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Abstract: By analyzing COSMIC data, found more than 50% reduction in electron density during a solar eclipse at the F2-layer and above, with the peak of ∼70% at 370km. So great eclipse effect on topside ionosphere was very abnormal and much different from previous studies. However, by comparing the cosmic data with IRI results, we find that the abnormal reduction comes mainly from the significant local time variation at sunrise, not from the eclipse effect. Furthermore, we simulated the eclipse effect by using a theoretical model to confirm our analysis. [Copyright &y& Elsevier]

Hydrogen is considered a truly clean energy source with great potential for replacing fossil fuels. However, the special physical and chemical properties of this source make large-scale, safe, and efficient storage challenging, thus limiting its widespread use. Consequently, an underground hydrogen storage system inspired by underground methane storage and CO 2 geological sequestration has been proposed, and it is increasingly becoming a focus of research. Depleted oil reservoirs are ideal sites for such systems. Nevertheless, research on these types of underground hydrogen storage systems is limited to a few feasibility assessments, and the hydrogen seepage laws in reservoirs with residual oil are not well understood. In this paper, a study was conducted involving mathematical modeling and numerical simulation of underground hydrogen storage, which was converted from the SSZ low-permeability depleted oil reservoir in Bohaiwan Basin, eastern China, to reveal the seepage patterns between hydrogen and complicated in situ fluids (oil, gas, and water). First, a comprehensive analysis was conducted using numerous rock samples and experimental data to identify the composition, genesis, and distribution patterns of the sandstone reservoir, detailing its internal pore structure and fluid distribution postdepletion characteristics. Then, the hydrogen seepage properties in the presence of oil films in the three main throat types of low-permeability sandstone were analyzed, and corresponding mathematical models of the different throats were established. Finally, a numerical simulation of underground hydrogen storage was conducted to assess the impacts of various parameters, such as injection speed, reservoir heterogeneity, and residual oil saturation, on hydrogen seepage. The planar and vertical diffusion patterns of hydrogen were clarified, and the key factors affecting the efficiency of underground hydrogen storage were analyzed, offering suggestions for the establishment of stable and efficient underground hydrogen storage systems. • Selection and description of typical low-permeability reservoirs for UHS. • Mathematical model establishment for hydrogen percolation in porous rock. • Numerical simulation of the storage process of hydrogen. • Percolation laws of hydrogen in rock porous. [ABSTRACT FROM AUTHOR]

Nanotechnology in recent years helps researcehers to design flow rate and profile in microsized channel via making surface charge heterogenous. This paper numerically simulates the electroosmotic flow inside a microchannel with non-uniform Zeta potential (ZP). The problem is a two-dimensional, incompressible, steady, and laminar channel flow between two parallel plates. The numerical results show that the flow rate changes compared to a constant ZP by ascending, descending, and parabolic modifications of the wall ZP at the mid-length of the microchannel. Results show that flow volume rate increases by microchannel width from 4 mm3/s to 6.5 mm3/s in best condition. [ABSTRACT FROM AUTHOR]

• The modified phase-field approach and the arbitrary Lagrangian–Eulerian one are able to give physically and quantitatively correct results for modeling electrocoalescence • The exponential relation between volume fraction and electrical conductivity has to be used in the phase-field approach when the conductivity of two phases differs significantly • The power of the volume fraction under the exponent has to be adjusted to centralize the space charge within the interface layer • The phase-field model needs for proper choice of the mobility turning parameter and the interface thickness and has a limited applicability for computing long-term processes • The arbitrary Lagrangian–Eulerian approach is more precise and less resource-intensive than the phase-field one The paper examines two numerical approaches to the simulation of electrical deformation and coalescence processes in water-in-oil emulsions: the phase-field method and the arbitrary Lagrangian–Eulerian approach. The former employs a diffuse interface, while the latter utilizes a sharp interface. The study analyzes the correctness of the computer simulation results and identifies less obvious limits of the applicability of these numerical techniques. The paper is based on a step-by-step comparison of data from two independent numerical models and quantitative verification using original experimental data, including data on unsteady-state droplet deformation and the threshold between coalescence and non-coalescence. The main findings are as follows. Both methods, the modified phase-field approach and the arbitrary Lagrangian–Eulerian one, are fundamentally capable of providing physically and quantitatively correct results for modeling electrohydrodynamic processes in two-phase immiscible liquids. On the one hand, the phase-field method demands thorough tuning and has limited applicability for simulating long-term processes. On the other hand, the arbitrary Lagrangian–Eulerian approach offers greater precision and requires fewer computational resources compared to the phase-field method, although it demands a manual adjustment of geometry when the system's topology changes. It is noteworthy that the phase-field method, without careful tuning, fails to yield quantitatively accurate results; errors, such as discrepancies in the time convergence of droplets under the influence of an electric field, can reach magnitudes of tens of percentages. [Display omitted] [ABSTRACT FROM AUTHOR]

IVR-ERVC (In-Vessel Retention – External Reactor Vessel Cooling) is a critical accident management method for ensuring the integrity of the reactor pressure vessel (RPV) lower head. One of the most crucial aspects within this method is to enhance the CHF (Critical Heat Flux) on the outer surface of the reactor pressure vessel (RPV) lower head. This paper explores the application of graphene nanofluids in IVR-ERVC. This paper uses computational fluid dynamics to numerically simulate the CHF characteristics of graphene nanofluids under different undercooling, mass flow rate, concentration, tilt angle, and gap size conditions and analyzes the impact of different factors on CHF and the coupling effects between different factors. The undercooling range is 5 K–100 K, the mass flow rate range is 150 k g / (m 2 ∙ s) to 3000 k g / (m 2 ∙ s) , the concentration range is 0–1%, the inclination angle range is 0°–90°, and the gap sizes are 10 mm and 20 mm. The results show that the CHF can be effectively improved by adding nano-graphene into the base solution, and the CHF increases with the increase of subcooling degree, mass flow rate, concentration, dip Angle and gap size. Within the simulation range, the strengthening effect on CHF weakens when raising the undercooling and mass flow rate. And the larger the concentration and inclination angle within the simulation range, the better the enhancement effect on CHF. The maximum increase was 290%, while the average increase was 75.6%. This article studies the coupling effects between different parameters through numerical simulation. It can be concluded that increasing the mass flow rate weakens the enhancement of subcooling and concentration on CHF, increasing the subcooling weakens the enhancement effect of mass flow rate and concentration on CHF, and increasing the concentration enhances the enhancement effect of subcooling and mass flow rate on CHF. Enhance the mass flow rate will weaken tilt angle effect, while increasing the concentration will enhance the strengthening effect of tilt angle on CHF. [ABSTRACT FROM AUTHOR]

The study of fluid–structure interactions in elastic structures is highly important in hydraulic structural engineering. This paper adopts the smooth particle hydrodynamics (SPH) coupling method to simulate dam failure water impact elastic plate flow and solid coupling problems. In addition, a numerical simulation is performed on the study of the free surface flow impact of the elastic plate structure on the main dynamic characteristics, including the impact force distribution and the change process. Additionally, the elastic structure of the vibration amplitude and frequency change rule, as well as the drastic changes in free surface flow, are also carried out. In this paper, the synchronous finite element algorithm is used to analyze the problem to obtain FEM results Additionally, two-dimensional benchmark physical tests are designed for dam-break water flow impacting an elastic plate are conducted, focusing on a comparative analysis of the numerical results of the SPH method with the results of physical tests and verifying the validity, accuracy, and superiority of the SPH coupling method for solving the problem of fluid‒solid coupling in elastic structures. On this basis, to explore the relevant physical quantities that cannot be measured or described during the test process, the flow–solid coupling characteristics of the elastic plate impacted by water flow are further understood by analyzing the nature of the flow field, the change in the flow–solid force of the elastic plate and the change rule of the frequency spectrum. The results show the following: (i) The jumps in velocity between the streams and the strong curvature of the free liquid surface lead to the creation of vortices at the cavities. (ii) The flow solid force under the impact of water flow increases and then decreases, and the smaller the deformation of the elastic structure is, the greater the force is. (iii) The vibration frequency of the fixed end of the elastic structure gradually decreases along the free end frequency, and the larger the deformation of the free end of the elastic plate is, the weaker its vibration response is. In addition, the natural frequency of the elastic plate under water flow impact is slightly lower than that under free vibration of the elastic plate. The related research results provide reference and guidance for the fluid–structure interaction problem. • Physical tests of elastic plates impacted by dam break water flow are studied. • Dynamic characteristics of elastic structures based on the SPH solver are analyzed. • The generation of vorticity, fluid-solid forces, and spectral changes are analyzed. • The water flow impacting the elastic plate based on SPH and FEM solver is studied. [ABSTRACT FROM AUTHOR]

The paper details some practical considerations associated with the numerical simulation of liquefaction in Wildlife site in Southern California. Two material constitutive models are implemented in the simulations: a pressure-dependent multi-yield-surface model (PDMY) and PM4Sand, both available in the OpenSees finite elements platform. Both uniaxial as well as biaxial simulations are presented in the paper. The uniaxial simulations only include the predominant horizontal shaking component while the biaxial simulations include both orthogonal horizontal shaking components. Two historical major earthquake events were simulated: the 1987 Superstition Hills and the 2010 El Mayor Cucapah earthquakes. Laboratory experimental data used for calibration of the material models was obtained from historical data published in the 1980's. This data is particularly valuable since they correspond to intact (undisturbed) samples extracted from Wildlife site about two years before occurrence of the 1987 earthquake. In all the simulations, the models were able to capture salient features of the deposit's behavior, such as the magnitude of surface accelerations, and dilative behavior of the soil. However, the excess pore water pressure rises earlier than what the site recordings indicates. This may be attributed to the fact that the constitutive models do not consider the concept of volumetric threshold shear strain below which no excess pore water pressure is generated during cyclic shear loading. It was also found that there was a significant overestimation of the excess pore pressure for the 2010 El Mayor Cucapah earthquake simulations. This may be attributed to the effect of the site shaking history which increased the site resistance to liquefaction. This added resistance was not reflected by the numerical model since it was calibrated with samples extracted about 25 years before the 2010 earthquake. • Wildlife case history in Southern California provides practical considerations in numerical liquefaction modeling. • Historical experimental data of intact samples from the 80s were used to calibrate PM4Sand and PDMY constitutive models. • Shaking history significantly changes the liquefaction behavior of the site. • Excess pore pressure is much more correlated to shear strains than shear stresses. [ABSTRACT FROM AUTHOR]

With the large-scale application of polymer flooding technology, the polymer concentration in produced water is increasing, which leads to incomplete regeneration of filter media by gravity field hydraulic backwashing technology only. In this study, the high-gravity backwashing technology is constructed by coupling gravity field and swirl field, which promotes the development of the oilfield. Based on the cascade theory, this paper establishes a mathematical expression of radial collision force in the high-gravity backwashing process in the vortex tube and solves a mathematical equation of high-gravity backwashing velocity gradient G based on the efficient zone of collision force action. Meanwhile, based on the discrete element method and computational fluid dynamics theory, the inter-particle collision regulation of the high-gravity backwashing process is simulated by the coupled FLUENT-EDEM method, and the high-efficiency zone of the backwashing process is verified. In this high-efficiency zone, the theoretical and simulated values of velocity gradient G for different high-gravity values match well, with differences ranging from –5.8 % to +7.1 %, indicating that the theoretical model of high-gravity backwashing is correct. When the high-gravity value is 210–240 g, the total impulse of the filter bed per unit time reaches a great value, and the backwashing velocity gradient G is 3047.1 s−1, which is much larger than the G value of combined air-water backwashing. The high-gravity backwashing technology breaks through the technical bottleneck of low efficiency in the action of the gravity field. It enriches and develops the gravity field hydraulic backwashing technology of the filter bed. • A new method of high-gravity backwashing is proposed, and a theoretical model of high-gravity backwashing is constructed. • The mathematical equations particle impact force and velocity gradient in high efficiency area of high-gravity backwashing are established. • The coupling method of FLUENT-EDEM is used to study the backwashing process, which provides a new idea for the backwashing of traditional water treatment filter bed. [ABSTRACT FROM AUTHOR]

• A novel discontinuous similar material for physical model experiments has been developed. • The bulking characteristics of the broken goaf roof under different roof cutting conditions have been revealed. • The protection effect of the roof cutting technology for the gob-side roadway has been obtained. • The excavation compensation effect of the bulking roof rock after failure by roof cutting has been proposed. The stability control of gob-side entry retaining (GSER) has consistently been an important topic of interest within the field of no-pillar mining. This paper presents a novel discontinuous similar material for conducting physical model experiments, in conjunction with discrete element numerical simulation, to investigate the goaf roof failure and bulking characteristics based on gob-side entry retaining by roof cutting. The results indicate that the application of roof cutting technology (RCT) can significantly expand the failure range of the goaf roof vicinity to the roof cutting line. This expansion leads to a 20% increase in the volume of broken roof rock, which in turn facilitates the formation of effective support and stress compensation for the overlying strata, and the possibility of failure and displacement in the overlying strata is reduced. RCT can decrease the length of the cantilever beam located on the gob-side roadway, which is beneficial for maintaining the stability of the roadway. This paper presents a rational approach for determining an appropriate roof cutting height and angle. The in-situ application results show that the deformation of the surrounding rock of GSER by RCT is small, indicating a high level of integrity, fully meeting the requirements of serving the production of the subsequent working face. This paper serves as a reference for future research on the stability control of gob-side roadways based on GSER approach. [ABSTRACT FROM AUTHOR]

A system of diffusion–reaction equations coupled with a dissolution–precipitation model is discussed in this paper. We start by introducing a microscale model together with its homogenized version. In the present paper, we first derive the corrector results to justify the obtained theoretical results. Furthermore, we perform the numerical simulations to compare the outcome of the effective (homogenized) model with the original heterogeneous microscale model. [ABSTRACT FROM AUTHOR]

Ningbo's seaport hydrogen refueling station was used as the research object. The effects of different leakage angles, wind direction, roof shape, leakage hole diameters, temperature, and humidity on the diffusion of hydrogen leakage were studied by numerical simulation. The influence of leakage angle on hydrogen leakage is mainly reflected in the presence or absence of obstacles. The volume of the flammable hydrogen cloud was reduced by 31.16%, and the volume of the hazardous hydrogen cloud was reduced by 63.22% when there was no obstacle. The wind direction can significantly impact hydrogen leakage, with downwind and sidewind accelerating hydrogen discharge and reducing the risk. At the same time, headwind significantly increases the volume of the flammable hydrogen cloud. Compared with no wind, the volume of the flammable hydrogen cloud increased by 71.73% when headwind, but the volume of the hazardous hydrogen cloud decreased by 24.00%. If hydrogen shows signs of accumulation under the roof, the sloping roof can effectively reduce the hydrogen concentration under the roof and accelerate the hydrogen discharge. When the leakage angle θ = 90°, the sloping roof reduced the volume of the flammable hydrogen cloud by 11.74%. The leakage process was similar for different leak hole diameters in the no wind condition. The inverse of the molar fraction of hydrogen on the jet centerline was linearly related to the dimensionless axial distance of the jet in different cases. Using a least squares fit, the decay rate was obtained as 0.0039. In contrast, temperature and humidity have almost no effect on hydrogen diffusion. Hydrogen tends to accumulate on the lower surface of the roof, near the roof pillars and the hydrogen dispenser. In this paper, a set of hydrogen detector layout schemes was developed, and the alarm success rate was verified to be 83.33%. •CFD numerical model for hydrogen refueling station at seaport is developed. •Pseudo-diameter model is used to describe simplified high-pressure hydrogen jet. •Effects of roof, leakage angles and wind on hydrogen diffusion are studied. •Recommendations on hydrogen detector layout are given based on parametric study. [ABSTRACT FROM AUTHOR]

• Dynamic stability of MDOF systems under parametric excitation was numerically simulated. • Responses of MDOF Mathieu-Hill equations were simultaneously obtained. • The conventional Hill ID method was numerically calibrated. • No resonances, simple resonances, combination additive and differential resonances were simultaneously determined. The stability and responses of dynamic systems under parametric excitation are often encountered in many fields of science and engineering, such as slender columns and thin plates under axial loadings. This paper proposes a novel numerical simulation method to simultaneously construct stability diagrams and predict the responses of multiple degree-of-freedom (DOF) dynamic systems under arbitrary parametric loadings. The method divides an arbitrary load into discrete segments to approximate the variable excitation function by a step function and then accumulates the system responses of each segment using a matrix method. Dynamic stability and response analysis of undamped and damped 1DOF, 2DOF, 3DOF, and multiple DOF systems are conducted, and numerical examples are compared to conventional methods to show the accuracy and advantage of the proposed numerical simulation method. The instability diagrams are also substantiated by vibration response curves obtained from the same method. The method is applied to calibrate the validity and ranges of applicability of the Hill infinite determinants in the Floquet theory of 1DOF Mathieu-Hill equations. The second order approximation of the first instability region from the Hill determinant is acceptable. However, the fourth order approximation of the second instability region must be used to obtain a relatively accurate result. For 2DOF, 3DOF, and multi-parameter linear periodic systems, the method can simultaneously render four types of instability regions in a single procedure: no resonances, simple parametric resonances, combination additive resonances, and combination differential resonances. These results could provide a better understanding of stability and responses of dynamic systems under parametric excitation. [ABSTRACT FROM AUTHOR]

In this paper, computational fluid dynamics (CFD) numerical simulation is used to analyze and discuss the horizontal propagation process of premixed hydrogen flame with obstacles. A total of three different obstacle channel arrangements at the blocking ratio of 0.5, which will affect the explosion flame and pressure development. The results show that the premixed flame is affected by flow instabilities and vortices when propagating through the obstacle channel, thereby distorting the flame. The vortices outside the flame boundary are more conducive to the acceleration of the flame. The continuous acceleration and synergistic promotion of the flame is more prominent due to the existence of the channel in the central axis of flame propagation, and the maximum velocity even achieved 307.91 m/s. The degree of the wrinkle of flame increases with the number of obstacle channels. The flame propagation process is always accompanied by pressure variations, and the dynamic pressure builds up at the flame front and intensifies periodically. But the downstream pressure gradually increases as the number of obstacle channels increases. CFD simulation of the explosion process clearly reveals the changing trends and interactions of explosion characteristic factors. • The vortex outside the flame boundary is more beneficial for flame acceleration. • Arrangement of obstacle channels effects the trend of flame front motion. • Pressure oscillation and magnitude can be changed by the obstacle arrangement. [ABSTRACT FROM AUTHOR]

This paper established the temperature differential model of temperature-controlled materials, performed the numerical simulation of the relationship between mechanical properties and temperature of temperature-controlled materials, and discussed the stress-strain relationship of temperature-controlled materials at different temperatures. The final stimulation experiment showed that temperature-controlled materials have the advantages of large energy storage density, approximately constant temperature and compact structure during phase change. The results of this paper provide a certain reference for the further researches on the numerical simulation of forced bending deformation of temperature-controlled materials based on the differential equation model. [ABSTRACT FROM AUTHOR]

Understanding the formation of impact craters on planetary surfaces has fundamental importance in geology, impact dynamics, and planetary sciences. The finite element-smoothed particle hydrodynamics (FE-SPH) adaptive method combines the advantages of smoothed particle hydrodynamics (SPH) and finite element method (FEM) in solving hypervelocity impact (HVI) problems. Employing FE-SPH adaptive method is a new idea for the analysis of planetary impact cratering which is different from impact-simplified arbitrary Lagrangian Eulerian (iSALE). In this paper, we establish a complete numerical model of planetary impact cratering through the FE-SPH method, including material failure criterion, thermodynamic analysis, gravity preloading, etc. We reproduce the numerical results by Collins et al. (2012) and highly consistent results are obtained through comparative analysis. This study simulates the formation process of simple and complex impact craters, and the temperature, pressure, density, and geometric shape of the impact zone can be quantitatively obtained. We further analyze the distribution of polymorphs and rock fragmentations in the impact zone based on the theories of shock metamorphism. The proposed analysis method may assist geologists in conducting geological studies. • We establish a complete numerical model of planetary impact cratering different from iSALE. • We analyze the distribution of high-pressure polymorphs based on shock metamorphism. • The FE-SPH model has higher numerical precision for planetary cratering impacts. [ABSTRACT FROM AUTHOR]

An accurate assessment of hydrogen storage mechanisms in an aquifer storage project requires detailed flow and transport modeling. The equation-of-state (EOS) based compositional phase equilibrium approaches make these models computationally expensive. This paper proposes using the black-oil simulation approach for the specific case of hydrogen storage in saline aquifers to reduce the computational burden of the flow simulations. We present a simple and efficient algorithm for converting hydrogen-brine phase equilibrium compositional data obtained from the Redlich and Kwong EOS into black-oil PVT data. The algorithm accurately predicts the hydrogen-brine transport properties required for the black-oil flow simulations of underground hydrogen storage. Numerical simulations for a simple cyclic hydrogen injection-production case reveal that the black-oil simulations are at least one order of magnitude faster than the compositional ones without loss of accuracy. These results support applying the black-oil PVT model and the simulation approach for numerical simulations of large-scale hydrogen storage in deep saline aquifers. • An algorithm for converting compositional data into black-oil PVT data is presented. • The PVT model accurately predicts hydrogen-brine phase equilibrium data. • A black-oil simulation approach is applied for hydrogen storage in saline aquifers. • Black-oil simulations are an order of magnitude faster than the compositional ones. [ABSTRACT FROM AUTHOR]

In this paper, microchannel flow boiling heat transfer and critical heat flux (CHF) are numerically characterized under both static and rolling conditions. The volume of fluid (VOF) based numerical model of a rectangular microchannel with the dimension of 4 × 400 mm is established. The additional force induced by rolling motion is loaded via a user defined function (UDF). Rolling amplitude and rolling period vary in the range of 10∼20° and 1∼2 s, respectively. The results demonstrate that bubble flow, slug flow, stretch bubble flow and annular flow are observed under static conditions. However, under rolling conditions, bubbles are more difficult to agglomerate and coalesce under the influence of additional forces. Rolling motion maximumly deteriorates CHF by 81.1% and wall temperature by 18.8%, respectively. Moreover, CHF decreases with the increase of rolling period while increases with the increase of rolling amplitude. The purpose of this research is to understand the microchannel CHF triggering mechanism under rolling conditions to aid in marine heat exchanger design. [ABSTRACT FROM AUTHOR]

The boom of renewable energy has been overshadowed by two problems: the intermittency and volatility of such energy. Largescale complementary energy storage has been required to solve these problems. This paper proposes a compressed CO 2 energy storage system in aquifer (CCES-A), aiming to storage energy efficiently at a low cost. Firstly, the feasibility of compressing CO 2 in the aquifer had been proved through numerical simulation, and the CO 2 compression in the aquifer had been emulated by a wellbore-reservoir coupling model. The operation of the CCES-A had been divided into the establishment stage of the initial airbag, and the cyclic stage of energy storage and release. The proposed wellbore-reservoir coupling model had been applied to analyze the wellhead pressure, energy flow and energy recovery rate of weekly, monthly, and seasonal cycles, as well as the energy recovery efficiency at different injection temperatures. The simulation results showed that under the three cycles, the wellhead pressure increased with the number of cycles. The energy flow and energy recovery efficiency decreased with the growing the number of cycles. The energy recovery became more efficient with the rise of the injection temperature. [ABSTRACT FROM AUTHOR]

The paper continues the numerical investigation for the problem of hypervelocity impact of a spherical projectile against thin-walled metallic containment that is a key process in the space vehicles shielding by composite honeycombs. The features of initial outward penetration process are studied for wide variation of projectile and containment material properties. The statements of the impact problem presented in the paper involve triple contact points. • Numerical investigation for the problem of hypervelocity impact. • Spherical projectile against thin-walled metallic containment made of different materials. • Space vehicles shielding by composite honeycombs concept. • The features of initial outward penetration process are studied for wide variation of material properties. • The statements of the impact problem involve triple contact points. [ABSTRACT FROM AUTHOR]

• The Basalt Fiber greatly improved the peak load and toughness of BFRC. • The fracture energy of BFRC had no size effect. • The addition of BF could effectively increase the fracture energy of concrete. • For notched beams, the initiation toughness increases as the specimen height increases. • As BF dosage increases, the initiation toughness of BFRC increases while unstable toughness varies irregularly. In this paper, three-point bending tests on precast notched beam and multiscale numerical simulation were used to evaluate and predict the effect of different Basalt Fiber (BF) dosages on the fracture resistance performance for Basalt Fiber Reinforced Concrete (BFRC). The three-point bending test was performed on a series of the notched beams in different sizes and volumetric fiber dosage to obtain the Load-Crack Mouth Opening Displacement (P-CMOD) curves during the loading process. The fracture energy and the double-K fracture parameters were calculated from P-CMOD curves to investigate the influences of fiber volume fraction and beam size on fracture parameters of BFRC. The results indicate that the numerical simulation results are in good coherence with the experimental results. The increase of BF dosage could markedly increase the peak load and the fracture energy of concrete. There was no size effect on fracture energy. Based on the two-parameter fracture theory, the initiation toughness had size effect and increased with the rise of specimen height, while size effect was not significant for unstable toughness. With the augment of fiber dosage, the initiation toughness increased linearly. The unstable toughness varied irregularly with the alteration of fiber dosage but higher than that of ordinary concrete. In addition, this paper developed a homogenization algorithm based on Mori-Tanaka and a multi-scale finite element simulation based on continuum progressive damage theory to evaluate and predict the fracture behavior of BFRC with different sizes and fiber volumetric dosages. The calculated P-CMOD curves from this algorithm were in good agreement with those from experiments and revealed the effects of fiber dosage and size effect on fracture behavior for BFRC. [ABSTRACT FROM AUTHOR]

• Simulation results can well predicate the actual cooldown process for 1.3 GHz 9-cell superconducting cavity. The deviation between the simulation results and the experimental test results is less than 7 %. • Heat transfer mechanism of the six different geometry structure for the 1.3 GHz 9-cell superconducting cavity were studied by CFD. The appropriate mechanical structure model was recommended. • The influence of inlet parameters on the cooling process was analyzed. And an efficient cooling strategy for the 1.3 GHz 9-cell superconducting cavity was obtained. As an indispensable component of X-ray free electron lasers and future ring electron-positron colliders, a 1.3 GHz 9-cell superconducting cavity provides higher acceleration voltage and higher RF power per unit length, and saves equipment space. During testing and operation, superconducting cavities often need to be cooled gradually from the ambient temperature (300 K) to the superconducting temperature (4.5 K or less). To avoid plastic deformation of materials and seal leaking caused by high thermal stress, the cooling rates in each stage and the temperature differences on the cavity must be properly controlled. Currently, a less effective manual control strategy is typically used, whose main limitations include a low level of automation, a high reliance on the experience of the operating personnel, and a fairly lengthy time due to low efficiency. In this paper, a 1.3 GHz 9-cell superconducting cavity and its helium vessel were taken as the research subjects, six different mechanical structures of the helium vessel were designed, and six different three-dimensional thermal-flow coupling models were established. For each structural model, the temperature distribution and cooling strategy were analyzed using fluid numerical simulation software. The influence of inlet parameters on the cooling process was analyzed, and the appropriate mechanical structure model was recommended. The results showed that: During the cooling process, the closer the superconducting cavity is to the inlet, the lower the temperature is. The cooling rate is faster in the early stage in which the temperature difference can be reduced by 50 % within the first 30 min. After experimental test verification, the total cooling time is about 650 min (10.8 h or so), and the deviation between the simulation results and the experimental test results is less than 7 %, which shows the simulation results can well predict the actual cooling process for 1.3 GHz 9-cell superconducting cavity. The research work in this paper can lay a good foundation for the further R&D status of the superconducting cavity. [ABSTRACT FROM AUTHOR]

• Vortex-inducing T-jet reactors greatly improve mixing performance. • Mixing effect can be significantly improved by vortex merging. • The change of inlet structure has an important effect on reactor performance. • The generation of unsteady symmetric flow was avoided by the vortex-inducing. Improving the jet reactor's mixing performance is critical and challenging. In this paper, a new type of vortex-inducing T-jet reactor proposed by researchers is studied. By designing the staggered inlet structure of the T-jet reactor, the vortex is induced in the flow field in the mixing channel to improve the mixing effect. Flow regimes and mixing characteristics in the vortex-inducing T-jet reactor were investigated through numerical simulations (CFD) at 30 ≤ Re ≤ 600. Results show that the staggered inlet channel induces vortices successfully, and the engulfment flow regime occurs at lower Reynolds numbers, thus promoting the mixing. The generation and evolution of vortex structures in the reactor were focused on. It was found that in the unsteady engulfment flow, the two fluids cross each other, which makes the vortex structure constantly twist and merge, which greatly improves the mixing effect. At larger Reynolds numbers, many attached small vortices are generated around the central vortex structure, and these vortices are wound together with the high-speed rotation of the central vortex, avoiding the unsteady symmetric flow pattern with a poor mixing effect. Finally, it is found that the mixing performance of the vortex-inducing T-jet reactor is greatly improved under all regimes. [Display omitted] [ABSTRACT FROM AUTHOR]

• The double helix vortex structure in a tangential chamber was obtained by means of numerical simulation. • Three regimes were simulated according to different swirl numbers. • Several recirculation zones were formed in the tangential chamber near its axis. • The frequency of the pressure pulsation was approximately twice the rotational frequency of the double helix structure. • The vorticity redistributes between branches of the double helix structure during its rotation and evolution. The paper investigates the flow structure in a tangential vortex chamber based on numerical simulation of unsteady turbulent flow by the LES method. The swirl flow in a cylindrical chamber was organized using 12 nozzles, supplying the flow tangentially. Three regimes were considered with different design swirl number S = 5.78, 8.67, and 17.34, which was varied by closing one or two nozzle rows. The unsteady computation shows the formation of a rotating double helix vortex structure in the regimes with S equal to 8.67 and 17.34, which is also verified by experimental observations. Several recirculation zones were formed in the tangential chamber near its axis, as well as along the wall at the lower part, and on the axis near the top lid. A dominant frequency was observed in the pressure pulsation spectrum, which increased with increasing swirl parameter, and for the S = 8.67 regime, it was approximately twice the rotational frequency of the double helix structure. In the course of rotation of the double helix structure, the vorticity redistributed between its branches from an approximately symmetric pattern and up to approaching a single-vortex structure at certain points in time. [ABSTRACT FROM AUTHOR]

This paper establishes the equivalent density and equivalent P-wave velocity models of coal bodies with different water saturation, and investigates the P-wave propagation evolution law of coal bodies with different water saturation from the perspective of numerical simulation. When the experimental coal samples continue to use high-pressure water after reaching the natural saturation state, the water saturation can be further increased, and the increase in water saturation is larger, and the corresponding P-wave velocity also appears to be increased more substantially, and this phenomenon also occurs in numerical simulation results, which indicates that the P-wave velocity will have an obvious increasing trend when the coal body is from nearly saturated to fully saturated. The experimental and numerical simulation results show that the P-wave velocity of coal samples increases with the water saturation degree in a similar exponential function, which further verifies the reasonableness and feasibility of the modelling based on the assumption of gas-liquid homogeneous medium. In addition, the propagation of P-wave in coal samples is affected by the pore and fracture structure, and the pore and fracture with small pore size has less influence on the P-wave, and vice versa. • Reveals the P-wave velocity evolution law from near saturation to full saturation in a coal body. • Equivalent density and equivalent P-wave velocity modelling of different water saturation were developed. • Numerical method for P-wave propagation in coals with different water saturations is realised. [ABSTRACT FROM AUTHOR]

• Mechanical response characteristics of beam-column substructures exposed to fire are analyzed. • Explicit calculation formulas for determining the collapse resistance are derived in detail. • Proposed theoretical calculated formulas agree well with these from numerical simulations. • Error analysis is conducted to reveal deviation reasons between theoretical model and numerical simulations. This paper provides a simplified analytical model for the restrained steel beam-column substructure under a fire-induced progressive collapse scenario, which is applied to predict the collapse resistance of substructures under fire. The simplified model is formulated for axially and rotationally restrained two-span steel beam-column substructures under column-loss scenarios and involves rigid and semi-rigid connections. The response characteristics of restrained substructures exposed to fire under column-loss scenarios in each response stage are elaborately analyzed. A "negative" catenary stage, in consideration of the unique negative axial force effects induced by the temperature thermal expansion, was first introduced in the five-stage simplified model for restrained substructures exposed to fire against progressive collapse. Subsequently, the explicit calculation formulas for determining the vertical loads and deflection of both rigid and semi-rigid joint substructures exposed to fire were derived in a quantified way, based on rigid-plastic mechanisms and restraint coefficient methods. In addition, the corresponding numerical simulation analysis on a restrained two-span steel beam-column substructure with different end constraints and fire conditions was carried out to verify the applicability and reliability of established theoretical formulas. Comparisons of vertical load-deflection relationships between the calculation formulas and corresponding numerical simulation shows good accuracy. For more accurate prediction results, the error analysis was further conducted, and several theoretical formulas were modified, which were verified to be accurate and reliable after correction. With derived resistance functions, the resistance of steel beam-column substructures in fire-induced progressive collapse scenarios can be predicted. [ABSTRACT FROM AUTHOR]

For the integrated design of the forebody and hypersonic inlet, the non-uniform inflows generated by the forebody have significant impacts on the inlet performance. Traditional inlet designed by the Internal Conical Flow C (ICFC) flowfield or Method of Characteristics (MOC) flowfield, is difficult to match non-uniform inflows, which can easily lead to reduced captured flow and total pressure recovery. Hence, this paper proposes a novel design method for inward-turning inlets to overcome these problems. The key of this method is the parent flowfiled called the Internal Conical Flow N (ICFN). A multi-objective design optimization is integrated into the design of the two-dimensional ICFN flowfield, which enables the "design-optimization" to implement simultaneously. The new ICFN flowfield makes full use of the high compression effect and avoids the existence of Mach reflection at the focal point. Complete details of the design method of ICFN flowfield and inward-turning inlet are presented. The flowfield structure of ICFN flowfield and inlet are analyzed. Numerical simulation results indicate that the new inward-turning inlet can effectively increase captured flow and total pressure recovery. This reveals that the design method gained here can be usefully applied to the design of high-performance inward-turning inlets. [ABSTRACT FROM AUTHOR]

Abstract In this paper, for the first time, fractional Taylor–Jumarie series expansion is used to solve a glass of time-fractional delay partial differential equation by piecewise interpolation reproducing kernel method (RKM), this class of equations describe sand motion model in beach formation. The aim of this work is to obtain more accurate numerical solution by fractional Taylor–Jumarie series expansion and piecewise interpolation technique. Three numerical experiments are provided to show the advantage of this method, the results show the characteristics of sand motion. The research in this paper is the theoretical basis for further sand motion study. [ABSTRACT FROM AUTHOR]

This paper focuses on 'self-initiated' strainbursts, and starts by providing an overview of these phenomena and their relevance to mining. This is used to set the framework for the numerical simulations presented in the second part of the paper. The numerical simulations examine and address challenges in modelling strainbursts related to the inherent difficulties in dynamic failure simulation. Existing methods either simulate dynamic failure under static or pseudo-static conditions while adopting some threshold factor (normally in terms of stress, strain, or energy) as an indicator of rockburst potential, or incorporate an assumed dynamic disturbance to cause rockburst damage. A distinct-element bonded block method is presented to simulate strainbursts. Instead of triggering failure by an assumed dynamic disturbance, the adopted method simulates the generation of a seismic event by self-initiated rock mass fracturing. This simulation of a self-initiated strainburst is interpreted using patterns of cracking, displacement and strain fields, ground velocities, and calculated kinetic and dissipated slip energies. The mechanisms of self-initiated strainbursting are successfully captured by the distinct-element bonded block method. [ABSTRACT FROM AUTHOR]

This paper presents an algorithm for calculating the stability of air flows in mine ventilation networks in case of random variations of air resistance. The analysis of the stability of air flows in the algorithm is based on two proposed criteria, which are calculated for each branch of mine ventilation network: the guaranteed minimum air flow and the relative deviation of the air flow. The algorithm calculates the distribution of both criteria in the mine ventilation network and allows detecting sections of the mine ventilation network with the least stable air flows. This information can be used to develop different measures to improve the stability of air flows in these sections, which is necessary to ensure the safety of mining operations. The advantages of the proposed algorithm are high calculating speed and intelligibility of the criteria for evaluating the airflow stability in each airway. The convergence of the algorithm is also studied in this paper for a set of ventilation networks. The results of numerical calculation of air flow stability for the undermining level of the Taimyrsky mine are presented. [ABSTRACT FROM AUTHOR]

When a suspended pipeline has corrosion defects, its failure is due to the combination of being suspended and corrosion. Compared with the probability reliability method, the non-probabilistic interval model that considers the factors to be independent only needs a small amount of data to obtain the variation bounds, and it is more economical for reliability analysis. Given that time-dependent reliability analysis based on a random process requires a large amount of data, an interval model for the suspended pipeline with corrosion defects based on the convex model method is proposed. First, based on the extreme suspended length's formula of pipeline through numerical simulation, this paper proposes a model that combines the time-accumulation effects of resistance and corrosion growth with time. Second, the time- dependent limit state equation is established considering the corrosion-defective suspended pipeline for the assessment of practical pipeline engineering. Finally, the non-probabilistic time-dependent reliability model is put forward for the decay characteristics of the resistance under the influence of multi-factors, which can be used as the effective complement of time-dependent reliability analysis based on random process theory. By combining numerical examples, the effectiveness of the present method is demonstrated. Thus, this paper provides a theoretical basis for the maintenance of buried oil and gas pipelines as well as the integrity management of pipelines. More importantly, an assessment standard for a suspended pipeline with corrosion defects is established that can work with poor information. It is of considerable significance for the safe operation of pipelines. [ABSTRACT FROM AUTHOR]

Abstract In this paper, numerical simulations are carried out to analyse the influence of geometrical parameters on the heat transfer and flow patterns for six spirally corrugated tubes at turbulent flow (R e = 25 × 10 3 ). Some previous studies are restricted to 2-D analyse or 3-D numerical simulations considering a reduced section length of the tubes as the computational domain in order to reduce the computation cost. The novelty of this paper is to perform a high cost numerical simulation using a computational domain with a length of the tube (L = 2 m) and dimensions similar to those used in commercial applications. In addition, a new non-dimensional parameter, the corrugation shape factor (C S F) is proposed, which takes into account the width of the corrugation, a geometrical dimension obviated in other studies. A 3-D unstructured tetrahedral mesh was created, and a grid independence analysis of the numerical solution was performed. The Realizable k − ε turbulence model with enhanced wall treatment was proposed to model the turbulence. Simulations were validated with experimental data available in the open literature. Regarding the ratio between height and diameter (H / D), the Nusselt number augmentation seems to augment as the H / D increases for low values of H / D (H / D < 0.05), whereas it decreases for values of H / D > 0.05. Considering the cases with the same diameter, in all the analysed cases, the pressure drop and Nusselt number augmentation decrease linearly as the P / D increases as well as both parameters increase linearly as the H / D , S I and C S F increase. The numerical results indicate that the augmentation of the Nusselt number and the friction factor (compared with the smooth tube) increases approximately linearly with the C S F in the range tested in this work (4 < C S F < 18), regardless of the tube diameter. [ABSTRACT FROM AUTHOR]

Highlights • An explicit kinetic simulation and test study of circular saw cutting is presented. • The interaction process between circular saw and branch can be clearly observed. • The cutting forces from the simulations match the experiment well. • The proposed method shows high efficiency in selecting the best working parameters. • The optimal working parameter combination can obtain smooth cutting surfaces. Abstract The paper describes a method of an explicit kinetic simulation and experimental study of circular saw blade cutting system of small mulberry cutting machine. This simulation is based on orthogonal test of numerical simulation. Firstly, main influencing factors and working conditions in the cutting process were considered according to principle of orthogonal test combined with specific working characteristics and material characteristics of circular saw blades. Large-scale CAE software ANSYS/LS-DYNA was used to respectively establish three-dimensional finite element models of the circular saw blade cutting system with different levels of factors. The boundary constraints and loads were given to conduct explicit kinetic analysis and calculation. The corrections processing and post-processing analysis of finite element analytical model was conducted by simulation tests. The Statistics software, Statistical Package for the Social Sciences (SPSS), is used to analyze the simulation analysis calculating results based on analysis of variance (ANOVA), thus to quickly find the best working parameters of circular saw blade cutting system. Experiments were conducted to measure cutting forces and to compare the surface quality of the mulberry branch under different conditions. The cutting force received by the circular saw blade under the optimal parameter matching was relatively small, and the cutting cross-section quality of the mulberry branches tended to be good, and the work efficiency could also be guaranteed. [ABSTRACT FROM AUTHOR]

Highlights • We accomplish a consistent and tractable numerical simulation of the thickening process. • The simulation includes the transport of a dynamic particle size distribution. • The simulation includes the thickeners underflow yield stress as an output variable. • The simulator can be used in the study of multivariable control strategies. Abstract The purpose of this paper is to extend existing mathematical models of tailings rheology and sedimentation to form a complete dynamic simulator. It is complete in the sense that it includes all important rheological variables for the development of multivariable control strategies and can be integrated with other stages of tailings management systems. This work extends a one-dimensional model for the dynamics of a flocculated suspension in a clarifier-thickener to include the discharge yield stress and particle size distribution in a manner that is computationally tractable. The paper also extends a static yield stress model to include the effect of particle size distribution, in a manner that is consistent with previous empirical and theoretical evidence. The dynamic simulator is validated through the simulation of a Proportional-Integral control strategy and proves to be a useful and flexible tool for the development of control strategies. [ABSTRACT FROM AUTHOR]

Abstract This paper reports the further study carried out by the authors on the technique of long-hole raising in one blast. In the previous work reporting the results of preliminary study, method of vertical crater retreat (VCR) multiple-deck shots with different and smaller slice heights was used to excavate the raise in one blast. A 32-m raise in the cover of an abandoned cavity was successfully broken through. In this paper, an improved technique is suggested to overcome the overbreak and freezing in a long-hole raising blast. In the raising process, long-hole presplitting is first performed at the periphery of the blasting pattern, and then inner VCR multiple-deck shots with the same slice height are conducted according to a specific initiation sequence without in-slice delays. The previously calibrated numerical model is used to simulate the blasting process. The rock mass behaviours and the raising mechanisms are examined. It is shown that after the introduction of long-hole presplitting, the overbreak and freezing are greatly relieved, and the direction of advance and timing pattern are vitally responsible for the evolution of rock damage. This suggested technique was then applied to field raising blasts, and a 29-m raise and a 24-m raise under special cavity conditions were successfully developed. It demonstrates that, compared to the method of purely VCR multiple-deck shots, the design process can be greatly simplified and the present technique leads to better blasting performances. [ABSTRACT FROM AUTHOR]

Highlights • A structural model for pipewall hydrate deposition is established. • Mechanical parameters of pipewall hydrate deposition are calculated. • Mechanical properties and stabilities of pipewall hydrate deposition are simulated. • Influences of flow rate, deposition thickness and deposition length are investigated. Abstract The mechanical properties and mechanical stabilities of pipewall hydrate deposition are of great importance to the prevention and removal of pipeline hydrate plugging. In this paper, the mechanical properties and mechanical stabilities of pipewall hydrate deposition are quantitatively investigated by modelling and numerical simulation. First, a structural model for pipewall hydrate deposition is established based on particle packing theory. Using this structural model, the main mechanical parameters of pipewall hydrate deposition can be calculated. Then, numerical simulations using finite element method and ANSYS Mechanical APDL 14.5 are conducted based on the calculated mechanical parameters. Through the simulations, the structure deformation, internal stress distribution and failure of pipewall hydrate deposition when it is under the action of external forces are studied and the influences of flow rate, deposition thickness and deposition length are investigated. The results of this paper can provide guidance for pipeline flow assurance. [ABSTRACT FROM AUTHOR]

Abstract Thermal spallation technology is a drilling method, which is potentially suitable for the exploitation of petroleum in hard rocks with low costs. In this paper, characteristics of reaction are investigated under relatively high pressure in thermal spallation drilling. The Peng-Robinson equation of state and eddy dissipation model are applied in the simulation. Effects of methane and oxygen flow rate, nitrogen fraction on the flow field are studied. Simulation results are validated in experiments that monitor the temperature of the flame jet using thermocouples. Results show that besides a portion of oxygen reacting with the methane, the left oxygen mainly flows towards the boundary of the reactor. The reaction between methane and oxygen mainly occurs at the central part of the reactor. Also, the temperature close to the wall of the reactor is only 1300 K, which can help to protect the reactor wall from damage due to high temperature. Increasing the methane flow rate within a certain range can help to obtain high temperature and high jet velocity simultaneously. Also, injecting mixture of oxygen and nitrogen can prevent too much excessive oxygen from existing in the wellbore during thermal spallation drilling. Results in this paper could provide guidance for field applications. Highlights • A model for simulation of reaction for thermal spallation drilling is proposed. • The reliability of the numerical model is validated in experiment. • Characteristics of reaction flow field are investigated. • Effects of injection parameters on the flow field are studied. [ABSTRACT FROM AUTHOR]

Activated natural fractures, poorly-propped and un-propped secondary hydraulic fractures may serve as the connection between reservoir fluids and the main hydraulic fractures (i.e., well-propped fractures). These branched fractures also contribute considerably to well after-fracturing productivity in unconventional tight/shale reservoirs. Rough fracture surface and its effects on fluid flow behavior in such fractures with very limited width is very important in understanding total mass transport in fractured rocks. In this paper, the effect of rough surface properties on fracture conductivity is studied through 3D numerical simulation of fluid flow behavior within the fractures. First, a tensile fracture was created on a core sample retrieved from the Montney formation, and the rough fracture surface topography was scanned via a high-resolution optical profilometer. The surface roughness characterizations were then used as reference to numerically reconstruct multiple three-dimensional fracture models. A finite element method was adopted to simulate fluid flow in the rough-wall fractures, using Navier-Stokes equation, for various fracture surface properties such as mean aperture, root mean square (RMS) asperity height, correlation length, anisotropy and shear displacement distance. Results showed that cubic law tends to overestimate the conductivity of the fractures with rough-wall surfaces, especially when the fracture aperture is small. Other surface properties, including correlation length, anisotropy and Hurst exponent also exert considerable impacts on fracture hydraulic properties. As the shear displacement distance increases, deviation of the fracture conductivity from cubic law first increases and then maintains at a constant level. The results of this paper have advanced the understanding of fracture conductivity and its dependence on fracture surface properties and will aid in improving production prediction and optimization in fractured tight reservoirs. [ABSTRACT FROM AUTHOR]

Hydrothermal jet is an alternative drilling method for the exploitation of oil and geothermal energy in deep hard formations. For the application of this novel technology, the successful generation of hydrothermal jet is very important. This paper focuses on investigating applications of different reaction, turbulence and radiation models to the supercritical water oxidation process in downhole reaction chamber of hydrothermal jet drilling. The objective is to identify the pros and cons of each model and determine a set of models that are the most appropriate for the reaction. Simulation models are tested and optimized through two different operating conditions. Simulation results are compared with experimental data. Results show that the entire space of the reaction chamber is in a high temperature state using the laminar finite rate model. The finite rate model is suitable for the simulation compared with other reaction models discussed. The Magnussen constant A and B in the finite rate model can be modified to be 7 and 0.5 to further reduce the error. In addition, the high temperature areas in k-omega model and SAS model are more concentrated, while they are more uniform in RNG k-epsilon model and standard k-epsilon model. The RNG k-epsilon model and DO or DTRM are the most appropriate turbulence and radiation models through comparison. Results in this paper can provide implications for the reaction simulation of hydrothermal jet drilling. [ABSTRACT FROM AUTHOR]

In this paper, the effects of different cavitation bubble on the natural frequency, mode shape and hydrodynamic damping of the NACA0009 hydrofoil are investigated by numerical simulation method. The cantilever truncated hydrofoil model is set in a high-speed water tunnel. The dynamic characteristics of the hydrofoil structure is affected by the fluid-structure coupling. Compared to the properties of water, the density of cavitation bubbles decreases, causing an increase in the natural frequency of the structure, and the decrease in the speed of sound also causes a change in the mode shape. The growth rate of frequency under unit chord length cavitation is nonlinear as the cavitation bubble length increases. By defining a modal displacement function to compare the structural mode shapes, cavitation intensifies the bending and torsional deformation of the hydrofoil. Even if the volume of cavitation bubbles is small, the inhomogeneous distribution of acoustic pressure and changes in cavitation bubble properties can cause changes in the structural mode shapes. The one-way FSI numerical method for hydrodynamic damping in cavitating flow is established and the applicability of this method is verified by the calculation of damping in water. For the first bending mode f c1 , the hydrodynamic damping with 50% chord length (0.5 l c) stably attaching cavitation is simulated. As the length of the cavitation bubble increases to 0.8 l c , the damping value becomes smaller. The research in this paper lays the foundation for analysing the dynamic characteristics of hydraulic machinery with cavitation using numerical simulation method. • The density and sound speed of cavitation are different from water, which can cause changes in frequency and mode shape. • The frequency growth rate of hydrofoil under unit chord cavitation changes nonlinearly. • Cavitation intensified the bending and torsional deformation of the hydrofoil. • Even if the cavitation volume is small,it can cause inhomogeneous pressure distribution and change the mode shape. • The one-way FSI numerical method for hydrodynamic damping in cavitating flow is established. [ABSTRACT FROM AUTHOR]

In this paper, we compare the failure behaviors of CFRP single and double (S–D) lap joints and analyze the effects of hygrothermal aging on these joints through a comprehensive experiment and simulation. Firstly, we analyze and compare the degradation pattern of the residual strength of S–D​ lap joints under three hygrothermal environments, and reveal the aging mechanism in conjunction with the macro/fine-view failure surfaces of the joints. Secondly, we elucidate the probability distribution of joint aging failure using the two-parameter Weibull distribution. Finally, we develop a finite element model to simulate the failure process of the cohesive behavior, and compare not only the bending moment and contact stress distribution of the two joints, but also analyze the damage condition of the CFRP matrix/fiber. We define environmental degradation factors to express the failure behavior of lap joints after aging. Through the above analysis methods, we find that hygrothermal aging can seriously damage the CFRP and adhesive properties. The mechanical performance of DLJs is significantly superior to that of SLJs, and they also exhibit better reliability. Therefore, DLJs can be substituted for SLJs in some application scenarios. Additionally, our paper provides new insights into the selection of an appropriate lap bonding method. • This paper evaluates the aging durability of single and double lap joints from multiple perspectives. • The failure behavior of single and double lap joints is comprehensively compared by numerical simulations. • This paper provides some new insights into the selection of an appropriate lap bonding method. [ABSTRACT FROM AUTHOR]

• Model prediction deviation less than 10%. • Aluminum agglomerate morphology close to experimental results. • Detailed information on particle size distribution of aluminum condensed phase products. Aluminum is an important additive in solid propellants used to improve energy efficiency, but agglomeration of aluminum particles can reduce the specific impulse of the engine, increase two-phase flow losses and cause ablation of the adiabatic layer. Therefore, it is important to understand the mechanism of formation, mode of movement and particle size characteristics of aluminum agglomerates in solid propellants to study the inhibition of agglomeration. In this paper, a three-dimensional numerical simulation of aluminum particle agglomeration near the burning surface of solid propellants was conducted using the discrete unit method based on direct tracking calculations of the detailed motion of individual particles. The model considered physical processes such as burning surface motion, aluminum particle precipitation, turbulent pulsation and the heating and melting of aluminum particle and used a grid-based contact detection method to accelerate the computational process. The agglomeration process of a solid propellant with specific formulation was experimentally investigated. Aluminum particle aggregates underwent splitting, and the final aluminum particle agglomerates were spherical droplets with typical structure. The agglomeration process of this propellant was investigated by means of a simulation. The accuracy of the agglomeration model was verified by comparing the results of the model for the agglomeration process and the shape and size distribution of agglomerates with available experimental data. Compared with the experimental results, the deviations of the equivalent particle sizes of agglomerates D 10 , D 50 , D 90 , D 4,3 , and D 3,2 obtained by using the simulation results were 6.3%, 6.3%, 9.4%, 7.5% and 6.7%, respectively. The aluminum particle agglomeration model established in this paper can predict the particle size distribution of aluminum agglomerates near the burning surface of solid propellants. The model was also used to further investigate the effects of aluminum particle content, ammonium perchlorate (AP) particle size and environmental pressure on aluminum particle agglomeration. Increasing the aluminum content or AP particle size aggravated aluminum particle agglomeration, whereas increasing pressure weakened it. [ABSTRACT FROM AUTHOR]

• Simulation on constituent separation and mass transfer in T-junction is performed. • Numerical simulation with mass transfer is compared to that without mass transfer. • The influence of the quality at inlet on the constituent separation is studied. • Flow characteristic and mass transfer of base case are discussed. • A correlation of mass transfer for annular flow in T-junction is proposed. The study of constituent separation in T-junction is important to realize the operation of the constituent adjustable system. This paper presents a numerical simulation on the constituent separation and mass transfer of R134a and R600a in T-junction. The multiphase flow model of volume of fluid (VOF) is adopted, and the interphase mass transfer of R134a and R600a is achieved by adding source terms in governing equations. The quality at inlet varies from 0.51 to 0.92. The mass flow rate at inlet and flow rate weighting of branch outlet are 10 g⋅s−1 and 0.3, respectively. Results show that the error of numerical simulation with mass transfer is lower than that of numerical simulation without mass transfer. When the quality at inlet is 0.81, the error of numerical simulation with mass transfer can be reduced by 50.07% compared with the numerical simulation without mass transfer. The higher the quality at inlet, the higher the separation efficiency of R134a when the quality at inlet is less than 0.81. When the quality at inlet is 0.81, the separation efficiency of R134a in the numerical simulation with mass transfer is the largest, whose value is 1.47%. Most of the flow patterns are annular flow. The pressure and flow pattern have an important influence on the constituent separation and the interphase mass transfer rate. A correlation with 10% error band of interphase mass transfer for annular flow in T-junction is proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, we study an intra- and interspecific competition system with the different diffusion rates in an unstirred chemostat. Due to the present of the different diffusion rates, the conservation principle for a classical standard chemostat model does not hold here. Firstly, we prove the existence, the uniqueness and asymptotic behaviors of positive solution of the single population system by using the degree theory. Secondly, by the degree theory and standard bifurcation theory, the existence and global structure of the coexistence solutions are investigated. The results show that when the maximum growth rates of two microorganisms with different diffusion abilities are not small, two competing microorganisms will coexist. Finally, numerical simulations are performed to illustrate that the interspecific interference can help the weaker competitor to win in the competition. [ABSTRACT FROM AUTHOR]

• 3D integrated model of PHENIX reactor primary system including cold and hot pool was established. • Overall flow paths in reactor vessel during PHENIX Dissymmetric Test were identified. • 3D asymmetric thermal stratification phenomena in cold pool, hot pool and local area of IHX inlet were captured. • 3D temperature distribution of internals during PHENIX Dissymmetric Test were obtained. Temperature distribution of internals under different transient events is important for the design and safety analysis of pool-type sodium-cooled fast reactor (SFR). It is influenced by overall flow and thermal stratification phenomena in the multi-scale sodium pool. Due to the difficulty to perform experiment, three-dimensional (3D) numerical method is usually adopted for obtaining the temperature distribution and analyzing complex phenomena in pool-type SFRs. It needs to be further validated using the published benchmark, such as PHENIX Dissymmetric Test. The simplified model in system code and 3D model of local area in current study cannot capture the complex coupling effect of cold and hot pool during dissymmetric test. In this paper, an integrated 3D model of PHENIX reactor primary system both including cold and hot pools is established. The steady and transient simulation with 1800 s of PHENIX Dissymmetric Test process are carried out. The key parameters of simulation are compared with the available experimental and predicted data, which achieves good agreement. Overall flow and asymmetric temperature distribution phenomena in cold pool, hot pool and local area of IHX inlet are simulated. There is a temperature difference between different sides of IHX inlet during a period after scram, with the maximum value of 80 ℃ approximately at 90 s. This validated numerical method can be further used for the analysis of thermal hydraulic characteristics in other pool-type SFR. The obtained temperature distribution of internals can provide the reference for the stress assess of structures in the engineering design. [ABSTRACT FROM AUTHOR]

Sediment compression during submarine hydrate depressurization production causes changes in physical and mechanical characteristics, which in turn affects production results. In this paper, based on geological conditions of SHSC-4 well in Shenhu area, a theoretical model considering sediment compression effects is established by COMSOL, and the effects on the evolution of reservoir physical and mechanical characteristics within 60 days during depressurization production is simulated. The results show that model dimension effects can be ignored when the size l ≥ 100 m within 60 days. The effects of sediment compression on the physical characteristics of the reservoir are mainly realized by affecting the evolution of porosity, and the porosity reduction leads to permeability reduction. The larger the sediment compression coefficient, the higher the pore pressure in the reservoir. Sediment compression hinders the propagation of low pore pressure and heat transfer in the reservoir, which is unfavorable for hydrate decomposition favorable to hydrate reformation. A larger or smaller sediment compression coefficient selected in the simulation can lead to under- or over-estimate of reservoir gas production, so choosing an appropriate sediment compression coefficient when considering sediment compression is necessary for rational assessment of reservoir production behavior. In the production test site, when the production pressure is higher than 3 MPa, the pore pressure gradient is the key factor to promote gas production from the reservoir. When the production pressure is lower than 3 MPa, the sediment compression is the key factor to impede gas production from the reservoir. [Display omitted] • Dimension effects can be ignored when model size l ≥ 100 m within 60 days. • Compression hinders production by affecting physical and mechanical characteristics. • An incorrect compression coefficient can lead to unreasonable production assessment. • When production pressure is below 3 MPa, compression becomes hindrance to production. [ABSTRACT FROM AUTHOR]

• An enhanced heat transfer structure is proposed, which can improve efficiency by 29 %. • The performance of the new structure was investigated by numerical simulation. • Experimental tests were conducted to prove the effectiveness of the new structure. To enhance the heat transfer efficiency of the helically coiled tubes heat exchangers, this paper proposes a double shell-passes structure designed for a multi-layer helically coiled tubes heat exchanger. Numerical simulation is employed to investigate the performance of the Double Shell-passes Multi-layer Helically Coiled Tubes Heat Exchanger (DSMHCTHE). Furthermore, an experimental test system is constructed to validate the simulation results, exploring the performance under different operating conditions. A comparative analysis is conducted with the traditional Multi-Layer Helical Tube Heat Exchanger (MHCTHE). The results indicate that, under identical experimental conditions, the heat transfer rate and thermal effectiveness of DSMHCTHE increased by 5.1 % to 12.9 %. The overall heat transfer coefficient showed an improvement ranging from 21.5 % to 29.0 %, while the shell-side heat transfer coefficient increased by 36.2 % to 47.5 %. However, the shell-side pressure drop increased by 60.7 % to 83.4 %. Utilizing the heat exchanger's comprehensive performance as the evaluation criterion, it was observed that DSMHCTHE exhibited superior comprehensive performance. In comparison to MHCTHE, the comprehensive performance of DSMHCTHE improved by 12 %. The design of the double shell-passes configuration has shown significant enhancements in both convective heat transfer and overall performance, highlighting the superior application potential of DSMHCTHE. [ABSTRACT FROM AUTHOR]

In response to the optimization problem of the motion law of the pectoral fins of biomimetic robotic fish, this paper uses computational fluid dynamics (CFD) methods to achieve the CFD optimization of two types of rigid biomimetic pectoral fins with three degrees of freedom (DOF): elliptical and 8-shaped swing curves. By analyzing the hydrodynamic characteristic curve of the pectoral fins, pressure distribution upstream and downstream of the fin surface, velocity vector of the surrounding flow field during pectoral fin swing, and three-dimensional vortex structure, it is found that when the pectoral fins are pushed forward in an elliptical swing curve, the resistance peak value decreases after two optimizations. However, at the same time, a certain amount of thrust is lost. When the pectoral fin advances in an 8-shaped swinging curve, after two optimizations, the pectoral fins resistance decreases while maintaining an enormous thrust, comprehensively improving the propulsive effect of the pectoral fin on the robotic fish. By substituting the optimized 8-shaped pattern into the robotic fish model, it is found that the flapping angle of 35 ° has better drag reduction performance, and the average swimming speed of the robotic fish is the fastest at this angle. • After secondary optimization, the elliptical pectoral fin swing curve with better drag reduction performance and smoother curve was obtained • Optimize the 8-shaped swing curve to comprehensively enhance the propulsion effect of pectoral fins on robotic fish • Substituting the optimized 8-shaped swing pattern into the robotic fish model to achieve self-propelled motion, it was found that p h i F L A = 35 d e g r e e had the best performance [ABSTRACT FROM AUTHOR]

The paper presents a study aimed at understanding the characteristics of an internal explosion within a chamber with limited venting. The study includes numerical simulations and analytical derivations. An in-house 3D code employing an improved weighted essentially non-oscillatory (WENO) conservative finite difference scheme was used to carry out the simulations. It is indicated that the proposed improved WENO scheme can resolve the shock waves with higher accuracy and resolution. Further, a simplified analytical model to predict the quasi-static overpressure was developed based on the conservation law of total energy and dimensional analysis theory. It is demonstrated that the proposed simplified approach for prediction of the quasi-static overpressure agrees well with simulation results for a wide range of explosive weights and venting hole sizes. The studies in this paper provide an efficient method to predict the blast load inside a partially confined chamber for the analysis of the consequences of explosion. [ABSTRACT FROM AUTHOR]