ERA modal identification method for hydraulic structures based on order determination and noise reduction of singular entropy

Lian, Jijian; Li, Huokun; Zhang, Jianwei

doi:10.1007/s11431-008-0200-z

Cited by 37 publications

(22 citation statements)

References 10 publications

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“…Based on this characteristic, singular entropy theory is used to determine the order of the modal system. The definition of singular entropy 18 is…”

Section: Stochastic Subspace Modal Identification Methods Based On Thementioning

confidence: 99%

Beat vibration mechanism of a sluice pier under high-speed flood discharge excitation

Zhong

Wei

et al. 2019

Journal of Low Frequency Noise, Vibration and Active Control

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The sluice pier prototype vibration test conducted in China Shuhe Hydropower Station shows that the vibration response of the measuring points exhibits a special form of vibration, which demonstrates intermittency and impact under high-speed flood discharge excitation. The waveform envelope increases or decreases sharply with time and shows the formation of beat vibration. Research on the mechanism of this type of vibration is rare. To analyze the characteristics and causes of the obvious beat phenomenon in the testing of the sluice pier prototype, we conduct research in the following manner. First, mathematical models of synthetic signals are built to analyze the influences of initial phase difference, frequency ratio, and amplitude ratio and determine the beat vibration formation condition. Second, the stochastic subspace identification method is used to identify the operational modal parameters (including the vibration order, frequency, damping ratio, and mode of vibration) on the basis of the measured prototype dynamic response. Last, the internal causes of the beat vibration phenomenon are analyzed based on the combination of the formation conditions of apparent beat vibration. Results show that the vibration of Shuhe sluice pier is dominated by the first two frequency components. The vibration frequency ratio is between 0.928 and 0.962 and satisfies the necessary conditions of beat vibration. The amplitude ratio is between 0.66 and 1.63 and thus makes the waveforms of beat vibration highly evident.

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“…Based on this characteristic, singular entropy theory is used to determine the order of the modal system. The definition of singular entropy 18 is…”

Section: Stochastic Subspace Modal Identification Methods Based On Thementioning

confidence: 99%

Beat vibration mechanism of a sluice pier under high-speed flood discharge excitation

Zhong

Wei

et al. 2019

Journal of Low Frequency Noise, Vibration and Active Control

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show abstract

“…Generally, the order k of the projection matrix O ie , which can be determined by the singular entropy (SE) method, 36 reflects the number of system non-zero singular values with the 033128-7 assumption that ðmi þ 2hÞ ! k. So, by performing SVD decomposition on the projection matrix O ie , the following can be obtained:…”

Section: A Hm-ssi Methodsmentioning

confidence: 99%

Operational modal identification of offshore wind turbine structure based on modified stochastic subspace identification method considering harmonic interference

Dong

Lian

Yang

2014

Journal of Renewable and Sustainable Energy

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The structural modal parameter information can be generally obtained from different vibration responses triggered by unknown excitations using the classic modal identification methods which are based on the assumption that the input to the structure is exactly the same or close to the stationary random white noise. For the actual projects such as the offshore wind turbine structure, however, the imposed loads cannot be considered as the pure white noise excitation because the harmonic components emerge obviously in vibration responses due to periodic rotation excitations of the rotor. When the created harmonic components have greater energy and their frequencies are close to any natural modal frequency of the structure, the classic methods can no longer separate harmonic modes from actual structural operational modes under this strong harmonic disturbance, thus false modes may be generated and the identification accuracy may be badly affected. To identify the actual structural operational modes accurately under strong harmonic excitation, a modified stochastic subspace identification (SSI) method considering harmonic interference called the harmonic modification SSI (HM-SSI) method was proposed in this paper assuming the input harmonic frequencies are known and time-invariant. Then the effectiveness and accuracy of the HM-SSI method were verified through a simple numerical model of cantilever beam excited by various harmonic inputs superimposed on random loads. Besides, the superior robustness and better accuracy of identification results affected by the level of noise and the proportion of harmonic energy were reflected. Finally, the modal parameter information under different operational conditions was obtained and the safety assessment of an operational wind turbine was made based on the measured data from one offshore wind turbine test prototype at high running speed.

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“…Compared with the operational modal parameter identification by eigensystem realization algorithm (ERA) on the same project [42], it is shown that the vibration appears as the vibration of an integral structure, rather than the independent vibration of each block, due to the transmission of shear forces through joints and thermal expansion (the tests were implemented in the summer). Therefore, the cementation between adjacent blocks is considered, with the integral numerical models built, and the frequencies of the dam and the guide wall are calculated for both dry and wet modes.…”

Section: Numerical Simulationmentioning

confidence: 99%

Analysis for the Vibration Mechanism of the Spillway Guide Wall Considering the Associated-Forced Coupled Vibration

et al. 2019

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During the flood discharge in large-scale hydraulic engineering projects, intense flow-induced vibrations may occur in hydraulic gates, gate piers, spillway guide walls, etc. Furthermore, the vibration mechanism is complicated. For the spillway guide wall, existing studies on the vibration mechanism usually focus on the vibrations caused by flow excitations, without considering the influence of dam vibration. According to prototype tests, the vibrations of the spillway guide wall and the dam show synchronization. Thus, this paper presents a new vibration mechanism of associated-forced coupled vibration (AFCV) for the spillway guide wall to investigate the dynamic responses and reveal coupled vibrational properties and vibrational correlations. Different from conventional flow-induced vibration theory, this paper considers the spillway guide wall as a lightweight accessory structure connected to a large-scale primary structure. A corresponding simplified theoretical model for the AFCV system is established, with theoretical derivations given. Then, several vibrational signals measured in different structures in prototype tests are handled by the cross-wavelet transform (XWS) to reveal the vibrational correlation between the spillway guide wall and the dam. Afterwards, mutual analyses of numeral simulation, theoretical derivation, and prototype data are employed to clarify the vibration mechanism of a spillway guide wall. The proposed mechanism can give more reasonable and accurate results regarding the dynamic response and amplitude coefficient of the guide wall. Moreover, by changing the parameters in the theoretical model through practical measures, the proposed vibration mechanism can provide benefits to vibration control and structural design.

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ERA modal identification method for hydraulic structures based on order determination and noise reduction of singular entropy

Cited by 37 publications

References 10 publications

Beat vibration mechanism of a sluice pier under high-speed flood discharge excitation

Beat vibration mechanism of a sluice pier under high-speed flood discharge excitation

Operational modal identification of offshore wind turbine structure based on modified stochastic subspace identification method considering harmonic interference

Analysis for the Vibration Mechanism of the Spillway Guide Wall Considering the Associated-Forced Coupled Vibration

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