Theoretical Model Calculations Research Articles

Solid–liquid interface disjoining pressure of frozen clay and its effect on water transport

To account for the influence mechanism of solid–liquid interface disjoining pressure on water migration during clay freezing, this study first provides a theoretical calculation model of solid–liquid interface disjoining pressure by combining the thermodynamic equilibrium relation of solid–liquid interface with the parallel plate capacitor model. This is done at the molecular level. An implicit equation for calculating the film thickness d of unfrozen water is also given and the accuracy of the model verified. Secondly, considering that unfrozen water film is anisotropic, the concept of tensor is introduced to show the distribution characteristics and functions of solid–liquid interface disjoining pressure in unfrozen water film. Finally, the effects of solution concentration and undercooling degree on film thickness d of unfrozen water are discussed. The results show that solid–liquid interface disjoining pressure can be expressed by the excess free energy on the surface of charged media, and it is a single-valued function of unfrozen water film thickness. Solid–liquid interface disjoining pressure not only provides an effective driving force for water migration, but also provides growth space for ice lenses; the thickness of unfrozen water film d is negatively correlated with solution concentration and undercooling degree. The research results can provide a theoretical reference for the study of frost heave mechanism in clay soils.

Theoretical analysis of betavoltaic cells based on pDSBD structure

Based on the interaction between β particles and matter and the physical properties of semiconductor devices, the Monte Carlo method was used to simulate the self-absorption effect of β radiation sources and their transport process in different metal/diamond devices. A theoretical calculation model of a p-diamond Schottky barrier diode (pDSBD) betavoltaic cell using an isotropic cuboid source (63Ni) is proposed. The results show that the optimal thickness of the 63Ni radiation source is 2 µm. For the metal materials Al, Au, Cu, Ni and Pt used in the preparation of Schottky contacts, the metal work function significantly affects the output of the pDSBD cells. Among them, the maximum output power density, filling factor, energy conversion efficiency and total energy conversion efficiency of the Al/pDSBD cell are 0.224 µW/cm2, 0.933, 14.53% and 2.06%, respectively.

Humidity field and moisture transfer of concrete with different pre-saturated recycled sand

The water absorption/desorption process of two kinds of recycled sand with parent concrete strength grade C20 and C50 respectively was tested. The influence of the pre-saturated recycled sand on the internal relative humidity development of concrete with strength grades of C30, C50, and C80 was tested. A critical water loss Wc of each concrete with pre-saturated recycled sand was calculated. The theoretical calculation model of concrete humidity considering the effect of pre-saturated recycled sand was established. The results show that the desorption process of recycled sand is closely related to its parent concrete strength grade (pore structure). The recycled sand with a weaker parent concrete induces a greater water release during the decline of ambient humidity. The use of recycled sand can prolong the humidity saturation period and improve the final humidity level of concrete. The effects are related to the pore size of the recycled sand and the new casting concrete. The recycled sand with a weaker parent concrete has stronger effect on the humidity of concrete. For the same recycled sand, it has a better effect on the humidity of high-strength concrete. The use of recycled sand can significantly increase the critical water loss of concrete. The introduction of pre-saturated recycled sand will increase the diffusion coefficient of concrete.

Optimization of Destressing Parameters of Water Jet Slits in Rock Burst Coal Seams for Deep Mining

Mining in deep coal seams is characterized by high ground stress, often accompanied by coal and rock dynamic disasters such as rock bursts. High-pressure water jet slotting technology can relieve pressure and reduce the stress concentration on the coal seam, which is one of the effective pressure relief measures in rock burst coal seams for deep mining. Reasonable pressure relief parameters are an important influence on the effectiveness of pressure relief achieved by a high-pressure water jet. This paper uses theoretical analysis and numerical simulation to analyze the principle of high-pressure water jet pressure relief and rock burst prevention, and a theoretical calculation model of six key pressure relief parameters is constructed. The optimal values of each pressure relief parameter are obtained, and good pressure relief effect is achieved in a certain rock burst risk area. The research results showed that (1) parameters such as drilling spacing–slit radius, drilling depth–slit length, and slotting cutting spacing–slotting cutting width have a great influence on the pressure relief effect, and there is a significant interaction between the parameters, while the strength of the coal seam also has a significant effect on the selection of the parameters and the pressure relief effect. (2) The displacement, vertical stress, plastic zone, elastic energy, impact risk index, and the cost of pressure relief can be used to comprehensively evaluate the quality and economy of the pressure relief effect, and the optimal pressure relief parameters of high-pressure water jet slotting under specific physical force properties of the coal seam can be obtained. (3) High-pressure water jet technology with optimal pressure relief parameters was applied to No. 3 connecting the roadway in the 730 mining area of a mine studied, and field monitoring showed that indicators such as microseismic frequency, total energy, and spatial concentration significantly decreased. Moreover, the accuracy of the theoretical model of high-pressure water jet slotting pressure relief parameter optimization is reliable in the relevant technical parameters of coal seam slotting. It is believed that the model can be used to design the high-pressure water jet slotting pressure relief parameters in deep rock burst coal seams.

Evaluating Ice Load during Submarine Surfacing and Ice Breaking

At present, the calculation method of ice load on surface navigation ships has been very mature, but the calculation method of submarine ice load is very few. The reasonable evaluation of submarine ice load has become an urgent problem to be solved. In this paper, the mechanical characteristics of the submarine surfacing ice-breaking process are systematically analyzed. Based on the theory of plate and shell, the theoretical calculation models of ice-breaking resistance of the submarine command tower and hull are established, respectively, and the ice load calculation method of the command tower and the hull is obtained. Then, the submarine model SUBOFF is used to perform the numerical simulation of the submarine’s ice-breaking and surfacing process. The numerical result is compared with the ice-breaking resistance calculation model. The results show that the ice-breaking resistance calculation model proposed in this paper is consistent with the numerical simulation results, and the influence of parameters such as ice mechanical properties, the upper area of the command tower, and initial crack length on ice-breaking resistance is established. The calculation model in this paper can provide a theoretical reference for the optimization design of polar submarine structures.

Estimation of fission barrier heights for even–even superheavy nuclei using machine learning approaches

With the fission barrier height information, the survival probabilities of super-heavy nuclei can also be reached. Therefore, it is important to have accurate knowledge of fission barriers, for example, the discovery of super-heavy nuclei in the stability island in the super-heavy nuclei region. In this study, five machine learning techniques, Cubist model, Random Forest, support vector regression, extreme gradient boosting and artificial neural network were used to accurately predict the fission barriers of 330 even–even super-heavy nuclei in the region 140 ≤ N ≤ 216 with proton numbers between 92 and 120. The obtained results were compared both among themselves and with other theoretical model calculation estimates and experimental results. According to the results obtained, it was concluded that the Cubist model, support vector regression and extreme gradient boosting methods generally gave better results and could be a better tool for estimating fission barrier heights.

Observation of coherent oscillations in the association of dimers from a thermal gas of ultracold atoms

We report the observation of coherent oscillations in conversion efficiency of weakly-bound dimers formed from a thermal gas of ultracold atoms. Finite thermal energy of the gas causes loss of coherence when a broad continuum is resonantly coupled to a discrete bound state. Restoration of the coherence can be achieved through non-adiabatic transitions of the dressed molecular energy level that are induced by a strong modulation pulse with fast envelope dynamics. Conditions to observe coherent oscillations are verified, and control of their properties is demonstrated. The main experimental findings are supported by theoretical modeling and numerical calculations. The observed results may lead to a renewed interest in general studies of a discrete energy level coupled to a broadband continuum when the properties of both are fully controlled.

Study on the ground impact vibration intensity model of high energy warhead explosion

Introduction: In the warhead explosion process, the ground impact vibration intensity will directly affect the target buildings and instruments safety, and it is also of great significance to accurately evaluate the ammunition explosion damage power.Methods: In this study, the finite element numerical simulation method was used to analyze the explosion shock wave pressure and ground shock vibration velocity of TNT explosive with a mass of 100 kg∼1000 kg, and the ground transmission medium of sandy soil, C35 and C140 concrete, and the shock wave pressure and ground shock vibration velocity propagation and distribution law was clarified. Based on the explosion similarity law and dimensional analysis method, a ground impact vibration velocity theoretical calculation model with clear physical significance is established by introducing the property ground propagation medium parameters, taking into account the factors affecting the ground impact vibration velocity.Results: The model calculation accuracy is verified by the measured data. The verification results show that the model calculation accuracy is higher than 91.8%, which improves the calculation accuracy of the explosion site ground impact vibration velocity.Discussion: This research provides more accurate and scientific theory and data support for the ammunition explosion damage power evaluation, and provides a reference for the shock and vibration resistance performance design of instruments, equipment and buildings. It has strong engineering application value.

Energy advantage of cold energy recovery system using water- and air-side free cooling technologies in semiconductor fabrication plant in summer

The semiconductor industry requires large amounts of energy. Of the total energy, semiconductor manufacturing facilities consume the most electricity, where 21–29% of the total energy is used to maintain a clean room environment at a constant temperature and humidity. The energy required for constant temperature and humidity has been developed and applied in various ways, e.g., waste heat recovery technology without a boiler. However, it is highly difficult to obtain the energy required for cooling without operating a chiller unless there is a climatic advantage. Therefore, with the perspective of introducing cold energy recovery system into outdoor air-conditioner, this paper suggests the analysis of the energy-saving effect of the recovery system which recovers wasted cold energy of the exhaust gas from the semiconductor fabrication plant located in high-temperature and humid region. Two systems have been proposed: a water-side free cooling system that recovers cold energy by connecting a cooling tower to exhaust gas, and an air-side free cooling system that recovers cold energy by connecting a membrane energy heat exchanger. When applied to the conventional outdoor air-conditioner after cold energy recovery in both systems, the energy-saving effect was estimated by a simulation program (i.e., engineer equation solver) using a theoretical calculation model. The result showed that the cooling load of the outdoor air-conditioner decreased by 10.2–13.1% and 8.5–11.2% when the water-side free cooling system and air-side free cooling system, respectively, were applied at an exhaust gas temperature of 24–28 °C and a humidity ratio of 0.00733 kg/kg’. However, with the consideration of the power consumed by the cold energy recovery system (i.e., water/air-side free cooling system), actual energy-saving rate was low. Consequently, the head and static pressure designs of the fluid transfer equipment (i.e., pumps and fans) of the cold energy recovery system should be considered with caution when the cold energy recovery system is applied.

Dynamic Response Analysis of Buried Aviation Oil Pipeline Under Heavy Vehicle Load

The risk of damage caused by the third party construction such as vehicle rolling is increasing day by day, which seriously threatens the production and operation of the aviation oil pipeline and the life and property safety of the people along the line. Based on the theoretical calculation model of vehicle rolling, the finite element models of pipeline, soil and pipe-soil are established respectively. At the same time, the moving load is loaded using the VLOAD subroutine, and the numerical simulation is carried out using ABAQUS. Finally, the influence of vehicle rolling load on the dynamic response of buried gas pipeline under different vehicle weight and speed conditions is analyzed. The research results have important guiding value for preventing the damage accident of aviation oil pipeline caused by vehicle crushing and guaranteeing the safe and smooth operation of aviation oil pipeline.

Optimization design of the sound absorbing structure of double-layer porous metal material with air layer based on genetic algorithm.

An acoustic absorption structure of a double-layer porous metal material with air layers is proposed. The Johnson-Champoux-Allard (JCA) model combined with the transfer matrix method (TMM) was used to establish the theoretical calculation model of the sound absorption coefficient (SAC). Meanwhile, the SAC between 500 and 6300 Hz were measured with an impedance tube. The errors between the theoretical and experimental values were compared to illustrate the good predictability of the theoretical model within the inverse estimations of the transport properties. The effects of the material placement order, material thickness, and cavity depth on the sound absorption performance from 200 to 5000 Hz were analyzed using the theoretical model. Further, a multi-objective function genetic algorithm was used to optimize the porous material's thickness and SAC to obtain an acoustic structure with a smaller thickness and higher sound absorption. A series of optimal solutions were obtained for acoustic structures with a total thickness of less than 70 mm. When the total thickness of the foam metal was 33.57 mm, the average SAC reached 0.853, which was significantly lower than the total thickness of the previous experiments. The multi-objective function genetic algorithm can provide a reliable solution for the optimal design of most sound-absorbing structures.

Grouting mechanism and experimental study of goaf considering filtration effect.

The filtration effect significantly affects the gangue slurry velocity and concentration, making it difficult to evaluate the gangue slurry diffusion range. Based on the Darcy seepage law, a seepage theoretical calculation model is established considering the filtration time and space effect. And the "water-cement ratio change matrix" in the seepage process of coal gangue slurry is deduced, revealing the basic mechanism of the porous media filtration effect, and the water-cement ratio gradually increases in the seepage process of gangue slurry. The visual test platform for slurry diffusion in goaf was independently developed for testing. The active heating optical fiber method (AHFO) was used to monitor the flow and diffusion of coal gangue slurry in the collapse zone of goaf, and the gravity gradient and water cement ratio of slurry in goaf were measured. The law of particle sedimentation in the gangue slurry flow process under the filtration effect was revealed, and engineering verification was carried out. The results show that the average slope of the gangue slurry in the gangue accumulation is 6.34%, and the overall flow law of the gangue slurry in the goaf is the first longitudinal expansion and then transverse diffusion. The water-cement ratio near the grouting mouth is smaller than the initial water-cement ratio, the near-end water-cement ratio is smaller, and the far-end water-cement ratio is larger. During on-site filling, the accumulated grouting volume of a single hole is 700 m3, and the gangue slurry diffusion distance is greater than 45m, indicating that the gangue slurry has good fluidity.

Modulation Doping Leads to Optimized Thermoelectric Properties in n‐Type Bi6Cu2Se4O6 due to Interface Effects

AbstractHeterogeneous composites consisting of Bi6Cu2Se3.6Cl0.4O6 and Bi2O2Se are prepared according to the concept of modulation doping. With prominently increased carrier mobility and almost unchanged effective mass, the electrical transport properties are considerably optimized resulting in a peak power factor ≈1.8 µW cm−1 K−2 at 873 K, although the carrier concentration is slightly deteriorated. Meanwhile, the lattice thermal conductivity is lowered to ≈0.62 W m−1 K−1 due to the introduction of the second phase. The modified Self‐consistent Effective Medium Theory is utilized to explain the deeper mechanism of modulation doping. The enhancement of apparent carrier mobility is derived from the highly active phase interfaces as fast carrier transport channels, while the reduced apparent thermal conductivity is ascribed to the existence of thermal resistance at the phase interfaces. Ultimately, an optimized ZT ≈0.23 is obtained at 873 K in Bi6Cu2Se3.6Cl0.4O6 + 13% Bi2O2Se. This research demonstrates the effectiveness of modulation doping for optimizing thermoelectric properties once again, and provides the direct microstructure observation and consistent theoretical model calculation to emphasize the role of interface effects in modulation doping, which should be probably applicable to other thermoelectrics.

Beam Energy Dependence of the Linear and Mode-Coupled Flow Harmonics Using the a Multi-Phase Transport Model

In the framework of the A Multi-Phase Transport (AMPT) model, the multi-particle azimuthal cumulant method is used to calculate the linear and mode-coupled contributions to the quadrangular flow harmonic (v4) and the mode-coupled response coefficient as functions of centrality in Au+Au collisions at sNN = 200, 39, 27 and 19.6 GeV. This study indicates that the linear and mode-coupled contributions to v4 are sensitive to beam energy change. Nevertheless, the correlations between different-order flow symmetry planes and the mode-coupled response coefficients show weak beam energy dependence. In addition, the presented results suggest that the experimental measurements that span a broad range of beam energies can be an additional constraint for the theoretical model calculations.

Probing the pressure dependence of sound speed and attenuation in bubbly media: Experimental observations, a theoretical model and numerical calculations

The problem of attenuation and sound speed of bubbly media has remained partially unsolved. Comprehensive data regarding pressure-dependent changes of the attenuation and sound speed of a bubbly medium are not available. Our theoretical understanding of the problem is limited to linear or semi-linear theoretical models, which are not accurate in the regime of large amplitude bubble oscillations. Here, by controlling the size of the lipid coated bubbles (mean diameter of ≈5.4μm), we report the first time observation and characterization of the simultaneous pressure dependence of sound speed and attenuation in bubbly water below, at and above microbubbles resonance (frequency range between 1–3 MHz). With increasing acoustic pressure (between 12.5–100 kPa), the frequency of the peak attenuation and sound speed decreases while maximum and minimum amplitudes of the sound speed increase. We propose a nonlinear model for the estimation of the pressure dependent sound speed and attenuation with good agreement with the experiments. The model calculations are validated by comparing with the linear and semi-linear models predictions. One of the major challenges of the previously developed models is the significant overestimation of the attenuation at the bubble resonance at higher void fractions (e.g. 0.005). We addressed this problem by incorporating bubble–bubble interactions and comparing the results to experiments. Influence of the bubble–bubble interactions increases with increasing pressure. Within the examined exposure parameters, we numerically show that, even for low void fractions (e.g. 5.1×10-6) with increasing pressure the sound speed may become 4 times higher than the sound speed in the non-bubbly medium.

Research and Perspectives on Fire-Fighting Systems in Tunnels under Strong Piston Wind Action

Guided by the technical requirements for tunnel fire safety, an overview of tunnel piston wind, combustion models, and full-size and small tunnel fire tests is presented. Firstly, the theoretical model and numerical calculation methods for piston wind tunnel fires are presented from the perspective of numerical simulation. Then, full-scale and small-scale test models for tunnel fires are presented, and the advantages and disadvantages of single-row, multi-row, single-fire source, and multi-fire source test methods are described. Finally, key breakthrough directions for future numerical and experimental research on piston winds and tunnel fires are proposed, specifically the mastery of underground tunnel fire development prediction methods. This involves mastering the full-scene elemental fire testing technology for underground tunnel operation systems; developing multi-channel data acquisition technology for fire tests under the effect of multiple disturbances such as high temperature and high humidity; and mastering the smoke flow law during fires in complex tunnel projects.

Analysis and Simulation Study on a Fault of Service Duty Test of Vacuum On-load Tap Changer

Aiming at a fault on service duty test of vacuum on-load tap changer (OLTC), the principle of the resonance test method is analyzed. Combined with the voltage and current waveform measured and the standard switching sequence, the cause and process of the test fault are qualitatively deduced. Based on the theoretical analysis, the simulation model of the test circuit and fault is built based on PSCAD. The voltage and current waveforms obtained by simulation are highly consistent with the test waveforms. The error of peak current between the simulation and the test waveform is 0.75%. The simulation results show the accuracy of the theoretical analysis and modeling calculation, they are verified by the follow-up inspection results of OLTC and vacuum tube solution. This paper provides a powerful technical means for fault analysis and fault mechanism research in the follow-up OLTC operation. It also has reference and guiding significance for the quality control, design, operation and maintenance, and monitoring of vacuum OLTC.

Understanding the yield strength difference in dual-phase eutectic high-entropy alloys

Face-centered cubic (FCC)/ordered body-centered cubic (B2)-structured Al–Co–Cr–Fe–Ni system eutectic high-entropy alloys (EHEAs) have a favorable combination of high strength and ductility in the as-cast state. However, the mechanical properties of this type of alloy vary significantly with composition. In this study, we attempted to determine the yield strength differences in FCC/B2 EHEAs. Based on reported Al0.8CrFeNi2.2, we successfully prepared three low-cost Co-free EHEAs: Al0.82Cr0.8Fe1.2Ni2.18, Al0.83Cr0.6Fe1.4Ni2.17, and Al0.85Cr0.4Fe1.6Ni2.15. All the EHEAs are shown to exhibit the same phase constituent (FCC/B2) and complete eutectic microstructure, with similar lamellar thickness but different tensile properties. We constructed a theoretical calculation model based on the Hall-Petch regime which fits the measured yield strength σ0.2. The yield differences for current FCC/B2 EHEAs results mainly from different intrinsic strengths of their soft FCC phases.

Experimental and Theoretical Investigation of the Mechanical Behavior of RC Beams Strengthened with Anchored Carbon–Glass-Fiber-Reinforced Polymer Plates

This paper focuses on the shear behavior of reinforced concrete (RC) beams strengthened with carbon–glass-fiber-reinforced polymer (C-GFRP) plates under different anchoring schemes. The study consisted of four reinforced specimens: specimen CS-1 with no reinforcement and three groups of reinforced specimens SR-1, SR-2 and SR-3. The studies used a four-point bending test to evaluate the reinforcement effect of mechanically anchoring C-GFRP plates. The results of the analysis of load–deflection, strain and bearing capacity indicated that a better reinforcement effect was observed with fiber-reinforced polymer. The test results suggested that the occurrence time of critical oblique cracks was delayed and the development speed of critical oblique cracks was limited by mechanically anchoring the C-GFRP plates. C-GFRP plates significantly increased the stiffness of the reinforced specimen and reflected the superiority of mechanical anchoring. The ultimate shear capacity of the mechanically anchored C-GFRP plates has been significantly improved. With a reasonable increase in the amount of C-GFRP plate, the shear resistance of the test beam became stronger. Compared with the CS-1 specimen without reinforcement, the yield load values of the reinforced specimens SR-1, SR-2 and SR-3 increased by 5.56%, 18.80% and 26.50%, respectively. The ultimate load of reinforced specimens SR-1, SR- 2 and SR-3 increased by 11.64%, 17.47% and 31.51%, respectively. The researchers deduced their theoretical calculation method from the bearing capacity of RC beams strengthened by anchoring with carbon–glass-fiber-reinforced polymer plates. The test findings were in good accord with the theoretical calculation model of bearing capacity suggested in this research.

Self-Intercalated 1T-FeSe2 as an Effective Kagome Lattice.

In kagome lattice, with the emergence of Dirac cones and flat band in electronic structure, it provides a versatile ground for exploring intriguing interplay among frustrated geometry, topology and correlation. However, such engaging interest is strongly limited by available kagome materials in nature. Here we report on a synthetic strategy of constructing kagome systems via self-intercalation of Fe atoms into the van der Waals gap of FeSe2 via molecular beam epitaxy. Using low-temperature scanning tunneling microscopy, we unveil a kagome-like morphology upon intercalating a 2 × 2 ordered Fe atoms, resulting in a stoichiometry of Fe5Se8. Both the bias-dependent STM imaging and theoretical modeling calculations suggest that the kagome pattern mainly originates from slight but important reconstruction of topmost Se atoms, incurred by the nonequivalent subsurface Fe sites due to the intercalation. Our study demonstrates an alternative approach of constructing artificial kagome structures, which envisions to be tuned for exploring correlated quantum states.