Prediction of random dynamic loads using second-order blind source identification algorithm

2020 ◽  
Vol 234 (9) ◽  
pp. 1720-1732
Author(s):  
You Jia ◽  
Zhichun Yang ◽  
Erqiang Liu ◽  
Yanhong Fan ◽  
Xuexia Yang
Keyword(s):  
Frequency Response ◽  
Frequency Domain ◽  
Source Identification ◽  
Second Order ◽  
Dynamic Loads ◽  
Modal Parameters ◽  
Frequency Domain Method ◽  
Identification Algorithm ◽  
Structural Dynamic ◽  
Comparison Results

Traditional load identification methods are based on the frequency response function matrix. However, in some cases, it is impossible to measure the frequency response functions directly, where only the measured structural dynamic response data are available. In this paper, a novel frequency domain method based on second-order blind source identification (SOBI) algorithm is proposed for identifying the random dynamic loads from some dynamic responses of limited test points. Firstly, the SOBI algorithm is applied to identify the modal parameters from the time histories of the measured displacement responses and then the modal loads are estimated by the identified modal parameters and modal responses in the modal space; finally, the random dynamic loads can be identified in the frequency domain. In order to control the error propagation, the theoretical formulas of the regularization process have been deduced, and the regularization parameters are selected by the generalized cross-validation method. A numerical simulation and an eight-storey spatial frame experimental model are studied to validate the proposed method; the comparison results show a good agreement between the identified random dynamic loads and the actually exerted loads.

scholarly journals Operational Modal Identification of Time-Varying Structures via a Vector Multistage Recursive Approach in Hybrid Time and Frequency Domain

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Si-Da Zhou ◽  
Li Liu ◽  
Wu Yang ◽  
Zhi-Sai Ma
Keyword(s):  
Parameter Estimation ◽  
Frequency Domain ◽  
Real Time ◽  
Time Estimation ◽  
Recursive Estimation ◽  
Modal Parameters ◽  
Time Varying ◽  
Modal Parameter ◽  
Structural Dynamic ◽  
Modal Parameter Estimation

Real-time estimation of modal parameters of time-varying structures can conduct an obvious contribution to some specific applications in structural dynamic area, such as health monitoring, damage detection, and vibration control; the recursive algorithm of modal parameter estimation supplies one of fundamentals for acquiring modal parameters in real-time. This paper presents a vector multistage recursive method of modal parameter estimation for time-varying structures in hybrid time and frequency domain, including stages of recursive estimation of time-dependent power spectra, frozen-time modal parameter estimation, recursive modal validation, and continuous-time estimation of modal parameters. An experimental example validates the proposed method finally.

scholarly journals Modal control based on direct modal parameters estimation

2017 ◽  
Vol 24 (12) ◽  
pp. 2389-2399 ◽  
Author(s):  
Baptiste Chomette ◽  
Adrien Mamou-Mani
Keyword(s):  
Frequency Domain ◽  
Controller Design ◽  
State Space Model ◽  
Parameters Estimation ◽  
Modal Parameters ◽  
Rational Fraction ◽  
Modal Control ◽  
Identification Algorithm ◽  
Human Intervention ◽  
Rational Fraction Polynomial

Modal active control is based on a state model that requires the identification of modal parameters. This identification can typically be done through a rational fraction polynomial algorithm applied in the frequency domain. This method generates numerical problems when estimating high-order models, particularly when moving from the basis of orthogonal polynomials for the modal basis. This algorithm must therefore be applied independently on multiple frequency ranges with a low order for each range. In this case, the controller design cannot be automated and requires a lot of human intervention, especially to build the state space model. To address this issue, this paper presents the application of the direct modal parameters estimation (DMPE) algorithm for active modal control design. The identification algorithm is presented in a simplified version with only positive frequencies. Unlike other classical identification methods in the frequency domain, the DMPE algorithm provides a solution with a great numerical stability and allows estimating models with a higher order. Using this method, the design of the controller can be largely automated and requires a minimum of human intervention. After a theoretical presentation, the proposed method is experimentally validated by controlling the vibration modes of a suspended plate.

A New Method of Time Series Analysis and its Application to Identifying Modal Parameters

1991 ◽  
Author(s):  
Yusheng He ◽  
Zhaoxiang Deng
Keyword(s):  
Time Series ◽  
Time Series Analysis ◽  
Time Domain ◽  
New Method ◽  
Modal Parameters ◽  
Frequency Domain Method ◽  
Identification Algorithm ◽  
Series Analysis ◽  
The Time Domain ◽  
Modeling Strategy

Abstract In the paper, the attention concentrates on the time domain modal analysis. A new method of time series analysis, which is formed mainly by an ideal modeling strategy and a new COR-IV method, is developed. In addition, an interesting parameter called as modal energy ratio, which is available for design reference, is defined and its identification algorithm is given. The new method presented in this paper and Frequency Domain Method (FDM) are performed on a frame of SG120 vehicle. It is shown by comparison between these two methods that the new method of time series analysis is practical.

scholarly journals Identification of Dynamic Loads Based on Second-Order Taylor-Series Expansion Method

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Xiaowang Li ◽  
Zhongmin Deng
Keyword(s):  
Series Expansion ◽  
Taylor Series ◽  
Time History ◽  
Taylor Series Expansion ◽  
Second Order ◽  
New Method ◽  
Dynamic Loads ◽  
Discrete Equation ◽  
System Response ◽  
Structural Dynamic

A new method based on the second-order Taylor-series expansion is presented to identify the structural dynamic loads in the time domain. This algorithm expresses the response vectors as Taylor-series approximation and then a series of formulas are deduced. As a result, an explicit discrete equation which associates system response, system characteristic, and input excitation together is set up. In a multi-input-multi-output (MIMO) numerical simulation study, sinusoidal excitation and white noise excitation are applied on a cantilever beam, respectively, to illustrate the effectiveness of this algorithm. One also makes a comparison between the new method and conventional state space method. The results show that the proposed method can obtain a more accurate identified force time history whether the responses are polluted by noise or not.

Efficient aerodynamic derivative calculation in three-dimensional transonic flow

2017 ◽  
Vol 121 (1244) ◽  
pp. 1464-1478 ◽  
Author(s):  
R. Thormann ◽  
S. Timme
Keyword(s):  
Steady State ◽  
Frequency Response ◽  
Frequency Domain ◽  
Time Domain ◽  
Transonic Flow ◽  
Frequency Domain Method ◽  
Flow Conditions ◽  
Non Linear ◽  
Order Of Magnitude ◽  
Computational Aeroelasticity

ABSTRACTOne key task in computational aeroelasticity is to calculate frequency response functions of aerodynamic coefficients due to structural excitation or external disturbance. Computational fluid dynamics methods are applied for this task at edge-of-envelope flow conditions. Assuming a dynamically linear response around a non-linear steady state, two computationally efficient approaches in time and frequency domain are discussed. A non-periodic, time-domain function can be used, on the one hand, to excite a broad frequency range simultaneously giving the frequency response function in a single non-linear, time-marching simulation. The frequency-domain approach, on the other hand, solves a large but sparse linear system of equations, resulting from the linearisation about the non-linear steady state for each frequency of interest successively. Results are presented for a NACA 0010 aerofoil and a generic civil aircraft configuration in very challenging transonic flow conditions with strong shock-wave/boundary-layer interaction in the pre-buffet regime. Computational cost savings of up to 1 order of magnitude are observed in the time domain for the all-frequencies-at-once approach compared with single-frequency simulations, while an additional order of magnitude is obtained for the frequency-domain method. The paper demonstrates the readiness of computational aeroelasticity tools at edge-of-envelope flow conditions.

scholarly journals The PolyMAX Frequency-Domain Method: A New Standard for Modal Parameter Estimation?

2004 ◽  
Vol 11 (3-4) ◽  
pp. 395-409 ◽  
Author(s):  
Bart Peeters ◽  
Herman Van der Auweraer ◽  
Patrick Guillaume ◽  
Jan Leuridan
Keyword(s):  
Parameter Estimation ◽  
Frequency Response ◽  
Least Squares ◽  
Frequency Domain ◽  
Real Life ◽  
Mode Shapes ◽  
Frequency Domain Method ◽  
Complex Frequency ◽  
Modal Parameter ◽  
Domain Method

Recently, a new non-iterative frequency-domain parameter estimation method was proposed. It is based on a (weighted) least-squares approach and uses multiple-input-multiple-output frequency response functions as primary data. This so-called “PolyMAX” or polyreference least-squares complex frequency-domain method can be implemented in a very similar way as the industry standard polyreference (time-domain) least-squares complex exponential method: in a first step a stabilisation diagram is constructed containing frequency, damping and participation information. Next, the mode shapes are found in a second least-squares step, based on the user selection of stable poles. One of the specific advantages of the technique lies in the very stable identification of the system poles and participation factors as a function of the specified system order, leading to easy-to-interpret stabilisation diagrams. This implies a potential for automating the method and to apply it to “difficult” estimation cases such as high-order and/or highly damped systems with large modal overlap. Some real-life automotive and aerospace case studies are discussed. PolyMAX is compared with classical methods concerning stability, accuracy of the estimated modal parameters and quality of the frequency response function synthesis.

Frequency Response Curves and Dynamic Characteristics of a Ginkgo Tree in Different Growth Periods

2020 ◽  
Vol 63 (6) ◽  
pp. 1673-1684
Author(s):  
Jie Zhou ◽  
Linyun Xu ◽  
Guanhua Liu ◽  
Yan Xuan ◽  
Hongping Zhou ◽  
...  
Keyword(s):  
Frequency Response ◽  
Frequency Domain ◽  
Dynamic Characteristics ◽  
Natural Frequencies ◽  
Excitation Frequency ◽  
Fruit Trees ◽  
Modal Parameters ◽  
Response Curves ◽  
Resonance Frequencies ◽  
Modal Parameters Identification

HighlightsThe frequency domain modal parameters identification method was applied to a ginkgo tree.Dynamic characteristics of the ginkgo tree were tested during five phenological periods.Almost all resonance frequencies were near the peaks of the frequency response curves.Leaves caused the number of natural frequencies of the ginkgo tree to be greatly reduced.Abstract. Understanding the dynamic characteristics of fruit trees is the premise of effective mechanized harvesting. This study performed a tracking test on a ginkgo tree in five phenological periods from the dormant period to the leaf-unfolding period. The frequency domain modal parameters identification method was applied to the ginkgo tree, and the relationship between the natural frequencies and resonance frequencies of the ginkgo tree was obtained. The main factors affecting the fundamental frequency and damping ratio of the ginkgo tree were not the elastic modulus and moisture content but rather the growth of the leaves. The growth of leaves caused the number of natural frequencies in the low-frequency band to be greatly reduced, and the value of the natural frequencies exhibited a slightly decreasing tendency. The damping caused by leaves had a significant weakening effect on the transmission of vibrational energy on the lateral branches. The resonance frequencies that caused strong response of the ginkgo tree were mostly near the peak frequencies of the frequency response curves (natural frequencies), but eccentric motor excitation could not effectively stimulate all the natural frequencies of the ginkgo tree to reach resonance. In the frequency response curves of the ginkgo tree, the main natural frequency with the maximum energy might not cause the maximum vibration response of the ginkgo tree, even if this excitation frequency could induce resonance. Resonance could be used to maximize the transfer of excitation energy, but each position of the tree had its own independent frequency spectrum characteristics. A single excitation frequency could not cause all positions of the ginkgo tree to resonate simultaneously. Changing the excitation frequency of harvesting equipment within a small frequency range could achieve the maximum resonance response of most positions on fruit trees. Keywords: Dynamic characteristics, Growth periods, Leaves, Natural frequencies, Resonance.

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