Propagation Speed Research Articles

Failure assessment of eccentric circular holes under compressive loading

AbstractThe present work aims to investigate the failure size effect on flattened disks containing an eccentric circular hole under mode I loading conditions. For this purpose, uniaxial compression tests are carried out on polymethyl methacrylate (PMMA) samples with holes. Depending on the hole radius and eccentricity, the energy release rate is either an increasing or decreasing function of the crack length, thus affecting the stability of crack propagation. Experimental results are interpreted and discussed through the coupled stress and energy criterion of Finite Fracture Mechanics. The approach lies on the assumption of a finite crack advance and it is implemented through the numerical estimation of the stress field and the Incremental Energy Release Rate functions. Finally, stability and crack speed propagation are discussed under the assumption of Linear Elastic Fracture Mechanics. Theoretical predictions reveal in agreement with experimental results thus demonstrating that the Coupled Criterion effectively captures the failure condition.

Infection spreading in tissue as a reaction-diffusion wave.

Viral infection develops in the organism due to virus replication inside infected cells and its transmission from infected to uninfected cells through the extracellular matrix or cell junctions. In this work, we model infection spreading in tissue with a delay reaction-diffusion system of equations for the concentrations of uninfected cells, infected cells and virus. We prove the wave existence, determine its speed of propagation and introduce a simplified one-equation model obtained from the complete model using a quasi-stationary approximation.

Study on the characteristics and predictive model of autoignition induced by shock wave from high-pressure hydrogen leakage

Faced with climate change and increasing environmental pollution, countries around the world are actively exploring strategies for clean, renewable energy. However, under high-pressure conditions, hydrogen leaks can lead to spontaneous combustion, which significantly raises the safety risk of hydrogen applications. This study employs fluid dynamic simulation methods to investigate the development process of shock waves within tubes. It analyzes the effect of release conditions on the propagation speed and shock wave intensity, revealing the impact of shock wave intensity on the temperature distribution and gas composition variation within the hydrogen-air mixture boundary layer. The results show that the tube length and bends have relatively little impact on the shock waves, while discharge pressure and tube diameter significantly affect the propagation speed and intensity of shock waves. Combined with dimensional analysis and data fitting, a predictive model for autoignition of high-pressure hydrogen leakage is established: (Pr/Pa)((DXrx(H₂)rO₂))/Vs2) = 1505(X/D)−1.329.

Investigations on conical lean turbulent premixed hydrogenated natural gas flames

Hydrogen's ability to enhance carbon neutrality in combustion processes puts forward the use of hydrogenated fuels, both in the form of fuel and an energy carrier as a potential decarbonization solution. However, because of the nature of hydrogen, blending it with hydrocarbons causes crucial structural changes in the flame structure, including higher flame propagation velocities and higher flame temperatures, decreased instantaneous flame thickness, and increased risks of flame flashback and an increasing potential of NOx emissions due to higher flame temperatures. These attributes encourage a thorough examination of hydrogenated blends of hydrocarbon fuels. Using lean premixed fuels is another technique to achieve efficient and cleaner combustion. However, due to the problem of flame instability in lean premixed combustion, forecasting the design points in terms of flame attributes is critical for better combustor designs.In this study, conical (Bunsen type) lean premixed turbulent flames of hydrogenated natural gas-air mixtures are experimentally studied. Through chemiluminescence measurements of the OH* and CH* radicals and laser-induced Mie scattering, lean natural gas-air premixed flames are examined with subsequently increasing hydrogen addition rates up to 20% by volume and keeping the premixture velocity constant. The obtained data is utilized for exploring the dynamics of the turbulent flame front. The main turbulent premixed flame parameters we identified relate to the instantaneous and average topology of the flame such as the turbulent flame brush thickness and flame height. We also inferred global combustion parameters like the turbulent flame propagation speed from the experimental findings.

KPP fronts in shear flows with cutoff reaction rates

AbstractWe consider the effect of a shear flow which has, without loss of generality, a zero mean flow rate, on a Kolmogorov–Petrovskii–Piscounov (KPP)‐type model in the presence of a discontinuous cutoff at concentration . In the long‐time limit, a permanent‐form traveling wave solution is established which, for fixed , is unique. Its structure and speed of propagation depends on (the strength of the flow relative to the propagation speed in the absence of advection) and (the square of the front thickness relative to the channel width). We use matched asymptotic expansions to approximate the propagation speed in the three natural cases , , and , with particular associated orderings on , while remains fixed. In all the cases that we consider, the shear flow enhances the speed of propagation in a manner that is similar to the case without cutoff (). We illustrate the theory by evaluating expressions (either directly or through numerical integration) for the particular cases of the plane Couette and Poiseuille flows.

Visualization experiment on the ignition performance and flame-spreading in different charging structures

In order to investigate the influence of different charging structures on the ignition performance and its influence on the particle movement before and after the film rupture of the chamber, a visualization experiment platform of the chamber was designed and built, and the stage tests of the ignition of the full particle charging, partial particle charging, mixed before and after the rod-particle charging and the full rod charging were carried out. The experiment shows that the free space will cause the flame propagation speed to increase significantly, from 77 m/s in the charge area to 575 m/s, and there will be pressure fluctuations in several areas of the chamber. The ignition performance of the rod is obviously better than that of the granular, and the pressure fluctuation in the chamber is smaller, the peak ignition gas pressure in the rod charge structure is only 50 % of that in the granular charge structure (1.6 MPa:3.2 MPa), and the maximum pressure difference is only 20 % of that in the granular propellant structure (0.5 MPa:2.5 MPa). The rod-particle mixed charge bed has good ignition consistency in the rod charge area, and when it reaches the granular charge area, the flame will be significantly hindered. The rod basically stays still during the ignition process in the chamber, while the granular will move with the gas flow when there is free space, and after the film is broken, the particle movement is faster than that before the film is broken.

Influence of finger joint length on the elastic modulus of reconstituted wood from Pinus taeda L.

The aim of this study was to evaluate the influence of three finger joint splice lengths on the dynamic modulus of elasticity of pieces of reconstituted wood from Pinus taeda L. Wooden specimens had finger joint splices of 5, 7 and 15 mm in length and were evaluated using the Stress Wave Time equipment, to analyze the wave propagation speed and dynamic modulus of elasticity, as well as the density of the pieces. As a result, increasing the finger joint’s length did not reduce the wave propagation speed through the wooden specimen. On the other hand, there was a reduction in the strength of the spliced wood as the much as the length of the finger joint increased. The density of the material may have influenced the reduction in the modulus of elasticity, even if it did not interfere with the wave propagation speed through the specimen.

Numerical and experimental study of attenuation inspection during FDM with ultrasonic leaky waveguide

ABSTRACT This work proposes an ultrasonic leaky waveguide (ULWG) for in-situ structural integrity inspection during fused deposition modeling (FDM). Since the ultrasonic wave propagation speed (m·s−1) is much higher than the deposition speed (mm·s−1), a quasi-static finite element model is first established to simulate the wave propagation during this dynamic process. The amplitude and energy attenuation coefficients (α and ζ) are chosen as the inspection features. Processing parameters including deposition layer thickness and number, inspection frequency, plate thickness and interface impedance are explored. For the first layer printing, a thinner thickness, higher frequency and proper interface impedance will enable a better inspection with high sensitivity. For multilayer printing, the multimodal dispersion curves change continuously and α oscillation is observed due to waveform aliasing that ζ is more reliable. Printing failures such as detachment can be predicted as well from the model established. The ULWG is then integrated into a commercial FDM machine to capture the attenuation coefficients of an “S” shape sample. The poor adhesion, local and global detachments, path planning impact can all be revealed by ζ experimentally. Moreover, being consistent to the simulation, the fluctuation of α in multilayer printing increases, which prevents a further printing evaluation.

Effect of lanthanum oxide on the radiation-shielding, dielectric, and physical properties of lithium zinc phosphate glasses

This study looked at the shielding properties, physical properties, and dielectric spectroscopy of various lanthanum oxide concentrations based on (65-x) P2O5-15 Li2O–15ZnO– 5Bi2O3- xLa2O3 with x = 0.0, 1.0, 2.0, 3.0, and 4.0 mol% glasses. When La2O3 is added, the molar volume quantities fall but the density values increase. The sample with the designation La-4.0 (4.0 mol% La2O3 content) had the highest density observed, 3.2182 g/cm3. Monte Carlo simulations and the Phy-x/PSD software were used to determine the critical gamma radiation attenuation characteristics, particularly linear attenuation coefficients and mass attenuation coefficients of glass samples under investigation. The half-value layer, mean free path, effective atomic number and effective electron density were then examined across a wide energy range (0.015–15 MeV). The findings of the investigation showed that the addition of La2O3 decreased the half-value layer and mean free path while increasing the mass attenuation coefficient, effective atomic number, and effective electron density. The results indicate that the inclusion of La2O3 appears to improve that glass system's ability to deflect gamma and neutron radiation. Over a broad frequency range, the dielectric properties were measured. The dielectric constant (ε′), which is typically steadily decreased with the addition of lanthanum, indicates an increase in the degree of electrical stiffness inside the glass network. Among the samples examined, the glass sample La-4.0 is thought to possess the best properties for electronic packaging due to its maximum propagation speed and lowest dielectric constant.

Seismic oceanography of internal solitary waves offshore the South Island, New Zealand

Seismic oceanography has been widely used in the study of internal solitary waves (ISWs) in recent years, and has achieved remarkable results. In this paper, we analyzed the multi-channel seismic reflection data in the Canterbury Basin offshore New Zealand from January 9 to January 29, 2000, collected by R/V Maurice Ewing. We observed 4 groups of ISWs (labeled ISW1s to ISW4s) on 4 seismic survey lines. We studied their waveforms and propagation speeds in detail. There are two theoretical structures used to describe the vertical waveform of ISWs: the first-order nonlinear vertical structure and the linear vertical structure. We found that ISW1s fit the nonlinear structure well, ISW3s and ISW4s fit the linear structure, and ISW2 does not fit either one. As the water depth increases, the waveforms of all ISWs gradually widen. Two satellite SAR images reveal that all ISWs generally travel shoreward across the isobaths. However, the propagation direction of ISW1s is about 354°-360° (clockwise from due north), different from the propagation directions of other ISWs (about 22°-26°), which explains why ISW1s have the largest characteristic half-height width. The estimated propagation speeds are close to the theoretical speeds, confirming our speed correction method. In the end, we also discuss the interaction of ISWs and eddies.

Experimental Study on Flame Spread of Pine Wood Dust Layer Under Horizontal Rotation Condition

ABSTRACT The rotating discs of wood polishing machines and the rotating bases of winding machines rotate horizontally during operation, and a layer of wood dust may be deposited on their surfaces. The study of flame spreading of wood dust layer in the rotating state has not been reported in the literature. Based on this situation, in this study, the flame spreading of pine wood dust layers in three particle size ranges under stationary and different rotating conditions were carried out and analyzed comparatively. The results show that the flame spreading speed of the pine wood dust layer from 74~100 micrometers positively correlates with the rotational angular velocity. The flame-spreading speed of a pine wood dust layer larger than 100 micrometers negatively correlated with the rotational angular velocity. This indicates that the flame spreading speed of the pine wood dust layer is affected by the combined effect of dust particle size and dust layer motion state. The flame propagation speed of the 74~100 micron pine dust layer was 3.3 mm/s when the rotational angular velocity was 0.167 rad/s, which was the maximum flame propagation speed in all experimental conditions. The maximum flame height of the pine dust layer in the rotating state was at least 55.6% higher than that in the stationary state.From the combined view of the three parameters of flame spreading speed, flame duration, and maximum flame height, the fire danger is greater in the rotating state than in the stationary state. Within a certain range, the larger the rotational angular velocity, the greater the fire hazard.

Process of cabin smoke and flame propagation and emergency evacuation characteristics of personnel during sudden fire of Boeing 737

Cabin fires and emergency evacuation of personnel are hot topics in aviation safety. To obtain the characteristics of cabin fires and personnel evacuation, a study is conducted on the Boeing 737, and the results show that after the fire occurs, smoke first spreads towards the top and then rapidly spreads towards both ends of the cabin. The propagation speed of smoke is greater than that of flame, as the spread of flame is limited by the oxygen concentration in the cabin. Although the partition between business class and economy class has a significant obstructive effect on the spread of smoke, the effectiveness of the partition in blocking heat and high temperature transfer is limited. When a fire occurs in the cabin and emergency evacuation is required, it takes 80.5 s to evacuate all personnel when all eight cabin doors are open. But when emergency hatches fail to open, it is not until 164.8 s that all personnel in the cabin are evacuated, mainly because people in the economy class can only be evacuated through the front and rear cabin doors, which reduces the evacuation rate. The research on cabin fire and emergency evacuation of personnel can provide reference for fire monitoring and firefighting rescue.

The combustion characteristics and stable limit of a novel combustor with gradient porous media for hydrogen-enriched natural gas

Injecting hydrogen into natural gas pipelines for delivery to end users is currently considered as one of the potential solutions to the challenges of hydrogen transportation and utilization. However, the blending of hydrogen accelerates the flame propagation speed of the mixture, leading to flame instability and other issues. In this paper, a gradient porous structural burner was proposed, then the effects of pore size gradient and porosity gradient on the combustion characteristics and stability limits of hydrogen-enriched natural gas flames were investigated numerically. This paper proposed a spatial gradient-based porous structure, and the results showed that the axial gradient porous structure with increasing pore size enhances the maximum temperature by approximately 26 %. The radial gradient structures with decreasing porosity and increasing pore size increased the maximum temperature by approximately 25.8 % and 24.8 %, respectively, and improved flame uniformity. Compared to the conventional two-stage uniform structure, the axial pore size increment structure improved the stability limit by approximately 117 %, while the radial pore size increment structure increased the stability limit by 47 %. The results provide reference for the design and optimization of new porous media burner structures that are applicable under wide power ranges and hydrogen blending conditions.

Slow traveling-wave solutions for the generalized surface quasi-geostrophic equation

In this paper, we systematically study the existence, asymptotic behaviors, uniqueness, and nonlinear orbital stability of traveling-wave solutions with small propagation speeds for the generalized surface quasi-geostrophic (gSQG) equation. Firstly we obtain the existence of a new family of global solutions via the variational method. Secondly we show the uniqueness of maximizers under our variational setting. Thirdly by using the variational framework, the uniqueness of maximizers and a concentration-compactness principle we establish some stability theorems. Moreover, after a suitable transformation, these solutions constitute the desingularization of traveling point vortex pairs.

Effect of low blockage ratio obstacle on explosion characteristic in methane/air mixture

Methane/air explosion is one of the common hazards in process and mining industries. In this study, the methane explosion propagation is studied, and two-dimensional configuration is considered. The gas phase equations are solved using an OpenFOAM code for compressible reacting flow, EXiFOAM. The effects of the low blockage ratio (LBR) obstacles are investigated. The results show that the flame propagation speed, flame structure, shock wave propagation, and gas flow are considerably affected by LBR obstacles. Specifically, the flame propagation speed first increases and then decreases. As the initial pressure increases, the flame propagation speed gradually increases. The maximum speed is up to 500 m/s, when the initial pressure is 1.5 MPa. If the flame propagation is prevented, resulting in the flame deformation. Moreover, the flame disruptive phenomenon is captured due to the reflected waves. In front of the obstacle, the cellular structures of the high-pressure distribution are formed. Note that the tiny cellular structures are produced in the wake of the leading shock. Furthermore, a high-speed flow region and two low-speed flow regions are produced around the LBR obstacles. It is found that as the initial pressure increases, the explosion pressure is larger, while the temperature change is not obvious. These research findings have implications for enhancing safety production in coal mines.

All-photonic artificial synapses based on photochromic perovskites for noncontact neuromorphic visual perception

Recently optoelectronic synapses generating light-driven electrical memories have played a vital role in the neuromorphic computing of visual perception. However, all the optoelectronic synapses demonstrate photoelectric conversion. Peripheral circuits are used for contact photocurrent measurement, leading to significant energy consumption and impeding the evolution of optical wireless communication. It is crucial to develop noncontact neuromorphic visual perception based on light-driven photonic memories. Herein, we report all-photonic artificial synapses based on photochromic perovskites. Triggered by ultraviolet and visible light pulses, cesium lead iodide bromine induces a structural disorder. Optical transmittance changes induced by the disorder last after the pulses are gone. Next, the photonic memories are propagated in the air and processed by a recurrent neural network. The accuracy of binary image recognition is instantly stabilized at 1.0, and accuracy above 0.8 after 7 epochs is achieved in the recognition of digitals from 0 to 9. The all-photonic synapses realize remote perception with zero in-situ energy consumption and enable artificial sensory systems with low-power computation, remote control, and ultrahigh propagation speed.

Evolution of the Leader Discharge in Bi‐Directional Propagation System in Altitude‐Triggered Lightning

AbstractOn 18 June 2023, comprehensive observations were conducted to an altitude‐triggered lightning flash. Upward positive leader (UPL) and downward negative leader (DNL) in a bi‐directional development system were detected simultaneously by a high‐speed camera, together with the coordinated measurements of magnetic field and very‐high‐frequency (VHF) emissions. High‐speed images reveal, for the first time, the enhancement of the UPL's propagation speed by DNL in the bi‐directional leader system. Concretely, the upward positive leader initially originates from a suspended wire tip and propagates at a two dimensional (2D) speed of 5.32 × 104 m/s, and after about 6.3 ms, its propagation speed was enhanced to 1.12 × 105 m/s when the stepped DNL started advancing at an average speed of 1.44 × 105 m/s. Additionally, based on the evolution of channel luminosity and the variations of magnetic radiation, it is found that there is a consistency in luminosity variation between the ascending channel and the descending channel in the bi‐directional leader system, and the amplitude of the magnetic field increases when the negative discharges start at the bottom wire end with intensive VHF emissions. Those facts indicate that the DNL has an effect, may be a positive one, on the UPL's development in the early stage of altitude‐triggered lightning.

Nonclassical wave propagation measurements in the high temperature vapor of D6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {D}_{6}$$\\end{document} with the asymmetric shock tube for experiments in rarefaction waves (ASTER)

A novel test setup called the asymmetric shock tube for experiments on nonideal rarefaction waves (ASTER) has been commissioned at Delft University of Technology. The ASTER, which works according to the principle of Ludwieg tubes, is designed to generate and measure the speed of small and finite amplitude waves propagating in the dense vapors of fluids formed by complex organic molecules, therefore in the nonideal compressible fluid dynamics regime. The ultimate goal of the associated research is to prove the existence of nonclassical gasdynamics. The setup consists of a high-pressure charge tube and a vacuum tank separated by a glass disk equipped with a breaking mechanism for rarefaction waves experiments. When the glass disk is broken, an expansion wave propagates into the tube in the direction opposite to the fluid flow. The propagation speed of this wave is measured using a time-of-flight method with the help of four fast-response pressure sensors placed equidistantly in the middle of the tube. The charge tube can withstand pressures and temperatures of up to 15 bar and 400∘C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }\\mathrm{C}$$\\end{document}. Preliminary rarefaction experiments were successfully conducted using dodecamethylcyclohexasiloxane, D6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {D}_{6}$$\\end{document}, as the working fluid and at pressures and temperatures of up to 9.4 bar and 372∘C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }\\mathrm{C}$$\\end{document} , respectively. The results of an experiment featuring the initial state for which a theoretical model predicts the nonclassical acceleration of rarefaction waves show that the propagation is qualitatively different from that put into evidence by experiments for which the propagation is classic. Upcoming setup improvements and experimental campaigns are planned with the objective of experimentally verifying the existence of nonclassical gasdynamics.Graphical abstract

Atomic simulations of crack propagation in Ni-Al binary single crystal superalloy with a central crack

Nickel (Ni)-based single-crystal superalloys are of great importance in the aircraft industry due to their excellent mechanical properties, and cracks as unavoidable defects may affect the mechanical performances of materials dramatically. In this paper, large scale molecular dynamics (MD) simulations are carried out to understand the deformation mechanisms of Ni-based single crystal with a central crack under tension. Here, the effects of matrixes (γ, γ′ and γ/γ′), strain rates (1 × 109 s−1 ∼ 3 × 109 s−1) and temperatures (300 K∼900 K) on the role of crack propagation are considered. It is observed that dislocations and slip systems in the γ′ model are concentrated near the crack, resulting in the rapid expansion of dislocation, which leads to the fastest crack growth speed and early fracture. While the crack propagation rate of γ and γ/γ′ models are relatively slow, due to the combined action of the Lomer-Cottrell lock and stacking fault tetrahedron structure and Stair-rod dislocation, which hinders crack propagation. In addition, deformation at increased strain rates and/or reduced temperatures, lead to superior yield stress and Young′s modulus for models with a central crack at γ/γ′ interface. On the other hand, high temperature and high strain rate will promote crack propagation in the γ phase, and the higher the strain rate and/or temperature, the faster the crack propagation speed will be. These results will enrich our understanding on the crack propagation and evolution mechanisms in Ni-based single crystal superalloy.

Experimental and numerical simulation of the attenuation effect of blast shock waves in tunnels at different altitudes

Traffic engineering such as tunnels in various altitudinal gradient zone are at risk of accidental explosion, which can damage personnel and equipment. Accurate prediction of the distribution pattern of explosive loads and shock wave propagation process in semi-enclosed structures at various altitude environment is key research focus in the fields of explosion shock and fluid dynamics. The effect of altitude on the propagation of shock waves in tunnels was investigated by conducting explosion test and numerical simulation. Based on the experimental and numerical simulation results, a prediction model for the attenuation of the peak overpressure of tunnel shock waves at different altitudes was established. The results showed that the peak overpressure decreased at the same measurement points in the tunnel entrance under the high altitude condition. In contrast, an increase in altitude accelerated the propagation speed of the shock wave in the tunnel. The average error between the peak shock wave overpressure obtained using the overpressure prediction formula and the measured test data was less than 15%, the average error between the propagation velocity of shock waves predicted values and the test data is less than 10%. The method can effectively predict the overpressure attenuation of blast wave in tunnel at various altitudes.