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.

An Improved Algorithm for Moving Force Identification

2013 ◽  
Vol 438-439 ◽  
pp. 935-938
Author(s):  
Zhen Chen ◽  
Jun Ling Han ◽  
Jun Jie Li
Keyword(s):  
Time Domain ◽  
Noise Immunity ◽  
Bending Moment ◽  
Identification Accuracy ◽  
Time Varying ◽  
Force Identification ◽  
Moving Force ◽  
Ill Posed ◽  
Preconditioned Matrix ◽  
The Time Domain

The pretreatment conjugate gradient method (PCGM) is proposed to improve the ill-posed problem of moving force identification. Compared with the time domain method (TDM), the identification accuracy of the time-varying bending moment responses is more obviously improved. Meanwhile, the pretreatment matrix is very important to the PCGM because it affects the identification accuracy and robust noise immunity as well as ill-posed problems identification to some extent, choosing proper preconditioned matrix can effectively improve both of identification accuracy and efficiency of the PCGM.

Theory Study by CGM for Moving Force Identification

2012 ◽  
Vol 238 ◽  
pp. 823-825
Author(s):  
Zhen Chen ◽  
Jun Ling Han
Keyword(s):  
Time Domain ◽  
Noise Immunity ◽  
Theoretical Study ◽  
Identification Accuracy ◽  
Acceptable Solution ◽  
Force Identification ◽  
Moving Force ◽  
Study Results ◽  
Ill Posed ◽  
The Time Domain

The conjugate gradient method (CGM) is proposed in this paper to improve the ill-posed problem of moving force identification. Based on theoretical analysis, the CGM formula is deduced and applied in moving force identification. Related research shows that the CGM have higher identification accuracy and robust noise immunity as well as producing an acceptable solution to ill-posed cases to some extent comparing with the time domain method (TDM), when they are used to identify the moving force. The theoretical study results by CGM are practical significant to selection properly method for moving force identification.

scholarly journals Experimental and simulated milling stability tests

Mechanik ◽  
2017 ◽  
Vol 90 (11) ◽  
pp. 965-967
Author(s):  
Piotr Andrzej Bąk ◽  
Krzysztof Jemielniak
Keyword(s):  
Numerical Simulation ◽  
Stability Analysis ◽  
Time Domain ◽  
Cutting Parameters ◽  
Milling Machine ◽  
Machined Surface ◽  
Simulation Results ◽  
The Stability ◽  
The Time Domain

Self-excited vibrations significantly reduce the milling productivity, deteriorate the quality of machined surface and tool life. One of the ways to avoid these vibrations is to modify the cutting parameters based on the stability analysis results. A method of numerical simulation of self-excited vibrations in the time domain can be used for this purpose. A comparison of numerical simulation results with those from experiments conducted using a milling machine is presented. The results confirm the correctness of applied modeling.

Effect of the circular microstructure on absorbing properties of carbonyl iron rubber radar absorbing patch

2019 ◽  
Vol 33 (01n03) ◽  
pp. 1940049 ◽  
Author(s):  
Bi-Cheng Zhou ◽  
Dong-Hong Wang ◽  
Bao-Yi Li ◽  
Ya-Juan Zhao ◽  
Jiang-Jiang Ma ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Absorption Band ◽  
Time Domain ◽  
Carbonyl Iron ◽  
Integral Method ◽  
Unit Size ◽  
Test Results ◽  
Finite Integral ◽  
Simulation Results ◽  
The Time Domain

A kind of radar absorber is designed and produced based on circular microstructure, which is composed of a circular microstructure, carbonyl iron rubber radar absorbing patch and metal backboard composition. Numerical simulation of effect of the circular microstructure on absorbing properties of carbonyl iron rubber radar absorbing patch is performed by means of the time domain finite integral method. Simulated results indicate that by using the holding absorber with the unchanged thickness of 2.5 mm, when the absorber unit size was P = 30 mm and the circular radius was R = 5 mm, the value of the minimum absorption peak can reach −43 dB, −10 dB absorption band shifted from 5.8–9.3 to 4.6–8.2 GHz, changing the parameters of circular microstructure greatly, expanding the absorbing bandwidth of microwave absorbing patch, reducing the reflectivity of resonance frequency. According to the simulation results, the samples are prepared and tested. The test results are in agreement with the simulation results.

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.

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