Inhomogeneous Temperature Field Research Articles

Effects of geometrical parameters on rarefied gas flows and Knudsen force in the system of triangular-rectangular beams with different temperatures

In the rarefied gas, the gas flows induced by the inhomogeneous temperature fields and the Knudsen force exerting on the immersed structure are potentially applicable to the micro/nano-electromechanical systems (MEMS/NEMS) and aerospace. The system composed of a series of triangle cold beams and rectangle hot beams is proposed, and the effects of the beam geometry, dimensions, and positions for different pressures on rarefied gas flows and Knudsen force are researched based on the direct simulation Monte Carlo (DSMC) method. The results reveal that both the gas flows and Knudsen force are highly sensitive to these factors. Particularly, the applications of triangular cross-section cold beams and large height-to-width ratios are necessary for a larger Knudsen force. Compared to the rectangle cold beam, when the triangle cold beam has an inclination of approximately 20°, the peak value of Knudsen force can increase by 142%. Moreover, Knudsen force monotonically reduces with the distance between the cold and hot beams increasing. However, the effects of the distance between the cold beam and substrate (substrate proximity) on Knudsen force depend on the ambient pressure. In general, an appropriate increase in substrate proximity appears to be a smart way to practically enhance the Knudsen force.

Thermal-magnetic coupling inhomogeneous temperature field analysis of cylindrical eddy current brakes

With the increasing requirements for safety and reliability, it is now necessary to analyze the thermal characteristics to the same extent as the electromagnetic design for eddy current brakes(ECB), because the working characteristic will be greatly influenced by temperature. In this paper, the transient thermal-magnetic coupling analysis of permanent magnet cylindrical eddy current brake, which is used as the recoil mechanism in artillery, is presented. First, the structure and working principle of this ECB are described in detail. Second, the analytical electromagnetic model is established by multilayer theory to derive the heat source of this ECB. Thirdly, the thermal-magnetic coupling model is established to calculate the dynamic inhomogeneous temperature field of the ECB. The heat conduction equation is solved in different regions with inhomogeneous internal heat source by Finite Difference method(FDM) in two-dimensional cylindrical coordinate. Finally, the validity of the proposed model is verified by commercial Finite Element software. The thermal characteristic and its effects on braking force is analyzed during working. The maximum value of temperature approximately rises by 16℃ in each firing. The braking force will decline by 8% considering temperature.

Comprehensive Distortion Analysis of a Laser Direct Metal Deposition (DMD)-Manufactured Large Prototype Made of Soft Martensitic Steel 1.4313

Additive manufacturing (AM) by using direct metal deposition (DMD) often causes erratic distortion patterns, especially on large parts. This study presents a systematic distortion analysis by employing numerical approaches using transient–thermal and structural simulations, experimental approaches using tomography, X-ray diffraction (XRD), and an analytical approach calculating the buckling distortion of a piston. The most essential geometrical features are thin walls situated between massive rings. An eigenvalue buckling analysis, a DMD process, and heat treatment simulation are presented. The eigenvalue buckling simulation shows that it is highly dependent on the mesh size. The computational effort of the DMD and heat treatment simulation was reduced through simplifications. Moreover, artificial imperfections were imposed in the heat treatment simulation, which moved the part into the buckling state inspired by the experiment. Although the numerical results of both simulations are successful, the eigenvalue and DMD simulation cannot be validated through tomography and XRD. This is because tomography is unable to measure small elastic strain fields, the simulated residual stresses were overestimated, and the part removal disturbed the residual stress equilibrium. Nevertheless, the heat treatment simulation can predict the distortion pattern caused by an inhomogeneous temperature field during ambient cooling in an oven. The massive piston skirt cools down and shrinks faster than the massive core. The reduced yield strength at elevated temperatures and critical buckling load leads to plastic deformation of the thin walls.

Equatorial modons in thermal rotating shallow water model

Exact steady eastward-moving vortex-dipole solutions, the equatorial modons, are constructed in the asymptotic limit of low divergence and small temperature variations in the thermal rotating shallow water (TRSW) model on the equatorial beta-plane. This regime is known to be relevant for the tropical atmosphere. The model itself is a generalization, allowing for horizontal temperature gradients, of the classical rotating shallow water model. The asymptotic modons can carry a temperature anomaly and exist also on the inhomogeneous temperature background. The modon configurations are then used to initialize numerical simulations, in order to check whether such coherent structures can exist in the full TRSW model. The results show that this is, indeed, the case. The parameter regimes and limitations on the structure of the temperature anomaly inside, in order for the modons to persist, are established. It is also shown that the modons keep their coherence even while evolving on the background of meridionally inhomogeneous temperature fields, or while interacting with sharp temperature fronts. A general scenario of disaggregation of the modons, if they are out of the stability domain, is exhibited and analysed.

Design of a Frequency Multiplier Based on Laterally Coupled Quantum Dots for Optoelectronic Device Applications in the Terahertz Domain: Impact of Inhomogeneous Indium Distribution, Strain, Pressure, Temperature, and Electric Field

Design of a Frequency Multiplier Based on Laterally Coupled Quantum Dots for Optoelectronic Device Applications in the Terahertz Domain: Impact of Inhomogeneous Indium Distribution, Strain, Pressure, Temperature, and Electric Field

The Role of Particle Inertia and Thermal Inertia in Heat Transfer in a Non-Isothermal Particle-Laden Turbulent Flow

We present an analysis of the effect of particle inertia and thermal inertia on the heat transfer in a turbulent shearless flow, where an inhomogeneous passive temperature field is advected along with inertial point particles by a homogeneous isotropic velocity field. Eulerian–Lagrangian direct numerical simulations are carried out in both one- and two-way coupling regimes and analyzed through single-point statistics. The role of particle inertia and thermal inertia is discussed by introducing a new decomposition of particle second-order moments in terms of correlations involving Lagrangian acceleration and time derivative of particles. We present how particle relaxation times mediate the level of particle velocity–temperature correlation, which gives particle contribution to the overall heat transfer. For each thermal Stokes number, a critical Stokes number is individuated. The effect of particle feedback on the attenuation or enhancement of fluid temperature variance is presented. We show that particle feedback enhances fluid temperature variance for Stokes numbers less than one and damps is for larger than one Stokes number, regardless of the thermal Stokes number, even if this effect is amplified by an increasing thermal inertia.

Influence of Interface Morphology on the Thermal Stress Distribution of SOFC under Inhomogeneous Temperature Field

Excessive thermal stress can cause the failure of a solid oxide fuel cell (SOFC), and an inhomogeneous temperature field is one of the reasons for thermal stress in the cell. In the present work, the bi-dimensional thermo-mechanical coupling models of SOFCs with different interface morphologies including planar and corrugated cells are proposed. The temperature distribution of two types of cells under the action of heat conduction is analyzed. Further, the inhomogeneous temperature field caused by gas flow is used as the thermal load to compare the thermal stress distribution of planar and corrugated cells. The influence of interface morphology on the temperature distribution, stress distribution and the contribution of the temperature gradient to stress distribution are investigated. This research provides a reference for reducing thermal stress and improving the stability of SOFC.

Refuelling tests of a hydrogen tank for heavy-duty applications

A transition towards zero-emission fuels is required in the mobility sector in order to reach the climate goals. Here (green) renewable hydrogen for use in fuel cells will play an important role, especially for heavy duty applications such as trucks. However, there are still challenges to overcome regarding efficient storage, infrastructure integration and optimization of the refuelling process. A key aspect is to reduce the refuelling duration as much as possible, while staying below the maximum allowed temperature of 85 °C. Experimental tests for the refuelling of a 320 l type III tank were conducted at different operating conditions and the tank gas temperature measured at the front and back ends. The results indicate a strongly inhomogeneous temperature field, where measuring and verifying the actual maximum temperatures proves difficult. Furthermore, a simulation approach is provided to calculate the average tank gas temperature at the end of the refuelling process.

Four-Dimensionally Printed Continuous Carbon Fiber-Reinforced Shape Memory Polymer Composites with Diverse Deformation Based on an Inhomogeneous Temperature Field.

Four-dimensionally printed continuous carbon fiber-reinforced shape memory polymer composite (CFSMPC) is a smart material with the ability to bear loads and undergo deformation. The deformation of CFSMPC can be driven by the electrothermal effect of carbon fibers. In this study, the effect of temperature on the shape memory recovery performance of polylactic acid (PLA) was first studied experimentally. Continuous carbon fibers were incorporated into PLA to design CFSMPCs with thickness gradients and hand-shaped structures, respectively. The distribution strategy of the carbon fibers was determined based on simulations of the electrically driven shape recovery process of the aforementioned structures. Both the simulations and experiments demonstrated that the electrification of the CFSMPC structures resulted in an inhomogeneous temperature field, leading to distinct deformation recovery processes. Eventually, a precise unfolding was achieved for the thickness gradient structure and the five fingers in the hand-shaped structure by utilizing a safe voltage of 6 V. This demonstrates that the 4D-printed CFSMPC with diverse deformations based on an inhomogeneous temperature field has potential applications in actuators, reconfigurable devices, and other fields.

Numerical Assessment of the Inhomogeneous Temperature Field and the Quality of Heat Extraction of Nb3Sn Impregnated Magnets for the High Luminosity Upgrade of the LHC

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN foresees the installation of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn-based quadrupole magnets at selected interaction points of the accelerator. The precise knowledge of each magnet's thermal characteristics and heat extraction performance in response to power depositions during both nominal and ultimate conditions is essential in determining safe operating margins. A 2D numerical framework has been developed to systematically assess the temperature distribution in the combined magnet structure-superfluid He system of each magnet and enveloping cold mass using open-source software. Here a full cross-section of a magnet cold mass is modelled, under the power density distribution expected at the most exposed longitudinal position during accelerator operation at an instantaneous luminosity of 5.0x10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , corresponding to the nominal conditions for HL-LHC. Temperature maps and margins are presented for the inner triplet magnets (MQXF) for both horizontal and vertical beam crossing conditions, along with the validation of the design of cold mass cooling channels for heat extraction.

Experimental and numerical study on welding temperature field by double-sided submerged arc welding for orthotropic steel deck

Orthotropic steel deck (OSD) is susceptible to fatigue damage when subjected to repeated traffic loads, and the welding residual stress (WRS) is an important factor contributing to fatigue damage in OSD. WRS is formed by the shrinkage of the welds due to the inhomogeneous temperature field during the welds fabrication process, and thus the study of the welding temperature field is of significance for accurately predicting the WRS. As an emerging welding technology, the double-sided submerged arc welding (DSSAW) technology can generate higher welding temperature and consequently higher welding penetration rate on U rib and deck for welding thicker base metal. However, the DSSAW technology generates more complex welding temperature field compared to the traditional arc welding technology, which has not been evaluated so far. In this study, the finite element model (FEM) of OSD with U rib-to-deck (RTD) welded joints is established to simulate the welding temperature field generated by DSSAW. Moreover, the temperature field in OSD by DSSAW is measured by using the infrared thermal imager (ITI) and the industrial temperature measurement gun (TMG) to verify the FEM simulated temperature results. It is found that large surface temperature gradient and large temperature gradient along the thickness direction would be formed at the weld toe of U rib and deck, which is generally the location where the maximum WRS is distributed and where the fatigue cracks are susceptible in OSD. Compared to the inside welding, the outside welding may generate higher welding temperature, higher temperature gradient, and larger molten pool area, resulting in larger WRS in the OSD. The findings in this study can help to an in-depth understanding of the welding temperature field caused by the new DSSAW technology and support further studies on WRS.

Numerical and experimental investigation of many-objective optimization for efficient temperature and velocity fields reconstruction via acoustic tomography

Accurate and high-quality measurement of temperature and velocity fields is important in combustion and flow diagnosis, especially for the control of boiler operations and optimization of combustion processes. Nonlinear acoustic tomography (NAT) is an appealing approach to simultaneously monitor temperature and velocity fields by observing the changes in sound speed they induce. However, the inherent ill-posedness of the tomographic inverse problem and the lack of a priori information may lead to poor robustness, low precision, and the presence of artifacts. On the other hand, the inclusion of a priori information, such as smoothness and box constraints, may require the use of hyperparameters that hinder quasi real-time reconstruction and may degrade performance in actual applications. In this study, we aim to ensure quasi real-time reconstruction and alleviate the ill-posedness of the NAT problem by eliminating the regularization parameters and transforming the inverse problem into a many-objective optimization problem with four objectives. The knee point-driven evolutionary algorithm with improved environmental selection strategy (KEA-IES) is proposed to simultaneously reconstruct the arbitrary inhomogeneous temperature and aerodynamic fields in a furnace. Apart from the investigation of the performance of KEA-IES and the influence of various factors, including measurement noise, function evaluation number, population size, and functional norms, on the quality of the reconstruction, an experimental AT system with independent 16 T/R channels is developed to evaluate the proposed method. The results show that combustion flame temperature and velocity fields can be monitored simultaneously by using the proposed KEA-IES with more accuracy, less consumed time, and better noise immunity compared with the state-of-the-art algorithms. The proposed method can provide valuable guidance in the development of a non-intrusive real-time pyrometry and velocimetry system, particularly for applications with large velocity fields and temperature gradients. Furthermore, its capability in complex combustion and flow diagnosis will offer benefits in terms of energy conservation, emission reduction, boiler operations supervision, and combustion process optimization.

METHODS FOR DETERMINING THERMAL ERRORS IN MACHINE TOOLS BY THERMO-ELASTIC SIMULATION IN CONNECTION WITH THERMAL MEASUREMENT IN A CLIMATE CHAMBER

Thermo-elastic deformation of the machine tool due to thermal expansion of machine components presents one of the biggest challenges in maintaining accuracy and product quality. The operation of the machine inevitably leads to waste heat due to friction losses of bearings and guides and electrical losses of motors and control cabinets. These internal heat sources lead to inhomogeneous and changing temperature fields, which also interact with the ambient temperature. An interaction with the environment takes place via natural or forced convection and radiation. During the design phase, these thermal effects are determined using thermal (typically FEM) simulations. For existing machines, thermal measurements are possible but require careful planning and execution. Thermo-elastic FEM simulations coupled with thermal measurements in a climate chamber with controlled ambient and foundation temperature, lead to an optimal understanding and management of thermal errors in machine tools. In this paper, the process of thermo-elastic FEM in connection with measurement principles in a climate chamber will be presented. The five-axis milling machine tool DMU 80 evo is used to demonstrate and validate the results of the thermo-elastic FEM with measurement data.

Experimental investigation of the seismic resistance of RC beam–column connections after freeze–thaw cycle treatment

The freeze–thaw cycle (FTC) is one of the major factors leading to damage to reinforced concrete (RC) structures in severely cold regions. The seismic resistance of FTC-damaged RC beam–column connections is critical to the assessment of structural safety. However, studies on the seismic resistance of FTC-damaged RC beam–column connections under severely cold environments are still scarce. In this study, the seismic resistance of FTC-damaged RC connections was investigated in terms of the failure process, hysteresis, energy consumption, core area shear behavior, etc. Furthermore, the effects of FTC action at the microscopic level and macroscopic level and the damage mechanisms of the connections were investigated. The results showed that the shear force ratio of the connections varied via the “diagonal compression strut model” and “truss model” propagation due to the FTC-induced deterioration of the bond performance between the longitudinal rebar and concrete in the beam end; this variation in the shear force ratio, in turn, led to the transformation of the failure mode of the connections. Moreover, as the number of FTCs increased, the ductility of the connections increased slightly, and the shear distortion in the core region as well as its contribution to the whole displacement gradually rose. When the shear–compression ratio is >0.208, increasing the axial force ratio will reduce the load carrying capacity and the shear distortion in the core zone. Based on the test results, a calculation model of the shear force–strain envelope curve of RC connections that integrates the effects of the inhomogeneous temperature field distribution and axial compression ratio was established.

Three-dimensional J-integral evaluation for thermomechanically loaded cracks and temperature-dependent incremental plasticity

In this paper, the J-integral is derived for temperature-dependent elastic–plastic materials described by incremental plasticity. It is implemented using the equivalent domain integral method for assessment of three-dimensional cracks based on results of finite-element calculations. The J-integral considers contributions from inhomogeneous temperature fields and temperature-dependent elastic and plastic material properties as well as from gradients in the plastic strains and the hardening variables. Different energy densities are considered, the Helmholtz free energy and the stress-working density, providing a physical meaning of the J-integral as a fracture criteria for crack growth. Results obtained for a plate with two different crack configurations each loaded by a cool-down thermal shock show domain-independence of the incremental J-integral for different energy densities even for high temperature gradients and significant temperature-dependence of the yield stress and the hardening exponent in the presence of large scale yielding. Hence, the derived J-integral is an appropriate parameter for the assessment of cracks in thermomechanically loaded components.

Conformational approach to the crystallization mechanisms of organosilicon liquids of PMS brand in a non-uniform temperature field

The possibility of using the conformational approach to describe the crystallization kinetics during melt-crystal phase transitions in an inhomogeneous temperature field and to determine the molar mass range corresponding to a change in the crystallization mechanism is shown using the example of PMS brand organosilicon liquids. It is established that the curve of dependence of the mean square of the dipole moment of a macromolecule on the average molar mass of an organosilicon polymer contains three sections, each of which has its own crystallization mechanism.

Electric fields in a counterflow nonpremixed flame: measurement and simulation

In electric field modified flames, the electric body force on fluid elements can play a role in modifying the flow field, affecting flame characteristics by this modified flow motion. Numerical studies have developed ion kinetic mechanisms and appropriate transport models for charged species, validating them with a voltage-current trend in 1D premixed flames. Recent experimental approaches have measured the electric field by adopting the Electric Field Induced Second Harmonic generation (EFISH) technique. However, the quantification has turned out very challenging due to the inherent distortion in the EFISH signal, as well as inhomogeneous temperature and concentration fields in the combustion field. Here, we propose measurement and calibration schemes to quantify the EFISH signal in a laminar counterflow nonpremixed flame and present comparison with numerical results using an in-house multi-physics CFD (Computational Fluid Dynamics) code. Overall, the quantified electric fields agreed well with those from numerical simulation, specifically capturing null electric fields near the flame in the sub-saturated regime due to the electric field screening effect. In the saturated regime, notable discrepancy was found in a fuel stream when electrons moved through it: experiment indicated a significant number of negative ions in the fuel stream, whereas numerical results predicted negligible negative ions, due to the implemented ion-mechanism. This suggested that the experimentally obtained electric fields may serve as validation data for modeling studies to improve transport models and ion-mechanism. In-situ measurement of charged species in the presence of external electric fields should be a future work.

Modelling of fast fueling of pressurized hydrogen tanks for maritime applications

This paper studies fast fueling of gaseous hydrogen into large hydrogen (H2) tanks suitable for maritime applications. Three modeling methods have been developed and evaluated: (1) Two-dimensional computational fluid dynamic (CFD) modeling, (2) One-dimensional wall discretized modeling, and (3) Zero-dimensional modeling. A detailed 2D CFD simulation of a small H2-tank was performed and validated with data from literature and then used to simulate a large H2-tank. Results from the 2D-model show non-uniform temperature distribution inside the large tank, but not in the small H2-tank. The 1D-model can predict the mean temperature in small H2-tanks, but not the inhomogeneous temperature field in large H2-tanks. The 0D-model is suitable as a screening tool to obtain rough estimates. Results from the modeling of the large H2-tank show that the heat transfer to the wall during fast filling is inhibited by heat conduction in the wall which leads to an unacceptably high mean hydrogen temperature.

STRESS-STRAIN STATE AND WEAR MODELLING FOR FUEL ROD – GRID CONTACT

The paper presents an approach for effective solution of the stress-strain state and wear prediction problem for the case of contact between fuel rod and grid surfaces of a nuclear reactor. Boundary-initial value elastic-plastic problem statement, due to the quasi-static character of the forced oscillations, which was approved by eigen frequencies analysis, was reduced to boundary one. The influence of inhomogeneous temperature field and varying pressure in the outer surface of fuel rod’s shell are considered. For this, a sequence of special procedures for searching the most effective ways of numerical simulation with limited computational resources was considered. The method of weighted residuals and the finite difference method were used to solve the problem of nonlinear forced oscillations under periodic loading of the fuel rod, described as beam under bending. The analytical solution for the fuel rod’s shell displacements in thermo-elasticity problem is obtained, approximated for spatial case and added to the general three-dimensional Finite Element model. The same procedure was adopted for the maximum amplitude values of the displacements which were obtained in the geometrically nonlinear beam problem solution. After that the general elastic-plastic contact problem of the interaction between the fuel rod and the grid surfaces was solved, taking into account preliminary obtained stress distributions achieved by temperature and amplitude displacements influence. The theory of plasticity of an isotropic material with isotropic hardening was used as a model. The limits of linear solutions for beam deflections as well as deflection dependencies upon time are demonstrated and analyzed. The numerically obtained distributions of strains and stresses are presented. By use of the obtained maximum stress values an attempt for the wear estimation in contact zone was done and the fuel rod’s operating time without critical wear during the contact with the grid surface was determined. The obtained results may be considered as corresponding to practical operating data.

Reference shape of bodies with finite incompatible deformations

The work develops differential-geometric methods for modeling of finite incompatible deformations of hyperelastic solids. Deformation incompatibility can be caused, for example, by inhomogeneous temperature fields and distributed defects. As a result, residual stresses and distortion of geometric shape of the body occur. These factors determine the critical parameters of modern high-precision technologies, in particular, in additive manufacturing technologies. In this regard, the development of methods for their quantitative description is an urgent problem of modern solid mechanics.&#x0D; The application of methods of differential geometry is based on the representation of a body as a smooth manifold equipped with a metric and a non-Euclidean connection. This approach allows one to interpret the body as a global stress-free shape and to formulate the physical response and material balance equations with respect to this shape. Within the framework of the geometric method, deformations are characterized by embeddings of non-Euclidean shape into physical space, which is still considered to be Euclidean. Measures of incompatibility are identified with the invariants of the affine connection, namely, torsion, curvature, and nonmetricity, and the connection itself is determined by the type of physical process.