Generic Friction Models for Time-Domain Vibration Analysis of Bladed Disks

2004 ◽  
Vol 126 (1) ◽  
pp. 184-192 ◽  
Author(s):  
E. P. Petrov ◽  
D. J. Ewins
Keyword(s):  
Time Domain ◽  
Normal Load ◽  
Contact Stiffness ◽  
Time Varying ◽  
Bladed Disks ◽  
Friction Forces ◽  
Friction Characteristics ◽  
Motion Trajectories ◽  
Friction Models ◽  
The Time Domain

New efficient models have been developed to describe dynamic friction effects in order to facilitate analysis of the vibration of bladed disks in the time domain. These friction models describe friction forces occurring at contact interfaces under time-varying normal load variations, including cases of separation. The friction models developed allow one to take into account time-varying friction contact parameters, such as friction coefficient and contact stiffness coefficients. Anisotropy and variation of the friction characteristics over the contact surfaces are included in the proposed models. The capabilities of the new friction models are demonstrated. Analysis of the friction forces is performed for different motion trajectories and different time variations of the normal load, and the effects of anisotropy, variation in time of the friction characteristics and normal load variation are discussed. A numerical analysis of transient vibrations of shrouded blades using the new models is presented.

Generic Friction Models for Time-Domain Vibration Analysis of Bladed Discs

2003 ◽  
Author(s):  
E. P. Petrov ◽  
D. J. Ewins
Keyword(s):  
Time Domain ◽  
Normal Load ◽  
Contact Stiffness ◽  
Time Varying ◽  
Friction Forces ◽  
Friction Characteristics ◽  
Load Variations ◽  
Motion Trajectories ◽  
Friction Models ◽  
The Time Domain

New efficient models have been developed to describe dynamic friction effects in order to facilitate analysis of the vibration of bladed discs in the time domain. These friction models describe friction forces occurring at contact interfaces under time-varying normal load variations, including cases of separation. The friction models developed allow one to take into account time-varying friction contact parameters, such as friction coefficient and contact stiffness coefficients. Anisotropy and variation of the friction characteristics over the contact surfaces are included in the proposed models. The capabilities of the new friction models are demonstrated. Analysis of the friction forces is performed for different motion trajectories and different time variations of the normal load, and the effects of anisotropy, variation in time of the friction characteristics and normal load variation are discussed. A numerical analysis of transient vibrations of shrouded blades using the new models is presented.

scholarly journals Identification of Methamphetamine Abstainers by Resting-State Functional Magnetic Resonance Imaging

2021 ◽  
Vol 12 ◽  
Author(s):  
Tingting Dong ◽  
Qiuping Huang ◽  
Shucai Huang ◽  
Jiang Xin ◽  
Qiaolan Jia ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Functional Magnetic Resonance Imaging ◽  
Time Domain ◽  
Resting State ◽  
Time Varying ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Normal People ◽  
The Time Domain

Methamphetamine (MA) can cause brain structural and functional impairment, but there are few studies on whether this difference will sustain on MA abstainers. The purpose of this study is to investigate the correlation of brain networks in MA abstainers. In this study, 47 people detoxified for at least 14 months and 44 normal people took a resting-state functional magnetic resonance imaging (RS-fMRI) scan. A dynamic (i.e., time-varying) functional connectivity (FC) is obtained by applying sliding windows in the time courses on the independent components (ICs). The windowed correlation data for each IC were then clustered by k-means. The number of subjects in each cluster was used as a new feature for individual identification. The results show that the classifier achieved satisfactory performance (82.3% accuracy, 77.7% specificity, and 85.7% sensitivity). We find that there are significant differences in the brain networks of MA abstainers and normal people in the time domain, but the spatial differences are not obvious. Most of the altered functional connections (time-varying) are identified to be located at dorsal default mode network. These results have shown that changes in the correlation of the time domain may play an important role in identifying MA abstainers. Therefore, our findings provide valuable insights in the identification of MA and elucidate the pathological mechanism of MA from a resting-state functional integration point of view.

On Vessel Motion Induced Vortex-Induced Vibrations of a Steel Lazy Wave Riser

2021 ◽  
Author(s):  
Decao Yin
Keyword(s):  
Vortex Shedding ◽  
Time Domain ◽  
Oscillatory Flow ◽  
Domain Model ◽  
Time Varying ◽  
Structure Interaction ◽  
Response Characteristics ◽  
Vortex Induced Vibrations ◽  
The Time Domain ◽  
Vessel Motion

Abstract Deepwater steel lazy wave risers (SLWR) subject to vessel motion will be exposed to time-varying oscillatory flow, vortices could be generated and the cyclic vortex shedding force causes the structure vibrate, such fluid-structure interaction is called vortex-induced vibrations (VIV). To investigate VIV on a riser with non-linear structures under vessel motion and oscillatory flows, time domain approaches are needed. In this study, a time-domain approach is used to simulate a full-scale SLWR. Two cases with simplified riser top motions are simulated numerically. By using default input parameters to the time domain approach, the key oscillatory flow induced VIV response characteristics such as response frequency, curvature and displacements are examined and discussed. More accurate VIV prediction could be achieved by using realistic hydrodynamic inputs into the time domain model.

scholarly journals Frequency and Vibration Characteristics of High-Speed Gear-Rotor-Bearing System with Tooth Root Crack considering Compound Dynamic Backlash

2019 ◽  
Vol 2019 ◽  
pp. 1-19 ◽  
Author(s):  
Jie Liu ◽  
Weiqiang Zhao ◽  
Weiwei Liu
Keyword(s):  
Time Domain ◽  
Crack Depth ◽  
Transmission System ◽  
Gear System ◽  
Time Varying ◽  
Tooth Root ◽  
Meshing Stiffness ◽  
The Time Domain ◽  
Center Distance ◽  
Root Crack

Considering the microstructure of tooth surface and the dynamic characteristics of the vibration responses, a compound dynamic backlash model is employed for the gear transmission system. Based on the fractal theory and dynamic center distance, respectively, the dynamic backlash is presented, and the potential energy method is applied to compute the time-varying meshing stiffness, including the healthy gear system and the crack fault gear system. Then, a 16-DOF coupled lateral-torsional gear-rotor-bearing transmission system with the crack fault is established. The fault characteristics in the time-domain waveform and frequency response and statistics data are described. The effect of crack on the time-varying meshing stiffness is analyzed. The vibration response of three backlash models is compared. The dynamic response of the system is explored with the increase in crack depth in detail. The results show that the fault features of countershaft are more obvious. Obvious fluctuations are presented in the time-domain waveform, and sidebands can be found in the frequency domain responses when the tooth root crack appears. The effect of compound dynamic backlash on the system is more obvious than fixed backlash and backlash with changing center distance. The vibration displacement along meshing direction and dynamic meshing force increases with the increase in crack depth. Backlash and variation of center distance show different tendencies with increasing crack depth under different rotational speeds. Amplitude of the sidebands increases with crack depth increasing. The amplitude of multiplication frequency of rotational frequency has an obvious variation with growing crack depth. The sidebands of the multiplication frequency of meshing frequency show more details on the system with complex backlash and crack fault.

scholarly journals Time-Domain Substructure Transient Vibration Transfer Path Analysis Based on Time-Varying Frequency Response Functions under Operational Excitations

2019 ◽  
Vol 2019 ◽  
pp. 1-16
Author(s):  
Rong He ◽  
Hong Zhou
Keyword(s):  
Path Analysis ◽  
Frequency Response ◽  
Time Domain ◽  
Time Varying ◽  
Response Functions ◽  
Transient Vibration ◽  
Transfer Path ◽  
Time Varying Systems ◽  
Transfer Path Analysis ◽  
The Time Domain

The time-domain substructure inverse matrix method has become a popular method to detect and diagnose problems regarding vehicle noise, vibration, and harshness, especially for those impulse excitations caused by roads. However, owning to its reliance on frequency response functions (FRFs), the approach is effective only for time-invariable linear or weak nonlinear systems. This limitation prevents this method from being applied to a typical vehicle suspension substructure, which shows different nonlinear characteristics under different wheel transient loads. In this study, operational excitation was considered as a key factor and applied to calculate dynamic time-varying FRFs to perform accurate time-domain transient vibration transfer path analysis (TPA). The core idea of this novel method is to divide whole coupled substructural relationships into two parts: one involved time-invariable components; normal FRFs could be obtained through tests directly. The other involved numerical computations of the time-domain operational loads matrix and FRFs matrix in static conditions. This method focused on determining dynamic FRFs affected by operational loads, especially the severe transient ones; these loads are difficult to be considered in other classical TPA approaches, such as operational path analysis with exogenous inputs (OPAX) and operational transfer path analysis (OTPA). Experimental results showed that this new approach could overcome the limitations of the traditional time-domain substructure TPA in terms of its strict requirements within time-invariable systems. This is because in the new method, time-varying FRFs were calculated and used, which could make the FRFs at the system level directly adapt to time-varying systems from time to time. In summary, the modified method extends TPA objects studied in time-invariable systems to time-varying systems and, thus, makes a methodology and application innovation compared to traditional the time-domain substructure TPA.

Numerical Simulation by CGM for Moving Force Identification

2012 ◽  
Vol 238 ◽  
pp. 826-829
Author(s):  
Zhen Chen ◽  
Jun Ling Han
Keyword(s):  
Numerical Simulation ◽  
Time Domain ◽  
Bending Moment ◽  
Identification Accuracy ◽  
Time Varying ◽  
Acceptable Solution ◽  
Moving Force ◽  
Ill Posed ◽  
Simulation Results ◽  
The Time Domain

The conjugate gradient method (CGM) is compared with the time domain method (TDM) in the paper. The numerical simulation results show that the CGM have higher identification accuracy and robust noise immunity as well as producing an acceptable solution to ill-posed problems to some extent when they are used to identify the moving force. When the bending moment responses are used to identify the time-varying loads, the identification accuracy is more obviously improved than the TDM, which is more suitable for the time-varying loads identification.

scholarly journals Time- and Quantile-Varying Causality between Investor Attention and Bitcoin Returns: A Rolling-Window Causality-in-Quantiles Approach

Complexity ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Jianqin Hang ◽  
Xu Zhang
Keyword(s):  
Time Domain ◽  
Time Varying ◽  
Investor Attention ◽  
Causality Test ◽  
Novel Approach ◽  
Rolling Window ◽  
Causality Tests ◽  
High Volatility ◽  
The Time Domain ◽  
Quantile Causality

This study proposes a novel approach that incorporates rolling-window estimation and a quantile causality test. Using this approach, Google Trends and Bitcoin price data are used to empirically investigate the time-varying quantile causality between investor attention and Bitcoin returns. The results show that the parameters of the causality tests are unstable during the sample period. The results also show strong evidence of quantile- and time-varying causality between investor attention and Bitcoin returns. Specifically, our results show that causality appears only in high volatility periods within the time domain, and causality presents various patterns across quantiles within the quantile domain.

scholarly journals Hydrological model performance and parameter estimation in the wavelet-domain

2009 ◽  
Vol 6 (2) ◽  
pp. 2451-2498 ◽  
Author(s):  
B. Schaefli ◽  
E. Zehe
Keyword(s):  
Time Series ◽  
Parameter Estimation ◽  
Time Domain ◽  
Model Performance ◽  
Time Varying ◽  
Wavelet Domain ◽  
Frequency Content ◽  
Time Varying Frequency ◽  
The Time Domain

Abstract. This paper proposes a method for rainfall-runoff model calibration and performance analysis in the wavelet-domain by fitting the estimated wavelet-power spectrum (a representation of the time-varying frequency content of a time series) of a simulated discharge series to the one of the corresponding observed time series. As discussed in this paper, calibrating hydrological models so as to reproduce the time-varying frequency content of the observed signal can lead to different results than parameter estimation in the time-domain. Therefore, wavelet-domain parameter estimation has the potential to give new insights into model performance and to reveal model structural deficiencies. We apply the proposed method to synthetic case studies and a real-world discharge modeling case study and discuss how model diagnosis can benefit from an analysis in the wavelet-domain. The results show that for the real-world case study of precipitation – runoff modeling for a high alpine catchment, the calibrated discharge simulation captures the dynamics of the observed time series better than the results obtained through calibration in the time-domain. In addition, the wavelet-domain performance assessment of this case study highlights which frequencies are not well reproduced by the model, which gives specific indications about how to improve the model structure.

Discrete Time, Discrete Frequency

2021 ◽  
pp. 106-155
Author(s):  
Victor Lazzarini
Keyword(s):  
Signal Processing ◽  
Fourier Transform ◽  
Discrete Time ◽  
Time Domain ◽  
Continuous Time ◽  
Time Varying ◽  
Discrete Frequency ◽  
The Fourier Transform ◽  
Definition Of ◽  
The Time Domain

This chapter is dedicated to exploring a form of the Fourier transform that can be applied to digital waveforms, the discrete Fourier transform (DFT). The theory is introduced and discussed as a modification to the continuous-time transform, alongside the concept of windowing in the time domain. The fast Fourier transform is explored as an efficient algorithm for the computation of the DFT. The operation of discrete-time convolution is presented as a straight application of the DFT in musical signal processing. The chapter closes with a detailed look at time-varying convolution, which extends the principles developed earlier. The conclusion expands the definition of spectrum once more.

Sign in / Sign up

Export Citation Format

Share Document