Effect Of Waviness Research Articles

Flow of liquid films over a single element of structured packing. Comparison of microtextures of various types

The paper deals with the theoretical analysis of viscous liquid films flowing down along a single element of a structured packing with large ribs and microtexture in the form of a wavy two-dimensional surface or three-dimensional surface of the “undulating” type. The effect of inertia forces, surface tension, coarse corrugation, and fine texture geometry on the averaged characteristics of the film flow is considered. New equations for calculating a three-dimensional film flow along a plate with double corrugation structure are obtained. In the calculations, the main attention is paid to the effect of various types of microtextures on film spreading. The type, amplitude, angle of fine texture inclination, and Reynolds number of liquid are varied. It is found that the microtexture of three-dimensional “undulating” type has a small effect on liquid film spreading over a single element of the structured packing; the averaged liquid flow rates along and across large ribs depend weakly on the amplitude and inclination angle of fine texture of this type. It is revealed that only the average film thickness is sensitive to a change in the amplitude of microsurface of the “undulating” type. This is very different from the effect that a wavy two-dimensional microtexture has on film spreading along and across the large ribs. In this case, the effect of waviness on spreading hydrodynamics depends substantially on fine texture amplitude and inclination angle.

Gas-driven thin liquid films: Effect of interfacial shear on the film waviness and convective heat transfer

This study is aimed at experimental investigation of hydrodynamics and convective heat transfer in gravity and gas-driven thin liquid wall films. The liquid film has been annularly applied on a vertically aligned heated tube mounted in a flow channel. In the arranged two-phase flow domain, both the liquid film flow and co-current air flow were thermally and hydrodynamically developing. The Reynolds numbers of liquid and gas flows have been varied between 80−800 and 104−105, respectively. The wall heat flux was kept constant at 15W/cm2. In order to elucidate the effect of the film waviness on the convective heat transfer between the heated wall and the liquid film, the wave frequencies and standard deviations of film thickness have been evaluated by applying high-speed shadowgraphy technique. The wall temperature distribution in streamwise direction has been measured. The experimentally obtained average Nusselt numbers have been compared with the wave frequencies and standard deviations of film thickness. Up to a gas Reynolds number of 4⋅104 and for liquid Reynolds numbers between 80 and 800, the convective heat transfer preliminary depends on the liquid Reynolds number rather than the Reynolds number of the gas flow. For this range, the average Nusselt numbers from the gas-driven film experiments are close to those for falling film flows. At the gas Reynolds numbers starting from 7⋅104, significant heat transfer enhancement with the gas flow has been registered over the full range of liquid Reynolds number.

Strut waviness and load orientation affected fracture toughness knockdown in biaxially woven square lattices

Material imperfection, especially struts waviness attributed to fabrication and service phase, may cause the decay of the fracture resistance of lattice structures. Accordingly, a cautionary step must be taken to ensure the correct fracture properties are employed in the analysis and design of lattices before further utilized in applications. Hence, strut waviness effects on the fracture toughness, KC, of square lattices with respect to numerous loading orientations are of concern in this paper. To examine these effects, square lattices with struts in flat (planar) and biaxially woven configurations are numerically considered. KC is assessed by introducing plane-tension to centrally-cracked lattices for various relative densities (ρ¯ = 0.05, 0.1, 0.15, and 0.2) and loading directions (α = 0°–90°). In all cases, KC of planar lattices are greater than those woven, with as high as 91.7% of performance knockdown in the latter due to the waviness and loading direction effects. In general, KC correlates directly with relative density but inversely with loading direction. KC enhancement is greater in planar lattices compared to those woven when the relative density is increased. Both lattices exhibit anisotropic KC, in which the effects on the planar lattices are more evident. Failure modes of both lattices are found to be independent of relative density but greatly influenced by loading orientations. A shifting in failure mode from plane-tension to plane-shear can be noticed in accordance with the transition angle α = αt as the loading orientation increases.

Fabrication, characterization and micromechanics modeling of the electrical conductivity of reduced graphene oxide/aramid nanofiber nanocomposites

Graphene-based materials with high graphene concentration are of great interest for multifunctional, structural electrode materials that simultaneously store electrical energy and carry structural loads. Graphene-based materials can have a high electrochemically active surface area, high electrical conductivity, and good stiffness and strength. Published analytical studies of electrical conductivity are mostly focused on graphene-based polymer nanocomposites with very low concentrations of conductive fillers, for percolation purposes. In the research reported herein, reduced graphene oxide (rGO) and aramid nanofiber (ANF) nanocomposite films with higher concentrations of rGO, up to 100 wt% rGO, were fabricated and characterized for their electrical conductivity. In addition, a hybrid micromechanical and phenomenological model of electrical conductivity was developed to include the effects of rGO waviness and conductivity, volume fraction of ANF, random orientation of rGO and ANFs, interphase thickness and interphase conductivity. The experimentally measured in-plane conductivity of rGO/ANF nanocomposite films decreases exponentially with the addition of ANFs. For example, the experimental in-plane conductivity of rGO/ANF nanocomposite films was increased 30-fold by decreasing the ANF loading from 25 wt% to 0 wt%. This exponential relationship can be explained by the model proposed. The model showed that the influence of the interphase thickness and interphase conductivity was more significant than that of waviness. The effective in-plane conductivity changed by 20% when the waviness was decreased from maximum observed value to minimum. The effective in-plane conductivity decreased by two orders of magnitude when the interphase thickness was changed from 0 to 0.5 nm and the interphase conductivity was 0.09 S m−1. The model results agreed with the experimental data when the interphase thickness and conductivity vary with the volume fraction of rGO. The addition of ANFs is significant due to the influence it has on the microstructure of the composite and the interphase structure and conductivity. This model can be used for composites with coated fibers or continuous polymeric matrix by adjusting the interphase morphology.

Numerical Investigation of the Effect of Two-Dimensional Surface Waviness on the Current Density of Ion-Selective Membranes for Electrodialysis

Ion-selective membranes are an important component of electrodialysis stacks for desalination. Manufacturing imperfections or slight inhomogeneity of the material can lead to minute membrane surface imperfections. Two-dimensional solutions of the coupled Poisson–Nernst–Planck and Navier–Stokes equations were sought for a perfectly smooth membrane and for membranes with well-defined small-amplitude harmonic surface roughness. The simulations were carried out with the validated rheoEFoam solver by Pimenta and Alves. In the overlimiting regime, the electric field is strong enough for an electrokinetic instability to occur. The instability leads to disturbance growth and the formation of electro-convection cells, which strongly increase the current density. The present simulations show that with an increasing ion concentration and applied voltage, the instability becomes stronger and the overlimiting regime is reached earlier. The limiting current density shows a noticeable dependence on the wavelength of the surface roughness. When the wavelength of the surface roughness is incommensurate with the wavelength of the naturally occurring instability, the limiting current density is increased. Since production membranes will always have some degree of surface roughness, this suggests that membrane surface treatments which favor certain wavelengths may have an effect on the overall membrane performance.

Wavy channels triple-tube LHS unit with sinusoidal variable wavelength in charging/discharging mechanism

A novel wavy channels triple-tube latent heat storage (LHS) unit accompanied by variable wavelength is examined in charging/discharging mechanisms. The LHS triple-tube LHS unit is filled with phase change material (PCM) in the middle tube while water is passed in the inner and outer tubes as the heat transfer fluid (HTF) in opposite directions. Different wavy configurations with variable sinusoidal wavelength and wave amplitude are studied and compared with the smooth channels unit. The performance of the unit is assessed based on the charging/ discharging time and heat storage/recovery rate using different contour plots for the temperature and liquid fraction. The results show the significant effects of channel waviness on the performance of the system. For the best unit, the charging and discharging times reduce by almost 50% and 48%, respectively, compared with the smooth walls LHS system. Moreover, the rates of heat storage and recovery for the best configuration are increased by 100% and 99%, respectively, compared with the LHS unit with no wavy walls. This study also aims to develop the possibility of the practical application of high-performance LHS units using geometry modification.

Effect of Nanocomposite Microstructure on Stochastic Elastic Properties: An Finite Element Analysis Study

Abstract This paper addresses the effect of microstructure uncertainties on elastic properties of nanocomposites using finite element analysis (FEA) simulations. Computer-simulated microstructures were generated to reflect the variability observed in nanocomposite microstructures. The effect of waviness, agglomeration, and orientation of carbon nanotubes (CNTs) were investigated. Generated microstructures were converted to image-based 2D FEA models. Two hundred different realizations of microstructures were generated for each microstructure type to capture the stochastic response. The results confirm previously reported findings and experimental results. The results show that for a given fiber volume fraction, CNTs orientation, waviness, and agglomeration result in different elastic properties. It was shown that while a given microstructural feature will improve the elastic property, it will increase the variability in the elastic properties.

Effects of interphase regions and tunneling distance on the electrical conductivity of polymer carbon nanotubes nanocomposites

In this paper, an analytical model is developed for electrical conductivity of nanocomposites, particularly polymer/carbon nanotubes nanocomposites. This model considers the effects of aspect ratio, concentration, waviness, conductivity and percolation threshold of nanoparticles, interphase thickness, wettability between polymer and filler, tunneling distance between nanoparticles and network fraction on the conductivity. The developed model is confirmed by experimental results and parametric studies. The calculations show good agreement with the experimental data of different samples. The concentration and aspect ratio of nanoparticles directly control the conductivity. Moreover, a smaller distance between nanoparticles increases the conductivity based on the tunneling mechanism. A thick interphase also causes an increased conductivity, because the interphase regions participate in the networks and enhance the effectiveness of nanoparticles.

МОДЕЛЮВАННЯ ГІДРОДИНАМІКИ КОРПУСА СУДНА З УРАХУВАННЯМ БІОЛОГІЧНОГО ЗАБРУДНЕННЯ

The article presents a study of the effect of roughness and waviness (including taking into account bioburden) on the hydrodynamic characteristics of the vessel. To carry out the experiments, a model of the hull of the vessel was developed, which includes the submerged underwater part of the vessel and a special channel in which the flow is modeled. Biological contamination (bio-fouling of the underwater hull) of seaships and river-ships is a problem for all fleets. To maintain the speed of a ship with biological contamination, the hull requires an increase in diesel power by increasing the fuel supply. To maintain the speed of a ship with biological contamination, the requires an increase in diesel power by increasing the fuel supply. It affects the economy and environmental friendliness of maritime transport. The model investigated the change in fluid velocity during flow around a "clean surface" with a roughness of 75, 100, 125 microns. Numerical modeling showed a slight effect of changes in coating roughness for a “clean surface”. Numerical modeling for a surface contaminated with biological contaminants (roughness of 750 micron) revealed a significant effect on the change in fluid velocity along the hull. The developed model can be used when conducting research for a comparative assessment of the energy efficiency of ships.

An approach for modeling non-ageing linear viscoelastic composites with general periodicity

The present work deals with the modeling of non-ageing linear viscoelastic composite materials and quasi-periodic microstructure. The stratified functions and the curvilinear coordinates play an important role in the design of different geometrical shapes. The main objective focuses on the application of two-scales Asymptotic Homogenization Method (AHM) to obtain the overall behavior of the viscoelastic composite materials. Although the whole process is based on the analysis of laminated configurations, a multi-step homogenization scheme to estimate the effective properties of a structure reinforced with long rectangular fibers and wavy effects is used. The associated local problems, the homogenized problem and the analytical expressions for the effective coefficients are obtained by using the correspondence principle and the Laplace-Carson transform. Also, the interconnection between the effective relaxation modulus and the effective creep compliance is performed. Finally, the inversion to the original temporal space is calculated. Some comparisons between the proposed approach and Finite Elements Method (FEM) results are displayed.

Comparative study of biocomposite reinforced with vegetable fiber and based on carbon nanotubes of different corrugated shapes with interphase problem

ABSTRACTIn order to further improve the properties of composite materials, particular attention has been paid to the additional reinforcements. One of the most promising reinforcements is the carbon nanotube “CNT”. Naturally, a double bound between carbon-carbon with an sp2 hybridized orbital in graphene is one of the most rigid of the bonds. The CNTs possess an ideal arrangement of these bonds in a cylindrical structure, which gives them extremely high modulus. For many researchers, it is the ideal reinforcement for new composites. Moreover, the material used in this study will be reinforced by one of the most cultivated vegetable fibers in Algeria, which is date palm fiber. In this study, the elastic modulus of a four-phase material (fiber, gmatrix, CNT, and interphase) is assessed. Firstly, an analytical approach is conducted with emphasizing on the effect of interphase thickness, intragallery enhancement factor and CNT size on nanocomposite elastic modulus. Then, a numerical study showing the effect of CNT waviness and interphase thickness on elastic modulus of the nanocomposite is conducted. The presented results show a significant effect of the abovementioned parameters on the behavior of the nanocomposite. These results give better insights into the real behavior of the nanocomposite and invite researchers to enhance the interfacial bonding of CNT/matrix and to control the undulation of CNT once embedded in a matrix.

The impact of vibration response due to rolling bearing components waviness on the performance of grinding machine spindle system

In this research, an analytical model based on a five-degrees-of-freedom nonlinear dynamical system was utilized to investigate the impact of vibration response due to inner race, outer race, and ball bearing waviness on the performance of grinding machine spindle system supported by two angular ball bearings. The waviness of rolling elements is modeled as a sinusoidal function is incorporated along the inner or outer races of bearing and ball surface. The elastic deflection and nonlinear contact force are calculated based on Hertzian contact model, while the shaft has five-degrees-of-freedom motions, three translational and two angular motions. The five–degrees-of-freedom nonlinear governing equations of the spindle system were developed taking into consideration the effect of outer race, inner race, and ball surface waviness, which are included in the kinematic constraints and force equilibrium equations of a ball. The developed model and its results are validated against results found in literature. Results by this paper indicate that the inner race waviness can significantly distort the tolerance and machining quality of grinding spindle-bearing systems more than does waviness in the outer race and ball elements. This is because the inner race waviness generates more complicated vibrations than the outer race and ball waviness. The most severe vibrations caused by the inner race waviness were found to occur when the waviness was of the order that is equal to multiple of number of balls in a bearing set plus or minus one ([Formula: see text]).

Vibrational characterization of wavy atomic structures of single walled boron nitride nanotubes

This paper illustrates the variation in the natural frequencies of different modes of vibration considering the different types of waviness of the atomic structures of single walled boron nitride nanotubes (SWBNNTs), i.e., sinusoidal, elliptical and parabolic. The waviness present in the atomic structures of SWBNNTs causes a variation in the localized stiffness in waviness regions, thereby affecting the natural frequency of the SWBNNTs. Thus, it is important to understand the effects of the different types of possible waviness present in the atomic structures of SWBNNTs on their natural frequency. A vibrational analysis was performed for the bridged configuration (with both ends fixed) of SWBNNTs. Continuum modelling based analytical and finite element method (FEM) simulation approaches were used to estimate the natural frequencies of SWBNNTs with different types of wavy curvatures. The FEM approach reflects the shear deformation on the natural frequency of wavy nanotubes, whereas inclusion of shear deformation in the analytical approach adds complexity to the model, which requires more computational time for analysis. The obtained results indicate that the sinusoidal curvature of wavy atomic structures of SWBNNTs is more sensitive compared to the parabolic and elliptical curvatures of wavy nanotubes. Mode shape analysis is also found to be useful for estimating the type of curvature in the atomic structures of the nanotube. As presented herein, understanding the effect of waviness on the variation in the natural frequency of the wavy atomic structure of SWBNNTs is found to be useful for the practical realization of wavy atomic structure based nano-mechanical resonators for applications such as in sensor systems on the nano-scale level.

A Simulation Study on the Effects of Race Surface Waviness on Cage Dynamics in High-Speed Ball Bearings

The effects of the race surface waviness on the cage dynamics, including cage slip ratios, cage instabilities, and time-averaged cage wear rates, in high-speed ball bearings are investigated. A dynamic model of high-speed ball bearings considering the cage effect and the race surface waviness is proposed. Based on the proposed dynamic model, the effects of the maximum wave amplitude (MWA) and the wave order (WO) of race surface waviness on cage slip ratio, cage instability, and time-averaged cage wear rate are investigated. The results show that the race surface waviness has a great effect on the cage dynamics. The waviness would increase the random impacts between balls and cage pockets and thus cause more instable motion of the cage. Although the ball skidding and the cage slip ratio decrease with the increase of MWA, the cage instability and the cage wear rate become severe when MWA increases. In addition, the effect of WO on cage dynamics is nonlinear. The current investigation could provide a theoretical tool for an in-depth understanding of the dynamics in a high-speed ball bearing.

Effects of raceway waviness on dynamic behaviors of deep groove ball bearing

Deep groove ball bearings (DGBB) are widely applied in the supporting structure of a variety of rotating machineries. A high rotating accuracy should be maintained for a more stable rotor system, which requires a carefully designed DGBB. For a designing purpose, dynamic behaviors of the DGBB under different structural parameters need to be investigated. Its dynamic responses are essentially excited by the contact forces induced by external loads. Besides the relative displacement between the inner- and the outer-raceway, and the clearance, ring waviness is the major factor that affects the values of the contact forces and the deformations of different rolling elements. Therefore, the control of ring waviness order and its corresponding amplitude is of great significance for the design of a high-precision DGBB and moreover a rotor system with high rotating accuracy. In this work, the effects of different waviness order and waviness amplitude are investigated to study the dynamic behavior of a DGBB under different waviness parameter.

Effect of carbon nanotube waviness on smart damping of geometrically nonlinear vibrations of fuzzy-fiber reinforced composite plates

In this article, we present a finite element model for the three-dimensional analysis of smart constrained layer damping of geometrically nonlinear vibrations of laminated fuzzy-fiber reinforced composite plates. The three-dimensional fractional derivative constitutive relation is implemented for the viscoelastic layer. The constraining layer of the smart constrained layer damping treatment is composed of the vertically/obliquely reinforced 1–3 piezoelectric composites. The von Kármán–type nonlinear strain–displacement relations are used to incorporate the geometric nonlinearity in the model. The main aim of this article is to numerically investigate the effect of carbon nanotube waviness on the nonlinear smart damping. Several thin laminated substrate fuzzy-fiber reinforced composite plates with straight carbon nanotubes and wavy carbon nanotubes with different waviness in different planes are considered with various boundary conditions and stacking sequences to numerically compute their effect on smart damping. The performance of the obliquely reinforced 1–3 piezoelectric composites is discussed and the efficacy of the present smart finite element model in terms of active control authority is also presented.

A Model of Mixed Lubrication Based on Non-Normalized Discretization and Its Application for Multilayered Materials

This study presents a generalized model of mixed elastohydrodynamic lubrication, in which the dimensional Reynolds equation is discretized according to a modified differential scheme based on the full analysis of the pressure balance within the lubrication region. The model is capable of a wide range of lubrication regimes from fully hydrodynamic down to boundary lubrication, and both the steady-state and the time-dependent conditions can be considered. A simplified computational procedure is proposed for elliptical contacts without the ellipticity parameters specified. The evolution of lubrication behavior at startup and shutdown conditions is investigated and the transient effect of surface waviness is discussed. The model application is then extended to contacts of multilayered materials, and the effects of the layer stiffness and the fabrication methods on the stress fields and lubrication performance are analyzed. The conclusions may potentially provide some insightful information for the design and analysis of functional materials and their engineering structures.

Melting and solidification characteristics of a double-pipe latent heat storage system with sinusoidal wavy channels embedded in a porous medium

The aim of this investigation is to explore the combined effects of porous medium and surface waviness on the melting and solidification of PCM inside a vertical double-pipe latent heat storage (LHTES) system. The results are compared with the cases of smooth channels and pure PCM. In the system, water is passed through the inner tube while composite PCM is placed in the annulus side. Different effective parameters including wavelength and wave amplitude of the sinusoidal wavy channels, porosity and pore size of the porous structure, Reynolds number and inlet temperature of water are examined to find the optimum geometric as well as operating conditions in both melting/solidification processes. The results show that utilizing both the high conductive porous structure and wavy channel reduces the melting/solidification times significantly. For the best case, the melting and solidification times of PCM reduce by 91.4% and 96.7%, respectively, compared with the smooth channels pure PCM system. The average rate of transferred heat for the wavy channel composite PCM are 10.4 and 18.9 times that for the smooth channel pure PCM case. Comparing with the pure PCM system, the presence of copper foam reduces the effect of channel waviness significantly for both melting/solidification processes.

Effect of Surface Waviness on Stability of Hydrodynamic Journal Bearing Systems

Effect of Surface Waviness on Stability of Hydrodynamic Journal Bearing Systems

Effects of Fiber Waviness and Misalignment of Reinforcing Fiber on Deformation Strength in Rubber-Composite Material

Effects of Fiber Waviness and Misalignment of Reinforcing Fiber on Deformation Strength in Rubber-Composite Material