Constant Temperature Field Research Articles

Formulation of the extended plane wave expansion for in‐plane and out‐of‐plane vibrations in viscoelastic phononic thin plates under a constant temperature field

AbstractIn this study, we develop an extended plane wave expansion method to determine the complex elastic band gaps for both in‐plane and out‐of‐plane vibrations in a viscoelastic phononic crystal (PnC) thin plate model under a constant temperature field. The periodic structure of the thin plate comprises a unit cell (UC) consisting of an epoxy matrix and circular steel inclusions. In this configuration, we consider the viscoelastic effects described by the generalized Maxwell model arising from the epoxy matrix. Furthermore, we incorporate thermal effects in the UC, accounting for the linear dependence of the Young's modulus on the temperature of the epoxy matrix, assuming the absence of heat flow in the dimensions of the UC. We present a band structure illustrating the displacement of the real and imaginary parts of the complex band structure for evanescent waves arising from the viscoelastic PnC thin plate, considering both in‐plane and out‐of‐plane vibrations.

Coupled thermomechanical analysis using isoparametric curved shell elements

This study focuses on the coupled thermo-mechanical formulation in isoparametric shell elements and its implementation in curved laminar structures. The formulation is based on the direct isoparametric formulation, specifically designed for flat and curved shell elements, and relies on the theory of degenerated solids. The research provides a comprehensive description of the coupled thermo-mechanical analysis, including the mechanical equilibrium equations, the interrelations between stress, temperature, displacement, deformation, and the conservation of thermal energy. It adopts a simultaneous approach to addressing the impacts of temperature and mechanical loads. The paper elaborates on various numerical examples that substantiate the formulation. These examples include simulations that encompass linear scenarios, which are then compared to analytical solutions and results derived from other numerical software. The examples highlighted include one-dimensional temperature diffusion, radial diffusion, and the thermal behavior of a cylindrical cover and a pipe under a linear temperature gradient. These simulations demonstrate the formulation's capacity to accurately capture the interactions between temperature variations and structural displacements. They also confirm the alignment of the proposed model with existing analytical and numerical solutions. In conclusion, the research provides a good framework for coupled thermo-mechanical analysis. The flexibility of the formulation is evidenced across different configurations and scenarios, accommodating various types of boundary conditions such as constant and linear temperature fields, distributed loads, and constraints on displacements and rotations. It effectively manages temperature flows across one, two, and three dimensions, highlighting its extensive applicability in the realm of structural analysis. This versatility underscores its broad applicability in the field of structural analysis.

Effect of temperature on tribofilm growth and the lubrication of the piston ring-cylinder liner system in two-stroke marine engines

This study is an optimized extension based on the authors’ previous research on the tribo-chemical reaction under constant temperature field of two-stroke internal combustion engines (ICEs). It establishes a coupled analysis model that considers the tribo-chemical reactions, dynamic contact, and interface lubrication of the piston ring-cylinder liner (PRCL) system under transient temperature conditions. In this study, for the first time, the prediction of the tribofilm thickness and its influence on the surface micro-topography (the comprehensive roughness) are coupled in the working temperature field of the PRCL system, forming an effective model framework and providing a model basis and analytical basis for subsequent research. This study findings reveal that by incorporating temperature and tribofilm into the simulation model, the average friction deviation throughout the stroke decreases from 8.92% to 0.93% when compared to experimental results. Moreover, the deviation during the combustion regime reduces from 39.56% to 7.34%. The proposed coupled model provides a valuable tool for the evaluation of lubrication performance of the PRCL system and supports the analysis software forward design in two-stroke ICEs.

Energy loss of heavy quarks in the presence of magnetic field

We study the heavy quark energy loss in the presence of a background magnetic field. The analysis considers the high magnetic field generated by spectators from initial hard collisions that were incorporated using the medium-modified Debye mass, determined from quark condensates at finite temperature and magnetic field via recent lattice quantum chromodynamics calculations. We analyse the impact of medium polarization on the heavy quark propagation in a quark–gluon plasma formed in relativistic heavy-ion colliders like relativistic heavy ion collider and large hadron collider. For simplification, we considered the static medium with constant temperature and magnetic field values. Then, we explore the nuclear modification factor (R AA) at different magnitudes of magnetic field strengths at fixed temperatures. The energy loss of heavy quarks significantly increases, leading to R AA suppression at higher magnetic field values.

Numerical simulation of fracking and gas production in shale gas reservoirs

AbstractIn this work, different stages of gas production in shale reservoirs are modelled. First, hydraulic fracturing is considered by injecting water at high pressures to crack the formation and increase the flow capacity of the reservoir. During the fluid injection, rock properties are modified and water appears in the stimulated area. Then, these changes can be detected through seismic monitoring. Finally, once the fracking stage is completed, the simulation of gas production begins. The simultaneous gas–water flow in the injection and production stages is modelled using the Black‐Oil formulation. Furthermore, a fracture criterion is applied under the hypothesis of constant temperature and constant stress field in this first analysis of the problem. The numerical simulations allow us to analyse the propagation of the fracture and the behaviour of the pore pressure and water saturation in the stimulated area. The advance of the fracturing fluid is delayed in relation to the breakdown of the rock. Besides, the presence of new fractures is detected by applying a poroviscoelastic wave propagation simulator that considers mesoscopic losses induced by heterogeneities in rock and fluids. After the fracture network is created, the injection well becomes a producer, allowing the extraction of gas and the flowback of the injected fluid. The simulated gas flow rates are compared with those obtained by a simplified single‐phase analytical solution used for practical applications, achieving optimum matching results.

Explicit Formulas for the Deformation of Chiral Porous Circular Beams in Gradient Thermoelasticity

Chirality and porosity are characteristic properties of nanostructured materials. Their effects on the mechanical behaviour of structural elements, such as shells, plates and beams, cannot be disregarded. In this paper, we study the thermoelastic deformation of a chiral porous circular beam loaded with an axial force and torque. The beam is also under the action of a constant temperature field. The analytical solution is obtained using the results established in a paper recently published by the Author within the context of the strain gradient theory proposed by Papanicopolous. In the constitutive equations, the chirality is introduced by a material constant parameter and the porosity is described by means of a scalar function. Displacements, microdilatation function, and stress and strain fields are expressed in explicit form and in terms of engineering constants. Explicit formulas of the stiffness of chiral porous circular beams are presented and the effects of right and left chirality are discussed.

Effect of fluid-particle interaction on 2D Rayleigh-Bénard laminar convection of a temperature-sensitive magnetic fluid

Rayleigh-Bénard (R–B) laminar convection of a temperature-sensitive magnetic fluid (TSMF) with an immersed nonmagnetic particle in a square cavity heated from the bottom and subject to an external magnetic field is investigated experimentally and numerically, which restricts to the initial constant temperature and stationary flow fields with perfect thermal insulated wall condition. The flow and particle behaviors as well as the heat transfer characteristic are examined at different Ra (Ra < 4 × 104) and Ram (Ram = 0, 1.89 × 108, and 3.14 × 108). The magnetic field slightly precipitates the onset of convection and the transition of the flow pattern. The particle may influence the early flow development and the final flow pattern, depending on the initial location of the particle, Ra, and Ram. Over certain ranges of the parameters, the particle stabilizes the flow by shifting the higher flow mode (bicellular) to the lower one (unicellular) and improves the heat transfer performance. The numerical results confirm the experimental findings and provide more detailed behaviors of the flow and temperature fields as well as the particle.

Study on wall-slipping mechanism of nano-injection polymer under the constant temperature fields

Abstract Polyphenylene sulfide (PPS) and copper (Cu) were used as the polymer and substrate material to simulate the nano-injection molding process by molecular dynamics method. The results show that the PPS chain obeys Einstein’s diffusion law in the early stage of injection molding then deviates from it in the late stage due to the entanglement and limitation of surrounding nanoparticles. In addition, the process of conformational isomerization of polymer chains is accompanied by the twisting and stretching of fixed chains. There are two kinds of adhesion phenomena, one is the macromolecular slides violently in small areas of some sure nanoscale groove to form multiple anchor points. The other case involves multiple nano-grooves along the metal interface, the polymer chain slides and is bolted as multiple anchors in different grooves due to the exerted wall-drag effect on the neighboring chains. These two slipping and anchoring mechanisms are consistent with de Gennes’ slipping theory. Through the quantitative analysis of the influence of pressure on injection filling, it is found that injection pressure should be kept within a certain range to achieve the positive effect of molding.

Acoustic pyrometry for flow velocity estimation: preliminary analysis

Acoustic pyrometry uses the variations of the speed of sound in a medium to determine its temperature. One of the assumptions at the base of this technique is that the flow velocity component in the direction of the acoustic path is negligible in comparison to the speed of sound. However, if the temperature of the medium is known, the acoustic pyrometry approach can be used to determine flow speed, as long as the flow is not perpendicular to the acoustic path. The combined approach of temperature and velocity determination is also known as acoustic tomography. This technique allows the determination of velocity and temperature maps in a flow region. Even though this is an interesting result, the mathematical approach to solve the velocity and temperature fields might be very complex and sensitive measurement set-up. In this study, a preliminary investigation is carried out to determine the flow velocity by starting from the time of flight of an acoustic signal moving along different acoustic paths in a constant temperature field. For this purpose, a simplified geometry is considered. The developed mathematical approach at the base of the methodology is presented in this study.

Approximate analytical method for calculating the heating process of concrete structures in heating formwork

The use of electric heating of concrete during construction in winter makes it possible to create an optimal thermal regime in which the hardening process takes place, and to obtain a structure of the required quality. When developing a system for automatic control of the heating process, it is necessary to determine the law of regulating the power of heaters. This article presents a method for calculating the thermal heating regime of concrete structures in heating formwork, the essence of which is to reduce the boundary value problem of thermal conductivity to a system of equivalent integral equations. To solve this problem, a theoretical study was carried out, a theoretical study of the heat transfer process in concrete structures heated during winter concreting was carried out, and a mathematical description of this process was presented in the form of a system of differential equations. After the transformations of the above system of equations and the application of the Green function of the second kind to it for the plate and rod, an approximate solution of the equivalent equation was obtained. As a result of the application of the asymptotic method to the solution of the integral equation, an analytical solution of the problem under consideration is obtained. The resulting solution makes it possible to determine the temperature fields on the concrete surface, as well as the value of the specific heat flux from electric heaters. In order to automate the process of performing the thermal calculation of heating concrete structures with the help of heating forms, a program for calculating temperature fields in heating forms has been developed based on the solution obtained, which makes it possible to effectively solve the tasks of monitoring and controlling the concrete hardening process. The developed program makes it possible to calculate temperature fields not only at constant heater power, but also when it changes with the help of regulators. The presented method of thermal calculation with a hardware and software complex for regulating the power of electric heaters allows solving a fairly wide range of tasks related to maintaining a constant temperature field.

Preparation and multilayer transfer of high-quality monocrystalline graphene grown on centimeter-Cu (111) substrate

Graphene, owing to its excellent mechanical properties, shows promising application prospects in the field of pressure sensing. Currently, chemical vapor deposition (CVD) is an effective method to synthesize graphene artificially. It is challenging to grow large monocrystals by single-point nucleation. However, meeting multiple requirements (e.g., monocrystal and monolayer) is difficult when graphene is grown by multipoint nucleation, which critically limits their practical applications. In this study, we report the growth of monocrystal and monolayer graphene on a centimeter-scale Cu (111) substrate using CVD. Multiphysics coupling establishes the guidance results of gradient and constant temperature fields, obtains a high-purity Cu (111) substrate in a gradient temperature field, and grows monolayer graphene in a constant temperature field. Experiments show that choosing the optimum time during the temperature drop of the monocrystal substrate can cause total area coverage of Cu foil transfer toward Cu (111). The concentration gradient grew larger monocrystals of graphene with the Young's modulus of 0.837 TPa on the Cu (111) substrate following multipoint nucleation. Furthermore, multilayer graphene with good uniformity was synthesized.

Engineering Method for Calculating the Process of Heating Concrete Structures in Heating Formworks

Issues related to the technology of winter concreting are very relevant. The organization of heating the erected monolithic enclosing structures with minimal thermal or electrical energy consumption is undoubted of scientific and practical interest. The use of electric heating of concrete during construction in winter allows one to create an optimal thermal regime. The hardening process takes place and obtains a structure of the required quality. When developing an automatic control system for the heating process, it is necessary to determine the law for regulating the power of the heaters. This article presents a methodology for calculating the thermal regime of heating concrete structures in heating formwork. The essence is to reduce the boundary value problem of thermal conductivity to a system of equivalent integral equations. A theoretical study of the heat transfer process in concrete structures heated during winter concreting was carried out. A mathematical description of this process was presented in a system of differential equations. After transformations of the above system of equations and applying Green's function of the second kind for the plate and the rod, an approximate solution of the equivalent equation was obtained. As a result of applying the asymptotic method to the integral equation, an analytical solution of the problem under consideration is obtained. The solution obtained makes it possible to determine the temperature fields on the concrete surface and the value of the specific heat flux from electric heaters. A program for calculating temperature fields in heating formworks has been developed. This program effectively solves the problems of monitoring and controlling the concrete hardening process to automate the thermal calculation of heating concrete structures with the help of heating formworks, based on the solution obtained. The developed program makes it possible to calculate the temperature fields at a constant power of the heaters and when it is changed with the help of regulators. The presented method of thermal calculation with a hardware-software complex for controlling the power of electric heaters allows solving a relatively wide range of problems associated with maintaining a constant temperature field.

Strength of Curvilinearly Reinforced Plates in a Polar Coordinate System

А computer simulation of flat structures to create a fiber composite with curved reinforcement along spiral trajectories in the polar coordinate system has been performed. Numerical comparisons of the reachability of limit states for various reinforcement structures by two families of continuous curved fibers have been made. The calculations take into account the influence of a constant temperature field. In this paper, analytical solutions of the reinforcement intensity function of the differential equation of the constancy of the fiber cross sections for the families of logarithmic and algebraic spirals are found. The analysis of the results shows that due to the choice of curved laying of reinforcing fibers, it is possible to obtain a structure with predetermined properties

Analysis of the ghost and mirror fields in the Nernst signal induced by superconducting fluctuations

We present a complete analysis of the Nernst signal due to superconducting fluctuations in a large variety of superconductors from conventional to unconventional ones. A closed analytical expression of the fluctuation contribution to the Nernst signal is obtained in a large range of temperature and magnetic field. We apply this expression directly to experimental measurements of the Nernst signal in ${\mathrm{Nb}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x}$ thin films and ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$ superconductors. Both magnetic field and temperature dependence of the available data are fitted with very good accuracy using only two fitting parameters, the superconducting temperature ${T}_{\mathrm{c}0}$ and the upper critical field ${H}_{\mathrm{c}2}(0)$. The obtained values agree very well with experimentally obtained values. We also extract the ghost lines (the maximum of the Nernst signal for constant temperature or magnetic field) from the complete expression and also compare it to several experimentally obtained curves. Our approach predicts a linear temperature dependence for the ghost critical field well above ${T}_{\mathrm{c}0}$. Within the errors of the experimental data, this linearity is indeed observed in many superconductors far from ${T}_{\mathrm{c}0}$.

Analysis of Nonlinear Vibrations of Slightly Curved Tripled-Walled Carbon Nanotubes Resting on Elastic Foundations in a Magneto-Thermal Environment

In this work, nonlocal elasticity theory is applied to analyze nonlinear free vibrations of slightly curved multi-walled carbon nanotubes resting on nonlinear Winkler and Pasternak foundations in a thermal and magnetic environment. With the aid of Galerkin decomposition method, the systems of nonlinear partial differential equations are transformed into systems of nonlinear ordinary differential equations which are solved using homotopy perturbation method. The influences of elastic foundations, magnetic field, temperature rise, interlayer forces, small scale parameter and boundary conditions on the frequency ratio are investigated. It is observed form the results that the frequency ratio for all boundary conditions decreases as the number of walls increases. Also, it is established that the frequency ratio is highest for clamped-simple supported and lowest for clamped-clamped supported. Further investigations on the controlling parameters of the phenomena reveal that the frequency ratio decreases with increase in the value of spring constant (k1) temperature and magnetic field strength. It is hoped that this work will enhance the applications of carbon nanotubes in structural, electrical, mechanical and biological applications especially in a thermal and magnetic environment.

Slow flocking dynamics of the Cucker-Smale ensemble with a chemotactic movement in a temperature field

We study slow flocking phenomenon arising from the dynamics of Cucker-Smale (CS) ensemble with chemotactic movements in a self-consistent temperature field. For constant temperature field, our situation reduces to the previous CS model with chemotactic movements. When a large CS ensemble with chemotactic movements is placed in a self-consistent temperature field, the dynamics of the CS ensemble can be effectively described by the kinetic thermodynamic CS (TCS) equation with chemotactic movements, which corresponds to the coupled collisional transport-reaction diffusion system. For the proposed coupled model, we provide a global solvability of strong solutions and their asymptotic flocking estimates which exhibit slow algebraic relaxation toward the flocking state. Our analytical results show that asymptotic flocking is robust with respect to a small perturbation of a constant temperature.

On the Cucker--Smale Ensemble with the q-Closest Neighbors in a Self-Consistent Temperature Field

We present emergent dynamics of the continuous and discrete Cucker--Smale (CS) type models with the q-closest neighbors in a self-consistent time-varying temperature field. Asymptotic flocking dynamics of the thermodynamic Cucker--Smale (TCS) ensemble has been extensively studied using particle, kinetic, and fluid models under several connection topologies that can be realized by the complete network, connected symmetric network, directed graph with a spanning tree, etc. In this paper, we propose sufficient frameworks for the monocluster flocking of the continuous and discrete TCS models on a digraph with a neighbor set determined by q-closest neighbors from the test particle. In our proposed frameworks, there can be a phase-transition-like phenomenon from local (multicluster) flocking to global (monocluster) flocking, depending on the size q of the neighbor set, as we increase q. When q is larger than half of the population, any initial configuration will tend to the monocluster flocking state in a positive coupling regime. In contrast, when q is smaller than half of the population, we need to impose some restrictive conditions on the initial data to guarantee the emergence of monocluster flocking. Thus, our results generalize Cucker and Dong's result [Math. Models Methods Appl. Sci., 26 (2016), pp. 2685--2708] for the CS ensemble in a homogeneous constant temperature field. We also provide several numerical examples and compare them with our analytical results.

Directional Gradientless Thermoexcited Rotating System Based on Carbon Nanotubes and Graphene

The simple and practicable intrinsic driving mechanism is of great significance for the design and development of nanoscale devices. This paper proposes a nanosystem that can achieve directional gradientless thermoexcited rotation at a relatively high temperature field (such as 300 K). In the case of a constant temperature field, the difference in atomic van der Waals (VDW) potentials in different regions of the rotor can be achieved by an asymmetric design of the structure, which provides torque for the rotation of the rotor. We studied the rotation and driving mechanism of the designed system through molecular dynamics (MD) simulation and discussed the influence of the chiral combination of carbon nanotubes, the chirality of graphene substrate, the length of graphene substrate, and the system temperature on rotation. At the same time, this paper also makes a qualitative analysis of the feasibility of the designed system from the perspective of molecular mechanics combined with energy. This research provides a new idea of nanoscale driving rotation, which has guiding significance for the design and application of related nanodevices in the future.

Flow behavior and heat transfer characteristics in Rayleigh-Bénard laminar convection with fluid-particle interaction

The present study experimentally and numerically investigates the Rayleigh-Bénard (R-B) laminar convection of a Newtonian fluid in a square cavity heated from the bottom wall at the initial conditions of constant temperature field and stationary flow field over the range of Rayleigh number Ra ≤ 4 × 104. The effect of a freely-moving particle in the cavity on the flow pattern and heat transfer characteristics is discussed. When the stable multi-stability patterns coexist, i.e. Ra is beyond a certain critical value, the final flow pattern can be manipulated by adjusting the initial position of the particle. The bicellular mode is established if the particle is located at the bottom center of the cavity while the unicellular mode is established if the particle is away from the center. The present results demonstrate that at the same Ra, the thermal performance is mainly determined by the flow pattern but not the presence of a particle. However, one can control the final flow pattern for R-B convection by adjusting the initial position of the particle, which consequently determines the thermal performance.

Nonlinear vibrations of single- and double-walled carbon nanotubes resting on two-parameter foundation in a magneto-thermal environment

The excellent mechanical, electrical, structural and thermal properties coupled with high strength to weight ratio of carbon nanotubes have tremendously expanded their applications in various industrial, engineering, physical and natural sciences processes. In this work, nonlocal elasticity theory is used to analyze nonlinear vibrations of single and double-walled carbon nanotubes resting on two-parameter foundation in a thermal and magnetic environment. With the aid of Galerkin decomposition method, the systems of nonlinear partial differential equations are transformed into systems of nonlinear ordinary differential equations which are solved using homotopy perturbation method. The developed analytical solutions are used to investigate the influences of elastic foundations, magnetic field, temperature rise, interlayer forces, small scale parameter and boundary conditions on the frequency ratio. From the results, it is observed that the frequency ratio for all boundary conditions decreases as the number of walls increases from single to double. Also, it is established that the frequency ratio is highest for clamped–simple supported and lowest for clamped–clamped supported. Additionally, the results revealed that the frequency ratio decreases with increase in the value of spring constant (k1) temperature and magnetic field strength. This work will enhance the applications of carbon nanotubes in structural, electrical, mechanical and biological applications especially in a thermal and magnetic environment.