Increasing Aspect Ratio Research Articles

A direct numerical simulation study of bubble–particle hydrodynamic interactions

The interactions between a spherical or non-spherical bubble and a solid sphere placed in tandem in a viscous flow are investigated by direct numerical simulation under different order of location, Reynolds numbers Re∈[50,200], dimensionless center-to-center separation distances S∈[1.25,6], and the bubble aspect ratios χ∈[1,2.5]. For the interactions between a spherical bubble and a sphere, the bubble's drag coefficient Cd generally decreases monotonically, while the sphere's Cd always first decreases and then increases when S decreases regardless of the order. For the interactions between a non-spherical bubble and a sphere, as the increase in the bubble's aspect ratio, the sphere's Cd decreases, but the downstream bubble's Cd decreases first and then increases with the decrease in S at a high aspect ratio, which is different from that of the spherical bubble. Furthermore, the sphere significantly reduces the bubble's Cd, but the sphere's Cd is hardly affected by the bubble when the bubble is located downstream of the sphere. However, the sphere's Cd is significantly affected by the bubble when the bubble is located upstream of the sphere. The mechanisms for the change of Cd are further unrevealed by analyzing the pressure drag coefficient Cdp and the viscous drag coefficient Cdμ. The observations reveal that the deformation of the bubble plays an important role for the bubble–particle interactions.

Multi-Physics Coupling of Rectangular Channels with Different Aspect Ratios in Solid Oxide Electrolysis Cells

To explore the impact of the aspect ratio of the channels in the flow fields of solid oxide electrolysis cells on the performance of the cell, we developed three-dimensional models for cells with varying aspect ratios. Our findings revealed that channels with low and high aspect ratios exhibit higher maximum pressure drops, whereas those with medium aspect ratios have the lowest pressure drops. Additionally, the mole fraction of the hydrogen decreases as the channel’s aspect ratio increases. We also computed the polarization curves for SOEC operating under three distinct aspect ratio channels. Our results suggest that structures with low aspect ratios exhibit the poorest electrochemical performance, suitable only for brief operations at low current densities; medium aspect ratio structures exhibit a balanced performance, making them suitable for various operating conditions; and high aspect ratio structures are best suited for operations at high current densities. This study on selecting different aspect ratios aids in determining the optimal channel parameters for different operating conditions, ultimately enhancing the performance of solid oxide electrolysis cells.

Exploratory study on the influences of geometric parameters on buckling behavior of composite cylindrical panels under external pressure

PurposeThis paper aims to study the effects of various geometric parameters, such as ply angles, side length, aspect ratio, and curvature, on the buckling behavior of composite cylindrical panels under external pressure.Design/methodology/approachA implicit nonlinear buckling analysis model is proposed, in which large strain and overall Lagrangian method are selected, and the pressure is gradually increased with equal steps to capture the buckling deformation process. The study results are investigated from mechanical and physical perspectives.FindingsStudy results indicate that the external pressure buckling behaviors of the cylindrical panels are greatly influenced by the geometric parameters: the buckling deformation reduces with increasing the content of the 90° layer, while which increases with increasing the side length and aspect ratio. The buckling external pressure rises with the increase of curvature and content of 0° layer, and declines with the increase of side length and aspect ratio. The shape and location of the buckling region change with the increase of the side length and curvature.Originality/valueThe buckling behaviors of composite cylindrical panels under external pressure are first presented by using implicit nonlinear buckling analysis. The study results can provide guidance for the structural design of composite cylindrical panels under external pressure.

Evolution of coherent vibrations in atomically precise gold quantum rods with periodic elongation.

The coherent vibrational dynamics of gold nanorods with varying aspect ratios have been extensively studied by time-resolved spectroscopy to reveal their mechanical properties, but quantum-sized rods (transverse diameter<2nanometers) remain unexplored. Here, we present a comprehensive study on the coherent vibrations of atomically precise gold quantum rods with distinct energy gaps (0.6 to 1.3electron volts), all sharing the same radial dimension but with increasing aspect ratios. Time-resolved spectroscopy reveals ultrafast internal conversion and intersystem crossing, along with oscillatory features superimposed on transient signals that unveil coherent vibrational dynamics. Two dominant modes are identified: a longitudinal mode scaling with rod length and a transverse mode independent of aspect ratio. Theoretical simulations support these findings and clarify the structural origins of the observed vibrational behavior. Our study provides a framework for designing atomically precise gold quantum rods with tailored optical and vibrational properties, advancing the understanding and application of anisotropic quantum materials.

Numerical analysis of bearing capacity of winged helical anchor in clayed soil

Adding wings is an effective method to improve the lateral bearing capacity of helical anchor to meet the requirement of combined loading. However, the study on winged helical anchors is scarce. Therefore, this paper used numerical method to investigate the lateral and vertical bearing capacities and failure modes of winged helical anchors in mixed soil (cohesive material with internal friction). The addition of wings at the top of the helical anchor enhances the ultimate lateral capacity (ULC) significantly when ULC is controlled by displacement of 10% helix diameter, which increases with the height and width of wings. But the effect of wing height is limited, once the height exceeds the maximum soil mobilization depth induced by wing or shaft under lateral loading, the ULC essentially stops increasing. As the relative wing width B/D increases, although the increase rate in ULC gradually slows down, obvious increase is still observed at B/D = 1.5. The ULC reaches 4 times that of a wingless helical anchor for the case of helical anchor with relative wing height h/D of 2 and width B/D of 1.5. The calculation method of ULC is proposed combining the analysis of displacement field at failure, and the safety factors for design are also suggested. The vertical tensile and compressive bearing capacities of wingless anchor are similar when installations are not considered. Each helix with a spacing greater than 1.53D exhibits an independent failure mode when using 0.1D as the failure criterion. And Terzaghi’s formula for the bearing capacity of circular foundations can effectively estimate the ultimate vertical bearing capacity of helical plates. The ultimate end resistance qcu of the wings decreases logarithmically with increasing aspect ratio of wing base B/t. The Meyerhof’s bearing capacity factors for deep strip foundations are recommended to calculate qcu of wings with B/t no less than 15. This study can provide reference for design engineers to estimate the lateral and vertical bearing capacities of winged helical anchors.

Enhancing the external quantum efficiency of GaN-based micro-LEDs using an InGaN quantum well/quantum dot composite structure with an AlGaN interlayer

InGaN/GaN self-organized quantum dots (QDs) exhibit stronger carrier localization due to their three-dimensional confinement. Utilizing a quantum well/quantum dot (QW/QD) composite structure as the active region in LED can significantly enhance luminous efficiency. This study investigates GaN-based micro-LEDs featuring a QW/QD composite structure with an (Al)GaN interlayer. Experimental results reveal that QDs with an (Al)GaN interlayer exhibit reduced diameters and increased aspect ratios. Notably, an AlGaN interlayer with 10% Al composition optimally enhances QD carrier localization, promoting radiation recombination. Consequently, the peak external quantum efficiency (EQE) of 5 μm micro-LEDs with an Al0.1Ga0.9N interlayer reaches 7.3%, an 87.4% improvement compared to those devices without an interlayer. Moreover, the micro-LEDs with an Al0.1Ga0.9N interlayer demonstrate enhanced wavelength stability, narrowest full-width at half maximum (FWHM), and the lowest reverse leakage current.

Impacts of Device Geometry and Layout on Temperature Profile during Large‐Area Photonic Curing

Photonic curing is a large‐area, high‐throughput thermal processing technique that uses high‐intensity pulsed light to selectively cure thin films on thermally sensitive substrates. This study employs 3‐dimensional (3D) simulation to show, for the first time, that gate geometry significantly impacts peak curing temperature during photonic curing. The simulation results are experimentally validated by photonically curing solution‐processed indium zinc oxide for thin‐film transistors with different bottom gate geometries and comparing their performance to thermally annealed control devices. Under the same photonic curing pulse, for a fixed aspect ratio, peak photonic curing temperature increases with larger gate area, while for a fixed area, peak photonic curing temperature decreases with increasing aspect ratio. For different gate areas and aspect ratios, the simulated peak photonic curing temperature varies from ≈200 to 450 °C, which strongly impacts metal‐hydroxide to metal‐oxide conversion in sol–gels. Thus, the subsequent transistor performance is strongly influenced by the gate geometry. For example, for increasing gate area with fixed aspect ratio of 1, the average mobility increases from 1.61 to 12.52 cm2 V−1 s−1, while the threshold voltage decreases from 2.14 to −5.68 V. Thus, this study provides valuable insights for adopting 3D simulation to design transistors for complex large‐area electronics using photonic curing.

Insight into the effect of air ingestion on the film characteristics of a special squeeze film damper

The research of unclear influence of air ingestion on the characteristics of squeeze film damper (SFD) oil film was carried out. The fluid domain was modeled. Influences of air ingestion were analyzed under different structure and working conditions. Mechanism of air ingestion on the characteristics of oil film was revealed. Results uncover that air ingestion occurs at the outlet boundary and have a significant inhibition on the cavitation effect. It is affected by whirl radius, clearance ratio, width, and oil supply pressure. Air ingestion has significant effects on maximum pressure, oil film force, moment at time T, oil film force in the x direction, oil film force in the y direction, oil film resultant force, and minimum pressure fraction. Moreover, the stability of damping and stiffness is improved due to air ingestion. Increasing aspect ratio, oil supply pressure, and reducing whirl frequency can improve dynamic characteristics. The results provide theoretical basis for the optimized design of SFD.

Influence of real particle morphology on single particle crushing behavior of rockfill based on FDEM

Influence of real particle morphology on single particle crushing behavior of rockfill based on FDEM

Computational Study on the Effect of Aspect Ratio of High-Pressure Hydrogen Tank on Explosion Characteristics

The explosion characteristics of 70 MPa high-pressure hydrogen tanks with varying aspect ratios were investigated using OpenFOAM computation. The tank volume (175 L) and stored hydrogen mass (7.26 kg) were fixed, and four tank geometries with aspect ratios ranging from 1.0 (spherical) to 10.0 (elongated) were analyzed to examine the spatial and temporal distributions of the overpressure and impulse. The results show that, as the aspect ratio increases, the initial blast wave pressure propagates more strongly in the radial direction than in the axial direction. In the radial and axial directions, the peak overpressure and impulse rapidly decrease with distance, followed by a secondary increase owing to the pressure reflected from the ground. The reflected pressure increases with the aspect ratio in the radial direction but decreases in the axial direction. Moreover, the blast wave dissipates more quickly in the axial direction as the aspect ratio increases, resulting in lower reflected and peak pressures. These findings highlight the significant impact of tank geometry on explosion behavior and offer valuable insights for safe design and mitigation strategies of hydrogen infrastructure.

Semi‐Analytical Solution for Passive Earth Pressure in Unsaturated Narrow Soils Behind Retaining Walls With a Log‐Spiral Failure Surface Based on the Principal Stress Trajectory Method

ABSTRACTMost existing passive earth pressure theories are not completely suitable for the calculation of unsaturated backfill in practical engineering, especially for narrow backfill cases. In view of this, this study establishes a modified analytical model for the passive earth pressure of narrow backfill behind a retaining wall under unsaturated steady‐state seepage conditions, based on the log‐spiral failure mechanism and the arched differential element method. The distribution, total force magnitude, and the height of the application point of passive earth pressure for narrow backfill under the rotation about the wall toe (RB) mode are calculated by the fourth order Runge–Kutta method within the framework of the generalized effective stress principle. To validate the proposed method, a comparative analysis is conducted by integrating experimental, theoretical, and OptumG2 simulation results. Moreover, the effect of main parameters on passive earth pressures is investigated through a parametric analysis. The results show that as the wall–soil interface friction angle increases gradually, the passive earth pressure distribution curve transitions from convex towards the wall back to concave towards the wall back; with the increase of aspect ratio, the passive earth pressure curve gradually shifts from curved to nearly straight; with a small air entry pressure parameter, the total passive earth pressure force increases as the air entry pressure parameter increases, while the height of the application point of total force initially decreases and then increases; the hysteresis effect reduces the total passive earth pressure force and decreases the height of the application point of the total force.

Motion of a deformable droplet in a rectangular, straight channel

The motion and deformation of a neutrally buoyant drop in a rectangular channel experiencing a pressure-driven flow at a low Reynolds number has been investigated both experimentally and numerically. A moving-frame boundary-integral algorithm was used to simulate the drop dynamics, with a focus on steady-state drop velocity and deformation. Results are presented for drops of varying undeformed diameters relative to channel height ( $D/H$ ), drop-to-bulk viscosity ratio ( $\lambda$ ), capillary number ( $Ca$ , ratio of deforming viscous forces to shape-preserving interfacial tension) and initial position in the channel in a parameter space larger than considered previously. The general trend shows that the drop steady-state velocity decreases with increasing drop diameter and viscosity ratio but increases with increasing $Ca$ . An opposite trend is seen for drops with small viscosity ratio, however, where the steady-state velocity increases with increasing $D/H$ and can exceed the maximum background flow velocity. Experimental results verify theoretical predictions. A deformable drop with a size comparable to the channel height when placed off centre migrates towards the centreline and attains a steady state there. In general, a drop with a low viscosity ratio and high capillary number experiences faster cross-stream migration. With increasing aspect ratio, there is a competition between the effect of reduced wall interactions and lower maximum channel centreline velocity at fixed average velocity, with the former helping drops attain higher steady-state velocities at low aspect ratios, but the latter takes over at aspect ratios above approximately 1.5.

Swimming dynamics of a spheroidal microswimmer near a wall.

In this work, we investigate the swimming dynamics of a spheroidal squirmer near a flat wall for various aspect ratios using the direct-forcing fictitious domain method. Our results show that the swimming mode of a strong pusher undergoes the transition from either oscillating or escaping to crawling as the aspect ratio increases. A strong puller exhibits an opposite transition: from crawling to escaping and then to oscillating as the aspect ratio increases. The mechanism for the near-wall swimming behavior of a strong puller and pusher is explored by analyzing the hydrodynamic force and torque on a swimmer with its height and orientation fixed. The results indicate that both collision and hydrodynamic toques are important to the near-wall swimming state of the squirmer. Additionally, we found that the initial orientation angle and the release distance do not influence the swimming mode when the squirmer initially swims toward the wall at an angle smaller than -π/8.

Effects of neutral beam injection on tearing mode stability: insights from hybrid simulations

Abstract In tokamak plasmas, tangential neutral beam injection (NBI) produces (a large fraction of) circulating energetic ions (CEIs) and induces plasma toroidal rotation, both of which play an important role in the stability of tearing mode (TM). In this study, the effect of NBI on TM is systematically investigated using kinetic-magnetohydrodynamic hybrid code M3D-K. Here, the effect of NBI is modeled as the combined effects of CEI and toroidal rotation. The analysis focuses on the dependency of NBI's effect on key physical parameters, including magnetic shear, total beta and plasma shape. The modification of rotation on equilibrium is self-consistently included in simulation, which can enhance the destabilizing effect of counter-CEI on TM and has a negligible contribution to the effect of co-CEI. Furthermore, the simulation results reveal that the co-NBI always reduces TM's growth rate due to the dominant stabilizing effect of rotation and the weak net effect of co-CEI, agreeing well with most experimental results. Whether the counter-NBI stabilizes or destabilizes TM depends on the competition between the stabilizing contribution from rotation and the destabilizing contribution from counter-CEI. Specifically, the counter-NBI tends to stabilize TM when elongation and triangularity decrease, while magnetic shear, total beta and aspect ratio increase.

Experimental study on wind load characteristics of rectangular high-rise buildings with varied aspect ratios

The wind load is one of the predominant factors for high-rise buildings and it has been found that the aspect ratio of the section affects the wind-induced forces on buildings significantly. In this paper, simultaneous wind pressure tests were conducted for three rectangular tall buildings in the wind tunnel, with different aspect ratios of 1:1, 1.5:1, and 2:1 (named Model I/II/III). The characteristics of wind pressure on buildings under different wind azimuths were analyzed and the following conclusions were obtained. When the longer sides of the buildings (Side I/III) are perpendicular to the wind, the variation tendency of the most unfavorable wind pressure coefficient along increasing aspect ratio has a critical value on the windward/leeward/top facades, and it was found the critical ratio equals 1.5 (Model II). Moreover, when the shorter sides of the buildings (Side II/IV) are perpendicular to the wind, it can be found that Model II presents the most unfavorable wind pressure on the crosswind side. Referring to the leeward side, the larger the aspect ratio, the more favorable the negative pressure appears. Furthermore, the horizontal correlation coefficients at points on the windward/leeward side are generally higher in Model II. The power spectrum of the measuring points on the axis of the crosswind and leeward sides gradually decreases in the low frequency range, while the energy in the high frequency range gradually increases. The comprehensive experimental data provided in this work can be used for further wind resistance studies.

Endothelial Cells Stably Infected with Recombinant Kaposi’s Sarcoma-Associated Herpesvirus Display Distinct Viscoelastic and Morphological Properties

PurposeKaposi’s sarcoma-associated herpesvirus (KSHV) is a γ-herpesvirus that has a tropism for endothelial cells and leads to the development of Kaposi’s sarcoma, especially in people living with HIV. The present study aimed to quantify morphological and mechanical changes in endothelial cells after infection with KSHV to assess their potential as diagnostic and therapeutic markers.MethodsVascular (HuARLT2) and lymphatic endothelial cells (LEC) were infected with recombinant KSHV (rKSHV) by spinoculation, establishing stable infections (HuARLT2-rKSHV and LEC-rKSHV). Cellular changes were assessed using mitochondria-tracking microrheology and morphometric analysis.ResultsrKSHV infection increased cellular deformability, indicated by higher mitochondrial mean squared displacement (MSD) for short lag times. Specifically, MSD at τ = 0.19 s was 49.4% and 42.2% higher in HuARLT2-rKSHV and LEC-rKSHV, respectively, compared to uninfected controls. There were 23.9% and 36.7% decreases in the MSD power law exponents for HuARLT2-rKSHV and LEC-rKSHV, respectively, indicating increased cytosolic viscosity associated with rKSHV infection. Infected cells displayed a marked spindloid phenotype with an increase in aspect ratio (29.7%) and decreases in roundness (26.1%) and circularity (25.7%) in HuARLT2-rKSHV, with similar changes observed in LEC-rKSHV.ConclusionsThe quantification of distinct KSHV-induced morpho-mechanical changes in endothelial cells demonstrates the potential of these changes as diagnostic markers and therapeutic targets.

Self-assembly of defined core-shell ellipsoidal particles at liquid interfaces.

Self-assembly of defined core-shell ellipsoidal particles at liquid interfaces.

The study of design and mixing characteristics of a micromixer based on DLV-SAR layered structure

Abstract This paper proposes a new and efficient micromixer (double-layer vortex split-and-recombine) based on the principles of splitting-recombination and vortex mechanisms, which employs a dual-layer vortex structure for split-composite and chaotic convection. Through numerical simulations and experimental studies of the micromixer, the advantages of its fluid mixing capabilities were outlined. Based on this, the Reynolds number (Re) and the aspect ratio (λ) of the micromixer’s channel were coordinated to comprehensively study the mixing performance and pressure loss. The results indicate that the mixing efficiency is optimal when Re = 25–100 and λ = 0.5. The mixing index (ϕ) decreases as the aspect ratio (λ) increases, and the effect of Re on pressure loss also diminishes. At Re = 25–100, the maximum mixing volume flow rate occurs at an aspect ratio of 1, and the mixer with an aspect ratio of 1 demonstrates superior performance in mixing volume flow rate as Re increases, compared to mixers with other aspect ratios. The overall performance index (Φ) of the micromixer increases with the aspect ratio (λ), with relatively better performance at λ = 1.25 and λ = 1.5. Both simulation and experimental results show that the micromixer not only has a simple channel structure and dual-layer stacking, but also exhibits excellent mixing performance, offering significant potential for applications in chemical and biological engineering.

Investigation on the Electron Emission Regularity of Sputtered Boron Nitride Thin Films and Microstructured Array Surfaces

Boron nitride (BN) ceramic is an important support material in aerospace, arc discharge devices, and vacuum electronics. The electron emission properties of BN surfaces are of significance among various space applications. In this work, by preparing BN thin films and microstructured BN bulks, we have investigated the influence of the surface physical properties on the electron emission coefficient (EEC). The results showed that the surfaces of BN films, which were prepared by magnetron sputtering, produced serious gas adsorption and organic contamination when they were left for 10 days, and these surface modifications made the EEC of BN film surface decrease to a certain extent. The argon ion cleaning experiments indicated that the process of ion cleaning was able to partly eliminate the surface adsorption and contamination for the BN film. The EEC of the cleaned BN film surface was significantly improved compared to that of the original polluted BN film surface, with an EEC peak value of about 3.2 instead of 3.0 for the original polluted surfaces. By contrast, the EEC curves of the BN bulk show some difference, with the peak values of the EEC curves being 2.62 for the untreated BN bulk. The results of laser etching on the BN bulk surface to form microarray structures show that the EEC of BN bulk decreases significantly with the increase of the average aspect ratio of the microstructures. The EEC peak values of the BN bulks decrease from 2.62 to 1.16 when the porosity of the BN bulk reaches 49.11% and the aspect ratio reaches 1.36, indicating that constructing a surface microstructure is an effective method to achieve EEC reduction. By employing the electron trajectory tracking algorithm and the phenomenological model of electron emission, the effect of microstructure on EEC for BN bulk was quantitatively explained. The results of the study are of engineering application significance for vacuum devices involving the electron emission process of BN ceramic.

Mechanism of the effect of plantar pressure on mechanical stress response in basketball sports

This study investigated the mechanisms of metatarsal cellular mechanical stress responses to plantar pressure during basketball activities. A comprehensive analysis was conducted using integrated biomechanical and cellular approaches, involving 120 professional basketball players divided by playing positions. Plantar pressure distribution was measured during specific basketball movements using a high-precision pressure measurement system, while cellular responses were analyzed through morphological, biochemical, and genetic markers. Results demonstrated a non-linear relationship between applied pressure and cellular stress response, with a threshold effect at 300 kPa. Significant position-specific differences were observed in pressure distribution patterns, with centers exhibiting higher peak pressures (698.3 kPa ± 52.4 kPa) compared to forwards (642.5 kPa ± 48.6 kPa) and guards (584.2 kPa ± 42.3 kPa). Cellular adaptation mechanisms showed peak activity between 24–48 hours post-stimulation, characterized by increased aspect ratios and upregulation of mechanosensitive genes. Multiple regression analysis identified peak pressure, loading duration, and recovery time as primary factors influencing cellular responses, accounting for 85% of observed variance. These findings provide novel insights into the relationship between basketball-specific mechanical loading and cellular adaptation mechanisms, offering implications for injury prevention and training program optimization.