Numerical Simulation Results Research Articles

The Impact of Different Excavation Support Structures on the Deformation and Stability of Adjacent Station and Tunnels

This study uses the finite element software Midas GTS NX (2019), combined with actual engineering projects, to establish numerical models and analyze the impact of different support types (pile-anchor support and double-row pile support) on the excavation of foundation pits near metro station tunnels. The results indicate that under both support methods, the vertical displacement of the tunnel is the greatest at the interface between the station and the tunnel, with greater vertical displacement occurring under double-row pile support. Under pile-anchor support, the horizontal displacement of the tunnel reaches its maximum value during the sixth excavation stage, while under double-row pile support, the horizontal displacement increases steadily, and the overall displacement is small. The horizontal displacement under pile-anchor support is significantly greater than that under double-row pile support. For the station, the maximum vertical displacement under pile-anchor support is smaller than that under double-row pile support. The horizontal displacement under pile-anchor support exhibits a linear change, while under double-row pile support, the displacement continuously increases from the end of the foundation pit farther from the excavation to the end closer to it. The model tests are consistent with the numerical simulation results, verifying the correctness of the numerical simulation. This study can provide references for relevant engineering projects to ensure the safety and stability of metro structures.

Multi-scale non-uniform hierarchical filtering model based on fractal theory.

Gasoline particulate filters (GPF) are widely used due to their superior environmental benefits, but its trapping efficiency is affected by many factors. We established a multi-scale non-uniform hierarchical filtering model (MNHF) based on the fractal theory to accurately analyze the dynamic changes of trapping efficiency during GPF operation. The multi-scale characteristics of the filter wall about trap diameter and pore size are presented. Additionally, filter theory and Brownian kinematics are used to precisely predict particle motion. The study focuses on the dynamic change of trapping efficiency of MNHF in different particle size ranges. The results indicate the following: By comparing the numerical simulation results of the model with experimental data, the maximum relative error range is found to be within 0.7%. The MNHF model accurately predicts the change in trapping performance at different times when particles move in the trap. The trapping efficiency of the upper layer of the single-layer trap is higher than that of the lower layer based on the particles' moving distance in unit time, and the trapping efficiency of the next layer is reduced by up to 29.34% compared to that of the upper layer. Additionally, it provides a more accurate simulation of the trapping efficiency for particles with sizes ranging from 0.01 μm to 0.5 μm under conditions of low wall flow velocity.

Detection of the Relationship Between the Inverse Variations of Sea Ice in the Okhotsk–Bering Sea During Spring and the 11‐Year Solar Cycle

ABSTRACTThe 11‐year solar cycle is a stable external forcing factor for the Earth system. However, its influence on decadal climate variability, including sea ice, remains uncertain. This study statistically analyses spring sea ice concentration (SIC) and annual sunspot numbers (SSNs) from 1960 to 2021, revealing a significant inverse correlation between the 11‐year solar activity cycle and spring sea ice variability in the Okhotsk Sea and Bering Sea. During solar maximum years, sea ice increases in the Okhotsk Sea while decreasing in the eastern Bering Sea. Further analysis shows that the spring sea ice concentration difference (SICD) index correlates closely with the preceding winter Pacific Meridional Mode (PMM) modulated by the 11‐year solar cycle. This suggests that solar activity may influence east–west sea ice variability in the North Pacific during spring through its impact on the winter PMM. Atmospheric circulation and numerical simulation results indicate that during high‐solar‐activity years in winter, changes in stratospheric ozone concentration lead to variations in stratospheric temperatures. This strengthens zonal westerlies in the subtropical stratosphere and troposphere. The propagation of planetary waves from the stratosphere to the mid‐ and high‐latitude troposphere converges over the Bering Sea, creating an easterly anomaly. This convergence stimulates a high pressure and a low pressure to its south, forming a pattern resembling the PMM in the North Pacific during winter. The sea surface temperature (SST) anomalies linked to the winter PMM persist into spring, influencing sea ice at high latitudes in the North Pacific and causing the observed inverse sea ice changes in the Okhotsk and Bering Seas. This study highlights the significant modulating effect of solar activity on sea ice variability, offering insights for understanding Arctic climate change and predicting sea ice changes.

The Effect of Contraction–Expansion Nozzle on High-Temperature Shock Tube Flow

To achieve higher enthalpy and pressure, the technique of variable cross-section drive is effectively combined with the heating of light gas to enhance the intensity of the incident shock wave. A study was conducted to predict the impact of variable cross-sections on the performance of high-temperature shock tube flow using a shock tube with a 2.6:1 diameter ratio between the driver and driven sections. The driver section was filled with a helium–argon gas mixture (mass ratio of 1:9), while the driven section contained dry air. Under total pressure conditions of 14.5 MPa and total temperature of 3404 K, as well as total pressure of 45 MPa and total temperature of 4845 K in the driver section, corresponding to driven section pressures of 10 kPa and 80 kPa, the results of chemical non-equilibrium numerical simulations were compared to experimental measurements of the incident shock Mach number and total pressure. The results indicated the following: First, after adding the contraction–expansion nozzle, the incident shock accelerated through the contraction section and reflected within the contraction section. Strong oscillations occurred during the flow, with increasing intensity as the throat size decreased. Second, without the nozzle, the shock velocity increased and then decreased. However, with the nozzle, the Mach number was highest near the nozzle exit and gradually decreased thereafter. Third, the presence of the nozzle led to the formation of a distinct fan-shaped wavefront, accompanied by significant variations in flow variables such as pressure, temperature, and Mach number in the region. This phenomenon was attributed to the interaction between the shock wave and the nozzle geometry, which altered the flow dynamics. Finally, as the throat size decreased, the intensity of the incident shock also decreased. After reflecting at the end of the shock tube, the total pressure in the driven section also decreased. The numerical simulations employed a multi-component, multi-temperature chemical non-equilibrium model, validated against experimental data, to accurately capture the complex flow behavior and wave interactions within the shock tube.

Detecting the droplet and bubble in the oil-gas-water three-phase medium via ultrasonic A-scan signal-assisted B-mode imaging method

Abstract Accurately detecting the parameters of bubbles and droplets in the oil-gas-water three-phase medium is essential to critical decision-making about industrial production. An ultrasonic A-scan signal-assisted B-mode imaging (AS-assisted-BI) method that combines a B-mode imaging (BI) method and an A-scan signal (AS) method is developed to simultaneously visualize the oil-gas-water three-phase medium, distinguish the gas bubble and oil droplet, and measure the parameters about their sizes and locations. The applicability of the plane wave imaging (PWI) method for visualizing the oil-gas-water three-phase medium with less computational cost was confirmed. Then, the influence of the bubble and droplet characteristics, such as acoustic impedance difference, size, and location, upon the ultrasonic propagation mechanism are studied to understand the B-mode image and A-scan signal as the design basis of the BI and AS method. The BI method locates the least key points from the B-mode image based on the PWI method compared with the conventional industrial B-mode image method. The AS method automatically locates the key point from the A-scan signal rather than manually marking it in the previous study. Two options for the AS-assisted-BI method, suitable for different detection requirements and applications, have been designed. The numerical simulation and experimental results demonstrated that the proposed method received excellent precision, robustness, and efficiency for detecting the acoustic impedance difference between the bubble and droplet, the longitudinal location of the bubble front surface, and the droplet’s size and center location.

Dike flow and heat transfer with geomembrane defects: experiment and simulation

The damage of geomembranes in dikes can result in leakage. In order to investigate the efficacy of heat tracing in the detection of geomembrane defects, a series of laboratory experiments were conducted utilising a self-made 2D sand trough and temperature sensors. The heat tracing response of geomembrane defects was evaluated. The findings indicate that the temperature distribution within the dike, resulting from geomembrane defects, exhibits a comparable spatial-temporal pattern to that of the seepage field. Furthermore, the heat tracing response is discernible. A flow-heat coupling model (FHCM) was constructed based on the heat transfer theory of porous media and the saturated-unsaturated seepage theory. The accuracy of the FHCM was tested by combining the laboratory experiment results. The The numerical simulation results show that the superposition of multiple geomembrane defects results in an acceleration of leakage. In order to reduce the amount of debugging work required for model parameters, the Morris method was employed to analyse the global sensitivity of six parameters within the FHCM. It was determined that the parameter exhibiting the greatest sensitivity is hydraulic conductivity. This work provides a reference for the wide application of heat tracing technique.

Research on the static and dynamic characteristics of porous air bearings considering annular groove air supply

Abstract The paper examines the dynamic characteristics of porous air bearings in the critical pneumatic hammer state (the transition state from the steady state to the pneumatic hammer state). The dynamic characteristics mainly include the critical load (film load capacity) and the critical frequency (vibration frequency) of the bearings. This study presents two fluid domain models: the first model depicts flow channels with annular grooves for air supply (annular grooved model), while the second model does not include annular grooves (non-grooved model). The effects of bearing permeability and air supply pressure are analyzed. Numerical simulation results show that the critical loads and the critical frequencies in the annular grooved model are quite different from those in the non-grooved model. When the permeability is 1.33×10−14 m2 and the supply pressures are 400kPa, 450kPa and 500kPa, the critical loads in the annular groove model are 54.5N, 48.9N and 45.9N, while the critical loads in the non-grooved model are 42N, 52.5N and 68N. Reducing the permeability of the air bearing significantly increases the critical load and the critical frequency. Finally, an experimental facility is set up to investigate the critical load and the critical frequency of the air bearings. The critical loads in the experiment are 59.1N, 52.5N and 49.3N. The fluid domain model and solution method's accuracy has been confirmed. The simulation results of the annular grooved model are closer to the experimental results.

Tunable nonlinear absorption properties of Ti3C2Tx MXene for all-optical bipolar modulation applications

The demand for ultrafast and multifunctional all-optical modulators based on two-dimensional nonlinear optical materials is continuously growing in the era of big data and artificial intelligence. Herein, we report the experimental realization of the first, to the best of our knowledge, all-optical bipolar modulator that is based on pump intensity-dependent nonlinear absorption of Ti3C2T x MXene. This tunable nonlinear absorption with a conversion threshold of approximately 65 GW/cm2 is characterized and analyzed by the Z-scan technology, and Ti3C2T x MXene shows a stronger nonlinear absorption coefficient of 102 cm/GW than most of two-dimensional materials. According to the proposed four-energy-level model, the numerical simulation results suggest that the tunable nonlinear absorption transition is from the interplay between the absorption cross section ratios of the first and second excited states relative to the ground state. Inspired by this, the all-optical bipolar modulation with a nanosecond-level response time is demonstrated by changing the pump intensity. This work opens up exciting possibilities for the design of innovative multifunctional all-optical modulation devices based on two-dimensional nonlinear media.

Migration and Transformation of Nitrogen in Clay-Rich Soil Under Shallow Groundwater Depth: In Situ Experiment and Numerical Simulation

Excessive use of nitrogen fertilizer in agricultural activities can easily induce nitrogen pollution in groundwater, which may deteriorate groundwater quality. Generally, nitrogen fertilizer passes through the unsaturated zone to groundwater. Therefore, it is of great significance to investigate the migration and transformation of nitrogen pollutants in unsaturated zones for the prevention and control of groundwater nitrogen pollution. Clay-rich soil is often considered a barrier layer to prevent pollutant leakage because of its lower relative permeability, while its prevention capacity is seldom reported under shallow groundwater table conditions. Motivated by this, an in situ experiment and numerical simulation were conducted to investigate the migration and transformation of nitrogen fertilizer in a clay-unsaturated zone with a shallow groundwater table. Systematic measurements and numerical simulation results revealed that nitrogen can pollute groundwater via the infiltration through clay-rich soil in the in situ experiment site. This finding clarified that the difference in hydraulic head under the shallow groundwater table, rather than soil permeability, is the dominant factor in controlling the downward migration of nitrogen pollutants in the clay-unsaturated zone. More importantly, the nitrogen migration is convection dominant during precipitation in this experiment, indicating nitrogen polluted groundwater much faster in humid climate areas. These findings suggest that nitrogen contaminates groundwater easily under shallow groundwater tables in humid climate areas, even with clay-rich soil texture.

Study on Bending Performance of High-Ductility Composite Slab Floor with Composite Ribs

In order to solve the problems of high production cost and complex control of the inverted arch of an unsupported prestressed concrete composite slab, a flange truss high-ductility concrete composite slab floor is proposed to change the structure and pouring material to meet the requirements of no support during construction. The crack distribution and bending performance of the flange truss high-ductile concrete composite slab floor (CRHDCS) under different structures are clarified through the test and numerical analysis of four different rib plate structure floors. According to the analysis results, the calculation formulas of the cracking moment and short-term stiffness before cracking are modified, and the equivalent short-term stiffness formula of a single web member of the “V” truss to this kind of bottom plate is established. The results show that, unlike the short-term stiffness-change law of typical concrete composite slabs after cracking, the short-term stiffness of the designed bottom plate in this paper includes a short-term increase stage. The numerical simulation results are the same as the experimental ones; the maximum error is 10%. The maximum errors between the modified cracking moment and the short-term stiffness calculation formula are 6% and 8%, respectively. The influence rates of removing flange plate, truss-inverted binding, and adding rib plate on the cracking bending moment of foundation structure are −81.5%, 11.0%, and 22.2% respectively, and the influence rates on short-term stiffness are −87.6%, −1.5%, and 37.5% respectively.

Transversal vibration of a multi-span axially moving beam with multiple elastic supports

Using the transfer matrix method for multibody systems (MSTMM), this paper presents a dynamical model of a multi-span axially moving system with multiple elastic supports under different boundary conditions. The complex transfer matrices of an axially moving beam and a spring-damping supporting element are derived. According to the system topology, the overall transfer equation is acquired for vibration characteristic analysis. However, when dealing with multi-span systems that involve a large number of components, numerical instability may arise due to the instability of the corresponding boundary value problems. To address this issue, the reduced complex transfer matrix method (RCTMM) is developed. The state vector is artificially partitioned corresponding to the boundary condition of the system input. Numerical simulation results show that the developed method has the same computational accuracy as the MSTMM. More importantly, the RCTMM exhibits superior numerical stability, as indicated by the condition numbers of the system transfer matrix. It will provide an efficient tool for the design of mechanical multi-span axially moving systems.

Bimodal Photothermal-driven Self-sustained Oscillator Based on MXene Structure

Soft robots capable of autonomous, continuous, fast, and adjustable motion speeds under constant external stimuli have great potential in environmental, industrial, military, and medical fields. Aiming at the difficulties of existing self-oscillators, including small oscillation range, difficulty of achieving non-reciprocal motion, and the slow forward speed of the resulting self-sustained soft robots. In this paper, a sunlight-driven self-oscillator based on MXene is prepared. By employing a bimorph structure and thermal regulation process, the self-oscillator exhibits two distinct oscillation modes: 'elastic' and 'plastic' deformation. These modes can be modulated within the same film by varying the light power. A broader amplitude range (3.6-302.3°, 3.3 times that of the existing studies) is achieved by attaching a load to the film's end to enhance the inertial force of movement. Non-reciprocal motion in both modes and stable oscillations in sunlight are achieved. Finally, a light-driven sailboat model is developed. The sailboat can achieve autonomous light-forward motion with a speed of up to 12.8 body length per minute (2.1 times that of existing studies), with its propulsion mechanism further explained through numerical simulation results. This research provides new strategies for constructing fast and large-amplitude self-oscillators and demonstrates the potential for applications in speed-adjustable autonomous forward devices.

Visualizing kinetics of diffusional penetration in tissues using OCT-based strain imaging.

We report a new application of the recently developed technique, Optical Coherence Elastography (OCE) to quantitatively visualize kinetics of osmotic strains due to diffusive penetration of various osmotically active solutions into biological tissues. The magnitude of osmotic strains may range from fractions of one per cent to tens per cent. The visualized spatio-tempotal dynamics of the strains reflect the rates of osmotic dehydration and diffusional penetration of the active solute, which can be controlled by concentration of the solution components. Main features of the OCE-visualized diffusion-front dynamics well agree with Fick's theory yielding diffusivity coefficients consistent with the literature data. The OCE technique may be used to study diffusion of a broad variety of osmotically-active substances - drugs, cosmetic agents, preservative solutions, so-called optical clearing agents enhancing the depth of optical visualization, etc. The corresponding experimental examples, some results of theoretical interpretations and numerical simulations are given.

Active control of cavity buffeting noise using a DBD plasma model based on interval uncertainty correction

This study established a corrected system for a dielectric barrier discharge plasma actuator (DBD-PA) model and applied the corrected plasma model in research on the control of vehicle buffeting noise. Firstly, experiments on static ion wind characteristics under different excitation voltages were conducted, and the spatial distribution of the body force vector field during actuator operation was estimated. Subsequently, on the basis of experimental index parameters, an interval uncertainty multi-objective optimization (IUMOO) algorithm was used to reconstruct the expression of charge density and the action area boundary of the core electric field force, making them consistent with experimental results. A DBD-PA was arranged upstream of the cavity opening in the reverse direction, and experimental and numerical simulation results showed that noise reduction by this control scheme exceeded 3.67 dB at the characteristic wind speed. Finally, on the basis of the corrected plasma model, the correlation between vortex impact and pressure feedback in the buffeting phenomenon was analysed, and the influence of shear layer dynamic flow parameters on cavity buffeting noise was quantified. Results indicate that the DBD-PA acts to control the flow evolution of vortex cores and pressure clusters, suppress vortex reconnection, and weaken the intensity of vortex impact, thereby reducing wind buffeting noise.

Research on the influence of turbulence models on numerical simulation results of cross wavy heat exchanger channels

At present, for the numerical simulation of heat transfer and flow in cross wavy channels, scholars have no unified understanding on the prediction results of different turbulence models. Using inappropriate turbulence models will lead to inaccurate results. In order to solve this problem, this paper studies the prediction accuracy on the overall performance and internal flow field based on the different turbulence models. The research finds that the Low Reynolds number k-ε model is not accurate in predicting the overall thermodynamic characteristics of the laminar range, and the maximum error of Nu is 15.54 %. In order to obtain information about the internal flow field, a water circulation optical measurement experiment bench is constructed in this research. The experimental results show that the errors between the experimental results and the internal flow field prediction results of the Laminar model and the SST k-ω model are between 3.10 % and 5.21 %. However, the maximum error of RNG k-ε model is 26.20 %. This shows that the Laminar model and SST k-ω model have good calculation accuracy in the Reynolds number range studied in this paper, which provides a reference for scholars to the numerical simulation study of cross wavy channels.

High-Pressure Hydrogen Charge Check-Valve Energy Loss-Based Correlation Analysis Affecting Internal Flow Characterizations

In this study, we analyzed changes in flow characteristics and energy-dissipation characteristics due to changes in hydrogen temperature and inlet/outlet differential pressure in a check valve, which affect the storage safety and reliability of high-pressure hydrogen refueling systems. The effects of flow separation and recirculation flow generation at the back end of the valve were investigated, and the pressure, flow rate, pressure coefficient, and energy dissipation at the core part (where the hydrogen inflow is blocked) and the outlet part (where the hydrogen is discharged) were numerically analyzed. The hydrogen-inlet temperature (Tin) was selected as 233 K, 293 K, and 363 K, and the differential pressure (∆P) was selected in the range of 2 to 10 MPa in 2 MPa steps. To ensure the reliability of the numerical results, mesh dependence was performed, and the effect of the mesh geometry on the results was less than 2%. The numerical simulation results showed that the hydrogen introduced into the core part is discharged into the discharge part, and the pressure decreases by up to 6% and the velocity increases by up to 16% at the 95 mm position of the L-shaped curved tube. In addition, for the hydrogen-inlet temperature of 233 K in the L-shaped curved tube, the flow velocity decreases by up to 60% and the pressure coefficient increases at the 2.3 mm point in the Y-axis direction, indicating that the main flow area is biased towards the bottom of the valve due to the constriction of the veins caused by flow separation. The TDR results showed that the hydrogen discharge to the discharge region increased by 96% at 95 mm compared to 90 mm, and the turbulent kinetic energy of the hydrogen was dissipated, resulting in a temperature increase of up to 4.5 K. The exergy destruction was maximized in the core region where flow separation occurs, indicating that the pressure, velocity, and TDR changes due to flow separation and recombination have a significant impact on the energy loss of the flow in the check valve.

Simulation and experimental study of single axis load of resin-based concrete at macro-micro scale

ABSTRACT This study focuses on resin-based concrete, a novel composite material in which resin replaces the traditional cementitious binder, forming a three-phase composite consisting of aggregate, resin matrix, and interfacial transition zones. Four random aggregate models were generated using the Monte Carlo method and their stability was verified. Subsequently, a two-dimensional micro-model was established, and the simulation results were compared with experimental data, yielding a maximum error of 8%, which validated the feasibility of the model. The findings indicate that circular aggregates exhibit lower load-bearing capacity, while irregular aggregates demonstrate higher capacity. Although the peak compressive strength is similar among different aggregate shapes, the crack propagation paths vary significantly. The load-bearing capacity of resin-based concrete increases with aggregate content up to an optimal value of approximately 80%, beyond which it decreases. At this optimal content, crack paths transition from branched to near-linear. In terms of aggregate grading, higher coarse aggregate proportions enhance load-bearing capacity and promote linear crack propagation, whereas higher fine aggregate proportions reduce capacity and result in multiple irregular crack paths. Finally, the numerical simulation results were used to guide macroscopic experiments, and orthogonal experiments were conducted to determine the optimal mixture proportions of different resin binders.

Generation of high squeezing for atomic ground states via cavity-assisted non-resonant Raman transition

Spin squeezing state is a critical physical resource for the realization of high-precision metrology. Here, using two ground states of atoms as pseudo spin degrees of freedom, we propose a simple scheme to create high squeezing via cavity-assisted non-resonant Raman transition. The numerical simulation results show that our scheme can achieve the same optimum squeezing and has the same advantages as the conventional two-axis counter twisting model. The scheme is robust against system dissipation and provides a feasible approach for the realization of Heisenberg limit squeezing within the reach of current experimental technologies.

Ultra‐Broadband Polarization‐Independent Terahertz Absorber Based on All‐Dielectric GaN Metamaterials

In this article, an ultra‐wideband wide‐angle absorber based on all dielectric gallium arsenide (GaN) is proposed. The proposed absorber comprises a all dielectric square GaN structure and a GaN substrate. Numerical simulation results demonstrate that the proposed absorber achieves over 90% ultra‐wideband absorption in the range of 0.26–1.7 THz, with a relative bandwidth of 146.9%. The ultra‐broadband absorption property of the proposed absorber is further validated by an equivalent circuit model, which agrees well with the full‐wave numerical simulation results obtained using the finite element method. The simulated electromagnetic field distribution indicates that ultra‐wideband absorption primarily originates from the excitation of Fabry–Perot interference modes and electromagnetic resonance. The proposed absorber exhibits wide‐angle incidence properties and polarization insensitivity in both transverse electric and transverse magnetic modes. Thus, the proposed GaN ultra‐wideband terahertz absorber holds significant potential for applications in fields such as imaging technology and biomedicine.

Transient dynamic analysis of cutter-head loads: effects of different cutter spacings during excavation

As a critical component in achieving the rock-breaking function during the operation of Tunnel Boring Machines (TBM), the cutterhead inevitably generates significant vibrations during the rock-breaking process. These vibrations can lead to localized damage to the cutterhead and cause the abnormal failure of key components, which, in turn, may compromise the overall tunneling efficiency of the machine. This study investigates the load and vibration characteristics of the cutterhead during the rock-breaking process, employing large-scale physical model experiments conducted at varying cutter spacings. Real-time acceleration data from the cutterhead can be obtained through the monitoring system integrated into the TBM (Tunnel Boring Machine) experimental platform. The whole time-domain curves are stepped and periodic, as demonstrated by the test results. During excavation, the monitoring curves vibrate suddenly if the cutter-head becomes stuck or if rocks begin to fracture. The cutter-head primarily exhibits vibrations in the 0∼3 Hz range, characteristic of low-frequency oscillations. To obtain the real-time mechanical properties of the cutter-head, transient dynamic analysis was employed, utilizing the collected data as driving parameters. According to numerical simulation results, the vibration pattern during excavation is the superposition of random vibrations generated by rock breaking and the unloading of the tunnel face. Moreover, it is important to monitor the wear of the edge cutters throughout the boring operation in real-world construction scenarios. To prevent and control cutterhead vibration, it is recommended that the cutter spacing be as small as possible during the tunneling process. At a smaller tool spacing, the cutterhead will exhibit higher structural integrity, which may lead to a delay in the response of mechanical vibration. The conclusions presented offer valuable insights for the study of the mechanical properties and stability design of TBM cutterheads.