Thermal Response Of Structure Research Articles

Critical implications of ion-surface energy accommodation and neutralization mechanism in hollow cathode physics

Self-heating thermionic hollow cathodes are essential components in modern plasma thrusters. To fully understand their operation, three interdependent physical domains must be considered: plasma discharge physics, thermal response of the cathode structure, and chemical evolution of plasma exposed surfaces. In this work, we develop the first self-consistently coupled plasma–thermal–chemical simulation platform for hollow cathode operation using lanthanum hexaboride (LaB6) and Xe and study its performance against our experimentally determined temperature measurements. Results show that the customary assumptions of single-step resonant neutralization and full energy accommodation in ion-surface collisions fail to reproduce our empirical observations. We propose a two-step neutralization mechanism that consists of resonant neutralization to the first excited state of xenon followed by Auger de-excitation to the ground state, along with system specific accommodation factors. In this way, the agreement between the results of the simulations and experiments was achieved. These fundamental processes could govern neutralization in other cathode technologies where low work function emitters are employed and should therefore be accounted for in physical models. In addition, the new simulation platform allows us to better estimate the equilibrium work function of LaB6 hollow cathode emitters. In the cathode studied here, we found that the effective work function is 2.25 eV, which is significantly lower than previous estimates, and leads to better than expected cathode material performance with important implications for space missions.

CSPACE for a simulation of core damage progression during severe accidents

CSPACE (Core meltdown, Safety and Performance Analysis CodE for nuclear power plants) for a simulation of severe accident progression in a Pressurized Water Reactor (PWR) is developed by coupling of verified system thermal hydraulic code of SPACE (Safety and Performance Analysis CodE for nuclear power plants) and core damage progression code of COMPASS (Core Meltdown Progression Accident Simulation Software). SPACE is responsible for the description of fluid state in nuclear system nodes, while COMPASS is responsible for the prediction of thermal and mechanical responses of core fuels and reactor vessel heat structures. New heat transfer models to each phase of the fluid, flow blockage, corium behavior in the lower head are added to COMPASS. Then, an interface module for the data transfer between two codes was developed to enable coupling. An implicit coupling scheme of wall heat transfer was applied to prevent fluid temperature oscillation. To validate the performance of newly developed code CSPACE, we analyzed typical severe accident scenarios for OPR1000 (Optimized Power Reactor 1000), which were initiated from large break loss of coolant accident, small break loss of coolant accident, and station black out accident. The results including thermal hydraulic behavior of RCS, core damage progression, hydrogen generation, corium behavior in the lower head, reactor vessel failure were reasonable and consistent. We demonstrate that CSPACE provides a good platform for the prediction of severe accident progression by detailed review of analysis results and a qualitative comparison with the results of previous MELCOR analysis.

Numerical tool for quantifying energy deposition effects on representative hypersonic vehicle structures

This paper presents a methodology to rapidly assess the transient thermal-structural response of a representative skin panel experiencing finite energy deposition over a hypersonic trajectory. The thermal state of the panel is calculated using reference-enthalpy heating with two-dimensional conduction. Panel thermal stress is calculated using a linear Levy sine series expansion model, complemented by a non-linear finite element analysis. Numerical results using the X-43A trajectory as a case study are presented. Energy deposition is observed to have a greater effect on the skin panel when it is already thermally and aerodynamically loaded. The panel is more structurally compromised for energy pulses of longer duration, and/or applied earlier during the X-43A trajectory.

Effect of uniform laser irradiation on thermal response of temperature sensitive structures

The analysis of the temperature distribution, thermal deformation, and stress of thin plate structures attributed to laser irradiation is of great significance because the thermal effects substantially affect a suite of properties. In this paper, based on the theory of thin plate thermal bending, the analytical expressions of deflection and thermal stress in the local uniform temperature field are derived and compared with the numerical simulation results. The influence of the boundary constraint and irradiation factor on the thermal response is analyzed. Considering the temperature sensitivity of material parameters, the effect of heat flux density on the structural response is analyzed by the finite element method. The results show that the analytical solutions of the circular plate deflections are consistent with the numerical results. The maximum values of both deflection and compressive stresses occur at the center. The maximum tensile stress occurs near the boundary of the spot. In the heat affected zone (HAZ), the deflection of a point shows a trend of the Gaussian decrease with the increase in the distance to the center, while the thermal stress almost does not change with the distance. Outside the HAZ, both deflection and thermal stress are related to the boundary conditions and irradiation factors. Considering that the material parameters change with temperature, the HAZ area, deflection, and von Mises stress are positively correlated with the heat flux density, but the change patterns are different.

Thermal Behavior and Stress Response of Steel-concrete Structures under Solar Radiation

Steel-concrete structures are widely used because of their large space and strong plasticity, but the long construction period, complex splicing process and other factors will make the main body of the structure directly exposed to solar radiation, resulting in temperature changes on the surface of steel structure and concrete structure. In order to obtain the stress changes of steel-concrete structures under solar radiation, two kinds of steel-concrete structures with different support forms were simulated. Under three temperature gradients, the thermal behavior and mechanical properties of two kinds of steel-concrete structures composed of upper steel roof and lower concrete support were analyzed. The results show that there is a linear relationship between the thermal behavior and stress response of steel-concrete structure and the daily temperature difference caused by solar radiation. Under the action of thermal effect, the stress difference between the lower steel frame of the full support structure and the lower steel frame of the support structure on both sides is about 10.7%.

Thermostructural Responses of Metallic Lattice-Frame Sandwich Structure for Hypersonic Leading Edges

Metallic lattice-frame materials, due to excellent heat transfer performance under high heat flux and mechanical property, are regarded as the potential candidates for a vehicle leading edge. This paper presents a new-style lattice-frame sandwich panel with active heat transfer wall-plate. The heat transfer performance and thermal–structural responses are numerically studied, considering the temperature-dependent mechanical and thermal properties. The effects of geometrical characteristics of the wall-plate channel on heat exchange and hydraulic behavior are explored. The different parent materials and channel types are respectively compared based on the thermal–structural responses of sandwich structure. A relatively optimized sandwich panel is employed as the vehicle leading edge, and the effects of attack angle on heat transfer and thermostructural behavior are discussed, subjected to intense localized heat flux. The metallic lattice-frame sandwich panel with an active heat exchange wall-plate shows attractive potential for a higher- temperature leading edge, which can withstand the hypersonic thermal–mechanical environment. It can still offer a great improvement space in thermal management as leading edges for hypersonic vehicles.

Femtosecond Laser-Induced Periodic Surface Structures on 2D Ti-Fe Multilayer Condensates.

2D Ti-Fe multilayer preparation has been attracting increased interest due to its ability to form intermetallic compounds between metallic titanium and metallic iron thin layers. In particular, the TiFe compound can absorb hydrogen gas at room temperature. We applied femtosecond laser pulses to heat Ti-Fe multilayer structures to promote the appearance of intermetallic compounds and generate surface nanostructuring. The surface pattern, known as Laser Induced Periodic Surface Structures (LIPSS), can accelerate the kinetics of chemical interaction between solid TiFe and gaseous hydrogen. The formation of LIPSS on Ti-Fe multilayered thin films were investigated using of scanning electron microscopy, photo-electron spectroscopy and X-ray diffraction. To explore the thermal response of the multiple layered structure and the mechanisms leading to surface patterning after irradiating the compound with single laser pulses, theoretical simulations were conducted to interpret the experimental observations.

Different Thermal Responses of Local Structures in Pd43Cu27Ni10P20 Alloy from Glass to Liquid

Different thermal responses of local atomic packing structures in a Pd43Cu27Ni10P20 alloy from glass to liquid have been studied by in situ high-energy X-ray diffraction together with ab initio mol...

Outstanding thermo-mechanical properties of graphene-like B3C3 and C3N3

Experimentally fabricated two-dimensional (2D) carbon-based nanomaterials have received significant attention because of their ultra-high physical properties, in recent years. In this manuscript, the thermal conductivity (TC) and mechanical response of 2D B3C3 and C3N3 structures are studied in detail, using molecular dynamics (MD) simulations. Their superior mechanical properties (Young’s modulus, ultimate tensile strength and failure strain) and TC make an excellent candidate for various applications of nanodevices. The mechanical properties of these 2D structures are also examined at five various temperatures up to 900 K along with the different loading directions and various strain rates from 107 to 109 s−1. MD results demonstrate that the mechanical properties of these 2D structures gradually decrease as temperature increases, due to the weakening effect of high temprerature. Additionally, when the strain rate increases, it is revealed that the mechanical properties show an increasing trend. Furthermore, at 300 K, the failure processes of these 2D structures are studied. MD simulations results demonstrate that these structures show brittle failure mechanism. On the other hand, various types of structural defects occurs during the production process and so these defects affect the physical properties of these structures adversely. Accordingly, the effects of various atom types, such as, N, B and C, vacancy defects on the mechanical properties and TC of these structures were investigated. The existence of vacancy defects in these structures reduces the TC and mechanical properties significantly by increasing the concentrations of defects. Finally, non-equilibrium MD simulations results indicate exceptionally high TC values of these structures.

Symmetric modeling of the thermal actions in a structural fire experiment on a long-span composite floor beam in a compartment

This paper presents symmetric modeling of the thermal actions in a structural fire experiment on a 12.8 m long composite floor beam in a compartment. A quarter of the fire compartment was modeled in FDS and a portion of about 1/160 of the composite beam was modeled in ANSYS. The FDS symmetry model gave consistent results with the FDS model of the entire compartment, the differences between the predicted upper layer gas temperatures were within 2 ∘C on average. The differences between the FDS symmetry model predicted upper layer gas temperatures and the experimental data were within 7% at the steady stage. Using the thermal boundaries predicted by the FDS symmetry model, the finite element symmetry model gave good prediction of the lower flange and mid web steel temperatures of the composite beam, the differences between predicted and measured maximum lower flange and maximum mid web temperatures were within 2%. The study indicates that symmetry model might be used to predict the thermal responses of structures in realistic fires.

Adhesion layer influence on controlling the local temperature in plasmonic gold nanoholes.

Gold films do not adhere well on glass substrates, so plasmonics experiments typically use a thin adhesion layer of titanium or chromium to ensure a proper adhesion between the gold film and the glass substrate. While the absorption of light into gold structures is largely used to generate heat and control the temperature at the nanoscale, the influence of the adhesion layer on this process is largely overlooked. Here, we quantify the role of the adhesion layer in determining the local temperature increase around a single nanohole illuminated by a focused infrared laser. Despite their nanometer thickness, adhesion layers can absorb a greater fraction of the incoming infrared light than the 100 nm thick gold layer leading to a significant increase of the local temperature. Different experimental designs are explored, offering new ways to promote or avoid the temperature increase inside nanoapertures. This knowledge further expands the plasmonic toolbox for temperature-controlled experiments including single molecule sensing, nanopore translocation, polymerization, or nano-optical trapping.

Study on the performance of inflatable decelerator under hypersonic aerodynamic load

In order to understand the influence of hypersonic aerodynamic force and aerodynamic heat on the performance of flexible structure of inflatable decelerator, a unidirectional thermal-fluid-structure three field coupling model under the extreme conditions of reentry trajectory is established in this paper. The temperature distribution of thermal protection structure (TPS) and structure response are obtained. The numerical results show that the TPS has a good insulation effect, and the cooling contribution of insulation layer in TPS is up to 80.90%. The stress is concentrated at the contact position between the flexible structure and the blunt head. The stress of TPS layer fluctuates greatly.

The coupled thermal-structural response of RC beams during fire events based on nonlinear numerical simulation

In this paper and based on a previous work, a parametric study was executed to capture the crucial parameters that affect the response of reinforced concrete beams, whether the thermal response or the structural response. The aim behind the used methodology from the previous work was reaching a reliable algorithm that has the capability to simulate any reinforced concrete element under both mechanical and fire loads. This algorithm is based on connecting thermal analysis and structural analysis with coupling technique called sequential coupling technique. This technique allow taking into consideration the non-linearity for thermal material properties such as conductivity, specific heat, and density, and also the non-linearity for mechanical properties such as stress-strain relationship, and thermal expansion coefficient, beside the nonlinearity for concrete compressive strength, and rebar ultimate strength. This algorithm is achieved through detailed numerical finite element models using ANSYS program. The main parameters that had been studied in this paper are the effect of increasing concrete compressive strength, increasing concrete cover, and the effect of increasing the lateral stiffness of the beam on the total response.

Design of an Athermal Interferometer Based on Tailored Subwavelength Metamaterials for On-Chip Microspectrometry

Temperature dependence is one of the main challenges of the silicon-on-insulator platform due to the large thermo-optic coefficient of its core material. In this work, to the best of our knowledge, we propose a design of an all-passive athermal silicon-on-insulator Mach-Zehnder interferometer (MZI) with the minimal temperature sensitivity reported to date. The MZI’s temperature compensation was achieved by optimizing the relative length of its wire and subwavelength arms and by tailoring the thermal response of the subwavelength structure. Simulations of the device performance showed that the overall temperature sensitivity of 7.5 pm/K could be achieved over a 100 nm spectral range near the 1550 nm region.

Hypersonic flow characteristics and relevant structure thermal response induced by the novel combined spike-aerodome and lateral jet strategy

Huge aerodynamic drag and severe aeroheating are the inevitable challenges for hypersonic vehicles, this paper proposes a novel combined spike-aerodome and lateral jet strategy for drag reduction and thermal protection. Meanwhile, the hypersonic flow characteristics and structure thermal response are numerically investigated by an in-house code. The obtained results demonstrate that this novel strategy not only further reduces the total drag, but also provides excellent thermal protection for both the blunt body and spike rod. Then the effects of lateral jet pressure ratio, spike length and aerodome diameter on the flow properties, drag and heat reduction performance are thoroughly explored. Increasing the lateral jet pressure ratio can effectively enhance the thermal protection. Surprisingly, in a certain range, higher lateral jet pressure ratio even leads to larger pressure peak value on the blunt body. Increasing the spike length would enhance the heat transfer along the blunt body surface, and the total drag changes non-monotonically as the spike length varies. The total drag rises significantly when the aerodome diameter increases, and it can be increased by 40.1% when the aerodome diameter ratio increases from 0.15 to 0.5. Besides, increasing the aerodome diameter is beneficial to remarkably enhance thermal protection.

Combined thermal phenomena of hypersonic vehicle

The combined thermal phenomena are a series of multi-factor coupling phenomena caused by the structural thermal response under the cumulative action of aerodynamic heating. The combined thermal phenomena, which will lead to a more significant time-space coupling effect on the multiple physics of hypersonic vehicle, is an important issue in the development of long-haul hypersonic vehicle in the future. This paper describes the connotation of the combined thermal phenomena by combining with the physical link of the aircraft system coupling phenomenon. The physical essence and prediction methods of the combined thermal problem are expounded in detail. The key issues affecting the combined thermal problem such as aerodynamics, aerodynamics/structure/trajectory coupling are discussed. The new progress in the research of coupling experimental verification is introduced. The extension of the combined thermal problem such as the multi-scale effect of the new composite thermal protection materials, the multi-system optimization design based on the multi-factor coupling method, and the influence of the cabin thermal effect on the heat protection system are discussed.

Gas-kinetic unified algorithm for computable modeling of Boltzmann equation and application to aerothermodynamics for falling disintegration of uncontrolled Tiangong-No.1 spacecraft

How to solve the hypersonic aerothermodynamics around large-scale uncontrolled spacecraft during falling disintegrated process from outer space to earth, is the key to resolve the problems of the uncontrolled Tiangong-No.1 spacecraft reentry crash. To study aerodynamics of spacecraft reentry covering various flow regimes, a Gas-Kinetic Unified Algorithm (GKUA) has been presented by computable modeling of the collision integral of the Boltzmann equation over tens of years. On this basis, the rotational and vibrational energy modes are considered as the independent variables of the gas molecular velocity distribution function, a kind of Boltzmann model equation involving in internal energy excitation is presented by decomposing the collision term of the Boltzmann equation into elastic and inelastic collision terms. Then, the gas-kinetic numerical scheme is constructed to capture the time evolution of the discretized velocity distribution functions by developing the discrete velocity ordinate method and numerical quadrature technique. The unified algorithm of the Boltzmann model equation involving thermodynamics non-equilibrium effect is presented for the whole range of flow regimes. The gas-kinetic massive parallel computing strategy is developed to solve the hypersonic aerothermodynamics with the processor cores 500~45,000 at least 80% parallel efficiency. To validate the accuracy of the GKUA, the hypersonic flows are simulated including the reentry Tiangong-1 spacecraft shape with the wide range of Knudsen numbers of 220~0.00005 by the comparison of the related results from the DSMC and N-S coupled methods, and the low-density tunnel experiment etc. For un-controlling spacecraft falling problem, the finite-element algorithm for dynamic thermal-force coupling response is presented, and the unified simulation of the thermal structural response and the hypersonic flow field is tested on the Tiangong-1 shape under reentry aerodynamic environment. Then, the forecasting analysis platform of end-of-life large-scale spacecraft flying track is established on the basis of ballistic computation combined with reentry aerothermodynamics and deformation failure/disintegration.

Experimental Model Design and Preliminary Numerical Verification of Fluid–Thermal–Structural Coupling Problem

Fluid–thermal–structural interactions in hypersonic flows is an extremely complex coupling problem, which puts forward higher requirements on the coupling calculation method and computational efficiency. It is of great significance to design a fluid–thermal–structural coupled ground test to verify the effectiveness of the coupling analysis tools. However, because of the demanding requirements of testing tools and equipment capabilities, no relevant research on full-coupling test has been reported. This study aims to design a reasonable test model, including the size, material, aerodynamic shape, and structure of the model, for verification of the fluid–thermal–structural coupling analysis tools. Based on existing materials and facilities, as well as coupling test requirements, the exploratory design of the test model is carried out. The feasibility of the model design is preliminarily verified using a stainless-steel model by a 10 s short-time test in the high-temperature hypersonic wind tunnel of China Aerodynamic Research and Development Center (CARDC) and in-house FL-CAPTER (Coupled Analysis Platform for Thermal Environment and Structure Response) platform, which is developed by CARDC. The 60 s long-time test model using superalloy is also calculated, which revealed that the effects of the fluid–thermal–structural coupling problem must be considered during the design of the new generation of airbreathing hypersonic vehicles.

Phase-field modeling of metallic powder-substrate interaction in laser melting process

Understanding fusion dynamics of metallic powders and powder-substrate interactions is important for reducing the defects, and thus improving surface and bulk quality of additive manufactured (AM) parts. Albeit recent advances in AM technology, there is a great need of theoretical analysis at the powder level to quantify and predict relevant mesoscale dynamics in the manufacturing process. We present a thermodynamically consistent phase-field modeling framework to integrate relevant thermal fluid phenomena and elastic structure response, including phase transition, thermal capillarity, interfacial deformation, and thermal stress induced by spot laser heating. The 2D results show that the fusion of pure titanium powder and titanium substrate can be significantly enhanced by the capillary effect when the partially melted powder is bridging the molten substrate, whereas the thermal-elastic deformation has a longer range effect, which is primarily influenced by the heating power of the laser beam.

Two-dimensional Modelling of Thermal Responses of GFRP Profiles Exposed to ISO-834 Fire

In the past three decades, one-dimensional (1-D) thermal model was usually used to estimate the thermal responses of glass fiber-reinforced polymer (GFRP) materials and structures. However, the temperature gradient and mechanical degradation of whole cross sections cannot be accurately evaluated. To address this issue, a two-dimensional (2-D) thermo-mechanical model was developed predict the thermal and mechanical responses of rectangular GFRP tubes subjected to one-side ISO-834 fire exposure in this paper. The 2-D governing heat transfer equations with thermal boundary conditions, discretized by alternating direction implicit (ADI) method, were solved by Gauss-Seidel iterative approach. Then the temperature-dependent mechanical responses were obtained by considering the elastic modulus degradation from glass transition and decomposition of resin. The temperatures of available experimental results can be reasonably predicted. This model can also be extended to simulate the thermo-mechanical responses of beams and columns subjected to multi-side fire loading, which may occur in real fire scenarios.