Dissipation Function Research Articles

Nonlinear constitutive model of CFRP composites under constant direct current: Combined effects of thermal damage and dielectric degradation

Prolonged exposure to low-density direct current (DC) can lead to mechanical degradation of carbon fiber-reinforced polymer (CFRP) composites, posing significant risks to material safety and reliability. This paper presents a nonlinear constitutive model to elucidate the mechanical degradation of CFRP composites when subjected to DC influences. Grounded in the principles of non-equilibrium thermodynamics, this model introduces two internal variables to account for the impact of thermal damage and dielectric degradation on the Helmholtz free energy. Furthermore, specialized dissipation functions are employed to derive the evolution equations governing these internal variables. Utilizing the model, we analyze the damage progression in carbon fiber–epoxy laminates subjected to constant DC loading. The theoretically projected resistivity and elastic modulus align closely with available experimental data in literature, thus confirming the rationality and accuracy of the proposed model. This model holds the potential to forecast the long-term evolution of mechanical properties in unidirectionally reinforced composite materials with varying carbon fiber contents under the influence of DC, thereby furnishing a theoretical foundation for enhancing the reliability design of CFRP composites in electrically-charged environments.

Seismic performance test of bolted U-shaped steel assembled shear wall

A new type of assembled shear wall with energy dissipation and seismic damping function was proposed for the damage mechanism and weak points of typical assembled shear wall structures under strong earthquake effects. Using a combination of model tests and numerical simulations, four new assembled shear wall specimens with a scaling ratio of 1:1.54 and a shear-to-span ratio of 1.52 were designed and fabricated. The corresponding seismic performance tests were carried out. The effects of the number of bolts, axial compression ratio and longitudinal reinforcement ratio of edge members on the damage mode, hysteresis performance, bearing capacity, deformation performance, stiffness degradation and energy dissipation capacity of the specimens were systematically analyzed. The test results show that the damage mode of each specimen is basically the same as that of the common shear wall with the same shear-to-span ratio, which is bending-shear type damage However, the new assembled shear wall has more excellent hysteresis performance and energy dissipation capacity. Friction between the steel plates of the horizontal joints consumes a lot of energy and further inhibits wall damage. The energy dissipation value at the point of destruction of the wall is significantly higher than that of ordinary cast-in-place wall. The energy consumption value of the specimen PFSW is about 6 times that of a cast-in-place wall. When the number of bolts decreases, hysteresis performance decreases and wall deformation increases. The decrease of axial pressure ratio or longitudinal reinforcement ratio of edge members leads to the decrease of bearing capacity and increase of ultimate displacement of shear wall. Finally, the finite element model of the corresponding specimens was established by ABAQUS software. The simulation results were in good agreement with the test results, which indicated the correctness of the proposed model. And it can be applied to the analysis of new assembled shear walls.

WarmSPy: a numerical study of cosmological perturbations in warm inflation

We present WarmSPy, a numerical code in Python designed to solve for the perturbations' equations in warm inflation models and compute the corresponding scalar power spectrum at CMB horizon crossing. In models of warm inflation, a radiation bath of temperature T during inflation induces a dissipation (friction) rate of strength Q ∝ Tc /ϕm in the equation of motion for the inflaton field ϕ. While for a temperature-independent dissipation rate (c = 0) an analytic expression for the scalar power spectrum exists, in the case of a non-zero value for c the set of equations can only be solved numerically. For c > 0 (c < 0), the coupling between the perturbations in the inflaton field and radiation induces a growing (decaying) mode in the scalar perturbations, generally parameterized by a multiplicative function G(Q) which we refer to as the scalar dissipation function. Using WarmSPy, we provide an analytic fit for G(Q) for the cases of c = {3,1,-1}, corresponding to three cases that have been realized in physical models. Compared to previous literature results, our fits are more robust and valid over a broader range of dissipation strengths Q ∈ [10-7,104]. Additionally, for the first time, we numerically assess the stability of the scalar dissipation function against various model parameters, inflationary histories as well as the effects of metric perturbations. As a whole, the results do not depend appreciably on most of the parameters in the analysis, except for the dissipation index c, providing evidence for the universal behaviour of the scalar dissipation function G(Q).

Nonlinear Vibration and Dynamic Buckling of Complex Curved Functionally Graded Graphene Panels Reinforced with Inclined Stiffeners

This paper presents a new semi-analytical approach for the nonlinear vibration and dynamic responses of functionally graded graphene platelet-reinforced composite (FG-GPLRC) panels with complex curvature reinforced by orthogonal and/or inclined stiffeners in the thermal environment resting on the nonlinear viscoelastic foundation with the nonlinearities of von Kármán in the framework of the higher-order shear deformation theory (HSDT). The three curvature types of complexly curved panels are considered to be cylindrical, sinusoid, and parabola panels. Orthogonal and/or inclined stiffeners are modeled utilizing an improved smeared stiffener technique. The stress function form is estimated by applying the like-Galerkin method for complexly curved panels. By applying the Lagrange function and Euler–Lagrange equation, the nonlinear equations of motion of the panels are obtained. The viscous damping effects of the viscoelastic foundation are considered by utilizing the Rayleigh dissipation function. Numerical results are examined utilizing the Runge–Kutta method to acquire the time-deflection curves, and by utilizing the Budiansky–Roth criterion, the critical dynamic buckling loads are determined. From the investigated results, it is possible to evaluate the nonlinear vibration and buckling dynamic responses of three forms of panels with stiffeners.

Enhance thermal conductivity via constructing a low heat resistance interface with quaternized graphene

Interfacial thermal resistance of fillers in thermal conductive polymer composites is a barrier restricting heat dissipation function. In-situ graft of quaternary ammonium group on the surface of graphene can form cation-π interaction, providing a medium for heat transfer between graphene layers. Accordingly, we fabricate polyvinyl alcohol (PVA)-based heat conductive composite containing quaternized graphene stacking structure. With the assistance of non-covalent bonding, the in-plane thermal conductivity of the composite formed by self-precipitation method reaches 9.97 W m−1 K−1 at a filling content of 30 vol%. Molecular dynamics (MD) simulation further explores the promoting effect of the interfacial structure constructed between the charged group and graphene on the interfacial heat transfer. The optimized interfacial structure not only alleviates the bottleneck of interface thermal resistance but also enhances the mechanical properties of composite. This strategy provides an ideal solution to preparation of high-performance thermal management materials for electronic equipment.

Anisotropic continuum framework of coupled gas flow – adsorption – deformation in sedimentary rocks

AbstractSolid deformation is always a crucial factor of gas transport in sedimentary rocks. While previous studies always adopt the assumption of isotropic poroelastic deformation, anisotropic poroelastoplastic deformation is rarely considered, despite anisotropy being a ubiquitous property of natural sedimentary rocks. In this work, an anisotropic poromechanical model is established to analyze the matrix porosity and apparent permeability evolutions during the process of gas migration. Using a thermodynamic formulation that treats the fluid–solid interface as an independent phase, we derive a rate form for matrix porosity and obtain the new dissipation function that contains three parts: dissipations from solid deformation, gas adsorption, and fluid flow. For gas adsorption, we justify the rationality of the adopted model; for fluid flow, the updated porosity can be substituted into sophisticated apparent permeability models for full‐scale analysis; and for solid deformation, a recently developed constitutive model appropriate for rocks exhibiting transverse isotropy in both the elastic and plastic responses is adopted in this work. Through the novel stress‐point simulation incorporating two effective stress measures and adsorption strain, new patterns of apparent permeability are obtained, which fit the experimental data quite well and cannot be reproduced from the assumption of isotropic poroelasticity. The advantages of our poromechanical model include thermodynamic consistency and the ability to employ finite‐element‐based formulation. Finally, an initial‐boundary value problem of gas production considering anisotropic plasticity is conducted, and the effects of the bedding plane and different adsorption models are highlighted.

Nonlinear vibration and dynamic buckling responses of stiffened functionally graded graphene‐reinforced cylindrical, parabolic, and sinusoid panels using the higher‐order shear deformation theory

AbstractThe nonlinear vibration and dynamic responses of functionally graded graphene‐reinforced composite (FG‐GRC) laminated cylindrical, parabolic, and sinusoid panels stiffened by FG‐GRC stiffeners in the uniformly distributed temperature variation are presented in this paper. An improved smeared stiffener technique is used to model the added stiffnesses of stiffeners to the total stiffnesses of panels. The higher‐order shear deformation shell theory (HSDT) with the geometrical nonlinearities of von Kármán is applied to establish the governing formulations. The stress function form is estimated using the approximated technique for complex curvature panels. Lagrange function and Euler‐Lagrange equations are applied, and the Rayleigh dissipation function is taken into account to obtain the nonlinear equation of motion. Numerical examples are investigated using the Runge‐Kutta method to obtain the dynamic responses of panels, and the critical dynamic buckling loads of panels are considered using the Budiansky‐Roth criterion. Some significant remarks on the nonlinear vibration and dynamic buckling responses of three types of stiffened panels can be recognized from the numerical examples.

Information geometry of dynamics on graphs and hypergraphs

We introduce a new information-geometric structure associated with the dynamics on discrete objects such as graphs and hypergraphs. The presented setup consists of two dually flat structures built on the vertex and edge spaces, respectively. The former is the conventional duality between density and potential, e.g., the probability density and its logarithmic form induced by a convex thermodynamic function. The latter is the duality between flux and force induced by a convex and symmetric dissipation function, which drives the dynamics of the density. These two are connected topologically by the homological algebraic relation induced by the underlying discrete objects. The generalized gradient flow in this doubly dual flat structure is an extension of the gradient flows on Riemannian manifolds, which include Markov jump processes and nonlinear chemical reaction dynamics as well as the natural gradient. The information-geometric projections on this doubly dual flat structure lead to information-geometric extensions of the Helmholtz–Hodge decomposition and the Otto structure in L2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$L^{2}$$\\end{document}-Wasserstein geometry. The structure can be extended to non-gradient nonequilibrium flows, from which we also obtain the induced dually flat structure on cycle spaces. This abstract but general framework can broaden the applicability of information geometry to various problems of linear and nonlinear dynamics.

Exact Response Theory for Time-Dependent and Stochastic Perturbations.

The exact, non perturbative, response theory developed within the field of non-equilibrium molecular dynamics, also known as TTCF (transient time correlation function), applies to quite general dynamical systems. Its key element is called the dissipation function because it represents the power dissipated by external fields acting on the particle system of interest, whose coupling with the environment is given by deterministic thermostats. This theory has been initially developed for time-independent external perturbations, and then it has been extended to time-dependent perturbations. It has also been applied to dynamical systems of different nature, and to oscillator models undergoing phase transitions, which cannot be treated with, e.g., linear response theory. The present work includes time-dependent stochastic perturbations in the theory using the Karhunen-Loève theorem. This leads to three different investigations of a given process. In the first, a single realization of the stochastic coefficients is fixed, and averages are taken only over the initial conditions, as in a deterministic process. In the second, the initial condition is fixed, and averages are taken with respect to the distribution of stochastic coefficients. In the last investigation, one averages over both initial conditions and stochastic coefficients. We conclude by illustrating the applicability of the resulting exact response theory with simple examples.

NUMERICAL INVESTIGATION OF THE DYNAMICS OF MAGNETIZED CASSON FLUID FLOW OVER A PERMEABLE WEDGE SUBJECT TO DISSIPATION AND THERMAL RADIATIONS

The streamline boundary layer Casson liquid flow via wedge inspired by magnetic field effects is considered in this study. The governing laws of Casson fluid are modified by adding the effects of radiative heat flux, viscous dissipation and the surface permeability. Afterward, the model is transformed into simplified form using similarity variables and then analyzed via numerical scheme. The significant influence of the physical parameters appeared due to acting magnetic field, radiative heat flux, dissipation function and Prandtl number is specially treated for the flow behavior and thermal transfer mechanism plotted and discussed in detail. Further, tabulated results are also provided to replicate the study in future and this model is validated with the date published in open literature and it is found that these results are accurate and aligned with existing results.

Thermodynamic Constitutive Model of the Gas Hydrate-Bearing Sediments Considering Anisotropy

Gas hydrate-bearing sediments (GHBS) are considered a significant potential energy source. However, the decomposition of hydrates can lead to various geological hazards. Therefore, a comprehensive investigation into the mechanical properties of GHBS is essential to ensure the safe extraction of gas hydrate. This paper presents a constitutive model for GHBS that incorporates anisotropy, based on the theory of thermodynamics. To account for the effects of hydrate filling and cementing, two parameters are introduced into the dissipation function of the model. The filling effect is expressed through the densification mechanism, which increases the density of the host sediment. The cementing effect is represented by the enhanced expansion of the yield surface. The yield function incorporates the spacing ratio [Formula: see text] and the teardrop shape parameter [Formula: see text], which govern the shape of the yield surface, as well as the anisotropy angle [Formula: see text], which signifies the anisotropic evolution law. The physical significance of these parameters is also elucidated. The anisotropic evolution is described by an exponential function. The proposed model is compared to both the test results and the existing constitutive model, and it is found that it provides more accurate predictions of the mechanical properties of GHBS.

Safety assessment of wireless chargers for electric vehicles considering thermal characteristics.

This study employs the transient finite element method and electromagnetic heat transfer theory to assess the heating generated by high-power wireless chargers during electric vehicle charging. The analysis includes simulating and analyzing the temperature distribution of two different types of shielding plates of the wireless charger and the specific absorption rate (SAR) and head temperature rise of both adults and children in close proximity to the charger. Simulation results show that the maximum temperature rise of the copper shielding plate is 16°C lower than that of the aluminum shielding plate after charging for 1h. This temperature increase does not affect the chassis' s equipment. Regarding human safety, the induced electric field strength and SAR values in the child's head tissue are higher than those in the adult, meeting the International Commission on Non-Ionizing Radiation Protection (ICNIRP) limits. When the initial temperature is set to 37°C, the temperature rise in the heads of both adults and children is approximately equal after 1h of charging, reaching a maximum temperature rise of 0.21 and 0.23°C, respectively. These values remain below the thermal limit of ICNIRP (2°C for Type 2 tissues). The findings indicate that the copper shielding plate can provide both electromagnetic shielding and heat dissipation functions, and the electromagnetic exposure absorbed by the human body and head temperature rise within safe ranges.

Ternary Metals in Phase Change Polymers for Efficient Thermal Management of Electronics

AbstractPhase change materials (PCMs) are paramount for the thermal management of electronics. However, the present PCMs encounter a dilemma in balancing the thermal conductivity and effective latent heat, compromising the heat dissipation function of PCMs for electronics. This work successfully integrates ternary metals and polymer science to design novel PCMs composed of a ternary metal (TM, Ga0.20In0.46Sn0.34) with precise composition and polyethylene glycol (PEG) by physical blending. Due to the introduction of PEG with high melting enthalpy, the ternary metal in PEG (TM@PEG) simultaneously has high thermal conductivity (7.086 W m−1 K−1), desirable effective latent heat (143.6 J cm−3), suitable phase change range, and durability. During thermal management, the thermal conductivity and effective latent heat of TM@PEG contribute to suppressing the working temperature and delaying the temperature rise rate of electronics, respectively. Hence, the TM@PEG effectively behaves as the thermally conductive grease for LEDs and CPU to control the working temperature of electronics in a reasonable range. This work offers a new perspective for TM applied in thermal management.

A variational approach to effective models for inelastic systems

Given a set of inelastic material models, a microstructure, a macroscopic structural geometry, and a set of boundary conditions, one can in principle always solve the governing equations to determine the system’s mechanical response. However, for large systems this procedure can quickly become computationally overwhelming, especially in three-dimensions when the microstructure is locally complex. In such settings multi-scale modeling offers a route to a more efficient model by holding out the promise of a framework with fewer degrees of freedom, which at the same time faithfully represents, up to a certain scale, the behavior of the system. In this paper, we present a methodology that produces such models for inelastic systems upon the basis of a variational scheme. The essence of the scheme is the construction of a variational statement for the free energy as well as the dissipation potential for a coarse scale model in terms of the free energy and dissipation functions of the fine scale model. From the coarse scale energy and dissipation we can then generate coarse scale material models that are computationally far more efficient than either directly solving the fine scale model or by resorting to FE2 type modeling. Moreover, the coarse scale model preserves the essential mathematical structure of the fine scale model. An essential feature for such schemes is the proper definition of the coarse scale inelastic variables. By way of concrete examples, we illustrate the needed steps to generate successful models via application to problems in classical plasticity, included are comparisons to direct numerical simulations of the microstructure to illustrate the accuracy of the proposed methodology.

Study on the performance of thin-film VCSELs on composite metal substrate

Thin film p-side up vertical-cavity surface-emitting lasers (VCSELs) with 940 nm wavelength on a composite metal (Copper/Invar/Copper; CIC) substrate has been demonstrated by twice-bonding transfer and substrate removing techniques. The CIC substrate is a sandwich structure with a 10 µm thick Copper (Cu) layer/30 µm thick Invar layer/10 µm thick Cu layer. The Invar layer was composed of Iron (Fe) and Nickel (Ni) with a proportion of 70:30. The thermal expansion coefficient of the composite CIC metal can match that of the GaAs substrate. It results that the VCSEL layers can be successfully transferred to CIC metal substrate without cracking. At 1 mA current, the top-emitting VCSEL/GaAs and thin-film VCSEL/CIC had a voltage of 1.39 and 1.37 V, respectively. The optical output powers of VCSEL/GaAs and VCSEL/CIC were 21.91 and 24.40 mW, respectively. The 50 µm thick CIC substrate can play a good heat dissipation function, which results in improving the electrical and optical characteristics of thin film VCSELs/CIC. The VCSEL/CIC exhibited a superior thermal management capability as compared with VCSEL/GaAs. The obtained data suggested that VCSELs on a composite metal substrate not only affected significantly the characteristics of thin film VCSEL, but also improved considerably the device thermal performance.Graphical

Exploration of entropy analysis and viscous dissipation on radially convective flow of (Cu‐Al2O3:H2O) hybrid nanofluid over a stretching disk

AbstractThe current research work deals with the impact of suction/injection on the thermally radiating convective flow generated by a nonlinear stretched disk. The energy equation is addressed by the presence of thermal radiation and the energy dissipative function. This work was carried out with the help of the Das and Tiwari (single‐phase nanofluid) models and the Maxwell Garnett and Brinkman nanofluid models for the analysis of entropy generation. In the present model, nanoparticles of copper (Cu) and alumina (Al2O3) are being used with water (H2O) as the base fluid. The governing nonlinear partial differential equations are transformed into ordinary differential equations with the assistance of appropriate similarity variables. These transformed equations are then solved using the bvp4c function, a built‐in function in MATLAB software. The investigation examines the influence of various factors on the velocity and temperature fields, entropy generation, skin friction, and heat transfer rate. The findings show that suction decreases velocity and temperature by 6.59%, while injection has the opposite effect. Viscous dissipation increases velocity by 5.13% and temperature by 17.94% in hybrid nanofluids. Higher Prandtl numbers reduce velocity and temperature by 6% in nanofluids but boost them by 5.45% and 18.81% in hybrid nanofluids with radiation growth. As volume fraction rises, Al2O3/H2O nanofluid speed falls by 5.37%, but Cu‐Al2O3/H2O hybrid nanofluid temperature increases by 13.09% and surface drag force increases by 12%. The entropy of the hybrid nanofluid increases by 5.84%, 8.19%, and 14.04% with Eckert number, suction, and Prandtl number but decreases by 10.08% with temperature difference. The Nusselt number of nanofluid decreases by 10.58% and 12.40% with Eckert number and radiation, but hybrid particles increase it by 10.31% with intensified Prandtl number. These findings offer valuable insights for potential applications of hybrid nanofluids in heat transfer and cooling systems.

Correction: Second law of thermodynamics and energy dissipation function

Correction: Second law of thermodynamics and energy dissipation function

Design and experiment of a low-temperature charging preheating system for power battery packs with an integrated dissipative balancing function

The performance degradation of lithium-ion batteries (LiB) at low temperatures, as well as variability among batteries after battery grouping, limit the application range of electric vehicles (EVs). A low-temperature preheating method for power battery packs with an integrated dissipative balancing function is proposed in this research. The system builds its topology structure and sets the placement of heating units in the battery pack, as well as using heating units as preheating elements and balancing resistors. Furthermore, this paper presents an online balancing control technique to completely utilize the minimal capacity single battery module and formulates the balancing control threshold for different SOCnew states. The results showed that the temperature rise and temperature difference caused by the battery pack balancing process are within the range of 7 °C under the full operation conditions of balancing resistance at an ambient temperature of 20 °C. Under a −20 °C ambient temperature, the preheating system can raise the average temperature of the battery pack to 16 °C within 40 min and keep the temperature inside the battery pack above 0 °C for the following 4 h. This paper provides a new idea for coupling the research of efficient balancing technology and low-temperature preheating technology for power battery packs.

Significance of radiated ternary nanofluid for thermal transport in stagnation point flow using thermal slip and dissipation function

Investigation of heat transfer is a potential research area to acquire the targets in engineering and various industries. Although, conventional liquids are good for many such applications but their heat transfer rate is limited and thus it is essential to study new fluids which meet the requirements. Therefore, a new ternary nanofluid model acquired using enhanced thermal conductivity, electrical conductivity, heat capacity, basic governing laws and similarity transforms. The model comprises the motivational aspects of thermal slip, convective condition, radiative flux and viscous dissipation and predict the parametric ranges for excellent heat transfer results. The nanoparticles (Al2O3, CuO and Cu) amount is kept up to 0.04. For the results simulation, the numerical technique based on shooting scheme is implemented and solved the model. It is scrutinized that induction of aforementioned physical quantities significantly improved thermal transport performance of ternary nanoliquid. These are an excellent sources to acquire the preferred amount of heat for industrial applications. Further, higher B1 near surface boosted the temperature with increasing B1 in the range of 0.1–0.4. The heat transfer rate at the surface effectively enhanced for thermal slip (α1), radiation number (Rd) and Biot number (B1) in the range of 0.1,0.3,0.5,0.7.

Study on the Effect of Different Sandwich Thicknesses on the Impact Resistance of Laminated Glass

Polyvinyl butyral (PVB) laminated glass is widely used in architectural structures and automotive glass due to its remarkable cushioning and cohesive properties, and its lamination thickness has a significant effect on the overall impact resistance of the glass. In this paper, two conventional laminated glass thicknesses of 0.76 mm and 1.52 mm were selected to study the dynamic performance and damage morphology of laminated glass under three different impact velocities using light gas gun impact tests combined with industrial CT scanning-3D reconstruction techniques. The results showed that the PVB sandwich thickness had a significant positive correlation with the energy absorption effect, but under different impact velocities and glass thickness, the sandwich thickness and impact resistance showed a differentiated “marginal effect”. At moderate impact velocities, the impact resistance was most sensitive to the change in sandwich thickness. With the increase in glass thickness, the sensitivity of impact resistance to the change of sandwich thickness decreased. According to the characterization of full-dimensional cracks under medium-velocity impact conditions, it could be seen that the sandwich had the function of buffering dissipation and gathering recovery in different stress directions, and the thickness of the sandwich was a key functional parameter to reduce the flying of glass fragments. Therefore, the results of this study can provide a reference for the analysis and design of the impact resistance of PVB laminated glass.