Dissipative Conditions Research Articles

Exponential stability for infinite-dimensional non-autonomous port-Hamiltonian Systems

We study the non-autonomous version of an infinite-dimensional linear port-Hamiltonian system on an interval [ a , b ] . Employing abstract results on evolution families, we show C 1 -well-posedness of the corresponding Cauchy problem, and thereby existence and uniqueness of classical solutions for sufficiently regular initial data. Further, we demonstrate that a dissipation condition in the style of the dissipation condition sufficient for uniform exponential stability in the autonomous case also leads to a uniform exponential decay rate of the energy in this non-autonomous setting.

Finite-Time Thermodynamics in Economics.

In this paper, we consider optimal trading processes in economic systems. The analysis is based on accounting for irreversibility factors using the wealth function concept. The existence of the welfare function is proved, the concept of capital dissipation is introduced as a measure of the irreversibility of processes in the microeconomic system, and the economic balances are recorded, including capital dissipation. Problems in the form of kinetic equations leading to given conditions of minimal dissipation are considered.

Changes in the daytime thermospheric gravity wave propagation characteristics over low-latitudes in response to the variation in solar flux

Gravity waves play an important role in the propagation of energy and momentum from the lower atmospheric regions into the upper atmosphere. Depending on the varying dissipation conditions, these waves generated in the lower atmosphere can propagate higher into the atmosphere. As the neutrals and plasma share the same volume in the upper atmosphere, these waves affect both these densities as they propagate. In our analysis, using the information on the variations in phase offsets at different heights corresponding to isoelectron density contours at several defined transmission frequencies of digisonde, vertical phase propagation speeds, and vertical scale sizes of gravity waves in the daytime thermosphere have been estimated. Investigation of gravity waves by radio measurements, unlike the conventional optical techniques, which are limited to clear sky conditions alone, enable an unhindered study of gravity wave dynamics in all weather conditions. We have found a very good semblance between the variations in derived vertical phase speeds of gravity waves in the thermosphere and Solar F10.7cm flux. Further, gravity wave activity, i.e., the number of gravity waves present in the thermosphere in daytime increases with increasing Solar flux. We quantify these inter-relationships and present linear relations of gravity wave activity and their propagation speeds as a function of variation in Solar flux.

Prediction of Weld Reinforcement Based on Vision Sensing in GMA Additive Manufacturing Process

In the gas-metal-arc (GMA) additive manufacturing process, the shape of the molten pool, the temperature field of the workpiece and the heat dissipation conditions change with the increase of cladding layers, which can affect the dimensional accuracy of the workpiece; hence, it is necessary to monitor the additive manufacturing process online. At present, there is little research about formation-dimension monitoring in the GMA additive manufacturing process; in this paper, weld reinforcement prediction in the GMA additive manufacturing process was conducted, the visual-sensing system for molten pool was established, and a laser locating system was designed to match every frame of the molten pool image with the actual weld location. Extracting the shape and location features of the molten pool as visual features, on the basis of a back-propagation (BP) neural network, we developed the prediction model for weld reinforcement in the GMA additive manufacturing process. Experiment results showed that the model could accurately predict weld reinforcement. By changing the cooling time between adjacent cladding layers, the generalization ability of the prediction model was further verified.

The dependence of the temperature cycle in the cylinder of the CI engine when burning methyl hydroxide

In the course of burning, the processes of gas movement intensively occur in the cylinder, which contribute to heat transfer to the cylinder walls. A diesel engine has different heat dissipation conditions than a gas engine. Due to the higher compression ratio, the temperature of the gases leaving the cylinder is much lower. The temperature of the gases in the cylinder in the course of burning reaches 2000-2300 °C. Using methyl hydroxide and changing the installing angles of advancing fuel injection there is a tendency to change the temperature of the cycle in the cylinder of the diesel engine. Starting from a certain position of the piston in the course of the compression stroke, the air temperature becomes higher than the wall temperatures, and the heat flux changes direction, i.e., heat is transferred from the air to the cylinder walls.

Performance investigation of a battery thermal management system with microencapsulated phase change material suspension

In electric vehicles, the performance of the battery thermal management system (BTMS) is closely related to the life and safety of the power batteries. Microencapsulated phase change material suspension (MEPCMS) has good thermal management property, and has been used in many fields of industry. In order to investigate the feasibility of applying MEPCMS to the BTMS, a BTMS model using liquid cold plates is established. It is found that compared with natural heat dissipation condition, using water or MEPCMS as the coolant can significantly reduce the maximum temperatures of the tabs and on the battery body at the end of 5C discharge, but increase the maximum temperature difference on the battery body. The effects of the flow rate of the MEPCMS, the volume fraction of the microencapsulated phase change material (MEPCM), the latent heat and the melting temperature range of the phase change material (PCM) on the thermal management performance are investigated. All these above design parameters can significantly affect the temperature distribution of the battery. Based on the analysis results, an improved design using MEPCMS as the coolant is obtained, and its performance is better than that using water.

Numerical study of heat transfer characteristics in positional wire and arc additive manufacturing

PurposeThis paper aims to fabricate inclined thin-walled components using positional wire and arc additive manufacturing (WAAM) and investigate the heat transfer characteristics of inclined thin-walled parts via finite element analysis method.Design/methodology/approachAn inclined thin-walled part is fabricated in gas metal arc (GMA)-based additive manufacturing using a positional deposition approach in which the torch is set to be inclined with respect to the substrate surface. A three-dimensional finite element model is established to simulate the thermal process of the inclined component based on a general Goldak double ellipsoidal heat source and a combined heat dissipation model. Verification tests are performed based on thermal cycles of locations on the substrate and the molten pool size.FindingsThe simulated results are in agreement with experimental tests. It is shown that the dwell time between two adjacent layers greatly influences the number of the re-melting layers. The temperature distribution on both sides of the substrate is asymmetric, and the temperature peaks and temperature gradients of points in the same distance from the first deposition layer are different. Along the deposition path, the temperature distribution of the previous layer has a significant influence on the heat dissipation condition of the next layer.Originality/valueThe established finite element model is helpful to simulate and understand the heat transfer process of geometrical thin-walled components in WAAM.

Quantum Transport in a Silicon Nanowire FET Transistor: Hot Electrons and Local Power Dissipation.

A review and perspective is presented of the classical, semi-classical and fully quantum routes to the simulation of electro-thermal phenomena in ultra-scaled silicon nanowire field-effect transistors. It is shown that the physics of ultra-scaled devices requires at least a coupled electron quantum transport semi-classical heat equation model outlined here. The importance of the local density of states (LDOS) is discussed from classical to fully quantum versions. It is shown that the minimal quantum approach requires self-consistency with the Poisson equation and that the electronic LDOS must be determined within at least the self-consistent Born approximation. To bring in this description and to provide the energy resolved local carrier distributions it is necessary to adopt the non-equilibrium Green function (NEGF) formalism, briefly surveyed here. The NEGF approach describes quantum coherent and dissipative transport, Pauli exclusion and non-equilibrium conditions inside the device. There are two extremes of NEGF used in the community. The most fundamental is based on coupled equations for the Green functions electrons and phonons that are computed at the atomically resolved level within the nanowire channel and into the surrounding device structure using a tight binding Hamiltonian. It has the advantage of treating both the non-equilibrium heat flow within the electron and phonon systems even when the phonon energy distributions are not described by a temperature model. The disadvantage is the grand challenge level of computational complexity. The second approach, that we focus on here, is more useful for fast multiple simulations of devices important for TCAD (Technology Computer Aided Design). It retains the fundamental quantum transport model for the electrons but subsumes the description of the energy distribution of the local phonon sub-system statistics into a semi-classical Fourier heat equation that is sourced by the local heat dissipation from the electron system. It is shown that this self-consistent approach retains the salient features of the full-scale approach. For focus, we outline our electro-thermal simulations for a typical narrow Si nanowire gate all-around field-effect transistor. The self-consistent Born approximation is used to describe electron-phonon scattering as the source of heat dissipation to the lattice. We calculated the effect of the device self-heating on the current voltage characteristics. Our fast and simpler methodology closely reproduces the results of a more fundamental compute-intensive calculations in which the phonon system is treated on the same footing as the electron system. We computed the local power dissipation and “local lattice temperature” profiles. We compared the self-heating using hot electron heating and the Joule heating, i.e., assuming the electron system was in local equilibrium with the potential. Our simulations show that at low bias the source region of the device has a tendency to cool down for the case of the hot electron heating but not for the case of Joule heating. Our methodology opens the possibility of studying thermoelectricity at nano-scales in an accurate and computationally efficient way. At nano-scales, coherence and hot electrons play a major role. It was found that the overall behaviour of the electron system is dominated by the local density of states and the scattering rate. Electrons leaving the simulated drain region were found to be far from equilibrium.

Magnon-induced optical high-order sideband generation in hybrid atom-cavity optomagnonical system.

The nonlinearity of magnons plays an important role in the study of an optomagnonical system. Here in this paper, we focus on the high-order sideband and frequency comb generation characteristics in the atom coupled optomagnonical resonator. We find that the atom-cavity coupling strength is related to the nonlinear coefficients, and the efficiency of sidebands generation could be reinforced by tuning the polarization of magnons. Besides, we show that the generation of the sidebands could be suppressed under the large dissipation condition. This study provides a novel way to engineer the low-threshold high-order sidebands in hybrid optical microcavities.

Coupled Magnetic Field-Thermal Network Analysis of Modular-Spoke-Type Permanent-Magnet Machine for Electric Motorcycle

Brushless modular spoke type permanent magnet (MSTPM) machine has exhibited prior electromagnetic (EM) performance over conventional surface-mounted PM machines for in-wheel traction system in electric vehicles (EVs). However, analysis of thermal behavior of MSTPM machines is rather insufficient, even accurate thermal analysis is of significant importance due to poor heat dissipation condition inside the wheel hub. Conventionally, the losses produced in electrical machines by EM prediction is equivalent to the heat source in normal thermal analysis, and only the resultant thermal behavior is investigated. However, the reaction of temperature rising on the EM performance is neglected. In this article, a bi-directional coupled electromagnetic-thermal analysis method is proposed and carried out by a combination of lumped parameter thermal network (LPTN) model and finite element method (FEM), where both steady-state temperature distribution and transient-state temperature rise are investigated for MSTPM machines. By finite number of iterations between magnetic and thermal fields, the electromagnetic performance and thermal behavior can be predicted more accurately due to the coupling effect considered. The coupled model-predicted results are verified by 3D-FEM and experimental measurement, which shows that the proposed method has advantages in both computational efficiency and accuracy as well as can be applied to other electrical machines.

Global well-posedness for systems of hyperbolic-parabolic composite type with center manifold

Concerning the global existence of classical solution to systems of hyperbolic-parabolic composite type, a well-known general theory was established by Kawashima in [4], where the dissipation condition (Kawashima-Shizuta condition) to the linearized system plays a fundamental role. Recently, systems with much weaker dissipations have attracted a lot of attentions, see [1,2,10,11] among others. The typical feature of this kind of system is that the corresponding linearized system has one eigenvalue with the real part equals to zero. This violates the Kawashima-Shizuta stability conditions. In this paper, we develop a general global well-posedness theory for this kind of system. Moreover, as the applications of the general theory, several examples are given.

Effect of ambient dissipation condition on thermal behavior of a lithium-ion battery using a 3D multi-partition model

The accurate prediction of lithium-ion batteries thermal behaviors is critical to design battery thermal management system. Herein, a three dimensional (3D) multi-partition thermal model coupled with a thermal network model is established to study the thermal behavior of an 18650 cylindrical lithium-ion battery under different ambient dissipation conditions. The validity of the proposed model is demonstrated experimentally via discharge tests and infrared thermal imaging. The developed model is applied to study the temperature distribution of the battery under different discharge rates and heat dissipation conditions. The results show that the 3D multi-partition thermal model has higher accuracy than lumped thermal method. The maximum error of averaging surface temperature between multi-partition model and experiment data is less than 3.5%. Through the analysis of volumetric heat generation rate, the battery cap is found as the one of heat concentrated areas and might cause the temperature gradient in the battery. Meanwhile, ambient dissipation condition plays an important role on the thermal behavior of batteries. With the increasing of convection heat transfer coefficient, the high temperature region of the battery is narrowed and the temperature of the battery tends to be uniform. The maximum surface temperature is decreased from 81.6 °C to 29.9 °C, and the maximum difference is decreased from 9.3 °C to 0.5 °C at 3C discharge rate.

Enhanced Cooling of LED Filament Bulbs Using an Embedded Tri-Needle/Ring Ionic Wind Device

Improving the heat dissipation ability for light-emitting diode (LED) filament bulb is very difficult. A tri-needle/ring ionic wind generator was developed to improve the heat dissipation condition of bulbs. The operation characteristics of the ionic wind generator, such as the electrode gap, inception voltage, and discharge current with regard to the operation voltage, were studied by experiments. The ionic wind velocity within the bulb was investigated under different electrode gaps and applied voltages. The temperature drop achieved by the ionic was were tested with the consideration of many operation parameters for analysis. The experiments showed that ionic wind can provide efficient and stable cooling effect for LED filament bulbs. The temperature drop of LED junction can reach 30 °C at best. Good stability and adjustability of the ionic wind generator were demonstrated by tracing the temperature history of LED filaments in long-term tests. Finally, the light efficiency of LED filament bulbs with ionic wind cooling was studied. The experimental results showed that light efficiency was improved by 7.3% under the best cooling case. The experimental results indicate that the embedded ionic wind generator can provide an effective solution for cooling LED filament bulbs.

Chemical-Fuel-Driven Assembly in Macromolecular Science: Recent Advances and Challenges.

In the past decade, chemical-fuel-driven processes have been integrated with synthetic self-assembled systems, in which both the formation and properties can be carefully controlled. This strategy can drive systems far away from equilibrium, tailor the lifetime window of transient self-assembled systems, thus holding promise for future smart, adaptive, self-regulated, and life-like systems. By judging whether the building blocks or transient self-assembled systems participate in the fuel-to-waste conversion, the reported systems can be divided into two classes: dissipative self-assembly and self-assembly under dissipative conditions. Among these systems, the utilization of macromolecular building blocks to design non-equilibrium self-assemblied systems is becoming common. Macromolecular systems capable of dissipating energy with a programmed time domain have found widespread application, and have therefore been an active field of scientific inquiry. This Minireview aims to highlight the recent progress and opportunities of chemical-fuel-driven assembly in macromolecules. We envision that chemical-fuel-driven approach will play an increasingly important role in polymer science in the near future.

Epitaxial laser deposition of single crystal Ni-based superalloys: Repair of complex geometry

Abstract A multi-track single crystal structure produced by laser cladding can be succeeded on a flat but failed on complex geometry for single crystal superalloys repair. It was always accompanied with stray grains and cracks when the complex shape defects were repaired by laser cladding. According to analysis, the geometrical profile of the defect may change the heat dissipation condition during laser cladding so that it promotes to form stray grains locally. In this paper, the off-axis heat flow angle (β) which was defined by the heat flow direction and the dendritic growth direction, was used to evaluate the formation of stray grains. Results showed that dendrites grew epitaxially along the preferred crystal orientation which was closer to heat flow. In addition, stray grains could not be formed in the epitaxial columnar dendrite region until the β was more than the critical value of 30°. Two preferred orientations competed for growth perpendicular to each other when the β was close to 45°. Therefore, the repair principle was proposed that the β was not more than 30° ensured by geometrical profile design, and a v-groove defect was successfully guided and repaired.

Boundedness for reaction–diffusion systems with Lyapunov functions and intermediate sum conditions

We study the uniform boundedness of solutions to reaction–diffusion systems possessing a Lyapunov-like function and satisfying an intermediate sum condition. This significantly generalizes the mass dissipation condition in the literature and thus allows the nonlinearities to have arbitrary polynomial growth. We show that two dimensional reaction–diffusion systems, with quadratic intermediate sum conditions, have global solutions which are bounded uniformly in time. In higher dimensions, bounded solutions are obtained under the condition that the diffusion coefficients are quasi-uniform, i.e. they are close to each other. Applications include boundedness of solutions to chemical reaction networks with diffusion.

On uniqueness and instability for some thermomechanical problems involving the Moore–Gibson–Thompson equation

It is known that in the case that several constitutive tensors fail to be positive definite the system of the thermoelasticity could become unstable and, in certain cases, ill-posed in the sense of Hadamard. In this paper, we consider the Moore–Gibson–Thompson thermoelasticity in the case that some of the constitutive tensors fail to be positive and we will prove basic results concerning uniqueness and instability of solutions. We first consider the case of the heat conduction when dissipation condition holds, but some constitutive tensors can fail to be positive. In this case, we prove the uniqueness and instability by means of the logarithmic convexity argument. Second we study the thermoelastic system only assuming that the thermal conductivity tensor and the mass density are positive and we obtain the uniqueness of solutions by means of the Lagrange identities method. By the logarithmic convexity argument we prove later the instability of solutions whenever the elasticity tensor fails to be positive, but assuming that the conductivity rate is positive and the thermal dissipation condition hold. We also sketch similar results when conductivity rate and/or the thermal conductivity fail to be positive definite, but the elasticity tensor is positive definite and the dissipation condition holds. Last sections are devoted to considering the case when a third-order equation is proposed for the displacement (which comes from the viscoelasticiy). A similar study is sketched in these cases.

The layout of Boussinesq couple-stress fluid flow over an exponentially stretching sheet with slip in porous space subject to a variable magnetic field

PurposeThe purpose of this study is to present the significance of Joule heating, viscous dissipation, magnetic field and slip condition on the boundary layer flow of an electrically conducting Boussinesq couple-stress fluid induced by an exponentially stretching sheet embedded in a porous medium under the effect of the magnetic field of the variable kind. The heat transfer phenomenon is accounted for under thermal radiation, Joule and viscous dissipation effects.Design/methodology/approachThe governing nonlinear partial differential equations are transformed to the nonlinear ordinary differential equations (ODEs) by using some appropriate dimensionless variables and then the consequential nonlinear ODEs are solved numerically by making the use of the well-known shooting iteration technique along with the standard fourth-order Runge–Kutta integration scheme. The impact of emerging flow parameters on velocity and temperature profiles, streamlines, local skin friction coefficient and Nusselt number are described comprehensively through graphs and tables.FindingsResults reveal that the velocity profile is observed to diminish considerably within the boundary layer in the presence of a magnetic field and slip condition. The enhanced radiation parameter is to decline the temperature field. The slip effect is favorable for fluid flow.Originality/valueTill now, slip effect on Boussinesq couple-stress fluid over an exponentially stretching sheet embedded in a porous medium has not been explored. The present results are validated with the previously published study and found to be highly satisfactory.

Asymptotic Dissipativity for Merged Stochastic Evolutionary Systems with Markov Switchings and Impulse Perturbations under Conditions of Lévy Approximation

Conditions for asymptotic dissipativity are established for the merged system of stochastic differential equations with Markov switchings and impulse perturbations under conditions of Levy approximation. In particular, it is analyzed how the behavior of the boundary process depends on the pre-limiting normalization of a stochastic evolution system in the ergodic Markovian environment under the conditions of Levy approximation.

Hard Alloy Production by SHS Compaction in Open Matrix

The possibility of performing SHS for the composition (wt %) 81.5Ti + 18.5B in air with subsequent compaction of combustion products in an open steel mold with the walls limiting their radial flow under severe heat dissipation conditions without using an intermediate loose heat insulator is investigated. The preparation modes of reaction powder mixtures to the synthesis is optimized. Process characteristics such as loose density, densification, and elastic aftereffect are performed, and the strength of compacts is evaluated. It is shown that the interrelation between the strength of charge compacts, combustion rate, and variation in the volume after combustion in air occurs. The optimal density of charge compacts is found to be 0.75, which corresponds to the maximum combustion rate without charge escapes and with a minimum change in volume. As a result of the optimization, the possibility of an efficient and safe synthesis process without using an intermediate insulator friable medium is shown. Hard-alloy plates 60 mm in diameter and 11 mm in thickness are prepared under the conditions of SHS compaction in an open steel mold. The structure of prepared hard alloy is unique with porosity smaller than 0.5% and consists of titanium diboride (~60 wt %) and binder titanium-based phase (~40 wt %). Such a structure, formed due to accelerated cooling, can be determined as nonequilibrium according to the phase diagram of the Ti–B system; titanium monoboride (TiB) should be the main phase for the composition under investigation. The microhardness of the fabricated hard alloy is HV = 18 000 MPa.