Search

Because the seabed is covered with deep slit soil and seawater layer, the characteristics between offshore and onshore ground motions are significantly different. Besides, compared with sea-crossing bridges and other marine structures, the seismic response of immersed tunnels buried under seabed can be influenced by the site condition more significantly. Therefore, it is necessary to study the effects of seawater depth, site condition and offshore ground motion on the seismic response of immersed tunnels. Firstly, offshore strong motion records from the K-NET are grouped with different epicentral distances, magnitudes, and stations, and the response spectra of offshore ground motions in different groups are compared. Then, a numerical simulation model with the water layer, offshore soil layer and immersed tube tunnel coupling is established. The seismic responses of the tunnel and the seabed site are compared by inputting offshore and onshore ground motions respectively. Finally, the effects of seawater depth, incidence angle, slit soft soil layer and buried depth on the seismic response of tunnel and local seabed site are systematically studied by inputting P wave and SV wave pulses respectively. The results show that the silt soft soil layer will make the horizontal seismic response of the immersed tunnel more serious under SV wave incidence. The vertical seismic responses of the immersed tunnel and seabed are suppressed by the seawater layer under P wave incidence, and the response will decrease with seawater depth increasing. Besides, the effect of the buried depth and incidence angle on the seismic response of the immersed tunnel is limited. [ABSTRACT FROM AUTHOR]

Fiber metal laminates (FMLs) are widely applied as protective structures in various high-tech industries owing to their excellent impact resistance. This paper presents an explicit finite element (FE) simulation to investigate the dynamic damage behavior of carbon fiber-reinforced aluminum laminates (CRALLs) under combined explosion and fragment loading. Johnson-Cook model is utilized to capture the damage response of aluminum material; 3D Hashin failure criteria are applied to predict the damage evolution of fiber composite material considering the high strain rate effect; cohesive elements are incorporated to simulate the inter-laminar delamination phenomena. The effectiveness of the proposed numerical model is verified through a comparison with available experimental data in ballistic impact conditions. In addition, a thorough analysis of the dynamic behavior and damage mechanism of FMLs is conducted, and the impact performance is extensively discussed in terms of the influences of explosion distance and explosion mass. This work serves as a valuable reference for future numerical studies on the explosive impact resistance of other FMLs structures. [ABSTRACT FROM AUTHOR]

3D woven fabrics possess excellent specific performance and processability, making them highly favorable in the field of protective engineering, particularly in applications such as body armor. It is critical to evaluate their ballistic response under various impact loadings for both material manufacturing and application purposes. This paper presents a full-size mesoscale finite element model to investigate the dynamic damage behavior of 3D angle-interlock woven fabric (3DAWF) under ballistic impact. The effectiveness of the proposed numerical model is verified through a comparison with available experimental data in terms of ballistic performance and damage morphology. The effects of projectile shape, impact angle, and pre-stretching loading on the ballistic performance of 3DAWF are discussed. It is observed that 3DAWF demonstrates different impact resistance with different projectile shapes due to variations in the impact area and damage mechanism. The friction generated by projectile sliding plays a significant role in dissipating projectile kinetic energy under oblique impact. Moreover, pre-stretching is found to enhance the ballistic limit and energy absorption of 3DAWF to a certain extent. [ABSTRACT FROM AUTHOR]

With the development of railway technology, high-speed trains have been invested in practical operation increasingly. The traffic accident that train runs at high speed will cause casualties and property losses. The energy absorption tube can effectively alleviate the damage of the vehicle in the collision process and protect passengers in the buffering process. In this paper, nested corrugation square energy-absorbing tubes (NCSTs) with circumferentially cosine profile and different inner structures are analyzed by adopting finite element (FE) simulation. The quasi-static compression tests and proposed theoretical model based on Simplified Super Folding Element (SSFE) theory are employed to validate the effectiveness of numerical models. The simulation results indicates that the crushing modes possess certain sensitiveness to cross-sectional conformation and the NCSTs present more stable and orderly deformation modes compared with non-nested tubes. The specific energy absorption (SEA) and crushing force efficiency (CFE) of NCST can be increased by 52.49 and 19.07% compared to ordinary corrugation tube, respectively. In addition, the tube with two-layers octagonal wall (SO1D) is selected as optimal structure because it is ranked first under cases of 40% by adopting the technique for order preference by similarity to ideal solution (TOPSIS) method. Finally, the sensitivity analyses based on SO1D are conducted. The results show that the parametric variation of trib and tout fairly effect on the deformation pattern. And increases in wall thickness t and section size of the middle wall Dmid will all result to increases in initial peak crushing force (IPCF) and significant variation on other crashworthiness criteria. This paper offers certain reference significance for the study of energy-absorbing structures. [ABSTRACT FROM AUTHOR]

The authors performed the optimizations of an auxetic tube considering different structural responses: mass, critical buckling load, natural frequency, Poisson's ratio, and maximum compression load compression. The response surface methodology was applied to generate a metamodeling with a set of non-linear equations. All data were generated via numerical modeling after experimental validation. The Lichtenberg Algorithm was used to find the best possible configurations. This paper shows something unprecedented in the literature when evaluating the static and modal performance of an auxetic tube in a multi-objective problem. The results showed an improvement of up to 43% compared to the initial model. [ABSTRACT FROM AUTHOR]

With bio-mimetic MAV (micro aerial vehicles) becoming increasingly important dual-use equipment, their crashworthiness under impact loads is also considered a key research direction. Based on the micro-morphology of the cross section of the beetle exoskeleton, we proposed the thin-walled structure protection design of several bionic MAV, and used the finite element method to compare the crushing process and energy absorption characteristics of each structure under axial loading, and obtained the thin-walled structure with excellent protection. On this basis, numerical simulation methods were used to study the optimal parameters of the structure, such as impact angle, number of protective layers, and wall thickness. The results show that the energy absorption characteristics of square structure with type #3 are higher than those of all other structures. With the increase of inclination angle, the energy absorption characteristics of the structure generally show a very obvious decreasing trend. The structure with wall thickness of 1.0 mm has better space accommodation and energy absorption ability for bio-mimetic MAV. [ABSTRACT FROM AUTHOR]

In this study, a dynamic caustic experimental system is used to examine the damage distribution characteristics as well as the crack formation/propagation mechanism in polymethyl methacrylate (PMMA) caused by uncoupled eccentric shaped charge blasting under different decoupling coefficients and charge positions. Using PMMA as the experimental material, the damage variables around the hole are calculated by the digital image processing method. The stress wave propagation law under different charge positions is revealed. Furthermore, based on the fractal theory, the damage values of shaped and unshaped cracks are calculated. The results show that the range of the crushed zone and failure zone on the coupled side around the hole of eccentric uncoupled charge is larger than that on the uncoupled side, which can reduce the damage on the reserved side and break the excavation side more fully. Under the condition of eccentric uncoupled charging, the range of the crack zone and failure zone decreases with the increase in the decoupling coefficient. When the decoupling coefficient is 2, the smoothness of the main crack is the best, and the total and average lengths of the main crack are also maximum. The damage distribution caused by explosive crack conforms to the fractal law, and the fractal dimension can accurately represent the damage degree of PMMA after the explosion. [ABSTRACT FROM AUTHOR]

This study focused on the water breakthrough issue that still occurred after water shutoff using gel plugging agents. Taking the heavy oil reservoir with edge-bottom water in the Y oilfield as an example, the study investigated the water cut variations after water shutoff and analyzed the types of water breakthrough characteristics in the wells of this reservoir. The CMG numerical simulation software was used to study the influence of geological parameters on the water cut variations after water shutoff. The research findings revealed that the water breakthrough characteristics in all the treated horizontal wells were classified into low water cut breakthrough, pulse-type breakthrough, step-type breakthrough, and high water cut breakthrough. Additionally, it was observed that horizontal wells in different geological conditions exhibited distinct water breakthrough characteristics under the same water shutoff process conditions. Through numerical simulation and statistical analysis of field data, the main factors influencing the variation of water cut after water shutoff were identified as reservoir permeability, oil saturation, interlayer position, water avoidance height, injection-production well distance, oil viscosity. The research findings allowed for the prediction of water breakthrough characteristics after water shutoff or the analysis of reservoir structure configuration based on known water breakthrough characteristics. [ABSTRACT FROM AUTHOR]

In Western Guizhou, China, multi-layer development is a successful way for CBM development, with drainage rate control being the essential technology. In this article, a coupled hydraulic-mechanical numerical model considering permeability velocity-sensitive damage was established to analyze the impact of drainage rate on the gas production and reservoir parameters of multi-layer CBM development. The CBM development in the study area can be divided into four stages. The permeability velocity-sensitive damage and Jamin effect mainly occurred in the first two stages. Increasing the drainage rate during the first two stages will cause more serious permeability velocity-sensitive damage. Reducing the drainage rate in the first two stages could alleviate the permeability velocity-sensitive damage and Jamin effect. During the stable production stage II, the gas seepage being dominant in the c409 coal seam, the gas production would be significantly reduced under the permeability stress-sensitive damage as the drainage rate increasing. Based on the simulation results, three recommendations concerning the drainage rate optimization of multi-layer CBM development were advanced, and gas production was successfully improved. This study has important theoretical and practical significance for guiding the multi-layer CBM development in Western Guizhou and Southern China. [ABSTRACT FROM AUTHOR]

With the increase of exploration resources of crude oil worldwide, how to decompose by recombination or long chain compounds to convert high viscosity heavy and inferior crude oil into high quality low viscosity oil and chemical raw materials has become the focus of the refining industry. Several types of oil were treated to reduce viscosity with a self-built heavy oil viscosity reduction device based on jet cavitation. Meanwhile, the viscosity-decreasing condition of different operating parameters was analyzed by CFD numerical simulation method. The results showed that the viscosity reduction of Saudi heavy oil is the best at 4 MPa, the viscosity reduction rate reaches 46.97%. The numerical simulation and analysis of different kinds of oil products were carried out, and the pressure, gas holdup, velocity, turbulent kinetic energy, mass transfer rate and cavitation number were used as evaluation criteria. Through the numerical simulation and experimental verification, the application of jet cavitation in viscosity reduction of heavy oil is deeply studied, and an innovative evaluation method for viscosity reduction of jet cavitation which integrated various factors is proposed, which provides theoretical guidance and data support for the oil treatment effect and device selection of jet cavitation in industrial application. [ABSTRACT FROM AUTHOR]

The overburden of marine hydrate sediment is usually a permeable cover, and the presence of permeable overburden directly affects the depressurization effect. However, previous studies have mainly focused on the effect of the permeable overburden without considering seawater infiltration, and the influence of seawater infiltration on the production of hydrate cannot be ignored. In this article, a new numerical model considering seawater infiltration is developed and this study is completed by numerical simulation. The results show that seawater infiltration significantly reduces hydrate dissociation, and the presence of seawater substantially reduces cumulative gas production and increases water production compared to non-permeable overburden, with higher permeability resulting in lower gas production and higher water production. It is an effective means to extract hydrates through lower bottom-hole pressure by increasing the gas–water ratio. It is of great significance to further understand the production characteristics of hydrate reservoirs. [ABSTRACT FROM AUTHOR]

The most widely used method in the self-healing of hot mix asphalt is the capsule method. In this method, the capsules effect the mechanical properties of asphalt mixtures. In order to determine the effect of capsules on the mechanical properties of asphalt mixtures, capsules containing waste vegetable oil in four different ratios (0.25%; 0.50%; 0.75% and 1.00%) were added to the mixtures. The mechanical properties of asphalt mixtures with and without capsules were determined by applying the creep test at single stress (450 kPa). Thanks to these test results, after the capsules written in 4 different ratios were randomly distributed into the sample with Python code, the creep test was carried out under three different constant stresses (300, 450 and 600 kPa) using the finite element method. Finally, the Response Surface Method (RSM) analysis was carried out to evaluate the relationship between variables and permanent deformations, thus it was aimed to gain a statistical perspective to the study. As a result of the simulation, differences caused by the capsules were observed. Accordingly, it was determined that the addition of capsules increased the permanent deformation rate of asphalt mixtures. As a result of the RSM analysis, it is seen that the model performs the analysis with high accuracy. [ABSTRACT FROM AUTHOR]

In this paper, a novel bioinspired hexagonal honeycomb (NBHH) is proposed. Different from the conventional honeycomb (CH), the core wall of the NBHH has a saw-tooth corrugated shape. Firstly, LS-DYNA R11.0 is used to construct a finite element model and conduct experimental verification; then, a comparative analysis is carried out with the CH and the bionic honeycomb sandwich panel (BHSP) with sinusoidal curves, and the proposed NBHH exhibits excellent energy absorption capability under dynamic impact. In particular, compared with the CH and the BHSP with the same wall thickness, the specific energy absorption of the NBHH is 58.60% higher than that of the CH. Compared with the BHSP, the specific energy absorption of the NBHH has increased by 7.23%. Finally, parametric research is carried out on the NBHH. [ABSTRACT FROM AUTHOR]

Deep within coal gangue hills, there is a substantial amount of wasted thermal energy. Prolonged accumulation of these hills leads to significant damage to the atmosphere and soil. Gravity heat pipes, as efficient heat transfer components, can safely, efficiently, and conveniently extract the accumulated heat in gangue hills to achieve effective thermal control. In this study, we first analyzed the optimal height of the heat dissipation fins through a single fin heat dissipation model. Then, we determined the optimum spacing between the heat dissipation fins through analysis with multiple fins. The results showed that when the height of the heat dissipation fins was 80 mm and the spacing between fins was 80 mm, the heat dissipation performance and economic costs were most reasonable. Through an engineering trial conducted for 143 days at the Maotergou coal mine gangue hill, it was found that the average heat dissipation rate of a single gravity heat pipe ranged from 243.52W to 494.32W. The total heat dissipation during the entire experimental process was 54.39 kJ, and the total heat dissipation at the elevation of 890 meters was 1087.71 kJ. This indicates that managing the internal temperature accumulation in coal gangue hills using gravity heat pipes is entirely feasible. [ABSTRACT FROM AUTHOR]

Coal is a major part to stable energy structure. Borehole Grouting is a primary method used for the prevention and control of coal spontaneous combustion in the regenerated roof. However, the construction design of high-position grouting for the regenerated roof lacks a sufficient theoretical foundation due to the limited advancement in theoretical research on the high-position grouting of fracture. To fill the theory research gap of high-position grouting in regenerated roof, a fracture network high-position grouting numerical model was established. Based on the numerical model and assumptions of the equivalent path, a mathematical model of fracture network high-position grouting was established and a global sensitivity analysis was conducted. The results showed that the morphology of slurry diffusion is influenced by gravity and fracture orientation. The diffusion front undergoes three successive phases of transformation: hemispherical diffusion, curved diffusion, and plane diffusion. Based on the mathematical model, the fracture aperture has the largest first-order sensitivity and total-sensitivity index to grouting pressure during the whole phase of grouting. The second-order sensitivity index between fracture aperture and slurry viscosity, grouting pipe radius, grouting rate, dip, and azimuth is greater than other parameters. By focusing on key parameters and their interactions, this research contributes to enhancing the effectiveness of grouting construction while simultaneously reducing design complexity. [ABSTRACT FROM AUTHOR]

Shale is a complex porous medium with multi-scale pores and well-developed fracture networks. This paper aims to use modeling and numerical simulation methods to study the transport of shale gas in a complex multi-scale matrix-fracture system. In this study, mathematical modeling and programming was used to establish digital models of shale gas multi-scale matrix and 3D discrete fracture network. Based on the transport mechanisms of shale gas, this study derives the mathematical models of shale gas transport in different transport media, and uses the finite element method to solve and analysis the transport of shale gas in the multi-scale matrix-fracture system. The model is verified by real shale gas field data. The results show that the fractal dimension of organic pores have great effects on shale gas transport. When the fractal dimension is greater than 1.4, the increase on gas production is particularly obvious. Compared with organic pores, the effect of fractal dimension of inorganic pores is smaller. The existence of the fracture network has an effect of up to 25% on gas production, and the optimal fracture density is 200. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced composite multilayer damping structures with different types of stiffeners demonstrate excellent mechanical properties. This paper deals with the bending properties analysis of carbon fiber reinforced composite multilayer damping structures with different types of stiffeners for the first time. A theoretical model was constructed to investigate the bending performance of the structure under static loading based on structural stress transfer mechanism between stiffener and composite plate. Moreover, the theoretical solution was compared with the numerical simulation results to confirm their validity. Finally, structural parameters were considered to discuss the change law of the structural center deflection. [ABSTRACT FROM AUTHOR]

Welding buckling deformation is one of the foremost failure modes of thin plate welded structures. It is important to estimate welding buckling for structural design and process optimization. Inherent strain-based welding buckling evaluation methods have been proved to be valid, but the existing methods have low efficiency due to requiring multiple inherent forces. In this study, a novel welding buckling evaluation method based on longitudinal shrinkage force was established. The effectiveness of the proposed method was validated using a butt welded joint. In addition, this method was applied in a large-scale thin plate structure for evaluating the structural stability, the effects of heat input, welding manner, and external constraints on welding deformation and buckling were also discussed. The results reveal that the proposed inherent strain-based welding buckling evaluation method can be used to judge whether welded structures are buckled. The reduction of welding heat input and the use of single-sided welding can mitigate welding deformation. Increasing external constraints can not only reduce the welding deformation, but also improve the welding critical buckling load for preventing welding buckling. [ABSTRACT FROM AUTHOR]

In the western region of China, the coal seam is shallowly buried. Overburden fissures readily develop upwards through the surface, and provide channels for wind to flow into the gob. Here, a model for the coal spontaneous combustion in gob caused by air leakage from fissures in shallow coal seams was established. The accuracy of the model is verified by comparing the oxygen concentration on the inlet and outlet sides of the field monitoring data with the results of numerical simulation. In addition, the distribution of oxygen concentration and wind speed in gob and their influence on spontaneous combustion dangerous zone were studied by numerical simulation when the air leakage volume varied from low to high (36–600 m3/min). The results showed no significant change in the distribution ranges of oxygen concentration and wind speed along the Z-direction when there is no air leakage from the gas conducting fissure in the gob. With the increase of air leakage, the oxidation zone defined by oxygen concentration moves to the depth of the gob, and the oxygen concentration near the fissure increases. In addition, the oxidation zone defined by the wind speed moves significantly deeper into the mining area, and the wind speed is higher at the location corresponding to the fissure close to the working face, and the overall symmetrical distribution of the flow field in the mining area. According to the oxygen concentration and wind speed, the size of dangerous zone initially increased, before decreasing and finally plateauing. [ABSTRACT FROM AUTHOR]

Existing mathematical models for deflector jet hydraulic amplifiers cannot accurately describe the influence of the deflector motion on the receiver jet, which results in calculation differences for the receiver pressure. To deeply investigate this problem, the momentum transfer model considering secondary jet velocity distribution was used to develop an improved model that is more aligned with the actual state of the flow field. In this model, the receiver jet velocity is calculated, for the first time, with a maximum error of 18% when compared with existing models. To verify the improved model, the recovery pressures in the receivers were verified by numerical simulations and experiments. The verification results show that the model can accurately predict the recovery pressures in the receivers within an 8.1% maximum error. This model fills the gaps in the theoretical research and lays a foundation for the structural design of deflector jet pressure servo valves. [ABSTRACT FROM AUTHOR]

In contemporary times, radar and infrared‐compatible stealth materials have emerged as a pivotal domain of research globally, aimed at augmenting the survivability of military assets. However, current candidates generally exhibit subpar compatibility performance in elevated temperature environments due to the imbalanced interplay between the two spectral bands. In this work, a meticulously designed sandwich‐structure SiO2/C@SiC/SiO2 composite is proposed to cope with the challenge. The middle layer of C@SiC composites possesses excellent microwave absorption performance even at high temperatures. The outer layers of SiO2 aerogels serve not only to inhibit the infrared radiation intensity, but also reinforce the microwave absorption capacity by optimizing the impedance matching and reducing the heat transferred to the middle layer. Based on the numerical simulation outcomes, the thickness of each layer has been optimized to attain a harmonious balance between microwave absorption and infrared radiation properties. Ultimately, the sandwich structured SiO2/C@SiC/SiO2 composites demonstrate low RL (reflection loss) values (←5 dB) across nearly the entire X band (8–12 GHz), alongside minimal surface temperatures hovering ≈44 °C at an ambient temperature of 200 °C. The comprehensive investigation into impact patterns and underlying mechanisms offers invaluable insights to develop radar and infrared‐compatible stealth materials for high‐temperature applications, which can be applied as stealth coatings on the skin of high Mach number aircraft. [ABSTRACT FROM AUTHOR]

AbstractThe research focuses on the comprehensive excavation face of Xida Lane in a coal mine belonging to Lu’an Group in Shanxi Province. A comprehensive research approach, combining theoretical analysis, numerical simulation and field measurement, is employed. A new dust isolation and collection device is utilized, along with a ventilation mode that combines upper and lower cylinders. A simulation model is established for the air curtain ventilation system formed by rectangular air outlet, studying the airflow and dust field of the comprehensive excavation face. The findings indicate that when high-speed airflow is injected from the rectangular air outlet, an air curtain forms in front of the comprehensive excavator operator. The majority of the dust generated during excavation is effectively controlled within a specific area, primarily between x = 0 m, x = 1 m, x = 2 m. With increasing distance from the comprehensive excavation face, the concentration of dust in the roadway gradually decreases. At the coordinates of comprehensive excavator operator (x = 5 m, y = 1.5 m, z = 0.4 m), the dust concentration has been successfully reduced to 9.31 mg/m³. This level meets the coal mine safety regulations, which mandate that dust concentrations remain below 10 mg/m³. [ABSTRACT FROM AUTHOR]

The longevity of solid oxide fuel cells is influenced by internal residual stresses, which may induce deformation or fracturing of components. This study investigates the residual stress distribution at the nonplanar cathode–electrolyte interface by approximating the actual interface with trigonometric functions and developing a three-dimensional (3D) model. The model reveals that the stress patterns at nonplanar interfaces can elucidate the genesis of interfacial cracks. During fabrication, anode contraction results in compressive stress within the electrolyte and tensile stress within the anode, with thermal discrepancies between layers being the primary cause of residual stresses. The reduction process diminishes these stresses, thus enhancing the mechanical integrity of the cell. Mitigating interface nonplanarity is beneficial for minimizing residual stress. At each interface crest, the electrolyte exhibits a local minimum in compressive stress, and a local maximum in shear stress occurs between each crest and trough. Furthermore, decreasing the initial porosity and NiO volume fraction can slightly lessen interlayer thermal discrepancies, with little effect on residual stresses. [ABSTRACT FROM AUTHOR]

Sea-crossing bridges face critical challenges due to scour, which can destabilize foundations. This study investigates the scour characteristics of the large-diameter main pier of the Haiwen Bridge, with a pile diameter of 4.3 meters. Seabed changes were monitored over 630 days using field tests and numerical simulations. The study analyzed the relationship between flow velocity and scour depth, revealing that the maximum recorded scour depth was 3.65 meters at the upstream side. A linear regression model, developed from 75 sets of field data, produced a formula to estimate maximum local scour depth. Validation against field measurements showed a strong correlation, with the calculated values deviating by less than 10% from observed data. The findings indicate that upstream scour pits were 1.5 times wider and deeper than those downstream, while a shallow triangular scour zone, extending 1.2 times the pile diameter, formed downstream. Recommendations for scour protection include hydrological considerations, particularly on the upstream side and areas lacking sediment sources. [ABSTRACT FROM AUTHOR]

Effective coalbed methane extraction from soft coal seams is essential for mine safety and energy supply. To enhance the extraction efficiency of coal mine methane (CMM) and reduce the risk of gas outbursts in coal mining areas, we developed an original and innovate horizontal well hydraulic cavitation method. A mathematical model that can quantitatively optimize construction parameters and improve the effectiveness of engineering applications was also constructed to calculate the technological parameters of this construction method. This technology differs from traditional approaches by relying on hydraulic erosion rather than water jets, and it can be implemented in cased horizontal wells. Utilizing the mathematical model grounded in porous media theory and Darcy’s law, numerical simulations with COMSOL Multiphysics were conducted and construction parameters optimized. The proposed technology significantly advances safe and efficient coalbed methane recovery, benefiting coal mine safety and environmental sustainability. [ABSTRACT FROM AUTHOR]

ABSTRACT Aiming at the treatment problem for water inflow in a high geothermal environment, we proposed a grouting simulation method in high‐temperature flowing water: temperature extended‐two‐fluid tracking (txTFT) method. First, a transport model for solving the residence time of slurry was derived. Furthermore, a temperature transport model was established to describe the heat transfer between slurry and water. Finally, according to the fitted equation of slurry viscosity with residence time and temperature, the fine characterization of slurry viscosity was realized, and then the whole process simulation of grouting was realized. This method was used to reveal the blocking mechanism for grouting in high‐temperature flowing water of rock fractures. The results show that high‐temperature water limited the parallel‐flow diffusion of slurry and increased the counterflow diffusion and transverse diffusion of slurry. The higher the water temperature, the larger the grouting rate, and the lower the inlet pressure, the better the blocking effect of flowing water. The research results can provide theoretical guidance and application value for the grouting treatment of water inflow in a high geothermal environment. [ABSTRACT FROM AUTHOR]

Driven by the dual-carbon goal, the utilization and promotion of hydrogen energy, as a sustainable, eco-friendly, and clean energy option, has been widely supported by the policies of countries around the world. Nevertheless, because of the distinctive physical and chemical characteristics of H 2 , there is a potential for leakage across the entire hydrogen energy industry chain, resulting in combustion or explosion accidents. Consequently, to guarantee the safety and reliability of hydrogen energy during its utilization process, the diffusion process of hydrogen jets after the leakage of hydrogen storage system needs to be studied and analyzed. After briefly classifying the types of leaking hydrogen jets in hydrogen storage systems, this paper focuses on classifying, summarizing and commenting on the dominant mechanism of hydrogen jets, hydrogen jet prediction model, high-pressure underexpanded hydrogen jet surge structure and computational fluid dynamics-based simulation of leaking jets. Finally, the shortcomings in the study of leaking hydrogen jets in hydrogen storage systems are elaborated, and suggesting the future research for the promotion of safer and more efficient utilization of H 2. • Summarized the physical and chemical properties of hydrogen gas. • Classified types of hydrogen jets leaking from hydrogen storage systems. • The current research content of hydrogen jet after leakage is summarized, concluded and reviewed. [ABSTRACT FROM AUTHOR]

Typhoons are strong natural events that significantly influence the marine environment. In 2018, Typhoon Mangkhut traveled over a moored station with a depth ~1900 m on continental slope in the northern South China Sea, the near-inertial oceanic responses are studied based on the Regional Ocean Modeling System (ROMS) model simulation combined with observation data. Near-inertial currents after Mangkhut can be divided into three layers: near-circular polarized in upper ocean, across-slope polarized in deep ocean and along-slope polarized near the bottom, thickness of the three layers depend on the slope steepness. According to across-slope and along-slope intensified currents, the near-bottom vertical velocities and near-inertial energy were intensified at the moored station. The across-slope forth/back near-inertial flows brought cold/warm and salty/fresh water from deeper/shallower depth, increased vertical excursions of near-bottom temperature/salinity isolines and near-inertial available potential energy. The near-inertial barotropic across-slope currents were much greater than along-slope currents, with net cooling and salinity increase of the whole water column at the moored station. The core responses to Mangkhut were within 100 km around the station. The near-inertial kinetic energy generated both at sea surface and bottom slope, then propagated vertically into ocean interior and horizontally into the South China Sea basin as well as some topography-trapped waves propagated along the slope. This work enriches the understanding of air–sea interactions in coastal regions and the effect of ocean topography, especially after a typhoon. [ABSTRACT FROM AUTHOR]

The combination of auxetic behavior with concrete offers promising advancements in structural materials, providing unique mechanical properties that enhance impact resistance and energy absorption. The study investigates the mechanical behavior of auxetic concrete cellular structures, focusing on elliptic and peanut-shaped unit cells as well as their modified stiffener configurations, under low-velocity impact loading. To compare their impact performance, traditional and stiffened models were analyzed numerically using finite element solver ANSYS/LS-DYNA. The findings indicate significant differences between traditional and stiffened models. Stiffened models, such as SEC and SPC, exhibit higher maximum impact forces compared to traditional models like TEC and TPC. The introduction of stiffeners delays the zero-force phenomenon, resulting in extended energy absorption periods. The TPC model absorbed the most significant proportion of the initial impact velocity among traditional models, whereas the SPC model exhibited the highest energy absorption in models with stiffeners. The study highlights the potential of stiffened auxetic concrete cellular structures to enhance impact resistance and energy dissipation, making them advantageous for applications requiring high structural resilience. Further research into varying impact velocities and loading directions is recommended to optimize these structures for diverse conditions. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to investigate the hydrodynamics performance of the three types (pusher, tractor and Schottel) of the azimuthing podded drive (AZIPOD) electric propulsion system. To evaluate the propulsive performance of the podded drive system, the Reynolds-Averaged Navier Stokes (RANS) solver is employed. KP-505 propeller as the research object, hydrodynamic open-water characteristics of this propeller was first calculated, and agreed well with test results. Then, numerical simulation of the thrust, torque and efficiency of the three types of the AZIPOD systems (Pusher, Tractor and Schottel) with KP-505 propeller at various yaw angles (from -30° to +30° with 15° increments) and different advance coefficients were compared. For the Schottel propulsion system, the effects of the number of propeller blades and the blade pitch-diameter ratio on performance are presented and discussed. Finally, the effect of sturt, support element and pod for pusher type on the pressure coefficient, thrust and torque of one blade and whole blades is investigated during one cycle. [ABSTRACT FROM AUTHOR]

A detailed model for heat and moisture dynamics within the maize piles drying is created to investigate thermal and moisture transfer, specifically using maize as the subject of research. 3D reconstructions of maize piles using image processing methods and computed tomography technology enabled accurate geometric modelling. The drying process was analysed using finite element simulations, validated through maize drying experiments. An investigation into how airflow rate, thermal conditions, and moisture levels affect the drying behaviours was conducted. This study revealed that velocity decreases incrementally from the core towards the edges of the pores. Along the direction of the airflow, pressure and temperature both continuously reduce, showing a clear stratification effect. The complex airflow distribution within grain piles leads to uneven temperature distribution in maize piles. Higher ventilation speeds enhance heat transfer within the maize pile, accelerating the temperature rise of the kernels. Heat transfer takes place at a much quicker rate than moisture transfer. The drying duration is primarily determined by moisture transfer rather than heat transfer. In contrast to heat transfer, moisture diffusion within the grain pile requires significantly more drying time. Increasing the temperature of the ventilating air can intensify heat transfer between the kernels and the air, while also promoting moisture diffusion. However, higher relative humidity in the ventilation air hinders moisture diffusion, impeding surface moisture reduction and adversely affecting the drying process. These methods and findings offer theoretical support and references for designing and optimising drying systems. • The heat and moisture transfer are studied by computed tomography and COMSOL. •The pressure and temperature show a stratification phenomenon in airflow direction. •The moisture diffusion necessitates more drying time compared to heat transfer. •Higher air temperatures and velocity enhance heat transfer and moisture diffusion. •Lower relative humidity promotes moisture diffusion while may hinder grain heating. [ABSTRACT FROM AUTHOR]

Conventionally, the airflow fields outside and inside the naturally ventilated livestock buildings are modelled simultaneously in one computational domain using CFD (Computational Fluid Dynamics). The presence of surrounding buildings, indoor facilities and animals for large scale cattle barns make the required computational power extremely high and even unfordable to achieve simulation results with reasonable accuracy. The Domain Decomposition Technique (DDT), dividing simulations into two separate steps, is an alternative CFD framework to provide sufficient accuracy with affordable computations at each step. The objective of this study was to verify the reliability of DDT on modelling the airflow fields inside a naturally ventilated cattle barn (NVCB) by employing wind tunnel measurements. The exterior airflow fields around the targeted NVCB, which was opened with varying opening ratios, were first simulated to obtain the airflow boundary conditions at sidewall openings by applying exterior wind conditions at the inlet of the computational domain. The interior airflow of the targeted NVCB, were secondly simulated by applying the achieved airflow boundary conditions at sidewall openings from the first step simulation. The interior airflow fields obtained by DDT were in good agreement with wind tunnel measurements. This indicates that DDT can provide an alternative for CFD application in large-scale NVCB with presence of surrounding buildings, indoor facilities and animals, though these had not been considered in this study. This work contributes to simulation technology by providing a novel computational fluid dynamics (CFD) framework which provides sufficient accuracy on optimising microclimate inside naturally ventilated intensive livestock buildings with less computational effort. The conventional CFD framework makes the required computational power extremely high and even unfordable when the presence of surrounding buildings, indoor facilities, and animals were included in one computational domain. The proposed CFD framework, domain decomposition technique (DDT), dividing simulations into two separate steps, makes the individual CFD simulations feasible with available computational capacity when modelling gaseous emissions inside and around cattle barns. Such information can be very valuable as support for scientific advice on regulatory aspects concerning ammonia and methane emission levels at barn level. • Domain Decomposition Technique (DDT) was verified against wind tunnel measurements. • DDT provides reasonable accuracy of airflow inside naturally ventilated cattle barns. • Opening ratios of sidewalls openings affected the accuracy of DDT. • DDT facilitates CFD modelling of airflow inside naturally ventilated cattle barns. [ABSTRACT FROM AUTHOR]

In internally post‐tensioned (PT) prestressed concrete (PC) structures, the prestressing system is usually made of high‐strength steel tendons embedded within concrete through either metallic or plastic ducts filled with cement grout or grease. Construction defects or degradation phenomena may lead to insufficient covering, exposing the prestressing steel to a harmful environment, potentially compromising the durability and load‐bearing capacity of the structure. Based on experimental tests on six 1:5 scaled PT specimens, this study presents accurate numerical simulations of four‐point bending tests on girders with unbonded and partially bonded tendons having different levels of initial prestress. Nonlinear finite element analyses (FEAs) were developed to reflect the friction‐type interaction mechanism between unbonded tendons and external ducts under increasing external load up to failure. Both global and local response parameters of the girders were studied validating numerical results against experimental findings. The numerical simulations provide insights on the stress pattern of unbonded and partially bonded strands, shedding light on the lower bearing capacity of defective girders compared to those with bonded tendons. Such findings contribute to a multi‐scale assessment and decision‐making framework for existing PT girders with defective grouting and low residual prestress levels, enhancing the understanding of their structural behavior and informing maintenance or retrofitting decisions. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete (RAC) is increasingly being used in the construction of structural elements. However, the performance of RAC elements under fire is usually considered to be inferior to that of normal concrete (NC) elements. This study investigates the fire behavior of RAC composite steel slabs with and without openings. Ten slabs of size of 1.0 m × 2.2 m were cast either with no opening, one or two circular openings, and one or two square openings. Five of the slabs were manufactured with 100% RAC, while the other five slabs were made with NC. The concrete slabs were loaded and subjected to fire tests at a temperature of about 900°C for 120 min. Test results show that RAC composite slabs have lower stiffness (thus larger mid‐span deflections) under fire exposure compared to their counterpart NC slabs. In terms of the recorded temperature–time curves, RAC slabs showed similar performance to that of NC slabs. The ratio of soffit temperature to the temperature at the top of slab was considerably smaller for RAC slabs compared to NC slabs. RAC slabs also showed more spalling than NC slabs. Experimental test results were numerically verified using PyroSim® software with the two showing good agreement. A series of new design charts for composite RAC slabs with desired fire endurance are proposed. This study is expected to promote the wider use of RAC in construction of structural elements, particularly of composite slabs exposed to extreme temperatures. [ABSTRACT FROM AUTHOR]

Drilled shafts with a larger diameter than columns are frequently adopted as the foundation of highway bridge columns due to their superior economic efficiency and lower impact on existing facilities in the urban built‐up area. Different section dimensions lead to a socket connection between the column and the oversized shaft and a noncontact lap splice of their longitudinal bars. The force‐transfer mechanism and failure process of column‐to‐drilled shaft connections were deeply revealed in this study. Detailed FE models were developed at the Diana platform and validated against previous experimental results. Subsequently, a parametric study investigated the effect of the shear span‐to‐depth ratio, diameter ratio of shaft‐to‐column, column embedment depth, and shaft stirrup ratio. Finally, a modified strut‐and‐tie model (STM) was proposed to design stirrups of the transition region efficiently considering the experimental failure mechanism. Results indicate that the numerical models built in the Diana platform can precisely simulate the mechanical behavior of column‐to‐drilled shaft connections. The failure mechanism of column‐to‐drilled shaft connections is shaft stirrups yield at the compressive side induced by extrusion between the embedded column and shaft. The lateral loading capacity of column‐to‐drilled shaft connections increases with the increase of shear span‐to‐depth ratio, diameter ratio of shaft‐to‐column, column embedment depth, and shaft stirrup ratio. The modified STM is able to reveal the variation tendency of shaft transverse reinforcement demand with the various design parameters and give an average stirrup stress ratio of 1.20 and a coefficient of variation of only 8.31%. [ABSTRACT FROM AUTHOR]

Although it has been shown that using recycled concrete aggregate in new structural concrete is economical and sustainable, the use of this material for such applications is still not widespread. One of the reasons is that manufacturers, designers, engineers, owners, and other market players are not familiar with specifying and utilizing this material—although standards are starting to incorporate provisions for recycled aggregate concrete, successful, practical example projects are needed. The current paper describes the results of a partnership between universities and a precast concrete manufacturer of hollow core slabs. Seven hollow core slabs with volumetric replacement ratios of natural aggregate with recycled aggregate from 0% to 60% were tested to failure in both bending and shear, and then undamaged portions of the slabs were subjected to punching shear until failure. The results showed only mild differences in strength, with different replacement percentages of recycled aggregate under the various loading scenarios. Numerical simulations performed in Abaqus demonstrated the feasibility of analyzing recycled aggregate concrete structural elements and provided important insights into their behavior. [ABSTRACT FROM AUTHOR]

Recently, laser energy has been widely utilized from applications ranging from machining to weapon systems. In this study, the objective is to derive a damage modeling that can rapidly predict the damage to metallic materials resulting from continuous-wave laser irradiation. To this end, two materials, steel and aluminum, were subjected to computational analysis, and the analysis techniques were validated by comparing their results to previously published experimental results. Based on the keyhole depths of the specimens, the computational analysis results deviated by 3 %–10 % from the experimental results. The damage to each material was predicted over time by applying laser energies of 15 kW to 80 kW to disk-shaped specimens. Based on the results, a damage modeling was proposed. The proposed damage modeling yielded accuracies of within 4 % for DP600 steel, 7 % for 304 stainless steel, and 9 % for aluminum over a range of laser powers. [ABSTRACT FROM AUTHOR]

Leading-edge protuberances (LEPs) suppress flow separation and improve the aerodynamic performance of fluid machinery. In this paper, bionic protuberance was added to the leading edge of the wind turbine blade. Three parameters were designed to control the protuberance shape (amplitude, attenuation, and number), and a comparative study was conducted using computational fluid dynamics. Results indicate that the bionic LEPs can influence the flow pattern. Under the rated condition with the wind speed of 11.4 m/s, using the LEPs with a larger attenuation can increase the output power of the wind turbine by 1.36 %. Research on the parameters of the LEP shows that when using LEPs with faster attenuation rate and fewer number, the vortex on the suction surface can be reduced, which brings positive gains. Unsteady characteristics indicate that LEPs can reduce the blade fluctuations during operation and can improve the operational stability. Therefore, bionic LEPs can effectively enhance the performance of wind turbines. [ABSTRACT FROM AUTHOR]

Blasts are a threat both in military and civil contexts due not only to explosive devices but also to gas leakages or other accidents. Numerical models could aid to plan response strategies in the short and long term. Nevertheless, due to modeling complexities, a standardized computational framework has not been established yet. In this challenging context, the present study assesses the prediction of blast‐induced traumas by using the total human model for safety (THUMS) human model, which has never been attempted before to the authors knowledge. The pedestrian model is publicly available, hence the demonstration of its suitability to predict blast injuries could benefit the establishment of a common modeling framework. Therefore, the THUMS human model was exposed to different blast scenarios both in free field and partially confined spaces and the response of vital organs was investigated. Trauma patterns to internal organs of the THUMS were consistent with available experimental data and injury thresholds. In conclusion, THUMS open‐source human model demonstrated its validity to reproduce primary blast‐related injuries, addressing the development of standardization of numerical simulations of human response to explosions. [ABSTRACT FROM AUTHOR]

Combustion is a complex physical and chemical process, which is considered both in the modeling of new propulsion systems with high energy efficiency and sufficient safety, and in the modeling of explosion safety and fire extinguishing problems. Fundamental research of this process is one of the key factors responsible for the safety of current and future space flights. Modeling the behavior of chemically reacting systems is computationally complex problem. It is necessary to take into account many details and processes, such as multicomponent structure, diffusion, turbulence, chemical transformations, etc. The modeling of chemical kinetics is the most computationally complex stage. In this paper, we consider the problem of approximating chemical kinetics for modeling the detonation of a hydrogen-air mixture using neural networks. The dataset for training the neural network were prepared using the principal component analysis from the results of numerical modeling of detonation in a narrow channel. The results of the obtained neural network showed that the presented model is capable of approximating chemical kinetics processes without significant restrictions on the range of pressure, temperature or the choice of the used time step. • Space flight safety issues in combustion were treated with machine learning. • The neural network for approximating the chemical kinetics of H 2 combustion was built. • The principal component analysis was used to prepare dataset. • The resulting neural network can predict the behavior of a chemical system many steps ahead. • The time step was taken into account in the work of neural network. [ABSTRACT FROM AUTHOR]

The study of the transient combustion modes is one of the key topics when considering the safety of space flights. Control of detonation onset has a dual application. First, the search for ways to prevent detonation modes in case of accidental fuel releases for fire safety issues of launch systems and the avoidance of accidents with rocket engines at a launch site and in near-Earth space. Second, the study of detonation and the possibility of using it to create propulsion systems based on detonation combustion of fuel. The paper shows the effect of the presence of spatial non-uniformities on the promotion of detonation in the chamber. Various geometries with and without obstacles and cavities are considered. It is demonstrated that the presence of obstacles accelerates the transition to the detonation process on the one hand, but on the other hand the presence of obstacles in combustion chamber could be the cause of incidental uncontrolled ignition, which ruins stable operation of an engine. The results of theoretical studies of the working cycle of the combustion chamber of a pulsed detonation engine are presented. Theoretical estimates for thrust characteristics are obtained. • The possibility of using detonation for developing new type of Space engine is demonstrated. • Different configuration of obstacles could both promote or inhibit the detonation onset. • Large distance between obstacles promotes uncontrolled self-ignition between engine cycles. • For each type of obstacles there exist optimal pitch for stable detonation onset. [ABSTRACT FROM AUTHOR]

The removal of inclusion particles is an important function of tundish metallurgy. During ladle change, the liquid level fluctuation around the ladle shroud is severe, which may affect the effectiveness of inclusion removal. In the present study, the fluid flow characteristics and inclusion‐removal behavior in the tundish during ladle change are investigated by numerical simulation method. And the effectiveness of flow control devices on the flow characteristics of molten steel is evaluated. It is found that the escape rate of inclusion particles during ladle change is ordered as emptying process < steady process < filling process. The proper combination of weir, dam, and turbulence inhibitor can optimize the conditions for the floating and removal of inclusion particles to the greatest extent. In the tundish with weir and dam, the escape rates of inclusion particles with sizes of 10, 50, and 100 μm throughout the entire ladle change period are respectively reduced by 9.8%, 1.6%, and 1.4%, compared to not using flow control devices. With a combination of weir, dam, and turbulence inhibitor, the escape rates of the three types of inclusion particles are reduced by 24.7%, 9.9%, and 1.2%, respectively. [ABSTRACT FROM AUTHOR]

The traditional new Austrian tunneling method (NATM) is inadequate for handling the excavation and support of deep soft-rock tunnels with significant deformation. Therefore, new steel structures and materials are needed to effectively manage such complex conditions. This study utilizes the coupling technology of negative Poisson's ratio (NPR) anchor cable structures and double-layer three-dimensional truss structures, as proposed by Academician He Manchao. Mechanical models, numerical simulations, and field monitoring were employed to investigate the support of large deformation soft-rock tunnels traversing multi-stage fault-fracture zones for the first time. The findings indicate that the support technology combining the flexible control and rigid constraint of "NPR anchor cable + double-layer three-dimensional truss" demonstrates remarkable mechanical compensation for large deformation in soft-rock tunnels. This approach effectively controls tunnel deformation to below 300 mm and maintains a constant resistance value around 350kN. This research provides a scientific basis for supporting other large-deformation soft-rock tunnels across multi-stage fault-fracture zones. Highlights: A comprehensive study of soft-rock large deformation tunnels across multi-stage faults has been carried out through numerical simulations, field monitoring and physical modeling tests. The first experimental study of stress compensation in soft-rock large deformation tunnels across multi-stage faults First coupling application of NPR anchor cables with negative Poisson's ratio effect structures to truss structures [ABSTRACT FROM AUTHOR]

Rock permeability is a critical parameter for assessing rock's ability to facilitate fluid flow. The pressure pulse decay method, characterized by its short testing duration and high accuracy, is widely employed for permeability testing of low-permeable rocks. This method acquires pressure differential data by conducting experiments on regular-shaped samples. Due to the theoretical solution's requirements (cross-sectional area and length), this method cannot be applied to rocks that are challenging to shape into regular samples, such as soft rock and soft coal. In this paper, a novel permeability determination method based on the numerical simulation of inverse problem is proposed. This method involves constructing a mathematical model that accurately describes the entire process of determining permeability using the pressure pulse decay method. The sample's pressure difference data over time is used as a penalty function, and the sample permeability is calculated by inverse problem numerical simulation. Specifically, a computation strategy is introduced to determine the initial range for permeability, aiming to avoid locally optimal issues in the inverse problem numerical simulation. Utilizing the new model, forward and inverse problem numerical simulations were conducted. The pressure difference decay data obtained from these calculations closely match the laboratory-measured data for regular samples, with correlation coefficient (R2) reaching 0.992 and 0.990, respectively. The permeability calculated by inverse simulation is determined to be 0.28 mD, showing minimal deviation from the theoretically derived permeability. This demonstrates the accuracy of the proposed model in describing the experimental process of the pressure pulse decay method and the precision of the obtaining permeability parameters. Furthermore, when applied to numerical experiments with irregular-shaped samples, the inverse simulation yields pressure difference data that closely matches the experimental data. The established new method effectively addresses limitations posed by the shape of samples, providing a novel approach for measuring rock permeability. The convenience of numerical experiments also offers a new and efficient means to investigate the competitive effects of permeability influencing factors. This provides promising applications in unconventional gas development, depleted reservoir carbon dioxide storage, and geological hydrogen storage, among other fields. Highlights: A mathematical model is developed to accurately describe gas mass transfer behaviour during the permeability testing by the transient method. A computational method for calculating permeability based on numerical solution is proposed. The new method proposed in this paper solves the limitation of the traditional method for the shape of the test sample. [ABSTRACT FROM AUTHOR]

A numerical simulation model is put forward to study the molten pool dynamic behavior and clarify its influencing mechanism on the undercut defects in laser‐arc hybrid welding (LAHW). The undercut defect is a common and challenging problem to address. However, a controversy exists on whether the dynamic process of molten pool can affect undercut defects, and the potential mechanism has been still unclear. The results suggest that profile variation of molten pool surface is driven by surface tension gradient, and the existence of eddy can alter the morphology and surface tension distribution of molten pool, which is the main factor to homogenize the flow field. Compared with the short‐circuit transfer mode, the molten metal flows toward the welds edge at a constant velocity (2.5–3.75 m min−1) in the spray transfer mode, which improves the stability of molten pool flow. It can be observed that the irregular fluctuation of molten metal during the solidification process can directly cause the undercut defects. [ABSTRACT FROM AUTHOR]

Upgrading the caisson-type quay wall could be conducted by strengthening the rubble mound beneath the front caisson toe. Subsequently, the rubble in front of the wall is removed to increase the front water depth. This study assessed the dynamic response of the upgraded quay wall under earthquake loading and compared it to the existing case using a centrifuge test and numerical study. The tests were performed in a dry condition under six consecutive input waves with increasing magnitude. The results indicated that the upgrade significantly reduced the displacements of the quay wall. The deformation trend of the caisson also changed from overturning to slipping. A numerical study of the upgraded case was conducted using the PLAXIS 2D program in the dry condition to validate the model. In addition, the simulation in water was performed to realize the difference between the models with and without water. The numerical results were in good agreement with the experimental model. The deformed mode of the quay wall in the dry condition did not differ from that in water. However, the horizontal displacement of the quay wall in water was higher than in the dry condition, whereas the vertical component was slightly lower. [ABSTRACT FROM AUTHOR]

• Boiling heat transfer of ammonia in a vertical rectangular microchannel at high pressure of 354–615 kPa was investigated. • The wake at lower end of the primary bubbles increases the local flow rate significantly. • Influence of saturation temperature on bubble growth and heat transfer performance was analyzed. Ammonia boilers are commonly used as expendable radiators during the return phase of spacecraft. The aim of this study is to investigate the bubble behavior and heat transfer characteristics within a vertical rectangular microchannel of a plate-fin ammonia boiler under gravity at an absolute pressure of 354–615 kPa. In order to achieve this, a single rectangular microchannel unit was intercepted from the ammonia boiler structure to construct a simulation model, and the high-pressure boiling process of ammonia in the rectangular microchannel was numerically investigated using the VOF model. Good agreement was obtained by comparing the numerical results with the experimental data with the error within 8 %. The results show that the wake flow at the lower end of the primary bubbles has an enhanced effect on the heat transfer, which is about 50–60 %. The maximum horizontal dimension of primary bubbles increases with increasing superheat, and significant bubble coalescence occurs when 45 % of the rectangular microchannel spacing is exceeded. In addition, the effect of different saturation temperatures on the heat transfer performance on the hot high temperature wall was investigated. Significant heat transfer deterioration was found to occur at saturation temperatures below 4 °C (superheat above 15 °C). The reason found in this study was that bubble coalescence significantly increases the percentage of gas-phase contact area on the high-temperature wall (from 25 % to 54 %) and weakens the wake enhancement effect. [ABSTRACT FROM AUTHOR]

• The total magnetic field in the gap of full-compensated nested Halbach cylinders (NHC) dependence on the rotation angle of inner array is described by the cosine modulus function. • High operating frequency, a large amount of working space, ease of use, and a small number of moving parts make NHC effectiveness in realizing the AMR cycle. • Phase shift angles between the rotation of the inner cylinder of NHC and the piston displacement processes in the range of 70 - 90° to ocure a maximum thermal span. • The volume of pumped heat transfer fluid through the regenerator must be 20–30 % of its voids volume. In this study, a numerical model of the Active Magnetic Regenerator (AMR) cycle, implemented in the reciprocal demonstrator, was developed using COMSOL Multiphysics. A nested Halbach cylinder (NHC) array served as the magnetic field source. Additional simulation of an operation of the NHC array was carried out. To eliminate the discrepancies between the heat exchange duration of the heat transfer medium (HTM) and the hot and cold ends of the regenerator, an adequate time dependence of the inner cylinder rotation angle was calculated. The latter provides the symmetrical sinusoidal form of time dependence of the magnetic flux density in the gap of NHC array, which is important for enhancing the performance of a magnetic refrigerator. It was established that in order to achieve a maximal temperature span, it is necessary to shift the phases of the magnetic field insertion/removal and heat transfer fluid pumping processes by nearly half of the operating cycle period. The latter brings the simulated cycle closer to the ideal AMR cycle. [ABSTRACT FROM AUTHOR]