This paper presents an experimental study on the behavior of circular concrete columns reinforced by BFRP-PVC tubes under uniaxial loading.A total of six specimens were prepared and tested under uniaxial loading.The m...This paper presents an experimental study on the behavior of circular concrete columns reinforced by BFRP-PVC tubes under uniaxial loading.A total of six specimens were prepared and tested under uniaxial loading.The main parameters varied in the tests were strengthening ratio and strengthening approach of BFRP.The performance,such as failure modes,ultimate bearing capacity and stress-strain curves,was investigated in details and a formula was proposed to predict the compressive ultimate strength.The results show that this kind of confined columns obviously improves the ultimate bearing capacity,and the ultimate bearing capacity increases with the strengthening layers.The formula proposed is applicable and efficient for prediction of the ultimate bearing capacity as well.展开更多
This research investigates the bending response of folded multi-celled tubes(FMTs)fabricated by folded metal sheets.A three-point bending test for FMTs with circular and square sections is designed and introduced.The ...This research investigates the bending response of folded multi-celled tubes(FMTs)fabricated by folded metal sheets.A three-point bending test for FMTs with circular and square sections is designed and introduced.The base numerical models are correlated with physical experiments and a static crashworthiness analysis of six FMT configurations to assess their energy absorption characteristics.The influences of thickness,sectional shape,and load direction on the bending response are studied.Results indicate that increasing the thickness of the tube and radian of the inner tube enhances the crashworthiness performance of FMT,yielding a 20.50%increase in mean crushing force,a 55.53%increase in specific energy absorption,and an 18.05%decrease in peak crushing force compared to traditional multi-celled tubes(TMTs).A theoretical analysis of the specific energy absorption indicates that FMTs outperform TMTs,particularly when the peak crushing force is prominent.This study highlights the innovative and practical potential of FMTs to improve the crashworthiness of thin-walled structures.展开更多
The behavior of reinforced concrete(RC)square columns strengthened with self-compacting concrete(SCC)-filled steel tubes under cyclic loading was experimentally investigated.Tests were carried out on eleven reinforced...The behavior of reinforced concrete(RC)square columns strengthened with self-compacting concrete(SCC)-filled steel tubes under cyclic loading was experimentally investigated.Tests were carried out on eleven reinforced columns and one unreinforced column.The parameters studied for the strengthened columns included axial compression ratio,reinforcement rate,defect rate,strength of SCC,and the section form of a reinforced steel tube.The results show that the steel tube SCC reinforcement method can effectively strengthen RC columns,exert the restraint effect of steel tube,and delay the development of internal concrete cracks.The method can also significantly improve the bearing capacity of RC columns.Regarding ductility,the improvement of the reinforced column is obvious,the deformation resistance of the specimen is enhanced,and the degradation of stiffness and strength is relatively slow,indicating that it has good seismic performance.展开更多
The fabrication of one-dimensional metal/N-doped carbon materials has shown a promising prospect as efficient electrocata-lysts for oxygen reduction reaction(ORR).Herein,CoNi alloy nanoparticles anchored on N-doped ca...The fabrication of one-dimensional metal/N-doped carbon materials has shown a promising prospect as efficient electrocata-lysts for oxygen reduction reaction(ORR).Herein,CoNi alloy nanoparticles anchored on N-doped carbon nanotubes(CoNi@NCNT)are prepared by a dual-template strategy,using polypyrrole(PPy)tubes and CoNi-based metal-organic framework as the precursors.The as-formed CoNi@NCNT catalyst displays a half-wave potential(0.83 V)as well as good durability under alkaline medium.The excellent electrocatalytic performance is ascribed to a synergistic coupling of hierarchically tubular structure,highly electronic conductivity,and abundantly alloy-type active sites.When the CoNi@NCNT catalyst is applied in zinc-air battery(ZAB),the device displays a stable charge-discharge cycling performance.The present work affords a useful approach to constructing alloy/nitrogen-incorporated carbon-aceous materials as bifunctional electrocatalysts for high-performance ZABs.展开更多
In the anticorrosive coating line of a welded tube plant, the current status and existing problems of the medium-frequency induction heating equipment were discussed.Partial renovations of the power control cabinet ha...In the anticorrosive coating line of a welded tube plant, the current status and existing problems of the medium-frequency induction heating equipment were discussed.Partial renovations of the power control cabinet have been conducted.Parameters such as the DC current, DC voltage, intermediate frequency power, heating temperature, and the positioning signal at the pipe end were collected.A data acquisition and processing system, which can process data according to user needs and provide convenient data processing functions, has been developed using LabVIEW software.This system has been successfully applied in the coating line for the automatic control of high-power induction heating equipment, production management, and digital steel tube and/or digital delivery.展开更多
Two cross⁃sectional configurations of thin⁃walled square tubes partially filled with lightweight metallic foams are proposed,and termed as double⁃cell configuration partially filled with foam(DC⁃PF)and double⁃tube con...Two cross⁃sectional configurations of thin⁃walled square tubes partially filled with lightweight metallic foams are proposed,and termed as double⁃cell configuration partially filled with foam(DC⁃PF)and double⁃tube configuration partially filled with foam(DT⁃PF),respectively.The bending crashworthiness is investigated based on three⁃point bending tests using finite element ABAQUS/Explicit code.The two key mechanical indicators including Crash Load Efficiency(CLE)and Specific Energy Absorption(SEA)are introduced to evaluate the effect of foams in comparison with empty square tubes and fully filled square tubes.The numerical results show that the two partially filled configurations,especially DT⁃PF,display dramatically excellent bending crashworthiness compared with empty and fully filled square tubes.There exists a foam density threshold,beyond which the CLE of DT⁃PF achieves a maximum constant.In addition,there seems to be another foam density threshold,beyond which the SEA of DT⁃PF gets to the maximum value.It is also shown that the foam density threshold corresponding to the maximum SEA varies with the thickness of thin⁃walled square tubes.展开更多
The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weld...The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weldability of components with thin walls after small punch sampling,such as ethylene cracking furnace tubes,requires further investigation.Therefore,the weldability of in-service ethylene cracking furnace tubes following small punch sampling was investigated through nondestructive testing,microstructural characterization,and mechanical testing.Additionally,the impact of small punch sampling size and residual stress on the creep performance of the specimens was studied using an improved ductility exhaustion model.The results indicate that both the surface and interior of the weld repair areas on new furnace tubes and service-exposed furnace tubes after small-punch sampling are defect-free,exhibiting good weld quality.The strength of the specimens after weld repair was higher than that before sampling,whereas toughness decreased.Weld repair following small punch sampling of furnace tubes is both feasible and necessary.Furthermore,a linear relationship was observed between specimen thickness,diameter,and creep fracture time.The residual stress of welding affects the creep performance of the specimen under different stresses.展开更多
This paper tackles uncertainties between planning and actual models.It extends the concept of RCI(robust control invariant)tubes,originally a parameterized representation of closed-loop control robustness in tradition...This paper tackles uncertainties between planning and actual models.It extends the concept of RCI(robust control invariant)tubes,originally a parameterized representation of closed-loop control robustness in traditional feedback control,to the domain of motion planning for autonomous vehicles.Thus,closed-loop system uncertainty can be preemptively addressed during vehicle motion planning.This involves selecting collision-free trajectories to minimize the volume of robust invariant tubes.Furthermore,constraints on state and control variables are translated into constraints on the RCI tubes of the closed-loop system,ensuring that motion planning produces a safe and optimal trajectory while maintaining flexibility,rather than solely optimizing for the open-loop nominal model.Additionally,to expedite the solving process,we were inspired by L2gain to parameterize the RCI tubes and developed a parameterized explicit iterative expression for propagating ellipsoidal uncertainty sets within closedloop systems.Furthermore,we applied the pseudospectral orthogonal collocation method to parameterize the optimization problem of transcribing trajectories using high-order Lagrangian polynomials.Finally,under various operating conditions,we incorporate both the kinematic and dynamic models of the vehicle and also conduct simulations and analyses of uncertainties such as heading angle measurement,chassis response,and steering hysteresis.Our proposed robust motion planning framework has been validated to effectively address nearly all bounded uncertainties while anticipating potential tracking errors in control during the planning phase.This ensures fast,closed-loop safety and robustness in vehicle motion planning.展开更多
The electric vertical takeoff and landing(e VTOL)aircraft shows great potential for rapid military personnel deployment on the battlefield.However,its susceptibility to control loss,complex crashes,and extremely limit...The electric vertical takeoff and landing(e VTOL)aircraft shows great potential for rapid military personnel deployment on the battlefield.However,its susceptibility to control loss,complex crashes,and extremely limited bottom energy-absorbing space demands higher comprehensive crashworthiness of its subfloor thin-walled structures.This study investigated the energy absorption capacity of novel concave polygonal carbon fiber reinforced plastics(CFRP)tubes under multi-angle collisions.Quasistatic compression experiments and finite element simulations were conducted to assess the failure mode and energy absorption.The influences of cross-section shapes,loading conditions,and geometry parameters on crashworthiness metrics were further analyzed.The results revealed that,under the similar weight,concave polygonal tubes exhibited superior energy absorption under axial loads compared to regular polygonal and circular tubes,attributed to the increased number of axial splits.However,both regular and concave polygonal tubes,particularly the latter,demonstrated reduced oblique energy absorption compared to traditional square tubes with the increasing ratio of SEA value decreased from 20%-16%.Notably,this reduction in energy absorption can be compensated for by the implementation of inward and outward crusher plugs,and with them,the concave polygonal tubes demonstrated outstanding overall crashworthiness performance under multiple loading conditions.This concave cross-sectional design methods could serve as a guidance for the development of the eVTOL subfloor.展开更多
The main purpose of this research is to optimize the hydrothermal performance of a dimpled tube by augmenting the surface area for heat transmission and thermal layer cracking.To achieve that,the impact of different d...The main purpose of this research is to optimize the hydrothermal performance of a dimpled tube by augmenting the surface area for heat transmission and thermal layer cracking.To achieve that,the impact of different dimple diameters and their distribution along the dimpled tube was investigated numerically using the ANSYS Fluent 2022 R1 software by considering two models,A and B.Both models consist of three regions;the first,second,and third have dimple diameters of 3,2,&1 mm,respectively.Model A included an in-line dimple arrangement,while model B involved a staggered dimple arrangement.The finite volume method(FVM)was used in the modeling techniques to address the turbulent flow problem,which ranged in this investigation from Re of 3000 to 8000.The cooling fluid used in this investigation is water,which concentrated primarily on single-phase flow conditions.The investigation results revealed that as the Re increased,all analyzed models showcased higher.A reduction in pressure drops,thermal resistance,Nu,and overall performance standards.Crucially,compared to the traditionalmodel,both suggested models demonstrated improved heat transmission capacities.Within all the models examined,the tube with dimples in(model B)as staggered showed the greatest enhancement in the Nu,which was almost double that of the conventional type.Model A and Model B have respective average total performance criteria of 1.23 and 1.34.展开更多
The grain size of TiAl alloy castings prepared by traditional casting process is coarse,thus showing poor mechanical properties.In this study,a new type of high performance Ti-46Al alloy tube prepared by vacuum centri...The grain size of TiAl alloy castings prepared by traditional casting process is coarse,thus showing poor mechanical properties.In this study,a new type of high performance Ti-46Al alloy tube prepared by vacuum centrifugal casting technology was introduced.This research comprehensively examined the influence of pouring time on the microstructure and mechanical performance of the castings,employing both experimental approaches and ProCast simulation methodologies.The findings indicate that prolonging the pouring time facilitates a microstructural evolution from coarse columnar grains to refined equiaxed grains.Under the condition of pouring temperature of 1,600℃,rotation speed of 800 r·min^(-1) and pouring time of 6 s,the tensile strength of Ti-46Al alloy at room temperature reaches 650 MPa,and the tensile strength at 800℃ reaches 705 MPa,which is significantly higher than that of traditional as-cast Ti-Al alloy.展开更多
In this paper,a distributed Event-Triggered(ET)collision avoidance coordinated control for Quadrotor Unmanned Aerial Vehicles(QUAVs)is proposed based on Virtual Tubes(VTs)with flexible boundaries in the presence of un...In this paper,a distributed Event-Triggered(ET)collision avoidance coordinated control for Quadrotor Unmanned Aerial Vehicles(QUAVs)is proposed based on Virtual Tubes(VTs)with flexible boundaries in the presence of unknown external disturbances.Firstly,VTs are constructed for each QUAV,and the QUAV is restricted into the corresponding VT by the artificial potential field,which is distributed around the boundary of the VT.Thus,the collisions between QUAVs are avoided.Besides,the boundaries of the VTs are flexible by the modification signals,which are generated by the self-regulating auxiliary systems,to make the repulsive force smaller and give more buffer space for QUAVs without collision.Then,a novel ET mechanism is designed by introducing the concept of prediction to the traditional fixed threshold ET mechanism.Furthermore,a disturbance observer is proposed to deal with the adverse effects of the unknown external disturbance.On this basis,a distributed ET collision avoidance coordinated controller is proposed.Then,the proposed controller is quantized by the hysteresis uniform quantizer and then sent to the actuator only at the ET instants.The boundedness of the closed-loop signals is verified by the Lyapunov method.Finally,simulation and experimental results are performed to demonstrate the superiority of the proposed control method.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
A rotary swaging machine was applied to fabricating pipe reduction for miniature inner grooved copper tube （MIGCT） heat pipes. Compared with conventional swaging method, the axial feed of the designed rotary swaging...A rotary swaging machine was applied to fabricating pipe reduction for miniature inner grooved copper tube （MIGCT） heat pipes. Compared with conventional swaging method, the axial feed of the designed rotary swaging machine was reached by a constant pushing force. The deformation of grooves in pipe reduced section during rotary swaging was analyzed. The shrinkage and extensibility of pipe reduction were measured and calculated. Furthermore, four aspects, including outer diameter, surface roughness, extensibility and processing time of pipe reduction, which were influenced by the pushing force, were considered. The results show that the tube wall thickness increases gradually along the z-axis at sinking section. However, the outer diameters, surface roughness and micro-cracks at reduced section tend to decrease along the z-axis. Besides, the effect of variation in the pushing force on the extensibility is limited while an increase in the pushing force results in a decrease of surface roughness. Therefore, a large pushing force within the limit is beneficial to pipe reduction manufacturing during rotary swaging process.展开更多
Two types of tube bundles are designed,which are,respectively,composed of six tubes arranged in the boiling chamber.The nucleate pool boiling performance of smooth tube bundles and sintered porous surface tube bundles...Two types of tube bundles are designed,which are,respectively,composed of six tubes arranged in the boiling chamber.The nucleate pool boiling performance of smooth tube bundles and sintered porous surface tube bundles with deionized water as a medium are experimentally studied at atmospheric and sub-atmospheric pressures,respectively.The experimental results indicate that the boiling heat transfer coefficients of the two types of tube bundles increase with the increase in pressure under vacuum conditions as they behave under ordinary pressure.As the pressure varies from 10 to 100 kPa,it also can be seen that the heat transfer coefficient of the sintered porous surface tube is increased by 0.2 to 4 times compared with the smooth one under the same operating parameters.In addition,the experimental data show that a definite bundle effect exists in both sintered porous surface tubes and smooth tubes under vacuum conditions.展开更多
Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of th...Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of the geometric and system parameters on heat transfer characteristics in helically coiled tubes are investigated by collecting large amounts of experimental data and analyzing the heat transfer mechanisms. The existing correlations are divided into two categories,and they are calculated with the experimental data.The Dn factor is introduced to take into account the effect of a complex geometrical structure on flow boiling heat transfer.A new correlation is developed for predicting the flow boiling heat transfer coefficients in the helically coiled tubes,which is validated by the experimental data of R134a flow boiling heat transfer in them;and the average relative error and root mean square error of the new correlation are calculated.The results show that the new correlation agrees well with the experimental data,indicating that the new correlation can be used for predicting flow boiling heat transfer characteristics in the helically coiled tubes.展开更多
In order to develop the warming bending technology of the large diameter thin-walled（LDTW） commercial pure titanium alloy CP-Ti tubes, the warm bending mechanism of the extrados and intrados of LDTW CP-Ti tubes was ...In order to develop the warming bending technology of the large diameter thin-walled（LDTW） commercial pure titanium alloy CP-Ti tubes, the warm bending mechanism of the extrados and intrados of LDTW CP-Ti tubes was researched. By EBSD analysis and Vickers hardness test, the changes of microstructure and strength of the tubes at different bending temperatures of 293, 423 and 573 K, were analyzed. The results show： 1） The extrados of the bent tube deforms mainly by slip, along with few twinning, and the preferred orientation is similar to that of the initial tube; the intrados of the bent tube experiences compression deformation mainly by {1 012} tensile twinning, and the twinning makes the preferred orientation of wall materials change sharply. 2） The Vickers hardness values of both the extrados and intrados of the samples after bending increase greatly; the Vickers hardness values of the intrados are much higher than those of the extrados, and Vickers hardness values of the RD-TD planes are always higher than those of the RD-LD planes, which are related to the different deformation mechanisms.展开更多
文摘This paper presents an experimental study on the behavior of circular concrete columns reinforced by BFRP-PVC tubes under uniaxial loading.A total of six specimens were prepared and tested under uniaxial loading.The main parameters varied in the tests were strengthening ratio and strengthening approach of BFRP.The performance,such as failure modes,ultimate bearing capacity and stress-strain curves,was investigated in details and a formula was proposed to predict the compressive ultimate strength.The results show that this kind of confined columns obviously improves the ultimate bearing capacity,and the ultimate bearing capacity increases with the strengthening layers.The formula proposed is applicable and efficient for prediction of the ultimate bearing capacity as well.
基金supported by the National Natural Science Foundation of China(Grant No.52475277)2022 Guangxi University Young and Middle-aged Teachers’Basic Research Ability Improvement Project(Grant No.2022KY0781)Scientific Research Funds of Guilin University of Aerospace Technology(Grant No.XJ22KT29).
文摘This research investigates the bending response of folded multi-celled tubes(FMTs)fabricated by folded metal sheets.A three-point bending test for FMTs with circular and square sections is designed and introduced.The base numerical models are correlated with physical experiments and a static crashworthiness analysis of six FMT configurations to assess their energy absorption characteristics.The influences of thickness,sectional shape,and load direction on the bending response are studied.Results indicate that increasing the thickness of the tube and radian of the inner tube enhances the crashworthiness performance of FMT,yielding a 20.50%increase in mean crushing force,a 55.53%increase in specific energy absorption,and an 18.05%decrease in peak crushing force compared to traditional multi-celled tubes(TMTs).A theoretical analysis of the specific energy absorption indicates that FMTs outperform TMTs,particularly when the peak crushing force is prominent.This study highlights the innovative and practical potential of FMTs to improve the crashworthiness of thin-walled structures.
基金Natural Science Foundation of Sichuan Province under Grant Nos.2022NSFSC0319 and 2022NSFSC0095the Science and Technology Research Projects of Mianyang,China under Grant No.15S-02-3。
文摘The behavior of reinforced concrete(RC)square columns strengthened with self-compacting concrete(SCC)-filled steel tubes under cyclic loading was experimentally investigated.Tests were carried out on eleven reinforced columns and one unreinforced column.The parameters studied for the strengthened columns included axial compression ratio,reinforcement rate,defect rate,strength of SCC,and the section form of a reinforced steel tube.The results show that the steel tube SCC reinforcement method can effectively strengthen RC columns,exert the restraint effect of steel tube,and delay the development of internal concrete cracks.The method can also significantly improve the bearing capacity of RC columns.Regarding ductility,the improvement of the reinforced column is obvious,the deformation resistance of the specimen is enhanced,and the degradation of stiffness and strength is relatively slow,indicating that it has good seismic performance.
基金support by the National Natural Science Foundation of China(No.22279047).
文摘The fabrication of one-dimensional metal/N-doped carbon materials has shown a promising prospect as efficient electrocata-lysts for oxygen reduction reaction(ORR).Herein,CoNi alloy nanoparticles anchored on N-doped carbon nanotubes(CoNi@NCNT)are prepared by a dual-template strategy,using polypyrrole(PPy)tubes and CoNi-based metal-organic framework as the precursors.The as-formed CoNi@NCNT catalyst displays a half-wave potential(0.83 V)as well as good durability under alkaline medium.The excellent electrocatalytic performance is ascribed to a synergistic coupling of hierarchically tubular structure,highly electronic conductivity,and abundantly alloy-type active sites.When the CoNi@NCNT catalyst is applied in zinc-air battery(ZAB),the device displays a stable charge-discharge cycling performance.The present work affords a useful approach to constructing alloy/nitrogen-incorporated carbon-aceous materials as bifunctional electrocatalysts for high-performance ZABs.
文摘In the anticorrosive coating line of a welded tube plant, the current status and existing problems of the medium-frequency induction heating equipment were discussed.Partial renovations of the power control cabinet have been conducted.Parameters such as the DC current, DC voltage, intermediate frequency power, heating temperature, and the positioning signal at the pipe end were collected.A data acquisition and processing system, which can process data according to user needs and provide convenient data processing functions, has been developed using LabVIEW software.This system has been successfully applied in the coating line for the automatic control of high-power induction heating equipment, production management, and digital steel tube and/or digital delivery.
基金Sponsored by National Natural Science Foundation of China (Grant Nos.12272064 and 12101086)University Natural Science Research Project of Anhui Province (Grant No.KJ2018A0481)+2 种基金Major Project of Basic Science (Natural Science) Research in Jiangsu Universities (Grant Nos.22KJA460001,23KJA580001)Changzhou Science and Technology Plan Project (Grant No.CE20235049)Changzhou Leading Innovative Talents C ultivation Project (Grant No.CQ20220092).
文摘Two cross⁃sectional configurations of thin⁃walled square tubes partially filled with lightweight metallic foams are proposed,and termed as double⁃cell configuration partially filled with foam(DC⁃PF)and double⁃tube configuration partially filled with foam(DT⁃PF),respectively.The bending crashworthiness is investigated based on three⁃point bending tests using finite element ABAQUS/Explicit code.The two key mechanical indicators including Crash Load Efficiency(CLE)and Specific Energy Absorption(SEA)are introduced to evaluate the effect of foams in comparison with empty square tubes and fully filled square tubes.The numerical results show that the two partially filled configurations,especially DT⁃PF,display dramatically excellent bending crashworthiness compared with empty and fully filled square tubes.There exists a foam density threshold,beyond which the CLE of DT⁃PF achieves a maximum constant.In addition,there seems to be another foam density threshold,beyond which the SEA of DT⁃PF gets to the maximum value.It is also shown that the foam density threshold corresponding to the maximum SEA varies with the thickness of thin⁃walled square tubes.
基金supports provided by the National Natural Science Foundation of China(No.52372330).
文摘The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weldability of components with thin walls after small punch sampling,such as ethylene cracking furnace tubes,requires further investigation.Therefore,the weldability of in-service ethylene cracking furnace tubes following small punch sampling was investigated through nondestructive testing,microstructural characterization,and mechanical testing.Additionally,the impact of small punch sampling size and residual stress on the creep performance of the specimens was studied using an improved ductility exhaustion model.The results indicate that both the surface and interior of the weld repair areas on new furnace tubes and service-exposed furnace tubes after small-punch sampling are defect-free,exhibiting good weld quality.The strength of the specimens after weld repair was higher than that before sampling,whereas toughness decreased.Weld repair following small punch sampling of furnace tubes is both feasible and necessary.Furthermore,a linear relationship was observed between specimen thickness,diameter,and creep fracture time.The residual stress of welding affects the creep performance of the specimen under different stresses.
基金Supported by National Natural Science Foundation of China(Grant Nos.52025121,52394263)National Key R&D Plan of China(Grant No.2023YFD2000301)+2 种基金Foundation of State Key Laboratory of Automobile Safety and Energy Saving of China(Grant No.KFZ2201)the Jiangsu Provincial Scientific Research Center of Applied Mathematics under(Grant No.BK20233002)Special Fund of Jiangsu Province for the Transformation of Scientific and Technological Achievements under(Grant No.BA2021023)。
文摘This paper tackles uncertainties between planning and actual models.It extends the concept of RCI(robust control invariant)tubes,originally a parameterized representation of closed-loop control robustness in traditional feedback control,to the domain of motion planning for autonomous vehicles.Thus,closed-loop system uncertainty can be preemptively addressed during vehicle motion planning.This involves selecting collision-free trajectories to minimize the volume of robust invariant tubes.Furthermore,constraints on state and control variables are translated into constraints on the RCI tubes of the closed-loop system,ensuring that motion planning produces a safe and optimal trajectory while maintaining flexibility,rather than solely optimizing for the open-loop nominal model.Additionally,to expedite the solving process,we were inspired by L2gain to parameterize the RCI tubes and developed a parameterized explicit iterative expression for propagating ellipsoidal uncertainty sets within closedloop systems.Furthermore,we applied the pseudospectral orthogonal collocation method to parameterize the optimization problem of transcribing trajectories using high-order Lagrangian polynomials.Finally,under various operating conditions,we incorporate both the kinematic and dynamic models of the vehicle and also conduct simulations and analyses of uncertainties such as heading angle measurement,chassis response,and steering hysteresis.Our proposed robust motion planning framework has been validated to effectively address nearly all bounded uncertainties while anticipating potential tracking errors in control during the planning phase.This ensures fast,closed-loop safety and robustness in vehicle motion planning.
基金financially supported by the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(Grant No.24qnpy041)the Science and Technology Innovation Key R&D Program of Chongqing(Grant No.CSTB2023TIAD-STX0030)。
文摘The electric vertical takeoff and landing(e VTOL)aircraft shows great potential for rapid military personnel deployment on the battlefield.However,its susceptibility to control loss,complex crashes,and extremely limited bottom energy-absorbing space demands higher comprehensive crashworthiness of its subfloor thin-walled structures.This study investigated the energy absorption capacity of novel concave polygonal carbon fiber reinforced plastics(CFRP)tubes under multi-angle collisions.Quasistatic compression experiments and finite element simulations were conducted to assess the failure mode and energy absorption.The influences of cross-section shapes,loading conditions,and geometry parameters on crashworthiness metrics were further analyzed.The results revealed that,under the similar weight,concave polygonal tubes exhibited superior energy absorption under axial loads compared to regular polygonal and circular tubes,attributed to the increased number of axial splits.However,both regular and concave polygonal tubes,particularly the latter,demonstrated reduced oblique energy absorption compared to traditional square tubes with the increasing ratio of SEA value decreased from 20%-16%.Notably,this reduction in energy absorption can be compensated for by the implementation of inward and outward crusher plugs,and with them,the concave polygonal tubes demonstrated outstanding overall crashworthiness performance under multiple loading conditions.This concave cross-sectional design methods could serve as a guidance for the development of the eVTOL subfloor.
文摘The main purpose of this research is to optimize the hydrothermal performance of a dimpled tube by augmenting the surface area for heat transmission and thermal layer cracking.To achieve that,the impact of different dimple diameters and their distribution along the dimpled tube was investigated numerically using the ANSYS Fluent 2022 R1 software by considering two models,A and B.Both models consist of three regions;the first,second,and third have dimple diameters of 3,2,&1 mm,respectively.Model A included an in-line dimple arrangement,while model B involved a staggered dimple arrangement.The finite volume method(FVM)was used in the modeling techniques to address the turbulent flow problem,which ranged in this investigation from Re of 3000 to 8000.The cooling fluid used in this investigation is water,which concentrated primarily on single-phase flow conditions.The investigation results revealed that as the Re increased,all analyzed models showcased higher.A reduction in pressure drops,thermal resistance,Nu,and overall performance standards.Crucially,compared to the traditionalmodel,both suggested models demonstrated improved heat transmission capacities.Within all the models examined,the tube with dimples in(model B)as staggered showed the greatest enhancement in the Nu,which was almost double that of the conventional type.Model A and Model B have respective average total performance criteria of 1.23 and 1.34.
基金financially supported by the Natural Science Foundation of China(52071065)the Fundamental Research Funds for the Central Universities(N2007007)the National Key R&D Program of China(2016YFB-0301201)。
文摘The grain size of TiAl alloy castings prepared by traditional casting process is coarse,thus showing poor mechanical properties.In this study,a new type of high performance Ti-46Al alloy tube prepared by vacuum centrifugal casting technology was introduced.This research comprehensively examined the influence of pouring time on the microstructure and mechanical performance of the castings,employing both experimental approaches and ProCast simulation methodologies.The findings indicate that prolonging the pouring time facilitates a microstructural evolution from coarse columnar grains to refined equiaxed grains.Under the condition of pouring temperature of 1,600℃,rotation speed of 800 r·min^(-1) and pouring time of 6 s,the tensile strength of Ti-46Al alloy at room temperature reaches 650 MPa,and the tensile strength at 800℃ reaches 705 MPa,which is significantly higher than that of traditional as-cast Ti-Al alloy.
基金supported in part by the National Key R&D Program of China(No.2023YFB4704400)in part by the National Natural Science Foundation of China(Nos.U23B2036,U2013201).
文摘In this paper,a distributed Event-Triggered(ET)collision avoidance coordinated control for Quadrotor Unmanned Aerial Vehicles(QUAVs)is proposed based on Virtual Tubes(VTs)with flexible boundaries in the presence of unknown external disturbances.Firstly,VTs are constructed for each QUAV,and the QUAV is restricted into the corresponding VT by the artificial potential field,which is distributed around the boundary of the VT.Thus,the collisions between QUAVs are avoided.Besides,the boundaries of the VTs are flexible by the modification signals,which are generated by the self-regulating auxiliary systems,to make the repulsive force smaller and give more buffer space for QUAVs without collision.Then,a novel ET mechanism is designed by introducing the concept of prediction to the traditional fixed threshold ET mechanism.Furthermore,a disturbance observer is proposed to deal with the adverse effects of the unknown external disturbance.On this basis,a distributed ET collision avoidance coordinated controller is proposed.Then,the proposed controller is quantized by the hysteresis uniform quantizer and then sent to the actuator only at the ET instants.The boundedness of the closed-loop signals is verified by the Lyapunov method.Finally,simulation and experimental results are performed to demonstrate the superiority of the proposed control method.
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Project (U0834002) supported by the Key Program of NSFC Guangdong Joint Funds of ChinaProjects (51005079, 20976055) supported by the National Natural Science Foundation of China+1 种基金Project (10451064101005146) supported by the Natural Science Foundation of Guangdong Province, ChinaProject (20100172120001) supported by Specialized Research Fund for the Doctoral Program of Higher Education, China
文摘A rotary swaging machine was applied to fabricating pipe reduction for miniature inner grooved copper tube （MIGCT） heat pipes. Compared with conventional swaging method, the axial feed of the designed rotary swaging machine was reached by a constant pushing force. The deformation of grooves in pipe reduced section during rotary swaging was analyzed. The shrinkage and extensibility of pipe reduction were measured and calculated. Furthermore, four aspects, including outer diameter, surface roughness, extensibility and processing time of pipe reduction, which were influenced by the pushing force, were considered. The results show that the tube wall thickness increases gradually along the z-axis at sinking section. However, the outer diameters, surface roughness and micro-cracks at reduced section tend to decrease along the z-axis. Besides, the effect of variation in the pushing force on the extensibility is limited while an increase in the pushing force results in a decrease of surface roughness. Therefore, a large pushing force within the limit is beneficial to pipe reduction manufacturing during rotary swaging process.
基金The National Natural Science Foundation of China(No.50706012)
文摘Two types of tube bundles are designed,which are,respectively,composed of six tubes arranged in the boiling chamber.The nucleate pool boiling performance of smooth tube bundles and sintered porous surface tube bundles with deionized water as a medium are experimentally studied at atmospheric and sub-atmospheric pressures,respectively.The experimental results indicate that the boiling heat transfer coefficients of the two types of tube bundles increase with the increase in pressure under vacuum conditions as they behave under ordinary pressure.As the pressure varies from 10 to 100 kPa,it also can be seen that the heat transfer coefficient of the sintered porous surface tube is increased by 0.2 to 4 times compared with the smooth one under the same operating parameters.In addition,the experimental data show that a definite bundle effect exists in both sintered porous surface tubes and smooth tubes under vacuum conditions.
基金The National Natural Science Foundation of China(No.50776055,51076084)
文摘Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of the geometric and system parameters on heat transfer characteristics in helically coiled tubes are investigated by collecting large amounts of experimental data and analyzing the heat transfer mechanisms. The existing correlations are divided into two categories,and they are calculated with the experimental data.The Dn factor is introduced to take into account the effect of a complex geometrical structure on flow boiling heat transfer.A new correlation is developed for predicting the flow boiling heat transfer coefficients in the helically coiled tubes,which is validated by the experimental data of R134a flow boiling heat transfer in them;and the average relative error and root mean square error of the new correlation are calculated.The results show that the new correlation agrees well with the experimental data,indicating that the new correlation can be used for predicting flow boiling heat transfer characteristics in the helically coiled tubes.
基金Projects(50905144,51275415)supported by the National Natural Science Foundation of ChinaProject supported by the Program for New Century Excellent Talents in University,ChinaProject(B08040)supported by the Program of Introducing Talents of Discipline to Universities,China("111"Project)
文摘In order to develop the warming bending technology of the large diameter thin-walled（LDTW） commercial pure titanium alloy CP-Ti tubes, the warm bending mechanism of the extrados and intrados of LDTW CP-Ti tubes was researched. By EBSD analysis and Vickers hardness test, the changes of microstructure and strength of the tubes at different bending temperatures of 293, 423 and 573 K, were analyzed. The results show： 1） The extrados of the bent tube deforms mainly by slip, along with few twinning, and the preferred orientation is similar to that of the initial tube; the intrados of the bent tube experiences compression deformation mainly by {1 012} tensile twinning, and the twinning makes the preferred orientation of wall materials change sharply. 2） The Vickers hardness values of both the extrados and intrados of the samples after bending increase greatly; the Vickers hardness values of the intrados are much higher than those of the extrados, and Vickers hardness values of the RD-TD planes are always higher than those of the RD-LD planes, which are related to the different deformation mechanisms.
