Accurate acquisition of the lithological composition of a tunnel face is crucial for efficient tunneling and hazard prevention in large-diameter slurry shield tunnels.While widely applied,current data-driven methods o...Accurate acquisition of the lithological composition of a tunnel face is crucial for efficient tunneling and hazard prevention in large-diameter slurry shield tunnels.While widely applied,current data-driven methods often face challenges such as indirect prediction,data sparsity,and data drift,which limit their accuracy and generalizability.This study develops an integrated method that combines a knowledge-driven method to directly compute distribution patterns of lithological components,which are used as a priori knowledge to guide the development of a data-driven method.Coupled Markov chain(CMC)and deep neural networks(DNNs)serve as the knowledge-driven and data-driven components,respectively.Additionally,a dynamic prediction strategy is proposed,where the model is continuously optimized as construction progresses and training samples accumulate,rather than being statically trained on post-construction data,as is common in data-driven methods.Finally,the proposed method is evaluated using a real-world project.The evaluation results show that the integrated method outperforms both individual data-and knowledge-driven methods,demonstrating higher predictive performance,greater stability,and greater robustness to data scarcity and data drift.Furthermore,the dynamic prediction strategy better captures the effects of gradual data accumulation and lithological spatial variability on prediction performance during construction,providing new insights for real-time prediction in practical tunneling applications.展开更多
Large-diameter drilling method is a prevalent method for preventing and controlling rock burst,and the spacing between the large-diameter drilling hole and anchoring hole is a critical factor influencing the roadway s...Large-diameter drilling method is a prevalent method for preventing and controlling rock burst,and the spacing between the large-diameter drilling hole and anchoring hole is a critical factor influencing the roadway stability and relief effectiveness.In this study,a mechanical model for optimal matching between the large-diameter drilling hole and anchoring hole was established following the principle of synergistic control.The influence of large-diameter drilling hole diameter on the optimal spacing under the synergistic relief effect was investigated by integrating theoretical analysis,numerical simulation,and field practice.The results suggest that the hole spacing achieved a synergistic effect in a certain range when the optimal hole spacing increased linearly with the hole diameter.For instance,when the anchoring hole diameter was 20 mm,an increase in the aperture ratio from 5 to 10 brought about an increase in the optimal spacing from 0.25 m to 0.45 m.Additionally,the vertical stress between the large-diameter drilling hole and anchor hole increased nonlinearly under the condition of constant pore ratio but varying hole spacing.Both excessively small and excessively large hole spacings were detrimental to the pressure relief effect.In the engineering practice,optimizing the hole spacing from 0.55 m to 0.45 m in the 1208 working face contributed to reducing coal body drilling cuttings and the roadway moving quantity by 33%and 19.2%,respectively.This demonstrates that the pressure relief-support reinforcement synergistic effect should be fully considered in optimization design.展开更多
Tube thinning control without wrinkling occurring is a key problem urgently to be solved for improving the forming qualities in numerical control （NC） bending processes of large-diameter Al-alloy thin-walled tubes ...Tube thinning control without wrinkling occurring is a key problem urgently to be solved for improving the forming qualities in numerical control （NC） bending processes of large-diameter Al-alloy thin-walled tubes （AATTs）. It may be a way solving this problem to exert axial compression loads （ACL） on the tube end in the bending. Thus, this article establishes a three-dimensional （3D） elastic-plastic explicit finite element （FE） model for the bending under ACL and has its reliability verified. Through a multi-index orthogonal experiment design, a combination of process parameters, each expressed by a proper range, for this FE model is derived to overcome the compression instability on tube ends. By combining the FE model with a wrinkling energy prediction model, an in-depth study is conducted on the forming characteristics of large-diameter AATTs with small bending radii and it can be concluded that （1） The larger the tube diameters and the smaller the bending radii, the larger the induced tangent tension stress zones on tube intrados, by which the tube maximum tangent compression stress zones will be partitioned in the bending processes; thus, the smaller the ACL roles in decreasing thinning degrees and the larger the compression instability possibilities on tube ends. （2） The tube wrinkling possibilities under ACL are larger than without ACL acting in the earlier forming periods, and smaller in the later ones. （3） For the tubes with a size factor less than 80, the ACL roles in decreasing thinning degrees are stronger than in increasing wrinkling possibilities.展开更多
The existing researches of the magnetic liquid rotation seal have been mainly oriented to the seal at normal temperature and the seal with the smaller shaft diameter less than 100 mm. However, the large-diameter magne...The existing researches of the magnetic liquid rotation seal have been mainly oriented to the seal at normal temperature and the seal with the smaller shaft diameter less than 100 mm. However, the large-diameter magnetic liquid rotation seal at low temperature has not been reported both in theory and in application up to now. A key factor restricting the application of the large-diameter magnetic liquid rotation seal at low temperature is the high breakaway torque. In this paper, the factors that influence the breakaway torque including the number of seal stages, the injected quantity of magnetic liquid and the standing time at normal temperature are studied. Two kinds of magnetic liquid with variable content of large particles are prepared first, and a seal feedthrough with 140 mm shaft diameter is used in the experiments. All experiments are carried out in a low temperature chamber with a temperature range from 200℃ to -100℃. Different numbers of seal stages are tested under the same condition to study the relation between the breakaway torque and the number of seal stages. Variable quantity of magnetic liquid is injected in the seal gap to get the relation curve of the breakaway torque and the injecting quantity of magnetic liquid. In the experiment for studying the relation between the breakaway torque and the standing time at the normal temperature, the seal feedtrough is laid at normal temperature for different period of time before it is put in the low temperature chamber. The experimental results show that the breakaway torque is proportional to the number of seal stages, the injected quantity of magnetic liquid and the standing time at the normal temperature. Meanwhile, the experimental results are analyzed and the torque formula of magnetic liquid rotation seal at low temperature is deduced from the Navier-Stokes equation on the base of the model of magnetic liquid rotation seal. The presented research can make wider application of the magnetic liquid seal in general. And the large-diameter magnetic liquid rotation seal at low temperature designed by using present research results are to be used in some special fields, such as the military field, etc.展开更多
The large-diameter cylinder structure, which is made of large successive bottomless cylinders placed on foundation bed or partly driven into soil, is a recently developed retaining structure in China. It can be used i...The large-diameter cylinder structure, which is made of large successive bottomless cylinders placed on foundation bed or partly driven into soil, is a recently developed retaining structure in China. It can be used in port, coastal and offshore works. The method for stability analysis of the large-diameter cylinder structure, especially for stability analysis of the embedded large-diameter cylinder structure, is an important issue. In this paper, an idea is presented that is, embedded large-diameter cylinder quays can be divided into two types, i.e. the gravity wall type and the cylinder pile wall type. A method for stability analysis of the large-diameter cylinder quay of the cylinder pile wall type is developed and a method for stability analysis of the large-diameter cylinder quay of the gravity wall type is also proposed. The effect of significant parameters on the stability of the large-diameter cylinder quay of the cylinder pile wall type is investigated through numerical calculation.展开更多
Considering the viscous damping of the soil and soil-pile vertical coupled vibration,a computational model of large-diameter pipe pile in layered soil was established.The analytical solution in frequency domain was de...Considering the viscous damping of the soil and soil-pile vertical coupled vibration,a computational model of large-diameter pipe pile in layered soil was established.The analytical solution in frequency domain was derived by Laplace transformation method.The responses in time domain were obtained by inverse Fourier transformation.The results of the analytical solution proposed agree well with the solutions in homogenous soil.The effects of the shear modulus and damping coefficients of the soil at both outer and inner sides of the pipe pile were researched.The results indicate that the shear modulus of the outer soil has more influence on velocity admittance than the inner soil.The smaller the shear modulus,the larger the amplitude of velocity admittance.The velocity admittance weakened by the damping of the outer soil is more obvious than that weakened by the damping of the inner soil.The displacements of the piles with the same damping coefficients of the outer soil have less difference.Moreover,the effects of the distribution of soil layers are analyzed.The results indicate that the effect of the upper soil layer on dynamic response of the pipe pile is more obvious than that of the bottom soil layer.A larger damping coefficient of the upper layer results in a smaller velocity admittance.The dynamic response of the pipe pile in layered soil is close to that of the pipe pile in homogenous soil when the properties of the upper soil layer are the same.展开更多
A method of coupled BEM-FEM analysis for the elastic spatial structure system is presented. It can be applied to the calculation of the stress and deformation of the large-diamater cylinder structure system and it is ...A method of coupled BEM-FEM analysis for the elastic spatial structure system is presented. It can be applied to the calculation of the stress and deformation of the large-diamater cylinder structure system and it is suitable for symmetric or non-symmetric structures under the distributed or concentrated load. Numerical examples show that the proposed method and computer program BEFEM are quite efficient in the analysis of the large-diameter cylinder structure problems in ocean engineering.展开更多
This study addresses the increasing demand for large-diameter production timber,and considers the time and space variability of half-sib families of Pinus massoniana.Height,diameter at breast height(DBH)and timber vol...This study addresses the increasing demand for large-diameter production timber,and considers the time and space variability of half-sib families of Pinus massoniana.Height,diameter at breast height(DBH)and timber volume of 440 open-pollinated half-sib progeny families were investigated in 14 progeny trials in different years and production regions.An evaluation of the genetic variation of all half-sib families was carried out during the sustainable rapid growth period and individual volumes were characterized as a major index.ANOVA analysis showed that there was considerable variance in the growth traits of most families in different years and on different sites.The variations caused by temporal and spatial changes of the mating system required three selection methods for analysis.The results show that there were differences among the heritabilities of different growth traits by different halfsib progenies.Average heritability values of height,DBH and volume were 0.33,0.34 and 0.36,respectively.Fortyfive superior families were selected in every progeny test,12 were selected in progeny trials by different years and five in different habitat progeny trials.Three superior families(Gui GC553A,Gui GC414A and Gui GC431A)were selected,although in different years and production regions.The genetic gains of timber volume of these selected r families ranged from 1.20 to 47.00%,which could provide a foundation for superior wood property selection and serve as material for seed improvement and extension in surrounding areas.展开更多
This paper aims to present a theoretical method to study the bearing performance of vertically loaded large-diameter pipe pile groups.The interactions between group piles result in different bearing performance of bot...This paper aims to present a theoretical method to study the bearing performance of vertically loaded large-diameter pipe pile groups.The interactions between group piles result in different bearing performance of both a single pile and pile groups.Considering the pile group effect and the skin friction from both outer and inner soils,an analytical solution is developed to calculate the settlement and axial force in large-diameter pipe pile groups.The analytical solution was verified by centrifuge and field testing results.An extensive parametric analysis was performed to study the bearing performance of the pipe pile groups.The results reveal that the axial forces in group piles are not the same.The larger the distance from central pile,the larger the axial force.The axial force in the central pile is the smallest,while that in corner piles is the largest.The axial force on the top of the corner piles decreases while that in the central pile increases with increasing of pile spacing and decreasing of pile length.The axial force in side piles varies little with the variations of pile spacing,pile length,and shear modulus of the soil and is approximately equal to the average load shared by one pile.For a pile group,the larger the pile length is,the larger the influence radius is.As a result,the pile group effect is more apparent for a larger pile length.The settlement of pile groups decreases with increasing of the pile number in the group and the shear modulus of the underlying soil.展开更多
A new technique for the analysis of the three-dimensional collapse failure mechanism and the ground surface settlements for the large-diameter shield tunnels were presented.The technique is based on a velocity field m...A new technique for the analysis of the three-dimensional collapse failure mechanism and the ground surface settlements for the large-diameter shield tunnels were presented.The technique is based on a velocity field model using more different truncated solid conical blocks to clarify the multiblock failure mechanism.Furthermore,the shape of blocks between the failure surface and the tunnel face was considered as an entire circle,and the supporting pressure was assumed as non-uniform distribution on the tunnel face and increased with the tunnel embedded depth.The ground surface settlements and failure mechanism above large-diameter shield tunnels were also investigated under different supporting pressures by the finite difference method.展开更多
Cooling strength is one of the important factors affecting microstructure and properties of gas cylinders during quenching process,and reasonable water spray volume can effectively improve the quality of gas cylinders...Cooling strength is one of the important factors affecting microstructure and properties of gas cylinders during quenching process,and reasonable water spray volume can effectively improve the quality of gas cylinders and reduce production costs.To find the optimal water spray parameters,a fluid-solid coupling model with three-phase flow was established in consideration of water-vapor conversion.The inner and outer walls of gas cylinder with the dimensions of d914 mm×38 mm×12000 mm were quenched using multi-nozzle water spray system.The internal pressure,average heat transfer coefficient(have)and stress of the gas cylinder under different water spray volumes during quenching process were studied.Finally,the mathematical model was experimentally verified.The results show that both the internal pressure and have increase along with the increase of spray volume.The internal pressure increases slowly first and then rapidly,but have increases rapidly first and then slowly.To satisfy hardenability of gas cylinders,the minimum spray volume should not be less than 40 m^3/(h·m).The results of stress indicate that water spray quenching will not cause deformation of bottle body in the range of water volume from 40 to 290 m^3/(h·m).展开更多
A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the...A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the soil along pile shaft is divided into slip and nonslip zones and the base soil is modeled as a fictitious-soil pile(FSP)to account for the wave propagation in the soil.True soil properties are adopted and slippage at the pile-soil interface is considered,allowing realistic representation of largediameter OEPP mechanics.The developed model is validated by comparing with conventional models and finite element method(FEM).It is further used to successfully simulate and interpret the behaviors of a steel OEPP during the offshore field test.It is found that the variation in the vertical vibrations of shaft soil along radial direction is significant for large-diameter OEPPs,and the velocity amplitudes of the internal and external soil attenuate following different patterns.The shaft soil motion may not attenuate with depth due to the soil slippage,while the wave attenuation at base soil indicates an influence depth,with a faster attenuation rate than that in the pile.The findings from the current study should aid in simulating the vibration behaviors of large-diameter OEPP-soil system under high-strain dynamic loading.展开更多
Introduction The predominant characteristics of high-altitude climates include low air pressure,low humidity,and large diurnal temperature fluctuations.In practical engineering scenarios in high-altitude regions,many ...Introduction The predominant characteristics of high-altitude climates include low air pressure,low humidity,and large diurnal temperature fluctuations.In practical engineering scenarios in high-altitude regions,many pier surface cracks only appear several months after erection,and cyclic thermal stress is identified as the main trigger for such cracking.The thermal stress in concrete structures has been investigated for decades but remains incompletely understood.Structural engineers typically regard concrete as an isotropic material and calculate the thermal stress using code-specified coefficients of thermal expansion(CTEs)along with temperature conditions and constraints.Because the CTE of hardened cement paste is more than twice that of many aggregates,reducing the CTE of coarse aggregates can further exacerbate the thermal deformation incompatibility between the coarse aggregate and mortar matrix.In this paper,a comprehensive thermal-elastic mechanics model for pier concrete was developed to analysis the temperature-induced surface stress.Methods A series of mechanical and thermophysical tests were conducted on the diorite aggregate,ITZ cement paste,and mortar,and concrete.A test pier was constructed on open ground near the Yarlung Zangbo River at an altitude of 3800 m.The pier had a diameter of 1.8 m and height of 2 m.Temperature sensors were embedded in the cross-section at a height of 1 m,positioned along the southnorth and east-west directions.The embedding depths(distances from the pier surface)were 0,1.5,3,4.5,6,7.5,9,12,15,20,25,30,35,40,50,60,70,80 cm,and 90 cm.A model of the bridge pier concrete for surface-level analysis was constructed.The model consists of a concrete unit formed as a sphere-shell-shell composite,including the aggregate,ITZ,and mortar layers,embedded in the surface layer of a bridge pier.Outside this unit,the pier concrete was treated as an isotropic,homogeneous elastic material.The real-time internal temperature fields of high-altitude concrete bridge piers,measured on-site,were incorporated into the model.By applying thermoelastic mechanics theory and finite element solutions for plane strain problems,the three-dimensional thermal stresses on the surface layer of high-altitude bridge piers were analyzed Results and discussion During the experimental period,the lowest and highest temperatures on the bridge pier in the high-altitude region were 9.6 ℃ and 42.6 ℃,respectively.These occurred before sunrise and sunset on sunny days,respectively,corresponding to the local maximum temperature gradients during the surface heating and cooling stages,as well as the maximum temperature difference between the surface and center during these stages.The thermal stress on the pier concrete surface was obtained by superimposing the stresses caused by the uneven distribution of the internal temperature field and those caused by the incompatible thermal deformation among the different components in the surface concrete Before the erection of the upper structures,the absolute values of the tangential and vertical stresses were the same;therefore,only one curve was observed.From 22:00 to 8:00,the pier concrete surface was in tension,whereas from 11:00 to 22:00,the pier concrete surface was in compression.The surface of the pier concrete was subjected to biaxial forces of equal magnitude with a maximum compressive stress of 12.52 MPa and maximum tensile stress of 2.15 MPa,respectively at 18:00 and 8:00.According to the fatigue equation,the concrete was predicted to crack after 21 d of temperature cycling.Moreover,if humidity-induced stress is added on top of this,the tensile stress may approach or even exceed the concrete's tensile strength,thereby posing a significant risk of cracking.After the erection of upper structures,the tangential and vertical stresses no longer coincide because the upper structures have been erected.The curve of the tangential stress is unchanged,whereas the curve of the vertical stress is translated downwards by 1.57 MPa due to the structural deadweight.Therefore,the maximum tangential compressive stress remained 12.52 MPa,whereas the maximum vertical compressive stress increased to 14.09 MPa.Additionally,the maximum tangential tensile stress was 2.15 MPa,and the maximum vertical tensile stress was 0.58 MPa.According to Appendix C of GB/T 50010 and the fatigue equation,stresses are unlikely to cause cracking of the pier concrete surface.Although a higher CTE of the coarse aggregate slightly increased the maximum compressive stress,the differences among the three groups of concrete were minimal and could be ignored.Specifically,the maximum compressive stresses on the pier concrete surface were 12.54,12.45 MPa,and 12.56 MPa when using diorite,limestone,and basalt,respectively.By contrast,a lower CTE of the coarse aggregate results in a greater maximum tensile stress on the pier concrete surface.For example,when using limestone,which has a low CTE,the maximum tensile stress on the pier concrete surface is 2.28 MPa,compared to 2.17 MPa when using diorite and 2.14 MPa when using basalt.The finite element simulation results indicated that the maximum compressive stress on the pier concrete surface was 11.72 MPa,whereas the maximum tensile stress was 2.10 MPa.These results are approximately consistent with the theoretical calculations.This consistency provides mutual verification.Conclusions Surface cracking in pier concrete occurs predominantly before the erection of upper structures.Under sunny conditions,the orthogonal decomposition of the superficial stress revealed that the maximum compressive stress during the day was approximately 12.52 MPa,whereas the maximum tensile stress was approximately 2.15 MPa.This tensile stress approached the tensile strength of the C35 concrete under biaxial tension.The risk of cracking increased significantly when humidity-induced stress was considered.After the erection of upper structures,the maximum tangential tensile stress on the pier surface remained at 2.15 MPa while the maximum vertical stress decreased to 0.58 MPa,both of which are well below the tensile strength of C35 concrete under biaxial tension.Although the use of coarse aggregates with a lower coefficient of thermal expansion reduced the tensile stress induced by temperature gradients,it increased the stress owing to material deformation incompatibility,leading to a slight increase in the maximum tensile stress on the pier concrete surface.展开更多
The synchronous construction of the secondary lining during the boring of large-diameter shield faces challenges such as the design of the lining jumbo,the high requirements on the performance for the lining jumbo,the...The synchronous construction of the secondary lining during the boring of large-diameter shield faces challenges such as the design of the lining jumbo,the high requirements on the performance for the lining jumbo,the organization of the construction activities in the small and confined area,the horizontal transportation for shield boring and high safety management requirements.A super-long invert lining construction jumbo,as well as the matching California switch,is developed,which provides solution for the confliction between the invert lining construction and the horizontal transportation.The procedure and method for the synchronous operation of the shield boring and the secondary lining are developed by referring to the synchronous construction of the secondary lining during the boring of the TBMs in hard rocks.Due to the adoption of the synchronous operation of the shield boring and the secondary lining,the construction period is shortened and the construction cost is reduced.The paper can provide reference for the synchronous construction of the secondary lining in similar projects in the future.展开更多
Objective To discuss the postoperative curative effects of two surgical techniques of minimally invasive total hip arthroplasty (THA) using metal-on-metal largediameter and conventional diameter femoral head for the e...Objective To discuss the postoperative curative effects of two surgical techniques of minimally invasive total hip arthroplasty (THA) using metal-on-metal largediameter and conventional diameter femoral head for the elderly patients展开更多
Scour around bridge pier foundations is a complex phenomenon that can threaten structural stability.Accurate prediction of scour depth around compound piers remains challenging for bridge engineers.This study investig...Scour around bridge pier foundations is a complex phenomenon that can threaten structural stability.Accurate prediction of scour depth around compound piers remains challenging for bridge engineers.This study investigated the effect of foundation elevation on scour around compound piers and developed reliable scour depth prediction models for economical foundation design.Experiments were conducted under clear-water conditions using two circular piers:(1)a uniform pier(with a diameter of D)and(2)a compound pier consisting of a uniform pier resting on a circular foundation(with a foundation diameter(D_(f))of 2D)positioned at various elevations(Z)relative to the channel bed.Results showed that foundation elevation significantly affected scour depth.Foundations at or below the bed(Z/D≥0)reduced scour,while those projecting into the flow field(Z/D<0)increased scour.The optimal foundation elevation was found to be 0.1D below the bed level,yielding a 57%reduction in scour depth compared to the uniform pier due to its shielding effect against downflow and horseshoe vortices.In addition,regression,artificial neural network(ANN),and M5 model tree models were developed using experimental data from this and previous studies.The M5 model outperformed the traditional HEC-18 equation,regression,and ANN models,with a coefficient of determination greater than 0.85.Sensitivity analysis indicated that flow depth,foundation elevation,and diameter significantly influenced scour depth prediction,whereas sediment size had a lesser impact.展开更多
Aiming at the problems of difficulty in balancing construction efficiency and quality,as well as the high safety risks of working at heights during the construction of main piers for highway bridges,this study takes a...Aiming at the problems of difficulty in balancing construction efficiency and quality,as well as the high safety risks of working at heights during the construction of main piers for highway bridges,this study takes a specific bridge project as an example to introduce the technology of hydraulically sliding formwork for the construction of main piers of highway bridges.An in-depth analysis of the project’s construction process found that this technology can effectively improve construction efficiency,ensure the quality of concrete pouring,and significantly reduce the potential safety hazards of working at heights.It provides a reliable technical solution for constructing the main piers of highway bridges and has important reference significance for similar projects.展开更多
Bridge pier failures from granular flow impacts are common.Installing defense piles upstream is an effective mitigation strategy,yet their protective mechanisms and standardized design guidelines are unclear.This stud...Bridge pier failures from granular flow impacts are common.Installing defense piles upstream is an effective mitigation strategy,yet their protective mechanisms and standardized design guidelines are unclear.This study employed 3D discrete element method to analyze the influence of defense pile size and placement on its performance across 219 scenarios,providing a detailed examination of their protective mechanisms.Results show that optimizing these factors can reduce the maximum impact force on bridge piers by up to 94%.In terms of size,a critical height threshold is identified,beyond which increasing pile height does not enhance protection.This threshold depends on the movement height of granular particles at the slope base.Protection effectiveness varies with pile size:when H≤0.05 h(H is the height of defense piles,h is the height of bridge),protection marginally improves with increasing height and diameter;for 0.05 h<H<0.15 h,protection strongly correlates with both parameters;for H≥0.15 h,diameter becomes the dominant factor.In terms of placement,an optimal longitudinal distance exists between the defense pile and the bridge pier.The larger the diameter,the greater the optimal longitudinal distance.However,the transverse distance is inversely related to protection effectiveness.Mechanistic analysis shows that defense piles are more effective at redirecting particles to prevent direct collisions with the pier(contributing 100%impact energy reduction before the non-dimensional travel time t*=7.01 and 63%–100%afterward)than at reducing particle velocity.This study provides insights into the protective mechanisms of defense piles and informs strategies for optimizing bridge pier protection in granular flow-prone regions.展开更多
In this study,the flow characteristics around a group of three piers arranged in tandem were investigated both numerically and experimentally.The simulation utilised the volume of fluid(VOF)model in conjunction with t...In this study,the flow characteristics around a group of three piers arranged in tandem were investigated both numerically and experimentally.The simulation utilised the volume of fluid(VOF)model in conjunction with the k–ɛmethod(i.e.,for flow turbulence representations),implemented through the ANSYS FLUENT software,to model the free-surface flow.The simulation results were validated against laboratory measurements obtained using an acoustic Doppler velocimeter.The comparative analysis revealed discrepancies between the simulated and measured maximum velocities within the investigated flow field.However,the numerical results demonstrated a distinct vortex-induced flow pattern following the first pier and throughout the vicinity of the entire pier group,which aligned reasonably well with experimental data.In the heavily narrowed spaces between the piers,simulated velocity profiles were overestimated in the free-surface region and underestimated in the areas near the bed to the mid-stream when compared to measurements.These discrepancies diminished away from the regions with intense vortices,indicating that the employed model was capable of simulating relatively less disturbed flow turbulence.Furthermore,velocity results from both simulations and measurements were compared based on velocity distributions at three different depth ratios(0.15,0.40,and 0.62)to assess vortex characteristic around the piers.This comparison revealed consistent results between experimental and simulated data.This research contributes to a deeper understanding of flow dynamics around complex interactive pier systems,which is critical for designing stable and sustainable hydraulic structures.Furthermore,the insights gained from this study provide valuable information for engineers aiming to develop effective strategies for controlling scour and minimizing destructive vortex effects,thereby guiding the design and maintenance of sustainable infrastructure.展开更多
This article provides an overview of the current development status of prestressed segmental precast and assembled piers,Emphasis was placed on analyzing the stress characteristics of bridge piers under impact.The con...This article provides an overview of the current development status of prestressed segmental precast and assembled piers,Emphasis was placed on analyzing the stress characteristics of bridge piers under impact.The concept of recoverable functional design and its application prospects were elaborated,and finally,the research on the impact resistance performance of prestressed segmental precast and assembled pierswas discussed.Research has shown that optimizing design and material selection can effectively enhance the impact resistance and structural durability of bridge piers.At the same time,the introduction of the concept of recoverable functionality provides new ideas for the rapid repair and functional recovery of bridge piers,which helps to improve the recovery efficiency of bridges after extreme events.Future research should focus on the evaluation methods of impact resistance performance,new connection technologies,in-depth application of recoverable functional design,a combination of impact simulation experiments and numerical analysis,and exploration of comprehensive disaster prevention and reduction strategies.These research results will also promote the further development and innovation of prefabricated assembly technology in bridge engineering,bringing new ideas and methods to the field of engineering construction.展开更多
基金supported by the Beijing Natural Science Foundation(Grant No.8252012)the National Natural Science Foundation of China(Grant No.52378475).
文摘Accurate acquisition of the lithological composition of a tunnel face is crucial for efficient tunneling and hazard prevention in large-diameter slurry shield tunnels.While widely applied,current data-driven methods often face challenges such as indirect prediction,data sparsity,and data drift,which limit their accuracy and generalizability.This study develops an integrated method that combines a knowledge-driven method to directly compute distribution patterns of lithological components,which are used as a priori knowledge to guide the development of a data-driven method.Coupled Markov chain(CMC)and deep neural networks(DNNs)serve as the knowledge-driven and data-driven components,respectively.Additionally,a dynamic prediction strategy is proposed,where the model is continuously optimized as construction progresses and training samples accumulate,rather than being statically trained on post-construction data,as is common in data-driven methods.Finally,the proposed method is evaluated using a real-world project.The evaluation results show that the integrated method outperforms both individual data-and knowledge-driven methods,demonstrating higher predictive performance,greater stability,and greater robustness to data scarcity and data drift.Furthermore,the dynamic prediction strategy better captures the effects of gradual data accumulation and lithological spatial variability on prediction performance during construction,providing new insights for real-time prediction in practical tunneling applications.
基金Project(52274086)supported by the National Natural Science Foundation of ChinaProject(2024KJH069)supported by the Shandong Provincial Youth Innovation and Technology Support Program,ChinaProject(tstp20221126)supported by the Project of Taishan Scholar in Shandong Province,China。
文摘Large-diameter drilling method is a prevalent method for preventing and controlling rock burst,and the spacing between the large-diameter drilling hole and anchoring hole is a critical factor influencing the roadway stability and relief effectiveness.In this study,a mechanical model for optimal matching between the large-diameter drilling hole and anchoring hole was established following the principle of synergistic control.The influence of large-diameter drilling hole diameter on the optimal spacing under the synergistic relief effect was investigated by integrating theoretical analysis,numerical simulation,and field practice.The results suggest that the hole spacing achieved a synergistic effect in a certain range when the optimal hole spacing increased linearly with the hole diameter.For instance,when the anchoring hole diameter was 20 mm,an increase in the aperture ratio from 5 to 10 brought about an increase in the optimal spacing from 0.25 m to 0.45 m.Additionally,the vertical stress between the large-diameter drilling hole and anchor hole increased nonlinearly under the condition of constant pore ratio but varying hole spacing.Both excessively small and excessively large hole spacings were detrimental to the pressure relief effect.In the engineering practice,optimizing the hole spacing from 0.55 m to 0.45 m in the 1208 working face contributed to reducing coal body drilling cuttings and the roadway moving quantity by 33%and 19.2%,respectively.This demonstrates that the pressure relief-support reinforcement synergistic effect should be fully considered in optimization design.
基金National Natural Science Foundation of China (59975076, 50175092)National Science Fund of China for Distinguished Young Scholars (50225518)
文摘Tube thinning control without wrinkling occurring is a key problem urgently to be solved for improving the forming qualities in numerical control （NC） bending processes of large-diameter Al-alloy thin-walled tubes （AATTs）. It may be a way solving this problem to exert axial compression loads （ACL） on the tube end in the bending. Thus, this article establishes a three-dimensional （3D） elastic-plastic explicit finite element （FE） model for the bending under ACL and has its reliability verified. Through a multi-index orthogonal experiment design, a combination of process parameters, each expressed by a proper range, for this FE model is derived to overcome the compression instability on tube ends. By combining the FE model with a wrinkling energy prediction model, an in-depth study is conducted on the forming characteristics of large-diameter AATTs with small bending radii and it can be concluded that （1） The larger the tube diameters and the smaller the bending radii, the larger the induced tangent tension stress zones on tube intrados, by which the tube maximum tangent compression stress zones will be partitioned in the bending processes; thus, the smaller the ACL roles in decreasing thinning degrees and the larger the compression instability possibilities on tube ends. （2） The tube wrinkling possibilities under ACL are larger than without ACL acting in the earlier forming periods, and smaller in the later ones. （3） For the tubes with a size factor less than 80, the ACL roles in decreasing thinning degrees are stronger than in increasing wrinkling possibilities.
基金supported by National Natural Science Foundation of China (Grant No. 50875017)
文摘The existing researches of the magnetic liquid rotation seal have been mainly oriented to the seal at normal temperature and the seal with the smaller shaft diameter less than 100 mm. However, the large-diameter magnetic liquid rotation seal at low temperature has not been reported both in theory and in application up to now. A key factor restricting the application of the large-diameter magnetic liquid rotation seal at low temperature is the high breakaway torque. In this paper, the factors that influence the breakaway torque including the number of seal stages, the injected quantity of magnetic liquid and the standing time at normal temperature are studied. Two kinds of magnetic liquid with variable content of large particles are prepared first, and a seal feedthrough with 140 mm shaft diameter is used in the experiments. All experiments are carried out in a low temperature chamber with a temperature range from 200℃ to -100℃. Different numbers of seal stages are tested under the same condition to study the relation between the breakaway torque and the number of seal stages. Variable quantity of magnetic liquid is injected in the seal gap to get the relation curve of the breakaway torque and the injecting quantity of magnetic liquid. In the experiment for studying the relation between the breakaway torque and the standing time at the normal temperature, the seal feedtrough is laid at normal temperature for different period of time before it is put in the low temperature chamber. The experimental results show that the breakaway torque is proportional to the number of seal stages, the injected quantity of magnetic liquid and the standing time at the normal temperature. Meanwhile, the experimental results are analyzed and the torque formula of magnetic liquid rotation seal at low temperature is deduced from the Navier-Stokes equation on the base of the model of magnetic liquid rotation seal. The presented research can make wider application of the magnetic liquid seal in general. And the large-diameter magnetic liquid rotation seal at low temperature designed by using present research results are to be used in some special fields, such as the military field, etc.
基金by the National Natural Science Foundation of China(Grant No.59679003)the Natural Science Foundation of Tianjin(Grant No.973606311)
文摘The large-diameter cylinder structure, which is made of large successive bottomless cylinders placed on foundation bed or partly driven into soil, is a recently developed retaining structure in China. It can be used in port, coastal and offshore works. The method for stability analysis of the large-diameter cylinder structure, especially for stability analysis of the embedded large-diameter cylinder structure, is an important issue. In this paper, an idea is presented that is, embedded large-diameter cylinder quays can be divided into two types, i.e. the gravity wall type and the cylinder pile wall type. A method for stability analysis of the large-diameter cylinder quay of the cylinder pile wall type is developed and a method for stability analysis of the large-diameter cylinder quay of the gravity wall type is also proposed. The effect of significant parameters on the stability of the large-diameter cylinder quay of the cylinder pile wall type is investigated through numerical calculation.
基金Project(U1134207)supported by the National Natural Science and High Speed Railway Jointed Foundation of ChinaProject(B13024)supported by the "111" Program of China+1 种基金Project(BK2012811)supported by the Nature Science Foundation of Jiangsu Province,ChinaProject(NCET-12-0843)supported by the Fund for New Century Excellent Talents in Universities,China
文摘Considering the viscous damping of the soil and soil-pile vertical coupled vibration,a computational model of large-diameter pipe pile in layered soil was established.The analytical solution in frequency domain was derived by Laplace transformation method.The responses in time domain were obtained by inverse Fourier transformation.The results of the analytical solution proposed agree well with the solutions in homogenous soil.The effects of the shear modulus and damping coefficients of the soil at both outer and inner sides of the pipe pile were researched.The results indicate that the shear modulus of the outer soil has more influence on velocity admittance than the inner soil.The smaller the shear modulus,the larger the amplitude of velocity admittance.The velocity admittance weakened by the damping of the outer soil is more obvious than that weakened by the damping of the inner soil.The displacements of the piles with the same damping coefficients of the outer soil have less difference.Moreover,the effects of the distribution of soil layers are analyzed.The results indicate that the effect of the upper soil layer on dynamic response of the pipe pile is more obvious than that of the bottom soil layer.A larger damping coefficient of the upper layer results in a smaller velocity admittance.The dynamic response of the pipe pile in layered soil is close to that of the pipe pile in homogenous soil when the properties of the upper soil layer are the same.
文摘A method of coupled BEM-FEM analysis for the elastic spatial structure system is presented. It can be applied to the calculation of the stress and deformation of the large-diamater cylinder structure system and it is suitable for symmetric or non-symmetric structures under the distributed or concentrated load. Numerical examples show that the proposed method and computer program BEFEM are quite efficient in the analysis of the large-diameter cylinder structure problems in ocean engineering.
文摘This study addresses the increasing demand for large-diameter production timber,and considers the time and space variability of half-sib families of Pinus massoniana.Height,diameter at breast height(DBH)and timber volume of 440 open-pollinated half-sib progeny families were investigated in 14 progeny trials in different years and production regions.An evaluation of the genetic variation of all half-sib families was carried out during the sustainable rapid growth period and individual volumes were characterized as a major index.ANOVA analysis showed that there was considerable variance in the growth traits of most families in different years and on different sites.The variations caused by temporal and spatial changes of the mating system required three selection methods for analysis.The results show that there were differences among the heritabilities of different growth traits by different halfsib progenies.Average heritability values of height,DBH and volume were 0.33,0.34 and 0.36,respectively.Fortyfive superior families were selected in every progeny test,12 were selected in progeny trials by different years and five in different habitat progeny trials.Three superior families(Gui GC553A,Gui GC414A and Gui GC431A)were selected,although in different years and production regions.The genetic gains of timber volume of these selected r families ranged from 1.20 to 47.00%,which could provide a foundation for superior wood property selection and serve as material for seed improvement and extension in surrounding areas.
基金supported by the Joint High Speed Railway Key Program of National Natural Science Foundation of China (Grant No.U1134207)the National Natural Science Foundation of China (Grant No.51378177)+1 种基金the Program for Excellent University Talents in New Century (Grant No.NCET-12-0843)the Fundamental Research Fund for the Central Universities (Grant No.106112014CDJZR200007)
文摘This paper aims to present a theoretical method to study the bearing performance of vertically loaded large-diameter pipe pile groups.The interactions between group piles result in different bearing performance of both a single pile and pile groups.Considering the pile group effect and the skin friction from both outer and inner soils,an analytical solution is developed to calculate the settlement and axial force in large-diameter pipe pile groups.The analytical solution was verified by centrifuge and field testing results.An extensive parametric analysis was performed to study the bearing performance of the pipe pile groups.The results reveal that the axial forces in group piles are not the same.The larger the distance from central pile,the larger the axial force.The axial force in the central pile is the smallest,while that in corner piles is the largest.The axial force on the top of the corner piles decreases while that in the central pile increases with increasing of pile spacing and decreasing of pile length.The axial force in side piles varies little with the variations of pile spacing,pile length,and shear modulus of the soil and is approximately equal to the average load shared by one pile.For a pile group,the larger the pile length is,the larger the influence radius is.As a result,the pile group effect is more apparent for a larger pile length.The settlement of pile groups decreases with increasing of the pile number in the group and the shear modulus of the underlying soil.
基金Project(41202220) supported by the National Natural Science Foundation of ChinaProject(2011YYL034) supported by the Fundamental Research Funds for the Central Universities,China
文摘A new technique for the analysis of the three-dimensional collapse failure mechanism and the ground surface settlements for the large-diameter shield tunnels were presented.The technique is based on a velocity field model using more different truncated solid conical blocks to clarify the multiblock failure mechanism.Furthermore,the shape of blocks between the failure surface and the tunnel face was considered as an entire circle,and the supporting pressure was assumed as non-uniform distribution on the tunnel face and increased with the tunnel embedded depth.The ground surface settlements and failure mechanism above large-diameter shield tunnels were also investigated under different supporting pressures by the finite difference method.
基金Project(51674096)supported by the National Natural Science Foundation of ChinaProject(E2016203119)supported by Hebei Natural Science Foundation of ChinaProject(18211045)supported by the Key Research and Development Foundation in Hebei Province of China
文摘Cooling strength is one of the important factors affecting microstructure and properties of gas cylinders during quenching process,and reasonable water spray volume can effectively improve the quality of gas cylinders and reduce production costs.To find the optimal water spray parameters,a fluid-solid coupling model with three-phase flow was established in consideration of water-vapor conversion.The inner and outer walls of gas cylinder with the dimensions of d914 mm×38 mm×12000 mm were quenched using multi-nozzle water spray system.The internal pressure,average heat transfer coefficient(have)and stress of the gas cylinder under different water spray volumes during quenching process were studied.Finally,the mathematical model was experimentally verified.The results show that both the internal pressure and have increase along with the increase of spray volume.The internal pressure increases slowly first and then rapidly,but have increases rapidly first and then slowly.To satisfy hardenability of gas cylinders,the minimum spray volume should not be less than 40 m^3/(h·m).The results of stress indicate that water spray quenching will not cause deformation of bottle body in the range of water volume from 40 to 290 m^3/(h·m).
基金support from the Exploring Youth Project of Zhejiang Natural Science Foundation (Grant No.LQ24E080009)the Key Project of Natural Science Foundation of Zhejiang Province (Grant No.LXZ22E080001)the National Natural Science Foundation of China (Grant No.52108347).
文摘A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the soil along pile shaft is divided into slip and nonslip zones and the base soil is modeled as a fictitious-soil pile(FSP)to account for the wave propagation in the soil.True soil properties are adopted and slippage at the pile-soil interface is considered,allowing realistic representation of largediameter OEPP mechanics.The developed model is validated by comparing with conventional models and finite element method(FEM).It is further used to successfully simulate and interpret the behaviors of a steel OEPP during the offshore field test.It is found that the variation in the vertical vibrations of shaft soil along radial direction is significant for large-diameter OEPPs,and the velocity amplitudes of the internal and external soil attenuate following different patterns.The shaft soil motion may not attenuate with depth due to the soil slippage,while the wave attenuation at base soil indicates an influence depth,with a faster attenuation rate than that in the pile.The findings from the current study should aid in simulating the vibration behaviors of large-diameter OEPP-soil system under high-strain dynamic loading.
文摘Introduction The predominant characteristics of high-altitude climates include low air pressure,low humidity,and large diurnal temperature fluctuations.In practical engineering scenarios in high-altitude regions,many pier surface cracks only appear several months after erection,and cyclic thermal stress is identified as the main trigger for such cracking.The thermal stress in concrete structures has been investigated for decades but remains incompletely understood.Structural engineers typically regard concrete as an isotropic material and calculate the thermal stress using code-specified coefficients of thermal expansion(CTEs)along with temperature conditions and constraints.Because the CTE of hardened cement paste is more than twice that of many aggregates,reducing the CTE of coarse aggregates can further exacerbate the thermal deformation incompatibility between the coarse aggregate and mortar matrix.In this paper,a comprehensive thermal-elastic mechanics model for pier concrete was developed to analysis the temperature-induced surface stress.Methods A series of mechanical and thermophysical tests were conducted on the diorite aggregate,ITZ cement paste,and mortar,and concrete.A test pier was constructed on open ground near the Yarlung Zangbo River at an altitude of 3800 m.The pier had a diameter of 1.8 m and height of 2 m.Temperature sensors were embedded in the cross-section at a height of 1 m,positioned along the southnorth and east-west directions.The embedding depths(distances from the pier surface)were 0,1.5,3,4.5,6,7.5,9,12,15,20,25,30,35,40,50,60,70,80 cm,and 90 cm.A model of the bridge pier concrete for surface-level analysis was constructed.The model consists of a concrete unit formed as a sphere-shell-shell composite,including the aggregate,ITZ,and mortar layers,embedded in the surface layer of a bridge pier.Outside this unit,the pier concrete was treated as an isotropic,homogeneous elastic material.The real-time internal temperature fields of high-altitude concrete bridge piers,measured on-site,were incorporated into the model.By applying thermoelastic mechanics theory and finite element solutions for plane strain problems,the three-dimensional thermal stresses on the surface layer of high-altitude bridge piers were analyzed Results and discussion During the experimental period,the lowest and highest temperatures on the bridge pier in the high-altitude region were 9.6 ℃ and 42.6 ℃,respectively.These occurred before sunrise and sunset on sunny days,respectively,corresponding to the local maximum temperature gradients during the surface heating and cooling stages,as well as the maximum temperature difference between the surface and center during these stages.The thermal stress on the pier concrete surface was obtained by superimposing the stresses caused by the uneven distribution of the internal temperature field and those caused by the incompatible thermal deformation among the different components in the surface concrete Before the erection of the upper structures,the absolute values of the tangential and vertical stresses were the same;therefore,only one curve was observed.From 22:00 to 8:00,the pier concrete surface was in tension,whereas from 11:00 to 22:00,the pier concrete surface was in compression.The surface of the pier concrete was subjected to biaxial forces of equal magnitude with a maximum compressive stress of 12.52 MPa and maximum tensile stress of 2.15 MPa,respectively at 18:00 and 8:00.According to the fatigue equation,the concrete was predicted to crack after 21 d of temperature cycling.Moreover,if humidity-induced stress is added on top of this,the tensile stress may approach or even exceed the concrete's tensile strength,thereby posing a significant risk of cracking.After the erection of upper structures,the tangential and vertical stresses no longer coincide because the upper structures have been erected.The curve of the tangential stress is unchanged,whereas the curve of the vertical stress is translated downwards by 1.57 MPa due to the structural deadweight.Therefore,the maximum tangential compressive stress remained 12.52 MPa,whereas the maximum vertical compressive stress increased to 14.09 MPa.Additionally,the maximum tangential tensile stress was 2.15 MPa,and the maximum vertical tensile stress was 0.58 MPa.According to Appendix C of GB/T 50010 and the fatigue equation,stresses are unlikely to cause cracking of the pier concrete surface.Although a higher CTE of the coarse aggregate slightly increased the maximum compressive stress,the differences among the three groups of concrete were minimal and could be ignored.Specifically,the maximum compressive stresses on the pier concrete surface were 12.54,12.45 MPa,and 12.56 MPa when using diorite,limestone,and basalt,respectively.By contrast,a lower CTE of the coarse aggregate results in a greater maximum tensile stress on the pier concrete surface.For example,when using limestone,which has a low CTE,the maximum tensile stress on the pier concrete surface is 2.28 MPa,compared to 2.17 MPa when using diorite and 2.14 MPa when using basalt.The finite element simulation results indicated that the maximum compressive stress on the pier concrete surface was 11.72 MPa,whereas the maximum tensile stress was 2.10 MPa.These results are approximately consistent with the theoretical calculations.This consistency provides mutual verification.Conclusions Surface cracking in pier concrete occurs predominantly before the erection of upper structures.Under sunny conditions,the orthogonal decomposition of the superficial stress revealed that the maximum compressive stress during the day was approximately 12.52 MPa,whereas the maximum tensile stress was approximately 2.15 MPa.This tensile stress approached the tensile strength of the C35 concrete under biaxial tension.The risk of cracking increased significantly when humidity-induced stress was considered.After the erection of upper structures,the maximum tangential tensile stress on the pier surface remained at 2.15 MPa while the maximum vertical stress decreased to 0.58 MPa,both of which are well below the tensile strength of C35 concrete under biaxial tension.Although the use of coarse aggregates with a lower coefficient of thermal expansion reduced the tensile stress induced by temperature gradients,it increased the stress owing to material deformation incompatibility,leading to a slight increase in the maximum tensile stress on the pier concrete surface.
文摘The synchronous construction of the secondary lining during the boring of large-diameter shield faces challenges such as the design of the lining jumbo,the high requirements on the performance for the lining jumbo,the organization of the construction activities in the small and confined area,the horizontal transportation for shield boring and high safety management requirements.A super-long invert lining construction jumbo,as well as the matching California switch,is developed,which provides solution for the confliction between the invert lining construction and the horizontal transportation.The procedure and method for the synchronous operation of the shield boring and the secondary lining are developed by referring to the synchronous construction of the secondary lining during the boring of the TBMs in hard rocks.Due to the adoption of the synchronous operation of the shield boring and the secondary lining,the construction period is shortened and the construction cost is reduced.The paper can provide reference for the synchronous construction of the secondary lining in similar projects in the future.
文摘Objective To discuss the postoperative curative effects of two surgical techniques of minimally invasive total hip arthroplasty (THA) using metal-on-metal largediameter and conventional diameter femoral head for the elderly patients
文摘Scour around bridge pier foundations is a complex phenomenon that can threaten structural stability.Accurate prediction of scour depth around compound piers remains challenging for bridge engineers.This study investigated the effect of foundation elevation on scour around compound piers and developed reliable scour depth prediction models for economical foundation design.Experiments were conducted under clear-water conditions using two circular piers:(1)a uniform pier(with a diameter of D)and(2)a compound pier consisting of a uniform pier resting on a circular foundation(with a foundation diameter(D_(f))of 2D)positioned at various elevations(Z)relative to the channel bed.Results showed that foundation elevation significantly affected scour depth.Foundations at or below the bed(Z/D≥0)reduced scour,while those projecting into the flow field(Z/D<0)increased scour.The optimal foundation elevation was found to be 0.1D below the bed level,yielding a 57%reduction in scour depth compared to the uniform pier due to its shielding effect against downflow and horseshoe vortices.In addition,regression,artificial neural network(ANN),and M5 model tree models were developed using experimental data from this and previous studies.The M5 model outperformed the traditional HEC-18 equation,regression,and ANN models,with a coefficient of determination greater than 0.85.Sensitivity analysis indicated that flow depth,foundation elevation,and diameter significantly influenced scour depth prediction,whereas sediment size had a lesser impact.
文摘Aiming at the problems of difficulty in balancing construction efficiency and quality,as well as the high safety risks of working at heights during the construction of main piers for highway bridges,this study takes a specific bridge project as an example to introduce the technology of hydraulically sliding formwork for the construction of main piers of highway bridges.An in-depth analysis of the project’s construction process found that this technology can effectively improve construction efficiency,ensure the quality of concrete pouring,and significantly reduce the potential safety hazards of working at heights.It provides a reliable technical solution for constructing the main piers of highway bridges and has important reference significance for similar projects.
基金supported by the National Natural Science Foundation of China(Grant numbers 41977233)。
文摘Bridge pier failures from granular flow impacts are common.Installing defense piles upstream is an effective mitigation strategy,yet their protective mechanisms and standardized design guidelines are unclear.This study employed 3D discrete element method to analyze the influence of defense pile size and placement on its performance across 219 scenarios,providing a detailed examination of their protective mechanisms.Results show that optimizing these factors can reduce the maximum impact force on bridge piers by up to 94%.In terms of size,a critical height threshold is identified,beyond which increasing pile height does not enhance protection.This threshold depends on the movement height of granular particles at the slope base.Protection effectiveness varies with pile size:when H≤0.05 h(H is the height of defense piles,h is the height of bridge),protection marginally improves with increasing height and diameter;for 0.05 h<H<0.15 h,protection strongly correlates with both parameters;for H≥0.15 h,diameter becomes the dominant factor.In terms of placement,an optimal longitudinal distance exists between the defense pile and the bridge pier.The larger the diameter,the greater the optimal longitudinal distance.However,the transverse distance is inversely related to protection effectiveness.Mechanistic analysis shows that defense piles are more effective at redirecting particles to prevent direct collisions with the pier(contributing 100%impact energy reduction before the non-dimensional travel time t*=7.01 and 63%–100%afterward)than at reducing particle velocity.This study provides insights into the protective mechanisms of defense piles and informs strategies for optimizing bridge pier protection in granular flow-prone regions.
文摘In this study,the flow characteristics around a group of three piers arranged in tandem were investigated both numerically and experimentally.The simulation utilised the volume of fluid(VOF)model in conjunction with the k–ɛmethod(i.e.,for flow turbulence representations),implemented through the ANSYS FLUENT software,to model the free-surface flow.The simulation results were validated against laboratory measurements obtained using an acoustic Doppler velocimeter.The comparative analysis revealed discrepancies between the simulated and measured maximum velocities within the investigated flow field.However,the numerical results demonstrated a distinct vortex-induced flow pattern following the first pier and throughout the vicinity of the entire pier group,which aligned reasonably well with experimental data.In the heavily narrowed spaces between the piers,simulated velocity profiles were overestimated in the free-surface region and underestimated in the areas near the bed to the mid-stream when compared to measurements.These discrepancies diminished away from the regions with intense vortices,indicating that the employed model was capable of simulating relatively less disturbed flow turbulence.Furthermore,velocity results from both simulations and measurements were compared based on velocity distributions at three different depth ratios(0.15,0.40,and 0.62)to assess vortex characteristic around the piers.This comparison revealed consistent results between experimental and simulated data.This research contributes to a deeper understanding of flow dynamics around complex interactive pier systems,which is critical for designing stable and sustainable hydraulic structures.Furthermore,the insights gained from this study provide valuable information for engineers aiming to develop effective strategies for controlling scour and minimizing destructive vortex effects,thereby guiding the design and maintenance of sustainable infrastructure.
基金supported by the Zhejiang Provincial Natural Science Foundation of China under Grant No.LTGG23E080001Scientific Research Foundation of Hangzhou City University under Grant Nos.X-202107 and X-202109Zhejiang Engineering Research Center of Intelligent Urban Infrastructure under Grant No.IUI2023-ZD-14.
文摘This article provides an overview of the current development status of prestressed segmental precast and assembled piers,Emphasis was placed on analyzing the stress characteristics of bridge piers under impact.The concept of recoverable functional design and its application prospects were elaborated,and finally,the research on the impact resistance performance of prestressed segmental precast and assembled pierswas discussed.Research has shown that optimizing design and material selection can effectively enhance the impact resistance and structural durability of bridge piers.At the same time,the introduction of the concept of recoverable functionality provides new ideas for the rapid repair and functional recovery of bridge piers,which helps to improve the recovery efficiency of bridges after extreme events.Future research should focus on the evaluation methods of impact resistance performance,new connection technologies,in-depth application of recoverable functional design,a combination of impact simulation experiments and numerical analysis,and exploration of comprehensive disaster prevention and reduction strategies.These research results will also promote the further development and innovation of prefabricated assembly technology in bridge engineering,bringing new ideas and methods to the field of engineering construction.
