Dispersion Characteristics Research Articles

Two-stage residual networks for damage identification and location of stiffened composite panel based on guided waves

The damage detection of the stiffened composite panel, as a typical aircraft structure, is a research hotspot in Structural Health Monitoring (SHM). where guided waves propagate with multi-modal and dispersion characteristics. The traditional damage detection method manually extracts the potential discriminative features of the signal to achieve damage identification, depending on expert experience. In this paper, we propose a two-stage residual networks (ResNets) framework based on guided waves to locate damage in the stiffened composite panel, which automatically mines the high-dimensional features with sensitive discriminant information. The guided wave signal acquisition system collects four types of data: health data, stringer damage data, damage data on the skin of the stringer-side, and damage data on the skin-side. The first-stage utilizes a ResNet to classify the structure condition, while in the second-stage, three separate ResNets are employed to locate the damage according to the classification results of the first-stage. The experimental results show that the accuracy of the first-stage damage classification and the damage localization of the stringer and the skin of the stringer-side in the second-stage has reached 100%, and that of the skin-side is 99.13%, which significantly outperforms single-stage methods. This strategy of inter-class discrimination and intra-class precise localization of damage can not only identify the damaged regions but also determine the specific location of the damage, which greatly increases the performance of SHM. The present two-stage method is a potential solution for future SHM strategies and further investigation is warranted.

Dispersion Behavior of a Droplet Impacting a Single Fiber.

The high-gravity reactor, known for its excellent mass transfer capability, plays a crucial role in the carbon capture process. The wire mesh packing serves as the core structure for enhancing mass transfer performance. Understanding the underlying dispersion mechanism requires a thorough exploration of the dynamics of droplet impact on a single fiber. This work aimed to numerically study the process of a droplet impacting a single fiber by applying the volume of fluid method. The effects of initial velocity (u0), initial diameter (D0), impact eccentric distance (e), and impact angle (θ) on the deformation evolution and dispersion characteristics of a droplet impacting a single fiber were systematically studied. Central or vertical impacts can be categorized into four main stages: splitting, merging, stretching, and breaking. Meanwhile, asynchronous breaking, sliding splitting, and oblique stages were observed during eccentric and nonvertical impacts. Subsequently, dimensionless time (t*) and the rate of increase of the gas-liquid interfacial area (η) were introduced to quantitatively analyze the dispersion characteristics postimpact. Increasing the initial velocity, reducing the droplet diameter, minimizing the impact eccentric distance, and maximizing the impact angle all contribute to enhanced dispersion performance. A correlation for the maximum increase rate of the gas-liquid interfacial area of the droplet was proposed, with errors less than ±15%. Finally, the deformation mechanism of droplet impact on a fiber was summarized by analyzing the influences of differential pressure inside and outside the liquid film, as well as gas vortices.

Computation and analysis of surface wave dispersion and attenuation in layered viscoelastic-vertical transversely isotropic media by the generalized R/T coefficient method

SUMMARY In this study, we propose a systematic and effective method, that is, an extended version of the generalized reflection/transmission (R/T) coefficient method, for computing the phase-velocity (${c}_r$) dispersion curves, attenuation coefficient ($\alpha $) curves, and eigenfunctions of both Rayleigh and Love waves as well as the ellipticity of Rayleigh waves in layered viscoelastic-vertical transversely isotropic (VTI) media. The numerical scheme of combining the root-searching method with the local optimization method is designed for determining the complex-valued modal solutions (i.e. complex wavenumber $k = {\omega {/ {\vphantom {\omega {{c}_r - i\alpha }}}} {{c}_r - i\alpha }}$) of surface waves. The near-surface sedimentary geological environment is taken as the model example because it is typical viscoelastic-VTI media. Besides the anisotropic-viscoelastic (AV) media, our algorithm can also compute surface waves in isotropic-elastic (IE), isotropic-viscoelastic (IV) and anisotropic-elastic (AE) media by resetting the corresponding parameters. Using the six-layer half-space models and in these four media, we verify the correctness of our algorithm by benchmarking the modal solutions against those from other methods. In the four-layer half-space model, by comparing the results of IE, IV, AE and AV media, we analyse the effects of velocity anisotropy, viscoelasticity and attenuation anisotropy on the dispersion and attenuation characteristics of both Rayleigh and Love waves in detail. Our study can provide a theoretical basis and useful tool for surface wave imaging considering the anisotropy and/or viscoelasticity of the medium, which has the potential to better investigate the solid Earth's internal structure.

A balanced outflow boundary condition for swirling flows

In open flow simulations, the dispersion characteristics of disturbances near synthetic boundaries can lead to unphysical boundary scattering interactions that contaminate the resolved flow upstream by propagating numerical artifacts back into the domain interior. This issue is exacerbated in flows influenced by real or apparent body forces, which can significantly disrupt the normal stress balance along outflow boundaries and generate spurious pressure disturbances. To address this problem, this paper develops a zero-parameter, physics-based outflow boundary condition (BC) designed to minimize pressure scattering from body forces and pseudo-forces and enhance transparency of the artificial boundary. This “balanced outflow BC” is then compared against other common BCs from the literature using example axisymmetric and three-dimensional open swirling flow computations. Due to centrifugal and Coriolis forces, swirling flows are known to be particularly challenging to simulate in open geometries, as these apparent forces induce non-trivial hydrostatic stress distributions along artificial boundaries that cause scattering issues. In this context, the balanced outflow BC is shown to correspond to a geostrophic hydrostatic stress correction that balances the induced pressure gradients. Unlike the alternatives, the balanced outflow BC yields accurate results in truncated domains for both linear and nonlinear computations without requiring assumptions about wave characteristics along the boundary.

Dispersion characteristics of arc-axis waveguides

Ultrasonic single mode excitation methods, mode separation algorithms and damage detection applications all require the calculation of the dispersion characteristics of the waveguide. However, existing dispersion calculation methods are mainly applicable to straight-axis waveguides. Therefore, in this paper, a novel semi-analytical finite element method in cylindrical coordinates (SAFEM-CC) is established and we focus on the dispersion characteristics of arc-axis waveguides. The cross-section of the waveguide can have arbitrary complex shapes, and the correctness of this method is verified by the finite element eigenfrequency method. At the same time, this paper takes the example of an arc-axis structure with a square cross-section and investigates the convergence of SAFEM-CC under different numbers of elements, element types, and element orders. This paper also establishes a finite element simulation model to study the waveform transmission law over a wide frequency range and the wave amplitude distribution law within the cross-section of arc-axis waveguides. The dispersion characteristics of arc-axis waveguides at different radii are also investigated. Finally, the correctness of the proposed method and the dispersion characteristics of arc-axis waveguides are verified by a large number of experiments. The main conclusions are as follows: the waveform transmission laws of the guided wave in arc-axis waveguides at each frequency agree with the dispersion curve; the theoretical wavestructure gives the distribution law of the amplitude within the cross-section; when the axis is arc, the displacement of the wavestructure on the inner and outer sides does not have symmetry, and the difference between the left and right sides gradually increases as the radius decreases.

Characteristics of bare rocky land evolution in karst mountain areas of Southwest China based on socio-ecological system perspectives: The case study of Huajiang Canyon

Rock exposure is a prerequisite for the emergence of bare rocky land (BRL), a severe ecological and environmental problem in karst mountain areas (KMA) of Southwest China, severely restricting the region’s sustainable development. An in-depth analysis of the evolution of BRL in KMA of Southwest China based on socio-ecological perspectives is significant for promoting the region’s sustainable development. This paper firstly analyzes the evolution of the social-ecological system and BRL and the transition of human-land relations in KMA of Southwest China, then selects a typical KMA, Huajiang Canyon in Guizhou Province, for a case study and applies ArcGIS to analyze the dynamics of the BRL of Huajiang Canyon in the past 60 years from 1969 to 2020, and reveals the reasons for the evolution of BRL. The results show that: (1) The evolution of BRL in KMA of Southwest China is closely related to the changes in the local socio-ecological environment. (2) The number, spatial distribution, and landscape pattern of BRL in the Huajiang Canyon from 1969 to 2020 underwent significant changes, with the area of BRL transitioning from an expansion phase to an accelerated shrinking phase and with prominent spatial dispersion characteristics. (3) The transition of the BRL of the Huajiang Canyon into forest grassland and economic and fruity forest land, and the transition of land use from production to ecology and eco-economy, have proved the greening of the KMA of Southwest China from a microscopic perspective. (4) This paper shows that the expansion and contraction of BRL areas can reflect the human-land relations in KMA of Southwest China. Finally, the development path proposed in this paper has a certain positive effect on promoting the future sustainable development of the KMA of Southwest China and can also provide a reference for developing other mountainous areas with similar situations.

Nanostructures and multi-scale aggregation of high ion exchange capacity short-side-chain perfluorosulfonic acid dispersion

Short-side-chain perfluorosulfonic acid (SSC-PFSA) ionomers with high ion-exchange-capacity are promising candidates for high-temperature proton exchange membranes (PEMs) and catalyst layer (CL) binders. The solution-casting method determines the importance of SSC-PFSA dispersion characteristics in shaping the morphology of PEMs and CLs. Therefore, a thorough understanding of the chain behavior of SSC-PFSA in dispersions is essential for fabricating high-quality PEMs and CLs. In this study, we have employed multiple characterization techniques, including dynamic light scatting (DLS), small-angle X-ray scattering (SAXS), and cryo-transmission electron microscope (Cryo-TEM), to fully study the chain aggregation behaviors of SSC-PFSA in water–ethanol solvents and elucidate the concentration-dependent self-assembly process. In dilute dispersions (2 mg/mL), SSC-PFSA assembles into mono-disperse rod-like aggregates, featuring a twisted fluorocarbon backbone that forms a hydrophobic stem, and the sulfonic acid side chains extending outward to suit the hydrophilic environment. As the concentration increases, the radius of rod particles increases from 1.47 to 1.81 nm, and the mono-disperse rod particles first form a “end-to-end” configuration that doubles length (10 mg/mL), and then transform into a swollen network structure in semi-dilute dispersion (20 mg/mL). This work provides a well-established structure model for SSC-PFSA dispersions, which is the key nanostructure to be inherited by PEMs.

Effects of In2O3 doping on the microstructure and electrical properties of ZnO–V2O5–Nb2O5 varistor ceramics

To understand the effects of In2O3 on the microstructure, grain size dispersion, density and nonlinear electrical characteristics, ZnO–V2O5–Nb2O5 varistor ceramics with 0.02, 0.05 and 0.1 mol.% In2O3 were fabricated via sintering at 950–975 °C for 1 h. The sintered samples were evaluated by x-ray diffraction, scanning electron microscopy, density measurements and electrical measurements through a voltage source meter. In2O3 addition improves relative density to ≥99 % and acts as an efficient grain growth inhibitor, resulting in a narrower grain dispersion and finer ZnO grains due to the formation of In–V–O intergranular phases. The breakdown potential (E1mA) increases sharply to 7.49 ± 0.3 kV/cm (from 1.66 ± 0.1 kV/cm) as a result of grain size reduction to 2.1 ± 0.1 μm (from 3.89 ± 0.2 μm) with In concentration of 0.1 mol.% (from 0.02 mol.%). Doping of In2O3 improves the nonlinear exponent and reduces the leakage current density as a direct consequence of enhanced Schottky barrier height.

Fragment dispersion characteristics of uncoupled charge structures with internal explosive loading

The demand for uncoupled charge structures has risen alongside advancements in warheads and protective design technologies in defense and public security sectors. Consequently, this work investigates the fragment dispersion characteristics of uncoupled charge structures and the impact of different structural parameters through numerical simulations. A modified equation derived from the Gurney formula is proposed using numerical simulation and the smoothed particle hydrodynamics method, tailored to the uncoupled charge concept and the foundational theory of the Gurney formula. To validate the fragment velocity prediction model for uncoupled charge structures, explosion experiments and other testing methods were utilized. By examining the theoretical underpinnings and the application of numerical simulation methods, this paper provides a robust foundation for the uncoupled charge structure, offering a crucial reference for designing protective measures against improvised explosive devices.

The Influence of Additively Manufactured Specimen Thickness on Laser-Induced Ultrasonic Signals

Selective laser melting (SLM) technology, employed in metal additive manufacturing, is widely utilised to fabricate components with precise dimensions and excellent mechanical properties by melting powder layer by layer. Laser ultrasonic testing is anticipated to be an efficient method for in-line monitoring in the additive manufacturing (AM) process. The conversion of specimens from thin to thick during the SLM manufacturing process has an impact on the ultrasonic signals. This paper focuses on the influence of AM specimen thickness changes on ultrasonic signals. In the finite element analysis, the incremental specimen thickness was maintained at 0.2 mm, which was the initial value. As the specimen thickness increased sequentially, ultrasonic signals were obtained from different specimens. The results demonstrate that Lamb waves are generated when the specimen is thin, and the dispersive characteristics weaken as the thickness increases. The dispersive phenomenon diminishes significantly once the specimen thickness exceeds 1 mm. By employing the f-k method, calculated dispersion curves for various specimen thicknesses were obtained. After fitting the derived dispersion curve, a mapping relationship is established with respect to the specimen thickness. Consequently, the fitting coefficient of the dispersion curve can therefore be utilized to characterize the thickness of the additive manufactured thin specimen.

An equivalent target plate damage probability calculation mathematics model and damage evaluation method

Aiming at the requirement of damage testing and evaluation of equivalent target plate based on the explosion of intelligent ammunition, this paper proposes a novel method for damage testing and evaluation method of circumferential equivalent target plate. Leveraging the dispersion characteristics parameters of fragment, we establish a calculation model of the fragment power situation and the damage calculation model under the condition of fragment ultimate penetration equivalent target plate. The damage model of equivalent target plate involves the fragment dispersion density, the local perforation damage criterion, the tearing damage model, and the damage probability. We use the camera to obtain the image of the equivalent target plate with fragment perforation, and research the algorithm of fragment distribution position recognition and fragment perforation area calculation method on the equivalent target plate by image processing technology. Based on the obtained parameters of the breakdown position and perforation area of fragments on equivalent target plate, we apply to damage calculation model of equivalent target plate, and calculate the damage probability of each equivalent target plate, and use the combined probabilistic damage calculation method to obtain the damage evaluation results of the circumferential equivalent target plate in an intelligent ammunition explosion experiment. Through an experimental testing, we verify the feasibility and rationality of the proposed damage evaluation method by comparison, the calculation results can reflect the actual damage effect of the equivalent target plate.

In-Plane Radiation of Surface Plasmon Polaritons Excited by Free Electrons.

Surface plasmon polaritons (SPPs) have become a research hotspot due to their high intensity and subwavelength localization. Through free-electron excitation, a portion of the momentum of moving electrons can be converted into SPPs. Converting highly localized SPPs into a radiated field is an approach with the potential to aid in the development of a light radiation source. Reducing losses of SPPs is currently a critical challenge that needs to be addressed. The lifetime of SPPs in metal films is longer than that in metal blocks. Traditional optical gratings can transform SPPs into radiation to avoid the decay of SPPs in metal; however, they are created by etching metal films, so they tend to alter the dispersion characteristics of these films and will emit radiation in the direction perpendicular to the metal surface. This paper proposes an approach to converting the SPPs of a metal film excited by free electrons into a radiation field via lateral grating and obtaining in-plane radiation. We investigate the properties of SPP lateral radiation. The study of lateral radiation from metal films holds significant importance for SPP radiation sources and SPP on-chip circuit development.

Effects of gas-pore sizes and locations on fatigue failure: A peridynamic study

Due to complicated features of gas-pores and great dispersions of fatigue lifetimes in additively manufactured metals, it is cumbersome to reveal the exact effects of gas-pores on fatigue failure by purely analyzing experiment data. In this paper, two-dimensional peridynamic virtual fatigue experiments (PD-VFE) are performed to investigate the effects of a singular circular gas-pore on the fatigue failure in smooth specimens. PD-VFE well captures three different modes of fatigue crack initiation (FCI), which are revealed to dominate the gas-pore impacts on fatigue lifetimes. Effects of two typical features of gas-pores, i.e. locations and sizes, are also clarified; to be specific, gas-pore location is the major factor to decide FCI mode and subsurface gas-pore is the most dangerous, while the role of gas-pore size is to scale the impacts of gas-pore location on fatigue lifetimes. The above PD-VFE results accord with experiment data in variation tendency, and can also explain assumptions and simplifications in Murakami approach.

Room-Temperature Polariton Lasing from CdSe Core-Only Nanoplatelets.

This paper reports how CdSe core-only nanoplatelets (NPLs) coupled with plasmonic Al nanoparticle lattices can exhibit exciton-polariton lasing. By improving a procedure to synthesize monodisperse 4-monolayer CdSe NPLs, we could resolve polariton decay dynamics and pathways. Experiment and theory confirmed that the system is in the strong coupling regime based on anticrossings in the dispersion diagrams and magnitude of the Rabi-splitting values. Notably, polariton lasing is observed only for cavity lattice periodicities that exhibit specific dispersive characteristics that enable polariton accumulation. The threshold of polariton lasing is 25-fold lower than the reported photon lasing values from CdSe NPLs in similar cavity designs. This open-cavity platform offers a simple approach to control exciton polaritons anticipated to benefit quantum information processing, optoelectronics, and chemical reactions.

Impact of Methods of Preparation on Mechanical Properties, Dissolution Behavior, and Tableting Characteristics of Ibuprofen-Loaded Amorphous Solid Dispersions.

This study aims to improve the biopharmaceutical, mechanical, and tableting properties of a poorly soluble drug, ibuprofen (IBP), by preparing amorphous solid dispersion (ASD) followed by a sustained-release tablet formulation. A suitable polymer to develop an ASD system was chosen by utilizing the apparent solubility of IBP in various polymer solutions. ASDs containing various ratios of IBP and selected polymer were prepared by the melt fusion (MF) method. ASD containing optimized drug-polymer ratio prepared by freeze-drying (FD) method was characterized and compared physicochemically. The solubility of IBP in water increased 28-fold and 35-fold when formulated as ASD by MF and FD, respectively. Precise formulations showed amorphization of IBP and increased surface area, improving solubility. The dissolution pattern of optimized ASD-IBP in pH 6.8 phosphate buffer after 60 min in MF and FD was enhanced 3-fold. In addition, direct compression tablets comprising optimized ASD granules from MF and FD were made and assessed using compendial and noncompendial methods. ASD-IBP/MF and ASD-IBP/FD formulations showed a similar drug release profile. In addition, 12 h of sustained IBP release from the ASD-IBP-containing tablets was obtained in a phosphate buffer with a pH of 6.8. From the dissolution kinetics analysis, the Weibull model fitted well. The drug release pattern indicated minimal variations between tablets formed using ASD-IBP prepared by both procedures; however, pre- and postcompression assessment parameters differed. From these findings, the application of ASD and sustained-release polymers in matrix formation might be beneficial in improving the solubility and absorption of poorly soluble drugs such as IBP.

Effect of bubble properties and dispersion characteristics in microbubble counter-current collision flotation column

ABSTRACT Cationic collectors are widely used in the flotation of hematite, silicate, oxides, etc. GE-601, as a new type of cationic collector, which was used in various mineral flotation process, has achieved excellent selection indexes. In order to study foaming performance of GE-601, the bubble characteristics are studied in an experimental scale two-phase flotation column. A high-speed camera recorder is used to take bubbles’ images and the distribution of bubble diameter under different conditions is measured by image analysis. Moreover, the surface tension of bubbles under different reagent concentrations is measured by a surface tension meter. Studies show that as GE-601 concentration increases, d 32 gradually decreases and after exceeding CCC, Sauter mean diameter (d 32) stabilizes at 0.562 mm. When the bubble diameter decay degree is 99%, 90% and 50%, GE-601 concentration reaches 0.112 mol/m3, 0.0643 mol/m3, and 0.0295 mol/m3, respectively. The adsorption concentration of GE-601 is about 0.0254 μmol·m−2. GE-601 reduces pulsation on the surface of bubbles in flowing liquid. During the rise of bubbles, d 32 is approximately linearly related to measured height, but the concentration of d 32 and GE-601 decrease varies linearly.

Dispersion behavior of silica fume in cementitious suspensions

The dispersion characteristics of silica fume are pivotal factors influencing the rheological properties, mechanical properties, and durability of cement-based materials. This study investigated the dispersion behavior of different types of silica fume including highly densified silica fume (HDSF), moderately densified silica fume (MDSF), and raw silica fume (RSF) in water and cement paste filtrate mediums. Optical microscopy (OM) was utilized to monitor the silica fume agglomerations in suspensions, and scanning electron microscopy (SEM) was employed to observe the agglomerates in hardened ultra-high performance concrete (UHPC) containing 25 wt% silica fume. The results revealed that RSF, MDSF, and HDSF have similar particle size distributions in water and cement paste filtrate, with D50 values of 10.9 μm, 15.0 μm, and 112.2 μm, respectively. The agglomeration degree of silica fume is virtually unaffected by superplasticizer. Additionally, the effects of dispersion methods (i.e., ultrasonic, aerodynamic, and aggregate premixing) on silica fume dispersions were also investigated. It was shown that the aerodynamic dispersion method significantly reduced silica fume agglomeration, and adequate ultrasonic treatment almost eliminated physical agglomeration. By contrast, premixing silica fume with aggregates and steel fibers partially mitigated agglomeration. This study provides a theoretical foundation and technical guidance for the effective utilization of different types of silica fume in concrete applications.

Migration characteristics and geohazards risk analysis of swelling clay in clayey silt hydrate sediments

The safe and long-term hydrate production in loose clayey silt sediments with high clay content is one of the research priorities, in which the fines migration is one of the key factors. The characteristics of montmorillonite swelling and dispersion make its migration behavior more challenging, which causes the evolution of reservoir seepage properties and potential geohazards risk cannot be predict. The migration behavior of montmorillonite induced by pore water was investigated, and discusses its potential impact on the geomechanical properties of the reservoir. The results show that the combined effects of montmorillonite swelling, which creates favorable conditions for blockage, and migration, which exacerbates permeability decline, make montmorillonite have a much greater effect on seepage characteristics in clayey silt sediments than illite. Higher montmorillonite content and low salinity increase the particle concentration in the pore water, which creates a source of particles for blockage. The low reynolds number indicates that the particles mainly detach from the pore wall with rolling in laminar flow and the lifting force can be neglected. As a result of this combined effect, the montmorillonite is more likely to readsorb and block the pore throat with bridging. This work will help to understand the migration behavior of montmorillonite in clayey silt formations with low permeability, which needs to be paid attention to when formulating gas production schemes and safety control strategies.

Melting phenomenon of thermally stratified MHD Powell–Eyring nanofluid with variable porosity past a stretching Riga plate

Abstract Recently, experts have become particularly interested in the treatment of disorders caused by magnesium shortage. Hypomagnesemia is produced by a magnesium deficit in the blood, which is an additional stimulation for different diseases such as vomiting, drowsiness, nausea, loss of appetite, and so on. To compensate for this shortage, magnesium is injected as a nanoparticle in the blood (base fluid). The properties of these magnesium nanoparticles specifically their size, dispersion, and surface characteristics are crucial for optimizing their bioavailability and therapeutic efficacy. Advanced material characterization techniques ensure the stability and enhanced performance of these nanoparticles in the physiological environment. Based on these applications, the current research aims to address magnesium deficiency via Powell–Eyring nanofluid flow distorted by the linearly stretchable sheet in the region of the stagnation point. Linear thermal stratification, viscous dissipation, and Joule heating are used to reveal the heat transport features. The magnetic field is applied to the nanofluid at an angle α to further control the fluid dynamics and nanoparticle behavior. Transformations are used to create a set of dimensionless governing equations. Comparative graphs are used to explain the physical behaviors of temperature and velocity fields, demonstrating how material properties impact fluid dynamics. The well-known convergence method (homotopy analysis method) is used to solve the model by comparing graphs.

Effect of Pyrolyzed Peach Pit Biomass on Dispersion and Sedimentation Characteristics of Saline Clay

Effect of Pyrolyzed Peach Pit Biomass on Dispersion and Sedimentation Characteristics of Saline Clay