotor blade. The computer simulation results are found in good agreement with experimentally measured natural frequencies. The important results are obtained as follows: (1) Natural frequencies are changed due to the variation of rotational speed and fiber angle of rotor blade, (2) Weak coupling between flapping mode shape and lead-lag mode shape are detected, (3) Centrifugal force has more effect on flapping modal frequency than lead-lag modal frequency.

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Modal Synthesis Method Using Interpolated Rotational DOF (회전자유도 보간에 의한 모드합성법)

  • 장경진;지태한;박영필
    • Journal of KSNVE
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    • v.5 no.4
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    • pp.503-514
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    • 1995
  • In the case of performing experimental modal analysis(EMA) and finite- element analysis(EFA) for a whole structure of automotive body that is composed of many complex parts, a trouble may arise from the calculation time, the capacity of memory in computers and the experimental conditions, etc. In this paper, for the vibrational analysis of automotive body model, the efficient modal synthesis method by means of dividing the whole structure into two parts and performing EMA and FEA for each part is studied. In addition, the method based on Lagrange interpolation is proposed for approximating rotational degrees-of-freedom information and linking FEA with EMA. In result, by measuring translational degrees-of-freedom information of only few points and adopting only few modes, the linking method based on Lagrange interpolation turned out to be efficient and accurate in the low frequency range.

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