Numerical Simulation Test Research Articles

Waterproof Performance of Sealing Gasket in Shield Tunnel: A Review

Rubber gaskets are commonly adopted as the waterproof component in shield tunnels for their outstanding sealing performance. The contact pressure between surfaces generated by the assembly stress ensures that the gaskets resist certain water pressure without leaking. However, with the continuous occurrence of leakage accidents, attention has been drawn to the topic of the waterproof performance of gasketed joint shield tunnels. In this article, prominent contributions to the waterproof performance of sealing gasket in shield tunnels are listed and sorted into four sections: (1) structural behavior of lining and joint; (2) material constitutive model and durability; (3) numerical simulation methods; (4) thermal-mechanical coupling analysis. First, examples of leakage are discussed and tests on gaskets are elucidated, which is followed by a summary of the progress on material mechanical properties and durability. Then, the development of the simulation methods is presented. Finally, the existing research on the thermal-mechanical coupling analysis is summarized. It is found that the contributions to gaskets’ waterproof performance are fruitful, however, with stringent construction conditions, such as the material constitutive model and aging mechanism under special conditions, such as high temperature, numerical simulation, and laboratory test methods, which need to be further explored.

A method for quantitative damage identification in a high-piled wharf based on modal strain energy residual variability

Damage may occur in the pile foundations of high-pile wharfs due to the complex and diverse working conditions. To identify the damage in pile foundations in early stage is very important for the operation and maintenance on wharfs. Research on pile damage identification based on modal strain energy is one of the hot research topics. This study presents the concept of the modal strain energy residual variability using the characteristics of sensor placement and pile mode shapes of high-pile wharfs, which provide a simple, accurate and practical method to identify the damage in pile foundations of high-pile wharfs in early stage. The qualitative and quantitative relationships between the modal strain energy residual variability and element damage extent are deduced. This concept not only enhances the sensitivity of the modal strain energy to damage but also realizes the decoupling of damage element identification, which is easy to calculate in practical engineering. A damage identification method is constructed base on the concept, and the accuracy of the method is verified by a finite element numerical simulation and model test. A sensor placement method for engineering detection is studied by comparing the damage identification effect in different sampling intervals. The results show that this method can accurately locate a damage area and accurately identify the damage extent in numerical simulation and model test, which provides a new method for the practice of pile foundation damage identification of high-pile wharfs.

Protective Efficiency of Railway Arbor-Shrub Windbreak Forest Belts in Gobi Regions: Numerical Simulation and Wind Tunnel Tests

The railways in the Gobi area have serious sand hazards. To prevent these hazards and ensure operational safety, plant-based sand prevention is a fundamental measure for the prevention and control of railway wind-sand hazards. This study considers the protective windbreak forest belts along the Lan-Xin Railway, Northwest China as the study area and evaluates its protective benefits from the perspectives of windproof efficiency and sand control efficiency using numerical simulations and wind tunnel testing. Our results show that the disrupting effect of the three shelterbelt rows on the airflow was significantly enhanced, and the wind velocity profile began to change at 2H. As the airflow continued to move forward, the wind velocity profile gradually deviated from the logarithmic law, and an obvious turning point appeared at 13H behind the forest belt. Under different incoming wind velocities, the maximum wind protection efficiency of the three shelterbelt rows appeared at 5H on the leeward side. The maximum wind protection efficiencies in the numerical simulation were 95.1, 90.4, and 88.6%, respectively. The minimum value appeared at 15H on the leeward side, and the minimum wind protection efficiencies were 58.3, 53.1, and 47.1%, respectively. The maximum wind protection efficiencies in the tunnel test were 94.3, 90.1, and 86.5%, and the minimum value appeared at 15H on the leeward side. As the wind velocity increased, the efficiency of wind protection tended to decrease. The sand control efficiencies of the shelterbelt were 93.8, 91.6, and 88.1%, and as the wind velocity increased, the sand control efficiency continued to decrease. In general, the forest belt had a significant effect on reducing the sand flux density, especially below the forest belt height, which can effectively control the wind and sand disasters in some Gobi areas along the Lan-Xin Railway.

Design and Analysis of Decentralized Dynamic Sliding Mode Controller for TITO Process

In this paper, a decentralized dynamic sliding mode control (DySMC) strategy is applied to a multivariable level control system. The time derivative of the control input of the DySMC is considered a new control variable for an augmented system which is composed of the original system and the integrator. This DySMC can transfer discontinuous terms to the first-order derivative of the control input and effectively reduce the chattering. The interactions between input/output variables are a common phenomenon and a challenging task in the design of multi-loop controllers for interacting multivariable processes. For reducing the interaction among variables, ideal decouplers are used. Independent diagonal controllers are designed for each decoupled subsystem, which is reduced to the first-order plus dead-time (FOPDT) model. A numerical simulation test has been carried out on a reactor system of the Industrial-Scale Polymerization (ISP). Experimental tests are performed to check the efficacy of the proposed controller using a laboratory-level coupled tank system. A comparison of the proposed approach and sliding mode controller (SMC) is presented. Simulation and experiment results show that the DySMC approach reduces the chattering, and compensates for the effect of the external disturbances, and parametric uncertainties.

Research and application of Gob-Side entry retaining with roof presplitting under residual coal pillar of upper coal seam

In the mining of close coal seam, the stress concentration under the residual coal pillar in the upper coal seam leads to serious deformation to roadway surrounding rock in the lower coal seam. Hence, it poses a huge challenge to the maintenance of entry surrounding rock. Based on this, an approach of entry surrounding rock control technology, directional pre-splitting, and roof-cutting pressure relief, was applied. The stress and deformation of entry surrounding rock utilizing directional pre-splitting and roof-cutting pressure relief were studied by numerical simulation and field test The results indicated that the depth of stress concentration under the residual coal pillar achieve 44 m. With the application of the roof presplitting, the vertical stress of the entry roof decreased. Utilizing the roof presplitting with a height of 7 m and an angle of 15°, the gangue filled the goaf and supported the overlying strata. Meanwhile, the surrounding rock of entry was controlled with a constant resistance anchor cable (9 m length) and gangue prevention support structure. Through field test monitoring, the roof pressure and the deformation of surrounding rock increases rapidly at 30 ∼ 110 m behind the working face. From 110 ∼ 160 m, the increased rate of roof pressure and surrounding rock deformation gradually slows down and tends to be stable at 160 m behind the working face. The maximum displacement of the roof to the floor is 511 mm, and the maximum displacement of the gangue rock wall to coal wall is 421 mm. The remaining roadway meets the demand of the adjacent working face.

Active and Passive Earth Pressure Calculation Method for Double-Row Piles considering the Nonlinear Pile Deformation

The double-row pile supporting structure has been widely used in foundation pit excavations. When analyzing the effect of earth pressure on the pile structure, previous research only considered the double-row piles as the rigid body and the pile-soil interaction has not been examined. In this study, a theoretical model was developed based on Duncan-Chang’s hyperbolic theory to calculate earth pressures in the active and passive zones of the double-row pile supporting structure. The model considered the nonlinear effect of the pile deformation on the active and passive earth pressures. The macroscopic pile-soil interaction was converted into a microscopic stress-strain relationship at a certain point in the soil body, reflecting the nonlinear effect of pile deformation on earth pressure. Numerical simulation and large-scale field tests have been conducted to verify the proposed model. The results show that the average values of the parameters obtained by numerical simulation are a ¯ = 0.38 , b ¯ = − 0.253 for the active zone and a ¯ = 0.00612 , b ¯ = − 0.729 for the passive zone. Based on the values of a ¯ and b ¯ , the predicted active and passive earth pressures stemming from the developed model agreed well with those obtained from field tests. The developed model in this study can be used to predict the distribution of active and passive earth pressures for double-row pile supporting structures.

Improved virtual extensometer measurement method in complex multi-fracture situation

To overcome the limitation of the virtual extensometer method in measuring the crack opening displacement (COD) in the process of complex multi-crack propagation of rock, the measurement error of Digital Image Correlation (DIC) local deformation is theoretically analyzed. An improved virtual extensometer method for measuring the COD is proposed, which considers the temporal and spatial characteristics of crack development in the process of complex crack propagation. The accuracy of the proposed method is verified by the strain localization band numerical simulation test and indoor single crack simulation test. Furthermore, the method is applied to the two-dimensional similarity simulation test of simulating complex multi-fractures in rock stratum. The COD obtained by the traditional and improved methods is compared with the measured COD. The results show that in the case of multiple complex cracks, to obtain the COD accurately, the relative distance between the virtual extensometer measuring point and the crack should be greater than half of the sum of the width of the crack strain localization zone and the subset size. With the development of the crack, the relative distance between the virtual extensometer measuring point and the crack should increase with the increase of the width of the crack strain localization zone. The error of the COD measured by the traditional method increases with fracture development, and the maximum is 21.20%. The maximum relative error between the COD measured by the improved method and the measured crack opening is 3.61%. The research results improve the accuracy of the virtual extensometer in measuring the COD under complex multi-crack conditions.

Fidelity assessment of Real-Time Hybrid Substructuring based on convergence and extrapolation

High quality of products and quick development cycles require reliable verification of the products. An applicable method for component testing is Real-Time Hybrid Substructuring (RTHS), which is a cyber–physical testing method combining numerical simulation and experimental testing. For the broad application of such testing methods, confidence in the test results must be gained. For this purpose, fidelity measures are required to indicate to the user how trustworthy the results are. The fidelity of an RTHS test does not only depend on the amount of errors in the loop, but also on the dynamics of the reference system and the interface locations. Current assessment measures do either not consider these dynamics/partitioning or require a reference solution or need knowledge about the dynamics of all involved components. This work proposes a novel strategy for fidelity assessment that circumvents these shortcomings: Fidelity Assessment based on Convergence and Extrapolation (FACE). The main idea is to deliberately vary the amount of error in the RTHS loop and monitor how this changes the RTHS result. From this relation, system understanding can be gained that is used in a further step to estimate the dynamics of the reference solution (i.e., if there was no error in the loop). The proposed method is applied to two application examples. In the first example, which is a virtual RTHS test of a linear system, the true reference solution is available and the prediction capability of the FACE method is verified. The second example uses data from a real RTHS test. Both examples reveal that the FACE method captures the dynamics influence of an error on the RTHS result and therefore helps the user to decide whether the conducted test was successful. This method can therefore be a valuable tool to assist users in the application of RTHS to a large variety of systems.

Influence of residual stresses on the fatigue life of welded joints. Numerical simulation and experimental tests

Residual stresses constitute an inevitable consequence of the most ordinary manufacturing processes, leading to high and not easily foreseeable stress field within a component. Fatigue design codes typically address residual stresses by means of very conservative assumptions, which may results in poorly optimized designs and unexpected failures. Nowadays, the increasing motivation towards an optimized material application require a more reliable fatigue assessment of welded joints and residual stress evaluation. This study investigates the influence of residual stresses on the fatigue assessment of a S355JR structural steel pipe-to-plate welded joint subjected to fully-reversed torsional and bending loading. Influencing factors, such as geometric discontinuities and the material heterogeneous microstructure were considered through numerical modelling and microstructural analysis respectively. Firstly, an uncoupled thermal–structural finite element simulation was carried out to assess the complete residual stress field within the specimen generated by a gas metal arc welding process. Both thermal and structural simulations were developed to achieve an optimal trade-off between simulation time and results accuracy. Then, residual stresses were mapped and included as initial condition in numerical models intended for fatigue damage factors calculation. Fatigue analysis was conducted by means of the Fatemi–Socie critical plane factor and the hydrostatic stress as local damage parameters. Experimental results were then used to corroborate numerical models and verify their capability in assessing the fatigue endurance. Both the experimental data and the applied damage factors have shown an effect of residual stresses on the fatigue life of welded joints when torsional loading was applied. Data further agreed that no influence of residual stresses was detected in the case of bending loading.

Gust Alleviation and Wind Tunnel Test by Using Combined Feedforward Control and Feedback Control

Gust alleviation is of great significance for improving aircraft ride quality and reducing gust load. Using aircraft response (feedback control) and gust disturbance information (feedforward control) to improve the gust alleviation effect is worthy of attention. In this paper, a combined control system (CCS) composed of feedforward control system (FFCS) and feedback control system (FBCS) is designed and analyzed. At the same time, the gust alleviation effect of the CCS, the single FFCS and the single FBCS are analyzed and compared by means of numerical simulation and wind tunnel test, respectively. Taking a flexible wing as the research object, the gust alleviation effects of three control systems under different forms of gust excitation (1-cos discrete gust, sine gust and Dryden turbulence) are analyzed by numerical simulation. In the wind tunnel test, the sine gust generated by a gust generator was used, and the gust alleviation test was carried out under different wind speeds and gust frequencies. The simulation and experimental results show that the CCS has better gust alleviation performance for various gust excitations. When comparing FFCS and FBCS, the FFCS has better robustness and control effect than the FBCS. When comparing FFCS and CCS, the better the alleviation effect of FFCS, the more difficult it is to achieve significant effect improvement by using CCS, which is obtained by adding FBCS on the FFCS.

Effects of bionic blades inspired by the butterfly wing on the aerodynamic performance and noise of the axial flow fan used in air conditioner

The axial flow fan, as a key part of the outdoor unit of air conditioner, has an important impact on the performance of air conditioner. In order to reduce the power consumption and aerodynamic noise of the outdoor unit, the outer edge profile with a depression structure, inspired by the effective control of butterfly wings for airflow, is reconstructed and adopted in the design of bionic blades. The effects of bionic blades with four different depression depths on the aerodynamic performance of the outdoor unit are investigated numerically. It is found that when the depression depth is 1.9 mm, the aerodynamic performance of the outdoor unit is the best. For the axial flow fan with the optimal design blade, the numerical simulation and experimental test on the noise of the outdoor unit are carried out. Based on the experimental results, the shaft power of the outdoor unit is reduced by 1% and the noise is reduced by 1.3 dB when the bionic blade with the depression depth of 1.9 mm is adopted. Based on the numerical results, the flow characteristics of the axial flow fan with the bionic blades is analyzed and the noise reduction mechanism of the depression structure is revealed. The studied results show that the depression structure with proper depth at the outer edge of the blades effectively changed the development and trajectory of the tip leakage vortex, which has a positive influence on the aerodynamic performance improvement and noise reduction of the axial flow fan.

The shear behaviors of concrete-gypsum specimens containing double edge cracks under four-point loading conditions

In this investigation, the fracture behavior of concrete-gypsum samples consisting of edge joints (planer and echelon joints) under four-point bending tests has been investigated using numerical simulation and experimental testing. For this purpose, concrete and gypsum rectangular samples with a dimension of 30 cm * 15 cm * 5 cm have been prepared. These slabs have edge notches in their volume. The lengths of these notches vary by 2 cm in increments of 2 cm, from 2 cm to 6 cm. The slabs were attached with glue. This complex was tested and simulated numerically under four-point loading conditions. The results indicate that the crack growth trajectory is affected by the type of slab material. The strength of samples is controlled by notch length. Numerical simulation outputs are in good accordance with experimental test results.

Literature Review on the Discrete Element Method in Asphalt Mixtures

Asphalt mixtures are commonly used in pavement engineering, especially for highway construction. The mechanism exploration and analysis of pavement distress are the main challenges for researchers and industry managers. Thereby, it is important to understand their properties and interaction mechanisms in asphalt mixtures. It is difficult to conduct some sophisticated or microscale tests in the laboratory, and numerical simulation and virtual tests can be solutions for these cases with low costs. The Discrete Element Method (DEM) is a promising tool for researchers to undertake these tasks. This paper mainly summarized and analyzed the research progress and development prospect of DEMs in asphalt mixtures from a series of technical sections. The laboratory test results were often used to calibrate the DEM simulations as well as Two-dimensional (2D) and Three-dimensional (3D) modeling. Several modeling methods were developed to generate digital samples, like user-defined, image-based, random-modeling. In addition, the conclusions can be referenced by researchers for the development of numerical simulations.

Face stability of shield tunnels considering a kinematically admissible velocity field of soil arching

Existing mechanism of simulating soil movement at tunnel face is generally based on the translational or rotational velocity field, which is, to some extent, different from the real soil movement in the arching zone. Numerical simulations are carried out first to investigate the characteristics of the velocity distribution at tunnel face and above tunnel vault. Then a new kinematically admissible velocity field is proposed to improve the description of the soil movement according to the results of the numerical simulation. Based on the proposed velocity field, an improved failure mechanism is constructed adopting the spatial discretization technique, which takes into account soil arching effect and plastic deformation within soil mass. Finally, the critical face pressure and the proposed mechanism are compared with the results of the numerical simulation, existing analytical studies and experimental tests to verify the accuracy and improvement of the presented method. The proposed mechanism can serve as an alternative approach for the face stability analysis. • A proper velocity field is proposed to agree with soil movement in soil arch zone. • An improved failure mechanism is constructed based on spatial discretization. • Proposed mechanism provides a better upper bound solution of critical face pressure. • Proposed mechanism corresponds well with numerical simulation and experiment test.

An improved four-dimensional variation source term inversion model with observation error regularization

Aiming at the Four-Dimensional Variation source term inversion algorithm proposed earlier, the observation error regularization factor is introduced to improve the prediction accuracy of the diffusion model, and an improved Four-Dimensional Variation source term inversion algorithm with observation error regularization (OER-4DVAR STI model) is formed. Firstly, by constructing the inversion process and basic model of OER-4DVAR STI model, its basic principle and logical structure are studied. Secondly, the observation error regularization factor estimation method based on Bayesian optimization is proposed, and the error factor is separated and optimized by two parameters: error statistical time and deviation degree. Finally, the scientific, feasible and advanced nature of the OER-4DVAR STI model are verified by numerical simulation and tracer test data. The experimental results show that OER-4DVAR STI model can better reverse calculate the hazard source term information under the conditions of high atmospheric stability and flat underlying surface. Compared with the previous inversion algorithm, the source intensity estimation accuracy of OER-4DVAR STI model is improved by about 46.97%, and the source location estimation accuracy is improved by about 26.72%.

Increasing the Energy Density and Power Ratio of a Staggered VAWT Wind Farm by Using the Rotor's Diameter as a Reference

The development of wind energy systems has achieved a higher technology readiness level for Horizontal Axis Wind Turbine (HAWT). Unfortunately, the HAWT is only suitable for high wind speed areas. The Vertical Axis Wind Turbine (VAWT) is considered the ideal model to utilize wind energy in the low wind speed region. However, VAWT has a lower power coefficient. Therefore, developing a VAWT wind farm can improve the overall energy density for power generation in the low wind speed region. In this study, staggered configuration for three turbine clusters is evaluated through numerical simulation and experimental tests. The pitch distance is set by using the rotor's diameter as a reference for placing the 3rd rotor at the second row. The turbulence intensity in the area wake superposition is highly affected by the position of the 3rd rotor. The flow characteristic indicates that the 3D layout has a high concentration at the front area of the 3rd rotor. It leads to higher achievement of power ratio for the clusters. The overall power ratio for 3D layout can achieve more than 0.9, whereas, at a speed 3 m/s, the highest power ratio is obtained at 1.0. The finding in this study can be set as an essential reference for developing a VAWT wind farm with a specific arrangement and improving the overall power density of the turbine clusters.

Two-Step Geometry Design Method, Numerical Simulations and Experimental Studies of Bioresorbable Stents.

The stent-implantation process during angioplasty procedures usually involves clamping the stent onto a catheter to a size that allows delivery to the place inside the artery. Finding the right geometrical form of the stent to ensure good functionality in the open form and to enable the clamping process is one of the key elements in the stent-design process. In the first part of the work, an original two-step procedure for stent-geometry design was proposed. This was due to the necessary selection of a geometry that would provide adequate support to the blood-vessel wall without causing damage to the vessel. Numerical simulations of the crimping and deployment processes were performed to verify the method. At the end of this stage, the optimal stent was selected for further testing. In addition, numerical simulations of selected experimental tests (catheter-crimping process, compression process) were used to verify the obtained geometrical forms. The results of experimental tests on stents produced by the microinjection method are presented. The digital image correlation (DIC) method was used to compare the results of numerical simulation and experimental tests. The two-step modeling approach was found to help select the appropriate geometry of the expanded stent, which is an extremely important step in the design of the crimping process. In the part of the paper where the results obtained by numerical simulation were compared with those gained by experiment and using the DIC method, a good compatibility of the displacement results can be observed. For both longitudinal and transverse (pinch) stent compression, the results practically coincide. The paper presents also the application of the DIC method which significantly expands the research possibilities, allowing for a detailed inspection of the deformation state and, above all, verification of local dangerous areas. This approach significantly increases the possibility of assessing the quality of the stents.

Automated framework for monitoring building structures through derivation of lateral stiffness using marker-free vision-based displacement sensor

Vision-based displacement sensors (VDSs) are drawing attention as next-generation methods for monitoring buildings due to easy installation, however, there is a further need to develop integrated techniques both to obtain displacement at desired positions and to assess dynamic characteristics with high-precision. This study aimed to develop an automated framework to assess the dynamic characteristics of buildings through the derivation of lateral stiffness using a marker-free vision-based displacement sensor (MVDS). The MVDS utilizes image convex hull optimization to measure displacement at user-defined positions without ancillary markers. Then, the dynamic characteristics were estimated from eigenvalue analysis by reconstructing the equation of motion based on lateral stiffness derived through linear regression in load-displacement curves using the measured displacement data. From numerical simulation and shake table test, the results showed that the proposed framework enables monitoring of the dynamic characteristics where frequency domain exceeded the Nyquist frequency of the sensor compared to FFT-based analysis.

Aerodynamic noise control of rearview mirror by steady and unsteady jets

Aerodynamic noise control of rearview mirror by steady and unsteady jets was investigated by combining numerical simulation and wind tunnel test. The maximum reduction of total turbulent pressure level for isolated rearview mirror is 1.2 dB when the jet ratio is 0.23. Whether it is an isolated or vehicle rearview mirror, numerical simulations without jet have obtained consistent results with experiments. Eight unsteady jets are quickly evaluated by subdomain method, where the turbulent pressure and sound pressure of the front side window were obtained by large eddy simulation and acoustic perturbation equations. The jet velocity ratio of 0.23, the best noise reduction effect, in the experiment was adopted, and the jet frequency of 78 Hz and phase were obtained by spectral proper orthogonal decomposition and phase analysis. The simulation results show that three jets have better noise reduction effect and the best jet2 can reduce the total sound pressure level by 0.7 dB. Sound pressure level at the frequencies from 200 Hz to 2000 Hz becomes small, and the maximum magnitude is about 1.5 dB.

Determination of Reasonable Width of Filling Body for Gob-Side Entry Retaining in Mining Face with Large Cutting Height

When gob-side entry retaining is adopted in the mining face with large cutting height, due to large stope space, strong dynamic pressure, and other reasons, the filling body is usually broken and unstable due to improper width of filling body, and the stability of surrounding rock of a roadway is poor. Taking the actual project of Shaqu mine as the background, we analyze the stability factors of gob-side entry retaining with large mining height, and considering the lateral pressure and overlying load on the filling body, the mechanical model of a gob-side retaining roadway is established, the calculation method of the reserved width of the filling body is simplified, and the reasonable width of the filling body is obtained quantitatively. Through the monitoring results of numerical simulation and field test, the rationality of the calculation results of the reserved width of filling body is verified. The results show that if the width of the filling body is too small, it will not be able to bear the load of the overlying strata, resulting in the fragmentation of the filling body. The larger the width of the filling body, the greater the cutting resistance provided, which can reduce timely the stress on the roadway and above the filling body, and the more stable the retaining roadway is, but when the width increases to a certain value, the displacement of the surrounding rock of the roadway has changed little. When the width of the filling body is 4 m, the stability of gob-side entry retaining can be guaranteed.