scholarly journals The Influence of Crack Modes on the Elastic Wave Propagation Characteristics in a Non-uniform Rotating Shaft

2018 ◽  
Author(s):  
Yimin Wei ◽  
Xuan Shi ◽  
Qi Liu ◽  
Wenhua Chen
Keyword(s):  
Elastic Wave ◽  
Elastic Waves ◽  
Transverse Crack ◽  
Propagation Characteristics ◽  
Mode Iii ◽  
Transverse Cracks ◽  
Rotating Shaft ◽  
Rotating Speed ◽  
Local Flexibility ◽  
The Media

The vibration propagates in a media such as a shaft in the form of elastic waves. The propagation characteristics of the waves are affected by the geometry of the media, the material properties as well as the cracks. The study to elastic waves propagating in a shaft with transverse cracks can help to detect them. The transverse crack possesses different crack modes due to different external loads. The influence of the crack mode, the location and the depth to the propagation characteristics is investigated in this paper. Firstly, the local flexibility coefficients with three different modes are deduced. And then, the transfer matrix of the elastic wave can be obtained. Finally, the influence of the crack mode, the location and the depth of the transverse crack as well as the rotating speed to the propagation characteristics is then studied, both in a numerical and an experimental way. It’s found that mode III is the most suitable mode in this paper, the location of the crack will make the stopbands fluctuating, the depth mainly affects the bandwidth of the stopbands, and the increase of the rotating speed will shift up the stopbands without changing their bandwidths.

scholarly journals The Influence of Crack Modes on the Elastic Wave Propagation Characteristics in a Non-Uniform Rotating Shaft

2018 ◽  
Vol 8 (11) ◽  
pp. 2105 ◽  
Author(s):  
Yimin Wei ◽  
Xuan Shi ◽  
Qi Liu ◽  
Wenhua Chen
Keyword(s):  
Wave Propagation ◽  
Elastic Wave ◽  
Transfer Matrix ◽  
Elastic Waves ◽  
Transverse Crack ◽  
Propagation Characteristics ◽  
Mode Iii ◽  
Rotating Shaft ◽  
Rotating Speed ◽  
Local Flexibility

The transverse crack in a non-uniform shaft possesses different crack modes, and it can affect the propagation characteristics of the elastic waves in the shaft. The influence of the crack mode as well as the location and the depth of the crack and the rotating speed to the propagation characteristics is investigated in this paper. Firstly, the transfer matrix for the elastic wave in a non-uniform shaft is obtained by deducing the local flexibility coefficients of the three typical crack modes, in which the transverse crack is modeled as a local spring. After that, the influence of the crack mode to the propagation characteristics is studied both in a numerical and an experimental way. Finally, the influence of the location and the depth of the transverse crack as well as the rotating speed of the shaft is studied too. It is found that Mode III is the most suitable mode in this paper, the location of the crack will make the stopbands fluctuating, the depth mainly affects the bandwidth of the stopbands, and the increase of the rotating speed will shift up the stopbands without changing the bandwidths. The results can help to detect and locate a transverse crack.

scholarly journals Numerical Modelling and Optimization of Two-Dimensional Phononic Band Gaps in Elastic Metamaterials with Square Inclusions

2021 ◽  
Vol 11 (7) ◽  
pp. 3124
Author(s):  
Alya Alhammadi ◽  
Jin-You Lu ◽  
Mahra Almheiri ◽  
Fatima Alzaabi ◽  
Zineb Matouk ◽  
...  
Keyword(s):  
Elastic Wave ◽  
Tungsten Carbide ◽  
Composite Structure ◽  
Elastic Waves ◽  
Wave Attenuation ◽  
Low Frequency ◽  
Filling Fraction ◽  
Carbide Composite ◽  
Elastic Metamaterials ◽  
Tungsten Carbide Composite

A numerical simulation study on elastic wave propagation of a phononic composite structure consisting of epoxy and tungsten carbide is presented for low-frequency elastic wave attenuation applications. The calculated dispersion curves of the epoxy/tungsten carbide composite show that the propagation of elastic waves is prohibited inside the periodic structure over a frequency range. To achieve a wide bandgap, the elastic composite structure can be optimized by changing its dimensions and arrangement, including size, number, and rotation angle of square inclusions. The simulation results show that increasing the number of inclusions and the filling fraction of the unit cell significantly broaden the phononic bandgap compared to other geometric tunings. Additionally, a nonmonotonic relationship between the bandwidth and filling fraction of the composite was found, and this relationship results from spacing among inclusions and inclusion sizes causing different effects on Bragg scatterings and localized resonances of elastic waves. Moreover, the calculated transmission spectra of the epoxy/tungsten carbide composite structure verify its low-frequency bandgap behavior.

A CALIBRATED MODEL SEISMIC SYSTEM

Geophysics ◽  
1972 ◽  
Vol 37 (3) ◽  
pp. 445-455 ◽  
Author(s):  
C. N. G. Dampney ◽  
B. B. Mohanty ◽  
G. F. West
Keyword(s):  
Wave Propagation ◽  
Elastic Wave ◽  
Elastic Waves ◽  
Critical Examination ◽  
Two Dimensional ◽  
Linear Filtering ◽  
Analog Model ◽  
Basic Assumptions ◽  
Electronic Circuitry ◽  
Seismic System

Simple electronic circuitry and axially polarized ceramic transducers are employed to generate and detect elastic waves in a two‐dimensional analog model. The absence of reverberation and the basic simplicity. of construction underlie the advantages of this system. If the form of the fundamental wavelet in the model itself, as modified by the linear filtering effects of the remainder of the system, can be found, then calibration is achieved. This permits direct comparison of theoretical and experimental seismograms for a given model if its impulse response is known. A technique is developed for calibration and verified by comparing Lamb’s theoretical and experimental seismograms for elastic wave propagation over the edge of a half plate. This comparison also allows a critical examination of the basic assumptions inherent in a model seismic system.

Vibration And Stability Of A Rotating Shaft Containing A Transverse Crack

1993 ◽  
Vol 162 (3) ◽  
pp. 387-401 ◽  
Author(s):  
S.C. Huang ◽  
Y.M. Huang ◽  
S.M. Shieh
Keyword(s):  
Transverse Crack ◽  
Rotating Shaft

Analytical Buckling Loads of Columns Weakened Simultaneously with Transverse Cracks and Partial Delamination

2019 ◽  
Vol 19 (03) ◽  
pp. 1950027 ◽  
Author(s):  
Igor Planinc ◽  
Simon Schnabl
Keyword(s):  
Mathematical Model ◽  
Analytical Solution ◽  
Boundary Conditions ◽  
Parametric Study ◽  
Transverse Crack ◽  
Transverse Cracks ◽  
Buckling Loads ◽  
Crack Location ◽  
Benchmark Solution ◽  
First Time

This paper focuses on development of a new mathematical model and its analytical solution for buckling analysis of elastic columns weakened simultaneously with transverse open cracks and partial longitudinal delamination. Consequently, the analytical solution for buckling loads is derived for the first time. The critical buckling loads are calculated using the proposed analytical model. A parametric study is performed to investigate the effects of transverse crack location and magnitude, length and degree of partial longitudinal delamination, and different boundary conditions on critical buckling loads of weakened columns. It is shown that the critical buckling loads of weakened columns can be greatly affected by all the analyzed parameters. Finally, the presented results can be used as a benchmark solution.

Reverse Time Migration of Elastic Waves Using the Pseudospectral Time-Domain Method

2018 ◽  
Vol 26 (01) ◽  
pp. 1750033 ◽  
Author(s):  
Jiangang Xie ◽  
Mingwei Zhuang ◽  
Zichao Guo ◽  
Hai Liu ◽  
Qing Huo Liu
Keyword(s):  
Elastic Wave ◽  
Time Domain ◽  
Elastic Waves ◽  
Sampling Rate ◽  
Fdtd Method ◽  
Time Domain Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Domain Method

Reverse time migration (RTM), especially that for elastic waves, consumes massive computation resources which limit its wide applications in industry. We suggest to use the pseudospectral time-domain (PSTD) method in elastic wave RTM. RTM using PSTD can significantly reduce the computational requirements compared with RTM using the traditional finite difference time domain method (FDTD). In addition to the advantage of low sampling rate with high accuracy, the PSTD method also eliminates the periodicity (or wraparound) limitation caused by fast Fourier transform in the conventional pseudospectral method. To achieve accurate results, the PSTD method needs only about half the spatial sampling rate of the twelfth-order FDTD method. Thus, the PSTD method can save up to 87.5% storage memory and 90% computation time over the twelfth-order FDTD method. We implement RTM using PSTD for elastic wave equations and accelerate it by Open Multi-Processing technology. To keep the computational load balance in parallel computation, we design a new PML layout which merges the PML in both ends of an axis together. The efficiency and imaging quality of the proposed RTM is verified by imaging on 2D and 3D models.

Electromagnetic damping of elastic waves: Experimental results

1968 ◽  
Vol 5 (4) ◽  
pp. 825-829 ◽  
Author(s):  
F. E. M. Lilley ◽  
C. M. Carmichael
Keyword(s):  
Magnetic Field ◽  
Elastic Wave ◽  
Applied Magnetic Field ◽  
Elastic Waves ◽  
Applied Field ◽  
Eddy Currents ◽  
Electrical Conductor ◽  
Electromagnetic Damping ◽  
The Waves ◽  
The Magnetic Field

The passage of an elastic wave causes straining and translation in the transmitting material. If a magnetic field is applied, and the medium is an electrical conductor, some of the energy of the wave is dissipated by the flow of electrical eddy currents. Usually the amount of energy lost is very small, but it may be greatly increased if the applied field is strongly non-uniform.Laboratory experiments are described which demonstrate this effect for standing elastic waves in a metal bar. The applied magnetic field changes from almost zero to its full strength over a distance which is short compared to the length of the standing wave. The result of this strong non-uniformity is that the energy lost due to the translation of the bar in the field greatly exceeds the energy lost due to the straining of the bar in the field.The dependence of the attenuation of the waves by the magnetic field is investigated for variation in frequency of vibration, bar thickness, and field gradient.

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