Dissipative Layer Research Articles

A viscoelastic harvester-absorber for energy generation and vibration control

Abstract A vibration energy harvester harnesses the oscillatory movement and
converts it into electrical energy. On the other hand, a (dynamic) vibration absorber
dissipates the mechanical energy of a host structure (primary system). The proposal for
a harvester-absorber device (HAD), comprinsing a piezoelectric element (conventional
harvester) bonded with a viscoelastic layer and a steel constrained layer, is based on the
dual purpose of generating energy and at the same time reducing the vibratory response
of the primary system. Introducing a viscoelastic dissipative layer in a conventional
harvester, also offers the advantage of simultaneously reducing wear on the piezoelectric
element, thereby extending its lifespan and preventing fatigue-related breakage. The
paper presents a model of a harvester-absorber built from a bimorph piezoelectric
beam, a layer of viscoelastic material (E-A-R C1002-01PSA) and a beam of steel, which
acts as a constrained layer. A lumped parameter model is proposed for the theoretical
description of the HAD which is successfully used to experimentally determine its
parameters. After that, and using the equivalent stiffness concept, the HAD was
coupled to a free-free beam with two masses at its ends to study its perfomance over a
real host structure. The inertance of the composite system and voltage/force frequency
response function of the HAD were obtained and compared with experimental results.
The accuracy of the results justifies and validate the model which has the advantage
of simplicity and can contribute to reducing wear and increasing the lifespan of brittle
piezoelectric structures.

An analytical study on the influence of magnetic field-dependent viscosity on viscous and ohmic dissipative second-grade fluid boundary layers

This article aims to investigate the magnetohydrodynamic (MHD) boundary layer flow of a second-grade non-Newtonian fluid over a horizontally stretching sheet, considering magnetic field-dependent (MFD) viscosity, as well as viscous and Ohmic dissipations. Analytical solutions for previously unexplored momentum and heat transfer equations involving MFD viscosity are derived. Two boundary conditions, namely Prescribed Surface Temperature (PST) and Prescribed Heat Flux (PHF), are taken into account. Governing dimensional partial differential equations (PDEs) are transformed into non-dimensional ordinary differential equations (ODEs) using similarity transformations. Closed-form analytical solutions for flow are derived, considering stretching velocity, MFD viscosity, second-grade fluid properties, and suction impacts. Heat transfer equations are transformed into Gauss-hypergeometric form, yielding solutions in terms of confluent hypergeometric functions. Analytical expressions for skin friction, local Nusselt number, and non-dimensional wall temperature are derived. A unique solution is obtained for the flow equation. It is found that both second-grade and magnetic viscosity parameters expand the momentum boundary layer while the magnetic parameter reduces thickness. Thermal boundary layer thickness increases with a higher second-grade parameter, magnetic viscosity, and Eckert number. Moreover, analytical solutions are validated against published results for a special case.

Super-Structured Wet-Adhesive Hydrogel with Ultralow Swelling, Ultrahigh Burst Pressure Tolerance, and Anti-Postoperative Adhesion Properties for Tissue Adhesion.

Wet-adhesive hydrogels have been developed as an attractive strategy for tissue repair. However, achieving simultaneously low swelling and high burst pressure tolerance of wet-adhesive hydrogels is crucial for in vivo application which remains challenges. Herein, a novel super-structured porous hydrogel (denoted as PVA/PAAc-N+ ) is designed via facile moisture-induced phase separation-solvent exchange process for obtaining porous polyvinyl alcohol (PVA) hydrogel as dissipative layer and in situ photocuring technology for entangling quaternary ammonium-functionalized poly(acrylic acid)-based wet-adhesive layer (PAAc-N+ ) with the porous surface of PVA layer. Benefitting from the ionic crosslinking between quaternary ammonium ions and carboxylate ions in PAAc-N+ wet-adhesive layer as well as the high crystallinity induced by abundant hydrogen bonds of PVA layer, the hydrogel has unique ultralow swelling property (0.29) without sacrificing adhesion strength (63.1kPa). The porous structure of PVA facilitates the mechanical interlock at the interface between PAAc-N+ wet-adhesive layer and tough PVA dissipative layer, leading to the ultrahigh burst pressure tolerance up to 493mm Hg and effective repair for porcine heart rupture; the PVA layer surface of PVA/PAAc-N+ hydrogel can prevent postoperative adhesion. By integrating ultralow swelling, ultrahigh burst pressure tolerance, and anti-postoperative adhesion properties, PVA/PAAc-N+ hydrogel shows an appealing application prospect for tissue repair.

Numerical study of dissipative SW/MWCNT-nanofluid coating flow from a stretching wall to a porous medium with shape factor effects

A mathematical model is developed for incompressible steady-state dissipative CNT-aqueous nanofluid boundary layer flow from a stretching sheet to a saturated isotropic porous medium. Three different CNT shapes (spheres, blades and platelets) are considered. Both single-walled (SWCNT) and multi-walled (MWCNT) carbon nanotubes are examined. A Darcy-Brinkman model is adopted for the porous medium and a modified viscous dissipation formulation is considered which features porous media influence in the energy conservation equation. Appropriate expressions are deployed for the CNT-modified nanofluid viscosity, density, specific heat capacity, thermal conductivity and CNT shape factor. Via similarity transformations, the governing conservation equations for mass, momentum and energy with associated boundary conditions are normalized to generate a coupled nonlinear ordinary differential boundary value problem. A numerical solution is presented with the robust MATLAB-based bvp4c method and 4th order Runge-Kutta shooting scheme. Validation with previous studies is included. Velocity, temperature, skin friction and Nusselt number are computed for a range of selected parameters. The computations show that elevation in CNT volume fraction parameter accelerates the boundary layer flow whereas increment in the Darcian (inverse permeability) parameter induces strong deceleration. MWCNTs produce higher velocities than SWCNTs. Temperature and thermal boundary layer thickness are found to be enhanced with increasing Eckert number, Darcian (inverse permeability) parameter, CNT volume fraction and CNT shape factor. Significantly greater temperatures are computed for MWCNTs.

Diffusiophoresis-Driven Stratification in Pressure-Sensitive Adhesive Films from Bimodal Waterborne Colloids.

The uses of pressure-sensitive adhesives (PSAs) are wide ranging, with applications including labels, tapes, and graphics. To achieve good adhesion, a PSA must exhibit a balance of viscous and elastic properties. Previous research has found that a thin, elastic surface layer on top of a softer, dissipative layer resulted in greater tack adhesion compared with the single layers. Superior properties were achieved through a bilayer obtained via successive depositions, which consume energy and time. To achieve a multilayered structure via a single deposition process, we have stratified mixtures of waterborne colloidal polymer particles with two different sizes: large poly(acrylate) adhesive particles (ca. 660 nm in diameter) and small poly(butyl acrylate) (pBA) particles (ca. 100 nm). We used two types of pBA within the particles: either viscoelastic pBA without an added cross-linker or elastic pBA with a fully cross-linked network. Stratified surface layers of deuterium-labeled pBA particles with thicknesses of at least 1 μm were found via elastic recoil detection and qualitatively verified via the analysis of surface topography. The extent of stratification increased with the evaporation rate; films that were dried slowest exhibited no stratification. This result is consistent with a model of diffusiophoresis. When the elastic, cross-linked pBA particles were stratified at the surface, the tack adhesion properties made a transition from brittle failure to tacky. For pBA without an added cross-linker, all adhesives showed fibrillation during debonding, but the extent of fibrillation increased when the films were stratified. These results demonstrate that the PSA structure can be controlled through the processing conditions to achieve enhanced properties. This research will aid the future development of layered or graded single-deposition PSAs with designed adhesive properties.

Tough-interface-enabled stretchable electronics using non-stretchable polymer semiconductors and conductors.

Semiconducting polymer thin films are essential elements of soft electronics for both wearable and biomedical applications1-11. However, high-mobility semiconducting polymers are usually brittle and can be easily fractured under small strains (<10%)12-14. Recently, the improved intrinsic mechanical properties of semiconducting polymer films have been reported through molecular design15-18 and nanoconfinement19. Here we show that engineering the interfacial properties between a semiconducting thin film and a substrate can notably delay microcrack formation in the film. We present a universal design strategy that involves covalently bonding a dissipative interfacial polymer layer, consisting of dynamic non-covalent crosslinks, between a semiconducting thin film and a substrate. This enables high interfacial toughness between the layers, suppression of delamination and delocalization of strain. As a result, crack initiation and propagation are notably delayed to much higher strains. Specifically, the crack-onset strain of a high-mobility semiconducting polymer thin film improved from 30% to 110% strain without any noticeable microcracks. Despite the presence of a large mismatch in strain between the plastic semiconducting thin film and elastic substrate after unloading, the tough interface layer helped maintain bonding and exceptional cyclic durability and robustness. Furthermore, we found that our interfacial layer reduces the mismatch of thermal expansion coefficients between the different layers. This approach can improve the crack-onset strain of various semiconducting polymers, conducting polymers and even metal thin films.

Design, Fabrication, and Characterization of an Impact Dissipative Layer for Fiber-Reinforced Polymer Composites.

This study presents the option of an effective low-impact energy dissipating material applied to GFRP (glass fiber reinforced plastic) composite laminates using auxectic technology in the case of planing hull vessels that use the same high-speed light materials that repeatedly impact the surface of the water when sailing, producing a slamming phenomenon. Research shows that the option to modify the laminate with an auxectic layer protects the laminate from damage. This work proposes the manufacturing of dissipative layers, introduced in laminates made with a polymeric matrix and fiberglass reinforcement, which are evaluated with weight drop tests under different impact energies. The data are collected and processed by a unidirectional gravitometer that gives the acceleration values of the impactor. The tests compare unmodified panels with modified panels, showing that the energy absorbed by the unmodified panel is greater at equal energy levels. The returned energy comparison curve is shown, and the benefits of its use are presented.

Transverse oscillations and damping of magnetic flux tubes with a thick transitional layer

ABSTRACT In this paper, the magnetohydrodynamic kink waves and their damping are investigated in a thin coronal flux tube model. The thickness of the inhomogeneous transitional layer is of the order of the tube’s radius. The governing equations are solved analytically in all regions of the tube except for the thin dissipative layer. The dispersion relation is derived and solved numerically. The oscillation frequency does not vary much when varying the thickness of the transitional layer. When the transitional layer is thin, the damping rate of the kink wave increases significantly with the increase in the thickness of the transitional layer; however, when the transitional layer is thick, the damping rate does not vary much with the increase in the thickness of the transitional layer. For small values of the thickness of the transitional layer, our results are in agreement with results obtained in the thin tube, thin boundary approximation. In flowing tubes, the effect of flow on the damping rate of the waves depends on the direction of the wave propagation and plasma flow. The resonant instability of the kink waves in flux tubes with flowing transitional layer has been investigated.

Adsorption and interaction mechanisms of Chi-g-P(AM-DMDAAC) assisted settling of kaolinite in a two-step flocculation process

Flocculation has been widely employed in treatment of mineral tailings and water management. In this study, a chitosan-graft-poly(acrylamide-dimethyl diallyl ammonium chloride) (Chi-g-P(AM-DMDAAC)) was synthesized in-house. The adsorption and interaction mechanisms of Chi-g-P(AM-DMDAAC) and an anionic polyacrylamide (APAM) in a two-step flocculation process of kaolinite were explored using settlement tests, zeta potential measurement, quartz crystal micro-balance with dissipation (QCM-D) and atomic force microscopy (AFM) technique. The type of primary flocculant was critical for the two-step flocculation process. The treatment of the kaolinite suspension using 1 mg/L of Chi-g-P(AM-DMDAAC) followed by adding 2 mg/L of APAM displayed more efficient flocculation performance. QCM-D results showed that three dissipative layers were assembled on model kaolinite surface after sequentially injecting 3.5 mg/L of Chi-g-P(AM-DMDAAC), 0.05 wt% kaolinite suspension and 2.5 mg/L of APAM. The above total adsorption amount (Δf of −64.9 Hz) was much higher than that of using the two flocculants in reverse order (Δf of −23.1 Hz). This result indicated that the adsorption layer of the positively charged Chi-g-P(AM-DMDAAC) on kaolinite surface provided active adsorption sites for APAM. Further AFM measurement confirmed that the average adhesion between the silicon tip adsorbed Chi-g-P(AM-DMDAAC) and model kaolinite surface in 2.5 mg/L APAM solution increased from 0.25 ± 0.1 nN to 4.2 ± 0.3 nN with the effective interaction range of 700 nm, which was stronger than that measured between a bare silicon tip and silica substrate in single-component-flocculant solutions. The highly efficient two-step flocculation process could be ascribed to the strong electrostatic attraction between the kaolinite and the oppositely charged Chi-g-P(AM-DMDAAC) and APAM. Findings in this study will benefit the development of environmentally friendly flocculant for mineral tailings and water treatment.

Kinetic Alfven Waves Near a Dissipative Layer

AbstractThe spatial structure of kinetic Alfven waves near a dissipative layer is examined. The type of dispersion for kinetic Alfven waves (KAWs) changes inside the dissipative layer: from ”cold,” when the transverse (across the magnetic shells) wavelength is determined by the electron skin depth in plasma, to ”warm” dispersion, when the wavelength is determined by the ion Larmor radius. The characteristic transverse length of a KAW is complex in the dissipative layer, because it decays strongly when interacting with background plasma electrons. The features of phase shifts between the transverse electromagnetic field components of Alfven oscillations are considered. Phase shift can be used to identify the type of Alfven waves observed by satellites in the vicinity of the dissipative layer. The Alfven wave energy absorption in the dissipative layer can lead to the formation of electron fluxes (with electron energies of 2–5 eV) toward the ionosphere and initiate here the stable auroral red (SAR) arcs. An analytical formula is proposed for determining the density of the electron flux toward the ionosphere and the flux of the energy transferred by them.

Analysis of variable magnetic field on chemically dissipative MHD boundary layer flow of Casson fluid over a nonlinearly stretching sheet with slip conditions

ABSTRACT Casson fluid model is a non-Newtonian fluid with yield stress which is widely used for modelling blood flow in narrow arteries. The present study investigates the slip flow analysis on magnetohydrodynamic flow of a Casson fluid over a nonlinearly permeable stretching sheet embedded in a porous medium. The heat transfer equation is modelled with the influences of thermal radiation, viscous dissipation, Joule heating and uniform heat source. Further, the chemically reactive species enriches the study of chemical reaction. Using similarity transformations the governing equations are converted into ordinary differential equations which are solved numerically using shooting technique. The influences of various pertinent parameters are explained through graphs and tables. It is found that suction and injection have opposite effects on velocity profiles. Further, Eckert number enhances the rate of heat transfer but reduces the mass transfer at the bounding surface.

Boundary-layer effects on electromagnetic and acoustic extraordinary transmission through narrow slits.

We study the problem of resonant extraordinary transmission of electromagnetic and acoustic waves through subwavelength slits in an infinite plate, whose thickness is close to a half-multiple of the wavelength. We build on the matched-asymptotics analysis of Holley & Schnitzer (2019 Wave Motion 91, 102381 (doi:10.1016/j.wavemoti.2019.102381)), who considered a single-slit system assuming an idealized formulation where dissipation is neglected and the electromagnetic and acoustic problems are analogous. We here extend that theory to include thin dissipative boundary layers associated with finite conductivity of the plate in the electromagnetic problem and viscous and thermal effects in the acoustic problem, considering both single-slit and slit-array configurations. By considering a distinguished boundary-layer scaling where dissipative and diffractive effects are comparable, we develop accurate analytical approximations that are generally valid near resonance; the electromagnetic-acoustic analogy is preserved up to a single parameter that is provided explicitly for both scenarios. The theory is shown to be in excellent agreement with GHz-microwave and kHz-acoustic experiments in the literature.

Resonant magnetohydrodynamic oscillations in flowing high beta plasmas

The plasma motion in the dissipative layer of a flowing high beta plasma is studied. The linearized magnetohydrodynamic (MHD) equations are used to study the plasma motion. Using the perturbation method presented by Ruderman (2009) the solution of equations of motion are determined. The effect of the plasma flow is to change the distance between the slow and Alfvenic resonant points as well as the thickness of the mixed dissipative layer.

Contact Electrification of Adhesion Films on Flat Panel Displays

Contact electrification of a protective adhesion film on a flat panel display may result in high charge accumulation on an electrically insulating surface affecting production yield and field failures. Tendency for triboelectric charging on planar surfaces was evaluated with the different film structures and different plane materials. Manual separation and constant speed separation techniques were adopted in the experiments. Triboelectrification had random effects that may be difficult to control without electrical conductivity. Electrostatic dissipative properties on the adhesion surface may increase charging of the insulating display. An inherently dissipative layer of the adhesion film significantly mitigated charge accumulation of the film itself.

Marangoni Convection Flow Along a Wavy Surface with Non-Linear Radiation

Abstract A boundary-layer analysis is presented for steady, two-dimensional, Marangoni convection along an irregular surface. Thick radiation limit is considered to express the radiative heat flux. A coordinate transformation is adopted to convert the physical domain into computational domain. Implicit finite difference method is then used to obtain the solutions of the problem. The main purpose of this study is to demonstrate the radiation effects on the dissipative layers. Numerical solutions are presented in the form of skin friction coefficient, heat transfer coefficient, velocity and temperature profiles, streamlines and isotherms. It is observed that thermal radiation has a pronounced effect on the flow field and amplitude of the harmonic oscillations also decay with R d $R_d$ . The momentum and thermal boundary-layer thickness increases as R d $R_d$ gets augmented.

EFFECTIVENESS RESEARCH OF POLYMER FILM-BASED VIBRATION ABSORBERS

The paper describes possibility of a significant improvement in the vibration performance of resonating plates with vibration absorbing coatings or mass-saving resonating vibration absorbers. Vinyl acetate polymer film was used for a dissipative layer in coatings and vibration absorbers.

Ohmic Heating Effect on Magneto Hydrodynamic Marangoni Mixed Convection Boundary Layer Nanofluid Flow

In surface driven flows, dissipative layers which occur along the surface of two immiscible fluids are known as marangoni boundary layers. Mixed connection takes place when buoyancy forces act beside marangoni effect. Consider a nanofluid flow along a flat surface experiencing marangoni convection with ohmic dissipation and magnetic field. Copper and Alumina are the nanoparticles with water as base fluid. The similarity equations are solved numerically by BVP solver ‘bcp4c”. The flow characteristics are analyzed graphically and discussed.

Reflection and Refraction of Solitons by the KdV–Burgers Equation in Nonhomogeneous Dissipative Media

We study the behavior of the soliton that encounters a barrier with dissipation while moving in a nondissipative medium. We use the Korteweg–de Vries–Burgers equation to model this situation. The modeling includes the case of a finite dissipative layer similar to a wave passing through air–glass–air and also a wave passing from a nondissipative layer into a dissipative layer (similar to light passing from air to water). The dissipation predictably reduces the soliton amplitude/velocity. Other effects also occur in the case of a finite barrier in the soliton path: after the wave leaves the dissipative barrier, it retains the soliton form, but a reflection wave arises as small and quasiharmonic oscillations (a breather). The breather propagates faster than the soliton passing through the barrier.

Nonlinear waves in layered media: Solutions of the KdV–Burgers equation

Abstract We use the KdV–Burgers equation to model a behaviour of a soliton which, while moving in non-dissipative medium encounters a barrier with dissipation. The modelling included the case of a finite width dissipative layer as well as a wave passing from a non-dissipative layer into a dissipative one. The dissipation results in reducing the soliton amplitude/velocity, and a reflection and refraction occur at the boundary(s) of a dissipative layer. In the case of a finite width barrier on the soliton path, after the wave leaves the dissipative barrier it retains a soliton form and a reflection wave arises as small and quasi-harmonic oscillations (a breather). The first order approximation in the expansion by the small dissipation parameter is studied.

Lie Group Transformation on MHD Double-Diffusion Convection of a Casson Nanofluid over a Vertical Stretching/Shrinking Surface with Thermal Radiation and Chemical Reaction

This paper is concern with the study of steady magnetohydrodynamic radiative dissipative boundary layer flow of a reactive Casson nanofluid over a permeable vertical nonlinear stretching/shrinking surface. We have incorporated the combined effects of viscous and Ohmic dissipation, thermophoresis and Brownian motion on heat and mass transfer in Casson nanofluid in the presence of chemical reaction. The governing equations are reduced to a system of nonlinear ordinary differential equations with associated boundary conditions using scaling group transformations. The reduced nonlinear ordinary differential equations are then solved numerically by Runge–Kutta–Fehlberg fifth-order method with shooting technique. The effects of magnetic field, suction/injection parameter, Prandtl number, Eckert number, Brownian motion parameter, thermophoresis parameter and Lewis number on local Nusselt number and local Sherwood number are analyzed. The results show that the physical parameters have significant influence on the flow velocity, surface shear stress, local Nusselt number and local Sherwood number.