Steady Temperature Field Research Articles

Self-galloping of a liquid crystal elastomer catenary cable under a steady temperature field

Thermally-driven self-sustained motion allows for direct absorption of heat from a steady temperature field to maintain its own continuous motion, making it a valuable technology for thermal sensors, harvesters, and soft robotics. Exploring a straightforward and durable system that operates with self-sustained motion driven by heat is a formidable challenge. Based on a thin liquid crystal elastomer (LCE) fiber, we propose a thermally-driven self-galloping catenary cable system in this paper. Experiments show that the LCE catenary cable can engage in continuous periodic self-galloping in a steady temperature field with gradient. Combining the well-established dynamic LCE model and catenary theory, the governing equations of the self-galloping LCE catenary cable are established and its dynamics are theoretically investigated. The LCE catenary cable always develops into two motion modes, i.e., static and self-galloping modes, according to numerical calculations. The theoretical predictions are in general agreement with the experimental results. The LCE catenary cable maintains the self-galloping by absorbing thermal energy to offset the damping dissipation. The effects of system parameters on the amplitude, frequency and equilibrium position of the self-galloping are also obtained. This LCE catenary cable has advantages in terms of simple structure, customizable size, minimal requirement for movement space, and flexible adjustment, and it is anticipated to satisfy the demands of actual complex scenarios such as thermal sensors, energy harvesters, and autonomous robots.

A real-time solution method for three-dimensional steady temperature field of transformer windings based on mechanism-embedded cascade network

To enhance the computation efficiency and accuracy of three-dimensional steady temperature field of transformer windings, we propose a new non-invasive Reduced Order Model (ROM) based on a mechanism-embedded cascade network. Initially, a snapshot matrix is formed from the Full Order Model (FOM) and then combined with Proper Orthogonal Decomposition (POD) to extract key modal features that characterize the temperature field. Subsequently, a cascade network architecture, integrating Multilayer Perceptron (MLP) and Radial Basis Function Neural Network (RBFNN), is devised to swiftly map working condition parameters to modal coefficients. Additionally, the cascade network is embedded with condition sensitivity and modal contribution mechanisms to further enhance prediction accuracy. Finally, by linearly weighting the modes with predicted modal coefficients, a rapid reconstruction of the steady temperature field in transformer windings is achieved. Validation against Fluent software simulations and experimental measurements demonstrate a close agreement, with computational errors of less than 4K and an impressive single solution time of only 0.0087 s, which is 48760 times faster compared to Fluent software.

Electromagnetic–Thermal Characteristics Analysis of a Tubular Permanent Magnet Linear Generator for Free-Piston Engines

Temperature rise of the tubular permanent magnet linear generator (TPMLG) might lead to insulation failure and demagnetization of permanent magnets, affecting the safe and stable operation of other equipment and the entire system. Herein, a bidirectional electromagnetic–thermal coupling method for analyzing the electromagnetic loss and thermal characteristics of a TPMLG considering the effect of increased temperature on the permanent magnet was proposed. To study the electromagnetic–thermal characteristics of the TPMLG under stable power generation, a two-dimensional electromagnetic field model and a three-dimensional temperature field model were established and coupled. The temperature field of the TPMLG was numerically calculated using computational fluid dynamics over finite volume method under natural air cooling and forced air cooling conditions. Effects of loss and air flow velocity on the steady temperature field were investigated. Results indicated that copper loss increased by 24.5% considering the influence of temperature rise. The windings’ top central position in the TPMLG was the spot with the highest temperature of 127.8 °C and there was a potential demagnetization risk for the permanent magnets. Some reference for future research of clarifying thermal characteristics and cooling design was provided.

An exact solution for the entropy base flow of electroosmotic magneto-nanofluid through microparallel channel

An exact solution of steady state, electroosmotic, transient magnetohydrodynamic (MHD) flow, and heat transfer of a viscous and incompressible electrically conducting nanofluid consists of water and Cu metal, through a microparallel channel under the combined effect of pressure and vertically acting magnetic field is found. An exact solution is calculated through Laplace transform using the software of Mathematica to find the steady velocity and temperature field depending on many dimensionless parameters. The electromagnetic couple effect, the volumetric generation of heat caused by the Joule heating effect, and viscous dissipation are considered to analyze the thermally fully formed heat flow problem based on the steady part of the velocity field. The exact result of the temperature field is obtained by taking the uniform boundary heat flux. The significant parameter of heat flow known as the Nusselt number, depending on the height of the microtube, is defined. At last, the entropy generation of MHD temperature flow is analyzed. The interpretation of variations that occurred in internal and external entropy generations is given and consequences are explained.

Study on the coupling relationship between wear and dynamics under steady uniform temperature field of planetary gear system

Study on the coupling relationship between wear and dynamics under steady uniform temperature field of planetary gear system

Effects of thermal dispersion on transient free convective flow in vertical porous channel filled with porous material

In this work, the effect of suction/injection on transient free convective flow in vertical porous (suction/injection on the channel surfaces) channel filled with porous material in the presence of thermal dispersion was studied. The Boussinesq assumption is applied and the nonlinear governing equations of motion and energy are developed. The time dependent problem is solved using implicit finite difference method while steady state problem is solved by perturbation technique method. The solution obtained is graphically represented and the effects of suction/injection, time, Darcy number, thermal dispersion, and Prandtl number on the fluid flow and heat transfer characteristics. During the course of computation, an excellent agreement was found between the well-known steady state solutions sand transient solutions at large value of time. Furthermore, the time required to reach steady state velocity and temperature field strongly dependent on suction/injection parameter, Prandtl number and thermal dispersion parameter. The introduction of suction/injection has distorted the symmetric nature of the flow formation.

A prediction model for suction cavitation erosion in a journal bearing

Suction damage occurred often in dynamically loaded journal bearings. A new theoretical model, including lubrication module, boundary module and prediction module, was proposed to investigate the suction damage in a journal bearing. The results showed that, a stable cavitation area with steady temperature fields formed in the film rupture region, but no suction cavitation erosion occurred in a constant load journal bearing. It was concluded that, suction cavitation erosion occurred within the region of suction cavitation, and higher dimensionless deformation coefficients stood for more muscular suction damage strength within suction cavitation regions. It was beneficial to reduce transient impact force applied to a journal bearing for resisting suction cavitation erosion, leading to an increase of a periodic pressure coefficient.

Dynamics of steady, unsteady flows and heat transfer in Casson fluid over a free stretching surface: stability analysis

The dynamics of the steady flow, heat transfer, and MHD in Casson fluid (CF) were currently studied in the literature. But studies on unsteady flow are rare. In those studies, the boundary conditions at the boundary layer, for the directed and perpendicular velocities, and the temperature field, were only taken constants. Or they were taken to depend linearly on the directed distance. The study of CF over a free-stretching surface is too complicated and was not considered in the literature. Our objective, here, is to study the dynamics of CF with boundary conditions at the free surface, where similar solutions of the the steady flow, unsteady flow and temperature are found. This is completely a novel problem. The exact solutions for the steady flow, unsteady flow and temperature field dynamic equations are found via the extended unified method. The only existing tool, to deal with this problem, is the use of Lie symmetry which requires a hierarchy of long steps. The solutions obtained are evaluated numerically and represented in graphs. It is found that the steady-state flow exhibits two, upper and lower, layers with variant behavior which agree with what is found in the literature. It is, also, observed that in the unsteady state case that the directed and perpendicular velocities tend to zero asymptotically when the lateral space variable and the time tend to infinity. While it is observed that the temperature attains a constant value. An approach is presented to study the stability of the steady-state flow and temperature. It is found that the steady-state temperature is unstable for varying the magnetic field strength, viscosity and mass density. While, when varying the Casson parameter Λ, it is stable when and it is unstable for . This is in contrast to the case of steady-state flow which is shown to be stable.

Fast optimization of multichip modules using deep learning coupled with Bayesian method

In this study, we develop an approach based on deep learning and the Bayesian method for fast optimization of the thermal placement of the multichip modules (MCMs). Specifically, a deep learning-based reduced-order model (ROM) is proposed to replace the CFD model to accelerate the optimization. The ROM applies the convolutional neural network (CNN) as the coding layers, the deconvolutional CNN as the decoding layers, and the signed distance function (SDF) as the input of the ROM network. It enables fast and accurate prediction of the steady temperature field and the junction temperature of each chip with various chip numbers, chip powers, and chip placements. According to the results, the average error of the temperature field is only 0.81%, and the time cost for each temperature field prediction is less than 0.01 s, which is three orders faster than the numerical simulations. Profiting from the excellent performance of the ROM, the Bayesian optimization speeds up two orders of magnitude, and the coefficient of determination, R2, reaches 0.9991, which shows the huge potential of the deep learning-based optimization method to achieve the fast and accurate thermal placement design of the MCMs.

Bifurcation and chaos analysis of a pretensioned moving printed electronic laminated membrane considering aerothermoelasticity

The bifurcation and chaotic motion characteristics are studied for a roll-to-roll flexible printed electronic laminated membrane subjected to initial tension in a steady temperature field. First, an aerodynamic model of the moving membrane is established by using an improved Newton's law for internal friction. Based on von Karman's large deflection theory, a nonlinear vibration differential equation is derived for the laminated membrane under multiple physical fields using Hamilton's principle and solved numerically using the fourth-order Runge-Kutta method. The effects of the temperature, air resistance and other parameters on the nonlinear vibration of the membrane are analyzed by using the bifurcation diagram, Lyapunov exponent diagram and corresponding phase diagram, Poincaré diagram and time history diagram. The results show that the membrane exhibits abundant chaos and bifurcation phenomena under a coupling field. The parameters of the membrane can be varied to control the nonlinear vibration characteristics. This study provides theoretical guidance for improving the transmission stability of electronic membranes and realizing high-precision overprinting.

Study on Steady-State Temperature Rise Characteristics of Motor Heat Balance under Load Rate

The influence of load rate and other factors is not considered in the temperature rise monitoring process of traditional motor, which will lead to the wrong diagnosis of motor health status. In this paper, the characteristics of motor temperature rise under different ambient temperatures and different load factors are studied. Taking an 11 kW three-phase asynchronous motor as an example, the temperature rise model of the motor is based on the finite element method established using ANSYS software. The thermal conductivity coefficient and surface heat dissipation coefficient of each part of the motor are determined. According to the electromagnetic field calculation, the motor loss distribution is obtained, and the temperature rise distribution curve of the motor is obtained by the simulation of the three-dimensional steady temperature field of the motor. In this paper, the temperature rise variation law of the motor considering the influence of environmental temperature and load factors is proposed, and combined with the temperature rise threshold curve of the motor under different load rates, a dynamic threshold judgment system is established to accurately warn the motor of overheating under any load rate. When the motor’s health status changes after running for a long time, it provides an important theoretical basis for accurate diagnosis of the motor’s health status.

Thermal–Structural Coupling Analysis of Subsea Connector Sealing Contact

Taking a subsea collet connector as an example, the contact characteristics of the sealing structure of the subsea connector under thermal–structural coupling were studied. Considering the heat transfer problem of the subsea connector in deep water, the heat transfer model of seawater layer between sealing structures was established, and the relationship between equivalent thermal conductivity, composite heat transfer coefficient, and temperature was determined. The steady-state temperature field distribution of the connector under the action of the internal high-temperature oil and gas and external low-temperature seawater was obtained. Considering the stress and deformation of the subsea connector under the thermal load, the thermal–structural coupling analysis model of the steady-state temperature field was established, and the thermal stress theoretical analysis and numerical simulation of the key sealing structures of the connector were compared and verified. Analysis of coupled stress calculation, for example, under a steady-state temperature field, was carried out on the sealing structure of the subsea connector. At the same time, the pressure shock mode under a steady temperature field was analyzed, which showed that the lenticular sealing gasket is sensitive to high pressure under high-temperature conditions.

Numerical and experimental investigation of cutting temperature in turning with a self-propelled rotary tool

This study focuses on the analysis of temperature distribution in a self-propelled rotary insert for dry turning of SKD11 steel both experimentally and numerically using ABAQUS solver. The simulation results showed that the tool temperature increased with increasing the cutting speed, feed rate, and depth of cut, and the self-propelled rotary tool exhibited a considerably lower temperature than that of the one with a fixed cutting edge. The simulation results were experimentally validated by capturing the steady temperature field in the cutting zone with an IR camera. Thanks to the continuous introduction of a fresh part of the cutting edge into the shear region of the self-propelled rotary tool, both simulated and experimental results revealed a large reduction in the tool temperature of more than 170oC at various cutting conditions.

Thermally Driven Self-Rotation of a Hollow Torus Motor.

Self-oscillating systems based on thermally responsive polymer materials can realize heat-mechanical transduction in a steady ambient temperature field and have huge application potential in the field of micro-active machines, micro-robotics and energy harvesters. Recently, experiments have found that a torus on a hot surface can rotate autonomously and continuously, and its rotating velocity is determined by the competition between the thermally induced driving moment and the sliding friction moment. In this article, we theoretically study the self-sustained rotation of a hollow torus on a hot surface and explore the effect of the radius ratio on its rotational angular velocity and energy efficiency. By establishing a theoretical model of heat-driven self-sustained rotation, its analytical driving moment is derived, and the equilibrium equation for its steady rotation is obtained. Numerical calculation shows that with the increase in the radius ratio, the angular velocity of its rotation monotonously increases, while the energy efficiency of the self-rotating hollow torus motor first increases and then decreases. In addition, the effects of several system parameters on the angular velocity of it are also extensively investigated. The results in this paper have a guiding role in the application of hollow torus motor in the fields of micro-active machines, thermally driven motors and waste heat harvesters.

Finite element analysis of electroresistive heating of a high pressure apparatus for studying the solubility of GaN in Fe

The advantages and disadvantages of methods for gallium nitride crystals production are considered. The convergence of the solution of the problem of electroresistive heating at determination of a thermal condition of the high pressure apparatus cell is investigated. The thermal state of the high pressure apparatus cell used to determine the solubility of gallium nitride in iron has been modeled and investigated. It is determined that the combined discretization with the use of triangular and quadrangular elements allows to reduce the time of solving the coupled problem of electrical and thermal conductivity under these conditions. The results of calculations are presented by steady temperature fields in various elements of the device. It was obtained that at the temperature in the cell control point of 1800 °С its axial difference in the volume of the investigated sample of iron was 62 °С , the maximum difference was 156 °С. The simulated cell configuration and the heating conditions defined for it are acceptable for experimental studies of the solubility of GaN in contact with Fe under conditions of high pressures and temperatures.

Analytical models for thermal deformation and mesh stiffness of spur gears under steady temperature field

Thermal effect is an important cause of engineering failure of gear system. However, the lack of accurate model limits the research on the thermal behavior of gear transmission system. Here, based on the linear thermal expansion theory, involute profile theory and energy method, the thermal expansion model, the mesh stiffness model, the load sharing ratio model and the loaded static transmission error model of spur gears are proposed which comprehensively consider the thermal changes of material properties, theoretical involute, thermal profile error and actual contact positions. The corresponding finite element models are established to verify the accuracy of the proposed model and published models. The results indicate that the proposed model is accurate enough. The increase of temperature leads to the decrease of mesh stiffness, the unevenness of load sharing ratio and the increase of loaded static transmission error, accompanied by the phenomenon of earlier meshing. The hub bore radius has obvious influences on the thermal profile error and mesh stiffness, and the load torque also has apparent influences on mesh stiffness. The research provides supports for gear thermal effect analysis and gear system design.

Thermally driven self-oscillation of an elastomer fiber with a hanging weight

Self-excited motion has been recently extensively explored for various applications ranging from autonomous systems to energy harvesting devices. Our recent experiment has discovered that an ultrathin thermally responsive liquid crystal elastomer (LCE) fiber with a hanging weight can self-oscillate in a steady temperature field. Compared to many systems previously studied, which can generate self-excited motions when subjected to time-invariant stimuli such as light and humidity, the LCE fiber–mass system is simple and its heat-driven self-oscillation is very robust. During the self-oscillation, the LCE fiber continuously converts thermal energy to mechanical work, making it capable of harvesting low-grade waste heat. In this paper, we formulate a nonlinear dynamic theory for the system to understand its heat driven self-oscillation behavior. We have further obtained asymptotic solutions of the system with a few assumptions.

Application of the Complex Variable Step Method and the Boundary Element Method for Sensitivity Analysis of Steady Heat Conduction Problems

The paper concerns the problems related to applying the complex variable step method for the sensitivity analysis of the steady temperature field in the solid body domain due to the perturbations of the geometrical and physical parameters. The optimization problem using the approach proposed is also discussed. At the stage of numerical modelling, the boundary element method is used. The first part of the paper is devoted to the shape sensitivity. The results obtained are compared with the solution resulting from the implicit approach of sensitivity analysis. In the second part, the practical problem concerning optimizing the geometry of continuous casting mould cross-section is considered. The project variable vector contains the cooling pipes' radius and the volume flow rate of the cooling water. The numerical results and the conclusions are presented in the final part of the paper.

Electrospun liquid crystal elastomer microfiber actuator.

Fibers capable of generating axial contraction are commonly seen in nature and engineering applications. Despite the broad applications of fiber actuators, it is still very challenging to fabricate fiber actuators with combined large actuation strain, fast response speed, and high power density. Here, we report the fabrication of a liquid crystal elastomer (LCE) microfiber actuators using a facile electrospinning technique. Owing to the extremely small size of the LCE microfibers, they can generate large actuation strain (~60 percent) with a fast response speed (<0.2 second) and a high power density (400 watts per kilogram), resulting from the nematic-isotropic phase transition of liquid crystal mesogens. Moreover, no performance degradation is detected in the LCE microfibers after 106 cycles of loading and unloading with the maximum strain of 20 percent at high temperature (90 degree Celsius). The small diameter of the LCE microfiber also results in a self-oscillatory behavior in a steady temperature field. In addition, with a polydopamine coating layer, the actuation of the electrospun LCE microfiber can be precisely and remotely controlled by a near-infrared laser through photothermal effect. Using the electrospun LCE microfiber actuator, we have successfully constructed a microtweezer, a microrobot, and a light-powered microfluidic pump.

Thermal characteristic of double-row cylindrical roller bearing of high-speed train using analytical solution and finite element analysis

The complicated thermal characteristics critically affect the reliability of double-row cylindrical roller bearing (DCRB) in the high-speed railway, which will cause the deformation and vibration and severely lead to bearing failure. Thus, research on the heat distribution and steady temperature field is essential for DCRB. In this paper, the Green’s function was established and programed with MATLAB under certain boundary conditions to verify the temperature field of DCRB. It computes fast than the finite element analysis (FEA), According to the simulation of ANSYS, temperature in outer ring is higher than inner ring and it is the maximum in roller, while the rib reduces the temperature in bearing and temperature near rib is larger, which result in asymmetry in raceway. All these results are consistent with the accrual working. This paper provided a heat portion equation between the rollers and the raceway and calculated more accurate and comprehensive than other equation. All results in this paper made sure the more exact temperature field in the DCRB with more convenient calculation and verification.