Search Results (62)

This study proposes an RBF-PSO hybrid framework for efficient inversion analysis of hydration heat parameters in mass concrete temperature fields, addressing the computational inefficiency and accuracy limitations of traditional methods. By integrating a Radial Basis Function (RBF) surrogate model with Particle Swarm Optimization (PSO), the method reduces reliance on costly finite element simulations while maintaining global search capabilities. Three objective functions—integral-type (F₁), feature-driven (F₂), and hybrid (F₃)—were systematically compared using experimental data from a C40 concrete specimen under controlled curing. The hybrid F₃, incorporating Dynamic Time Warping (DTW) for elastic time alignment and feature penalties for engineering-critical metrics, achieved superior performance with a 74% reduction in the prediction error (mean MAE = 1.0 °C) and <2% parameter identification errors, resolving the phase mismatches inherent in F₂ and avoiding F₁’s prohibitive computational costs (498 FEM calls). Comparative benchmarking against non-surrogate optimizers (PSO, CMA-ES) confirmed a 2.8–4.6× acceleration while maintaining accuracy. Sensitivity analysis identified the ultimate adiabatic temperature rise as the dominant parameter (78% variance contribution), followed by synergistic interactions between hydration rate parameters, and indirect coupling effects of boundary correction coefficients. These findings guided a phased optimization strategy, as follows: prioritizing high-precision calibration of dominant parameters while relaxing constraints on low-sensitivity variables, thereby balancing accuracy and computational efficiency. The framework establishes a closed-loop “monitoring-simulation-optimization” system, enabling real-time temperature prediction and dynamic curing strategy adjustments for heat stress mitigation. Robustness analysis under simulated sensor noise (σ ≤ 2.0 °C) validated operational reliability in field conditions. Validated through multi-sensor field data, this work advances computational intelligence applications in thermomechanical systems, offering a robust paradigm for parameter inversion in large-scale concrete structures and multi-physics coupling problems. Full article

For investigating the effect of temperature and strain rate on martensitic transformation and establishing the corresponding kinetic model for newly TRIP (transformation-induced plasticity) aided duplex stainless steel (DSS), the tensile tests are conducted at temperatures of 20–150 °C and strain rates of 0.0001–150 s⁻¹. The stepped cross-section tensile specimen is proposed and designed for obtaining microstructure at specific strain during dynamic tensile testing. The results demonstrate that the deformation mechanism of austenite in TRIP-aided DSS is highly sensitive to temperature and strain rate. As the deformation temperature increases, strain-induced martensitic transformation is inhibited, and the deformation mechanism transforms from martensitic transformation to the co-occurrence of martensitic transformation and twinning, and finally, twinning is the main deformation mechanism. This leads to reduced strength with an initial increase followed by a decrease in elongation. As the strain rate increases, martensitic transformation is inhibited, resulting in a reduction in strength and plasticity during quasi-static tensile testing, while during dynamic tensile testing, strength increases due to enhanced resistance to dislocation motion, and plasticity displays no significant variation because of the combination of adiabatic softening and martensitic transformation suppression. Moreover, during tensile deformation, a plastic temperature rise model is established for newly developed DSSs. Based on this model, the Ludwigson–Berger model for martensitic transformation was modified to couple the effect of temperature and strain rate by considering the non-uniform distribution of temperature rise within the material and its variation with strain rate, as well as the suppression of dynamic strain rate on martensitic transformation. This new model could accurately describe the characteristics of martensitic transformation in newly developed DSSs at different deformation temperatures and strain rates. Full article

Sodium-ion batteries (SIBs) share similar working principles with lithium-ion batteries while demonstrating cost advantages. However, the current understanding of their safety characteristics remains insufficient, and the thermal runaway mechanisms of different SIB systems have not been fully elucidated. This study investigated the following two mainstream sodium-ion battery systems: polyanion-type compound (PAC) and layered transition metal oxide (TMO) cathodes. Differential scanning calorimetry (DSC) was employed to evaluate the thermal stability of cathodes and anodes, examining the effects of state of charge (SOC), cycling, and overcharging on electrode thermal stability. The thermal stability of electrolytes with different compositions was also characterized and analyzed. Additionally, adiabatic thermal runaway tests were conducted using an accelerating rate calorimeter (ARC) to explore temperature–voltage evolution patterns and temperature rise rates. The study systematically investigated heat-generating reactions during various thermal runaway stages and conducted a comparative analysis of the thermal runaway characteristics between these two battery systems. Full article

Propellants play a crucial role in the propulsion systems of aerospace vehicles, and their combustion characteristics are susceptible to external environmental conditions. This study systematically investigated the impact of various initial conditions on the combustion process of ADN-based propellant, including combustion products, equilibrium pressure, adiabatic temperature, and ignition delay time. The results indicate that the primary combustion products of ADN-based propellant include N₂O, N₂, CO₂, OH, and others. ADN-based propellant exhibits a distinct two-stage combustion process under low pressure and temperature conditions (P₀ = 2 atm, T₀ = 586 K). Conversely, under high pressure and temperature conditions (P₀ = 10 atm, T₀ = 2930 K), the two stages of combustion occur almost simultaneously, making them difficult to distinguish. Furthermore, as the initial temperature increases, the ignition delay time decreases significantly, and the combustion rate accelerates. When the initial temperature rises from 400 K to 2800 K at a pressure of P₀ =10 atm, the ignition delay time decreases from 3.5 ms to 0.6 μs. Interestingly, changes in initial pressure have a relatively minor impact on the ignition delay time compared to changes in temperature. Therefore, temperature has a more crucial influence on the combustion characteristics of ADN-based propellant than pressure. This study holds promise for providing new combustion optimization strategies for the aerospace industry and promoting the development of aircraft designs towards higher performance and sustainability. Full article

The hot deformation behaviors and dynamic softening mechanisms of XM-19 super austenitic stainless steel (SASS) were investigated using the isothermal compression test in the temperature range from 1025 to 1250 °C and a compression rate of 0.01–10 s⁻¹. A hot processing map with a strain of 0.9 was constructed, and the analysis results show that the optimal thermal deformation parameters are a temperature range of 1200–1250 °C and a strain rate range of 0.03–0.2 s⁻¹. The thermal activation energy at 0.7 strain is calculated to be 614.3 kJ/mol by developing constitutive equations under various deformation parameters, which is essentially higher than the range of thermal deformation activation energy of typical austenitic stainless steels. At a high temperature of 1250 °C, the synergistic effect of adiabatic heating and increased dislocation density drives the recrystallization fraction to surge from 20% to 78% as the strain rate rises from 0.01 to 10 s⁻¹, while at a fixed strain rate of 0.1 s⁻¹, the increase in deformation temperature from 1025 °C to 1250 °C promotes dynamic recrystallization (DRX), leading to a parallel rise in recrystallization fraction to 25%. The nucleation mechanism of XM-19 SASS is primarily driven by discontinuous dynamic recrystallization (DDRX), with a supporting role of continuous dynamic recrystallization (CDRX). The contribution of CDRX decreases gradually with increasing deformation temperature. Full article

A novel amorphous Fe₈₈Pr₆Ce₄B₂ ribbon with better magnetocaloric properties near 285 K is reported in the present work. The Fe₈₈Pr₆Ce₄B₂ ribbon exhibits a typical second-order ferromagnetic–paramagnetic transition near its Curie temperature (T_c, ~284 K), with a maximum magnetic entropy change (−ΔS_m^peak) of ~4.15 J/(kg × K) under 5 T and a maximum adiabatic temperature rise (ΔT_ad) of ~2.57 K under 5 T, both of which are almost the largest amongst the iron-based metallic glasses with T_c = 285 ± 10 K. The high −ΔS_m^peak enables several amorphous hybrids with table-like −ΔS_m–T curves to be synthesized by appropriately proportioning the Fe₈₈Pr₆Ce₄B₂ ribbon and other amorphous ribbons with different T_c. The larger average −ΔS_m and effective refrigeration capacity, as well as the appropriate temperature range, make the two amorphous hybrids potential candidates for use as refrigerants in household magnetic air conditioners. Full article

In this study, the flow condensation of R-410A within 18 square microchannels arranged horizontally in parallel was experimentally investigated. All components of pressure drop, including expansion, contraction, deceleration, and friction, were quantified specifically for microchannels. The test conditions included saturation temperature, vapor quality, and mass flux, ranging from 18.86 to 24.22 bar, 0.09 to 0.92, and 200 to 445 kg/m²·s, respectively. The frictional pressure loss made up approximately 92.89% of the overall pressure reduction. The findings demonstrate that the pressure drop rises with higher mass flux and a lower saturation temperature. By comparing with correlations and semi-empirical models outlined in the literature across various scales, specimen types, and refrigerant media, correlations developed for two-phase adiabatic flows in multi-channel configurations can effectively predict the pressure drop in microchannel condensation processes. The model introduced by Sakamatapan and Wongwises demonstrated the highest predictive accuracy, with a mean absolute deviation of 8.4%. Full article

The concrete used in the main structures of subway stations has a high degree of constraint. Consequently, temperature changes and shrinkage during construction frequently lead to significant constraint stress, which can result in structural cracking. Therefore, cement with low hydration heat is commonly used in engineering to reduce the temperature of concrete during its age. Aiming at the problem of hydration and heat release caused by concrete construction, based on the principles of concrete hydration heat release and a numerical analysis method, an optimized semi-adiabatic temperature rise test method has been introduced to investigate concrete temperature rise characteristics with different mineral admixtures. The following conclusions were obtained: The effect of reducing the heat of hydration is related to the content and material properties of different mineral admixtures, but not the type of mineral admixture to be incorporated. The temperature rise performance of four common mineral admixtures is as follows: ① total cooling capacity: limestone powder > slag, fly ash > metakaolin; ② early heat generation rate: metakaolin > slag > fly ash > limestone powder; ③ heat reduction rate in the middle and late periods: metakaolin > limestone powder > fly ash > slag. Full article

On 4 November 2021, during the rising phase of solar cycle 25, an intense geomagnetic storm (Kp = 8−) occurred. The effects of this storm on the outer magnetospheric region up to the ionospheric heights have already been examined in previous investigations. This work is focused on the analysis of the solar wind conditions before and during the geomagnetic storm, the high-latitude electrodynamics conditions, estimated through empirical models, and the response of the atmosphere in both hemispheres, based on parameters from the ECMWF ERA5 atmospheric reanalysis dataset. Our investigations are also supported by counter-test analysis and Monte Carlo tests. We find, for both hemispheres, a significant correspondence, within 1–2 days, between high-latitude electrodynamics variations and changes in the temperature, specific humidity, and meridional and zonal winds, in both the troposphere and stratosphere. The results indicate that, in the complex solar wind–atmosphere relationship, a significant role might be played by the intensification of the polar cap potential. We also study the reciprocal relation between the ionospheric Joule heating, calculated from a model, and two adiabatic invariants used in the analysis of solar wind turbulence. Full article

Phase change materials can be converted between solid, liquid, and gaseous states, absorbing or releasing a large amount of heat. PCM is incorporated into concrete to adjust the temperature difference between inside and outside of concrete, which can reduce cracking. In this paper, the finite element analysis method is used to establish the model of an ordinary concrete structure, doped with phase change materials, on the basis of mechanical properties and a temperature regulation test performed by calculating the adiabatic temperature rise of concrete with different contents of composite phase change material, comparing the experimental and simulation results of the ordinary concrete structures with phase change materials, and analyzing the change in temperature field of the concrete structure with the content of self-prepared composite phase change materials. It is found that the addition of self-prepared composite phase change materials reduces the temperature peak of the concrete structure in the stage of hydration heat and delays the time taken to reach the temperature peak. Then, the temperature field of the phase change mass concrete structure is established, and the influence law of composite phase change material admixture on the temperature field of mass concrete is summarized through the time–temperature curves of different admixture amounts and positions so as to predict the possibility of cracks in mass concrete. Full article

The rise in early-age temperature concrete structures, driven by the exothermic reactions during cement hydration, significantly increases the risk of thermal cracking. To address this issue, the construction industry employs several strategies, including the partial substitution of cement with ground granulated blast furnace slag (GGBS) due to its lower heat of hydration. Accurately predicting the hydration temperature of concrete is critical for preventing thermal cracking. This task becomes more complex, with fluctuating ambient temperatures influencing hydration kinetics and heat dissipation. Previous studies often assume adiabatic or isothermal conditions, thus overlooking the impact of ambient temperature variations. This paper presents an innovative finite element modelling (FEM) approach to simulate the hydration temperature progression in in situ concrete slabs, incorporating the effects of ambient temperature fluctuations. Isothermal calorimetry curves were adjusted using the Arrhenius-based approach to express the cement hydration rate as a function of ambient temperature. The FEM outcomes, validated with semi-adiabatic calorimetry tests, demonstrate the model’s capability to forecast temperature development in in situ concrete under varying ambient conditions. Additionally, the study examines the influence of partial cement replacement with GGBS on thermal behaviour, revealing that while GGBS effectively reduces thermal reactions at higher contents, its efficacy diminishes with rising ambient temperatures. Full article

Past studies have reported a decreasing planetary albedo and an increasing absorption of solar radiation by Earth since the early 1980s, and especially since 2000. This should have contributed to the observed surface warming. However, the magnitude of such solar contribution is presently unknown, and the question of whether or not an enhanced uptake of shortwave energy by the planet represents positive feedback to an initial warming induced by rising greenhouse-gas concentrations has not conclusively been answered. The IPCC 6th Assessment Report also did not properly assess this issue. Here, we quantify the effect of the observed albedo decrease on Earth’s Global Surface Air Temperature (GSAT) since 2000 using measurements by the Clouds and the Earth’s Radiant Energy System (CERES) project and a novel climate-sensitivity model derived from independent NASA planetary data by employing objective rules of calculus. Our analysis revealed that the observed decrease of planetary albedo along with reported variations of the Total Solar Irradiance (TSI) explain 100% of the global warming trend and 83% of the GSAT interannual variability as documented by six satellite- and ground-based monitoring systems over the past 24 years. Changes in Earth’s cloud albedo emerged as the dominant driver of GSAT, while TSI only played a marginal role. The new climate sensitivity model also helped us analyze the physical nature of the Earth’s Energy Imbalance (EEI) calculated as a difference between absorbed shortwave and outgoing longwave radiation at the top of the atmosphere. Observations and model calculations revealed that EEI results from a quasi-adiabatic attenuation of surface energy fluxes traveling through a field of decreasing air pressure with altitude. In other words, the adiabatic dissipation of thermal kinetic energy in ascending air parcels gives rise to an apparent EEI, which does not represent “heat trapping” by increasing atmospheric greenhouse gases as currently assumed. We provide numerical evidence that the observed EEI has been misinterpreted as a source of energy gain by the Earth system on multidecadal time scales. Full article

Continuous dynamic recrystallization (CDRX) is widely acknowledged to occur during hot forming and plays a significant role in microstructure development in alloys with moderate to high stacking fault energy. In this work, the flow stress and CDRX behaviors of the TC18 alloy subjected to hot deformation across a wide range of processing conditions are studied. It is observed that deformation leads to the formation of new low-angle grain boundaries (LAGBs). Subgrains rotate by absorbing dislocations, resulting in an increase in LAGB misorientation and the transition of some LAGBs into high-angle grain boundaries (HAGBs). The HAGBs migrate within the material, assimilating the (sub)grain boundaries. Subsequently, an internal state variable (ISV)-based CDRX model is developed, incorporating parameters such as the dislocation density, adiabatic temperature rise, subgrain rotation, LAGB area, HAGB area, and LAGB misorientation angle distribution. The values of the correlation coefficient (R), relative average absolute error (RAAE), and root-mean-square error (RMSE) between the anticipated true stress and measured stress are 0.989, 6.69%, and 4.78 MPa, respectively. The predicted outcomes demonstrate good agreement with experimental findings. The evolving trends of the subgrain boundary area under various conditions are quantitatively analyzed by assessing the changes in dynamic recovery (DRV)-eliminated dislocations and misorientation angles. Moreover, the ISV-based model accurately predicts the decreases in grain and crystallite sizes with higher strain rates and lower temperatures. The projected outcomes also indicate a transition from a stable and coarse-grained microstructure to a continuously recrystallized substructure. Full article

Under the action of cement hydration heat, the construction environment, thermal insulation measures, and pipe cooling systems, a mass concrete pile cap is subject to a complex internal temperature field, which makes it difficult to control its internal surface temperature difference (T_ISTD), the internal adiabatic temperature rise (T_IATR), and the surface temperature (T_ST). In this study, a mass concrete pile cap of a very large bridge (the length, width, and height were 26.40 m, 20.90 m, and 5.00 m, respectively, and the central-pier pile cap was constructed with C40 concrete) was taken as the research object. The control factors affecting the temperature field of the pile cap were determined by comparing the field temperature measurements with the values calculated with finite element software simulation analysis. By using Midas Civil (2022 v1.2) and Midas FEA (NX 2022) finite element software, these factors (the concrete mold temperature, the concrete surface convection coefficient, the ambient temperature, the pipe cooling system parameters, etc.) were numerically analyzed, and their influence laws and degrees were determined. Full article

In the present study, first, the environmental challenges and cracking characteristics during the construction of plateau concrete on the Sichuan–Tibet route were revealed. Then, using a multi-field coupled shrinkage model with hydration temperature humidity constraints, the early and long-term cracking risks in the core of plateau pier bodies were investigated. Later, the effects of tensile strength, pouring interval age and adiabatic temperature rise on the cracking risk were analyzed. Finally, various control measures for high-altitude concrete cracking were proposed. The results indicated that the complex environment of the plateau led to different forms of cracks in the pier body, especially vertical cracks in the straight sections. The long-term risk of core cracking in the plateau pier body is significantly greater than the risk of early cracking. This risk was strongly influenced by factors such as the concrete tensile strength, pouring interval age and adiabatic temperature rise, which should be given more attention. Deformation compensation can significantly enhance the peak and residual deformation capacities of plateau concrete, with peak values greater than 900 με and residual deformation greater than 200 με at day 60, as well as its resistance to cracking. Strategies such as adopting radiant cooling techniques, improving construction techniques and implementing effective management measures can all play a vital role in improving the cracking resistance of highland concrete. Full article