A bolt preload monitoring method based on the refocusing capability of virtual time reversal

2019 ◽  
pp. e2370 ◽  
Author(s):  
Fei Du ◽  
Chao Xu ◽  
Jie Zhang
Keyword(s):  
Time Reversal ◽  
Monitoring Method ◽  
Bolt Preload ◽  
Virtual Time

scholarly journals M-ary nonlinear sine chirp spread spectrum for underwater acoustic communication based on virtual time-reversal mirror method

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Songzuo Liu ◽  
Habib Hussain Zuberi ◽  
Yi Lou ◽  
Muhmmad Bilal Farooq ◽  
Shahabuddin Shaikh ◽  
...  
Keyword(s):  
Acoustic Communication ◽  
Time Reversal ◽  
Spread Spectrum ◽  
Underwater Acoustic Communication ◽  
Half Cycle ◽  
Spreading Factor ◽  
Underwater Acoustic ◽  
Virtual Time ◽  
Chirp Spread Spectrum ◽  
Time Reversal Mirror

AbstractLinear chirp spread spectrum technique is widely used in underwater acoustic communication because of their resilience to high multipath and Doppler shift. Linear frequency modulated signal requires a high spreading factor to nearly reach orthogonality between two pairs of signals. On the other hand, nonlinear chirp spread spectrum signals can provide orthogonality at a low spreading factor. As a result, it improves spectral efficiency and is more insensitive to Doppler spread than the linear counterpart. To achieve a higher data rate, we propose two variants (half cycle sine and full cycle sine) of the M-ary nonlinear sine chirp spread spectrum technique based on virtual time-reversal mirror (VTRM). The proposed scheme uses different frequency bands to transmit chirp, and VTRM is used to improve the bit error rate due to high multipath. Its superior Doppler sensitivity makes it suitable for underwater acoustic communication. Furthermore, the proposed method uses a simple, low-power bank of matched filters; thus, it reduces the overall system complexity. Simulations are performed in different underwater acoustic channels to verify the robustness of the proposed scheme.

OFDM Demodulation Using Virtual Time Reversal Processing in Underwater Acoustic Communications

2015 ◽  
Vol 23 (04) ◽  
pp. 1540011 ◽  
Author(s):  
Yanling Yin ◽  
Songzuo Liu ◽  
Gang Qiao ◽  
Yue Yang ◽  
Yue Yang
Keyword(s):  
Time Reversal ◽  
Orthogonal Frequency Division Multiplexing ◽  
Estimation Methods ◽  
Delay Spread ◽  
Underwater Acoustic Communications ◽  
Ofdm Systems ◽  
Acoustic Communications ◽  
Underwater Acoustic ◽  
Single Input Single Output ◽  
Virtual Time

The extremely long underwater channel delay spread causes severe inter-symbol interference (ISI) for underwater acoustic communications. Passive time reversal processing (PTRP) can effectively reduce the channel time dispersion in a simple way via convolving the received packet with a time reversed probe signal (PS). However, the PS itself may introduce extra noise and interference (self-correlation of the PS). In this paper, we propose a virtual time reversal processing (VTRP) for single input single output (SISO) orthogonal frequency division multiplexing (OFDM) systems. It convolves the received packet with the reversed estimated channel, instead of the PS to reduce the interference. Two sparse channel estimation methods, matching pursuit (MP), and basis pursuit denoising (BPDN), are adopted to estimate the channel impulse response (CIR). We compare the performance of VTRP with the PTRP and without any time reversal processing through MATLAB simulations and the pool experiments. The results reveal that VTRP has outstanding performance over time-invariant channels.

Numerical Investigation of Nonlinear Lamb Wave Time Reversing for Fatigue Crack Detection

2019 ◽  
Author(s):  
Junzhen Wang ◽  
Yanfeng Shen
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Time Reversal ◽  
Lamb Wave ◽  
Crack Detection ◽  
Guided Waves ◽  
Fatigue Cracks ◽  
Contact Dynamics ◽  
Virtual Time ◽  
Fatigue Crack Detection

Abstract This paper presents a numerical study on nonlinear Lamb wave time reversing for fatigue crack detection. An analytical framework is initially presented, modeling Lamb wave generation, propagation, wave crack linear and nonlinear interaction, and reception. Subsequently, a 3D transient dynamic coupled-field finite element model is constructed to simulate the pitch-catch procedure in an aluminum plate using the commercial finite element software (ANSYS). The excitation frequency is carefully selected, where only single Lamb wave mode will be generated by the Piezoelectric Wafer Active Sensor (PWAS). The fatigue cracks are modelled nucleating from both sides of a rivet hole. In addition, contact dynamics are considered to capture the nonlinear interactions between guided waves and the fatigue cracks, which would induce Contact Acoustic Nonlinearity (CAN) into the guided waves. Then the conventional and virtual time reversal methods are realized by finite element simulation. Advanced signal processing techniques are used to extract the distinctive nonlinear features. Via the Fast Fourier Transform (FFT) and time-frequency spectral analysis, nonlinear superharmonic components are observed. The reconstructed signals attained from the conventional and virtual time reversal methods are compared and analyzed. Finally, various Damage Indices (DIs), based on the difference between the reconstructed signal and the excitation waveform as well as the amplitude ratio between the superharmonic and the fundamental frequency components are adopted to evaluate the fatigue crack severity. The DIs could provide quantitative diagnostic information for fatigue crack detection. This paper finishes with summary, concluding remarks, and suggestions for future work.

Baseline-free Damage Imaging Algorithm using Spatial Frequency Domain Virtual Time Reversal

2021 ◽  
pp. 1-1
Author(s):  
Bruno Albuquerque Castro ◽  
Fabricio Guimaraes Baptista ◽  
Jorge Alfredo Ardila ◽  
Francesco Ciampa
Keyword(s):  
Spatial Frequency ◽  
Frequency Domain ◽  
Time Reversal ◽  
Imaging Algorithm ◽  
Damage Imaging ◽  
Virtual Time ◽  
Spatial Frequency Domain
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