Total Dissipation Research Articles

Assessment of subgrid-scale modeling for large-eddy simulation of a spatially-evolving compressible turbulent boundary layer

Abstract The performance of three standard subgrid-scale (SGS) models, namely the wall-adapting local eddy-viscosity (WALE) model, the Dynamic Smagorinsky model (DSM) and the Coherent Structures model (CSM), are investigated in the case of a spatially-evolving supersonic turbulent boundary layer (STBL) over a flat plate at M ∞ = 2 and Reθ ≈ 2600. A high-order split-centered scheme is used to discretize the convective fluxes of the Navier–Stokes equations, and is found to be highly effective to overcome the dissipative character of the standard shock-capturing WENO scheme. The consistency and the accuracy of the simulations are evaluated using direct numerical simulations taken from the literature. It is demonstrated that all SGS models require a comparable minimum grid refinement in order to capture accurately the near-wall turbulence. Overall, the models exhibit correct behavior when predicting the dynamic properties, but show different performances for the temperature distribution in the near-wall region even for cases with satisfactory energy resolution of more than 80%. For a well-resolved LES, the SGS dissipation due to the fluctuating velocity gradients is found to dominate the total SGS dissipation.

Shock finding on a moving-mesh – II. Hydrodynamic shocks in the Illustris universe

Hydrodynamical shocks are a manifestation of the non-linearity of the Euler equations and play a fundamental role in cosmological gas dynamics. In this work, we identify and analyse shocks in the Illustris simulation, and contrast the results with those of non-radiative runs. We show that simulations with more comprehensive physical models of galaxy formation pose new challenges for shock finding algorithms due to radiative cooling and star-forming processes, prompting us to develop a number of methodology improvements. We find in Illustris a total shock surface area which is about 1.4 times larger at the present epoch compared to non-radiative runs, and an energy dissipation rate at shocks which is higher by a factor of around 7. Remarkably, shocks with Mach numbers above and below $\mathcal{M}\approx10$ contribute about equally to the total dissipation across cosmic time. This is in sharp contrast to non-radiative simulations, and we demonstrate that a large part of the difference arises due to strong black hole radio-mode feedback in Illustris. We also provide an overview of the large diversity of shock morphologies, which includes complex networks of halo-internal shocks, shocks on to cosmic sheets, feedback shocks due to black holes and galactic winds, as well as ubiquitous accretion shocks. In high redshift systems more massive than $10^{12}\,\mathrm{M}_\odot$ we discover the existence of a double accretion shock pattern in haloes. They are created when gas streams along filaments without being shocked at the outer accretion shock, but then forms a second, roughly spherical accretion shock further inside.

Arbuscular Mycorrhizal Fungal Hyphae Alter Soil Bacterial Community and Enhance Polychlorinated Biphenyls Dissipation

We investigated the role of arbuscular mycorrhizal fungal (AMF) hyphae in alternation of soil microbial community and Aroclor 1242 dissipation. A two-compartment rhizobox system with double nylon meshes in the central was employed to exclude the influence of Cucurbita pepo L. root exudates on hyphal compartment soil. To assess the quantitative effect of AMF hyphae on soil microbial community, we separated the hyphal compartment soil into four horizontal layers from the central mesh to outer wall (e.g., L1–L4). Soil total PCBs dissipation rates ranged from 35.67% of L4 layer to 57.39% of L1 layer in AMF inoculated treatment, which were significant higher than the 17.31% of the control (P < 0.05). The dissipation rates of tri-, tetrachlorinated biphenyls as well as the total PCBs were significantly correlated with soil hyphal length (P < 0.01). Real-time quantitative PCR results indicated that the Rhodococcus-like bphC gene was 2–3 orders of magnitude more than that of Pseudomonas-like bphC gene, and was found responded positively to AMF. Phylogenetic analyses of the 16S rDNA sequenced by the Illumina Miseq sequencing platform indicated that AMF hyphae altered bacterial community compositions. The phylum Betaproteobacteria and Actinobacteria were dominated in the soil, while Burkholderiales and Actinomycetales were dominated at the order level. Taxa from the Comamonadaceae responded positively to AMF and trichlorinated biphenyl dissipation, while taxa from the Oxalobacteraceae and Streptomycetaceae responded negatively to AMF and PCB congener dissipation. Our results suggested that the AMF hyphal exudates as well as the hyphae per se did have quantitative effects on shaping soil microbial community, and could modify the PCBs dissipation processes consequently.

Force-based dynamic contact angle measurements in liquid-liquid-solid systems

Under flow conditions, the dynamic contact angle replaces the equilibrium contact angle. Correlation of dynamic contact angles as a function of the capillary number in liquid-liquid-solid systems is important in a number of applications. For instance, it is one of the ways used to predict water penetration into an oil-filled porous medium. The Cahn-Thermo device is used to measure the excess force needed to plunge a plate vertically into a liquid-liquid interface or pull it out. This force is used to calculate the dynamic contact angle. Polydimethylsiloxane (PDMS) with different viscosities were used for the upper phase and water for the lower phase (viscosity ratios of 95–485). An algebraic expression that predicts the dynamic contact angles has been derived using the concept that the total viscous dissipation is equal to the surface work in the contact line region. This result, together with a result based on a regular hydrodynamic theory, was compared to the experiments on the advancing dynamic contact angles. The advancing dynamic contact angles measured were from 90° to 105°, agreed with the theory and one adjustable parameter related to the ratio of microscopic to the macroscopic length scale that is recovered is found to depend inversely on the viscosity ratio. The parameter itself varies from 2 to 70. The receding contact angles showed significant scatter. A closer photographic examination showed the meniscus to be unstable.

Efficiency fluctuations of small machines with unknown losses.

The efficiency statistics of a small thermodynamic machine has been recently investigated assuming that the total dissipation is a linear combination of two currents: the input and output currents. Here, we relax this standard assumption and consider the question of the efficiency fluctuations for a machine involving three different currents, first in full generality and second for two different examples. Since the third current may not be measurable and/or may decrease the machine efficiency, our motivation is to study the effect of unknown losses in small machines.

Particle-resolved direct numerical simulation of homogeneous isotropic turbulence modified by small fixed spheres

A statistically stationary homogeneous isotropic turbulent flow modified by 64 small fixed non-Stokesian spherical particles is considered. The particle diameter is approximately twice the Kolmogorov length scale, while the particle volume fraction is 0.001. The Taylor Reynolds number of the corresponding unladen flow is 32. The particle-laden flow has been obtained by a direct numerical simulation based on a discretization of the incompressible Navier–Stokes equations on 64 spherical grids overset on a Cartesian grid. The global (space- and time-averaged) turbulence kinetic energy is attenuated by approximately 9 %, which is less than expected. The turbulence dissipation rate on the surfaces of the particles is enhanced by two orders of magnitude. More than 5 % of the total dissipation occurs in only 0.1 % of the flow domain. The budget of the turbulence kinetic energy has been computed, as a function of the distance to the nearest particle centre. The budget illustrates how energy relatively far away from particles is transported towards the surfaces of the particles, where it is dissipated by the (locally enhanced) turbulence dissipation rate. The energy flux towards the particles is dominated by turbulent transport relatively far away from particles, by viscous diffusion very close to the particles, and by pressure diffusion in a significant region in between. The skewness and flatness factors of the pressure, velocity and velocity gradient have also been computed. The global flatness factor of the longitudinal velocity gradient, which characterizes the intermittency of small scales, is enhanced by a factor of six. In addition, several point-particle simulations based on the Schiller–Naumann drag correlation have been performed. A posteriori tests of the point-particle simulations, comparisons in which the particle-resolved results are regarded as the standard, show that, in this case, the point-particle model captures both the turbulence attenuation and the fraction of the turbulence dissipation rate due to particles reasonably well, provided the (arbitrary) size of the fluid volume over which each particle force is distributed is suitably chosen.

Effect of junction temperature on heat dissipation of high power light emitting diodes

The effect of junction temperature on heat dissipation of high power light emitting diodes (LEDs) is investigated. The theoretical aspect of junction temperature dependency of two major parameters—the forward voltage and the radiant flux—on heat dissipation is reviewed. Actual measurements of the heat dissipation over a wide range of junction temperatures are followed to quantify the effect of the parameters using commercially available LEDs. The results show that (1) the effect of the junction temperature dependency on heat dissipation is governed largely by the LED power efficiency and (2) each parameter contributes to the total heat dissipation in an opposite way so that the absolute changes of the heat dissipation are not significant over a wide range of junction temperature. An empirical model of heat dissipation is proposed for applications in practice.

Surf-Swash Interactions on a Low-Tide Terraced Beach

ABSTRACT Almar, R.; Almeida, P.; Blenkinsopp, C., and Catalan, P., 2016. Surf-swash interactions on a low-tide terraced beach. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 348-352. Coconut Creek (Florida), ISSN 0749-0208. Through an integrated approach, this paper investigates the role of coupled surf-swash dynamics on outgoing waves using data collected at a low-tide terraced beach, Grand Popo, Benin (Gulf of Guinea, West Africa). Observed reflection is 8 %. Analyses are conducted from deep water directional wave spectra measurements, daily beach surveys and remote video measurements. Our results show that the swash can be a non-negligible component of the nearshore energy balance (14% of total dissipation) and is closely tied to reflection. Reflection thus depends on waves at swash inception (offshore waves and surf zone saturation), and shor...

Analysis of critical thermal issues in 3D integrated circuits

Several key attributes of a 3D integrated chip structure are analyzed in this work. Critical features related to the effect of the size of the substrate, heat sink, device layer, through silicon vias (TSVs), thermal interface material (TIM), and the pitch and arrangement of core processors and TSVs as well as variation of thermal conductivity and total heat dissipation and distribution of power within the device layers core processors are investigated in depth. The effects of variation of pertinent features of the 3D integrated circuit (IC) structure on thermal hotspots are established and an optimization route for its reduction is clarified. In addition, a revealing analysis that shows the effect of the number of layers in the 3D structure is presented. Furthermore, the features that have insufficient effect on reduction of thermal hotspots are also established and discussed.

Transport of water and ions in partially water-saturated porous media. Part 1. Constitutive equations

I developed a model of cross-coupled flow in partially saturated porous media based on electrokinetic coupling including the effect of ion filtration (normal and reverse osmosis) and the multi-component nature of the pore water (wetting) phase. The model also handles diffusion and membrane polarization but is valid only for saturations above the irreducible water saturation. I start with the local Nernst–Planck and Stokes equations and I use a volume-averaging procedure to obtain the generalized Ohm, Fick, and Darcy equations with cross-coupling terms at the scale of a representative elementary volume of the porous rock. These coupling terms obey Onsager's reciprocity, which is a required condition, at the macroscale, to keep the total dissipation function of the system positive. Rather than writing the electrokinetic terms in terms of zeta potential (the double layer electrical potential on the slipping plane located in the pore water), I developed the model in terms of an effective charge density dragged by the flow of the pore water. This effective charge density is found to be strongly controlled by the permeability and the water saturation. I also developed an electrical conductivity equation including the effect of saturation on both bulk and surface conductivities, the surface conductivity being associated with electromigration in the electrical diffuse layer coating the grains. This surface conductivity depends on the CEC of the porous material.

Assessment of two different optimization principles applied in heat conduction

Optimization principles play a crucial role in the intensification of the heat-transfer process. In this study, we assess and compare two principles, i.e., the entransy dissipation extremum (EDE) principle and the minimum entropy generation (MEG) principle, used in a typical “area to point” heat conduction problem solved via a cellular automaton algorithm. The simulated results indicate that both rules can ameliorate the tree-network conductive path, leading to a more uniform thermal field and lower average and maximum temperatures. In contrast to the MEG principle, the EDE principle is more appropriate to be linked to the algorithm when dealing with the “area to point” heat conduction optimization, especially with a higher conductivity ratio, kp/k0, between the high conductivity material and the low conductivity material and the fraction of high conductivity, ϕ0. With the analysis of total entransy dissipation rate and entropy generation of the domain optimized by two principles, the results indicate that the EDE principle is more suitable for the heat-transfer processes without heat–work conversion. Moreover, optimization via reducing the total entransy dissipation rate exhibits better performance in decreasing the equivalent resistance theoretically.

Introducing a novel model based on particle wave duality for energy dissipation analysis in MQCA circuits

In recent years, the limitations of the physical dimensions and high consumption of energy in electronic systems have been a major challenge. In order to decrease the physical size and energy consumption, various technologies have been investigated at the nano-scale. One of which is quantum cellular automata (QCA). This paper elaborates on the advantages of molecular QCA (MQCA) and proposes a new idea based on particle wave duality of free electron in QCA for energy dissipation analysis. The first stage is to calculate the dissipation of the internal dynamical and statically power of the cells considering the inner interaction of molecules. In return, by elaborating the inner calculation and consideration the distances and real size of the cells, energy dissipation values of MQCAs is calculated. Then, energy dissipation values for MQCA circuits consisting of binary wire and a majority gate are calculated. The achieved results show that in MQCA circuits, energy dissipation is very low. In addition, most of the energy dissipation in such circuits is related to the dynamical dissipation of the system. Our new concept proposes the separate use of classical physics and quantum mechanics properties in the calculation. Cell polarization changes simulated stage by stage based on current situation of electron and in each stage, the best conditions for calculations considered. The main innovation of this work is to introduce a new model based on particle wave duality for free electrons in MQCAs. In addition we presented equations to calculate total dissipation consisting dynamical and statically dissipation of MQCA circuits.

The Effects of Prone with Respect to Supine Position on Stress Relaxation, Respiratory Mechanics, and the Work of Breathing Measured by the End-Inflation Occlusion Method in the Rat.

The working hypothesis is that the prone position with respect to supine may change the geometric configuration of the lungs inside the chest wall, thus their reciprocal mechanical interactions, leading to possible effects on stress relaxation phenomena and respiratory mechanics. The effects of changing body posture from supine to prone on respiratory system mechanics, particularly on stress relaxation, were investigated in the rat by the end-inflation occlusion method. In the prone with respect to supine position, an increment of the frictional resistance of the airway (from 0.13 ± 0.01 to 0.19 ± 0.02 cm H2O/l sec(-1), p < 0.05) and a decrement of the stress relaxation-linked pressure dissipation (from 0.51 ± 0.05 to 0.45 ± 0.05 cm H2O/l sec(-1), p < 0.01) were found. Respiratory system elastance and total resistive pressure dissipation did not change significantly. Accordingly, a significant increase of the frictional "ohmic" mechanical inspiratory work of breathing and a decrease of the visco-elastic work of inspiration were demonstrated, while no significant changes occurred for the total mechanical work of breathing and its total resistive and elastic components. It is concluded that postural changes affect the visco-elastic characteristics of the respiratory system and the related stress relaxation phenomena by influencing the disposition and relation of the lungs inside the chest wall and their relative geometrical configuration, and the interaction phenomena of the constitutive parenchymal structures, i.e., elastin and collagen fibers. Since the prone position resulted in no serious or disadvantageous respiratory system mechanical derangement, it is suggested it may be usefully applied in nursing or for therapeutic goals.

Disruption of states by a stable stratification

We identify ‘minimal seeds’ for turbulence, i.e. initial conditions of the smallest possible total perturbation energy density $E_{c}$ that trigger turbulence from the laminar state, in stratified plane Couette flow, the flow between two horizontal plates of separation $2H$, moving with relative velocity $2{\rm\Delta}U$, across which a constant density difference $2{\rm\Delta}{\it\rho}$ from a reference density ${\it\rho}_{r}$ is maintained. To find minimal seeds, we use the ‘direct-adjoint-looping’ (DAL) method for finding nonlinear optimal perturbations that optimise the time-averaged total dissipation of energy in the flow. These minimal seeds are located adjacent to the edge manifold, the manifold in state space that separates trajectories which transition to turbulence from those which eventually decay to the laminar state. The edge manifold is also the stable manifold of the system’s ‘edge state’. Therefore, the trajectories from the minimal seed initial conditions spend a large amount of time in the vicinity of some states: the edge state; another state contained within the edge manifold; or even in dynamically slowly varying regions of the edge manifold, allowing us to investigate the effects of a stable stratification on any coherent structures associated with such states. In unstratified plane Couette flow, these coherent structures are manifestations of the self-sustaining process (SSP) deduced on physical grounds by Waleffe (Phys. Fluids, vol. 9, 1997, pp. 883–900), or equivalently finite Reynolds number solutions of the vortex–wave interaction (VWI) asymptotic equations initially derived mathematically by Hall &amp; Smith (J. Fluid Mech., vol. 227, 1991, pp. 641–666). The stratified coherent states we identify at moderate Reynolds number display an altered form from their unstratified counterparts for bulk Richardson numbers $\mathit{Ri}_{B}=g{\rm\Delta}{\it\rho}H/({\it\rho}_{r}{\rm\Delta}U^{2})=O(\mathit{Re}^{-1})$, and exhibit chaotic motion for larger $\mathit{Ri}_{B}$. We demonstrate that at hith Reynolds number the suppression of vertical motions by stratification strongly disrupts input from the waves to the roll velocity structures, thus preventing the waves from reinforcing the viscously decaying roll structures adequately, when $\mathit{Ri}_{B}=O(\mathit{Re}^{-2})$.

The Prediction of Velocity Distribution of Plate Jet with a EMMS Model

The energy minimization multi-scale model is applied to the plane jet. The stability conditions of plane jets is adopted to predict the velocity distribution of plane jet. When the ratio of total dissipation to viscous dissipation tends to the maximum is used as the optimization condition and entrancement factor is considered as a constant, the Gauss velocity distribution can be concluded in the plane jet.

Estimating total body heat dissipation in air and water from skin surface heat flux telemetry in Weddell seals

Accurate estimates of thermoregulatory costs in air and water are necessary to predict the impacts of changing habitats to individuals and populations of ice-obligate seals. Investigations that would provide such estimates of thermoregulatory physiology over natural activities in free-ranging marine mammals have been limited. This study describes a biotelemetry method for measuring skin surface heat flux in free-ranging Weddell seals. These data are then applied to estimations of thermoregulatory heat dissipation from multiple point measurements. Data loggers collecting skin surface heat flux telemetry at four body locations (head, neck, axilla and flank) from 40 free-ranging Weddell seals were deployed and recovered over periods of 1–13 days in Erebus Bay, Antarctica. We derive equations for estimating total body heat dissipation from these point measurements and demonstrate the subsequent calculation of heat dissipated from obligate thermoregulatory costs. Heat lost to air or water was described by heat flux sensor data extrapolated across the whole-body surface, as informed by skin surface infrared thermal patterns. Heat lost directly to the ice surface during haul-out was best described by physical features of the seal, rather than environmental variables. Heat flux inputs from the four sensors could be reduced to two principal components, and corresponding regressions indicated that the axilla and flank sensors were most correlated with total body heat dissipation in air and water. Variability in head sensor heat flux was least described by the two principal components. This method can be used to estimate total body heat dissipation during daily activities in marine mammals, and under steady-state conditions, it can be used to identify obligate thermoregulatory heat costs. Ultimately this type of data will provide relevant empirical information for parameterizing models of thermoregulatory energetics in ice-obligate seals, which may improve our ability to predict outcomes of altered ice conditions at high latitudes.

A synthetic layout optimization of discrete heat sources flush mounted on a laminar flow cooled flat plate based on the constructal law

A synthetic optimization is presented for the Pareto layouts of discrete heat sources (with uniform heat flux) flush mounted on a flat plate over which laminar flow serves for cooling purpose. The peak temperatures and the flow drag loss are minimizing simultaneously provided that the total heat dissipation rate and the plate length are held constant. The impact of the manufacturing limit, i.e. the minimum length of the heated or the adiabatic patch, on the optimum layout is discussed. The results in general comply with analytical deduction based on the constructal theory. However in a finite length scenario, geometric constraints on the adiabatic spacing differ from that fits the situation in which maximum heat transfer performance alone is to be achieved.

Ill posedness of Bingham-type models for the downhill flow of a thin film on an inclined plane

In this paper we consider the flow of a thin layer of a Bingham-type material over an inclined plane with “small” tilt angle. A Bingham-type continuum is a material which behaves as a viscous fluid above a certain threshold (tied to the shear stress) and as a solid below such a threshold. We consider creeping flow and that the ratio between the thickness and the length of the layer is small, so that the lubrication approach is suitable. The unknowns of the model are the layer thickness, the position of the yield surface and the position of the advancing front. We first show that, though diverging in a neighborhood of the wetting front, the shear stress is integrable so that total dissipation is bounded. We then prove that the mathematical problem is inherently ill posed independently on the constitutive model selected for the solid domain. We therefore conclude that either the Bingham-type models are inappropriate to describe the thin film motion on an inclined surface or the lubrication technique fails in approximating such flows.

Kinetics of interstitial segregation in Cottrell atmospheres and grain boundaries

Trapping of interstitial (e.g. carbon) atoms is driven by the reduction in energy in the system. Diffusion of interstitials, together with their trapping in dislocation cores and/or grain boundaries, is studied by the thermodynamic extremal principle. In addition to the total Gibbs energy, a well-established formulation of the total dissipation is applied. Dimension-free evolution equations are derived, whose solution is well approximated by an easy to handle kinetic equation. Cottrell’s power law can be verified in the initial stage.

A numerical study of non-linear crack tip parameters

Crack closure concept has been widely used to explain different issues of fatigue crack propagation. However, different authors have questioned the relevance of crack closure and have proposed alternative concepts. The main objective here is to check the effectiveness of crack closure concept by linking the contact of crack flanks with non-linear crack tip parameters. Accordingly, 3D-FE numerical models with and without contact were developed for a wide range of loading scenarios and the crack tip parameters usually linked to fatigue crack growth, namely range of cyclic plastic strain, crack tip opening displacement, size of reversed plastic zone and total plastic dissipation per cycle, were investigated. It was demonstrated that: i) LEFM concepts are applicable to the problem under study; ii) the crack closure phenomenon has a great influence on crack tip parameters decreasing their values; iii) the ?Keff concept is able to explain the variations of crack tip parameters produced by the contact of crack flanks; iv) the analysis of remote compliance is the best numerical parameter to quantify the crack opening level; v) without contact there is no effect of stress ratio on crack tip parameters. Therefore it is proved that the crack closure concept is valid.