Based on the electro-hydraulic servo pressure tester and 100 mm SHPB test platform, four kinds of saturated red sandstone samples were subjected to static compression test and six kinds of strain rate dynamic impact test.Drawing on the concept of macroscopic phenomenological damage mechanics and Lemairte’s damage model, the constitutive relation of water softening-strain damage was obtained according to the static compression test results of different saturated water.Finally, the results of static compression test were analyzed by using the constitutive relation.SHPB impact test results show that: ①The saturated sandstone shows a significant strain rate effect.The peak stress, peak strain and peak modulus increase with strain rate.②In the water-rock-force response system, there is a softening effect of water on the rock, and there is coupling reinforcement between the strain rate, the pore water and the rock structure.Both of these effects are always present, but with the change of the strain rate, the effect of the two effects is floating, which in turn affects the performance of the red sandstone.
An approach for super resolution patch near-field acoustic holography was proposed based on sparse Bayesian learning.The interpolation and extrapolation models were first established by use of the Gaussian kernel functions and the sparse Bayesian learning, and then the measured pressure was simultaneously interpolated and extrapolated to obtain a larger and denser virtual measurement.Finally, the interpolated and extrapolated pressures were used to perform near-field acoustic holography.Results of the simulation and experiment show that the aperture effect was greatly suppressed and the super resolution reconstruction can be achieved when using the Fourier-based near-field acoustic holography.It also shows that the measurement noise was suppressed in the process of interpolation.
In view of the fact that the ensenble empirical mode decomposition (EEMD) algorithm selects the effective intrinsic mode function (IMF) in the past, the phenomenon of misjudgment was considered.A de-noising method combining EEMD with cloud similarity theory was proposed.First, through the simulation experiment in which we constructed continuous acoustic emission signals and used the correlation coefficient method to select the intrinsic mode function compared with the signal-to-noise ratio and mean square error as the index, we verified that this method can improve the signal-to-noise ratio.Second, when we used the improved EEMD algorithm for frequency characteristics of the red sand rock acoustic emission, the signal extraction results showed that the acoustic emission signal was a decomposed intrinsic mode function.The first three IMF components have high cloud similarity value, with difference range of 0.346-0.906 from other components.The experimental statistical analysis to select the threshold is 0.655.Finally, we analyzed the power spectrum, 0-25 kHz, corresponding to IMF4, IMF5, IMF6, IMF7, IMF8 low frequency components; 25-150 kHz, corresponding to IMF1, IMF2, IMF3 high frequency components, and the red sandstone rupture of the effective frequency of the acoustic emission signals for 25-150 kHz.
To reduce urban railway vehicle bodies’ vertical vibration and improve passenger comfort based on the characteristics of magnetorheological elastic material, whose stiffness and natural frequency are adjustable, the vertical vibration model with semi-active vibration absorber including magnetorheological elastomer was established.The method of designing a dynamic vibration absorber using a magnetorheological elastomer, which is suitable for urban railway vehicles, was presented.Because urban railway vehicle traffic and speed change frequently, the best design frequency expression of the magnetorheological absorber can be obtained by multiple regression analysis.The vehicle body’s vertical vibration reduction characteristics with semi-active magnetorheological vibration absorber after-stiffness optimization was studied.Then the advantages of the magnetorheological vibration absorber were further established.The results show that the vibration absorptive capacity of the semi-active magnetorheological vibration absorber is superior to that of the passive vibration absorber at each of the vehicle body’s frequency points within the effective working frequency band of magnetorheological vibration absorbers.So the advantages of the broadband vibration damping are obvious.The magnetorheological absorber, which is modified by the best design frequency expression, can be in a resonant state with the vehicle body at all times to keep the vehicle consistently running at superior quality levels.The study provides a reference basis for the application of a semi-active vibration absorber utilizing a magnetorheological elastomer, which is used in urban railway vehicles.
To overcome the limitations of the traditional linear wavelet transform when dealing with a ground target’s vibration signals, the update lifting morphological wavelet was employed to extract the target signals’ feature information.The simulated signals and vibration signals measured from two kinds of vehicle targets were analyzed, and the results show that, compared with the traditional wavelet and max-lifting scheme, the update lifting scheme can effectively extract the target signals’ feature information in strong noise environments.It can also eliminate the interference of low frequency signals, thereby providing a new method for the precise identification of ground targets based on seismic signals.
Piezoelectric actuators and sensors are widely applied in structural health monitoring (SHM).To simulate the elastic wave propagation in piezoelectric coupled structures, a 3-D piezoelectric coupled solid time-domain spectral element method (SEM) was proposed in this paper.The propagation of guided waves was analyzed in the cases in which the piezoelectric patches work as actuators or sensors by using the proposed method and the traditional finite element method (FEM).The experimental study was carried out to further validate the proposed SEM method.The results show that, compared to the FEM, the proposed SEM can reduce the computational cost and required memory space dramatically, and it has better convergence capability to simulate the A0 mode wave.The experimental work further validates the proposed method’s effectiveness.
The key problem of the wavelet packet de-noising algorithm is effectively eliminating noise while retaining as many of the original signal wavelet packet coefficients as possible.Due to the lack of adjustable parameters and the fixed de-noising form, the traditional threshold function fails to adjust adaptively based on the noise contribution of wavelet packet decomposition coefficients, and the de-noising effects have yet to be improved.Therefore, Shannon entropy was introduced as the adjusting parameter in the wavelet packet threshold function.To shrink wavelet packet coefficients on a large scale under a strong noise background and a smooth transition for threshold shrinkage under weak noise background, an adjustable wavelet packet threshold de-noising algorithm based on Shannon entropy was proposed.The signal was decomposed by the wavelet packet method, and the Shannon entropy of wavelet packet coefficients in the largest decomposition dimension was calculated for the adjustment of threshold function.The de-noising analysis of the simulation signal, the bearing vibration experimental signal based on the method above, and other wavelet threshold de-noising algorithms show that the new method has a greater de-noising effect and effectively retains original features of the signal while removing noise.
For the spherical hinge’s connection of a 1D deployable truss, the stiffness of the spherical hinge was investigated based on dynamic model updating.The deployable structure was simplified to be in locked condition, considering the stiffness of the spherical hinge only.First, we established the elaborate FEM of a locked truss unit and calculated the initial stiffness values by carrying out the contact analysis.Then we substituted the initial value with the parameterized model with six-directional stiffness spring elements linearizing the spherical hinges’ connection.Afterward, we carried out the modal tests for this locked truss unit, using these modal parameters to identify the spherical hinge’s stiffness.Finally, we utilized the identified stiffness for the finite element modeling of the deployable structure and verified the identified results by using the multi-layer’s modal parameters.The results show that the stiffness identification method of the spherical hinge based on dynamic model updating presented by this paper is effective.
Extraction of various order signals from the original beam vibration response signals is required in bridge damage detection.In this paper, a new method of signal extraction based on custom harmonic window function was proposed.The definition of custom harmonic window function and the process of decomposition and reconstruction were demonstrated.Five order vibration signals were extracted after decomposing and reconstructing the original vibration response signals of reinforced concrete beams.The results indicated that the custom harmonic window function could be used to achieve the free division of the signal frequency band.The extracted signal had no data loss, phase shift, or small signal distortion, and the noise was filtered simultaneously during signal extraction.
To improve the sound absorption ability of a single-layer microperforated panel (MPP), an MPP backed by an L-type division cavity was designed.Based on the MPP theory and electro-acoustical equivalent circuit principle, the sound absorption model of a microperforated panel backed by a two-cavity L-type division cavity was built.Simulation and experiment results show that that an MPP with a designed cavity structure has better sound absorption performance and a broader absorption bandwidth than an MPP with a single-cavity structure.This structure is extended to N-cavity segmentation.The experimental results are in agreement with the numerical results.
