Showing papers on "Dissipation published in 2021"

Observation of a Dissipative Time Crystal.

Abstract: We present the first experimental realization of a time crystal stabilized by dissipation. The central signature in our implementation in a driven open atom-cavity system is a period doubled switching between distinct checkerboard density wave patterns, induced by the interplay between controlled cavity dissipation, cavity-mediated interactions, and external driving. We demonstrate the robustness of this dynamical phase against system parameter changes and temporal perturbations of the driving.

Melting heat transportation in radiative flow of nanomaterials with irreversibility analysis

Abstract: Melting phenomenon of PCMs (phase change materials) is mostly complemented with resilient variation in density of thermal heat. Thermal energy created from numerous sources can be stored in form of latent heat combination throughout melting process of a phase change materials. Thermal energy can be unconfined during the solidification processes. MPCS (microencapsulated phase change slurry) has noteworthy advantages particularly in high energy density and narrow temperature range for various heat energy application. Melting heat transportation has attracted the consideration of scientists and engineers due to its tremendous applications of technological, solidification, casting and industrial processes. A variety of phase change materials with low cost are commercially accessible and do significant work in different circumstances of temperature. Main motivation here is to investigate irreversibility in MHD convection flow of viscous liquid with melting effect over a stretched surface. Slip condition and Lorentz force behaviors are accounted. Energy expression is developed through dissipation, heat radiation and Joule heating. Irreversibility exploration is modeled through second law of thermodynamics. Brownian diffusion and thermophoresis are taken. First order chemical reaction is deliberated. Nonlinear expressions are reduced to ordinary one employing transformation. The obtained systems are solved for the convergent solutions through ND-solve method. Variation of velocity field, entropy rate, temperature, Bejan number and concentration distribution are scrutinized. Velocity filed rises versus higher melting variable. Larger melting parameter decreases the temperature distribution. Concentration and temperature have similar effects against thermophoresis variable. Bejan number and entropy rate have opposite outcome via melting parameter. Higher radiation parameter reduces the entropy rate. For higher radiation both entropy rate and Bejan number have same effect. Main observations are concluded.

Electro-magnetohydrodynamic flow and heat transfer of a third-grade fluid using a Darcy-Brinkman-Forchheimer model

Abstract: The purpose of this paper is to examine the electro-magnetohydrodynamic behavior of a third-grade non-Newtonian fluid, flowing between a pair of parallel plates in the presence of electric and magnetic fields. The flow medium between the plates is porous. The effects of Joule heating and viscous energy dissipation are studied in the present study.,A semi-analytical/numerical method, the differential transform method, is used to obtain solutions for the system of the nonlinear differential governing equations. This solution technique is efficient and may be adapted to solve a variety of nonlinear problems in simple geometries, as it was confirmed by comparisons between the results using this method and those of a fully numerical scheme.,The results of the computations show that the Darcy–Brinkman–Forchheimer parameter and the third-grade fluid model parameter retards, whereas both parameters have an inverse effect on the temperature profile because the viscous dissipation increases. The presence of the magnetic field also enhances the temperature profile between the two plates but retards the velocity profile because it generates the opposing Lorenz force. A graphical comparison with previously published results is also presented as a special case of this study.,The obtained results are new and presented for the first time in the literature.

An explicit dissipative model for isotropic hard magnetorheological elastomers

Abstract: Hard magnetorheological elastomers ( h -MREs) are essentially two phase composites comprising permanently magnetizable metallic inclusions suspended in a soft elastomeric matrix. This work provides a thermodynamically consistent, microstructurally-guided modeling framework for isotropic, incompressible h -MREs. Energy dissipates in such hard-magnetic composites primarily via ferromagnetic hysteresis in the underlying hard-magnetic particles. The proposed constitutive model is thus developed following the generalized standard materials framework, which necessitates suitable definitions of the energy density and the dissipation potential. Moreover, the proposed model is designed to recover several well-known homogenization results (and bounds) in the purely mechanical and purely magnetic limiting cases. The magneto–mechanical coupling response of the model, in turn, is calibrated with the aid of numerical homogenization estimates under symmetric cyclic loading. The performance of the model is then probed against several other numerical homogenization estimates considering various magneto–mechanical loading paths other than the calibration loading path. Very good agreement between the macroscopic model and the numerical homogenization estimates is observed, especially for stiff to moderately-soft matrix materials. An important outcome of the numerical simulations is the independence of the current magnetization to the stretch part of the deformation gradient. This is taken into account in the model by considering an only rotation-dependent remanent magnetic field as an internal variable. We further show that there is no need for an additional mechanical internal variable. Finally, the model is employed to solve macroscopic boundary value problems involving slender h -MRE structures and the results match excellently with experimental data from literature. Crucial differences are found between uniformly and non-uniformly pre-magnetized h -MREs in terms of their pre-magnetization and the associated self-fields.

Dissipative spin dynamics in relativistic matter

Abstract: Using the classical description of spin degrees of freedom, we extend recent formulation of the perfect-fluid hydrodynamics for spin-polarized fluids to the case including dissipation. Our work is based on the analysis of classical kinetic equations for massive particles with spin $1/2$, with the collision terms treated in the relaxation time approximation. The kinetic-theory framework determines the structure of viscous and diffusive terms and allows to explicitly calculate a complete set of new kinetic coefficients that characterize dissipative spin dynamics.

A computational frame work on magnetohydrodynamic dissipative flow over a stretched region with cross diffusion: Simultaneous solutions

Abstract: In this report, the hydromagnetic dissipative Newtonian/non-Newtonian fluid flow over a stretched surface is examined numerically. Brownian moment, Joule heating, thermophoresis effects are considered. Similarity variables are employed to transform the non-linear PDEs into ODEs. The eminent shooting scheme is employed to determine the solution of the nonlinear equations. Solutions are achieved for different benefits of parameters of the model and the consequences are predicted in plots and tables. The Brownian moment imposed to accelerate the energy field and the dissipation influences to expand both the thermal and momentum fields. Also, simultaneous solutions are exhibited and found that the heat transport in Casson fluids has superior properties than the regular fluid.

Experimental study on energy storage and dissipation characteristics of granite under two-dimensional compression with constant confining pressure

Abstract: To study the energy storage and dissipation characteristics of deep rock under two-dimensional compression with constant confining pressure, the single cyclic loading-unloading two-dimensional compression tests were performed on granite specimens with two height-to-width (H/W) ratios under five confining pressures. Three energy density parameters (input energy density, elastic energy density and dissipated energy density) in the axial and lateral directions of granite specimens under different confining pressures were calculated using the area integral method. The experimental results show that, for the specimens with a specific H/W ratio, these three energy density parameters in the axial and lateral directions increase nonlinearly with the confining pressure as quadratic polynomial functions. Under constant confining pressure compression, the linear energy storage law of granite specimens in the axial and lateral directions was founded. Using the linear energy storage law in different directions, the elastic energy density in various directions (axial elastic energy density, lateral elastic energy density and total elastic energy density) of granite under any specific confining pressures can be calculated. When the H/W ratio varies from 1:1 to 2:1, the lateral compression energy storage coefficient increases and the corresponding axial compression energy storage coefficient decreases, while the total compression energy storage coefficient is almost independent of the H/W ratio.

Correlating the Molecular Structure of Polyimides with the Dielectric Constant and Dissipation Factor at a High Frequency of 10 GHz

Abstract: The relationships between the structure and the dielectric properties of polyimides (PIs) were extensively studied to construct universal correlations of dielectric constant (Dk) and dissipation fa...

3D Printing of Liquid Crystal Elastomer Foams for Enhanced Energy Dissipation Under Mechanical Insult.

Abstract: Polymer foams are an essential class of lightweight materials used to protect assets against mechanical insults, such as shock and vibration. Two features are important to enhance their energy absorption characteristics: the foam structure and the matrix phase mechanical behavior. This study investigates novel approaches to control both of these features to enhance the energy absorption capability of flexible lattice foams. First, we consider 3D printing via digital light processing (DLP) as a method to control the foam mesostructure across a suite of periodic unit cells. Second, we introduce an additional energy dissipation mechanism in the solid matrix phase material by 3D printing the lattice foams with polydomain liquid crystal elastomer (LCE), which undergo a mechanically induced phase transition under large strains. This phase transition is associated with LC mesogen rotation and alignment and provides a second mechanism for mechanical energy dissipation in addition to the viscoelastic relaxation of the polymer network. We contrast the 3D printed LCE lattices with conventional, thermomechanically near-equivalent elastomer lattice foams to quantify the energy-absorbing enhancement the LCE matrix phase provides. Under cyclic quasi-static uniaxial compression conditions, the LCE lattices show dramatically enhanced energy dissipation in uniaxial compression compared to the non-LCE equivalent foams printed with a commercially available photocurable elastomer resin. The lattice geometry also plays a prominent role in determining the energy dissipation ratio between the LCE and non-LCE foams. We show that when increasing the lattice connectivity, the foam deformation transitions from bending-dominated to stretching-dominated deformations, which generates higher axial strains in the struts and higher energy dissipation in the lattice foam, as stretching allows greater mesogen rotation than bending. The LCE foams demonstrate superior energy absorption during the repeated dynamic loading during drop testing compared with the non-LCE equivalent foams, demonstrating the potential of LCEs to enhance physical protection systems against mechanical impact.

Superconducting-like Heat Current: Effective Cancellation of Current-Dissipation Trade-Off by Quantum Coherence.

Abstract: Quantum coherence is a useful resource for increasing the speed and decreasing the irreversibility of quantum dynamics. Because of this feature, coherence is used to enhance the performance of various quantum information processing devices beyond the limitations set by classical mechanics. However, when we consider thermodynamic processes, such as energy conversion in nanoscale devices, it is still unclear whether coherence provides similar advantages. Here we establish a universal framework, clarifying how coherence affects the speed and irreversibility in thermodynamic processes described by the Lindblad master equation, and give general rules for when coherence enhances or reduces the performance of thermodynamic devices. Our results show that a proper use of coherence enhances the heat current without increasing dissipation; i.e., coherence can reduce friction. In particular, if the amount of coherence is large enough, this friction becomes virtually zero, realizing a superconducting-like "dissipation-less" heat current. Since our framework clarifies a general relation among coherence, energy flow, and dissipation, it can be applied to many branches of science from quantum information theory to biology. As an application to energy science, we construct a quantum heat engine cycle that exceeds the power-efficiency trade-off bound on classical engines and effectively attains the Carnot efficiency with finite power in fast cycles.

Boundary layer flow with forced convective heat transfer and viscous dissipation past a porous rotating disk

Abstract: The Coriolis effect with forced convective heat transfer on steady ferrohydrodynamic flow past a rotating porous disk in the presence of viscous dissipation has been investigated. The basic idea of the Neuringer-Rosensweig model has been used for the equation of motion of the nanofluid flow. With help of suitable transformations, the governing non-linear system of coupled partial differential equations is simplified into the dimensionless system of ordinary differential equations. Further, the dimensionless system of equations is solved numerically by the MATLAB routine bvp4c solver package. The findings for the motivating parameters of physical interest are expressed by the table and discussed with graphs. The outcomes show that heat transfer rate and thermal boundary layer thickness increase due to the higher value of the dissipation parameter.

New Results on Stabilization of Port-Hamiltonian Systems via PID Passivity-Based Control

Abstract: In this article, we present some new results for the design of PID passivity-based controllers (PBCs) for the regulation of port-Hamiltonian (pH) systems. The main contributions of this article are: (i) new algebraic conditions for the explicit solution of the partial differential equation required in this design; (ii) revealing the deleterious impact of the dissipation obstacle that limits the application of the standard PID-PBC to systems without pervasive dissipation; (iii) the proposal of a new PID-PBC which is generated by two passive outputs, one with relative degree zero and the other with relative degree one. The first output ensures that the PID-PBC is not hindered by the dissipation obstacle, while the relative degree of the second passive output allows the inclusion of a derivative term. Making the procedure more constructive and removing the requirement on the dissipation significantly extends the realm of application of PID-PBC. Moreover, allowing the possibility of adding a derivative term to the control, enhances its transient performance.

Hydrodynamic magneto-transport in charge density wave states

Abstract: In this paper we study the dynamical properties of charged systems immersed in an external magnetic field and perturbed by a set of scalar operators breaking translations either spontaneously or pseudo-spontaneously. By combining hydrodynamic and quantum field theory arguments we provide analytic expressions for all the hydrodynamic transport coefficients relevant for the diffusive regime in terms of thermodynamic quantities and DC thermo-electric conductivities. This includes the momentum dissipation rate. We shed light on the role of the momentum dissipation rate in the transition between the pseudo-spontaneous and the purely explicit regimes in this class of systems. Finally, we clarify several relations between the hydrodynamic transport coefficients which have been observed in the holographic literature of charge density wave models.

Velocity transformation for compressible wall-bounded turbulent flows with and without heat transfer.

Abstract: In this work, a transformation, which maps the mean velocity profiles of compressible wall-bounded turbulent flows to the incompressible law of the wall, is proposed. Unlike existing approaches, the proposed transformation successfully collapses, without specific tuning, numerical simulation data from fully developed channel and pipe flows, and boundary layers with or without heat transfer. In all these cases, the transformation is successful across the entire inner layer of the boundary layer (including the viscous sublayer, buffer layer, and logarithmic layer), recovers the asymptotically exact near-wall behavior in the viscous sublayer, and is consistent with the near balance of turbulence production and dissipation in the logarithmic region of the boundary layer. The performance of the transformation is verified for compressible wall-bounded flows with edge Mach numbers ranging from 0 to 15 and friction Reynolds numbers ranging from 200 to 2,000. Based on physical arguments, we show that such a general transformation exists for compressible wall-bounded turbulence regardless of the wall thermal condition.