Search Results (101)

This article presents the results of a study on the possibility of using a single-speed multiphase model with free surface allowance for simulating boiling and condensation processes. The simulation is based on the VOF method, which allows the position of the interphase boundary to be tracked. To increase the stability of the iterative procedure for numerically solving volume fraction transfer equations using a finite volume discretization method on arbitrary unstructured grids, the basic VOF method is been modified by writing these equations in a semi-divergent form. The models of Tanasawa, Lee, and Rohsenow are considered models of interphase mass transfer, in which the evaporated or condensed mass linearly depends on the difference between the local temperature and the saturation temperature with accuracy in empirical parameters. This paper calibrates these empirical parameters for each mass transfer model. The results of our study of the influence of the values of the empirical parameters of models on the intensity of boiling and evaporation, as well as on the dynamics of the interphase boundary, are presented. This research is based on Stefan’s problem of the movement of the interphase boundary due to the evaporation of a liquid and the problem of condensation of vapor bubbles water columns. As a result of a series of numerical experiments, it is shown that the average error in the position of the interfacial boundary for the Tanasawa and Lee models does not exceed 3–6%. For the Rohsenow model, the result is somewhat worse, since the interfacial boundary moves faster than it should move according to calculations based on analytical formulas. To investigate the possibility of condensation modeling, the results of a numerical solution of the problem of an emerging condensing vapor bubble are considered. A numerical assessment of its position in space and the shape and dynamics of changes in its diameter over time is carried out using the VOF method, taking into account the free surface. It is shown herein that the Tanasawa model has the highest accuracy for modeling the condensation process using a VOF method taking into account the free surface, while the Rohsenow model is most unstable and prone to deformation of the bubble shape. At the same time, the dynamics of bubble ascent are modeled by all three models. The results obtained confirm the fundamental possibility of using a VOF method to simulate the processes of boiling and condensation and taking into account the dynamics of the free surface. At the same time, the problem of the studied models of phase transitions is revealed, which consists of the need for individual selection of optimal values of empirical parameters for each specific task. Full article

The purpose of this paper is to study the shear performance of reinforced concrete corbels under a synergistic change in the main stirrup inclination angle to explore the synergistic mechanism of the main reinforcement and the stirrup inclination angle, and to evaluate the applicability of existing design specifications. The shear performance test was carried out by designing RC corbel specimens with an inclination angle of the main reinforcement and stirrup. The test results show that a 15° inclination scheme significantly improves the shear performance: the yield load is increased by 28.3%, the ultimate load is increased by 23.6%, the strain of the main reinforcement of the 15° specimen is reduced by 51.3%, the stirrup shows a delayed yield (the yield load is increased by 11.6%) and lower strain level (250 kN is reduced by 23.7%), and the oblique reinforcement optimizes the internal force transfer path and delays the reinforcement yield. A CDP finite element model was established for verification, and the failure mode and crack propagation process of the corbel were accurately reproduced. The prediction error of ultimate load was less than 2.27%. Based on the test data, the existing standard method is tested and a modified formula of the triangular truss model based on the horizontal inclination angle of the tie rod is proposed. The prediction ratio of the bearing capacity is highly consistent with the test value. A function correlation model between the inclination angle of the steel bar and the bearing capacity is constructed, which provides a quantitative theoretical tool for the optimal design of RC corbel inclination parameters. Full article

In this paper, we present a fast and accurate numerical approach applied to specific American-style derivatives, namely American power call and put options, whose main feature is that the underlying asset is raised to a power. The study is set in the Black–Scholes framework, and we consider continuously paying dividends assets and arbitrary positive values for the power. It is important to note that although a log-normal process raised to a power is again log-normal, the resulting change in variables may lead to a negative dividend rate, and this case remains largely understudied in the literature. We derive closed-form formulas for the perpetual options’ optimal boundaries and for the fair prices. For finite maturities, we approximate the optimal boundary using some first-hitting properties of the Brownian motion. As a consequence, we obtain the option price quickly and with relatively high accuracy—the error is at the third decimal position. We further provide a comprehensive analysis of the impact of the parameters on the options’ value, and discuss ordinary European and American capped options. Various numerical examples are provided. Full article

Insufficient structural stiffness is a key technical challenge that restricts the increase in span of multi-tower cable-stayed bridges. In order to clarify the application effect of crossing cables in long-span, multi-tower cable-stayed bridges, theoretical analysis and the finite element method were used to study the influence of the cable sag effect on the longitudinal constraint stiffness of crossing cables. The longitudinal constraint stiffness formula of the crossing cable was modified by introducing the equivalent elastic modulus to consider the cable sag effect. Based on the stiffness formula, the influence of the main span, initial stress of the crossing cable, and the ratio of the crossing cable area on its restraining effect was analyzed. The finite element model of a three-tower cable-stayed bridge with main span length of 1000 m and 1500 m is established to verify the accuracy of the formula, and the influence of the number of crossing cables and the tower height on the restraining effect of crossing cables is explored. The research results indicate that as the main span length increases, the location of maximum restraining stiffness of crossing cables moves closer to the mid span; increasing the area of crossing cables connected to the mid tower can effectively suppress the deviation of the tower. In addition, increasing the main span length will reduce the restraining effect of the crossing cables, while changes in the height of the towers do not affect the enhancement effect of the crossing cables on structural rigidity. Full article

This study investigates the impact of the bearing plate position on the uplift bearing capacity of low-header concrete expanded pile (CEP) foundations using the ANSYS finite element simulation method. Nine models of low-header CEP single piles with varying bearing plate positions are constructed. Incremental loading is applied to obtain relevant data, including load–displacement curves for vertical tensile forces, displacement contours, and shear stress distributions. The study analyzes the characteristics of load–displacement curves under different loading conditions, the axial force distribution along the pile shaft, the failure state of the surrounding soil, and how the uplift bearing capacity varies with changes in the bearing plate position. Based on the findings, a calculation model for the uplift bearing capacity of low-header CEP single-pile foundations is proposed. Given that the uplift bearing capacity decreases to varying degrees depending on the bearing plate position, the slip-line theory from previous studies is applied to refine the corresponding calculation formula for uplift bearing capacity. The results from the ANSYS finite element simulation confirm that the bearing plate position significantly influences the uplift bearing performance of low-header CEP single-pile foundations. The uplift bearing capacity increases with the distance between the bearing plate and the low header, reaching a peak before decreasing beyond a certain threshold. Considering the influence of the bearing plate position on bearing capacity, the affected area of soil beneath the foundation, and the time required for the system to enter its working state, the optimal bearing plate position is found to be at a distance of d₁ = 4R₀ to 5R₀ from the top of the pile. Full article

Based on the equal-stress formula and equal-strain formula of material mechanics, a new formula for predicting Young’s modulus of sheet-reinforced composite is derived by taking sheet-graphene composite as an example. The effectiveness of the formula is verified by comparing it with the mixing rate (ROM), Halpin–Tsai equation, and finite-element simulation. This formula is used to discuss the effect of interface-layer properties on the modulus of composite materials. Compared with the case without interface, when the graphene content is 3% and the interface-layer properties are linearly distributed and exponentially distributed, respectively, the embedded RVE modulus prediction increases by 5.06%, and the sandwich RVE modulus prediction increases by 56.5% and 31.75%, respectively. The influence of the change in interface-layer thickness from 0 to 1.5 nm (determined according to the existing literature) is also discussed. The predicted modulus of embedded RVE and sandwich RVE increases by 73% and 11.3%, respectively. The results show that the influence of the thickness and properties of the interface layer on the modulus prediction of graphene composites cannot be ignored. Combined with the analysis of experimental data, it is found that the experimental data fall within the prediction range of the modulus of the formula, indicating that the formula can be used for the preliminary trend analysis of the mechanical test of graphene-composite materials in the early stage, saving testing costs and time. Full article

Aiming at the requirement of high stress ratio reinforcement in space steel structures, a novel method for enshancing the load-bearing capacity of casings through indirect welding to produce a reinforced steel pipe is introduced. To investigate how the mechanical properties of steel pipe members change when reinforced using this method, a series of welding reinforcement axial compression tests were designed, incorporating local reinforcements at various positions and with different initial stress ratios. By comparing the reinforced specimens with those left unreinforced, we obtained insights into the failure modes, ultimate bearing capacities, and strain data of the steel pipes. To further validate the findings, 236 finite element models were developed. These models allowed for a comprehensive analysis of the numerical results alongside the experimental data, taking into account the thermal effects of welding. Quantitative analyses were performed to assess the impact of the initial stress ratio, initial defects, welding heat effects, slenderness ratio, the area ratio between the reinforcement and the pipe, and the length of the reinforcement on the ultimate bearing capacity of the reinforced members. The findings indicate that residual stresses resulting from the welding process have a minimal influence on the ultimate bearing capacity. The method maintains over 75% of its efficiency even at initial stress ratios up to 0.8. Additionally, the study elucidates the rules governing the impact of localized reinforcement on the mechanical properties of loaded steel pipe members. Combining the theoretical calculations with numerical simulations, an empirical formula for estimating the ultimate bearing capacity of the reinforced pipe specimens was derived. The relative error of the formula is less than 10% with the experimental outcomes and the finite element analysis results thereby offering a reliable tool for engineering applications. Full article

Based on the Zhuyuan–Bailonggang sewage interconnection pipe project in Shanghai, the ABAQUS finite element software was used in numerical simulations to study the fine control of stratum disturbances caused by pipe jacking parameter deviation in soft soil areas. Combining the simulation results with onsite measured data, the Peck formula was used to predict surface settlement. The results indicate the following: (1) The jacking speed and face pressure are negatively correlated with surface settlement. Under the maximum positive deviation and negative deviations in the jacking speed, after the tail passes through the monitoring section D₀ 16 ring, the maximum value of settlement at point B8 increases by 21.6% and decreases by 12.8%, respectively. Increasing the jacking speed increases the area with stress change ratio R < 0 at monitoring section D₀, and the arch foot at the tail of the pipe jacking machine decreases the surface settlement. In contrast, when the face pressure deviates from its average value, the variation range is less than 1%. (2) The pipe slurry coefficient and surface subsidence are positively correlated. Under the maximum positive deviation and the maximum negative deviation, the tail passes through the monitoring section D₀ 16 ring, and the maximum settlement value at B8 decreases by 4.9% and increases by 16.5%, respectively. The increase in the coefficient reduces the area with R < 0 at D₀ and increases the surface settlement. (3) In the order of descending strength, surface settlement is affected by the jacking speed, slurry friction coefficient, and face pressure. (4) To predict the maximum surface settlement value due to deviations in the jacking parameters, the Peck formula was modified using a correction factor $\alpha$ ranging from 0.6 to 3.0 and a settlement trough width correction factor $\beta$ ranging from 1.6 to 4.0. The modified prediction curve is in closer agreement with the actual conditions. Full article

Deep coal mining is faced with high temperature, high seepage pressure, and high ground stress, and there is a complex nonlinear coupling relationship between the temperature of water in deep rock mass and its seepage. Based on the background of deep mining in Zhaolou Coal Mine in Shandong Province, China, the hydraulic conductivity of artificial rock samples with similar materials was tested indoors under different water temperatures of 30~80 °C. On the basis of deep rock samples collected in the field, the hydraulic conductivity has a nonlinear positive correlation with the rise of water temperature. The difference in hydraulic conductivity at the highest and lowest temperatures is two to three times. By means of multi-physics coupling finite element software (COMSOL Multiphysics, COMSOL Inc., Stockholm, Sweden), combined with the actual geological background, the regularity was found to be consistent with the laboratory experiment and further proves that the inlet pressure has no effect on the hydraulic conductivity. Subsequent analyses revealed that the influence of temperature on the seepage field is mainly reflected in the change of fluid kinematic viscosity with temperature, which causes the change in the hydraulic conductivity. According to the formula, the hydraulic conductivity of the rock at 80 °C is 2.31 times higher than its hydraulic conductivity at 30 °C, which is matched by the indoor test results. The engineering performance is that as the temperature of the deep rock body increases, the ability of water to penetrate rocks increases, and the water inflow of the working face increases. The results can be applied to the prevention of water hazard threats in deep coal mining. Full article

This paper proposes a method for modifying brick masonry walls using ultra-high-performance concrete (UHPC) to effectively reduce the beam section width in composite members. First, a detailed finite element model of UHPC–brick masonry composite beams was established using the finite element software ABAQUS 2022 and validated through comparison with the existing literature. Then, the effects of factors such as the tensile reinforcement ratio, UHPC layer thickness, and UHPC strength grade on the load–midspan deflection curve of composite members were analyzed, along with a study of the bending performance under vertical loads. Based on the results of the finite element analysis, a calculation formula for the positive section bending capacity of UHPC–brick masonry composite beams was proposed. The study found that longitudinal tensile reinforcement yielded first, followed by the crushing of the compressive region of UHPC and brick masonry, resulting in overall bending failure. With the increase in the tensile reinforcement ratio and UHPC layer thickness, both the yield load and peak load significantly increased, while the UHPC layer thickness had a notable impact on the cracking load of the composite member. When the UHPC strength grade ranged from 150 MPa to 180 MPa, the bearing capacity of the composite member changed little. The proposed calculation method for bearing capacity correlated well with the finite element results, providing a theoretical basis for the design and analysis of UHPC–brick masonry composite beams. Full article

The natural caving method, as a new technique in underground mining, has been promoted and applied in several countries worldwide. The destruction of the bottom rock mass structure directly impacts the structural stability of underground engineering, resulting in damage and collapse of underground tunnels. Therefore, based on the principles of explosion theory and field monitoring data, a scaled three-dimensional numerical simulation model of underground blasting was constructed using LS-DYNA19.0 software to investigate the attenuation patterns of underground blasting vibrations and their impact on nearby tunnels. The results show that the relative error range between the simulated blasting vibration velocities based on the FEM-SPH (Finite Element Method–Smoothed Particle Hydrodynamics) algorithm and the measured values is between 7.75% and 9.85%, validating the feasibility of this method. Significant fluctuations in blasting vibration velocities occur when the blast center increases to within a range of 10–20 m. As the blast center distance exceeds 25 m, the vibration velocities are increasingly influenced by the surrounding stress. Additionally, greater stress results in higher blasting vibration velocities and stress wave intensities. Fitting the blasting vibration velocities of various measurement points using the Sadovsky formula yields fitting correlation coefficients ranging between 0.92 and 0.97, enabling the prediction of on-site blasting vibration velocities based on research findings. Changes in propagation paths lead to localized fluctuations in the numerical values of stress waves. These research findings are crucial for a deeper understanding of underground blasting vibration patterns and for enhancing blasting safety. Full article

This study aims to examine the effects of local corrosion on the axial compression performance of concrete-filled steel tubular (CFST) members. Nineteen CFST short columns with local corrosion were designed and fabricated to undergo axial compression mechanical property tests, with the radial corrosion depth of the local corrosion area as the key test parameter. The failure mechanism and mechanical property change laws of CFST axial compression short columns with circumferential full corrosion at the ends and middle were studied. Combined with finite element modeling, the influence laws of the three-dimensional geometrical characteristics of the local corrosion zone, i.e., the axial length, the annular width and the radial depth, on the structural bearing performance were thoroughly explored and discussed. The results revealed that the main reason for the reduction in load-carrying capacity of circular CFST axial columns due to local corrosion is attributed to the reduction of the effective cross-sectional area of the steel tube in the corrosion area. When local corrosion occurs at different axial positions, the variation range of the bearing capacity of CFST columns is within 10%. Regarding the impact of the three dimensions of local corrosion on the axial load-carrying capacity of CFST, the radial corrosion depth was identified as the most influential factor, followed by the annular corrosion width, and finally by the axial corrosion length. When the axial corrosion length exceeds 20% of the specimen length, its further influence on the load-carrying capacity is considered limited. Finally, a practical calculation formula for the bearing capacity of locally corroded CFST columns is proposed. The predicted results of this formula fit well with the test results and can quickly estimate the remaining bearing capacity of the structure by measuring the geometric parameters of the local corrosion area, providing a reference for the assessment and maintenance of CFST structures. Full article

This study focuses on developing an advanced anti-lock braking system (ABS) for motorcycles, specifically targeting the challenges associated with cornering. Significant roll angles during motorcycle turns can often lead to slipping and the loss of control, increasing the risk of accidents. Existing ABSs primarily address longitudinal dynamics and fail to provide optimal braking control during cornering. To address this gap, this study utilizes BikeSim and MATLAB/Simulink for simulations and experiments to design an ABS that adapts to varying roll angles by analyzing motorcycle dynamics during cornering. A tire model is constructed using the Magic Formula to examine both longitudinal and lateral characteristics under different conditions, which helps determine the current tire slip set-point. The controller, designed with a finite-state machine combined with bang-off-bang control, uses tire slip as the control variable. It adjusts the slip set-point based on changes in roll angle and sends control signals to the hydraulic actuator to regulate braking pressure, ensuring optimal braking performance without the loss of control. Finally, hardware-in-the-loop experiments are conducted, with real-time control commands sent to the hardware platform’s actuator via BikeSim RT. These experiments validate the effectiveness of the designed controller, significantly enhancing braking stability during cornering and improving safety for motorcycle riders. Full article

To study the flexural performance of fiber-reinforced polymer (FRP) grid–polymer cement mortar (PCM)-composite-strengthened RC beams, the finite element numerical simulation of FRP grid–PCM composite RC beams is carried out using ABAQUS to analyze the effects of the amount of FRP grid reinforcement, the type of FRP grid material, and the geometry of FRP grid on the flexural performance of reinforced concrete beams and to establish the flexural capacity calculation formula of FRP grid–PCM-reinforced RC beams in case of debonding failure, based on analysis of the influencing factors. The results show that increasing the reinforcement of the FRP grid and increasing the stiffness of the FRP grid can improve the flexural bearing capacity of RC beams, and the change of FRP grid geometry has little effect on the flexural bearing capacity of RC beams. The established formula for calculating the flexural bearing capacity of FRP grid-reinforced concrete beams can better predict the flexural capacity of reinforced concrete beams under peeling failure. Full article

Mathematical models of heat and moisture transfer for anisotropic materials, based on the use of the fractional calculus of integro-differentiation, are considered because such two-factor fractal models have not been proposed in the literature so far. The numerical implementation of mathematical models for determining changes in heat exchange and moisture exchange is based on the adaptation of the fractal neural network method, grounded in the physics of processes. A fractal physics-informed neural network architecture with a decoupled structure is proposed, based on loss functions informed by the physical process under study. Fractional differential formulas are applied to the expressions of non-integer operators, and finite difference schemes are developed for all components of the loss functions. A step-by-step method for network training is proposed. An algorithm for the implementation of the fractal physics-informed neural network is developed. The efficiency of the new method is substantiated by comparing the obtained numerical results with numerical approximation by finite differences and experimental data for particular cases. Full article