最新刊期
卷 55 ， 期 5 ， 2023
- 摘要：The deformation of the isolated structure is mostly concentrated in the isolation layer due to its low stiffness. Isolation bearings commonly meet the requirement of a large deformation well under strong earthquakes. However, it is difficult for the bearings to recover to their initial state after such large deformation under some earthquakes. Significant residual deformations of base isolators may disrupt structural serviceability and reduce the capability of base isolators to withstand immediate aftershocks and future earthquakes. In addition, it is difficult to repair and return to the original position after the earthquakes. For this reason, the provisions of the current design codes on the restoring capability of the isolation bearing were investigated. By combining the super-elastic behavior of the shape memory alloy (SMA) and lead rubber bearing (LRB), a novel self-centering isolation bearing (SMA–LRB) was proposed. The mechanical behaviors of traditional LRB and SMA–LRB were compared through compression-shear cyclic loading tests. Nonlinear time-history analyses of the single-degree-of-freedom isolated systems designed according to different code requirements and the SMA–LRB system were carried out. The results show that SMA–LRB exhibits excellent self-centering capability. Considerable residual deformation of LRBs may be observed even though the traditional LRBs can meet the code requirements. However, the residual deformation is not directly related to the maximum deformation of the isolation layer, which may be more prone to residual deformation under moderate earthquakes (such as design-based earthquakes). By contrast, the SMA–LRB isolation system exhibits excellent self-centering capability.关键词：seismically isolated structure;lead rubber bearing;self-centering;shape memory alloy;residual deformation;normal functionality
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发布时间：2024-01-10 - 摘要：The inerter system can control multiple performance objectives of the structures, but the existing inerter-based structural design methods mainly focus on a single performance indicator. To meet the safety and functional requirements of structures, a compound multi-objective targeted control design method for inerter-based seismic mitigation structures combined with nonlinear viscous damping elements was proposed. The method aims at both displacement and acceleration control indices, e.g. the inter-story drift angle and the absolute acceleration. To determine the parameters of the inerter system and the installation position of the inerter, the principle of master degree of freedom and analytical design formulas are utilized. In this method, the relative deformation at the installation location is considered as the master degree-of-freedom, and the shape of the targeted control mode is considered as a structural deformation shape. By transforming the complex original structure into a master oscillator structure with the inerter, the parameters can be easily determined based on the use of closed-form design formulae. A standard model is taken as an example to demonstrate the applicability of the proposed method. Nonlinear damping elements are used in the inerter system, and the influence of the support stiffness on the mitigation performance is considered. The results show that this method can satisfy the performance indicators of inter-story drift and floor absolute acceleration with smaller inerter system design parameters. The structural safety and normal use function requirements are met, which comply with the latest codes and standards. This multi-objective performance control strategy is expected to provide powerful guidance for practical engineering structure design.关键词：inerter;compound targeted control;multi-objective control;functionality
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发布时间：2024-01-10 - 摘要：Traditional Chinese pavilion-type timber structure consists of a column base layer, column frame layer, paving layer and roof truss layer, of which the response of each layer under seismic waves indicates that the pavilion-type timber frame is a highly non-linear structural system, which contains a wealth of seismic mitigation and isolation mechanism. The seismic mechanism of the overall pavilion-type timber frame is sophisticated and the coordinated working mechanism, dynamic and energy dissipation performance have not been fully revealed. To investigate the dynamic and energy dissipation performance of the pavilion-type timber frame, a shaking table test of a 1/16 scaled simplified Guanyin Pavilion timber frame was carried out based on the previous study. Three seismic waves were scaled down and adjusted for peak ground acceleration (PGA) to analyze the dynamic response of the timber frame under unidirectional seismic excitation. The test results show that the response of the timber frame is little with little input acceleration, and the structural response, such as column rocking, column base sliding and column base uplifting occur with large input acceleration. The inter-story drift is mainly provided by the column frame layer, the inter-story displacement of the column frame layer decreases and the inter-story displacement of the paving layer increases as the PGA increases. Based on the displacement and acceleration responses of the specimen, the hysteresis characteristics of the timber frame are analyzed. Hysteretic curves of the timber frame present large initial stiffness before column rocking, as well as small positive second-stiffness after column rocking and negative stiffness when column base uplifting occurs. At the same time, the cumulative energy dissipation and energy dissipation proportion of each part of the specimen under different seismic excitations are analyzed. With an increasing PGA, the column base sliding becomes the main energy dissipation mode, and the greater the PGA, the more energy dissipation proportion of the column rocking of the column frame layer and the less energy dissipation proportion of the paving layer are.关键词：pavilion-type timber frame;shaking table test;column base uplifting;hysteretic curve;cumulative energy dissipation
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发布时间：2024-01-10 - 摘要：Freestanding cultural relics (FCR) often suffer serious damage in earthquakes. Seismic isolation technology is an effective means to protect the safety of FCR. In this study, a modular metal seismic isolation bearing (MMSIB) was proposed. The effectiveness of MMSIB was verified by conducting a shaking table test of a freestanding vase. The MMSIB was composed of mental plates, linear guides and sliders, springs, and friction dampers. The MMSIB was able to decouple the horizontal seismic action with a feature of the double-layer bidirectional arrangement. Linear guide rails were used to restrict movement direction and to prevent overturning of MMSIB; springs were used to adjust the horizontal stiffness of MMSIB, and to provide self-centering ability through pre-tension; friction dampers were used to control horizontal deformations of MMSIB with adjustable energy dissipation ability. The MMSIB was modularly assembled so the numbers and locations of springs and friction dampers were adjustable according to design demand. The results show that MMSIB exhibits excellent seismic isolation performance. The acceleration response at the top of MMSIB can be reduced to 28.10%～78.01% of that of the shaking table. The seismic isolation effect of MMSIB is relevant to peak ground acceleration (PGA), the larger the PGA, the better the acceleration reduction. The actual residual deformation of MMSIB is less than the reference value ignoring the input ground motion types and earthquake intensities. Residual displacements can be controlled by adjusting the parameters of friction dampers and springs. The sliding and overturning of FCR are consistent with the theoretical calculations. The MMSIB can prevent cultural relics from overturning under seismic excitations. Nevertheless, traditional seismic measures are still necessary to improve the anti-overturning ability of FCR. In the design of MMSIB for small cultural relics, the reduction ratio of acceleration, demand of bearing displacement, limitation of bearing deformation, self-centering ability, etc., should be fully considered. These targets are sometimes difficult to meet at the same time, trade-offs are needed.关键词：freestanding cultural relics;modular metal seismic isolation bearing;shaking table tests;overturning;slip;self-centering
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发布时间：2024-01-10 - 摘要：The stability control of the unrestrained connecting segment of buckling-restrained braces (BRB) is key to the energy dissipation behavior. Based on the failure modes and failure characteristics of BRB observed in the previous research, the failure process and failure mechanism of the unrestrained connecting segment were analyzed, and the factors influencing the buckling failure under different failure modes were studied to improve the end configurations of connecting segment and enhance the stability behavior. Then the calculation formulas for axial force and bending moment on the control section of the outer constrained sleeve and unrestrained connecting segment under different failure modes were derived based on theoretic analysis, and the stability analysis model of the unrestrained connecting segment was established. According to the proposed end configurations and stability analysis model, BRB specimens were designed and tested through quasi-static tests to verify the reasonability of the end configurations and the effectiveness of the stability analysis model. The results demonstrated that the instability failure of the unrestrained connecting segment was caused by the fact that the compression-bending effect on the control section of the restraint element or the unrestrained connecting segment exceeded its ultimate capacity. The stability of the unrestrained connecting segment was closely related to the end rotation of BRB, which was directly caused by the high-order multi-wave buckling deformation of the BRB core plate. Under the condition that the stability design criteria were satisfied, reducing the length of the unrestrained connecting segment and the gap between core steel and outer constrained sleeve, or enlarging the restrained transition segment could improve the stability behavior. Moreover, no stability failure was found in the BRBs designed by the proposed method, and the stress caused by the compression-bending effect on the control section of the unrestrained connecting segment was in the elastic range. The results obtained in this paper could provide a theoretical reference for the stability design and stability control of the unrestrained connecting segment of BRB.关键词：buckling-restrained brace;extended connection segment;instability failure;quasi-static test
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发布时间：2024-01-10
SEISMIC ISOLATION AND ENERGY DISSIPATION FOR ENGINEERING STRUCTURES
- 摘要：Calibration of micro parameters of particles based on the mechanical properties of rock and soil mass is essential to solve various geotechnical problems by using the granular discrete element method. If the strength reduction method is employed in the granular discrete element method to assess slope stability, the shear strength of rock and soil mass will be continuously adjusted according to the reduction factor, and then, micro parameters of particles should be constantly calibrated. In this case, the trial-and-error method is cumbersome and time-consuming. To solve the issue, take MatDEM as an example, an overdetermined BP neural network was built by setting micro parameters of particles as input and the shear strength of rock and soil mass as output. A technique was developed to carry out biaxial compression numerical tests in parallel. Then, a reverse-iterative-correct strategy was proposed to calibrate micro parameters of particles for a prescribed value of shear strength, by executing the “reversely determination—error check—sample correction” process repeatedly. Results of numerical tests verified that the new strategy apparently had a higher precision than the underdetermined BP neural network by taking the shear strength as input and micro parameters as output. Micro parameters obtained by the new strategy had a remarkable level of compliance with the specified shear strength, and the relative error between the prescribed values and the numerical test results was less than one percent. Two exam problems, a homogeneous soil slope and a rockfill dam, suggested by ACADS are adopted to verify the ability of the proposed strategy in slope stability analysis based on the strength reduction method. Results showed that the new strategy satisfied the calibration requirement on micro parameters of particles when executing the strength reduction method in MatDEM and the resulting safe factors agree with the safe factors recommended by ACADS. The proposed strategy provides a reliable approach for MatDEM and other granular discrete element software to calibrate micro parameters when assessing slope stability by the strength reduction method.关键词：granular discrete element method;strength reduction method;micro parameters;BP neural network;MatDEM
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发布时间：2024-01-10 - 摘要：To investigate the post-fire residual capacity and failure mode of the concrete beam-slab specimens, the mechanical tests of three fire-damaged specimens and two reference specimens were conducted. The cracks, failure modes, deflections, and concrete and steel strains were observed during each test. Based on the conventional yield line method, the stiffness and deflection of the beam were considered to establish the theoretical method, and the residual ultimate load and failure modes of the specimens can be analyzed, and the predicted results were compared to the experimental results. Results showed that different mechanisms of the reference and fire-damaged specimens led to different failure modes, including the first-panel failure and the first beam failure. In addition, due to the post-fire spalling, the concrete cover of the fire-damaged panel fell off, and its effective thickness and bond strength degraded. Thus, apart from the flexural failure, the punching failure mode of the fire-damaged specimen also occurred. Compared to the reinforcement layout, the reinforcement ratio had a considerable effect on the ultimate loads of the beam-slab specimens, increasing the reinforcement ratio of the panel led to its higher carrying capacity and the brittle failure easily appeared. The conventional simply supported and fixed yield line method tended to underestimate or overestimate the ultimate loads of the specimens. For the present method, the effect of the edge beam’s stiffness and the vertical deflection was considered, and thus it could reasonably predict the ultimate loads, the failure mode and the reinforcement or repair method of the fire-damaged beam-slab specimens.关键词：concrete floor slab;failure mode;residual carrying capacity;flexural stiffness;torsional stiffness
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发布时间：2024-01-10 - 摘要：To explore both static and seismic performances of stainless steel beam-to-column minor-axis joints, a total of four minor-axis joints with end-plate connections were designed and fabricated, involving two austenitic stainless steel joint specimens and two duplex stainless steel counterparts. All specimens were reinforced with the box panel zone. Both monotonic and cyclic loading were applied to joints, respectively, and the structural behavior of joints and the characteristics of the local zone were obtained, including failure modes, load-displacement curves, and bolt force development of joints under both static and cyclic loading. The stiffness and strength deterioration and energy dissipation capacity of joints under cyclic loading were also acquired. The test results indicated that the butt welds between the skin plate and the column flange of tested joints subject to both static and cyclic loading experienced fracture failure. The initial stiffness of austenitic stainless steel joint specimens was close to 90% of that of duplex ones, and the plastic resistance of austenitic joints was about 60%～70% of that of the latter. Hysteresis curves of joints under cyclic loading were relatively plump without a noticeable pinching phenomenon, and the degradation of stiffness and strength was observed. The energy dissipation capacity of an austenitic stainless steel joint was about three times that of a duplex stainless steel counterpart. Higher quality control of the welds was needed for beam-to-column minor-axis joints with box panel zone, and the development of the excellent ductility of stainless steels was undermined by the premature fracture of welds. The structural behavior of tested joints was simulated by elaborate finite element (FE) models generated using the ABAQUS software package. The developed FE models were validated against the test results. The obtained test results and developed FE models can be used for further studies on the structural behavior of stainless steel beam-to-column minor-axis joints with box panel zones.关键词：stainless steel;beam-to-column minor-axis joints;end-plate connections;box panel zone
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发布时间：2024-01-10 - 摘要：The attenuation of effective potential leads to the poor effect of electroosmosis in the later stage, and the influence of the change of effective potential cannot be considered in the classical electroosmotic consolidation theory. Aiming at this problem, in the rectangular layout, taking the point electrode unit as the research model, by focusing on the contradiction between the effective potential attenuation and the restriction conditions when introducing the intermediate variable, the Riemann summation form is introduced to segment the effective potential attenuation by polymorphism, which ensures the establishment of the intermediate variable equation in the Riemann state segment. By considering the unity of the effective potential attenuation and electroosmotic consolidation in the time dimension, the initial condition is adopted. The unsteady state solution in the time domain is transformed into the updating iteration of the initial conditions between the state segments. The finite element form of the method is given based on Galerkin’s method, and is programmed with Python. The results show that: 1) in the process of electroosmosis, the change of the effective potential at the anode is affected by the length of the seepage path, and the effective potential of the far anode is increasing, and the other two parts are in the state of attenuation; 2) the results of the multi-state algorithm can reflect the distribution of the effective potential on the pore pressure compared with the classical results, and the change is mainly concentrated in the middle of the element. 3) The mutation of pore pressure amplitude caused by the inheritance of initial conditions decreases with the increase of the number of state segments. When the pore pressure curve is smooth, the increase of the number of state segments by inheritance has limited improvement on the calculation accuracy. This method is simple, clear and more in line with the real situation.关键词：two-dimensional electro-osmosis consolidation theory;effective potential decay;punctiform electrode unit;python scientific computation
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发布时间：2024-01-10 - 摘要：With the increase of water content (humidity), red bed clay (rock) shows the characteristics of volume expansion and water-softening simultaneously, which is the main reason for geological hazards, such as landslides and subgrade uplifts in red bed regions. To understand the influence of water content on the deformation regulation of loaded geo-materials, a water-softening model based on relative humidity (normalized water content) was proposed and a corresponding expansive analysis model was established. Firstly, taking consolidated clay and red bed clay rock as research objects, expansion, and water-softening tests were carried out to calibrate the steady parameters of the model. The expansive tests show that the confining expansion rate of clay rock and consolidated soil are 0.345 and 0.205, and the expansion stress is 225.0 kPa and 112.5 kPa respectively, which reflected that the clay rock has a stronger expansion capacity than the consolidated clay. Meanwhile, the test also shows that the consolidated soil absorbs water more quickly and can reach the expansion equilibrium state faster. The water-softening test shows that the compression modulus of clay rock is larger than consolidated clay in the dry state, and the decrease of compression modulus with water content is also faster. The compression modulus of consolidated clay and clay rock is basically the same in the saturated state. Then, the confining expansion test was numerically simulated based on the calibrated analysis model, and the applicability of the method in terms of steady analysis was verified. Meanwhile, the average diffusivity K (which is a transient parameter) was calibrated by the comparison of tests and numerical results. Finally, taking the problem of circular cavern encountering water as an example, the steady theoretical analysis and the transient numerical calculation were carried out to illustrate the superiority of the model in expansive large deformation conditions. In summary, the parameters of the novel model are easy to obtain, and the numerical result is accord with tests, which can guide the engineering practice in the red bed expansive clay or swelling rock areas.关键词：red bed clay rocks;humidity stress field;expansive constitutive model;water-softening;numerical simulation;diffusion coefficient of the relative humidity
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发布时间：2024-01-10 - 摘要：Tunnels with non-circular cross-sections such as rectangles, straight walls, and arches are becoming more and more common in engineering construction. It is also a basic fact that natural soils are mostly permeable anisotropic media due to geological movement and their own gravity. The existing analytical research theories on the seepage field of underwater tunnels often assume that the shape of the tunnel cross-section is circular, to simplify the calculation of the seepage field of underwater tunnels. Few analytical studies on tunnels with non-circular cross-sections also fail to consider the effect of anisotropy of permeation of the surrounding medium on the seepage field. Based on this, two mutually perpendicular permeability coefficients are used to represent the permeability anisotropy of the surrounding soil of the tunnel. Based on groundwater seepage theory, coordinate transformation, conformal mapping, and optimization techniques, the sub-regions of the seepage area of underwater non-circular tunnels are mapped into concentric rings. On this basis, the steady seepage continuity equations are solved separately, and then simultaneously solved according to the seepage continuity principle, and the analytical formulas of seepage flow and water head in underwater non-circular tunnels in semi-infinite porous media with the permeation anisotropy are derived. Based on an elliptical underwater tunnel, the correctness of the analytical solution is verified by numerical simulation, and compared with the equivalent perimeter method and the equivalent area method, it is found that this method is more consistent with the numerical simulation results. The study also finds that if the seepage anisotropy of the surrounding soil is not considered, the seepage flow of the tunnel and the water head outside the lining will be underestimated, which will bring safety hazards to the design of the tunnel support structure. The method is suitable for the analytical study of the seepage field of any shape underwater tunnel considering the seepage anisotropy and provides support for the rapid and accurate prediction of the seepage flow of the non-circular section tunnel and the external water pressure of the support structure.关键词：non-circular tunnel;conformal mapping;permeation anisotropy;lining;analytical solution
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发布时间：2024-01-10 - 摘要：In order to quantitatively analyze the relationship between electromagnetic radiation (EMR) parameters and the deformation and failure of tunnel surrounding rock, and improve the prediction accuracy of tunnel deformation, the correlation between EMR parameters and tunnel deformation (including deformation amount and deformation rate) were analyzed by correlation analysis method based on 219 sets of field test data of Zhongyi Tunnel on Lixiang Railway. The most relevant parameters among the intensity, pulse and energy indexes were used to develop the new multi-parameter models for tunnel deformation amount and deformation rate. The developed model was verified by the monitoring data. The tunnel deformation amount and deformation rate after excavation were predicted by the developed models of this study. The results showed that: 1) Among the EMR intensity, pulse and energy indexes, the most relevant parameters of tunnel deformation amount are the maximum peak events of EMR intensity in total events, the peak events which exceeding average energy in total events and pulse number, respectively. Their fluctuation rate are the most relevant parameters of the tunnel deformation rate. 2) The three-parameter PLSR models of deformation amount and deformation rate were established by the Partial Least Squares Regression (PLSR) method. The correlation coefficients between the calculated values and the measured values of tunnel deformation amount and deformation rate were 0.838 and 0.927, respectively. It showed the effectiveness of these proposed models. 3) According to the field application results, the prediction results by the three-parameter PLSR models of this study were closer to the field data than those by the unitary regression models. The prediction accuracy of the proposed models was more stable. In practical engineering, the multi-parameter model of tunnel deformation should be established by integrating the intensity, pulse and energy indexes of EMR, which can accurately reflect the actual deformation law of tunnel surrounding rock and promote the field application of EMR technology in engineering practice.关键词：tunnel deformation;electromagnetic radiation;deformation rate;partial least square regression
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发布时间：2024-01-10 - 摘要：Considering the characteristics of multi-index, fuzziness, and uncertainty of collapse in mountain tunnels, the set pair analysis (SPA) method and information entropy theory were combined and applied for risk assessment of collapse. Firstly, the risk environment and risk factors of tunnel collapse were considered, and the main influencing factors, such as surrounding rock grade, groundwater, unfavorable geology, initial support stiffness, excavation method, construction technology level, and construction management level, were selected as evaluation indices. Second, the SPA method was introduced into the tunnel collapse risk assessment, and the certainty-uncertainty problem of tunnel stability-instability was analyzed from the perspectives of identity, discrepancy, and contrary, and a set pair system of evaluation indexes and classification standards was constructed. Then, the evaluation indices of collapse were divided into two main types: benefit type and cost type indices. Based on SPA, the single index connection degrees of evaluation indices were calculated. At the same time, the information entropy theory was introduced to determine the objective weight of the evaluation index, and it was coupled to the single index connection degree of the evaluation index, and the entropy weight-set pair comprehensive connection degree evaluation model of tunnel collapse risk assessment was constructed. Finally, the credible degree recognition criterion was used to determine the risk level collapse. Taking Binfang 2# tunnel as an example, the shallow-buried section of the right tunnel K31+500～K31+660 was emphatically analyzed. The results showed that the determination uncertainty of tunnel stability instability based on the set pair analysis method could better solve the multi-index and uncertainty in the risk assessment of mountain tunnel collapse. The modified entropy weight method was used to determine the index weight, which reduced the influence of human factors; The confidence recognition criterion was introduced to identify the risk of tunnel collapse, which made up for the distortion of evaluation results caused by the maximum membership principle. The evaluation process of this method is reasonable, and the results are reliable. It is an effective collapse risk evaluation method and provides a new research idea for the collapse risk evaluation of mountain tunnel.关键词：mountain tunnel;collapse;risk assessment;entropy weight method;set pair analysis method;credible degree recognition criterion
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发布时间：2024-01-10
CIVIL ENGINEERING
- 摘要：Hydrologic data are crucial to sustainable management and utilization of water resources, but they are limited by monitoring cost and technology, which brings pressure to the acquisition of hydrological data and the establishment of long-term monitoring network. Citizen science is a way for the citizen to participate in science and it is a promising and cost-effective means of data acquisition, which can effectively alleviate the problem of data’s shortage, uneven distribution, and low spatial and temporal resolution. It has been studied and applied in the international hydrology field. However, there is little related research in China, and no summary analysis of the research results and future development prospects have been conducted. Citizen science promotes the interaction and feedback process between hydrology and society. Firstly, this paper systematically introduced citizen science from the aspects of its definition, form and scientific research stage of citizen participation, and the interaction with hydrological development. Secondly, the current status of citizen science in the field of hydrology was analyzed through literature review and project statistics. The results showed that the research of citizen science in hydrology was on the rising trend, especially in the past five years. The research was widely studied in American and European, while China was still in the initial stage of development. The contribution of citizen science to hydrology was mainly data acquisition and supplement. It also has great potential for citizens to deeply participate in multi-stage hydrological research. At the same time, citizen science has certain applications in rainfall, flow/water level, water quality, soil moisture and so on. The development of sensors, internet of things and emerging technologies can better serve hydrological research. Finally, the frontier problems and future prospects of this research in terms of data market, hydrological analysis technology and hydrological knowledge exploration were discussed, in order to point out the direction for the development of citizen science in this field in the future.关键词：citizen science;hydrology;data monitoring;public participation;public hydrology
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发布时间：2024-01-10 - 摘要：A coupled LBM–DEM numerical model was developed by modifying the Lattice Bhatnagar Gross Krook evolution equation based on the theory of lattice Boltzmann method (LBM) and discrete element method (DEM). The immersed moving boundary method (IMB) was introduced for solving complex fluid-particle interactions using a fast linear approximation of partially intersected volume between a particle and a lattice cell. MATLAB was used to develop an LBM–IMB–DEM coupling solving program to simulate the movement of suspended particles in the aquifer medium. The accuracy of the model and the solution method was verified by using a chromatographic column forced seepage experiment and simulation of the drafting, kissing and tumbling (DKT) phenomenon. The effects of groundwater dynamics, particle morphology and size effect on aquifer permeability were analyzed on the pore scale. The results showed that when the suspension of spherical silica powder was injected with an inlet velocity of 5×10–5 m/s, the seepage velocity in the aquifer presented three successive stages of declining, rising and stabilizing. While the seepage velocity decreased, particle retention rate increased by 47.4% and recovery rates for the average velocity of each section declined. After the suspended particle was changed from spherical silica powder to non-spherical silica powder, the maximum drop of the average velocity of each section increased by 15%, 11.4%, and 2.6%, respectively, whereas the recovery rate decreased by 37.5%, 69.6%, and 71.9%, and the particle retention rate increased by 47.9%. According to the particle force balance analysis, spherical silica powders can be easily detached from the grain surface of the aquifer medium due to their low rotary inertia. Since the specific surface area of the non-spherical silica powder with the equivalent volume is larger and the flocculating lumping is often observed in it, the probability of the attachment in matrix surface or being captured by the pore throat are enhanced during transport, and it is difficult for non-spherical silica powders to re-release after deposition. While the seepage velocity decreases and the calculation area of the aqueous medium increases, the influence degree of suspended particle morphology on the hydrodynamic evolution of the aquifer is strengthened.关键词：particles transportation;lattice Boltzmann method (LBM);discrete element method (DEM);morphology characteristics;size effect
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发布时间：2024-01-10 - 摘要：Open intake is an important hydraulic structure in small and medium-size pump stations. The air-entrained vortex is prone to occur in the open intake when the structural size design is unreasonable, and cavitation may occur in serious cases, affecting the safe and stable operation of the pumping station. The previous studies have revealed that the floor clearance C has a great influence on the flow in the intake, but the influence on the air-entrained vortex is not given. According to the value range of floor clearance given in the design code of pump station, this paper uses the S-CLSVOF method to capture the water air interface, and carries out numerical simulation based on Bifurcation model, and analyzes the variation law of air-entrained vortex with the floor clearance of bell mouth. Combining the vorticity at the bell mouth and the Reynolds-averaged enstrophy, the mechanism of this variation law is analyzed. The results show that the size of air-entrained vortex is related to the relative air-entrainment rate β in the inlet pipe, the average of which was 3×10–4～7×10–4. The value of β basically decreased with the increase of floor clearance, but there was a sudden drop at C=0.35D (D is the bell mouth diameter). The variation law of vorticity with time in each scheme is analyzed, and the vorticity can quantitatively reflect the intensity of air-entrained vortex. Through the analysis of Reynolds-averaged enstrophy transport equation, it is found that the tilting effect of the vortex determines the variation of the average relative air-entrainment rate, which is consistent with the change law of the air-entrainment rate, and also reveals the mechanism of the sudden drop. When designing the intake, by considering the degree of air-entrained vortex and the installation of pump, C=0.35D is the optimal choice.关键词：intake;air-entrained vortex;floor clearance;S-CLSVOF;air-entrainment rate
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发布时间：2024-01-10 - 摘要：The erosion of the soil bank slope by waves in the Three Gorges Reservoir Area (TGRA) significantly affects the ecological and geological environment safety of the reservoir area. The prediction of the erosion range of the bank slope by waves will be an important measure for disaster prevention and mitigation in the TGRA. However, the existing erosion prediction is mainly based on empirical methods, and it is difficult to obtain accurate results. Therefore, by using the energy conservation theory and considering the wave layer thickness and wave velocity changes during the wave run-up, the wave run-up potential energy equation and the friction energy consumption equation were respectively established, from which the prediction equation for the erosion range of the soil bank slope caused by waves was established. In order to obtain the key parameters of the prediction equation, the physical model test of the wave run-up bank slope was carried out, and the flow velocity, layer thickness and run-up law were studied. In order to verify the reliability of the prediction equation, the wave-induced bank slope erosion model test was carried out to obtain the erosion evolution process of the soil bank slope. The results of wave run-up model test shown that the greater the slope of the bank slope is, the higher the wave run-up reaches, and the thickness of the water flow increases, but the velocity of the water flow decreases. According to the test results, the distribution interval of the water flow thickness parameter and the flow velocity parameter were obtained, and the relationship equation among the water flow thickness parameter, the flow velocity parameter and the slope of the bank slope was constructed. The model test results of wave erosion bank slope showed that the greater the dry density of soil, the stronger the erosion resistance of the bank slope, and the longer the time required for the bank slope to reach the final steady state. With more gravel content contained, the stronger the anti-erosion ability of the bank slope was, and the stable time of bank slope erosion was shortened due to the effect of gravel protection. By comparing the final steady state results of bank slope erosion with the results of the prediction equation, it was proven that the prediction equation of erosion range proposed in this paper is reliable. The wave erosion range prediction equation proposed in this paper can be widely used in the prevention and control of erosion disasters on soil bank slopes of reservoirs.关键词：energy conservation;wave erosion;Three Gorges Reservoir Area;model test
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发布时间：2024-01-10 - 摘要：For the optimal design of a new type of artificial block featured with high permeability and the better understanding of its hydrodynamic characteristics, a numerical model based on Dualsphysics was conducted to simulate the regular wave transformation on the slope breakwater with this type of block. The numerical model was verified according to the measured data from the physical experiment, showing that the deviations between the numerical model and the measured data were less than 6% and 9%, respectively for wave run-up and wave overtopping, which demonstrated that the model was reliable to capture the wave evolution on the breakwater of artificial blocks. By using this model, the hydrodynamic performances of this block with different design details were analyzed, and the block design parameters including the optimal relationship between block radius and block length presenting the optimal wave-damping effect were determined. This selection was for the overall consideration of wave run-up, reflection, overtopping, block porosity and material consumption. It was revealed that the wave damping effects were mainly from holes existing between adjacent blocks which have a retarding effect on the climbing and falling of waves. These holes inside the blocks could accommodate the water and reduce the turbulence energy efficiently, which then contributed to reduce wave run-up. The results also indicated that the optimized TB-CUBE block climbing height increased with the increase of wave height and decrease of wave steepness. The wave run-up, however, revealed a unimodal curve with the rise of breakwater slope. Moreover, the empirical formula that could reflect the true wave climbing phenomenon on this type of artificial block was suggested through data-fitting in which the correlation coefficient was 0.981. This study paves the way for future application of this block in practice.关键词：smoothed particle hydrodynamics;new type of artificial block;TB–CUBE;wave run-up;overtopping;empirical formula
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发布时间：2024-01-10
HYDRAULIC ENGINEERING
- 摘要：Thin film plays an important role in the field of aerospace because of its advantages of light weight, small folding volume and good mechanical properties. Thin film is a flexible material with characteristics of small thickness and bending stiffness. The local buckling phenomenon of the thin film is easy to occur at large external loads, leading to undesirable wrinkles. Folding is one of the important factors affecting the structure and properties of spatial thin films. Therefore, it is crucial to study the characteristics of film folding and its inhibition for the application of film structure in the field of aerospace. In this paper, the effects of the structural parameters and boundary conditions on the fold characteristics of thin films are studied. Aiming at square membrane structure under tensile load, wrinkling simulation analysis of the structure is carried out by using the explicit dynamic method, and the simulation results are compared with the theoretical calculation results to verify the simulation model and analysis results. In order to explore the change law of wrinkles characteristics under tensile loads, we analyze how the wrinkles characteristics and deformation of square membrane are affected by the structural parameters including membrane aspect ratio, internal angle, clamping width, and side cable structure. The results show that the out-of-plane deformation of membrane increases and the wrinkle distribution area expands when the aspect ratio of membrane increases from 1.0 to 1.5. The wrinkles are mainly distributed in the corner area with an acute angle between two sides of membrane when the internal angle in the membrane is less than 75°. In addition, the occurrence of wrinkles can be effectively suppressed by increasing the clamping width of membrane and the side cable structure. To further verify the analysis results, fold tests under different clamping widths were carried out. The simulation model is validated by the trend analysis of the experimental results of fold number and amplitude as well as their comparison with the simulation results, which provides a certain theoretical basis for the tensile analysis of thin film structure.关键词：square membrane;explicit dynamic method;wrinkles characteristics;out-of-plane deformation
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发布时间：2024-01-10 - 摘要：To alleviate the problems of parking difficulty in rush hours, long waiting time in queue and low efficiency of stereo vehicles, a stereo garage with efficient parallel storage is designed. First, we make full use of the three-dimensional garage bottom space to design sub-mother vehicle buffer pool storage scheme, and improve the efficiency of vehicle storage and extraction through the buffer pool’s continuous handling work. A mother car is arranged in each layer of the garage, and the multi-layer circular parking space allocation strategy is adopted to realize the parallel storage function of the multi-layer mother car in the garage, and the parallel storage efficiency of the stereo garage is calculated by analyzing the working sequence characteristics of the stereo garage in the case of multiple storage requests. Second, the M/M/n queuing model for vehicle storage is established based on the customer’s vehicle storage process, and the queuing theory is used to analyze the average utilization rate of elevators under different customer arrival rates, and the average queuing time, queue length and the waiting probability for customers under different number of elevators. Finally, a reasonable capacity of the vehicle storage buffer pool is designed based on the actual vehicle parameters, garage structure size, the movement parameters of the sub-mother vehicle handling system, and the occupied area of stereo garage. In addition, the customer vehicle storage indexes before and after the buffer pool are compared to verify the significant reduction in customer waiting time of vehicle storage by the buffer pool. The results show that the stereo garage system increases the storage efficiency by 39% compared with the traditional stacker stereo garage under parallel storage condition of five vehicles. The average queuing time of customers is reduced by 47.8% when the customer vehicle arrival rate is 75 vehicle/h and the capacity of the sub-car buffer pool is set to 4. Therefore, the parallel car storage scheme of the stereo garage with buffer pool can significantly improve the efficiency of car storage and reduce customer waiting time, which can further meet the requirements of customer’s car storage.关键词：stereo garage;sub-mother vehicle;buffer pool;parallel vehicle storage;queuing model
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发布时间：2024-01-10 - 摘要：Carbon fiber reinforced polymer composites (CFRP) are widely used in the field of aerospace but it is prone to suffer from riveting damage. This work experimentally investigated the riveting damage behaviors of the CFRP riveted joints with gaskets and evaluated the tensile shearing properties of joints at different width-diameter ratios and edge displacement-diameter ratios. The results demonstrated that the rivet tail’s excessive expansion in the radial direction and extrusion deformation in the axial direction led to high local stress on the CFRP hole and thus riveting damage. The most critical damage occurred on the plies near the riveted head. The gasket can effectively limit the uneven expansion near the rivet tail and can reduce axial stress of the hole surface by dispersing the local axial extrusion force to the gasket coverage area around the hole, which helped reduce riveting damage. The load-displacement response curves of all specimens were dominated by rivets, accompanied by rivet shearing failure. During tensile shearing testing, the gasket was un-deformed but local extrusion damage occurred at the local region near the hole of CFRP along with fiber tensile fracture noise. The width to diameter ratio exhibited an obvious influence on the specimen stiffness and failure strength, while the edge displacement to diameter ratio had little influence on them. In order to explore a more efficient riveting method compared to traditional riveting, this paper focused on CFRP/CFRP composite riveted structures and introduced a novel riveting method with gaskets. Through riveting and tensile-shear tests and microscopic observation of the riveted specimens, it was found that gaskets could reduce riveting damage by suppressing the expansion of the rivet head and dispersing stress around the hole. The width-to-diameter ratio of the riveted specimens had a more significant influence on their stiffness and failure strength compared to the edge-to-diameter ratio. In the tensile-shear tests, all the failure modes of the riveted specimens were rivet fracture.关键词：composite;riveting;gasket;damage;failure
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发布时间：2024-01-10 - 摘要：Negative Poisson’s ratio metamaterials are widely used in various engineering fields due to their excellent properties. In this paper, the tribological properties of negative Poisson’s Ratio (NPR) specimens and solid specimens were prepared by 3D printing technology (fused deposition melding) based on the typical concave hexagonal negative Poisson’s ratio structure using acrylonitrile-butadiene-styrene (ABS) material as the carrier. Combined with ring-block friction and wear test, SEM, white light confocal three-dimensional topography instrument, finite element static analysis and other tests, the difference of tribological properties between NPR specimens and solid specimens under different loads (10, 30, 50 N) was comparatively studied. The results show that: 1) under different loads, the stress and deformation of the NPR specimens were larger than those of the solid specimen, and the stress appears at the joints of the internal units of the NPR specimens with a more obvious effect of negative Poisson’s ratio as the load increases; 2) under the same load, the NPR specimens had a smaller friction coefficient and larger wear amount, and furrows appeared in the friction contact interface along with an abrasive wear on the substrate. The wear mechanism turned into adhesive wear with the increasing load because partial abrasive chip adheres to the friction surface of the NPR specimens; 3) under large load (50 N), the negative Poisson’s ratio effect of NPR specimens was enhanced, which exhibited better performance in vibration and impact resistance and energy absorption. Both friction coefficient and wear amount became lower than those under low load (30 N), which helped improve the tribological properties of the specimens. The research results have enriched and improved the research system of negative Poisson’s ratio tribological materials, and made exploratory attempts at the frontier of materials science research, providing basic data and technical support for the application of negative Poisson’s ratio materials in the field of tribological engineering.关键词：negative Poisson’s ratio;metamaterials;tribological properties
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发布时间：2024-01-10
MECHANICAL ENGINEERING
- 摘要：Accidents of the rail electric locomotive in the underground are frequently occurring due to the poor coal mine roadway environment and fatigue-limited manual driving. To address this issue, an improved YOLOv4–Tiny framework, called YOLOv4–Tiny–4S, is proposed to achieve multi-object real-time detection for rail electric locomotive. A 4–scale prediction head is designed to enhance the detection ability of small objects based on the 2–scale prediction of YOLOv4–Tiny. Spatial pyramid pooling (SPP) is introduced into the neck network to extend the receptive field and enrich the fused features. In this work, the detection objects concern person, locomotive, stone and lamp in the coal mine roadway, and a new dataset is constructed to validate the proposed approach. The K–means and K–means++ algorithms are applied to re-cluster the samples, and K–means++ has a better performance in this dataset. The ablation studies over YOLOv4–Tiny are conducted to validate the technical improvements in this work. The result comparison over other baselines demonstrates that the proposed approach can detect and recognize the required objects in the underground rail electric locomotive with considerable high performance, achieving 95.35% mean average precision. Specifically, the average precision for small object “stone” reaches 86.69%, yielding 12.38% and 41.66% improvements over YOLOv4–Tiny. The average detection speed of the proposed approach is 58.7 frames per second (FPS), with only 26.3 Mb memory. The proposed multi-object real-time detection method is expected to provide technical support for the unmanned driving of mine electric locomotive.关键词：mine electric locomotive;YOLOv4–Tiny;multi-object real-time detection;unmanned driving
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发布时间：2024-01-10 - 摘要：Hydraulic machinery and equipment (such as gates, trash racks, etc.) inevitably suffered from corrosion on their structural surfaces due to the long-term usage in the water environment. If the severity of corrosion cannot be accurately detected, the maintenance and strengthening of important key stress-bearing structural components may fail to be timely implemented, which further threatens people’s life around the damaged structure. Currently, the identification of corrosion features of hydraulic machinery and equipment mainly depends on manual visual inspection, resulting in strong subjectivity, poor detection accuracy limited by visual fatigue. To address this issue, a corrosion-rating evaluation method is proposed by incorporating the attention mechanism and bilinear pooling into the VGG–16 (visual geometry group, VGG) backbone. Considering that different components in the RGB (red green and blue) and HSV (hue saturation and value) color spaces present distinctive features on the rust image, a multi-branch neural architecture is designed to learn informative features by taking different color spaces as inputs. The attention mechanism is embedded in the branch network to recalibrate the features of the rust image by the learnable weights, focusing on the learning of task-oriented features to support the evaluation. The bilinear pooling is applied to fuse the extracted representations of branch networks to enhance the fine-grained features, which improves the ability to utilize the contrastive details. A rust image dataset is constructed to validate the proposed approach using the salt spray corrosion test . Experimental results demonstrate that the proposed approach outperforms the selective baselines, achieving a 0.953 detection and other measurements, including the precision, recall andF1 scores, are also greatly improved. Most importantly, the proposed approach can achieve better performance for irregular corrosions, which has huge potential for the application of the engineering practice.关键词：rust image;VGG–16;attention mechanism;bilinear pooling;rust grade
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发布时间：2024-01-10
INFORMATION ENGINEERING
- 摘要：Aiming at the low adsorption capacity and slow adsorption rate caused by the narrow pores in the traditional β-cyclodextrin (β–CD) media in the separation and purification of flavonoids, a surfactant swelling strategy was adopted to construct macroporous β–CD microspheres (LCDM), achieving the high adsorption capacity and fast adsorption rate. The macropores not only provide wide mass transfer channels and accelerate the adsorption rate, but also shorten the distance between the adsorbates in the solution and the adsorption sites in the interior of LCDM, thus improving the utilization of adsorption sites for high adsorption capacity. The pore-forming mechanism is that surfactant forms micelles in the β–CD solution when its concentration exceeds the critical micelle concentration. During the emulsification, the external oil phase is attracted into the β–CD droplet by the surfactant micelles due to their internal hydrophobic core, forming the oil phase channel. As β–CD is cross-linked, the oil-phase channels are transformed into macropores. Experimental results showed that the pore distributions of LCDM are in the range of 20~200 nm, which can be controlled by adjusting the surfactant concentration. Permeability experiments showed that LCDM had lower back pressures than traditional microporous β–CD microspheres (SCDM) at the same flow rate, and the maximum permeability of LCDM increased by 70.65% compared with SCDM. Taking rutin as the model representative of flavonoids, the adsorption properties of LCDM and SCDM microspheres were compared. The maximum rutin adsorption capacity of LCDM reached 29.62 mg·mL–1, 3.42 times higher than that of SCDM (8.66 mg·mL–1); the ratio of effective pore diffusion coefficient to free diffusion coefficient (De/D0) of rutin in LCDM reached 1.29, 10.75 times higher than that of SCDM .关键词：cyclodextrin;flavonoids;surfactant;adsorption
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发布时间：2024-01-10
CHEMICAL ENGINEERING & MATERIAL ENGINEERING
- 摘要：Secure multiparty computation is valuable for studying data privacy protection issues due to its decentralization, input privacy, fairness, etc. One of the most fundamental problems is to confidentially compute the maximum and the minimum of multiple data. In this paper, an efficient secure multipart computation scheme that can compute the maximum and the minimum simultaneously without a trusted third party was proposed to address the problems of existing secure multi-party computation protocols, such as inability of computing the maximum and the minimum at one time, low efficiency, and security risks caused by unique designated decryption key holder. In the scheme, an encoding method that can simultaneously compute the maximum and the minimum was first provided, whose basic idea was to give a complete set of ordinal numbers with potential l (l ≥ the number of participants n), and each participant encodes its data into an array with length l where the location of the data in the complete set was coded as a random number and the other positions were coded as 1. The positions of the leftmost and rightmost non-1 values in the product array were the positions of the maximum and minimum in the whole set. Based on the proposed encoding method, the ElGamal homomorphic encryption algorithm was used to guarantee the confidentiality of all participants’ data, and the maximum threshold decryption was used to make each participant hold part of the decryption key, which avoids the security threats caused by centralized decryption of calculation result by designated key holder. The proposed scheme was proven to be resistant to collusive attacks by any participant under a semi-honest model based on an ideal-realistic simulation paradigm. Finally, the efficiency analysis and performance comparison with related maximum (minimum) computing schemes were given, which showed that the proposed protocol has advantages over existing schemes in terms of computational complexity and communication complexity under the premise of higher security.关键词：secure multi-party computation;maximum and minimum;ElGamal homomorphic encryption;threshold decryption;simulation paradigm
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发布时间：2024-01-10 - 摘要：In order to solve the problems of imperfect transaction legitimacy verification strategies for protecting account balances and transaction amounts in privacy protection of consortium blockchain, and the low efficiency of the basic encryption algorithm Paillier, a +HomElG zero-knowledge proof protocol for consortium blockchain transfer privacy protection was proposed. A consortium blockchain transfer privacy protection application was constructed based on PBFT, which expounded the consensus interaction scenario of zero-knowledge proof of homomorphic encryption. The transaction amount and balance of account were encrypted by the +HomElG algorithm, and the zero-knowledge proof of the ciphertext was designed with the Σ protocol. The non-interactive zero-knowledge was designed through the idea of the Fiat-Shamir algorithm processes such as the proof of equality, the amount of the transaction greater than zero and the balance of the transfer party not less than zero in the proof of range. The protocol was proved to be correct, complete and zero-knowledge under the DDH. A consortium blockchain transfer privacy protection prototype system based on Hyperledger Fabric was constructed. The results verified that the protocol can realize ciphertext transactions to protect balance of account and transaction amount under the condition of non-interactive zero-knowledge proof. When the key length is 3072 bit and the data length is a 12-bit decimal integer, the efficiency of the +HomElG algorithm is 150.3 ms, and the efficiency of the proof of equality, the amount of the transaction greater than zero and the balance of the transfer party not less than zero in the proof of range are 482.3 ms, 209.3 ms and 261.3 ms respectively. Compared with the existing protocols, the proposed +HomElG algorithm is more efficient, and its transaction legitimacy verification strategies such as equality proof and range proof are more perfect and efficient. The proposed protocol can meet the privacy protection requirements of consortium blockchain transfer transactions.关键词：consortium blockchain;zero-knowledge proof;privacy protection;homomorphic encryption;+HomElG
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发布时间：2024-01-10
CYBERSPACE SECURITY
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