Tangential Surface Research Articles

The Effect of Different Densification Levels on the Mechanical Properties of Southern Yellow Pine

Plantations, typically involving the cultivation of fast-growing trees like southern yellow pine, offer avenues to enhance sustainability and manage limited resources more effectively. However, fast-growing trees suffer from low mechanical properties due to less dense wood. Densification and the development of engineered wood products represent approaches to developing high-performance products from fast-growing tree species. In this study, the correlation between the densification levels and mechanical properties of a fast-growing species, loblolly pine (Pinus taeda L.), was established to improve resource utilization. Wood specimens were densified at three compression ratios: 16.67%, 33.33%, and 50.00%. The impact of densification levels on bending strength, bending stiffness, shear strength, and hardness was studied. The findings highlighted the positive impact of densification on structural integrity, as bending stiffness consistently improved, eventually reaching a 42% enhancement at a compression ratio of 50.00%. However, bending strength showed an initial increasing trend but reached a plateau at higher densification levels. Densification levels showed minimal changes in shear strength parallel to the grain. Notably, densification significantly enhanced hardness properties, particularly on the tangential surface, where a fourfold increase was observed at a 50% compression ratio. Overall, these findings reveal the relation between the compression ratio and the mechanical properties of lumber and are beneficial for utilizing lower-quality wood species in construction and engineering applications.

The mechanism of EP/SiC coating modulated DC flashover characteristics of epoxy composites in SF6/N2 mixtures

Surface flashover is an inevitable insulation issue for basin-type insulators in gas-insulated switchgears/lines, which significantly challenges the reliability of the electrical power systems. Previous studies have indicated that polymer/semiconductor-filler composite coatings effectively improve the insulation properties; however, the influence mechanism of the coating materials on flashover has not been demonstrated from a molecular perspective. In this work, epoxy/silicon-carbide (EP/SiC) composites were coated onto an EP substrate. The energy-level structure, surface trap, surface charging, and DC flashover voltage in SF6/N2 were calculated and characterized, and the process by which the tailored molecular energy level influences surface charge transport and flashover characteristics was elucidated. The incorporating of SiC particles reduced the width of the bandgap and introduced shallow traps, which improved carrier mobility and surface conductivity. Quantitative analysis of charge transport indicated that the improved carrier mobility and reduced surface trap level accelerated the surface charge dissipation. This reduced the tangential electrical field distortion and surface charge density and further impeded gas ionization. When the SiC concentration was 15 wt%, the flashover performance improved by 20.88%. This study describes the mechanism by which the EP/SiC coating regulates the surface charge distribution to improve the surface flashover performance by establishing a relationship among the microscopic molecular energy-level structures, mesoscopic charge transport, and macroscopic discharge phenomena.

Chemical Composition and Mechanical Properties of Wood after Thermal Modification in Closed Process under Pressure in Nitrogen.

In this study, silver birch (Betula pendula) and Scots pine (Pinus sylvestris) wood planks (1000 × 100 × 25 mm) were thermally modified in pilot-scale equipment. Research extended our knowledge of the thermal modification (TM) process in a closed system under nitrogen pressure, as well as how process parameters affect the chemical composition and mechanical strength of wood. Various TM regimes were selected-maximum temperature (150-180 °C), modification time (30-180 min), and initial nitrogen pressure (3-6 bar). Chemical analyses were performed to assess the amount of extractives, lignin, polysaccharides and acetyl group content following the TM process. The mechanical properties of TM wood were characterized using the modulus of rupture (MOR), modulus of elasticity (MOE), and Brinell hardness. The MOR of both studied wood species following TM in nitrogen was reduced, but MOE changes were insignificant. The Brinell hardness of TM birch wood's tangential surface was much higher than that of the radial surface, although Scots pine wood showed the opposite pattern. TM birch and pine wood specimens with the highest mass loss, acetone soluble extractive amount, and the lowest xylan and acetyl group content had the lowest MOR and Brinell hardness.

The Hydrophilicity of Samama Wood Surface Quality after Boron, Methyl Methacrylate Impregnation, and Heat Treatment

Indicators of surface roughness and surface-free energy can represent the improvement in wood surface quality. In this study, those two indicators were used to determine the change in the samama (Anthocephalus macrophyllus) wood surface following two modification steps, namely impregnation and heat treatment. The first step was boron impregnation in two forms applied separately, i.e., boric acid and borax. The second step was impregnation of methyl methacrylate followed by heat treatment at 90°C and 180°C. Surface roughness was determined following the ISO 4287:1997 standard, and surface free energy was analyzed using the Rabel Method. The results showed that the radial surface of samama wood naturally had a lower roughness than the tangential surface. Impregnation with boric acid, borax, and methyl methacrylate increased the wood surface roughness. However, heat treatment at 180°C tended to smooth the rough surface. Total surface free energy was altered after borax and methyl methacrylate impregnation. However, heat treatment seemingly withdrew the alteration. The polar components and dispersion contributed to total surface free energy with different compositions. In this study, the change in surface roughness was not congruent with the change in total surface free energy. Keywords: boron, heat treatment, impregnation, samama, surface free energy

Numerical implications of including drifts in SOLPS-ITER simulations of EAST

The inclusion of drifts in plasma edge codes like SOLPS-ITER is required to match simulation data with experimental profiles. However, this remains numerically challenging. In this paper, the effect of some numerical factors on the final plasma solution is investigated. This study is performed on three EAST simulations in the upper single null configuration: an attached purely deuterium case, an attached case with limited Ne-seeding, and a detached Ne-seeded case. The effects of the anomalous conductivity and anomalous thermo-electric coefficient on the plasma potential are investigated. Next, the effect of the employed grids is shown. In order to investigate these effects, accurate drift simulations are needed. Therefore, the employed time step and numerical parameters are discussed for the three studied simulations. For all presented simulations, it is verified that the restriction of the grid to the first flux surface tangent to the main chamber wall is sufficient within the context of non-extended simulations. This means that the main power dissipation takes place inside the simulated domain, and only a small fraction of the power is leaving the B2.5 grid through the grid boundary closest to the first wall. Finally, the effect of drifts on the asymmetry between the inner and outer target for EAST simulations is demonstrated.

Toward Optimal Robot Machining Considering the Workpiece Surface Geometry in a Task-Oriented Approach

Robot workpiece machining is interesting in industry as it offers some advantages, such as higher flexibility in comparison with the conventional approach based on CNC technology. However, in recent years, we have been facing a strong progressive shift to custom-based manufacturing and low-volume/high-mix production, which require a novel approach to automation via the employment of collaborative robotics. However, collaborative robots feature only limited motion capability to provide safety in cooperation with human workers. Thus, it is highly necessary to perform more detailed robot task planning to ensure its feasibility and optimal performance. In this paper, we deal with the problem of studying kinematic robot performance in the case of such manufacturing tasks, where the robot tool is constrained to follow the machining path embedded on the workpiece surface at a prescribed orientation. The presented approach is based on the well-known concept of manipulability, although the latter suffers from physical inconsistency due to mixing different units of linear and angular velocity in a general 6 DOF task case. Therefore, we introduce the workpiece surface constraint in the robot kinematic analysis, which enables an evaluation of its available velocity capability in a reduced dimension space. Such constrained robot kinematics transform the robot’s task space to a two-dimensional surface tangent plane, and the manipulability analysis may be limited to the space of linear velocity only. Thus, the problem of physical inconsistency is avoided effectively. We show the theoretical derivation of the proposed method, which was verified by numerical experiments.

Growth stress and wood properties of 10-year-old fast-growing teak grown in Gunungkidul, Yogyakarta

Abstract The establishment of fast-growing teak plantations in Indonesia provides opportunities for shorter harvesting periods. However, it also poses challenges on wood utilization due to juvenility and growth stress-related defects. This study investigated growth stress levels and some wood properties of 10-year-old fast-growing teak grown in Gunungkidul Regency, Yogyakarta. The strain gauge method was used to measure longitudinal surface released-strains (LRS), tangential surface released-strains (TRS), and longitudinal internal residual strains (IRS). Wood specimens were also collected near each strain measurement point for the analysis of wood properties. The results showed LRS values ranging from −1243 to 320 με, TRS values ranging from −779 to 382 με, and IRS values ranging from −589 to 786 με. Meanwhile, radial variations in fiber length, modulus of elasticity, and lignin content were observed. Significant correlations were found between IRS values and microfibril angle, fiber length, modulus of elasticity, lignin content, and hemicellulose content, while no significant correlations were observed between LRS and TRS values and wood properties. These findings suggest a moderate level of growth stress. Additionally, the results also indicate that this 10-year-old fast-growing teak is still in the juvenile stage. Therefore, its utilization should be performed with caution.

Elastic Stress Field beneath a Sticking Circular Contact under Tangential Load

Based on a potential theoretical approach, the subsurface stress field is calculated for an elastic half-space which is subject to normal and uniaxial tangential surface tractions that—in the case of elastic decoupling—correspond to rigid normal and tangential translations of a circular surface domain. The stress fields are obtained explicitly and in closed form as the imaginary parts of compact complex-valued expressions. The stress state in the surface and on the central axis are considered in detail. As, within specific approximations that have been discussed at length in the literature, any tangential contact problem with friction can be understood as a certain incremental series of such rigid translations, the solutions presented here can serve as the basis of very fast superposition algorithms for the analysis of subsurface stress fields in general tangential contact problems with friction. This idea is demonstrated by means of the frictional tangential contact between an elastic half-space and a rigid cylindrical flat punch with rounded corners.

An extended M-K model under surface traction with adjustable gradient distribution

The forming limit of sheets usually corresponds to the strain accumulation before localized necking and is closely related to the loading state. In the viscous pressure forming (VPF) method, the surface traction generated by the force-transmitting medium with high-viscosity fluid-flow characteristics on the sheet exhibits the obvious gradient distribution near the necking region. However, existing necking instability theories have not factored in the surface traction gradient distribution (STGD) and can't accurately explain the inherent mechanism of the VPF method with this loading state to improve the forming limit. To deal with the issue, STGD-related ‘stress balance’ equations are established and an extended M-K model with STGD response under 3D stress state (STGD-3D-MK model) is proposed, based on the analysis of the adjustable STGD generated in the VPF method during the necking development. The proposed model is used to explore the influence and mechanism of the STGD on the forming limit, as well as to provide suggestions on how to achieve the full positive effect of tangential surface traction. This research demonstrates that the forming limit is sensitive to the STGD, which affects the ability of surface traction to improve the forming limit. The STGD changes the stress path of the groove, affecting the development of necking. In addition, the critical STGD that can increase the limit strain is also provided and its magnitude is related to the strain path. Finally, the VPF-based experimental results are provided to support the effectiveness of the analysis of the STGD-3D-MK model. This work provides a new perspective on the loading method to improve the forming limit.

Non-local modelling of multiphase flow wetting and thermo-capillary flow using peridynamic differential operator

AbstractInterfaces in multiphase flows are affected by surface tension, and when temperature gradients occur in the flow domain, tangential surface tensions along the interface also arise. As the behaviour of fluids contacting on a solid surface is also governed by surface tension, the description of the wetting phenomenon is challenging. Peridynamic differential operator (PDDO) can express partial differentials of any order by integral equations. Therefore, the governing equations for multiphase fluid motion, such as the Navier–Stokes equations and energy equations, can be reformulated in terms of integral equations. In this study, a novel non-local method is developed for modelling the multiphase fluid flow motion using the PDDO, and the thermal effect on surface tension force is considered. To describe the surface tension forces in the normal and tangential directions, the non-local form of the continuum surface force (CFS) model is presented. Besides, to overcome the inaccuracy of the unit normal vectors at the three-phase flow intersection region, an additional treatment for this region is presented. Finally, several benchmark multiphase fluid flow cases, such as square droplet deformation, surface wetting, and droplet migration in thermo-capillary flow are presented and validated. The results demonstrate that the developed non-local model can accurately capture the surface tension effect in multiphase fluid flow motion.

A novel approach to compute the spatial gradients of enriching functions in the X-FEM with a hybrid representation of cracks

The eXtended Finite Element Method (X-FEM) is a versatile technique to model discontinuities by enriching the trial functions with a prior solution. In the X-FEM, a crack can be explicitly represented by a set of triangles or implicit signed distances, i.e., level set functions, of the points of interest from the crack surface and the crack front. In the explicit representations, it is crucial to accurately evaluate surface normal, conormal, and tangent vectors along crack fronts for computations of the gradients of the enriching functions. The solution is very sensitive to these directional vectors, especially for non-planar 3D cracks. We here propose a novel approach to compute these gradients without evaluating the directional vectors. Level set functions are first set up in a hexahedral grid independent of the background mesh in the X-FEM. We can thus implement the Weight Essentially Non-Oscillatory (WENO) scheme to compute the gradients of level sets. The gradients of the enriching functions at any integration point can therefore be computed by interpolations and chain rules. We compare the implementation procedures of the explicit representation and the proposed hybrid representation in detail. A three-dimensional lens crack problem is studied to demonstrate the accuracy of the proposed method, especially for coarse meshes.

Swimming of an inertial squirmer and squirmer dumbbell through a viscoelastic fluid

We investigate the hydrodynamics of a spherical and dumbbell-shaped swimmer in a viscoelastic fluid, modelled by the Giesekus constitutive equation. The ‘squirmer’, a model of a micro-swimmer with tangential surface waves at its boundaries, is simulated utilizing a direct-forcing fictitious domain method. We consider the competitive effects of the fluid inertia and elasticity on the locomotion of the swimmers. For the neutral squirmer, its speed increases monotonically with increasing Reynolds number in the Giesekus fluid, in contrast to holding a constant speed in a Newtonian one. Meanwhile, the speed of the finite inertial squirmer increases monotonically with fluid elasticity, as measured by the Weissenberg number. Regarding the dumbbell-shaped swimmers in the Giesekus fluid, we find the pusher–puller (the puller is in front of the pusher) dumbbell swimming to be significantly faster than other dumbbells, providing practical guidance in assembling the complex micro-swimming devices. We further consider the squirmer's (or the dumbbell-shaped squirmer's) energy expenditure and hydrodynamic efficiency, finding that swimming in viscoelastic fluids expends less energy than its Newtonian counterpart, and the neutral squirmer expends more energy than a pusher or puller. The energy expenditure and hydrodynamic efficiency are relevant to steady swimming speeds, in which a faster counterpart squirmer (dumbbell-shaped squirmer) expends less energy but has higher hydrodynamic efficiency.

Diffusion of tangential tensor fields: numerical issues and influence of geometric properties

Abstract We study the diffusion of tangential tensor-valued data on curved surfaces. For this purpose, several finite-element-based numerical methods are collected and used to solve a tangential surface n-tensor heat flow problem. These methods differ with respect to the surface representation used, the geometric information required, and the treatment of the tangentiality condition. We emphasize the importance of geometric properties and their increasing influence as the tensorial degree changes from n = 0 to n ≥ 1. A specific example is presented that illustrates how curvature drastically affects the behavior of the solution.

Application of machine learning techniques in environmentally benign surface grinding of Inconel 625

This work explores the grinding performance of Inconel 625 by comparing tangential forces and surface roughness under dry, wet, and minimum quantity lubrication (MQL) environments. Response surface methodology (RSM) and machine learning (ML) techniques establish correlations between inputs and outputs. RSM shows the quadratic regression model effectively captures experimental variability. Four ML models, namely: multilayer perceptron, KNN, and SVM with two kernels, were implemented to predict outcomes, among which KNN appeared as a better-suited model. Lower tangential forces and better ground surface quality support the suitability of MQL grinding compared with dry and wet grinding. Micro-graph investigations of the ground surfaces and chip morphology findings also upkeep the emergence of MQL grinding as a sustainable alternative for Inconel 625 grinding.

NTPP-MVSNet: Multi-View Stereo Network Based on Neighboring Tangent Plane Propagation

Although learning-based multi-view stereo algorithms have produced exciting results in recent years, few researchers have explored the specific role of deep sampling in the network. We posit that depth sampling accuracy more directly impacts the quality of scene reconstruction. To address this issue, we proposed NTPP-MVSNet, which utilizes normal vector and depth information from neighboring pixels to propagate tangent planes. Based on this, we obtained a more accurate depth estimate through homography transformation. We used deformable convolution to acquire continuous pixel positions on the surface and 3D-UNet to account for the regression of depth and normal vector maps without consuming additional GPU memory. Finally, we applied homography transformation to complete the mapping of the imaging plane and the neighborhood surface tangent plane to generate a depth hypothesis. Experimental trials on the DTU and Tanks and Temples datasets demonstrate the feasibility of NTPP-MVSNet, and ablation experiments confirm the superior performance of our deep sampling methodology.

Influence of heterogeneity or shape on the locomotion of a caged squirmer

The development of novel drug delivery systems, which are revolutionizing modern medicine, is benefiting from studies on microorganisms’ swimming. In this paper we consider a model microorganism (a squirmer) enclosed in a viscous droplet to investigate the effects of medium heterogeneity or geometry on the propulsion speed of the caged squirmer. We first consider the squirmer and droplet to be spherical (no shape effects) and derive exact solutions for the equations governing the problem. For a squirmer with purely tangential surface velocity, the squirmer is always able to move inside the droplet (even when the latter ceases to move as a result of large fluid resistance of the heterogeneous medium). Adding radial modes to the surface velocity, we establish a new condition for the existence of a co-swimming speed (where squirmer and droplet move at the same speed). Next, to probe the effects of geometry on propulsion, we consider the squirmer and droplet to be in Newtonian fluids. For a squirmer with purely tangential surface velocity, numerical simulations reveal a strong dependence of the squirmer's speed on shapes, the size of the droplet and the viscosity contrast. We found that the squirmer speed is largest when the droplet size and squirmer's eccentricity are small, and the viscosity contrast is large. For co-swimming, our results reveal a complex, non-trivial interplay between the various factors that combine to yield the squirmer's propulsion speed. Taken together, our study provides several considerations for the efficient design of future drug delivery systems.

Zero Thickness Surface Susceptibilities and Extended GSTCs—Part I: Spatially Dispersive Metasurfaces

A simple method to describe spatially dispersive metasurfaces is proposed where the angle-dependent surface susceptibilities are explicitly used to formulate the zero thickness sheet model of practical metasurface structures. It is shown that if the surface susceptibilities of a given metasurface are expressed as a ratio of two polynomials of tangential spatial frequencies, k|| with complex coefficients, they can be conveniently expressed as spatial derivatives of the difference and average fields around the metasurface in the space domain, leading to extended forms of the standard generalized sheet transition conditions (GSTCs) accounting for the spatial dispersion. Using two simple examples of a short electric dipole and an all-dielectric cylindrical puck unit cells, which exhibit purely tangential surface susceptibilities and reciprocal/symmetric transmission and reflection characteristics, the proposed concept is numerically confirmed in 2D. A Lorentzian representation with angle-dependent parameters is further proposed and found to accurately model the complex temporal-spatial frequency response via their electric and magnetic susceptibilities of two unit cell examples - a metallic dipole and a dielectric puck resonator. For both cases, the appropriate spatial boundary conditions are derived.

Duality for certain multi-Frobenius nonclassical curves in higher dimensional spaces

We show how a type of multi-Frobenius nonclassicality of a curve defined over a finite field Fq of characteristic p reflects on the geometry of its strict dual curve. In particular, in such cases we may describe all the possible intersection multiplicities of its strict dual curve with the linear system of hyperplanes. Among other consequence, using a result by Homma, we are able to construct nonreflexive space curves such that their tangent surfaces are nonreflexive as well, and the image of a generic point by a Frobenius map is in its osculating hyperplane. We also obtain generalizations and improvements of some known results of the literature.

Differences in Some Physical and Chemical Properties of Beechwood with False Heartwood, Mature Wood and Sapwood

The article presents the differences in some physical and chemical properties of wood with false heartwood, mature wood, and sapwood of Fagus sylvatica L.: density of wood in the dry state, color in the color space CIE L*a*b* on the tangential surface and the planed surface at w = 10 ± 0.5%, as well as moisture and acidity of wet wood. As part of chemical analyses, the relative proportion of cellulose, hemicelluloses, lignin, and extractive substances in individual zones of beechwood in trunks with false heartwood was determined. From the carried out analyses, it follows that the biggest difference between the wood of false heartwood, mature wood, and sapwood is the color of the wood. The red-brown color of the wood with false heartwood in the color space CIE L*a*b* is described by the following coordinate values: L* = 64.9 ± 4.9; a* = 12.9 ± 1.4; b* = 19.6 ± 1.7. The most significant differences between the values of the color space are on the lightness coordinate, where the light ochre-white of mature wood shows a decrease of ∆L* = −14.0 compared with the color of false heartwood, and the white—pale grey color of sapwood shows a decrease of ∆L* = −17.5. The density of dry beechwood with false heartwood is higher by ∆ρ0 = 4.7% than the density of mature wood, and the density of sapwood is ∆ρ0 = 12.3% lower than the density of wood with false heartwood. The exact opposite applies to the acidity of wet beechwood. The results of wet wood acidity measurements also point to certain differences. While the acidity of the wet wood of false heartwood is pH = 5.32 ± 0.13, the acidity of the sapwood is 5.1% lower. The higher acidity of beech heartwood is attributed to the presence of organic acids in polyphenols during heartwood formation. From the comparison of the representation of cellulose, hemicellulose, lignin, and extractive substances, it follows that the relative content of lignin and hemicelluloses is higher in false heartwood than in mature wood and sapwood. On the contrary, the content of holocellulose and cellulose is highest in sapwood. The presented divisions in the physical and chemical properties of beechwood with false heartwood do not limit the use of beechwood in industrial applications, except for a change in color; the definition of color boundaries in the color space CIE L*a*b* creates space for sorting beechwood according to color and can be used to increase the color variety of compositions of construction-carpentry products.

A versatile immersed boundary method for high-fidelity simulation of Conjugate Heat Transfer

A numerical strategy based on an immersed boundary method (IBM) is presented for performing high-fidelity simulation of thermal hydraulics while including Conjugate Heat Transfer (CHT). The well documented pipe flow is considered which, despite its academic nature, can be seen as a prototype of complex geometry in the sense that the computational mesh, only regular and Cartesian, is not in any way designed to fit the wall. An original strategy is proposed to impose Neumann boundary conditions in this generic situation where the wall geometry is disconnected from the mesh organization. As a first validation step, the technique is used in the context of heat transfer in pipe flow with isoflux conditions (IF). The actual order of accuracy is assessed in laminar regime and then direct numerical simulation (DNS) results are compared to turbulent data of reference, including first- and second-order one-point statistics, as well as budgets of temperature variance for a Reynolds number Re=5300 and two Prandtl numbers Pr=0.025,0.71. The technique is then used to develop a versatile methodology for CHT simulations, where the coupling between fluid and solid thermal solution is performed by an immersed boundary technique that translates the information from the normal and tangential surface directions into the Cartesian grid directions. Consistent results are presented in laminar and turbulent regimes, through the check of the accuracy order for the former and the analysis of turbulent statistics for the latter, including the assessment of the discontinuity of the temperature variance dissipation across the fluid-solid interface.