This study focuses on the time-varying modal frequency identification of space solar power satellites. Accordingly, an improved recursive subspace identification algorithm based on the variable ...forgetting factor is proposed to enhance the tracking adaptability of the original method in time-varying systems. Considering the changes in the structural configuration induced by the rotation of the solar concentrator mirror, a time-varying attitude-vibration coupling dynamic model of a space solar power satellite with an integrated symmetrical concentrator configuration is developed based on the modal synthesis technology and the substructure method. Moreover, based on the projection subspace theory, the time-varying forgetting factor is determined by minimizing the mean square deviation of the system estimator. Subsequently, the variable forgetting factor subspace algorithm is adopted to recursively identify the time-varying pseudo modal frequency parameters. A finite element model of the space solar power satellite is established via numerical simulations, and several optimal sensor placement methods are applied to determine the positions of the vibration sensors. Based on the output signals obtained from the optimal sensor placement results, the time-varying frequency parameters of the system are obtained using the proposed algorithm. The computational results reveal that a decrease in the average relative error by 4.2% compared with that obtained via the conventional recursive subspace method is observed when the signal-to-noise-ratio of the measured output is selected as 15 dB. In addition, the results also reveal that an average relative error reduction of approximately 0.4%–1.4%, over two other methods with a fixed forgetting factor, can be achieved using the proposed algorithm when the rotation speed of the solar concentrator mirror is increased. The findings of this study confirm that the proposed algorithm demonstrates a high noise-immune ability and tracking performance for fast time-varying systems.
•The tower-line coupling effect is considered in the modal parameter identification.•An aeroelastic model of the tower-line system is fabricated.•An advanced 3D motion capture system is used to ...measure the response.•The parametric analysis is also carried out.
The modal parameters of transmission tower-line systems constitute the basis of their wind and seismic design. However, such structures become complicated spatial systems due to the coupling effects between the towers and lines, making it difficult to evaluate the modal parameters of a transmission tower. To study the tower-line coupling effects on the frequencies and mode shapes of a tower, a stochastic subspace identification (SSI) method for identifying modal parameters is first introduced. Then, a finite element model of a transmission tower-line system is established, and the influences of three transmission line parameters, namely, the total span length, span ratio and height difference angle, on the modal parameters are analyzed. An aeroelastic model of the tower-line system is fabricated, and a percussion experiment is performed. The simulated and experimental results both show that the first-order frequency increases with an increase in the total span length but is only slightly affected by changes in the span ratio and the height difference angle. For the wind and seismic design of transmission towers, to obtain reliable natural vibration characteristics, a complete tower-line system model should be established instead of a single tower model.
An improved identification method is proposed for the modal parameter identification of multi-modal vibration attenuation signals based on the analytical mode decomposition and the particle swarm ...optimization. Through examples of analog signals, it is proved that the proposed method can identify modal parameters under a strong colored noise environment. Field tests were carried out on four in-service aluminum alloy reticulated structures to obtain the acceleration response of the structures. The improved identification method proposed in this paper is used to identify the modal parameters of each acceleration response curve, based on which the damping characteristics of the aluminum alloy reticulated structures are analyzed. The results show that the damping characteristics of such structures obey a three-stage change rule, with the increase of the acceleration amplitude. In addition, a practical calculation method of the damping ratios of aluminum alloy reticulated structures is proposed on the basis of the experimental results.
•An improved modal parameter identification method is proposed based on AMD and PSO.•The proposed modal parameter identification method is effective in dealing with signals with colored noise.•Damping characteristics of aluminum alloy reticulated spatial structures satisfy a three-stage change rule.•Practical calculation method of the damping ratios of aluminum alloy reticulated structures is proposed.
•A vision modal analysis framework for modal parameter identification is developed.•The vision data is shown pertaining to the vision modal decomposition.•Additional higher-order harmonics arise for ...finite motion or non-smoothing video.•The DOFs are dramatically reduced by using edge pixels in the ZOIs as vision data.•The effectiveness is verified by numerical and experimental examples.
Testing of structures by non-contact and possibly-remote video camera measurement has emerged as a promising topic in engineering fields. This paper develops a vision modal analysis framework for output-only structural modal parameter identification using vision measurement. The establishment of this framework is mainly twofold. On the one hand, the vision data as the intensities of some selected pixels on a vibrating structure is elaborately derived upon the optical flow theory to possess the vision modal decomposition. Under small motion and proper smoothness assumptions, such a decomposition is similar to the conventional structural modal decomposition, indicating that the structural modal parameters are directly implicated in the vision data. While in the case of finite motion or a non-smoothing video, additional higher-order harmonics as combinations of basic frequencies may arise. On the other hand, with the vision modal decomposition, the frequency domain decomposition is utilized to identify the vision modal parameters from the vision data and then, the structural mode shapes are recovered from the vision modal shapes by some motion extraction processing. Numerical examples and an experimental case are studied to see the feasibility and accuracy of the proposed vision modal analysis.
The active imaging blue light high-speed three-dimensional digital image correlation (3D-DIC) system was combined with a transient aerodynamic heating system and random pulse excitation technology to ...establish a high-frequency thermal vibration optical test system capable of multi-temperature zone testing at 900 °C to accurately obtain the thermal modal parameters of thin-walled structures. The full-field temperature distribution of a novel honeycomb thin-walled composite structure (HTWCS) with pit defects under non-uniform temperature was accurately simulated through reinforcement learning. The first six modal frequencies of honeycomb thin-walled composite structure with pit defects at room temperature increased compared with the non-destructive honeycomb thin-walled composite structure, and the third and fourth modal shapes interchanged. An adaptive modal parameter identification method for full-field three-dimensional vibration measurements under high-temperature environments was developed by combining the successive multivariate variational mode decomposition (VMD) with the modal superposition method. This method can effectively identify close modes. The area ratio-based approach was used to evaluate the damping of the measured response. The finite element model (FEM) of the HTWCS with pit defects at different temperatures was updated using a multi-state step-by-step model updating method and the temperature-dependent material properties were established. The results showed that the introduction of a damping ratio improved the accuracy of the updated FEM of HTWCS with pit defects. The proposed technique is anticipated to provide an effective method for high-frequency thermal vibration optical measurement and modal identification of thin-walled structures under multi-temperature regions.
•Establish a multi-temperature region thermal vibration optical test system.•Output-only modal identification based on full-field 3D vibration measurement.•Propose a new model updating method for structures.•Full-field heat transfer analysis of structures using reinforcement learning.
As the penetration of renewable energy increases to a large scale and power electronic devices become widespread, power systems are becoming prone to synchronous oscillations (SO). This event has a ...major impact on the stability of the power grid. The recent research has been mainly concentrated on identifying the parameters of sub-synchronous oscillation. Sub/Super synchronous oscillations (Sub/Sup-SO) simultaneously occur, increasing the difficulty in accurately identify the parameters of SO. This work presents a novel method for parameter identification that effectively handles the Sub/Sup-SO components by utilizing the Rife-Vincent window and discrete Fourier transform (DFT) simultaneously. To mitigate the impact of spectral leakage and the fence effect of DFT, we integrate the tri-spectral interpolation algorithm with the Rife–Vincent window. We use the instantaneous data of the phasor measurement unit (PMU) to identify Sub/Sup-SO-related parameters (Sub/Sup-SO damping ratio, frequency, amplitude and phase). First, the spectrum of the Sub/Sup-SO signals is analyzed after incorporating the Rife-Vincent window, and the characteristics of the Sub/Sup-SO signal are determined. Then, the signal spectrum is identified using a three-point interpolation algorithm, and the damping ratio, amplitude, frequency, and phase of the Sub/Sup-SO signals are obtained. In addition, we consider the identification accuracy of the algorithm under various complex conditions, such as the effect of Sub/Sup-SO parameter variations on parameter identification in the presence of a non-nominal frequency and noise. The proposed algorithm accurately identifies the parameters of multiple Sub/Sup-SO components and two Sub-SO components that are in close proximity. Testing with synthetic and real data demonstrates that the proposed algorithm outperforms existing methods in terms of identification accuracy, identification bandwidth, and adaptability.
•Sub/Sup-SO parameter identification is proposed via tri-spectral line interpolation.•This method obtains wide identification band range and high measurement accuracy.•Parameter identification is proposed for parameters containing Sub-SO and Sup-SO frequencies.•The deviation of parameter identification was less than 1 % in most cases.
•Transmissibility-based operational modal analysis is a recent research area in developing.•Transmissibility-based method cannot identify closely spaced modes.•For that, a combined method based on ...transmissibility functions and blind source separation techniques is proposed.•The combined method is based on new way to define the transmissibility functions with the use the recovered sources signals.•A numerical simulation and experimental test show that the method is able to identify closely spaced modes.
Transmissibility-based operational modal analysis is a recent and alternative approach used to identify the modal parameters of structures under operational conditions. This approach is advantageous compared with traditional operational modal analysis because it does not make any assumptions about the excitation spectrum (i.e., white noise with a flat spectrum). However, common methodologies do not include a procedure to extract closely spaced modes with low signal-to-noise ratios. This issue is relevant when considering that engineering structures generally have closely spaced modes and that their measured responses present high levels of noise. Therefore, to overcome these problems, a new combined method for modal parameter identification is proposed in this work. The proposed method combines blind source separation (BSS) techniques and transmissibility-based methods. Here, BSS techniques were used to recover source signals, and transmissibility-based methods were applied to estimate modal information from the recovered source signals. To achieve this combination, a new method to define a transmissibility function was proposed. The suggested transmissibility function is based on the relationship between the power spectral density (PSD) of mixed signals and the PSD of signals from a single source. The numerical responses of a truss structure with high levels of added noise and very closely spaced modes were processed using the proposed combined method to evaluate its ability to identify modal parameters in these conditions. Colored and white noise excitations were used for the numerical example. The proposed combined method was also used to evaluate the modal parameters of an experimental test on a structure containing closely spaced modes. The results showed that the proposed combined method is capable of identifying very closely spaced modes in the presence of noise and, thus, may be potentially applied to improve the identification of damping ratios.
•Establish a multi-temperature region thermal vibration coupled optical test system.•Visualization of modal shapes based on full-field 3D-DIC output-only response.•Propose a multi-state non-uniform ...temperature field FEM updating method for structures.•Full-field non-uniform heat transfer analysis of structures using Q-learning algorithm.•The proposed structure can serve as a structural component in reusable hypersonic vehicles.
Thermal effects in hypersonic vehicles, such as severe aerodynamic heating, can greatly influence their thermodynamic behavior. These effects can cause uneven temperature distributions and drastic vibrations, which in turn impact the vibration characteristics of the vehicle structure. To address this issue, a comprehensive approach was developed to study the behavior of honeycomb sandwich structures in high-temperature environments. Firstly, a full-field thermal vibration testing system was established, which allowed for free-boundary multi-temperature region heating at 900 °C while applying unconnected excitation. Through this setup, we were able to obtain modal frequencies and modal shapes of the honeycomb sandwich structures under high-temperature conditions. To accurately simulate the heat transfer distribution of the honeycomb sandwich structure, the Q-learning algorithm was employed, which proved effective in achieving accurate and detailed predictions of the full-field heat transfer distribution. Furthermore, for the purpose of further enhancing the accuracy of the finite element model, a multi-state non-uniform temperature field model updating method was utilized. This updated model accounted for the influence of the multi-temperature region heating, resulting in a more reliable representation of the structure's behavior. Additionally, a variational mode decomposition (VMD) framework was applied to visualize and analyze the modal shapes of the honeycomb sandwich structures. By decomposing the time-domain signals with VMD, it is possible to efficiently obtain the modal shapes of the output-only response signals. Experimental results demonstrated that the identification method used in this study produced modal frequencies and modal shapes that closely matched those obtained using the PolyMAX method at room temperature. Therefore, the proposed approach offers an effective means of identifying the modal characteristics of structures subjected to non-uniform temperature fields, particularly in output-only scenarios.
The Natural Excitation Technique (NExT) is widely used in structural modal parameter identification. However, the cross-correlation function is susceptible to the mode shape of each order, which is ...obtained by the traditional NExT method combined with other modal identification methods between the two measuring points, resulting in large errors of the identified frequency and damping ratio of various modes. Therefore, in this study, to obtain the modal responses of the target order correctly and eliminate interaction of various modes, a new combined NExT method with improved Empirical Mode Decomposition (EMD) method is developed. The improved NExT method is introduced firstly, then, the structural modal parameters are identified by five different methods, which are Ibrahim Time Domain Technique, Sparse Time Domain Algorithm, Autoregressive Moving Average timing method, Least Square Complex Exponential and Eigensystem Realization Algorithm respectively. The correction and improvement of the new method are verified through a simple-supported beam experiment and a shaking table test of a 12-story benchmark tall building at Tongji University. The structural modal parameters are identified and compared through adopting traditional NExT method and the proposed new NExT algorithm. Results illustrate that the improved NExT algorithm in this paper has a higher accuracy and effectiveness than the traditional one in structural modal parameter identification.
This paper develops a novel stochastic subspace modal identification method in which the uncertainty quantification of structural modal parameters is considered. On the basis of a 4-degree-of-freedom ...(4DOF) simulation model, the detailed procedure of the proposed approach is first demonstrated. Then, by conducting a series of numerical simulations on the 4DOF model, the accuracy and effectiveness of the proposed method are verified for the cases of structural responses containing high-level noise and non-stationary properties. Furthermore, the proposed approach is applied to field measurements on a 260-m-high supertall building under ambient excitations, and the estimated modal parameters are further compared with the results determined by the forced vibration test performed on the building. The good agreement between these two sets of estimated modal parameters verifies the applicability and effectiveness of the developed modal identification method for field measurements. The objective of this study is to provide an efficient instrument for the accurate modal identification of civil structures.
