Effect Of Line Tension Research Articles

Transmission Line Icing Prediction Based on Dynamic Time Warping and Conductor Operating Parameters

Aiming to improve on the low accuracy of current transmission line icing prediction models and ignoring the objective law of icing of transmission lines, a transmission line icing prediction model considering the effect of transmission line tension on the bundle of icing thickness is proposed, based on a convolutional neural network (CNN) and bidirectional gated recurrent unit (BiGRU). Firstly, the finite element calculation model of the conductor and insulator system was established, and the change rule between transmission line tension and icing thickness was studied. Then, the convolutional neural network and bidirectional gated recurrent unit were used to construct a transmission line icing thickness prediction model The model incorporated a weighted fusion of soft−dynamic time warping (Soft−DTW) and the icing change rule as the loss function. Optimal weights were determined through the utilization of the grid search algorithm and cross−validation, contributing to an enhancement of the model’s generalization capabilities and a reduction in prediction errors. The results indicate that the proposed prediction model can consider the impact of line operating parameters, avoiding the shortcomings of prediction results conflicting with actual physical laws. Compared with traditional non−mechanical models, the proposed model showed reductions in root mean square error (RMSE), mean absolute error (MAE), and mean absolute percentage error (MAPE) by 0.26–0.51%, 0.24–0.44%, and 5.77–13.33%, respectively, while the coefficient of determination (R2) increased by 0.07–0.13.

Numerical study of implosion instability mitigation in magnetically driven solid liner dynamic screw pinches

Magnetized liner inertial fusion experiments on the Z accelerator suffer from magneto-Rayleigh–Taylor instabilities (MRTI) that compromise integrity of the imploding cylindrical liner, limiting achievable fusion fuel conditions and ultimately reducing magneto-inertial fusion target performance. Dynamic screw pinches (DSP) provide a method to reduce MRTI in-flight via application of magnetic field line tension to the imploding liner outer surface. In contrast with z-pinches that drive implosions with an azimuthal magnetic field, dynamic screw pinches enforce an additional axial drive magnetic field component, making the overall drive magnetic field helical. As the liner implodes, cumulative MRTI development is reduced by dynamically shifting the orientation of the fastest growing instability modes. Three-dimensional magnetohydrodynamic simulations show that the DSP mechanism effectively stabilizes initially solid cylindrical liner implosions driven by Z-scale current pulses, indicating that MRTI mitigation increases with the ratio of axial to azimuthal drive magnetic field components (i.e., the drive field ratio). We also performed a spectral analysis of the simulated imploding density distributions, extracting wavelength and pitch angle of the simulated MRTI structures to study their dynamics during the implosion. Simulations of liners initially perturbed with drive-field-aligned sinusoidal structures indicate that MRTI mitigation in DSP implosions decreases with perturbation wavelength, once again suggestive of magnetic field line tension effects.

Line tension of sessile droplets: Thermodynamic considerations.

We deduce a thermodynamically consistent diffuse interface model to study the line tension phenomenon of sessile droplets. By extending the standard Cahn-Hilliard model via modifying the free energy functional due to the spatial reflection asymmetry at the substrate, we provide an alternative interpretation for the wall energy. In particular, we find the connection of the line tension effect with the droplet-matrix-substrate triple interactions. This finding reveals that the apparent contact angle deviating from Young's law is contributed by the wall energy reduction as well as the line energy minimization. Besides, the intrinsic negative line tension resulting from the curvature effect is observed in our simulations and shows good accordance with recent experiments [Tan etal. Phys. Rev. Lett. 130, 064003 (2023)0031-900710.1103/PhysRevLett.130.064003]. Moreover, our model sheds light upon the understanding of the wetting edge formation which results from the vying effect of wall energy and line tension.

Effect of line tension on domain formation of fluorinated compounds at alkane/water interface

Condensed domain formation of fluorinated compounds (alcohol and ester) in adsorbed films at alkane/water interfaces was investigated by interfacial tensiometry, X-ray reflectometry, and BAM observation. The results obtained are explained by the effects of contact energy and dipole-dipole interaction, which are competitive contributions to the line tension acting at the domain boundary. Estimation of the two contributions indicated that the former is more dominant than the latter for the domain formation. In the adsorbed films of fluorinated alcohol, F8H2OH, at alkane/water interfaces, the domain formation was suppressed with increasing alkane chain length due to an increase in contact energy. The mixing of hybrid alcohol with fluorocarbon and hydrocarbon chains of the same carbon number, F6H6OH, in adsorbed film reduces contact energy. This stabilizes the dispersion of many domains with small size. On the other hand, when F8H2OH molecules are mixed with a cationic surfactant, C12TAB, in the adsorbed film, an attractive dipole-ion interaction between the hydrophilic groups relaxes the repulsive dipole-dipole interaction between F8H2OH molecules, resulting in the formation of domains with smooth boundary and large size. Furthermore, fluorinated ester, FC12Me molecules form flower shaped domains with intricate boundary mainly due to a larger dipole moment of FC12Me than F8H2OH.

Cloaking Transition of Droplets on Lubricated Brushes.

We study the equilibrium properties and the wetting behavior of a simple liquid on a polymer brush, with and without the presence of lubricant by multibody Dissipative Particle Dynamics simulations. The lubricant is modeled as a polymeric liquid consisting of short chains that are chemically identical with the brush polymers. We investigate the behavior of the brush in terms of the grafting density and the amount of lubricant present. Regarding the wetting behavior, we study a sessile droplet on top of the brush. The droplet consists of nonbonded particles that form a dense phase. Our model and choice of parameters result in the formation of a wetting ridge and in the cloaking of the droplet by the lubricant; i.e., the lubricant chains creep up onto the droplet and eventually cover its surface completely. Cloaking is a phenomenon that is observed experimentally and is of integral importance to the dynamics of sliding droplets. We quantify the cloaking in terms of its thickness, which increases with the amount of lubricant present. The analysis reveals a well-defined transition point where the cloaking sets in. We propose a thermodynamic theory to explain this behavior. In addition, we investigate the dependence of the contact angles on the size of the droplet and the possible effect of line tension. We quantify the variation of the contact angle with the curvature of the contact line on a lubricant free brush and find a negative value for the line tension. Finally we investigate the effect of cloaking/lubrication on the contact angles and the wetting ridge. We find that lubrication and cloaking reduce the contact angles by a couple of degrees. The effect on the wetting ridge is a reduction in the extension of the brush chains near the three phase contact line, an effect that was also observed in experiments of droplets on cross-linked gels.

Enhanced dimensional stability of lightweight SBR/EVA foam by an inorganic scaffold structure constructed in the cell wall

The poor dimensional stability of lightweight rubber-based foam directly restricts its application. The realization of its higher dimensional stability contributes to being widely applied in the automobile industry, military equipment, aerospace, national defense engineering, medical and health care. However, this remains a huge challenge because the crystallization of rubber is too low to counterbalance the internal stresses and strains created by the rubber chains during the foaming process. Hence, An inorganic scaffold structure, containing the organically-modified lamellar montmorillonite (KDMMT) and rod-like attapulgite (KHATP) with a carbon-carbon double bond (>C C<), has been successfully constructed in the cell wall of styrene butadiene rubber/ethylene vinyl acetate (SBR/EVA) foam, which can improve the dimensional stability of SBR/EVA foam and reduce its density. The construction of the inorganic scaffold structure ascribed to a double cross-linking network structure (-C-C- and -C-S x -C-), which is based on the cellular heterogeneous nucleation while taking line tension effects at the melt-nucleator interface into account. The results indicate that when the density of SBR/EVA/KDMMT/KHATP composites foam with the inorganic scaffold structure was 0.24 g/cm 3 , the shrinkage and post shrinkage was reduced by 56.6% and 50.6%, respectively, compared with that of SBR/EVA foam (0.28 g/cm 3 ). Meanwhile, shoe soles constructed from this material have exceptional folding resistance compared to EVA foam. The inorganic scaffold structure was constructed in the cell wall of SBR/EVA/KDMMT/KHATP foam reduced its post shrinkage by 50.6%. • An inorganic scaffold structure was constructed by two shaped inorganic particles. • This structure was constructed in the cell wall based on cell heterogeneous nucleation. • The construction was ascribed to a double cross-linking network structure. • The post shrinkage of SBR/EVA composite foam reduced by 50.6%. • The foam with the inorganic scaffold structure has excellent folding resistance.

Abnormal interactions between high-speed edge dislocation and microvoid in BCC metals

The interaction between a high speed edge dislocation and a microvoid has been investigated by molecular dynamics (MD) simulations in BCC crystals of Ta, Fe, V and W in the present work. The focus is placed on the dynamic effect on the dislocation-microvoid interaction. Three interaction scenarios different from static cases, i.e., repeated dislocation oscillations around microvoids, dislocation depinning from microvoid like releasing an elastic slingshot, and formation of abnormal “pull forward” dislocation configuration, have been found for the first time. The “repeated oscillations” can be attributed to the dislocation line tension and dynamic effect, which is analogous to under-damped mechanical oscillator system. For the “releasing slingshot” case, the dislocation first bows out after breaking away from the microvoid, and then a stable “drag backward” dislocation configuration is formed. When further increasing the applied shear stress, the dislocation can accelerate to subsonic speed of roughly0.7CT, with CT being the transverse sound speed, leading to a stable “pull forward” configuration. These different dislocation configurations are closely related to the formation of superjog driven by the dislocation-microvoid interaction. By careful analysis, it is found that the variation of relative mobility between the original edge dislocation on the (110) plane and the superjog segments on the (112) plane with shear stresses perfectly coincides with the above three dislocation configurations. In fact, when the applied shear stress is high enough and the dislocation speed is subsonic, the friction stress on the superjog segments turns to be smaller than that of the original edge dislocation, resulting in the formation of abnormal “pull forward” configuration.

Investigations into the Complete Spreading Dynamics of a Viscoelastic Drop on a Spherical Substrate.

We study the spreading dynamics of a sphere-shaped elastic non-Newtonian liquid drop on a spherical substrate in the capillary-driven regime. We use the simplified Phan-Thien-Tanner model to represent the rheology of the elastic non-Newtonian drop. We consider the drop to be a crater on a flat substrate to calculate the viscous dissipation near the contact line. Following the approach compatible with the capillary-viscous force balance, we establish the evolution equation for describing the temporal evolution of the contact line during spreading. We show that the contact line velocity obtained from the theoretical calculation matches well with our experimental observations. Also, as confirmed by the present experimental observations, our analysis deems efficient to capture the phenomenon during the late stage of spreading for which the effect of line tension becomes dominant. An increment in the viscoelastic parameter of the fluid increases the viscous dissipation effect at the contact line. It is seen that the higher dissipation effect leads to an enhancement in the wetting time of the drop on the spherical substrate. Also, we have shown that the elastic nature of the fluid leads to an increment in the dynamic contact angle at any temporal instant as compared to its Newtonian counterpart. Finally, we unveil that the phenomenon of the increasing contact angle results in the time required for the complete wetting of drop, which becomes higher with increasing viscoelasticity of the fluid. This article will fill a gap still affecting the existing literature because of the unavailability of experimental investigations of the spreading of the elastic non-Newtonian drop on a spherical substrate.

Temperature Dependence of Liquid Contact Angle at a Deformable Solid Surface

To date, it has been reliably shown by direct methods that a sessile droplet on a solid surface causes deformation of the substrate. For solids with rather low elasticity moduli, in particular, elastomers, this phenomenon becomes observable, and the deformation work reaches values sufficiently large to take it into account in the theory when necessary. Within the framework of the current theory of capillarity and the generalized Young equation, it is most convenient to introduce the deformation work (realized along and inside the three-phase contact line) into the line tension. The resultant effective line tension is several orders of magnitude higher than the usual one (for undeformable solids); therefore, it manifests itself even in macroscopic (although small) droplets. While the usual line tension is just a small correction to the classical Young equation, when elastomers are used as substrates, the effective line tension may become the main term and govern surface phenomena. In this communication, the results of work [Budziak, C.J., Varcha-Butler, E.I., and Neumann, A.W., J. Appl. Polym. Sci., 1991, vol. 42, p. 1959], which is devoted to studying the temperature dependence of liquid contact angles at elastomers, are discussed from the aforementioned points of view. The following facts have been explained: the higher the surface tension of a liquid the larger the contact angle at the same substrate; most probably, the contact angle increases with temperature; the temperature dependence of a contact angle cannot be strong because of the mutual compensation of the temperature dependences of the surface tension of a wetting liquid and the elasticity modulus of an elastomeric substrate.

Assessment of Wind Turbine Aero-Hydro-Servo-Elastic Modelling on the Effects of Mooring Line Tension via Deep Learning

As offshore wind turbines are moving to deeper water depths, mooring systems are becoming more and more significant for floating offshore wind turbines (FOWTs). Mooring line failures could affect power generations of FOWTs and ultimately incur risk to nearby structures. Among different failure mechanics, an excessive mooring line tension is one of the most essential factors contributing to mooring failure. Even advanced sensing offers an effective way of failure detections, but it is still difficult to comprehend why failures happened. Unlike traditional parametric studies that are computational and time-intensive, this paper applies deep learning to investigate the major driven force on the mooring line tension. A number of environmental conditions are considered, ranging from cut in to cut out wind speeds. Before formatting input data into the deep learning model, a FOWT model of dynamics was simulated under pre-defined environmental conditions. Both taut and slack mooring configurations were considered in the current study. Results showed that the most loaded mooring line tension was mainly determined by the surge motion, regardless of mooring line configurations, while the blade and the tower elasticity were less significant in predicting mooring line tension.

Thermodynamic analysis of steady wetting state of droplet on single microstructure surface

A three dimension thermodynamic model is used to investigate the steady wetting state of droplet on a single microstructure surface based on the lowest principle of droplet free energy. The cone, frustum (upright and inverted) and sphere in micro-scale are selected as studied structures. The results show that both the intrinsic contact angle and morphology parameters of microstructure surface affect the wetting depth and normalized Helmholtz free energy (NFE) of droplet. The wetting maps for minimum points of NFE of droplet on cone and frustum surfaces with respect to intrinsic contact angle and morphology parameters have been presented. These wetting maps provide a guidance for fabricating microstructures that is used to enhance droplet adhesion. The effect of three phase contact line tension on droplet NFE has been studied. Results indicate that the line tension slightly increases the droplet NFE and that causes the decrease of droplet wetting stability. The absolute differences between Fτ* (NFE with line tension) and F * (NFE without line tension) are small both for 1 μL and 1 nL droplets. But the relative differences, (Fτ*-F *)/F *, of 1 nL droplet are significantly larger than that of 1 μL droplet. Therefore, for a droplet with small volume, the line tension effect on droplet free energy is relatively large and that results in the increase of instability of droplet wetting state.

Operating windows for oscillatory interfacial shear rheology

Interfacial rheology becomes important when surface active species such as surfactants, particles, or proteins are present in sufficient quantities at liquid-liquid interfaces and interact between them. Interfacial rheometry measurements are challenging for various reasons. The mechanical response of the thin interface is often weaker compared to that of bulk materials and so one is often measuring close to the lower force and torque limits of rheometers, hence signal-to-noise ratios merit closer attention. In addition, the role of both instrument and sample inertia is more important for interfacial rheometry compared to bulk rheometry. Effects of misalignment and imperfections of the measurement geometries lead to effects of surface and line tension. Finally, peculiar for interfacial rheometry is the need to deconvolute the contributions of flow and deformation in the surrounding phases from that at the interface. Whereas some of these aspects have received attention in previous works, a clear and unambiguous view on the operating limits of interfacial rheometers has been missing. In the present work, we investigate the different experimental challenges and develop a generic methodology, which provides a clear definition of the operating limits of various interfacial rheometers including the interfacial needle shear rheometer, the double wall ring, and the bicone geometries. We validate this methodology by investigating the limitations defined intrinsically by the instrument as well as the ones emerging from the properties of the interface of interest for an interface composed of fatty alcohols which represents a challenging test case. The results provide cautionary examples and clear guidelines for anyone measuring interfacial rheology with these direct rheological techniques.

Wetting of single crystalline and amorphous silicon surfaces: effective range of intermolecular forces for wetting

ABSTRACTWetting at nanoscale is a property of a three-dimensional region with a finite length into the solid domain from the surface. Understanding the extent of the solid region effective on wetting is important for recent coating applications as well as for both crystalline and amorphous solids of different atomic ordering. For such a case, we studied the wetting behaviour of silicon surfaces at various crystalline and amorphous states. Molecular distributions of amorphous systems were varied by changing the amorphisation conditions of silicon. Semi-cylindrical water droplets were formed on the surfaces to be large enough to remain independent of line tension and Tolman length effects. Contact angles showed up to 38% variation by the change in the atomic orientation of silicon. Instead of a homogeneous solid density definition, we calculated different solid densities for a given surface measured inside different extents from the interface. We correlated the observed wetting variation with each of these different solid densities to determine which extent governs the wetting variation. We observed that the variation of solid density measured inside a 0.13 nm extent from the surface reflected the variation of wetting angle better for both single crystalline and amorphous silicon surfaces.

Dynamics of particle uptake at cell membranes.

Receptor-mediated endocytosis requires that the energy of adhesion overcomes the deformation energy of the plasma membrane. The resulting driving force is balanced by dissipative forces, leading to deterministic dynamical equations. While the shape of the free membrane does not play an important role for tensed and loose membranes, in the intermediate regime it leads to an important energy barrier. Here we show that this barrier is similar to but different from an effective line tension and suggest a simple analytical approximation for it. We then explore the rich dynamics of uptake for particles of different shapes and present the corresponding dynamical state diagrams. We also extend our model to include stochastic fluctuations, which facilitate uptake and lead to corresponding changes in the phase diagrams.

Effect of line tension on axisymmetric nanoscale capillary bridges at the liquid-vapor equilibrium.

The effect of line tension on the axisymmetric nanoscale capillary bridge between two identical substrates with convex, concave, and flat geometry at the liquid-vapor equilibrium is theoretically studied. The modified Young's equation for the contact angle, which takes into account the effect of line tension, is derived on a general axisymmetric curved surface using the variational method. Even without the effect of line tension, the parameter space where the bridge can exist is limited simply by the geometry of substrates. The modified Young's equation further restricts the space where the bridge can exist when the line tension is positive because the equilibrium contact angle always remains finite and the wetting state near the zero contact angle cannot be realized. It is shown that the interplay of the geometry and the positive line tension restricts the formation of capillary bridge.

Compare numerical modeling and improved understanding of dynamic sessile drop contact angle analysis in Liquid-Solid-Gas system

Dynamic contact angle measurement; as a standard method for surface wettability analysis, is usually conducted through the analysis of sessile drops formed following the low rate injection of fluid from beneath through a drilled hole via an injection needle. However, understanding/characterizing the changes of drop contact angle from the point where the flat solid surface begins is not well discussed yet. Moreover, during the evaluation of size-dependent behavior of contact angle of millimeter-scale drops, the effect of the drilled hole is ignored. In this regard, in the current study, the experimental and thermodynamic characterizations of the sessile drop advancing contact angle measurements for a liquid-solid-air system are presented. To do this, a set of dynamic contact angle experiments for a water-calcite-air system with different devised hole diameters and roughness is conducted, and Gibbs free energy analysis is then utilized to propose a modeling scheme. Experimental results revealed a transient region from zero infinite contact angle at the hole to infinite contact angle of the solid surface, which was equal to 74.61° and 69.05° for nanoscale, and microscale surface roughness. In addition, it was shown that with a decrease in the hole diameter, the transient region met a lower value of contact angle at different dimensionless volumes. The result of higher advancing contact angle measured for the system with smaller drilled hole diameter was attributed to higher contact-line velocity. However, the assumption of low rate advancing contact angle was not violated for the hole diameter larger than 1.4 mm. Numerical studies demonstrated that in the case of zero line tension, two straight lines with positive slop could be fitted to the data; attributed to drilled hole effect. Besides, it was concluded that this behavior should not be interpreted as a negative line tension effect. The obtained values of line tension and equilibrium advancing contact angle, as matching parameters, were in agreement with those reported in the previous studies. Results of this work could help for better analyzing the size-dependent behavior of millimeter-scale drop through a suggested size-dependent model.

Extracellular and intercellular force distribution in circularly shaped epithelia

Stress homeostasis in multicellular organisms is essential to tissue growth, development, and repair. However, how cellular forces are generated and transmitted within a multicellular organism to maintain stress homeostasis remains poorly understood. Here we employ cellular force microscopies to quantify extracellular traction and intercellular tension of circularly shaped cohesive epithelia seeded on hydrogels of various stiffness. Our experimental measurements show that the traction force is both colony size and gel stiffness dependent. A minimal mechanics model is developed and predicts exponential decay of extracellular traction from the periphery to the center of the epithelial monolayers, which agrees with the experimental data. Our modeling analyses further show that the colony size and gel stiffness dependent traction is originated from the line tension effect and stiffness-dependent cell contractility, respectively. Our study lays down a foundation for future modeling and experimental measurements of cellular force generation, transmission, and distribution in multicellular organisms, which is critical to mechanobiological understanding of normal and disease development.

Thermodynamic Analysis of Adsorption and Line-Tension Contributions to Contact Angles of Small Sessile Droplets

Relations for the contact angles of sessile liquid droplets with axially symmetric or cylindrical shapes and different equilibrium sizes have been considered using a general thermodynamic approach. For a multicomponent system comprising a liquid droplet, a vapor–gas medium, and a solid substrate, influence of dependence of the surface tension on the chemical potentials related to equilibrium droplet size (i.e., the effect of adsorption) and the effect of size-dependent line tension on the contact angles have been discussed. It has been shown that, for an axially symmetric sessile droplet, the effects of adsorption and line tension are, in the general case, comparable and manifest themselves already at the first order with respect to the droplet curvature. For a cylindrical droplet, the effect of adsorption is observed already in the first order with respect to the droplet curvature, while the influence of the line tension manifests itself only in the second order and is governed by the droplet-size dependence of the line tension.

Stability of a twisted Plateau border with line tension and bending stiffness

The stability of a Plateau border between three soap films is considered, taking into account the effects of line tension and bending stiffness in the border. A simple geometry is considered, in which the border initially lies in equilibrium along the axis of a circular cylinder, with three equally-spaced films radiating outwards to meet the inside wall of the cylinder. The films are pinned at the two ends of the cylinder with a fixed relative twist, so the initial film surfaces are helicoids. The stability of this system to small perturbations, involving both the films and the border, is investigated as a function of the cylinder aspect ratio, twist angle, film surface tension, border line tension, and border bending stiffness. Analytically, the stability problem is reduced to finding the first occurrence of a zero eigenvalue of an infinite matrix, which is then estimated numerically. The results from this calculation are in good agreement with full numerical simulations.

Nanodroplets at Membranes Create Tight-Lipped Membrane Necks via Negative Line Tension.

The response of biomembranes to aqueous-phase separation and to the resulting water-in-water droplets has been recently studied on the micrometer scale using optical microscopy and elasticity theory. When such a droplet adheres to the membrane, it forms a contact area that is bounded by a contact line. For a micrometer-sized droplet, the line tension associated with this contact line can usually be ignored compared with the surface tensions. However, for a small nanoscopic droplet, this line tension is expected to affect the membrane-droplet morphology. Here, we use molecular simulations to study nanodroplets at membranes and to gain insight into these line tension effects. The latter effects are shown to depend strongly on another key parameter, the mechanical tension experienced by the membrane. For a large membrane tension, a droplet adhering to the membrane is only partially engulfed by the membrane, and the membrane-droplet system exhibits an axisymmetric morphology. A reduction of the membrane tension leads to an increase in the contact area and a decrease in the interfacial area of the droplet, initially retaining its axisymmetric shape, which implies a circular contact line and a circular membrane neck. However, when the tension falls below a certain threshold value, the system undergoes a morphological transition toward a non-axisymmetric morphology with a non-circular membrane neck. This morphology persists until the nanodroplet is completely engulfed by the membrane and the membrane neck has closed into a tight-lipped shape. The latter morphology is caused by a negative line tension, which is shown to be a robust feature of membrane-droplet systems. A closed membrane neck with a tight-lipped shape suppresses both thermally activated and protein-induced scission of the neck, implying a reduction in the cellular uptake of nanodroplets by pinocytosis and fluid-phase endocytosis. Furthermore, based on our results, we can also draw important conclusions about the time-dependent processes corresponding to the surface nucleation and growth of nanodroplets at membranes.