Tangential Slip Research Articles

Spreading model of single droplet impacting the banana leaf surface and computational fluid dynamics simulation analysis

The droplet deposition behavior is an important indicator of precision agriculture and sustainable agriculture 4.0. Comprehensive analysis of the behavior and modeling of pesticide droplets impacting target leaves is an important basis for achieving efficient spray deposition. In this study, banana leaves were taken as the research object, the spreading model and computational fluid dynamics (CFD) model of single droplet impacting on the target leaf surface were studied from the micro and macro perspectives. The aim is to clarify and obtain the quantitative mapping relationship between droplet deposition performance and related operating parameters. The results showed that the pesticide droplets were asymmetrically spread and slipped on the surface of the inclined banana leaves. The maximum lateral spreading diameter Dnmax was only affected by the normal component of Weber number Wen, while the maximum tangential spreading diameter Dtmax and slip distance L were affected by the normal component of Weber number Wen and the inclination angle α. As the impact velocity increases, the pesticide droplets interact with the non-smooth morphology of the banana leaf surface to form a large number of pinning sites on the edge contact line. Combining the microscopic characteristics of banana leaves with the physicochemical characteristics of the droplets, a CFD model was established to carry out single-drop impact simulation verification. The impact velocity and inclination angle were set as variables to carry out CFD simulation of the dynamic process. The numerical simulation results are consistent with the spreading model obtained from the experimental study, which can quantitatively reflect the impact process of pesticide droplets. The spreading model and CFD model of pesticide droplets impacting on the banana leaf surface established in this study, can provide guidance for the selection of pesticide application for the spray droplet deposition behavior. At the same time, it can also provide methodological reference for other crop spray research and spray technology research in other fields.

Short Fiber-Reinforced Polymer Polyamide 6 Lugs and Selective Laser-Melted Ti-6Al-4V Bushing Contact Cohesive Zone Model Mode II Parameters’ Evaluation

This paper discusses an approach to estimating the parameters of the cohesive zone model (CZM) by mode II by extruding the bushing along the lug axis. This method of evaluation requires small samples, which is particularly relevant when investigating short fiber-reinforced polymers (SFRPs) with additively manufactured embedded elements. Adhesion is investigated on the example of 30% carbon fiber-reinforced polyamide-6 molded to Ti-6Al-4V (VT6) selective laser-melted (SLM) alloy bushing in cases of a roughness Ra = 2.66 μm (vibratory finishing), Ra = 8.79 μm (sandblasting), and Ra = 10.02 (directly from SLM). The values of the maximum equivalent tangential contact stress were in a range from 1.1 MPa to 9.5 MPa, while the critical fracture energy for tangential slip was estimated at 15 N/mm for all cases. Experimental validation of the obtained CZM mode II was carried out by evaluating the load-carrying capacity of the lugs with different bushings. In both the experiment and the calculation, greater bushing roughness provides greater lug load-bearing capacity. The ribbed bushings added significant strength in the experiments, which confirmed the importance of considering the tangential mode in the contact model. The presented models can be used for the preliminary evaluation of short fiber-reinforced polyamide-6 parts with titanium-embedded elements bearing capacity.

An Approach to Measure Slips in Friction Contacts Using a Self-Powered Sensor

The accumulation of small tangential slip will occur on the contact surfaces of components in mechanical structures when subjected to cyclic loadings, which will lead to system failure. However, the small tangential slip is difficult to measure directly. In this paper, a method for measuring the contact slip by using a self-powered displacement sensor based on triboelectric nanogenerator (TENG) is proposed, and the accuracy is verified by the finite element analysis (FEA). The contact slips for a flat-on-flat contact configuration are measured by this method. When the test piece is subjected to a cyclic tangential load with a frequency of 10Hz, the average obtained slip displacement of the test piece under single load cycle is less than 10μm. Then the finite element simulation of the contact configuration is carried out using software Abaqus 6.14. The analysis results are close to the test results, which verifies the effectiveness of the measurement method. Moreover, the slips of the flat-on-flat contact configuration under different frequency and amplitude of cyclic tangential load are investigated.

Effect of maximum applied cyclic stress on fretting fatigue stress distribution of flat-on-flat modified 9Cr-1Mo steel contact: Finite element analysis

Fretting fatigue experiments were conducted on a modified 9Cr-1Mo (P91) steel under flat-on-flat contact with maximum applied cyclic stress (σmax) levels of 450 MPa, 500 MPa and 550 MPa at a stress ratio of 0.3 and a contact pressure of 100 MPa. A decrease in the cyclic life was observed with an increase in σmax. Chaboche model with isotropic and kinematic hardening was employed in finite element analysis to evaluate the stress distribution near the contact pad and along the contact surface under fretting fatigue conditions. In addition, the contact-related parameters such as contact pressure, contact shear stress and relative tangential motion were also assessed. The relative tangential motion was found to increase with increasing σmax. Besides, the peak values of normal stress (parallel to the applied loading direction) and maximum principal stress were observed around the leading and trailing edges of the contact pad at the σmax. The amplitude of relative tangential motion and slip zone increases with σmax. The orientations of the principal plane and shear plane to the applied cyclic loading direction are −89.5° and −134.5°, irrespective of the σmax. The fracture surface of the failed specimen revealed that the direction of the crack was nearly perpendicular to the applied stress. Smith-Watson-Topper parameter was used for estimating the crack initiation life with σmax. It has been noticed that the fraction and dominance of crack initiation or propagation phase depend on the imposed cyclic condition for the steel.

Numerical simulation of pressure relief stress distribution of diamond beaded rope saw cutting in low permeability coal seam

The diamond bead slit is a practical method for changing the stress distribution of low permeability coal seam and achieving pressure relief and reflection improvement. The stress distribution of coal seam in large scale is not clear due to the influence of diamond bead slit parameters and geological parameters, making it difficult to identify. In this paper, the finite element model with built-in Coulomb friction contact surface is used to simulate the stress distribution in coal with different angles, seam length, working face length, seam friction coefficient and different in-situ stress difference. This investigation is conducted to examine the stress distribution of parallel working face, vertical coal seam, and advance working face. The simulation results show that the mechanism of stress transfer in large scale diamond beaded rope saw cutting coal seam is mainly due to the tangential slip of coal body on both sides of seam surface, forming concentrative zone and pressure relief zone with axial distribution, center symmetry and phase. The pressure relief range and maximum pressure relief range of all three direction present a "single peak" distribution with the change of angel α between slit and maximum in-situ stress, i.e. when α = 45°, both of them are maximum. The slit length mainly affects the stress distribution in the advancing direction of the working face, and the length of working face mainly affects the stress distribution in the direction of parallel working face and vertical coal seam, both of which are positively correlated with the pressure relief range and the maximum pressure relief amplitude. The friction coefficient of seam surface and the difference of in-situ stress affect the relative dislocation of coal body on both sides of seam surface, and they inhibit and promote the pressure relief range and the maximum pressure relief amplitude respectively, and are greatly affected by α. The simulation results above suggest that it is reasonable to select fracture and geological parameters in practical engineering.

Behavior of Reinforced Concrete Beams without Stirrups and Strengthened with Basalt Fiber–Reinforced Polymer Sheets

This paper reports on a series of four-point bending experiments to investigate the shear capacity of reinforced concrete (RC) beams strengthened with externally bonded basalt fiber–reinforced polymer (BFRP) sheets. The experimental results show that BFRP sheets can significantly increase RC beams’ shear capacity and ductility. To analyze the fracture and mechanical behaviors of BFRP sheet–strengthened RC beams, a three-dimensional (3D) finite-element model (FEM) based on the application of cohesive elements was developed. Mixed-mode constitutive models of the BFRP–concrete interface, the concrete potential fracture surface, and the reinforcement–concrete interface were proposed. The proposed constitutive models were able to characterize the interface’s normal separation, tangential slip, and friction. A comparison of the simulation and experimental results indicates that the proposed numerical model can appropriately simulate the mechanical response, crack propagation, and crack distribution of BFRP sheet–strengthened RC beams. Finally, based on the proposed 3D FEM, a series of numerical tests were conducted to investigate the influence of key parameters (i.e., sheet elastic modulus, sheet bonding area, and sheet bonding angle) on the shear capacity of BFRP sheet–strengthened RC beams.

Lie-group method solutions for a viscous flow in a dilating-squeezing permeable channel with velocity slip

The investigation focuses on the effects of wall velocity slip on the solution of a viscous, laminar, incompressible channel flow subjected to small-scaled contraction and expansion of the weakly permeable walls. The study of such flow systems is often contextual for fluid transport in biological organisms. In the considered flow configuration, the vertically moving porous walls enable the fluid to enter or exit with a constant rate. The tangential slip velocity of the flow at the porous walls is modeled with the Navier slip boundary condition. The flow dynamics inside the channel is governed by the full Navier–Stokes equations. The Lie symmetry analysis and the invariant method are adopted to reduce the number of independent variables in the system of governing equations. Consequently, a single fourth-order ordinary differential equation is obtained, which is solved analytically by the double perturbation method and the variation of iteration method. The solutions are compared for different arrangements. Furthermore, the approximated analytical solutions are likened to the numerical solutions obtained from a fourth-order Runge–Kutta solver embedding the Shooting method to check the accuracy. It is observed that the boundary layers are formed, and the flow rapidly turns near the walls, when suction and wall contraction coexist. Alternatively, if injection and wall expansion are paired, the flow adjacent to the walls is delayed. The existence of wall velocity slip advances the near-wall velocity and cuts down the speed of centerline velocity. It results in a change in the volumetric flow rate and shear rate. The overall pressure is also varied by higher wall velocity slip. The results are explored for different values of the permeation Reynold number and the dimensionless wall dilation rate to capture all possible impacts of the flow parameters. The current analysis rectifies the existing errors in the work of Boutros et al. [“Lie-group method solution for two-dimensional viscous flow between slowly expanding or contracting walls with weak permeability,”Appl. Math. Model. 31(6), 1092–1108 (2007)] with the no-slip boundary condition and discusses the overall influences of slip boundary condition on the Lie symmetry solution of the flow system.

Equivalent Dynamic Modeling for the Relative Rotation of Bolted Joint Interface Using Valanis Model of Hysteresis

Dynamic modeling of the joint interface is critical to the performance analysis of bolt-jointed structures. In this work, an equivalent modeling method was presented for modeling the relative rotation of the joint interface in bolt-jointed beam structures. As the transverse vibration of the studied structure is closely related to the rotation of the joint, which is different from previous studies that focused on the tangential slip of the joint interface, the Valanis model is used to model the relative rotation of the joint. In addition, the shear deformation and rotational inertia of the beam were considered in the modeling, using a finite element method that employed Timoshenko beam elements. The parameters of the Valanis model were determined by fitting a series of hysteresis loops obtained from the transient nonlinear analysis of a 3D FEM model. The results show that the proposed equivalent modeling method can accurately simulate the dynamic response and dissipation of the jointed beam structure with a significantly high computational efficiency. The maximum errors of the dynamic response amplitude and the energy dissipation are 5.5% and 8.3%.

Parallel and perpendicular flows of a couple stress fluid past a solid cylinder in cell model: Slip condition

The axisymmetric steady flow of a couple stress fluid between two concentric cylinders with a slip effect is investigated with the help of the cell model technique. Here, the inner cylinder is rigid, and the outer cylinder is fictitious. The tangential slip, vanishing of normal velocity, and zero couple stress conditions are applied on the inner cylindrical surface. In addition, zero shear stress (Happel's model), continuity of normal velocity component, and zero couple stress conditions are used on the outer cylindrical surface. We consider two flow problems: the first is the parallel flow, and the second is the perpendicular flow to the cylinder in the cell model. Also, we have discussed the random case. For all the cases, the Kozeny constant is calculated. We described some special cases and compared them with well-known results. The effects of slip and couple stress parameters on the Kozeny constant with fixed value of couple stress viscosity parameter are presented graphically. The influence of the couple stress viscosity parameter on the Kozeny constant with fixed values of couple stress, and slip parameters for parallel flow are expressed graphically. The numerical values for the Kozeny constant for different values of fractional void volume are tabulated. We also obtained the results of the consistent couple stress theory as a special case.

Practical wheel/rail tangential contact force model for vehicle dynamics analysis combining Levi-Chartet’s formula with adhesion coefficient-velocity relational expression

This paper describes a practical wheel/rail tangential contact force model for railway dynamics analysis under running in rainy conditions. In our previous studies, it was confirmed that experimental results of tangential contact force measurement are agree well with Kalker’s rolling contact theory under dry condition with low humidity around contact surfaces. Here, it can be considered that if the ambient humidity around the contact surface become high infinity, the contact surface is under wet lubrication conditions. On the basis of this assumption, in this study, a practical estimation model for characteristics of tangential contact force under running in rainy conditions is proposed by combining the relationship between the adhesive coefficient and velocity measured on running experiments using actual railway vehicles and Kalker’s linear rolling contact theory. Therefore, to verify the proposed model, the tangential contact force measurement experiment using a twin-disk rolling sliding machine was carried out. As a result, it is confirmed that estimated formulae based on the proposed model are well agreed with experimental results even under different velocity conditions, comparing the relationship between tangential contact force coefficient and slip ratio. From these verified results, the proposed model is considered to be a practical wheel/rail tangential contact force model for vehicle dynamics analysis under rain conditions, because the proposed model has the advantage of low calculation cost and can be easily applied to vehicle dynamics analysis based on multi-body dynamics theories.

Swirling bioconvective nanofluid flow from a spinning stretchable disk in a permeable medium

ABSTRACT Medical engineering is increasingly deploying nanotechnology and bio-inspired designs in the 21st century. Motivated by studying the spin coating of bio-nanofluid materials, gyrotactic bioconvection nanofluid swirling coating flow from a spinning disk to an isotropic permeable medium is analysed. The balance equations for mass, momentum, thermal, concentration and microorganism species including blowing effects are transformed into ordinary differential equations and then the solutions are obtained numerically through MATLAB bvp4c quadrature. These solutions are further validated with Adomian decomposition method (ADM). Increasing radial momentum slip reduces the radial skin friction and increasing tangential slip suppresses the tangential skin friction. Nusselt number, nanoparticle Sherwood number and micro-organism density number gradient are, respectively, decreased with increment in thermal slip, nanoparticle mass slip and micro-organism slip factors. Combinations of bioconvection and nanofluids provide excellent advantages in designing anti-bacterial and resilient bio-coatings for many devices.

Analytical approach to estimating the influence of friction slip contact between surrounding rock and concrete lining on mechanical response of deep rheological soft rock tunnels

For a deep-buried tunnel in soft ground, the contact condition between the surrounding rock and lining significantly affects the mechanical response. This is because the slip bond relationship on the contact surface has a direct influence on the tangential slip, resulting in the redistribution of displacement and stress on the contact surface between the surrounding rock and lining. However, previous studies have not paid sufficient attention to this problem, and a well-established method for quantitatively evaluating this influence remains unavailable. Therefore, the influence of the contact behavior between the surrounding rock and lining was examined in this study using an analytical method. First, the concept of friction slip contact and corresponding theoretical equations are proposed based on the real contact behavior between the surrounding rock and lining. Second, considering the friction slip contact between the surrounding rock and lining, a mechanical model of the tunnel excavation-support process was established, and analytical solutions for the stress and displacement of the tunnel within a viscoelastic rock material were realized. Third, the effectiveness and reliability of the proposed solutions were validated. The results could be degenerated to those that do not consider the influence of the mechanical behavior of the contact surface. In addition, there was good agreement between the analytical results and further numerical calculation results. Finally, a comprehensive parametric investigation was conducted, including the influences of the initial release coefficient, friction coefficient, and installation time of the lining. Some useful recommendations for tunnel lining design are provided herein.

Single-asperity failure mechanism driven by morphology and multiaxial loading using molecular dynamics simulation

Single-asperity contact behavior under multiaxial loading is of considerable effect between mechanical contact surfaces. Taking α-Fe as the paradigm material, a single-asperity model under multiaxial loading is established using molecular dynamics (MD) methods. The displacement behavior of the rigid plane, normal loading and asperity radius effects on the failure mechanism are analyzed. The results show that: (i) Normal loading affects the asperity normal deformation state, leading to different failure mechanisms in tangential slip. The failure tends to occur near the contact surface under low normal loading, but inside both the asperity and substrate under high normal loading. (ii) Different asperity radii may cause the asperities to be in different initial deformation states. The failure mode could be judged by combining the normal loading and asperity radius. The results provide detailed description of the asperity failure mechanism and could be applied in the analysis and design of contact interfaces.

Bödewadt flow of non‐Newtonian fluid with single‐walled TiO2 nanotubes suspensions

AbstractThe present study analyzes the boundary layer flow behavior of single‐walled Titania nanotube (SWTNT)–water nanofluid over a rotating disk. The main motivation behind such an investigation is that single‐walled Titania nanotubes (SWTNTs) exhibit significant results due to their extensive applications, low cost, high thermal conductivity, dielectric properties, and photocatalytic activities compared to prevalently existing single‐walled carbon nanotubes. The radial and azimuthal slip conditions are implemented. Fourth order Runge–Kutta method along with the shooting technique is applied to obtain the appropriate numerical solution. The relevant outcomes include the fact that the Casson fluid parameter controls the radial velocity of SWTNT‐water nanofluid and radial and tangential slip parameters exhibit the same trend of radial velocity in the presence of SWTNT in the base fluid. The descending trend of radial velocity is due to a rise in the Casson fluid parameter in the range . The ranges of other parameters influencing the flow behavior are . The non‐Newtonian fluid model helps in controlling the momentum transfer of SWTNT‐water nanofluid. Boundary layer flow of SWTNT‐water nanofluid due to radial stretching is the novelty of our study. The present work may be extended to the Darcy and non‐Darcy medium, which is beyond the scope of our work.

A Simple and Low-Cost Numerical Model for FRP-Masonry Interface Behavior

In recent years, strengthening with Fiber Reinforced Polymers (FRPs) has emerged as an effective way for the structural upgrading of masonry elements. In such typology of external reinforcement, the bond quality is crucial for the increase of the load bearing capacity. The bond efficacy beyond the elastic limit can be studied analytically or numerically via several different models, where the most important issue to tackle is the reproduction of the typical brittle behavior of the substrate. In this paper, a simple numerical approach which models FRP as elastic and lumps all non-linearity on the FRP/masonry interface is proposed. The non-linear behavior of such interface is modeled in a simplified but effective way integrating numerically the differential equations deduced from equilibrium and compatibility (once that a non-linear constitutive relationship between tangential stress and slip is assumed at the interface). Such integration is carried out by means of a particularly simple forward scheme that requires the estimation of the slip value and its derivatives on specific knot points. A comparison against existing literature indicated that the proposed numerical procedure can adequately reproduce global load-displacement curves in standard single lap shear tests, as well predict the local slip behavior.

Hydrodynamics of gas flow in a rotating packed bed under floating motions: Experimental and simulation study

As a typical process intensification device, a rotating packed bed (RPB) is promising for marine gas separation and purification. Previous studies have focused on the gas-phase characteristics of onshore RPBs without the function of floating motions. In this study, the effect of the six degrees of freedom floating motions on the gas-phase characteristics was investigated by experiments and simulation. Compared to the pressure drop under stationary conditions, the pressure drop under floating motions is generally lower and fluctuates. The heave motion causes a significant deviation and oscillation in the pressure drop. The simulation results revealed that the turbulence-enhanced zone (T-E zone) and the turbulence-weakened zone (T-W zone) appeared alternately and caused an evolution of the maldistribution factor. The floating motions enhance or weaken the radial, axial, and tangential slip velocities of the gas phase, which leads to the presence of a T-E/T-W zone and variation of flow direction. The results provided a deep understanding of offshore RPBs performance.

Practical wheel/rail tangential contact force model for vehicle dynamics analysis under running in rainy conditions

This paper describes a practical wheel/rail tangential contact force model for railway dynamics analysis under running in rainy conditions. In our previous studies, it was confirmed that experimental results of tangential contact force measurement are agree well with Kalker’s rolling contact theory under dry condition with low humidity around contact surfaces. Here, it can be considered that if the ambient humidity around the contact surface become high infinity, the contact surface is under wet lubrication conditions. On the basis of this assumption, in this study, a practical estimation technique for characteristics of tangential contact force under running in rainy conditions is proposed by combining the relationship between the adhesive coefficient and velocity measured on running experiments using actual railway vehicles and Kalker’s linear rolling contact theory. Therefore, to verify the proposed technique, the tangential contact force measurement experiment using a twin-disk rolling sliding machine was carried out. As a result, it is confirmed that estimated formulae based on the proposed technique are well agreed with experimental results even under different velocity conditions, comparing the relationship between tangential contact force coefficient and slip ratio. From these verified results, the proposed technique is considered to be a practical wheel/rail tangential contact force model for vehicle dynamics analysis under rain conditions, because the proposed technique has the advantage of low calculation cost and can be easily applied to vehicle dynamics analysis based on multibody dynamics theories.

Analytical Solution of Composite Curved I-Beam considering Tangential Slip under Uniform Distributed Load

An analytical solution of composite curved I-beam considering the partial interaction in tangential direction under uniform distributed load is obtained. Based on the Vlasov curved beam theory, the global balance condition of the problem has been obtained by means of the principle of virtual work; integrating this by parts, the governing system of differential equations and corresponding boundary conditions have been determined. Analytical expressions for the composite beam considering the partial interaction have been developed. In order to verify the validity and the accuracy of this study, the analytical solutions are presented and compared with other three FEM results using the space beam element and the shell element. The deflection and the tangential slip of the composite curved I-beam are investigated.

Asymptotic analysis of initial flow around an impulsively started circular cylinder using a Brinkman penalization method

The initial flow past an impulsively started translating circular cylinder is asymptotically analysed using a Brinkman penalization method on the Navier–Stokes equations. The asymptotic solution obtained shows that the tangential and normal slip velocities on the cylinder surface are of the order of $1/\sqrt {\lambda }$ and $1/\lambda$ , respectively, within the second approximation of the present asymptotic analysis, where $\lambda$ is the penalization parameter. This result agrees with the estimation of Carbou & Fabrie (Adv. Diff. Equ., vol. 8, 2003, pp. 1453–1480). Based on the asymptotic solution, the influence of the penalization parameter $\lambda$ is discussed on the drag coefficient that is calculated using the adopted three formulae. It can then be found that the drag coefficient calculated from the integration of the penalization term exhibits a half-value of the results of Bar-Lev & Yang (J. Fluid Mech., vol. 72, 1975, pp. 625–647) as $\lambda \to \infty$ .

Magnetohydrodynamic flow of viscous fluid and heat transfer analysis between permeable discs: Keller-box solution

In this study, we looked at a two-dimensional constant, laminar, and incompressible viscous flow between two porous discs in the presence of an external magnetic field. The proper similarity transformations simplify the complicated governing problem to nonlinear differential equations with suitable velocity slip and other boundary conditions. The Keller-box method, an efficient finite-difference approach, is used to get its solutions. The purpose of this analysis is to investigate the effect of non-zero tangential slip velocity on velocity, temperature profiles, and shear stress for various relevant parameters. The data is then displayed in tables and graphs to examine velocity and temperature profiles for different flow parameters such as Reynolds number, Hartmann number, Prandtl number, and slip coefficient. In the absence of slip, the results were quite similar to previous findings.