Geometric Effects Research Articles

Forced Wetting of Shear-Thinning Fluids in Confined Capillaries.

Dynamic wetting in confined spaces is pivotal for the functional efficiency of biological organisms and offers significant potential for optimizing microdevices. The fluids encountered in such scenarios often exhibit shear-thinning behavior, which gives rise to complex interfacial phenomena. Here, we present an intriguing wetting phenomenon for shear-thinning fluids in confined capillary spaces. The employed shear-thinning fluids, carboxymethyl cellulose aqueous solutions with mass fractions of 0.5, 1.0, and 1.5 wt %, exhibit an intermediate state between ideal viscoelastic liquids, viscoelastic solids, and gel-like properties. We elucidate the geometric effect on its capillary wetting behavior, demonstrating that distortion of the moving contact line alters flow dynamics near the front corner, modifying the viscous resistance. This intricate interplay between the modified viscous resistance and the driving force results in a novel dynamic equilibrium distinct from that in Newtonian fluids. We further reveal that the viscous resistance in confined capillaries is controlled by both the morphology of the moving contact line and the shear-thinning exponent, particularly within the range of 0.7 to 1. This novel mechanism provides a pathway for manipulating the wetting dynamics of complex fluids in confined spaces.

Superelliptic quantum rings under orthogonally applied electric and magnetic fields: Electronic and thermal properties

A systematic study was undertaken to analyze the electronic and thermal properties of a single electron within a superelliptic quantum ring under orthogonal magnetic and electric fields. The corresponding Schrödinger equation for this system was numerically solved using the finite element method within the effective mass approximation. The influence of geometric effects associated with the morphology of the inner and outer contours of the superellipse, as well as the impact of external fields on electronic and thermal properties, were analyzed. The flexibility of the superellipse shape parameters considered in this study allows the consideration of different types of rings and the derivation of several electronic properties previously published in the literature as particular cases of our model. It was observed that thermal properties are highly sensitive to external fields and the geometrical potential linked to the topological variations experienced by the superellipse during the growth of the quantum rings.

Numerical investigation of the geometric parameters effect of helical blades installed on horizontal geo heat exchanger

In this study, we investigate the enhancement of horizontal geothermal heat exchangers equipped with helical fins on the pipe's exterior and internally ribbed turbulators. Our approach focuses on the interplay between geometry and thermal efficiency through innovative design modifications. Utilizing the finite element method, three-dimensional numerical simulations assessed the effects of varying geometric parameters such as the diameter and thickness of the fins. Our findings indicate significant increases in heat transfer efficiency with the addition of helical fins; specifically, increasing the fin diameter from 5 mm to 10 mm results in a 15 % increase in the heat transfer rate, while doubling the fin thickness from 2 mm to 4 mm enhances the rate by 10 %. These improvements are due to the expanded surface area facilitating greater heat exchange. Optimization using the desirability function approach yielded models with high performance, achieving desirability scores of 0.9879 for outlet temperature and 0.9534 for the heat transfer coefficient. This reflects the effective tuning of geometric parameters to maximize thermal performance. The study also introduces two predictive mathematical models for the outlet temperature and convective heat transfer coefficient of the U-shaped pipe equipped with these enhancements. These models, derived from extensive numerical data, provide practical tools for future design and operational applications of geothermal heat exchangers. This research advances the design and operational efficiency of geothermal heat exchange systems, establishing new benchmarks for thermal efficiency in the field with actionable insights and robust mathematical tools.

The roles of geometry and viscosity in the mobilization of coarse sediment by finer sediment

In rivers, the addition of finer sediment to a coarser riverbed is known to increase the mobility of the coarser fraction. Two mechanisms have been suggested for this: a geometric mechanism whereby smaller sizes smooth the bed, increasing near-bed velocity and thus mobility of the larger sizes, and a viscous mechanism whereby a transitionally smooth turbulent boundary layer forms, rendering the coarser grains more mobile. Here, we report on experiments using two sediment mixtures to better understand these proposed mechanisms. In Mixture 1, we used 0.5 and 5 mm grains, and in Mixture 2, we used 2 and 20 mm grains. If the entrainment of coarse gravel by finer sediment is a purely geometric effect, then the addition of finer material should produce the same effect on the mobility of the coarser material for both mixtures because they have the same size ratio. We show that addition of finer material has a different effect on the two mixtures. We observed an increase in the mobility of the coarse fraction for both mixtures, but the increase in coarse fraction mobility for Mixture 1 was almost twice that for Mixture 2. Our experiments show that in addition to the geometric effect, enhancement of coarse gravel transport by finer sediment is also driven by a viscous effect.

Geometrical nonlinear Hall effect induced by Lorentz force

Geometrical nonlinear Hall effect induced by Lorentz force

Contribution of geometrical infill pattern on mechanical behaviour of 3D manufactured polylactic acid specimen: Experimental and numerical analysis

Additive manufacturing is regarded as a very efficient fabrication technique since it permits the manufacturing of any three-dimensional product. The present work determines the effect of various infill pattern on the mechanical properties in term of tensile strength, yield strength and hardness of poly-lactic acid (PLA) samples fabricated by fused deposition modeling method. The mechanical behaviour of the 3D-printed PLAs investigated using dog-bone specimens with six distinct infill patterns: line, triangle, tri-hexagon, cubic, octet, and gyroid. The mechanical characteristics were evaluated using the uniaxial tensile test and shore D type hardness tester. The strain and deformation criteria were employed to substantiate the ductile and brittle characteristics. The fractural surface morphology analyzed using the field emission scanning electron microscope. Nonlinear Finite Element Analysis (FEA) was employed to simulate the uniaxial tensile test and establish a Yeoh third order hyperelastic material model for the predictions of the stress-strain response. This model is chosen for its precise ability to predict the nonlinear stress-strain responses for significant deformation and is crucial in applications that involve high degrees of flexibility and elasticity, such as in tire modeling, polymer and elastomer analysis, sports equipment designing, 3D printed components etc. Results revealed that the cubic infill had a maximum tensile strength 32.648 ± 1.42 MPa and octet infill had a minimum tensile strength 22.373 ± 0.79 MPa. The majority of experimental data indicated a brittle behaviour for line-infilled, but triangular, trihexagonal, cubic, octet, and gyroid infill patterns demonstrated ductile behaviour. In comparison to other geometrical infills, cubic shown relatively superior mechanical responses. Consequently, the geometrical infill effect plays a significant role in finding the appropriate mechanical property for industrial applications. The developed material model possesses potential utility in non-linear FEA investigations pertaining to 3D printed PLA objects that are predicted to sustain tensile strength.

Controlling Vibronic Coupling in Chlorophyll Proteins: The Effects of Excitonic Delocalization and Vibrational Localization.

Vibrational-electronic (vibronic) coupling plays a critical role in excitation energy transfer in molecular aggregates and pigment-protein complexes (PPCs). But the interplay between excitonic delocalization and vibronic interactions is complex, often leaving even qualitative questions as to what conceptual framework (e.g., Redfield versus Förster theory) should be used to interpret experimental results. To shed light on this issue, we report here on the interplay between excitonic delocalization and vibronic coupling in site-directed mutants of the water-soluble chlorophyll protein (WSCP), as reflected in 77 K fluorescence spectra. Experimentally, we find that in PPCs where excitonic delocalization is disrupted (either by mutagenesis or heterodimer formation), the relative intensity of the vibrational sideband (VSB) in fluorescence spectra is suppressed by up to 37% compared to that of the native protein. Numerical simulations reveal that this effect results from the localization of high-frequency vibrations in the coupled system; while excitonic delocalization suppresses the purely electronic transition due to H-aggregate-like dipole-dipole interference, high-frequency vibrations are unaffected, leading to a relative enhancement of the VSB. By comparing VSB intensities of PPCs both in the presence and absence of excitonic delocalization, we extract a set of "local" Huang-Rhys (HR) factors for Chl a in WSCP. More generally, our results suggest a significant role for geometric effects in controlling energy-transfer rates (which depend sensitively on absorption/fluorescence line shapes) in molecular aggregates and PPCs.

Combined effects of pores and cracks on the effective thermal conductivity of materials: a numerical study

Porous solids are commonplace in engineering structures and in nature. Material properties are inevitably affected by the internal inhomogeneity. The effective thermal conductivity of porous materials has been and remains to be a subject of extensive research. Less attention has been devoted to thermal conductivity impacted by internal cracks. This study is devoted to theoretical analyses of the combined effects of pores and cracks on the effective thermal conductivity. Systematic numerical simulations using the finite element method are performed based on two-dimensional models, with periodic distributions of internal pores and cracks. The parametric investigations seek to address how individual geometric layout can influence the overall thermal conduction behavior. In addition to circular pores and isolated cracks, angular pores with cracks extending from their sharp corners are also considered. It is found that both isolated cracks and cracks connected to existing pores can significantly reduce the effective thermal conductivity in porous materials. Since it is much easier to microscopically detect internal pores than thin cracks, care should be taken in using the apparent porosity from microscopic images and density measurements to estimate the overall thermal conductivity. Quantitative analyses of the detailed geometric effects are reported in this paper.

Defect prediction and performance optimization of A413 vertical centrifugal castings through FEA-based simulation

This study benefits from advanced simulation based on finite element analysis, where finite element analysis possesses robust numerical algorithms to confront critical industrial challenges, including prediction and optimization techniques. The primary goal is to predict the location and quantity of shrinkage porosity and air entrainment, and to mitigate them by optimizing key casting process factors while considering the geometric effects. Virtual experiments designed through the Taguchi method, with three parameters (aspect ratio, pouring temperature, and mold rotation speed) at five levels each, were conducted using the finite element analysis software ProCAST. Post-experimentation, comprehensive data analyses, including signal-to-noise ratio and response surface methods, were employed to determine optimal conditions. Additionally, a sophisticated regression model was developed to clarify the complex relationship between key parameters and defect aspects. Optimal conditions to reduce shrinkage porosity were identified within parameter ranges of (50–75) rpm, (750–800) °C, and (1.75–2) aspect ratio. Similarly, optimal parameters to reduce air entrainment were identified as 150 rpm, 800 °C, and (1) aspect ratio.

Concerning the Parameterization of Geometric and Criticality Effects on Detonation Amplification

This study investigates the role of geometric effects and detonation criticality on the behavior of a detonation transition through an area expansion of finite length. Three reinitiation behaviors that result in an amplified pressure impulse were observed and are referred to as steady, spike, and endwall amplification. Steady amplification was characterized by an amplification event with a peak pressure impulse 2 times that of the inlet detonation, followed by a near-linear attenuation toward Chapman–Jouguet conditions. Spike amplification displayed a larger peak pressure amplification that was 3 to 5 times greater than the inlet detonation, followed by a rapid and nonlinear attenuation. Endwall behavior represents a Craven–Grieg deflagration to detonation transition scenario. These behaviors are shown to be factors of area expansion ratio and the degree to which the incoming detonation is subcrtical. A decoupling parameter, Ψd, was devised to combine these effects into a single correlation metric. The finite length of the expansion chamber also plays a role in the reinitiation behavior as observed by the endwall reinitiation behavior. A critical chamber length parameter was devised to explain this behavior and then theorized to have a relationship to Ψd with this being explored theoretically and with the limited data set available.

Renormalization of networks with weak geometric coupling.

The renormalization group is crucial for understanding systems across scales, including complex networks. Renormalizing networks via network geometry, a framework in which their topology is based on the location of nodes in a hidden metric space, is one of the foundational approaches. However, the current methods assume that the geometric coupling is strong, neglecting weak coupling in many real networks. This paper extends renormalization to weak geometric coupling, showing that geometric information is essential to preserve self-similarity. Our results underline the importance of geometric effects on network topology even when the coupling to the underlying space is weak.

Phase-resolved Spectroscopy of Low-frequency Quasiperiodic Oscillations from the Newly Discovered Black Hole X-Ray Binary Swift J1727.8-1613

Low-frequency quasiperiodic oscillations (LFQPOs) are commonly observed in X-ray light curves of black hole X-ray binaries (BHXRBs); however, their origin remains a topic of debate. In order to thoroughly investigate variations in spectral properties on the quasiperiodic oscillation (QPO) timescale, we utilized the Hilbert–Huang transform technique to conduct phase-resolved spectroscopy across a broad energy band for LFQPOs in the newly discovered BHXRB Swift J1727.8–1613. This is achieved through quasi-simultaneous observations from Neutron Star Interior Composition Explorer, Nuclear Spectroscopic Telescope Array, and Hard X-ray Modulation Telescope. Our analysis reveals that both the nonthermal and disk–blackbody components exhibit variations on the quasiperiodic oscillation (QPO) timescale, with the former dominating the QPO variability. For the spectral parameters, we observe modulation of the disk temperature, spectral indices, and reflection fraction with the QPO phase with high statistical significance (≳5σ). Notably, the variation in the disk temperature is found to precede the variations in the nonthermal and disk fluxes by ∼0.4–0.5 QPO cycles. We suggest that these findings offer further evidence that the type-C QPO variability is a result of geometric effects of the accretion flow.

The Velocity Aberration Effect of the CSST Main Survey Camera* *This research has been generously supported by the National Natural Science Foundation of China (NSFC, Grant Nos. 12073047 and 12273077) and the National Key Research and Development (Grant No. 2022YFF0711500).

In this study, we conducted simulations to find the geometric aberrations expected for images taken by the Main Survey Camera of the Chinese Space Station Telescope (CSST) due to its motion. As anticipated by previous work, our findings indicate that the geometric distortion of light impacts the focal plane's apparent scale, with a more pronounced influence as the size of the focal plane increases. Our models suggest that the effect consistently influences the pixel scale in both the vertical and parallel directions. The apparent scale variation follows a sinusoidal distribution throughout one orbital period. Simulations reveal that the effect is particularly pronounced in the center of the Galaxy and gradually diminishes along the direction of ecliptic latitude. At low ecliptic latitudes, the total aberration leads to about a 0.94 pixel offset (a 20 minute exposure) and a 0.26 pixel offset (a 300 s exposure) at the edge of the field of view. Appropriate processings for the geometric effect during the CSST pre- and post-observation phases are presented.

The flaring activity of blazar AO 0235+164 in 2021

Context. The blazar AO 0235+164, located at redshift z = 0.94, has displayed interesting and repeating flaring activity in the past, with recent episodes in 2008 and 2015. In 2020, the source brightened again, starting a new flaring episode that peaked in 2021. Aims. We study the origin and properties of the 2021 flare in relation to previous studies and the historical behavior of the source, in particular the 2008 and 2015 flaring episodes. Methods.We analyzed the multiwavelength photo-polarimetric evolution of the source. From Very Long Baseline Array images, we derived the kinematic parameters of new components associated with the 2021 flare. We used this information to constrain a model for the spectral energy distribution of the emission during the flaring period. We propose an analytical geometric model to test whether the observed wobbling of the jet is consistent with precession. Results. We report the appearance of two new components that are ejected in a different direction than previously, confirming the wobbling of the jet. We find that the direction of ejection is consistent with that of a precessing jet. Our derived period agrees with the values commonly found in the literature. Modeling of the spectral energy distribution further confirms that the differences between flares can be attributed to geometrical effects.

Local joint flexibility of two-planar tubular DY-joints in jacket-type substructures of offshore wind turbines: parametric study of geometrical effects and design formulation

ABSTRACT The present paper discusses the results of a parametric study conducted on the local joint flexibility (LJF) of two-planar tubular DY-joints in jacket-type substructures of offshore wind turbines. A set of finite element (FE) analyses were carried out on 81 FE models subjected to two types of axial loading to study the effects of geometrical characteristics of two-planar DY-joint on the LJF factor (f LJF). The f LJF values in two-planar DY- and uniplanar Y-joints were compared. Results showed that the multi-planarity effect on the LJF is significant and consequently the application of equations already available for uniplanar Y-joints to calculate the f LJF in two-planar DY-joints may result in highly over- or under-predicting results. To tackle this problem, FE results were used to develop a new parametric equation for the prediction of the f LJF in axially loaded two-planar DY-joints and the derived equation was checked against the UK DoE acceptance criteria.

Numerical investigation on flow characteristics and heat transfer of mixed convection in a packed bed

Flow characteristic and heat transfer of mixed convection in the packed bed were investigated numerically comparing with the previous experimental studies. For the fixed packed bed and sphere diameters of 0.06 m and 0.01 m, the ratios of bed height to sphere diameter and Reynolds numbers were varied from 5 to 20, and from 1 to 300, respectively for both buoyance aided and opposed flows. The temperatures difference between fluid and sphere was 78.85 K. The packed bed structure was modeled by generating location coordinates through the random number with an in-house code and computational analyses were performed using ANSYS FLUENT software. Laminar mixed convection behaviors were observed: heat transfer enhancement for buoyancy aided flow and impairment for buoyancy opposed flow. For larger bed heights, even under a laminar flow condition, turbulent behaviors were observed: heat transfer impairment for buoyance aided flow and enhancement for buoyance aided flow. The same trend was observed in the analysis of turbulence intensity. Local flow analysis within the packed bed confirmed that this is due to the vortices and the wakes resulting from the interaction between mixed convection flows and the randomly stacked spheres in the packed bed. This study unveiled mixed convection phenomena accompanied by the geometric effects of the packed bed on vortices and wakes, which exhibit turbulence-like behavior.

Fatigue life prediction of notched components based on energy gradient using reconstructed critical distance theory

AbstractIn this paper, a reasonable explanation is given to unify notch effect and geometric size effect into notch geometric feature effect (NGFE), and energy gradient is utilized to depict the influence of the NGFE on the critical distance. The correlation of energy gradient with critical distance and fatigue life is discussed respectively. The weight index of the high energy region is used to quantify the contribution of the high energy region to the fatigue damage. Finally, a model of the reconstructed critical distance theory considering the geometric notch characteristic effect is established. The fatigue test of Q355 (D) alloy steel notched components was carried out, and the evaluation precision of the presented method is compared with Yang’ model and Shen’ model combining with the existing fatigue test data of En8. The results indicate that prediction results of the proposed method are consistent with the test results.

Superlubric Graphullerene.

Graphullerene (GF), an extended quasi-two-dimensional network of C60 molecules, is proposed as a multicontact platform for constructing superlubric interfaces with layered materials. Such interfaces are predicted to present very small and comparable sliding energy corrugation regardless of the identity of the underlying flat layered material surface. It is shown that, beyond the geometrical effect, covalent interlinking between the C60 molecules results in reduction of the sliding energy barrier. For extended GF supercells, negligible sliding energy barriers are found along all sliding directions considered, even when compared to the case of the robust superlubric graphene/h-BN heterojunction. This suggests that multicontact architectures can be used to design ultrasuperlubric interfaces, where superlubricity may persist under extreme sliding conditions.

A broadband acoustic metamaterial lens for sub-wavelength imaging based on bandwidth enhancement

Acoustic metamaterials manufactured from natural materials can exhibit exotic characteristics that cannot be found in nature materials through the design of geometric structures and resonance effects, and acoustic metamaterials can be used to achieve sub-wavelength acoustic imaging as the acoustic metamaterial lens (AML). Currently, the AMLs based on the Fabry–Pérot (FP) resonance principle are all with single effective length hole, which is directly related to the thickness of its structure. They can only achieve acoustic imaging in a relatively narrow frequency range, and there is no AML which can achieve broadband sub-wavelength acoustic imaging. In this paper, a kind of broadband acoustic metamaterial lens (BAML) is introduced. While maintaining a constant overall thickness of the AML, a design which is composed of the supercell consisting of a cross distribution of different effective length holes is proposed. This design enables the AML formed by these supercells to encompass multiple operating frequencies corresponding to various holes, thereby broadening the frequency range of acoustic imaging. Finite element simulation and imaging experiments were conducted, and results demonstrated that the BAML consisting of multiple effective length holes has the ability to enhance bandwidth of acoustic imaging. Compared to AML with single effective length hole, it offers a broader range of imaging frequencies, this design offers a general method of bandwidth enhancement. BAML has potential application value in ultrasonic imaging, sound absorption, intelligent thermal control and medical diagnosis.

Understanding molecular geometric phase effects with exact effective force: case study of a model system

In this work, molecular geometric phase effects are studied using the idea of exact factorization (EF) (Abediet al2010Phys. Rev. Lett.105123002) and exact effective force (Liet al2022Phys. Rev. Lett.128113001). In particular, we performed dynamics simulations for a two-state vibronic coupling model, and interpreted the results in three different perspectives: the Born-Huang expansion, the exact time-dependent potential energy surface (TDPES) and the exact effective force. We find that (i) at particular moment, while the vanishing nuclear density that occurs periodically in space is conventionally attributed to destructive interference of the nuclear wave packet owing to the geometric phase, such phenomenon can be equally well interpreted through the energy perspective, as manifested in the exact TDPES in the EF scheme; (ii) when combined with trajectory-based classical dynamics, the exact effective force obtained through EF qualitatively reproduces the correct nuclear density, while the adiabatic force gives the wrong density, particularly in the interference region. Our results suggest that the exact effective force is a potential starting point for making approximations and improving trajectory-based computational methods towards an accurate description of geometric phase effects.