Concrete-filled fiber-reinforced polymer tubes (CFFTs) have attracted interest for their structural applications in corrosive environments. However, a weak interfacial strength between the ...fiber-reinforced polymer (FRP) tube and the concrete infill may develop due to concrete shrinkage and inadequate concrete compaction during concrete casting, which will destroy the confinement effect and thereby reduce the load bearing capacity of a CFFT. In this paper, the lead zirconate titanate (PZT)-based ultrasonic time-of-flight (TOF) method was adopted to assess the concrete infill condition of CFFTs. The basic idea of this method is that the velocity of the ultrasonic wave propagation in the FRP material is about half of that in concrete material. Any voids or debonding created along the interface between the FRP tube and the concrete will delay the arrival time between the pairs of PZT transducers. A comparison of the arrival times of the PZT pairs between the intact and the defected CFFT was made to assess the severity of the voids or the debonding. The feasibility of the methodology was analyzed using a finite-difference time-domain-based numerical simulation. Experiments were setup to validate the numerical results, which showed good agreement with the numerical findings. The results showed that the ultrasonic time-of-flight method is able to detect the concrete infill condition of CFFTs.
Butt welding is extensively applied in long-distance oil and gas pipelines, and it is of great significance to conduct non-destructive ultrasonic testing of girth welds in order to avoid leakage and ...safety accidents during pipeline production and operation. In view of the limitations of large transducer size, single fixed beam angle, low detection resolution and high cost of conventional ultrasonic inspection technologies, a 16-channel piezoelectric micro ultrasonic transducer (PMUT) array probe was developed through theoretical analysis and structural optimization design. After the probe impedance characterization, the experimental results show that the theoretical model can effectively guide the design of the ultrasonic transducer array, offering the maximum operating frequency deviation of less than 5%. The ultrasonic echo performance tests indicate that the average −6 dB bandwidth of the PMUT array probe can be up to 77.9%. In addition, the fabricated PMUT array probe has been used to successfully detect five common internal defects in pipeline girth welds. Due to the multiple micro array elements, flexible handling of each element, large bandwidth and high resolution of defect detection, the designed PMUT array probe can provide a good application potential in structural health monitoring and medical ultrasound imaging fields.
Impact force refers to a transient phenomenon with a very short-acting time, but a large impulse. Therefore, the detection of impact vibration is critical for the reliability, stability, and overall ...life of mechanical parts. Accordingly, this paper proposes a method to indirectly characterize the impact force by using an impact stress wave. The LS-DYNA software is utilized to establish the model of a ball impacting the steel plate, and the impact force of the ball and the impact response of the detection point are obtained through explicit dynamic finite element analysis. In addition, on this basis, a correspondence between the impact force and the impact response is established, and finally, an experimental platform for impact force detection is built for experimental testing. The results obtained by the finite element method are in good agreement with the experimental measurement results, and it can be inferred that the detected piezoelectric signal can be used to characterize the impact force. The method proposed herein can guide the impact resistance design and safety assessment of structures in actual engineering applications.
Incoherent scattered waves are generated when seismic waves propagate through heterogeneous media. These scattered waves contain statistical information, such as random heterogeneity. In order to ...study the influence of random heterogeneity on seismic waveforms, four series of simulation experiments were performed in the presents study, as follows: (1) Waves were excited by the same source and propagated through four models with different parameters; (2) Waves were excited by different frequencies, but spread in the same model (0.25, 0.50, 1.00, 2 MHz); (3) Waves were excited by the same source and propagated through three different velocity fluctuation models (5%, 10% and 15%); (4) Waves were excited by the same source and propagated through three different propagation distances (30, 60, and 90 mm). In the present study, the correlation between coherent waveforms and observed waveforms, the energy distribution with respect to the elapsed time, and the statistical distribution of the waveform correlation coefficient were calculated. Next, the variation of the waveform parameters with the normalized scale parameter ka was investigated. Stronger scattered waves and more complicated waveforms were observed when the ka value increased, indicating the transition from an equivalent homogeneous medium to a heterogeneous medium.
Since light propagation in a multimode fiber (MMF) exhibits visually random and complex scattering patterns due to external interference, this study numerically models temperature and curvature ...through the finite element method in order to understand the complex interactions between the inputs and outputs of an optical fiber under conditions of temperature and curvature interference. The systematic analysis of the fiber’s refractive index and bending loss characteristics determined its critical bending radius to be 15 mm. The temperature speckle atlas is plotted to reflect varying bending radii. An optimal end-to-end residual neural network model capable of automatically extracting highly similar scattering features is proposed and validated for the purpose of identifying temperature and curvature scattering maps of MMFs. The viability of the proposed scheme is tested through numerical simulations and experiments, the results of which demonstrate the effectiveness and robustness of the optimized network model.
Scattering due to small-scale heterogeneities in the rock formation surrounding a wellbore can significantly change the acoustic waveform from a logging measurement which in turn can be used to ...characterize the formation heterogeneities. This study simulates the elastic heterogeneity scattering in monopole and dipole acoustic logging and analyse the resulting effects on the waveforms. The results show that significant coda waves are generated in both monopole and dipole waveforms and the dipole coda is dominated by S-to-S scattering, which can be effectively utilized to diagnose the heterogeneity in the rock formation. The coda wave modelling and analysis were used to characterize dipole acoustic data logged before and after fracturing a reservoir interval, with significant coda wave in the after-fracturing data indicating fracturing-induced heterogeneous property change in the rock volume surrounding the borehole.
An active sensing approach using piezoceramic induced stress wave is proposed to provide monitoring and early warning for the development of interface debonding damage of precast segmental concrete ...beams (PSCBs). Three concrete specimens with toothed interfaces were fabricated and bonded with high-strength epoxy resin adhesive to form PSCBs. Smart aggregates (SAs) embedded in concrete specimens are used as actuators and sensors. The PSCBs are subjected to periodic loading with hydraulic jack to test the different degrees of debonding damage. The experimental results of time-domain and frequency-domain analysis clearly show that the amplitude of the signal received by the piezoceramic sensor is reduced when debonding crack occurs. The energy analysis and damage index based on wavelet packet can be used to determine the existence and severity of interface debonding damage in PSCBs. The experimental research validates the feasibility of monitoring the interface debonding damage in PSCBs using SA transducers based on active sensing technique.
Single-well acoustic imaging in logging-while-drilling (LWD) has important application potential in evaluating cluster-well drilling safety as it can be applied to the real-time detection of an ...existing cased borehole from a new well during drilling. Forward modelling can help us understand the mechanism of elastic-wave radiation, scattering and reception. In this work, we investigate the characteristics of acoustic wavefields associated with LWD in an unconsolidated formation. We use the time-domain finite difference (FDTD) method to simulate the wavefields corresponding to a ring dipole source. The modeling results reveal the existence of a new Mach wave apart from the conventional P- and S-waves. The Mach waves are secondary waves resulting from the constructive interference of the collar waves. Such wave is often overlooked in the previous studies of single-well acoustic imaging in LWD. We found that not only P- and S-waves but also the Mach waves could be scattered by the nearby cased borehole and propagate back to the original borehole. The simulations indicate that both the scattered P-waves and the scattered Mach S-waves exhibit strong amplitudes. This study provides a theoretical foundation for the borehole detection by LWD single-well acoustic imaging technique in unconsolidated formations.
Wireless sensor networks (WSNs) are adopted in a variety of fields where coverage enhancing is a critical challenge because of the requirements of service quality, cost, and energy consumption. ...Coverage-enhancing approaches have currently attracted a lot of interest owing to their superior abilities in the deployment of the WSNs, e.g., maximum coverage, minimum sensors, and minimum energy. In this paper, a differential evolution-based regional coverage-enhancing algorithm is proposed for directional 3D WSNs, which is able to maximizing coverage while minimize the number of sensors. First, a directional cone perception model is designed to better display the actual sensing performance of sensor nodes. Subsequently, the coverage region is established to describe the perceptual range of nodes. Thereafter, a three-stage coverage-enhancing method is derived, which includes the pitch angle optimization, the deflection angle optimization and the redundant node sleeping. These strategies are designed to maximize the perception range of a single sensor node, maximize the coverage rate, and minimize the number of nodes, respectively. Finally, simulation results show that our method is able to ensure better performance compared to the state-of-the-art frameworks.
In this paper, a method to quantitatively evaluate the status of bolted connection by using a single piezoceramic transducer and coda wave is proposed. The so-called coda wave was inherited from the ...seismological community to name the late part of a seismogram. Coda wave is a slowly decaying wave after being scattered multiple times due to medium heterogeneities or boundaries, and it is extremely sensitivity to small changes and highly repeatable. The bolt connection is good application of coda wave since the presence of the microscopically rough surfaces and the boundary along the bolt interface generate scattering events. Stress wave generated by a Lead Zirconate Titanate (PZT) transducer is often used to evaluate the status of bolted connection. However, with the aging of a PZT transducer, the amplitude of the excitation signal decreases, and the signal energy does not correctly reflect the real status of the bolt connection. In this paper, a single PZT transducer, acting as both an actuator and a sensor, is used to transmit and receive stress wave signal. The stress wave signal received by PZT sensor consists of two parts, one is the direct wave whose amplitude is related to the excitation signal, and the other part is the backscatter wave (coda wave) produced by microscopically rough surfaces and the boundary along the interface of a bolt connection. Coda wave amplitude is affected by both heterogeneity of microscopically rough surfaces and PZT performance. To eliminate the effects of PZT aging, coda wave is normalized through the amplitude of the direct wave, and the magnitude of coda wave energy (CWE) only reflects the change of connection states. The main innovation of this paper is to establish the quantitative relationship between the bolt connection status and the CWE with a single PZT transducer. An experiment on the evaluation of the bolt connection status was carried out in this research. The results indicate that quantitative evaluation on the bolt-connected structure can be achieved through CWE, thus verifying the proposed method.
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