Evaluation of the characterization of acoustic emission of brittle rocks from the experiment to numerical simulation

Acoustic emission (AE) characterization is an effective technique to indirectly capture the failure process of quasi brittle rock. In previous studies, both experiments and numerical simulations were adopted to investigate the AE characteristics of rocks. However, as the most popular numerical model, the moment tensor model (MTM) cannot be constrained by the experimental result because there is a gap between MTM and experiments in principle, signal processing and energy analysis. In this paper, we developed a particle-velocity-based model (PVBM) that enabled direct monitoring and analysis of the particle velocity in the numerical model and had good robustness. The PVBM imitated the actual experiment and could fill in gaps between the experiment and MTM. AE experiments of marine shale under uniaxial compression were carried out, and the results were simulated by MTM. In general, the variation trend of the experimental result could be presented by MTM. Nevertheless, the magnitudes of AE parameters by MTM presented notable differences of more than several orders of magnitude compared with those by the experiment. We sequentially used PVBM as a proxy to analyse these discrepancies and systematically evaluate the AE characterization of rocks from the experiment to numerical simulation, considering the influence of wave reflection, energy geometrical diffusion, viscous attenuation, particle size and progressive deterioration of rock material. The combination of MTM and PVBM could reasonably and accurately acquire AE characteristics of the actual AE experiment of rocks by making full use of their respective advantages.

Surface Dyakonov–Cherenkov radiation

Recent advances in engineered material technologies (e.g., photonic crystals, metamaterials, plasmonics, etc.) provide valuable tools to control Cherenkov radiation. In all these approaches, however, the particle velocity is a key parameter to affect Cherenkov radiation in the designed material, while the influence of the particle trajectory is generally negligible. Here, we report on surface Dyakonov–Cherenkov radiation, i.e. the emission of directional Dyakonov surface waves from a swift charged particle moving atop a birefringent crystal. This new type of Cherenkov radiation is highly susceptible to both the particle velocity and trajectory, e.g. we observe a sharp radiation enhancement when the particle trajectory falls in the vicinity of a particular direction. Moreover, close to the Cherenkov threshold, such a radiation enhancement can be orders of magnitude higher than that obtained in traditional Cherenkov detectors. These distinct properties allow us to determine simultaneously the magnitude and direction of particle velocities on a compact platform. The surface Dyakonov–Cherenkov radiation studied in this work not only adds a new degree of freedom for particle identification, but also provides an all-dielectric route to construct compact Cherenkov detectors with enhanced sensitivity.

Effect of Spray Distance and Powder Feed Rate on Particle Velocity in Cold Spray Processes

Cold spray technology using micron-sized particles to produce coatings is increasingly used for reparative tasks in various industries. In a cold spray setup, the gun is usually connected to a robotic arm to deposit coatings on components with complex geometries. For these components, the standoff distance used in the cold spray process has to be large enough for easy maneuverability of the gun around a small radial feature. However, a small standoff distance is commonly found in most studies, which is thought to prevent a velocity drop of the particles over a larger distance. Here, a study was carried out by measuring the Inconel 625 particle velocity at different spray distances, ranging from 3 to 40 cm. The highest average velocity of 781 m/s was found at a spray distance of 8 cm. Furthermore, a study with varying powder feed rates was also conducted. An increase in the powder feed rate was found to have a minimal effect on the particle velocity. Inconel 625 coatings deposited at the optimum standoff distance (8 cm) were found to have low porosity and high hardness. The results in this study demonstrate that a larger standoff distance can be applied without a significant drop in velocity for cold spray applications requiring high maneuverability.

Nearfield acoustic holography in a moving medium based on particle velocity input using nonsingular propagator

Nearfield acoustic holography in a moving medium is a technique which is typically suitable for sound sources identification in a flow. In the process of sound field reconstruction, sound pressure is usually used as the input, but it may contain considerable background noise due to the interactions between microphones and flow moving at a high velocity. To avoid this problem, particle velocity is an alternative input, which can be obtained by using Laser Doppler Velocimetry in a non-intrusive way. However, there is a singular problem in the conventional propagator relating the particle velocity to the pressure, and it could lead to significant errors or even false results. In view of this, in this paper nonsingular propagators are deduced to realize accurate reconstruction in both cases that the hologram is parallel to and perpendicular to the flow direction. The advantages of the proposed method are analyzed, and simulations are conducted to verify the validation. The results show that the method can overcome the singular problem effectively, and the reconstruction errors are at a low level for different flow velocities, frequencies, and signal-to-noise ratios.

Effect of external sound superimposed on the self-excited oscillation in loop-tube thermoacoustic system

The influence of application of external sound to loop-tube type thermoacoustic system on the energy conversion efficiency is experimentally examined. The investigation is carried out by paying attention on the effect of loudspeaker (SP) set as external sound source. As a result, it is found that the setting of SP affects the sound field in the system and the amount of energy generation increases or decreases. The increasing or decreasing effect differs depending on the setting position of SP. Furthermore, it is confirmed that, provided SP is set near the node of particle velocity, the sound energy can be increased by more than the input power to SP, without changing the sound field in the tube. From these results it can be confirmed that, similar to straight-tube type thermoacoustic system, the energy conversion efficiency can be enhanced by setting SP at suitable position even in loop-tube type without end surfaces.

The General Relativistic Perspective

The Equations from General Einstein's Relativity Theory can also be framed from a Relativistically distorted perspective. General relativity slows gravitons reducing the force, so escape velocity is limited to c. Atomic structure bosons slowing makes all elements subject to decay. Energy from slowing boson structure particles would increase matter particle velocity. The lower the atomic weight, the greater the speed, so hydrogen escapes in the most significant amounts. Distortion would never be imaginary.

Artificial Neural Network Optimized by Modified Particle Swarm Optimization for Predicting Peak Particle Velocity Induced by Blasting Operations in Open Pit Mines

Blasting is an indispensable part of the open pit mining operations. It plays a vital role inpreparing the rock mass for subsequent operations, such as loading/unloading, transporting, crushing, anddumping. However, adverse effects, especially blast-induced ground vibrations, are considered one of themost dangerous problems. In this study, artificial intelligence was supposed to predict the intensity ofblast-induced ground vibration, which is represented by the peak particle velocity (PPV). Accordingly, anartificial neural network was designed to predict PPV at the Coc Sau open pit coal mine with 137 blastingevents were collected. Aiming to optimize the ANN model, the modified version of the particle swarmoptimization (MPSO) algorithm was applied to optimize the ANN model for predicting PPV, called theMPSO-ANN model. For the comparison purposes, two forms of empirical equations, namely UnitedStates Bureau of Mining (USBM) and U Langefors - Kihlstrom, were also developed to predict PPV andcompared with the proposed MPSO-ANN model. The results showed that the proposed MPSO-ANNmodel provided a better performance with a mean absolute error (MAE) of 1.217, root-mean-squared error(RMSE) of 1.456, and coefficient of determination (R2) of 0.956. Meanwhile, the empirical models onlyprovided poorer performances with an MAE of 1.830 and 2.012, RMSE of 2.268 and 2.464, and R2 of0.874 and 0.852 for the USBM and U Langefors – Kihlstrom empirical models, respectively.

Time-Domain Sound Field Reproduction with Pressure and Particle Velocity Jointly Controlled

Particle velocity has been introduced to improve the performance of spatial sound field reproduction systems with an irregular loudspeaker array setup. However, existing systems have only been developed in the frequency domain. In this work, we propose a time-domain sound field reproduction method with both sound pressure and particle velocity components jointly controlled. To solve the computational complexity problem associated with the multi-channel setup and the long-length filter design, we adopt the general eigenvalue decomposition-based approach and the conjugate gradient method. The performance of the proposed method is evaluated through numerical simulations with both a regular loudspeaker array layout and an irregular loudspeaker array layout in a room environment.