Dissipative Layer Research Articles

Finite element computation of transient dissipative double diffusive magneto-convective nanofluid flow from a rotating vertical porous surface in porous media

This article aimed to investigate the transient dissipative magnetohydrodynamic double diffusive free convective boundary layer flow of electrically conducting nanofluids from a stationary or moving vertical porous surface in a rotating high permeability porous medium, considering buoyancy, thermal radiation and first-order chemical reaction. Thermo-diffusion (Soret) and diffuso-thermo (Dufour) effects are also considered. Darcy’s law is employed. The mathematical model is formulated by considering water-based nanofluids containing metallic nano-particles for both stationary and moving plate cases. Three nanofluids are examined, namely copper, aluminium oxide or titanium oxide in water. The transformed non-linear, coupled, dimensionless partial differential equations describing the flow are solved with physically appropriate boundary conditions using Galerkin weighted residual scheme. For prescribed permeability, numerical results are presented graphically for the influence of a number of emerging parameters. Validation of finite element solutions for skin friction and Nusselt number is achieved via comparison with the previously published work as special cases of the present investigation and very good correlation obtained. Increasing rotational parameter is observed to reduce both primary and secondary velocity components. Primary and secondary velocities are consistently elevated with increasing Soret, Dufour, thermal Grashof and solutal Grashof numbers. Increasing Schmidt number, chemical reaction and suction parameter both suppress nano-particle concentration whereas the converse behavior is computed with increasing Soret number. The study is relevant to high-temperature rotating chemical engineering systems exploiting magnetized nanofluids and also electromagnetic nanomaterial manufacturing processes.

Dispersion and Attenuation of Guided Waves in Tubular Section with Multi-Layered Viscoelastic Coating — Part II: Circumferential Wave Propagation

In the second part of the study on guided wave motions in a hollow cylinder with epoxy layers, shear and longitudinal modes propagating in the circumferential direction are investigated. The corresponding dispersion and attenuation characteristic equations are derived by incorporating a complex, frequency-dependent constitutive law for the viscoelastic coating material. Continuous displacement boundary conditions are implemented to model perfect interfacial bonds between the tubular section and applied epoxy coatings. The presence of thin dissipative viscoelastic layers has profound impact on the propagation of both the circumferential shear and longitudinal waves. The number of admissible propagating modes increases with increasing number of viscoelastic layers and higher order modes dissipate significantly less at high frequencies than the lower order modes at low frequencies. Over the frequency range considered, all the circumferential propagating modes are significantly more attenuating than their axial propagating counterparts studied in Part 1 of the paper. Generation of the lowest shear wave mode is suppressed at approximately 0.2 MHz in the coated tubular. However, no such definitive cutoff frequencies are observed for the longitudinal modes regardless of how many viscoelastic layers are considered.

Internal dissipative boundary layers in the cross-equatorial flow of a grounded deep western boundary current

It is known that dissipative adjustment must occur in the cross-equatorial dynamics of a deep western boundary current (DWBC) that is in planetary-geostrophic balance away from the equator. Theoretical modelling and numerical simulations suggest that the dissipative zones correspond to “small” isolated zonally-elongated regions within the trough and crest of a nonlinear stationary equatorial planetary wave that is formed as the DWBC flows eastward along the equator. An internal frictional boundary layer theory is advanced to describe the leading order structure of the DWBC in the dissipative regions, which asymptotically matches with the large scale inviscid flow characteristics in the equatorial region.

Multiple slow waves in metaporous layers for broadband sound absorption

Sound absorption for a broad frequency range requires sound dissipation. The mechanics of acoustic metamaterials for non-dissipative applications has been extensively studied, but sound absorption using dissipative porous metamaterials has been less explored because of the complexity resulting from the coupling of its dissipative mechanism and metamaterial behavior. We investigated broadband sound absorption by engineering dissipative metaporous layers, which absorb sound by the mechanism of multiple slow waves, and combined local and global resonance phenomena. A set of rigid partitions of varying lengths was elaborately inserted in a hard-backed porous layer of a finite thickness. An effective medium theory was used to explain the physics involved; high performance at a low-frequency range was found to be mainly due to the formation of global resonances caused by multiple slow waves over the thickness of the metaporous layer, while enhancement at a high-frequency range was attributed to the combined effects of the global resonances and the local resonances directly related to the sizes of the inserted partitions.

Deposition Kinetics of Bioinspired Phenolic Coatings on Titanium Surfaces.

Polyphenols can form functional coatings on a variety of different materials through auto-oxidative surface polymerization in a manner similar to polydopamine coatings. However, the mechanisms behind the coating deposition are poorly understood. We report the coating deposition kinetics of the polyphenol tannic acid (TA) and the simple phenolic compound pyrogallol (PG) on titanium surfaces. The coating deposition was followed in real time over a period of 24 h using a quartz crystal microbalance with dissipation monitoring (QCM-D). TA coatings revealed a multiphasic layer formation: the deposition of an initial rigid layer was followed by the buildup of an increasingly dissipative layer, before mass adsorption stopped after approximately 5 h of coating time. The PG deposition was biphasic, starting with the adsorption of a nonrigid viscoelastic layer which was followed by layer stiffening upon further mass adsorption. Coating evaluation by ellipsometry and AFM confirmed the deposition kinetics determined by QCM-D and revealed maximum coating thicknesses of approximately 50 and 75 nm for TA and PG, respectively. Chemical characterization of the coatings and polymerized polyphenol particles indicated the involvement of both physical and chemical interactions in the auto-oxidation reactions.

A study of sodium oleate adsorption on Ca2 + activated quartz surface using quartz crystal microbalance with dissipation

The adsorption kinetics, density and structural property of sodium oleate on Ca2+ activated quartz surface have been studied using the techniques of quartz crystal microbalance with dissipation (QCM-D) and atomic force microscope (AFM). The real-time measurements of frequency (Δf) and dissipation shifts (ΔD) with SiO2 coated sensor have revealed the changes in surface property of the quartz during the entire activation and adsorption process at different Ca2+ concentrations and pH's. An activation layer with an adsorption density of 89ng/cm2 was observed at pH=12.0. Since pseudo-first-order model fitted well with adsorption process of sodium oleate, the mass transfer (diffusion-controlled) was the rate determining step at pH12.0. Therefore, the reactions of RCOO−/(RCOO)22− and Ca(OH)+/Ca2+ is considered to be the dominant process in the solution at pH12.0 which generated (RCOO)2Ca precipitation and formed poorly-organized dissipative adsorption layer on activated quartz surface. Two distinct adsorption stages were identified from the different slopes K2>K3 and K3≤0.2 of ΔD−Δf plots which demonstrated the existence of conformational changes in the adsorption layer.

Facile one-step fabrication of 2-layered and 4-quadrant type phosphor-in-glass plates for white LEDs: an insight into angle dependent luminescence

Phosphor-in-glass (PiG) when used in combination with a blue light emitting diode (LED) chip in a remote phosphor configuration offers precise tuning and yields higher luminous efficiencies at elevated temperatures, compared to the conventional conformal LED packaging. However, drawbacks such as spectral overlapping of the constituent phosphors and resultant reabsorption remain unresolved in multi phosphor color conversion plates. These issues were solved up to a desired extent by arranging different color-emitting PiGs, via cutting and reassembly. However, the interface of the multicolored plates acted as a dissipative layer. In this work, a novel fabrication technique was proposed to overcome this drawback by eliminating the interfacial layer through a one-step process. PiGs were fabricated using glass frits at a low softening temperature of 600 °C. As a result, a higher efficacy of the studied prototypes, i.e., a horizontal 2-layered PiG and a 4-quadrant PiG, was obtained as compared with their counterparts. The angular dependency of the luminescence of the segmented 4-quadrant type PiG was studied, and the results were discussed.

Ionic strength dependent vesicle adsorption and phase behavior of anionic phospholipids on a gold substrate.

The authors report on the effect of ionic strength on the formation of supported vesicle layers of anionic phospholipids 1,2-dimyristoyl-sn-glycero-3-phospho-rac-glycerol (DMPG) and dimyristoylphosphatidylserine (DMPS) onto gold. Using quartz crystal microbalance with dissipation monitoring the authors show that vesicle adsorption is mainly governed by NaCl concentration, reflecting the importance of electrostatic interactions in anionic lipids, as compared to zwitterionic 1,2-dimyristoyl-sn-glycero-3-phosphocholine. At low ionic strength, low or no adsorption is observed as a result of vesicle-vesicle electrostatic repulsion. At medium ionic strength, the negative charges of DMPG and DMPS are screened resulting in larger adsorption and a highly dissipative intact vesicle layer. In addition, DMPS exhibits a peculiar behavior at high ionic strength that depends on the temperature of the process.

Predicting the Dynamic Response of Friction Dissipative Foundations Using a Modified Newmark Model

This paper analyses the dynamic behaviour of a seismic isolation technology adopted for the foundations of the towers of two recent long-span bridges, consisting of a dissipative layer of granular soil placed at the contact of the foundation caisson with a group of foundation piles. The fundamental aspects of this isolation device is studied through a three-dimensional modified Newmark model that accounts for the multi-directionality of the seismic motion and includes a simplified description of the dynamic response of the superstructure. This simplified model is expressed in a rigorous non-dimensional formulation and is validated against the results of three-dimensional dynamic analysis of the soil-structure interaction for a specific case of a suspension bridge. Taking advantage of the non-dimensional formulation of the simplified dynamic model, a parametric study of general validity is carried out, that highlights the most significant factors influencing the performance of the dissipative device.

In situ kinetics and conformation studies of dodecylamine adsorption onto zinc sulfide using a quartz crystal microbalance with dissipation (QCM-D)

Abstract The adsorption behavior and kinetics of dodecylamine onto zinc sulfide (ZnS) coated quartz crystal sensor (referred to as ZnS sensor hereafter) were investigated using quartz crystal microbalance with dissipation (QCM-D). The QCM-D data showed that the adsorption interactions, conformations and kinetics were critically dependent on the species distribution of dodecylamine in the solution. When the dodecylamine was primarily ion form or molecular form in the solution, the dodecylamine was adsorbed to a lesser extent, forming a thick and rigid adsorption layer without any change in conformation. Meanwhile, the pseudo-second order provided the best fit to the adsorption process. With an increase in pH and concentration, the micelle, or precipitation, of dodecylamine became the dominant species in the solution. The micelle of dodecylamine was adsorbed faster and in larger amounts onto the ZnS sensor, with two distinguishable adsorption stages: the first stage, characterized by a dissipative adsorption layer; and the second stage, which had a more compact adsorption layer. The initial stage was best fitted by the pseudo-first order model and the second stage was best fitted by the Elovich model. The pseudo-second order and Elovich model fittings demonstrated that the interactions between the adsorbed layer and the ZnS sensor involved chemisorption. The morphology of the adsorbed layer was also examined using AFM. AFM imaging of the adsorbed layer illustrated that the adsorption of dodecylamine onto the ZnS sensor was heterogeneous, and that the dodecylamine aggregated and scattered on the ZnS sensor, resulting in the formation of discrete surface agglomerations.

Surface participation and dielectric loss in superconducting qubits

We study the energy relaxation times (T1) of superconducting transmon qubits in 3D cavities as a function of dielectric participation ratios of material surfaces. This surface participation ratio, representing the fraction of electric field energy stored in a dissipative surface layer, is computed by a two-step finite-element simulation and experimentally varied by qubit geometry. With a clean electromagnetic environment and suppressed non-equilibrium quasiparticle density, we find an approximately proportional relation between the transmon relaxation rates and surface participation ratios. These results suggest dielectric dissipation arising from material interfaces is the major limiting factor for the T1 of transmons in 3D circuit quantum electrodynamics architecture. Our analysis also supports the notion of spatial discreteness of surface dielectric dissipation.

Design of metaporous supercells by genetic algorithm for absorption optimization on a wide frequency band

The optimization of acoustic absorption by metaporous materials made of complex unit cells with 2D resonant inclusions is realized using genetic algorithm. A nearly total absorption over a wide frequency band can be obtained for thin structures, even for frequencies below the quarter wavelength resonances i.e., in a sub-wavelength regime. The high absorption performances of this material are due to the interplay of usual visco-thermal losses, local resonances and trapped modes. The density of resonant and trapped modes in this dissipative porous layer, is a key parameter for broadband absorption. The best configurations and critical coupling conditions are found by genetic algorithm optimization. Several types of resonators are included gradually in the studied configurations (split-rings, Helmholtz resonators, back cavities) with increasing complexity. The optimization leads to a metaporous structure with a 2-cm sub-wavelength layer thickness, exhibiting a nearly total absorption between 1800Hz and 7000Hz. The influence of the incidence angle on the absorption properties is also shown.

Modeling nonlinear wave–wave interactions with the elliptic mild slope equation

An approach is developed to simulate wave–wave interactions using nonlinear elliptic mild-slope equation in domains where wave reflection, refraction, diffraction and breaking effects must also be considered. This involves the construction of an efficient solution procedure including effective boundary treatment, modification of the nonlinear equation to resolve convergence issues, and validation of the overall approach. For solving the second-order boundary-value problem, the Alternating Direction Implicit (ADI) scheme is employed, and the use of approximate boundary conditions is supplemented, for improved accuracy, with internal wave generation method and dissipative sponge layers. The performance of the nonlinear model is investigated for a range of practical wave conditions involving reflection, diffraction and shoaling in the presence of nonlinear wave–wave interactions. In addition, the transformation of a wave spectrum due to nonlinear shoaling and breaking, and nonlinear resonance inside a rectangular harbor are simulated. Numerical calculations are compared with the results from other relevant nonlinear models and experimental data available in literature. Results show that the approach developed here performs reasonably well, and has thus improved the applicability of this class of wave transformation models.

Analytical study of MHD free convective, dissipative boundary layer flow past a porous vertical surface in the presence of thermal radiation, chemical reaction and constant suction

An analytical solution of MHD free convective, dissipative boundary layer flow past a vertical porous surface in the presence of thermal radiation, chemical reaction and constant suction, under the influence of uniform magnetic field which is applied normal to the surface is studied. The governing equations are solved analytically using a regular perturbation technique. The expressions for velocity, temperature and concentration fields are obtained. With the aid of these, the expressions for the coefficient of skin friction, the rate of heat transfer in the form of Nusselt number and the rate of mass transfer in the form of Sherwood number are derived. Finally the effects of various physical parameters of the flow quantities are studied with the help of graphs and tables. It is observed that the velocity and concentration increase during a generative reaction and decrease in a destructive reaction. The same observed to be true for the behavior of the fluid temperature. The presence of magnetic field and radiation diminishes the velocity and also the temperature.

Coulomb collision effects on linear Landau damping

Coulomb collisions at rate ν produce slightly probabilistic rather than fully deterministic charged particle trajectories in weakly collisional plasmas. Their diffusive velocity scattering effects on the response to a wave yield an effective collision rate νeff ≫ ν and a narrow dissipative boundary layer for particles with velocities near the wave phase velocity. These dissipative effects produce temporal irreversibility for times t ≳ 1/νeff during Landau damping of a small amplitude Langmuir wave.

Similarity Solutions of Marangoni Convection Boundary Layer Flow with Gravity and External Pressure

This study is focused on a steady dissipative layer, which is generated by Marangoni convection flow over the surface resulted from an imposed temperature gradient, coupled with buoyancy effects due to gravity and external pressure. A model is proposed with Marangoni condition in the boundary conditions at the interface. The similarity equations are determined and approximate analytical solutions are obtained by an efficient transformation, asymptotic expansion and Padé approximant technique. For the cases that buoyancy force is favorable or unfavorable to Marangoni flow, the features of flow and temperature fields are investigated in terms of Marangoni mixed convection parameter and Prantl number.

Three-layer in-plane dynamical track model for metro applications

In the study a linear dynamical model suitable for metroapplications is constructed and analysed in the framework of the Winkler-foundation theory. The metro track is allocated within the inner space of the tube of big diameter. The tube is considered as a beam on elastic and damped foundation. The track itself consists also of two elastically supported beams, namely the basement beam made of steel-reinforced concrete is situated at the bottom of the tube and connected to the lower-inner surface of the tube by an elastic and dissipative "carpet-pad". The concrete beam supports the rails through an elastic and dissipative layer. The wheel loads acting on the rails are moving horizontally along the track. The set of partial dierential equations describing the vertical motion of the three-layer dynamical system is composed and the method of solution in the case of travelling wheel loads is elaborated.

Rheology of bubble suspensions using dissipative particle dynamics. Part I: A hard-core DPD particle model for gas bubbles

In this paper, the rheology of dilute bubble suspensions is studied using dissipative particle dynamics (DPD). Each gas bubble is modeled by a hard-core DPD particle. The approach addresses the issue of zero-viscosity arising from modeling of a gas bubble by a set of DPD particles. Moreover, it helps to reduce significantly the computational demand due to a much less number of DPD particles required in the simulation. A dissipative layer is created outside the effective region of the hard-core DPD particle to manage the hydrodynamic force acting on it, and different phases can be defined accordingly. The model is further examined in the simulation of dilute bubble suspensions, and measurements on the Newtonian viscosity for the volume fraction less than 15% are consistent with experimental results and results from theoretical models in continuum mechanics at low Ca limit.

A combined finite element/parabolic equation formulation for acoustic wave propagation over and within a rigid porous ground

This paper describes a finite-element (FEM) marching scheme for a standard wide-angle parabolic equation (PE) formulation for calculating the sound fields over and within a rigid porous ground. The study has an application for exploring the effect of snow cover on the propagation of horizontal acoustic waves under refractive atmospheric conditions. Instead of using the standard Crank Nicholson method to solve for the finite difference marching scheme, a FEM discretization approach has been advocated in the present study. By using this approach, the boundary conditions, i.e., the continuity of acoustic pressure and velocity, can be incorporated directly at the air/ground and ground/ground interfaces that facilitates the simultaneous calculations of the sound fields over and within the rigid porous ground. The FEM/PE formulation yields a complete set of information on the acoustic pressure and its spatial derivatives at any receiver locations. In addition, the perfectly matched layer (PML) technique has been adopted that simulates a dissipative layer especially designed to absorb sound waves without reflections from the uppermost layers. Numerical simulations have confirmed that the application of such impedance-matched PML has efficiently eliminated reflections and reduced the overall computational time.

Power generation in thermochemical and electrochemical systems – A thermodynamic theory

In this paper power limits and other performance indicators are investigated in various power generation systems with downgrading or upgrading of resources. Energy flux (power) is created in a power generator located between a resource fluid (‘upper’ fluid 1) and the environmental fluid (‘lower’ fluid, 2). Transfer phenomena, fluid properties and conductance values of dissipative layers or conductors influence the rate of power yield. While temperatures Ti of participating media are only necessary variables to describe purely thermal systems, in the present work both temperatures and chemical potentials μk are essential. This case is associated with engines propelled by fluxes of both energy and substance (chemical and electrochemical engines).Optimization methods are applied to determine power generation limits which are important performance indicators for various energy converters, such as thermal, solar, chemical, and electrochemical engines. Methodological similarity is shown when analysing power limits in thermal machines and fuel cells. Numerical approaches are based on the methods of dynamic programing (DP) or Pontryagin’s maximum principle. In view of the limitation of DP to systems with low dimensionality of state vector, we focus here on the Pontryagin’s method, which involves discrete canonical algorithms derived from the process Hamiltonian. Some new or relatively unknown properties of these algorithms are described in the context of their application to power systems.In fuel cells and other electrochemical systems downgrading or upgrading of resources may also occur. However, we restrict here to the steady-state fuel cells. An approximate (topology-ignoring) analysis shows that, in linear systems, only at most 1/4 of power dissipated in the natural transfer process can be transformed into mechanical or electric power. This indicator may be viewed as a new form of the second law efficiency. The relevant experimental data obtained at the institute of Power Engineering are also presented in this paper.