Particle Velocity Research Articles

Influence of in-flight thermal dynamics of metal powder on directed energy deposition process

During the laser directed energy deposition (LDED) process, the in-flight thermal dynamics of metal powders lead to the formation of detrimental by-products such as fumes, flames, and metal vapors. In this work, we use a high-speed camera to investigate the nuanced thermal stage changes of the powders, examining how gas flow rates and laser beam powers influence them. We identify distinct stages in the powder's journey: heating up, fusion and vaporization, flaming, tailing, and accelerated falling. Notably, the latter stages adversely affect both the processing environment and surface quality. Control over gas flow rate and laser beam power dictates the trajectory, duration, and intensity of tailing. Additionally, laser irradiation accelerates the falling speed of particles by 6.8–22.8% compared to non-irradiated ones. Higher laser beam powers increase vaporization-induced propulsion, culminating in escalated particle velocities. Optimal gas flow rates enhance the surface quality by significantly minimizing high-temperature spatter. Through this work, the in-flight thermal dynamic behaviors of metal particles and their impact on LDED processing are explained.

Adaptive unified gas-kinetic scheme for diatomic gases with rotational and vibrational nonequilibrium

Multiscale nonequilibrium physics at large variations of local Knudsen number are encountered in applications of aerospace engineering and micro-electro-mechanical systems, such as high-speed flying vehicles and low pressure of the encapsulation. An accurate description of flow physics in all flow regimes within a single computation requires a genuinely multiscale method. The adaptive unified gas-kinetic scheme (AUGKS) is developed for such multiscale flow simulation. The AUGKS applies discretized velocity space to accurately capture the non-equilibrium physics in the multiscale UGKS, and adaptively employs continuous distribution functions following Chapman–Enskog expansion to efficiently recover near-equilibrium flow region in GKS. The UGKS and GKS are dynamically connected at the cell interface through the fluxes from the discretized and continuous gas distribution functions, which avoids any buffer zone between them. In this study, the AUGKS with rotation and vibration non-equilibrium is developed based on a multiple temperature relaxation model. The real gas effect in different flow regimes has been properly captured. To capture aerodynamic heating accurately, the heat flux modifications from the rotation and vibration modes are also included in the current scheme. Unstructured discrete particle velocity space is adopted to further improve the computational performance of the AUGKS. Numerical tests, including Sod tube, normal shock structure, high-speed flow around the two-dimensional cylinder and three-dimensional sphere and space vehicles, and an unsteady nozzle plume flow from the continuum flow to the background vacuum, have been conducted to validate the current scheme. In comparison with the original UGKS, the current scheme speeds up the computation, reduces the memory requirement, and maintains the equivalent accuracy for multiscale flow simulation, which provides an effective tool for nonequilibrium flow simulations, especially for the flows at low and medium speed.

An Inventive Approach for Simultaneous Prediction of Mean Fragmentation Size and Peak Particle Velocity Using Futuristic Datasets Through Improved Techniques of Genetic XG Boost Algorithm

An Inventive Approach for Simultaneous Prediction of Mean Fragmentation Size and Peak Particle Velocity Using Futuristic Datasets Through Improved Techniques of Genetic XG Boost Algorithm

Sensitivity enhancement of thermal acoustic particle velocity sensor based on metal film optimization

Thermal acoustic particle velocity sensors find widespread application in sound field measurements and sound source localization, owing to their capacity to capture vectorial information. This paper focuses on enhancing the sensitivity of detecting weaker signals by elevating the temperature coefficient of resistance (TCR) in the platinum thin film on the sensor's sensing wires. The study delves into the impact of annealing on the TCR of Pt thin films applied to small-sized elongated wires for thermal acoustic particle velocity sensors. The augmented effects of annealing Pt thin films with three adhesion layer metals—Chromium (Cr) and Titanium (Ti), previously commonplace in this sensor, and the newly introduced Tantalum (Ta) are scrutinized. Additionally, the influence of the deposition of Au electrodes, employed for wire bonding, both before and after annealing, on the annealing effect is also explored. In conclusion, a Pt thin film annealing process tailored for thermal acoustic particle velocity sensors is proposed, along with the recommendation of the optimal adhesion layer metal. This approach results in a substantial 20 % improvement in the TCR of the Pt thin film on the sensing wires, coupled with a corresponding 2.2 dB increase in sensor sensitivity.

Shock response of two epoxy resins at up to 330 GPa pressure

Experimental studies of the shock wave properties of two epoxy resins with the same composition but different curing temperatures (160 and 200 °C) at up to 330 GPa pressure have been carried out. Laser interferometry was used to record particle velocity profiles at up to 73 GPa pressure while measuring the shock wave velocity. The release sound velocity was experimentally determined in the 3–73 GPa pressure range. Cumulative explosive shock wave generators were used to study the shock Hugoniot of epoxy resins at pressures above 100 GPa. It was shown that the shock compressibility data of both samples are approximated by a single shock Hugoniot within the experimental error. A kink on Hugoniot recorded close to 25 GPa pressure indicates a chemical decomposition in epoxy resin. Above this kink, a change in the shock wave front structure was recorded. Hugoniots of epoxy resin and unidirectional carbon/epoxy composite were compared at up to 370 GPa pressure.

The Elevation Effect of Vibration Induced by Pneumatic Rock Breaking with Carbon Dioxide Ice Powder

In traditional explosive blasting, the elevation amplification effect is an important aspect that cannot be ignored in the study of vibration disasters. Compared with this type of vibration, the elevation amplification effect of vibration induced by pneumatic rock breaking with carbon dioxide ice pow-der was explored through on-site vibration monitoring experiments. The results showed peak particle velocity increased when the sensor was higher than the vibration source, indicating that vibration induced by pneumatic rock breaking with carbon dioxide ice powder, like explosive blasting, has an elevation amplification effect. However, the elevation effect of vibration induced by pneumatic rock breaking with carbon dioxide ice powder mainly manifests as an amplification of the low-frequency vibration component, suppressing and weakening the high-frequency vibration. Others, the elevation amplification effect is only reflected within a certain distance. As the distance to the vibration source increases, peak particle velocity returns to its standard value and follows the existing attenuation rule. The elevation factor no longer affects the propagation and attenuation of vibration within the rock mass.

Observation of acoustic meron textures

Merons, as a member of quasiparticle family characterized by half-integer of the skyrmion topological charge with nontrivial topological textures, are of great interest in various branches of physics. Here, we report the first experimental observation of a meron texture configuration in acoustic waves. A squared metastructure is designed to support the spoof acoustic surface wave, forming meron lattice patterns in the acoustic velocity field vectors. The experimental results indicate that the meron textures can be moved and shaped by tuning the phase and amplitude differences between the excited sound sources, respectively. To demonstrate the topologically protected character of meron against structure defects, we further measure the acoustic pressure and velocity field distributions on a defective surface. The acoustic meron texture not only provides potential applications toward topologically robust ways to manipulate vectorial characteristics of the acoustic waves but also instills confidence for exploring other members of the quasiparticle family, such as the acoustic hopfion in acoustic waves.

Research Progress on Numerical Simulation of the Deposition and Deformation Behavior of Cold Spray Particles

It is of significant theoretical and practical value to study the deposition process and deformation behavior of cold-sprayed particles to find the deposition mechanism of cold-sprayed coatings, further improve the coating performance, and expand its application scope. However, observing the deposition process and particle behavior through experiments is difficult due to the brief deposition duration of cold spray particles. Numerical simulation offers a means to slow the deposition process and predict the critical velocity, deformation behavior, bonding mechanism, and residual stress of cold-sprayed particles. This paper uses finite element analysis software, including ANSYS LS Dynamic-2022 R1 and ABAQUS-6.14, alongside various prevalent finite element methods for numerically simulating cold spray particle deposition. These methods involve the Lagrange, Euler, arbitrary Lagrange-Euler (ALE), and Smoothed Particle Hydrodynamics (SPH) to investigate the cold spray particle deposition process. The recent literature primarily summarizes the simulation outcomes achieved by applying these methodologies for simulating the deposition process and deformation characteristics of different particles under varying cold spraying conditions. In addition, the reliability of these simulation results is analyzed by comparing the consistency between the simulation results of single-particle and multi-particle and the actual experimental results. On this basis, these methods’ advantages, disadvantages, and applicability are comprehensively analyzed, and the future simulation research work of particle deposition process and deformation behavior of cold spraying prospects is discussed. Future research is expected to provide a more in-depth study of the micro-mechanisms, such as the evolution of the inter-particle and internal organization of the particles, near the actual situation.

Erratum to “Acoustic wave velocities and effective Debye temperature in potassium alum KAl(SO4)2·12H2O crystal”[Solid State Sci. 154 (2024) 107595]

Erratum to “Acoustic wave velocities and effective Debye temperature in potassium alum KAl(SO4)2·12H2O crystal”[Solid State Sci. 154 (2024) 107595]

Weak shock compaction on granular salt

This study conducted integrated experiments and computational modeling to investigate the speeds of a developing shock within granular salt and analyzed the effect of various impact velocities up to 245 m/s. Experiments were conducted on table salt utilizing a novel setup with a considerable bore length for the sample, enabling visualization of a moving shock wave. Experimental analysis using particle image velocimetry enabled the characterization of shock velocity and particle velocity histories. Mesoscale simulations further enabled advanced analysis of the shock wave’s substructure. In simulations, the shock front’s precursor was shown to have a heterogeneous nature, which is usually modeled as uniform in continuum analyses. The presence of force chains results in a spread out of the shock precursor over a greater ramp distance. With increasing impact velocity, the shock front thickness reduces, and the precursor of the shock front becomes less heterogeneous. Furthermore, mesoscale modeling suggests the formation of force chains behind the shock front, even under the conditions of weak shock. This study presents novel mesoscale simulation results on salt corroborated with data from experiments, thereby characterizing the compaction front speeds in the weak shock regime.

Revisiting flat rotation curves in Chern-Simons modified gravity

We revisit slow rotating black hole (BH) solutions in Chern-Simons modified gravity (CSMG) by considering perturbative solution about Schwarzschild BH. In particular, the case when nondynamical CSMG with noncanonical CS scalar is considered. We provide a new solution different from the previously obtained one [1] which we refer to as KMT model. The present solution accounts for frame dragging effect which includes not only radial dependence as in the KMT. Nevertheless, it reduces to KMT as a particular case. We show that the tidal gravitational force (Kretschmann invariant) associated to the present solution contains a term of order 1/r3 additional to Schwarzschild but absent from directional divergence, unlike KMT model which diverges along the axis of symmetry. We derive the corresponding circular velocity of a massive test particle in which the KMT velocity is recovered in addition to an extra term ∝r. We investigate possible constraints on KMT and the present solutions from the observed rotation curve of UGC11455 galaxy as an example. We show that perturbation solutions cannot physically explain the flattening of galactic rotation curves.

Research on multi-velocity measurement method of solid particles based on interdigital electrostatic sensor

Abstract In gas-solid two-phase flow, the velocities of solid particles will show different distributions as the flow pattern changes, and it is a challenging task to achieve the measurement of different velocity parameters in the flow field. To obtain the velocity information of solid particles in the flow field, a novel method to achieve multi-velocity measurement of solid particles is proposed by using the spatial filtering characteristics of interdigital electrostatic sensor with variational mode decomposition (VMD). Firstly, a three-dimensional model of the interdigital electrostatic sensor is established using COMSOL simulation software. Based on its spatial dynamic sensitivity, a theoretical analysis of its spatial filtering characteristics is conducted to obtain a mathematical relationship for velocity measurement. Subsequently, the VMD decomposition method is applied to an experiment involving charged wires, with the experimental results verifying the effectiveness of VMD in achieving multi-scale decomposition of electrostatic signals. Finally, the proposed measurement method is validated on a gravity feeding device and a pneumatic conveying system. The experimental results demonstrate that the method exhibits good feasibility.

Reconstruction of particle distribution for tomographic particle image velocimetry based on unsupervised learning method

The development of deep learning has inspired some new methods to solve the 3D reconstruction problem for Tomographic Particle Image Velocimetry (Tomo-PIV). However, the supervised learning method requires a large number of data with ground truth as training information, which is very difficult to gather from experiments. Although synthetic datasets can be used as alternatives, they are still not exactly the same with the real-world experimental data. In this paper, an Unsupervised Reconstruction Technique based on U-net (UnRTU) is proposed to reconstruct volume particle distribution explicitly. Instead of using ground truth data, a projection function is used as an unsupervised loss function for network training to reconstruct particle distribution. The UnRTU was compared with some traditional algebraic reconstruction algorithms and supervised learning method using synthetic data under different particle density and noise level. The results indicate that UnRTU outperforms these traditional approaches in both reconstruction quality and noise robustness, and is comparable to the supervised learning methods AI-PR. For experimental tests, particles dispersed in cured epoxy resin are moved by an electric rail with a certain speed to obtain the ground truth data of particle velocity. Compared with other algorithms, the reconstructed particle distribution by UnRTU has the best reconstruction fidelity. And the accuracy of the 3D velocity field estimated by UnRTU is 12.9% higher than that from the traditional MLOS-MART algorithm. It demonstrates significant potential and advantages for UnRTU in 3D reconstruction of particle distribution. Finally, UnRTU was successfully applied to the high-speed planar cascade airflow field, demonstrating its applicability for measuring complex fluid flow fields at higher particle density.

Lifting of Transversely Forced Turbulent Nonpremixed Coaxial Jet Flames

The lifting behavior of turbulent nonpremixed coaxial jet flames was investigated experimentally as a function of the center jet Reynolds number, annular-to-center jet velocity ratio, acoustic frequency, and acoustic amplitude, all with and without transverse acoustic disturbances acting on the flames situated at a pressure antinode. Global lifting regimes were mapped and consisted of attached flames, periodically lifted flames, and permanently lifted flames. With one exception, all flames were attached in the absence of acoustics and lifted only because of the applied acoustic excitation. The exception occurred at the highest Reynolds number and velocity ratio, where the flames were unconditionally lifted in all cases. Between these two extremes, a range of lifting regimes was observed. Lower applied frequencies and smaller amplitudes were found to generally promote attachment to the burner. Flow visualizations using high-speed Schlieren and OH* chemiluminescence imaging revealed a lateral spreading effect near the jet exit. The lateral spreading was hypothesized to be caused by an axially oriented counterflow collision between the downstream flowing jets and presumed local upstream portion of the acoustic velocity fluctuations. Physical mechanisms were hypothesized based on this observation, which appear to consistently explain most of the observed behavior.

Predicting Blast-Induced Damage and Dynamic Response of Drill-and-Blast Tunnel Using Three-Dimensional Finite Element Analysis

The significance of predicting the dynamic response and damage of an existing concrete tunnel during underground blasting has increased owing to the close proximity between the newly built and existing tunnels. Peak particle velocity (PPV) is a commonly used criterion in the assessment of blast-induced structural damage. However, such structural damage is also associated with the frequency content of the blast wave. Nevertheless, the recommended threshold PPVs, which are based on empirical criteria, predict conservative estimations. Using stringent and regulated blasting methods often results in project delays and escalates the total project expenditure. In this paper, a three-dimensional finite element model of an underground tunnel has been developed in LS-DYNA to analyze damage to the concrete tunnels under blast loading. A suite of analyses was performed to examine the potential damage induced in the underground tunnel. A lower frequency load was found to have a greater potential for producing damage compared with a high frequency blast load. The results showed that the location of the cracking within the tunnel, such as the arch foot or tunnel wall, was also influenced by the frequency of the blast wave. The maximum allowable PPV for the concrete tunnel was determined for a range of frequencies based on predicted free field PPV and additional factors of safety of 1.2 and 1.5 were established, depending on the safety needs and importance of the tunnel construction. Thus, our findings provide useful information for improving the evaluation of tunnel damage and guaranteeing the safety of underground tunnels.

Source characterization of a ducted source using acoustic free velocity

A common method to characterize linear time invariant ducted acoustic sources is the electro-acoustic analogy. The sources are typically defined by their internal source strength and source impedance. Various methods have emerged to determine the source characteristics, broadly categorized into direct and indirect methods. Direct methods involve using a secondary source with significantly higher amplitude to measure source impedance but cannot determine source strength. Indirect methods vary acoustic loads to obtain both source strength and source impedance, accuracy depends on appropriate load combinations. In this research, we propose an inverse method to determine the acoustic source strength from the measured acoustic transfer function and the operational acoustic pressure. This approach yields what we term as the "acoustic free velocity," corresponding to a plane monopole source that characterizes the original sound source. Subsequently, the source impedance is obtained using the acoustic free velocity in conjunction with the load impedance and acoustic pressure in the acoustic circuit. The method is demonstrated using a compressor driver source attached to a 1 3/8" impedance tube. Validation of the measured source strength and source impedance is conducted using a two-load method. Additionally, prediction of muffler insertion loss shows a good correlation with experimental measurements, affirming the efficacy of the proposed methodology.

Transfer learning with cross-domain adaptation of vibro-acoustic signals for electric motor mechanical fault detection and diagnosis.

Contact-based vibration measurement techniques involving accelerometers are typically utilized for machine health monitoring and manufacturing end-of-line quality control. Acoustic signals, encompassing sound pressure and particle velocity, carry crucial information about the operational status of underlying equipment and can be utilized for detecting various machine faults. Utilizing one-dimensional Convolution Neural Networks (1D-CNN) based on deep learning for processing raw acoustic time signals has proven to be a valuable approach in detecting machinery faults, offering an effective alternative to using traditional accelerometer signals. However, the success of deep learning methods is heavily dependent on the quantity and availability of data for robust network training. When transitioning to new non-contact type sensor technology, manufacturers may face challenges due to insufficient data for training deep learning models. In such cases, leveraging existing historical accelerometer-based data becomes crucial. Transfer learning emerges as a promising solution, allowing deep learning models trained on a source domain (SD) to be applied to a separate but related target domain (TD). This paper hence introduces a domain adaptation methodology by implementing transfer learning, where the SD 1D-CNN network is trained on accelerometer signals, then the trained model weights are transferred to the TD 1D-CNN network that can process acoustic signals.

Microstructural and material property changes in severely deformed Eurofer-97

Severe plastic deformation changes the microstructure and properties of steels, which may be favourable for their use in structural components of nuclear reactors. In this study, high-pressure torsion (HPT) was used to refine the grain structure of Eurofer-97, a ferritic/martensitic steel. Electron microscopy and X-ray diffraction were used to characterise the microstructural changes. Following HPT at room temperature to a maximum shear strain of 230, the average grain size reduced by a factor of ∼30, with a marked increase in high-angle grain boundaries. Dislocation density also increased by more than one order of magnitude. The thermal stability of the deformed material was investigated via in-situ annealing during synchrotron X-ray diffraction. This revealed substantial recovery between 450 K – 800 K. Irradiation with 20 MeV Fe-ions to ∼0.1 dpa caused a 20% reduction in dislocation density compared to the as-deformed material. However, HPT deformation prior to irradiation only had a minor effect in mitigating the irradiation-induced reductions in thermal diffusivity and surface acoustic wave velocity of the material. Microstructural and material property changes are dominated by deformation compared to irradiation. In light of this, the benefits of using HPT to improve the irradiation resistance of Eurofer-97 are limited. These results provide a multi-faceted view of the changes in ferritic/martensitic steels due to severe plastic deformation, and how these changes can be used to alter material properties.

Development of a characterization method for high-speed vehicle-induced vibrations in the built environment

A methodology was developed to analyze vehicle-induced vibration on street-adjacent structures. In partnership with an international racing organization, acceleration data was recorded during vehicle pass-by events during measurement campaigns at three locations involving cars traveling at high-speed. Net peak particle velocities were then calculated from the acceleration data. A unique filtering approach was developed for removing non-vehicle-induced signal noise from the measured data prior to analysis. Finally, an adaptation of the frequency domain composition (FDD) method was used to identify peak frequencies of interest for each event. By comparing the processed data to existing standards for cosmetic damage in buildings, the level of structural excitation caused by the measured vehicles was able to be assessed.

Surface construction vibration impacts on underground tunnels: Approaches for using measurements and finite-element modeling to predict vibration in the frequency and time domain

Quantitative analyses of vibration impacts on underground tunnel structures were carried out on two projects. The first project was a new facility situated above an existing physics laboratory accelerator tunnel embedded in soil where the concern was vibration interference with sensitive research. Published and in-house data for construction equipment source levels were combined with measured transfer functions, between the ground surface and the tunnel, to estimate vibration transmitted to the tunnel in the frequency domain. This case study presents an approach for site-specific evaluations of construction vibration where spectral data are needed for evaluating vibration-sensitive equipment/receivers. The second project was a new facility situated above a storm relief tunnel embedded in rock where the concern was for potential vibration damage to the tunnel. A 3-D finite-element model of the rock and tunnel structure was developed to calculate the peak particle velocity and strain response of the tunnel walls in the time domain. This case study presents an approach for site-specific evaluations of construction vibration where peak velocity amplitudes and strain data are needed for evaluating structural damage potential.