scholarly journals Identification of Structural Parameters Based on HHT and NExT

2021 ◽  
Vol 4 (1) ◽  
pp. 5
Author(s):  
Yongli Zhang ◽  
Ruixin Li
Keyword(s):  
Signal Processing ◽  
Earthquake Engineering ◽  
Mode Shape ◽  
Structural Parameters ◽  
Damping Ratio ◽  
Type Structure ◽  
Modal Parameters ◽  
Modal Frequency ◽  
Shear Type ◽  
Natural Excitation Technique

Signal processing approaches are widely used in the field of earthquake engineering, especially in the identification of structural modal parameters. Hilbert-Huang Transformation (HHT) is one new signal processing approach, which can be used to identify the modal frequency, damping ratio, mode shape, even the interlayer stiffness of the shear-type structure, incorporating with Natural Excitation Technique (NExT) method to take information from the response records of the structure. The stiffness of the structure is of great importance to judge the loss of its bearing capacity after earthquake. However, all of modal parameters are required to calculate the stiffness of the structure by use of HHT and NExT, which means that the response records shall contain all of modal information. However, it has been found that the responses of the structure recorded only contain the former order modal information; even it is excited by earthquake. Therefore, it is necessary to found a formula (formulas) to calculate the stiffness only using limited modal parameters. In this paper, the calculation formulas of the interlayer stiffness of shear-type structure are derived by using of the flexibility method, which indicate that all of interlayer stiffnesses could be worked out as long as any one set of modal parameters is obtained. After that, Taking Sheraton-Universal Hotel subjected to North Bridge earthquake in 1994 as an example, HHT and NExT are used to identify its modal parameters, the derived formulas are used to calculate the interlayer stiffnesses, and their applicability and accuracy are verified.

The Comparative Modal Analysis of Simulation and Experiment on the Electronic Button-Sewing Machine Shell

2013 ◽  
Vol 668 ◽  
pp. 612-615
Author(s):  
Li Zhang ◽  
Guang Yuan Nie ◽  
Hong Wu ◽  
Jie Chen
Keyword(s):  
Comparative Analysis ◽  
Modal Analysis ◽  
Natural Frequency ◽  
Mode Shape ◽  
Damping Ratio ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Ansys Software ◽  
Sewing Machine ◽  
Simulation And Experiment

In this paper, the simulation with ANSYS software and the experimental modal analysis by impacting are carried out on the electronic button-sewing machine shell. The modal parameters, such as the natural frequency, the damping ratio and the mode shape, are obtained. Comparative analysis of their results shows that the mode shapes of the machine shell are mainly the outward-expanding and inward-contracting vibrations, which provides a useful reference for vibration and noise reduction of the electronic button-sewing machine.

Application of Digital Videometrics in the Vibration Test of Suspension Cable

2013 ◽  
Vol 333-335 ◽  
pp. 2401-2406
Author(s):  
Sheng Hong Fan ◽  
Zhi Yang Gou ◽  
Ya Jun Wu ◽  
Cong Li ◽  
Qiang Wang ◽  
...  
Keyword(s):  
Signal Processing ◽  
Parameter Identification ◽  
Damping Ratio ◽  
Dynamic Performance ◽  
High Accuracy ◽  
Modal Parameters ◽  
Vibration Test ◽  
Special Focus ◽  
Scaled Model ◽  
Suspension Cable

This paper devotes to vibration test based on digital videometrics. The new non-contact measuring technology has good dynamic performance and high accuracy. It is applied to the suspension cable of an indoor scaled model of FAST telescope and successfully gets the identified modal parameters such as natural frequency and damping ratio. Special focus is put on the principle of digital videometrics and the testlayout. Besides, the related signal processing before parameter identification is also discussed.

Fluid-Structure Interaction Effects of a Partially Immersed, Cantilevered Hydrofoil

2021 ◽  
Author(s):  
Yongshun Zeng ◽  
Xin Qi ◽  
Lingfeng Shu ◽  
Zhifeng Yao ◽  
Lingjiu Zhou ◽  
...  
Keyword(s):  
Free Surface ◽  
Mode Shape ◽  
Guide Vane ◽  
Damping Ratio ◽  
Fluid Structure Interaction ◽  
Side Wall ◽  
Added Mass ◽  
Modal Parameters ◽  
Structure Interaction ◽  
Operating Stability

Abstract Knowledge of the modal parameters of the guide vane is essential for evaluating the operating stability of pump-turbines. In the present investigation, experiments and simulations are designed to analyze the influence of submergence level and sidewall clearance on the vibration characteristics of a guide vane-like structure. The results show that the type of mode shape remains unchanged at different submergence levels, while the position of the node line (NL) demonstrates a slight shift. According to the angle of the NL and the free surface, the mode types are divided into parallel NL, vertical NL and slanted NL modes. The added mass tends to increase with increasing submergence levels, while the slope of added mass in conjunction with the submergence level, is dependent on the mode type. In particular, in relation to the parallel NL mode, the slope is almost zero, if the free surface is close to the NL region; with regard to the slanted NL mode, the slope in the NL region is significant smaller than that outside this region; in the case of the vertical NL mode, the slope remains approximately constant. The damping ratio increases with increasing submergence level for the vertical NL mode. While the damping ratios for the parallel and slanted NL modes are decreased, if the free surface is close to the NL regions. In addition, as the side wall clearance increases, both the added mass and damping ratio tend to decrease.

scholarly journals Numerical and Experimental Investigation on Parameter Identification of Time-Varying Dynamical System Using Hilbert Transform and Empirical Mode Decomposition

2014 ◽  
Vol 2014 ◽  
pp. 1-15
Author(s):  
Jun Chen ◽  
Guanyu Zhao
Keyword(s):  
Free Vibration ◽  
Empirical Mode Decomposition ◽  
Hilbert Transform ◽  
Instantaneous Frequency ◽  
Structural Parameters ◽  
Damping Ratio ◽  
Modal Parameters ◽  
Time Varying ◽  
Mode Decomposition ◽  
Definition Of

This paper proposes an approach to identifying time-varying structural modal parameters using the Hilbert transform and empirical mode decomposition. Definition of instantaneous frequency and instantaneous damping ratio based on Hilbert transform for single-degree-of-freedom (SDOF) system is first introduced. The following is the definition of Hilbert damping spectrum from which the time-varying damping ratio of multi-degree-of-freedom (MDOF) system can be calculated. Identification procedures for both instantaneous frequency and damping ratios based on their definition are then introduced. Applicability of the proposed identification algorithm has been validated through several numerical examples. The instantaneous frequency and damping ratios of SDOF system under free vibration and under sinusoidal and white noise excitation have been identified. The proposed method is also applied to MDOF system with slow and sudden changing structural parameters. The results demonstrate that when the system modal parameters are slowly changing, the instantaneous frequency could be easily and well identified with satisfied accuracy for all cases. However, the instantaneous damping ratio could be extracted only when the system is lightly damped. The damping results are better for free vibration situation than for the forced vibration cases. It is also shown that the suggested method can easily track the abrupt change of system modal parameter under free vibration. The proposed method is then applied to a 12-story short-lag shear wall structure model tested on a shaking table. The instantaneous dynamic properties of the structure were identified and were then introduced as known parameters into a finite element model. Comparisons with the numerical results using constant structural parameters demonstrate that the calculated structural responses using the identified time-varying parameters are much closer to the experimental results.

scholarly journals Chatter identification in turning process based on vibration analysis using Hilbert-Huang transform

2020 ◽  
Vol 14 (2) ◽  
pp. 6856-6868
Author(s):  
Agus Susanto ◽  
K. Yamada ◽  
R. Tanaka ◽  
Y. A. Handoko ◽  
M. F. Subhan
Keyword(s):  
Signal Processing ◽  
Damping Ratio ◽  
Machining Process ◽  
Frequency Resolution ◽  
Modal Parameters ◽  
High Time Resolution ◽  
Chatter Vibration ◽  
Cutting Depth ◽  
Hilbert Huang Transform ◽  
Short Time

In machining process, the increasing cutting depth is aimed to accelerate machining operations in a short time. However, the increasing cutting depth can cause chatter vibration at any time. Chatter can accelerate tool wear and lead to poor machined surface. This paper studied the application of Hilbert-Huang transform (HHT) to analyse chatter caused by the increasing cutting depth during operation. Chatter vibration is typical of non-stationary and non-linear vibration signals, therefore it should be analysed by appropriate signal processing; HHT. In this research, initially “hammering tests” were conducted to observe dynamic modal parameters of cutting system; modal mass, damping ratio, and stiffness. Then stability lobe chart was generated based on those dynamic modal parameters to determine cutting parameters. Second, turning tests were conducted and then vibrations obtained in turning tests were analysed using HHT for chatter detection. The results were then compared by conventional signal processing; short-time Fourier (STFT) transforms. The results show that the empirical mode decomposition (EMD) of HHT process separated complex vibrations into simple components and isolated chatter from the others. The chatter was isolated in the first IMF. Therefore, chatter can be identified by EMD process. In the spectrum analysis, HHT spectra showed its superiority over STFT spectra. HHT spectra provided high time resolution and high frequency resolution both rather than STFT spectra that provided blurry and blocked spectra. The implication is that HHT can be applied to monitor the machining process.    

A validated robust and automatic procedure for vibration analysis of bridge structures using MEMS accelerometers

2020 ◽  
Vol 14 (3) ◽  
pp. 327-354
Author(s):  
Mohammad Omidalizarandi ◽  
Ralf Herrmann ◽  
Boris Kargoll ◽  
Steffen Marx ◽  
Jens-André Paffenholz ◽  
...  
Keyword(s):  
Vibration Analysis ◽  
Damping Ratio ◽  
Fem Analysis ◽  
Cost Effective ◽  
Analysis Procedure ◽  
Modal Parameters ◽  
Bridge Structure ◽  
Modal Damping ◽  
Mems Accelerometers ◽  
Better Than

AbstractToday, short- and long-term structural health monitoring (SHM) of bridge infrastructures and their safe, reliable and cost-effective maintenance has received considerable attention. From a surveying or civil engineer’s point of view, vibration-based SHM can be conducted by inspecting the changes in the global dynamic behaviour of a structure, such as natural frequencies (i. e. eigenfrequencies), mode shapes (i. e. eigenforms) and modal damping, which are known as modal parameters. This research work aims to propose a robust and automatic vibration analysis procedure that is so-called robust time domain modal parameter identification (RT-MPI) technique. It is novel in the sense of automatic and reliable identification of initial eigenfrequencies even closely spaced ones as well as robustly and accurately estimating the modal parameters of a bridge structure using low numbers of cost-effective micro-electro-mechanical systems (MEMS) accelerometers. To estimate amplitude, frequency, phase shift and damping ratio coefficients, an observation model consisting of: (1) a damped harmonic oscillation model, (2) an autoregressive model of coloured measurement noise and (3) a stochastic model in the form of the heavy-tailed family of scaled t-distributions is employed and jointly adjusted by means of a generalised expectation maximisation algorithm. Multiple MEMS as part of a geo-sensor network were mounted at different positions of a bridge structure which is precalculated by means of a finite element model (FEM) analysis. At the end, the estimated eigenfrequencies and eigenforms are compared and validated by the estimated parameters obtained from acceleration measurements of high-end accelerometers of type PCB ICP quartz, velocity measurements from a geophone and the FEM analysis. Additionally, the estimated eigenfrequencies and modal damping are compared with a well-known covariance driven stochastic subspace identification approach, which reveals the superiority of our proposed approach. We performed an experiment in two case studies with simulated data and real applications of a footbridge structure and a synthetic bridge. The results show that MEMS accelerometers are suitable for detecting all occurring eigenfrequencies depending on a sampling frequency specified. Moreover, the vibration analysis procedure demonstrates that amplitudes can be estimated in submillimetre range accuracy, frequencies with an accuracy better than 0.1 Hz and damping ratio coefficients with an accuracy better than 0.1 and 0.2 % for modal and system damping, respectively.

Analysis of Modal Parameters of Adhesively Bonded Double-Strap Joints by the Modal Strain Energy Method

1993 ◽  
Author(s):  
Mohan D. Rao ◽  
Krishna M. Gorrepati
Keyword(s):  
Strain Energy ◽  
Natural Frequencies ◽  
Structural Parameters ◽  
Flexural Vibration ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Adhesively Bonded ◽  
Modal Strain Energy ◽  
Joint System ◽  
Damping Material

Abstract This paper presents the analysis of modal parameters (natural frequencies, damping ratios and mode shapes) of a simply supported beam with adhesively bonded double-strap joint by the finite-element based Modal Strain Energy (MSE) method using ANSYS 4.4A software. The results obtained by the MSE method are compared with closed form analytical solutions previously obtained by the first author for flexural vibration of the same system. Good agreement has been obtained between the two methods for both the natural frequencies and system loss factors. The effects of structural parameters and material properties of the adhesive on the modal properties of the joint system are also studied which are useful in the design of the joint system for passive vibration and noise control. In order to evaluate the MSE and analytical results, some experiments were conducted using aluminum double-strap joint with 3M ISD112 damping material. The experimental results agreed well with both analytical and MSE results indicating the validity of both analytical and MSE methods. Finally, a comparative study has been conducted using various commercially available damping materials to evaluate their relative merits for use in the design of these joints.

scholarly journals Influence of Structure on the Aseismic Stability and Dynamic Responses of Liquefiable Soil

2021 ◽  
Author(s):  
Pengfei Dou ◽  
Chengshun Xu ◽  
Xiuli Du ◽  
Su Chen
Keyword(s):  
Earthquake Engineering ◽  
Damping Ratio ◽  
Free Field ◽  
Shaking Table ◽  
Dynamic Responses ◽  
Seismic Stability ◽  
Geotechnical Earthquake Engineering ◽  
Liquefiable Soil ◽  
Porewater Pressure ◽  
Lateral Displacements

Abstract In previous major earthquakes, the damage and collapse of structures located in liquefied field which caused by site failure a common occurrence, and the problem of evaluation and disscusion on site liquefaction and the seismic stability is still a key topic in geotechnical earthquake engineering. To study the influence of the presence of structure on the seismic stability of liquefiable sites, a series of shaking table tests on liquefiable free field and non-free field with the same soil sample was carried out. It can be summarized from experimental results as following. The natural frequency of non-free field is larger and the damping ratio is smaller than that of free field. For the weak seismic loading condition, the dynamic response of sites show similar rules and trend. For the strong ground motion condition, soils in both experiments all liquefied obviously and the depth of liquefaction soil in the free field is significantly greater than that in the non-free field, besides, porewater pressure in the non-free field accumulated relately slow and the dissapited quikly from analysis of porewater pressure ratios(PPRs) in both experiments. The amplitudes of lateral displacements and acceleration of soil in the non-free field is obviously smaller than that in the free field caused by the effect of presence of the structure. In a word, the presence of structures will lead to the increase of site stiffness, site more difficult to liquefy, and the seismic stability of the non-free site is higher than that of the free site due to soil-structure interaction.

Sign in / Sign up

Export Citation Format

Share Document